Target isotope effect in high energy photon production atE/A=10 MeV

A comparison has been made between the production of high energy (E _γ≧30 MeV)γ rays from the bombardment of¹²⁴Sn and¹¹²Sn targets withE/A= 10 MeV¹²C ions. The results are well explained by then-p bremsstrahlung model and do not indicate the need for any new processes.     

Isotope dynamic mixing and vibronic structure

Existing theories which deal with the isotope dependence of vibronic structure have neglected the isotope dependence of vibration dynamics. The latter dependence (isotope dynamic mixing) is an adiabatic correction to vibronic structure theory. A theory of vibronic structure, which includes isotope dynamic mixing, is developed. The results of model calculations are presented.     

On the dimerization of BH3 and the associated delocalization (resonance) energy

SCF calculations utilizing a basis of all s-type Gaussians have been performed to investigate the dimerization of BH₃ to B₂H₆. Localized molecular orbitals and pseudonatural orbitals are calculated. The dimerization energy obtained (11.5 kcal/mole) supports the assumption that the non-Hartree-Fock interactions (electron correlation) play a dominant role (Exp = 40–60 kcal/mole). The energy of the principal type of resonance structure based on the SCF-MO 's of the separated-but-distorted BH₃ systems is rigorously calculated and found to be 150 kcal/mole higher in energy than the SCF energy of B₂H₆. Thus, resonance stabilization (delocalization) is shown to be extremely important to the stability of the “three-center” bonds in B₂H₆, as has been suspected for many years.     

An animal model of solar-aged skin: histological, physical, and visible changes in UV-irradiated hairless mouse skin

Albino hairless mice (Skh:HR-l) exposed to sub-erythemal doses of UVB or UVA radiation display physical, visible, and histological alterations. Skin surface replicas, transepidermal water loss, and skin fold thickness were found to change with irradiation. Visibly, the skin wrinkled with UVB and sagged with UVA exposure. These changes were graded on 3-point scales. Histological alterations included tissue thickening, loss of elastic fibers, elastosis, loss of collagen, and increases in muco-substances. The UVB alterations occur to a much lesser extent with an SPF-15 (7% PABA and 3% oxybenzone) sunscreen product. This sunscreen product had little effect on development of UVA-induced changes. However, an efficient UVA sunscreen (Parsol 1789) did reduce the UVA-induced changes. Many of the UVB-induced alterations regressed after UVB irradiation was stopped. No regression in UVA-induced alterations was observed when UVA irradiation was stopped. Qualitatively, the effects with UVA irradiation were like those observed in mouse chronological aging. These models and the convenient physical and visible grading methods described can be used to determine the effectiveness of topical treatments, such as sunscreens.     

One-pot synthesis of chiral azetidines from chloroaldehyde and chiral amines

A variety of chiral azetidinepiperidines have been synthesized utilizing an expedient one-pot union of piperidine chloroaldehyde with chiral amines. This two step one-pot procedure provides access to an interesting set of compounds that retain the chiral purity of the starting chiral amine.     

Redetermination of the X-ray structure of nitroxylcobalamin: base-on nitroxylcobalamin exhibits a remarkably long Co-N(dimethylbenzimidazole) bond distance

The X-ray structures of three new crystals of nitroxylcobalamin (NOCbl) have been determined. Unlike our earlier reported structure in which NOCbl was partially oxidized (L. Hannibal, C. A. Smith, D. W. Jacobsen and N. E. Brasch, Angew. Chem., Int. Ed. 2007, 46, 5140), the O atom of the nitroxyl ligand is located in a single position with a N=O bond distance of 1.12-1.14 ?, consistent with a double bond. The Co-N-O angle is in the 118.9-120.3 ? range. The α-axial Co-N(dimethylbenzimidazole) (Co-NB3) bond distance is a remarkable 2.32-2.35 ? in length, ~0.1 ? longer than that reported for all other cobalamin structures. The change in the Gibbs free energy for the base-on/base-off equilibrium now correlates extremely well with the Co-NB3 bond distance, as observed for other cobalamins.     

Crystal structure of cyanocalix[4]arene methyl ether

The title compound has been prepared by the addition of bromocalix[4]arene methyl ether to CuCN in N-methylpyrrolidone. The crystals belong to the monoclinic space groupP2₁/n witha=13.591(3),b=24.778(5),c=11.057(3)Å,=93.58(2)°, andD _c=1.09 g cm^–3 forZ=4. Refinement based on 1118 observed reflections led to a finalR value of 0.085. The molecule exhibits the partial cone conformation.     

Mode-to-mode vibrational energy transfer in D2CO: Evidence of coriolis-enhanced rotational selectivity

Infrared—ultraviolet double resonance spectroscopy is used to demonstrate rapid collision-induced V-V transfer between the v₆ and v₄ vibrational manifolds of D₂CO. The rate of transfer is at least gas-kinetic and is explained in terms of Coriolis coupling and rotationally specific, quasi-resonant relaxation channels