Quantum mechanical estimation of Abraham hydrogen bond parameters using 1:1 donor–acceptor complexes

Hydrogen bond donor strength () and acceptor strength () have been successfully used in models of many environmental and chemical systems, and a number of computational methods have been developed to predict them. In this work, a quantum chemical Møller–Plesset perturbation (MP2) method is applied to estimate the binding free energies (ΔG_hbond) of several 1:1 hydrogen‐bonded complexes. A correlation between the binding free energies and hydrogen bond strength is established. This relationship can be used to develop an accurate computational model for predicting and using binding free energies. The accuracy of the method in predicting Abraham (root mean squared deviation (RMSD) = 0.0693) and (RMSD = 0.0677) are comparable to the empirical, fragment‐based ABSOLV method (RMSD = 0.1144 and 0.1281 for and , respectively). The binding free energy has been decomposed into its thermodynamic components, and it is demonstrated that the linear relationships in the dataset and the existence of magic point can be attributed to a constant entropy of reaction. Copyright © 2014 John Wiley & Sons, Ltd.     

Determining the excited‐state substituent constants of meta‐substituent from 3,4'‐disubstituted stilbenes

In this paper, 61 samples of 3,4'‐disubstituted stilbenes and 18 samples of 3,3'‐disubstituted stilbenes were synthesized, and their UV data were measured in anhydrous ethanol. Based on the UV absorption energy (wavenumber) of 3,4'‐disubstituted stilbenes, the excited‐state substituent constants of meta‐substituent were determined by means of curve‐fitting. The availability of was confirmed by the good correlation with the UV absorption energy of 3,4'‐disubstituted stilbenes and 4,4'‐disubstituted stilbenes. Further, using the obtained constants and the correlation equation, we calculated the UV wavenumbers of 3,3'‐disubstituted stilbenes, and the calculated wavenumbers are in good agreement with the experimental values. These results verified that the excited‐state substituent constants of meta‐substituent are reliable parameter to scale the effect of meta‐substituent on the UV absorption energy. Copyright © 2012 John Wiley & Sons, Ltd.     

Density functional theory study of methoxide promoted and Zn(II)‐complexed methoxide promoted cleavages of aryl‐ and alkyl acetates in methanol. Transition from concerted to stepwise processes as a function of leaving group ability

Density functional theory calculations were performed for the methanolysis reactions of a set of aryloxy and alkoxy acetates ( 1a , 1b , 1c , 1d , 1e , 1f , 1g , 1h , 1i , 1j , 1k , 1l , 1m ) promoted by methoxide and a 1,5,9‐triazacyclododecane‐complexed Zn^(II)‐methoxide [2(OCH₃)]⁺ in order to give free energies and structural data for the various intermediates and transition states along the reaction pathway. The methoxide‐promoted reactions experience a transition of pathways from enforced‐concerted addition of CH₃O^? to the C = O unit for substrates having a good aryloxy leaving groups (LGs) with strong electron withdrawers ( 1a , 1b , 1c , 1d , 1e ) to a two step process with rate‐limiting CH₃O^‐ attack on aryloxy acetates having higher (the pK_a of the parent phenol of the LG in methanol) values. Only in the case of the substrates 1i‐m having alkoxy LGs is there an observed change in rate‐limiting step that occurs at the quasi‐symmetrical point where the . The methanolysis process for the 2,4‐dinitrophenoxy substrate ( 1a ) promoted by [2(OCH₃)]⁺ involves transient binding of the substrate to the metal complex followed by a rate‐limiting, enforced‐concerted attack of Zn^(II)‐coordinated ^–OCH₃, with fast breakdown of an addition intermediate that does not have a significant lifetime. For substrates 1b,c having slightly less electron withdrawing substituents, the reaction has two steps with rate‐limiting attack and an unassisted LG departure. As the increases, the reaction still has two steps with rate‐limiting attack, but departure of the LG is now assisted by its coordination to the metal ion. For alkoxy containing substrates, a change in rate‐limiting step occurs centered at methoxy acetate, 1j , (when ) for which the second step of metal ion assisted departure of methoxide becomes partially rate‐limiting. The Brønsted plots computed for the methoxide‐promoted and [2(OCH₃)]⁺‐promoted methanolyses are compared with the previously determined experimental data and are analyzed as arising not from a common line attributable to all substrates but rather in terms of separate, but intersecting, plots for aryl‐ and alkyl acetates. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and thermochemical study of quinoxaline‐N‐oxides: enthalpies of dissociation of the N–O bond

