Kinetics investigation of the hydrogen abstraction reaction between CH<Subscript>3</Subscript>SS and CN radicals

The reaction mechanisms and rates for the H abstraction reactions between CH₃SS and CN radicals in the gas phase were investigated with density functional theory (DFT) methods. The geometries, harmonic vibrational frequencies, and energies of all stationary points were obtained at B3PW91/6-311G(d,p) level of theory. Relationships between the reactants, intermediates, transition states and products were confirmed, with the frequency and the intrinsic reaction coordinate (IRC) analysis at the same theoretical level. High accurate energy information was provided by the G3(MP2) method combined with the standard statistical thermodynamics. Gibbs free energies at 298.15 K for all of the reaction steps were reported, and were used to describe the profile diagrams of the potential energy surface. The rate constants were evaluated with both the classical transition state theory and the canonical variational transition state theory, in which the small-curvature tunneling correction was included. A total number of 9 intermediates (IMs) and 17 transition states (TSs) were obtained. It is shown that IM1 is the most stable intermediate by the largest energy release, and the channel of CH₃SS?+?CN?→?IM3?→?TS10?→?P1(CH₂SS?+?HCN) is the dominant reaction with the lowest energy barrier of 144.7 kJ mol^?1. The fitted Arrhenius expressions of the calculated CVT/SCT rate constants for the rate-determining step of the favorable channel is k =7.73?×?10⁶? T ^1.40exp(?14,423.8/T) s^?1 in the temperature range of 200–2000 K. The apparent activation energy E _a(app.) for the main channel is ?102.5 kJ mol^?1, which is comparable with the G3(MP2) energy barrier of ?91.8 kJ mol^?1 of TS10 (relative to the reactants).     

The addition reactions of germylenoid H<Subscript>2</Subscript>GeAlCl<Subscript>3</Subscript> with ethylene: a theoretical investigation

Theoretical calculations using the M062X and QCISD methods were performed on the addition reactions of the aluminum germylenoid H₂GeAlCl₃ with ethylene. The most two stable structures of germylenoid H₂GeAlCl₃, i.e., the p-complex and three-membered ring structures, respectively, were employed as reactants. The calculated results indicate that, for the p-complex, H₂GeAlCl₃ there are two pathways, I and II, of which path I involves just one transition state, while path II involves two transition states between reactants and products. Comparing the reaction barrier heights of path I (44.6 kJ mol^?1) and II (37.6 kJ mol^?1), the two pathways are competitive, with similar barriers under the same conditions, while for the three-membered ring structure, another two pathways, III and IV, also exist. Path III has one transition state; however, in path IV, two transition states exist. By comparing their barrier heights, path III (barrier height 39.2 kJ mol^?1) could occur more easily than path IV (barrier height 92.8 kJ mol^?1). Considering solvent effects on these addition reactions, the PCM model and CH₂Cl₂ solvent were used in calculations, and the calculated results demonstrate that CH₂Cl₂ solvent is unfavorable for the reactions, except for path II. In CH₂Cl₂ solvent, paths II and III are more favorable than paths I and IV.     

Multi-spectroscopic and voltammetric evidences for binding,conformational changes of bovine serum albumin with thiamine

The interaction between thiamine hydrochloride (TA) and bovine serum albumin (BSA) was investigated by fluorescence, FTIR, UV–vis spectroscopic and cyclic voltammetric techniques under optimised physiological condition. The fluorescence intensity of BSA is gradually decreased upon addition of TA due to the formation of a BSA–TA complex. The binding parameters were evaluated and their behaviour at different temperatures was analysed. The quenching constants (K_sv) obtained were 2.6 × 10⁴, 2.2 × 10⁴ and 2.0 × 10⁴ L mol^?1 at 288, 298 and 308 K, respectively. The binding mechanism was static-type quenching. The values of ΔH° and ΔS° were found to be 26.87 kJ mol^?1 and 21.3 J K^?1 mol^?1, and indicated that electrostatic interaction was the principal intermolecular force. The changes in the secondary structure of BSA upon interaction with TA were confirmed by synchronous and 3-D spectral results. Site probe studies reveal that TA is located in site I of BSA. The effects of some common metal ions on binding of BSA–TA complex were also investigated.     

