DFT and quantum chemical investigation of molecular properties of substituted pyrrolidinones

The DFT, quantum-chemical calculations and thermodynamics parameters of 1-{2-[(2-hydroxyethyl)thio]ethyl}pyrrolidin-2-one (HTEP); [2-(2-oxo-pyrrolidin-1-yl)-ethyl]-phosphonic acid diethyl ester (EOEP); {[2-(2-oxopyrrolidin-1-yl)ethyl]thio}acetic acid (OETA); (2-pyridin-4-yl-ethyl]thio}acetic acid (PTA) and pyridine (PY) have been calculated with Gaussian 94 and Hybrid B3LYP functional density with 6-31G* basis set. Moreover, the electronic properties such as highest occupied molecular orbital (HOMO), lowest unoccupied orbital (LUMO) energy and molecular densities have been investigated.     

Solvation of the Electrolytic Components of Seawater

A new modification of the adiabatic compressibility method of investigating solvation in solutions is presented and applied to the analysis of the following structurally-related characteristics of hydrated complexes of seawater electrolytes (NaCl, KCl, MgCl₂, CaCl₂, Na₂SO₄, MgSO₄) at different concentrations (0.1 to 5.0 mol⋅kg⁻¹) and temperatures (278.15 to 308.15 K): solvation numbers (h) and their dependences on concentration, volumes of stoichiometric mixtures of ions without their hydration shells (V _2h ), compressibilities (β _1h ) and molar volumes of water in their solvation shells (V _1h ), their dependences on concentration and temperature, etc.     

Two Novel Thermal Biradical Cyclizations of Enyne-Ketenimines: Theory,Experiment, and Synthetic Potential

Both benzocarbazoles and quinolines can be synthesized from enyne ketenimines 1 generated in situ via biradical intermediates (see reaction below). Which of the heterocyclic ring systems is formed depends on the choice of the substituent R¹ at the alkyne terminus.     

Reactions in Anhydrous Liquid Ammonia: Syntheses and Crystal Structures of [M(NH3)8]I2 (M = Eu,Yb) with Bicapped Trigonal-Prismatic Octaammine Lanthanoid(II) Cations

The compounds [M(NH₃)₈]I₂ (M = Eu, Yb) were obtained from reactions in anhydrous liquid ammonia solutions as side products. They were characterized by single-crystal X-ray diffraction and found to be isotypic to the compounds [Ca(NH₃)₈]X₂ (X = Cl, Br, I). The coordination sphere of the lanthanoid(II) cations is not square-antiprismatic but much better described as bicapped trigonal-prismatic. In contrast, quantum-chemical gas-phase calculations show the square-antiprismatic coordination polyhedron (point group S₈) to be energetically favored over the bicapped trigonal prism and the latter is not even a true local minimum. Obviously, hydrogen bonding and eventually other weak interactions have an impact on the observed bicapped trigonal-prismatic coordination sphere of the [M(NH₃)₈]²⁺ cations in the solid state.     

Sorbifuranones A-C, sorbicillinoid metabolites from Penicillium strains isolated from Mediterranean sponges

Three novel natural products, sorbifuranones A-C (4-6), were isolated from a Penicillium chrysogenum fungus isolated from the marine sponge Ircinia fasciculata. Sorbifuranones B (5) and C (6) and 2′,3′-dihydrosorbicillin, a putative precursor to sorbifuranone B, were also found in the culture of another Penicillium strain, which was isolated from the sponge Tethya aurantium. Their constitutions were elucidated mainly by 2D NMR. NOE correlations in combination with quantum chemical calculations and comparison of experimental and calculated electronic circular dichroism (CD) spectra permitted assignment of the absolute configuration of sorbifuranone C. The structures hint at a two-step cleavage-cyclization sequence of sorbifuranone A (4) leading to the spiro compound sorbifuranone C, while sorbifuranone B is likely to be the respective cleavage product of a putative 2′,3′-dihydrosorbifuranone A, which cannot cyclize further.     

