Towards the understanding of molecular mechanisms in the early stages of heat-induced aggregation of beta-lactoglobulin AB

Heat-induced aggregation of bovine β-lactoglobulin AB (10 mg/ml) was studied at 68.5 °C at two different pH values (6.7, 4.9) using gel electrophoresis techniques and matrix-assisted laser desorption ionization mass spectrometry (MALDI–TOF MS). Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS–PAGE) analysis under non-reducing and reducing conditions showed that in the early stages of the aggregation of β-lactoglobulin disulfide linked aggregates were formed on heating at pH 6.7, but not at pH 4.9. We related this result to the pH-dependent activity of the free thiol group at C121. Mass spectrometric analyses were conducted in two steps. The first involved the analysis of intact non-native monomers and dimers following their ultrasonic passive elution into a suitable solvent mixture in order to confirm the identity of the different gel bands. The second step comprises the analysis of in-gel digests for the determination of disulfide patterns in non-native monomers, covalent dimers and trimers. The results of in-gel digestions analyzed by mass spectrometry suggest that non-native dimers could result from the formation of inter-molecular disulfide bonds C121–C66, C160–C160, or C121–C160. Moreover, two inter-molecular bonds C121–C66 and C160–C160 between two and the same monomer units have been detected, which may play an important role in limiting the process of covalent β-lactoglobulin network formation. The combination of SDS–PAGE and MALDI–TOF MS enables us to understand the mechanism of β-lactoglobulin aggregation at the macromolecular level.     

A simultaneous TG–DTA study of the thermal decomposition of 2-hydroxybenzoic acid, 2-carboxyphenyl ester (salsalate)

Simultaneous thermogravimetry–differential thermal analysis (TG–DTA) and gas and liquid chromatography with mass spectrometry detection have been used to study the kinetics and decomposition of 2-hydroxybenzoic acid, 2-carboxyphenyl ester, commercially known as salsalate. Samples of salsalate were heated in the TG–DTA apparatus in an inert atmosphere (100 ml min⁻¹ nitrogen) in the temperature range 30–500 °C. The data indicated that the decomposition of salsalate is a two-stage process. The first decomposition stage (150–250 °C) had a best fit with second-order kinetics with E_a=191–198 kJ/mol. The second decomposition stage (300–400 °C) is described as a zero-order process with E_a=72–80 kJ/mol. The products of the decomposition were investigated in two ways:

(a)Salsalate was heated in a gas chromatograph at various isothermal temperatures in the range 150–280 °C, and the exit gas stream analyzed by mass spectrometry (GC–MS). This approach suggested that salsalate decomposes with the formation of salicylic acid, phenol, phenyl salicylate, and cyclic oligomers of salicylic acid di- and tri-salicylides.

(b)One gram samples of salsalate were heated in a vessel under nitrogen to 150 °C, and the residues were analyzed by liquid chromatography–mass spectrometry (LC–MS). The major compound detected was a linear tetrameric salicylate ester.

     

Phase behavior, conformations, thermodynamic properties, and molecular motion of multicomponent paraffin waxes: A Raman spectroscopy study

Variable-temperature (72–20 °C) studies of Raman spectra (3100–800 cm⁻¹) and thermal analysis of multicomponent paraffin wax have been carried out. The disorder–order transition under liquid–solid transition was observed and their temperature ranges were obtained through the S_lateral order parameter as a function of temperature. From 56 to 43 °C, the paraffin undergoes a conformational state transition of non-extended chain state (NECS) to extended chain state (ECS). The enthalpy and entropy change for the transition obtained by van’t Hoff analysis were 214.286 ± 21 kJ/mol and 0.661 ± 0.066 kJ/mol/K, respectively. The enthalpy determined by differential scanning calorimetry (DSC) was 52.165 ± 5.2 kJ/mol, which is smaller than the van’t Hoff enthalpy due to larger effective non-extended chain state. The variation of Raman spectra with decreasing temperature presents the structure evolution and molecular motion during the crystallization of paraffin wax.     