The synthesis of three new quinoxaline mono‐N‐oxides derivatives, namely, 2‐tert‐butoxycarbonyl‐3‐methylquinoxaline‐N‐oxide, 2‐phenylcarbamoyl‐3‐ethylquinoxaline‐N‐oxide, and 2‐carbamoyl‐3‐methylquinoxaline‐N‐oxide, from their corresponding 1,4‐di‐N‐oxides is reported. Samples of these compounds were used for a thermochemical study, which allowed derivation of their gaseous standard molar enthalpies of formation, , from their enthalpies of formation in the condensed phase, , determined by static bomb combustion calorimetry, and from their enthalpies of sublimation, , determined by Calvet microcalorimetry. Finally, combining the for the quinoxaline‐N‐oxides derived in this work with literature values for the corresponding 1,4‐di‐N‐oxides and atomic oxygen, the bond dissociation enthalpies for cleavage of the first N?O bond in the di‐N‐oxides, DH₁(N–O), were obtained and compared with existing data. Copyright © 2011 John Wiley & Sons, Ltd.     

Solution properties of phenothiazine drug promazine hydrochloride with cationic hydrotropes in aqueous/electrolyte solution at different temperature

The current work deals with the mixed micellization phenomena of surface active promazine hydrochloride (PMZ) drug with cationic hydrotropes (para‐toluidine hydrochloride and ortho‐toluidine hydrochloride) in absence and occurrence of 50 mmol kg^?1 NaCl at five different temperature (293.15–313.15 K). PMZ is an amphiphilic phenothiazine drug and employed for the cure of mania and schizophrenia. Conductometry measurement was employed to gain a detailed picture of the interactions between drug and hydrotrope molecules. The experimental data were analyzed according to different mixing models within the outline of the pseudophase separation model. The evaluated values of critical micelle concentration (cmc) were found to be inferior than cmc^id values signifying attractive interactions involving the both components in the solutions. NaCl further reduces the cmc of pure amphiphiles and their mixed systems as a result of screening of the electrostatic repulsion between the polar head groups. The micellar mole fractions (X₁) of hydrotropes evaluated by various proposed models were constantly more than ideal values ( ) signifying high involvements of hydrotrope in mixed micelles. Activity coefficients ( and ) were always below one in all cases signifying synergism in mixed micelles. Thermodynamic parameters favor the process of micellization which is found to be entropy driven. The negative values of free energies of mixing demonstrated the stability of the mixed systems of drug and hydrotrope. Copyright © 2016 John Wiley & Sons, Ltd.     

Kinetics and mechanisms of gas‐phase decarbonylation of α‐methyl‐trans‐cinamaldehyde and E‐2‐methyl‐2‐pentenal under homogeneous catalysis of hydrogen chloride

The kinetics of the gas‐phase elimination of α‐methyl‐trans‐cinamaldehyde catalyzed by HCl in the temperature range of 399.0–438.7 °C, and the pressure range of 38–165 Torr is a homogeneous, molecular, pseudo first‐order process and undergoing a parallel reaction to produce via (A) α‐methylstyrene and CO gas and via (B) β‐methylstyrene and CO gas. The decomposition of substrate E‐2‐methyl‐2‐pentenal was performed in the temperature range of 370.0–410.0 °C and the pressure range of 44–150 Torr also undergoing a molecular, pseudo first‐order reaction gives E‐2‐pentene and CO gas. These reactions were carried out in a static system seasoned reactions vessels and in the presence of toluene free radical inhibitor. The rate coefficients are given by the following Arrhenius expressions:

• Products formation from α‐methyl‐trans‐cinamaldehyde
• α‐methylstyrene :
• β‐methylstyrene :
• Products formation from E‐2‐methyl‐2‐pentenal
• E‐2‐pentene :

The kinetic and thermodynamic parameters for the thermal decomposition of α‐methyl‐trans‐cinamaldehyde suggest that via (A) proceeds through a bicyclic transition state type of mechanism to yield α‐methylstyrene and carbon monoxide, whereas via (B) through a five‐membered cyclic transition state to give β‐methylstyrene and carbon monoxide. However, the elimination of E‐2‐methyl‐2‐pentenal occurs by way of a concerted cyclic five‐membered transition state mechanism producing E‐2‐pentene and carbon monoxide. The present results support that uncatalyzed α‐β‐unsaturated aldehydes decarbonylate through a three‐membered cyclic transition state type of mechanism. Copyright © 2014 John Wiley & Sons, Ltd.     