Molecular dynamics simulation of d-Benzedrine transmitting through molecular channels within D3R

Dex-Benzedrine (known as d-Benzedrine or SAT) acts in dopamine receptors of central nerve cell system. In clinic, SAT is used to treat a variety of diseases; meanwhile, it has dependence and addiction. In order to investigate the pharmacology and addiction mechanisms of SAT as a medicine, in this paper, we have studied the structure of D₃R complex protein with SAT, and based on which, using potential mean force with umbrella samplings and the simulated phospholipid bilayer membrane (or POPC bilayer membrane), the molecular dynamics simulation was performed to obtain free energy changes upon the trajectories for SAT moving along the molecular channels within D₃R. The free energy change for SAT transmitting toward the outside of cell along the functional molecular channel within D₃R is 83.5 kJ mol^?1. The change of free energy for SAT to permeate into the POPC bilayer membrane along the protective molecular channel within D₃R is 87.7 kJ mol^?1. Our previous work gave that the free energy for Levo-Benzedrine (RAT) transmitting toward the outside of cell along the functional molecular channel within D₃R is 91.4 kJ mol^?1, while it is 117.7 kJ mol^?1 for RAT to permeate into the POPC bilayer membrane along the protective molecular channel within D₃R. The values of free energy suggest that SAT relatively prefers likely to pass through the functional molecular channel within D₃R for increasing the release of dopamine molecules resulting in a variety of functional effects for SAT. The obtained results show that the pharmacology and addiction mechanisms of SAT as a drug are closely related to the molecular dynamics and mechanism for SAT transmitting along molecular channels within D₃R.     

Homologous yeast lipases/acyltransferases exhibit remarkable cold-active properties

Lipases/acyltransferases catalyse acyltransfer to various nucleophiles preferentially to hydrolysis even in aqueous media with high thermodynamic activity of water (a _w >0.9). Characterization of hydrolysis and acyltransfer activities in a large range of temperature (5 to 80 °C) of secreted recombinant homologous lipases of the Pseudozyma antarctica lipase A superfamily (CaLA) expressed in Pichia pastoris, enlighten the exceptional cold-activity of two remarkable lipases/acyltransferases: CpLIP2 from Candida parapsilosis and CtroL4 from Candida tropicalis. The activation energy of the reactions catalysed by CpLIP2 and CtroL4 was 18–23 kJ mol^?1 for hydrolysis and less than 15 kJ mol^?1 for transesterification between 5 and 35 °C, while it was respectively 43 and 47 kJ mol^?1 with the thermostable CaLA. A remarkable consequence is the high rate of the reactions catalysed by CpLIP2 and CtroL4 at very low temperatures, with CpLIP2 displaying at 5 °C 65 % of its alcoholysis activity and 45 % of its hydrolysis activity at 30 °C. These results suggest that, within the CaLA superfamily and its homologous subgroups, common structural determinants might allow both acyltransfer and cold-active properties. Such biocatalysts are of great interest for the efficient synthesis or functionalization of temperature-sensitive lipid derivatives, or more generally to lessen the environmental impact of biocatalytic processes.     

The thermodynamic parameters of the interaction of concanavalin A with glycosyl-free liposomes: a microcalorimetric study

The nonspecific interaction of the mitogenic lectin Concanavalin A (Con A) with glycosyl-free liposomes of various composition has been investigated by microcalorimetric titration measurements. The results obtained show the following features of main interest: (1) the affinity constants (K_a) of the interaction of Con A with liposomal bilayers are in the order of magnitude 10⁵–10⁶M^?1. The reaction enthalpies (ΔH) are positive, and small (approximately 0.1 KJ mol^?1 lipid), compared to the free energy terms (?ΔG = 30–40 KJ mol^?1 lipid). All lectin–lipid interactions are strongly entropy-controlled (ΔH/TΔS < 1.0). These thermodynamic features are characteristic for hydrophobic interaction processes. (2) The liposomal head-group charge does not significantly affect the lipid-affinity of Con A. Electrostatic forces thus appear to play a minor role in lectin–lipid interactions. (3) The lipid affinity of Con A is sensitive to the fluidity of the liposomal bilayers, increasing with increasing fluidity. Below the gel to liquid-crystal phase transition temperature, the lectin binding to liposomal bilayers is inhibited. (4) The binding isotherms, corresponding to the interaction of Con A with liposomes, composed of tightly packed, saturated phospholipids, exhibit pronounced positive cooperativity. This phenomenon is absent in the binding curves, corresponding to the interaction of Con A with more fluid liposomal bilayers. (5) The Con A specific inhibitor α-D -methylmannopyranoside (50 mM) drastically increases the molar reaction enthalpy. The K_a term is significantly reduced in presence of the inhibitor sugar. Urea induces analogous changes in the thermodynamic parameters of the lectin–lipid interaction. The effects of α-D -methylmannopyranoside are thus not Con A specific, but are attributable to solvent effects. (6) It was shown that the binding of one Con A molecule affects a large number (approximately 1000) of phospholipid molecules in the liposomal bilayer. (7) The affinity constants (K_a) of the interaction of Con A with glycosyl-free lipids are smaller by a factor of approximately 10, compared to the K_a terms, reported for Con A binding to biological membranes. The presence of glycosidic receptor groups thus controls the specificity of lectin–membrane interactions, whereas the nonspecific lectin–lipid interactions appear to represent the main driving force for the strong attachment of the lectin to membrane surfaces.     

