Microscopic mechanism for cold denaturation

We elucidate the mechanism of cold denaturation through constant-pressure simulations for a model of hydrophobic molecules in an explicit solvent. We find that the temperature dependence of the hydrophobic effect induces, facilitates, and is the driving force for cold denaturation. The physical mechanism underlying this phenomenon is identified as the destabilization of hydrophobic contact in favor of solvent-separated configurations, the same mechanism seen in pressure-induced denaturation. A phenomenological explanation proposed for the mechanism is suggested as being responsible for cold denaturation in real proteins.     

Test of cold denaturation mechanism for proteins as a function of water's structure

At low temperatures and high pressures (ranging from approximately 200 up to 700 MPa), some proteins become thermodynamically unstable by means of a phenomenon know as cold denaturation. A microscopic understanding of the mechanisms leading to cold denaturation is very difficult to develop, due in part to the complexity of the protein–solvent interactions. A possible proposal to explain the cold denaturation of proteins based on a relation between hydrophobicity and the loss of the local low-density water structure at high pressures is explained in detail. In the present paper, this mechanism is tested for the first time by means of full atom numerical simulations. In good agreement with the proposal, cold denaturation resulting in the unfolded state has been found at the high-density liquid (HDL) state of water, at which the amount of open tetragonal hydrogen bonds decreases at cooling.     

液态簧振动力学谱在蛋白质水凝胶脱水变性过程的应用研究

本文用液态簧振动力学谱(RMS-L)方法, 对典型蛋白质水凝胶鸡蛋清的脱水变性过程进行了测量, 结果表明, 随水含量的减少, 鸡蛋清至少存在4个力学谱的显著变化过程. 基于此结果并结合力学谱的理论分析, 作者推测, 随水含量的减少, 鸡蛋清可能依次存在下述4个状态: 1) 类体水(bulk-likewater) 的蛋白质水凝胶态; 2) 键合水 (bond water) 的蛋白质水凝胶态; 3) 键合水和键合蛋白质(bonding protein) 的混合态; 4) 键合蛋白质态. 而蛋白质的空间构型(spatial configuration)转变即变性, 主要发生在拥有键合水的蛋白质通过失水向键合蛋白质转变的混合态. 这表明RMS-L对鸡蛋清脱水变性过程的检测是有效的, 所得结果对蛋白质变性机理、以及蛋白质水凝胶态的深入研究也应具有参考价值. 关键词： 力学谱 蛋白质水凝胶 蛋白质变性     

MOLECULAR MORPHOLOGY AND CRYSTALLIZATION IN THE QUANTUM LIMIT

The effects of phonons on crystallization and crystal morphology are investigated. It is shown that the commensuration of the lattice vibrations with the lattice will favor certain crystal morphologies. Vibrational effects can also be important for the molecular structure of chain molecules. In this case, the contribution from quantum mode forces to denaturation is estimated by using a simple phenomenological model describing the molecule as a continuum. The frequencies of the vibrational modes depend on the molecular dimensionality; hence, the zero-point energies for the folded and the denatured protein are estimated to differ by several electron volts. For a biomolecule, such energy is significant and may contribute to cold denaturing as seen for proteins. This is consistent with the empirical observation that cold denaturation is exothermic and hot denaturation endothermic.     

A Nuclear Magnetic Resonance study of the reversible denaturation of hydrated lysozyme

The understanding of the physical processes that occur below the threshold of protein thermal denaturation is of fundamental importance. In this thermal region proteins undergo a reversible folding/unfolding process whose evolution depends upon temperature and time. When the kinetics of the folding is altered, the specific biological activity of the protein is altered as well and aggregation phenomena usually intervene. The most important role in driving these processes is played by the solvent and water is certainly the solvent par excellence. It is well known that proteins become biologically active with no less than a water monolayer covering their surface. The knowledge of the physical properties of this monolayer is of basic importance to prevent folding alterations. We present a proton Nuclear Magnetic Resonance study at very high resolution of the thermodynamic properties of lysozyme hydration water as a function of temperature and time in the thermal region of the reversible denaturation.     

生物药品液氮辅助冻干机的设计与分析

随着生物技术的高速发展,多肽蛋白质类药物不断涌现,可应用于临床的多肽、蛋白酶、激素、疫苗、细胞生长因子等成为开发重点.为防止药品变性,目前广泛采用冷冻干燥法制备成固态药品.液氮冻干机,以液氮作为冷源,采用直接膨胀相变制冷的方式,解决了常规压缩机制冷的冻干机存在降温速率较慢、冷阱极限温度不够低等问题;同时也弥补了由于随着...     

Effects of thermal denaturation on the longitudinal relaxation time (T1) of water protons in protein solutions: study of the factors determining the T1 of water protons

The factors determining the longitudinal relaxation time (T1) of water protons in protein solutions were investigated by analyzing the effects of thermal denaturation on the T1 of the water protons. We treated the water protons and the protein protons "on a protein surface" as a dipole-dipole coupled two-spin system where relative translational diffusion is the dominant mechanism, and measured the change in the time development of the nuclear Overhauser effect (NOE) factors of the water protons. The T1 of the water protons was shortened markedly when the proteins were thermally denatured. Our analysis indicates that this relaxation enhancement is due to an increase in the value of the translational correlation time as well as the fraction of hydration water molecules, though the influence of "proton exchange" between the water protons and the labile protein protons cannot be completely neglected.     

