Electrochemical Oxidation of Sanguinarine and of Its Oxidation Products at a Glassy Carbon Electrode – Relevance to Intracellular Effects

The electrochemical behavior of sanguinarine, a quaternary benzophenanthridine glycoside alkaloid with antimicrobial, anti‐inflammatory, antioxidant and/or immune‐stimulatory activities, was studied at a glassy carbon electrode using cyclic, differential pulse, and square wave voltammetry. The oxidation of sanguinarine is a quasireversible, diffusion‐controlled process and occurred in a cascade mechanism with the formation of several oxidation products which adsorbed at the electrode surface. The oxidation of sanguinarine is pH dependent and involves the transfer of the same number of electrons and protons. The adsorbed sanguinarine oxidation products are reversibly oxidized at the glassy carbon electrode surface and their oxidation for a wide range of pHs was also studied by differential pulse and square wave voltammetry. A mechanism for the oxidation of sanguinarine at glassy carbon electrode is proposed.     

Selective isolation-detection of two different positively charged peptides groups by strong cation exchange chromatography and matrix-assisted laser desorption/ionization mass spectrometry: application to proteomics studies

We report here a procedure for the independent analysis of two groups of peptides by liquid chromatography-matrix-assisted laser desorption/ionization mass spectrometry (LC-MALDI MS/MS), using a selective isolation-detection procedure. In this procedure all primary amino groups of tryptic peptides derived from mouse liver proteins are blocked, restricting their positive charge, at acidic pH, to the presence of histidine and arginine residues. After strong cation exchange chromatography, multiply charged peptides (R + H > 1) are retained on the column and separated with high selectivity from singly (R + H = 1) and neutral peptides (R + H = 0) which are together collected in the flow-through. Using LC-MALDI-MS/MS analysis, the retained fraction displayed a 94% of enrichment of multiply charged peptides while in the flow-through; peptides with at least one arginine or histidine residue were exclusively identified, which suggests that MS detection in this fraction is restricted only to those peptides with ionizable side chains, arginine and histidine amino acids.     

Controlling optical properties and function of BODIPY by using asymmetric substitution effects

Asymmetrically substituted BODIPY analogues of the dye PM567 have been synthesised from 2-acylpyrroles and pyrroles that bear indene, fluorene or difluorene units. The type of linkage between the fluorene and the BODIPY core plays an important role in the photophysics of the BODIPY chromophore. Indeed, an aliphatic bridge gives rise to an energy-transfer process between the chromophores, whereas a vinyl spacer allows an electronic interaction between them, leading to a large red shift of the spectral bands. The laser action of the new dyes has been analysed under transversal pumping at 10 Hz repetition rate, in both liquid phase and incorporated into solid polymeric matrices. Lasing efficiencies of up to 40% were reached with high photostabilities with the laser output remaining at the initial level after 1×10(5) pump pulses in the same position of the sample. The laser action of the new dyes outperforms the laser behaviour of commercial dyes that emit in the same spectral region. The replacement of fluorene by indene quenches the fluorescence and laser emission, but allows the development of an iron cation fluorescent sensor.     

Tuning the spin ground state in heterononanuclear nickel(II)-copper(II) cylinders with a triangular metallacyclophane core

Two new heterometallic Ni(II)(n)Cu(II)((9-n)) complexes [n = 1 (2) and 2 (3)] have been synthesized following a multicomponent self-assembly process from a n:(3 - n):2:6 stoichiometric mixture of Ni(2+), Cu(2+), L(6-), and [CuL'](2+), where L and L' are the bridging and blocking ligands 1,3,5-benzenetris(oxamate) and N,N,N',N',N'-pentamethyldiethylenetriamine, respectively. Complexes 2 and 3 possess a unique cyclindrical architecture formed by three oxamato-bridged trinuclear linear units connected through two 1,3,5-substituted benzenetris(amidate) bridges, giving a triangular metallacyclophane core. They behave as a ferromagnetically coupled trimer of two (2)/one (3) S = (1)/(2) Cu(II)(3) plus one (2)/two (3) S = 0 Ni(II)Cu(II)(2) linear units with overall S = 1 Ni(II)Cu(II)(8) (2) and S = (1)/(2) Ni(II)(2)Cu(II)(7) (3) ground states.     