Determining the excited‐state substituent constants of furyl and thienyl groups

Six series of styrene derivatives XCH═CHArY (total of 65) containing the styrene parent molecular skeleton were synthesized (here, Y is OMe, Me, H, F, Cl, CF₃, CN, and NO₂, and X is 2‐furyl, 3‐furyl, 2′‐methyl‐2‐furyl, 2‐thienyl, 3‐thienyl, and 2′‐methyl‐2‐theniyl). Their ultraviolet absorption spectra were measured in anhydrous ethanol, and their wavelength of absorption maximum λ_max was recorded. For the wavenumber ν_max (cm^?1, ν_max = 1/λ_max) of the obtained λ_max, a quantitative correlation analysis was performed, and 6 excited‐state substituent constants of groups X were obtained by means of curve‐fitting method. Taking the ν_max values of total 90 compounds of styrene derivatives as a data set (including 25 compounds from reference and 65 compounds of this work), a quantitative correlation analysis was performed, and the reliability of the obtained was verified. In addition, 12 samples of disubstituted Schiff bases (XCH═NArY) involving the above groups X were synthesized, and their ν_max values were recorded. Using these 12 ν_max together with the 14 ν_max values of Schiff bases taken from reference (total of 26 compounds), it was further verified that the values are reliable by means of quantitative correlation method.     

Conformation/Tautomerization effect on the pKa values of lumazine and 6‐thienyllumazine

Density functional theory [B3LYP/6‐311+G(d,p)] was used in combination with the conductor‐like polarizable continuum model (CPCM) solvation model to investigate the relative stability and site‐specific values of neutral and ionized tautomers of lumazine (LM) and 6‐thienylLM (TLM). Two types of populations should be taken into consideration when calculating the , tautomers, and conformers. The major tautomer of neutral LM in aqueous solution is 13‐LM (the 13 notation refers to the acidic protons being in positions 1 and 3 of LM) TLM has decreased acidity at N₈ relative to LM. Further, the trans conformer of TLM is more acidic than cis. Similar to the case of LM, for TLM, N₁ is more acidic than N₃ in the uracil part. However, N₈ is predicted to be a stronger acid than N₁ for TLM. This acidity enhancement is essentially because of a specific stabilization of the anion when the thienyl group replaces H. Two factors are responsible for the acidity strength of N₈: The thienyl ring upon deprotonation acts inductively as an electron‐withdrawing group, and the excess electron density is dispersed better when the system is trans and contains second‐row atoms. Accurate pK_a calculation requires that all conformers/tautomers be included into the calculation. Copyright © 2014 John Wiley & Sons, Ltd.     

CTED: the new aromaticity index based on corrected total electron density at bond critical points

In this work, the corrected total electron density based on ellipticity (ε) at C–C bond critical points in a given ring and bond length alternations was introduced to estimate π‐electron density distributions in the ring. Then, to evaluate aromaticity of rings with any number of members, the was normalized relative to a system assumed as a full aromatic, which is named as the corrected total electron density (CTED) aromaticity index. For a wide range of aromatic, nonaromatic and antiaromatic compounds, we have compared CTED index with the other commonly used aromatic indices, such as HOMA, PDI, FLU, NICS and recently introduced EL. CTED index was seen to be in agreement with the defined indices, and with general expectations. Hence, as similar to the other indices except from PDI, we have proposed that CTED index could be applied to study the aromaticity of rings without any restriction in the number of members of rings and used to analyze both the local and global aromatic character of rings as a new aromaticity index. Copyright © 2014 John Wiley & Sons, Ltd.     

