Publications

2025

1. Chemical waves in reaction-diffusion networks of small organic molecules

   Paikar A., Li X., Avram L., Smith B. S., Sütő I., Horváth D., Rennert E., Qiu Y., Tóth Á., Vaikuntanathan S., Semenov S. N. et al. (2025) Chemical Science. 16, 2, p. 659-669  Abstract

   Chemical waves represent one of the fundamental behaviors that emerge in nonlinear, out-of-equilibrium chemical systems. They also play a central role in regulating behaviors and development of biological organisms. Nevertheless, understanding their properties and achieving their rational synthesis remains challenging. In this work, we obtained traveling chemical waves using synthetic organic molecules. To accomplish this, we ran a thiol-based reaction network in an unstirred flow reactor. Our observations revealed single or multiple waves moving in either the same or opposite directions, a behavior controlled by the geometry of our reactor. A numerical model can fully reproduce this behavior using the proposed reaction network. To better understand the formation of waves, we varied the diffusion coefficient of the fast inhibitor component of the reaction network by attaching polyethylene glycol tails with different lengths to maleimide and studied how these changes affect the properties of the waves and conditions for their sustained production. These studies point towards the importance of the molecular titration network motif in controlling the production of chemical waves in this system. Furthermore, we used machine learning (ML) tools to identify phase boundaries for classes of dynamic behaviors of this system, thus demonstrating the applicability of ML tools for the study of experimental nonlinear reaction-diffusion systems.

   [All authors]

2024

1. A Pseudo-catalytic Network Motif for Thiol-based Chemical Reaction Networks

   Zhigileva E. A., Puchkin I. A. & Semenov S. N. (2024) ChemSystemsChem. e202400072.  Abstract

   The construction of chemical reaction networks (CRNs) is a formidable challenge because of their holistic and nonlinear nature. One approach to constructing CRNs involves combining fragments with distinctive properties, known as network motifs. Thiol chemistry is widely used in the construction of CRNs, with motifs available for positive and negative feedback loops. However, a simple catalytic motif has been lacking. Here, we developed a pseudo-catalytic motif using the reaction between cystamine and organic thiocyanates, which operates through a nucleophilic chain mechanism. Although similar to thiol autocatalytic systems, this reaction does not involve a doubling of the number of thiol species at any stage. The reaction is high-yielding and produces 2-amino-2-thiazoline. Its pseudo-catalytic nature manifests itself in the nearly linear relationship between the reaction rate and the amount of free thiols added at the beginning of the reaction. We demonstrated that this reaction can be regulated by external, time-dependent thiol signals and integrated into larger CRNs. We believe that this system will be a valuable addition to thiol chemistry, enabling the construction of CRNs with interesting functionalities.

2. Altering the structures of 3D supramolecular assemblies from melamine and cyanuric acid derivatives in water

   Orekhov N., Bukhtiiarova N., Brushevich Z. A., Muravev A. A., Nadav E., Tsarfati Y., Kossoy A., Feldman I., Zelenina A., Rubekina A. A., Semenov S. N., Skorb E. V. et al. (2024) Chemical Communications. 60, 77, p. 10680-10683  Abstract

   Herein, we obtained two supramolecular assemblies with layered structures from melamine, N-methylmelamine, and hexynyl-cyanuric acid in water. By combination of X-ray diffraction, electron microscopy, and molecular dynamics studies, we found that introducing one methyl group in melamine alters the arrangement of the layers in these structures.

   [All authors]
3. Selenium catalysis enables negative feedback organic oscillators

   Li X., Fomitskaya P., Smaliak V. A., Smith B. S., Skorb E. V. & Semenov S. N. (2024) Nature Communications. 15, 3316.  Abstract

   The construction of materials regulated by chemical reaction networks requires regulatory motifs that can be stacked together into systems with desired properties. Multiple autocatalytic reactions producing thiols are known. However, negative feedback loop motifs are unavailable for thiol chemistry. Here, we develop a negative feedback loop based on the selenocarbonates. In this system, thiols induce the release of aromatic selenols that catalyze the oxidation of thiols by organic peroxides. This negative feedback loop has two important features. First, catalytic oxidation of thiols follows Michaelis-Menten-like kinetics, thus increasing nonlinearity for the negative feedback. Second, the strength of the negative feedback can be tuned by varying substituents in selenocarbonates. When combined with the autocatalytic production of thiols in a flow reactor, this negative feedback loop induces sustained oscillations. The availability of this negative feedback motif enables the future construction of oscillatory, homeostatic, adaptive, and other regulatory circuits in life-inspired systems and materials.

2023

1. Interplay between autocatalysis and liquid-liquid phase separation produces hierarchical microcompartments

   Hanopolskyi A. I., Mikhnevich T. A., Paikar A., Nutkovich B., Pinkas I., Dadosh T., Smith B. S., Orekhov N., Skorb E. V., Semenov S. N. et al. (2023) Chem. 9, 12, p. 3666-3684  Abstract

   Our ability to synthesize life-inspired systems and materials is intimately connected to our understanding of the interplay between reactions, diffusion, phase separation, and self-assembly. The interaction between non-linear reactions (autocatalysis) and liquid-liquid phase separation is particularly interesting because of the emergence of functional properties and structures through instabilities, which are hard to predict theoretically without the help of experimental model systems. In this work, we studied systems where chemical autocatalysis is coupled to complex coacervation and the formation of oil-in-water droplets. The autocatalysis is driven by a nucleophilic chain reaction and is coupled to complex coacervation through the formation of tri- and tetracationic species. Interestingly, we observed the formation of hierarchical colloids when we used reactants that can form oil droplets in addition to coacervate droplets. This work illustrates a mechanism for the formation of complex, hierarchical microstructures by kinetically controlled self-assembly regulated by non-linear chemical reaction networks.

   [All authors]
2. Collectively autocatalytic sets

   Ashkenasy G., Kauffman S., Lancet D., Otto S., Ruiz-Mirazo K., Semenov S. & Xavier J. (2023) Cell Reports Physical Science. 4, 10, 101594.  Abstract

   The origins of life probably involved autocatalysis. Kauffman's 1986 description of collectively autocatalytic setsself-replicating reaction networksand related ideas have influenced efforts to study the properties of reaction networks that may have given rise to life. Here, researchers discuss the impact of collectively autocatalytic sets on the field.

