Triphenylmethane Research Articles

Fine Copper Nanoparticles on Amine Functionalized SBA-15 as an Effective Catalyst for Mannich Reaction and Dye Reduction

Copper nanoparticles dispersed on amine functionalised mesoporous silica SBA-15 (Cu/NH2-SBA-15) were synthesised by a simple sol–gel and impregnation method using sodium borohydride (NaBH4) as a reducing agent. The morphology, mesostructure and functionality of the ordered mesoporous Cu/NH2-SBA-15 were evaluated by powder X-ray diffraction (PXRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Nitrogen adsorption–desorption isotherms (BET) and Fourier transform infrared spectroscopy (FTIR). The results obtained revealed, that the amine functionalised SBA-15 holds hexagonal lamelliform with surface area and pore size of 250 m2/g, 2.2 nm respectively. Moreover, these short vertical channels have a substantial role in the uniform dispersion of copper nanoparticles within the meso-channels of amine functionalised SBA-15. Cu nanoparticles in the size range of 4–7 nm were dispersed on the NH2-SBA-15 support. To confirm the potential catalytic activity, Cu/NH2-SBA-15 was tested in Mannich reaction. The catalyst showed an excellent catalytic activity for the yield (90%) of β-amino carbonyl compounds that serve as a building block for the synthesis of lactams, peptides, amino alcohols and precursor for various amino acids. Further, the activity of the catalyst was also tested for the reduction of dyes. The structural influence over the reduction pathways was studied on triphenyl methane dyes.

Estrogenic activity of multicyclic aromatic hydrocarbons in rainbow trout (Oncorhynchus mykiss) in vitro assays

A representative group of multicyclic aromatic hydrocarbons (MAHC) which can be further classified as bridged-ring (bridged-MAHC) or fused-ring (fused-MAHC) were examined for their ability to interact with the estrogen receptor of rainbow trout (rtER) in a hepatic cytosolic estrogen receptor competitive binding assay (cyto rtERαβ) and the vitellogenin (Vtg) mRNA gene activation liver slice assay. All five fused-MAHCs; naphthalene (NAFT), fluorene (FE), Fluoranthene (FAT), pyrene (PY), and 9,10-dihydroanthracene (DAC) had no estrogenic activity in the in vitro assays used. Five of the eight bridged-MAHCs; triphenylethylene (3PE), o-terphenyl (OTP), triphenylmethane (TPM), 1,1-diphenylethylene (DPE), and cis-stilbene (CSB) were positive in the rtER-binding assay. The additional three bridged-MAHC’s; trans-stilbene (TSB), tetraphenylethylene (4PE), and 4,4-di-tertbutylphenyl (DtBB) were determined to be non-binders due to isomeric configuration, solubility limitation, and possible steric hinderance. It is possible that the bridged-MAHCs bind to the rtER through a proposed aromatic-aromatic stacking (π-π interaction) facilitated by perpendicular ring orientation achieved through free rotation of the bridged rings. The fused-ring structures are locked in a planar configuration which doesn’t allow for rotation of rings perpendicular to one another. This first report of the rtER-binding of bridged-MAHCs in fish demonstrates binding for a class of chemicals normally not thought of as having an affinity for the estrogen receptor and further supports the versatility or promiscuity of ER ligand selectivity.

Superior adsorption performance of metal-organic-frameworks derived magnetic cobalt-embedded carbon microrods for triphenylmethane dyes

In this work, magnetic Co/C microrods were successfully synthesized using direct carbonization of [Co3(BTC)2(H2O)12] precursors. After the carbonization, the original shape of the precursors was well-maintained, while the magnetic Co nanoparticles were well dispersed in the carbon matrix. The Co/C microrods were used as adsorbents for the adsorption of methyl blue (MB), acid fuchsin (AF), malachite green (MG), rhodamine B (Rh B), methyl orange (MO) and methylene blue (MTB) from their aqueous solutions. The results show that Co/C microrods can selectively adsorb triphenylmethane (TPM) dyes, while the adsorption capacities are about 13960, 11,610 and 4893 mg/g for MB, AF and MG dyes, respectively. The adsorption mechanism can be attributed to π-π interaction forces between the sp2 graphitic carbon in Co/C microrods and the triphenyl structure of dyes. In addition, the synthesized magnetic Co/C microrods can be easily removed from water using magnetic separation, and subsequently, regenerated using ethanol treatment.

