Recovery of rhodium(III) from solutions and industrial wastewaters by a sulfate-reducing bacteria consortium

A quantitative analysis of the rate of removal of rhodium(III) by a resting sulfate-reducing bacteria (SRB) consortium under different initial rhodium and biomass concentrations, pH, temperature, and electron donor was studied. Rhodium speciation was found to be the main factor controlling the rate of its removal from solution. SRB cells were found to have a higher affinity for anionic rhodium species, as compared to both cationic and neutral species, which become abundant when speciation equilibrium was reached. Consequently, a pH-dependent rate of rhodium removal from solution was observed. The maximum SRB uptake capacity for rhodium was found to be 66 mg of rhodium per gram of resting SRB biomass. Electron microscopy studies revealed a time-dependent localization and distribution of rhodium precipitates, initially intracellularly and then extracellularly, suggesting the involvement of an enzymatic reductive precipitation process. When a purified hydrogenase enzyme was incubated with rhodium chloride solution under hydrogen, 88% of the rhodium was removed within 1 h, whereas with a soluble extract from SRB 77% was removed within 10 min. Due to the low pH of the industrial effluent (1.31), the enzymatic reduction of rhodium by the purified hydrogenase was greatly limited, and it was apparent that an industrial effluent pretreatment was necessary before the application of an enzymatic treatment. In the present study, however, it was established that SRB are good candidates for the enzymatic recovery of rhodium from both aqueous solution and industrial effluent.     

Analysis of Data on the Cross Sections for Electron-Impact Ionization and Excitation of Electronic States of Atomic Hydrogen (Review)

A review is given of experimental and theoretical data on the cross sections for ionization, excitation, and deexcitation of atomic hydrogen. The set of the cross sections required to calculate the electron energy distribution function and find the level-to-level rate coefficients needed to solve balance equations for the densities of neutral and charged particles in hydrogen plasma is determined.     

Regulation of energy dissipation in photosystem I by the redox state of the plastoquinone pool

The effect of exogenous plastoquinone (PQ) on the different deexcitation pathways of photosystem I (PSI) was investigated. Addition of oxidized decyl-plastoquinone (dPQ) and PQ-2 strongly quenched the chlorophyll (Chl) emission spectra of PSI submembrane fractions over all wavelengths. This quenching increased with the concentration of exogenous PQ added and followed the modified Stern-Volmer law. The Stern-Volmer constants found for dPQ and PQ-2 were 1.25 x 10(6) M-1 and 0.55 x 10(6) M-1, respectively, and the fraction of fluorescence accessible to the quencher was 0.7 for both exogenous PQ. dPQ and PQ-2 also retarded the P700 photooxidation measured under limiting actinic light irradiances. Photoacoustic measurements showed that addition of dPQ increased the heat dissipation and decreased the photochemical capacity of PSI. From these results, exogenous oxidized PQ were shown to efficiently quench the Chl excited state in the PSI antenna and change the balance between Chl deexcitation pathways. Moreover, reduction of the endogenous PQ pool in whole thylakoid membranes by NADPH increased PSI fluorescence by 65%, indicating the importance of the redox state of the PQ pool on PSI energy dissipation.     

A highly enantioselective rhodium catalyst for the hydrogenation of aliphatic α-keto esters

The enantioselective hydrogenation of several α-keto acid derivatives with rhodium diphosphine catalysts has been investigated using a random screening approach. The neutral rhodium catalyst prepared in situ from bis(2,5-norbornadiene rhodium chloride) and NORPHOS has been found to be an excellent catalyst for preparing aliphatic α-hydroxy esters in high optical purities. The reaction parameters for the hydrogenation of ethyl 2-oxo-4-phenyl-butyrate, an intermediate for the ACE inhibitor Benazepril, were optimized and the best optical yields obtained were 96%.     

Structure of a photoactive rhodium complex intercalated into DNA

Intercalating complexes of rhodium(III) are strong photo-oxidants that promote DNA strand cleavage or electron transfer through the double helix. The 1.2 A resolution crystal structure of a sequence-specific rhodium intercalator bound to a DNA helix provides a rationale for the sequence specificity of rhodium intercalators. It also explains how intercalation in the center of an oligonucleotide modifies DNA conformation. The rhodium complex intercalates via the major groove where specific contacts are formed with the edges of the bases at the target site. The phi ligand is deeply inserted into the DNA base pair stack. The primary conformational change of the DNA is a doubling of the rise per residue, with no change in sugar pucker from B-form DNA. Based upon the five crystallographically independent views of an intercalated DNA helix observed in this structure, the intercalator may be considered as an additional base pair with specific functional groups positioned in the major groove.     