3. Stirring-Free Scalable Electrosynthesis Enabled by Alternating Current

   Bortnikov E. O., Smith B. S., Volochnyuk D. M. & Semenov S. N. (2023) Chemistry - A European Journal. 29, 18, e202203825.  Abstract

   Alternating current (AC) electrolysis is receiving increased interest as a versatile tool for mild and selective electrochemical transformations. This work demonstrates that AC can enable the concept of a stirring-free electrochemical reactor where the periodic switch of electrode polarity, inherent to AC, provides uniform electrolysis across the whole volume of the reactor. Such design implies a straightforward approach for scaling up electrosynthesis. This was demonstrated on the range of electrochemical transformations performed in three different RVC-packed reactors on up to a 50-mmol scale. Redox-neutral, oxidative, and reductive processes were successfully implemented using the suggested design and the applicable frequency ranges were further investigated for different types of reactions. The advantages of the AC-enabled design such as the absence of stirring and a maximized surface area of the electrodes provide the possibility for its universal application both for small-scale screening experimentation and large-scale preparative electrosynthesis without significant optimization needed in between.

2022

1. Designed assembly and disassembly of DNA in supramolecular structure: From ion regulated nuclear formation and machine learning recognition to running DNA cascade

   Aliev T. A., Timralieva A. A., Kurakina T. A., Katsuba K. E., Egorycheva Y. A., Dubovichenko M. V., Kutyrev M. A., Shilovskikh V. V., Orekhov N., Kondratyuk N., Semenov S. N., Kolpashchikov D. M., Skorb E. V. et al. (2022) Nano Select. 3, 11, p. 1526-1536  Abstract

   Abstract In this paper, we introduce a novel encapsulation system for DNA oligonucleotides. Supramolecular assembly of melamine cyanurate encapsulates DNA at pH 7 and start to release it at pH less than 6.5. We study the assembly and disassembly in time in specially designed reaction-diffusion system. Magnesium ions allow spatial separation of DNA with the highest DNA concentration in the core of melamine cyanurate capsule. Molecular dynamics (MD) simulation shows that DNA acts as a nucleation centre for melamine cyanurate. Dataset of fluorescent images analysed by machine learning algorithms indicates correlation between structure of melamine cyanurate capsules for DNA trapping and concentration of magnesium ions. The concentration of magnesium ions can be recognized with 96% accuracy proving that all environmental conditions are extremely important during the self-assembly and should be considered for laboratory and industrial applications of the suggested approach. Moreover, the encapsulated DNA can undergo a cascade reaction consisting of hybridization with complementary strand and its cleavage at a designated site. This reactivity opens a fresh avenue for various applications in biosensing, diagnostics, DNA compartmentalization, and even gives new hints for the origin-of-life questions.

   [All authors]
2. Unconventional approaches for organic electrosynthesis: Recent progress

   Bortnikov E. O. & Semenov S. N. (2022) Current Opinion in Electrochemistry. 35, 101050.  Abstract

   Modern organic electrochemistry enables a broad range of synthetic transformations in a convenient and \u201cgreen\u201d manner. However, the limitations, inherent in the established design of an electrochemical experiment such as mass and heat transfer and the non-homogeneity of an electric field may sometimes limit the effectivity of the method. The development of novel unconventional approaches to conduct electrochemical experiments may help to overcome these problems by introducing significant modifications to the traditional experimental design. In this review, the most notable emerging fields in organic electrochemistry are briefly surveyed microflow electrosynthesis, alternating current electrolysis, and bipolar electrochemistry with a particular emphasis on recent synthetic progress using these methods.

3. Ternary host-guest complexes with rapid exchange kinetics and photoswitchable fluorescence

   Gemen J., Białek M. J., Kazes M., Shimon L. J. W., Feller M., Semenov S. N., Diskin-Posner Y., Oron D. & Klajn R. (2022) Chem. 8, 9, p. 2362-2379  Abstract

   Confinement within molecular cages can dramatically modify the physicochemical properties of the encapsulated guest molecules, but such host-guest complexes have mainly been studied in a static context. Combining confinement effects with fast guest exchange kinetics could pave the way toward stimuli-responsive supramolecular systemsand ultimately materialswhose desired properties could be tailored \u201con demand\u201d rapidly and reversibly. Here, we demonstrate rapid guest exchange between inclusion complexes of an open-window coordination cage that can simultaneously accommodate two guest molecules. Working with two types of guests, anthracene derivatives and BODIPY dyes, we show that the former can substantially modify the optical properties of the latter upon noncovalent heterodimer formation. We also studied the light-induced covalent dimerization of encapsulated anthracenes and found large effects of confinement on reaction rates. By coupling the photodimerization with the rapid guest exchange, we developed a new way to modulate fluorescence using external irradiation.

4. Spatiotemporal Regulation of Hydrogel Actuators by Autocatalytic Reaction Networks

   Paikar A., Novichkov A. I., Hanopolskyi A. I., Smaliak V. A., Sui X., Kampf N., Skorb E. V. & Semenov S. N. (2022) Advanced materials (Weinheim). 34, 13, 2106816.  Abstract

   Regulating hydrogel actuators with chemical reaction networks is instrumental for constructing life-inspired smart materials. Herein, hydrogel actuators are engineered that are regulated by the autocatalytic front of thiols. The actuators consist of two layers. The first layer, which is regular polyacrylamide hydrogel, is in a strained conformation. The second layer, which is polyacrylamide hydrogel with disulfide crosslinks, maintains strain in the first layer. When thiols released by the autocatalytic front reduce disulfide crosslinks, the hydrogel actuates by releasing the mechanical strain in the first layer. The autocatalytic front is sustained by the reaction network, which uses thiouronium salts, disulfides of beta-aminothiols, and maleimide as starting components. The gradual actuation by the autocatalytic front enables movements such as gradual unrolling, screwing, and sequential closing of "fingers." This actuation also allows the transmission of chemical signals in a relay fashion and the conversion of a chemical signal to an electrical signal. Locations and times of spontaneous initiation of autocatalytic fronts can be preprogrammed in the spatial distribution of the reactants in the hydrogel. To approach the functionality of living matter, the actuators triggered by an autocatalytic front can be integrated into smart materials regulated by chemical circuits.

2021

1. Kinetic selection in the outofequilibrium autocatalytic reaction networks that produce macrocyclic peptides

   Semenov S. N., Miao X., Paikar A., Lerner B., Diskin-Posner Y. & Shmul G. (2021) Angewandte Chemie (International ed.). 60, 37, p. 20366-20375  Abstract

   Autocatalytic reaction networks are instrumental for validating scenarios for the emergence of life on Earth and for synthesizing life de novo . It is well understood how the selection of specific molecules occurs in reaction networks driven by template-assisted ligation; however how selection could occur in strongly interconnected, nonselective, autocatalytic networks is less clear. Here, we demonstrate that dimeric thioesters of tripeptides with the general structure (Cys-Xxx-Gly-SR) 2 form strongly interconnected autocatalytic reaction networks that predominantly generate macrocyclic peptides up to 69 amino acids long. Some macrocycles of 6-12 amino acids were isolated from the product pool and were characterized by NMR spectroscopy and single-crystal X-ray analysis. We studied the autocatalytic formation of macrocycles in a flow reactor in the presence of acrylamide, whose conjugate addition to thiols served as a model \u201cremoval\u201d reaction. These results indicate that autocatalytic production and competing removal of molecular species in an open compartment could be a feasible route for selecting functional molecules during the pre-Darwinian stages of molecular evolution.

