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The introduction of nanoparticles (MNPs) at the surface of cationic poly-porphyrin films, obtained by electrostatic interaction between the bis-porphyrin copolymer and the Preyssler type polyoxometalate P5W30@MNPs, enhances the photocurrent (up to 2.5-3 times greater as a function of the used nanoparticle).

This review focuses on the electrochemical and spectroelectrochemical studies that gave insight into redox potentials of the four mitochondrial complexes and their homologues from bacterial respiratory chains using O2 as a terminal acceptor, thus providing crucial information about their reaction mechanism. Advantages and limitations of the use of the different techniques for the study of membrane proteins are presented. Electrocatalytic experiments are described that revealed specific features of the reaction with the substrates and inhibitors. An overview is given on the great variability of the redox and catalytic properties of the enzymes in different organisms that may be due to adaptation to the specific environments in which these enzymes function. The adaptation of the redox chain to the different types of quinone and substrates is analyzed, and future studies are discussed.

5 pages, 3 figures, 2 tables, The quantification of uncertainties affecting satellite ocean color products is a fundamental step to ensure their compliance with mission and science requirements. This work investigated a methodology relying on the use of in situ radiometric data with known uncertainties to determine those affecting matching satellite data. By exploiting in situ radiometric data from the Ocean Color component of the Aerosol Robotic Network (AERONET-OC), an advanced method was applied to radiometric data products from the Ocean and Land Color Instruments onboard the Sentinel-3A satellite (OLCI-A) and the Visible Infrared Imager Radiometer Suite onboard the Suomi National-Polar Orbiting Partnership satellite (VIIRS-S). The results from the analysis support the relevance of the method proposed, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

Uncertainty estimates are needed to assess ocean color products and qualify the agreement between missions. Comparison between field observations and satellite data, a process defined as validation, has been the traditional way to assess satellite products. However validation statistics can provide only an approximation for satellite data uncertainties as field measurements have their own uncertainties and as the validation process is imperfect, comparing data potentially differing in temporal, spatial or spectral characteristics. This study describes a method to interpret in terms of uncertainties the validation statistics obtained for ocean color remote sensing reflectance RRS knowing the uncertainties associated with field data. This approach is applied to observations collected at sites part of the Ocean Color component of the Aerosol Robotic Network (AERONET-OC) located in coastal regions of the European seas, and to RRS data from the VIIRS sensors on-board the SNPP and JPSS1 platforms. Similar estimates of uncertainties σVRS (term accounting for non-systematic contributions to the uncertainty budget) are obtained for both missions, decreasing with wavelength from the interval 0.8–1.4 10−3 sr−1 in the blue to a maximum of 0.24 10−3 sr−1 in the red, values that are at least twice (but up to 8 times) the uncertainties reported for the field data. These uncertainty estimates are then used to qualify the agreement between the VIIRS products, defining the extent to which they agree within their stated uncertainty. Despite significant biases between the two missions, their RRS products appear fairly compatible.

International audience; The chemical oxidation of a hydrogen bonded network, formed upon combination of a hydrogen bond donor dication (1 2+ , , a dicationic bis-amidinium organic moieties bearing four propyl chains) with [Fe III/II (CN) 6 ] 3-/4anions has been studied using vibrational spectroscopies. The post synthetic oxidation of the microcrystalline powder of X 2 1 3-[Fe II (CN) 6 ] 2 (X = Na, K and Cs) by S 2 O 8 2into 1 3-[Fe III (CN) 6 ] 2 appeared to be partial for X = K + and Cs + and total for Na 2 1 3-[Fe II (CN) 6 ] 2. It corresponds to a two-step process involving a second order reaction. The reaction time appears to be dependent on the nature of the alkali cation and is faster for X = Na +. The integrity of the hydrogen bonded network, after oxidation, was also confirmed by XRPD. The flexible nature of 2 the hydrogen bonded network allows alkali cation motions within the network during the oxidation process. In addition, the investigation of the electrochemical behavior evidenced an amorphous deposition on a gold electrode immersed into a solution containing (1 2+ and [Fe III (CN) 6 ] 3-) after 100 cycles. This is the first evidence of an electrochemical ion intercalation for a molecular hydrogen bonded network.

