Enthalpies Of Transfer Research Articles

Critical analysis of radical scavenging properties of atorvastatin in methanol recently estimated via density functional theory

In this communication we draw attention on serious flaws that plague recently reported antioxidant properties of atorvastatin (ATV) in methanol. First and foremost, we emphasize that the O-H bond dissociation energies (BDE) of about 400kcal/mol previously reported are completely wrong. Further, we present results refuting the previous claim that the proton affinity (PA) of ATV is smaller than that of the ascorbic acid. That unfounded claim relies on incorrect data for PA’s ascorbic acid (which we correct here) circulated in the literature. Further, we correct the values of the chemical reactivity indices (e.g., chemical hardness, electrophilicity index, electroaccepting and electrodonating powers), which were inadequately estimated previously via Kohn–Sham HOMO and LUMO energies. Finally, our updated values for O-H bond dissociation enthalpy (BDE = 91.4kcal/mol) and electron transfer enthalpy (ETE = 105.7kcal/mol) tentatively suggest that direct H-atom transfer (HAT) and sequential proton loss electron transfer (SPLET) may coexist.

Disclosing the distribution regularities for chiral recognition exemplified by R-and RS- of new antifungal: Impact of pH and temperature

The overall investigation of the distribution behavior for the enantiomer (R-98) and racemic (RS-186) antifungal compounds was carried out to the aim of disclosing the possibility of chiral differentiation. To this end, the study on the thermodynamics of the distribution coefficients in the model systems 1-octanol/water and n-hexane/water was performed. The impact of pH on the transferring of the compounds was revealed by using buffer solutions at pH 2.0 and pH 7.4 as an aqueous phase. The transferring mechanisms for different distribution systems were disclosed based on the complex analysis of the enthalpy and entropy contributions to the Gibbs energy and involved in chiral discrimination. A separation factor or enantioselectivity, as well as the differences between the transfer Gibbs free energy, enthalpy and entropy (excess thermodynamic functions) were determined and discussed. The maximal value of the separation factor in the 1-octanol/buffer pH 7.4 system was shown. The impact of the hydrogen binding potential of the substances on the enantioselectivity was detected.

Antioxidant Potential of Santowhite as Synthetic and Ascorbic Acid as Natural Polymer Additives.

A wide variety of additives are used to improve specific characteristics of the final polymeric product. Antioxidant additives (AAs) can prevent oxidative stress and thus the damage of polymeric materials. In this work, the antioxidant potential and thus the applicability of Santowhite (SW) as synthetic and ascorbic acid (Asc) as natural AAs were explored by using computational tools. Two density functional theory (DFT) methods, M05-2X and M06-2X, have been applied in combination with the 6-311++G(2d,2p) basis set in gas phase. Three antioxidant mechanisms have been considered: hydrogen atom transfer (HAT), single electron transfer-proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET). Bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA), and electron transfer enthalpy (ETE) have been computed for each potential hydrogen donor site. The results indicate that the antioxidant potential of Asc is higher than SW. Furthermore, some of the C-H bonds, depending on their position in the structures, are potent radical scavengers, but O-H groups are more prone to donate H-atoms to free radicals. Nonetheless, both additives can be potentially applied to safeguard common polymers and prohibit oxidative stress-induced material deterioration.

Fisetin and Robinetin antiradical activity under solvent effect: density functional theory study

