A Copper(II) Ion-Selective Potentiometric Sensor Based on N,N′,N″,N′′′-Tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane in PVC Matrix

Dinuclear silver(i) complexes with a pyridine-based macrocyclic type of ligand as antimicrobial agents against clinically relevant species: the influence of the counteranion on the structure diversification of the complexes

New dinuclear silver(i) complexes with N,N',N'',N'''-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc), [Ag2(NO3)(tpmc)]NO3·1.7H2O (1), [Ag2(CF3SO3)2(tpmc)] (2), and [Ag2(tpmc)](BF4)2 (3) were synthesized and characterized by NMR (1H and 13C), IR and UV-Vis spectroscopy, cyclic voltammetry and molar conductivity measurements. The molecular structures of the complexes were determined by single-crystal X-ray diffraction analysis. The spectroscopic and crystallographic data showed that the structure of the complexes strongly depends on the nature of the counteranion of silver(i) salt used for their synthesis. The antimicrobial activity of complexes 1-3 was examined against Gram-positive and Gram-negative bacteria and different species of unicellular fungus Candida spp. The ability of these complexes to inhibit the formation of Candida biofilms and to eradicate the already formed biofilms was tested in the standard microtiter plate-based assay. In addition, a bioelectrochemical testing of the antimicrobial activity of complex 1 against early biofilm was also performed. The obtained results indicated that complexes 1-3 showed increased activity toward Gram-negative bacteria and Candida spp. and could inhibit the formation of biofilms. In most cases, these complexes had positive selectivity indices and showed similar or even better activity with respect to the clinically used silver(i) sulfadiazine (AgSD). The values of the binding constants for complexes 1-3 to bovine serum albumin (BSA) were found to be high enough to indicate their binding to this biomolecule, but not so high as to prevent their release upon arrival at the target site. Moreover, the positive values of partition coefficients for these complexes indicated their ability to be transported through the cell membrane. Once inside the cell, complexes 1-3 could induce the formation of the reactive oxygen species (ROS) in C. albicans cells and/or interact with DNA. Taken together, silver(i) complexes with the tpmc ligand could be considered as novel antimicrobial compounds with favourable pharmacological properties, being safer than AgSD.

Potentiometric detection and removal of copper using porphyrins

Background

Copper is an essential trace element with a great importance in industry, environment and biological systems. The great advantage of ion-selective sensors in comparison with other proposed techniques is that they are measuring the free metal ion activity which is responsible for their toxicity. Porphyrins are known to be among the best ionophores in formulation of ion-selective sensors.

Results

A symmetrically substituted meso-porphyrin, namely: 5,10,15,20-tetrakis(4-allyloxyphenyl)porphyrin (TAPP) was used in the construction of a new copper selective-sensor and was also tested for the removal of copper from waste waters. The potentiometric response characteristics (slope and selectivity) of copper-selective electrodes based on TAPP in o-nitrophenyloctylether (o-NPOE), dioctyl phtalate (DOP) and dioctyl sebacate (DOS) plasticized with poly(vinyl chloride) membranes are compared.

Conclusions

The best results were obtained for the membrane plasticized with DOP. The sensor has linear response in the range 1x10^-7 – 1x10^-1 M with 28.4 ± 0.4 mV/decade near-Nernstian slope towards copper ions and presents good selectivity. Due to its chelating nature, the same porphyrin was also tested for the retention of copper from synthetic copper samples, showing a maximum adsorption capacity of 280 mg/g.

Electrochemical Analysis of Some Toxic Metals by Ion-Selective Electrodes

An overview of potentiometric sensors that are capable of detecting toxic heavy metal ions in environmental samples is presented and discussed. Notwithstanding the tremendous work performed so far, it is obvious that still several limitations do exist in terms of selectivity, limits of detection, dynamic ranges, applicability to specific problems, and reversibility. A survey on important advances in potentiometric sensors with regard to high selectivity, lower detection limit, fast response time, and on-line environmental analysis is presented in this review article. [Supplemental materials are available for this article. Go to the publisher's online edition of Critical Reviews in Analytical Chemistry to view the free supplemental file.].

New Cu (II) and Co(II) octaazamacrocyclic complexes with 2-amino-3-phenyl-propanoic acid

New cationic Cu(II) and Co(II) complexes with N,N',N'',N'''-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane (tpmc) and the anion of 2-amino-3-phenyl-propanoic acid (S-phenylalanine) were prepared. The complexes were analyzed and characterized by elemental analysis, conductometric, polarimetric, magnetic and cyclic voltammetric measurements, as well as by spectroscopic data (UV/Vis, IR). Both complexes are binuclear with the general formula [M2(S-Phe)tpmc](ClO4)3?nH2O; S-PheH = S-phenylalanine, M(II) = Cu, n = 7; Co, n = 0. Based on previously reported data for some familiar complexes and the present results, pentacoordinated geometry was proposed. Both of the central metal ions are coordinated with two pyridyl and two cyclam nitrogens and bridged with -N-(CH2)3-N- portions of the cyclam ring and oxygen atoms of the S-phenylalaninate ion. Antimicrobial screening of the complexes, solvent, starting salts and ligands alone was performed against fungi, mould and some bacteria. In certain cases, enhanced activity of Co(II) complex towards bacteria compared with the relevant free ligands and starting salts was detected.