Cytochrome bd oxidase is a bacterial terminal oxygen reductase that was suggested to enable adaptation to different environments and to confer resistance to stress conditions. An electrocatalytic study of the cyt bd oxidases from Escherichia coli, Corynebacterium glutamicum and Geobacillus thermodenitrificans gives evidence for a different reactivity towards oxygen. An inversion of the redox potential values of the three hemes is found when comparing the enzymes from different bacteria. This inversion can be correlated with different protonated glutamic acids as evidenced by reaction induced FTIR spectroscopy. The influence of the microenvironment of the hemes on the reactivity towards oxygen is discussed.

The crystal structure of the title salt, (C6H16N)2[MoO4], results from N—H⋯O hydrogen-bonded rings formed through inter­connections between the (iPr2NH2)+ cations and [MoO4]2− anions., The organic–inorganic title salt, (C6H16N)2[MoO4] or (iPr2NH2)2[MoO4], was obtained by reacting MoO3 with diiso­propyl­amine in a 1:2 molar ratio in water. The molybdate anion is located on a twofold rotation axis and exhibits a slightly distorted tetra­hedral configuration. In the crystal structure, the diiso­propyl­ammmonium (iPr2NH2)+ cations and [MoO4]2− anions are linked to each other through N—H⋯O hydrogen bonds, generating rings with R 12 12(36) motifs that give rise to the formation of a three-dimensional network. The structure was refined taking into account inversion twinning (ratio of ca 4:1 between the two domains).

International audience; Two new organiceinorganic materials based on MoePOM, namely (iPr2NH2)2.((CH3)2NH2)2.[Mo8O26] (1) and (Pr2NH2)4$[Mo8O26] (2), have been synthesized by a non-hydrothermal method at room temperature and characterized by single crystal X-ray diffraction, thermal gravimetric analysis (TGA) and vibrational spectroscopy. The compound (1) is a b-[Mo8O26]4- anion which crystallizes as a mixed salt of both dimethylammonium [(CH3)2NH2]þ and diisopropylammonium [iPr2NH2]þ. The interaction between anions and cations leads to an inorganic-organic band structure. Similarly, in compound (2), the interconnection of b-[Mo8O26]4- anions with dipropylammonium [Pr2NH2]þ cations gives an inorganicorganic band structure. In both compounds, the cations interact with two different sites of the cluster: a fundamental site formed by four highly nucleophilic terminal oxo ligands, and a second site which is composed of Ot, m2-O and/or m3-O oxygen groups. A remarkable difference between the two compounds is that in compound (2) interactions between the bands involve only Van der Waals forces, whereas in compound (1) the bands interact also through hydrogen bonds.

The coupling of the reaction of a tightly bound ubiquinone with the reduction of O2 in cytochrome bo3 of Escherichia coli was investigated. In the absence of the quinone, a strongly diminished rate of electrocatalytic reduction of oxygen is detected, which can be restored by adding quinones. The correlation of previous EPR data with the electrocatalytic study on mutations in the binding site at positions, Q101, D75, F93, H98, I102 and R71 reveal that the stabilization of the radical is not necessary for the oxygen reaction. The Q101 and F93 variants exhibit both well-defined catalytic i-V curves, whereas D75H, H98F, I102W and R71H exhibit broad i-V curves with large hysteresis pointing toward a strong alteration in their catalytic activity.

Spectroelectrochemistry, in combination with plasmonic approaches and infrared spectroscopy, has emerged as a powerful tool in the study of membrane protein redox reactions, both for immobilized monolayer samples and those reintroduced into their native environment. Here the use of nanostructured electrodes for surface enhanced spectroelectrochemistry are discussed.

