Song-Sheng Qu

A solution-reaction isoperibol calorimeter and standard molar enthalpies of formation of Ln(hq)2Ac (Ln = La, Pr)

Abstract An on-line solution-reaction isoperibol calorimeter has been constructed. The performance of the apparatus was evaluated by measuring the molar enthalpy of solution of KCl in water at 298.15xa0K. The uncertainty and the inaccurary of the experimental results were within ±0.3% compared with the recommended reference data. Using the calorimeter, the molar enthalpies of reaction for the following two reactions: LaCl3·7H2O(s)+2Hhq(s)+NaAc(s)=La(hq)2Ac(s)+NaCl(s)+2HCl(g)+7H2O(l) and PrCl3·6H2O(s)+2Hhq(s)+NaAc(s)=Pr(hq)2Ac(s)+NaCl(s)+2HCl(g)+6H2O(l), were determined at T=298.15xa0K, as −(78.3±0.6) and −(97.3±0.5)xa0kJxa0mol−l, respectively. From the above molar enthalpies of reaction and other auxiliary thermodynamic quantities, the standard molar enthalpies of formation of La(hq)2Ac and Pr(hq)2Ac, at T=298.15xa0K, have been derived to be −(1535.5±0.7) and −(1536.7±0.6)xa0kJxa0mol−l, respectively.

Heat capacity and thermochemical study of trifluoroacetamide (C2H2F3NO)

Abstract The low-temperature heat capacities of trifluoroacetamide were precisely determined with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 404xa0K. A solid-to-solid phase transition, a fusion and a phase transition from a liquid crystalline phase to fully liquid phase have been observed at the temperatures of 336.911±0.102, 347.622±0.094 and 388.896±0.160xa0K, respectively. The molar enthalpies of these phase transitions as well as the chemical purity of the substance were determined to be 5.576±0.004, 11.496±0.007, 1.340±0.005xa0kJxa0mol −1 and 99.30xa0mol%, respectively, on the basis of the heat capacity measurements. The molar entropies of the three phase transitions were calculated to be 16.550±0.012, 33.071±0.029 and 3.447±0.027xa0Jxa0mo1 −1 xa0K −1 , respectively. Further researches of the thermochemical properties for this compound have been carried out by means of TG and DSC techniques.

Microcalorimetric study of Escherichia coli growth inhibited by the selenomorpholine complexes.

The inhibitory or antibiotic action of four kinds of the selenomorpholine complex on a strain of Escherichia coli was studied by microcalorimetry. Differences in their capacities to inhibit the metabolism of this bacterium were observed. The extent and duration of the inhibitory effect on the metabolism as judged from the rate constant, k, and the half-inhibitory concentration, IC50, varied with the different drugs. The rate constant (k) of Escherichia coli (in the log phase) in the presence of the drugs decreased with increasing concentrations of the drugs (C). The relationship of k and C is nearly linear for (1) selenomorpholine and (2) selenomorpholine hydrochloride, but for (3) N,N′-methylene bisselenomorpholine and (4) N-dodecyl selenomorpholine, it is not linear. The experimental results reveal that the sequence of antibiotic activity of selenomorpholines is (3) and (4)>(1)>(2).

Thermodynamics of binding of cadmium to bovine serum albumin

The binding isotherm of Cd2+ ion to bovine serum albumin (BSA) has been investigated by microcalorimetry at 310.15 K and pH 7.0. The thermodynamic parameters of the binding reaction have been determined, and the stoichiometry of the complex is 2:1, indicating that there exist two identical binding sites of BSA with Cd2+ ion. The value of deltarHthetam is -28.4+/-1.7 kJ mol(-1), the free energy of binding deltarGthetam is -25.2 kJ mol(-1), and the entropy of binding deltarSthetam is -10.3 J mol(-1) K(-1). The negative deltarHthetam and deltarSthetam values are observed for the binding reaction of Cd2+ ion and BSA, suggesting that the binding reaction is mainly enthalpy-driven and the entropy is unfavorable for it.

A thermochemical study of the solid-state coordination reactions of two α-amino acids with copper(II) acetate

Abstract The two solid-state coordination reactions (1) CuAc 2 · H 2 O ( s )+2 Ala ( s )→trans- Cu ( Ala ) 2 ( s )+2 HAc ( l )+ H 2 O ( l ) (2) CuAc 2 · H 2 O ( s )+2 Gly ( s )→trans- Cu ( Gly ) 2 · H 2 O ( s )+2 HAc ( l ) have been studied by solution calorimetry. The molar dissolution enthalpies of the reactants and the products in some solvents (such as 2xa0molxa0l−1 HCl or its solutions) of these solid–solid coordination reactions have been measured by an isoperibol solution calorimeter. The standard molar formation enthalpies of [trans-Cu(Ala)2(s), 298.15xa0K] and [trans-Cu(Gly)2(s), 298.15xa0K] have been determined to be −1015.42 ± 0.06 and 1252.36 ± 0.05xa0kJxa0mol−1, respectively, from the results of the molar dissolution enthalpies and other auxiliary thermodynamic data.