Deexcitation of cardiac cells.

Excitation and deexcitation are fundamental phenomena in the electrophysiology of excitable cells. Both of them can be induced by stimulating a cell with intracellularly injected currents. With extracellular stimulation, deexcitation was never observed; only cell excitation was found. Why? A generic model with two variables (FitzHugh) predicts that an extracellular stimulus can both excite the cell and terminate the action potential (AP). Our experiments with single mouse myocytes have shown that short (2-5 ms) extracellular pulses never terminated the AP. This result agrees with our numerical experiments with the Beeler-Reuter model. To analyze the problem, we exploit the separation of time scales to derive simplified models with fewer equations. Our analysis has shown that the very specific form of the current-voltage (I-V) characteristics of the time-independent potassium current (almost no dependence on voltage for positive membrane potentials) is responsible here. When the shape of the I-V characteristics of potassium currents was modified to resemble that in ischemic tissues, or when the external potassium concentration (K0) is increased, the AP was terminated by extracellular pulses. These results may be important for understanding the mechanisms of defibrillation.     

Synthesis, spectroscopy, and structures of new rhodium(I) and rhodium(III) corroles and catalysis thereby

The syntheses and molecular structures of six- and five-coordinated rhodium(III) corroles (by pyridines and a chiral amine, respectively) and the rhodium(I) complex of a chiral corrole are described, together with some interesting features in the NMR spectra of the complexes and their utilization as carbene-transfer catalysts.     

Catalytic properties of water-soluble rhodium and iridium complexes: the influence of the ligand structure

Rhodium and iridium complexes of trisulfonated triarylphosphanes, TPPTS (tris(3-sulfonatophenyl)phosphane), T(p-A)PTS (tris(3-sulfonato-4-methoxyphenyl)phosphane), T(2,4-X)TS (tris(2,4-dimethyl-5-sulfonatophenyl)phosphane), have been tested in biphasic hydrogenation of aldehydes. T(2,4-X)TS could not stabilize the rhodium complex under the applied conditions. Guanidium salt of T(2,4-X)TS has been characterized by X-ray crystallography, and Tolman cone angle of the phosphane has been determined from crystallographic data. The large cone angle (196°, 210°) explains the instability of the rhodium complex. Contrary to the T(2,4-X)TS/rhodium system, the T(2,4-X)TS/iridium catalyst has been found to be stable and effective in hydrogenation of benzaldehyde and caproaldehyde.     

Tripodal oxygen and tripodal nitrogen ligands in hydroformylation reactions: formation of novel rhodium(III) carbonyl bis(acyl) complexes

The rhodium(I) complexes TpmsRh(CO)₂ (1) and TpmsRh(cod) (2) of the tripodal nitrogen ligand tris(pyrazolyl)methanesulfonate, Tpms⁻=[(pz)₃CSO₃]⁻, catalyze the hydroformylation of 1-hexene. Addition of phosphine has a negative effect on the activity. The hydroformylation activity reaches a maximum at about 60 °C. At temperatures above 80 °C hydrogenation becomes an important secondary reaction. When the catalysis is performed at 60 °C in acetone with 1 or 2 as catalyst precursor all of the rhodium is recovered in the form of the rhodium(III) bis(acyl) complex TpmsRh(CO)(COC₆H₁₃)₂ (9). A similar behaviour is observed with rhodium(I) complexes bearing the tripodal oxygen ligand L_OMe⁻=[(cyclopentadienyl)tris(dimethylphosphito-P) cobalt O,O^′,O″]⁻. In this case all of the rhodium is transformed into L_OMeRh(CO)(COC₆H₁₃)₂ (10). These hitherto unknown bis(acyl) rhodium(III) complexes show the same catalytic activity as the rhodium(I) starting compounds.     

Inhibiting prolyl isomerase activity by hybrid organic–inorganic molecules containing rhodium(II) fragments

A small molecule containing a rhodium(II) tetracarboxylate fragment is shown to be a potent inhibitor of the prolyl isomerase FKBP12. The use of small molecules conjugates of rhodium(II) is presented as a general strategy for developing new protein inhibitors based on distinct structural and sequence features of the enzyme active site.     

