Probing the electronic properties of ternary A MB ( = 1: A = Ca, Sr; M = Rh, Ir and = 3: A = Ca, Sr; M = Rh) phases: observation of superconductivity.

We follow the evolution of the electronic properties of the titled homologous series when as well as the atomic type of A and M are varied where for = 1, A = Ca, Sr and M = Rh, Ir while for = 3, A = Ca, Sr and M = Rh. The crystal structure of = 1 members is known to be CaRhB-type (), while that of = 3 is CaRhB-type (); the latter can be visualized as a stacking of structural fragments from AMB (6/) and AMB. The metallic properties of the = 1 and 3 members are distinctly different: on the one hand, the = 1 members are characterized by a linear coefficient of the electronic specific heat ≈ 3 mJ mol K, a Debye temperature ≈ 300 K, a normal conductivity down to 2 K and a relatively strong linear magnetoresistivity for fields up to 150 kOe.

DNA or RNA oligonucleotide 2'-hydrazides for chemoselective click-type ligation with carbonyl compounds.

An efficient method for the synthesis of DNA or RNA oligonucleotide 2'-hydrazides is described. Fully deprotected oligonucleotides containing a hydrazide group at the 2'-position of a uridine residue were obtained by a novel two-step procedure: periodate cleavage of an oligonucleotide with 1,2-diol group followed by conversion of the aldehyde to hydrazide with an extended linker arm using a homobifunctional reagent succinic dihydrazide and NaBH(3)CN. The resulting oligonucleotide 2'-hydrazides were efficiently conjugated by a click-type reaction at acidic pH to aliphatic or aromatic aldehydes with or without NaBH(3)CN reduction to afford novel 2'-conjugates.

Metal ion CHElate-aSSisted LIGAtion (CHESS LIGA) for SNP detection on microarrays.

We developed a metal ion chelate-assisted ligation for SNP detection by microarray. An oligonucleotide probe was separated into two 9-10-mers bearing iminodiacetic residues at the gap point. Duplex formation with the DNA target was possible only if nickel ions were added, but a nucleotide substitution opposite the gap point prevented duplex formation.

Preparation of 2'-hydrazino oligonucleotides and their reaction with aldehydes and 1,3-diketones.

Oligodeoxyribonucleotides that contain a hydrazino nucleoside, 2'-O-(2-hydrazinoethyl)uridine were prepared and shown to react with aldehydes or 1,3-diketones with the formation of hydrazones or pyrazoles, respectively. The method may be applicable for the preparation of oligonucleotide-peptide conjugates.

A convenient solid-phase method for the synthesis of novel oligonucleotide-folate conjugates.

We describe the preparation of two batches of a polymer support for the incorporation of folic acid into oligonucleotides. The method permits the regioselective attachment of a target nucleic acid sequence through its 3'-end to either the alpha-or gamma-carboxyl group of L-glutamic acid, respectively. The supports have been tested in solid-phase synthesis of oligonucleotide-folate conjugates for cell delivery studies.

Incorporation of side-chain groups of basic amino acids into oligonucleotides via the 2'-position of uridine.

Certain amino acids and short peptides are known to act as enhancers of ribozyme-mediated RNA cleavage at low concentration of magnesium ion. Thus, covalent conjugates of oligonucleotides and some amino acids may have a potential for development as sequence-specific artificial ribonucleases. Here we would like to report an incorporation of basic amino acids, lysine and histidine, into oligonucleotides at the 2'-position of a uridine residue.

2'-Hydrazine oligonucleotides: synthesis and efficient conjugation with aldehydes.

Oligodeoxyribonucleotides that contain a novel nucleoside, 2'-O-(2-hydrazinoethyl)uridine, were synthesized by sodium cyanoborohydride reduction of hydrazones formed from 2'-aldehyde oligonucleotides and FmocNHNH2 followed by ammonia deprotection. 2'-Hydrazine oligonucleotides were used successfully to obtain a series of conjugates with various aldehydes by hydrazone formation. The method was shown to be suitable for the preparation of oligonucleotide-peptide conjugates.

Structure-based cross-linking of NF-kappaB p50 homodimer and decoy bearing a novel 2'-disulfide trapping site.

Double-stranded oligodeoxyribonucleotides with engineered disulfide units were successfully used for covalent trapping of cysteine containing proteins. In particular, an efficient cross-linking of NF-kappaB p50 homodimer to a sequence-specific decoy was demonstrated. The results suggest that the synthetic oligonucleotides bearing a novel 2'-disulfide trapping site can be used as new tools to study and manipulate biological systems.

Oligonucleotides containing 2'-O-[2-(2,3-dihydroxypropyl)amino-2-oxoethyl]uridine as suitable precursors of 2'-aldehyde oligonucleotides for chemoselective ligation.

2'-O-[2-(2,3-Diacetoxypropyl)amino-2-oxoethyl]uridine 3'-phosphoramidite was prepared and used in solid-phase synthesis to obtain oligonucleotides containing a 1,2-diol group, which may then be converted into a 2'-aldehyde group. The oligonucleotides were conjugated efficiently to various molecules by chemoselective ligation that involves an addition-elimination reaction between the 2'-aldehyde group and a suitable nucleophile, such as a hydrazine, a O-alkylhydroxylamine or an 1,2-aminothiol. The method was applied successfully to the conjugation of peptides to oligonucleotides at the 2'-position.

Use of carbonyl group addition--elimination reactions for synthesis of nucleic acid conjugates.

This review outlines the synthesis of covalent conjugates of oligonucleotides and their analogues that are obtained by reactions of carbonyl compounds with various nucleophiles such as primary amines, N-alkoxyamines, hydrazines, and hydrazides. The products linked by imino, oxime, hydrazone, or thiazolidine groups are shown to be useful intermediates for a wide range of chemical biology applications. Methods for their preparation, isolation, purification, and analysis are highlighted, and the comparative stabilities of the respective linkages are evaluated.

Oligonucleotides with 2'-O-carboxymethyl group: synthesis and 2'-conjugation via amide bond formation on solid phase.

An efficient method for synthesis of oligonucleotide 2'-conjugates via amide bond formation on solid phase is described. Protected oligonucleotides containing a 2'-O-carboxymethyl group were obtained by use of a novel uridine 3'phosphoramidite, where the carboxylic acid moiety was introduced as its allyl ester. This protecting group is stable to the conditions used in solid-phase oligonucleotide assembly, but easily removed by Pd(0) and morpholine treatment.

Synthesis of oligonucleotide 2'-conjugates via amide bond formation in solution.

An efficient method for synthesis of 2'-O-carboxymethyl oligonucleotides is described. Fully deprotected oligonucleotides containing a carboxymethyl group at the 2'-position of sugar residue were obtained by a two-step procedure by periodate cleavage of an oligonucleotide containing 1,2-diol group followed by oxidation of the 2'-aldehyde resulted with sodium chlorite. 2'-O-Carboxymethyl oligonucleotides prepared were efficiently coupled in aqueous solution in the presence of a water-soluble carbodiimide to a number of amino acid derivatives or short peptides to afford novel 2'-conjugates of high purity in good yield.