A pillared metal-organic framework incorporated with 1,2,3-triazole moieties exhibiting remarkable enhancement of CO(2) uptake

The replacement of the pillar ligand, 4,4'-bipyridine, in the prototypal pillared MOF, MOF-508, with the custom-designed ligand, 4,4'-(2H-1,2,3-triazole-2,4-diyl)dipyridine, affords a porous metal-triazolate framework, MTAF-3, which demonstrates remarkable enhancement of CO(2) uptake capacity by a factor of ～3 compared to the parent MOF-508.     

Studies on the Michael addition of naphthoquinones to sugar nitro olefins: first synthesis of polyhydroxylated hexahydro-11H-benzo[a]carbazole-5,6-diones and hexahydro-11bH-benzo[b]carbazole-6,11-diones

A strategy for the synthesis of the novel (6bR,7R,8S,9S,10S,10aR)-8-(benzyloxy)-7,9,10-trihydroxy-6b,7,8,9,10,10a-hexahydro-11H-benzo[a]carbazole-5,6-dione is reported. The key steps were the Michael addition of 2-hydroxy-1,4-naphthoquinone to 1-nitrocyclohexene or 3-O-benzyl-5,6-dideoxy-1,2-O-isopropylidene-6-nitro-α-d-xylo-hex-5-enefuranose and the diastereoselective intramolecular Henry reaction of 3-O-benzyl-5,6-dideoxy-5-C-(3′-hydroxy-1′,4′-naphthoquinon-2′-yl)-1,2-O-isopropylidene-6-nitro-α-d-glucofuranose to give the key (1S,2S,3S,4R,5R,6R)-3-(benzyloxy)-1,2,4-trihydroxy-5-(3′-hydroxy-1′,4′-naphthoquinon-2′-yl)-6-nitrocyclohexane. When 2-hydroxy-1,4-naphthoquinone was replaced by (1,4-dimethoxynaphthalen-2-yl)lithium, the novel (1R,2S,3S,4R,4aS,11bS)-2-(benzyloxy)-1,3,4-trihydroxy-1,2,3,4,4a,5-hexahydro-11bH-benzo[b]carbazole-6,11-dione was obtained.     

H-bonds superstructures built by aquacomplexes and an azapurine derivative: a case of molecular recognition

The crystal structures of six compounds involving the divalent cations of Mn, Zn and Cd, the anionic form of the heterocycle 4,6-dimethyl-1,2,3-triazolo[4,5-d]pyrimidin-5,7-dione (Hdmax) and bipyridyl based spacer ligands are reported. The most important feature of these structures is the presence, in all cases, of a topologically identical 1-D polymeric superstructure (tape), involving tetra- or hexaaqua complex cations and triazolopyrimidine anions, built through hydrogen bonds. Adding these results to others previously published, we may consider these tapes as robust supramolecular synthons where a defined/clear case of molecular recognition between these two moieties takes place.     

1,2-disubstituted ferrocenyl carbohydrate chloroquine conjugates as potential antimalarial agents

This work presents a new family of organometallic antimalarial compounds consisting of ferrocene bearing a chloroquine-derived moiety as well as a 1,2;3,5-diisopropylidene glucofuranose moiety at a cyclopentadienyl scaffold in a 1,2-substitution pattern. The synthetic route proceeds via a stereoselective functionalization of ferrocene carboxaldehyde to the 1,2-disubstituted conjugates. After complete characterization of these new, trifunctional conjugates, they were examined for their cytotoxicity in two cancerous cell lines (MDA-MB-435S and Caco2) and one non-cancerous cell line (MCF-10A), showing that increased cytotoxicity can be observed for the chloroquine ferrocenyl conjugates compared to their carbohydrate-substituted precursors. The antiplasmodial activity of the conjugates in a chloroquine-sensitive strain of Plasmodium falciparum (D10) and a chloroquine-resistant strain (Dd2) was determined. Monosubstituted conjugates 13, 14 and 15 exhibit decreasing activity with increasing alkyl chain length between the ferrocene and quinoline moiety, bifunctional conjugates 16, 17, 18 show constant activity, performing better than chloroquine in the Dd2 strain.     

