Nanostructured thin films of C60-aniline dyad clusters: electrodeposition, charge separation, and photoelectrochemistry

Clusters of C60-aniline dyads are deposited as thin films on nanostructured SnO2 electrodes under the influence of an electric field. At low applied DC voltage (<5 V) the clusters in toluene/acetonitrile (1:3) mixed solvent grow in size (from 160 nm to approximately 200 nm in diameter) while at higher voltages (>50 V) they are deposited on the electrode surface as thin films. The C60- aniline dyad cluster films when cast on nanostructured SnO2 films are photoelectrochemically active and generate photocurrent under visible light excitation. These nanostructured fullerene films are capable of delivering relatively large photocurrents (up to approximately 0.2 mA cm(-2), photoconversion efficiency of 3-4%) when employed as photoanodes in photoelectrochemical cells. Both luminescence and transient absorption studies confirm the formation of charge transfer product (C60 anion) following UV/Vis excitation of these films. Photo-induced charge separation in these dyad clusters is followed by the electron injection from C60-anion moiety into the SnO2 nanocrystallites. The oxidized counterpart is reduced by the redox couple present in the electrolyte, thus regenerating the dyad clusters. The feasibility of casting high surface area thin fullerene films on electrode surfaces has opened up new avenues to utilize dyad molecules of sensitizer bridge donor type in light energy conversion devices, such as solar cells.     

Alkali metal zinc vanadates

The phase composition of the M₂O-ZnO-V₂O₅ (M = Li, Na, K, Rb, Cs) systems at subsolidus temperatures is investigated. Three groups of double vanadates are identified: M₂Zn(VO₃)₄ for M = K, Rb, or Cs; M₂ZnV₂O₇ for M = Na, K, or Rb; and MZnVO₄ for M = Li or Cs. Double pyrovanadate Rb₂ZnV₂O₇ is synthesized for the first time. Phase diagrams are designed for all systems. Comparative phase-formation features of the systems in the alkali oxide series are considered.     

ZERO FIELD OPTICAL DETECTION OF MAGNETIC RESONANCE OF TRIPLET STATE OF CHLOROPHYLL a IN LIPID BILAYER VESICLES

Abstract The zero-field ODMR of triplet state of chlorophyll a incorporated in phosphatidylcholine (PC) vesicles (Chi a : PC = 1:100) has been carried out. The zero-field ODMR frequencies and intersystem crossing rate constants have been measured at various fluorescence wavelengths. The ODMR data suggest that the chlorophyll is present in mono- and biligated species. The nature of the ligand and the role of the medium (phospholipid) are also discussed.     

Photocatalytic reduction of azo dyes Naphthol Blue Black and Disperse Blue 79

Photocatalytic reduction of two textile azo dyes, Naphthol Blue Black (NBB) and Disperse Blue 79 (DB79) has been carried out in colloidal WO₃ and TiO₂ suspensions. Under bandgap excitation of the semiconductor colloids these dyes undergo irreversible reduction as they react with the trapped electrons. The quantum efficiency for the photocatalytic reduction of these dyes were 5.4% and 4.8% for NBB and DB79 respectively. The kinetics and mechanism of the interfacial charge transfer in these colloidal suspension has been elucidated with transient absorption spectroscopy. The reaction between the dye and trapped electrons is diffusion limited and occurs with rate constants of 1.1×10⁸ M⁻¹s⁻¹ and 4.0×10⁷ M⁻¹s⁻¹ for NBB and DB79 respectively.     

Reconstruction of the Water-Oxidizing Complex in Manganese-Depleted Photosystem II Preparations Using Mononuclear Manganese Complexes

