29Si NMR研究TEOS/DDS双前驱体体系的水解动力学

原位引入有机组分对氧化硅体系改性是合成有机-无机杂化硅材料的重要方法. 利用原位的²⁹Si液体核磁, 研究了甲醇为溶剂、氨水催化条件下的四乙氧基硅烷(TEOS)和二甲基二乙氧基硅烷(DDS)原位共水解的动力学过程. 通过改变反应体系中氨和水的浓度, 拟合出单体及中间产物浓度随时间的变化曲线, 得到了TEOS和DDS各自的水解速率常数以及相应各反应物的反应级数. 与单前驱体水解一致的是, 在双前驱体系中TEOS和DDS自身的反应级数仍保持一级, 但是氨和水的反应级数都有不同程度的增大. 与单前驱体水解速率方程相比, 混合体系中TEOS的水解速率常数增大. 同时, DDS在双前驱体中比单前驱体中的水解速率常数有很大程度的减少. 水解动力学表明, TEOS和DDS在双前驱体体系中显示出更平行的水解速率. 利用固体²⁹Si MAS NMR, XPS及小角X射线散射(SAXS)手段对双前驱体体系研究得到的信息显示, 碱催化条件下原位的TEOS水解中间物与DDS中间产物的原位共缩聚程度很弱.     

Ammonia Catalyzed Hydrolysis-Condensation Kinetics of Tetraethoxysilane/Dimethyldiethoxysilane Mixtures Studied by <Superscript><Emphasis Type="Bold">29</Emphasis></Superscript>Si NMR and SAXS

In-situ ²⁹Si liquid-state nuclear magnetic resonance (NMR) was used to investigate the ammonia catalyzed hydrolysis and condensation of the mixed systems of tetraethoxysilane (TEOS) and dimethyldiethoxysilane (DDS) dissolved in methanol. With ammonia catalysis, the hydrolysis reaction orders for TEOS and DDS in the mixed systems remained first order, which is similar to that observed for their corresponding single silane component precursor systems. The hydrolysis rate constant for TEOS in the mixed systems was larger than that of TEOS in the single silane component precursor systems. Meanwhile, the hydrolysis rate constants of DDS in the mixed precursor systems were smaller than those of DDS in the single silane component precursor systems. The hydrolysis and condensation kinetics showed more compatible hydrolysis-condensation relative rates between TEOS and DDS, which remarkably affected the final microstructure of the resulting silica particles. Small angle X-ray scattering (SAXS) experiments showed a typical double fractal structure in the particulate networks.     

Enzymatic hydrolysis of protein: Mechanism and kinetic model

The bioreaction mechanism and kinetic behavior of protein enzymatic hydrolysis for preparing active peptides were investigated to model and characterize the enzymatic hydrolysis curves. Taking into account single-substrate hydrolysis, enzyme inactivation and substrate or product inhibition, the reaction mechanism could be deduced from a series of experimental results carried out in a stirred tank reactor at different substrate concentrations, enzyme concentrations and temperatures based on M-M equation. An exponential equation dh/dt = aexp(-bh) was also established, where parameters a and b have different expressions according to different reaction mechanisms, and different values for different reaction systems. For BSA-trypsin model system, the regressive results agree with the experimental data, i.e. the average relative error was only 4.73%, and the reaction constants were determined as K _m = 0.0748 g/L, K _s = 7.961 g/L, k _d = 9.358/min, k ₂ = 38.439/min, E _a = 64.826 kJ/mol, E _d = 80.031 kJ/mol in accordance with the proposed kinetic mode. The whole set of exponential kinetic equations can be used to model the bioreaction process of protein enzymatic hydrolysis, to calculate the thermodynamic and kinetic constants, and to optimize the operating parameters for bioreactor design. __________ Translated from Journal of Tianjin University, 2005, 38(9) (in Chinese)     

Interactive influence and optimization of reaction parameters in the hydrolysis of olive and coconut triacylglycerols byC. cylindracea andR. javanicus lipases in reverse micellar media