A target-focused library of small molecules, containing a set of quinones, quinolones, coumarins, flavonoids and other diverse drugs was screened to identify potential inhibitors of the cytochrome bd-I oxidase from Escherichia coli by means of an electrochemical assay based on the immobilization of the proteins on gold nanoparticles. As primary hits, three quinolone fragments were identified with inhibition activity in this study. As a hit-to-lead optimization approach, a series of more complex natural product-based quinolones substituted in position 3 by an isoprenyl chain of various lengths were synthetized in order to increase the inhibitory efficiency of the initial hit fragments. We show that the efficiency of these molecules depends on the length of their isoprenyl side chain.

The structure-property relationships were compared for the iron and iron-copper complexes of two functional cytochrome c oxidase models, 1 and 2 , both constructed upon a phenanthroline-strapped porphyrin bearing respectively pyridyl or picolinyl built-in proximal and distal ligands. The behavior of these heme models in the absence and in the presence of copper was studied by 1 H NMR, UV–visible absorption, EPR, Raman and FTIR spectroscopies, electrochemistry in solution and deposited on a rotating ring-disk graphite electrode. The distal binding site within the phenanthroline pocket of both 1 and 2 is available for the coordination of exogenic ligands, yet the oxygen binding affinity is higher for all complexes of 2 than for 1 . Despite this difference, [ 1Fe II Cu I ] more efficiently reproduced the electrocatalyzed reduction of oxygen to water than [ 2Fe II Cu I ]. The oxygenated complexes of both iron(II)-copper(I) species mimic the ability of cytochrome c oxidase to reversibly bind O 2 , as shown by competitive binding studies in the presence of CO. Differences in the binding and electrocatalytic properties of these models stem from difference in rigidity of scaffolds upon binding of both the proximal and distal ligands, as well as from the bulkiness of the distal ligand.

PMID: 27664317; Cytochrome cbb3 (also known as C-type) oxidases belong to the family of heme-copper terminal oxidases which couple at the end of the respiratory chain the reduction of molecular oxygen into water and the pumping of protons across the membrane. They are expressed most often at low pressure of O2 and they exhibit a low homology of sequence with the cytochrome aa3 (A-type) oxidases found in mitochondria. Their binuclear active site comprises a high-spin heme b3 associated with a CuB center. The protein also contains one low-spin heme b and 3 hemes c. We address here the redox properties of cbb3 oxidases from three organisms, Rhodobacter sphaeroides, Vibrio cholerae and Pseudomonas stutzeri by means of electrochemical and spectroscopic techniques. We show that the redox potential of the heme b3 exhibits a relatively low midpoint potential, as in related cytochrome c-dependent nitric oxide reductases. Potential implications for the coupled electron transfer and proton uptake mechanism of C-type oxidases are discussed.

Hemes switch spots in a terminal oxidase Reduction of molecular oxygen to water is the driving force for respiration in aerobic organisms and is catalyzed by several distinct integral membrane complexes. These include an exclusively prokaryotic enzyme, cytochrome bd–type quinol oxidase, which is a potential antimicrobial target. Safarian et al. determined a high-resolution cryo–electron microscopy structure of this enzyme from the enteric bacterium Escherichia coli . Comparison to a homolog reveals a complete relocation of the site of oxygen binding and reduction caused by a change in the arrangement of heme cofactors and channels in the protein scaffold. This switch illustrates the diversity of structure and function in this family of enzymes and might reflect different biochemical roles of these homologs. Science , this issue p. 100

International audience; Three new dinuclear molybdenum(VI) oxalate (Pr2NH2)4·[Mo2O6(C2O4)2] (1), (iPr2NH2)4·[Mo2O6(C2O4)2] (2) and (HDabco)4[Mo2O6(C2O4)2]·2H2O (3) compounds, have been prepared by one pot-synthesis at room temperature and characterized by single crystal X-ray diffraction and vibrational spectroscopies. Each compound contains the binuclear [Mo2O6(C2O4)2]4− anion where each molybdenum is in an octahedral MoO6 environment. In compound (3), the interconnection between [Mo2O6(C2O4)2]4− anions, [HDabco]+ cations and water molecules (H2O) leads to an infinite inorganic-organic chain structure. Similarly, in compounds (1) and (2) the interactions between [Mo2O6(C2O4)2]4− anions and respectively [Pr2NH2]+ and [iPr2NH2]+ cations leads to an infinite inorganic-organic chain structure. A remarkable difference between the compounds is that in compounds (1) and (2) interactions between the chains involve only Van der Waals forces giving rise to layer-like structures, which also interact between them only by Van der Waals forces, whereas in compound (3) the chains interact also through hydrogen bonds giving a 3D supramolecular structure. The thermal properties of the compounds were investigated through thermogravimetric and differential thermal analyzes. The differences in the thermal decomposition of the compounds in the solid state are discussed in relation with their crystal structure. Cyclic voltammetry shows that the [Mo2O6(C2O4)2]4− anion can be reduced in both aprotic solvent and water.

