Adjacent Cd Research Articles

Coordination Polymers Self-Assembling from Cadmium(II) Ions and Flexible Pyridine-Based Bridging Ligands

Abstract This paper describes coordination polymers assembled from cadmium nitrate and flexible bridging ligands, py–X–py (py = 4-pyridyl, 1a: X = CH2, 1b: X = C(=CH2), 1c: X = CH2CH2). The X-ray structure analysis of these complexes showed that their infinite topologies are quite different from each other, despite the structural similarity of ligands 1a—1c. Upon treatment with Cd(NO3)2, 1a gave an infinite two-dimensional sheet structure with a stoichiometry of ML2 (M and L denote metal and ligand, respectively). Ligand 1b also afforded an infinite polymer possessing the same ML2 composition. However, the polymer structure is characterized by one-dimensionally bounded macrocyclic frameworks where adjacent Cd ions are linked by two ligand molecules. Interestingly, ligand 1c gave an infinite polymer of M2L3 composition whose structure was shown to be a unique one-dimensional framework having macrocyclic frameworks (M2L2) linked together by the third L molecules.

Preparation of a β-Cyclodextrin-Modified N-Carboxymethylchitosan and Its Chromatographic Behavior as a Chiral HPLC Stationary Phase

Chitosan, whose deacetylation degree was 0.95, was N-carboxymethylated and subsequently modified with 6-amino-6-deoxy-β-cyclodextrin. The 1H NMR spectra of the carboxymethylated chitosan (NCMC) and the β-cyclodextrin- modified NCMC (β-CD-NCMC) showed introductions of ca. 8.4 of the carboxymethyl groups and 8.2 of β-CD moieties per 10 units, respectively. β-CD-NCMC was covalently attached to a macroporous silica gel and used as a stationary phase for chiral HPLC separations of 2, 4-dinitrophenyl-α-amino acids and related racemates. The chiral discrimination was influenced more strongly by the size of an alkyl group on the chiral center of the aliphatic amino acids, compared to a Cyclobond I bearing monomeric β-CD molecules. The distance between two aromatic moieties on the aromatic amino acids and related racemates was also discriminated. The strict recognition required the high substitution degree of the β-CD moiety, permitting us to propose a simultaneous inclusion of the 2, 4-dinitrophenyl group and another aromatic substituent or an alkyl group with a proper size into the two adjacent CD cavities on the polymer chain.

Linear-Chain Structure of Bis(O,O'-dimethyldithiophosphato)cadmium(II)

The two ligands in the title compound, catenapoly[cadmium-μ-bis(O,O'-dimethyl­dithio­phosphatoS:S')], [Cd{S2P(OCH3)2}2], bridge two adjacent Cd atoms forming a linear chain along the c axis. The chain has a twofold symmetry axis through the Cd atoms. The Cd atom is coordinated by four S atoms in a distorted tetrahedral arrangement. The Cd—S bond lengths are 2.565 (2) and 2.571 (2) A.

Structure and Function of Activated Rhodopsin

AbstractAfter cis/trans isomerization of retinal and early photoproducts, activated rhodopsin (R*) develops signaling states for different proteins in a time‐ordered sequence. Rhodopsin kinase binds all Meta forms, including the early Meta I, while interaction with transducin (Gt) or arrestin requires the deprotonated Schiff base form, Meta II (MII). Gt recognizes a specific conformation, termed MIIb, which arises from an additional, spectrally silent conversion, linked to proton uptake. Collisional coupling with the GDP‐bound Gt holoprotein induces the release of GDP and formation of a stable R*—Gt complex, in which the nucleotide binding site of Gt is empty. The empty site complex, once formed, remains stable, even if the retinal is re‐isomerized to the cis configuration. The cytoplasmic surface of rhodopsin appears to provide the majority of interaction sites for other proteins. Physical analyses and mutagenesis have emphasized the loops connecting helices C/D and E/F of the seven‐helix structure. Any interaction between R* and Gt depends on a conserved charge pair at the interface between the helix C and the adjacent loop CD. Replacements or deletions in loops CD and EF were found to cause more specific functional defects, including slow release of GDP or failure of GTP‐induced complex dissociation. In the dark, signaling states with low activity can be generated by reversible binding of all‐trans‐retinal to opsin. These light‐independent signaling states are different from the Meta forms.