Permeability of lipid bilayer to anthracycline derivatives. Role of the bilayer composition and of the temperature

The uptake of three anthracycline derivatives: doxorubicin, daunorubicin and pirarubicin, into large unilamellar vesicles (LUV) in response to a driving force provided by DNA encapsulated inside the LUV has been investigated as a function of the temperature and of the bilayers lipid composition. The kinetics of the decay of the anthracycline fluorescence in the presence of DNA-containing liposome was used to follow the diffusion of the drug through the membrane. For the three drugs, the permeability coefficient of the neutral form of the drug (P⁰) decreases as the amount of negatively charged phospholipid in the bilayers increases. This can be explained by the fact that the kinetics of passive diffusion of the drugs depends on the amount of neutral form embedded in the polar head group region, which decreases as the quantity of negatively charged phospholipids increases. P⁰ also decreases as the amount of cholesterol, that makes the bilayer more rigid, increases. The activation energies, E_a, for the passage of the neutral form of these anthracyclines through the bilayers lie within 100±15 kJ·mol⁻¹, except for pirarubicin and doxorubicin through anionic phospholipid-rich membranes (E_a=57 kJ·mol⁻¹) and cholesterol-rich membranes (E_a=167 kJ·mol⁻¹).     

Theoretical study of chemisorption of cyanuric fluoride and S-triazine on the surface of Al-doped graphene

We studied the adsorption of cyanuric fluoride (CF) and s-triazine (ST) molecules on the surface of pristine as well as Al-doped graphenes using density functional theory calculations. Our results reveal low adsorption on the surface of pristine graphene; but by modification of surface using aluminium, resulted Al-doped graphene becomes more reactive towards both CF and ST molecules. We aimed to focus on the adsorption energy, electronic structure, charge analysis, density of state and global indices of each system upon adsorption of CF and ST molecules on the above-mentioned surfaces. Our calculated adsorption energies for the most stable position configurations of CF and ST on Al-doped graphene were ?76.53 kJ mol^?1 (?57.45 kJ mol^?1 BSSE corrected energy) and ?115.55 kJ mol^?1 (?86.87 kJ mol^?1 BSSE corrected energy), respectively, which point to the chemisorption process. For each CF and ST molecule, upon adsorption on the surface of Al-doped graphene, the band gap of HOMO-LUMO was reduced considerably and it becomes a p-type semiconductor, whereas there is no hybridisation between the above-mentioned molecules and pristine graphene.     

Quercetin and daidzein β-apo-14’-carotenoic acid esters as membrane antioxidants

Abstract

Esterification by β-apo-14’-carotenoic acid was found to have opposite effects on antioxidant activity of quercetin (at B4’, B3’ hydroxyl) as of daidzein (at A7 hydroxyl) in phosphatidylcholine liposomes. The daidzein ester had increased activity, while quercetin had a significant decreased activity. Quantum mechanical calculations using density function theory (DFT) indicate a modest decrease in bond dissociation enthalpy, BDE, for (weakest) hydrogen–oxygen phenolic bond in daidzein from 368.4 kJ·mol^{? 1} to 367.7 kJ·mol^{? 1} compared to a significant increase in quercetin from 329.5 kJ·mol^{? 1} to 356.6 kJ·mol^{? 1} upon derivatization. These opposite changes in tendency for hydrogen atom transfer from phenolic groups to lipid radicals combined with an increase in A-to-B dihedral angle from 0.0° to 36.4° and in dipole moment from 0.40 D to 6.01 D for quercetin upon derivatization, while less significant for daidzein (36.4°–36.7° and 3.26 D–7.87 D, respectively), together provide a rationale for the opposite effect of esterification on antioxidation.     