Identification of a sugar flexible glycosyltransferase from Streptomyces olivaceus, the producer of the antitumor polyketide elloramycin

BACKGROUND: Elloramycin is an anthracycline-like antitumor drug related to tetracenomycin C which is produced by Streptomyces olivaceus Tü2353. Structurally is a tetracyclic aromatic polyketide derived from the condensation of 10 acetate units. Its chromophoric aglycon is glycosylated with a permethylated L-rhamnose moiety at the C-8 hydroxy group. Only limited information is available about the genes involved in the biosynthesis of elloramycin. From a library of chromosomal DNA from S. olivaceus, a cosmid (16F4) was isolated that contains part of the elloramycin gene cluster and when expressed in Streptomyces lividans resulted in the production of a non-glycosylated intermediate in elloramycin biosynthesis, 8-demethyl-tetracenomycin C (8-DMTC). RESULTS: The expression of cosmid 16F4 in several producers of glycosylated antibiotics has been shown to produce tetracenomycin derivatives containing different 6-deoxysugars. Different experimental approaches showed that the glycosyltransferase gene involved in these glycosylation events was located in 16F4. Using degenerated oligoprimers derived from conserved amino acid sequences in glycosyltransferases, the gene encoding this sugar flexible glycosyltransferase (elmGT) has been identified. After expression of elmGT in Streptomyces albus under the control of the erythromycin resistance promoter, ermEp, it was shown that elmG can transfer different monosaccharides (both L- and D-sugars) and a disaccharide to 8-DMTC. Formation of a diolivosyl derivative in the mithramycin producer Streptomyces argillaceus was found to require the cooperative action of two mithramycin glycosyltransferases (MtmGI and MtmGII) responsible for the formation of the diolivosyl disaccharide, which is then transferred by ElmGT to 8-DMTC. CONCLUSIONS: The ElmGT glycosyltransferase from S. olivaceus Tü2353 can transfer different sugars into the aglycon 8-DMTC. In addition to its natural sugar substrate L-rhamnose, ElmGT can transfer several L- and D-sugars and also a diolivosyl disaccharide into the aglycon 8-DMTC. ElmGT is an example of sugar flexible glycosyltransferase and can represent an important tool for combinatorial biosynthesis.     

Bifurcations of the normal modes of the Ne?Br2 complex

We study the classical dynamics of the rare gas-dihalogen Ne?Br₂ complex in its ground electronic state. By considering the dihalogen bond frozen at its equilibrium distance, the system has two degrees of freedom and its potential energy surface presents linear and T-shape isomers. We find the nonlinear normal modes of both isomers that determine the phase space structure of the system. By means of surfaces of section and applying the numerical continuation of families of periodic orbits, we detect and identify the different bifurcations suffered by the normal modes as a function of the system energy. Finally, using the Orthogonal Fast Lyapunov Indicator (OFLI), we study the evolution of the fraction of the phase space volume occupied by regular motions.     

Brillouin light scattering characterization of the surface acoustic wave velocity in sp<Superscript>2</Superscript> allotropes thin films

Carbon thin films have been deposited by DC magnetron sputtering at different substrate temperatures ranging from 200 K to 400 K. The influence of the preparation substrate temperature on the elastic properties has been evidenced by means of the High Resolution Brillouin Spectroscopy. Thus, the surface acoustic wave (SAW) velocity evolution could be assessed for the different samples. The observed variation is analysed in terms of the relative population of sp² allotropes phases forming the film.     

Transfer of naturally occurring radionuclides to wheat under laboratory controlled conditions

Knowledge of soil–plant transfer of naturally occurring radionuclides can be essential to assure an adequate radiological protection. Available data are mainly for anthropogenic radionuclides and biased for temperate climates. Wheat plantlets were grown using soil collected in Mediterranean regions and transfer factors, TF, for ^234,238U, ²²⁶Ra, ²¹⁰Po and stable elements (K, Na, Ca and Mg) were determined. U, Ra and Po were mainly located in roots. Calcium presented the highest TF values, whereas for radionuclides were much lower. Uranium TFs were correlated with total and exchangeable potassium concentration in soil. Calcium and radium TFs were correlated with total calcium concentration in soil.

     

Desingularization and integralityof the automorphism scheme of a finite field extension

Let be the automorphism scheme of a finite purely inseparable field extension (in fact, we consider a wide class of finite ring extensions). Let be the splitting algebra of K (see 2.8) and the splitting field of K. It is proved that is integral if and only if . This may be formulated as a condition on the degree of and generalizes a result of Chase. Surprisingly, may be defined intrinsically, since is the scheme parametrizing the maximal smooth subgroups of . It is also proved that the desingularization of is the universal maximal smooth subgroup of and coincides with the blowing up along a closed subscheme canonically defined from the action of on . Received June 4, 1997; in final form July 22, 1998