The four reaction parameters—pH, reaction temperature, molar ratio (R) of water to surfactant, and Aerosol-OT concentration—have significant linear, quadratic., and interactive effects on the initial rate and the degree of hydrolysis for lipase-mediated hydrolysis of triacylglycerols (TAG) in Aerosol-OT/iso-octane reverse micellar media. Reaction temperature and pH had the most significant influence on the rate and the degree of hydrolysis, whereas Aerosol-OT concentration had the least influence on those parameters. The initial rate was most influenced by the interactive effect of pH with all other variables, whereas the degree of hydrolysis was the most influenced by the interactive effect of reaction temperature with other variables. Lowerlevel variable combinations were favorable over higher-level variable combinations to TAG hydrolysis in reverse micellar media. Regression models, developed for the initial rate and the degree of hydrolysis as a function of reaction variables, accounted for up to 96% of the variation in the two responses. The optimum reaction condition ranges were determined based on maximization of both the rate and the degree of hydrolysis. The differences in the physicochemical characteristics of substrates had no significant effect on the optimum condition ranges. However, the noticeable differences were observed for these ranges between the systems withRhizopus javanicus andCandida cylindracea lipases. Lipase-catalyzed hydrolysis of TAG in Aerosol-OT/iso-octane reverse micellar media was optimum at about 22‡C, 140 mM Aerosol-OT concentration, pH 6.8, andR value of 14.     

Aqueous phase size exclusion chromatography of polyvinylalcohols of different degrees of hydrolysis

The aqueous-phase size exclusion chromatography (SEC) represents a suitable method for the analysis of molecular weight distribution (MWD) of polyvinylalcohols (PVOHs) of different degree of hydrolysis ranging from 72 to 98 mol-% applying the Suprema columns. Eluents of different composition were used consisting of either a mixture of water and acetonitrile for the lower degrees of hydrolysis (72 - 88 mol-%) or 0.1 M LiNO₃ solution for the higher degrees of hydrolysis (88 - 98 mol-%). By knowing the M̄_w̄ values of commercially available PVOHs samples of a given degree of hydrolysis and using the commercial water soluble narrow distribution standards, a principle of the constant hydrodynamic equivalence ratios was applied to obtain the absolute values of the molecular weights of PVOHs of different degree of hydrolysis. The effect of a various number of extrusion cycles on MWD of different PVOHs was used to demonstrate the sensitivity of the selected SEC conditions.     

Selenomethionine Extraction from Selenized Yeast: an LC-MS Study of the Acid Hydrolysis of a Synthetic Selenopeptide

A synthetically prepared seleno-peptide (AHPDVLTVXLQMLDDGR) was used as a model system for the acid hydrolysis of selenized yeast proteins. The seleno-peptide is a tryptic peptide of a heat shock protein 104 from Saccharomyces cerevisiae, was subjected to acid hydrolysis using methanesulfonic acid over a time period of 8 hours. Aliquots of the solution were sub-sampled at predetermined time intervals and the peptide fragments characterized by reversed phase LC MSⁿ. Similarly, the appearance of amino acid residues in the solution was monitored. It was found that after about 8 hours the synthetic peptide completely hydrolyzed. The use of a selenopeptide as a model for hydrolysis of selenized yeast hydrolysis was validated by comparing the decomposition time profile of the synthetic peptide with that of a selenized yeast sample. The rate of hydrolysis was identical in both systems, suggesting that the employed acid hydrolysis yields to the complete decomposition of the Se containing proteins in yeast and consequently to the liberation of selenomethionine.     

Enzymatic Resolution of Ethyl α-Hydroxyphosphinates in a Modified Reaction Environment

The enzymatic resolutions of two racemic ethyl hydroxyalkane(P-phenyl)phosphinates were performed by both esterification and hydrolysis approaches. The first reaction was performed in anhydrous diisopropyl ether with triethylamine or pyridine as additives by using lipases from three different sources (Candida cylindracea, Aspergillus niger, and Mucor javanicus). The increase in enantioselectivity was observed when NEt₃ was applied. The second reaction—lipase-catalysed hydrolysis of ethyl butyryloxyalkane(P-phenyl)phosphinates—was carried out by Candida cylindracea lipase in diisopropyl ether saturated with water or in aqueous solutions containing MgCl₂, LiCl, or Triton X-100. The usefulness of biphasic systems consisting of diisopropyl ether and water or aqueous solution of MgCl₂, LiCl, or Triton X-100 also were tested. The use of biphasic system in the presence of Triton X-100 resulted in the higher conversion of the substrates.     

