Viscoelastic characterization of selected foods over an extended frequency range

Three disparate food systems (gummy candy, Mozzarella cheese, and cooked ham) were characterized for their viscoelastic behavior under isothermal conditions over an extended frequency range of 10⁻³ to 10⁴ Hz using broadband viscoelastic spectroscopy (BVS). The materials were tested for any stress-induced fluid flow. However, no evidence of fluid flow was found under the tested frequency range. Validity of time–temperature superposition for the selected materials was also tested and compared with data from BVS.     

On the power of white pebbles

We construct a family (G _p |p) of directed acyclic graphs such that any black pebble strategy forG _p requiresp ² pebbles whereas 3p+1 pebbles are sufficient when white pebbles are allowed.Supported by the National Science Foundation under contract no. DCR-8407256 and by the office of Naval Research under contract no. N0014-80-0517.     

Quantum chaology: The photoeffect and beyond

I will show how aspects of quantum chaology are relevant even in a seemingly well understood quantum phenomenon like the photoelectric effect. This example together with recent experiments in atom optics are used to define and discuss the larger questions, recent progress made by us in resolving some of these issues and future directions.     

Synthesis, spectral and thermal studies of some transition metal mixed ligand complexes: modeling of equilibrium composition and biological activity

Several mixed ligand Ni(II), Cu(II) and Zn(II) complexes of 2-amino-3-hydroxypyridine (AHP) and imidazoles viz., imidazole (him), benzimidazole (bim), histamine (hist) and L-histidine (his) have been synthesized and characterized by elemental and spectral (vibrational, electronic, 1H NMR and EPR) data as well as by magnetic moment values. On the basis of elemental analysis and molar conductance values, all the complexes can be formulated as [MAB]Cl except histidine complexes as MAB. Thermogravimetric studies reveal the presence of coordinated water molecules in most of the complexes. From the magnetic measurements and electronic spectral data, octahedral structure was proposed for Ni(II) and Cu(II)-AHP-his, tetrahedral for Cu(II)-AHP-him/bim/hist, but square planar for the Cu(II)-AHP complex. The g∥/A∥ calculated supports tetrahedral environment around the Cu(II) in Cu(II)-AHP-him/bim/hist and distorted octahedral for Cu(II)-AHP-his complexes. The morphology of the reported metal complexes was investigated by scanning electron micrographs (SEM). The potentiometric study has been performed in aqueous solution at 37 °C and I=0.15 mol dm(-3) NaClO4. MABH, MAB and MAB2 species has been identified in the present systems. Proton dissociation constants of AHP and stability constants of metal complexes were determined using MINIQUAD-75. The most probable structure of the mixed ligand species is discussed based upon their stability constants. The in vitro biological activity of the complexes was tested against the Gram positive and Gram negative bacteria, fungus and yeast. The oxidative DNA cleavage studies of the complexes were performed using gel electrophoresis method. Cu(II) complexes have been found to promote DNA cleavage in presence of biological reductant such as ascorbate and oxidant like hydrogen peroxide.     

Conformational energy map for a pair of peptide units using the bond polarisability method

A method recently developed for the calculation of intramolecular nonbonded interactions based on experimental bond polarisabilities and atomic charges and transition π-charges obtained from MO calculations has been applied to the alanyl dipeptide. The potential energy contours in the ?, ψ plane obtained by this method compare favourably with those derived from the frequency of occurrence of conformations in globular proteins. An analysis of the various components of the nonbonded interaction energy indicates that the fairly frequent occurrence of conformations around ? = ?80°, ψ=0° is presumably due to a favourable interaction of the π-polarisation.     

Structures of mixed ligand copper(II) complexes coordinating through S,O and N. E.p.r. studies

Summary The formation of near square planar mixed ligand Cu^II complexes with diethyldithiocarbamate (dtc) as one of the ligands and 8-hydroxyquinolinate (Hy) or salicylaldehydate (Sal) as the second ligand by exchange reactions, has been detected by e.p.r. spectroscopy. The concentrations of the mixed ligand complexes in the reaction mixtures are small compared to those of the reactants. Six different tests were used to identify the m₁=3/2,⁶³Cu hyperfine transition of the near square planar complexes, based upon the relative concentrations of the different Cu^II species in the reaction mixture, ligand hyperfine structures, the minium linewidths observed in a temperature dependent study and the isotropic g₀ estimated from the e.p.r. spectra in solution.