The structural and antioxidant activity of two flavonols, namely, Fisetin and Robinetin, have been investigated employing the density functional theory (DFT) using B3LYP functional and 6-311++G (d, p) basis set. The calculations were performed in the gas phase and under the solvent effect of water, dimethylsulfoxide (DMSO), methanol, and benzene. The Hydrogen-Atom Transfer (HAT), single Electron Transfer Followed by Proton Transfer (SET-PT), and sequential Proton Loss Electron Transfer (SPLET) mechanisms were investigated to rationalize the radical scavenging capacities and to identify the favored antioxidant mechanism. Hence, the bond dissociation enthalpies (BDE) ionization potential (IP), IE, proton dissociation enthalpy (PDE), proton affinity (PA), and electron Transfer enthalpy (ETE) related to each mechanism were reported and discussed in function of the solvent effect. For both flavonols, the results showed that 4'-OH hydroxyl is the preferred active site following the trend 4'-OH > 3'-OH > 3-OH > (5'-OH) > 7-OH. Besides, the HAT mechanism is energetically the most favored pathway. The energetically favored solvents follow the trends water > DMSO > benzene > methanol and benzene > DMSO > methanol > water, for Fisetin and Robinetin, respectively.

Thermochemical characteristics of some glycylpeptides interaction with anionic micelles in a phosphate-buffered saline solution of sodium dodecyl sulfate

The dissolution enthalpies of glycylglycine (GlyGly), glycylglycylglycine (GlyGlyGly) and glycyl-L-tyrosine (GlyTyr) in phosphate-buffered saline solution and micellar solution (sodium dodecyl sulfate (SDS) + phosphate-buffered saline solution) were measured calorimetrically at pH = 7.4 and T = 298.15 K. The thermochemical characteristics of the interaction of peptides with micelles are defined as the transfer enthalpies of peptides into a micellar solution of sodium dodecyl sulfate in a phosphate-buffered saline solution. A comparison of the obtained results revealed the influence of the ionic state, chain length and hydrophobicity of peptides on the characteristics of their interaction with anionic micelles. The effect of micelle contraction upon interaction with peptide zwitterions was found. The differences in the dissolution enthalpies in the buffer and in pure water are described by the contributions of acid dissociation of peptides, which is accompanied by a change in the fractions of the zwitter-ionic and anionic forms with a change in pH.

Phenolic acids and their carboxylate anions: Thermodynamics of primary antioxidant action

Phenolic acids represent naturally occurring antioxidants and play important role in free radicals scavenging. In this work, we have studied thermodynamics of the first step of primary antioxidant action for phenolic OH groups of benzoic and cinnamic acid derivatives, and their carboxylate anions. M06–2X/6–311++G(d,p) reaction enthalpies related to Hydrogen Atom Transfer (HAT), Single Electron Transfer – Proton Transfer (SET-PT), and Sequential Proton-Loss Electron-Transfer (SPLET) mechanisms were computed for model non-polar environment (benzene) and aqueous solution. The effect of acid structure on found reaction enthalpies was investigated, as well. For HAT, representing relevant reaction path in both environments, the lowest O–H bond dissociation enthalpies, BDE, were found for sinapic acid (347 kJ mol−1 in benzene and 337 kJ mol−1 in water). With two exceptions, carboxylate anions show lower BDEs than parent acids. In aqueous solution, enthalpies of the first step of SPLET from phenolic OH groups are low (135–199 kJ mol−1). It indicates thermodynamic feasibility of the mechanism for acids, as well as their carboxylate anions. Although enthalpies of electron transfer from dianions formed after successive deprotonations of carboxyl and phenolic groups in water are usually higher than BDEs, differences are within 25 kJ mol−1. Demethylation of OCH3 groups may affect radical scavenging activity of studied substances due to O–CH3 BDE considerably lower (230–269 kJ mol−1) in comparison to O–H ones.

Computational study of synthetic and natural polymer additives — Antioxidant potential of BHA, TBHQ, BHT, and curcumin

The antioxidant potential of commonly used synthetic and natural antioxidant additives, including butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), tert‑butylhydroquinone (TBHQ), and natural additive, curcumin have been studied and compared by calculating the bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA), and electron transfer enthalpy (ETE) values for each potential hydrogen donor site. The results indicate that, in each additive an OH group has the highest antioxidant potential (lowest BDE value). The studied molecules can be ranked based on their antioxidant potential as follows: BHT > BHA ≈ TBHQ > curcumin A > curcumin D. By comparing with commonly used polymers, in each studied species, there is at least one X-H bond which has a lower BDE value than in the corresponding polymeric material. Thus, all studied additives are potentially applicable to protect polymeric materials. BHT is the best radical scavenger additive in case of the hydrogen atom transfer (HAT), and the sequential proton loss electron transfer (SPLET) mechanisms to donate a H atom, but in single electron transfer proton transfer (SETPT) curcumin could also be suitable.