Anisotropic charge transport properties of chrysene derivatives as organic semiconductor: A computational study

We used density functional theory to calculate the angular resolution anisotropic charge mobility of the substituted chrysene molecules, viz, 4,10‐diphenoxychrysene (DPC), 4,10‐bis(phenylsulfanyl)chrysene (BPSC), and ethyl 8,9,12‐trimethoxychrysene‐6‐carboxylate (ETCC). The highest occupied molecular orbital–lowest unoccupied molecular orbital gap for DPC, BPSC, and ETCC was calculated to be 3.92, 3.83, and 3.81 eV, respectively, which inferred the compounds to be wide‐band‐gap semiconductors indicating that the compounds should have high stability in atmospheric conditions. The fact is also supported by electronic band‐structure calculation. In addition, higher electron affinity of studied compounds as compared with the bare chrysene molecule imparts enhancement of n‐type character in the compounds. The maximum hole ( ) and electron mobilities ( ) for DPC compound were found to be 0.739 cm²V^?1s^?1 and 0.319 cm²V^?1s^?1, respectively, at Φ = 0°. On the other hand, in the case of BPSC crystal, comparatively larger anisotropic electron mobility (0.709 cm²V^?1s^?1 at Φ = 0° and Φ = 179.90°) than the hole mobility (0.208 cm²V^?1s^?1 at Φ = 127.19° and Φ = 307.10°) was noted. Similarly, in ETCC, the parallel dimers were found to contribute maximum and of 0.052 and 0.102 cm²V^?1s^?1, respectively, at Φ = 0°. The substitution of ‐SPh in BPSC and ‐OCH₃ and ‐CO₂CH₂CH₃ in ETCC have relatively more impact on band reduction than ‐OPh in DPC, thus facilitating electron transport in BPSC and ETCC.     

Gas‐phase elimination kinetics of selected aliphatic α,β‐unsaturated aldehydes catalyzed by hydrogen chloride

The gas‐phase elimination of 2‐methyl‐2‐propenal catalyzed by HCl yields propene and CO gas, while E‐2‐pentenal with the same catalyst gives butene and CO gas. The kinetics determinations were carried out in a static system with the reaction vessels deactivated with allyl bromide and the presence of the free radical inhibitor toluene. Temperature and pressure ranges were 350.0–410.0 °C and 34–76 Torr. The elimination reactions are homogeneous and unimolecular, and follow a first‐order rate law. The rate coefficients for the reactions are expressible by the following Arrhenius equations: Data from the kinetic and thermodynamic parameters of these catalyzed elimination reactions implies a mechanism of a concerted five‐membered cyclic transition state structure for the formation of the corresponding olefin and carbon monoxide. Copyright © 2015 John Wiley & Sons, Ltd.     

Genotoxic halofuranones in water: isomerization and acidity of mucohalic acids

Among the genotoxic halofuranones formed by chlorination in water are mucochloric acid (MCA, 3,4‐dichloro‐5‐hydroxyfuran‐2(5H)‐one) and mucobromic acid (MBA, 3,4‐dibromo‐5‐hydroxyfuran‐2(5H)‐one). These acids are direct genotoxins and potential carcinogens, with the capacity to alkylate the DNA bases. In recent years, they have also attracted attention in the synthesis of furanone derivatives. Mucohalic acids (MXA) exist in solution as an equilibrium between three species; a cyclic lactone‐lactol , an open‐chain aldehyde‐acid , and the dissociated form of the latter . The distribution of the three species in the equilibrium has synthetic, toxicological, and environmental implications owing to their different functionalization. The case of the neutral open‐chain form is of special interest, since it is expected to be highly reactive. We have experimentally determined the apparent dissociation constant of the cyclic species . Their values suggest that at neutral pH MXA are mostly present as the dissociated carboxylate‐aldehyde. The dissociation constant of the open‐chain neutral species and the cyclization equilibrium constant were determined in water and organic solvents, using density functional theory and ab initio methods. The results suggest that the undissociated aldehyde is a minor species at any given pH. The structure of MXA in solution and the influence of the level of theory on the calculated geometry are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Gas‐phase acidity of bis[(perfluoroalkyl)sulfonyl]imides. Effects of the perfluoroalkyl group on the acidity

The gas‐phase acidity (GA) values were determined for a number of perfluoroalkyl‐substituted sulfonylimides by measuring proton‐transfer equilibria using a Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer. The GA scale below 286.5 kcal mol^?1 for (CF₃SO₂)₂NH was extended and partially revised. The GA value of (C₄F₉SO₂)₂NH which is currently the strongest acid was revised from 284.1 to 278.6 kcal mol^?1. The effect of fluorine atoms on the acidity of perfluoroalkyl‐substituted sulfonylimides was described with the following model where N_(α), N_(β), N_(γ), and N_(δ) are the numbers of fluorine atoms at α, β, γ, and δ position in R_fSO₂ (R_f = perfluoroalkyl group), respectively. This correlation indicates that the electron‐withdrawing ability of the R_fSO₂ group can be described in terms of the number of fluorine atoms in the perfluoroalkyl group corrected by taking into account their positions. Copyright © 2014 John Wiley & Sons, Ltd.     