Theoretical Calculation of the Geometry and Vibrational Frequencies of Triphenylmethane

Raman spectra of polycrystalline triphenylmethane (TPM) are recorded at room temperature in the range 4000–400 cm–1. The optimum structure and vibrational (Raman and IR) spectra of TPM are calculated using the B3LYP/6-311G(d,p) approximation. Theoretical modes and bands corresponding to them in the experimental Raman spectrum are assigned to stretching and bending vibrations of certain bonds in the TPM molecule based on visualization of the vibrations. Most bands, in particular, the strongest ones in the Raman spectra of TFM, are due to vibrations in monosubstituted benzene rings. Some of the theoretical modes and the corresponding experimental bands are assigned to benzene modes in Wilson notation.

Influence of Dyes on Metal Removal: a Study Using Live and Dead Cells of Penicillium simplicissimum in Single-Metal and Dye-Metal Mixtures

The metal removal efficiency of live and dead fungal cells of Penicillium simplicissimum (isolate 10, KP713758) was tested against 100 ppm toxic metals Cd, Cu, Pb, Zn and trivalent Cr in single-metal solutions and in mixtures with 50 ppm triphenylmethane (TPM) dyes (Cotton Blue, Crystal Violet, Methyl Violet, and Malachite Green). Results revealed that live cells were more effective at removing metals from single (10.8–70.0%) and dye-metal mixtures (5.3–62.2%) than dead cells (5.1–27.4%). The dyes in dye-metal mixtures influenced metal uptake capacity. All four dyes inhibited the uptake of Cd (0.9–7.1%), Zn (5.3–7.7%), Cu (5.0–25.8%) and Cr (47.3–60.7%) by live cells. The exception was the enhance removal of Pb by live cells (48.6 to 56.3–62.2%) in the presence of dye (MG or CB). Pb uptake was not affected by MV (51.8%), but was inhibited by CV (31.9%). For dead cells, uptake of metals (Cd, Cr and Zn) in single (3.2–27.4%) and dye-metal solutions (0.7–27.4%) was similar, whilst removal of Cu (6.4–13.5%) and Pb (33.6–44.0%) was inhibited by all four dyes. P. simplicissimum is concluded to have potential to remove toxic metals even in the presence of TPM dyes, with preferred use of live cells than dead cells.

Isolation and Characterization of a Molybdenum-reducing and Methylene Blue-decolorizing Serratia marcescens strain KIK-1 in Soils from Nigeria

Bioremediation of toxic compound in polluted environment is currently considered as the most economical and ecofriendly approach, particularly at a lower concentration of the toxicant, where other physicochemical techniques are ineffective. In this work, molybdenum-reducing bacterium with the capacity to decolorize various azo and triphenyl methane dyes independent of molybdenum reduction was isolated from contaminated soil. The bacterium reduces molybdate to Mo-blue optimally at pH between 5.8 and 6.5, temperature, between 34 and 37 oC, molybdate concentration between 10 and 25 mM and phosphate concentration, 5.0 mM. Glucose was the best electron donor supporting molybdate reduction followed by sucrose, maltose, trehalose, d-mannose, glycerol, d-mannitol, d-sorbitol, myo-inositol, d-adonitol and salicin in descending order. The absorption spectrum of Mo-blue produced was similar to other previous Mo-reducing bacteria, and closely resembles a reduced phosphomolybdate. About 78.1, 63.4, 45.5 and 17.8% of the molybdenum reduction in this bacterium was inhibited by 2 ppm mercury (ii), silver (i), copper (ii) and chromium (vi), respectively. The biochemical analysis resulted in a tentative identification of the bacterium as Serratia marcescens strain KIK-1. The ability of this bacterium to detoxify molybdenum and decolorize azo dye makes this bacterium an important tool for bioremediation.
 

