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71.
Enzymatic degradation of two lignin-based polymers (lignophenols), lignocatechol and lignocresol, prepared by selectively grafting catechol and p-cresol to Cα positions of lignin, respectively, were carried out in aqueous organic solvents. Both lignophenols showed high reactivity in the peroxidase-catalyzed oxidation. Structural analyses by NMR spectroscopies revealed that the degraded lignophenols contained aliphatic chain content, which might be mainly formed in the reduction of the intermediate initially generated by the aromatic ring cleavage. Lower amount of aromatic units in the lignophenols after degraded by peroxidase also indicted the cleavage of aromatic rings. Due to the substitution of phenols at Cα positions of lignin, the degraded lignophenols did not have carbonyl structure, which was abundant in the biodegradation products of native lignin. The two lignophenols were also degraded by Rhus vernicifera laccase. But the degree of degradation was lower than that of the degradation by peroxidase, which might be due to the low activity of laccase on the lignin moieties in lignophenols. 相似文献
72.
Eberhard Hohaus 《Monatshefte für Chemie / Chemical Monthly》1980,111(4):863-875
The i.r., u. v.,1H n.m.r.,13C n.m.r., and11B n.m.r. spectra of several substituted diphenylboron chelates derived from salicylaldehyde azomethines were compared with respect to the influence of the amine substituentR. O–B–N-6-ring constitution of the chelates29–32 [R=OH, NH2, NHC6H5, N(CH3)2] can be deduced from the spectra.
Als 3. Mitt. gilt:F. Umland undE. Hohaus mit Beiträgen vonW. Riepe, K. Brodte, C. Schleyerbach undD. Szonn. Untersuchungen über borhaltige Ringsysteme vom Chelattyp. Forschungsbericht des Landes Nordrhein-Westfalen Nr. 2538. Opladen: Westdeutscher Verlag. 1976. 相似文献
73.
Charles B. de Koning Sunnyboy S. Manzini Joseph P. Michael Edwin M. Mmutlane Tefo R. Tshabidi Willem A.L. van Otterlo 《Tetrahedron》2005,61(3):555-564
The synthesis of substituted anthracenes from naphthalene precursors is described. The key step involved heating ortho-allyl substituted naphthalene-2-carbaldehydes and potassium t-butoxide in DMF with concomitant irradiation from a high pressure mercury lamp to afford anthracenes in yields of 76-98%. 相似文献
74.
Cossy J 《Chemical record (New York, N.Y.)》2005,5(2):70-80
The synthesis of optically active substituted piperidines has been achieved by using four different methodologies. The first one is an intramolecular nucleophilic displacement of activated alcohol moieties that was used to build up the piperidine ring of (-)-prosophylline and (-)-slaframine, and the second one is a ring-closing metathesis of unsaturated amines which was employed in the synthesis of (+)-sedamine and 4a,5-dihydrostreptazoline. The third methodology is the alpha-functionalization of N-Boc piperidines which was particularly useful in the synthesis of argatroban, and the fourth one is a ring expansion of prolinols to 3-chloropiperidines or 3-hydroxypiperidines which was utilized to synthesize (-)-paroxetine, (-)-pseudoconhydrine, the piperidine ring of (-)-velbanamine and (+)-zamifenacin. 相似文献
75.
Conformations of 2-methoxytetrahydropyran as a model for the six-membered ring in aldopyranosides have been calculated by the PCILO method using the algorithm of the conjugated gradient to optimize the geometry. The calculated geometry of the fourteen basic forms of 2-methoxytetrahydropyran was found to be in agreement with the available data obtained by X-ray diffraction of pyranosides. The results indicate differences in the geometry of 2-methoxytetrahydropyran resulting from the change of the axial vs. equatorial position of the methoxyl group. These changes are particularly meaningful in the values of bond angles and they are in agreement with the anomeric and exoanomeric effects. The experimentally found differences in the energies of an axial (4
C
1) and equatorial (1
C
4) conformer, G = 2.9–3.7 kJ/mol, and the dipole moment, = 1.20 ± 0.05 D (1D = 3.33 10–30mAs) agree well with the calculated values E = 3.18 kJ/mol and <> = 1.18 D which, in turn, suggest that the axial conformer is preferred over the equatorial one by a ratio a:e = 78:22. 相似文献
76.