Minimal Bosonization of Supersymmetry with ‐graded Parity

In this paper we consider the ‐graded parity generalizing the ordinary (or Z₂‐graded ) parity. Using the ‐graded parity operator, we discuss the minimal bosonization of the N=2 SUSY with ‐graded parity. The lowest energy level is shown to be infinitely degenerate. In order to avoid the infinite degeneracy of the ground state we introduce the paraboson algebra to obtain the para‐supersymmetry. Finally, we discuss the hidden SUSY with Z₃‐graded parity.     

inflation from scale invariant supergravity and anomaly free superstrings with fluxes

The scale invariant gravity theory coupled to conformally invariant matter is investigated. We show that in the non‐supersymmetric case the conformally coupled scalars belong to an manifold, while in the supersymmetric case the scalar manifold becomes isomorphic to the Kählerian space =. In both cases when the underlying scale symmetry is preserved the vacuum corresponds to de Sitter space. Once the scale symmetry is broken by quantum effects, a transition to flat space becomes possible. We argue that the scale violating terms are induced by anomalies related to a symmetry. The anomaly is resolved via the gauging of a Peccei‐Quinn axion shift symmetry. The theory describes an inflationary transition from de Sitter to flat Minkowski space, very similar to the Starobinsky inflationary model. The extension to metastable de Sitter superstring vacua is also investigated. The scalar manifold is extended to a much richer manifold, but it contains always as a sub‐manifold. In superstrings the metastability is induced by axions that cure the anomalies in chiral (or even ) supersymmetric vacua via a Green‐Schwarz/Peccei‐Quinn mechanism generalized to four dimensions. We present some typical superstring models and discuss the possible stabilization of the no‐scale modulus.     

Higher‐Dimensional Unification with continuous and fuzzy coset spaces as extra dimensions

We first review the Coset Space Dimensional Reduction (CSDR) programme and present the best model constructed so far based on the , 10‐dimensional E₈ gauge theory reduced over the nearly‐Kähler manifold with the additional use of the Wilson flux mechanism. Then we present the corresponding programme in the case that the extra dimensions are considered to be fuzzy coset spaces and the best model that has been constructed in this framework too. In both cases the best model appears to be the trinification GUT .     

New Gaugings and Non‐Geometry

We discuss the possible realisation in string/M theory of the recently discovered family of four‐dimensional maximal gauged supergravities, and of an analogous family of seven‐dimensional half‐maximal gauged supergravities. We first prove a no‐go theorem that neither class of gaugings can be realised via a compactification that is locally described by ten‐ or eleven‐dimensional supergravity. In the language of Double Field Theory and its M theory analogue, this implies that the section condition must be violated. Introducing the minimal number of additional coordinates possible, we then show that the standard S ³ and S ⁷ compactifications of ten‐ and eleven‐dimensional supergravity admit a new class of section‐violating generalised frames with a generalised Lie derivative algebra that reproduces the embedding tensor of the and gaugings respectively. The physical meaning, if any, of these constructions is unclear. They highlight a number of the issues that arise when attempting to apply the formalism of Double Field Theory to non‐toroidal backgrounds. Using a naive brane charge quantisation to determine the periodicities of the additional coordinates restricts the gaugings to an infinite discrete set and excludes all the gaugings other than the standard one.     

algebras and field theory

We review and develop the general properties of algebras focusing on the gauge structure of the associated field theories. Motivated by the homotopy Lie algebra of closed string field theory and the work of Roytenberg and Weinstein describing the Courant bracket in this language we investigate the structure of general gauge invariant perturbative field theories. We sketch such formulations for non‐abelian gauge theories, Einstein gravity, and for double field theory. We find that there is an algebra for the gauge structure and a larger one for the full interacting field theory. Theories where the gauge structure is a strict Lie algebra often require the full algebra for the interacting theory. The analysis suggests that algebras provide a classification of perturbative gauge invariant classical field theories.