Enthalpy Of Hydrolysis Research Articles

Thermodynamic and Vibrational Aspects of Peptide Bond Hydrolysis and Their Potential Relationship to the Harmfulness of Infrared Radiation

The primary physicochemical effect upon exposure to infrared radiation (IR) is the temperature increase of cells. The degradation of proteins via the hydrolysis of peptide bonds is related to cell malfunction. In this work, the degradation of proteins/peptides under the influence of IR radiation is theoretically studied. It is shown that the low value of enthalpy of peptide bond hydrolysis has two consequences: (a) the enthalpy of hydrolysis is sensitive to small variations in the bond strength, and the hydrolysis of weak peptide bonds is exothermic, while the hydrolysis of stronger bonds is endothermic; (b) the increase in temperature (e.g., due to IR exposure) changes the enthalpy of the reaction of some weak peptide bonds from exothermic to endothermic (that is, their hydrolysis will be favored upon further increase in temperature). Simple calculations reveal that the amount of absorbed energy during the overtone and hot band transitions of the H–O–H and C–N stretching vibrations is comparable to the activation energy of the (uncatalyzed) hydrolysis. A critical discussion is provided regarding the influence of different IR wavelengths on peptide bond hydrolysis.

In Silico Simulations Reveal Molecular Mechanism of Uranyl Ion Toxicity towards DNA-Binding Domain of PARP-1 Protein.

The molecular toxicity of the uranyl ion (UO22+) in living cells is primarily determined by its high affinity to both native and potential metal-binding sites that commonly occur in the structure of biomolecules. Recent advances in computational and experimental research have shed light on the structural properties and functional impacts of uranyl binding to proteins, organic ligands, nucleic acids, and their complexes. In the present work, we report the results of the computational investigation of the uranyl-mediated loss of DNA-binding activity of PARP-1, a eukaryotic enzyme that participates in DNA repair, cell differentiation, and the induction of inflammation. The latest experimental studies have shown that the uranyl ion directly interacts with its DNA-binding subdomains, zinc fingers Zn1 and Zn2, and alters their tertiary structure. Here, we propose an atomistic mechanism underlying this process and compute the free energy change along the suggested pathway. Our Quantum Mechanics/Molecular Mechanics (QM/MM) simulations of the Zn2-UO22+ complex indicate that the uranyl ion replaces zinc in its native binding site. However, the resulting state is destroyed due to the spontaneous internal hydrolysis of the U-Cys162 coordination bond. Despite the enthalpy of hydrolysis being +2.8 kcal/mol, the overall reaction free energy change is -0.6 kcal/mol, which is attributed to the loss of domain's native tertiary structure originally maintained by a zinc ion. The subsequent reorganization of the binding site includes the association of the uranyl ion with the Glu190/Asp191 acidic cluster and significant perturbations in the domain's tertiary structure driven by a further decrease in the free energy by 6.8 kcal/mol. The disruption of the DNA-binding interface revealed in our study is consistent with previous experimental findings and explains the loss of PARP-like zinc fingers' affinity for nucleic acids.

ChemInform Abstract: Heats of Reaction of Cyclic and Acyclic Phosphate and Phosphonate Esters. “Strain Discrepancy” and Steric Retardation.

The millionfold enhancement of the rate of hydrolysis of five-membered cyclic phosphate esters compared to their acyclic analogues is purely enthalpic and arises at least partially from destabilization of the four-coordinate cyclic reactant compared to the acyclic analogue, assuming that both react with hydroxide through unstrained five-coordinate transition states. Calorimetric analysis of the hydrolysis of cyclic and acyclic phosphates and phosphonates is reported in which the absolute value of the difference in enthalpy of hydrolysis of the cyclic and acyclic species is considerably less than the difference in activation enthalpies (about 2 kcal/mol discrepancy)

A calorimetric study of the enthalpy of enzymatic hydrolysis of components of a product from vegetable raw materials for enteral feeding

The enthalpy of hydrolysis of potato starch and some starch-containing components of Lider-1 nutrition product for enteral (tube) feeding in the presence of α-amylase enzyme was studied on a DAK-1-1 differential microcalorimeter.

