The replacement of five-membered N-donor heterocycles from aminotrichlorogold(III) complexes. A comparison with pyridines

The kinetics of the process AuCl₃(nu) + Cl⁻→ AuCl ₄ ⁻ + nu (nu = one of a number of five-membered N-donor heterocycles covering a wide range of basicity, namely: oxazole, 2,4,5-trimethyloxazole, thiazole, 5-methylthiazole, 4-methylthiazole, 4,5-dimethylthiazole, 2,4-dimethylthiazole, 2,4,5-trimethylthiazole, imidazole and 2-methylimidazole) have been studied in methanol at 25 °C. The reactions follow the usual two-term rate law, rate = (k ₁ + k ₂[Cl⁻])[complex], observed in a square-planar substitution associative-mechanism. The second-order rate constants, k ₂, indicate that the discriminating ability of Au^(III) in these complexes is good and markedly influenced by the nature of the leaving group. A linear-free-energy relationship, logk ₂ = 0.53pK _a + constant, is observed between the rate constant and the basicity of the leaving group for its replacement by chloride. The results are compared with data from the literature regarding a series of complexes of the type AuCl₃(py) (py = one of a number of pyridines) reacting with the Cl⁻ anion under the same experimental conditions. The reactivity depends not only upon ligand basicity but also upon the nature of the ligand in the order: pyridines> five-membered heterocycles. Steric factor due to the presence of a single methyl group ortho to the sp² nitrogen atom in the ring has no influence on the rate of substitution while, surprisingly, when there are two ortho methyl groups a remarkable steric retardation effect is observable. The results are discussed in terms of reaction-profile in the associative-substitution reaction and bonding interactions in the ground and transition states.     

STUDIES OF ADHESION OF METAL PARTICLES TO SILICA PARTICLES BASED ON ZETA POTENTIAL MEASUREMENTS

The zeta-potentials of silica, copper, platinum and gold particles have been measured as a function of pH. The isoelectric points were found to be at pH 3.0, 5.8, 3.0 and 3.5, respectively. In the pH range 3.0 to 5.8 copper and silica particles are oppositely charged and accordingly the coating of silica with copper particles could be demonstrated. In the case of gold and platinum the sign of the charge is such that direct adhesion to silica particles cannot be expected and this was also demonstrated in the case of platinum.     

The development of an integrated platform to identify breast cancer glycoproteome changes in human serum

Protein glycosylation represents one of the major post-translational modifications and can have significant effects on protein function. Moreover, changes in the carbohydrate structure are increasingly being recognized as an important modification associated with cancer etiology. In this report, we describe the development of a proteomics approach to identify breast cancer related changes in either concentration and/or the carbohydrate structures of glycoprotein(s) present in blood samples. Diseased and healthy serum samples were processed by an optimized sample preparation protocol using multiple lectin affinity chromatography (M-LAC) that partitions serum proteins based on glycan characteristics. Subsequently, three separate procedures, 1D SDS-PAGE, isoelectric focusing and an antibody microarray, were applied to identify potential candidate markers for future study. The combination of these three platforms is illustrated in this report with the analysis of control and cancer glycoproteomic fractions. Firstly, a molecular weight based separation of glycoproteins by 1D SDS-PAGE was performed, followed by protein, glycoprotein staining, lectin blotting and LC–MS analysis. To refine or confirm the list of interesting glycoproteins, isoelectric focusing (targeting sialic acid changes) and an antibody microarray (used to detect neutral glycan shifts) were selected as the orthogonal methods. As a result, several glycoproteins including alpha-1B-glycoprotein, complement C3, alpha-1-antitrypsin and transferrin were identified as potential candidates for further study.     

Some problems in non-linear elasticity of crystalline solids

The author reviews some results of his concerning the kinematics and the analysis of equilibria for non-linearly elastic solids whose constitutive equations have the invariance group postulated by Ericksen [6]. The last part of the paper contains an unpublished characterization of complex lattices which was in the back of the author's mind in [23], and thus provides a more satisfactory background for that paper as well as for its consequences in [24].     

The reactions between tetrachloroplatinate(II) anion and bidentate sulphur-nitrogen chelating agents: A direct route for the synthesis of the neutral dichloro species

A direct route for the synthesis of the neutral dichloro complexes [Pt(NS)Cl₂], (NS = 2-[(ethylthio)methyl]pyridine and 2-[(phenylthio)methyl]pyridine) in dimethylformamide, which avoids the formation of bis-chelate cations, is reported.     

<Emphasis Type="Italic">N</Emphasis>-arachidonoyl glycine,an abundant endogenous lipid,potently drives directed cellular migration through GPR18, the putative abnormal cannabidiol receptor

Background  

Microglia provide continuous immune surveillance of the CNS and upon activation rapidly change phenotype to express receptors that respond to chemoattractants during CNS damage or infection. These activated microglia undergo directed migration towards affected tissue. Importantly, the molecular species of chemoattractant encountered determines if microglia respond with pro- or anti-inflammatory behaviour, yet the signaling molecules that trigger migration remain poorly understood. The endogenous cannabinoid system regulates microglial migration via CB₂ receptors and an as yet unidentified GPCR termed the 'abnormal cannabidiol' (Abn-CBD) receptor. Abn-CBD is a synthetic isomer of the phytocannabinoid cannabidiol (CBD) and is inactive at CB₁ or CB₂ receptors, but functions as a selective agonist at this G_i/o-coupled GPCR. N-arachidonoyl glycine (NAGly) is an endogenous metabolite of the endocannabinoid anandamide and acts as an efficacious agonist at GPR18. Here, we investigate the relationship between NAGly, Abn-CBD, the unidentified 'Abn-CBD' receptor, GPR18, and BV-2 microglial migration.     

Chelate polypyridine ligand rearrangement in Au(III) complexes

The reaction of gold(III) neutral complexes AuBr(CN)₂(N–N) {N–N = 2,2′-bipyridine (bpy), 5,5′-dimethyl-2,2′-bipyridine (^Me2bpy), 1,10-phenanthroline (phen)} with a stoichiometric amount of K[AuCl₄] · 2H₂O in nitromethane at room temperature led to the formation of 1:1 electrolytes which were characterized by NMR and IR spectroscopy, conductivity measurements, elemental analyses and X-ray diffraction. Both the anions and the cations of these salts are singly charged square-planar Au(III) complexes and the cations have general formula [AuCl₂(N–N)]⁺. A hypothesis on the possible reaction mechanisms is presented to give an explanation for the formation of the reaction products.