Isolation and Structural Characterization of Di‐ and Tetra‐protonated Forms of the Macrocyclic Hexaamine trans‐6,13‐Dimethyl‐1,4,8‐11‐tetraazacyclodecane‐6,13‐diamine

Cations derived by protonation of the ligand title compound (L¹) have been structurally characterized in their di‐ and tetra‐ protonated forms in the salts [H₂L¹][ClO₄]₂·2H₂O and [H₄L¹][ZnCl₄]₂·4H₂O. In both structures, one half of the formula unit comprises the asymmetric unit of the structure, the macrocycle being centrosymmetric, with the two macrocycles adopting similar conformations. In both salts, a pair of diagonally opposed macrocyclic secondary amine groups are protonated; in the [H₄L¹]⁴⁺ salt, the additional pair of protons are accommodated on the exocyclic pendant amine groups. The dispositions of the pendent amines differ between the two structures, being ‘equatorial’ with respect to the macrocyclic ring in the [H₂L¹]²⁺ salt, and ‘axial’ in the [H₄L¹]⁴⁺ salt. In other structurally characterized compounds containing [H₄L¹]⁴⁺ the equatorial disposition was found in the ferricyanide adduct, while in the tetraperchlorate salt the axial disposition was identified. The differences in disposition of the exocyclic groups are ascribed to the extensive H‐bonding in the lattices.     

Quantitative analysis of perchlorate in extracts of whole fish homogenates by ion chromatography: comparison of suppressed conductivity detection and electrospray ionization mass spectrometry

The perchlorate anion (ClO ₄ ^– ) is an anthropogenic contaminant of increasing concern in water supplies, and has been shown to disrupt thyroid activity. Most perchlorate analyses are currently carried out by ion chromatography (IC) with suppressed conductivity detection (SCD). While this procedure has been demonstrated to provide acceptable performance for analysis of water samples, the determination of perchlorate in high-conductivity aqueous extracts of plant or animal material is not readily accomplished by IC-SCD unless lengthy cleanup protocols are applied. With the addition of electrospray ionization mass spectrometry (ESI-MS) to IC, it was hypothesized that the interference imposed by various ionic species could be significantly reduced without the need for purification; however, the analysis of perchlorate in relatively unpurified extracts of biologically derived homogenates by IC-ESI-MS has not previously been described in the literature. The research presented here represents a comparison of the capabilities of IC-SCD and IC-ESI-MS to detect perchlorate in reagent water and in crude extracts of perchlorate-exposed fish (threespine stickleback, Gasterosteus aculeatus). ESI-MS was found to compare favorably to SCD for the detection of perchlorate in deionized water, and to exceed SCD performance in perchlorate analysis of fish-derived extracts.     

Macrocyclic cobalt(III) complexes as precursors for metal-polythiophene hybrid materials

A thiophene-functionalised macrocyclic ligand trans-6,13-dimethyl-6-((thiophen-3-ylmethyl)amino)-1,4,8,11-tetraazacyclotetradecane-13-amine (L¹) has been prepared and complexed with Co^III. The ligand L¹ binds as a pentadentate in the crystallographically characterised complexes [CoL¹(OAc)](ClO₄)₂ and [CoL¹Cl]Cl₂. Electro-copolymerisation of [CoL¹Cl]Cl₂ with 3,4-ethylenedioxythiophene (EDOT) in a 1:2 ratio on a preformed poly-3,4-ethylenedioxythiophene (PEDOT) film resulted in metal–polymer hybrid films of high quality, consistency and uniformity in appearance. The copolymerised films were characterised by XPS indicating a 1:11 ratio of incorporation of complex to EDOT. Electrochemistry of the Co-PEDOT film (cast on an indium-doped tin oxide working electrode) in water revealed a Co^III/II redox couple at a potential ca. −600 mV (vs Ag/AgCl) which is similar to that seen in solution for the monomeric aqua complex [CoL¹(OH₂)]³⁺.     

The non-selective voltage-activated cation channel in the human red blood cell membrane: reconciliation between two conflicting reports and further characterisation

Using the patch-clamp technique, the non-selective, voltage-activated cation channel in the human red blood cell (RBC) membrane was further characterised. Activity of the cation channel could be demonstrated at a range of salt concentrations with the current-voltage characteristics for monovalent cations going from linear to superlinear functions, depending on the cation concentration in the range of 100-500 mM. The non-selective voltage-activated cation channel was demonstrated to be permeable to the divalent cations Ca2+ and Ba2+, and even Mg2+. The current-voltage relations for the divalent cations were superlinear even at 75 mM salt concentration, but indicated outward rectification in contrast to the I-V curve for monovalent cations. The degree of activation at a given membrane potential depended strongly on the prehistory of the channel. The gating exhibited hysteretic-like behaviour, since the quasi steady-state deactivation and activation curves were displaced by approximately 25 mV. This result fully explains apparent discrepancies between V0.5-values previously obtained by slightly different experimental protocols. The possible physiological/pathophysiological role of the channel is discussed in the context of the demonstrated permeability for divalent cations.     