International audience; In this work, we report the formation of a coloured inorganic–organic hybrid material generated from the [Ti10O12(cat)8(py)8] (catecholato (cat), pyridine (py)) oxo-cluster and poly(4-vinylpyridine). The titanium oxo-cluster is linked to the organic polymer through Ti–N coordination bonds. Vibrational spectroscopies (FT-IR and Raman scattering) and thermogravimetric analysis highlight the quantitative incorporation of the cluster in the polymeric matrix with no degradation of the inorganic core of the starting complex, and also highlight the good homogeneity of the resulting materials. Solid-state NMR measurements (13C CP-MAS) also reveal that the hybrid material results only from the substitution of the labile pyridine ligands within [Ti10O12(cat)8(py)8] by the pyridines of the P4VP polymer. Next, the functionalization of SiO2 surfaces with monolayer or multilayer films composed of alternate layers of the oxo-cluster and of the polymer is detailed. The thickness of these films, as evaluated by ellipsometry, ranges from a few nanometers to tens of nanometers for the monolayer films and the multilayer films, respectively

International audience; Two new hybrid inorganic–organic compounds, namely (iPr2NH2)2(NH4)2[Mo8O26] (1) and (C4H7N2)4[Mo8O26(C4H6N2)2]·2H2O (2), have been synthesized from room temperature, and characterized by vibrational spectroscopies, thermal gravimetric analysis (TGA) and single-crystal X-ray diffraction. Compound (1) contains a β-octamolybdate anionic cluster (β-[Mo8O26]4−) stabilized with two ammonium [NH4]+ and two diisopropylammonium [iPr2NH2]+ cations. Compound (2) is built upon a γ-octamolybdate anionic cluster (γ-[Mo8O26]4−) functionalized by two neutral 2-methylimidazole (C4H6N2) molecules, and stabilized by four protonated 2-methylimidazolium [C4H7N2]+ cations. Single-crystal X-ray diffraction analyses reveal that the compounds have 2D and 3D supramolecular structures resulting from electrostatic and H-bonding interactions between inorganic and organic entities. Both compounds exhibit distinct solid-state photochromic properties at room temperature which vary with the nature of both the polyoxometalate clusters and the organoammonium cations.

The cytochrome bd oxidase catalyzes the reduction of oxygen to water in bacteria and it is thus an interesting target for electrocatalytic studies and biosensor applications. The bd oxidase is completely embedded in the phospholipid membrane. In this study, the variation of the surface charge of thiol-modified gold nanoparticles, the length of the thiols and the other crucial parameters including optimal phospholipid content and type, have been performed, giving insight into the role of these factors for the optimal interaction and direct electron transfer of an integral membrane protein. Importantly, all three tested factors, the lipid type, the electrode surface charge and the thiol length mutually influenced the stability of films of the cytochrome bd oxidase. The best electrocatalytic responses were obtained on the neutral gold surface when the negatively charged phosphatidylglycerol (PG) was used and on the charged gold surface when the zwitterionic phosphatidylethanolamine (PE) was used. The advantages of the covalent binding of the membrane protein to the electrode surface over the non-covalent binding are also discussed.