Hydrolysis of neptunium(V) at variable temperatures (10–85°C)

Neptunium is one of the few radioactive elements that are of great concern in the disposal of nuclear wastes in the geological repository, due to its hazards and the long half-life of the isotope, 237Np ( t 1/2 = 2.14 × 10 6 years). To understand and predict the migration behavior of neptunium in the geological media, it is of importance to study its hydrolysis at elevated temperatures, because the temperature in the waste package and the vicinity of the repository could be high. Moreover, the chemical analogy between neptunium(V) and plutonium(V) adds even greater value to this investigation, because the latter could exist at tracer levels in neutral and slightly oxidizing waters but is difficult to study due to its rather labile redox behavior. In this work, the hydrolysis of neptunium(V) was studied at variable temperatures (10 to 85°C) in tetramethylammonium chloride (1.12 mol kg −1). Two hydrolyzed species of neptunium(V), NpO 2OH(aq) and NpO 2(OH) 2 −, were identified by potentiometry and Near-IR absorption spectroscopy. The hydrolysis constants (* β n) and enthalpy of hydrolysis (Δ H n) for the reaction NpO 2 + + nH 2O = NpO 2(OH) n (1−n)+ + nH + ( n = 1 and 2) were determined by titration potentiometry and microcalorimetry. The hydrolysis constants, * β 1 and * β 2, increased by 0.8 and 3.4 orders of magnitude, respectively, as the temperature was increased from 10 to 85°C. The enhancement of hydrolysis at elevated temperatures is mainly due to the significant increase of the degree of ionization of water as the temperature is increased. The hydrolysis reactions are endothermic but become less endothermic as the temperature is increased. The heat capacities of hydrolysis, Δ C p1 and Δ C p2 , are calculated to be −(71 ± 17) J K −1 mol −1 and −(127 ± 17) J K −1 mol −1, respectively. Approximation approaches to predict the effect of temperature, including the constant enthalpy approach, the constant heat capacity approach and the DQUANT equation, have been tested with the data.

Hydrolysis of uranium(VI) at variable temperatures (10-85 degrees C).

The hydrolysis of uranium(VI) in tetraethylammonium perchlorate (0.10 mol dm(-3) at 25 degrees C) was studied at variable temperatures (10-85 degrees C). The hydrolysis constants (*beta(n,m)) and enthalpy of hydrolysis (Delta H(n,m)) for the reaction mUO(2)(2+) + nH(2)O = (UO(2))(m)(OH)(n)((2m-n))+) + nH(+) were determined by titration potentiometry and calorimetry. The hydrolysis constants, *beta(1,1), *beta(2,2), and *beta(5,3), increased by 2-5 orders of magnitude as the temperature was increased from 10 to 85 degrees C. The enthalpies of hydrolysis, Delta H(2,2) and Delta H(5,3), also varied: Delta H(2,2) became more endothermic while Delta H(5,3) became less endothermic as the temperature was increased. The heat capacities of hydrolysis, Delta C(p(2,2)) and Delta C(p(5,3)), were calculated to be (152 +/- 43) J K(-1) mol(-1) and -(229 +/- 34) J K(-1) mol(-1), respectively. UV/Vis absorption spectra supported the trend that hydrolysis of U(VI) was enhanced at elevated temperatures. Time-resolved laser-induced fluorescence spectroscopy provided additional information on the hydrolyzed species at different temperatures. Approximation approaches to predict the effect of temperature were tested with the data from this study.

Standard enthalpy of formation of hexamethyldisilane

The standard (p°= 0.1 MPa) enthalpy of formation at 298.15 K of liquid hexamethyldisilane was determined by measuring the enthalpy of its reaction with bromine to produce trimethylsilicon bromide. The required ΔfH°m[(CH3)3SiBr, I]/kJ mol–1=–330.4 ± 2.7 was determined from its enthalpy of hydrolysis in aqueous hydrobromic acid. The final result, ΔfH°m[(CH3)6Si2, I]/kJ mol–1=–341.1 ± 5.5 differs considerably from previous determinations and the consequences for the thermochemistry of silicon–methyl species are discussed. In particular the enthalpies of formation of the silylenes, SiH2, SiHMe and SiMe2, were derived as 266, 201 and 140 kJ mol–1, respectively, with uncertainties < ±6 kJ mol–1.

