Electron donor-acceptor complex of ICl with diethyl ether - He I photoelectron spectroscopy and ab initio molecular orbital study

The He I photoelectron spectrum of the diethyl ether-ICl complex has been obtained. The oxygen orbitals are shifted to higher binding energies and that of ICl to lower binding energies owing to complex formation. Ab initio molecular orbital (MO) calculations of the complex molecule showed that the bonding is between the sigma-type lone pair of oxygen and the I atom and that the complex has C-2v symmetry. The binding energy of the complex is computed to be 8.06 kcal mol(-1) at the MP2/3-21G* level. The orbital energies obtained from the photoelectron spectra of the complex are compared and assigned with orbital energies obtained by MO calculations. Natural bond orbital analysis (NBO) shows that charge transfer is from the sigma-type oxygen lone pair to the iodine atom and the magnitude of charge transfer is 0.0744 e.

Lectin binding to complex carbohydrate at the interface: a study by resonance energy transfer

The binding affinity of the oligosaccharide moiety of a neutral glycosphingolipid, asialoGM1, towards Ricinus communis agglutinin (RCAI) was determined for the first time by fluorescence resonance energy transfer (RET). The asialoGM1 was incorporated into a phospholipid (DMPC) vesicle doped with dansylated DPPE and then titrated with an increasing amount of the galactose specific RCAI. The efficiency of RET was determined by a saturable increase in the quenching of 'donor' fluorescence, i.e. the 'trp' residue of RCAI, due to the energy transfer from the 'acceptor' dansyl group on the surface of the vesicle. The apparent binding constant was found to be in the range of 10(5)-10(6) M-1 at 27 degrees C.

Identification of the active-site peptide of 2,3-dihydroxybenzoic acid decarboxylase from Aspergillus oryzae

The non-oxidative decarboxylation of aromatic acids is a poorly understood reaction. The transformation of 2,3-dihydroxybenzoic acid to catechol in the fungal metabolism of indole is a prototype of such a reaction. 2,3-Dihydroxybenzoic acid decarboxylase (EC 4.1.1.46) which catalyzes this reaction was purified to homogeneity from anthranilate induced cultures of Aspergillus oryzae using affinity chromatography. The enzyme did not require cofactors like NAD(+), PLP, TPP or metal ions for its activity. There was no spectral evidence for the presence of enzyme bound cofactors. The preparation, which was adjudged homogeneous by the criteria of SDS-PAGE, sedimentation analysis and N-terminal analysis, was characterized for its physicochemical and kinetic parameters. The enzyme was inactivated by group-specific modifiers like diethyl pyrocarbonate (DEPC) and N-ethylmaleimide (NEM). The kinetics of inactivation by DEPC suggested the presence of a single class of essential histidine residues, the second order rate constant of inactivation for which was 12.5 M(-1) min(-1). A single class of cysteine residues was modified by NEM with a second order rate constant of 33 M(-1) min(-1). Substrate analogues protected the enzyme against inactivation by both DEPC and NEM, suggesting the Location of the essential histidine and cysteine to be at the active site of the enzyme. The incorporation of radiolabelled NEM in a differential labelling experiment was 0.73 mol per mol subunit confirming the presence of a single essential cysteine per active-site. Differentially labelled enzyme was enzymatically cleaved and the peptide bearing the label was purified and sequenced. The active-site peptide LLGLAETCK and the N-terminal sequence MLGKIALEEAFALPRFEEKT did not bear any similarity to sequences reported in the Swiss-Prot Protein Sequence Databank, a reflection probably of the unique primary structure of this novel enzyme. The sequences reported in this study will appear in the Swiss-Prot Protein Sequence Databank under the accession number P80402.

Interactions of 3' terminal and 5' terminal regions of physalis mottle virus genomic RNA with its replication complex

Physalis mottle virus (PhMV) belongs to the tymogroup of positive-strand RNA viruses with a genome size of 6 kb. Crude membrane preparations from PhMV-infected Nicotiana glutinosa plants catalyzed the synthesis of PhMV genomic RNA from endogenously bound template. Addition of exogenous genomic RNA enhanced the synthesis which was specifically inhibited by the addition of sense and antisense transcripts corresponding to 3' terminal 242 nucleotides as well as the 5' terminal 458 nucleotides of PhMV genomic RNA while yeast tRNA or ribosomal RNA failed to inhibit the synthesis. This specific inhibition suggested that the 5' and 3' non-coding regions of PhMV RNA might play an important role in viral replication.

