Structures of the BrF(4)(+) and IF(4)(+) cations

The large discrepancies between the calculated and observed structures for BrF(4)(+) and IF(4)(+) (Christe, K. O.; Zhang, X.; Sheehy, J. A.; Bau, R. J. Am. Chem. Soc. 2001, 123, 6338) prompted a redetermination of the crystal structures of BrF(4)(+)Sb(2)F(11)(-) (monoclinic, P2(1)/c, a = 5.2289(6) A, b = 14.510(2) A, c = 14.194(2) A, beta = 90.280(1) degrees, Z = 4) and IF(4)(+)SbF(6)(-) (orthorhombic, Ibca, a = 8.2702(9) A, b = 8.3115(9) A, c = 20.607(2) A, Z = 8). It is shown that for BrF(4)(+), the large differences were mainly due to large errors in the original experimental data. For IF(4)(+)SbF(6)(-), the geometry previously reported for IF(4)(+) was reasonably close to that found in this study despite a very large R-factor of 0.15 and a refinement in an incorrect space group. The general agreement between the calculated and the redetermined geometries of BrF(4)(+) and IF(4)(+) is excellent, except for the preferential compression of one bond angle in each ion due to the influence of interionic fluorine bridges. In BrF(4)(+), the fluorine bridges are equatorial and compress this angle. In IF(4)(+), the nature of the fluorine bridges depends on the counterion, and either the axial (in IF(4)(+)SbF(6)(-)) or the equatorial (in IF(4)(+)Sb(2)F(11)(-)) bond angle is preferentially compressed. Therefore, the geometries of the free ions are best described by the theoretical calculations.     

X-ray crystal and molecular structure of upper rim monoformylated calix[4]arene system

Selective formylation under controlled conditions leads to the formation of a monoformylated compound 11-formyl-25,27-bis(ethoxycarbonylmethoxy)-calix[4]arene (1). The spectroscopic results indicated that the calix[4]arene is present in a cone conformation. The crystal and molecular structure of (1) has been determined by X-ray diffraction methods. The crystal data are monoclinic, space group P2 ₁/c, M= 624.66, a= 10.341(1), b=15.176(1), c= 20.121(1) Å, = 91.90°(1), V= 3156.0(4) ų, Z= 4, D _c = 1.315 g cm^–3. The structure confirms the cone conformation for the molecule in the solid state as well.     

Design,synthesis, in silico and in vitro evaluation of novel diphenyl ether derivatives as potential antitubercular agents

Molecular Diversity - Diphenyl ether derivatives inhibit mycobacterial cell wall synthesis by inhibiting an enzyme, enoyl-acyl carrier protein reductase (InhA), which catalyses the last step in the...     

Solution conformation of d(C(4)ACAC(4)TGT)(2); an intramolecularly folded i-motif from the insulin minisatellite

A 28-mer sequence taken from the insulin minisatellite is shown, through NMR and UV thermal melting studies, to form an intramolecular i-motif with two ACA and one TGT loop that persists to near neutral pH and room temperature.     

Single-Pot Synthesis of Spiroannulated Dihydrofurans by Iodine–Ammonium Acetate–Mediated Reaction of Dimedone with Aldehydes

Iodine–ammonium acetate–mediated annealation of dimedone with aldehydes led to facile formation of spirodihydrofuran in good yields through tandem Knoevenagel–Michael iodonation and cyclodehydroiodonation reactions in a single pot.     

Benign methodology and improved synthesis of 5-(2-chloroquinolin-3-yl)-3-phenyl-4,5-dihydroisoxazoline using acetic acid aqueous solution under ultrasound irradiation

In the present paper, we have executed the synthesis of substituted 5-(2-chloroquinolin-3-yl)-3-phenyl-4,5-dihydroisoxazolines via the reactions of substituted 3-(2-chloroquinolin-3-yl)-1-phenylprop-2-en-1-ones with hydroxylamine hydrochloride and sodium acetate in aqueous acetic acid solution in 72-90% yields at room temperature under ultrasound irradiation. This method provides several advantages such as operational simplicity, higher yield, safety and environment friendly protocol. The resulting substituted isoxazolines were characterized on the basis of (1)H NMR, (13)C NMR, IR, elemental analysis, and mass spectral data.     

