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271.
Marchand P. Lefebvre L. Perez G. Counioux J.-J. Coquerel G. 《Journal of Thermal Analysis and Calorimetry》2002,67(1):37-47
Computer modelling of time dependences of radon release rate during hydration of 3CaO·SiO2 was carried out. It was demonstrated that the emanation thermal analysis (ETA) can be used for the characterisation of morphology changes during hydration of Portland cement clinker minerals. The presence of various additives and increased temperature affecting kinetics of hydration were simulated by the mathematical model of the radon release rate during hydration of 3CaO·SiO2. A good agreement between the mathematical model and ETA experimental results was found.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
272.
Gref R Lück M Quellec P Marchand M Dellacherie E Harnisch S Blunk T Müller RH 《Colloids and surfaces. B, Biointerfaces》2000,18(3-4):301-313
Nanoparticles possessing poly(ethylene glycol) (PEG) chains on their surface have been described as blood persistent drug delivery system with potential applications for intravenous drug administration. Considering the importance of protein interactions with injected colloidal dug carriers with regard to their in vivo fate, we analysed plasma protein adsorption onto biodegradable PEG-coated poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA) and poly(-caprolactone) (PCL) nanoparticles employing two-dimensional gel electrophoresis (2-D PAGE). A series of corona/core nanoparticles of sizes 160–270 nm were prepared from diblock PEG-PLA, PEG-PLGA and PEG-PCL and from PEG-PLA:PLA blends. The PEG Mw was varied from 2000–20 000 g/mole and the particles were prepared using different PEG contents. It was thus possible to study the influence of the PEG corona thickness and density, as well as the influence of the nature of the core (PLA, PLGA or PCL), on the competitive plasma protein adsorption, zeta potential and particle uptake by polymorphonuclear (PMN) cells. 2-D PAGE studies showed that plasma protein adsorption on PEG-coated PLA nanospheres strongly depends on the PEG molecular weight (Mw) (i.e. PEG chain length at the particle surface) as well as on the PEG content in the particles (i.e. PEG chain density at the surface of the particles). Whatever the thickness or the density of the corona, the qualitative composition of the plasma protein adsorption patterns was very similar, showing that adsorption was governed by interaction with a PLA surface protected more or less by PEG chains. The main spots on the gels were albumin, fibrinogen, IgG, Ig light chains, and the apolipoproteins apoA-I and apoE. For particles made of PEG-PLA45K with different PEG Mw, a maximal reduction in protein adsorption was found for a PEG Mw of 5000 g/mole. For nanospheres differing in their PEG content from 0.5 to 20 wt %, a PEG content between 2 and 5 wt % was determined as a threshold value for optimal protein resistance. When increasing the PEG content in the nanoparticles above 5 wt % no further reduction in protein adsorption was achieved. Phagocytosis by PMN studied using chemiluminescence and zeta potential data agreed well with these findings: the same PEG surface density threshold was found to ensure simultaneously efficient steric stabilization and to avoid the uptake by PMN cells. Supposing all the PEG chains migrate to the surface, this would correspond to a distance of about 1.5 nm between two terminally attached PEG chains in the covering ‘brush’. Particles from PEG5K-PLA45K, PEG5K-PLGA45K and PEG5K-PCL45K copolymers enabled to study the influence of the core on plasma protein adsorption, all other parameters (corona thickness and density) being kept constant. Adsorption patterns were in good qualitative agreement with each other. Only a few protein species were exclusively present just on one type of nanoparticle. However, the extent of proteins adsorbed differed in a large extent from one particle to another. In vivo studies could help elucidating the role of the type and amount of proteins adsorbed on the fate of the nanoparticles after intraveinous administration, as a function of the nature of their core. These results could be useful in the design of long circulating intravenously injectable biodegradable drug carriers endowed with protein resistant properties and low phagocytic uptake. 相似文献
273.
Synthesis and rearrangement of ethylenic 17-hydroxy steroids, with a cis or trans configuration of the 18-methyl and 17-hydroxy groups, is described. The cis compounds lead, in acidic media, to backbone-rearranged steroids, whereas the trans compounds lead to C-nor spiroketones. A concerted mechanism is postulated for the rearrangement of the C and D rings, in every case different from the one occurring for the transposition of ABC rings. 相似文献
274.
Design of a triple-helix-specific cleaving reagent 总被引:5,自引:0,他引:5
Zain R Marchand C Sun J Nguyen CH Bisagni E Garestier T Hélène C 《Chemistry & biology》1999,6(11):771-777
BACKGROUND: Double-helical DNA can be recognized sequence specifically by oligonucleotides that bind in the major groove, forming a local triple helix. Triplex-forming oligonucleotides are new tools in molecular and cellular biology and their development as gene-targeting drugs is under intensive study. Intramolecular triple-helical structures (H-DNA) are expected to play an important role in the control of gene expression. There are currently no good probes available for investigating triple-helical structures. We previously reported that a pentacyclic benzoquinoquinoxaline derivative (BQQ) can strongly stabilize triple helices. RESULTS: We have designed and synthesized the first triple-helix-specific DNA cleaving reagent by covalently attaching BQQ to ethylenediaminetetraacetic acid (EDTA). The intercalative binding of BQQ should position EDTA in the minor groove of the triple helix. In the presence of Fe(2+) and a reducing agent, the BQQ-EDTA conjugate can selectively cleave an 80 base pair (bp) DNA fragment at the site where an oligonucleotide binds to form a local triple helix. The selectivity of the BQQ-EDTA conjugate for a triplex structure was sufficiently high to induce oligonucleotide-directed DNA cleavage at a single site on a 2718 bp plasmid DNA. CONCLUSIONS: This new class of structure-directed DNA cleaving reagents could be useful for cleaving DNA at specific sequences in the presence of a site-specific, triple-helix-forming oligonucleotide and also for investigating triple-helical structures, such as H-DNA, which could play an important role in the control of gene expression in vivo. 相似文献
275.