Realtime kinetic analysis of antigen-antibody interaction using solid phase binding: Transformation of hCG-monoclonal antibody complex

Kinetic constants of MAb-hCG interactions have been determined using solid phase binding of I-125[hCG] to immobilized MAb. While association has been shown to follow the expected pattern, dissociation consists of at least two reversible steps, one with a rate constant of 0.0025 min(-1), and a second with a rate constant of 0.00023 min(-1). Validity of affinity constant measurements in the light of the complex reaction kinetics is discussed, A comparison between the method of surface plasmon resonance technology (BIAcore) and solid phase binding (SPB) for determination of kinetic parameters shows that SPB provides not only a cost-effective approach for determination of realtime kinetic parameters of macromolecular ligand-ligate interaction but also a method with several advantages over the BIAcore system in investigating the mechanism of antigen-antibody interaction.

Synthesis, characterisation and superoxide dismutase activity of a manganese(II) complex

A potent superoxide dismutase mimic; Mn-II(HL)(2) [H(2)L = 2,6-bis(benzimidazol-2-yl)pyridine] has been synthesised and characterised by its crystal structure determination and EPR spectroscopy.

A novel zinc bis(thiosemicarbazone) complex for live cell imaging

Fluorescent zinc complexes have recently attracted a lot of interest owing to their vast applications in cellular imaging. We report the synthesis as well as physical, chemical and biological studies of a novel zinc glyoxalbis(4-methyl-4-phenyl-3-thiosemicarbazone), Zn (GTSC)](3), complex. As compared with the well-studied zinc biacetylbis(4-methyl-3-thiosemicarbazone), Zn(ATSM), complex, which was used as a reference, Zn(GTSC)](3) had 2.5-fold higher fluorescence. When cellular fluorescence was measured using flow cytometry, we observed that Zn(GTSC)](3) had 3.4-fold to 12-fold higher fluorescence than Zn(ATSM) in various cell lines (n = 9) of different tissue origin. Confocal fluorescence microscopy results showed that Zn(GTSC)](3) appeared to have a nuclear localization within 30 mm of addition to MCF7 cells. Moreover, Zn(GTSC)](3) showed minimal cytotoxicity compared with Zn(ATSM), suggesting that Zn(GTSC)](3) may be less deleterious to cells when used as an imaging agent. Our data suggest that the novel Zn(GTSC)](3) complex can potentially serve as a biocompatible fluorescent imaging agent for live cells.

Raman Spectroscopy of the Charge Transfer Complex (TTF)x C60 Br8

We report Raman studies on powder samples of the charge transfer complex (TTF)(x)C60Br8 at room temperature. The phonons show considerable softening with respect to the frequencies observed in the Raman spectrum of solid C60Br8. The strongest mode at 1464 cm(-1) in C60Br8 is red shifted to a doublet with peaks at 1414 and 1421 cm(-1), implying an average phonon softening Delta omega of -47 cm(-1). A comparison with the phonon softening of the corresponding A(g)(2) mode in alkali-doped C-60 (Delta omega similar to -36 cm(-1) for A(6)C(60), A = K, Rb or Cs) suggests that 8 electrons are transferred per C60Br8 molecule in the charge transfer complex. The mode at 503 cm(-1) in C60Br8 is shifted upwards, similar to that in A(6)C(60) compounds.

