Deamination process in the formation of a copper(II) complex with glutamic acid and a new ligand derived from guanidinoacetic acid: Synthesis,characterization, and molecular modeling studies

A deamination process was observed after copper(II) complexation reaction with guanidinoacetic (Gaa) and glutamic acids (Glu), forming the binuclear copper(II) complex K₂Cu₂C₁₆H₂₃N₇O₁₂ · 1/2H₂O (1), which was characterized by elemental analysis (CHN), spectroscopy methods (IR and EPR), powder X-ray diffraction, thermogravimetric analysis (TGA), and mass spectrometry. A new ligand, namely biguanide-1,5-diethanoate (Bge) (C₆H₉N₅O₄), was formed during complexation, probably due to the reaction between two Gaa species and the consequent release of a significant amount of ammonia, thus, characterizing the deamination process. In complex 1, Bge behaved as a tetradentated ligand, using its oxygen and nitrogen atoms as coordinating sites to both Cu(II) ions. In addition, Glu has coordinated to Cu(II) through its α-N and O atoms. Theoretical calculations of the cis–cis, cis–trans, and trans–trans isomers of 1, considering three prototropic forms of the Bge ligand, were carried out using semi-empirical quantum mechanics (PM3/d). DFT (B3LYP and B3P86) calculations of complex 1, in which a hydrogen atom replaced the side chain of Glu, were also carried out using the 6-31G(d) basis set and the LanL2DZ effective core potential for the transition metal. Based on experimental and theoretical data, we concluded that the trans–trans isomer of the binuclear copper(II) complex 1 should be the most stable, although the occurrence of other isomers, even if in minor quantities, should not be disregarded.     

Model calculations for the phase transition in SmS

Assuming a simple model for the compound SmS we have performed calculations which indicate a definite tendency toward the observed semiconductor-metal phase transition under pressure. Our results lend support to the hypothesis that the transition is associated with a change in 4f occupancy of the Sm ion.     

Activation of Elemental Sulfur at a Two‐Coordinate Platinum(0) Center

Platinum dichalcogenides have been known to exhibit two‐dimensional layered structures. Herein, we describe the syntheses, isolation, and characterization of air‐stable crystalline cyclic alkyl(amino) carbene (cAAC)‐supported monomeric platinum disulfide three‐membered ring complex [(cAAC)₂Pt(S₂)] ( 2 ). The highly reactive platinum(0) [(cAAC)₂Pt] complex ( 1 ) with two‐coordinate platinum activates elemental sulfur to give 2 . The brown crystals of bis‐carbene platinum(II)monosulfate [(cAAC)₂Pt(SO₄)_x(S₂)_1?x] ( 4 ) have been isolated when the reaction was performed in air. The dioxygen analogue of 2 was formed upon exposing the THF solution of 1 to aerial oxygen (O₂). The binding of oxygen at the Pt⁰ center was found to be reversible. Additionally, DFT study has been performed to elucidate the electronic structure and bonding scenario of 2 , 3 , and 4 . Quantum chemical calculations showed donor–acceptor‐type interaction for the Pt?S bonds in 2 and Pt?O bonds in 3 and 4 .     

