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.     

Water exchange on beryllium complexes: part VIII – influence of neutral electron pair donors

In this article, water exchange reactions on [Be(L)(H₂O)₃]²⁺ (L?=?NH_{3? x} (CH₃) _x , PH_{3? x} (CH₃) _x , AsH_{3? x} (CH₃) _x , OH_{2? x} (CH₃) _x , SH_{2? x} (CH₃) _x , SeH_{2? x} (CH₃) _x , pyridine, 4-fluoropyridine, 4-bromopyridine, 4-chloropyridine, 4-hydroxypyridine, 4-thiolopyridine, 4-selenidopyridine, 4-nitrilopyridine, 1,4-diazine, 1,3,5-triazine, HCN, acetonitrile, and benzonitrile) are examined, utilizing the B3LYP//6-311?+?G** density functional for geometry optimizations, and B3LYP//6-311?+?G** both with and without the CPCM solvent model as well as MP2(full)//6-311?+?G** for subsequent single-point energy calculations. In all examined cases, the results prove that these complexes show associative interchange mechanisms for water exchange. With the exception of the NH _x (CH₃)_{3? x} series of ligands, activation energy barriers vary little, making these ligands mostly spectator ligands. Geometrical parameters vary mainly with the ligand size.     

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.     

Synthesis, structure and dynamic stereochemistry of (O → Si)-chelate N-(trifluorosilylmethyl)-[N-(S)-(1-phenylethyl)]acetamide and 1-(trifluorosilylmethyl)-2-oxoperhydroazepine: Retention of the O → Si coordination in the adduct with KF and 18-crown-6

The novel compounds, N-(trifluorosilylmethyl)-[N-(S)-(1-phenylethyl)]-acetamide (1a) and 1-(trifluorosilylmethyl)-2-oxoperhydroazepine (1b) have been prepared from the corresponding NH-compounds using ClCH₂SiCl₃/Et₃N or ClCH₂SiCl₃/(Me₃Si)₂NH followed by methanolysis or hydrolysis of the reaction mixture in the presence of Lewis bases, and then BF₃ etherate. Potassium-(18-crown-6)-(2-oxoperhydroazepinomethyl)tetrafluorosilicate (2) was synthesized by reaction of the trifluoride (1b) with KF in the presence of 18-crown-6. Using ¹⁹F, ²⁹Si NMR and X-ray diffraction techniques it was established that the silicon atom is pentacoordinate in the trifluorides (1a, b) and hexacoordinate in the adduct 2. Thus the internal coordination of the O → Si bond present in the trifluoride (1b) is retained in the adduct 2.The stereochemical non-rigidity of the trifluorides (1a, b) and the N-(trifluorosilylmethyl)-N-methylacetamide (1c) was investigated using dynamic ¹⁹F NMR spectroscopy. The activation barriers for permutational isomerization are in the range 9.5-10 kcal mol⁻¹. Lower values of ΔG^# for permutation of trifluorides (1a-c) compared to the monofluorides with the coordination core OSiC₃F together with small negative values for the activation entropy implies a non-dissociative mechanism. Quantum-chemical analysis suggests a mechanism involving a turnstile rotation.     

Theoretical investigations on the conversions of cyclic polysulfides to acyclic polysulfide diradicals and subsequent reactions of biological interest

Sulfur is one of the most necessary biogenic elements in nature that must be assimilated by all organisms; it is an essential macronutrient for living organisms and has multiple roles in plant development. The oxidation of elemental sulfur is a complex process involving the contact of cells with sulfur particles, the oxidation of sulfur to sulfite, and the oxidation of sulfite to sulfate. To provide hypothesis concerning the most probable processes in the early states, we determined, by quantum-chemical calculations, the energies of some allotropic forms containing up to 32–40 sulfur atoms and energetics of their reactions with triplet dioxygen. The most probable reactions occurred with methylpolysulfane anions with an electron transfer to give the superoxide anion radical (and thiyls radicals) and especially the formation of peroxydic polysulfane anions. Calculations confirmed that the triplet diradical is more stable than the singlet one for acyclic polysulfide chains.     

An experimental and theoretical study of dipole moments of N-[4-(9-acridinylamino)-3-methoxyphenyl]methanesulfonamide

The excited state (S1) dipole moment of m-AMSA (1), an acridine derivative with antitumor activity, was determined from solvatochromic shifts of the lowest energy absorption band in several organic solvents. The effect of the solute shape and the values of polarizability on the determined change of dipole moment between ground and excited state was discussed. The dipole moments in S0 and S1 state were calculated in gas phase with semiempirical quantum-chemical and DFT and CIS methods and in solvents with SM5.4A solvation model and compared with values obtained experimentally. All the results show that the dipole moment of compound 1 in the excited state is higher than that in the ground state. These methods quite well predict the values of Deltamicro between two states of an investigated compound.     

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).     

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.     

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.     

Synthesis and Theoretical Study of Vanadium Oxotrichloride Complex of Hexachlorotriphosphazene and Ab Initio Investigations of Some Simple Cyclic Triphosphazenes

N₃P₃Cl₆·VOCl₃ results from the reaction between vanadium oxotrichloride and hexachlorotriphosphazene in dichloroethane. Vanadium oxotrichloride coordination with nitrogen atom in the phosphonitrile ring was detected from the IR spectrum of the product. Quantum-chemistry calculations for (NPX₂)₃ (X = H, F, Cl, NH₂) were carried out as well. A comparative study of some basic characteristics of the simple cyclotriphosphazenes' electronic structures was carried out. Quantum-chemistry calculations also were done for the complex of hexachlorophosphazene with vanadium oxotrichloride. It is shown that the nitrogen atom in phosphazenes plays an essential role for donor-acceptor interactions and is the most preferable atom for binding with a vanadium atom.