2. Autocatalytic and oscillatory reaction networks that form guanidines and products of their cyclization

   Novichkov A. I., Hanopolskyi A. I., Miao X., Shimon L. J. W., Diskin-Posner Y. & Semenov S. N. (2021) Nature Communications. 12, 1, 2994.  Abstract

   Autocatalytic and oscillatory networks of organic reactions are important for designing life-inspired materials and for better understanding the emergence of life on Earth; however, the diversity of the chemistries of these reactions is limited. In this work, we present the thiol-assisted formation of guanidines, which has a mechanism analogous to that of native chemical ligation. Using this reaction, we designed autocatalytic and oscillatory reaction networks that form substituted guanidines from thiouronium salts. The thiouronium salt-based oscillator show good stability of oscillations within a broad range of experimental conditions. By using nitrile-containing starting materials, we constructed an oscillator where the concentration of a bicyclic derivative of dihydropyrimidine oscillates. Moreover, the mixed thioester and thiouronium salt-based oscillator show unique responsiveness to chemical cues. The reactions developed in this work expand our toolbox for designing out-of-equilibrium chemical systems and link autocatalytic and oscillatory chemistry to the synthesis of guanidinium derivatives and the products of their transformations including analogs of nucleobases.

3. Previously unknown type of protein crosslink discovered

   Fass D. & Semenov S. (2021) Nature (London). 593, 7859, p. 343-344  Abstract

   Molecular crosslinks known as disulfides stabilize the 3D structures of many proteins, and sometimes regulate protein function. But disulfides are not alone another type of regulatory protein crosslink has been discovered.

4. De novo Design of Chemical Reaction Networks and Oscillators and Their Relation to Emergent Properties

   Semenov S. N. (2021) OutofEquilibrium (Supra)molecular Systems and Materials. p. 91-130  Abstract

   Chemical reaction networks (CRNs) cascades of chemical reactions where products of one reaction influence the rate of another reaction are important in many fields of natural sciences. CRNs orchestrate cellular metabolism and guide the growth and movement of cells and multicellular organisms in heterogeneous environments. The chapter emphasizes two important conclusions from phenomenological nonequilibrium thermodynamics for the design of CRNs: quantitative requirements for the free energy of reactions and the importance of using open chemical systems. It considers two fundamental laws governing CRNs: mass conservation that results in stoichiometric restrictions and mass action. The stoichiometry significantly restricts the number of ways that concentrations of compounds can change during reactions. Continuously stirred tank reactor is the most common type of flow reactor employed in experimental studies. The current synthetic CRNs, the networks that are supposed to regulate artificial cells and smart therapeutic agents, are incomparable in their complexity to cellular regulatory networks.

5. Autocatalysis: Kinetics, Mechanisms and Design

   Hanopolskyi A. I., Smaliak V. A., Novichkov A. I. & Semenov S. N. (2021) ChemSystemsChem. 3, 1, e2000026.  Abstract

   The importance of autocatalysis spans from practical applications such as in chemically amplified photoresists, to autocatalysis playing a fundamental role in evolution as well as a plausible key role in the origin of life. The phenomenon of autocatalysis is characterized by its kinetic signature rather than by its mechanistic aspects. The molecules that form autocatalytic systems and the mechanisms underlying autocatalytic reactions are very diverse. This chemical diversity, combined with the strong involvement of chemical kinetics, creates a formidable barrier for entrance to the field. Understanding these challenges, we wrote this Review with three main goals in mind: (i) To provide a basic introduction to the kinetics of autocatalytic systems and its relation to the role of autocatalysis in evolution, (ii) To provide a comprehensive overview, including tables, of synthetic chemical autocatalytic systems, and (iii) To provide an in-depth analysis of the concept of autocatalytic reaction networks, their design, and perspectives for their development.

6. Coupling of Alternating Current to Transition-Metal Catalysis: Examples of Nickel-Catalyzed Cross-Coupling

   Bortnikov E. O. & Semenov S. N. (2021) Journal of Organic Chemistry. 86, 1, p. 782-793  Abstract

   The coupling of transition-metal to photoredox catalytic cycles through single-electron transfer steps has become a powerful tool in the development of catalytic processes. In this work, we demonstrated that transition-metal catalysis can be coupled to alternating current (AC) through electron transfer steps that occur periodically at the same electrode. AC-assisted Ni-catalyzed amination, etherification, and esterification of aromatic bromides showed higher yields and selectivity compared to that observed in the control experiments with direct current. Our mechanistic studies suggested the importance of both reduction and oxidation processes in the maintenance of the AC-assisted catalytic reactions. As described in presented examples, the AC assistance should be well-suited for catalytic cycles involving reductive elimination or oxidative addition as a limiting step.

2019

1. Robustness, Entrainment, and Hybridization in Dissipative Molecular Networks, and the Origin of Life

   Cafferty B. J., Wong A. S. Y., Semenov S. N., Belding L., Gmur S., Huck W. T. S. & Whitesides G. M. (2019) Journal of the American Chemical Society. 141, 20, p. 8289-8295  Abstract

   How simple chemical reactions self-assembled into complex, robust networks at the origin of life is unknown. This general problem-self-assembly of dissipative molecular networks-is also important in understanding the growth of complexity from simplicity in molecular and biomolecular systems. Here, we describe how heterogeneity in the composition of a small network of oscillatory organic reactions can sustain (rather than stop) these oscillations, when homogeneity in their composition does not. Specifically, multiple reactants in an amide-forming network sustain oscillation when the environment (here, the space velocity) changes, while homogeneous networks-those with fewer reactants-do not. Remarkably, a mixture of two reactants of different structure-neither of which produces oscillations individually-oscillates when combined. These results demonstrate that molecular heterogeneity present in mixtures of reactants can promote rather than suppress complex behaviors.
2. Mathematical Analysis of a Prototypical Autocatalytic Reaction Network

   Skorb E. & Semenov S. N. (2019) Life. 9, 2, 42.  Abstract

   Network autocatalysis, which is autocatalysis whereby a catalyst is not directly produced in a catalytic cycle, is likely to be more common in chemistry than direct autocatalysis is. Nevertheless, the kinetics of autocatalytic networks often does not exactly follow simple quadratic or cubic rate laws and largely depends on the structure of the network. In this article, we analyzed one of the simplest and most chemically plausible autocatalytic networks where a catalytic cycle is coupled to an ancillary reaction that produces the catalyst. We analytically analyzed deviations in the kinetics of this network from its exponential growth and numerically studied the competition between two networks for common substrates. Our results showed that when quasi-steady-state approximation is applicable for at least one of the components, the deviation from the exponential growth is small. Numerical simulations showed that competition between networks results in the mutual exclusion of autocatalysts; however, the presence of a substantial noncatalytic conversion of substrates will create broad regions where autocatalysts can coexist. Thus, we should avoid the accumulation of intermediates and the noncatalytic conversion of the substrate when designing experimental systems that need autocatalysis as a source of positive feedback or as a source of evolutionary pressure.