Kinetics and thermodynamics of catalysis and thermal inactivation of a novel α-amylase (Tp-AmyS) from Thermotoga petrophila

Abstract

This research is focussed on kinetic, thermodynamic and thermal inactivation of a novel thermostable recombinant α-amylase (Tp-AmyS) from Thermotoga petrophila. The amylase gene was cloned in pHIS-parallel1 expression vector and overexpressed in Escherichia coli. The steady-state kinetic parameters (V_max, K_m, k_cat and k_cat/K_m) for the hydrolysis of amylose (1.39?mg/min, 0.57?mg, 148.6?s^?1, 260.7), amylopectin (2.3?mg/min, 1.09?mg, 247.1?s^?1, 226.7), soluble starch (2.67?mg/min, 2.98?mg, 284.2?s^?1, 95.4) and raw starch (2.1?mg/min, 3.6?mg, 224.7?s^?1, 61.9) were determined. The activation energy (E_a), free energy (ΔG), enthalpy (ΔH) and entropy of activation (ΔS) at 98?°C were 42.9?kJ mol^?1, 74?kJ mol^?1, 39.9?kJ mol^?1 and ?92.3 J mol^?1 K^?1, respectively, for soluble starch hydrolysis. While ΔG of substrate binding (ΔG_E-S) and ΔG of transition state binding (ΔG_E-T) were 3.38 and ?14.1?kJ mol^?1, respectively. Whereas, EaD, Gibbs free energy (ΔG*), increase in the enthalpy (ΔH*) and activation entropy (ΔS*) for activation of the unfolding of transition state were 108, 107, 105?kJ mol^?1 and ?4.1 J mol^?1 K^?1. The thermodynamics of irreversible thermal inactivation of Tp-AmyS revealed that at high temperature the process involves the aggregation of the protein.     

Multispectroscopic studies of the interaction of folic acid with glycated human serum albumin

Abstract

The interaction between glycated human serum albumin (gHSA) and folic acid (FA) was investigated by various spectroscopic techniques, such as fluorescence, circular dichroism, UV–vis absorption spectroscopy and electrophoretic light scattering technique. These methods characterize the binding properties of an albumin–folic acid system. The binding constants values (K_a) at 300 and 310 K are about 10⁴ M^?1. The standard enthalpy change (ΔH) and the standard entropy change (ΔS) were calculated to be ～?20?kJ mol^?1 and ～16 J mol^?1 K^?1, respectively, which indicate characteristic electrostatic interactions between gHSA and folic acid. The CD studies showed that there are no significant conformational changes in the secondary structure of the protein. Moreover, the zeta potential measurements proved that under physiological conditions the gHSA–folic acid complex shows instability. No significant changes in the secondary structure of the protein and reversible drug binding are the desirable effect from pharmacological point of view.

Communicated by Ramaswamy H. Sarma     

Thermodynamic Prediction of Glycine Polymerization as a Function of Temperature and pH Consistent with Experimentally Obtained Results

Prediction of the thermodynamic behaviors of biomolecules at high temperature and pressure is fundamental to understanding the role of hydrothermal systems in the origin and evolution of life on the primitive Earth. However, available thermodynamic dataset for amino acids, essential components for life, cannot represent experimentally observed polymerization behaviors of amino acids accurately under hydrothermal conditions. This report presents the thermodynamic data and the revised HKF parameters for the simplest amino acid “Gly” and its polymers (GlyGly, GlyGlyGly and DKP) based on experimental thermodynamic data from the literature. Values for the ionization states of Gly (Gly⁺ and Gly^?) and Gly peptides (GlyGly⁺, GlyGly^?, GlyGlyGly⁺, and GlyGlyGly^?) were also retrieved from reported experimental data by combining group additivity algorithms. The obtained dataset enables prediction of the polymerization behavior of Gly as a function of temperature and pH, consistent with experimentally obtained results in the literature. The revised thermodynamic data for zwitterionic Gly, GlyGly, and DKP were also used to estimate the energetics of amino acid polymerization into proteins. Results show that the Gibbs energy necessary to synthesize a mole of peptide bond is more than 10 kJ mol^?1 less than previously estimated over widely various temperatures (e.g., 28.3 kJ mol^?1 → 17.1 kJ mol^?1 at 25 °C and 1 bar). Protein synthesis under abiotic conditions might therefore be more feasible than earlier studies have shown.     

