Enthalpic interaction coefficients of amides dissolved in N,N-dimethylformamide

Enthalpies of dilution of propionamide, butyramide, pentanamide, hexanamide, N-pentylacetamide, N,N-dipentylacetamide, N-ethylhexanamide and N,N-diethylhexanamide dissolved in N,N-dimethylformamide as solvent have been measured calorimetrically at 25°C. The results are interpreted in terms of the McMillan-Mayer theory. Enthalpic interaction parameters are obtained for pairs, triplets and some quadruplets of solute molecules. All enthalpic pair interaction coefficients are negative, whereas those for triplets are positive. For unsubstituted amides the change of the enthalpic coefficients with the number of C-atoms differs considerably from that of the substituted compounds. The concept of polarophobic interaction is used for the interpretation of the results in connection with the assumption of formation of solute-solvent associates. For solutes with longer alkyl chains the results cannot be described satisfactorily in terms of the additivity approach of Savage and Wood. Probably the pair interactions of these compounds are not the result of interaction in a random way. Also the linear dependence of the pair interaction coefficients of the larger molecules with the number of C-atoms and the results for the unsubstituted amides support the occurrence of preferential orientations for these compounds.     

A study of solute-solute interactions of amides dissolved in N-methylformamide by enthalpic interaction coefficients

Enthalpies of dilution of formamide, acetamide, propionamide, butyramide and hexanamide, dissolved in N-methylformamide have been measured calorimetrically at 25°C. From the results McMillan-Mayer coefficient related enthalpic pair and triplet interaction coefficients have been calculated. Except for those of formamide, all pair coefficients are negative, whereas the triplet terms are positive. The values in the protic solvent N-methylformamide presented in this paper together with those published before are compared with results for corresponding solutes dissolved in the aprotic solvent N,N-dimethylformamide. A discussion of the dependence of the interaction coefficients on the applied concentration scale is given and conversion factors are presented. The influence of hydrogen bonding, of substituent effects on this hydrogen bonding, and of polarophobic interaction is discussed. The latter is comparable in N,N-dimethyl-and N-methylformamide. The enthalpic pair interaction coefficients have been correlated with the Excess Group Additivity approach.To whom correspondence should be addressed.     

Enthalpies of dilution of aqueous solutions of formamide,acetamide, propionamide,andN,N-dimethylformamide

The enthalpies of dilution of aqueous solutions of formamide, acetamide, propionamide,N,N-dimethylformamide, and sucrose have been measured from about 0.15 to 2.0 moles-kg ^–1 at 25.0°C. The results of the enthalpy measurements were used to calculate the pairwise enthalpies of interaction for each compound with itself. The equation of Savage and Wood together with their interaction parameters are used to predict the experimental results. All of the predictions are within the standard deviation of the original correlation of Savage and Wood (±220 J-kg-mole ^–2 ). Detailed examination of the results shows that specific effects are present but they are less than 220 J-kg-mole ^–2 . Results on urea and substituted ureas are used to determine interaction coefficients for a urea group with itself and with another CH ₂ group. The result,H _U,U =–280 andH _{U,CH 2} =29 J-kg-mole ^–2 , is an improvement on the previous arbitrary assignment of parameters for urea interactions.     

Enthalpies of Dilution and Enthalpies of Mixing of Amino Acids with Sucrose in Aqueous Solutions at 298.15 K

The enthalpies of mixing of aqueous solutions have been determined for sucrose with six different amino acids (glycine, l-alanine, l-serine, l-valine, l-proline and l-threonine) at 298.15 K, by using a LKB-2277 flow microcalorimetric system. These results, along with the enthalpies of dilution of these solutes for the initial solutions, were used to determine the enthalpic interaction coefficients (h _xy, h _xyy, h _xxy) of the McMillan–Mayer Theory. The pair-wise cross interaction coefficients of amino acids and sucrose are discussed from the viewpoint of solute–solute interactions.     

