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91.
S. Montserrat P. Cortés Y. Calventus J. M. Hutchinson 《Journal of Thermal Analysis and Calorimetry》1997,49(1):79-85
Structural relaxation in different epoxy-anhydride and epoxy-diamine resins has been investigated by differential scanning calorimetry using annealing and cooling rate experiments. The annealing experiments lead to the determination of enthalpy loss,H, at an equivalent annealing temperatureT
a=T
g-20, and for periods of annealing time, ta, between 1 h and 4 months. The variation ofH with logta, defines a relaxation rate per decade,rrpd, which is very sensitive to changes of the epoxy network. The cooling rate experiments allow the determination of the apparent activation energy,h
*. The effect of the degree of crosslinking, the addition of a reactive diluent, which acts as flexibilizer, and the length of cross-link onrrpd and h* was studied.Financial support has been provided by DGICYT (Project no.PB93/1241). The authors are grateful to CIBA-GEIGY for supplying the epoxies and hardeners, and to HUNTSMAN CORPORATION EUROPE for supplying the JEFFAMINE*, J.M.H. wishes to acknowledge assistance for a sabbatical period from theMinisterio de Education y Ciencia. 相似文献
92.
Montserrat Barquín María J. Gonzlez Garmendia Liher Larrínaga Elena Pinilla María R. Torres 《无机化学与普通化学杂志》2005,631(11):2151-2155
The two complexes of composition Cu2(OAc)4(phen)(H2O)2 ( 1 ) andCu2(OAc)4(phen)2(H2O) ( 2 ) have been synthesized and characterized by chemical analysis and IR and electronic spectroscopies. Compound 2 has the structure of a dimer with a phenanthroline molecule and two monodentate acetate groups coordinated to each copper atom and a water molecule as the only bridging ligand between them. Each copper atom has a distorted square‐planar pyramidal coordination, determined by two oxygen atoms at 1.94(3) and 1.959(3) Å, two nitrogen atoms at 2.023(4) Å and the oxygen atom of the bridging water molecule at 2.289(2) Å. The distance between the two copper atoms is of 4.29 Å and the angle Cu(1)‐O(3)‐Cu(1A) 139.2(2)°. The water molecule is involved in two intramolecular hydrogen bonds with non coordinated oxygen atoms. The distance between the molecules of phenanthroline is 3.75 Å. Magnetic and EPR results for Cu2(OAc)4(phen)(H2O)2 ( 1 ), Cu2(OAc)4(phen)2(H2O) ( 2 ), Cu2(OAc)4(bipy) ( 3 ) and Cu2(OAc)4(bipy)2(H2O)2 ( 4 ) have been analysed and compared. For 1 and 3 an antiferromagnetic dimer unit [Cu2(μ‐OAc)4] with 2J = ?325 and ?292 cm?1, respectively, and other two copper atoms without significant magnetic interaction are present. Triplet signals are detected in the EPR spectra. In 2 and 4 there is no practically magnetic exchange and the orthorhombic signals are observed in the EPR spectra. 相似文献
93.
Montserrat Domínguez-Prez Julieta Jimnez de Llano Luisa Segade Oscar Cabeza Carlos Franjo Eulogio Jimnez 《Thermochimica Acta》2004,420(1-2):45-49
This paper reports excess molar enthalpies, HmE, and excess molar volumes, VmE, of the binary systems {propyl propanoate + o-xylene}, {propyl propanoate + m-xylene} and {propyl propanoate + p-xylene} at the temperature 298.15 K and atmospheric pressure, over the whole composition range. VmE was calculated from the experimental measurement of the corresponding densities, while HmE was measured directly. The excess magnitudes were correlated to a Redlich-Kister type equation. Finally, we will discuss the results of the three mixtures studied here and by comparison with other binary systems containing propyl propanoate and a benzene-based compound previously published. 相似文献
94.
Calculation and reporting procedures are described, which aim to improve the quality and comparability of published formation constant values obtained by glass-electrode potentiometry. Ways in which the processing of data by computer optimization programs can be standardized are the main concern, particularly in respect of improving the usefulness of equilibrium data through incorporation into large publically available databases. These recommendations may be particularly valuable to researchers beginning in this field as well as to those who determine formation constants only occasionally. 相似文献
95.