Key parameters for outdoor biomass production of Scenedesmus obliquus in solar tracked photobioreactors

The biomass productivity of Scenedesmus obliquus was investigated outdoors during all seasons in solar tracked flat panel photobioreactors (PBR) to evaluate key parameters for process optimization. CO₂ was supplied by flue gas from an attached combined block heat and power plant. Waste heat from the power plant was used to heat the culture during winter. The parameters pH, CO₂, and inorganic salt concentrations were automatically adjusted to nonlimiting levels. The optimum biomass concentration increased directly with the photosynthetic active radiation (PAR) from 3 to 5 g dry weight (DW)?L^?1 for a low PAR of 10 mol photons m^?2 day^?1 and high PAR of 40–60 mol photons m^?2 day^?1, respectively. The annual average biomass yield (photosynthetic efficiency) was 0.4?±?0.5 g DW mol^?1 photons. However, biomass yields of 1.5 g DW mol^?1 photons close to the theoretical maximum were obtained at low PAR. The productivity (including the night biomass losses) ranged during all seasons from ?5 up to 30 g DW m^?2 day^?1 with a mean productivity of 9?±?7 g DW m^?2 day^?1. Low night temperatures of the culture medium and elevated day temperatures to the species-specific optimum increased the productivity. Thus, continuous regulation of the biomass concentration and the culture temperature with regard to the fluctuating weather conditions is essential for process optimization of outdoor microalgal production systems in temperate climates.     

Biochemical and thermodynamic characteristics of thermo-alkali-stable xylanase from a novel polyextremophilic Bacillus halodurans TSEV1

The purified extracellular xylanase of polyextremophilic Bacillus halodurans TSEV1 has been visualized as a single band on SDS-PAGE and eluted as single peak by gel filtration, with a molecular mass of 40 kDa. The peptide finger print and cloned xylanase gene sequence analyses indicate that this enzyme belongs to GH family 10. The active site carboxyl residues are mainly involved in catalysis, while tryptophan residues are involved in substrate binding. The enzyme is optimally active at 80 °C and pH 9.0, and stable in the pH range of 7.0–12.0 with T _1/2 of 35 min at 80 °C (pH 9.0). Activation energy for birch wood xylan hydrolysis is 30.51 kJ mol^?1. The K _m, V _max and k _cat (birchwood xylan) are 2.05 mg ml^?1, 333.33 μmol mg^?1 min^?1 and 3.33 × 10⁴ min^?1, respectively. The pKa₁ and pKa₂ of ionizable groups of the active site that influence V _max are 8.51 and 11.0. The analysis of thermodynamic parameters for xylan hydrolysis suggests this as a spontaneous process. The enzyme is resistant to chemical denaturants like urea and guanidinium-HCl. The site-directed mutagenesis of catalytic glutamic acid residues (E196 and E301) resulted in a complete loss of activity. The birch wood xylan hydrolyzate contained xylobiose and xylotriose as the main products without any trace of xylose, and the enzyme hydrolyzes xylotetraose and xylopentaose rapidly to xylobiose. Thermo-alkali-stability, resistance to various chemical denaturants and mode of action make it a useful biocatalyst for generating xylo-oligosaccharides from agro-residues and bleaching of pulp in paper industries.     

The Interaction of Chromium(VI) with Urease in Solution

The interaction between K₂Cr₂O₇ and urease was investigated using fluorescence, UV-vis absorption, and circular dichroism (CD) spectroscopy. The experimental results showed that the fluorescence quenching of urease by K₂Cr₂O₇ was a result of the formation of K₂Cr₂O₇–urease complex. The apparent binding constant K _A between K₂Cr₂O₇ and urease at 295, 302, and 309 K were obtained to be 2.14?×?10⁴, 1.96?×?10⁴, and 1.92?×?10⁴ L mol^?1, respectively. The thermodynamic parameters, ΔH° and ΔS° were estimated to be ?5.90 kJ mol^?1, 43.67 J mol^?1 K^?1 according to the Van’t Hoff equation. The electrostatic interaction played a major role in stabilizing the complex. The distance r between donor (urease) and acceptor (K₂Cr₂O₇) was 5.08 nm. The effect of K₂Cr₂O₇ on the conformation of urease was analyzed using UV-vis absorption, CD, synchronous fluorescence spectroscopy, and three-dimensional fluorescence spectra, the environment around Trp and Tyr residues were altered.     