The wide range of values found for the redox potentials of the hemes in proteins allows them to catalyze several proton-coupled redox reactions. This article summarizes the redox properties of the cytochromes which are involved in the transfer of electrons in aerobic respiratory chains, with a special emphasis on the diversity found within bacterial system as well as in the mitochondrial respiration. The article includes both, the membrane-bound enzymes, such as the cytochrome bc 1 complex or the cytochrome c oxidase, as well as proteins that are loosely associated with the membrane, such as cytochrome c . An overview is given on the electrochemical and spectroscopic techniques that give access to the redox properties of these redox proteins. Structural and functional aspects are described including the known structures, the reaction mechanism, electron transfer pathways, and the respective redox properties.

Succinate: quinone reductases (SQRs) are the enzymes that couple the oxidation of succinate and the reduction of quinones in the respiratory chain of prokaryotes and eukaryotes. Herein, we compare the temperature-dependent activity and structural stability of two SQRs, the first from the mesophilic bacterium Escherichia coli and the second from the thermophilic bacterium Thermus thermophilus, using a combined electrochemical and infrared spectroscopy approach. Direct electron transfer was achieved with full membrane protein complexes at single-walled carbon nanotube (SWNT)-modified electrodes. The possible structural factors that contribute to the temperature-dependent activity of the enzymes and, in particular, to the thermostability of the Thermus thermophilus SQR are discussed. journal article research support, n.i.h., extramural research support, non-u.s. gov't research support, u.s. gov't, non-p.h.s. 2014 Nov 10 2014 08 19 imported

PMID: 27314676; Cytochrome bd oxidases are membrane proteins expressed by bacteria including a number of pathogens, which make them an attractive target for the discovery of new antibiotics. An electrochemical assay is developed to study the activity of these proteins and inhibition by quinone binding site tool compounds. The setup relies on their immobilization at electrodes specifically modified with gold nanoparticles, which allows achieving a direct electron transfer to/from the heme cofactors of this large enzyme. After optimization of the protein coverages, the assay shows at pH7 a good reproducibility and readout stability over time, and it is thus suitable for further screening of small molecule collections.

Polyynes spanning from a diyne to a dodecayne with adamantyl endgroups have been synthesized using the Fritsch–Buttenberg–Wiechell rearrangement as a key step to construct the acetylenic framework. Molecular properties as a function of polyyne length have been analyzed by UV–Vis spectroscopy, cyclic voltammetry, differential scanning calorimetry, and X-ray crystallography. Copyright © 2011 John Wiley & Sons, Ltd.

PMID: 21557598; The electrochemical behavior of three proteins fragments from the respiratory chain of the extremophilic bacterium Thermus thermophilus , namely, cytochrome c(1) (Cyt-c(1)), cytochrome c(552) (Cyt-c(552)), and Cu(A), immobilized on three-dimensional gold nanoparticles electrodes was investigated by cyclic voltammetry. The gold nanoparticles were modified by either dithiobissuccinimidyl propionate (DTSP) or a mixed self-assembled monolayer of 6-mercaptohexan-1-ol and hexanethiol, depending on the surface of the protein. High surface coverages with enzymes and good electron transfer rates were achieved in the case of Cyt-c(1) immobilized on DTSP-modified gold nanoparticles and Cyt-c(552) or Cu(A) immobilized on mixed SAMs-modified gold nanoparticles. Interestingly, high surface coverages with Cu(A) were also observed on DTSP-modified gold nanoparticles, but a slower electron transfer rate was determined in this case. The gold nanoparticle/protein assemblies were characterized by surface-enhanced IR spectroscopy and transmission electron microscopy.

Papillomavirus E6 oncoproteins bind and often provoke the degradation of many cellular proteins important for the control of cell proliferation and/or cell death. Structural studies on E6 proteins have long been hindered by the difficulties of obtaining highly concentrated samples of recombinant E6. Here, we show that recombinant E6 proteins from eight human papillomavirus strains and one bovine papillomavirus strain exist as oligomeric and multimeric species. These species were characterized using a variety of biochemical and biophysical techniques, including analytical gel filtration, activity assays, surface plasmon resonance, electron microscopy and Fourier transform infrared spectroscopy. The characterization of E6 oligomers is facilitated by the fusion to the maltose binding protein, which slows the formation of higher-order multimeric species. The proportion of each oligomeric form varies depending on the viral strain considered. Oligomers appear to consist of folded units, which, in the case of high-risk mucosal human papillomavirus E6, retain binding to the ubiquitin ligase E6-associated protein and the capacity to degrade the proapoptotic protein p53. In addition to the small-size oligomers, E6 proteins spontaneously assemble into large organized multimeric structures, a process that is accompanied by a significant increase in the beta-sheet secondary structure content. Finally, co-localisation experiments using E6 equipped with different tags further demonstrate the occurrence of E6 self-association in eukaryotic cells. The ensemble of these data suggests that self-association is a general property of E6 proteins that occurs both in vitro and in vivo and might therefore be functionally relevant.

