Inmaculada Peral

Protein and solvent dynamics: How strongly are they coupled?

Analysis of Raman and neutron scattering spectra of lysozyme demonstrates that the protein dynamics follow the dynamics of the solvents glycerol and trehalose over the entire temperature range measured 100-350 K. The proteins fast conformational fluctuations and low-frequency vibrations and their temperature variations are very sensitive to behavior of the solvents. Our results give insight into previous counterintuitive observations that protein relaxation is stronger in solid trehalose than in liquid glycerol. They also provide insight into the effectiveness of glycerol as a biological cryopreservant.

A comparison of united atom, explicit atom, and coarse-grained simulation models for poly(ethylene oxide).

We compare static and dynamic properties obtained from three levels of modeling for molecular dynamics simulation of poly(ethylene oxide) (PEO). Neutron scattering data are used as a test of each models accuracy. The three simulation models are an explicit atom (EA) model (all the hydrogens are taken into account explicitly), a united atom (UA) model (CH(2) and CH(3) groups are considered as a single unit), and a coarse-grained (CG) model (six united atoms are taken as one bead). All three models accurately describe the PEO static structure factor as measured by neutron diffraction. Dynamics are assessed by comparison to neutron time of flight data, which follow self-motion of protons. Hydrogen atom motion from the EA model and carbon/oxygen atom motion from the UA model closely follow the experimental hydrogen motion, while hydrogen atoms reinserted in the UA model are too fast. The EA and UA models provide a good description of the orientation properties of C-H vectors measured by nuclear magnetic resonance experiments. Although dynamic observables in the CG model are in excellent agreement with their united atom counterparts, they cannot be compared to neutron data because the time after which the CG model is valid is greater than the neutron decay times.

Amorphization Induced by Pressure: Results for Zeolites and General Implications

We report an ab initio study of pressure-induced amorphization (PIA) in zeolites, which are model systems for this phenomenon. We confirm the occurrence of recently reported low-density amorphous phases that preserve the crystalline topology, and explain the role of the zeolite composition regarding PIA. Our results support the correctness of existing models for the basic PIA mechanism, but suggest that energetic, rather than kinetic, factors determine the irreversibility of the transition.

Structure and Dynamics of Propylene Oxide and Trimethylene Oxide Clathrate Hydrates

We present results from studies of the structure and dynamics of clathrate hydrates of three cyclic ethers by neutron diffraction and preliminary results on molecular dynamics simulations. Recent results from neutron powder diffraction and quasielastic neutron scattering of studies of propylene oxide (PO, C 3 H 6 O) and its isomer trimethyelene oxide (TMO, C 3 H 6 O), are compared with structural results obtained previously for tetrahydrofuran (THF, C 3 H 5 O). Experimental evidence of distortions of the host structures with temperature is discussed in light of the findings from quasielastic neutron scattering, which indicate distinct regions of high-temperature and low-temperature rotational dynamics and a temperature dependence related to the size of the guest. Preliminary MD results indicate a general expansion of the lattice with temperature resulting in increased volume available to PO.