Structure, reactivity and aromaticity of acenes and their BN analogues: a density functional and electrostatic investigation

Density functional calculations have been carried out on a series of linearly annelated acenes and their BN analogues. Even though borazine shows aromatic and reactivity behavior parallel with that of benzene, its condensed derivatives show patterns different from those of their hydrocarbon analogues. Nucleus independent chemical shift (NICS) values in acenes suggest that the aromaticity of the inner rings is more than that of benzene, whereas in BN-acenes there is no substantial change in the aromaticity of the individual rings. Molecular electrostatic potential (MESP) is employed to obtain further insights into the bonding and reactivity trends for these systems. The MESP topography patterns of acenes and BN-acenes are substantially different, with BN-acenes showing more localized pi electron features compared to those of acenes. The MESP values at the critical points (CPs) indicate overall lowering of aromaticity in these annelated systems. However, this change is gradual among the BN-acenes.     

Synthesis of phthalide derivatives using nickel-catalyzed cyclization of o-haloesters with aldehydes

The reaction of o-bromobenzoate (1 b) with benzaldehyde (2 a) in the presence of [NiBr(2)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane) and zinc powder in THF (24 hours, reflux temperature), afforded 3-phenyl-3H-isobenzofuran-1-one (3 a) in an 86 % yield. Similarly, o-iodobenzoate reacts with 2 a to give 3 a, but in a lower yield (50 %). A series of substituted aromatic and aliphatic aldehydes (2 b, 4-MeC(6)H(4)CHO; 2 c, 4-MeOC(6)H(4)CHO; 2 d, 3-MeOC(6)H(4)CHO; 2 e, 2-MeOC(6)H(4)CHO; 2 f, 4-CNC(6)H(4)CHO; 2 g, 4-(Me)(3)CC(6)H(4)CHO; 2 h, 4-C(6)H(5)C(6)H(4)CHO; 2 i, 4-ClC(6)H(4)CHO; 2 j, 4-CF(3)C(6)H(4)CHO; 2 k, CH(3)(CH(2))(5)CHO; 2 l, CH(3)(CH(2))(2)CHO) also underwent cyclization with o-bromobenzoate (1 b) producing the corresponding phthalide derivatives in moderate to excellent yields and with high chemoselectivity. Like 1 b, methyl 2-bromo-4,5-dimethoxybenzoate (1 c) reacts with tolualdehyde (2 b) to give the corresponding substituted phthalide 3 m in a 71 % yield. The methodology can be further applied to the synthesis of six-membered lactones. The reaction of methyl 2-(2-bromophenyl)acetate (1 d) with benzaldehyde under similar reaction conditions afforded six-membered lactone 3 o in a 68 % yield. A possible catalytic mechanism for this cyclization is also proposed.     

Chloride, -Hydride and -Borohydride Derivatives of Difluorenyl Thallium(III)

Chloride¹), borohydrides²) and hydrides³) of dicyclopentadienyl thallium (III) and diindenyl thallium (III) have already been reported. The present communication deals with a study on the preparation and characterization of difluorenyl thallium (III) chloride, -hydride and -borohydride.     

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.     

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.     

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.     

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.     

Physico-mechanical and free volume behaviour of guar gum filled polyurethane/polyacrylonitrile biodegradable composites

A series of different weight ratios of guar gum viz. 5, 10, 20 and 30 were incorporated into polyurethane/polyacrylonitrile (PU/PAN, 50/50) semi interpenetrating polymer networks (SIPNs) using polyethylene glycol-400, 4,4′-diphenyl methane diisocyanate, acrylonitrile, benzoyl peroxide and new metallic catalyst. The obtained polymer composites were subjected to biodegradation studies using specific fungi Aspergillus niger. The composites are characterized for physico-mechanical properties like density and tensile behaviour of the specimens before and after biodegradation. The positron annihilation lifetime spectroscopy (PALS) was used to monitor the content of free volume before and after biodegradation. The extent of degradation was examined by change in tensile behaviour and surface morphology. The influences of fungi on mechanical and morphological behaviour of filled IPNs are found to be interesting. The free volume changes in the composite systems correlates well with the mechanical properties.