Facile synthesis of cis-2-Alkyl-3-trialkylsilyloxycycloalkanones via the non-aldol aldol rearrangement of 2,3-epoxycycloalkanols

Silyl triflate-promoted rearrangement of cis-2,3-epoxycycloalkanols A, prepared by epoxidation of the cyclic allylic alcohol and then silylation, afforded good yields ( approximately 70-75%) of the cis-2-alkyl-3-silyloxycycloalkanones B, presumably via the intermediates C and D, even with quite large alpha-substituents, e.g., tert-butyl. Finally, it has been shown that the stereochemistry of the epoxy alcohol is crucial as one would expect from the mechanism.     

Vicinal deuterium perturbations on hydrogen NMR chemical shifts in cyclohexanes

The substitution of a deuterium for a hydrogen is known to perturb the NMR chemical shift of a neighboring hydrogen atom. The magnitude of such a perturbation may depend on the specifics of bonding and stereochemical relationships within a molecule. For deuterium-labeled cyclohexanes held in a chair conformation at -80 degrees C or lower, all four possible perturbations of H by D as H-C-C-H is changed to D-C-C-H have been determined experimentally, and the variations seen, ranging from 6.9 to 10.4 ppb, have been calculated from theory and computational methods. The predominant physical origins of the NMR chemical shift perturbations in deuterium-labeled cyclohexanes have been identified and quantified. The trends defined by the Delta delta perturbation values obtained through spectroscopic experiments and by theory agree satisfactorily. They do not match the variations typically observed in vicinal J(H-H) coupling constants as a function of dihedral angles.     

Sulfur X-ray absorption and vibrational spectroscopic study of sulfur dioxide, sulfite, and sulfonate solutions and of the substituted sulfonate ions X3CSO3- (X = H, Cl, F)

Sulfur K-edge X-ray absorption near-edge structure (XANES) spectra have been recorded and the S(1s) electron excitations evaluated by means of density functional theory-transition potential (DFT-TP) calculations to provide insight into the coordination, bonding, and electronic structure. The XANES spectra for the various species in sulfur dioxide and aqueous sodium sulfite solutions show considerable differences at different pH values in the environmentally important sulfite(IV) system. In strongly acidic (pH < approximately 1) aqueous sulfite solution the XANES spectra confirm that the hydrated sulfur dioxide molecule, SO2(aq), dominates. The theoretical spectra are consistent with an OSO angle of approximately 119 degrees in gas phase and acetonitrile solution, while in aqueous solution hydrogen bonding reduces the angle to approximately 116 degrees . The hydration affects the XANES spectra also for the sulfite ion, SO32-. At intermediate pH ( approximately 4) the two coordination isomers, the sulfonate (HSO3-) and hydrogen sulfite (SO3H-) ions with the hydrogen atom coordinated to sulfur and oxygen, respectively, could be distinguished with the ratio HSO3-:SO3H- about 0.28:0.72 at 298 K. The relative amount of HSO3- increased with increasing temperature in the investigated range from 275 to 343 K. XANES spectra of sulfonate, methanesulfonate, trichloromethanesulfonate, and trifluoromethanesulfonate compounds, all with closely similar S-O bond distances in tetrahedral configuration around the sulfur atom, were interpreted by DFT-TP computations. The energy of their main electronic transition from the sulfur K-shell is about 2478 eV. The additional absorption features are similar when a hydrogen atom or an electron-donating methyl group is bonded to the -SO3 group. Significant changes occur for the electronegative trichloromethyl (Cl3C-) and trifluoromethyl (F3C-) groups, which strongly affect the distribution especially of the pi electrons around the sulfur atom. The S-D bond distance 1.38(2) A was obtained for the deuterated sulfonate (DSO3-) ion by Rietveld analysis of neutron powder diffraction data of CsDSO3. Raman and infrared absorption spectra of the CsHSO3, CsDSO3, H3CSO3Na, and Cl3CSO3Na.H2O compounds and Raman spectra of the sulfite solutions have been interpreted by normal coordinate calculations. The C-S stretching force constant for the trichloromethanesulfonate ion obtains an anomalously low value due to steric repulsion between the Cl3C- and -SO3 groups. The S-O stretching force constants were correlated with corresponding S-O bond distances for several oxosulfur species.     

Denaturation of hen egg white lysozyme in electromagnetic fields: a molecular dynamics study

Nonequilibrium molecular dynamics simulations of hen egg white lysozyme have been performed in the canonical ensemble at 298 K in the presence of external electromagnetic fields of varying intensity in the microwave to far-infrared frequency range. Significant nonthermal field effects were noted, such as marked changes in the protein's secondary structure which led to accelerated incipient local denaturation relative to zero-field conditions. This occurred primarily as a consequence of alignment of the protein's total dipole moment with the external field, although the enhanced molecular mobility and dipolar alignment of water molecules is influential on sidechain motion in solvent-exposed regions. The applied field intensity was found to be highly influential on the extent of denaturation in the frequency range studied, and 0.25-0.5 V Arms-1 fields were found to induce initial denaturation to a comparable extent to thermal denaturation in the 400 to 500 K range. In subsequent zero-field simulations following exposure to the e/m field, the extent of perturbation from the native fold and the degree of residual dipolar alignment were found to be influential on incipient folding.     

