Based on three-state renaturation process of denatured proteins, an equation describing the effect of denaturant concentration on renaturation yield of denatured proteins was presented. By this equation, two parameters n(m1 -m2) and Ka can be obtained. The former indicates the difference in the number of denaturant molecules between the renaturation process of n number of refolding intermediates from refolding intermediate state to native state and their aggregate process from refolding intermediate state to aggregate state, the latter denotes the apparent aggregate equilibrium constant for protein molecules aggregated from native state to aggregate state, and from them, the characteristics of the renaturation process of denatured proteins in denaturant solution can be identified. This equation was tested by the renaturation processes of denatured egg white lysozyme in guanidine hydrochloride and urea solutions, with the results to show that when guanidine hydrochloride and urea concentrations were separately higher than 1.25 and 3.00 mol/L or separately lower than 1.00 and 3.00 mol/L, the refolding intermediates of egg white lysozymes were more easily aggregated to aggregate state or more easily renatured to native state, respectively. Under different initial total egg white lysozyme concentrations in urea solution, the refolding egg white lysozyme intermediates could be deduced to have a tendency to form a bimolecular intermediate aggregate, and this inference was further confirmed by their nonreducing SDS-PAGE and size exclusion chromatography. 相似文献
It remains a challenge to precisely tailor the morphology of polymer monolayers to control charge transport. Herein, the effect of the dissolution temperature (Tdis) is investigated as a powerful strategy for morphology control. Low Tdis values cause extended polymer aggregation in solution and induce larger nanofibrils in a monolayer network with more pronounced π–π stacking. The field‐effect mobility of the corresponding monolayer transistors is significantly enhanced by a factor of four compared to devices obtained from high Tdis with a value approaching 1 cm2 V?1 s?1. Besides that, the solution kinetics reveal a higher growth rate of aggregates at low Tdis, and filtration experiments further confirm that the dependence of the fibril width in monolayers on Tdis is consistent with the aggregate size in solution. The generalizability of the Tdis effect on polymer aggregation is demonstrated using three other conjugated polymer systems. These results open new avenues for the precise control of polymer aggregation for high‐mobility monolayer transistors. 相似文献
The Simha and Somcynsky (S‐S) lattice‐hole theory has been shown to represent accurately the pressure‐volume‐temperature (PVT) surface of chain molecular melts and their mixtures. Proceeding beyond its original intent, it has led to correlations with other properties and extension into the steady state and relaxing glass. The equilibrium results appear as the solutions of two coupled equations, involving the variables of state and the hole fraction, h = h (V, T) – a kind of free volume quantity. These are to be solved numerically. Notwithstanding the theory's quantitative success, its implicit form has on some occasions been a practical limitation. We remedy this situation by fitting the scaled and thus general solutions of the coupled equations to accurate algebraic equations, V = V (T, P) and h = hV, T). In this manner, explicit analytical expressions for configurational thermodynamic functions and their derivatives are now available. The new expressions for V and h are simple to employ; the convergence of the non‐linear least‐squares fit is obtained in seconds. The numerical values of the scaling parameters so derived are nearly identical to those computed from the original coupled equations. Having h and V from the original theory, the cohesive energy density [CED = δ2V, T)] was also considered. The results are again well represented by a simple algebraic expression. An expression for the reduced solubility parameter δ = δ (T, P) is also given. The usefulness of these solutions is further illustrated by an application to the PVT surfaces of polystyrene and polyphenylene ether blends. 相似文献
We studied the thermodynamic stability of a small monomeric protein, staphylococcal nuclease (Snase), as a function of both temperature and pressure, and expressed it as a 3D free‐energy surface on the p,T‐plane using a second‐order Taylor expansion of the Gibbs free‐energy change ΔG upon unfolding. We took advantage of a series of different techniques (small‐angle Xray scattering, Fourier‐transform infrared spectroscopy, differential thermal analysis, pressure perturbation calorimetry and densitometry) in the evaluation of the conformation of the protein and in evaluating the changes in the thermodynamic parameters upon unfolding, such as the heat capacity, enthalpy, entropy, volume, isothermal compressibility and expansivity. The calculated results of the free‐energy landscape of the protein are in good agreement with experimental data of the p,T‐stability diagram of the protein over a temperature range from 200 to 400 K and at pressures from ambient pressure to 4000 bar. The results demonstrate that combined temperature–pressure‐dependent studies can help delineate the free‐energy landscape of proteins and hence help elucidate which features and thermodynamic parameters are essential in determining the stability of the native conformational state of proteins. The approach presented may also be used for studying other systems with so‐called re‐entrant or Tamman loop‐shaped phase diagrams.相似文献
Four chiral 1,2‐diaminocyclohexane (DACH)‐based molecules (R,R/S,S‐ 2 and R,R/S,S‐ 4 ) incorporating 1,8‐naphthalimide fluorophores exhibit strong circularly polarized luminescence (CPL) emission signals in common organic solvents. Interestingly, the reversed CPL signals can be observed in the aggregated state, which is due to the orderly aggregation. 相似文献