Controlled Release of Perfumery Alcohols by Neighboring‐Group Participation. Comparison of the Rate Constants for the Alkaline Hydrolysis of 2‐Acyl‐, 2‐(Hydroxymethyl)‐, and 2‐Carbamoylbenzoates

A series of 2‐acylbenzoates 1 and 2 , 2‐(hydroxymethyl)benzoates 3 , 2‐carbamoylbenzoates 4 – 6 , as well as the carbamoyl esters 7 or 8 of maleate or succinate, respectively (see Fig. 2), were prepared in a few reaction steps, and the potential use of these compounds as chemical delivery systems for the controlled release of primary, secondary, and tertiary fragrance alcohols was investigated. The rate constants for the neighboring‐group‐assisted alkaline ester hydrolysis were determined by anal. HPLC in buffered H₂O/MeCN solution at different pH (Table 1). The rates of hydrolysis were found to depend on the structure of the alcohol, together with the precursor skeleton and the structure of the neighboring nucleophile that attacks the ester function. Primary alcohols were released more rapidly than secondary and tertiary alcohols, and benzoates of allylic primary alcohols (e.g., geraniol) were hydrolyzed 2–4 times faster than their homologous saturated alcohols (e.g., citronellol). For the same leaving alcohol, 2‐[(ethylamino)carbonyl]benzoates cyclized faster than the corresponding 2‐(hydroxymethyl)benzoates, and much faster than their 2‐formyl and 2‐acetyl analogues (see, e.g., Fig. 4). Within the carbamoyl ester series, 2‐[(ethylamino)carbonyl]benzoates were found to have the highest rate constants for the alkaline ester hydrolysis, followed by unsubstituted 2‐(aminocarbonyl)benzoates, or the corresponding isopropyl derivatives. To rationalize the influence of the different structural changes on the hydrolysis kinetics, the experimental data obtained for the 2‐[(alkylamino)carbonyl]benzoates were compared with the results of density‐functional computer simulations (Table 2 and Scheme 4). Based on a preliminary semi‐empirical conformation analysis, density‐functional calculations at the B3LYP/6‐31G** level were carried out for the starting precursor molecules, several reaction intermediates, and the cyclized phthalimides. For the same precursor skeleton, these simple calculations were found to model the experimental data correctly. With an understanding of the influence of structural parameters on the rate constants obtained in this work, it is now possible to influence the rates of hydrolysis over several orders of magnitude, to design tailor‐made precursors for a large variety of fragrance alcohols, and to predict their efficiency as controlled‐release systems in practical applications.     

Phosphate Diester Cleavage Promoted by the Metallomicelles of Ce(III) Complexes of Aza-Crown Ether with Different Numbers of Nitrogen Atoms

The design of artificial hydrolase has attracted extensive attention due to their scientific significance and potential application in the field of gene medicine and molecular biology. This work reports the catalytic activation of two aza-crown ether Ce(III) complexes and their metallomicelles as artificial hydrolase in bis(4-nitrophenyl) phosphate ester (BNPP) hydrolysis. The chemical composition of two complexes was determined by the fluorescence spectra and the mole ratio method for electronic absorption spectra. The bonding effect of BNPP and solubilizing effect of the complexes were proved by a method of fluorescence spectroscopy. The catalytic activity of different catalytic systems in BNPP hydrolysis was measured with UV-vis spectrophotometric method. These catalytic systems showed high catalytic activity for promoting BNPP hydrolysis at the almost physiological conditions. BNPP hydrolysis rate in these catalytic system is about 10⁷- to 10⁹-fold faster than that of the BNPP spontaneous hydrolysis in aqueous solution at the same conditions. The metallomicelle systems exhibited higher catalytic activity compared with the complex solution systems in BNPP hydrolysis, and hexadecyltrimethyl ammonium bromide micelle provides a useful catalytic environment for reaction. The acid effect of the catalytic system is ascribed to the formation of metal-bound hydroxide serving as a better kind of nucleophile.     