A comprehensive two-dimensional map of cytosolic proteins of Bacillus subtilis

Proteomics relying on two-dimensional (2-D) gel electrophoresis of proteins followed by spot identification with mass spectrometry is an excellent experimental tool for physiological studies opening a new perspective for understanding overall cell physiology. This is the intriguing outcome of a method introduced by Klose and O'Farrell independently 25 years ago. Physiological proteomics requires a 2-D reference map on which most of the main proteins were identified. In this paper, we present such a reference map with more than 300 entries for Bacillus subtilis proteins with an isoelectric point (pI) between 4 and 7. The most abundant proteins of exponentially growing cells were compiled and shown to perform mainly housekeeping functions in glycolysis, tricarboxylic acid cycle (TCC), amino acid biosynthesis and translation as well as protein quality control. Furthermore, putative post-translational modifications were shown at a large scale, with 47 proteins in total forming more than one spot. In a few selected cases evidence for phosphorylation of these proteins is presented. The proteome analysis in the standard pI range was complemented by either stretching the most crowded regions in a narrow pH gradient 4.5-5.5, or by adding other fractions of the total B. subtilis proteome such as alkaline proteins as well as extracellular proteins. A big challenge for future studies is to provide an experimental protocol covering the fraction of intrinsic membrane proteins that almost totally escaped detection by the experimental procedure used in this study.     

Novel one-dimensional structures and solution behaviour of copper(II) bromide and chloride complexes of a new pentapyridyldiamine ligand

Copper(II) bromide and chloride complexes of the new heptadentate ligand 2,6-bis(bis(2-pyridylmethyl)amino)methylpyridine (L) have been prepared. For the bromide complexes, chains of novel, approximately C2-symmetric, chiral [Cu2(L)Br2]2+ 'wedge-shaped' tectons are found. The links between the dicopper tectons and the overall chirality and packing of the chains are dictated by the bromide ion content, not the counter anion. In contrast, the chloride complexes exhibit linked asymmetric [Cu2(L)Cl3]+ tectons with distinct N3CuCl2 and N4CuCl2 centres in the solid. The overall structures of the dicopper bromide and chloride units persist in solution irrespective of the halide. The redox chemistry of the various species is also described.     

Immobilisation of electroactive macrocyclic complexes within titania films

The 4-carboxyphenyl-appended macrocyclic ligand trans-6,13-dimethyl-6-((4-carboxybenzyl)amino)-1,4,8,11-tetraazacyclotetradecane-6-amine (HL10) has been synthesised and complexed with Co(III). The mononuclear complexes [Co(HL10)(CN)]2+ and [CoL10(OH)]+ have been prepared and the crystal structures of their perchlorate salts are presented, where the ligand is bound in a pentadentate mode in each case while the 4-carboxybenzyl-substituted pendent amine remains free from the metal. The cyano-bridged dinuclear complex [CoL10-mu-NC-Fe(CN)5]2- was also prepared and chemisorbed on titania-coated ITO conducting glass. The adsorbed complex is electrochemically active and cyclic voltammetry of the modified ITO working electrode in both water and MeCN solution was undertaken with simultaneous optical spectroscopy. This experiment demonstrates that reversible electrochemical oxidation of the Fe(II) centre is coupled with rapid changes in the optical absorbance of the film.     

Intra- vs intermolecular photoinduced electron transfer reactions of a macrocyclic donor-acceptor dyad

The synthesis, structural characterization, and photophysical behavior of a 14-membered tetraazamacrocycle with pendant 4-dimethylaminobenzyl (DMAB) and 9-anthracenylmethyl groups is reported (L3, 6-((9-anthracenylmethyl)amino)-trans-6,13-dimethyl-13-((4-dimethylaminobenzyl)amino)-1,4,8,11-tetraazacyclotetradecane). In its free base form, this compound displays rapid intramolecular photoinduced electron transfer (PET) quenching of the anthracene emission, with both the secondary amines and the DMAB group capable of acting as electron donors. When complexed with Zn(II), the characteristic fluorescence of the anthracene chromophore is restored as the former of these pathways is deactivated by coordination. Importantly, it is shown that the DMAB group, which remains uncoordinated and PET active, acts only very weakly to quench emission, by comparison to the behavior of a model Zn complex lacking the pendant DMAB group, [ZnL2]2+ (Chart 1). By contrast, Stern-Volmer analysis of intermolecular quenching of [ZnL2]2+ by N,N-dimethylaniline (DMA) has shown that this reaction is diffusion limited. Hence, the pivotal role of the bridge in influencing intramolecular PET is highlighted.     

Diverse solid-state and solution structures within a series of hexaamine dicopper(II) complexes

Mono- and dicopper(II) complexes of a series of potentially bridging hexaamine ligands have been prepared and characterized in the solid state by X-ray crystallography. The crystal structures of the following Cu(II) complexes are reported: [Cu(HL3)](ClO4)(3), C11H31Cl3CuN6O12, monoclinic, P2(1)/n, a = 8.294(2) A, b = 18.364(3) A, c = 15.674(3) A, beta = 94.73(2) degrees, Z = 4; ([Cu2(L4)(CO3)](2))(ClO4)(4).4H2O, C40H100Cl4Cu4N12O26, triclinic, P1, a = 9.4888(8) A, b = 13.353(1) A, c = 15.329(1) A, alpha = 111.250(7) degrees, beta = 90.068(8) degrees, gamma = 105.081(8) degrees, Z = 1; [Cu2(L5)(OH2)(2)](ClO4)(4), C13H36Cl4Cu2N6O18, monoclinic, P2(1)/c, a = 7.225(2) A, b = 8.5555(5) A, c = 23.134(8) A, beta = 92.37(1) degrees, Z = 2; [Cu2(L6)(OH2)(2)](ClO4)(4).3H2O, C14H44Cl4Cu2N6O21, monoclinic, P2(1)/a, a = 15.204(5) A, b = 7.6810(7) A, c = 29.370(1) A, beta = 100.42(2) degrees, Z = 4. Solution spectroscopic properties of the bimetallic complexes indicate that significant conformational changes occur upon dissolution, and this has been probed with EPR spectroscopy and molecular mechanics calculations.