Modes of interaction and thermodynamic behavior of aggregation of CTAB + BSA mixtures in diols media: effects of diols composition and temperature

The micellization of cetyltrimethylammonium bromide (CTAB) and bovine serum albumin (BSA) mixture has been studied conductometrically in aq. solutions of different diols (1,2-propanediol (1,2-PrD), 2,3-butanediol (2,3-BD), and 1,5-pentanediol (1,5-PD)) media over the temperature range from 298.15 K to 323.15 K to gain insight into the mode and degree of interaction amongst the investigated constituents. The critical micelle concentration (cmc) values of the CTAB + BSA mixtures were attained initially low but enhanced with the rise in temperature in all the media studied. The values of the CTAB + BSA mixtures in the different diols media followed the order: The degree of micelle ionization (α) increased with increasing carbon chain length of diols and temperature. The Gibbs free energy () values associated with the micellization of the CTAB + BSA mixture were negative and revealed a lowering of the spontaneity of micellization with increasing carbon chain length of the diols. The enthalpy () and entropy () changes of micellization revealed that the micellization was exothermic and mainly an enthalpy-controlled process in aq.1,2-PrD and 2,3-BD media while the process being endothermic, and entropy controlled in the 1,5-PD medium. The contribution of the solvent to the thermodynamic parameters was assessed from free energy of transfer (), enthalpy of transfer (), and entropy of transfer () values. The enthalpy–entropy compensation parameters were also studied and discussed with proper reasoning.

Antioxidant activity of erlotinib and gefitinib: theoretical and experimental insights

Erlotinib and gefitinib are quinazoline derivatives with antineoplastic properties. Usually, intake of antineoplastic agents results in much a greater degree of oxidative stress, i.e. the production of free radicals, than induced by cancer itself. Hence, anticancerous drugs must also exhibit antioxidant activity but this has not been studied thus far. In this study, the antioxidant activity of erlotinib and gefitinib was examined by experimental and computational studies. It was found that erlotinib and gefitinib exhibit good 2,2-dipheny l-1-picrylhydrazyl (DPPH) radical and hydroxyl radical scavenging (HRS) activities. In DPPH assay, the IC50 for erlotinib and gefitinib were 0.584 and 0.696 mM, respectively, while IC50 for HRS assay were 0.843 and 1.03 mM for erlotinib and gefitinib, respectively. Structural characteristics such as frontier molecular orbitals (FMOs), molecular electrostatic potential maps (MESPs), and global descriptive parameters were calculated at DFT/B3LYP/6-311++G (d,p) on the optimized geometries of erlotinib and gefitinib. UV–visible spectroscopy revealed the possible electronic transitions between the FMOs and their associated excitation energies of both drugs and found that erlotinib has π to π* transitions while gefitinib has π to π* and σ to π* transitions. To elucidate the antioxidant activity of erlotinib and gefitinib, three mechanisms namely hydrogen atom transfer (HAT), single electron transfer proton transfer (SETPT), and sequential proton-loss electron-transfer (SPLET) were employed and articulated the results in arithmetic parameters like bond dissociation energy (BDE), proton affinity (PA), ionization potential (IP), electron transfer enthalpy (ETE), and proton dissociation enthalpy (PDE). Further, molecular docking studies have been carried out to have a better understanding of binding sites and modes of interaction with a well-known antioxidant target protein monoamine oxidase-B (MAO-B) employing docking scores and types of interactions. All the calculated parameters point out that though gefitinib and erlotinib were interchangeable, erlotinib requires a lesser amount of energy for proton transfer and electron transfer, moreover it scavenges radicals easily.

