The thermochemical characteristics of solution of DL-α-alanylglycine and DL-α-alanylalanine in water-alcohol mixtures at 298.15 K

The integral enthalpies of solution of DL-α-alanylglycine and DL-α-alanylalanine in water-ethanol, water-n-propanol, and water-isopropanol mixtures were measured calorimetrically at alcohol concentrations x ₂ = 0?0.4 mole fractions. The standard enthalpies of solution (Δ_sol H°) of the peptides and their transfer (Δ_tr H°) from water into the mixed solvents were calculated. The influence of the structure and properties of the solutes and mixture composition on the enthalpy characteristics were considered. The Δ_sol H° = f(x ₂) and Δ_tr H° = f(x ₂) dependences were found to have extrema. The enthalpy coefficients of pair interactions (h _xy ) between the peptide and alcohol molecules were calculated. The coefficients were positive and increased in the series ethanol, n-propanol, isopropanol.     

Thermochemistry of the dissolution of DL-α-alanyl-DL-norleucine in aqueous solutions of amides at 298.15 K

Enthalpies of the dissolution of DL-α-alanyl-DL-norleucine are determined by calorimetry in aqueous solutions of formamide (FA), N-methylformamide (MFA), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) at a concentration of amides of x ₂ = 0–0.4 molar parts and T = 298.15 K. Standard values of enthalpies of dissolution Δ_sol H ^o and Δ_tr H ^o of DL-α-alanyl-DL-norleucine transfer from water to binary solvent are calculated, along with the enthalpy coefficients of pair interactions h _xy of DL-α-alanyl-DL-norleucine with amide molecules. The effect of the composition of water-organic mixtures and the structure of amides on the enthalpy characteristics of dissolution and transition of DL-α-alanyl-DL-norleucine is considered. Quantitative estimates of the contributions to energy from DL-α-alanyl-DL-norleucine-amides pair interactions determined by the polarity, polarizability, and electron acceptor and electron donor ability of organic cosolvents are given using the Kamlet-Taft correlation equation.     

Response of D-, L- and DL-α-alanines to ionizing radiations

There is no statistically significant difference in the response of the enantiomers and the racemate of -alanine to -radiation (⁶⁰Co) and accelerated electrons (10 MeV). The response was measured by the yield of ammonia, one of the separated final products of solid alanine radiolysis and the concentration of free radical CH₃·CH·COO^–, the intermediate product of radiolysis. Some of the properties of the racemate may affect the precision of measurements. The_DL-alanine shows different crystal structure, morphology of crystals, specific density and bulk density than the enantiomers. The response of_L and_DL alanines built into composites may be different because of different reactivity of the enantiomer and the racemate with components during the processing and irradiation.     

The enthalpy of solution of DL-α-alanyl-DL-α-valine depending on the composition of water-alcohol binary solvents at 298.15 K

The integral enthalpies of solution of DL-α-alanyl-DL-α-valine in water-ethanol, water-n-propanol, and water-isopropanol mixtures at alcohol concentrations x ₂ = 0–0.4 mole fractions were measured calorimetrically. The enthalpies of solution of the peptide Δ_sol H° and transfer from water to a mixed solvent Δ_tr H° were calculated. The effect of the structure and properties of the peptide and mixture composition on the enthalpy characteristics of the peptide are discussed. The enthalpy coefficients of pair interactions h _xy of DL-α-alanyl-DL-α-valine with alcohol molecules were calculated. It was found that they were positive and increased in the series ethanol, n-propanol, isopropanol. An analysis of the results allows the general features of changes in the thermodynamic parameters of solution of peptides of the DL-α-alanine series with different amino acid residues in water-alcohol mixtures to be established.     

Dependence of the solution and transfer enthalpies of DL-α-alanyl-DL-α-asparagine on the composition of water-amide binary solvents at 298.15 K

Solution enthalpies of DL-α-alanyl-DL-α-asparagine (AlaAsn) in water-formamide, water-N-methylformamide, water-N,N-dimethylformamide, and water-N,N-dimethylacetamide mixtures were measured in the range of amide mole fractions x ₂ = 0–0.3. The standard enthalpies of solution (Δ_sol H°) and transfer (Δ_tr H°) of AlaAsn from water to the binary solvent and enthalpy coefficients of pair-wise interactions (h _xy ) of AlaAsn with amide molecules were calculated. The influence of the composition of the water-organic mixture on the enthalpy characteristics of AlaAsn is discussed. It is shown that the enthalpy characteristics of solution and transfer of AlaAsn are related to the structure of amides.     

磷钼酸催化合成DL-α-生育酚

以磷钼酸(H3PMo12O40)为催化剂,通过2,3,5-三甲基氢醌与异植醇在室温下缩合得到DL-α-生育酚(维生素E),发现H3PMo12O40是合成DL-α-生育酚的一种高活性、易于分离和能够重复使用的催化剂。     

Thermochemistry of the Dissolution of Dipeptides Containing DL-α-Alanine in Aqueous Solutions of Sodium Dodecyl Sulfate at 298.15 K

Enthalpies of the dissolution of DL-α-alanylglycine (AlaGly), DL-α-alanyl-DL-α-alanine (AlaAla), DL-α-alanyl-DL-α-valine (AlaVal), and DL-α-alanyl-DL-norleucine (AlaNln) in an aqueous solution of sodium dodecyl sulfate (SDS) at SDS concentration of m = 0–0.07 mol kg^?1 and temperature Т = 298.15 K are measured via calorimetry. The standard values of the enthalpy of dissolution (Δ_solH ^m ) and the transfer of dipeptides (Δ_trH ^m ) from water to aqueous SDS solutions are calculated using the experimental data. The dependences of Δ_solH ^m and Δ_trH ^m the SDS concentration at a constant concentration of dipeptide are established. Thermochemical characteristics of the transfer of AlaGly, AlaAla, AlaVal, and AlaNln in the investigated range of SDS concentrations are compared. The results are interpreted by considering ion–ion, ion–polar, and hydrophobic–hydrophobic interactions between SDS and dipeptide molecules.     

