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101.
Nestor J Esquena J Solans C Levecke B Booten K Tadros TF 《Langmuir : the ACS journal of surfaces and colloids》2005,21(11):4837-4841
The use of a new class of graft polymer surfactants, based on inulin, in emulsion polymerization of poly(methyl methacrylate) (PMMA) and polystyrene (PS) particles is described. PS and PMMA were synthesized by emulsion polymerization, and stable particles with a high monomer content (50 wt %) were obtained with a very small amount of polymeric surfactant ([surfactant]/[monomer] = 0.0033). The latex dispersions were characterized by dynamic light scattering and by transmission electron microscopy to obtain the average particle size and the polydispersity index, and the stability was determined by turbidimetry measurements and expressed in terms of critical coagulation concentration. The last section gives a comparison of PMMA particles prepared by emulsion polymerization using classical surfactants from different types as emulsifiers with that obtained using the copolymer surfactant. It shows the superiority of INUTEC SP1 as it is the only one that allows stable particles at 20 wt % monomer content, with a smaller ratio [surfactant]/[monomer] = 0.002. 相似文献
102.
Transition metal-mediated intramolecular [2+2+2] cycloisomerizations of cyclic triynes and enediynes
Torrent A González I Pla-Quintana A Roglans A Moreno-Mañas M Parella T Benet-Buchholz J 《The Journal of organic chemistry》2005,70(6):2033-2041
[reaction: see text] Nitrogen-containing 15-membered triacetylenic macrocycles known as 1,6,11-tris(arylsulfonyl)-1,6,11-triazacyclopentadeca-3,8,13-triynes (1) and enediynic macrocycles called 1,6,11-tris(arylsulfonyl)-1,6,11-triazacyclopentadeca-3-ene-8,13-diynes (4 and 5) were satisfactorily prepared. [2+2+2] cycloisomerization processes catalyzed by transition metals were tested in the above-mentioned macrocycles. Readily available and familiar cyclotrimerization precatalysts were examined for efficiency. Among them, the RhCl(CO)(PPh(3))(2) complex was found to catalyze the cycloisomerization reaction giving the desired cycloadducts in high yields. 相似文献
103.
Fernández CE Mancera M Holler E Bou JJ Galbis JA Muñoz-Guerra S 《Macromolecular bioscience》2005,5(2):172-176
Low-molecular-weight poly(alpha-methyl beta,L-malate) made of approximately 25-30 units was prepared from microbial poly(beta,L-malic acid) by treatment with diazomethane. The thermal characterization of the polymalate methyl ester was carried out and its crystalline structure was preliminary examined. Its ability to crystallize both from solution and from the melt was comparatively evaluated. 相似文献
104.
Anbarasan Kalaiselvan Ponnambalam Venuvanalingam Jordi Poater Miquel Sol 《International journal of quantum chemistry》2005,102(2):139-146
The stereochemical course of the deamination of cis‐2,3‐dimethylaziridine by nitrosyl chloride was investigated at the QCISD/6‐31G(d) level. Calculations reveal that the reaction takes place in two steps. In the first step, the reactants form a pre‐reactive complex, followed by a spiro‐type bicyclic transition state, which on dissociative cycloelimination gives the N‐nitrosoaziridine intermediate. In the second step, this intermediate undergoes cycloreversion through a slightly asynchronous concerted transition state to form an alkene with the same stereochemistry, which is in total agreement with experiment. In the whole reaction, the denitrosation step is found to be rate‐determining. For comparison, geometry optimizations and energies were also obtained at the B3LYP/6‐31G(d) level. It was found that the B3LYP energy results differed significantly from the QCISD ones. To analyze the reason for this difference, B3LYP calculations were repeated by varying the contribution of exact exchange in the Becke functional. With respect to the QCISD results, it has been shown that the functional with 0% exact exchange yields the best activation barriers, whereas the functional with 30% exact exchange is the most suitable one to carry out the complexation and reaction energy calculations. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
105.
106.
Summary The addition of dienes to the system [(Cp2TiCl)2] LiAlH4toluene changes the system so that the complex [Cp2TiAlH4] is quantitatively formed instead of a titanocene hydride — aluminium hydride cluster. The complex [Cp2TiAlH4] is further converted into 3-allyltitanocene derivatives ([Cp2TiA]) if the diene structure is suitable for formation of stable [Cp2TiA] compounds and if the equilibrium [Cp2TiAlH4]+diene[Cp2TiA]+A1H3 is shifted towards the formation of [Cp2TiA] by the excess of diene. All the compounds [Cp2TiA] exhibit high-resolution e.s.r. spectra at g=1.993, showing interaction of the unpaired electron with the cyclopentadienyl and 3-allyl protons. The e.s.r. spectra clearly reveal the presence of alkyl substituents atsyn-1,3-positions of 3-allyl ligand, and show a triplet of multiplets for (3-allyl)titanocene, doublets of multiplets for (1-alkyl-3-allyl)titanocenes and single multiplets for (1,3-dialkyl-3-allyl)-titanocenes. thermal isomerization of (1,3-dimethyl-3-allyl)-titanocene and (1-methyl-3-ethyl-3-allyl)titanocene, hitherto considered as the stable Cp2TiA compounds, into (1-alkyl-3-allyl)titanocenes was confirmed by e.s.r. and electronic absorption spectroscopy as well as by chemical means. 相似文献
107.
Michele Tomasini Dr. Lucia Caporaso Jonathan Trouvé Dr. Jordi Poater Dr. Rafael Gramage-Doria Dr. Albert Poater 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(57):e202201970
Non-biological catalysts following the governing principles of enzymes are attractive systems to disclose unprecedented reactivities. Most of those existing catalysts feature an adaptable molecular recognition site for substrate binding that are prone to undergo conformational selection pathways. Herein, we present a non-biological catalyst that is able to bind substrates via the induced fit model according to in-depth computational calculations. The system, which is constituted by an inflexible substrate-recognition site derived from a zinc-porphyrin in the second coordination sphere, features destabilization of ground states as well as stabilization of transition states for the relevant iridium-catalyzed C−H bond borylation of pyridine. In addition, this catalyst appears to be most suited to tightly bind the transition state rather than the substrate. Besides these features, which are reminiscent of the action modes of enzymes, new elementary catalytic steps (i. e. C−B bond formation and catalyst regeneration) have been disclosed owing to the unique distortions encountered in the different intermediates and transition states. 相似文献
108.
Gas detection is important for controlling industrial and vehicle emissions, household security and environmental monitoring. In recent decades many devices have been developed for detecting CO(2), CO, SO(2), O(2), O(3), H(2), Ar, N(2), NH(3), H(2)O and several organic vapours. However, the low selectivity or the high operation temperatures required when most gas sensors are used have prompted the study of new materials and the new properties that come about from using traditional materials in a nanostructured mode. In this paper, we have reviewed the main research studies that have been made of gas sensors that use nanomaterials. The main quality characteristics of these new sensing devices have enabled us to make a critical review of the possible advantages and drawbacks of these nanostructured material-based sensors. 相似文献
109.
110.
In this paper we propose a method for carrying out variational transition state theory calculations without first obtaining
a converged minimum-energy path (MEP). We illustrate the method in two ways, first of all by employing an unconverged MEP
and secondly by using a dynamically optimized distinguished reaction path. Preliminary tests of the algorithm for the reactions
OH+H2→H2O+H and C2H5→C2H4+H are very encouraging.
Received: 22 January 1997 / Accepted: 11 March 1997 相似文献