Kb/Ka X-ray intensity ratios in calcium and potassium compounds

Summary Kb/Ka X-ray intensity ratios of some K and Ca compounds were studied. The samples were excited with 59.5 keV g-rays emitted from 75 mCi ²⁴¹Am radioisotope source and characteristic K X-ray from the samples were counted by means of an Si(Li) detector which has a resolution 155 eV at 5.9 keV. We found that Kb/Ka X-ray intensity ratios are changed by chemical effect for different K and Ca compounds. The experimental values were compared with the calculated theoretical values for elemental K and Ca.     

Trennung,Identifizierung und Bestimmung von Bactericiden auf der Basis von halogenierten Aromaten mittels Gas-Chromatographie

The separation of a mixture of 22 bactericides has been achieved by gas chromatography on columns with silicone rubber W-982 as stationary phase with temperatures between 100° and 300°C. The unchanged compounds as well as their silylation products have been used. The latter are more conveniently used especially for the quantitative determination. To be able to calculate the retention indices after Kovats gas chromatography has been performed isothermally at 180°C for the more volatile compounds and at 250°C for all other bactericides.The retention indices obtained under these conditions are tabulated together with the limits of detection.     

Efficient synthesis of 3H-imidazo[4,5-b]pyridines from malononitrile and 5-amino-4-(cyanoformimidoyl)imidazoles

1-Aryl-5-amino-4-(cyanoformimidoyl)imidazoles 2 were reacted with malononitrile under mild experimental conditions and led to 3-aryl-5,7-diamino-6-cyano-3H-imidazo[4,5-b]pyridines 5, when the reaction was carried out in the presence of DBU, or to 3-aryl-5-amino-6,7-dicyano-3H-imidazo[4,5-b]pyridines 3, in its absence. Both reactions evolved from the adduct formed by nucleophilic attack of the malononitrile anion to the carbon of the cyanoformimidoyl substituent. A 5-amino-1-aryl-4-(1-amino-2,2-dicyanovinyl)imidazole 4 was isolated when this reaction was carried out in the presence of DBU. The structure of compound 4 was confirmed by spectroscopic methods and by reaction with triethyl orthoformate and with acetic anhydride, leading respectively to 9-aryl-6-(cyanomethylidene)purines 11 and 12. Imidazole 2b was also reacted with ethyl acetoacetate, a carbon acid with a pK(a) comparable to that of malononitrile. Similar reaction conditions were used and the product isolated was a 6-carbamoyl-1,2-dihydropurine 10, showing that a different mechanism was operating in this case.     

2-Amino-4-bromobutanoic Acid

(2S)- and (2R)-2-Amino-4-bromobutanoic acid were prepared starting from N-Boc-glutamic acid α tert-butyl ester. The double tert-butyl protection was necessary to prevent a partial racemisation during Barton’s radical decarboxylation used to transform the γ-carboxylic group into a bromide. This bromide reacted with different nitrogen, oxygen and sulphur nucleophiles to give nonnatural amino acids characterised by basic or heterocyclic side chains. The title compound was also used to prepare a conformationally constrained peptidomimetic.     

Crystal engineering of urea alpha-network via I...O2N synthon and design of SHG active crystal N-4-iodophenyl-N'-4'-nitrophenylurea

Crystalline nitrodiphenyl ureas adopt the N-H...O tape alpha-network only when stabilization accrues from the I...O(2)N or C[triple bond]C-H...O(2)N synthon, otherwise the ureanitro motif is preferred; soft, weak interactions can direct polar self-assembly in strong N-HO hydrogen-bonded crystals.     

Pharmacomodulation of a ligand targeting the HBV capsid hydrophobic pocket

Hepatitis B virus (HBV) is a small enveloped retrotranscribing DNA virus and an important human pathogen. Its capsid-forming core protein (Cp) features a hydrophobic pocket proposed to be central notably in capsid envelopment. Indeed, mutations in and around this pocket can profoundly modulate, and even abolish, secretion of enveloped virions. We have recently shown that Triton X-100, a detergent used during Cp purification, binds to the hydrophobic pocket with micromolar affinity. We here performed pharmacomodulation of pocket binders through systematic modifications of the three distinct chemical moieties composing the Triton X-100 molecule. Using NMR and ITC, we found that the flat aromatic moiety is essential for binding, while the number of atoms of the aliphatic chain modulates binding affinity. The hydrophilic tail, in contrast, is highly tolerant to changes in both length and type. Our data provide essential information for designing a new class of HBV antivirals targeting capsid–envelope interactions.

Small-molecule binding to the Hepatitis B virus core protein hydrophobic pocket, a possible strategy for targeting viral particle assembly.     

Halogenation in Fungi: What Do We Know and What Remains to Be Discovered?

In nature, living organisms produce a wide variety of specialized metabolites to perform many biological functions. Among these specialized metabolites, some carry halogen atoms on their structure, which can modify their chemical characteristics. Research into this type of molecule has focused on how organisms incorporate these atoms into specialized metabolites. Several families of enzymes have been described gathering metalloenzymes, flavoproteins, or S-adenosyl-L-methionine (SAM) enzymes that can incorporate these atoms into different types of chemical structures. However, even though the first halogenation enzyme was discovered in a fungus, this clade is still lagging behind other clades such as bacteria, where many enzymes have been discovered. This review will therefore focus on all halogenation enzymes that have been described in fungi and their associated metabolites by searching for proteins available in databases, but also by using all the available fungal genomes. In the second part of the review, the chemical diversity of halogenated molecules found in fungi will be discussed. This will allow the highlighting of halogenation mechanisms that are still unknown today, therefore, highlighting potentially new unknown halogenation enzymes.     

A molecular mechanics approach for analyzing tensile nonlinear deformation behavior of single-walled carbon nanotubes

In this paper, by capturing the atomic information and reflecting the behaviour governed by the nonlinear potential function, an analytical molecular mechanics approach is proposed. A constitutive relation for single-walled carbon nanotubes (SWCNT’s) is established to describe the nonlinear stress-strain curve of SWCNT’s and to predict both the elastic properties and breaking strain of SWCNT’s during tensile deformation. An analysis based on the virtual internal bond (VIB) model proposed by P. Zhang et al. is also presented for comparison. The results indicate that the proposed molecular mechanics approach is indeed an acceptable analytical method for analyzing the mechanical behavior of SWCNT’s. The project supported by the National Natural Science Foundation of China (10121202, 90305015 and 10328203), the Key Grant Project of Chinese Ministry of Education (0306) and the Research Grants Council of the Hong Kong Special Administrative Region, China (HKU 7195/04E).     

Selective CO2 reduction into formate using Ln-Ta oxynitrides combined with a binuclear Ru(Ⅱ)complex under visible light

Hybrid materials constructed from a visible-light-absorbing semiconductor and a functional metal complex have attracted attention as efficient photocatalysts for CO₂ reduction with high selectivity to a desired product.In this work,defect fluorite-type Ln-Ta oxynitrides LnTaO_xN_y(Ln=Nd,Sm,Gd,Tb,Dy and Ho)were examined as the semiconductor component in a hybrid photocatalyst system combined with known Ag nanoparticle promoter and binuclear ruthenium(Ⅱ)complex(RuRu’).Among the LnTaO_xN_y examined,TbTaO_xN_y gave the highest performance for CO₂ reduction under visible light(k>400 nm),with a Ru Ru0-based turnover number of 18 and high selectivity to formate(>99%).Physicochemical analyses indicated that high crystallinity and more negative conduction band potential of Ln Ta O_xN_ywith the absence of Ln-4 f states in the band gap structure contributed to higher activity of the hybrid photocatalyst.