Effect of the composition of a water-alcohol solvent on the thermodynamics of dissolution of DL-α-alanyl-β-alanine at 298.15 K

Enthalpies of solution for DL-α-alanyl-β-alanine in H₂O-ethanol, H₂O-1-propanol, and H₂O-2-propanol mixed solvents with the alcohol mole fraction x ₂ = 0–0.3 are measured at 298.15 K. Standard enthalpies of solution (Δ_sol H ^°), standard enthalpies of transfer of DL-α-alanyl-β-alanine from water to binary solvent (Δ_tr H ^°), and coefficients of enthalpies of pair interactions with alcohol molecules (h _xy ) are calculated. The effect the structure and properties of alcohols and the composition of a water-alcohol mixture have on the enthalpy of dissolution for DL-α-alanyl-β-alanine are discussed. The h _xy values for dipeptides of the alanine series in water-alcohol binary solvents are compared.     

Thermodynamics of DL-α-aminobutyric acid induced solvation mechanism in aqueous KCl solutions at 288.15–308.15 K

The solubilities of DL-α-aminobutyric acid in KCl solutions of different concentrations are measured at 288.15–308.15 K. Gibbs energies and entropies have been determined for transfer of α-aminobutyric acid form water to aqueous KCl solution at 298.15 K. The cavity, dipole-dipole and other interactions affecting the solubility, as well as stability of the amino acid in solution are also evaluated. Gibbs energy and entropy of transfer due to interactions are computed to create the model of the complex solute-solvent and solventsolvent interactions. Molar volume, densities, dipole moment of solvent and diameter of co-solvent in aqueous potassium chloride are also evaluated.     

Effect of temperature on the thermodynamic characteristics of the protolytic equilibria of DL-α-alanyl-β-alanine in aqueous solutions in the range of 298 to 318 K

Protolytic equilibria in aqueous solutions of DL-α-alanyl-β-alanine are studied by calorimetry. Measurements are performed at temperatures of 298.15, 308.15, and 318.15 K; and at ionic strengths of 0.5, 1.0, and 1.5 (against a background of potassium nitrate). Thermodynamic characteristics (pK, ΔG, ΔH, and ΔS) of the stepwise dissociation of dipeptides both in water-salt and standard solutions are obtained for the first time.     

DL-乳酸-ε-己内酯无规共聚物改性聚DL-乳酸

合成了高分子量DL乳酸-ε-己内酯无规共聚物(PLCA),其结构经1H NMR表征.通过溶液共混制备了用PLCA改性DL-聚乳酸(PDLLA)的复合材料PDLLA/PLCA(PLC).研究了PLC的微观形态,力学性能,降解性等.结果表明,PLCA与PDLLA具有良好相容性;与PDLLA比较,PLC的柔韧性得到显著提高,降解速度加快.     

DL-对羟基苯甘氨酸的合成新工艺

DL-对羟基苯甘氨酸简称DL-HPG,是一种白色固体,熔点为225～227℃.该化合物经拆分可得D-HPG,它是合成广谱抗生素羟氨苄青霉素和羟氨苄头孢菌素的重要原料.该药物的抗菌性能已超过青霉素.因此DL-HPG 的合成研究具有广阔的应用价值.     

α-Thioureidoalkylation of urea heteroanalogs

α-Thioureidoalkylation of urea heteroanalogs such as thiosemicarbazide, amino-guanidine, sulfamide, and sulfonamides with 4,5-dihydroxyimidazolidine-2-thiones has been studied. Previously unknown 4,5-bis[thiosemicarbazido(guanidinoamino)]imidazolidine-2-thiones, 5,7-dialkylperhydroimidazo[4,5- e][1,2,4]triazine-3,6-dithiones, 4,6-diethyl-5(3H)-thioxotetrahydro-1 H-imidazo[4,5- c][1,2,5]thiadiazole 2,2-dioxide, and 1,3-dialkyl-4-[guanidinoimino(arylsulfonylimino)]imidazolidine-2-thiones have been synthesized.     

Hydrazones ofα-pyrazolidinylacetoacetic ester

The p-nitrophenylhydrazones and acetylhydrazones of trans--(1-acetyl-2-phenyl-3-methyl-5-pyrazolidinyl)-acetoacetic ester have been obtained in the form of a mixture of diastereomeric pairs of syn-isomers. Individual diastereomeric pairs that have been isolated do not undergo any tautomeric conversions in nonpolar solvents. Heterocyclization of these hydrazones is difficult.M. V. Lomonosov Moscow State University, Moscow 119899. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 311–320, March, 1998.     

流动注射化学发光法测定DL-酪氨酸

在甲醛存在下 ,高锰酸钾与DL 酪氨酸能够发生化学发光反应 ,产生很强的化学发光。据此采用流动注射技术 ,建立了一种测定DL 酪氨酸的化学发光分析法。方法的检出限为 2 .9× 1 0 - 8g/mL ,相对标准偏差为 1 .5 % ( 1 .0× 1 0 - 6g/mLDL 酪氨酸 ,n =1 1 ) ,线性范围为 1 .0× 1 0 - 7g/mL～ 5 .0× 1 0 - 6g/mL。