Dinuclear ruthenium(ii) complexes with flexible bridges as non-duplex DNA binding agents

The stereoisomers of a series of dinuclear ruthenium(ii) complexes [{Ru(phen)(2)}(2)(micro-BL)](4+) (phen = 1,10-phenanthroline) with flexible bridging ligands (BL) bb2 {1,2-bis[4(4'-methyl-2,2'-bipyridyl)]ethane}, bb5 {1,5-bis[4(4'-methyl-2,2'-bipyridyl)]pentane}, bb7 {1,7-bis[4(4'-methyl-2,2'-bipyridyl)]heptane}, and bb10 {1,10-bis[4(4'-methyl-2,2'-bipyridyl)]decane} have been synthesised. Their binding to a control dodecanucleotide, d(CCGGAATTCCGG)(2), and a tridecanucleotide, d(CCGAGAATTCCGG)(2), which contains a single adenine bulge have been studied using fluorescence displacement assays involving intercalating and groove-binding dyes, equilibrium dialysis and binding affinity chromatography. The fluorescence intercalator displacement (FID) assay indicated that LambdaLambda-[{Ru(phen)(2)}(2)(micro-bb7)](4+) had the greatest binding affinity with all the oligonucleotides, whereas an analogous fluorescence technique using a minor-groove binding dye, equilibrium dialysis and affinity binding chromatography showed that DeltaDelta-[{Ru(phen)(2)}(2)(micro-bb7)](4+) had the strongest binding. An (1)H NMR study of the binding of the DeltaDelta-enantiomer of [{Ru(phen)(2)}(2)(micro-bb7)](4+) to d(CCGAGAATTCCGG)(2) confirmed the selectivity of the metal complex for the bulge site and provided the basis for an energy-minimised binding model of the dinuclear ruthenium complex with the single adenine bulge containing trinucleotide. The binding model demonstrated the ability of the flexibly-linked complex to follow the curvature of the DNA minor groove.     

Theoretical studies of l-ascorbic acid (vitamin C) and selected oxidised, anionic and free-radical forms

Calculations were carried out at the restricted and unrestricted B3LYP/6-311++G(d,p) and B3LYP/EPR-II levels for two conformers (1 and 2) of l-ascorbic acid and their respective oxidation products to di- and monodehydroascorbates. For the didehydroascorbates, corresponding to Conformer 1, free radical properties are compared with previously published calculations in the gaseous and aqueous solution states and with experimental EPR values. Calculated molecular structures, EPR and vibrational spectral and energetic properties are reported including some proposed changes to previous EPR assignments. Conformer 2 of l-ascorbic acid is predicted to have lower energy than Conformer 1, under the method and basis sets used, by between 11 and 26 kJ mol⁻¹ and is stabilised by internal hydrogen bonding. For particular monodehydroascorbates, formed by loss of H from the chain CH(OH) group, calculated properties of conformers of five neutral mono-radicals and the corresponding five anionic di-radicals are reported. Relaxed potential energy surface (PES) scans were carried out for two proton transfer processes and relative energies of stable minima and barriers between them determined. The physiological significance of the protective oxidation of l-ascorbic acid by free radicals is briefly described.     

Reverse task as a designing of mechatronic vibrating branched systems

In this paper a new approach for designing mechatronic vibrating branched structures has been presented. Mechatronic structures have been built from mechanical discrete systems connected to piezoelectric actuator and externalL_xR_xC_x network, with different configurations. Modeling simplification has been performed by use of non dimensional transformations and retransformations. In each case reverse task has been solved by distribution into partial fraction method in respect to required dynamic properties in form of frequency spectrum: resonant and anti resonant frequencies. Furthermore, different configurations of final L_xR_xC_x network have been presented. These considerations have been supported by calculation examples, and all results have been presented in the graphical form. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

An experimental and theoretical investigation of gas-phase reactions of Ca2+ with glycine

The gas-phase reactions between Ca(2+) and glycine ([Ca(gly)](2+)) have been investigated through the use of mass spectrometry techniques and B3-LYP/cc-pWCVTZ density functional theory computations. The major peaks observed in the electrospray MS/MS spectrum of [Ca(gly)](2+) correspond to the formation of the [Ca,C,O(2),H](+), NH(2)CH(2) (+), CaOH(+), and NH(2)CH(2)CO(+) fragment ions, which are produced in Coulomb explosion processes. The computed potential energy surface (PES) shows that not only are these species the most stable product ions from a thermodynamic point of view, but they may be produced with barriers lower than for competing processes. Carbon monoxide is a secondary product, derived from the unimolecular decomposition of some of the primary ions formed in the Coulomb explosions. In contrast to what is found for the reactions of Ca(2+) with urea ([Ca(urea)](2+)), minimal unimolecular losses of neutral fragments are observed for the gas-phase fragmentation processes of [Ca(gly)](2+), which is readily explained in terms of the topological differences between their respective PESs.