A new glycine‐based reversible phase transition compound diglycine methanesulfonate ( 1 ) has been successfully synthesized. Differential scanning calorimetry (DSC) measurements of 1 showed a pair of broad peaks around 134 K (Tc=phase transition temperature) with a slight thermal hysteresis during the heating/cooling cycle, thereby indicating that this compound undergoes a reversible second‐order phase transition. Dielectric measurements further confirmed the phase transition and revealed a switchable response to the ambient temperature change for the dielectric constants of 1 , namely, the dielectric constants have a distinctive step‐like anomaly switching between a high dielectric state in the room temperature phase (RTP) and a low state in the low temperature phase (LTP). Variable‐temperature single‐crystal X‐ray diffraction analyses show that 1 undergoes an atypical transition from the space group P21/m in the RTP to P21/c in the LTP. The origin of the switchable dielectric phase transition is ascribed to the movement of the moieties in 1 from the equilibrium position, and this stems from the twisting of the molecules in the compound. We believe that these findings will be useful in exploring switchable dielectric phase transition materials. 相似文献
The effects of pressure on the temperature-induced coacervation of copoly( N-vinylformamide–vinylacetate) and copoly( N-vinylacetylamide–vinylacetate) in aqueous solution were investigated by measuring the apparent light scattering, and the effects of the concentrations of polymer and inert salt were also studied. At lower pressures, the apparent temperature of transition, Tc, increased with an increase in the pressure, but further increases in pressure decreased Tc. In contrast, the apparent pressure of transition, Pc, monotonously increased with decreasing fixed temperature. The T– P diagram was elliptical, but the curvature was not large and extrema were not observed in the low-temperature and high-pressure range. Anions with low lyotropic numbers induced an almost linear decrease in the Tc and Pc, whereas anions with a high number increased the Tc and Pc. In both polymers, the Tc and Pc depended on the concentrations of the polymers, reflecting the association/aggregation mechanism of coacervation. This is in contrast to typical thermoresponsive polymers such as poly( N-isopropylacrylamide) and poly( N-vinylisobutyramide), which show the coil-collapse transition as a single molecular event. 相似文献
The ability of positively charged aggregates of the surfactant (1R ,2S )‐dodecyl(2‐hydroxy‐1‐methyl‐2‐phenylethyl)dimethylammonium bromide (DMEB) to incorporate D‐tryptophan or L‐tryptophan in the gas phase has been investigated by electrospray ion mobility mass spectrometry (ESI‐IM‐MS). Strongly impacted by the pH of the electrosprayed solutions, both protonated (T+) and deprotonated (T−) tryptophan are effectively included into the aggregates, whereas, tryptophan in zwitterionic (T0) form is practically absent in singly charged DMEB aggregates but can be found in multiply charged ones. The ability to incorporate tryptophan increases with the aggregation number and charge state of aggregates. More than 1 tryptophan species can be entrapped (aggregates including up to 5 tryptophan are observed). Collision induced dissociation experiments performed on the positively singly charged DMEB hexamer containing 1 T− show that at low collision energies the loss of a DMEB molecule is preferred with respect to the loss of the DMEB cation plus T− species which, in turn, is preferred with respect to the loss of mere tryptophan, suggesting that the deprotonated amino acid is preferentially located in proximity of a DMEB head group and with the ionic moiety pointing towards the core of the aggregate. The analysis of the collision cross sections (CCS) of bare and tryptophan containing aggregates allowed evaluating the contributions of tryptophan and bromide ions to the total aggregate CCS. No significant discrimination between D‐tryptophan and L‐tryptophan by the chiral DMEB aggregates has been evidenced by mass spectra data, CID experiments, and CCS values. 相似文献
The rubber elastic behaviors of long polymethylene (PM) chains are investigated using Monte Carlo simulations and considering the rotational‐isomeric‐state model. Through the Monte Carlo method we can generate many PM chains in the equilibrium states, and obtain the average Helmholtz free energy 〈A〉 and average energy 〈U〉. Chain dimensions and thermodynamic statistical properties of long PM chains under various elongation ratios λ are also calculated. We find that the elastic force f increases with elongation ratio λ, and that energy contribution fu to the elastic force is negative and significant. The ratio fu /f ranges from –0.37 to –0.32 at T = 300 K and from –0.53 to –0.40 at T = 413 K, and decreases with increasing temperature, which agrees with the experimental data. Our calculations may provide some insights into the macroscopic phenomena of rubber elasticity. 相似文献
It remains a challenge to precisely tailor the morphology of polymer monolayers to control charge transport. Herein, the effect of the dissolution temperature (Tdis) is investigated as a powerful strategy for morphology control. Low Tdis values cause extended polymer aggregation in solution and induce larger nanofibrils in a monolayer network with more pronounced π–π stacking. The field-effect mobility of the corresponding monolayer transistors is significantly enhanced by a factor of four compared to devices obtained from high Tdis with a value approaching 1 cm2 V−1 s−1. Besides that, the solution kinetics reveal a higher growth rate of aggregates at low Tdis, and filtration experiments further confirm that the dependence of the fibril width in monolayers on Tdis is consistent with the aggregate size in solution. The generalizability of the Tdis effect on polymer aggregation is demonstrated using three other conjugated polymer systems. These results open new avenues for the precise control of polymer aggregation for high-mobility monolayer transistors. 相似文献
Summary: In a low‐molecular‐weight polyethylene‐block‐poly(ethylene oxide) (PE‐b‐PEO) diblock copolymer, two pathway‐dependent melting processes were observed: Upon slow heating, the PE lamellar crystals melted at ≈97 °C into a disordered state. However, when the temperature rapidly jumped to above the melting point (e.g., 100 °C), the PE lamellar crystals transformed directly into an ordered lamellar melt, followed by an isothermal conversion into a disordered melt. This isothermal order‐to‐disorder transition was explained by superheating of the PE crystals using a G‐T diagram.