ChemInform Abstract: THE SOLVENT EFFECT ON THE ENTHALPY OF HYDROLYSIS OF CYCLIC ADENOSINE 3′,5′‐MONOPHOSPHATE. A QUANTUM CHEMICAL STUDY

The solvent effect on the enthalpy of hydrolysis has been studied by the Extended-Huckel method for the hydrolysis reactions of cyclic adenosine 3',5'-monophosphate (cyclic 3',5'-AMP) and related cyclic phosphate diesters. The results show that the difference in enthalpy of hydrolysis between cyclic 3',5'-AMP and related phosphate diesters is explained by the difference in net solvation enthalpy. The larger exothermic net solvation enthalpy of cyclic 3',5'-AMP can be ascribed to an extra stabilization of the hydrolysis product with respect to the reactants, which does not occur for the other cyclic phosphate diesters. The extra stabilization is due to hydrogen bonding with water between O(1') and O(5') in both adenosine 5' - and 3'-monophosphate.

ChemInform Abstract: THE ENTHALPY OF FORMATION OF RHENIUM PENTAFLUORIDE OXIDE

The enthalpy of hydrolysis of solid ReF5O in alkaline aqueous solution at 298.2 K is –717 kJ mol–1. Thence its enthalpy of formation has been calculated to be –1 229 kJ mol–1.

The solvent effect on the enthalpy of hydrolysis of cyclic adenosine 3′,5′‐monophosphate. A quantumchemical study

AbstractThe solvent effect on the enthalpy of hydrolysis has been studied by the Extended‐Hückel method for the hydrolysis reactions of cyclic adenosine 3′,5′‐monophosphate (cyclic 3′,5′‐AMP) and related cyclic phosphate diesters. The results show that the difference in enthalpy of hydrolysis between cyclic 3′,5′‐AMP and related phosphate diesters is explained by the difference in net solvation enthalpy. The larger exothermic net solvation enthalpy of cyclic 3′,5′‐AMP can be ascribed to an extra stabilization of the hydrolysis product with respect to the reactants, which does not occur for the other cyclic phosphate diesters. The extra stabilization is due to hydrogen bonding with water between O(1′) and O(5′) in both adenosine 5′ ‐ and 3′‐monophosphate.

The enthalpy of formation of rhenium pentafluoride oxide

The enthalpy of hydrolysis of solid ReF5O in alkaline aqueous solution at 298.2 K is –717 kJ mol–1. Thence its enthalpy of formation has been calculated to be –1 229 kJ mol–1.

ChemInform Abstract: ENTHALPY OF FORMATION OF RHENIUM HEPTAFLUORIDE

The enthalpy of hydrolysis of ReF7(c) in Na[OH](1 mol dm–3 at 298.2 K) is –972 ± 11 kJ mol–1. From this result rhe enthalpy of formation of ReF7(c) is estimated to be –1 432 ± 11 kJ mol–1.

ChemInform Abstract: THE STANDARD ENTHALPIES OF HYDROLYSIS AND FORMATION OF TRICYANOPHOSPHINE

By use of a solution calorimeter the standard enthalpy of hydrolysis of P(CN)3(c) at 298.15 K has been determined as –44.9 ± 0.1 kcal mol–1 and the derived standard enthalpy of formation as 117.9 ± 6.0 kcal mol–1. The enthalpy of sublimation of P(CN)3 was determined by effusion manometry as 18.0 ± 0.7 kcal mol–1 and the P–CN mean bond dissociation energy was estimated as 84 kcal mol–1.

Enthalpy of formation of rhenium heptafluoride

The enthalpy of hydrolysis of ReF7(c) in Na[OH](1 mol dm–3 at 298.2 K) is –972 ± 11 kJ mol–1. From this result rhe enthalpy of formation of ReF7(c) is estimated to be –1 432 ± 11 kJ mol–1.

The enthalpy of hydrolysis and thermodynamic properties of carbonyl bromide

By use of an adiabatic solution-reaction calorimeter, the standard enthalpy of formation of carbonyl bromide, ΔH f o(COBr 2, 1, 298 K), was determined as −(34.7 ± 0.2) kcal mol −1.

Enthalpy and Free Emergy of Formation of the Hexachlororhenate(IV) Ion and Its Enthalpy of Hydrolysis1

Enthalpy and Free Emergy of Formation of the Hexachlororhenate(IV) Ion and Its Enthalpy of Hydrolysis¹