Seit dem ersten Fund von endohedralen Metallofullerenen (EMFs) hat sich die Suche nach Kohlenstoffkafigen mit eingeschlossenen Metallen oder kleinen Molekulen rasch zu einem sehr aktiven Forschungsgebiet entwickelt. EMFs weisen besondere elektronische und Struktureigenschaften auf und finden vielfache Anwendungsmoglichkeiten. Noch mehr Potenzial bieten funktionalisierte EMFs, die besser loslich sind und durch Rontgenkristallographie und andere Techniken leicht charakterisiert werden konnen. Wir geben hier eine Ubersicht uber das allgemeine Gebiet der EMFs und insbesondere der funktionalisierten EMFs. Wir befassen uns in diesem Aufsatz mit der Struktur und den (elektrochemischen) Eigenschaften dieser faszinierenden Verbindungen und werden auch auf Anwendungen eingehen.

Accessible and hindered phenanthroline-strapped Zn(II) porphyrin receptors exhibited suitable topography tailored to strongly and selectively bind N(1)-unsubstituted imidazoles and imidazoles appended to free-base porphyrins. Distal binding was clearly driven by the formation of strong bifurcated hydrogen bonds with the phenanthroline unit of the receptors. An extensive physicochemical study emphasized the influence of bulkiness of the substrate and of the porphyrin receptor on the binding and self-assembly mechanism. Knowledge of the corresponding spectroscopic, thermodynamic, and kinetic data were of fundamental importance to elucidate and to model the photoinduced properties which occur within the self-assembled porphyrin dyads.

While the trimetallic nitrides of Sc, Y and the lanthanides between Gd and Lu preferentially template C(80) cages, M(3)N@C(80), and while those of Ce, Pr and Nd preferentially template the C(88) cage, M(3)N@C(88), we show herein that the largest metallic nitride cluster, La(3)N, preferentially leads to the formation of La(3)N@C(96) and to a lesser extent the La(3)N@C(88). This is the first time that La(3)N is successfully encapsulated inside fullerene cages. La(3)N@C(2n) metallofullerenes were synthesized by arcing packed graphite rods in a modified Krätschmer-Huffman arc reactor, extracted from the collected soot and identified by mass spectroscopy. They were isolated and purified by high performance liquid chromatography (HPLC). Different arcing conditions were studied to maximize fullerene production, and results showed that yields have a high La(2)O(3)/C dependence. Relatively high yields were obtained when a 1:5 ratio was used. Three main fractions, La(3)N@C(88), La(3)N@C(92), and La(3)N@C(96), were characterized by UV/Vis-NIR and cyclic voltammetry. Unlike other trimetallic nitride metallofullerenes of the same carbon cage size, La(3)N@C(88) exhibits a higher HOMO-LUMO gap and irreversible reduction and oxidation steps.

High-performance liquid chromatography was used to isolate two new trimetallic nitride endohedral fullerenes, Gd3N@C2n (n = 42 and 44), and they were characterized by MALDI-TOF mass spectrometry, UV-vis-NIR, and cyclic voltammetry. It was found that their electronic HOMO-LUMO gaps depend pronouncedly on the size of the cage, from a large band gap for Gd3N@C80 (2.02 V) to a small band gap for Gd3N@C88 (1.49 V). The electrochemical properties also change dramatically with the size of the cage, going from irreversible for the C80 cage to reversible for Gd3N@C88. The latter is the largest trimetallic cluster inside C88 isolated and characterized to date. Gd3N@C88 has one of the lowest electrochemical energy gaps for a nonderivatized metallofullerene.