Theoretical insights into the radical scavenging activity of glipizide: DFT and molecular docking studies

Glipizide is an N-sulfonylurea compound used in the treatment of hyperglycemia in patients with type 2 diabetes mellitus. In the present study, DFT-based computational methods and molecular docking studies have been performed to systematically evaluate the radical scavenger behavior of the title molecule. Structural characteristics such as molecular descriptors, frontier molecular orbitals, molecular potential mapping, and Mulliken charge population have been investigated. Thermodynamic parameters like proton affinity (PA), ionization potential (IP), bond dissociation energy (BDE), electron transfer enthalpy (ETE), and proton dissociation enthalpy (PDE) related to three antiradical mechanisms namely hydrogen atom transfer (HAT), sequential electron transfer proton transfer (SETPT) and sequential proton loss electron transfer (SPLET) have been studied. Also, molecular docking studies have been carried out to have a theoretical understanding of the molecular mechanism and for the elucidation of binding mode/modes of a compound targeted through non-covalent interactions. The obtained results are of great significance in better understanding the reaction mechanism of the title molecule and opens a new perspective for the design of potent antioxidant agents.

EXTRAÇÃO DE CORANTES TÊXTEIS UTILIZANDO SISTEMAS AQUOSOS BIFÁSICOS COMPOSTOS POR 2-PROPANOL E SAIS DE SULFATO

EXTRACTION OF TEXTILE DYES USING TWO-PHASE AQUEOUS SYSTEMS COMPOSED OF 2-PROPANOL AND SULFATE SALTS. Aqueous Two Phase Systems (ATPS) composed of 2-propanol + inorganic salt (Na2SO4/MgSO4) + water, at different temperatures T = (20, 30, 40 and 50) °C were applied in the partition studies of the textile dyes Yellow, Blue Royal and Red Dianix CC. The thermodynamic parameters of the free transfer energy (ΔGtr), enthalpy (ΔHtr) and entropy (ΔStr), respectively, were determined for dye partitioning, using the Van’t Hoff equation. The values of the partition coefficients of textile dyes Yellow, Royal Blue and Red Dianix CC, ranged from 14.21 to 1610.00, 15.15 to 994.00 and 17.32 to 311.75, respectively; and with dye extraction yields ranging from 93.17 to 99.93; 94.53 to 99.89 and 97.19 to 99.64, respectively. Based on the ΔGtr results, it was verified that the dyes partition process was thermodynamically spontaneous, in all evaluated systems. For the 2-propanol + sodium sulfate ATPS, there was a prevalence of the enthalpic contribution over the entropic contribution (ΔHtr > ΔStr), while for the 2-propanol + magnesium sulfate systems, a greater predominance of the entropic contribution was observed (ΔHtr < ΔStr). The recovery yields (Y) values obtained were above 90% for all systems.

Variable-Temperature NMR Analysis of the Thermodynamics of Polymer Partitioning between Aqueous and Drug-Rich Phases and Its Significance for Amorphous Formulations.