SCF and electron correlation studies on structure, force constants and vibrational spectra of borane monoammoniate complex

Effects of basis set and electron correlation on the equilibrium geometry, force constants and vibrational spectra of BH3NH3 have been studied. A series of basis sets ranging from double zeta to triple zeta including polarization and diffuse functions have been utilized. All the SCF based calculations overestimate the dative B-N bond distance and considerable improvement occurs when the treatment for electron correlation is introduced. Detailed vibrational analysis for BH3NH3 has been carried out. The mean absolute percentage deviation of the ab initio predicted vibration frequencies of (BH3NH3)-B-11 from the experiment is about 10% for the SCF based calculations and the MP2 method shows better agreement, the overall deviation being 5-6%. The ground state effective force constants of BH3NH3 were obtained using RECOVES procedure. The RECOVES sets of force constants are found to be highly satisfactory for the prediction of the vibrational frequencies of different isotopomers of BH3NH3. The mean absolute percentage deviation of the calculated frequencies of different isotopomers from the experiment is much less than 1%. The RECOVES-MP2/augDZP set of force constants was found to be the best set among the different sets for this molecule. Theoretical infrared intensities are in fair agreement with the observed spectral features.

Unusual ribose conformation in a ternary copper(II) 2?deoxyribonucleotide complex

The ternary metal deoxyribonucleotide complex [Cu(bzim)(5?-dGMP)(H2O)3](bzim = benzimidazole, 5?-dGMP = 2?-deoxyguanosine 5?-monophosphate) has been prepared and the structure analysed by X-ray diffraction. The compound crystallizes in the space group P1 with a= 7.069(6), b= 13.959(10), c= 14.204(12)Å, ?= 75.12(6), ?= 94.15(6), ?= 97.98(6)° and Z= 2. The structure was solved by the heavy-atom method and refined by full-matrix least-squares procedures on the basis of 2813 observed [I[gt-or-equal] 3?(I)] reflections to final R and R? values of 0.050 and 0.052 respectively. There are two independent molecules in the asymmetric unit and both copper(II) centres have square-pyramidal co-ordination geometry. An unusual feature of the structure is the co-ordination of the metal by N(7) of the base, in the presence of a ?-aromatic amine, bzim. The structure is stabilized by intermolecular base�bzim stacking. The nucleotides of both the molecules have an anti conformation about the glycosyl bond, and a gauche-gauche conformation about the C(4?)�C(5?) bond. A feature of particular interest is the unusual sugar conformation. The base furanose rings of the two nucleotide molecules adopt C(3?)-exo/C(2?)-endo pucker and C(3?)-exo pucker respectively.

Modeling of angiogenin-3 '-NMP complex

Angiogenin belongs to the Ribonuclease superfamily and has a weak enzymatic activity that is crucial for its biological function of stimulating blood vessel growth. Structural studies on ligand bound Angiogenin will go a long way in understanding the mechanism of the protein as well as help in designing drugs against it. In this study we present the first available structure of nucleotide ligand bound Angiogenin obtained by computer modeling. The importance of this study in itself notwithstanding, is a precursor to modeling a full dinucleotide substrate onto Angiogenin. Bovine Angiogenin, the structure of which has been solved at a high resolution, was earlier subjected to Molecular Dynamics simulations for a nanosecond. The MD structures offer better starting points for docking as they offer lesser obstruction than the crystal structure to ligand binding. The MD structure with the least serious short contacts was modeled to obtain a steric free Angiogenin - 3' mononucleotide complex structure. The structures were energetically minimized and subjected to a brief spell of Molecular Dynamics. The results of the simulation show that all the li,ligand-Angiogenin interactions and hydrogen bonds are retained, redeeming the structure and docking procedure. Further, following ligand - protein interactions in the case of the ligands 3'-CMP and 3'-UMP we were able to speculate on how Angiogenin, a predominantly prymidine specific ribonuclease prefers Cytosine to Uracil in the first base position.