Time-Resolved Fluorescence Studies on Bovine Serum Albumin Denaturation Process

The denaturation of Bovine Serum Albumin (BSA) by a chaotropic agent, guanidinium hydrochloride (GuH+Cl-) was studied by fluorescence lifetime analysis. The BSA was labelled with 1-anilino-8-naphthalene sulfonate (ANS) at two different molar ratios (1:1) and (1:10). The non-exponential fluorescence kinetics of the BSA-ANS complex at different stages of denaturation is analysed using three different models: a discrete tri-exponential sum, stretched exponential, and Gaussian lifetime distribution. In all cases, the fluorescence decay times decreased with protein denaturation. The results from the models show that there are at least two different binding sites located in the BSA protein with different water accessibility.     

Denaturation transition of stretched DNA

We generalize the Poland-Scheraga model to consider DNA denaturation in the presence of an external stretching force. We demonstrate the existence of a force-induced DNA denaturation transition and obtain the temperature-force phase diagram. The transition is determined by the loop exponent c, for which we find the new value c = 4 nu-1/2 such that the transition is second order with c = 1.85 < 2 in d = 3. We show that a finite stretching force F destabilizes DNA, corresponding to a lower melting temperature T(F), in agreement with single-molecule DNA stretching experiments.     

Fluctuations in order–disorder transitions in the DNA–ligand complexes with various binding mechanisms

The melting of the DNA–ligand complex is considered theoretically for the ligands binding with the DNA by two mechanisms. The obtained results describe the experimentally observed behavior of such quantities as the denaturation degree and the correlation length depending on the concentration of ligands. It is shown that the heat and cold denaturations of the DNA–ligand complexes exhibit the same cooperativity, as the heat denaturation of the pure DNA. At the same time, the temperature range of the cold denaturation is essentially narrower than the interval for the heat denaturation of the pure DNA and the DNA–ligand complexes.     

New results on the melting thermodynamics of a circular DNA chain

We investigate the impact of supercoil period and nonzero supercoil formation energy on the thermal denaturation of a circular DNA. Our analysis is based on a recently proposed generalization of the Poland-Scheraga model that allows the DNA melting to be studied for plasmids with circular topology, where denaturation is accompanied by formation of supercoils. We find that the previously obtained first-order melting transition persists under the generalization discussed. The dependence of the size of the order-parameter jump at the transition point and the associated melting temperature are obtained analytically.     

New ultrasonic assisted technology of freezing,cooling and thawing in solid food processing: A review

Solid foods include fish, shrimp, shellfish, and other aquatic products, fruits, and vegetables. These products are commonly used for food freezing, cooling, and thawing. However, traditional freezing, cooling, and thawing of solid food technologies have limitations in quality, such as protein denaturation and water loss in food. Ultrasound-assisted technology has become a useful method in solid food processing due to improved preservation quality of solid food. This paper comprehensively reviews the mechanism and application of ultrasonic in solid food processing technology. Although the application of ultrasound-assisted ultrasound in solid food processing is relatively comprehensive, the energy saving of food cold processing is essential for practical application. This paper analyzes the optimization of ultrasonic in solid food processing, including orthogonal/multi-frequency technology and the combination of ultrasonic and other technologies, which provides new ideas for freezing, cooling, and thawing of solid food processing.     

A Euclidean perspective on the unfolding of azurin: spatial correlations

We investigate the stability to structural perturbation of Pseudomonas aeruginosa azurin using a previously developed geometric model. Our analysis considers Ru(2,2′,6′,2^″-terpyridine)(1,10-phenanthroline)(His83)-labelled wild-type azurin and five variants with mutations to Cu-ligating residues. We find that in the early stages of unfolding, the β-strands exhibit the most structural stability. The conserved residues comprising the hydrophobic core are dislocated only after nearly complete unfolding of the β-barrel. Attachment of the Ru-complex at His83 does not destabilize the protein fold, despite causing some degree of structural rearrangement. Replacing the Cys112 and/or Met121 Cu ligands does not affect the conformational integrity of the protein. Notably, these results are in accord with experimental evidence, as well as molecular dynamics simulations of the denaturation of azurin.     

The effect of temperature and viscoelasticity on cavitation dynamics during ultrasonic ablation

Inertial cavitation has been shown to enhance heating rates during high intensity focused ultrasound treatments. Cavitation dynamics will be affected by heating and by the changes in mechanical properties of tissue resultant from thermal denaturation; however, the nature of the change is not known and forms the focus of the current study. A Keller-Miksis equation is used to find the variation in inertial cavitation threshold with temperature in water and, when coupled with a Kelvin-Voigt viscoelastic model, in biological tissue. Simulated thermal ablation treatments in liver and muscle are used to explore the changes in cavitation dynamics, and the resultant frequency spectra of secondary acoustic emissions, due to tissue denaturation. Results indicate that viscosity is the key parameter controlling cavitation dynamics in biological tissues. The increase in viscosity during denaturation is predicted to increase inertial cavitation thresholds, leading to a substantial decrease in the higher harmonic content of the emitted pressure signal across a wide range of bubble radii. Experimental validation of these observations could offer improved methods to monitor therapeutic ultrasound treatments.     