Presence versus Proximity: The Role of Pendant Amines in the Catalytic Hydrolysis of a Nerve Agent Simulant

Amino‐functionalized zirconium‐based metal‐organic frameworks (MOFs) have shown unprecedented catalytic activity compared to non‐functionalized analogues for hydrolysis of organophosphonate‐based toxic chemicals. Importantly, the effect of the amino group on the catalytic activity is significantly higher in the case of UiO‐66‐NH₂, where the amino groups reside near the node, compared to UiO‐67‐m‐NH₂, where they are directed away from the node. Herein, we show that the proximity of the amino group is crucial for fast catalytic activity towards hydrolysis of organophosphonate‐based nerve agents. The generality of the observed amine‐proximity‐dictated catalytic activity has been tested on two different MOF systems which have different topology. DFT calculations reveal that amino groups on all the MOFs studied are not acting as Brønsted bases; instead they control the microsolvation environment at the Zr₆‐node active site and therefore increase the overall catalytic rates.     

Kinetics and Mechanism for Hydrolysis of α-Amino Acid Esters in Mixed Ligand Complexes with Zn(II)–Nitrilo-tris(methyl phosphonic Acid)

The kinetics of base hydrolysis of the alanine ethyl ester, in addition to glycine, histidine and methionine methyl esters in the presence of the Zn-NTP complex, were studied in aqueous solution by the pH-potentiometric technique, where NTP denotes the nitrilo-tris(methyl phosphonic acid) ligand. The kinetic data fits assumed that hydrolysis proceeds through formation of a M–OH complex, followed by an intramolecular OH⁻ attack. The effect of an organic solvent on the hydrolysis of coordinated esters was investigated by measuring the rate of hydrolysis in dioxane–water solutions of different compositions at t=25.0 °C and I=0.1 mol⋅dm⁻³. The kinetics of base hydrolysis of the glycine methyl ester was studied at different temperatures. Activation parameters for the base hydrolysis of the complexes were evaluated.     

Temperature effect on the ease of aggregation

The effect of temperature on the critical aggregate concentration (CAgC) has been investigated for the first time, by measurement of the hydrolytic rate constants of p-nitrophenyl dodecanoate (C12) and hexadecanoate (C16) at different temperatures in the 30:70 V/V (Φ=0.30) and 40:60 V/V (Φ= 0.40) dioxane (DX)-H2O systems. The CAgC values of C12 and C16 increase with the increase of the temperature, i.e., high temperatures disfavor aggregation. Activation energies for the hydrolysis of C12 in the monomeric and aggregated concentration domains have also been discussed.     

Kinetic resolution of both 1-phenylethanol enantiomers produced by hydrolysis of 1-phenylethyl acetate with <Emphasis Type="Italic">Candida antarctica</Emphasis> lipase B in different solvent systems

The enzymatic resolution of (R, S)-1-phenylethanol produced by hydrolysis of (R, S)-1-phenylethyl acetate catalyzed by immobilized Candida antarctica lipase B (CALB) was successfully carried out in different solvent systems. A systematic screening and optimization of the reaction parameters such as enzyme amount, the nature and the content of organic solvent, pressure and temperature in supercritical carbon dioxide (SC-CO₂) and phosphate buffer, with respect to the conversion rate, were performed. CALB exhibits high enantioselectivity in both tert-butanol with 0.025 mol/l phosphate buffer (pH 7.5) and SC-CO₂ with 0.025 mol/l phosphate buffer (pH 7.5) systems. The conversion rate was 41.2% higher in SC-CO₂ with 0.025 mol/l phosphate buffer (pH 7.5) then in tert-butanol with 0.025 mol/l phosphate buffer (pH 7.5) and the reaction time decreased from 8 h to 90 min.     

