arXiv subjects

Xiang-qiang Chu

Publications and source records attributed to Xiang-qiang Chu.

4 recordsLinked to original sources

arXiv2016

Effect of Nanodiamond surfaces on Drug Delivery Systems

The prospect of RNA nanotechnology is increasing because of its numerous potential applications especially in medical science. The spherical Nanodiamonds (NDs) are becoming popular because of their lesser toxicity, desirable mechanical, optical properties, functionality and available surface areas. On other hand RNAs are stable, flexible and easy to bind to the NDs. In this work, we have studied the tRNA dynamics on ND surface by high-resolution quasi-elastic neutron scattering spectroscopy and all atom molecular dynamics simulation technique to understand how the tRNA motion is affected by the presence of ND. The flexibly of the tRNA is analyzed by the Mean square displacement analysis that shows tRNA have a sharp increase around 230K in its hydrated form. The intermediate scattering function (ISF) representing the tRNA dynamics follows the logarithmic decay as proposed by the Mode Coupling theory (MCT). But most importantly the tRNA dynamics is found to be faster in presence of ND within 220K to 310K compared to the freestanding ones. This is as we have shown, is because of the swollen RNA molecule due the introduction of hydrophilic ND surface.

physics.bio-ph↗

arXiv2008

Pressure Effects in Supercooled Water: Comparison between a 2D Model of Water and Experiments for Surface Water on a Protein

Experiments in bulk water confirm the existence of two local arrangements of water molecules with different densities, but, because of inevitable freezing at low temperature $T$, can not ascertain whether the two arrangements separate in two phases. To avoid the freezing, new experiments measure the dynamics of water at low $T$ on the surface of proteins, finding a crossover from a non-Arrhenius regime at high $T$ to a regime that is approximately Arrhenius at low $T$. Motivated by these experiments, Kumar et al. [Phys. Rev. Lett. 100, 105701 (2008)] investigated, by Monte Carlo simulations and mean field calculations, the relation of the dynamic crossover with the coexistence of two liquid phases in a cell model for water and predict that: (i) the dynamic crossover is isochronic, i.e. the value of the crossover time $τ_{\rm L}$ is approximately independent of pressure $P$; (ii) the Arrhenius activation energy $E_{\rm A}(P)$ of the low-$T$ regime decreases upon increasing $P$; (iii) the temperature $T^*(P)$ at which $τ$ reaches a fixed macroscopic time $τ^*\geq τ_{\rm L}$ decreases upon increasing $P$; in particular, this is true also for the crossover temperature $T_{\rm L}(P)$ at which $τ=τ_{\rm L}$. Here, we compare these predictions with recent quasi elastic neutron scattering (QENS) experiments performed by X.-Q. Chu {\it et al.} on hydrated proteins at different values of $P$. We find that the experiments are consistent with these three predictions.

cond-mat.soft↗

arXiv2008

Pressure Dependence of the Dynamic Crossover Temperatures in Protein and its Hydration Water

Recently we have shown experimental evidence for a fragile-to-strong dynamic crossover (FSC) phenomenon in hydration water around a globular protein (lysozyme) at ambient pressure. In this letter we show that when applying pressure to the protein-water system, the FSC crossover temperatures in hydration water of lysozyme tracks the similar Widom line emanating from the existence of a liquid-liquid critical point in a 1-D confined water (in MCM-41-S). The mean squared displacements (MSD) of hydrogen atoms in lysozyme and in its hydration water show a sudden change of slopes at the same characteristic temperature, which decreases with an increasing pressure. These results taken together give support of the idea that the dynamic crossover (or so-called glass transition) of the protein is a function of both temperature and pressure, following the FSC of its hydration water.

physics.bio-ph↗

arXiv2007

Observation of a Dynamic Crossover in RNA Hydration Water which Triggers the Glass Transition in the Biopolymer

High-resolution quasi-elastic neutron scattering spectroscopy was used to measure H2O and D2O hydrated RNA samples. The contribution of scattering from RNA was subtracted out by taking the difference of the signals between the two samples. The measurements were made at a series of temperatures from 270 K down to 180 K. The Relaxing-Cage Model was used to analyze the difference quasi-elastic spectra. We observed clear evidence of a fragile-to-strong dynamic crossover (FSC) at TL = 220 K in RNA hydration water. We further show that the mean-square displacement of the hydrogen atoms in both RNA and its hydration water exhibit a sharp change in slope at approximately the same temperature 220 K. This latter fact suggests that the dynamic transition (or the glass transition) in RNA is triggered by the abrupt change of mobility of the hydration water at its FSC temperature TL.

physics.bio-ph↗