Molecular structure and conformational stability of allylisocyanate—post-Hartree–Fock and density functional theory studies

The molecular structure and conformational stability of allylisocyanate (CH₂CHCH₂NCO) molecule was studied using the ab initio and DFT methods. The geometries of possible conformers, C-gauche (δ=120°, θ=0°) (δ=C=C–C–N and θ=C–C–N=C) and C-cis N-trans (δ=0° and θ=180°) were optimized employing HF/6-31G^*, MP2/6-31G^* levels of theory of ab initio and BLYP, B3LYP, BPW91 and B3PW91 methods of DFT implementing the atomic basis set 6-311+G(d,p). The structural and physical parameters of the above conformers were discussed with the experimental and theoretical values of the related molecules, methylisocyanate and 3-fluoropropene. It has been found that the N=C=O bond angle is not linear as the experimental result for both the conformers and the theoretical bond angle is 173°. The rotational potential energy surfaces have been performed at the HF/6-31G^*, and MP2/6-31G^* levels of theory. The Fourier decomposition potentials were analysed at the HF/6-31G^*, and MP2/6-31G^* levels of theory. The HF/6-31G^* level of theory predicted that the C-gauche conformer is more stable than the C-cis N-trans conformer by 0.41 kJ/mol, but the MP2 and DFT methods predicted the C-cis N-trans conformer is found to be more stable than the C-gauche conformer. The calculated chemical hardness value at the HF/6-31G^* level of theory predicted the C-cis N-trans form is more stable than C-gauche form, whereas the chemical hardness value at the MP2/6-31G^* level of theory favours the slight preference towards the C-gauge conformer.     

Extraordinary chiral discrimination in inclusion gas chromatography. Thermodynamics of enantioselectivity between a racemic perfluorodiether and a modified γ-cyclodextrin

The enantiomers of the perfluorodiether “compound B” [2-(fluoromethoxy)-3-methoxy-1,1,1,3,3-pentafluoropropane], a decomposition product of the inhalational anesthetic sevoflurane [2-(fluoromethoxy)-1,1,1,3,3,3-hexafluoropropane], were separated by gas chromatography on octakis(3-O-butanoyl-2,6-di-O-n-pentyl)-γ-cyclodextrin (Lipodex E), dissolved in polysiloxane PS 255 (30% w/w), with an unexpectedly high separation factor of =10.6 at 26 °C. Using the concept of the retention increment R′, non-enantioselective and enantioselective contributions to retention were separated and thus reliable thermodynamic parameters of enantioselectivity, i.e. −Δ_S,R(ΔG)=5.7 (0.05) kJ/mol at 303 K, −Δ_S,R(ΔH)=20.1 (0.64) kJ/mol, Δ_S,R(ΔS)=−47.4 (2.0) J/K mol and T_isoenant=424 (30) K or 150 °C, were determined by temperature-dependent measurements. The enantiomeric bias represents the largest values ever measured in enantioselective gas chromatography. An equation is presented which allows calculation of the non-enantioselective contributions to retention from measurements at two arbitrary concentrations of Lipodex E in polysiloxane. Surprisingly, the enantioselectivity is greatly reduced when employing the β-cyclodextrin analogue and breaks down completely with the -cyclodextrin analogue of Lipodex E.     

Formation of colloidal silver nanoparticles stabilized by Na+-poly(gamma-glutamic acid)-silver nitrate complex via chemical reduction process

Macromolecular and polyanionic Na⁺–poly(γ-glutamic acid) (PGA) silver nitrate complex acted as both a metal ion provider and a particle protector to fabricate nanosized silver colloids under chemical reduction by dextrose. The formation and size of particles have been characterized from transmission electron microscopy (TEM), dynamic light scattering analysis and UV–vis spectrophotometer. The results showed that the average particle size was 17.2 ± 3.4 to 37.3 ± 5.5 nm, apparently depending on the complex concentration. It was found that the rate constant and conversion of silver nanoparticles were proportional to the concentration of PGA. The growth mechanism of nanosized silver colloid was fully discussed. In addition, the in vitro cytotoxicity evaluated by L929 fibroblasts proliferation and antibacterial activity against Gram-positive strain (methicillin-resistant S. aureus (MRSA)) and Gram-negative strain (P. aeruginosa) bacteria have been assessed.     