The electrochemical behavior of three cytochrome c oxidase models has been investigated. All the models are derived from a phenanthroline-strapped, porphyrin framework that binds zinc(II) or iron(III) chloride in the porphyrin subunit, and copper(I) in the phenanthroline site. The iron complex and the bimetallic zinc(II) copper(I) complex of the parent ligand have been characterized by X-ray diffraction. One model consists of the parent structure on which C 12 alkyl chains have been added. This soluble model achieves electrochemical 2-electron reduction of oxygen in organic solvents without the addition of an exogenous axial base, and in the presence of an organic or inorganic source of protons. The two other models comprise the parent phenanthroline-strapped porphyrin framework, on which two pendant imidazoles have been incorporated. These models adsorbed on ring-disk electrodes with an edge-oriented, pyrolytic graphite (EOPG) disk and a platinum ring, efficiently catalyze the 4-electron reduction of oxygen in dioxygen saturated water at neutral pH.

PMID: 25637325; Two different pathways through which protons access cytochrome c oxidase operate during oxygen reduction from the mitochondrial matrix, or the bacterial cytoplasm. Here, we use electrocatalytic current measurements to follow oxygen reduction coupled to proton uptake in cytochrome c oxidase isolated from Paracoccus denitrificans. Wild type enzyme and site-specific variants with defects in both proton uptake pathways (K354M, D124N and K354M/D124N) were immobilized on gold nanoparticles, and oxygen reduction was probed electrochemically in the presence of varying concentrations of Zn(2+) ions, which are known to inhibit both the entry and the exit proton pathways in the enzyme. Our data suggest that under these conditions substrate protons gain access to the oxygen reduction site via the exit pathway.

PMID: 25879256; Drosophila melanogaster cryptochrome is one of the model proteins for animal blue-light photoreceptors. Using time-resolved and steady-state optical spectroscopy, we studied the mechanism of light-induced radical-pair formation and decay, and the photoreduction of the FAD cofactor. Exact kinetics on a microsecond to minutes timescale could be extracted for the wild-type protein using global analysis. The wild-type exhibits a fast photoreduction reaction from the oxidized FAD to the FAD(•-) state with a very positive midpoint potential of ~ +125 mV, although no further reduction could be observed. We could also demonstrate that the terminal tryptophan of the conserved triad, W342, is directly involved in electron transfer; however, photoreduction could not be completely inhibited in a W342F mutant. The investigation of another mutation close to the FAD cofactor, C416N, rather unexpectedly reveals accumulation of a protonated flavin radical on a timescale of several seconds. The obtained data are critically discussed with the ones obtained from another protein, Escherichia coli photolyase, and we conclude that the amino acid opposite N(5) of the isoalloxazine moiety of FAD is able to (de)stabilize the protonated FAD radical but not to significantly modulate the kinetics of any light-inducted reactions.

The combination of FTIR spectroscopy with electrochemical techniques for the study of the reaction mechanism of proteins on molecular level is presented. Different cell types combining transmission or reflection modes with surface-enhanced approaches are discussed. Examples are given on contributions to the understanding of the reaction mechanism of proteins, including cytochrome c, hydrogenases, cytochrome c oxidases, and photosystem.

In addition to the need for functional models of cytochrome c oxidase, structural models are still required for a better understanding of the small reorganizations occurring during the catalytic cycle. An efficient synthetic approach has been designed to prepare several phenanthroline-strapped porphyrins, two of them bearing two pendant imidazoles. These built-in bases are both potentially able to act as axial bases for the metalloporphyrin and as complementary ligands for copper if necessary. Diamagnetic zinc(II) was used to demonstrate that the distal/proximal selectivity demonstrated by exogenic bases binding studies can be extended to the coordination of iron(III). Combination of EPR and paramagnetic 1H NMR shows that the imidazole binding on the zinc species can be further extended to the iron(III) species in dilute conditions.

