Infrared spectroscopic characterization of copper–polyhistidine from 1,800 to 50 cm−1: model systems for copper coordination

Iridium-Coordinated Histidyl Bolaamphiphile Self-Assemblies as Heterogeneous Catalysts for Water Oxidation

Catalysts that can promote oxygen evolution from water are necessary for green energy production. In this study, colloidal heterogeneous catalysts for oxygen evolution were prepared by coordination of Ir species to self-assemblies of histidyl bolaamphiphiles. When dissolved in water, the histidyl bolaamphiphiles self-assembled to form particulate structures with the exposure of densely packed histidine imidazoles on their surface. Subsequent coordination of the Ir species to the bolaamphiphile assembly gave rise to catalytic activity toward the oxygen evolution reaction. The oxygen evolution was examined by using the catalytic assemblies in the presence of a sacrificial oxidant, cerium ammonium nitrate. The Ir-coordinated assemblies showed a turnover frequency of 13 min^-1 , which was comparable to those previously reported for molecular water oxidation catalysts. The catalytic activity increased with increasing histidine imidazole/Ir molar ratio, which suggested that multiple coordination of Ir to imidazoles facilitated the formation of active Ir intermediates. This study demonstrates the feasibility of constructing catalytically active interfaces from colloidal bolaamphiphile assemblies with biochemical ligands.

Far infrared spectra of solid state L-serine, L-threonine, L-cysteine, and L-methionine in different protonation states

In this study, experimental far infrared measurements of L-serine, L-threonine, L-cysteine, and L-methionine are presented showing the spectra for the 1.0-13.0 pH range. In parallel, solid state DFT calculations were performed on the amino acid zwitterions in the crystalline form. We focused on the lowest frequency far infrared normal modes, which required the most precision and convergence of the calculations. Analysis of the computational results, which included the potential energy distribution of the vibrational modes, permitted a detailed and almost complete assignment of the experimental spectrum. In addition to characteristic signals of the two main acid-base couples, CO2H/CO2(-) and NH3(+)/NH2, specific side chain contributions for these amino acids, including CCO and CCS vibrational modes were analyzed. This study is in line with the growing application of FIR measurements to biomolecules.

Imidazole derivatives: a comprehensive survey of their recognition properties

Due to its amphoteric nature the imidazole ring can function as selective and effective anion and/or cation and even neutral organic molecules receptor system. As a result, the design of new multichannel imidazole-based receptors capable of recognizing different types of analytes is strongly demanded. This review summarizes the most recent and relevant advances in this area.

Determination of copper(II) ion concentration by lifetime measurements of green fluorescent protein

The understanding of cellular processes and functions and the elucidation of their physiological mechanisms is an important aim in the life sciences. One important aspect is the uptake and the release of essential substances as well as their interactions with the cellular environment. As green fluorescent protein (GFP) can be genetically encoded in cells it can be used as an internal sensor giving a deeper insight into biochemical pathways. Here we report that the presence of copper(II) ions leads to a decrease of the fluorescence lifetime (τ(fl)) of GFP and provide evidence for Förster resonance energy transfer (FRET) as the responsible quenching mechanism. We identify the His(6)-tag as the responsible binding site for Cu(2+) with a dissociation constant K(d) = 9 ± 2 μM and a Förster radius R(0) = 2.1 ± 0.1 nm. The extent of the lifetime quenching depends on [Cu(2+)] which is comprehended by a mathematical titration model. We envision that Cu(2+) can be quantified noninvasively and in real-time by measuring τ(fl) of GFP.

Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+ and Zn2+) and water coordination on the structure and properties of L-histidine and zwitterionic L-histidine

Interactions between metal ions and amino acids are common both in solution and in the gas phase. The effect of metal ions and water on the structure of L-histidine is examined. The effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+ and Zn2+) and water on structures of His·M(H2O)m, m=0.1 complexes have been determined theoretically employing density functional theories using extended basis sets. Of the five stable complexes investigated the relative stability of the gas-phase complexes computed with DFT methods (with one exception of K+ systems) suggest metallic complexes of the neutral L-histidine to be the most stable species. The calculations of monohydrated systems show that even one water molecule has a profound effect on the relative stability of individual complexes. Proton dissociation enthalpies and Gibbs energies of L-histidine in the presence of the metal cations Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+ and Zn2+ were also computed. Its gas-phase acidity considerably increases upon chelation. Of the Lewis acids investigated, the strongest affinity to L-histidine is exhibited by the Cu2+ cation. The computed Gibbs energies ΔG are negative, span a rather broad energy interval (from -130 to -1,300 kJ/mol), and upon hydration are appreciably lowered.

Monitoring the redox and protonation dependent contributions of cardiolipin in electrochemically induced FTIR difference spectra of the cytochrome bc(1) complex from yeast

Biochemical studies have shown that cardiolipin is essential for the integrity and activity of the cytochrome bc(1) complex and many other membrane proteins. Recently the direct involvement of a bound cardiolipin molecule (CL) for proton uptake at center N, the site of quinone reduction, was suggested on the basis of a crystallographic study. In the study presented here, we probe the low frequency infrared spectroscopy region as a technique suitable to detect the involvement of the lipids in redox induced reactions of the protein. First the individual infrared spectroscopic features of lipids, typically present in the yeast membrane, have been monitored for different pH values in micelles and vesicles. The pK(a) values for cardiolipin molecule have been observed at 4.7+/-0.3 and 7.9+/-1.3, respectively. Lipid contributions in the electrochemically induced FTIR spectra of the bc(1) complex from yeast have been identified by comparing the spectra of the as isolated form, with samples where the lipids were digested by lipase-A(2). Overall, a noteworthy perturbation in the spectral region typical for the protein backbone can be reported. Interestingly, signals at 1159, 1113, 1039 and 980 cm(-1) have shifted, indicating the perturbation of the protonation state of cardiolipin coupled to the reduction of the hemes. Additional shifts are found and are proposed to reflect lipids reorganizing due to a change in their direct environment upon the redox reaction of the hemes. In addition a small shift in the alpha band from 559 to 556 nm can be seen after lipid depletion, reflecting the interaction with heme b(H) and heme c. Thus, our work highlights the role of lipids in enzyme reactivity and structure.