Abstract— The water-oxidizing complex of chloroplast photosystem II is composed of a cluster of four manganese atoms that can accumulate four oxidizing redox equivalents. Depletion of manganese from the water-oxidizing complex fully inhibits oxygen evolution. However, the complex can be reconstituted in the presence of exogenous manganese in a process called photoactivation. In the present study, mononuclear manganese complexes with ligands derived from either nitrosonaphthol and ethylenediamine (Niten) or from diaminohexane and salicylaldehyde (Salhxn) are used in photoactivation experiments. Measurements of photoinduced changes of chlorophyll fluorescence yield, thermal dissipation using photoacoustic spectroscopy, photoreduction of 2,6-dichorophenolindophenol and oxygen evolution in manganese-depleted and in reconstituted photosystem II preparations demonstrate that photoactivation is more efficient when Niten and Salhxn complexes are used instead of MnCl₂. It is inferred that the aromatic ligands facilitate the interaction of the manganese atoms with photosystem II. The addition of CaCl₂ and of the extrinsic polypeptide of 33 kDa known as the manganese-stabilizing protein during photoactivation further enhances the recovery of electron transport and oxygen evolution activities. It is proposed that mononuclear manganese complexes are able to contribute to re-constitution of the water-oxidizing complex by sequential addition of single ions similarly to the current model for assembly of the tetranuclear manganese cluster and that these complexes constitute suitable model systems to study the assembly of the water-oxidizing complex.     

Synthesis and crystal structure of Ln2MGe4O12, Ln=rare-earth element or Y; M=Ca, Mn, Zn

The crystal structure of the promising optical materials Ln₂M²⁺Ge₄O₁₂, where Ln=rare-earth element or Y; M=Ca, Mn, Zn and their solid solutions has been studied in detail. The tendency of rare-earth elements to occupy six- or eight-coordinated sites upon iso- and heterovalent substitution has been studied for the Y_2−xEr_xCaGe₄O₁₂ (x=0-2), Y_2−2xCe_xCa_1+xGe₄O₁₂ (x=0-1), Y₂Ca_1−xMn_xGe₄O₁₂ (x=0-1) and Y_2−xPr_xMnGe₄O₁₂ (x=0-0.5) solid solutions. A complex heterovalent state of Eu and Mn in Eu₂MnGe₄O₁₂ has been found.     

Molecular calculations with the nonempirical ab initioMODPOT,VRDDO, and MODPOT/VRDDO procedures. IX. Carcinogenic benzo(a)pyrene and its metabolites using a MERGE technique

Ab initio MODPOT /VRDDO calculations have been carried out on carcinogenic benzo(a)pyrene and its metabolites. The MODPOT /VRDDO method incorporates two very desirable options into our fast ab initio Gaussian programs: MODPOT —ab initio effective core model potentials—and a charge-conserving integral prescreening approximation which we named VRDDO (variable retention of diatomic differential overlap). For orbital energies and population analyses the MODPOT /VRDDO results agree to essentially three decimal places with completely ab initio calculations using the same valence atomic basis set. For this series of very closely related congeners a new MERGE technique was implemented that allows reuse of integrals of a common skeletal fragment. Since our program computes integrals efficiently by blocks, reusing information common to the block, it was more difficult to implement a MERGE technique than for integral programs which calculate the integrals one-byone. The MODPOT /VRDDO calculations were performed for benzo(a)pyrene (BP), BP oxides, BP dihydrodiols, and BP dihydrodiol epoxides. The metabolites investigated were BP-7,8-oxide, BP-4,5-oxide, BP-7,8-dihydrodiol [cis(e, a), cis(a, e), trans(e, e), and trans(a, a)], and BP-7,8-dihydrodiol-9,10-epoxide [β,β,β (the most stable), β,β,α; α,α,β, and α,α,α all derived from cis-BP-7,8-dihydrodiol and β,α,β; α,β,β and α,β,β derived from trans-BP-7,8-dihydrodiol]. Several different conformations were calculated for each of the BP dihydrodiols and BP dihydrodiol epoxides. Calculations were carried out for the opening of the C₉—O—C₁₀ epoxide ring both toward C₉ and C₁₀ for the, most stable β,β,β isomer of BP-7,8-dihydrodiol-9,10-epoxide. Opening the epoxide ring between C₁₀ and O leads to a more stable intermediate than opening the epoxide ring between C₉ and C₁₀. However, there is no buildup of positive charge in C₁₀ as has been postulated by some cancer researchers, but rather the C₁₀ becomes slightly more negative. Nor is there a buildup of negative charge on the O atom. rather it becomes slightly less negative. As the epoxide ring is opened further than 90° for the O—C₉—C₁₀ or O—C₁₀—C₉ angles, there appears to be a possible mixing of configurations that is being investigated further.