Effect of inorganic ions on the ultrasound initiated degradation and product formation of triphenylmethane dyes

Triphenylmethane (TPM) dyes are an important category of dyes with a variety of industrial applications and consequently, these are found in the aquatic environment at relatively higher concentrations. Here, we report the degradation of two important TPM dyes (para rosaniline (PRA) and ethyl violet (EV)) in an aqueous medium by ultrasound which is one among the Advanced Oxidation Processes (AOPs). The main objective of this work is to study the effect of various inorganic ions on the degradation and the product formation of TPM dyes from the sonochemical reactions. Using a typical concentration of 10 ppm dyes and an ultrasonic frequency of 350 kHz and power of 60 W, a complete degradation of EV and PRA was observed with a pseudo first order rate constant of 0.2339 min−1 and 0.1956 min−1, respectively. The product analyses using high-resolution mass spectrometry (LC-Q-TOF-MS) revealed the formation of hydroxylated, de-alkylated, and other collapsed conjugated structure destructed products. The evolution of these products in the presence of various inorganic ions (Cl−, SO42−, NO3−, and CO3−) showed that only carbonate ions had a significant impact on the product evolution. The carbonate ions facilitated the formation of conjugated structure destructed product for both the dyes. This is attributed to the reactivity of carbonate radical, which facilitated the formation of carbon-centered radicals. This carbon-centered radical further undergoes reaction to cause the destruction of conjugated structures. This is confirmed by the identification of the corresponding product peaks in the mass spectra. The scavenging effect of carbonate ions was also reflected in the product study where there is a reduction in the formation of most of the hydroxylated products. One of the major inorganic species in any wastewater is carbonate ions and therefore the present result is very relevant to the understanding of oxidation based treatment protocol.

The concentration and probabilistic health risk assessment of pesticide residues in commercially available olive oils in Iran

This study was undertaken to analyze 29 pesticides residues in 37 commercially olive oil collected samples from Iran's markets using Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) approach along with acetonitrile for the extraction, surface adsorbents for clean-up procedure, following with a gas chromatography-mass spectroscopy (GC-MS). In order to eliminate the matrix effect, the calibration curves were drawn using spiked samples with the Area under curve (AUC) portion calculation of pesticide residue to AUC internal standard (Triphenyl Methane (TPM)). Moreover, the probabilistic health risk assessment includes non-carcinogenic and carcinogenic risk were estimated by target hazard quotient (THQ), total target hazard quotient (TTHQ) and cancer risk (CR) using the Monte Carlo Simulation (MCS) method. The calibration curves were linear in the range of 10–1500 ng/g, and R2 was higher than 0.994. All pesticides recoveries as average were in the range of 77.97–112.65%. The respective numbers attributed to LOD and LOQ were 3–5 ng/g and 8–15 ng/g. Results showed that 29.7% of samples were contaminated by pesticides which according to Iranian regulation, while in 7 cases banned pesticides were detected. Only 4 samples are noncompliant with EU regulation. The rank order of pesticides based on THQ was Heptachlor > DDT > Pretilachlor. Also, TTHQ for adults was 0.139; and children 0.467. The rank order of pesticides based on CR was Heptachlor > DDT. Consumers (adults and children) are not at non-carcinogenic risk due to ingestion of oil olive content (THQ and TTHQ < 1 value) but are at considerable carcinogenic (CR > 1E-6). According to the observed profile of pesticide in olive oil samples, which are mostly banned according to Iranian regulation, further improvements in agriculture procedures of cultivated olive in Iran, as well as required assessments of imported olive oil, was recommended.