Amperometric electrode for determination of urea using electrodeposited rhodium and immobilized urease

An amperometric biosensor was developed for determination of urea using electrodeposited rhodium on a polymer membrane and immobilized urease. The urease catalyzes the hydrolysis of urea to NH₄⁺ and HCO₃⁻ ions and the liberated ammonia is catalytically and electrochemically oxidized by rhodium present in the rhodinized membrane on the Pt working electrode. Three types of rhodinized polymer membranes were prepared by varying the number of electrodeposition cycles: membrane 1 with 10 deposition cycles, membrane 2 with 40 cycles and membrane 3 with 60 cycles. The morphologies of the rhodinized membranes were investigated by scanning electron microscopy and the results showed that the deposition of rhodium was like flowers with cornices-like centers. The influence of the amount of electrodeposited rhodium over the electrode sensitivity to different concentrations of ammonia was examined initially based on the cyclic voltammetric curves using the three rhodium modified electrodes. The obtained results convincingly show that electrode with rhodinized membrane 1, which contain the lowest amount of electrodeposited rhodium is the most active and sensitive regarding ammonia. It was found that the anodic oxidation peak of ammonia to nitrogen occurs at 0.60 V. In order to study the performance of urease amperometric sensor for the determination of urea, experiments at constant potential (0.60 V) were performed. The current–time experiments were carried out with urease rhodinized membrane 1 (10 cycles). The amperometric response increased linearly up to 1.75 mM urea. The detection limit was 0.05 mM. The urea biosensor exhibited a high sensitivity of 1.85 μA mM⁻¹ cm⁻² with a response time 15 s. The Michaelis–Menten constant K_m for the urea biosensor was calculated to be 6.5 mM, indicating that the immobilized enzyme featured a high affinity to urea. The urea sensor showed a good reproducibility and stability. Both components rhodium and urease contribute to the decreasing of the production cost of biosensor by avoiding the use of a second enzyme.     

Laurdan solvatochromism: solvent dielectric relaxation and intramolecular excited-state reaction.

Absorption, steady-state, and time-resolved fluorescence measurements have been performed on laurdan dissolved either in white viscous apolar solvents or in ethanol as a function of temperature. The heterogeneity of the absorption spectra in white oils or in ethanol is consistent with semiempirical calculations performed previously on Prodan. From steady-state and time-resolved fluorescence measurements in apolar media, an excited state reaction is evidenced. The bimodal lifetime distribution determined from the maximum entropy method (MEM) analysis is attributed to the radiative deexcitation of a "locally excited" (LE) state and of a "charge transfer" (CT) state, whereas a very short component (20 ps), the sign and the amplitude of which depend on the emission wavelength, is attributed to the kinetics of the interconvertion reaction. The observation of an isoemissive point in the temperature range from -50 degrees C to -110 degrees C in ethanol suggests an interconvertion between two average excited-state populations: unrelaxed and solvent-relaxed CT states. A further decrease in temperature (-190 degrees C), leading to frozen ethanol, induces an additional and important blue shift. This low temperature spectrum is partly attributed to the radiative deexcitation of the LE state. Time-resolved emission spectra (TRES) measurements at -80 degrees C in the ethanol liquid phase show a large spectral shift of approximately 2500 cm(-1) (stabilization energy of the excited state: 7.1 kcal x M(-1)). The time-dependent fluorescence shift (TDFS) is described for its major part by a nanosecond time constant. The initial part of the spectral shift reveals, however, a subnanosecond process that can be due to fast internal solvent reorientation and/or to intramolecular excited-state reactions. These two relaxation times are also detected in the analysis of the fluorescence decays in the middle range of emission energy. The activation energy of the longest process is approximately 3 kcal x M(-1). At -190 degrees C, one subnanosecond and one nanosecond excited-state reactions are also evidenced. They are likely due to intramolecular rearrangements after the excitation, leading to the CT state and not to solvent relaxation, which is severely hindered in these temperature conditions. Therefore, both intramolecular and solvent relaxations are responsible for the large Stokes shift displayed by this probe as a function of solvent polarity. A possible scheme is proposed for the deexcitation pathway, taking into account the kinetics observed in these different solvents.     

Hydroformylation of alkenes catalyzed by new dinuclear aryloxide- and carboxylate-bridged rhodium complexes

The new dinuclear aryloxide- and carboxylate-bridged rhodium complexes bis[μ-(2-methylphenolato)]bis[(η²:η²-cycloocta-1,5-diene)rhodium], di(μ-docosanoato)bis[(η²:η²-norborna-2,5-diene)rhodium] and bis[(μ-(adamant-1-yl)carboxylato]bis[(η²:η²-norborna-2,5-diene)rhodium] have been prepared. The complexes were tested as catalysts in the hydroformylation of styrene with a total pressure of CO/H₂ (1:1) of 1000 psi, at 25 and 60 °C, and displayed a regioselectivity towards the branched aldehyde of up to 97%. The same complexes as catalysts in the hydroformylation of 1-octene displayed a regioselectivity for the linear aldehyde of up to 55%.     