2018

1. Autocatalytic Cycles in a Copper-Catalyzed Azide-Alkyne Cycloaddition Reaction

   Semenov S. N., Belding L., Cafferty B. J., Mousavi M. P. S., Finogenova A. M., Cruz R. S., Skorb E. V. & Whitesides G. M. (2018) Journal of the American Chemical Society. 140, 32, p. 10221-10232  Abstract

   This work describes the autocatalytic copper-catalyzed azid-alkyne cycloaddition (CuAAC) reaction between tripropargylamine and 2-azidoethanol in the presence of Cu(II) salts. The product of this reaction, tris-(hydroxyethyltriazolylmethyl)amine (N(C3N3)(3)), accelerates the cycloaddition reaction (and thus its own production) by two mechanisms: (i) by coordinating Cu(II) and promoting its reduction to Cu(I) and (ii) by enhancing the catalytic reactivity of Cu(I) in the cycloaddition step. Because of the cooperation of these two processes, a rate enhancement of >400x is observed over the course of the reaction. The kinetic profile of the autocatalysis can be controlled by using different azides and alkynes or ligands (e.g., ammonia) for Cu(II). When carried out in a layer of 1% agarose gel, and initiated by ascorbic acid, this autocatalytic reaction generates an autocatalytic front. This system is prototypical of autocatalytic reactions where the formation of a product, which acts as a ligand for a catalytic metal ion, enhances the production and activity of the catalyst.

2. Four-Variable Model of an Enzymatic Oscillator Based on Trypsin

   Semenov S. N., Ainla A., Skorb E. V. & Postma S. G. J. (2018) Israel Journal of Chemistry. 58, 6-7, p. 781-786  Abstract

   This paper describes a four-variable model for an enzymatic oscillator based on trypsin. Variables in this model are concentrations of the essential proteins (trypsin and trypsinogen) and small molecules (masked and active inhibitors of trypsin) within the network. Importantly, to simplify the model, non-essential side reactions are neglected and essential reactions are assumed to follow first or second order kinetics. Numerical solutions of this reduced model semi-quantitatively reproduce experimentally determined periods, amplitudes, and phase shifts of oscillations in the concentrations of several species in the network. Moreover, linear stability analysis shows that oscillations in the trypsin oscillator emerge and disappear through Hopf bifurcation. The model will be helpful in situations where simplicity is necessary such as detailed analysis of dynamics and modeling of reaction-diffusion systems.
3. Photocatalytic Regulation of an Autocatalytic Wave of Spatially Propagating Enzymatic Reactions

   Lanchuk Y., Nikitina A., Brezhneva N., Ulasevich S. A., Semenov S. N. & Skorb E. V. (2018) ChemCatChem. 10, 8, p. 1798-1803  Abstract

   Bioinspiration is an attractive way to develop new robust chemistry. In biological cell, chemical reactions form complex networks (e.g. signaling and metabolic) that communicate with each other and control cell division, growth, and interaction with environment. Thus, combining multiple chemical subsystems into a single network is an attractive way to design a chemical system with new functions. In this paper, we combined two chemical networks: i) a photocatalytic oxidation/ reduction on TiO₂ particles, and ii) an autocatalytic formation of enzyme trypsin (Tr) from its precursor trypsinogen (Tg). Moreover, we put the combined network in hydrogel media, where all reactions are coupled to diffusion, to achieve a photocatalytic regulation of an autocatalytic wave. We showed that TiO₂ particles affected the fluorescence quenching of Tr, but, without irradiation, had no effect on the autocatalytic formation of Tr. With irradiation, however, a cascade of photocatalytic reactions causes media acidification that suppress the autocatalytic formation of Tr and propagation of the autocatalytic wave.

2017

1. 3D unsteady computations of evaporative instabilities in a sessile drop of ethanol on a heated substrate

   Semenov S., Carle F., Medale M. & Brutin D. (2017) Applied Physics Letters. 111, 24, 241602.  Abstract

   Droplets are ubiquitous and have been studied for a century; however, their internal flow pattern and related instabilities that occur in the course of evaporation arc not fully understood yet. In this paper, we report our investigation results on an ethanol drop evaporating onto a heated substrate under weightlessness conditions and with a pinned contact line. They have been obtained from both experiments and 3D unsteady computations in order to determine what kind of instabilities develop. Our one-sided model demonstrates quantitative agreement with experiments and confirms that experimentally observed instabilities are driven by thermo-capillary stress and not by the gas convection. Post-processed infrared images drawn from computations led us to conclude that the experimentally observed thermo-convective instabilities, which look, very similar to hydrothermal waves in the infrared spectrum, are actually nothing else than unsteady Benard-Marangoni instabilities. Published by AIP Publishing.
2. Magnetic Levitation To Characterize the Kinetics of Free-Radical Polymerization

   Ge S., Semenov S. N., Nagarkar A. A., Milette J., Christodouleas D. C., Yuan L. & Whitesides G. M. (2017) Journal of the American Chemical Society. 139, 51, p. 18688-18697  Abstract

   This work describes the development of magnetic levitation (MagLev) to characterize the kinetics of free-radical polymerization of water insoluble, low-molecular-weight monomers that show a large change in density upon polymerization. Maglev measures density, and certain classes of monomers show a large change in density when monomers covalently join in polymer chains. MagLev characterized both the thermal polymerization of methacrylate-based monomers and the photopolymerization of methyl methacrylate and made it possible to determine the orders of reaction and the Arrhenius activation energy of polymerization. MagLev also made it possible to monitor polymerization in the presence of solids (aramid fibers, and carbon fibers, and glass fibers). MagLev offers a new analytical technique to materials and polymer scientists that complements other methods (even those based on density, such as dilatometry), and will be useful in investigating polymerizations, evaluating inhibition of polymerizations, and studying polymerization in the presence of included solid materials (e.g., for composite materials).

