New Routes to a Series of σ‐Borane/Borate Complexes of Molybdenum and Ruthenium

A series of agostic σ‐borane/borate complexes have been synthesized and structurally characterized from simple borane adducts. A room‐temperature reaction of [Cp*Mo(CO)₃Me], 1 with Li[BH₃(EPh)] (Cp*=pentamethylcyclopentadienyl, E=S, Se, Te) yielded hydroborate complexes [Cp*Mo(CO)₂(μ‐H)BH₂EPh] in good yields. With 2‐mercapto‐benzothiazole, an N,S‐carbene‐anchored σ‐borate complex [Cp*Mo(CO)₂BH₃(1‐benzothiazol‐2‐ylidene)] ( 5 ) was isolated. Further, a transmetalation of the B‐agostic ruthenium complex [Cp*Ru(μ‐H)BHL₂] ( 6 , L=C₇H₄NS₂) with [Mn₂(CO)₁₀] affords a new B‐agostic complex, [Mn(CO)₃(μ‐H)BHL₂] ( 7 ) with the same structural motif in which the central metal is replaced by an isolobal and isoelectronic [Mn(CO)₃] unit. Natural‐bond‐orbital analyses of 5–7 indicate significant delocalization of the electron density from the filled σ_B?H orbital to the vacant metal orbital.     

Prevalence of eNOS Glu298Asp polymorphism in healthy volunteers from a region of Northern India

OBJECTIVE: Endothelial nitric oxide synthase (eNOS) Glu298Asp polymorphisms are under extensive study worldwide due to their suggested role in cardiovascular disorders. This polymorphism had gained more attention since several reports suggest its association with hypertension and coronary artery disease (CAD). Asian Indians are highly susceptible to ischemic heart dis eases. We determined the prevalence of eNOS Glu298 Asp polymorphism in 139 healthy volunteers from Delhi and the surrounding areas. The subjects were recruited from those who willingly participated in this study in response to a publicized call and a standard questionnaire. Male to female ratio was 2.7:1 due to the larger number of male participants in this investigation. This, however, does not represent normal male to female distribution in the area. Despite the male bias, this investigation was justified. The prevalence of CAD in males is about 3 times higher in this region and no data had so far been available on the distribution of this polymorphism from India. METHOD: The eNOS Glu298Asp polymorphism was studied by PCR-RFLP. RESULTS: Distribution of genotype GG, GT and TT in the study subjects was found to be 71.22, 28.06 and 0.72%, respectively, and allele frequency was G,0.853;T,0.147. CONCLUSION: T allele had been described as susceptibility allele for CAD in several population studies. The frequency of the T allele was found to be two times higher in our subjects than that reported for Japanese and Korean populations. This study does not provide any direct evidence for eNOS gene disease associations but is the first report on the prevalence of eNOS Glu298Asp gene polymorphism in Indian subjects. Whether the observed pattern of eNOS Glu298Asp polymorphism contributes to the greater susceptibility of Asian Indians to CAD as compared to the other population groups, needs to be investigated.     

Vibrational spectra of melamine diborate,C3N6H62H3BO3

IR and Raman spectra of melamine diborate have been recorded and analysed. Band assignments are given based on the vibrations of melamine and boric acid molecules. Three sets of frequencies observed for the N-H stretching mode region is ascribed to different types of hydrogen bonds in the amino groups of the triazine ring. Due to the lower symmetry of the melamine and boric acid molecules in the crystal, activation of inactive modes and lifting of the degeneracy of certain vibrational modes are observed. Lower symmetry of the melamine molecule in the crystal has resulted in the decrease of intensity of the Raman active melamine band around 1490 cm(-1). All the internal modes of boric acid molecule were identified. All the ring breathing modes of melamine molecule show frequency shift towards the high wavenumber side. In other words, hydrogen bonding affects the ring breathing modes of melamine.     

Conduction in magnesium phthalocyanine thin films with aluminium electrodes

The various electrical properties and the nature of conduction mechanisms of magnesium phthalocyanine thin film devices with top and bottom aluminium electrodes have been investigated. The conduction mechanism was identified as injection limited essentially due to the electrode material. Even with the same electrode materials, the device showed asymmetric conduction behavior in the forward and reverse bias. In general the conduction was interpreted as a Schottky emission with barrier height Φ_s=1.07 eV for the forward bias and Φ_s=1.09 eV in the reverse bias. The effect of oxygen on the conductivity of the device has also been investigated. In the oxygen doped samples the conductivity is decreased which may be attributed to an interfacial layer between the electrode and the organic layer. Further in the oxygen doped sample while a Schottky emission is observed at lower voltages Poole-Frenkel conductivity was identified in the higher voltage region.     

