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71.
The effect of confinement, number of branches (functionality), and size of the molecules on various properties as a function of temperature of star-branched polymers confined between two walls was studied using Monte Carlo simulations with the parallel tempering technique. The coil-to-globule transition and the liquidlike to solidlike transition, similar to those observed for linear chains, were characterized in all systems by changes in the heat capacity, internal energy, and radius of gyration. The transitions were also characterized by the most probable isomeric structure at a given temperature. The radius of gyration of the star polymers was smaller than the values of linear chains when the number of arms f increased. For star chains with more than f=5 arms the values of the radius of gyration, and therefore the size of the molecules, were similar for every condition of confinement studied, especially at higher temperatures. As confinement was increased, the difference in the radius of gyration of linear chains and star polymers became even larger. The coil-to-globule transition temperatures shifted to higher temperatures as the size of the chains and the number of arms in a molecule were increased. Effects of confinement were higher on the properties of the system at the smallest separations (less than twice the monomer diameter), where the coil-to-globule transition shifted to lower temperatures. The liquidlike to solidlike transition was present at almost the same temperature for different conditions of confinement, chain size, and number of arms. The behavior of the systems for separations between the walls greater than five bead diameters was similar to the behavior in the unconfined case. Hence, no considerable effect of confinement was found above this separation. 相似文献
72.
Roitershtein D Domingos A Pereira LC Ascenso JR Marques N 《Inorganic chemistry》2003,42(23):7666-7673
Reaction of yttrium and lanthanum trichloride with 1 equiv of sodium or potassium hydrotris(3,5-dimethylpyrazolyl)borate and 1 equiv of 2,2'-bipyridine gives good yields of the complexes [MCl(2)(Tp(Me2))(C(10)H(8)N(2))] (M = Y (1), La (2)). The analogous compounds with 1,10-phenanthroline, [MCl(2)(Tp(Me2))(C(12)H(8)N(2))] (M = Y (3), La (4)), have been obtained by a similar procedure. The solid-state structures of 2-4 were determined by single-crystal X-ray diffraction and revealed that the compounds are all seven-coordinate with capped octahedral geometry. In contrast, reaction of yttrium trichloride with 1 equiv of sodium hydrotris(3,5-dimethylpyrazolyl)borate in the presence of 1 equiv of neocuproine affords [YCl(3)(Tp(Me2))][Na(neoc)(3))] (5). Compounds 1 and 2 provide an entry for the synthesis of complexes containing the bipyridyl ligand in a radical anionic form or in a dianionic form. Reaction of 1 and 2 with an excess of sodium amalgam gives [Y(Tp(Me2))(bipy)(THF)(2)] (6) and [La(Tp(Me2))(2)(bipy)] (7), respectively. The structures of both compounds have been determined by X-ray crystallography. Compound 7 can be oxidized with iodine to give [La(Tp(Me2))(2)(bipy)]I (8). 相似文献
73.
Important parameters to consider when developing a liquid chromatography/mass spectrometry (LC/MS) method are buffer type and concentration, and column geometry. In the work presented here the choice of buffer for the analysis of basic compounds using a polar embedded phase (HyPURITYtrade mark ADVANCE) is illustrated for the analysis of tricyclic antidepressants. Method transfer from a 4.6 mm i.d. column to a 2.1 mm i.d. column is demonstrated for the analysis of triazines and anabolic steroids and their metabolites, with no change in selectivity and with added speed of analysis. Analysis of eight beta-blockers is achieved in 65 seconds by using a short 30 x 4.6 mm C18 column. 相似文献
74.
Rafael Fogel Rafaela Rodrigues Garcia Rebeca da Silva Oliveira Denise Neves Menchero Palacio Luciana da Silva Madeira Nei Pereira Jr. 《Applied biochemistry and biotechnology》2005,122(1-3):741-752
The dilute-acid hydrolysis of sugarcane bagasse was optimized using a statistical experimental design resulting in hydrolysates
containing 57.25 g/L of xylose, which were fermented with a high inoculum concentration (10 g/L of the yeast Candida guilliermondii IM/UFRJ 50088). The addition of urea reduced the time of conversion (t
C) to 75 h (without nitrogen source addition t
C>127 h), and, consequently, improving the rates of xylitol bioproduction. Fermentator experiments, using the optimized conditions,
resulted in enhanced conversion rates, reducing t
C to 30 h. The stability of the yeast in the hydrolysate was also verified in a 480-h cultivation. 相似文献
75.