2016

1. Autocatalytic, bistable, oscillatory networks of biologically relevant organic reactions

   Semenov S. N., Kraft L. J., Ainla A., Zhao M., Baghbanzadeh M., Campbell V. E., Kang K., Fox J. M. & Whitesides G. M. (2016) Nature. 537, 7622, p. 656-+  Abstract

   Networks of organic chemical reactions are important in life and probably played a central part in its origin(1-3). Network dynamics regulate cell division(4-6), circadian rhythms(7), nerve impulses(8) and chemotaxis(9), and guide the development of organisms(10). Although out-of-equilibrium networks of chemical reactions have the potential to display emergent network dynamics(11) such as spontaneous pattern formation, bistability and periodic oscillations(12-14), the principles that enable networks of organic reactions to develop complex behaviours are incompletely understood. Here we describe a network of biologically relevant organic reactions (amide formation, thiolate-thioester exchange, thiolate-disulfide interchange and conjugate addition) that displays bistability and oscillations in the concentrations of organic thiols and amides. Oscillations arise from the interaction between three subcomponents of the network: an autocatalytic cycle that generates thiols and amides from thioesters and dialkyl disulfides; a trigger that controls autocatalytic growth; and inhibitory processes that remove activating thiol species that are produced during the autocatalytic cycle. In contrast to previous studies that have demonstrated oscillations and bistability using highly evolved biomolecules (enzymes(15) and DNA(16,17)) or inorganic molecules of questionable biochemical relevance (for example, those used in Belousov-Zhabotinskii-type reactions)(18,19), the organic molecules we use are relevant to metabolism and similar to those that might have existed on the early Earth. By using small organic molecules to build a network of organic reactions with autocatalytic, bistable and oscillatory behaviour, we identify principles that explain the ways in which dynamic networks relevant to life could have developed. Modifications of this network will clarify the influence of molecular structure on the dynamics of reaction networks, and may enable the design of biomimetic networks and of synthetic self-regulating and evolving chemical systems.

2. Field-induced conductance switching by charge-state alternation in organometallic single-molecule junctions

   Schwarz F., Kastlunger G., Lissel F., Egler-Lucas C., Semenov S. N., Venkatesan K., Berke H., Stadler R. & Loertscher E. (2016) Nature Nanotechnology. 11, 2, p. 170-176  Abstract

   Charge transport through single molecules can be influenced by the charge and spin states of redox-active metal centres placed in the transport pathway. These intrinsic properties are usually manipulated by varying the molecule's electrochemical and magnetic environment, a procedure that requires complex setups with multiple terminals. Here we show that oxidation and reduction of organometallic compounds containing either Fe, Ru or Mo centres can solely be triggered by the electric field applied to a two-terminal molecular junction. Whereas all compounds exhibit bias-dependent hysteresis, the Mo-containing compound additionally shows an abrupt voltage-induced conductance switching, yielding high-to-low current ratios exceeding 1,000 at bias voltages of less than 1.0 V. Density functional theory calculations identify a localized, redox-active molecular orbital that is weakly coupled to the electrodes and closely aligned with the Fermi energy of the leads because of the spin-polarized ground state unique to the Mo centre. This situation provides an additional slow and incoherent hopping channel for transport, triggering a transient charging effect in the entire molecule with a strong hysteresis and large high-to-low current ratios.

3. Tunneling across SAMs Containing Oligophenyl Groups

   Bowers C. M., Rappoport D., Baghbanzadeh M., Simeone F. C., Liao K. C., Semenov S. N., Zaba T., Cyganik P., Aspuru-Guzik A., Whitesides G. M. et al. (2016) Journal of Physical Chemistry C. 120, 21, p. 11331-11337  Abstract

   This paper reports rates of charge tunneling across self-assembled monolayers (SAMs) of compounds containing oligophenyl groups, supported on gold and silver, using Ga₂O₃/EGaIn as the top electrode. It compares the attenuation constant, β, and the pre-exponential parameter, J₀, of the simplified Simmons equation across oligophenyl groups (R = Ph_n; n = 1, 2, 3) with three different anchoring groups (thiol, HSR; methanethiol, HSCH₂R; and acetylene, HC≡CR) that attach R to the template-stripped gold or silver substrate. The results demonstrate that the structure of the molecular linker between the anchoring group (-S- or -C≡C-) and the oligophenyl moiety significantly influences the rate of charge transport. SAMs of SPh_n and C≡CPh_n on gold show similar values of β and log |J₀| (β = 0.28 ± 0.03 Å^-1 and log |J₀| = 2.7 ± 0.1 for Au/SPh_n; β = 0.30 ± 0.02 Å^-1 and log |J₀| = 3.0 ± 0.1 for Au/C≡CPh_n). The introduction of a single intervening methylene (CH₂) group between the anchoring sulfur atom and the aromatic units generates SAMs of SCH₂Ph_n and increases β to ca. 0.66 ± 0.06 Å^-1 on both gold and silver substrates. (For n-alkanethiolates on gold, the corresponding values are β = 0.76 ± 0.03 Å^-1 and log |J₀| = 4.2 ± 0.2). Density functional theory calculations indicate that the highest occupied molecular orbitals (HOMOs) of both SPh_n and C≡CPh_n extend beyond the anchoring group and onto the phenyl rings; SAMs composed of these two groups of molecules result in indistinguishable rates of charge transport. The introduction of the CH₂ group, to generate SCH₂Ph_n, disrupts the delocalization of the orbitals, localizes the HOMO on the anchoring sulfur atom, and results in the experimentally observed increase in β to a value closer to that of a SAM of n-alkylthiolate molecules.

   [All authors]

2015

1. Influence of Molecular Structure on the Properties of Out-of-Equilibrium Oscillating Enzymatic Reaction Networks

   Wong A. S. Y., Postma S. G. J., Vialshin I. N., Semenov S. N. & Huck W. T. S. (2015) Journal of the American Chemical Society. 137, 38, p. 12415-12420  Abstract

   Our knowledge of the properties and dynamics of complex molecular reaction networks, for example those found in living systems, considerably lags behind the understanding of elementary chemical reactions. In part, this is because chemical reactions networks are nonlinear systems that operate under conditions far from equilibrium. Of particular interest is the role of individual reaction rates on the stability of the network output. In this research we use a rational approach combined with computational methods, to produce complex behavior (in our case oscillations) and show that small changes in molecular structure are sufficient to impart large changes in network behavior.

2. Rational design of functional and tunable oscillating enzymatic networks

   Semenov S. N., Wong A. S. Y., van der Made R. M., Postma S. G. J., Groen J., van Roekel H. W. H., de Greef T. F. A. & Huck W. T. S. (2015) Nature Chemistry. 7, 2, p. 160-165  Abstract

   Life is sustained by complex systems operating far from equilibrium and consisting of a multitude of enzymatic reaction networks. The operating principles of biology's regulatory networks are known, but the in vitro assembly of out-of-equilibrium enzymatic reaction networks has proved challenging, limiting the development of synthetic systems showing autonomous behaviour. Here, we present a strategy for the rational design of programmable functional reaction networks that exhibit dynamic behaviour. We demonstrate that a network built around autoactivation and delayed negative feedback of the enzyme trypsin is capable of producing sustained oscillating concentrations of active trypsin for over 65 h. Other functions, such as amplification, analog-to-digital conversion and periodic control over equilibrium systems, are obtained by linking multiple network modules in microfluidic flow reactors. The methodology developed here provides a general framework to construct dissipative, tunable and robust (bio) chemical reaction networks.

