- and β-cyclodextrin complexes with n-alkyl carboxylic acids and n-alkyl p-hydroxy benzoates. A molecular mechanics study of 1:1 and 1:2 associations

Molecular mechanics (MM) methods were employed to evaluate stabilization upon formation of inclusion compounds between two different guest molecules and - and β-cyclodextrins (CDs) for two different stoichiometries 1:1 and 1:2. The two guest molecules studied were n-alkyl carboxylic acids and n-alkyl p-hydroxy benzoates with variety of chain lengths. The computed stability for the inclusion compounds between -CDs and n-alkyl carboxylic acids reproduced experimental data reported in the literature. The transition between 1:1/1:2 complexes occurred at an alkyl chain length of n_C=9. It was previously demonstrated by diffusion coefficients measures that a stable 1:2 stoichiometry inclusion compound could be formed between n-alkyl p-hydroxy benzoates and -CD for the chain length n_C>4. The computed results reproduced the experimental ones. The combination between OPLS and GB/SA resulted in better agreements with experiments than those obtained with MM2 and MM3.     

A study of biodegradation/γ-irradiation on the degradation of p-chloronitrobenzene

A microbial strain, Vagococcus sp. B32, was isolated and applied to degrade p-chloronitrobenzene (p-CNB) in aqueous solutions. Three degradation methods: biodegradation, direct γ-irradiation and ⁶⁰Co-γ pre-irradiation with biodegradation by B32 were carried out. The decrease of p-CNB and the net increase of Cl⁻ were investigated to evaluate the degradation efficiency. The preliminary results showed that the combined method of pre-irradiation with biodegradation of B32 was more effective than the two others.     

Ethylp-(2-methyl-3-oxopropyl)- andp-(2-methyl-3-oxo-1-propenyl)benzoates: preparation and use in the synthesis of biologically active derivatives ofp-(nor-polyprenyl)benzoic acids

Novel ways for preparing the title compounds have been developed. Saturated (1) and unsaturated (2) aldehydoesters, which are easily accessible by a Pd-catalyzed reaction of ethyl 4-bromobenzoate with methallyl alcohol and aldol condensation of ethyl 4-formyl-benzoate with propanal, respectively, are strategically advantageous intermediates for the synthesis. The results of thein vitro assays of some of the synthesized compounds are compared with the known data on their pharmacological effectsin vivo.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2126–2129, December, 1993.     

CuI/amino acid catalysis in coupling and cyclization of β‐bromo‐α,β‐unsaturated carboxylic acids with terminal alkynes leading to alkylidenefuranones

β‐Bromo‐α,β‐unsaturated carboxylic acids are coupled and cyclized with terminal alkynes in DMF at 110°C in the presence of a catalytic amount of CuI and amino acid along with a base to give alkylidenefuranones in good yields. Similar reaction under microwave irradiation also gave alkylidenefuranones in higher yields. Copyright © 2013 John Wiley & Sons, Ltd.     

Electronic spectra of the linear magnesium-containing carbon chains MgC2nH (n = 1–5): A CASPT2 study

Complete active space self-consistent-field (CASSCF) approach has been used for the geometry optimization of the X²Σ⁺ and A²Π electronic states for the linear magnesium-containing carbon chains MgC_2nH (n = 1–5). Multireference second-order perturbation theory (CASPT2) has been used to calculate the vertical excitation energies from the ground to selected seven excited states, as well as the potential energy curves of two ²Σ⁺ and two ²Π electronic states. The studies indicate that the vertical excitation energies of the A²Π ← X²Σ⁺ transition for MgC_2nH (n = 1–5) are 2.837, 2.793, 2.767, 2.714, and 2.669 eV, respectively, showing remarkable linear size dependence. Compared with the previous TD-DFT and RCCSD(T) results, our estimates for MgC_2nH (n = 1–3) are in the best agreement with the available observed data of 2.83, 2.78, and 2.74 eV, respectively. In addition, the dissociation energies in MgC_2nH (n = 1–5) are also been evaluated.     