We previously reported that the polymers used in amorphous solid dispersion (ASD) formulations, such as polyvinylpyrrolidone (PVP), polyvinylpyrrolidone/vinyl acetate (PVP-VA), and hypromellose (HPMC), distribute into the drug-rich phase of ibuprofen (IBP) formed by liquid-liquid phase separation, resulting in a reduction in the maximum drug supersaturation in the aqueous phase. Herein, the mechanism underlying the partitioning of the polymer into the drug-rich phase was investigated from a thermodynamic perspective. The dissolved IBP concentration in the aqueous phase and the amount of polymer distributed into the IBP-rich phase were quantitatively analyzed in IBP-supersaturated solutions containing different polymers using variable-temperature solution-state nuclear magnetic resonance (NMR) spectroscopy. The polymer weight ratio in the IBP-rich phase increased at higher temperatures, leading to a more notable reduction of IBP amorphous solubility. Among the polymers, the amorphous solubility reduction was the greatest for the PVP-VA solution at lower temperatures, while HPMC reduced the amorphous solubility to the greatest extent at higher temperatures. The change in the order of polymer impact on the amorphous solubility resulted from the differences in the temperature dependency of polymer partitioning. The van't Hoff plot of the polymer partition coefficient revealed that both enthalpy and entropy changes for polymer transfer into the IBP-rich phase from the aqueous phase (ΔHaqueous→IBP-rich and ΔSaqueous→IBP-rich) gave positive values for most of the measured temperature range, indicating that polymer partitioning into the IBP-rich phase was an endothermic but entropically favorable process. The polymer transfer into the IBP-rich phase was more endothermic for HPMC than for PVP and PVP-VA. The solid-state NMR analysis of the IBP/polymer ASD implied that the newly formed IBP/polymer interactions in the IBP-rich phase upon polymer incorporation were weaker for HPMC, providing a rationale for the larger positive transfer enthalpy for HPMC. The change in Gibbs free energy for polymer transfer (ΔGaqueous→IBP-rich) showed negative values across the experimental temperature range, decreasing with an increase in temperature, indicating that the distribution of the polymer into the IBP-rich phase is favored at higher temperatures. Moreover, ΔGaqueous→IBP-rich for HPMC showed the greatest decrease with the temperature, likely reflecting the temperature-induced dehydration of HPMC in the aqueous phase. This study contributes fundamental insights into the phenomenon of polymer partitioning into drug-rich phases, furthering the understanding of achievable supersaturation levels and ultimately providing information on polymer selection for ASD formulations.

Solubility of N-(9-fluorenylmethoxycarbonyloxy)-succinimide in several aqueous co-solvent solutions revisited: Solvent effect, preferential solvation and dissolution and transfer properties

Preferential solvation of N-(9-fluorenylmethoxycarbonyloxy)-succinimide (Fmoc-OSu) in mixtures of DMF (1) + water (2), ethanol (1) + water (2), ethylene glycol (EG, 1) + water (2) and DMSO (1) + water (2) was investigated by inverse Kirkwood–Buff integrals method. In ethanol-rich and intermediate contents, ethanol preferentially solvated Fmoc-OSu; and for the four aqueous co-solvent blends in water-rich composition regions, Fmoc-OSu was preferentially solvated by water. The solvent effect was described through modeling the Gibbs energy change of Fmoc-OSu solubility by linear solvation energy relationships. The main contribution to solubility variation of Fmoc-OSu was the solvent dipolarity-polarizability and solubility parameter. The dissolution and transfer enthalpy, entropy and Gibbs free energy were discussed in detail. Analysis outcomes of thermodynamic dissolution and enthalpy–entropy compensation demonstrated that two different mechanisms, enthalpy-driven and entropy-driven controlled the solubility variation of Fmoc-OSu in the DMF/EG/DMSO + water mixtures; and enthalpy-driven, in the ethanol + water mixture.

Current view on the assessment of antioxidant and antiradical activities: A mini review

The main problems in assessing the antioxidant properties of plant biologically active compounds are discussed in this review. Antioxidant potential should be considered as a combination of antioxidant and antiradical activities, since antiradical activity is part of the antioxidant activity and does not always coincide with antioxidant activity. The mechanisms of action and the existing experimental and computational methods for their evaluation were reviewed. Methods like FRAP, CUPRAC etc. could be used for assessment of antioxidant activity of plant compounds, but it is necessary to perform studies on cell cultures or laboratory animals in order to determine mechanisms of action on the antioxidant system of a living organism. The current methodological approaches for studying antiradical activity and its mechanisms include experimental methods such as DPPH, ABTS and ORAC, and computational methods based on density functional theory. The main thermodynamic parameters for evaluating antiradical mechanisms (HAT, SET-PT and SPLET) are the bond dissociation enthalpy, ionization potential, proton dissociation enthalpy, proton affinity, and electron transfer enthalpy, among others. The existing approaches for determining the antiradical mechanisms of antioxidants are quite informative, but can still cannot predict or determine by in vitro methods the antioxidant mechanism of these compounds in organisms consisting of many complex individual systems.

