Descripción: The title compound, C 9H 14N +· CHB 11Cl 11 -, was obtained in the course of our continuing studies of the low-melting salts of closo- and nido-carborane cage anions with alkyl-pyridinium and dialkyl-imidazolium cations. The title compound is the first example of a pyridinium salt of a perchlorinated carborane anion. The structure consists of one N-butyl-pyridinium cation counterbalanced by one perchlorinated carborane cage anion per asymmetric unit. By changing the counter-ion, different packings are observed, and to try to understand this the new structure is compared with five similar compounds. © 2011 International Union of Crystallography.

Descripción: A-homopregnanes and 5β-methylpregnanes were prepared from the easily available 3β-hydroxy-20β-acetoxy-4β,5β-methylenepregnane by cationic and radical rearrangements respectively. The A-homopregnane was formed in a single step upon spontaneous rearrangement and elimination by treatment of the cyclopropyl alcohol with BF3·Et2O. The 5β-methylpregnane was obtained by cleavage of the hydrazone of the corresponding cyclopropylketone followed by rearrangement mediated by mercury(II) hydrides. ©ARKAT.

Descripción: The set of 1:1 and 2:1 complexes of XOOX′ (X, X′ H, CH 3) with lithium cation has been studied to determine if they are suitable candidates for chiral discrimination in an isotropic medium via nuclear magnetic resonance spectroscopy. Conventional nuclear magnetic resonance is unable to distinguish between enantiomers in the absence of a chiral solvent. The criterion for experimental detection is valuated by the isotropic part of nuclear shielding polarisability tensors, related to a pseudoscalar of opposite sign for two enantiomers. The study includes calculations at coupled Hartree-Fock and density functional theory schemes for 17O nucleus in each compound. Additional calculations for 1H are also included for some compounds. A huge static homogeneous electric field, perpendicular to the magnetic field of the spectromer, as big as ≈1.7 108 V m -1 should be applied to observe a shift of ≈1 ppm for 17O magnetic shielding in the proposed set of complexes. © 2011 American Institute of Physics.

Descripción: The α9 and α10 cholinergic nicotinic receptor subunits assemble to form the receptor that mediates efferent inhibition of hair cell function within the auditory sensory organ, a mechanism thought to modulate the dynamic range of hearing. In contrast to all nicotinic receptors, which serve excitatory neurotransmission, the activation of α9α10 produces hyperpolarization of hair cells. An evolutionary analysis has shown that the α10 subunit exhibits signatures of positive selection only along the mammalian lineage, strongly suggesting the acquisition of a unique function. To establish whether mammalian α9α10 receptors have acquired distinct functional properties as a consequence of this evolutionary pressure, we compared the properties of rat and chicken recombinant and native α9α10 receptors. Our main finding in the present work is that, in contrast to the high (pCa 2+/pMonovalents ∼10) Ca 2+ permeability reported for rat α9α10 receptors, recombinant and native chicken α9α10 receptors have a much lower permeability (∼2) to this cation, comparable to that of neuronal α4β2 receptors. Moreover, we show that, in contrast to α10, α7 as well as α4 and β2 nicotinic subunits are under purifying selection in vertebrates, consistent with the conserved Ca 2+ permeability reported across species. These results have important consequences for the activation of signaling cascades that lead to hyperpolarization of hair cells after α9α10 gating at the cholinergic-hair cell synapse. In addition, they suggest that high Ca 2+ permeability of the α9α10 cholinergic nicotinic receptor might have evolved together with other features that have given the mammalian ear an expanded high-frequency sensitivity.

Descripción: Two copper complex solvatomorphs, namely (3,10-C-meso-3,5,7,7,10,12,14,14- octamethyl-1,4,8,11-tetraazacyclotetradecane)bis(perchlorato-κO)copper(II) 1.2-hydrate, [Cu(ClO4)2(C18H 40N4)]·1.2H2O, (I), and (3,10-C-meso-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane) bis(perchlorato-κO)copper(II), [Cu(ClO4)2(C 18H40N4)], (II), are described and compared with each other and with a third, already reported, anhydrous diastereomer, denoted (III). Both compounds present very similar centrosymmetic coordination environments, with the CuII cation lying on an inversion centre in a distorted 4+2 octahedral environment, defined by the macrocyclic N4 group in the equatorial sites and two perchlorate groups in trans-axial positions [one of the perchlorate ligands in (I) is partially disordered]. The most significant difference in molecular shape is seen in the orientation of the perchlorate anions, and the influence of this on the intramolecular hydrogen bonding is discussed. The (partially) hydrated state of (I) favours the formation of chains along [011], while the anhydrous character of (II) and (III) promotes loosely bound structures with low packing indices. © 2013 International Union of Crystallography.