Establishing effective simulation protocols for β‐ and α/β‐peptides. III. Molecular mechanical model for acyclic β‐amino acids

All‐atom molecular mechanics (MM) force field parameters are developed for the backbone of acyclic β‐amino acid using an improved version of the multiobjective evolutionary algorithm (MOEA). The MM model is benchmarked using β³‐homo‐Alanine (β³‐hAla) diamide in water with SCC‐DFTB/MM simulations as the reference. Satisfactory agreements are found between the MM and SCC‐DFTB/MM results regarding the distribution of key dihedral angles for the β³‐hAla diamide in water. The MM model is further applied to a β‐hepta‐peptide in methanol solution. The calculated NOE values and ³J coupling constants averaged over different trajectories are consistent with experimental data. By contrast, simulations using parameters directly transferred from the CHARMM22 force field for proteins lead to much worse agreement, which highlights the importance of careful parameterization for non‐natural peptides, for which the improved MOEA is particularly useful. Finally, as an initial application of the new force field parameters, the behaviors of a short random copolymer consisting of β amino acids in bulk solution and membrane/water interface are studied using a generalized Born implicit solvent model (GBSW). Results for four selected sequences show that segregation of hydrophobic and cationic groups occur easily at the membrane/solution interface for all sequences. The sequence that features alternating short blocks exhibits signs of lower stability at the interface compared to other sequences. These results confirm the hypothesis in recent experimental studies that β‐amino‐acid based random copolymers can develop a high degree of amphiphilicity without regular three‐dimensional structure. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

Theoretical study of electronic spectra of linear carbon clusters HC2nS (n = 1–5)

In this work we report the structures and stabilities of linear carbon clusters HC_2nS (n = 1–5) in their ground states using the B3LYP density functional. The rotational constants at the optimized geometries give excellent agreement with the experimental and previous theoretical values. The vertical excitation energies of the 2²Π ← X²Π transitions at the CASPT2 level are 3.16, 2.66, 2.05, 1.78, and 1.55 eV, respectively, in good agreement with the corresponding observed values of 3.01, 2.48, 2.10, 1.84, and 1.65 eV. Also, the exponential-decay curves for these vertical excitation energies obtained from experiments and theoretical calculations are illuminated.     

Nickel‐Catalyzed Decarboxylative C–Si Bond Formation: A Regioselective Cross‐Coupling Between Trialkyl Silanes and α,β‐Unsaturated Carboxylic Acids

This report presents the first example of nickel‐catalyzed mild decarboxylative cross‐coupling reaction for the regioselective formation of C–Si bond. An easily accessible and significantly stable Ni (dmg)₂ owes the role of key promoter. This reaction is highly functional group tolerant and offers α,β‐unsaturated silanes in synthetically useful yields. The reaction gives access to the successful utilization of otherwise difficult trialkyl silanes as coupling partners and operates at a moderate temperature, which is beneficial to deal with highly volatile silanes.     

H NMR titration and quantum calculation for the inclusion complexes of styrene and α-methyl styrene with α, β and γ-cyclodextrins

The inclusion behavior between styrene (α-methyl styrene) and cyclodextrins (CDs) was studied by using ¹H NMR titration in solution. The results indicate that 1:1 inclusion complexes were formed. The association constants of the inclusion complexes were determined by nonlinear least-square method. The inclusion process was also studied by using PM3 quantum-mechanical semi-empirical method. The calculated results are in agreed with the experimental data.     

Inelastic neutron scattering and vibrational spectra of 2-(N-methyl-α-iminoethyl)-phenol and 2-(N-methyliminoethyl)-phenol: Experimental and theoretical approach

The infrared, Raman, and inelastic neutron scattering (INS) spectra of two ortho-hydroxy aryl Schiff’s bases, 2-(N-methyliminoethyl)-phenol and 2-(N-methyl-α-iminoethyl)-phenol, were recorded. Ab initio molecular orbital calculations employing the DFT (B3LYP) method with the 6-31G** basis set for both compounds were done. Assignments of vibrational modes within the 3500–50 cm⁻¹ spectral region were carried out. On the basis of the DFT calculations, four rotomers of 2-(N-methyl-α-iminoethyl)-phenol were analysed.     

Linear relationships in α,β-unsaturated carbonyl compounds between the half-wave reduction potentials, the frontier orbital energies and the Hammett σp values

A linear relationship between the half-wave reduction potentials of α,β-unsaturated carbonyl compounds R–CHCH–COX and the Hammett σ_p values of R and X is proposed: E_1/2=−1.341σ_p(X)σ_p(R)+1.123σ_p(X)+1.746σ_p(R)−1.694. A linear relationship is also observed for the LUMO's energy values, the absolute chemical hardness η, the chemical potential μ, the electrophilicity power ω, or the polarisation of the ethylenic double bond with the Hammett σ_p values of R and X.     