Correlation of solute-solute interaction enthalpies in dimethylformamide by group additivity

The Savage and Wood group additivity method has been applied to enthalpic pair interaction coefficients of more than 30 solutes dissolved in N,N-dimethylformamide. The results are not satisfactory. Better results are obtained by using a method which accounts for the differences in the numbers of molecular groups between solute and solvent molecules. With this excess group additivity method reasonable correlations are obtained even for solutes as large as dipeptide amides.     

Interactions between terminally substituted amino acids in an aqueous and a non-aqueous environment. Enthalpic interaction coefficients in water and in N,N-dimethylformamide at 25°C

Enthalpies of dilution of the N-acetyl amides of glycine, L-alanine, L-valine, L-leucine, and L-phenylalanine, dissolved in N,N-dimethylformamide (DMF) as a solvent have been measured at 25°C. The results obtained have been analyzed to give the enthalpic interaction (or virial) coefficients of the solutes and these are compared with information previously obtained in aqueous systems. There are marked differences in the interaction properties in the two solvents and, while the additivity approach of Savage and Wood is applicable to the solutes in water it is not suitable for representing the interactions in DMF. A correlation is presented between the enthalpic second virial coefficients in DMF and the propensity of side-chains to be in proximity in globular proteins.     

D-甘露醇与D-山梨醇在纯水和卤化钠水溶液中的稀释焓

应用等温流动微量热技术测定了298.15 K下D-甘露醇和D-山梨醇在纯水和卤化钠水溶液中的稀释焓,利用M cM illan理论计算了D-甘露醇和D-山梨醇在纯水和卤化钠水溶液中焓相互作用系数.结果表明,D-甘露醇和D-山梨醇在纯水和卤化钠水溶液中的二阶焓相互作用系数均为正值,并随着卤离子半径的变化而相应变化;且同种溶剂中,D-甘露醇的二阶焓相互作用系数要大于D-山梨醇的.结合两分子结构的差异,通过溶质-溶质相互作用和溶剂-溶质相互作用对这一结果进行了讨论.     

Enthalpic interaction coefficients of formamides dissolved in N,N-dimethylformamide

Enthalpies of dilution of formamide, N-methylformamide, N-ethylformamide, N-propylformamide, N-butylformamide, N-pentylformamide, N,N-diethyl-formamide, N,N-dipropylformamide, N,N-dibutylformamide, and N,N-dipentyl-formamide dissolved in N,N-dimethylformamide as solvent have been measured calorimetrically at 25°C. The results are interpreted in terms of the McMillan-Mayer theory. Enthalpic interaction parameters are obtained for pairs, triplets, and in some cases, quadruplets of solute molecules. In general, the enthalpic pair interaction coefficients are negative, whereas the triplet coefficients are positive. The interaction enthalpies are positive only for N-methylformamide and formamide. The magnitudes of the enthalpic pair and triplet interaction coefficients increase with increasing number of C atoms in the N-alkyl groups. The results for the formamides presented in this paper are compared with those for corresponding acetamides published earlier. Although the trends are comparable, distinct differences are observed. The contribution of the -CH₃ group at the CO side of the dialkylacetamides to the enthalpic interaction coefficients appears to be negligible. The same is true for -CH₂ groups at the NH side of a number of amides and related compounds. The enthalpic pair interaction coefficients of the mono-N-alkylsubstituted formamides show a shift of about 100 J-kg-mol^–2 as compared with isomeric N-alkylacetamides. This is discussed in terms of the difference in proton donating and accepting ability of several types of amide molecules. It is concluded that substitution effects should be incorporated in additivity models for these type of systems.     

