Fluorescent probe and NMR studies of the aggregation of bile salts in aqueous solution

The binding of the fluorescent probes 1-anilino-8-naphthalene sulfonate and dansyl cadaverine to the sodium salts of cholic, deoxycholic and dehydrocholic acids has been investigated. Enhanced probe solubilisation accompanies aggregation. Monitoring of fluorescence intensities as a function of bile salt concentration permits the detection of primary micelle formation, as well as secondary association. The transition concentrations obtained by fluorescence are in good agreement with values determined for the critical micelle concentrations, by other methods. Differences in the behaviour of cholate and deoxycholate have been noted. Fluorescence polarisation studies of 1,6-diphenyl-1,3,5-hexatriene solubilised in bile salt micelles suggest a higher microviscosity for the interior of the deoxycholate micelle as compared to cholate. 1H NMR studies of deoxycholate over the range 1–100 mg/ml suggest that micelle formation leads to a greater immobilisation of the C18 and C19 methyl groups as compared to the C21 methyl group. Well resolved 13C resonances are observed for all three steroids even at high concentration. Both fluorescence and NMR studies confirm that dehydrocholate does not aggregate.

Conformational studies of phynyl and isoxazolyl penicillins

Conformational energy calculations have been carried out on a few representative b-lactamase resistant and susceptible, phenyl and isoxazolyl penicillins. These studies, in agreement with those of earlier workers, show that the 6b-side chains of resistants penicillins are highly rigid as compared to those of susceptible penicillins. The present studies also suggest that the degree of resistant to b-lactamases depends not only on the rigidity of the side chain but also on the nature and orientation of the substituent, beyond the amide carbonyl group in the side chain. The overall shapes of these penicillins correlate well with their antibacterial properties.

Scanning electron microscopy studies of wear in LM13 and LM13-graphite particulate composite

Examination of the structure of worn surfaces has shown that the wear of LM13 and LM13-graphite particulate composite is controlled by the nature and extent of subsurface deformation. The addition of graphite influences the wear characteristics by affecting the plastically deformed zone. The possible mechanisms of wear are discussed.

Dielectric studies of As-Se glasses

Dielectric constants and loss tangents of As-Se glasses have been measured between 300 K and the respective glass transition temperatures and between 1 kHz and 20 kHz. The variation of dielectric constants has been interpreted in terms of both heteropolarity of bonds and average bond energies employing a chemically ordered network model. Various contributions to total molar polarizations have been estimated. Rapid rise of loss tangent in the vicinity of glass transitions has been interpreted in terms of rapid increase; of d.c. conductivity.

Structural Studies of Analgesics and Their Interactions. VIII.* Rotational Isomerism and Disorder in the Crystal Structure of Meelofenamie Acid

Meclofenamic acid, C I4HIICI2NO2, probably the most potent among analgesic fenamates, crystallizes in the triclinic space group P1, with a = 8.569 (5), b = 8.954(8), c -- 9.371 (4) A, ct = 103.0 (2), fl -- 103.5 (2), y = 92.4 (2) ° , Z = 2, D m = 1.43 (4), D c = 1.41 Mg m -3. The structure was solved by direct methods and refined to R = 0.135 for 1062 observed reflections. The anthranilic acid moiety in the molecule is nearly planar and is nearly perpendicular to the 2,6-dichloro-3-methylphenyl group. The molecules, which exist as hydrogen-bonded dimers, have an internal hydrogen bond involving the imino and the carboxyl groups. The methyl group is disordered and occupies two positions with unequal occupancies. The disorder can be satisfactorily explained in terms of the rotational isomerism of the 2,6-dichloro-3-methylphenyl group about the bond which connects it to the anthranilic acid moiety and the observed occupancies on the basis of packing considerations.

Spectroscopic studies of micro-explosions

NONEL tube finds vast applications in civil and military because of its safe and confined explosion technique. Spectroscopic and chemical analysis of a NONEL tube with an uniform mixture of HMX and Al is reported here. Peak temperature obtained at the open end of the NONEL tube due to the detonation of the explosive has been calculated using Planck’s radiation law. The products of the chemical reaction taking place due to the ignition of HMX + Al are characterized using FTIR spectroscopy.

Studies of phosphazenes. 12. Reactions of N4P4Cl8 with dibenzylamine- isolation of an unusual "bicyclic" phosphazene, N4P4[N(CH2Ph)2]6(NCH2Ph)

Octachlorocyclotetraphosphazene, N4P4CIa, reacts with dibenzylamine to give the chloro(dibenzy1amino) derivatives, N4P,C18,[N(CH2Ph)2],,, n = 1, 2 (two isomers), and 4 (three isomers). Nongeminal structures have been assigned to these compounds on the basis of ‘H and jlP NMR spectra. The presence of at least two tris(dibenzylamin0) derivatives in some reaction mixtures is also inferred from NMR spectra. Steric effects become important at the tetrakis stage of chlorine replacement, and further substitution by dibenzylamine to give monocyclic tetrameric derivatives does not occur. A “bicyclic” phosphazene, N4P4[N(CH2Ph)2]6(NCHzPh)is, obtained from the reaction of N4P4Claw ith an excess of dibenzylamine in boiling methyl cyanide. The formation of this derivative and its spectroscopic data are discussed.