Investigation on crystal growth and characterization of organic nonlinear optical triphenylmethane single crystal by vertical Bridgman technique

An organic triphenylmethane (TPM) single crystal of length 58 mm and diameter 12 mm was grown by vertical Bridgman technique. The cell parameters of the grown crystal were confirmed by single crystal X-ray diffraction studies. Powder X-ray diffraction analysis was used to determine the crystalline nature of the triphenylmethane crystal. The functional groups of the triphenylmethane crystal were identified by Fourier transform infrared analysis. The linear optical property of the grown triphenylmethane crystal was studied by UV–Vis–NIR spectroscopic analysis which shows that the crystal has low cutoff wavelength at 281 nm and exhibits optical band gap value at 4.15 eV. The fluorescence spectrum indicates that the grown crystal emits blue light. The second harmonic conversion efficiency of the crystal was determined using Kurtz and Perry powder technique. The thermal property of the grown crystal was analysed using thermo gravimetric analysis, differential thermal analysis and differential scanning calorimetry. The dielectric constant, dielectric loss and AC conductivity of the grown crystal was investigated for different frequency range upto 1 MHz at various temperatures. The strength of the crystal was estimated by Vicker’s hardness test and laser damage studies.

Biodegradation and Detoxification of Malachite Green Dye Using Novel Enzymes from Bacillus cereus Strain KM201428: Kinetic and Metabolite Analysis

Enzyme based degradation of organic pollutants is a promising detoxifying approach due to the promiscuous nature of the enzyme, efficiency, cost effective and ecofriendly. In the present study, we have carried out detailed decoloration and degradation studies on a model triphenyl methane group of dyes (Malachite Green dye (MG)) using a newly isolated enzyme from Bacillus cereus KM201428 under the static condition. Biodegradation of dyes was monitored by UV-VIS spectrophotometer and the resultant metabolites analyzed by Liquid Chromatography–Hybrid Quadrupole Time of Flight Mass Spectrometry (LC–QToF-MS) and Gas Chromatography/Mass Spectrometry (GC - MS). Metabolite analysis results revealed that enzymatic degradation of MG dye resulted in complete mineralization and benzene ring-removal; the latter known for organic dye toxicity. Kinetic study results revealed that first-order kinetic model was best applicable for describing MG dye decoloration. Michaelise-Menten kinetics, Lineweaver–Burk plot and Eadie-Hofstee plot models were used to establish the kinetic parameters for the dye decoloration. Lineweaver–Burk plot provided the best theoretical correlation of the experimental data with maximum rate (Vmax) of 17.70 mg l-1h-1 and Michaelis constant (Km) of 124 mgl-1. Results provide evidence that crude enzyme from Bacillus cereus strain KM201428 offers an effective, renewable, ecofriendly and affordable biotechnology for treatment of industrial effluents polluted with organic dye.

Synthesis and characterization of novel organo-soluble poly(ether-imide)s containing bulky moiety of triphenyl methane in the main chain

This paper describes the synthesis of novel thermally stable and organo-soluble poly(ether-imide)s (PEIs) by polycondensation reaction of a new synthesized diamine with different dianhydrides. Bis [4-(4-amino phenoxy)-2,5-dimethyl phenyl] paratolyl methane (6) as a new compound containing ether groups and bulky moiety of triphenyl methane was successfully prepared by a three step reaction. First, the diol compound (3) was prepared by a solvent free reaction of 2,5-dimethylphenol (1) with 4-methylbenzaldehyde (2). Then, the diol (3) was converted to dinitro (5) by reaction with 4-fluoronitrobenzene. Finally, dinitro (5) was reducted through the reaction with Pd/C 10 %. The structure of diamine (6) and resulting poly(ether-imide)s (8a-d) confirmed by 1HNMR, FTIR spectroscopy and elemental analysis (CHN). Also the properties of poly(ether-imide)s (8a-d) were investigated by mean of thermal gravimetric analysis (TGA), differantial thermal gravimetric (DTG), differential scanning calorimetry (DSC), solubility tests and inherent viscosity. The resulted polymers show excellent thermal stability, good solubility in aprotic polar solvent and inherent viscosities between 0.37-0.50 dl/g.

