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91.
A general stochastic theory of size exclusion chromatography (SEC) able to account for size dependence on both pore ingress and egress processes, moving zone dispersion and pore size distribution, was developed. The relationship between stochastic-chromatographic and batch equilibrium conditions are discussed and the fundamental role of the 'ergodic' hypothesis in establishing a link between them is emphasized. SEC models are solved by means of the characteristic function method and chromatographic parameters like plate height, peak skewness and excess are derived. The peak shapes are obtained by numerical inversion of the characteristic function under the most general conditions of the exploited models. Separate size effects on pore ingress and pore egress processes are investigated and their effects on both retention selectivity and efficiency are clearly shown. The peak splitting phenomenon and peak tailing due to incomplete sample sorption near to the exclusion limit is discussed. An SEC model for columns with two types of pores is discussed and several effects on retention selectivity and efficiency coming from pore size differences and their relative abundance are singled out. The relevance of moving zone dispersion on separation is investigated. The present approach proves to be general and able to account for more complex SEC conditions such as continuous pore size distributions and mixed retention mechanism. 相似文献
92.
Patrick Maestro Gerard Demazeau Michel Pouchard 《Journal of solid state chemistry》1981,40(1):101-108
A new solid solution Cr1?xIrxO2 (0 ≤ x ≤ 1) has been prepared using oxidizing agents under pressure. The magnetic study shows the importance of the spin-orbit coupling and the weakening of the ferromagnetic interactions with increasing iridium content. 相似文献
93.
Biswajit Pradhan Christopher Engelhard Sebastiaan Van Mulken Xueyan Miao Gerard W. Canters Michel Orrit 《Chemical science》2020,11(3):763
Monitoring the fluorescence of single-dye-labeled azurin molecules, we observed the reaction of azurin with hexacyanoferrate under controlled redox potential yielding data on the timing of individual (forward and backward) electron transfer (ET) events. Change-point analysis of the time traces demonstrates significant fluctuations of ET rates and of mid-point potential E0. These fluctuations are a signature of dynamical heterogeneity, here observed on a 14 kDa protein, the smallest to date. By correlating changes in forward and backward reaction rates we found that 6% of the observed change events could be explained by a change in midpoint potential, while for 25% a change of the donor–acceptor coupling could explain the data. The remaining 69% are driven by variations in complex association constants or structural changes that cause forward and back ET rates to vary independently. Thus, the observed spread in individual ET rates could be related in a unique way to variations in molecular parameters. The relevance for the understanding of metabolic processes is briefly discussed.Observing electron transfer events in individual azurin molecules, we relate the spread in transfer rates in a unique way to variations in molecular parameters. 相似文献
94.
Abdennbi Lekchiri Joëlle Morcellet Michel Morcellet 《Journal of polymer science. Part A, Polymer chemistry》1987,25(8):2231-2240
The complexes formed between palladium (II) and a polymeric ligand derived from L -asparagine, poly(N-methacryloyl-L -asparagine) (PNMAsn) have been investigated by electronic absorption and circular dichroism. N-isobutyroyl-L -asparagine (NIBAsn) was also synthesized and studied with the purpose of comparison with its polymeric analog. NIBAsn gives two complexes: at low pH, an optically active complex between one carboxylate and one secondary amide nitrogen (so-called 1N complex), and at higher pH, a 2N complex involving the primary and secondary amide group. This complex is also optically active. PNMAsn gives at low pH a 1N complex similar to that of NIBAsn, but at higher pH the 2N complex is formed between two carboxylate groups and two secondary amide groups of two different side chains of the polymer. At very high pH this 2N complex is hydrolyzed, i.e., the carboxylate-palladium bonds are replaced by hydroxyle-palladium bonds, and the complex becomes optically inactive. 相似文献
95.
