Isotopic hydration of cellobiose: vibrational spectroscopy and dynamical simulations

The conformation and structural dynamics of cellobiose, one of the fundamental building blocks in nature, its C4' epimer, lactose, and their microhydrated complexes, isolated in the gas phase, have been explored through a combination of experiment and theory. Their structures at low temperature have been determined through double resonance, IR-UV vibrational spectroscopy conducted under molecular beam conditions, substituting D(2)O for H(2)O to separate isotopically, the carbohydrate (OH) bands from the hydration (OD) bands. Car-Parrinello (CP2K) simulations, employing dispersion corrected density functional potentials and conducted "on-the-fly" from ～20 to ～300 K, have been used to explore the consequences of raising the temperature. Comparisons between the experimental data, anharmonic vibrational self-consistent field calculations based upon ab initio potentials, and the CP2K simulations have established the role of anharmonicity; the reliability of classical molecular dynamics predictions of the vibrational spectra of carbohydrates and the accuracy of the dispersion corrected (BLYP-D) force fields employed; the structural consequences of increasing hydration; and the dynamical consequences of increasing temperature. The isolated and hydrated cellobiose and lactose units both present remarkably rigid structures: their glycosidic linkages adopt a "cis" (anti-? and syn-ψ) conformation bound by inter-ring hydrogen bonds. This conformation is maintained when the temperature is increased to ～300 K and it continues to be maintained when the cellobiose (or lactose) unit is hydrated by one or two explicitly bound water molecules. Despite individual fluctuations in the intra- and intermolecular hydrogen bonding pattern and some local structural motions, the water molecules remain locally bound and the isolated carbohydrates remain trapped within the cis potential well. The Car-Parrinello dynamical simulations do not suggest any accessible pathway to the trans conformations that are formed in aqueous solution and are widespread in nature.     

The Bi-Hamiltonian Structures of the DR and DZ Hierarchies in the Approximation up to Genus One

Functional Analysis and Its Applications - In a recent paper, given an arbitrary homogeneous cohomological field theory ( CohFT), Rossi, Shadrin, and the first author proposed a simple formula for...     

Arene ruthenium metallacycles containing chelating thioamide ligands

Cationic, chiral arene ruthenium complexes of the type [Ru(η⁶-cym)(PPh₃){κ²N,S-PhNC(S)R}]BPh₄ were prepared in high yields by refluxing a mixture containing [(η⁶-cym)RuCl₂]₂, Ph₃P, PhNHC(S)R, NaBPh₄ and Et₃N in MeOH. A series of seven complexes with different thioamide ligands was prepared and fully characterised by spectroscopic methods including NMR spectroscopy and electrospray mass spectrometry. The solid-state structures of two complexes were determined by single crystal X-ray diffraction.     

Decay and polarization of luminescence pulses in the 440 nm emission band of KI:In

Model suggestions for the impurity luminescence center in KI:In crystals from the literature are found to agree with experimental results obtained by excitation of KI:In at 80 K with polarized light pulses in the A, B and C impurity absorption bands. By excitation in the C absorption band the population of the metastable M state goes not only via A state, but directly from the C state too.     

Kristalldaten von einigen Alkalihalogeno-auraten(III)

The lattice dimensions of the monoclinic unit cells of the compounds CsAuCl₄, CsAuBr₄, RbAuCl₄, and RbAuBr₄ were determined by means of single crystal X-ray diffraction photographs. The three first mentioned compounds are isostructural(space group I2/c). RbAuBr₄ has a different space group (P2₁/a) but a closely related crystal structure.