Calorimetric study on oxidation of alumina supported rhodium by dioxygen

Rhodium particles in nanometer size were prepared by impregnating alumina powders with aqueous solutions containing rhodium salts. The dispersion (D) of rhodium crystallites on the prepared samples was estimated by dioxygen adsorption measured at 300 K. Phenomena of oxidizing the supported crystallites with 2.5 × 10⁴ Pa O₂ in a temperature range between 280 and 870 K were calorimetrically studied. Extent of oxidation may be distinguished into three stages, i.e., adsorption on surface (T < 300 K), progressive penetration into bulk, and formation of a stable bulk oxide (T> 700 K), on raising the oxidation temperature. Heat of dioxygen adsorption varies only slightly with the dispersion (D) of rhodium and has a value of 294 ± 6 kJ (mol O₂)⁻¹. Chemical stoichiometry of the bulk oxide formed, however, varies with the dispersion of rhodium crystallites. A dioxide (RhO₂) (_f H = 225 ± 3 kJ (mol O₂)⁻¹) and a sesquioxide (Rh₂O₃) (_f H = 273 ± 3 kJ (mol O₂)⁻¹) was formed at D < 60% and D> 80%,     

Systematic design of profile control chemistry. Control of gelation of mixed poly(vinyl alcohol-co-vinylamine) crosslinked with dialdehydes

Quantitative chemistry and modeling allow us to predict the behavior of a new, environmentally friendly, non-heavy-metal-containing profile control agent as a function of well-bore conditions. We present an analysis of the kinetics and mechanism of gelation delay for dialdehyde crosslinking of mixed poly(vinyl alcohol-co-vinylamine) (PVA-VAM) copolymers. In the present system, gelation at 90–110°C takes place within minutes at pH below 6.5 and not at all at pH above 7.5 when the crosslinking agent is the acetal-protected form of the dialdehyde. We exploit this sharp pH transition by buffering to pH 9–12 and then allowing the pH to drop by in situ hydrolysis of triethyl phosphate. The fact that a pH much below 7 is not needed for gelation means that consumption of acid by carbonate rock will not be a problem as far as gelation is concerned. In fact, neutralization by rock carbonate after gelation can be expected to promote gel stability.

The kinetics of the gelation are determined by the hydrolysis kinetics of triethyl phosphate and the stability of the dialdehyde. Triethyl phosphate hydrolysis has both base-catalyzed and uncatalyzed kinetics so it is advantageous to avoid a high pH in order to extend the gel time. It is also important to avoid a high pH in order to minimize the attack of clay minerals. Gelation systems using NaOH, Na₄EDTA, and Na₃PO₄ at initial pH below 10 were developed along with a mathematical model which satisfactorily predicts their gelation times.

Spectroscopic analysis indicates that the crosslinks formed initially in the mixed polymer system are different from those in poly(vinyl alcohol) (PVA). In PVA the crosslinks are hemiacetal and 1,3-dioxane groups formed from adjacent OH groups but in PVA-VAM the amine function is more reactive and the crosslinks are hemiaminal and dihydro-1,3-oxazine groups. These are potentially more stable than the crosslinks in PVA. We have not determined the nature of the crosslinks formed after aging, but there is some evidence that the oxazine linkages convert to dioxane links. Gels stable at 110°C for 40 weeks have been demonstrated.     

Geminale substituenteneffekte : Teil I. Thermochemie von 1-nitro-, 2-nitro-, 2,2-dinitro-und 2-cyano-2-nitroadamantan

The heats of combustion of 1-nitroadamantane (1), 2-nitroadamantane (2), 2,2-di-nitroadamantane (3) and 2-cyano-2-nitroadamantane (4) were measured by combustion calorimetry, and the heats of sublimation were derived from the temperature dependence of the vapour pressure measured in a flow system. The results for ΔH^XXX_c(c) and ΔH_Sub (in kJ mol⁻¹, standard deviation in parentheses) are: 1, −5824.1 (±2.2) and 63.6 (±1.0); 2, −5841.0 (±2.2) and 58.0 (±2.3); 3, −5685.2 (±1.0) and 96.4 (±1.4); 4, −6238.4 (±1.5) and 70.0 (±1.9).