Dynamical changes in hydration water accompanying lysozyme thermal denaturation

We study the dynamics of the first hydration shell of lysozyme to determine the role of hydration water that accompanies lysozyme thermal denaturation. We use nuclear magnetic resonance spectroscopy to investigate both the translational and rotational contributions. Data on proton self-diffusion and reorentational correlation time indicate that the kinetics of the lysozyme folding/unfolding process is controlled by the dynamics of the water molecules in the first hydration shell. When the hydration water dynamics change, because of the weakening of the hydrogen bond network, the three-dimensional structure of the lysozyme is lost and denaturation is triggered. Our data indicates that at temperatures above approximately 315 K, water behaves as a simple liquid and is no longer a good solvent.     

在高压诱导蛋白质变性过程中水产生的压缩对它的影响

实验表明水的压缩系数随着压强的改变会发生变化,这种改变将对高压致蛋白质变性的充分含水动力学模拟结果产生直接影响,然而很多高压变性的分子动力学模拟并没有考虑这一点.在温度为300 K,压强为200 MPa、1000 MPa时,利用GROMACS软件包对两种小蛋白Chignolin和Trpcage进行了总计300ns的分子动力学模拟,模拟中考虑了水的压缩系数随压强的改变情况,然后将模拟结果与压缩系数维持在O.1 MPa时的情况进行了比较.结果发现,压缩系数对蛋白质高压变性的影响很大,依据实验数据对不同压强的压缩系数进行调整后,小蛋白Chignolin在高压变性中出现完全去折叠.这为分子动力学模拟研究蛋白质高压变性提供了正确的途径和理论依据.     

双热源空调-热水器一体机冬季制热的实验研究

冬季室外温度低时,空气源热泵系统的蒸发器会结霜,使系统COP降低。所设计的空调-热水器一体机可以制冷、制热、一年四季提供生活用热水。冬季室外温度低时,用太阳能加热后的水作为热泵的低温热源,可以提高热泵的效率。分别用空气源蒸发器和水源蒸发器独立工作使系统给房间制热,实验结果发现水源蒸发器工作时系统的COP平均值为3.56,空气源蒸发器工作时的COP平均值为2.51。     

Improving NMR sensitivity in room temperature and cooled probes with dipolar ions

The response of inverse triple resonance cold and conventional probes to ionic strength has been compared under a variety of conditions relevant to protein NMR. Increasing the salt concentration degrades probe performance in terms of sensitivity, and the effect is more severe for cold probes and with increasing magnetic field strength. This is especially noticeable for experiments that involve a spin lock or decoupling, where sensitivity losses compared with pure water can be more than 2-fold. We have investigated the use of glycine as a substitute for salt as a supporting solute for proteins, and we show that it has a minimal effect on probe tuning or performance. Readily available d5-Gly is a useful co-solute for protein NMR, especially at high magnetic field strengths and on cold probes, as it maintains solubility while not degrading probe performance.     

冷聚变的全原子论

早在1989年我首先就以原子分子物理和晶体物理为基础,提出了一个冷聚变机理的初步理论.按照此理论,在晶体中两个氘核可以实现冷聚变,产生超热和聚变产物~4He.在此理论提出后,我们在实验研究中观测到以Pd或Ti为阴极电解重水过程中产生的明显的超热效应与聚变产物~4He.这表明我们提出的理论预言是正确的.但在过去长时间里,仍有很多学者对冷聚变产生的机理一直很不理解.为了对冷聚变机理有一个更清楚的解释,使其易于被理解和接受,我们在过去的20年中进行了反复深入的理论与实验研究.经过进一步深入分析,我们发现晶体中的冷聚变实际上是两个氘原子以全原子状态相互作用而产生的.因此提出了冷聚变的全原子论,并在本文中详细阐述.按照此理论进行分析,发现我们还可以用冷聚变的办法,得到~3He产物.这是很重要的发现,因为我们可以在地面上人造出核能原料~3He,就不一定要跑到月球上面去开采~3He了.     

荧光光谱法研究蛋白质构象的电磁-温度协同效应

长期以来电磁生物效应受到人们普遍关注，近年来从各个角度进行了相关研究。电磁－温度协同效应是当前的热点。本研究通过电磁场及温度协同对蛋白质影响的研究，发现蛋白质在电磁场作用下的不可逆变性，而且这种变性也遵循Arrhenius规律，并进一步得出电磁－温度协同作用的蛋白质变性模型。本文从分子反应动力学的角度解释了电磁－温度协同效应，并对非热效应作了一定的探讨。