Synthesis of nonsymmetric chain end functionalized polyisobutylenes

We present the synthesis of nonsymmetric α‐ω‐functionalized polyisobutylenes (PIBs) bearing different functional moieties on their chain ends. Thus, on one chain end either, a short tri‐ethylene oxide chain (TEO) or a phosphine oxide ligand is attached, whereas the other chain end is substituted by hydrogen bonding moieties (thymine/2,6‐diaminotriazine). The nonsymmetric PIBs were synthesized via living cationic polymerization using methyl‐styrene epoxide as initiator, followed by quenching reaction with 3‐bromopropyl‐benzene. Subsequent bromide/azide exchange and the use of the azide/alkyne click reaction allowed the synthesis of (a) (α)‐TEO‐(ω)‐thymine‐telechelic PIB ( 7a ), (b) (α)‐triethyleneoxide‐(ω)‐triazine telechelic PIB ( 7b ), and (c) (α)‐phosphinoxide‐(ω)‐thymine‐telechelic PIB ( 13 ) with molecular weights M_n ～ 4000 g mol^?1 and low polydispersities (M_w/M_n = 1.3). The chemical identity of the final structures was proven by extensive ¹H NMR investigations and matrix‐assisted laser desorption/ionization‐mass spectroscopy (MALDI). The presented method for the first time offers a simple and highly versatile approach toward supramolecular nonsymmetric α‐ω‐functionalized PIB. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Uniqueness of the Ground State in the Feshbach Renormalization Analysis

In the operator theoretic renormalization analysis introduced by Bach, Fr?hlich, and Sigal, we prove uniqueness of the ground state.     

Synthesis and clustering of supramolecular “graft” polymers

The synthesis and melt rheology of supramolecular poly(isobutylene) polymers bearing statistically distributed hydrogen‐bonding moieties is reported, aiming at understanding the formation of the underlying supramolecular networks for self‐healing polymers. Two different hydrogen bonds were incorporated into a poly(isobutylene) (PIB) copolymer, one based on a (weak) pyridinium/pyridine interaction, the other based on a (stronger) 2,6‐diaminotriazine/thymine interaction. A direct copolymerization based on living cationic polymerization of isobutene and the comonomers 1 , 2 , and 4 in amounts of 1 mol % lead to the copolymers PIB‐ 1 , PIB‐ 2 , and PIB‐ 4 with a content of ～1 mol % of comonomer and molecular weights ranging from ～2000 to 19,000 g mol^?1 (M_w/M_n ～ 1.2–1.5). Subsequent azide/alkyne “click” chemistry enabled the attachment of 2,6‐diaminotriazine‐ and thymine‐moieties to yield the copolymers PIB‐ 5 , PIB‐ 6 , and PIB‐ 7 . Proof of the statistical incorporation of ～1 mol % of hydrogen‐bonding moieties was achieved by ¹H NMR spectroscopy and matrix‐assisted laser desorption ionization measurements. The true presence of a supramolecular network in PIB‐ 1 (pyridinium/pyridine interaction) as well as with 1/1 blends of PIBs interacting via the 2,6‐diaminotriazine/thymine interaction (PIB‐ 5 /PIB‐ 6 ) was proven via the increasing plateau modulus with increasing molecular weights (5.5k, 9.9k, 12.4k, 16k, and 19k). Dynamics of the hydrogen bonds in the melt state was investigated by determining the effective cluster lifetime ( τ ) observing a clear difference in the (weaker) pyridinium/pyridine interaction ( τ ～ 1 s) to the 2,6‐ (stronger) diamintriazine/thymine interaction ( τ ～ 100 s). The so‐generated materials will be useful as a basis for self‐healing polymers, as dynamics plays a major role in such polymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Catechol derivatives-coated Fe3O4 and γ-Fe2O3 nanoparticles as potential MRI contrast agents

Superparamagnetic iron oxide nanoparticles, Fe₃O₄ and γ-Fe₂O₃, were produced by the so-called polyol process. In order to stabilize the particles in a physiological environment as potential contrast agents for Magnetic Resonance Imaging (MRI), the as-prepared particles were successfully transferred to an aqueous medium through ligand exchange chemistry of the adsorbed polyol species with the dopamine or the catechaldehyde. The ligands were able to participate in bidentate binding to the nanoparticles surface and to improve the stability of aqueous suspensions of the nanoparticles. Analysis was performed by various techniques including X-ray diffraction, transmission electron microscopy, infrared spectroscopy and thermal analysis. The results of magnetic measurements and initial in vitro magnetic resonance imaging essays are presented for the pre- and post-surface modified nanoparticles, respectively and discussed in relation with their structure and microstructure.