A comparison of the resulting heats of formation ΔH^XXX_f(g) (in kJ mol⁻¹, standard deviation in parentheses) for 1 = −191.1 (± 2.4), 2 = −179.8 (±3.2), 3 = −154.3 (±1.7) and 4 = −21.0 (±2.5) reveals a destabilizing interaction of the geminal substituents in 3 and 4 amounting to 59 kJ mol⁻¹ (nitro/nitro) and 33 kJ mol⁻¹ (nitro/cyano) respectively.     

The direct synthesis of dimethyl ether from syngas over hybrid catalysts with sulfate-modified γ-alumina as methanol dehydration components

A series of γ-Al₂O₃ samples modified with various contents of sulfate (0–15 wt.%) and calcined at different temperatures (350–750 °C) were prepared by an impregnation method and physically admixed with CuO–ZnO–Al₂O₃ methanol synthesis catalyst to form hybrid catalysts. The direct synthesis of dimethyl ether (DME) from syngas was carried out over the prepared hybrid catalysts under pressurized fixed-bed continuous flow conditions. The results revealed that the catalytic activity of SO₄²⁻/γ-Al₂O₃ for methanol dehydration increased significantly when the content of sulfate increased to 10 wt.%, resulting in the increase in both DME selectivity and CO conversion. However, when the content of sulfate of SO₄²⁻/γ-Al₂O₃ was further increased to 15 wt.%, the activity for methanol dehydration was increased, and the selectivity for DME decreased slightly as reflected in the increased formation of byproducts like hydrocarbons and CO₂. On the other hand, when the calcination temperature of SO₄²⁻/γ-Al₂O₃ increased from 350 °C to 550 °C, both the CO conversion and the DME selectivity increased gradually, accompanied with the decreased formation of CO₂. Nevertheless, a further increase in calcination temperature to 750 °C remarkably decreased the catalytic activity of SO₄²⁻/γ-Al₂O₃ for methanol dehydration, resulting in the significant decline in both DME selectivity and CO conversion. The hybrid catalyst containing the SO₄²⁻/γ-Al₂O₃ with 10 wt.% sulfate and calcined at 550 °C exhibited the highest selectivity and yield for the synthesis of DME.     

Influence of whey protein denaturation on κ-carrageenan gelation

Response surface methodology was applied to study the effect of different heating temperature/time treatments on whey protein denaturation and its effect on κ-carrageenan gelation in milk. The path of gel formation was followed using small deformation rheology and the extent of whey protein denaturation was determined by gel permeation chromatography. κ-Carrageenan did not influence the rate of whey protein denaturation and it was unlikely that whey protein denaturation played a significant role on κ-carrageenan gelation in milk. In skim milk serum or skim milk ultrafiltrate the path of gel formation and gel strength were not influenced by the severity of heat treatment but increasing the concentration of whey proteins enhanced the gel strength. Heat treatment became important for carrageenan gelation in skim or recombined milks (i.e. in the presence of casein micelles) by influencing the gelation temperature and gel strength. Increasing the concentration of whey proteins in the recombined milks had a beneficial effect on gel strength.     

Infrared and Raman spectra, conformational stability, ab initio calculations of structure, and vibrational assignment of 2-hexyne

