The study of the interactions among metals, minerals, and humic substances is essential in understanding the migration of inorganic pollutants in the geosphere. A considerable amount of organic ...matter in the environment is associated with clay minerals. To understand the role of organic matter in the environment and its association with clay minerals, a hybrid clay-based material (HCM), montmorillonite (STx-1)–melanoidin, was prepared from l-tyrosine and l-glutamic acid by the Maillard reaction. The HCM was characterized by elemental analysis, nuclear magnetic resonance, x-ray photoelectron spectroscopy (XPS), scanning transmission x-ray microscopy (STXM), and thermal analysis. The presence of organic materials on the surface was confirmed by XPS and STXM. The STXM results showed the presence of organic spots on the surface of the STx-1 and the characterization of the functional groups present in those spots. Thermal analysis confirmed the existence of organic materials in the montmorillonite interlayer, indicating the formation of a composite of melanoidin and montmorillonite. The melanoidin appeared to be located partially between the layers of montmorillonite and partially at the surface, forming a structure that resembles the way a cork sits on the top of a champagne bottle.
2-Ammoniumethanethiolate, -SCH2CH2NH3 +, the first structurally characterized zwitterionic ammoniumthiolate, is the stable form of cysteamine (HL) in the solid state and in aqueous solution. ...Reactions of ZnCl2, Cd(Oac)2, and HgCl2 with cysteamine and NaOH in a 1:2:2 ratio, respectively, lead to the homoleptic complexes ML2. Their single-crystal X-ray structures demonstrate basic differences in the coordination chemistry of ZnII, CdII, and HgII. While chelating N,S-coordination modes are found for all metal ions, ZnII forms a mononuclear complex with a distorted tetrahedral Zn(N2S2) coordination mode, whereas HgII displays a dimer with Hg(N2S2) coordinated monomers being connected by two long Hg···S contacts. Solid-state 199Hg NMR spectra of HgL2 and Hg(HL)2Cl2 reveal a low-field shift of the signals with increasing coordination number. Strong and nearly symmetric Cd−S−Cd bridges in solid CdL2 lead to a chain structure, CdII displaying a distorted square pyramidal Cd(N2S3) coordination mode. The ab initio MP2/LANL2DZ(d,f) structures of isolated ML2 show a change from a distorted tetrahedral to bisphenoidal coordination mode in the sequence ZnII−CdII−HgII. A natural bond orbital analysis showed a high ionic character for the M−S bonds and suggests that the S−M−S fragment is best described by a 3c4e bond. The strength of the M···N interactions and the stability of ML2 toward decomposition to M and L−L decreases in the sequence Zn > Cd > Hg. Ab initio calculations further suggest that a tetrahedral S−M−S angle stabilizes ZnII against substitution by CdII and HgII in a M(N2S2) environment. Such geometry is provided in zinc-finger proteins, as was found by a database survey.
6Li and 13C NMR investigations on ethyl α-lithioisobutyrate (EiBLi) and quantum-chemical (DFT) calculations on methyl α-lithioisobutyrate (MiBLi) were performed to study the structure of active ...centers in anionic polymerization of methacrylates in toluene in the presence of tetramethylammonium chloride/triethylaluminum complexes NMe4Al n Et3 n Cl (n = 1, 2). The results support the existence of several complex species (EiBLi·Al n Et3 n ClNMe4) m varying in composition (n = 1, 2) and degree of association (m = 1, 2). In the presence of methyl pivalate (MPiv), a model compound for monomer/polymer ester groups, a nonassociated complex NMe4EiBLi·MPiv·AlEt3Cl is preferably formed.
6Li and 13C NMR on ethyl α-lithioisobutyrate (EiBLi) and quantum-chemical (DFT) calculations on methyl α-lithioisobutyrate (MiBLi) were used to elucidate the structure of the active center in the ...anionic polymerization of methacrylates in the presence of triethylaluminum (AlEt3) in toluene. This study reveals ester enolate/aluminum alkyl complexes with different degrees of association, (MiBLi·AlEt3) n (n = 1, 2, 4), and different stoichiometries, MiBLi·xAlEt3 (x = 1, 2). In the presence of methyl pivalate (MPiv), which is taken as a model compound for the monomer and polymer, complexes such as (MiBLi·MPiv·AlEt3) n (n = 1, 2) are formed. These complexes can dissociate into MiBLi·2AlEt3 and MPiv·AlEt3 when AlEt3 is used in excess.
Different ways have been used to synthesize glycidonitrile, the epoxide of acrylonitrile. The reaction product has been characterized by n.m.r. spectroscopy. While glycidonitrile-induced strand ...breaks in SV40 phage DNA in vitro, acrylonitrile did not.
