לוח שנה משולב

Dynamic Nuclear Polarization (DNP) is the most widespread and ubiquitous technique for signal enhancement in Nuclear Magnetic Resonance (NMR). The gain in signal intensity is achieved by polarization transfer from the highly-polarized electron spins to the nuclear spins of interest. The home-build DNP/EPR spectrometer in the laboratory of Prof. Songi Han at UCSB allowed for the first time direct observation of the electron spin dynamics in the course of DNP experiment at NMR-relevant magnetic field (≥ 7 Tesla); measurement of electron relaxation times T1 and T2 and electron-electron spin diffusion rate by Electron-Electron DOuble resonance (ELDOR) under DNP conditions. I will present how the addition of 200 GHz arbitrary pulse shaping extended the ability to manipulate the electron spins in both EPR and DNP experiments. Specifically, up to a factor of five improvement in DNP performance was observed when a train of chirp pulses (chirp-DNP) was substituted for conventional, continuous wave microwave irradiation. The combination of shaped-pulse ELDOR together with DNP profile lineshape analysis allowed us to conclude that the gain in performance in chirp-DNP is due to recruitment of additional electron spins that participate in DNP via cross effect (CE) mechanism as opposed to the indirect CE (iCE) mechanism that dominates in the conventional CW DNP experiments under similar conditions.
In addition to serving as the source of the polarization, the electron spins can have other, sometimes detrimental, effects on the NMR spectra such as shifting the position of the peaks (Paramagnetic Shift) and decreasing resolution by linewidth increase (Paramagnetic relaxation) collectively known as paramagnetic effects (PE). We have recently observed the reversal of PE upon microwave irradiation in DNP experiments at liquid helium temperatures. WE suggest that the the origin of the observed effect stems from the REversal of PRE by electron Spin SaturatION (REPRESSION) effect which was traced to the shortening of the electron phase memory time, Tm, with electron spin bath saturation by microwave irradiation.

Much of our understanding of the biological mechanisms that underlie cellular functions, such as migration, differentiation and force sensing has been garnered from studying cells cultured on two-dimensional (2D) substrates. In the recent years there has been intense interest and effort to understand cell mechanics in three-dimensional (3D) cultures, which more closely resemble the in vivo microenvironment. However, a major challenge unique to 3D settings is the dynamic feedback between cells and their surroundings. In many 3D matrices, cells remodel and reorient local extracellular microenvironment, which in turn alters the active mechanics and in many cases, the cell phenotype. Most models for matrices to date do not account for such positive feedback. Such models, validated by experiments, can provide a quantitative framework to study how injury related factors (in pathological conditions such as fibrosis and cancer metastasis) alter extracellular matrix (ECM) mechanics. They can also be used to analyze tissue morphology in complex 3D environments such as during morphogenesis and organogenesis, and guide such processes in engineered 3D tissues. In this talk, I will present discrete network simulations to study how cells remodel matrices and how this remodeling can lead to force transmission over large distances in cells. I will also discuss an active tissue model to quantitatively study the influence of mechanical constraints and matrix stiffness on contractility and stability of micropatterned tissues.