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11.
Leila S. Boulos Mona H. N. Arsanious El-Sayed M. A. Yakout 《Monatshefte für Chemie / Chemical Monthly》2007,41(9):979-984
The reaction of 3-amino-2-phenyl-4(3H)-quinazolinone with oxovinylidenetriphenylphosphorane afforded 5-phenylpyrazolo[1,5-c] quinazoline-2(3H)-one and triphenylphosphine oxide. On the other hand, when quinazolinone reacts with phosphorus ylides, the corresponding
phosphorane adducts were obtained. Moreover, quinazolinone reacts with trisdialkylaminophosphines to give the new (dialkylamino)oxophosphonium
dipolar products. Possible reaction mechanisms are considered and the structural assignments are based on analytical and spectroscopic
results. 相似文献
12.
Sherif El-Basil 《International journal of quantum chemistry》1982,21(5):779-792
Kekulé structures of 10 nonlinear acenes comprising 83 graphs are studied through the use of connectivities [M. Randi?, J. Am. Chem. Soc. 97 , 6609 (1975)] of their corresponding submolecules [H. Joela, Theor. Chim. Acta 39 , 241 (1975)]. In certain rare cases states were identified to have identical branching indices but different Kekulé indices [A. Graovac, I. Gutman, M. Randi?, and N. Trinajsti?, J. Am. Chem. Soc. 95 , 6267 (1973)]. Such states are termed pseudodegenerate states. A method is described to forecast and another to remedy such situations. The method emphasizes the relation between VB (resonance) and MO theories using graph-theoretical concepts. 相似文献
13.
Four myrosinase (β-thioglucosidase EC. 3.2.3.1) and seven disaccharase (β-fructofuranosidase, EC. 3.2.1.26) isoenzymes were isolated from turnip leaves. The most active enzymes were isolated in pure
form. Myrosinase and disaccharase mol wt was 62.0 × 103 and 69.5 × 103 dalton, respectively, on the basis of gel filtration on Sephadex G-200.
Myrosinase pH profile showed high activity between pH 5 and 7 with the optimum at pH 5.5. The purified enzyme was heat-stable
for 60 min at 30°C with only loss of 24% of activity. Its activity is strongly inhibited (100%) by Pb2+, Ba2+, Cu2+ and Ca2+ ions, and activated (70%) by EDTA at 0.04M. The pure enzyme failed to hydrolyze amylose, glycogen, lactose, maltose, and
sucrose. TheK
m andV
max values of myrosinase using sinigrin as specific substrate was 0.045 mM and 2.5 U, respectively.
The maximal activity of disaccharase enzyme was obtained at pH 4–5 and 35–37°C. The enzyme was heat-stable at 30°C for 30
min with only 10% loss of its activity. Its activity is strongly activated (70–240%) by Ca2+, Ba2+, Cu2+, and EDTA at 0.01M. The enzyme activity is specific to the disaccharide sucrose and failed to hydrolyze other disaccharides (maltose and lactose).
TheK
m andV
max of disaccharase were 0.123 mM and 3.33 U, respectively. 相似文献
14.
Summary The reactions of aldehydic and ketonic Schiff bases derived from hydrazine-S-methyl dithiocarboxylate and thiosemicar-bazide with cobalt(II) acetate were investigated. Octahedral tris ligand cobalt(III) chelates were formed with aldehydic Schiff bases whereas tetrahedral bis ligand cobalt (II) chelates were isolated with ketonic Schiff bases.N-isopropylidene hydrazine-S-methyldithiocarboxylate, however, gave both octahedral tris cobalt(III) and tetrahedral bis cobalt(II) chelates. These results are interpreted in terms of the steric requirements of the Schiff base used. 相似文献
15.
Sherif El-Basil 《International journal of quantum chemistry》1982,21(5):793-797
Molecular connectivities of submolecules [H. Joela, Theor. Chim. Acta 39 , 241 (1975)] corresponding to Kekulé structures of nine nonalternate hydrocarbons and four nonbenzenoid hydrocarbons containing four-membered rings are correlated with their Kekulé indices. In the latter class of compounds it was observed that the corresponding submolecules contain cut vertices and bridges in contrast to submolecules of benzenoid hydrocarbons which are devoid of such bridges. It was observed, furthermore, that the branching index goes up with the number of bridges in the submolecule. The results present an application to the abstract relation [D. Cvetkovi?, I. Gutman, and N. Trinajsti?, J. Chem. Phys. 61 , 2700 (1974)] between resonance and MO theories. 相似文献
16.
Summary The effect of some surfactants and protective colloids on the absorbance of the iron(III)-phenylfluorone complex has been investigated. The binary complex formed at pH 9.0 show a molar absorptivity of 7.5×104 l · mol–1 · cm–1 at 530 nm. In the presence of 2% Triton X-100, at the same pH, the molar absorptivity of the sensitized complex was 1.19×105 l · mo–1 · cm–1 at 555 nm. Full colour development of the sensitized complex occurred within 25 min and Beer's law was followed up to 0.53 ppm of iron. The molar ratio and continuous variation methods indicated a 13 metal-ligand ratio for the sensitized complex. The effect of various amounts of different ions has been studied under the experimental conditions and some masking agents were recommended. The method has been applied to the determination of iron in copper and nickel metals and some non-ferrous alloys.