2014

1. Threshold Sensing through a Synthetic Enzymatic Reaction-Diffusion Network

   Semenov S. N., Markvoort A. J., de Greef T. F. A. & Huck W. T. S. (2014) ANGEWANDTE CHEMIE-INTERNATIONAL EDITION. 53, 31, p. 8066-8069  Abstract

   A wet stamping method to precisely control concentrations of enzymes and inhibitors in place and time inside layered gels is reported. By combining enzymatic reactions such as autocatalysis and inhibition with spatial delivery of components through soft lithographic techniques, a biochemical reaction network capable of recognizing the spatial distribution of an enzyme was constructed. The experimental method can be used to assess fundamental principles of spatiotemporal order formation in chemical reaction networks.
2. Fluorescent hydrogels for studying Ca2+-dependent reaction-diffusion processes

   Semenov S. N., Postma S. G. J., Vialshin I. N. & Huck W. T. S. (2014) Chemical Communications. 50, 23, p. 3089-3092  Abstract

   Here, we report a convenient experimental platform to study the diffusion of Ca2+ in the presence of a Ca2+-binding protein (Calbindin D28k). This work opens up new possibilities to elucidate the physical chemistry of complex Ca2+-dependent reaction-diffusion networks that are abundant in living cells.

2013

1. Ultrasensitivity by Molecular Titration in Spatially Propagating Enzymatic Reactions

   Semenov S. N., Markvoort A. J., Gevers W. B. L., Piruska A., de Greef T. F. A. & Huck W. T. S. (2013) Biophysical Journal. 105, 4, p. 1057-1066  Abstract

   Delineating design principles of biological systems by reconstitution of purified components offers a platform to gauge the influence of critical physicochemical parameters on minimal biological systems of reduced complexity. Here we unravel the effect of strong reversible inhibitors on the spatiotemporal propagation of enzymatic reactions in a confined environment in vitro. We use micropatterned, enzyme-laden agarose gels which are stamped on polyacrylamide films containing immobilized substrates and reversible inhibitors. Quantitative fluorescence imaging combined with detailed numerical simulations of the reaction-diffusion process reveal that a shallow gradient of enzyme is converted into a steep product gradient by addition of strong inhibitors, consistent with a mathematical model of molecular titration. The results confirm that ultrasensitive and threshold effects at the molecular level can convert a graded input signal to a steep spatial response at macroscopic length scales.
2. Probing cellular heterogeneity in cytokine-secreting immune cells using droplet-based microfluidics

   Chokkalingam V., Tel J., Wimmers F., Liu X., Semenov S., Thiele J., Figdor C. G. & Huck W. T. S. (2013) Lab on a Chip. 13, 24, p. 4740-4744  Abstract

   Here, we present a platform to detect cytokine (IL-2, IFN-γ, TNF-α) secretion of single, activated T-cells in droplets over time. We use a novel droplet-based microfluidic approach to encapsulate cells in monodisperse agarose droplets together with functionalized cytokine-capture beads for subsequent binding and detection of secreted cytokines from single cells. This method allows high-throughput detection of cellular heterogeneity and maps subsets within cell populations with specific functions.

2010

1. [W(CO)(dppe)(2)] Cumulenylidene and Acetylide Complexes Accessed via Stannylated Acetylenes and Butadiynes

   Semenov S. N., Blacque O., Fox T., Venkatesan K. & Berke H. (2010) Organometallics. 29, 23, p. 6321-6328  Abstract

   The tungsten butatrienylidenes [cis-W(CO)(dppe)(2){C=C=C=C(R)(SnMe3)}] (R = SnMe3 (2) and SiMe3 (3); dppe = 1,2-bis(diphenylphosphinoethane)) were prepared from the reactions of [trans-W(CO)(N-2)(dppe)(2)] (1) and the respective butadiynes displaying a 1,4-shift of the respective SnMe3 groups along the butadiyne chains. Stannyl deprotection of 2 with NBu4F center dot 3H(2)O led to the anionic butadiyne derivative [trans-W(CO)(dppe)(2)(C CC CH)][NBu4] (10). The reaction of 1 with stannylated acetylenes gave the vinylidene derivatives [cis-W(CO)(dppe)(2){C=C(SnMe3)(R)}](R = Ph (5) or SnMe3 (6)), which lost a SnMe3 group, yielding W(I) acetylides of the type [trans-W(CO)(dppe)(2)(C CR)] (R = Ph (7), SnMe3 (8), and SiMe3 (9)). They were studied by cyclic voltammetry and EPR spectroscopy.
2. Syntheses, structures, and spectroscopy of mono- and polynuclear lanthanide complexes containing 4-acyl-pyrazolones and diphosphineoxide

   Marchetti F., Pettinari C., Pizzabiocca A., Drozdov A. A., Troyanov S. I., Zhuravlev C. O., Semenov S. N., Belousov Y. A. & Timokhin I. G. (2010) Inorganica Chimica Acta-Articles. 363, 14, p. 4038-4047  Abstract

   Lanthanide coordination compounds are important due to their unique luminescence and magnetic properties. Direct synthesis of oligo- and polymeric Ln complexes with a predicted structure is hampered due to high coordination numbers and unstable coordination polyhedra. A "building blocks" strategy for the synthesis of Ln(Q)(3)L polymers (Ln = Eu, Tb or Gd; HQ = 1-phenyl-3-methyl-4-RC(=O)pyrazol-5-one in general, in detail HQ(S), R = thienyl; HQ(CP): R = cyclopentyl; L = bis(diphenylphosphine) methane dioxide dppMO(2), bis(diphenylphosphine) ethane dioxide dppEO(2), and bis(diphenylphosphine) butane dioxide dppBO(2)) has been used: {Ln(Q)(3)} mononuclear fragments have been linked by dppXO(2) bridges when X = E or B, while monomeric molecular derivatives have been isolated with dppMO(2). Eighteen new complexes were prepared, 12 of them showing a polymeric nature and 6 being monomers. Three compounds have been structurally characterized, further confirming the hypothesized connectivity where metal centers have been found to exist in LnO(8) square antiprismatic environments. Luminescence properties have been also investigated. (C) 2010 Elsevier B.V. All rights reserved.