Rimsulfuron solubility in several aqueous solutions revisited: Solvent effect, dissolution behavior and preferential solvation

Preferential solvation was analyzed with the help of the inverse Kirkwood–Buff integrals method based on the available equilibrium solubility of rimsulfuron in four solutions of EG (1) + water (2), ethanol (1) + water (2), DMF (1) + water (2) and methanol (1) + water (2). Rimsulfuron was preferentially surrounded by water solvent in water-rich composition regions. For the aqueous ethanol/methanol mixtures in intermediate and methanol/ethanol-rich composition ranges, methanol/ethanol preferentially solvated rimsulfuron; while EG/DMF didn’t preferentially solvate the rimsulfuron for the EG/DMF in the ranges. Selective solvation of rimsulfuron by methanol/ethanol was perhaps resulted from higher basicity of methanol/ethanol that was in favor of interactions with the acidic groups of rimsulfuron. The performance of rimsulfuron solubility was investigated by means of Hansen solubility parameter concept in detail. The study on relative prominence of solvent–solvent and solute–solvent molecule interactions on rimsulfuron solubility variation identified the hydrogen-bond basicity, dipolarity-polarizability and solubility parameter of solution descriptors analyzed in terms of the linear solvation energy relationships. As well, the dissolution and transfer Gibbs free energy change, enthalpy and entropy were resulted, representing the solubilization capacity more favorable with the rising compositions of EG/ethanol/DMF/methanol. Thermodynamic analysis of enthalpy–entropy compensation demonstrated a shift of dominant dissolution mechanism from entropy-driven (water-rich regions) to enthalpy-driven (organics-rich regions).

Comparative theoretical researches on the anti-oxidant activity of δ-viniferin and ε-viniferin

Viniferin, the dimer of resveratrol, is an important natural product class with anti-oxidant activities. δ-viniferin and ε-viniferin are two different isomers of viniferin. In this context, a systematic theoretical study by density functional theory (DFT) calculations is carried out on these two isomers’ radical scavenging activity, which focuses on the thermodynamically preferred mechanism, anti-oxidant sites, and anti-oxidant activity sequence of δ-viniferin and ε-viniferin. Three radical scavenging mechanisms named hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) were discussed. The anti-oxidative capacities of δ-viniferin and ε-viniferin in the gas phase and solvents were elucidated by comparing the thermodynamic parameters such as bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA), and electron transfer enthalpy (ETE). The computational results showed that δ-viniferin is a more potent anti-oxidant than ε-viniferin. The obtained results may have some important implications for better understanding the relationship between structure and anti-oxidant activity, designing more active anti-oxidants, and providing theoretical guidance for developing and utilizing resveratrol derivatives.

A thermodynamic study of capillary electrochromatographic retention of aromatic hydrocarbons on a lauryl acrylate porous polymer monolithic column with measured phase ratio.

The phase ratio of a chromatographic system is an important measurement that has long been estimated or calculated, but rarely directly measured. This study utilized a nanoflow liquid chromatography instrument to more accurately measure the phase ratio for a lauryl acrylate porous polymer monolith. Direct measurement of the phase ratio, and its dependence on temperature, allows for a better understanding of the thermodynamics of retention of small analytes. This study investigates the retention of an alkyl benzene series, toluene to octylbenzene, via capillary electrochromatography. The phase ratio was determined to be 0.202 at 303 K and 0.213 at 333K. Using the directly measured phase ratio, entropic contributions to retention can also be obtained. Therefore, the Gibbs free energy calculations from these measurements and methods can give insight to modes of retention. The free energy of retention for toluene is -3.97kJ/mol at 303 K and -3.78kJ/mol at 333K. The trends for enthalpy, entropy, and Gibbs free energy of transfer show that retention is enthalpically driven in this capillary electrochromatography (CEC) porous polymer monolith system.