Enthalpies of solution of n-alcohols in formamide and ethylene glycol

The enthalpies of solution of 1-pentanol, 1-hexanol and 1-heptanol and water were determined in formamide and in ethylene glycol, at 25‡C, by macrosolution calorimetry. The observed enthalpies of solution for the n-alcohols are positive in the two solvents, and of similar magnitude. The enthalpy of solution of water is positive in formamide, and negative in ethylene glycol. From the enthalpies of solution, the enthalpies of solvation and the enthalpies of transfer for organic solvent↿ water were calculated. Using our values and literature data for alkanols, it was possible to see that both the enthalpies of solution and the enthalpies of solvation presented a constant CH₂ increment for the entire series, in contrast with their behavior in water. The methylene increments for these properties in different solvents are compared with parameters considered to reflect the cohesive energy of the solvent.     

Enthalpies of dilution of electrolyte solutions by flow microcalorimetry

The enthalpies of dilution of NaCl, Me₄NBr, andn-Bu₄NBr were measured in water at 25°C with a new flow microcalorimeter. The data were analyzed with a polynomial equation, and the derived relative apparent molal enthalpies _L are in good agreement with literature values. Provided care is taken that mixing is complete, flow calorimeters are as reliable and much less time-consuming than cell-type instruments for enthalpies of dilution measurements.     

Enthalpies of dilution of l-cystine in aqueous solutions of sodium hydroxide, potassium hydroxide and hydrochloric acid

The enthalpies of dilution of l-cystine in solutions of two strong alkalis and one strong acid have been determined by isothermal flow-mix calorimetry at the temperatures 298.15 K, 303.15 K, 308.15 K, 313.15 K and 318.15 K. Equations of apparent enthalpies of dilution have been obtained from the experimental data in terms of the improved McMillan-Mayer theory. Enthalpic interaction coefficients, h₂, h₃, and h₄, are obtained and the values of pair-wise enthalpic interaction coefficient, h₂, discussed in the light of solute-solute and solute-solvent interactions.     

D-山梨醇在纯水和卤化钠水溶液中293.15K～318.15K的稀释焓

应用流动式等温精密微量热技术测定4个温度(293.15、303.15、308.15和318.15 K)下D-山梨醇在纯水和卤化钠水溶液中的稀释焓.根据改进的McMillan-Mayer理论对所测数据进行关联,得到了表观摩尔稀释焓对浓度变化的经验方程和各阶焓相互作用系数(h2,h3和h4)和二阶熵相互作用系数(s2),根...     

Infinite dilution activity coefficients and gas-to-liquid partition coefficients of organic solutes dissolved in 1-sec-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and in 1-tert-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Inverse gas chromatography was used to measure infinite dilution activity coefficients and gas-to-liquid partition coefficients for 48 organic solute probes in either 1-sec-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-tert-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in the temperature range from 323.15 to 373.15 K. Partial molar excess enthalpies of solution were calculated from the variation of the infinite dilution activity coefficients with temperature. Abraham model correlations were also derived from the experimental partition coefficient data. The derived Abraham model correlations describe the observed partition coefficients to within 0.11 log units.     

木糖醇在纯水和碱金属卤化物水溶液中的稀释焓

应用等温流动微量热法测定了298.15 K时木糖醇在纯水和碱金属卤化物水溶液中的稀释焓, 根据McMillan- Mayer理论计算了木糖醇在溶液中的二到四阶焓相互作用系数. 结果表明, 木糖醇在碱金属卤盐溶液中的焓对相互作用系数h₂均为正值, h₂值随着碱金属阳离子或卤素阴离子半径的增大皆依次增大. 根据木糖醇参与的溶质-溶质, 溶质-溶剂等弱相互作用, 对该种多元醇在碱金属卤盐水溶液中的焓相互作用系数的变化进行了解释.     

Enthalpies of dilution of alkaline and alkaline earthp-toluenesulfonates

Enthalpies of dilution (H_D, c0.002 mol-dm^–3) of aqueous solutions of lithium, sodium, potassium, cesium, calcium, magnesium, and strontium salts of p-toluenesulfonic acid were measured at several temperatures between 0° and 40°C, and over a broad concentration range. For monovalent ions the following results were obtained: (i) the enthalpy of dilution for lithium p-toluenesulfonate became more exothermic on increasing the concentration, while those of sodium, potassium, and cesium salts exhibited a maximum, (ii) enthalpies of dilution were strongly dependent on the ionic radius of the cation, and the-H_D values increase in the order, Li>Na>K>Cs. This parallels the behavior of the same quantity in alkaline poly(styrenesulfonate) solutions. For divalent ions the situation was different; Mg, Ca, and Sr p-toluenesulfonates showed little temperature dependence and almost no dependence on the nature of the ion. In contrast with poly(styrenesulfonate) solutions, the enthalpies of dilution were exothermic for all temperatures and salts.     