Trichoderma asperellum laccase mediated crystal violet degradation–Optimization of experimental conditions and characterization

Biodegradation of crystal violet (CV) by Trichoderma asperellum laccase was herein reported. The process parameters viz., enzyme concentration, dye concentration, pH and incubation time were experimentally optimized for the maximum dye degradation. The degradation of CV was physico-chemically characterized by UV–vis spectroscopy, FTIR, HPTLC, HPLC and GC–MS analyses. In UV–vis spectroscopy, a major reduction in characteristic peak from 588nm to 575nm has suggested the disappearance of triphenyl methane chromophore. From the FT-IR spectra, the formation of new peaks at 3707cm−1 (OH stretching) and 1726cm−1 (CO stretching) indicates the successful transformation of the crystal violet. Similarly, the existence of a prominent peak (Rf−0.39) in HPTLC and a significant reduction in peak intensity of crystal violet had suggested the laccase mediated dye degradation. GC–MS analysis of crystal violet degraded metabolites were identified as Leucocrystal violet, Olivetol dimethyl ether (1,3-Dimethoxy-5-pentylbenzene) and 1,3,5-trimethoxybenzene by a hydride ion (H-) transfer followed by oxidative methylation. The genotoxicity studies by Allium cepa assay has shown that the degraded intermediates of CV are minimally toxic than the original dye. Owing to the above-discussed significance, T.asperellum laccase may be considered for the development of more environmental friendly treatment processes.

Reversible Insulin Hexamer Assembly Promoted by Ethyl Violet: pH-Controlled Uptake and Release.

Therapeutically improved long-acting insulin preparations require in-depth understanding of the hexamer assembly, structural selectivity, and its stability in solution. This Letter demonstrates, for the first time, an efficient method for the hexamerization of human insulin by a structure-specific triphenylmethane (TPM) dye, Ethyl Violet (EV), particularly, in the absence of Zn2+. Upon detailed spectroscopic evaluation and comparison with other TPM homologues, we establish that the diethylamino phenyl arms of EV are specific and effective in clipping the three dimer helices in a hexameric assembly. We establish that at physiological pH 7.4 and in the presence of the EV, insulin exists predominantly in its hexameric form, a condition appropriate for storage and preparation of long-acting insulin formulations. On the other hand, the disassembly of the hexamer into the monomeric form is accomplished at pH 5, highlighting its potential as a delivery vehicle for such custom-modified dyes/drugs.

MOLYBDENUM-REDUCING AND AZO-DYE DECOLORIZING SERRATIA MARCESCENS STRAIN NENI-1 FROM INDONESIAN SOIL

Heavy metals and organic xenobiotics including dyes are important industrial components with their usage amounting to the millions of tonnes yearly. Their presence in the environment is a serious pollution issue globally. Bioremediation of these pollutants using microbes with multiple detoxification capacity is constantly being sought. In this work we screen the ability of a molybdenum-reducing bacterium isolated from contaminated soil to decolorize various azo and triphenyl methane dyes. The bacterium reduces molybdate to molybdenum blue (Mo-blue) optimally at pH 6.0, and temperatures of between 25 and 40oC. Glucose was the best electron donor for supporting molybdate reduction followed by sucrose, trehalose, maltose, d-sorbitol, d-mannitol, d-mannose, myo-inositol, glycerol and salicin in descending order. Other requirements include a phosphate concentration of between 5.0 and 7.5 mM and a molybdate concentration between 10 and 20 mM. The absorption spectrum of the Mo-blue produced was similar to previous Mo-reducing bacterium, and closely resembles a reduced phosphomolybdate. Molybdenum reduction was inhibited by copper, silver and mercury at 2 ppm by 43.8%, 42.3% and 41.7%, respectively. We screen for the ability of the bacterium to decolorize various dyes. The bacterium was able to decolorize the dye Congo Red. Biochemical analysis resulted in a tentative identification of the bacterium as Serratia marcescens strain Neni-1. The ability of this bacterium to detoxify molybdenum and decolorize azo dye makes this bacterium an important tool for bioremediation.