Theoretical investigations on the antioxidant potential of a non-phenolic compound thymoquinone: a DFT approach.

Thymoquinone (TQ) is a natural compound present in black cumin which possesses potent antioxidant activity without having any phenolic hydroxyl group which is responsible for antioxidant activity. In the present study, computational calculation based on density functional theory (DFT) was executed to assess systematically the antioxidant behavior of this compound by considering geometrical characteristics, highest occupied molecular orbital - lowest unoccupied molecular orbital (HOMO-LUMO), and molecular electrostatic potential (MEP) surface. Thermochemical parameters correlated to the leading antioxidant mechanisms such as hydrogen atom transfer (HAT), single electron transfer-proton transfer (SETPT), and sequential proton loss electron transfer (SPLET) were studied in gas and water media. In addition, the changes of thermochemical parameters such as free energy change (∆G) and enthalpy change (∆H) were computed for hydrogen abstraction (HA) from TQ to hydroxyl radical in gas and water phases to investigate its free radical scavenging potency. The low and comparable values of bond dissociation enthalpy (BDE), proton dissociation enthalpy (PDE), ionization potential (IP), proton affinity (PA), and electron transfer enthalpy (ETE) revealed the antioxidant activity. The ∆G and ∆H also indicated apposite thermodynamic evidence in favor of antiradical capability of TQ. The attack of the free radical occurred preferentially at 3CH position of the molecule.

Thermochemical investigation of glycyl-L-alanine dissolution in aqueous solution of some acetamides and formamides at T = 298.15 K (Similarities and differences)

The paper presents data on the glycyl-L-alanine dissolution enthalpies in aqueous solutions of formamide (FA), N-methyl-formamide (MFA), N,N-dimethylformamide (DMF), acetamide (AM), N-methyl-acetamide (NMA), and N,N-dimethylacetamide (DMA) at an organic co-solvent concentration x2 = 0 ÷ 0.25 - mole fraction and T = 298.15 K, obtained by calorimetry. The standard values of dissolution enthalpies (ΔsolHo), transfer enthalpies (ΔtrHo), and enthalpic coefficients of pairwise interaction (hxy) were calculated from these data. The dependences of the enthalpic characteristics of glycyl-L-alanine dissolution on the mixture composition and the interaction energy between the mixture components have been established. A comparative analysis of the values of the enthalpic coefficients of pairwise interactions of glycyl-L-alanine, glycyl-glycine, and glycyl-L-tyrosine in similarly mixed solvents has been carried out. A quantitative assessment of the enthalpy contributions of the side-chains of glycyl-L-alanine and glycyl-L-tyrosine to the energetics of interaction with amide molecules in an aqueous solution is given.

Identification of new biologically active synthetic molecules: comparative experimental and theoretical studies on the structure-antioxidant activity relationship of cyclic 1,3-ketoamides.

Antioxidant agent is a chemical that prevents the oxidation of other chemical substances. Its use is the most effective means of protecting the organism by neutralizing the harmful effects of free radicals caused by oxidative stress. In the present work, a series of β-ketoamides containing a variety of monosubstituted amide groups were synthesized and tested as antioxidant agents. In order to establish a possible structure-antioxidant activity relationship, we are presenting a systematic theoretical study of these molecules with the aim of clarifying the active sites. In particular, we discuss the selectivity resulting from the choice of a free radical/antioxidant system. The theoretical study of these molecules was carried out using density functional theory (DFT) calculations at the B3LYP/6-311G (d,p) level of theory. In order to shed light on the antioxidant properties of β-ketoamides, O-H bond dissociation enthalpies (BDEs), ionization potentials (IPs), electron affinities (EAs), proton affinities (PAs), and electron transfer enthalpies (ETEs) are performed in the gas phase and in ethanol. The results obtained show that the HAT mechanism is thermodynamically more favored in the gas phase, while the SPLET is preferred in the polar solvent.