The infrared spectra (3500–50 cm⁻¹) of the gas and solid and the Raman spectra (3500–50 cm⁻¹) of the liquid and solid have been recorded for 2-hexyne, CH₃–CC–CH₂CH₂CH₃. Variable temperature studies of the infrared spectrum (3500–400 cm⁻¹) of 2-hexyne dissolved in liquid krypton have also been recorded. Utilizing four anti/gauche conformer pairs, the anti(trans) conformer is found to be the lower energy form with an enthalpy difference of 74±8 cm⁻¹ (0.88±0.10 kJ/mol) determined from krypton solutions over the temperature range −105 to −150 °C. At room temperature it is estimated that there is 42% of the anti conformer present. Equilibrium geometries and energies of the two conformers have been determined by ab initio (HF and MP2) and hybrid DFT (B3LYP) methods using a number of basis sets. Only the HF and DFT methods predict the anti conformer as the more stable form as found experimentally. A vibrational assignment is proposed based on the force constants, relative intensities, depolarization ratios from the ab initio and DFT calculations and on rotational band contours obtained using the calculated equilibrium geometries. From calculated energies it is shown that the CH₃ group exhibits almost completely free rotation which is in agreement with the observation of sub-band structure for the degenerate methyl vibrations from which values of the Coriolis coupling constants, ζ, have been determined. The results are compared to similar properties of some corresponding molecules.     

Conformational and structural studies of 1-chloropropane and 1-bromopropane from temperature-dependant FT-IR spectra of rare gas solutions and ab initio calculations

Variable temperature (−55 to −150°C) studies of the infrared spectra (3500–400 cm⁻¹) of 1-chloropropane (CH₃CH₂CH₂Cl) and 1-bromopropane (CH₃CH₂CH₂Br) dissolved in liquid krypton and xenon, respectively, have been recorded. Utilizing two conformer pairs in krypton solution for chloride and three conformer pairs in xenon solution for bromide, enthalpy differences of 52±3 cm⁻¹ (0.62±0.06 kJ/mol) and 72±7 cm⁻¹ (0.86±0.08 kJ/mol) were obtained for the chloride and bromide, respectively, with the gauche form being the more stable conformer for both molecules. From these data, it is estimated that 28 and 26% of trans form are present at ambient temperature for the chloride and bromide, respectively. The conformation stabilities, harmonic force constants, fundamental frequencies, infrared intensities and Raman activities have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations for both halopropanes and these quantities have been compared to the experimental values when appropriate. The optimized geometries have also been obtained with several different ab initio basis sets with full electron correlation by the perturbation method up to MP2/6-311+G(2d,2p). The r₀ structural parameters of both halopropanes have been obtained by combining the ab initio data with the previously reported microwave rotational constants for both conformers. The quantities are compared to the corresponding results for some similar molecules.     

Conformational stability of 1-bromo-2-fluoroethane from temperature dependent FT-IR spectra of rare gas solutions

Variable temperature (−55 to −135°C) studies of the infrared spectra (3500–400 cm⁻¹) of 1-bromo-2-fluoroethane, BrCH₂CH₂F, dissolved in liquid krypton and xenon have been recorded. From these data, the enthalpy difference has been determined to be 108±9 cm⁻¹ (1.296±0.113 kJ/mol) and 112±8 cm⁻¹ (1.346±0.098 kJ/mol) from the krypton and xenon solutions, respectively, with the trans conformer the more stable rotamer. Complete vibrational assignments are presented for both conformers which are consistent with the predicted frequencies obtained from the ab initio MP2/6-31G^* calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been obtained from RHF/6-31G^* and/or MP2/6-31G^* ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate. Structural parameters and conformational stability have also been obtained from MP2/6-311+G^** calculations. Combining the ab initio predicted structural parameters with the microwave rotational constants, r_o parameters have been obtained for the gauche conformer.     

Thermodynamic stabilities of NiTeO3 and Ni3TeO6 by solid oxide electrolyte e.m.f. method

The e.m.f. of the galvanic cells Pt,C,Te(l),NiTeO₃,NiO/15 YSZ/O₂ (P_o2 = 0.21 atm),Pt and Pt,C,NiTeO₃,Ni₃TeO₆,NiO/15 YSZ/O₂ (P_o2 = 0.21 atm),Pt (where 15 YSZ=15 mass% yttria-stabilized zirconia) was measured over the ranges 833–1104 K and 624–964 K respectively, and could be represented by the least-squares expressions E₍₁₎±1.48 (mV) = 888.72 − 0.504277 (K) and E_(II) ±4.21 (mV) = 895.26 − 0.81543T (K).

