Linquats: Synthesis,Characterization, and Properties of Linear Extended Diquats

We report an innovative synthetic route to linear extended diquats (linquats). Our approach is short and efficient and features a highly modular reaction sequence based on two‐fold quaternization followed by the key intramolecular [2+2+2] alkyne cycloaddition. The physico‐chemical properties of four new linquats were characterized by spectroscopic methods, X‐ray crystallography, and electrochemistry complemented by information obtained from DFT calculations. Electron deficient N‐heteroaromatic cations with linear extended diquat motif with high electron affinities have been recently recognized as attractive n‐type semiconductors for chemical and biological sensing. Their advantageous redox properties such as very fast reversible electron transfers make the title compounds interesting for applications.     

SERS-activating effect of chlorides on borate-stabilized silver nanoparticles: formation of new reduced adsorption sites and induced nanoparticle fusion

Changes in morphology, surface reactivity and surface-enhancement of Raman scattering induced by modification of borate-stabilized Ag nanoparticles by adsorbed chlorides have been explored using TEM, EDX analysis and SERS spectra of probing adsorbate 2,2'-bipyridine (bpy) excited at 514.5 nm and evaluated by factor analysis. At fractional coverages of the parent Ag nanoparticles by adsorbed chlorides <0.6, the Ag colloid/Cl(-)/bpy systems were found to be constituted by fractal aggregates of Ag nanoparticles fairly uniform in size (10 +/- 2 nm) and SERS spectra of Ag(+)-bpy surface species were detected. The latter result was interpreted in terms of the presence of oxidized Ag(+) and/or Ag(n)(+) adsorption sites, which have been encountered also in systems with the chemically untreated Ag nanoparticles. At chloride coverages >0.6, a fusion of fractal aggregates into the compact aggregates of touching and/or interpenetrating Ag nanoparticles has been observed and found to be accompanied by the formation of another surface species, Ag-bpy, as well as by the increase of the overall SERS enhancement of bpy by factor of 40. The same Ag-bpy surface species has been detected under the strongly reducing conditions of reduction of silver nitrate by sodium borohydride in the presence of bpy. The formation of Ag-bpy is thus interpreted in terms of the stabilization of reduced Ag(0) adsorption sites by adsorbed bpy. The formation of reduced adsorption sites on Ag nanoparticle surfaces at chloride coverages >0.6 is discussed in terms of local changes in the work function of Ag. Finally, the SERS spectral detection of Ag-bpy species is proposed as a tool for probing the presence of reduced Ag(0) adsorption sites in systems with chemically modified Ag nanoparticles.     

Measurement of sodium ion concentration in undiluted urine with cation-selective polymeric membrane electrodes after the removal of interfering compounds

The measurement of sodium ion concentration in urine can provide diagnostic information and guide therapy. Unfortunately, neutral-carrier-based ion-selective electrodes show a large positive drift and loss in selectivity in undiluted urine. The extraction of electrically neutral lipids from the urine into the sensing membrane was suggested as the main source of the drift, loss of selectivity and the consequent incorrect concentration readings.In this work, (i) solvent-solvent extraction, (ii) membrane-immobilized solvent extraction and (iii) solid phase extraction were used to remove interfering compounds from urine samples. The “cleaned” urine samples were subsequently analyzed using a calixarene (sodium ionophore X)-based, solid-contact, sodium-selective electrode in a flow-through manifold. The solid-contact sodium sensors had excellent stability in cleaned urine and an acceptable bias compared to commercial clinical analyzers.     

Modular and practical synthesis of 6-substituted pyridin-3-yl C-nucleosides

A novel modular and practical methodology for preparation of 6-substituted pyridin-3-yl C-nucleosides was developed. The Heck reaction of 2-chloro-5-iodopyridine with a 3'-TBDMS-protected glycal gave a 6-chloropyridin-3-yl nucleoside analogue, which was then desilylated, selectively reduced, and reprotected to give the TBDMS-protected 6-chloropyridin-3-yl C-2'-deoxyribonucleoside as a pure beta-anomer in a total yield of 39% over four steps. This key intermediate was then subjected to a series of palladium-catalyzed cross-coupling reactions, aminations, and alkoxylations to give a series of protected 1beta-(6-alkyl-, 6-aryl-, 6-hetaryl, 6-amino-, and 6-tert-butoxypyridin-3-yl)-2'-deoxyribonucleosides. 6-Unsubstituted pyridin-3-yl C-nucleoside was prepared by catalytic hydrogenation of the chloro derivative and 6-oxopyridine C-nucleoside by treatment of the 6-tert-butoxy derivative with TFA. Deprotection of all the silylated nucleosides by Et3N.3HF gave a series of free C-nucleosides (10 examples).     

Contribution to cation–π interaction of the univalent silver cation with racemic [7]helicene in the solid state

Structural Chemistry - Yellow crystals of the complex [7]helicene–silver perchlorate (i.e., C30H18–AgClO4 or more accurately [Ag(η4-C30H18)]ClO4, respectively), crystallizing in...     

Hydroxycamptothecin deactivation rates and binding to model membranes and HSA determined by fluorescence spectra analysis

Camptothecins (CPTs) are fluorescent compounds exhibiting anticancer activity. They can exist in two forms, a lactone and a carboxylate. In neutral and base solution, lactone forms hydrolyse and convert into carboxylates. Only the lactone forms of CPTs are biologically active. Because of strong affinity of the carboxylate form of the parent drug camptothecin to human serum albumin (HSA), this protein promotes the deactivation of this compound. On the other hand, the lactone forms of camptothecins do not hydrolyse and are stabilized when bound to membranes. The following three hydroxycamptothecins, 10 hydroxycamptothecin (10-OH-CPT), 7-ethyl-10-hydroxy-camptothecin (SN-38) and 7-tert-butyldimethylsil-10-hydroxycamptothecin (DB-67) were studied. Factor analysis of a set of fluorescence excitation spectra recorded during lactone hydrolysis facilitated the high-throughput determination of the deactivation rates of camptothecin and each hydroxycamptothecin in phosphate buffered saline. The fluorescence spectra of hydroxycamptothecins diluted in HSA solution or suspended in DMPC liposomes were recorded, and the association constants of these drugs to membranes and plasma proteins were calculated. Among the analysed agents, DB-67 exhibited the most desirable properties including low affinity of the carboxylate form for albumin and high affinity of its lactone form for model membranes.     

Synthesis of 2'-deoxyadenosine nucleosides bearing bipyridine-type ligands and their Ru-complexes in position 8 through cross-coupling reactions

The synthesis of the title 2'-deoxyadenosine derivatives bearing bipyridine, phenanthroline or terpyridine ligands and their corresponding RuII-complexes in position 8 linked via acetylene or phenylene tethers was accomplished through cross-coupling reactions. The Suzuki-Miyaura reactions of boronic acids or the Sonogashira reactions of terminal acetylene derivatives of oligopyridine ligands were performed either on protected 8-bromoadenosines in organic solvents or, more efficiently, directly on unprotected nucleosides in aqueous acetonitrile or DMF. Direct cross-coupling reactions of unprotected nucleosides with RuII-complexes or the oligopyridine-boronic acids or -acetylenes gave the Ru-labelled nucleosides in one step in fair to good yields. This method was also proven to be applicable for direct Ru-labelling of dATP. Terpyridine-containing 2'-deoxyadenosine exerted significant antiviral and cytostatic effects.