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51.
Optimum Obtention of Proferrorosamine A from Pseudomonas roseus fluorescens J. C. MARCHAL 1937. We have developed the best conditions for the culture of Pseudomonas roseus fluorescens, and a quantitative isolation of the Proferrorosamine A produced in the culture solution, in order to study the incorporation of 1-[14C]-glycerol in this propigment. 相似文献
52.
Setzer MJ 《Journal of colloid and interface science》2001,235(1):170-182
In contrast to the triple-point condition of bulk material, condensed matter in porous media can coexist stably as liquid, solid, and vapor over a wide temperature range. The necessary conditions are found by a thermodynamic approach starting with the potential which reflects the grand canonical distribution and is characterized by heat and matter exchange. The other parameters are volume and surface. Therefore, it is designated the free mechanical potential. General expressions for mechanical stability are given. On condensation and melting the nonwetting phases vanish. These are thermodynamically stable phase transitions. For the opposing effects evaporation and fusion, an energy barrier must be transgressed either by nucleation or by intrusion as discussed here. These are metastable states. Phase transitions are the conditions which limit the triple-phase region. Within this region high negative pressures are generated in the unfrozen liquid independent of the pore size where it exists. The findings are applied to water in the disperse matrix of hardened cement paste. They are the basis for "micro ice lens pumping". Copyright 2001 Academic Press. 相似文献
53.
Max Herberhold Udo Drfler Bemd Wrackmeyer 《Journal of organometallic chemistry》1997,530(1-2):117-120
1,2-Bis(dimethylamino)-1,2-dibora-[2]ferrocenophane (1) was prepared by the reaction of 1,1′-dilithioferrocene with 1,2-dichlorobis(dimethylamino)diborane(4). In addition to hindered rotation about the B-N bond (ΔG‡ > 80 kJ mol−1), another dynamic process was revealed by 1H and 13C NMR in solution at low temperature, and interpreted as motion of the cyclopentadienyl rings between staggered and eclipsed conformations (ΔG(233 K)‡ = 44 ± 1 kJ mol−1). 相似文献
54.
Andrea Schfer Manfred Hesse Max Viscontini Henning Paul Berthold Fischer 《Helvetica chimica acta》1995,78(7):1763-1776
The experimental conditions developed for the detection of rather stable radical cations in solution by electrospray-ionization mass spectrometry (ESI-MS) of a FeII complex of 2-amino-5,6,7,8-tetrahydro-5-methylpteridin-4 (3H)-one ( 1c ) are used to observe the formation of the more unstable radical cations formed from 2-amino-5,6,7,8-tetrahydropteridin-4(3H)-one ( 1a ) and tris(pentane-2,4-dionato)iron(III) ([FeIII(acac)3]; 4 ) and to monitor their oxidation to the corresponding p-quinonoid dihydropterin complexes. These results contribute to the understanding of the important role played by 6β-5,6,7,8-tetrahydro-L -biopterin ( 1b ; a homologue of 1a ) together with iron as constituent of some cofactors. The complexes obtained from 1a and iron may be considered, e.g. as a model of the cofactor of the phenylalanine hydroxylase. Moreover, we describe an improved synthesis of 1c . 相似文献
55.
We have performed two molecular-dynamics simulations to study the structural and dynamical properties of water at the interface with phospholipid bilayers. In one of the simulations the bilayer contained neutral phospholipid molecules, dioleoylphosphatidylcholine (DOPC); in the second simulation the bilayer contained charged lipid molecules, dioleoylphosphatidylserine (DOPS). From the density profile of water we observe that water next to the DOPS bilayer is more perturbed as compared to water near the DOPC bilayer. Using an energetic criterion for the determination of hydrogen bonding we find that water molecules create strong hydrogen bonds with the headgroups of the phospholipid molecules. Due to the presence of these bonds and also due to the confinement of water, the translational and orientational dynamics of water at the interface are slowed down. The degree of slowing down of the dynamics depends upon the location of water molecules near a lipid headgroup. 相似文献
56.