The influence of hydrophobic amines on hydrolysis of bis(p-nitrophenyl) methylphosphonate in micellar solutions of cetylpyridinium bromide

The kinetics of hydrolysis of bis(p-nitrophenyl) methylphosphonate in the presence of primary aliphatic amines in aqueous micellar solutions of cetylpyridinium bromide was studied. The reaction proceedsvia two routes, alkaline hydrolysis and amine-catalyzed hydrolysis according to the general basic catalysis mechanism. The contributions of these routes and the catalytic effect of micelles depend on the hydrophobicity of the amines. The formation of different types of micelles was found, and their characteristic parameters were determined by tensiometry and high-resolution¹H NMR spectroscopy with a magnetic field pulse gradient. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya No. 2, pp. 267–272, February, 2000.     

An Atomistic Modeling and Quantum Mechanical Approach to the Hydrolytic Degradation of Aliphatic Polyesters

This paper reports computational simulations at two different scales employed to investigate the hydrolytic degradation of two homopolyesters: polyglycolide, PGA and poly(L-lactide), PLLA. Atomistic bulk models were used to investigate the dry and various hydrated states of the two systems. In addition, the first moments of contact between the polymers and water were studied employing atomistic interface models. A higher affinity of water to polyglycolide in comparison with poly(L-lactide) was observed, while diffusion of water was found to be lower in the first polymer. Quantum chemical calculations for the first step of the water-assisted hydrolysis revealed a higher resistance to hydrolytical scission of the L-lactyl units in comparison to glycolyl units.     

Hydrolytic Cleavage of Paraoxon by Octanohydroxamate Ion in Cationic Microemulsions

The hydrolysis reaction of O,O‐diethyl O‐p‐nitrophenylphosphate (Paraoxon) with the octanohydroxamate ion (OHA^?) was studied in a cationic oil‐in‐water (O/W) microemulsion system over a pH range 7.5–12.0 at 300 K. The O/W systems are stabilized by using cationic surfactant, cetyltrimethylammonium bromide (CTAB), and n‐butanol as cosurfactants. In a microemulsion, the rate enhancement by OHA^? is greater toward the cleavage of paraoxon than its spontaneous (2.1 × 10⁷ s^?1) hydrolysis. The k_obs values for the reaction of paraoxon with OHA^? were determined in different microemulsion compositions with varying chain length of alcohols (n‐butanol, n‐pentanol, n‐octanol, and n‐dodecanol) and alkanes (n‐hexane, n‐heptane, and n‐decane). The effects of water content, pH, and size of the oil pool have been discussed.     

Effect of the structures of microemulsions on chemical reactions

Two kinds of chemical reactions were studied in two different microemulsion systems: cetyltrimethylammonium bromide/1-butanol/10 and 25% n-octane/water and sodium dodecyl sulfonate/1-butanol/20% styrene/water. One reaction is a hydrolysis reaction, in which aspirin and 2,4-dinitrochlorobenzene were used as the hydrolysis substrates. The second reaction is the polymerization of styrene, which was initiated by using two initiators, water-soluble K₂S₂O₈ and oil-soluble 2,2′-azobis(isobutyronitrile), and, at the same time, the polymerization of acrylamide, which was initiated by NaHSO₃, was also studied. All the hydrolysis reaction experimental results show that the hydrolysis is greatly affected by the structures and the structural transitions of microemulsions. The hydrolysis rates are higher in water-in-oil (W/O) microemulsion media and decrease with the addition of water. The rates increase in bicontinuous (BC) microemulsions and decrease in oil-in-water (O/W) microemulsions. The transition points of the hydrolysis rates occurred at the two microemulsion structural transition points from W/O to BC and from BC to O/W. The polymerization relationships between the conversions of styrene, the molecular weights of polystyrene and the water contents of the microemulsion system were obtained. The effects of microemulsion structures on the sizes of the polystyrene particles and on the molecular weights of the polymers are discussed. Polystyrene particles with diameters of 10–60 nm were observed by microscopy. Our experimental polymerization results show that microemulsions are suitable as media for the production of polymers, the molecular weights and the particle sizes of which can be controlled and predicted by variations in microemulsion structures. Received: 11 July 1999/Accepted: 26 July 1999     

