Necessary protection of the O6-position of guanine during the solid phase synthesis of oligonucleotides by the phosphoramidite approach

It has been observed that the use of O⁶-protected deoxyguanosine phosphoramidites leads to a significant improvement in the automated synthesis of oligonucleotides on an insoluble support.     

Chemical synthesis of branched RNA: novel trinucleoside diphosphates containing vicinal 2′–5′ and 3′–5′ phosphodiester linkages

The phosphite-triester synthesis of four triribonucleotides containing novel vicinal 2′–5′ and 3′–5′ phosphodiester linkages is described.     

Non-perturbative effects in two-dimensional lattice O(N) models

Non-abelian analogues of Kosterlitz-Thouless vortices may have important effects in two-dimensional lattice spin systems with O(N) symmetries. Renormalization group equations which include these effects are developed in two ways. The first set of equations extends the renormalization group equations of Kosterlitz to O(N) spin systems, in a form suggested by Cardy and Hamber. The second is derived from a Villain-type O(N) model using Migdal's recursion relations. Using these equations, the part played by topological excitations in the crossover from weak to strong coupling behavior is studied. Another effect which influences crossover behavior is also discussed: irrelevant operators which occur naturally in lattice theories can make important contributions to the renormalization group flow in the crossover region. When combined with conventional perturbative results, these two effects may explain the observed crossover behavior of these models.     

News Release

The forms of the dependences on the vibrational and rotational quantum numbers in the series representation of the vibration-rotational energies of diatomic molecules are discussed. It is concluded that the most convenient forms for diatomic molecules in ^lσ electronic states are (v+1/2) and (J+1/2)² respectively.     

Infrared spectra of CO in absorption and evaluation of radial functions for potential energy and electric dipolar moment

From quantum-chemical calculations of rotational g factor and new experimental measurements of strengths of lines in infrared spectra of vibration–rotational bands v′–0 in absorption, with 1≤v′≤4, of ¹²C¹⁶O, and from analysis of 16,947 frequencies and wave numbers assigned to pure rotational and vibration–rotational transitions within electronic ground state X ¹Σ⁺, including new measurements of band 4–0 of ¹²C¹⁶O, we evaluate radial functions for potential energy and electric dipolar moment, the latter both in polynomial form and as a rational function that has qualitatively correct behaviour under limiting conditions. Received: 8 November 2001 / Accepted: 5 February 2002 / Published online: 14 August 2002     

A SPECTROSCOPIC STUDY OF THE PHOTODECOMPOSITION OF DIAZOMETHANE

Abstract— The decomposition of diazomethane by photolytic means has been studied both in inert gas matrices near 4°K and in the gas phase near 295°K. The direct detection of the diazomethyl radical, HCNN and DCNN, and evidence for the participation of methanal azine, H₂C=‐N=CH₂, by vibrational spectroscopy proved that both species play a significant role in the decomposition schemes under the conditions of investigation. The present results make possible the reinterpretation of the data from earlier published experiments to conform to these schemes. The isomerisation of diazomethane is also discussed, and evidence is presented for the production of both diazirine and isodiazomethane under certain photolytic conditions, the former by an intramolecular process and the latter by the recombination of the diazomethyl radical with a hydrogen atom. The vibronic absorption spectra of gaseous diazomethane at 295°K are presented, and deductions concerning photochemical processes are drawn.