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91.
Francisco López-Suevos Christian Eyholzer Nico Bordeanu Klaus Richter 《Cellulose (London, England)》2010,17(2):387-398
Suspensions of commercial refined beech pulp (RBP) were further processed through mechanical disintegration (MD-RBP), chemical
modification (CM-RBP) and through chemical modification followed by mechanical disintegration (CM-MD-RBP). Nanocomposites
were prepared by compounding a poly(vinyl acetate) (PVAc) latex adhesive with increasing contents of the different types of
nanofibrils, and the resulting nanocomposites were analyzed by dynamic mechanical analysis (DMA). Also, the suitability of
using the CM-RBP fibrils to formulate PVAc adhesives for wood bonded assemblies with improved heat resistance was studied.
The presence of cellulose nanofibrils had a strong influence on the viscoelastic properties of PVAc latex films. For all nanocomposites,
increasing amounts of cellulose nanofibrils (treated or untreated) led to increasing reinforcing effects in the glassy state,
but especially in the PVAc and PVOH glass transitions. This reinforcement primarily resulted from interactions between the
cellulose fibrils network and the hydrophilic PVOH matrix that led to the complete disappearance of the PVOH glass transition
(tan δ peak) for some fibril types and contents. At any given concentration in the PVOH transition, the CM-MD-RBP nanofibrils
provided the highest reinforcement, followed by the MD-RBP, CM-RBP and the untreated RBP. Finally, the use of the CM-RBP fibrils
to prepare PVAc reinforced adhesives for wood bonding was promising since, even though they generally performed worse in dry
and wet conditions, the boards showed superior heat resistance (EN 14257) and passed the test for durability class D1. 相似文献
92.
Jaime G. Mayoral Francisco J. Alarcón Tomás F. Martínez Pablo Barranco F. Noriega 《Applied biochemistry and biotechnology》2010,160(1):1-8
A novel end-point fluorimetric procedure based on the use of rhodamine-110-labeled specific substrate was developed to determine
trypsin activities in biological samples. We evaluated the ability of trichloroacetic acid and acetic acid to stop the enzymatic
reaction without hindering the detection of the fluorescence of rhodamine-110 released into the reaction mixture from the
specific substrate (CBZ-l-alanyl-l-arginine)2-rhodamine-110. Trichloroacetic acid decreased markedly the fluorescence of rhodamine-110, even at low concentrations. On
the other hand, the addition of 50 mmol/l acetic acid inactivated efficiently trypsin activity, causing minor effects on rhodamine-110
fluorescence. The proposed procedure was more sensitive than the spectrophotometric end-point method using N-α-benzoyl-dl-arginine-p-nitroanilide as substrate. The possibility of carrying out end-point fluorimetric assays improves the performance of monocell
fluorimeters by setting specific conditions optimal for each enzyme activity independently of the fluorimeter. This method
also allows replicate assays to be conducted simultaneously, resulting in considerable time saving and in increased performance
of low-cost equipment. 相似文献
93.
Dr. José A. González-Delgado Dr. Miguel A. Romero Dr. Francisco Boscá Dr. Jesús F. Arteaga Prof. Dr. Uwe Pischel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(62):14229-14235
The light-gated organocatalysis via the release of 4-N,N-dimethylaminopyridine (DMAP) by irradiation of the [Ru(bpy)2(DMAP)2]2+ complex with visible light was investigated. As model reaction the acetylation of benzyl alcohols with acetic anhydride was chosen. The pre-catalyst releases one DMAP molecule on irradiation at wavelengths longer than 455 nm. The photochemical process was characterized by steady-state irradiation and ultrafast transient absorption spectroscopy. The latter enabled the observation of the 3MLCT state and the spectral features of the penta-coordinated intermediate [Ru(bpy)2(DMAP)]2+. The released DMAP catalyzes the acetylation of a wide range of benzyl alcohols with chemical yields of up to 99 %. Control experiments revealed unequivocally that it is the released DMAP which takes the role of the catalyst. 相似文献
94.
José L. García Ruano Alejandro ParraLeyre Marzo Francisco YusteVirginia M. Mastranzo 《Tetrahedron》2011,67(16):2905-2910
Room temperature ultrasonic irradiation of neat mixtures of methyl sulfinates and primary or secondary amines (1.5 equiv) produced sulfinamides, which on m-CPBA oxidation (in dichloromethane) were converted into the corresponding sulfonamides. The two steps can be accomplished in one pot, in good overall yields, when using secondary amines, but primary amines give better sulfonamide yields when the peracid oxidation is effected on the purified sulfinamide. This constitutes a mild, efficient, and potentially scalable route to sulfonamides, which obviates the use of water sensitive, often lachrymatory sulfonyl chlorides and large reagent excesses. 相似文献
95.
Francisco M. Fernndez Eduardo A. Castro 《International journal of quantum chemistry》1983,23(3):915-919
A very general form of the hypervirial theorems, which can be applied to several quantum systems of great interest for the theoretical quantum chemists is presented. 相似文献
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The equilibrium between propionaldehyde + propane-1,1-diol + 2,4,6-triethyl-1,3,5-trioxane has been characterized, for the first time, in aqueous solution using NMR techniques. The diffusion coefficients and the molar percentages at different temperatures have been also reported. 相似文献