3. An Iron-Capped Metal-Organic Polyyne: {[Fe](C C)(2)[W] CC CC [W](C C)(2)[Fe]}

   Semenov S. N., Taghipourian S. F., Blacque O., Fox T., Venkatesan K. & Berke H. (2010) Journal of the American Chemical Society. 132, 22, p. 7584-+  Abstract

   The organometallic conjugated complex H(C C)(2)[W] CC CC [W](C C)(2)H {[W] = W(dppe)(2); dppe = 1,2-bis(diphenylphosphino)ethane} containing a ditungstenatetradecaheptayne unit was synthesized by utilizing a new and efficient coupling method. The stannylated derivative was converted to the tetranuclear complex, which exhibits efficient long-range electron transfer.
4. Electronic Communication in Dinuclear C-4-Bridged Tungsten Complexes

   Semenov S. N., Blacque O., Fox T., Venkatesan K. & Berke H. (2010) Journal of the American Chemical Society. 132, 9, p. 3115-3127  Abstract

   The dinuclear tungsten carbyne [X(CO)(2)(dppe)WC4W(dppe)(CO)(2)X] (dppe = 1,2-bis(diphenylphosphino)ethane; X = 1 (3), Cl (7)) complexes were prepared from the bisacetylide precursor Li-2[(CO)(3)(dppe)WC4W(CO)(3)(dppe)] (2) via oxidative replacement of one CO group at each tungsten center with a halide substituent. The iodide ligand in 3 could be substituted with isothiocyanate or triflate resulting in [X(CO)(2)(dppe)WC4W(dppe)(CO)(2)X] complexes (X = NCS (8), OTf (9)). Substitution of two and all four CO ligands in 3 was achieved via subsequent photolytic or thermal activation with dppe. The "half-substituted" complex [I(CO)(2)(dppe)WC4W(dppe)(2)I] (11) allows reversible one-electron oxidation which results in the monocationic species [I(CO)(2)(dppe)WC4W(dppe)(2)I][PF6] (11[PF6]). The "all-dppe substituted" complex [I(dppe)(2)WC4W(dppe)(2)I] (10) possesses two reversible redox states leading to the stable monocationic [I(dppe)(2)WC4W(dppe)(2)I][PF6] (10[PF6]) and the dicationic [I(dppe)(2)WC4W(dppe)(2)I][PF6](2) (10[PF6](2)) Compounds. The complexes 2, 3, [W(CO)(3)(dppe)(C CPh)(I)] (4), [X(CO)(2)(dppe)W C-C(Me)=C(Me)-C W(dppe)(CO)(2)X] (X = 1 (5), Cl (6)), 7, 8, 10, 11 and 11[PF6] were characterized by single crystal X-ray diffraction. The electronic properties of complexes 10, 10[PF6], 10[PF6](2), as well as of compounds 11 and 11[PF6], were investigated using cyclic voltammetry (CV), EPR, IR, near-IR spectroscopy, and magnetization measurements. These studies showed that the [W] C-C C-C [W] canonical form of the bridged system with strong tungsten-carbon interaction contributes significantly to the electronic coupling in the mixed-valent species 10[PF6] (comproportionation constant K-c 7.5 x 10(4)) and to the strong antiferromagnetic coupling in the dicationic complex 10[PF6](2) (exchange integral J = -167 cm(-1)). In addition, the rate for electron transfer between the tungsten centers in 10[PF6] was evaluated by near-IR and IR studies.

2009

1. New Helical Zinc Complexes with Schiff Base Derivatives of beta-Diketonates or beta-Keto Esters and Ethylenediamine

   Kotova O., Semenov S., Eliseeva S., Troyanov S., Lyssenko K. & Kumina N. (2009) European Journal of Inorganic Chemistry. 2009, 23, p. 3467-3474  Abstract

   The tetradentate Schiff bases H(2)L = H(2)AC [N,N'-ethylenebis(4-iminopentan-2-one)], H(2)MAL1 [N,N'-ethylene-bis(methyl-3-iminobutanoate)], and H(2)MAL(2) [N,N'-ethylenebis(tert-butyl-3-iminobutanoate)] were found to possess sufficient flexibility and were tailored to self assemble with zinc ions to form neutral bimetallic helicates with the overall composition Zn(2)L(2). In solution for all ligands, an equilibrium between the tautomeric forms exists, which was confirmed by IR and NMR spectroscopy. X-ray single-crystal analysis performed for H(2)MAL1 (1) and H(2)MAL2 (2) reveals that they have similar geometrical parameters and crystallize in a trans conformation. In the crystal structures of the zinc complexes [Zn(2)(AC)(2)]center dot C(6)H(6) (3), [Zn(2)(MAL1)(2)]center dot 0.5C(7)H(8) (4), and [Zn(2)(MAL(2))(2)]center dot C(7)H(8) (5), the Schiff base ligands are helically wrapped around the two four-coordinate metal ions, which leads to an idealized D(2) symmetry. The coordination polyhedron around the Zn ions in 3-5 can be described as a tetrahedral geometry comprising two O- and two N-donor atoms of the Schiff base ligands. The intramolecular separation Zn center dot center dot center dot Zn varies from 3.465 to 3.628 angstrom. The total length of the helix is 5.85, 5.84, and 6.01 angstrom for structures 3, 4, and 5, respectively, while the helical pitch values are in the range 7.8-9.2 angstrom. Both the ligands H(2)L and the zinc helicates are thermally stable up to similar to 150-160 degrees C, as shown by thermogravimetric analysis under a nitrogen atmosphere. The formation of the zinc complexes in solution is confirmed by spectrophotometric titrations, along with ESI-MS, and has almost no effect on the absorption spectra of H(2)L. The Schiff bases and the Zn(2)L(2) complexes display broad-band, blue emission in the range 350-600 nm under a 337-nm excitation at 77 K. Finally, the impact of electronic effects of the Schiff base substituents on the structure of the Zn complexes, especially on bond lengths within the chelate rings, and the absorption and photoluminescence spectra, are discussed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

2. Self-Coupling of a 4-H-Butatrienylidene Tungsten Complex

   Semenov S. N., Blacque O., Fox T., Venkatesan K. & Berke H. (2009) ANGEWANDTE CHEMIE-INTERNATIONAL EDITION. 48, 28, p. 5203-5206  Abstract

2008

1. First direct assembly of molecular helical complexes into a coordination polymer

   Semenov S. N., Rogachev A. Y., Eliseeva S. V., Pettinari C., Marchetti F., Drozdov A. A. & Troyanov S. I. (2008) Chemical Communications. 17, p. 1992-1994  Abstract

   Luminescent triple-stranded helicates, formed between Tb(III) ions and bis-acylpyrazolones, were directly assembled into a 1-D polymeric system.
2. Role of the Ancillary Ligand N,N'-Dimethylaminoethanol in the Sensitization of Eu(III) and Tb(III) Luminescence in Dimeric β-Diketonates

   Eliseeva S. V., Kotova O. V., Gumy F., Semenov S. N., Kessler V. G., Lepnev L. S., Bünzli\u202c J. G. & Kuzmina N. P. (2008) Biotechnology and Bioengineering. 112, 16, p. 3614-3626  Abstract