Synthesis, Structures, and Magnetic Behavior of a Series of Copper(II) Azide Polymers of Cu-4 Building Clusters and Isolation of a New Hemiaminal Ether as the Metal Complex

Four new neutral copper azido polymers, Cu-4(N-3)(8)(L-1)(2)](n) (1), Cu-4(N-3)(8)(L-2)(2)](n) (2), Cu-4(N-3)(8)(L-3)(2)](n) (3), and Cu-9(N-3)(18)(L-4)(4)](n) (4) L1-4 are formed in situ by reacting pyridine-2-carboxaldehyde with 22-(methylamino)ethyl]pyridine (mapy, L-1), N,N-dimethylethylenediamine (N,N-dmen, L-2), N,N-diethylethylenediamine (N,N-deen, L-3), and N,N,2,2-tetramethylpropanediamine (N,N,2,2-tmpn, L-4)], have been synthesized by using 0.5 mol equiv of the chelating tridentate ligands with Cu-(NO3)(2)center dot 3H(2)O and an excess of NaN3. Single-crystal X-ray structures show that the basic unit of these complexes, especially 1-3, contains very similar Cu-4(II) building blocks. The overall structure of 3 is two-dimensional, while the other three complexes are one-dimensional in nature. Complex 1 represents a unique example containing hemiaminal ether arrested by copper(R). Complexes 1 and 2 have a rare bridging azido pathway: both end-on and end-to-end bridging azides between a pair of Cu-II centers. Cryomagnetic susceptibility measurements over a wide range of temperature exhibit dominant ferromagnetic behavior in all four complexes. Density functional theory calculations (B3LYP functional) have been performed on complexes 1-3 to provide a qualitative theoretical interpretation of their overall ferromagnetic behavior.

Oxidation of aqueous sulphur dioxide catalysed by poly-4-vinylpyridine-Cu(II) complex .2. Combined homogeneous and heterogeneous phase oxidation

Aqueous phase oxidation of sulphur dioxide at low concentrations catalysed by a PVP-Cu complex in the solid phase and dissolved Cu(II) in the liquid phase is studied in a rotating catalyst basket reactor (RCBR). The equilibrium adsorption of Cu(II) and S(VI) on PVP particles is found to be of the Langmuir-type. The diffusional effects of S(IV) species in PVP-Cu resin are found to be insignificant whereas that of product S(VI) are found to be significant. The intraparticle diffusivity of S(VI) is obtained from independent tracer experiments. In the oxidation reaction HSO3- is the reactive species. Both the S(IV) species in the solution, namely SO2(aq) and HSO3- get adsorbed onto the active PVP-Cu sites of the catalyst, but only HSO3- undergoes oxidation. A kinetic mechanism is proposed based on this feature which shows that SO2(aq) has a deactivating effect on the catalyst. A rate model is developed for the three-phase reaction system incorporating these factors along with the effect of concentration of H2SO4 on the solubility of SO2 in the dilute aqueous solutions of Cu(II). Transient oxidation experiments are conducted at different conditions of concentration of SO2 and O-2 in the gas phase and catalyst concentration, and the rate parameters are estimated from the data. The observed and calculated profiles are in very good agreement. This confirms the deactivating effect of nonreactive SO2(aq) on the heterogeneous catalysis.

Petri net-based modeling of a class of complex digital systems

We present through the use of Petri Nets, modeling techniques for digital systems realizable using FPGAs. These Petri Net models are used for logic validation at the logic design phase. The technique is illustrated by modeling practical circuits. Further, the utility of the technique with respect to timing analysis of the modeled digital systems is considered. Copyright (C) 1997 Elsevier Science Ltd

Exact complex-wave reconstruction in digital holography

We address the problem of exact complex-wave reconstruction in digital holography. We show that, by confining the object-wave modulation to one quadrant of the frequency domain, and by maintaining a reference-wave intensity higher than that of the object, one can achieve exact complex-wave reconstruction in the absence of noise. A feature of the proposed technique is that the zero-order artifact, which is commonly encountered in hologram reconstruction, can be completely suppressed in the absence of noise. The technique is noniterative and nonlinear. We also establish a connection between the reconstruction technique and homomorphic signal processing, which enables an interpretation of the technique from the perspective of deconvolution. Another key contribution of this paper is a direct link between the reconstruction technique and the two-dimensional Hilbert transform formalism proposed by Hahn. We show that this connection leads to explicit Hilbert transform relations between the magnitude and phase of the complex wave encoded in the hologram. We also provide results on simulated as well as experimental data to validate the accuracy of the reconstruction technique. (C) 2011 Optical Society of America