New Group 6 metal carbonyl derivatives of 2-(2'(-pyridyl)benzimidazole: synthesis and spectroscopic studies

Reaction of Cr(CO)(6) with 2-(2'-pyridyl)benzimidazole (pbiH) under reduced pressure resulted in the formation of the dinuclear complex [Cr(2)(CO)(6)(pbiH)(2)]. Infra-red (IR) spectroscopy revealed the presence of terminal and bridge Cr-CO bonds. Interaction of M(CO)(6), M=Cr, Mo and W, with pbiH in the presence of 2,2'-bipyridine (bpy) gave the tetracarbonyl complexes [M(CO)(4)(pbiH)].bpy. Spectroscopic studies of the complexes indicated the presence of hydrogen bonding between the bpy nitrogen and the NH group of pbiH. Reactions of M(CO)(6) with pbiH in the presence of PPh(3) gave the tricarbonyl monosubstituted derivatives [M(CO)(3)(PPh(3))(pbiH)]. The spectroscopic studies of the complexes suggested the proposed structures.     

Reaction of some coumarin and 4,6-diaryl-2H-pyran derivatives with secondary amines

The reaction of piperidine, morpholine, piperazine or dimethylamine with several coumarins, 3-bromocoumarin, 4,6-diaryl-2H-pyran-2-ones and 3-bromo-4,6-diaryl-2H-thiopyran-2-ones gave o-hydroxycinnamic acid amides, benzofurans, open-chain δ-oxoamides and thiophene derivatives, respectively.     

Partial dehydration of the retinal binding pocket and proof for photochemical deprotonation of the retinal Schiff base in bicelle bacteriorhodopsin crystals

In bicelle bacteriorhodopsin (bcbR) crystals, the protein has a different structure from both native bacteriorhodopsin (bR) and in-cubo bR (cbR) crystals. Recently, we studied the ability of bcbR crystals to undergo the photocycle upon laser excitation, characterized by the appearance of the M intermediate by single crystal resonance Raman spectroscopy. Calculation of the M lifetime by flash photolysis experiments demonstrated that in our bcbR crystals, the M rise time is much faster than in the native or cbR crystals, with a decay time that is much slower than these other two forms. Although it is now known that the bcbR crystals are capable of photochemical deprotonation, it is not known whether photochemical deprotonation is the only way to create the deprotonated Schiff base in the bcbR crystals. We measured both the visible and Raman spectra of crystals dried under ambient lighting and dried in the dark in order to determine whether the retinal Schiff base is able to thermally deprotonate in the dark. In addition, changes in the visible spectrum of single bcbR crystals under varying degrees of hydration and light exposure were examined to better understand the retinal binding environment.     

Selective adsorption from methanol/water mixtures by C60 fullerene nanospheres

Micro-Raman spectroscopy was used to investigate the selective adsorption of methanol/water mixtures on the surface of [60] fullerene nanospheres. C₆₀ molecules were dispersed in methanol/water mixtures with different methanol molar fractions ranging between 1 and 0.5. The Raman active pentagon pinch mode shifted significantly (±4 cm⁻¹) as the mixture composition was changed. The shift in the Raman mode was sinusoidal in nature indicating that methanol then water is adsorbed preferentially on the fullerene surface at different mixture compositions. The observed behavior is attributed to structure forming effects of alcohol/water mixtures and the shape and size effect of fullerene surface.     

Spectrophotometric determination of molybdenum with phenylfluorone

Spectrophotometric studies on the reaction between molybdenum as molybdate (MoO₄^2?) and phenylfluorone are presented. The reaction conditions are optimized to develop an intense color (molar absorptivity is 3.8 × 10³) selective and sensitive for the Spectrophotometric determination of molybdenum. The absorbance is measured at 560 nm, at a pH of 1.5–3. The colored complex is stable for up to 24 hr, Beer's law is obeyed, over the concentration range of 1 to 4 μg/25 ml. The relative standard deviation is 2% and the sensitivity of the method is 1.60 × 10^?4 mg/ml.     

Structural Elucidation of {[(CH3)2SnCl2·H2O]2·18-crown-6} n and its Hydrogen Bonding in Solution by HMBC Spectroscopy

Behavior of {[(CH₃)₂SnCl₂·H₂O]₂·18-crown-6}_n in solution have been investigated by HMBC NMR. The results show that coordination of water to tin containing species and its hydrogen bonding to crown ether remains intact in non-coordinating solvent in contrast to coordinating solvent. H-NMR reveals that the chemical shift of water in complex varies by solvent of crystallization.     

Conversion of sugarcane bagasse to carboxylic acids using a mixed culture of mesophilic microorganisms

Using the MixAlco process, biomass can be converted into carboxylic acids, which can be chemically converted into mixed alcohol fuels. This study focused on the use of countercurrent fermentation to anaerobically convert sugarcane bagasse and chicken manure to mixed carboxylic acids using a mixed culture of mesophilic microorganisms from terrestrial and marine sources. Bagasse was pretreated with lime to increase digestibility. The continuum particle distribution model (CPDM) simulated continuous fermentors based on data collected from batch experiments. This model saves considerable time in determining optimum operating conditions. For an 80% bagasse/20% chicken manure fermentation with terrestrial inoculum at a volatile solids loading rate (VSLR) of 7.36 g/(L of liquid·d) and a liquid residence time (LRT) of 8.88 d, total carboxylic acid productivity, total acid selectivity, and yield were 2.49 g/(L of liquid·d), 0.581 g of total acid/g of VS digested, and 0.338 g of total acid/g of VS fed, respectively, at a concentration of 18.7 g of total acid/L. At the same VSLR and LRT, fermentation with marine inoculum gave higher total acid productivity, total acid selectivity, and yield than fermentation with terrestrial inoculum. For an 80% bagasse/20% chicken manure fermentation with marine inoculum at a VSLR of 3.83 g/(L of liquid·d) and an LRT of 12.1 d, total carboxylic acid productivity, total acid selectivity, and yield were 1.38 g/(L of liquid·d), 0.667 g of total acid/g of VS digested, and 0.359 g of total acid/g of VS fed, respectively, at a concentration of 16.2 g of total acid/L.     

Diammonium Hydrogen Phosphate as an Efficient and Inexpensive Catalyst for the Synthesis of Bis(indolyl)methanes under Solvent-Free Conditions

Bis(indolyl)methanes were synthesized by the reaction of indole derivatives and aromatic and aliphatic aldehydes in the presence of diammonium hydrogen phosphate as a solid catalyst under solvent-free conditions. This methodology offers significant improvements for the synthesis of bis(indolyl)methanes with regard to the yield of products, simplicity in operation, and green aspects by avoiding toxic catalysts and solvents.     

13C NMR of indazoles

The carbon-13 chemical shifts and some selected coupling constants of 183 indazoles are reported. The main conclusions of the original references are briefly summarized.Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1159–1179, September, 1995.     

Theoretical study on interaction of different coordination modes of BH4 ligand with transition metal in [TM(BH4)(CO)4] (TM = Cr, Mo)

Density functional calculations were performed on bonding and structural features of [(ηⁿ-BH₄)TM(CO)₄]⁻ (n = 1, 2, 3; TM = Cr, Mo) complexes. Calculations show that the ground state is bidentate which is in good agreement with experimental results. It has been found that the bridge and terminal hydrogen atoms will interchange by two pathways: (i) twist of BH₄ about one of the bridge B-H and (ii) twist of BH₄ about one of the terminal B-H. The molecular orbital calculations and natural bond orbital methodologies for different isomers of these complexes have been evaluated. The final results indicate that case (i) is more preferable relative to another case.