Spectroscopic and semiempirical studies of a proton channel formed by the methyl ester of monensin A

Monensin A is an ionophore able to carry protons and cations through the cell membrane. Its methyl ester (MON1) and its hydrates have been studied in acetonitrile, and its deuterated analogue by Fourier transform infrared (FTIR) and (1)H and (13)C NMR spectroscopies as well as by vapor pressure osmotic and PM5 semiempirical methods. Interestingly, these hydrates show new and unexpected biophysical and biochemical properties. The formation of the hydrates starts with a transfer of a proton from the O(IV)-H hydroxyl group of MON1 to an oxygen atom of a water molecule, which is subsequently hydrated by other water molecules forming the (MON1 + 3H(2)O) species. This hydrate exhibits a ringlike structure in which the water molecules form an almost linear hydrogen-bonded chain. Within this chain, the excess proton fluctuates very fast inside the water cluster as indicated by a continuous absorption in the FTIR spectra. The formation of the (MON1 + 3H(2)O) species is accompanied by a self-assembly process, leading to the formation of a proton channel made up of eight (MON1 + 3H(2)O) units with a length of 60 A, in which the proton can fluctuate over the whole distance. Semiempirical calculations suggest that due to the hydrophobic surface the channel can be incorporated readily in a lipid bilayer. This hypothetical new channel is thought to be able to transport protons through the cell membrane. Thus it is a suitable model for studying proton-transfer processes, and in addition, it may open interesting new fields of application.     

From nanostrips to nanorings: the elastic properties of gold-glued polyauronaphthyridines and polyacenes

The previously proposed flat 2,6-diauro-1,5-naphthyridine polymers were bent to closed rings with up to 12 monomers. Their bending energies and lowest in-plane deformation frequencies were calculated at the DFT level using quasirelativistic pseudopotentials for gold. The ring-formation energies were compared with those for polyacene rings and found to be of the same order of magnitude, suggesting sufficient stability for the predicted polyauronaphthyridines. As function of the ring radius, r, the frequencies and deformation energies were shown to behave as r(-2) and r(-1), respectively. The molecules thus behave as classical elastic bodies.     

Basis-set limit of the aurophilic attraction using the MP2 method: the examples of [ClAuPH3]2 dimer and [P(AuPH3)4]+ ion

The basis-set limit of the aurophilic attraction is studied at the MP2 level for the free model dimer [ClAuPH(3)](2) and for a [P(AuPH(3))(4)](+) ion. The latter system is found to prefer a C(4v) symmetry, instead of T(d), in agreement with Li and Pyykko [Inorg. Chem. 32, 2630 (1993)] but in contradiction to recent results of Fang and Wang [J. Phys. Chem. A. 111, 1562 (2006)]. The Karlsruhe split valence and the Dunning correlation-consistent basis sets converge to the same limit.     

Structure and bonding of the MCN molecules, M=Cu,Ag,Au,Rg

High-precision calculations are reported for the title series with M=Cu, Ag, Au, using CCSD(T) with the latest pseudopotentials and basis sets up to cc-pVQZ. The bond lengths for M=Cu, Ag, Au agree with experiment within better than 1 pm. The role of deep-core excitations is studied. The second-order spin-orbit effects are evaluated at the density functional theory level, including M=Rg. A qualitative bonding analysis suggests multiple M-C bonding. The calculated vibrational frequencies are expected to be more accurate than the available experimental estimates. The M-C bond lengths obey Cu相似文献   

Superhydrophobic properties of cotton woven fabrics with conducting 3D networks of multiwall carbon nanotubes,MWCNTs

This article presents the findings concerning the preparation and properties of cotton woven fabrics with a conductive network made of multiwall carbon nanotubes deposited on the fiber surface by the padding method. The next stage of treatment consisted of imparting superhydrophobic properties to the fabrics in solution with methyltrichlorosilane (MTCS) in a waterless medium. The tests performed show that the state of surface and water content in cotton fibers exerts a significant influence on the hydrophobic properties of the analyzed samples. In order to explain the differences in hydrophobic properties, the morphology of the cotton fabric surface was examined using samples with various water contents. The formation mechanism of MTCS coatings on cotton fabric has been proposed.     

Exciton Binding Energies in Conjugated Polyelectrolyte Films

Molecular design: The electronic structure of conjugated polyelectrolytes as a function of ionization potential (IP) and electron affinity (EA) is determined using X‐ray absorption and emission spectroscopy (see figure). Different functional groups give rise to dissimilar transport gaps and exciton binding energies.

     

A study of the possible and preferred site of protonation in 7-methyl-1,5,7-triazabicyclo[4,4,0]dec-5-ene by vibrational spectroscopic methods

The normal co-ordinate analysis have been carried out for 7-methyl-1,5,7-triazabicyclo[4,4,0]dec-5-ene (MTBD) and its three possible protonated tautomeric forms. The calculations and measured infrared (IR) spectra are consistent with a tautomeric species in which the proton is attached to an imine nitrogen atom.     

The [ν]-M relationship for linear polydimethylsiloxane (PDMS)

Weight-average molecular weights for PDMS fractions were determined by light scattering and the Archibald method in the range of 3000–300,000; the [ν]-M? relationship for toluene, 25°, was found to be

$\text{[?]=1.87 × 10}{}^{\mathrm{?2}}\text{M}{}_{\mathrm{<mtext>w</mtext>}}{}^{03658}\text{,}\text{cm3/g}$

This relationship was compared with those previously used. No upward curvature of the linear relation, log $\text{[ν] = ?(}\text{M}\text{)}$, at lower molecular weights was observed. Over the whole range of molecular weights, the [ν]-values in toluene were higher than [ν]_θ-values in bromocyclohexane at 28°.