Solvation dynamics of a protein in the pre molten globule state

The nature of solvent molecules around proteins in native and different non-native states is crucial for understanding the protein folding problem. We have characterized two compact denatured states of glutaminyl-tRNA synthetase (GlnRS) under equilibrium conditions in the presence of a naturally occurring osmolyte, l-glutamate. The solvation dynamics of the compact denatured states and the fully unfolded state has been studied using a covalently attached probe, acrylodan, near the active site. The solvation dynamics progressively becomes faster as the protein goes from the native to the molten globule to the pre molten globule to the fully unfolded state. Anisotropy decay measurements suggest that the pre-molten-globule intermediate is more flexible than the molten globule although the secondary structure is largely similar. Dynamic light scattering studies reveal that both the compact denatured states are aggregated under the measurement conditions. The implications of solvation dynamics in aggregated compact denatured states have been discussed.     

Enthalpy of dissociation and hydration number of methane hydrate from the Clapeyron equation

The enthalpies of the reactions in which methane hydrate is dissociated to methane vapor and either (1) water, or (2) ice are determined by a new analysis using the Clapeyron equation. The difference in enthalpies of the two reactions is used to infer the hydration number at the quadruple point where hydrate, ice, liquid water, and methane vapor coexist. By appropriate corrections, the hydration number at points removed from the quadruple point is also determined. The most important feature of the new analysis is the direct use of the Clapeyron equation. The method avoids the use of certain simplifying assumptions that have compromised the accuracy of previous analyses in which the Clausius-Clapeyron equation was used. The analysis takes into account the finite volumes of all phases, the non-ideality of the vapor phase, and the solubility of methane in water. The results show that the enthalpy of dissociation and hydration number are constant within experimental error over the entire (hydrate, liquid, vapor) coexistence region. The results are more accurate than but entirely consistent with almost all previous studies.     

Vapor-liquid equilibrium of hexadecapolar fluids from a perturbation-based equation of state

In this work a numerically tractable expression for the interaction potential between two point hexadecapoles with octahedral symmetry and a molecular-based equation of state derived by perturbation theory for hexadecapolar fluids are presented. The polar system is modeled by square-well particles with a point hexadecapole with octahedral symmetry at their centers. This equation of state is analytical in the state variables and in the potential parameters and allows us to study the effects of the hexadecapolar moment strength on the thermodynamic properties and liquid-vapor phase diagram. The equation presented here is applied to the thermodynamics of sulfur hexafluoride and gives very good predictions for the saturation pressures and the vapor-liquid phase diagram.     

Thermodynamic properties of polar fluids from a perturbed-dipolar-hard-sphere equation of state

Based on theoretical results for a system of hard spheres with dipoles, a new equation of state is applied to the correlation of thermodynamic properties for four fluids: argon, ammonia, water and acetonitrile. The reference system has the same dependence on density as that given by the Carnahan-Starling equation, but the coefficients are now functions of temperature through the reduced dipole moment. These coefficients are chosen to match the Padé approximant developed by Rushbrooke, Stell and Hoye for the Helmholtz energy of dipolar hard spheres. The reference system proposed here shows a phase transition for reduced dipole moments greater than 1.9. A simple, empirical perturbation term is added to the reference system to account for induction and dispersion forces. For polar fluids, the equation gives results significantly better than those obtained from conventional cubic equations of state, when using the same limited experimental data for determining equation-of-state parameters.     

Synthesis of new bis(thiosemicarbazone) derivatives and DFT analysis of antioxidant characteristics in relation to HAT and SET reactions

A series of new bis(thiosemicarbazones) have been synthesized from terephthalaldehyde and various thiosemicarbazides. IR, ¹H NMR, ¹³C NMR spectroscopic methods, and elemental analysis were used to characterize the identification of the synthesized compounds. The in vitro antioxidant activity determinations were made using the 1,1-Diphenyl-2-Picryl Hydrazil (DPPH) method. The compounds exhibited very different inhibition activities with the change of groups attached to the bis(thiosemicarbazone) structure. The spectral and electronic properties of the compounds were investigated by DFT calculation. Intramolecular interactions were analyzed by QTAIM and IRI calculations. Intrinsic bond strength index values of the N–H bonds, Fukui indices and the local electron affinities of the compounds were calculated, and the relationships between the compounds and their antioxidant activity properties were investigated. The SET and HAT mechanisms in the reactions of the compounds with DPPH were affected by the concentration of the compounds, and the possible effects of the parameters supporting the dominant characteristics in these reactions were examined using theoretical data.     

