Icosahedral irreducible tensors and their applications

After a discussion of different concepts of anisotropy with reference to the icosahedron, the unusual problems surrounding the construction of icosahedral irreducible tensors are discussed. Tables of these tensors are then presented and applied to orbital problems, molecular polarization phenomena and to the construction of projection operators.     

FURTHER CHARACTERIZATION OF MONOCLONAL ANTIBODY INDICATES SPECIFICITY FOR (6–4)-DIPYRIMIDINE PHOTOPRODUCTS

Abstract
Monoclonal antibody aUVssDNA-1 is produced by hybridoma cell line 25JF.C3B6 originally selected from cell fusions using spleen cells from mice immunized with UV-irradiated polydeoxynucleotides (Strickland and Boyle, Photochem. Photobiol. 34 , 595–601, 1981). Original and subsequent studies of the binding characteristics of aUVssDNA-1 indicated that it was specific for cyclobuta-dithymidine photoproducts. Those investigations examined action spectrum, short-wavelength photo-reversal, nucleotide sequence effects, and photoreactivation using E. coli photolyase and incandescent tight. However, the more recent studies reported here examined acetophenone-UV-B photosensitization, UV-B photoisomerization, and photoreactivation using cloned E. coli photolyase and filtered incandescent light. The results indicate that aUVssDNA-1 recognizes photoproducts with characteristics of (6–4)-dipyrimidines. Thus, previous studies in which relatively rapid repair of cyclobuta-dithymidine photoproducts was inferred using this antibody, require re-interpretation in light of these new findings.     

The symmetry of molecular polarization tensors

Polarization tensors are discussed in terms of their intrinsic symmetry group which is a direct product of the point group and the subgroup of the permutation group relevant to the experiment. The study of these latter groups is simplified by use of the isomorphism with certain point groups and permutations of suffixes can be visualized by rotations and reflections of the vertices of various objects in space. The approach unites the previous treatments and provides a means of constructing the bases for the irreducible tensor components. The difficulties introduced by Laplace's equation are explained and the information obtainable from induced birefringence experiments (Kerr and Cotton–Mouton effects) discussed for various systems.     

Fragmentation dynamics of fullerenes in intense femtosecond-laser fields: loss of small neutral fragments on a picosecond time scale

The fragmentation dynamics of C60 irradiated with intense femtosecond laser pulses is studied with one-color pump-probe spectroscopy. Small neutral fragments (C, C2, and C3) are formed by an 800-nm pump pulse which are then postionized by a delayed probe pulse. The respective ion signals detected by the time-of-flight mass spectrometry dramatically increase on a time scale of 10-20 ps.     

Low-temperature behaviour of water in nafion membranes

Proton NMR measurements of T₁, T₁π and T₂ in “Nafion” perfluorosulphonate membranes, together with neutron- scattering and dielectric data, show that the aqueous phase in Nafion solidifies at a glass transformation whose temperature T_g is 168 K in water-saturated acid membranes. T_g is higher for the salt forms. Mo¨ssbauer measurements on Eu³⁺ Nafion confirm that the cations are present in an aqueous phase with T_g ≈ 220 K.     

203,205Tl NMR studies of crystallographically characterized thallium alkoxides. X-ray Structures of [TI(OCH2CMe3)]4 and [TI(OAr)]infinity, where OAr = OC6H3(Me)2-2,6 and OC6H3(CHMe2)2-2,6

[Tl(OCH2Me)]4 (1) was reacted with excess HOR to prepare a series of [Tl(OR)]n, where OR = OCHMe2 (2, n = 4), OCMe3 (3, n = 4), OCH2CMe3 (4, n = 4), OC6H3(Me)2-2,6 (5, n = infinity), and OC6H3(CHMe2)2-2,6 (6, n = infinity). Single-crystal X-ray diffraction experiments revealed that in the solid state the alkoxide-ligated compound 4 adopts a cubane structure, whereas the aryloxide derivatives, 5 and 6, formed polymeric chains. Compounds 1-6 were also characterized by 203,205Tl solution and 205Tl solid-state NMR spectroscopy. In solution it was determined that 1-4 retained the [Tl-O]4 cube structure, whereas the polymeric species 5 and 6 appeared to be fluxional. Variations in the solution and solid-state structures for the [Tl(OR)]4 cubes and polymeric [Tl(OAr)]infinity are influenced by the steric hindrance of the ligand. The acidity of the parent alcohol influences the degree of covalency at the Tl metal center, which is reflected in the 203,205Tl chemical shifts for 1-6.     

Synthesis of mono- and difluoronaphthoic acids

Aryl carboxamides are useful structural units found in several biologically active compounds. Unlike their benzoic acid counterparts, fluorinated versions of naphthoic acids are relatively unknown. In connection with a recent project, we needed viable syntheses of several mono- and difluorinated naphthoic acids. Herein we describe the synthesis of 5-, 6-, 7-, and 8-fluoro-1-naphthalenecarboxylic acids and 5,7-, 5,8-, 6,7-, and 4,5-difluoro-1-naphthalenecarboxylic acids. The 5-fluoro derivative 1was obtained from the corresponding 5-bromo compound via electrophilic fluorination of the lithio-intermediate. The rest of the monofluoro (2, 3, and 4) and the difluoro acids (5, 6, and 7) were prepared by a new, general route which entailed the elaboration of commercial fluorinated phenylacetic acids to 2-(fluoroaryl)glutaric acids with differential ester groups; selective hydrolysis to a mono acid, intramolecular Friedel-Crafts cyclization, and aromatization furnished the target structures. An alternative process to assemble a naphthalene skeleton is also presented for the difluoro acids 5 and 6. Finally, 4,5-difluoro-1-naphthalenecarboxylic acid (8) was prepared expeditiously from 1,8-diaminonaphthalene by adapting classical reactions.     

Synthetic applications of metal-stabilized carbenium ions.IV. preparation of 1,5-ene-ynes via coupling of [(propargyl) dicobalt hexacarbonyl] cations with allyl silanes.

A highly selective and flexible route to 1,5-ene-ynes is provided by the reactions of [(propargyl) dicobalt hexacarbonyl] cations with allyl silanes.