After correcting for the standard state of oxygen in the air reference electrode, and by combining with the standard Gibbs energies of formation of NiO and TeO₂ from the literature, the following expressions could be derived for the ΔG^°_f of NiTeO₃ and Ni₃TeO₆: ΔG_f^°(NiTeO₃) ± 2.03 (kJ mol⁻¹) = −577.30 + 0.26692T (K) and ΔG^°_f(Ni₃TeO₆)±2.54 (kJ mol⁻¹) = −1218.66 + 0.58837T (K).     

Synthesis and crystal structure of 9,10-dihydro-9,10-etheno-1,8-dichloro-11-diphenylphosphinyl-12-(diphenylphosphinylethynyl)anthracene

The title compound, 9,10-dihydro-9,10-etheno-1,8-dichloro-11-diphenylphosphinyl-12-(diphenylphosphinylethynyl)anthracene (1), has been synthesized and its crystal structure has been determined. The compound 1 crystallized into the triclinic space group P-1 with =74.837(4)°, β=88.156(4)°, γ=65.398(4)°, Z=2, D_c=1.352 gcm⁻³. In the crystal structure of 1a, one chloroform molecule was included by the compound 1 with a 1:1 ratio and the existence of non-classical intermolecular C–HO hydrogen bonds, intramolecular C–HCl and C–HO hydrogen bonds and π–π stacking were observed.     

Conformational stabilities of dimethylmethoxyphosphine and dimethyl(methylthio)phosphine from temperature dependent infrared spectra of rare gas solutions

Variable temperature (−55 to −150°C) studies of the infrared spectra (3500 to 400 cm⁻¹) of dimethylmethoxyphosphine, (CH₃)₂POCH₃ and dimethyl(methylthio)phosphine, (CH₃)₂PSCH₃ dissolved in liquid krypton and/or xenon have been recorded. From these data, the enthalpy differences have been determined to be 393±50 cm⁻¹ (4.71±0.60 kJ/mol), for (CH₃)₂POCH₃ with the near-cis conformer the more stable rotamer and 80±10cm⁻¹ (0.96±0.12 kJ/mol) for (CH₃)₂PSCH₃ with the cis conformer the more stable form. Complete vibrational assignments are presented for both molecules, which are consistent with the predicted frequencies obtained from the ab initio MP2/6-31G(d) calculations. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, and depolarization ratios have been obtained from RHF/6-31G(d) and/or MP2/6-31G(d) ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with some corresponding results for some similar molecules.     

Determination of the free activation energy for the breaking of the P---Ag bond in [(η-p-cymene)Ru(μ-pz)3Ag(PPh3)]

The Arrhenius equation corresponding to the process P---Ag+P*---Ag*→---P---Ag*+P*---Ag has been determined for [(η⁶-p-cymene)Ru(μ-pz)₃Ag(PPh₃)] (1) by complete line-shape analysis of the ³¹P NMR spectra between −40°C and +30°C. It has the form K = 10^11.8± e^{(−46±5 kJ mol−1/RT)}. The preexponential term, log A = 11.8 corresponds to a small activation entropy, whereas the activation energy, 46 kJ mol⁻¹ is comparable to those determined for other phosphorus—metal compounds.     

煤的缔合结构研究 Ⅰ 溶液缔合动力学

研究了煤可溶组分——吡啶不溶物（PI）在溶液中的缔合动力学，该PI系二硫化碳/N-甲基-2-吡咯烷酮（CS2/NMP）混合溶剂可溶组分。结果表明PI在NMP溶液中的缔合属于反应控制机理，并提出了二步动力学反应过程，即基本缔合单元的生成和缔合单元之间的缔合。通过实验获得了有关缔合的动力学参数，PI在NMP溶液中二步缔合的活化能分别为73.3 kJ/mol和21.6 kJ/mol。温度对缔合速率的影响显著，随着温度的升高，缔合速率增加。由于PI分子在CS2/NMP混合溶剂中相对NMP具有较高的扩散性，因而其在CS2/NMP混合溶剂中缔合速率较NMP快。此外，还讨论了PI在溶液中的缔合机理。