   Two types of dimeric complexes [Ln2(hfa)6(μ2-O(CH2)2NHMe2)2] and [Ln(thd)2(μ2,η2-O(CH2)2NMe2)]2 (Ln = YIII, EuIII, GdIII, TbIII, TmIII, LuIII; hfa- = hexafluoroacetylacetonato, thd- = dipivaloylmethanato) are obtained by reacting [Ln(hfa)3(H2O)2] and [Ln(thd)3], respectively, with N,N-dimethylaminoethanol in toluene and are fully characterized. X-ray single crystal analysis performed for the TbIII compounds confirms their dimeric structure. The coordination mode of N,N-dimethylaminoethanol depends on the nature of the β-diketonate. In [Tb2(hfa)6(μ2-O(CH2)2NHMe2)2], eight-coordinate TbIII ions adopt distorted square antiprismatic coordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with a Tb1···Tb2 separation of 3.684(1) Å. In [Tb(thd)2(μ2,η2-O(CH2)2NMe2)]2, the N,N-dimethylaminoethanol acts as chelating-bridging O,N-donor anion and the TbIII ions are seven-coordinate; the Tb1···Tb1A separation amounts to 3.735(2) Å within centrosymmetric dimers. The dimeric complexes are thermally stable up to 180 °C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublimation under reduced pressure. The EuIII and TbIII dimers display metal-centered luminescence, particularly [Eu2(hfa)6(O(CH2)2NHMe2)2] (quantum yield= 58%) and [Tb(thd)2(O(CH2)2NMe2)]2 (32%). Consideration of energy migration paths within the dimers, based on the study of both pure and EuIII- or TbIII-doped (0.01−0.1 mol %) LuIII analogues, leads to the conclusion that both the β-diketone and N,N-dimethylaminoethanol ligands contribute significantly to the sensitization process of the EuIII luminescence. The ancillary ligand increases considerably the luminescence of [Eu2(hfa)6(O(CH2)2NHMe2)2], compared to [Ln(hfa)3(H2O)2], through the formation of intra-ligand states while it is detrimental to TbIII luminescence in both β-diketonates. Thin films of the most luminescent compound [Eu2(hfa)6(O(CH2)2NHMe2)2] obtained by vacuum sublimation display photophysical properties analogous to those of the solid-state sample, thus opening perspectives for applications in electroluminescent devices.

2007

1. 5-Nitroaminotetrazole as a building block for extended network structures: Syntheses and crystal structures of a number of heavy metal derivatives

   Semenov S. N., Rogachev A. Y., Eliseeva S. V., Belousov Y. A., Drozdov A. A. & Troyanov S. I. (2007) Polyhedron. 26, 17, p. 4899-4907  Abstract

   The lead, mercury, copper and silver derivatives of 5-nitroaminotetrazole (5-H(2)NATZ) were obtained by the reaction between the metal nitrate and potassium 5-nitroaminotetrazolate. The lead and mercury complexes were crystallized and characterized by single crystal X-ray diffraction. The lead complex has a polymeric structure formed by (PbO2)(n) chains and anions of 5-NATZ, where each lead atom is surrounded by ten oxygen atoms. The mercury salt is constructed from neutral (Hg-NATZ)(n) chains, where the mercury atom has a linear coordination. The influence of chemical hardness and charge distribution on the reactivity and coordination properties of 5-NATZ was estimated based on density functional calculations. The thermal stability of the salts was also studied. (C) 2007 Elsevier Ltd. All rights reserved.

2006

1. Syntheses, spectroscopic characterization and X-ray structural studies of lanthanide complexes with adamantyl substituted 4-acylpyrazol-5-one

   Pettinari C., Marchetti F., Pettinari R., Natanti P., Drozdov A., Semenov S., Troyanov S. I. & Zolin V. (2006) Inorganica Chimica Acta-Articles. 359, 12, p. 4063-4070  Abstract

   Synthesis and spectroscopic characterization of new lanthanide complexes [Ln(Q(AD))(3)(EtOH)(H2O)], (Ln = Tb, Eu; HQ(AD) = 1-phenyl-3-methyl-4-adamantylcarbonyl-pyrazol-5-one), [H3O][Tb(Q(AD))(4)] [Ln(Q(AD))(3)(N-N)] (Ln = Tb, Eu; N-N = 1,10-phenanthroline (Phen), 2,2'-bipyridyl (Bipy), 4,4'-dimethyl-2,2'-bipyridyl (4,4'-Me(2)Bipy)) are reported. The crystal structures of the proligand HQ(AD) and of complexes [H3O][Tb(Q(AD))(4)] and [Tb(Q(AD))(3)(4,4'-Me(2)Bipy)] have been determined. In both complexes the lanthanide ions are in a square antiprismatic environment, the H3O+ cation in the former acid complex being stabilized by H-bonding. Luminescence studies have been performed on selected derivatives. (c) 2006 Elsevier B.V. All rights reserved.
2. A new rare-earth metal acylpyrazolonate containing the Zundel ion H5O2+ stabilized by strong hydrogen bonding

   Pettinari C., Archetti F., Pettinari R., Drozdov A., Semenov S., Troyanov S. & Zolin L. (2006) Inorganic Chemistry Communication. 9, 6, p. 634-637  Abstract

   A new luminescent europium derivative [H5O2][Eu(Q(Cy))(4)] (1) (HQ(Cy) = 1-phenyl-3-methyl-4-cyclohexanecarbonylpyrazole-5-one), achievable in high yield, characterized by high thermal stability, ionic in acetone and ethanol solution, contains the Zundel cations H5O2+ stabilized by strong hydrogen bonding with the N atoms of the anionic heterocyclic ligand (Q(Cy)). (C) 2006 Elsevier B.V. All rights reserved.

2005

1. Crystal structures of tin(IV) chloride hydrates

   Semenov S., Maltsev E., Timokhin I., Drozdov A. & Troyanov S. (2005) Mendeleev Communications. 15, 5, p. 205-207  Abstract

   As determined by single crystal X-ray crystallography, SnCl4 center dot 2H(2)O and SnCl4 center dot 3H(2)O have a molecular structure with cis-[SnCl4(H2O)(2)] units linked to each other by a system of hydrogen bonds.

2003

1. The role of reaction medium on the coordination environment of terbium in complexes with 4-acylpyrazol-5-ones

   Pettinari C., Pettinari R., Marchetti F., Drozdov A., Timokhin I. G., Semenov S. & Troyanov S. (2003) Inorganic Chemistry Communication. 6, 12, p. 1423-1425  Abstract

   [Tb(Q)(3)(H2O)] and [Tb(Q)(3)(H2O)(EtOH)] derivatives of novel 1-phenyl-3-methyl-4-R-pyrazol-5-one (HQ = HQ(CP): R = cyclopentylcarbonyl, HQ(ETCP): R = cyclopentylpropionyl) have been prepared and shown to be seven- and eight-coordinate, respectively, by IR, X-ray and elemental analyses. The role of the reaction medium on the coordination number of Tb is discussed. (C) 2003 Elsevier B.V. All rights reserved.

1. See list of publications here

   List of publications