A simpler and greener protocol for the preparation of β-acetylamino ketones by a one-pot reaction of aryl aldehydes, enolisable ketones, acetyl chloride and acetonitrile in the presence of zeolite Hβ as a reusable catalyst

β-Acetylamino ketones have been obtained in a one-pot coupling of an aldehyde with an enolisable ketone, acetyl chloride and acetonitrile in the presence of zeolite Hβ as catalyst at room temperature (26-28 °C). The procedure has the advantages of mild workup, circumvention of high temperature and inert atmosphere. The catalyst was found to be recyclable.     

Conformational stability of helical peptides containing a thioamide linkage

[structure: see text] Thioxo peptide analogues of the alpha-helical peptide GCN4-p1 were synthesized and evaluated for helicity and oligomeric state. Sedimentation equilibrium and CD measurements indicate that the thioxo peptides fold into parallel alpha-helical coiled coil structures essentially identical to the native structure. This work marks the first incorporation of a thioamide linkage into the backbone of an alpha-helix and demonstrates that a thioamide linkage is compatible with positions within the helix as well as near the C-terminus.     

Spectrophotometric determination of mercury(II) as the ternary complex with rhodamine 6g and iodide

The formation of a pink-coloured product when rhodamine 6G is treated with tetraiodomercurate(II) is used to determine mercury (5–25 μg) in a final volume of 25 ml. The reaction occurs immediately over the pH range 1–7 and, when the system is stabilized with gelatin, the absorbance remains unchanged at 575 nm for at least 24 h. The few interfering ions can be masked by the addition of appropriate reagent solutions. The method is simple and reliable and provides a molar absorptivity of 7.0·10⁴ l mole^-1 cm^-1.     

Hydrophobicity dependence of oxidation of tetrapeptides of elastin sequences with Mn(III): Synthesis,characterization, kinetics,and mechanistic study

The analogues of elastin sequences, glycyl‐glycyl‐alanyl‐proline (GGAP), glycyl‐glycyl‐phenylalanyl‐proline (GGFP), and glycyl‐glycyl‐isoleucyl‐proline (GGIP) were synthesized by classical solution phase method and characterized. The kinetics of oxidation of these tetrapeptides (TETP) by Mn(III) has been studied in the presence of sulphate ions in acidic solution at 25°C. The reaction was followed spectrophotometrically at λ_max = 500 nm. A first‐order dependence of rate on both [Mn(III)] and [TETP] was observed. The rate is independent of the concentration of the reduction product, Mn(II), and hydrogen ions. The effects of varying the dielectric constant of the medium and addition of anions such as sulphate, chloride, or perchlorate were studied. Activation parameters have been evaluated using Arrhenius and Erying plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of TETP with Mn(III) in the rate‐limiting step is suggested. An apparent correlation was noted between the rate of oxidation and the hydrophobicity of these sequences, where increased hydrophobicity results in increased rate of oxidation. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 39–48, 2002     

Design and construction of an open multistranded beta-sheet polypeptide stabilized by a disulfide bridge

The design and characterization of an open eight-stranded beta-sheet in a synthetic, 2-fold symmetric 70-residue peptide is described. The design strategy involves the generation of a 35-residue four-stranded beta-sheet peptide in which successive hairpins are nucleated by appropriately positioned (D)Pro-Xxx sequences. Oxidative dimerization using a single Cys residue positioned at the center of the C-terminal strand results in a disulfide-bridged eight-stranded structure. Nuclear Overhauser effects firmly establish an eight-stranded beta-sheet in methanol. In water, the outer strands are frayed, but a well-defined four-stranded beta-sheet stabilized by a disulfide bridge and a hydrophobic cluster is determined from NMR data. Comparison of the precursor peptide with the disulfide-bridged dimer reveals considerable enhancement of beta-sheet content in the latter, suggesting that the disulfide cross-link is an effective strategy for the stabilization of beta-sheets.     

Recovery of americium from nitric acid solutions containing calcium by different co-precipitation methods

Recovery of americium from nitric acid solutions was studied by co-precipitation as hydroxide with various ions like calcium, ferric, nickel using sodium hydroxide and ammonium hydroxide. Studies were also carried out to recover americium using lanthanum fluoride and bismuth phosphate co-precipitation. All the methods are able to co-precipitate Am quantitatively. However, co-precipitation of Am with optimum concentration iron using ammonia is found to be better from nitric acid solutions containing large concentrations of calcium ions. Approximately 2 g of Am was recovered from 150 litres of solution batch wise using iron.     

Di-μ-hydroxy-bis(N,N,N′,N′-tetramethylenediamine)-copper(II) chloride [Cu(OH)·TMEDA]2Cl2: an efficient, practical catalyst for benzylation and allylation of amides

An efficient protocol for the benzylation or allylation of amides using the corresponding benzyl or allyl chlorides as electrophiles under basic conditions with commercially available 5 mol % of [Cu(OH)TMEDA]₂Cl₂ as catalyst was developed. Under these conditions, unprotected amino acids were benzylated without any racemization.     

Regio- and stereoselective transfer of p-toluenesulfonamido group from sulfur to carbon: preparation of aminoalcohol derivatives from allylalcohols

A novel methodology for the regio- and stereoselective synthesis of amino alcohol derivatives from allylalcohols/ethers via intramolecular nucleophilic participation by the sulfilimine moiety is disclosed. The sulfilimine moiety is stereospecifically transformed to a sulfinyl moiety with an inverted configuration. The reaction is general and affords highly functionalised products.     

Exchange interactions in some low-dimensional metal dithiolene complexes

Low-dimensional systems are formed by planar metal dithiolene complexes which stack as columnar structures in the solid state. Stronger interactions among units within a chain leads to highly anisotropic magnetic properties. The magnetic effects are a manifestation of exchange interaction,J and can be studied through detailedepr techniques in conjunction with magnetic susceptibility and x-ray crystal structure. A brief review of such studies carried out mostly in our laboratory is presented along with the relevant background materials.     

Some analytical applications of aromatic sulfonyl haloamines: Estimation of indigocarmine by chloramine-B,bromamine-T,and dibromamine-T

Sodium N-chlorobenzenesulfonamide (chloramine-B, CAB), sodium N-bromo-p-toluenesulfonamide (bromamine-T, BAT) and N,N′-dibromo-p-toluenesulfonamide (dibromamine-T, DBT) are employed as analytical reagents for estimating indigocarmine (IC) in solution. A four-electron stoichiometry is observed within 30 min in the following media: CAB, 0.1–1.0 N HCl or H₂SO₄ and pH 1 buffer; BAT, 0.01–0.10 N NaOH; DBT, glacial acetic acid. The back titration methods are fairly rapid, simple, and accurate. The product of oxidation, isatinsulfonate, was estimated by spectrophotometric measurements at 410 nm. The sulfonamides formed by reduction of the haloamines are detected by TLC and paper chromatography.