Spirolactams as conformationally restricted pseudopeptides: synthesis and conformational analysis 总被引:1,自引:0,他引:1
Fernández MM Diez A Rubiralta M Montenegro E Casamitjana N Kogan MJ Giralt E 《The Journal of organic chemistry》2002,67(22):7587-7599
The synthesis of 1-(tert-butoxycarbonyl)-7-[1-(tert-butoxycarbonyl)-3-methylbutyl]-6-oxo-1,7-diazaspiro[4.5]decanes (S,S)-1a and (S,R)-1b is described. Derivatives 17a,b and 19a are prepared for use in peptide synthesis as constrained surrogates of the Pro-Leu and Gly-Leu dipeptides. The Ac-[Gly-Leu]-Met-NH(2) derivatives (S,S,S)-2a and (S,R,S)-2b, with the tripeptidic C-terminal region present in tachykinins, are also synthesized. Conformational analyses of these tripetide analogues by NMR experiments and molecular modeling calculations show that both (S,S,S)-2a and (S,R,S)-2b epimers are gamma-turn/distorted type II beta-turn mimetics. 相似文献
96.
Montserrat Cano Mark Ladlow Shankar Balasubramanian 《The Journal of organic chemistry》2002,67(1):129-135
The solution-phase preparation of the 3',5'-dialkoxybenzoin photolabile safety-catch linker 16 is described. Pivotal to this convenient synthesis is the selection of appropriate orthogonal protecting groups for the alkoxy functionalities present. The new linker can be readily loaded onto any standard amine-terminating resin under peptide-coupling conditions, without the need to protect the secondary alcohol functionality, and subsequently loaded with substrate. Alternatively, the loading efficiency of sterically hindered substrates can be enhanced by preloading the semiprotected linker variant 10 in solution prior to immobilization onto the resin. This second generation of benzoin photolabile safety-catch linkers provides greater control of both linker loading and resin attachment and should prove to be a more versatile and convenient form of the linker. 相似文献
97.
Torrens J Riu-Aumatell M López-Tamames E Buxaderas S 《Journal of chromatographic science》2004,42(6):310-316
The behavior of four fibers [polydimethylsiloxane (PDMS), PDMS-divinylbenzene (DVB), carboxen (CAR)-PDMS, PDMS-DVB-CAR), is tested for the analysis of volatile compounds of white and red wine. The PDMS-DVB-CAR fiber is the most appropriate to obtain the most wide volatile profile of wines. The better extraction conditions are 40 min at 35 degrees C. Satisfactory data about the reproducibility and uptake are obtained for more than 40 volatile compounds of red and white wine. 相似文献
98.
99.
A method based on an analytical technique, initially developed for quantifying aquatic refractory organic matter (often called
humics), has been applied to commercial samples claiming to contain humic-type substances. At present, no method exists for
quantifying the humic content on this type of sample. The analytical method is based on measuring the peak current obtained
by adsorptive stripping voltammetry of the complex formed by refractory organic matter in the presence of trace amounts of
Mo(VI). The quantification procedure requires the response obtained for the unknown sample to be compared with the response
obtained with International Humic Substance Society (IHSS) reference humic substances. A very simple procedure that enables
the humic content of any sample to be expressed as IHSS standard equivalents is described in detail. The method is highly
selective, reproducible and suitable for routine analysis. 相似文献
100.
In complex domains it is usually quite difficult to introduce context information. However, sometimes that information should be taken into account to make decisions, because it provides some relevant knowledge that cannot be expressed using an attribute-value representation. This is the case of the determination of risk of contamination of soils. In this paper, we propose to use conjunctive rules to introduce additional background knowledge to a MCDM sorting method called ClusDM. ClusDM is based on the aggregation of the data with unsupervised clustering techniques. The paper presents a new algorithm to incorporate rules to guide the clustering process in a semi-supervised way. The paper also describes how it works in the case sorting a set of possible contaminated soils, and compares the results obtained by ClusDM when rules are used or not. 相似文献