A synthesis of 12-oxa-3,5,9,10-tetrachlorohexacyclo[5.4.1.02,6.03,10.05,9.08,11]dodecane-4-one (6) from 4,4-dimethoxy-2,3,5,6-tetrachloropentacyclo [[5.4.0.02,6.03,10.05,9]undecane-8,11-dione (1) is described. Reaction of 6 with sodium hydroxide in refluxing benzene, toluene, or tetrahydrofuran affords 11-oxa-3,4,5-exo-6-tetrachloropentacyclo [[6.2.1.02,7.04,10.05,9]undecane-endo-3-carboxylic acid (7a, 80·2% yield). The corresponding reaction of 6 with refluxing aqueous sodium hydroxide solution affords 4,12-dioxa-8,11-dichlorohexacyclo-[5.4.1.02,6.03,10.05,9.08,11]dodecane-1-carboxylic acid (8a, 66·5% yield). A mechanism which accounts for the formation of 7a and 8a from 6 is presented. 相似文献
276.
N. Achard J. J. Counioux G. Marichy A. Marchand 《Journal of Thermal Analysis and Calorimetry》2000,59(3):927-934
The electrical properties of ZnO varistors are induced by a sintering step. The phenomena occurring during this thermal treatment
have been studied through model systems whose nature and composition are well defined. The pure BiSbO4 and Bi3 Zn2 Sb3 O14 phases have been synthetised by Direct Oxidation of a Precursory Alloy (DOPA) and characterized using XRD method. Each one
of these phases can react with zinc monoxide through an invariant isobaric reaction in the ZnO–Bi2 O3 –Sb2 O3 system:
– at 998°C 17/3<ZnO>+2/3<Bi3 Zn2 Sb3 O14 > arrow <Zn7 Sb2 O12 > + ((Bi2 O3 ))
– at 1058°C 7<ZnO>+2<BiSbO4 > arrow <Zn7 Sb2 O12 >+((Bi2 O3 ))
These thermodynamic considerations can explain the thermal domain of the sintering reaction described in the literature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
277.
Marchand M Dewez D Franck F Popovic R 《Journal of photochemistry and photobiology. B, Biology》2004,75(1-2):73-80
The protochlorophyllide transformation process was investigated by using comparative analysis of 77 K fluorescence spectral changes occurring in isolated bundle sheath (BS) cells of etiolated Zea mays leaves after being exposed to a 200 ms saturating flash. Deconvolution analysis of the fluorescence spectra showed essential differences in the ratio of protochlorophyll(ides) and chlorophyll(ides) spectral forms indicating for BS cells to have a characteristic pathway of protochlorophyllide transformation. Bundle sheath cells showed a high ratio between non-photoactive protochlorophyll(ide)-F632 and photoactive protochlorophyllide-F655. In those cells, the 200 ms flash triggered a preferential formation of chlorophyll(ide)-F675 which remained stable in the dark for at least 90 min. Isolated BS cells showed an accumulation of chlorophyll(ide)-F675 resulting in the formation of inactive photosystem II. However for mesophyll cells of intact leaves, it was found to have a high ratio between photoactive and non-photoactive protochlorophyll(ide), showing the succession of chlorophyll(ide) forms usually known in C(3) plants. Protochlorophyllide phototransformation pathway in BS cells related to early stages of plastid differentiation triggered by light may indicate specific conditions for PSII assembly process leading to inactive PSII forms. 相似文献
278.
Previous work suggests that pi-pi interactions between certain solutes and both phenyl and cyano columns can contribute to sample retention and the selectivity of these two column types versus alkylsilica columns. Recent studies also suggest that dipole-dipole interactions are generally unimportant for retention on cyano columns. The present study presents data for 44 solutes, three columns and two different mobile phases that were selected to further test these conclusions. We find that pi-pi interactions can contribute to retention on both cyano and phenyl columns, while dipole-dipole interactions are likely to be significant for the retention of polar aliphatic solutes on cyano columns. When acetonitrile/water mobile phases are used, both pi-pi and dipole-dipole interactions are suppressed, compared to the use of methanol/water. 相似文献
279.
Photoelectron spectra of six 8,11-disubstituted pentacycloundecanes (1, 3 - 7) are reported; the results suggest that the through-space interaction betweeen unsaturation centers in 1 and 3 dominates over the through-bond interaction mechanism. 相似文献
280.
M. Guillot F. Tchéou A. Marchand P. Feldmann R. Lagnier 《Zeitschrift für Physik B Condensed Matter》1981,44(1):53-57
Specific heat measurements have been carried out on single crystals of Erbium and Yttrium Iron garnets between 5 and 210K. The ErIG specific heat presents two anomalies. The first one situated at (77±4)K corresponds approximatively to the compensation temperature at which the bulk magnetization vanishes; the second one was found at (54±2)K below which temperature the |100| direction appears to be the easy direction. Both anomalies are to be associated with second order transitions and correspond to the onset of an umbrella structure and a change of the easy direction. 相似文献