Spektralphotometrische Bestimmung von Eisen als Phenylfluoronkomplex sensibilisiert mit Triton X-100相似文献
17.
Huang X El-Sayed IH Yi X El-Sayed MA 《Journal of photochemistry and photobiology. B, Biology》2005,81(2):76-83
Nicotinamide adenine dinucleotide is an important coenzyme involved in the production of ATP, the fuel of energy, in every cell. It alternates between the oxidized form NAD(+) and the reduced form dihydronicotinamide adenine dinucleotide (NADH) and serves as a hydrogen and electron carrier in the cellular respiratory processes. In the present work, the catalytic effect of gold nanoparticles on the oxidization of NADH to NAD(+) was investigated. The addition of gold nanoparticles was found to quench the NADH fluorescence intensities but had no effect on the fluorescence lifetime. This suggested that the fluorescence quenching was not due to coupling with the excited state, but due to changing the ground state of NADH. The intensity of the 340 nm absorption band of NADH was found to decrease while that of the 260 nm band of NAD(+) was found to increase as the concentration of gold nanoparticles increased. This conversion reaction was further supported by nuclear magnetic resonance and mass spectroscopy. The effect of the addition of NADH was found to slightly red shift and increase the intensity of the surface plasmon absorption band of gold nanoparticles at 520 nm. This gives a strong support that the conversion of NADH to NAD(+) is occurring on the surface of the gold nanoparticles, i.e. NADH is surface catalyzed by the gold nanoparticles. The catalytic property of this important reaction might have important future applications in biological and medical fields. 相似文献
18.
Mohamed El-Sayed Hardy Müller Gerd Rheinwald Heinrich Lang Stefan Spange 《Monatshefte für Chemie / Chemical Monthly》2003,50(11):361-370
N-(2′-Hydroxy-4′-N,N-dimethylaminobenzylidene)-4-nitroaniline [HDBN] has been used as a model for investigating intra- and intermolecular D–A (donor–acceptor) interactions in various environments
by means of UV/Vis spectroscopy. UV/Vis spectra of HDBN have been measured in various solvents, ethanolic solutions of different pH, adsorbed on silica, and in the solid state. A bathochromic shift of νmax is observed with increasing the dipolarity/polarizability and HBD (hydrogen bond donor) capacity of the solvent, which is
described by means of a multiple LSE (linear solvation energy) relationship in terms of the empirical Kamlet-Taft solvent polarity parameters. The adsorption of HDBN on Aerosil? 300-silica particles in non-HBA (hydrogen bond acceptor) solvents is explained in the same sense. Mobile protons and sol–gel
entrapping cause a hypsochromic shift due to protonation of the lone electron pair of the 4′-N,N-dimethylamino group. Hydroxide ions attack the 2′-hydroxy group which causes a bathochromic shift. A strong intramolecular
hydrogen bond between the 2′-hydroxyl hydrogen and the imine nitrogen atom is present in the solid-state structure causing
an unprecedented bathochromic shift. 相似文献
19.
The photoluminescence (PL) of CdSe quantum dots (QD) in aqueous media has been studied in the presence of gold nanoparticles (NP) with different shapes. The steady state PL intensity of CdSe QD (1.5-2 nm in size) is quenched in the presence of gold NP. Picosecond bleach recovery and nanosecond time-resolved luminescence measurements show a faster bleach recovery and decrease in the lifetime of the emitting states of CdSe QD in the presence of quenchers. Surfactant-capped gold nanorods (NR) with aspect ratio of 3 and surfactant-capped and citrate-capped nanospheres (NS) of 12 nm diameter were used as quenchers in order to study the effect of shape and surface charge on the quenching rates. The Stern-Volmer kinetics model is used to examine the observed quenching behavior as a function of the quencher concentration. It was found that the quenching rate of NR is more than 1000 times stronger than that of NS with the same capping material. We also found that the quenching rate decreases as the length of the NR decreases, although the overlap between the CdSe emission and the NR absorption increases. This suggests that the quenching is a result of electron transfer rather than long-range (Forster-type) energy transfer processes. The quenching was attributed to the transfer of electron with energies below the Fermi level of gold to the trap holes of CdSe QD. The observed large difference between NR and NS quenching efficiencies was attributed to the presence of the [110] facets only in the NR, which have higher surface energy. 相似文献
20.
While the nanocatalysis field has undergone an explosive growth during the past decade, there have been very few studies in the area of shape-dependent catalysis and the effect of the catalytic process on the shape and size of transition metal nanoparticles as well as their recycling potential. Metal nanoparticles of different shapes have different crystallographic facets and have different fraction of surface atoms on their corners and edges, which makes it interesting to study the effect of metal nanoparticle shape on the catalytic activity of various organic and inorganic reactions. Transition metal nanoparticles are attractive to use as catalysts due to their high surface-to-volume ratio compared to bulk catalytic materials, but their surface atoms could be so active that changes in the size and shape of the nanoparticles could occur during the course of their catalytic function, which could also affect their recycling potential. In this Feature Article, we review our work on the effect of the shape of the colloidal nanocatalyst on the catalytic activity as well as the effect of the catalytic process on the shape and size of the colloidal transition metal nanocatalysts and their recycling potential. These studies provide important clues on the mechanism of the reactions we studied and also can be very useful in the process of designing better catalysts in the future. 相似文献