Numerical simulation of the liquid phase in SnO<Subscript>2</Subscript> thin film deposition by sol-gel-dip-coating

The fluid flow of the liquid phase in the sol-gel-dip-coating process for SnO₂ thin film deposition is numerically simulated. This calculation yields useful information on the velocity distribution close to the substrate, where the film is deposited. The fluid modeling is done by assuming Newtonian behavior, since the linear relation between shear stress and velocity gradient is observed. Besides, very low viscosities are used. The fluid governing equations are the Navier–Stokes in the two dimensional form, discretized by the finite difference technique. Results of optical transmittance and X-ray diffraction on films obtained from colloidal suspensions with regular viscosity, confirm the substrate base as the thickest part of the film, as inferred from the numerical simulation. In addition, as the viscosity increases, the fluid acquires more uniform velocity distribution close to the substrate, leading to more homogenous and uniform films.     

Chiral bis(amino amides) as chiral solvating agents for enantiomeric excess determination of α-hydroxy and arylpropionic acids

A family of bis(amino amides) derived from natural amino acids has been synthesized and tested for the NMR enantiodiscrimination, as chiral solvating agents, for enantiomeric excess determination of some carboxylic acids. Those bis(amino amide) receptors contain different structural modifications and the splitting of the signals of the acids, after addition of the corresponding CSAs, depends on those structural variables. The influence of aminoacid side chain and the nature of the aliphatic spacer are important parameters to obtain good chiral discriminations. The results obtained clearly show the chiral recognition abilities of these bis(amino amide) ligands and suggest their advantageous use as chiral solvating agents for carboxylic acids. The binding between bis(amino amides) and carboxylic acids has been studied by ESI-MS, NMR, DSC, and molecular modeling. The data suggest that enantiodiscrimination involves the formation of an ionic pair after proton transfer from the carboxylic substrate to the bis(amino amides).     

Synthesis,Spectroscopic Characterization,DFT Calculations,and Dynamic Behavior of Mononuclear Macrocyclic Diorganotin(IV) Bis‐Dithiocarbamate Complexes

Nine mononuclear diorganotin(IV) dithiocarbamate complexes 1 – 9 with 19‐, 20‐ and 21‐membered macrocyclic structures were synthesized from dimethyl, di‐n‐butyl, and diphenyltin(IV) dichloride and three bis‐dithiocarbamate ligands derived from secondary bis‐amines having aromatic spacer groups. All compounds were characterized by elemental analysis, mass spectrometry, and spectroscopic methods (IR and ¹H, ¹³C, and ¹¹⁹Sn NMR). Additionally, quantum chemical DFT calculations were performed for the dimethyltin(IV) derivatives in order to model the molecular structures. For one compound series the NMR spectra showed a concentration‐dependent behavior in solution, which was analyzed in detail and permitted to postulate the existence of an equilibrium with the corresponding [2+2] macrocycles.     

Quantitative proton magnetic resonance determination of N,N‐dimethylformamide in one intermediate of the Quimi‐Hib vaccine

Quimi‐Hib is a conjugate vaccine against Haemophilus influenza type b (Hib) where the Hib antigen is the only one produced by chemical synthesis. NMR has become the alternative of choice for the identity of intermediates during the chemical synthesis of Hib antigen. We explore a rapid quantitative proton magnetic resonance (qHNMR) assay for the determination of N,N‐dimethylformamide (DMF) as a residual in one of the critical intermediates. The proposed assay has been shown to be accurate, precise for intermediate precision conditions (relative standard deviation <3% for spectrometer‐to‐spectrometer variations), specific (no detected interferences), and rugged (percentage difference <3% for day‐to‐day and spectrometer‐to‐spectrometer variations). The quantitative NMR assay can replace the common chromatographic methods for monitoring the DMF contents in one crucial step of the synthetic scheme. Copyright © 2012 John Wiley & Sons, Ltd.