13C NMR pattern of Sc3N@C68. Structural assignment of the first fullerene with adjacent pentagons

Sc3N@C68 is assigned to isomer Sc3N@C68:6140 on the grounds of relative energies, geometrical data, and its 13C NMR pattern. Sc3N@C68:6140 is an endohedral fullerene where each Sc atom is coordinated to the center of an equatorial pentalene unit. Static and dynamic computer simulations explain the different point groups observed in NMR and X-ray experiments. Computed and experimental 13C NMR pattern are in close agreement except for one low-intensity signal. The competing isomer Sc3N@C68:6275 is found to be 409 kJ/mol less stable and shows a different 13C NMR pattern.     

The effect of carbon dioxide on xylose fermentation byPichia stipitis

Carbon dioxide was found to reduce the xylose fermentation rate of two different strains ofPichia stipitis (CBS 5773 and CBS 5776) significantly in anaerobic batch fermentations. The maximum specific fermentation rate in a carbon dioxide atmosphere was about 45% lower than the fermentation rate in nitrogen atmosphere. Further-more, the fermentation rate was found to be correlated to the growth rate. It is probable that the carbon dioxide influences the fermentation rate partly through decreasing the growth rate. It was also found that the fermentation rate of CBS 5773 was higher than for CBS 5776 and that the specific fermentation rate was lower at a higher cell density.     

Copper(II) complexes of N-terminal protected tri- and tetra-peptides containing histidine residues

Copper(II) complexes of peptides containing two or three histidyl residues (Ac-HisGlyHis-OH, Ac-HisGlyHis-NHMe, Ac-HisHisGlyHis-OH and Ac-HisHisGlyHis-NHMe) have been studied by potentiometric, UV-Vis, EPR and CD spectroscopic measurements. The imidazole nitrogen atoms are described as the primary metal binding sites of all ligands resulting in the formation of various macrochelates in the pH range 4 to 7. The (Nim, N-, Nim)-co-ordinated [CuH-1L]0+ complexes were mainly detected in samples containing free carboxylates at the C-termini, whilst the [CuH-2L]-(0) complexes were the predominant species in slightly alkaline solution and their binding modes were described via 4N-co-ordination (Nim, N-, N-, Nim) in (7,5,6)-membered fused chelate rings. Deprotonation and co-ordination of the third amide nitrogens were detected above pH approximately 9 in all cases.     

A three‐dimensional framework of bis­[tris­(ethyl­enediamine)zinc] tetra­iodo­cadmate diiodide assisted by N—H⋯I hydrogen bonds

The title salt, [Zn(C₂N₂H₈)₃]₂[CdI₄]I₂, conventionally abbreviated [Zn(en)₃]₂[CdI₄]I₂, where en is ethyl­enediamine, contains discrete [Zn(en)₃]²⁺ cations and [CdI₄]²⁻ anions with distorted octa­hedral and nearly tetra­hedral geometries, respectively, as well as uncoordinated I⁻ ions. The cation and the free I⁻ anion lie on twofold rotation axes and the [CdI₄]²⁻ anion lies on a axis in the space group I2d. The structure exhibits numerous weak inter‐ionic hydrogen bonds of two types, viz. N—H⋯I⁻(free ion) and N—H⋯I([CdI₄]²⁻), which support the resulting three‐dimensional framework.     

Diverse spreading behavior of binary polymer nanodroplets

Molecular dynamics simulations are used to study the spreading of binary polymer nanodroplets in a cylindrical geometry. The polymers, described by the bead-spring model, spread on a flat surface with a surface-coupled Langevin thermostat to mimic the effects of a corrugated surface. Each droplet consists of chains of length 10 or 100 monomers with approximately 350,000 monomers total. The qualitative features of the spreading dynamics are presented for differences in chain length, surface interaction strength, and composition. When the components of the droplet differ only in the surface interaction strength, the more strongly wetting component forms a monolayer film on the surface even when both materials are above or below the wetting transition. In the case where the only difference is the polymer chain length, the monolayer film beneath the droplet is composed of an equal amount of short chain and long chain monomers even when one component (the shorter chain length) is above the wetting transition and the other is not. The fraction of short and long chains in the precursor foot depends on whether both the short and the long chains are in the wetting regime. Diluting the concentration of the strongly wetting component in a mixture with a weakly wetting component decreases the rate of diffusion of the wetting material from the bulk to the surface and limits the spreading rate of the precursor foot, but the bulk spreading rate actually increases when both components are present. This may be due to the strongly wetting material pushing out the weakly wetting material as it moves toward the precursor foot.     

Theoretical studies on the smallest fullerene: from monomer to oligomers and solid States

Hybrid B3LYP and density-functional-based tight-binding (DFTB) computations on the solid-state structures and electronic properties of the C(20) fullerene monomer and oligomers are reported. C(20) cages with C(2), C(2h), C(i), D(3d), and D(2h) symmetries have similar energies and geometries. Release of the very high C(20) strain is, in theory, responsible for the ready oligomerization and the formation of different solid phases. Open [2+2] bonding is preferred both in the oligomers and in the infinite one-dimensional solids; the latter may exhibit metallic character. Two types of three-dimensional solids, the open [2+2] simple cubic and the body-centered cubic (bcc) forms, are proposed. The energy of the latter is lower due to the better oligomer bonding. The open [2+2] simple cubic solid should be a conductor, whereas the bcc solids are insulators. The most stable three-dimensional solid-state structure, an anisotropically compressed form of the bcc solid, has a HOMO-LUMO gap of approximately 2 eV and a larger binding energy than that of the proposed C(36) solid.     

The change of aromaticity along a Diels-Alder reaction path

[reaction: see text] Quinodimethanes are highly reactive toward dienophiles since Diels-Alder cycloaddition results in an aromatic product. Density functional-based (13)C, (1)H NMR, NICS, and MO-NICS calculations indicate that the increase of aromatic character of the developing benzenoid ring along the reaction path is especially pronounced after the transition state is reached, even though the number of pi orbitals decreases. The forming aliphatic ring exhibits large ring current effects during the reaction.