Descripción: The molecular structure of the title compound, [Zn(CH3COO) 2(C12H12N2)], consists of isolated molecules bisected by a twofold rotation axis which goes through the ZnII cation and halves the organic base through the central C-C bond. The Zn II ion is coordinated by two N atoms from one molecule of the aromatic base and four O atoms from two bidentate, symmetry-related acetate anions, which coordinate asymmetrically [Zn-O distances of 2.058(2) and 2.362(3)Å], while the two Zn-N bond distances are equal as imposed by symmetry [2.079(2)Å]. The crystal structure is supported by a number of weak C-H⋯O interactions and C-H⋯π contacts, with no π-π interactions present, mainly hindered by the substituent methyl groups and the relative molecular orientation. The result is a three-dimensional structure in which each molecule is linked to eight different neighbors.

Descripción: The three transition-metal complexes, (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetra azacyclo tetra decane-κ4 N)bis (perchlorato-κO)copper(II), [Cu(ClO4)2(C18H40N4)], (I), (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetra azacyclo tetra decane-κ4 N)bis (nitrato-κO)zinc(II), [Zn(NO3)2(C18H40N4)], (II), and aqua chlorido (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetraazacyclo tetra decane-κ4 N)copper(II) chloride, [CuCl(C18H40N4)(H2O)]Cl, (III), are described. The mol ecules display a very similarly distorted 4+2 octa hedral environment for the cation [located at an inversion centre in (I) and (II)], defined by the macrocycle N4 group in the equatorial sites and two further ligands in trans-axial positions [two O-ClO3 ligands in (I), two O-NO2 ligands in (II) and one chloride and one aqua ligand in (III)]. The most significant difference in mol ecular shape resides in these axial ligands, the effect of which on the intra- and inter molecular hydrogen bonding is discussed. In the case of (I), all strong hydrogen-bond donors are saturated in intra molecular inter actions, while weak inter molecular C - H⋯O contacts result in a three-dimensional network. In (II) and (III), instead, there are N - H and O - H donors left over for inter molecular inter actions, giving rise to the formation of strongly linked but weakly inter acting chains. © 2013 International Union of Crystallography.

Descripción: Vertical excitation and electron detachment energies associated with the optical absorption of iodide ions dissolved in supercritical ammonia at 420 K have been calculated in two limiting scenarios: as a solvated free I- ion and forming a K+ I- contact ion pair (CIP). The evolution of the transition energies as a result of the gradual building up of the solvation structure was studied for each absorbing species as the solvent's density increased, i.e., changing the N H3 supercritical thermodynamic state. In both cases, if the solvent density is sufficiently high, photon absorption produces a spatially extended electron charge beyond the volume occupied by the solvated solute core; this excited state resembles a typical charge-transfer-to-solvent (CTTS) state. A combination of classical molecular dynamics simulations followed by quantum mechanical calculations for the ground, first-excited, and electron-detached electronic states have been carried out for the system consisting of one donor species (free I- ion or K+ I- CIP) surrounded by ammonia molecules. Vertical excitation and electron detachment energies were obtained by averaging 100 randomly chosen microconfigurations along the molecular dynamics trajectory computed for each thermodynamic condition (fluid density). Short- and long-range contributions of the solvent-donor interaction upon the CTTS states of I- and K+ I- were identified by performing additional electronic structure calculations where only the solvent interaction due to the first neighbor molecules was taken into account. These computations, together with previous experimental evidence that we collected for the system, have been used to analyze the solvent effects on the CTTS transition. In this paper we have established the following: (i) the CTTS electron of free I- ion or K+ I- CIP presents similar features, and it gradually localizes in close proximity of the iodine parent atom when the ammonia density is increased; (ii) for the free I- ion, the short-range solvent interaction contributes to the stabilization of the ground state more than it does for the CTTS excited state, which is evidenced experimentally as a blueshift in the maximum absorption of the CTTS transition when the density is increased; (iii) this effect is less noticeable for the K+ I- ion pair, because in this case a tight solvation structure, formed by four N H3 molecules wedged between the ions, appears at very low density and is very little affected by changes in the density; (iv) the long-range contribution to the solvent stabilization can be neglected for the K+ I- CIP, since the main features of its electronic transition can be explained on the basis of the vicinity of the cation; (v) however, the long-range solvent field contribution is essential for the free I- ion to become an efficient CTTS donor upon photoexcitation, and this establishes a difference in the CTTS behavior of I- in bulk and in clusters. © 2007 American Institute of Physics.