Comparative Reactivity of Phosphate Ester Hydrolysis Catalyzed by Mononuclear and Hetero-Dinuclear Complexes Containing the Lanthanum Ion (III)

The hydrolysis of bis(p-nitrophenyl phosphate)(BNPP) and p-nitrophenyl phosphate (NPP) were strongly promoted by the mononuclear La^III[(N,N-bis(3-carboxyl)-2-hydroxysalicylidene)ethylenediamine] and the hetero-dinuclear Cu^IILa^III[(N,N-bis(3-carboxyl)-2-hydroxysalicylidene)ethylenediamine] complexes at 35 °C in 50% aqueous DMSO. The results indicated that the hetero-dinuclear Cu^IILa^III complex exhibited a relatively higher catalytic function on NPP hydrolysis, while the hydrolysis of BNPP was slightly more efficient in the presence of the mononuclear La^III complex than that in the presence of the Cu^IILa^III complex, and this case was discussed by the different spacer requirements for NPP and BNPP hydrolysis. In addition, widely differing pH-rate profiles were obtained: saturated curves for NPP hydrolysis and bell-shaped curves for BNPP hydrolysis, and thus different kinetic treatments were employed to obtain the relative parameters.     

Studies on PNPP Hydrolysis Catalyzed by Schiff Base Cobalt（Ⅱ） Complexes Containing Benzoaza-15-crown-5

Three novel Schiff base cobalt（Ⅱ） complexes containing benzoaza-15-crown-5, CoL^1, CoL^2 and CoL^3 were synthesized and characterized, and these complexes were used in catalytic hydrolysis of carboxylic ester （PNPP, p-nitrophenyl picolinate） as mimic hydrolytic metalloenzyme. The analysis of specific absorption spectra of the hydrolytic reaction systems indicated that the catalytic hydrolysis involved the key intermediates formed by PNPP with cobalt（Ⅱ） complexes. The CoL^3 bearing the electron withdrawing group shows better catalytic activity due to its stabilization effect on active species MLS^-. The catalytic mechanism of PNPP hydrolysis was also proposed. The kinetic parameter of PNPP catalytic hydrolysis has been calculated and the activation energy for the catalytic hydrolysis is 43.69, 39.76 and 35.44 kJ·mol^-1, respectively.     

Studies on BNPP Cleavage by Schiff Base Complexes Containing Benzoaza‐15‐Crown‐5 in DHAB Micellar Solution

Two novel benzoaza‐crown Schiff base cobalt (II) and manganese (III) complexes were synthesized and characterized. The hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP) catalyzed by the two complexes was studied in buffer solution containing dihexadecyldimethylammonium bromide (DHAB) at 25°±0.1°C and different pH values. The kinetic mathematical model of BNPP hydrolysis was proposed, and the effects of different reaction conditions on BNPP hydrolysis were discussed. The results indicate that the two complexes (MnLCl and CoL) can efficiently accelerate the catalytic cleavage of BNPP in DHAB micellar solution. The pseudo‐first‐order rate constants (k _obsd) of BNPP hydrolysis catalyzed by the metallomicelles of MnLCl/DHAB and CoL/DHAB are 2.32×10⁷ times and 1.45×10⁷ times higher than that of the BNPP spontaneous hydrolysis, respectively. Possible reasons for the huge rate accelerations include the lower critical micelle concentration (cmc) of DHAB and formation of metallomicelles made of complexes and DHAB. Furthermore, the BNPP cleavage catalyzed only by the two complexes was investigated in buffer solution. It was found that the hydrolytic rates of BNPP catalyzed only by the two complexes were about 1% of those catalyzed by MnLCl/DHAB and CoL/DHAB systems at 25°C, pH=7.00, and [BNPP]=2.0×10^?4 mol · dm^?3.