Murat Acemoglu Peter Uebelhart Max Rey Conrad Hans Eugster 《Helvetica chimica acta》1988,71(5):931-956
Syntheses of Enantiomerically Pure Violaxanthins and Related Compounds The epoxides 16 and ent- 16 , prepared by Sharpless-Katsuki oxidation of 15 in excellent yield and very high enantiomeric purity, were used as synthons for the preparation of (+)-(S)-didehydrovomifoliol (45) , (+)-(6S, 7E, 9E)-abscisic ester 46 , (+)-(6S, 7E, 9Z)-abscsic ester 47 , (?)-(3S, 7E, 9E)-xanthoxin (49) , (?)-(3R, 7E, 9E)-xanthoxin (50) , (3S, 5R, 6S, 3′S,5′R, 6′S, all-E)-violaxanthin (1) (3R, 5R,6S,3′R,5′R,6′S, all-E)-violaxanthin (55) and their (9Z) (see 53 , 57 ), (13Z) (see 54 , 58 ), and (15Z) (see 60 ) isomers. The novel violadione ( 61 ) was prepared from 1 by oxidation with DMSO/Ac2O. By base treatment, 61 was converted into violadienedione (62) , a potential precursor of carotenoids with phenolic end groups. 相似文献
57.
Roland Prewo Jost H. Bieri Subhendu Narayan Ganguly Max Viscontini 《Helvetica chimica acta》1982,65(3):1094-1099
The Configuration at C(6) of Natural 5,6,7,8-Tetrahydro-L-biopterin and of its Pentaacetate The structure of (6.R)-pentaacetyl-5,6,7,8-tetrahydro-L-biopterin, one of two diastereoisomers obtained by catalytic hydrogenation and subsequent acetylation of L-biopterin, has been determined by X-ray diffraction analysis. The space group is P212121, a=8,053(l), b=14,955(3), c= 21,502 (4) Å. The asymmetric unit contains one molecule of the biopterin derivative and one of ethyl acetate. The R-configuration can be assigned to C(6) by reference to the known configurations of the other asymmetric C-atoms. As hydrolysis of this diastereoisomer yields the natural 5, 6,7,8-tetrahydro-L-biopterin, the latter also possesses the (6 R)-configuration. 相似文献
58.
Conformational analysis of 5,6,7,8-tetrahydropteroic acid and 5,6,7,8-tetrahydro-L -folic acid In the 360-MHz-1H-NMR.-spectrum of (6R, S)-9,9-dideuterio-5, 6, 7, 8-tetrahydropteroic acid (racemic) (XIII) (AMX-System, Fig. 4) and (6R, S)-9,9-dideuterio-5, 6, 7, 8-tetrahydro-L -folic acid (diastereomeric) (XVI) the Ha–C(6) and Ha–C(7) show a vicinal coupling constant of 6,7 Hz and the Ha–C(6) and He–C(7) one of 3,2 Hz. The first coupling constant provides evidence for an approximate trans-diaxal arrangement of Ha–C(6) and Ha–C(7), and the second for a gauche conformation of Ha–C(6) and He–C(7). The tetrahydropyrazine ring in the racemic 5, 6, 7, 8-tetrahydropteroic acid (III) and in the diastereomeric 5, 6, 7, 8-tetrahydro-L -folic acid (XVII) exists therefore in a half-chair conformation with a pseudoequatorial position of the side chain at C(6) (Fig.5). 相似文献
59.
PHOTOTROPISM IN PHYCOMYCES MUTANTS LACKING β-CAROTENE 总被引:1,自引:0,他引:1
Abstract. β-carotene and riboflavin are considered as the major candidates for the photoreceptor for physiological responses to blue light in Phycomyces and a number of other organisms. Mutants of Phycomyces blocked in all six steps of the biosynthesis of β-carotene from phytoene contain no detectable β-carotene (less than 4 times 10-5 of wild-type amount) but exhibit phototropic responses identical to wild-type. Moreover, wild-type Phycomyces , while abundant in trans -β-carotene, contains no detectable cis -β-carotene, sometimes proposed as a photoreceptor candidate on the basis of the close similarity of the cis -species absorption spectrum in the near UV region to many action spectra for blue-light responses. These results indicate that β-carotene cannot be the photoreceptor for phototropism in Phycomyces. 相似文献
60.