Spectroscopic Studies on the Interaction of Fluorine Containing Triazole with Bovine Serum Albumin

The binding of one fluorine including triazole (C₁₀H₉FN₄S, FTZ) to bovine serum albumin (BSA) was studied by spectroscopic techniques including fluorescence spectroscopy, UV–Vis absorption, and circular dichroism (CD) spectroscopy under simulative physiological conditions. Fluorescence data revealed that the fluorescence quenching of BSA by FTZ was the result of forming a complex of BSA–FTZ, and the binding constants (K _a) at three different temperatures (298, 304, and 310 K) were 1.516?×?10⁴, 1.627?×?10⁴, and 1.711?×?10⁴?mol L^?1, respectively, according to the modified Stern–Volmer equation. The thermodynamic parameters ΔH and ΔS were estimated to be 7.752 kJ mol^?1 and 125.217 J?mol^?1?K^?1, respectively, indicating that hydrophobic interaction played a major role in stabilizing the BSA–FTZ complex. It was observed that site I was the main binding site for FTZ to BSA from the competitive experiments. The distance r between donor (BSA) and acceptor (FTZ) was calculated to be 7.42 nm based on the Förster theory of non-radioactive energy transfer. Furthermore, the analysis of fluorescence data and CD data revealed that the conformation of BSA changed upon the interaction with FTZ.     

1,3‐Propanediol adsorption on a cation exchange resin: Adsorption isotherm,thermodynamics, and mechanistic studies

1,3‐Propanediol (1,3‐PD) is widely used in cosmetics, foods, antifreezes, and polyester. A low‐cost cation exchange resin, 001×7 H‐form resin, was selected for 1,3‐PD adsorption obtained from microbial fermentation of crude glycerol. The thermodynamics and kinetics of adsorption were studied. To identify the characteristics of the adsorption process, the influence of 1,3‐PD concentration, temperature, and resin particle diameters was studied. The temperature dependence of the adsorption equilibrium in the range of 288 to 318 K was observed to satisfy the Langmuir isotherm well. The thermodynamic parameters, adsorption enthalpy, entropy, and Gibbs free energy, were determined as 36.2 kJ·moL^?1, 160 mol^?1·K^?1, and ?11.2 kJ·moL^?1, respectively, which indicated that the adsorption was spontaneous and endothermic. The adsorption kinetics was accurately represented by the shell progressive model and indicated that the particle diffusion was the rate‐limiting step. Based on the kinetic simulation, the rate constant of exchange (k₀), order reaction (α), and the apparent activation energy reaction (E_a) were obtained as 3.11×10^?3, 0.644, and 11.5 kJ·moL^?1, respectively. This kinetic and thermodynamic analysis of 1,3‐PD recovery presented in this article is also applicable for the separation of other polyols by resin adsorption, which will promote value‐added utilization of glycerol.     

The responses of spatial situation,surface structure characteristics of leaves and sensitivity of two local rice cultivars to enhanced UV-B radiation under terraced agricultural ecosystem