Theoretical Study of the Dimerization of Chlorophyll (a) and Its Hydrates: Implication for Chlorophyll (a) Aggregation

Dimeric structures chlorophyll (a) (Chla) and their mono‐ and dihydrated have been suggested to play an important role in the mechanism of photoreaction center chlorophyll special pairs PSI and PSII. Despite their functional importance, the molecular basis structures for interacting two Chla molecules and the structural stabilization role of H₂O in the formation of hydrated Chla dimer complexes is poorly understood. In this article, the different coordination modes between two interacting Chla molecules and the configurational (orientation and distance) features between the dimer and bound H₂O molecules are characterized by means of super molecule approach the density functional theory DFT. An estimation of the thermodynamic quantities is made for Chla dimerization and hydration processes. The results indicate that structure including ester linkages via H₂O hydrogen bonding is the most favorable conformation for the dihydrated chlorophyll (a) dimer at B3LYP/6‐31G*‐DCP level of calculation. The dispersion interaction is shown to be of great significance for the Chla dimer stabilization. In aqueous nonpolar solvent, the thermodynamics show that Chla has a slightly stronger driving force for full hydration than for dimerization and that hydration of the dimers is rather weakly exergonic. The tetrahydrated dimers having a similar arrangement to that in crystals of ethyl chlorophyllide (a) dihydrate are found to be more stable than the Chla dihydrated dimer. The data underscore the key role of H‐bonding in the stability of Chla‐H₂O adducts and, in particular, the great importance of the Chla monomeric dihydrated species in the hydration and dimerization of Chla in aqueous media. Clearly, the Chla dihydrates (Chla‐2 H₂O) are found more stable than the monohydrates (Chla‐H₂O) and the Chla dimers (Chla₂), owing to a particular structure in which cooperative interactions occur between the H₂O molecules and Chla. Calculations also indicate that the most thermodynamically preferred pathway for the formation of Chla dimer hydrates can be represented by two steps: the first corresponds to the formation of Chla monomeric dihydrates and the second is the dimerization of the dihydrates on to tetrahydrated Chla dimers. These results allow to obtain a new possible pathway for Chla dimer formation processes and could provide new insights to the aggregation of chlorophyll (a) in solution.     

Communication: inferring the equation of state of a metastable hard-sphere fluid from the equation of state of a hard-sphere mixture at high densities

A possible approximate route to obtain the equation of state of the monodisperse hard-sphere system in the metastable fluid region from the knowledge of the equation of state of a hard-sphere mixture at high densities is discussed. The proposal is illustrated by using recent Monte Carlo simulation data for the pressure of a binary mixture. It is further shown to exhibit high internal consistency.     

Nucleus-independent chemical shift (NICS) profiles in a series of monocyclic planar inorganic compounds

A series of monocyclic planar inorganic compounds have been optimized at the B3LYP/6-311+G^∗ level. GIAO-B3LYP nucleus-independent chemical shifts (NICS) profiles calculated in the perpendicular direction of each ring show that the series of analyzed compounds can be classified in three groups according to their aromatic, non-aromatic or antiaromatic character. Our results suggest exercising caution in the use of single-point NICS calculations as a quantitative measure of aromaticity for these species.     