Compton profile of tantalum

The Compton profile of tantalum (Ta) has been measured using IGP type coaxial photon detector. The target atoms were excited by means of 59.54 keV γ-rays from Am-241. The measurements were carried out on a high purity thin elemental foil. The data were recoreded in a 4 K multichannel analyzer. These data duly corrected for various effects are presented and compared with theoretical and measured values. Best agreement with experiment is found for the 5d³6s² electron configuration     

meso -Tetrathienylporphyrins: Steady-state emission and structural properties

meso-Tetra (2′- and 3′-thienyl)porphyrins and their Zn(II)-complexes were examined by steady-state fluorescence measurements. These molecules exhibit significant bathochromic shift in their emission bands with decreased quantum yields relative to their correspondingmeso-tetraphenylporphyrin derivatives. The crystal structure of 5,10,15,20-tetrakis(3′-thienyl)porphinato zinc(II) shows planar and nonplanar stereochemical features of the macrocycle. One of the macrocycle shows nearly planar while the other exhibited predominantly saddle-shaped geometry. The extent of displacement of the Β-pyrrole carbons in the nonplanar (saddle) conformation is as high as ± 0·422 ?.     

Cooperative and FRET‐Assisted Brightness Enhancement in Oligo(phenylene ethynylene): Quantum Dot Organic–Inorganic Nanohybrids

Herein, we combine the ideas of concerted emission from fluorophore ensembles and its further amplification through FRET in an organic–inorganic hybrid approach. Spherical and highly fluorescent organic nanoparticles (FONPs, Φ_f=0.38), prepared by the self‐assembly of oligo(phenylene ethynylene) (OPE) molecules, were selected as a potential donor material. This organic core was then decorated with a shell of fluorescent CdSe/ZnS core–shell quantum dots (QDs; <d>?5.5 nm, Φ_f=0.27) with the aid of a bifunctional ligand, mercaptopropionic acid. Its high extinction coefficient (?≈4.1×10⁵ m ^?1 cm^?1) and good spectral match with the emission of the FONPs (J(λ)≈4.08×10¹⁶ m ^?1 cm^?1 nm⁴) made them a better acceptor candidate to constitute an efficient FRET pair (Φ_FRET=0.8). As a result, the QD fluorescence intensity was enhanced by more than twofold. The fundamental calculations carried out indicated an improvement in all the FRET parameters as the number of QDs around the FONPs was increased. This, together with the localization of multiple QDs in a nanometric dimension (volume≈1.8×10⁶ nm³), gave highly bright reddish luminescent hybrid particles as visualized under a fluorescence microscope.     

Adamantoid Scaffolds for Multiple Cargo Loading and Cellular Delivery as β-Cyclodextrin Inclusion Complexes

There is huge demand for developing guests that bind β-CD and can conjugate multiple cargos for cellular delivery. We synthesized trioxaadamantane derivatives, which can conjugate up to three cargos per guest. ¹H NMR titration and isothermal titration calorimetry revealed these guests form 1 : 1 inclusion complexes with β-CD with association constants in the order of 10³ M⁻¹. Co-crystallization of β-CD with guests yielded crystals of their 1 : 1 inclusion complexes as determined by single-crystal X-ray diffraction. In all cases, trioxaadamantane core is buried within the hydrophobic cavity of β-CD and three hydroxyl groups are exposed outside. We established biocompatibility using representative candidate G4 and its inclusion complex with β-CD (β-CD⊂ G4 ), by MTT assay using HeLa cells. We incubated HeLa cells with rhodamine-conjugated G4 and established cellular cargo delivery using confocal laser scanning microscopy (CLSM) and fluorescence-activated cell sorting (FACS) analysis. For functional assay, we incubated HeLa cells with β-CD-inclusion complexes of G4 -derived prodrugs G6 and G7 , containing one and three units of the antitumor drug (S)-(+)-camptothecin, respectively. Cells incubated with β-CD⊂ G7 displayed the highest internalization and uniform distribution of camptothecin. β-CD⊂ G7 showed higher cytotoxicity than G7 , camptothecin, G6 and β-CD⊂ G6 , affirming the efficiency of adamantoid derivatives in high-density loading and cargo delivery.