Cu-nanoparticles: a chemoselective catalyst for the aza-Michael reactions of N-alkyl- and N-arylpiperazines with acrylonitrile

A novel method for effecting the aza-Michael reactions of N-alkyl- and N-arylpiperazines with acrylonitrile using Cu-nanoparticles is described. The method features the use of 10 mol % Cu (14-17 nm) nanoparticles under mild reaction conditions to afford the addition products in good to excellent yields. The Cu-nanoparticles selectively catalysed the aza-Michael reaction of N-alkyl- and N-arylpiperazines in the presence of aromatic amino or aliphatic hydroxy groups.     

Sc(OTf)3-catalyzed alkylation of indoles with propargyl alcohols: an expeditious synthesis of 3-substituted indoles

Indoles undergo smooth alkylation with propargylic alcohols in the presence of 10 mol % of scandium triflate under mild conditions to produce 3-propargylated indoles in excellent yields with high selectivity.     

Facile reduction of aromatic nitro/azido functionality on solid support employing Al/NiCl2·6H2O and Al/NH4Cl: synthesis of pyrrolo[2,1-c][1,4]benzodiazepines

An efficient and mild method for the reduction of aromatic nitro and azido groups on solid support using Al/NiCl₂·6H₂O and Al/NH₄Cl is described. This solid phase reduction technique has been applied towards the synthesis of DNA binding pyrrolo[2,1-c][1,4]benzodiazepine antitumour antibiotics.     

Conversion of ammonia to dinitrogen in wastewater by Nitrosomonas europaea

Because Nitrosomonas europaea contains ammonia-oxidizing enzyme, nitrite reductase, and nitrous oxide reductase, the conversion of ammonia to dinitrogen was tried with different reaction conditions. In aerobic reaction conditions, ammonium was converted to nitrite (NO ₂ ⁻ ), while under oxygen-limiting or oxygen-free conditions, NO ₂ ⁻ -N formed from ammonia oxidation by N. europaea was reduced to N₂O and dinitrogen with 22% conversion. During denitrification, optimal pH for the production of N₂O and dinitrogen was found to be 7.0–8.0. Dinitrogen was not produced in acidic pH<7.0. A low partial oxygen pressure as well as oxygen-free conditions are favorable for high production of dinitrogen.     

Redox reactions in nonaqueous media : Determination of organoisothiocyanates and organoisocyanates

A simple and accurate method has been developed for the determination of organoisothiocyanates and organoisocyanates based on their quantitative reaction with n-butylamine in dimethylformamide medium to form substituted thioureas and ureas, respectively. The solution is mixed with 6 to 7 times its volume of acetonitrile and an excess of carbon disulphide, which converts the residual amine quantitatively into the corresponding n-butylammonium n-butyl dithiocarbamate. The determination is completed by titrating the resulting dithiocarbamate with iodine monobromide solution in acetonitrile. The end point is detected visually by the yellow color imparted to the solution by the first drop of oxidant solution in excess. The dithiocarbamates are quantitatively oxidized to the corresponding thiuram disulphides.     

Spin crossover studies in cationic complexes of iron by using Mössbauer spectroscopy

The spin transitions in two new cationic complexes of iron, i. e., iron bipyridine formate, [Fe/bipy/₃]/HCOO/₂. 5/HCOOH/ and iron bipyridine tetrafluoro borate, [Fe/bipy/₃]/BF₄/₂. 2H₂O have been studied by using Mössbauer spectroscopy. From quadrupole splitting values, at different temperatures, it has been established that both the complexes show the coexistence of both the high spin state and the low spin state at 300 K while complete transformation to low spin state occurs at 77 K. Both compounds were prepared by electrochemical technique.     

2-(2-Selenocyanic acid ethyl ester)-1H-benz[de] isoquinoline-1,3-(2H)-dione, synthesis photophysics and interaction with bovine serum albumin: a spectroscopic approach

The compound 2-(2-selenocyanic acid ethyl ester)-1H-benz[de] isoquinoline-1,3-(2H)-dione (SEBID), a ubiquitous, bioactive naphthalimide derivative is expected to possess an anticancer, anti-tumor and other important therapeutic activities of significant potency with low systematic toxicity. In this paper, the synthesis of the compound, photophysics of the newly prepared naphthalimide derivative and its interaction with model transport protein Bovine serum albumin (BSA) have been reported using the absorption and steady state fluorescence spectroscopic techniques exploiting the intrinsic fluorescence emission properties of BSA as a probe. Interaction of this organoselenium compound in different dioxane-water mixtures with increase in the polarity of the medium has been studied spectroscopically. Interaction of SEBID with BSA leads to a dramatic decrease in the fluorescence intensity of BSA, which suggests the binding of SEBID with the tryptophan residue of BSA. Furthermore, different thermodynamic parameters for SEBID-BSA interaction have been calculated. Rationalization of the data has been attempted, particularly in relation to prospective applications in the biomedical research.     

THE weighted histogram analysis method for free-energy calculations on biomolecules. I. The method

The Weighted Histogram Analysis Method (WHAM), an extension of Ferrenberg and Swendsen's Multiple Histogram Technique, has been applied for the first time on complex biomolecular Hamiltonians. The method is presented here as an extension of the Umbrella Sampling method for free-energy and Potential of Mean Force calculations. This algorithm possesses the following advantages over methods that are currently employed: (1) It provides a built-in estimate of sampling errors thereby yielding objective estimates of the optimal location and length of additional simulations needed to achieve a desired level of precision; (2) it yields the “best” value of free energies by taking into account all the simulations so as to minimize the statistical errors; (3) in addition to optimizing the links between simulations, it also allows multiple overlaps of probability distributions for obtaining better estimates of the free-energy differences. By recasting the Ferrenberg–Swendsen Multiple Histogram equations in a form suitable for molecular mechanics type Hamiltonians, we have demonstrated the feasibility and robustness of this method by applying it to a test problem of the generation of the Potential of Mean Force profile of the pseudorotation phase angle of the sugar ring in deoxyadenosine. © 1992 by John Wiley & Sons, Inc.     

Non-aqueous cerimetric determination of thioureas

Ammonium hexanitratocerate (in acetonitrile) solution has been used as an oxidimetric reagent for the visual and potentiometric determination of thiourea and its alkyl derivatives in acetonitrile medium. The thioureas are oxidized to their corresponding disulphides. The method is simple, accurate, reliable and widely applicable.     

Supramolecular peptide helix from a novel double turn forming peptide containing a β-amino acid

A single-crystal X-ray diffraction study of the terminally protected tetrapeptide Boc-β-Ala-Aib-Leu-Aib-OMe 1 (Aib: α-aminoisobutyric acid; β-Ala: β-Alanine) reveals that it adopts a new type of double turn structure which self-associates to form a unique supramolecular helix through intermolecular hydrogen bonds. Scanning electron microscopic studies show that peptide 1 exhibits amyloid-like fibrillar morphology in the solid state.