Structures of the cadmium halide complexes [{CdCl2(dmso)(MeOH)}n] and [{CdBr2(dmso)(MeOH)}n] with coordinated dimethyl sulfoxide and methanol

Cadmium chloride and bromide form halogen-bridged polymeric chain complexes catena-poly-[{(dimethyl sulfoxide)(methanol)cadmium}di-μ-chloro] [{CdCl 2 (dmso)(MeOH) n ] (dmso=dimethyl sulfoxide) and catena-poly[{(dimethyl sulfoxide)(methanol)cadmium}-di-μ-bromo] [{CdBr 2 (dmso)(MeOH)} n ] with Cd in octahedral coordination. With the chloride, the dmso and MeOH ligands are in trans positions. The hydroxylic proton of the coordinated methanol enters into hydrogen bonding with the O atom of a dmso ligand coordinated to an adjacent Cd centre in the same chain

An electron diffraction study of the gas-phase structure of a sterically hindered cadmium amide, bis(hexamethyldisilylamido)cadmium(II), Cd{N(Si(CH 3) 3) 2} 2

Gaseous bis(hexamethyldisilylamido)cadmium(II), Cd{N(SiMe 3) 2}, 2, has been studied by electron diffraction at a nozzle temperature of ca. 375K. The diffraction data are consistent with a model including only monomers. By assuming a linear NCdN chain and planar environments about the nitrogen atoms, an equilibrium conformer with a staggered Si 2NCdNSi 2 skeleton ( D 2d symmetry) may be brought into a nice agreement with the data. The large value of the amplitude of vibration for the inter-ligand Si…Si distances, 0.31(10) A, indicates that the ligands undergo large-amplitude vibrations about the NCdN axis. The value of the barrier to internal rotation about this axis is estimated to be in the range 1–2 kcal mol −1. A model with an eclipsed, co-planar Si 2NCdNSi 2 backbone ( D 2h symmetry) could not be brought into agreement with the observed intensity data. Some key parameters, including bond lengths ( τ a ) and valence angles, are: CdN 2.03(2) A, SiN 1.727(7) A, SiC 1.881(3) A; ∠CdNSi 114.0(0.6)°, ∠SiNSi 132.0(1.2)°, ∠NSiC 113.6(1.2)° and ∠SiCH 111.0(1.2) 0 (Parenthesized values denote least-squares standard deviations multiplied by a factor of three). The SiMe, groups are twisted 20(3) 0 away from the reference position typified by one SiC bond of each such group eclipsing the adjacent CdN bond, while the methyl groups themselves are essentially in staggered positions, the value of the relevant twist angle being 8(6) 0.

Applications of Cd N.M.R to Polycadmium Complexes. III. Effects of Zn/Cd and of Se/S Substitution in the Tetra-Adamantanoid Cage [S4Cd10(Sph)16]4- in Relation to Heterometal Metallothioneins

Cadmium-113 n.m.r . spectra at 66.6 MHz of various mixtures of the six cage compounds [X4M10( SPh )16]4- (1; X = S, Se; M = Zn, Cd ) and [M4( SPh )10]2- (M = Zn, Cd ), have revealed the exchange reactions of M and of X which occur within the different structural elements of (1), namely the triply bridging chalcogenide ligands X, the inner metal atoms Mi, and the outer metal atoms Mo. At laboratory temperature the exchange time scales range from days (X) through hours (Mi) to seconds (Mo and SPh ), according to the extent of atomic connection to each of these structural components of the aggregate. Metal exchange does not always follow random statistics, with biases towards equilibrium association of the same metal. The M- and X-substituted products, with lower symmetry than the high-symmetry precursors, reveal the mutual influences of the various structural elements on Cd chemical shift: S → Se substitution causes changes ( ΔδCd ) of -37 ppm at one bond, -3 ppm and -1.5 ppm at three bonds, and + 1 ppm five bonds distant; Cd → Zn substitution causes δCd to change by + 13 ppm and + 5 ppm at a connection of two bonds and by -3 ppm over four bonds. These effects of adjacent Cd → Zn substitution on δCd provide well defined models in support of the hypothesis of similar effects in the Cd n.m.r . spectra of mixed Zn, Cd metallothionein proteins.

Resonant Raman study of Cl in CdS

Raman scattering of vibrational modes of Cl in CdS is reported. From the resonance enhancement of these modes with excitons bound to Cl atoms they are identified with either (1) isolated Cl atoms or (2) complexes consisting of a Cl atom and an adjacent Cd vacancy. Our results support an earlier suggestion of Thomas et al. that Cl-Cd vacancy complexes form shallow acceptors in CdS.