MOLYBDENUM-REDUCING AND AZO-DYE DECOLORIZING SERRATIA MARCESCENS STRAIN NENI-1 FROM INDONESIAN SOIL

Heavy metals and organic xenobiotics including dyes are important industrial components with their usage amounting to the millions of tonnes yearly. Their presence in the environment is a serious pollution issue globally. Bioremediation of these pollutants using microbes with multiple detoxification capacity is constantly being sought. In this work we screen the ability of a molybdenum-reducing bacterium isolated from contaminated soil to decolorize various azo and triphenyl methane dyes. The bacterium reduces molybdate to molybdenum blue (Mo-blue) optimally at pH 6.0, and temperatures of between 25 and 40oC. Glucose was the best electron donor for supporting molybdate reduction followed by sucrose, trehalose, maltose, d-sorbitol, d-mannitol, d-mannose, myo-inositol, glycerol and salicin in descending order. Other requirements include a phosphate concentration of between 5.0 and 7.5 mM and a molybdate concentration between 10 and 20 mM. The absorption spectrum of the Mo-blue produced was similar to previous Mo-reducing bacterium, and closely resembles a reduced phosphomolybdate. Molybdenum reduction was inhibited by copper, silver and mercury at 2 ppm by 43.8%, 42.3% and 41.7%, respectively. We screen for the ability of the bacterium to decolorize various dyes. The bacterium was able to decolorize the dye Congo Red. Biochemical analysis resulted in a tentative identification of the bacterium as Serratia marcescens strain Neni-1. The ability of this bacterium to detoxify molybdenum and decolorize azo dye makes this bacterium an important tool for bioremediation.

Synthesis and properties of highly organosoluble and low dielectric constant polyimides containing non-polar bulky triphenyl methane moiety

Novel fluorinated aromatic polyimides were prepared by the conventional two-step imidization of 4.4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and diamines (TriPMPDA and TriPMMDA) bearing triphenyl methane moiety. Both of the flexible and tough polyimide films exhibited an intrinsic low dielectric constant (low-k) values of 2.56 and 2.33 at the frequency of 10kHz, respectively, due to the introduction of the bulky triphenyl methane side groups and the tortuous backbone structures. In addition, they showed light color, high thermal stability, moderate mechanical property, and more importantly, excellent solubility in common organic solvents (even completely dissolved in dichloromethane and chloroform). Thus, both of the functional polyimides possessed attractive potential applications in the field of high performance flexible polymer interlayer materials.

Novel Exploration of Endophytic Diaporthe sp. for the Biosorption and Biodegradation of Triphenylmethane Dyes

An endophytic isolate identified as Diaporthe sp. was explored for its biosorption and biodegradation potential on triphenylmethane (TPM) dyes. Treatment with live cells demonstrated strong decolorization activities towards methyl violet (MV, 100 mg L−1), crystal violet (CV, 100 mg L−1), and malachite green (MG, 50 mg L−1), with 84.87, 78.81, and 87.80 %, respectively. These values are far greater than decolorization by dead cells via biosorption (DE% of 18.82–48.32 %). The absence of peaks in the UV-vis spectra after 14 days further suggested degradation of dye chromophores. Results revealed that Diaporthe sp. removed TPM dyes through biodegradation and biosorption, with the former as a more desirable mechanism due to its ability to degrade most dye chromophore and enhance decolorization efficiency, and as a mechanism to tolerate toxic MG. As such, application of live cells of Diaporthe sp. is advantageous as it allows biodegradation to occur.

