2-Arylallyl as a new protecting group for amines, amides and alcohols

Amines, amides and ethers containing 2-arylallyl groups are selectively and easily deprotected with tert-butyllithium. This transformation probably involves a carbolithiation reaction of the styrenyl moiety followed by a beta-elimination process.     

A new class of DNA quadruplexes formed by oligodeoxyribonucleotides containing a 3'-3' or 5'-5' inversion of polarity site

Unprecedented DNA quadruplex structures containing a 3'-3' or 5'-5' inversion of polarity site in the G-tract are presented; the quadruplexes are characterized by different elements of symmetry and glycosidic angle conformations.     

Essential oil composition of the different parts of Eryngium bourgatii Gouan from Spain

The essential oil extracted from the different parts of Eryngium bourgatii Gouan: stems + leaves (E.b.SL), inflorescences (E.b.I) and roots (E.b.R), have been extracted by steam distillation and analysed by gas chromatography (GC) and gas chromatography coupled to mass spectrometry (GC-MS). Quantitative but not qualitative differences have been found between the analysed parts. The principal compounds from the inflorescences oil were found to be phyllocladene (37.6%) and bicyclogermacrene (15.1%), while the oil from stems and leaves showed phyllocladene (20.4%), gamma-muurolene (11.8%) and (E)-caryophyllene (10.1%) as main ones. The oil from the roots presented gamma-muurolene (15.4%) and phyllocladene (15.0%) as major constituents. It is worth mentioning the presence of a diterpene, phyllocladene, as main compound of the essential oil. This is the first report on the essential oil of this species.     

Equation of state and pressure induced amorphization of beta-boron from X-ray measurements up to 100 GPa

The equation of state of boron has been measured up to 100 GPa by single-crystal x-ray diffraction with helium as the pressure transmitting medium. Rhombohedral beta-boron is the stable structure up to 100 GPa under hydrostatic conditions. Nonhydrostatic stress stabilizes a different rhombohedral structure. At about 100 GPa a pressure-induced amorphization is observed. The amorphous phase can be quenched to ambient pressure. An explanation is proposed based on the different stability under pressure between intraicosahedra and intericosahedra bonds.     

An Extension of the Hirsch Symbolic Calculus

The symbolic calculus developed by Francis Hirsch (in several papers, between 1972 and 1976) is an already classical theory that introduces and studies the operators f(A) associated to a non-negative linear operator A on a Banach space and to the Stieltjes transform f of a Radon measure . It is required that the operator A has a dense domain and that the measure , as well as the value f()), are real and non-negative. These three conditions are essential in the proof of the main results, but they are very restrictive, since important cases are excluded, as the fractional powers A of complex exponent , or of base A non-densely defined. In this paper we present a reconstruction of the Hirsch theory, without using those hypothesis.     

Coxeter groups and interpolation of operators

Let V be a finite dimensional real Euclidean space and let G be a finite irreducible group generated by orthogonal reflections across hyperplanes in V. We study interpolation of operators in G-invariant norms on V. A collection of G-invariant norms is called G-sufficient if any G-invariant norm is a strict interpolation norm for this collection. Using the general theory of sufficient collections we calculate explicitly two remarkable minimal sufficient collections and study their extremal properties.To our teacher, Professor S.G. Krein, on his 75^th birthdayThe research was supported in part by a grant from the Ministry of Absorption and the Rashi Foundation.The research was supported in part by a grant from the Ministry of Science and Maagara — a special project for absorption of new immigrants, at the Department of Mathematics, Technion     

Automatic search for maximum similarity between molecular electrostatic potential distributions

Summary A new computer program has been developed to automatically obtain the relative position of two molecules in which the similarity between molecular electrostatic-potential distributions is greatest. These distributions are considered in a volume around the molecules, and the similarity is measured by the Spearman rank coefficient. The program has been tested using several pairs of molecules: water vs. water; phenylethylamine and phenylpropylamine vs. benzylamine; and methotrexate vs. dihydrofolic acid.