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111.
A new series of photoactivated DNA oxidizing agents in which an acridine moiety is covalently linked to viologen by an alkylidene spacer was synthesized, and their photophysical properties and interactions with DNA, including DNA cleaving properties, were investigated. The fluorescence quantum yields of the viologen-linked acridines were found to be lower than that of the model compound 9-methylacridine (MA). The changes in free energy for the electron transfer reactions were found to be favorable, and the fluorescence quenching observed in these systems is explained by an electron transfer mechanism. Intramolecular electron transfer rate constants were calculated from the observed fluorescence quantum yields and singlet lifetime of MA and are in the range from 1.06x10(10) s(-1) for 1 a (n=1) to 6x10(8) s(-1) for 1 c (n=11), that is, the rate decreases with increasing spacer length. Nanosecond laser flash photolysis of these systems in aqueous solutions showed no transient absorption, but in the presence of guanosine or calf thymus DNA, transient absorption due to the reduced viologen radical cation was observed. Studies on DNA binding demonstrated that the viologen-linked acridines bind effectively to DNA in both intercalative and electrostatic modes. Results of PM2 DNA cleavage studies indicate that, on photoexcitation, these molecules induce DNA damage that is sensitive to formamidopyrimidine DNA glycosylase. These viologen-linked acridines are quite stable in aqueous solutions and oxidize DNA efficiently and hence can be useful as photoactivated DNA-cleaving agents which function purely by the co-sensitization mechanism. 相似文献
112.
Stephen K. Boyer Joseph McKenna Jerrold Karliner Michael Nirsberger 《Tetrahedron letters》1985,26(31):3677-3680
Polychlorinated biphenyls (PCBs) were effectively dechlorinated to biphenyl under mild conditions using an aqueous solution of sodium hypophosphite in the presence of a palladium catalyst. 相似文献
113.
114.
Donna C Arnold Olga Kazakova Guillaume Audoit Joseph M Tobin Jaideep S Kulkarni Sergey Nikitenko Michael A Morris Justin D Holmes 《Chemphyschem》2007,8(11):1694-1700
The synthesis of marokite CaMn(2)O(4) nanowires using a hydrothermal method is reported. Transmission electron microscopy and electron diffraction measurements show that the nanowires are polycrystalline in nature with diameters between 10 and 20 nm and lengths ranging from approximately 100 to 500 nm. Most interestingly, in contrast with the bulk material, magnetization measurements show that these nanowires exhibit ferromagnetic ordering with a Curie temperature (T(C)) of approximately 40 K. 相似文献
115.
Joseph T. Repine Douglas S. Johnson Andrew D. White Michael A. Stier Trent Rankin Samarendra N. Maiti 《Tetrahedron letters》2007,48(31):5539-5541
A series of regioisomerically monofluorinated 1-(naphthalen-1-yl)piperazines is described. 相似文献
116.
Ananthakrishnan Gunasekaran Thiruvalam Jayachandran Joseph H. Boyer Mark L. Trudell 《Journal of heterocyclic chemistry》1995,32(4):1405-1407
The reaction of glyoxime ( 4 ) and hydroxylamine hydrochloride in aqueous sodium hydroxide was found to be a safe and inexpensive method for the preparation of multigram quantities of diaminoglyoxime ( 5 ). Potassium hydroxide mediated dehydration of 5 furnished diaminofurazan ( 1 ) in good yield of exceptional purity. The ready availability of 1 and 5 has facilitated the synthesis of new energetic furazan derivative 8 . 相似文献
117.
The reaction of pyridyl functionalized porphyrins with Re(CO)(5)Cl in THF results in the formation of porphyrin dimers which, despite incorporation of rhenium into the assemblies, remain fluorescent. The rigid compounds provide an efficient geometry and/or orbital pathway for singlet energy transfer, rendering these compounds suitable, in principle, for the study of both through-bond and through-space energy transfer. Derivatives containing both metallated and freebase porphyrins connected via the metal corners display efficient porphyrin-porphyrin energy transfer. The photophysical properties of the assemblies have been studied by both steady-state and time-resolved fluorescence techniques, yielding approximate rates and efficiencies for porphyrin-porphyrin energy transfer. 相似文献
118.