Enhanced photocatalytic activity of degradation of azo, phenolic and triphenyl methane dyes using novel octagon shaped BiOCl discs/MWCNT composite

Novel octagon disc-like multiwall carbon nanotubes (MWCNT)/bismuth oxychloride (BiOCl) composite photocatalysts have been prepared through a one-pot hydrothermal process in the presence of hexamine as surfactant. The crystallanity and morphology of as prepared samples were studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The MWCNT/BiOCl composite photocatalysts exhibited an obvious improved photocatalytic performance for congo red (CR), malachite green (MG) and bromophenol blue (BP) dye degradation. The photocatalytic studies shows that MWCNT could disperse and combine with BiOCl nanodiscs on its surface, which facilitated electron–hole separation, and contributed to improve the photocatalytic activity. A possible mechanism for the enhanced photocatalytic activity of MWCNT/BiOCl composite was also discussed.

Isolation and characterization of a molybdenum-reducing and orange G-decolorizing &lt;i&gt;Enterobacter&lt;/i&gt; sp. strain Zeid-6 in soils from Sudan

Chemical toxins and organic contaminants such as hydrocarbons and dyes are major global contaminants with countless tones of those chemicals are created yearly with a significant amount release to the environment. In this work we screen the ability of a molybdenum-reducing bacterium isolated from contaminated soil to decolorize various azo and triphenyl methane dyes independent of molybdenum reduction. Biochemical analysis resulted in a tentative identification of the bacterium as Enterobacter sp. strain Zeid-6. The bacterium was able to decolorize the azo dye Orange G. The bacterium reduces molybdate to Mo-blue optimally at pH between 5.5 and 8.0 and temperatures of between 30 and 37 oC. Other requirements include a phosphate concentration of 5 mM and a molybdate concentration of 20 mM. The absorption spectrum of the Mo-blue produced was similar to previous Mo-reducing bacterium, and closely resembles a reduced phosphomolybdate. Molybdenum reduction was inhibited by copper, lead, mercury and silver which showed 36.8, 16.9, 64.9 and 67.6% inhibition to Mo-reducing activity of Enterobacter sp. strain Zeid-6, respectively. The resultant molybdenum blue spectrum closely resembles the spectrum of molybdenum blue from the phosphate determination method. The ability of this bacterium to detoxify molybdenum and decolorize azo dye makes this bacterium an important tool for bioremediation.

Effect of Molecular Coupling on Ultrafast Electron-Transfer and Charge-Recombination Dynamics in a Wide-Gap ZnS Nanoaggregate Sensitized by Triphenyl Methane Dyes.

Wide-band-gap ZnS nanocrystals (NCs) were synthesized, and after sensitizing the NCs with series of triphenyl methane (TPM) dyes, ultrafast charge-transfer dynamics was demonstrated. HRTEM images of ZnS NCs show the formation of aggregate crystals with a flower-like structure. Exciton absorption and lumimescence, due to quantum confinement of the ZnS NCs, appear at approximately 310 and 340 nm, respectively. Interestingly, all the TPM dyes (pyrogallol red, bromopyrogallol red, and aurin tricarboxylic acid) form charge-transfer complexes with the ZnS NCs, with the appearance of a red-shifted band. Electron injection from the photoexcited TPM dyes into the conduction band of the ZnS NCs is shown to be a thermodynamically viable process, as confirmed by steady-state and time-resolved emission studies. To unravel charge-transfer (both electron injection and charge recombination) dynamics and the effect of molecular coupling, femtosecond transient absorption studies were carried out in TPM-sensitized ZnS NCs. The electron-injection dynamics is pulse-width-limited in all the ZnS/TPM dye systems, however, the back electron transfer differs, depending on the molecular coupling of the sensitizers (TPM dyes). The detailed mechanisms for the above-mentioned processes are discussed.