76.
Luis Adrio Gemma Alberdi Adriana Amoedo Darío Lata Alberto Fernndez Javier Martínez M. Teresa Pereira Jos M. Vila 《无机化学与普通化学杂志》2005,631(11):2197-2203
Reaction of the thiosemicarbazone ligands C4H4NC(H)=NN(H)C(S)NHR (R = Me, a ; Et, b ) with Li2[PdCl4] gave the dinuclear complexes [Pd{C4H4NC(H)=NNC(S)NHR}(μ‐Cl)]2 (R = Me, 1a ; Et, 1b ) with a central Pd2Cl2 core and with deprotonation of the thiosemicarbazones at the hydrazinic nitrogen atom. Treatment of 1a and 1b with triphenylphosphine gave the mononuclear compounds [Pd{C4H4C(H)=NNC(S)NHR}(Cl)(PPh3)] (R = Me, 2a ; Et, 2b ), whereas reaction of 1a and 1b with tertiary diphosphines gave mono‐ and dinuclear compounds, as appropriate, with the corresponding diphosphine acting as a monodentate ( 6b ), chelating ( 3a ) and bridging ligand ( 4a, 5a , 4b, 5b ). Treatment of 1a and 1b with (Ph2PCH2CH2PPh2)W(CO)5 gave the new heterobimetallic complexes 7a and 7b . The crystal structures of complexes 3a and 4a are described. 相似文献
77.
78.
Jun Liu Kelton A. Schleyer Tyrel L. Bryan Changjian Xie Gustavo Seabra Yongmei Xu Arjun Kafle Chao Cui Ying Wang Kunlun Yin Benjamin Fetrow Paul K. P. Henderson Peter Z. Fatland Jian Liu Chenglong Li Hua Guo Lina Cui 《Chemical science》2021,12(1):239
Heparanase (HPA) is a critical enzyme involved in the remodeling of the extracellular matrix (ECM), and its elevated expression has been linked with diseases such as various types of cancer and inflammation. The detection of heparanase enzymatic activity holds tremendous value in the study of the cellular microenvironment, and search of molecular therapeutics targeting heparanase, however, no structurally defined probes are available for the detection of heparanase activity. Here we present the development of the first ultrasensitive fluorogenic small-molecule probe for heparanase enzymatic activity via tuning the electronic effect of the substrate. The probe exhibits a 756-fold fluorescence turn-on response in the presence of human heparanase, allowing one-step detection of heparanase activity in real-time with a picomolar detection limit. The high sensitivity and robustness of the probe are exemplified in a high-throughput screening assay for heparanase inhibitors.Heparanase, a critical enzyme involved in the remodeling of the extracellular matrix, activates a disaccharide probe HADP to give a strong fluorescence signal. 相似文献
79.
An electrochemical biosensor for the specific detection of short DNA sequences from the E. coli pathogen is described. This hybridization device relies on the immobilization of a 25-mer oligonucleotide probe, from the E. coli lacZ gene, onto a screen-printed carbon electrode. Chronopotentiometric detection of the Co(bpy)3+3 indicator is used for monitoring the hybridization event. Numerous variables of the assay protocol, including those of the probe immobilization step, the hybridization event, and the indicator association/detection, are characterized and optimized. Hybridization times of 2- and 30-min are sufficient for detecting 300- and 50 ng/mL, respectively, of the E. coli DNA target. Applicability to analysis of untreated environmental water samples is illustrated. Such single-use electrochemical sensors hold great promise for decentralized environmental and food testing for the E. coli pathogen. 相似文献
80.
L. C. R. Andrade J. A. Paixo M. J. M. de Almeida C. Siquet F. Borges 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(2):o95-o97
The molecule of the title compound, C23H40O4Si2, features an approximate non‐crystallographic C2 symmetry axis. The aldehyde group is disordered over two positions with similar occupancies. The geometry of the isolated molecule was studied by ab initio quantum mechanical calculations employing a molecular orbital Hartree–Fock method. The calculations reproduce well the equilibrium geometry but slightly overestimate the value of the Si—O bond lengths of the trioxadisilepine ring. 相似文献