A novel synthesis of silyl enol ethers from α-silylbenzylthiols and carboxylic acid derivatives via C---C bond formation; thermal rearrangement of S-α-silylbenzyl thioesters

A new procedure for the synthesis of silyl enol ethers from S-α-silylbenzyl thioesters without need for either bases or catalysts via C---C bond formation is described. Solutions of S-α-silylbenzyl thioesters were simply heated at 180°C for 24 h in a sealed tube to give silyl enol ethers in good yields with high stereoselectivity. Cyclization of the dipoles generated by thermal rearrangement of the silyl group and elimination of sulfur afforded silyl enol ethers.     

The combination of 2-NsNH2/NCS and MeCN as the nitrogen sources for the regio- and stereoselective formation of imidazolines from α,β-unsaturated ketones

A new nitrogen source combination was found for the regio- and stereoselective diamination of α,β-unsaturated ketones. This combination employs the readily available and inexpensive combination of NCS and 2-NsNH₂ as the electrophilic nitrogen source, and acetonitrile as the nucleophilic nitrogen source, respectively. The reaction is easily performed by mixing olefin, 2-NsNH₂, NCS and 4 Å molecular sieves in freshly distilled acetonitrile at room temperature. The reaction is chemoselective without the formation of any haloamine side products. A new aziridinium ion formed from enones and 2-NsNHCl is suggested to exist and to react with nitrile via a [2+3] cycloaddition mechanism, which is responsible for the excellent regio-, stereoselectivity of the resulting diamination products.     

Intramolecular chelation of Zn2+ by α‐ and β‐mercaptocarboxamides. A parallel ab initio and polarizable molecular mechanics investigation. Assessment of the role of multipole transferability

α‐ and β‐mercaptocarboxamides constitute the Zn²⁺‐ligating entity of several highly potent metalloenzyme inhibitors. We have studied their interaction energies with Zn²⁺ using the polarizable molecular mechanics procedure SIBFA, and compared them to the corresponding ab initio supermolecule ones. Such validations are necessary to subsequently undertake simulations on complexes of Zn²⁺–metalloenzymes with inhibitors. If the distributed multipoles and polarizabilities are those derived for each ligand in its appropriate Zn²⁺‐binding conformation, a close reproduction of the ab initio binding energies is afforded. However, this representation is not tractable upon increasing the size of the ligands and/or to explore a continuum of binding conformations. This makes it necessary to construct the ligands by resorting to a library of constitutive fragments, namely in this case methanethiolate, formamide, and methane covalently connected together. A close reproduction of the ab initio interaction energies is enabled, but only if the ligand–ligand interactions are computed simultaneously with those occurring with Zn²⁺. This representation accounts for the nonadditivity occurring in the Zn²⁺–methanethiolate–formamide complex, and justifies the use of the distributed multipoles on the fragments for the construction of larger and flexible molecules. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1038–1047, 2001     

A novel method for the synthesis of (Z)-α-selenyl-α,β-unsaturated ketones via acylation of (E)-α-selanylvinylstannanes

The (E)-α-selenylvinylstannanes react with acyl halides in presence of a catalytic amount of Pd(PPh₃)₄ to give the corresponding (Z)-α-selenyl-α,β-unsaturated ketones in good yield.     

Reaction of 2-(2-oxoethylidene)furan-3(2H)-ones with isopropylidenehydrazides of aromatic carboxylic acids: Synthesis of 3-hydroxy-3-(2-oxoethyl)-2,3-dihydropyridazin-4(1H)-ones

3-Hydroxy-3-(2-oxoethyl)-6-phenyl-2,3-dihydropyridazin-4(1H)-ones were obtained by the reaction of methyl 3-oxo-5-phenylfuran-2(3H)-ylideneacetate or 2-[2-(4-chlorophenyl)-2-oxoethylidene]-5-phenylfuran-3(2H)-one with benzoic or p-nitrobenzoic isopropylidenehydrazides. Equilibrium C₍₅₎H and C₍₅₎H₂ tautomeric forms were detected in solutions of the 4-chlorophenyl derivatives in DMSO-d₆. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1156–1158, August, 2007.