A general method is described for the resolution of cycloprop-2-ene carboxylic acids via diastereomeric N-acyloxazolidines prepared from enantiomerically pure oxazolidinones. Although a number of oxazolidinones were shown to resolve cyclopropene carboxylic acids, the oxazolidinones of S-phenylalaninol, S-phenylglycine and (1S,2R)-cis-1-amino-2-indanol are optimal in terms of resolving power and cost effectiveness. Separations were performed using simple flash chromatography, and because there is typically a large difference in Rf values it is possible to separate gram quantities of pure diastereomers in a single chromatogram. The cycloprop-2-ene carboxylic acids that can be resolved include those that are substituted at the 1-position by H, Ph, α-naphthyl, CO2Me, CH2OMOM, and trans-styryl; alkene substituents include Me, n-alkyl, Ph and tethered alkynes. Remarkably, 2-methyl-3-propylcycloprop-2-ene carboxylic acid can also be resolved with ease. The relative configurations of four diastereomerically pure oxazolidines were determined by X-ray crystallography. Reduction of the N-acyloxazolidinones with LiBH4 give enantiomerically pure derivatives of 3-hydroxymethylcyclopropene that react with either MeMgCl or vinylMgCl and catalytic CuI to give enantiomerically pure products of syn-addition. 相似文献
119.
Allwyn G Cole Laurie M Yoder Joseph J Shiang Neil A Anderson Larry A Walker Mark M Banaszak Holl Roseanne J Sension 《Journal of the American Chemical Society》2002,124(3):434-441
An ultrafast transient absorption study of the primary photolysis of ethyl- and n-propylcobalamin in water is presented. Data have been obtained for two distinct excitation wavelengths, 400 nm at the edge of the UV gamma-band absorption, and 520 nm in the strong visible alphabeta-band absorption. These data are compared with results reported earlier for the B(12) coenzymes, methyl- and adenosylcobalamin. The data obtained for ethylcobalamin and n-propylcobalamin following excitation at 400 nm demonstrate the formation of one major photoproduct on a picosecond time scale. This photoproduct is spectroscopically identifiable as a cob(II)alamin species. Excitation of methyl-, ethyl-, and n-propylcobalamin at 520 nm in the low-lying alphabeta absorption band results in bond homolysis proceeding via a bound cob(III)alamin MLCT state. For all of the cobalamins studied here competition between geminate recombination of caged radical pairs and cage escape occurs on a time scale of 500 to 700 ps. The rate constants for geminate recombination in aqueous solution fall within a factor of 2 between 0.76 and 1.4 ns(-1). Intrinsic cage escape occurs on time scales ranging from 相似文献
120.
Ignacy Gryczynski Henryk Szmacinski Joseph R. Lakowicz 《Photochemistry and photobiology》1995,62(4):804-808
Abstract— We show that the calcium fiuorophore Indo-1 can be excited by simultaneous absorption of three-photons at 885 nra, a wavelength readily available from Ti:sapphire lasers. Three-photon excitation was demonstrated by the emission intensity of Indo-1 which depended on the cube of the laser power, and by a higher anisotropy than was observed for two-photon excitation. Excitation of Indo-1 becomes a two-photon process when the wavelength is decreased to 820 nm. Three-photon excitation was accomplished at a low 17μ concentration of Indo-1. Examination of the spatial profile of the excited Indo-1 showed a smaller volume for three- versus two-photon excitation. These results suggest that three-photon excitation may be useful in fluorescence microscopy using the long wavelength output of Tksapphire lasers, and may provide higher spatial resolution than available using two-photon excitation. 相似文献