Optical and magnetic resonance studies of the interaction of metallo tetraphenylporphyrins with nitrobenzofuroxan

Metallo tetraphenylporphyrins form I : I molecular complexes with 4,6-dinitrobenzofuroxan. The molecular association is described in terms of T-n. interaction with porphyrins functioning as donors. The association constants and thermodynamic parameters have been evaluated using optical absorption and 'H nmr spectral methods. Based on the binding constants, the donor ability of various metalloporphyrins can be arranged in the following order: Pd(I1) > Co(I1) > Cu(I1) > Ni(I1) - VO(1V) - 2H > Zn(l1). Electron paramagnetic resonance studies of the complexes reveal that the IT-complexation results in changes in the electronic structure of the central metal ions which are reflected in the changes in the M-N 5 bonding. The dipolar contribution to the acceptor proton chemical shifts in the CoTPP complex has been partitioned from ring current contributions using the shifts observed in the ZnTPP complex. The shifts, along with the line broadening ratios observed for the CoTPP complex, are used to arrive at the possible solution structures of the complexes.

Electron Spectroscopic Studies of Oxygen and Carbon Dioxide Adsorbed on Metal Surfaces

Adsorption of oxygen on Ni, Cu, Pd, Ag, and Au surfaces has been investigated by employing UV and X-ray photoelectron spectrscopy as well as electron energy loss spectroscopy (EELS). Molecularly chemisorbed (singlet) oxygen is found on Ni, Cu, Ag, and Au surfaces showing features such as stabilization of the rB* orbital, destabilization of the .nu orbital, higher O(1s) binding energy than the atomic species, and a band 2-3 eV below the Fermi level due to metal d-O(2p)u* interaction. 0-0 and metal-oxygen stretching frequencies have been observed in EELS. Physical adsorption of O2 is found to occur on Pd and Ni surfaces, only at high exposures in the latter case. Physical adsorption and multilayer condensation of CO, on metal surfaces are distinguished by characteristic relaxation shifts in UPS as well as O(1s) binding energies. Adsorption of CO on a Ni surface covered with presorbed atomic oxygen gives rise to C02.

Structural studies of analgesics and their interactions. II. The crystal structure of a 1:1 complex between antipyrine and salicyclic acid (salipyrine)

The complex crystallizes in the space group P21/c with four formula units in a unit cell of dimensions a= 12.747, b= 7.416, c= 17.894 A and/3= 90.2 °. The structure has been solved by the symbolic addition procedure using three-dimensional photographic data and refined to an R value of 0.079 for 2019 observed reflexions. The pyramidal nature of the two hetero nitrogen atoms in the antipyrine molecule is inter:nediate between that observed in free antipyrine and in some of its metal complexes. The molecule is more polar than that in crystals of free antipyrine but less so compared with that in metal complexes. In the salicylic acid molecule, the hydroxyl group forms an internal hydrogen bond with one of the oxygen atoms in the carboxyl group. The association between the salicylic acid and the antipyrine molecules is achieved through an intermolecular hydrogen bond with the other carboxyl oxygen atom in the salicylic acid molecule as the proton donor and the carboxyl oxygen atom of the antipyrine molecule as the acceptor.

Mossbauer effect studies of the thermal decomposition of iron(II) oxalate in hydrogen

Mössbauer-effect and X-ray studies were carried out on the product samples of the thermogravimetric analysis (TGA) and of the isothermal decomposition of iron(II) oxalate in flowing H2. Two types of sample configurations were employed for isothermal studies between 280 to 420°C for various periods of heating. Low temperature Mossbauer measurements at liquid nitrogen temperature were carried out to examine the superparamagnetic (SPM) contributions. From the spectra of samples decomposed at 340°C, in vertical experiments, the percentage SPM and percentage ferromagnetic (FM) area of Fe3O4 were estimated and an average size (˜167Å) for Fe3O4 was derived. Mossbauer measurements (at high temperatures) were carried out on Fe3C formed in horizontal experiments, for two samples decomposed at ˜320°C for 1 hr and 2 hr. An estimate of SPM and FM Fe3C was obtained by calculating KV, the anisotropy energy for the Fe3C in these two samples and values of 5.07 × 10−16 and 7.02 × 10−16 erg/sec, respectively, were obtained.

Dielectric and Electron Spin Resonance Spectroscopic Studies of Glassy Crystalline States of Organic Compounds

Dielectric studies of the glassy crystalline states of cyclohexanol, cyclohexanone, and camphor obtained by upercooling the plastic crystalline phase demonstrate the presence of characteristic a- and p-relaxations. The parameters of the a-relaxation fit the Vogel-Tammann-Fulcher (VTF) equation. ESR spin-probe studies of the glassy crystalline phase of cyclohexanol show that there is a marked decrease in the correlation time above the glasslike transition temperature. The present studies suggest the similarity between glassy crystals having long-range orientational disorder and glasses which are known to betra nslationally disordered.

Structural studies of analgesics and their interactions. III. The crystal and molecular structure of amidopyrine

Amidopyrine (1-phenyl-2,3-dimethyl-4-dimethylaminopyrazolone), C13HzvN30, a dimethylamino derivative of antipyrine and an important analgesic and antipyretic agent, crystallizes in the triclinic space group P1 with four molecules in a unit cell of dimensions a= 7.458 (5), b = 10.744 (5), c= 17.486 (15)/~,, e=98.6 (2),/~= 85.6 (3), y= 108-6 (2) . The structure was solved by direct methods and refined to an R value of 0.055 for 3706 photographically observed reflexions. The dimensions of the two crystallographically independent molecules are very nearly the same. The pyrazolone moiety in the molecule has dimensions comparable to those in antipyrine. Unlike antipyrine, the molecular dimensions of amidopyrine in the free state (the present structure) are close to those found in some of its hydrogenbonded complexes. Thus it appears that the presence of the dimethylamino group makes the molecule more resistant to changes in its dimensions resulting from molecular association. An attempt has also been made to correlate the polar nature of the pyrazolone moiety and the hybridization state of the hetero nitrogen atoms in antipyrine, amidopyrine and their complexes.