Search results for "Trap"
showing 10 items of 2144 documents
Polyelectrolytes Revisited: Reliable Determination of Intrinsic Viscosities
2007
The linear extrapolation of (hh0)/(h0c) towards c !0 constitutes the basis of traditional methods to determine intrinsic viscosities (h), where h is the viscosity of polymer solutions of concentration c and h0 is the viscosity of the pure solvent. With uncharged macromolecules this procedure works well; for polyelectrolytes it fails because of the pronounced non-linearity of the above dependence at high dilution resulting from the increasing electrostatic inter- actions. This contribution presents a new method for the determination of (h). It rests upon the application of the laws of phenomenological thermodynamics to the viscosity of polymer solutions and introduces a generalized intrinsic…
N-(tert-butoxycarbonylglycyl-alpha,beta-dehydrophenylalanylglycylphenylalanyl)-4-nitroaniline.
2000
In the crystal structure of the tetrapeptide Boc0–Gly1–ΔPhe2–Gly3–Phe4–p-NA (p-NA is para-nitroaniline), C33H36N6O8, there are two independent molecules differing in conformation in the asymmetric part of the unit cell. All the amino acids in the peptide are linked trans to each other. The torsion angles in the main chain of both molecules are close to the values of the type β-II turn. Two intramolecular and three intermolecular N—H⋯O hydrogen bonds stabilize the conformation of each of the molecules.
Trapping of Different Lipase Conformers in Water-Restricted Environments
1996
Based on a recently reported strategy to rationally activate lipolytic enzymes for use in nonaqueous media [Mingarro, I., et al. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 3308-3312], we compared the behavior in water-restricted environments of activated vs nonactivated forms of different lipases toward their natural substrates, triacylglycerols. To this end, nine lipases from varied origins (mammalian, fungal, and bacterial) were assayed using simple acidolyses as nonaqueous model reactions. The experimental results for several (though not all) lipases, discussed in the light of current structural and functional information, were collectively consistent with a model where, depending on the "…
Lipase-enhanced activity in flavour ester reactions by trapping enzyme conformers in the presence of interfaces
1998
In order to improve the lipase-catalyzed synthesis of flavour esters, we have used the reported strategy of interfacial activation-based molecular (bio)imprinting [Mingarro et al. 1995. Proc. Natl. Acad. Sci. U.S.A. 92: 3308], later called trapping in the presence of amphiphile interfaces (TPI) [Mingarro et al. 1996. Biochemistry 35: 9935]. Five lipases of fungal and mammalian origin typically used for esterification process have been explored to improve production by TPI treatment. A marked enhancement of enzymatic activity has been observed in all TPI-treated lipases assayed and the activation factor obtained was up to 90-fold. The dependence on chain length of acyl donors in the esterifi…
The ion trap aerosol mass spectrometer: improved design, first field deployment, and the capability of differentiating organic compound classes via M…
2016
Abstract. Further development and optimisation of a previously described ion trap aerosol mass spectrometer (IT-AMS) are presented, which resulted in more reproducible and robust operation and allowed for the instrument’s first field deployment. Results from this 11-day long measurement indicate that the instrument is capable of providing quantitative information on organics, nitrate, and sulphate mass concentrations with reasonable detection limits (0.5–1.4 µg m−3 for 1 h averages), and that results obtained with the IT-AMS can directly be related to those from Aerodyne aerosol mass spectrometers. The capability of the IT-AMS to elucidate the structure of fragment ions is demonstrated via …
Characterization of industrial alkylpolyphosphonates by infusion electrospray ionization-ion trap mass spectrometry with identification of the impuri…
2005
Technical grade diethylene-triaminepentakis(methylenephosphonic acid) (I), dihexamethylene-triaminepentakis(methylenephosphonic acid) (II), ethylene-diaminetetrakis(methylenephosphonic acid) (III), hexamethylene-diaminetetrakis(methylenephosphonic acid) (IV), amino-tris(methylenephosphonic acid) (V), hydroxyethyl-aminobis(methylenephosphonic acid) (VI), 1-hydroxyethylidene-1,1-diphosphonic acid (VII), and 2-phosphonobutane-1,2,4-tricarboxylic acid (VIII) were characterized by ion trap mass spectrometry with electrospray ionization (ESI-ITMS). Using the negative ion mode and acid and alkaline media, peak series corresponding to the nominal compounds and to impurities with a lower number of p…
Photoreactivity of Iron-Doped Titanium Dioxide Powders for Dinitrogen Reduction to Ammonia
1989
The production of NH3 from N2 and H2O on Fe/TiO2 has been studied in a continuous photoreactor under UV radiation. An ESR study of the catalysts shows that Fe3+ ions are better electron traps than Ti4+ ions. This trapping can be irreversible if the corresponding holes originate stable species adsorbed on the catalyst surface. The charge separation, thus favoured by the Fe3+ ions, helps the N2 adsorption by its reaction with surface species activated by holes. The best activity is found when no excess Fe is segregated at the surface; overall turnover for N2 reduction as high as 6 e−/Fe atom can be reached before catalyst deactivation.
Large-Scale Synthesis of Mammalian Gonadoliberin without protection of side-chain functions
1991
A simple, Large-scale preparation of mammalian gonadoliberin was elaborated using classical solution methods without protecting side-chain functions. At the final stage, a hexapeptide segment was condensed with the corresponding tetrapeptide and the obtained decapeptide was purified by a single chromatographic procedure on silica gel. The total efficiency of the whole synthesis and the purity of the product amounted to 34% and 98.3%, respectively.
Low-energy decay pathways of doubly charged silver clusters $Ag_{n}^{2+}$ (n = 9 - 24)
1997
The low-energy dissociation channels of mass selected silver cluster ions Ag n 2+ (n = 9–24) are determined by collision induced dissociation (CID) in a Penning trap. While all clusters of the size n ≥ 17 evaporate neutral monomers, most smaller clusters undergo asymmetric fission of the form Ag n 2+ → Ag −3 + + Ag {3} + . However, Ag 15 2+ and Ag 11 2+ emit monomers which indicates shell or odd-even effects. The observed fragmentation pathways are different from previous reports of measurements with sputtered Ag n 2+ .
Photoinduced electron transfer in supramolecular complexes of a π-extended viologen with porphyrin monomer and dimer
2012
A π-extended viologen has been synthesized, forming supramolecular complexes with a freebase tetraphenylporphyrin (H2TPP) and the cofacial porphyrin dimer with an anthracene spacer [H4(DPA)] through π–π interaction in benzonitrile (PhCN). Formation of the H2TPP-BHV2+ supramolecular complex was probed by UV-vis and fluorescence spectra. The fluorescence of H2TPP was strongly quenched by electron transfer from the singlet excited state (1H2TPP*) to BHV2+ in the supramolecular complex. The transient absorption spectrum of the charge-separated (CS) state (H2TPP•+ and BHV•+) was successfully detected by the laser flash photolysis measurements of the H2TPP-BHV2+ supramolecular complex in PhCN. Th…