Phytoplankton abundance, biomass and species composition of the Caspian Sea were evaluated by using samples collected from the Iranian (southern Caspian Sea) and southern Kazakhstan (eastern Caspian Sea) surface waters in March 2001. A total of 45 taxa were found in the samples (20 diatoms, 17 dinoflagellates and 8 others). Abundance and biomass of diatoms were high at the eastern stations, while dinoflagellates were dominant in terms of both biomass and abundance in the southern region. Average abundance and biomass were 40 000 ± 35 000 cell l−1 and 580 ± 690 μg l−1. The mean biomass value found here for the Middle and southern Caspian Sea in March are difficult to compare with the past due to limited information, but seems higher than previously registered values. Higher chlorophyll values were also apparent from the SeaWIFS images in 2001 compared to those in 1998. This is suggested to be due to decreased grazing of phytoplankton by zooplankton which is voraciously preyed by the recent invasive ctenophore Mnemiopsis leidyi.

Cytochrome aa3 from Paracoccus denitrificans and cytochrome ba3 from Thermus thermophilus, two distinct members of the heme-copper oxidase superfamily, were immobilized on electrodes modified with gold nanoparticles. This procedure allowed us to achieve direct electron transfer between the enzyme and the gold nanoparticles and to obtain evidence for different electrocatalytic properties of the two enzymes. The pH dependence and thermostability reveal that the enzymes are highly adapted to their native environments. These results suggest that evolution resulted in different solutions to the common problem of electron transfer to oxygen.

Imidazole-porphyrin coordination has become an important tool in the design of self-assembled materials. A combination of spectrophotometric and stopped-flow techniques has been used to gain insight into the control of imidazole binding in the distal pocket of phenanthroline-strapped porphyrins. The binding studies of a variety of imidazole substrates in combination with both hindered and accessible receptors have permitted the determination of the thermodynamic and kinetic parameters associated with the imidazole binding.

A practically simple top-down process for the exfoliation of graphene (GN) and few-layer graphene (FLG) from graphite is described. We have discovered that a biocompatible amphiphilic pyrene-based hexahistidine peptide is able to exfoliate, functionalize, and dissolve few layer graphene flakes in pure water under exceptionally mild, sustainable and virtually innocuous low intensity cavitation conditions. Large area functionalized graphene flakes with the hexahistidine oligopeptide (His(6)-TagGN = His(6)@GN) have been produced efficiently at room temperature and characterized by TEM, Raman, and UV spectroscopy. Conductivity experiments carried out on His(6)-TagGN samples revealed superior electric performances as compared to reduced graphene oxide (rGO) and non-functionalized graphene, demonstrating the non-invasive features of our non-covalent functionalization process. We postulated a rational exfoliation mechanism based on the intercalation of the peptide amphiphile under cavitational chemistry. We also demonstrated the ability of His(6)-TagGN nanoassemblies to self-assemble spontaneously with inorganic iron oxide nanoparticles generating magnetic two-dimensional (2D) His(6)-TagGN/Fe3O4 nanocomposites under mild and non-hydrothermal conditions. The set of original experiments described here open novel perspectives in the facile production of water dispersible high quality GN and FLG sheets that will improve and facilitate the interfacing, processing and manipulation of graphene for promising applications in catalysis, nanocomposite construction, integrated nanoelectronic devices and bionanotechnology.

Integral membrane proteins are encountered in fundamental natural processes, such as photosynthesis and respiration. The relation between the structure of the proteins and their function and dynamics are still not clear in most cases. Once fully understood, these processes could ultimately help researchers to develop alternative methods for producing energy, either from light or biomass. They could also lead to more efficient antibiotics, which would selectively inhibit a specific membrane protein of pathogenic bacteria. Since the chemical reactions involved in both photosynthesis and respiration are redox reactions, electrochemical methods can play a considerable role in uncovering their mechanisms. The electrochemical characterization of membrane proteins is, however, quite challenging. An overview on the techniques used for the characterization of membrane proteins, including classical approaches such as voltammetry and spectroelectrochemistry, and recent developments, such as their combination with surface-enhanced techniques is given.