Determination of aromatic primary amines at microg l(-1) level in environmental waters by gas chromatography-mass spectrometry involving N-allyl-n'-arylthiourea formation and their on-line pyrolysis to aryl isothiocyanates

Derivatization of aromatic primary amines to N-allyl-N'-arylthioureas by reaction with allyl isothiocyanate and GC-MS of the derivatives, when pyrolysis to aryl isothiocyanates occurs in the heated injector, has been used to determine aromatic amines in the range 0.5-50 microg l(-1) with a correlation coefficient, r, in the range 0.9902-0.9992. The limit of detection ranged 8 to 30 ng l(-1) when 60 ml of sample were preconcentrated, after derivatization, on a styrene-divinylbenzene copolymer sorbent. The pyrolytic cleavage of sym- and unsym-diaryl or alkyl-/arylthioureas has been rationalized. The chromatography of isothiocyanates is much superior to that of aryl amines and the specific mass fragmentation permits positive identification of amines. The method has been applied to spiked drinking water, groundwater and river water samples, when the recovery ranged from 84 to 109% with RSD of 5-9%, and to detect aromatic amines formed by reductive cleavage of azo dyes in effluents when the recovery of amine was in the range 81-95% with RSD 8-15%. The method is not applicable to nitroanilines.     

Catalytic dehydrocoupling of thienyl/furyl-substituted carbosilanes – Synthesis and characterization of functional poly(hydrosilane)s [RMe2Si(CH2)xSiH]n, (R = 2-Th, 4-Me-2-Th, 2-Fu, 5-Me-2-Fu; x = 2 and 3)

The carbosilanes RMe₂Si(CH₂)_xSiH₃, [R = 2-Th (1a, 2a), 4-Me-2-Th (3a, 4a), 2-Fu (5a, 6a), 5-Me-2-Fu (7a, 8a); x = 2 and 3], with primary SiH₃ end groups undergo a facile dehydropolymerization under ambient conditions (50 °C, 48 h) in presence of Cp₂TiCl₂/2.2 n-BuLi catalyst to afford the corresponding poly(hydrosilane)s 1–8 bearing carbosilyl side chains appended with thienyl/furyl groups. These have been characterized by GPC, IR, multinuclear (¹H, ¹³C{¹H}, ²⁹Si{¹H}) NMR, UV and PL spectral studies.     

Near-UV induced interstrand cross-links in anthraquinone-DNA duplexes

Anthraquinone (AQ) has been extensively used as a photosensitizer to study charge transfer in DNA. Near-UV photolysis of AQ induces electron abstraction in oligonucleotides leading to AQ radical anions and base radical cations. In general, this reaction is followed by the transport of base radical cations to sites of low oxidation potential, that is, GG, and conversion of G radical cations to DNA breaks. Here, we show that AQ also produces interstrand cross-links in DNA duplexes. About half of the cross-links collapse to single strands in hot piperidine treatment. The structure of stable interstrand cross-links was deduced by MS, NMR, and sequence substitution. The cross-links consist of a covalent link between the methyl group of T on one strand with either C6 or C7 of AQ on the other strand. The formation of interstrand cross-links decreased in O2 compared to deoxygenated solutions. In the presence of O2, the yield of breaks at GG doublets was 10-fold greater than that of cross-links for end tethered AQ, while cross-links exceeded breaks for centrally located AQ. The formation of stable cross-links can be explained by initial charge transfer from T to excited AQ, deprotonation of T radical cations, and condensation of the latter species with AQ radicals. These studies reveal a novel pathway of damage in the photolysis of AQ-DNA duplexes.     

Microscopic examination of the 2,300-year-old excavated steel plowshare from northern India

In the present investigation, X-ray diffractometer, optical microscope, and scanning electron microscope were used to analyze the plowshare excavated from Ganwaria, UP, India. The main objective of the investigation was to determine the type of alloy, analysis of slag inclusion, and corrosion behavior. X-ray diffraction analysis showed the presence of α-iron. Microstructure consists of ferrite and pearlite grains; ferrite phase was soft in comparison to the pearlite. Optical micrograph at lower magnification revealed slag inclusions aligned in a specific direction, which indicates that the forge welding technique was used in the manufacturing of the object. The microstructural examination revealed that the object was manufactured from carbon steel. Entrapped slag inclusions were observed by scanning electron microscope and X-ray mapping, and slags were identified as SiO₂ and MgO. Goethite and lepidocrocite corrosion compound were found on the surface of the object.