Under the situ terraced field experiments, effects of artificial UV-B radiation enhancement (0, 2.5, 5.0, 7.5 kJ m^?2) on spatial situation and surface structure of leaves and responses index of two local cultivars rice (Oryza sativa L.)—Yuelianggu and Baijiaolaojin in Yuanyang County, China in shooting stage were studied. The results showed that: (1) due to the enhanced UV-B radiation, leaf apex–base distance, leaf pedestal height, leaf rolling degree and wax content in leaves increased, while leaf apex–stem distance, distance between leaves and leaf angle decreased. The response index of growth was positive when UV-B levels were 2.5 and 5.0 kJ m^?2, which showed some adaptation. (2) The enhanced UV-B radiation resulted in smaller stomata with higher density and more papilla for both rice cultivars. (3) The enhanced UV-B radiation also leaded to larger silica cells and significantly increases the amount of papilla, spike and epidermal hair for both rice cultivars. (4) Yuelianggu cultivar showed an excellent adaptation on the aspect of spatial situation with UV-B radiation of 2.5 and 5.0 kJ m^?2, while Baijiaolaojin exhibited better adaptation respecting the surface structure of leaves when UV-B was 2.5 kJ m^?2. By changing spatial situation of leaves, structure and density of stomata, and non-stomatal structures (wax layer, silica cell, cork cell, papilla, spike and epidermal hair), two self-retention rice cultivars could adapt to the increased UV-B radiation. On the aspect of the response index, Baijiaolaojin showed better adaptation than Yuelianggu did when the UV-B was 2.5 kJ m^?2.     

The role of CS<Subscript>2</Subscript> in CS<Subscript>2</Subscript>/NMP mixed solvent in weakening the hydrogen bond of OH–N in coal: a DFT investigation

The interaction processes of trace amounts of N-methyl-2-pyrrolidinone (NMP), CS₂/NMP (1:1 by volume) and pure NMP solvent with the hydrogen bond of OH?N in coal were constructed and simulated by density functional theory methods. The distances and bond orders between the main related atoms, and the hydrogen bond energy of OH?N were calculated. The calculated results show that pure NMP solvent does not weaken the hydrogen bond of OH?N in coal. However, trace amounts of NMP and CS₂/NMP (1:1 by volume) have a strong capacity to weaken the hydrogen bond of OH?N in coal. The H2–N3 distances are elongated from 1.87 Å to 3.80 Å and 3.44 Å, the bond orders of H2–N3 all disappear, and the corresponding hydrogen bond energies of OH?N in coal decrease from 45.72 kJ mol^?1 to 7.06 and 11.24 kJ mol^?1, respectively. These results show that CS₂ added to pure NMP solvent plays an important role in releasing the original capacity of NMP to weaken the hydrogen bond of OH?N in coal, in agreement with experimental observations.     

Dynamics of molecular organization in agarose sulphate

Nongelling solutions of structurally regular chain segments of agarose sulphate show disorder–order and order–disorder transitions (as monitored by the temperature dependence of optical rotation) that are closely similar to the conformational changes that accompany the sol–gel and gel–sol transitions of the unsegmented polymer. The transition midpoint temperature (T_m) for formation of the ordered structure on cooling is ～25 K lower than T_m for melting. Salt-induced conformational ordering, monitored by polarimetric stopped-flow, occurs on a millisecond time scale, and follows the dynamics expected for the process 2 coil ? helix. The equilibrium constant for helix growth (s) was calculated as a function of temperature from the calorimetric enthalpy change for helix formation (ΔH_cal = ?3.0 ± 0.3 kJ per mole of disaccharide pairs in the ordered state), measured by differential scanning calorimetry. The temperature dependence of the nucleation rate constant (k_nuc), calculated from the observed second-order rate constant (k_obs) by the relationship k_obs = k_nuc(1 ? 1/s) gave the following activation parameters for nucleation of the ordered structure of agarose sulphate (1 mg mL^?1; 0.5M Me₄NCl or KCl): ΔH* = 112 ± 5 kJ mol^?1; ΔS* = 262 ± 20 J mol^?1 K^?1; ΔG*₂₉₈ = 34 ± 6 kJ mol^?1; (k_nuc)₂₉₈ = (7.5 ± 0.5) × 10⁶ dm³ mol^?1 s^?1. The endpoint of the fast relaxation process corresponds to the metastable optical rotation values observed on cooling from the fully disordered form. Subsequent slow relaxation to the true equilibrium values (i.e., coincident with those observed on heating from the fully ordered state) was monitored by conventional optical rotation measurements over several weeks and follows second-order kinetics, with rate constants of (2.25 ± 0.07) × 10^?4 and (3.10 ± 0.10) × 10^?4 dm³ mol^?1 s^?1 at 293.7 and 296.2 K, respectively. This relaxation is attributed to the sequential aggregation processes helix + helix → dimer, helix + dimer → trimer, etc., with depletion of isolated helix driving the much faster coil–helix equilibrium to completion. Light-scattering measurements above and below the temperature range of the conformational transitions indicate an average aggregate size of 2–3 helices.