Study on thermodynamic properties of polypyromellitimide molding powder

Abstract Polypyromellitimide molding powder has been prepared. In the 78–370xa0K range, the dependence of the specific heat capacity ( c p ) on the temperature ( T ) is given by the polynomial: c p =0.8163+0.4592 X +0.02468 X 2 +0.1192 X 3 +0.05659 X 4 (Jxa0K −1 xa0g −1 ), where X =( T −225.5)/144.5. Thermal decomposition in air starts at 716xa0K, and is complete at 1034xa0K. The standard combustion enthalpy is Δ c H =−26.442xa0kJxa0g −1 .

Thermokinetic method for faster enzyme-catalyzed reactions

Abstract This paper describes the application of dynamic microcalorimetry to determine the thermokinetics of short-time enzymatic reactions. A thermokinetic double-parameter method for faster enzyme-catalyzed reactions is proposed on the basis of the double-parameter theoretical model of the conduction calorimeter. By analyzing the calorimetric curves of faster enzyme-catalyzed reactions, this method can be conveniently used to calculate both molar reaction enthalpy ( Δ r H m ) and kinetic parameters ( K m , ν max ) of these reactions. Thermokinetics of the oxidation of xanthine catalyzed by xanthine oxidase in the presence of excess oxygen has been studied using microcalorimetry. This faster enzyme-catalyzed reaction obeyed the Michaelis–Menten kinetics, and the Michaelis constant ( K m ) for xanthine and the overall molar reaction enthalpy ( Δ r H m ) of this oxidation were determined by this method to be 1.04×10 −3 xa0molxa0dm −3 and −5.25xa0kJxa0mol −1 , respectively, at 298.15xa0K and pH 7.5. The reliability of the double-parameter method for faster enzyme-catalyzed reactions was verified by the experimental results.

Kinetics of action of Schiff bases on Aerobacter aerogenes as studied by microcalorimetry

Abstract Microcalorimetry was used to study the kinetics of action of five kinds of Schiff base on a strain of Aerobacter aerogenes. Differences in their capacities to suppress the metabolism of this bacterium were observed. The extent and duration of the inhibitory effect on the metabolism as judged from the multiplication rate constant, k, varied with the different Schiff bases. The multiplication rate constants, k, of Aerobacter aerogenes (in log phase) in the presence of Co(III)ue5f8NG and Niue5f8NG (NG: D-glucosamine-β-naphthol aldehyde) decreased with the increasing concentrations of the compounds C, but the relationship between k and C was not of good linearity. For Fe(III)ue5f8NG, the multiplication rate constants are constant irrespective of variations in concentration. Similarly over the concentration range 50–200 μg mL−1. there is nearly change in the inhibitory effects of NG on Aerobacter aerogenes, while they are slightly reduced beyond 200 μg mL−1. The experimental results revealed that the sequence of antibiotic activity of Schiff base drugs is: Co(III)-NG > Niue5f8NG > NG > Fe(III)ue5f8NG.

Thermokinetic models of enzyme-catalyzed reactions in batch and plug-flow reactors

Abstract This paper reports the thermokinetic models of single-substrate, enzyme-catalyzed reactions occurring in batch and plug-flow reactors, respectively. By analyzing the calorimetric curves of these reactions, these models can be used to produce not only the thermodynamic data ( Δ r H m ) but also the kinetic data ( K m and k 2 ). Using a LKB-2107 batch microcalorimeter and an LKB-2277 Bioactivity Monitor, the catalase-catalyzed decomposition of hydrogen peroxide was studied and its molar reaction enthalpy ( Δ r H m ) measured as −88.88±0.6 kJ mol −1 . The Michaelis constant ( K m ) for H 2 O 2 was determined by the batch and plug-flow thermokinetic models to be 5.03±0.18×10 −3 mol dm −3 and (5.27±0.11)×10 −3 mol dm −3 , respectively. The reliability of these models for determination of the thermokinetics of single-substrate, enzyme-catalyzed reactions occurring in these two types of reactors was verified by the experimental results.

A thermochemical study of the reactions of 8-hydroxyquinoline with Co(Ac)2·4H2O and Zn(Ac)2·2H2O

Abstract The solid-state coordination reactions: 2 HQ ( s )+ Co ( Ac ) 2 ·4 H 2 O ( s )→ Co ( HQ ) 2 ·2 H 2 O ( s )+2 HAc ( l )+2 H 2 O ( l ) 2 HQ ( s )+ Zn ( Ac ) 2 ·2 H 2 O ( s )→ Zn ( HQ ) 2 · H 2 O ( s )+2 HAc ( l )+ H 2 O ( l ) have been studied by solution calorimetry. The molar dissolution enthalpies of the reactants and the products in a certain solvent, 4xa0molxa0l −1 HCl, of this solid–solid coordination reaction have been measured using an isoperibol calorimeter. From the results and other auxiliary quantities, the standard molar formation enthalpies of [Co(HQ) 2 ·2H 2 O(s), 298.15xa0K], [Zn(HQ) 2 ·H 2 O(s), 298.15xa0K] and have been determined to be Δ f H m Θ (Co(HQ) 2 ·2H 2 O(s), 298.15xa0K)=−766.9±3.0xa0kJxa0mol −1 , Δ f H m Θ (Zn(HQ) 2 ·H 2 O(s), 298.15xa0K)=−580.7±3.0xa0kJxa0mol −1 .