L-丝氨酸在乙醇-水混合溶剂中的稀释焓

氨基酸是重要的生物活性物质,是组成蛋白质的基本结构单位．氨基酸的稀释焓是氨基酸溶液热力学性质研究的一个重要方面［１,２］,即溶质 溶质相互作用．目前氨基酸的稀释焓研究大多集中在纯水溶液中．然而,大多数蛋白质的天然环境并不是单纯的水溶液,而是含有许多有机物质的复杂环境．有机溶剂对蛋白质的溶解度、变性行为、解缔成次一级结构和酶的活性等都有很大影响［３］,蛋白质在非水介质环境条件下的热力学性质与其在水溶液环境条件下的性质是大不相同的．由混合溶剂中稀释焓的研究可以获得溶剂介入的溶质分子间的相互作用信息．…     

Enthalpies of Dilution of Colchicine in Aqueous NaCl Solutions

The concentration effect on the dilution enthalpies (Δ_dil H _m) of colchicine (COL) in aqueous NaCl solutions has been investigated by isothermal titration microcalorimetry at 298.15 K. The corresponding homogeneous enthalpic interaction coefficients have been calculated according to the excess enthalpy concept. The results show that the dilution enthalpies of COL in aqueous NaCl solutions at different mass fractions are positive. The overall trend is that enthalpies of dilution become more positive with the increase of the salt mass fraction. The values of enthalpic pair-wise interaction coefficients, h ₂, have been obtained by fitting the data of the enthalpies of dilution with a viral expansion. The results can be interpreted from the view of solute-solute and solute-solvent interactions involved in the solvent effects.     

Enthalpies of transfer of N-methylformamide,formamide, and N,N-dimethylformamide from methanol to methanol+dimethylsulfoxide mixtures

The enthalpies of transfer of formamide, N-methylformamide and N,N-dimethylformamide from methanol to methanol+dimethylsulfoxide solvent systems have been measured. These data are analysed in terms of a recently developed model of solvation in mixed solvents. The results of the data analyses indicate that preferential solvation of the different functional groups of the amides differs, the carbonyl oxygen being preferentially solvated by methanol and the nitrogen protons are by dimethylsulfoxide.     

Enthalpies of dilution of aqueous solutions of amides and alcohols

Enthalpies of dilution of aqueous systems containing formamide, dimethyl-formamide, the mixture of these amides, and each amide separately with mannitol, inositol, and cyclohexanol have been determined at 25°C. The data have been treated in terms of the Savage-Wood additivity principle and in combination with literature data. New values for the methylene-amide, carbinol-amide, and amide-amide group interaction enthalpies are presented. These may be used with data on a wider variety of solute systems to obtain interaction enthalpies for new groups.     

Enthalpies of solution of tetra-n-butylammonium bromide in binary mixtures of water,formamide, N-methylformamide,and N,N-dimethylformamide

The enthalpies of solution of tetra-n-butylammonium bromide have been measured in mixtures of formamide (F) with water, N-methylformamide (NMF) with water, N,N-dimethylformamide (DMF) with water, F with NMF, DMF with F, and NMF with DMF at 25°C in the whole mole-fraction range. The enthalpies of solution vs composition profiles show a maximum value in the DMF-H₂O and in the DMF-F systems. In the F-NMF and NMF-DMF mixturesn-Bu₄NBr displays a nearly ideal behavior, whereas in the other solvent systems the excess enthalpy of solution deviates substantially from zero.