Margarita Valero Brígida Esteban Rafael Peläez Licesio J. Rodrïguez 《Journal of inclusion phenomena and macrocyclic chemistry》2004,48(3-4):157-163
The aim of the present study was to investigate the effect of the presence of thewater-soluble polymer polyvinylpyrrolidone (PVP) MW = 24000 g/mol, on thecomplexation of the phototoxic anti-inflammatory drug naproxen, in its sodiumsalt form, with hydroxypropil-β-cyclodextrin (HP-β-CD). The datashown that the polymer interacts with the free naproxen and with thenaproxen:HP-β-CD inclusion complex. The presence of different proportions of PVP, in the 0–1%(w/w) rangesystematically increased the Kapp of the naproxen:HP-β-CD inclusioncomplex formation. The cause of this increase is that the polymer interactswith the HP-β-CD with a binding constant of K2 = 29000 ± 53 M-1; and with the naproxen:HP-β-CD inclusion complex, to givea ternary complex naproxen:HP-β-CD:PVP. The binding constant of thisprocess was K3 = 5350 ± 1 M-1. NMR data revealed that in the ternary system, PVP is outside of the cyclodextrin, and therefore must be wholly or partially recovering the naproxen:HP-β-CD inclusion complex. 相似文献
96.
[reaction: see text] An effective strategy has been developed for the rapid and efficient one-pot synthesis of 2-aryl-5-substituted-2,3-dihydrobenzofurans from readily available o-nitrotoluenes and aromatic aldehydes. This strategy allows access to a structurally diverse array of products for further manipulation. 相似文献
97.
Berger A Djukic JP Pfeffer M de Cian A Kyritsakas-Gruber N Lacour J Vial L 《Chemical communications (Cambridge, England)》2003,(5):658-659
In the presence of large amounts of [Me4N]Cl, the reaction of ortho-chloromercurated 2-[(eta6-phenyl)tricarbonylchromium]pyridine with mu-chloro cyclopalladated aromatic compounds yields a series of new heteroleptic heterodinuclear cis-(C--N)2Pd(II) complexes, which are valuable precursors of planar chiral cyclopalladated (eta6-arene)Cr(CO)3 complexes. 相似文献
98.
EDA-complexes of bicyclo[2,2,n]alkadienes (n = 1, 2, 3, 4) ( 1 (n)-series), 1,4-cyclohexadiene ( 2 ) and various other cyclic monoenes, dienes and trienes as donors and tetracyanoethylene (TCNE) as acceptor were investigated. Spectroscopic and thermodynamic constants of the complexes were determined and correlated with the ionisation potentials (ID) of the hydrocarbon donors obtained from PE. spectroscopy. The nature of the dominant energy contributions to the ground state and the two lowest CT-states of these weak complexes is discussed and structural conclusions are drawn. The role of the complexes in the addition reaction of the hydrocarbon components and TCNE is discussed. The homo Diels-Alder addition product of 1 (2) and TCNE, 9,9,10,10-tetracyanoquadricyclo[2,2,2,02,6,23,5]decane, and the ‘ene’-addition product of 2 and TCNE, 5-[1′,1′,2′,2′-tetracyanoethyl]-1,3-cyclohexadiene were prepared and characterized. Preliminary results for the mechanistic scheme governing the dehydrogenation of 2 by TCNE are reported. 相似文献
99.
Reaction of N-tert-butyloxycarbonylasparagine (Boc-Asn) with 2 equiv of benzyl bromide in presence of cesium carbonate led to N-benzyl-3-Boc-amino-pyrrolidin-2,5-dione 1a (N-benzyl-3-Boc-aminosuccinimide). Borane dimethylsulfide reduced 3-Boc-aminopyrrolidine-2,5-dione 1a into 3-Boc-aminopyrrolidin-2-one 2a. The same procedure could also be used to prepare derivatives 1 and 2 substituted on the aromatic ring. 相似文献
100.
In the presence of a catalytic amount of BH3·Me2S, TiCl4 or Me3SiCl, LiBH4 or NaBH4 are capable of hydroborating alkenes by following the unusual order of decreasing reactivity: tetramethylethylene > 1-methylcyclohexene > cyclohexene; the key step of the catalytic cycle is the exchange reaction between LiBH4 and the mono- or dialkylboranes resulting from hydroboration of the more substituted alkenes with BH3. 相似文献