The reactivity of ferrocenylalkyl azoles under the conditions of electrospray ionization

Under the conditions of electrospray ionization of ferrocenylalkyl azoles FcCH(R)X (Fc-η⁵-C₅H₅Fe-η⁵-C₅H₄, R - H, Me, XH - 2-methyl imidazole, pirazole) the processes of oxidation, protonation, fragmentation and ferrocenylalkylation to form, molecular ions [М]⁺, protonated molecules [М+Н]⁺, ferrocenylalkyl cations [FсCHR]⁺ and bisferrocenylalkyl azole cations [(FcCHR)2X]⁺, respectively, take place. Using special experimental techniques (deuterated solvents, saturation of ionic source of an ESI mass-spectrometer by the vapors of solvents, the experiments under the “inverse” ESI conditions when the solvent is subjected to electrospray in the presence of ferrocenylalkyl derivative vapours) and quantum-chemical calculations at the level of the B3LYP/LanL2DZ theory the scheme of the formation of these ions in a gas phase according to the mechanism of “activating protonation” was suggested. it was found that all these ions are formed through the protonation stage, which is taking place mainly in a gas phase. The key stage is the exothermic process of the protonation of the initial compounds by hydroxonium ions giving rise to protonated [M+H]⁺ molecules which further oxidize and alkylate ferrocenylalkylazoles to form molecular radical cations and bisferrocenylalkyl azole ions [FcCH(Me)-X-CH(Me)Fc]⁺. The decomposition of protonated ions with the elimination of the azole molecule gives rise to ferrocenylalkyl cations [FсCHR]⁺ capable in turn of oxidizing and alkylating the initial compounds.     

Lactamomethylation of alkylphenols: Synthesis and quantum-chemical study of the reaction pathway

Six novel lactamomethyl derivatives of 2,5-dimethylphenol and 2,3,5-trimethylphenol were prepared with moderate yields by the reaction of corresponding phenols with 1-(hydroxymethyl)lactams in the presence of an acid catalyst. In all cases, the substitution occurred at position 4 to the phenolic hydroxyl group. The structures of all synthesized compounds were confirmed by FT-IR, ¹H and ¹³C NMR, 2D NMR and elemental analysis. The selectivity and possible pathways of the lactamomethylation reaction were studied by quantum-chemical methods. In silico calculations showed that the substitution at para-position to the hydroxyl group of the corresponding phenols was more preferable due to the higher stability of forming intermediates.     

A new 3D-aromatic organoboron species on the basis of CB6 unit: Two states of carbon hypercoordination and structural isomerism of non-classical forms

Calculations using the DFT B3LYP/6-311+G(df,2p) and wb97XD/6-311+G(df,2p) methods predict the stability of a new three-dimensional aromatic organoboron species based on the CB₆ unit. Derived systems containing carbon atoms in two hypercoordination states (planar hexacoordination and inverted-umbrella heptacoordination) can be used as building blocks for constructing various stable condensed systems with many hypercoordinated carbon centers.     

The structure and spectra of 1,1-bis(trimethylsilylethynyl)-cyclopropane: a priori calculated force field and vibrational effects

The molecular structure of 1,1-bis(trimethylsilylethynyl)cyclopropane has been studied by the gas electron diffraction method, by vibrational spectroscopic methods and by ab initio calculations at the RHF and MP2 levels. A scaled quantum-chemical force field was used for band assignment in the experimental IR (4000-100 cm⁻¹) and Raman (4000-200 cm⁻¹) spectra. The root-mean-square vibrational amplitudes and harmonic shrinkage corrections were calculated taking into account non-linear relations between Cartesian and internal vibrational coordinates at the level of first-order perturbation theory (h1) and with the use of the traditional scheme (h0).     

Development of a five-parameter cubic equation of state

A five-parameter van der Waals type cubic equation of state has been developed specifically for representing pure-component volumetric properties. The justification of such an equation is based on the analysis of the variation of the attraction term contribution with reduced density. The parameters have been evaluated on the basis of optimal representation of the three saturated properties (vapor pressure, liquid volume and vapor volume) and the compressed liquid volume, and generalized in terms of critical temperature and the acentric factor. The calculated densities for 17 fluids are compared with those obtained from seven selected equations of state.In addition, individual parameters for carbon dioxide, ethylene, ethane and propane are presented for predicting volumetric behaviors in the critical region useful for supercritical fluid extraction processes.