The yield of chlorophyll a fluorescence as a means to test the various deexcitation mechanisms in the antenna system of green plants

With the aid of measurements of the fluorescence yield, the efficiency of the various deexcitation mechanisms of an exciton in the light-harvesting system has been determined. For this purpose, the fluorescence of dark-adapted as well as of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-treated and preilluminated leaves of Zea mays L. was excited by single ultrashort laser pulses of different energies. The experimental results have served for the fitting of solutions of rate equations, which describe the deexcitation by linear relaxation processes like fluorescence and radiationless transitions, by annihiation of excitons, and by traps both in the ground state and in an excited state. We have obtained the following results: a ratio of antenna chlorophyll molecules to Photosystem II traps of 600:1, an annihilation constant γ = 2·10^?8 cm³·s^?1, a mean trapping time of $\text{t}\text{?}\text{=0.5}\text{ns}$, a trapping probability for traps in the ground state of 2·10^?8 cm³·s^?1, and 6·10^?9 cm³·s^?1 for traps in an excited state.     

Energetics and chronology of phototransients in the light response of the purple membrane of Halobacterium halobium

Arrhenius parameters for formation and decay of phototransients in suspensions of purple membrane fragments in H₂O and ²H₂O have been determined in the temperature range 0–60 °C. Kinetic isotope effects are found which show that proton transfer steps are involved in both formation and decay of the two longest-lived transients absorbing at 410 nm and 660 nm, respectively. The results also suggest that these transients do not occupy a single pathway in the spontaneous deexcitation of bacteriorhodopsin within the purple membrane. Purple membrane undergoes a phase transition at 25–30 °C in both H₂O and ²H₂O.     

Rhodium complexes possessing S-phosphinite ligands with or without an amino group: application to hydroformylation of styrene

A chelate cationic rhodium(I) complex with a hemilabile amino- and sulfur-containing phosphinite ligand has been synthesized and, according to the NMR data, the ligand is bound to the metal in a P,S-bidentate coordination mode without any Rh-N interaction. This complex efficiently catalyzes the hydroformylation of styrene. The chelate rhodium complex with the analogous ligand without the amino group has also been synthesized and examined as a catalyst for the same hydroformylation reaction. The reaction rate is higher using the former complex compared to the latter one without the amino group, with, however, a slightly lower regioselectivity towards the formation of the branched aldehyde.     

Twisted paddlewheel rhodium complexes: Contribution of central and axial chirality to ECD,VCD, and NMR spectra

Dirhodium complexes bearing N-substituted chiral amino acid ligands are investigated. These complexes have an unusual twisted paddlewheel structure, showing inherent chirality. We would like to demonstrate that parallel application of chiroptical spectroscopic methods (ECD and VCD) and NMR spectroscopy combined with quantum chemical calculations constitutes a powerful tool to determine the configuration of the complexes unequivocally. Two chiroptical methods are needed to determine the absolute configuration: ECD for the coordinated nitrogen atom and VCD for the rhodium core. A quick to use NMR method is also presented: Upon the coordination of small molecules in the axial position, the relative configuration of both the rhodium core and the nitrogen atom can be determined simultaneously by studying spatial proximities provided by 1D NOE spectra.     

Synthesis and biological evaluation of novel 4"-alkoxy avermectin derivatives

Novel 4"-alkoxy avermectin derivatives were synthesized via rhodium carbenoid mediated O-H insertion reaction and tested for antiparasite activity against Artemia salina and Caenorhabditis elegans.     

Rhodium-catalyzed deuterioformylation of the ketal-masked β-isophorone: Evidence for a tertiary alkyl rhodium intermediate as a precursor of the main reaction product acetaldehyde derivative

The rhodium-catalyzed deuterioformylation of the ketal-masked β-isophorone 7,9,9-trimethyl-1,4-dioxa-spiro[4.5]dec-7-ene (1) under 100 atm of syngas, at 100 °C, gives the trideuterated acetaldehyde derivative 2 as the main product, originating from a primary alkyl rhodium intermediate c via isomerization of the tertiary one a. Theoretical calculations indicate that secondary and tertiary rhodium alkyl intermediates are formed in a similar amount and hence their evolution to aldehydes occurs with different rates.