A schematic G‐T diagram explaining the pathway‐dependent double melting for a crystalline polyethylene‐block‐poly(ethylene oxide) copolymer. 相似文献
A N‐2‐phenylethyl‐substituted 1,4‐dihydropyridine derivative (NDHP) containing 5,5‐dimethylcyclohexane‐1,3‐dione and naphthylethylene was designed and synthesized. NDHP acts as a multifunctional fluorescent sensor in dual phases. The crystal structure analysis confirms that the NDHP molecules have highly twisted conformations. The twisted conformation results in aggregation‐induced emission properties and solid‐state emission, by restricting the intramolecular free rotation in the aggregated or solid state. In the solid state, NDHP exhibits reversible mechanochromic properties as a result of the transition between the amorphous and crystalline states. NDHP also exhibits a rare phenomenon of acid‐fumed solid‐state emission enhancement owing to the change in packing mode from a zigzag arrangement to J‐aggregation. The solid‐state stimuli‐responsive fluorescence switching is applied to realize a rewritable optical recording media and a multiple output combinational logic system. In solution, NDHP shows a selective fluorescence response for environmentally harmful Hg2+, with a limit of detection of 2.7 nm . This results from the “turn‐on” responsive behavior owing to the Hg2+‐triggered aggregation of the NDHP molecules. NDHP is also used in the imaging of intracellular Hg2+ in HeLa cells. These findings provide a feasible and attractive route for developing multifunctional fluorescent sensors for use in dual phases. 相似文献
In this work we present experimental results of P, T, x, y, for the vapor–liquid equilibrium of the ternary system: nitrogen in an equimolar hexane+decane mixture at 258, 273, and 298 K in the range 1.5–20 MPa. The solubility of nitrogen in the liquid mixture of hexane+decane is increased when the pressure is increased; however, a considerable change in the solubility values is not observed as a function of temperature in the range studied. We have correlated the experimental results using the Peng–Robinson equation of state. The standard deviation of the fit shows that the data are well correlated (within the experimental error) in the ranges of pressure and temperature studied. 相似文献
Fluorine substitutions on the furanose ring of nucleosides are known to strongly influence the conformational properties of oligonucleotides. In order to assess the effect of fluorine on the conformation of 3′‐deoxy‐3′‐fluoro‐5‐methyluridine (RTF), C10H13FN2O5, we studied its stereochemistry in the crystalline state using X‐ray crystallography. The compound crystallizes in the chiral orthorhombic space group P212121 and contains two symmetry‐independent molecules (A and B) in the asymmetric unit. The furanose ring in molecules A and B adopts conformations between envelope (2E, 2′‐endo, P = 162°) and twisted (2T3, 2′‐endo and 3′exo, P = 180°), with pseudorotation phase angles (P) of 164.3 and 170.2°, respectively. The maximum puckering amplitudes, νmax, for molecules A and B are 38.8 and 36.1°, respectively. In contrast, for 5‐methyluridine (RTOH), the value of P is 21.2°, which is between the 3E (3′‐endo, P = 18.0°) and 3T4 (3′‐endo and 4′‐exo, P = 36°) conformations. The value of νmax for RTOH is 41.29°. Molecules A and B of RTF generate respective helical assemblies across the crystallographic 21‐screw axis through classical N—H…O aand O—H…O hydrogen bonds supplemented by C—H…O contacts. Adjacent parallel helices of both molecules are linked to each other via O—H…O and O…π interactions. 相似文献