Antonio Alberola Rebecca J. Collis Robert J. Less Jeremy M. Rawson 《Journal of organometallic chemistry》2007,692(13):2743-2749
A general three-step synthesis to a range of benzo-fused-1,3,2-dithiazolylium salts bearing both electron-withdrawing (CN) and electron-donating (Me) groups is described. This methodology has also been extended to pyridyl derivatives and offers a potential route to a diversity of 1,3,2-dithiazolylium rings and their corresponding 1,3,2-dithiazolyl free radicals. The key steps in the reaction are treatment of a substituted 1,2,-dichlorobenzene with two equivalents of [tBuS]Na, followed by chlorination to yield the corresponding bis(sulfenyl chloride). Subsequent ring closure with Me3SiN3 yields the target 1,3,2-dithiazolylium ring system in good yield. The preparation and crystal structures of 3′-methyl-benzo-1,3,2-dithiazolylium chloride and 3′-methyl-benzo-1,3,2-dithiazolyl are described and the electronic properties of the radical examined through EPR spectroscopy, DFT calculations and variable temperature magnetic susceptibility measurements. 相似文献
77.
Shinichi Yamabe Noriko Tsuchida Tsutomu Minato Takahisa Machiguchi 《Theoretical chemistry accounts》2005,113(2):95-106
Cheletropic additions forming cyclopropane rings were studied theoretically. Ten addition paths were traced by means of density-functional-theory calculations. Two 1,4-dienes, 1,4-pentadiene, and tricyclo[5.3.1.04,9]undeca-2,5-diene were adopted as substrates. CO, SO2, C2H5PCl2, CCl2 and SiCl2 were employed as cheletropic reagents (Xs). An orbital correlation diagram of the Woodward–Hoffmann (W–H) rule and frontier molecular orbital (FMO) interactions between them were investigated in detail. The FMO interactions, HOMO (1,4-diene)lumo (X) and homo (X)LUMO (diene), work reasonably for the progress of the reactions. Those cause the formation of two C–X bonds and a cyclopropane ring, and alternation of double bonds to single bonds. All the additions are concerted. The easiness of the ring formation depends upon the energy gap between HOMO and lumo and that between homo and LUMO, and the spatial directions of HOMO and LUMO extensions. Symmetry conservation of the W–H rule does not hold necessarily for those addition paths. The symmetry-breaking was discussed in terms of FMO interactions.Acknowledgement This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, Japan and by Nishida Memorial Foundation for Fundamental Chemical Research. 相似文献
78.
Reinhard Haase Dorit S. Meinhold Berthold Thomas Edwin Weber Gerd Rheinwald 《Structural chemistry》2002,13(5-6):471-477
The crystal structures of inclusion compounds of 3,3-bis(9-hydroxy-9-fluorenyl)-2,2-binaphthyl host (1) and its chloro (2) or bromo (3) derivatives substituted in 2,7-positions of the fluorene units with acetone guests (1A–3A) were determined by X-ray studies as well as by 1H-CRAMPS solid-state NMR. Using this NMR technique allows identification of differently bound guest molecules due to their different chemical shifts caused by the influence of the ring current effects of the host aryl units. 相似文献
79.
A new C19 hydroxylated enyne 15, as potential A-ring building block of vitamin D analogues, was synthesized in enantiomerically pure form in nine steps from (−)-(S)-limonene. This short synthesis involved ozonolyzis of 1,2-limonene oxide followed by a Criegee rearrangement, epoxide trans diaxial ring opening by lithium acetylide, elimination, epoxidation and syn β-elimination of the resulting homopropargylic oxirane. 相似文献
80.
Tsuneo Okubo 《Colloid and polymer science》2006,284(12):1395-1401
Sedimentation and drying dissipative structural patterns formed in the course of drying colloidal silica spheres (1.2 μm in diameter) in aqueous suspension have been studied in a glass dish and a polystyrene dish. The broad ring patterns are formed within a short time in suspension state by the convection flow of water and colloidal spheres. The broad ring patterns are not formed when a dish is covered with a cap, which demonstrates the important role of the convectional flow of silica spheres and water accompanied with the evaporation of water on the air-suspension interface. The sedimentary spheres always move by the convectional flow of water, and the broad ring patterns became sharp with time. Broad ring and microscopic fine structures are formed in the solidification processes on the bases of the convectional and sedimentation patterns. Drying patterns of the colloidal suspensions containing sodium chloride are star-like ones, which strongly supports the synchronous cooperative interactions between the salt and colloidal spheres. 相似文献