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Determined Spectroscopically (determine + spectroscopically)
Selected AbstractsTheoretical and experimental luminescence quantum yields of coordination compounds of trivalent europiumINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Wagner M. Faustino Abstract An appraisal of a semiempirical methodology recently introduced by us for the theoretical calculation of luminescence quantum yields is presented. Six coordination compounds of Eu3+ were considered, possessing either benzoylacetonate or benzoyltrifluoroacetonate, together with either water, 2,2,-bipyridine, or 1,10-phenanthroline as ligands. Their geometries were calculated using the SMLC/AM1 method. The ligand,Eu3+ energy transfer rates were calculated in terms of a model of intramolecular energy transfer processes in lanthanide coordination compounds developed earlier by our group. The luminescence quantum yields of the complexes were calculated by solving numerically a system of rate equations for each compound, and by comparing them with the quantum yields determined spectroscopically. Finally, we show that the theoretical quantum yields correlate linearly with the experimental yields, within their error bars. Such linear correlation indicates that the theoretical approach can be useful for the a priori design of highly luminescent lanthanide coordination compounds. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Infrared intensities of benzene derivatives as a measure of the substituent resonance effectJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2001Karel Palát Jr Abstract Infrared spectra of 39 benzene mono-derivatives were recorded in the region 1000,1800,cm,1 and the intensities of the bands ,16a and ,16b were determined by computer separation. The intensities correlated with the squared resonance substituent constants ,Ro as found by Katritzky and co-workers, but band separation does not represent any essential improvement compared with the earlier simpler technique. With substituents including an NH2 group, there is still an interference with the NH2 scissoring deformation band: in these cases deuteration is more effective than band separation. Several new constants ,Ro were determined spectroscopically for substituents of interest in pharmacology and these constants were also calculated by a quantum chemical model. The latter procedure seems to be most efficient and reasonably reliable for calculating new ,Ro constants; the only problem may be with the conformation in the case of axially unsymmetrical substituents. Copyright © 2001 John Wiley & Sons, Ltd. [source] Primary Photoprocesses in a Fluoroquinolone Antibiotic Sarafloxacin,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Fernando Lorenzo The photophysical properties of the fluoroquinolone antibiotic sarafloxacin (SFX) were investigated in aqueous media. SFX in water, at pH 7.4, shows intense absorption with peaks at 272, 322 and 335 nm, (, = 36800 and 17000 dm3 mol,1 cm,1, respectively). Both the absorption and emission properties of SFX are pH-dependent; pKa values for the protonation equilibria of both the ground (5.8 and 9.1) and excited singlet states (5.7 and 9.0) of SFX were determined spectroscopically. SFX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Laser flash photolysis and pulse radiolysis studies have been carried out in order to characterize the transient species of SFX in aqueous solution. Triplet,triplet absorption has a maximum at 610 nm with a molar absorption coefficient of 17,000 ± 1000 dm3 mol,1 cm,1. The quantum yield of triplet formation has been determined to be 0.35 ± 0.05. In the presence of oxygen, the triplet reacts to form excited singlet oxygen with quantum yield of 0.10. The initial triplet (3A*) was found to react with phosphate buffer to form triplet 3B* with lower energy and longer lifetime and having an absorption band centered at 700 nm. SFX triplet was also found to oxidize tryptophan to its radical with concomitant formation of the anion radical of SFX. Hence the photosensitivity of SFX could be initiated by the oxygen radicals and/or by SFX radicals acting as haptens. [source] Primary Photophysical Properties of Moxifloxacin, A Fluoroquinolone AntibioticPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2008Fernando Lorenzo The photophysical properties of the fluoroquinolone antibiotic moxifloxacin (MOX) were investigated in aqueous media. MOX in water, at pH 7.4, shows two intense absorption bands at 287 and 338 nm (, = 44 000 and 17 000 dm3 mol,1 cm,1, respectively). The absorption and emission properties of MOX are pH-dependent, pKa values for the protonation equilibria of both the ground (6.1 and 9.6) and excited singlet states (6.8 and 9.1) of MOX were determined spectroscopically. MOX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Phosphorescence from the excited triplet state in frozen ethanol solution has a quantum yield of 0.046. Laser flash photolysis and pulse radiolysis studies have been carried out to characterize the transient species of MOX in aqueous solution. On laser excitation, MOX undergoes monophotonic photoionization with a quantum yield of 0.14. This leads to the formation of a long-lived cation radical whose absorption is maximum at 470 nm (,470 = 3400 dm3 mol,1 cm,1). The photoionization process releases hydrated electron which rapidly reacts (k = 2.8 × 1010 dm3 mol,1 s,1) with ground state MOX, yielding a long-lived anion radical with maximum absorption at 390 nm (,390 = 2400 dm3 mol,1 cm,1). The cation radical of MOX is able to oxidize protein components tryptophan and tyrosine. The bimolecular rate constants for these reactions are 2.3 × 108 dm3 mol,1 s,1 and 1.3 × 108 dm3 mol,1 s,1, respectively. Singlet oxygen sensitized by the MOX triplet state was also detected only in oxygen-saturated D2O solutions, with a quantum yield of 0.075. [source] Synthesis and DNA-Recognition and -Cleavage Properties of Multiply Charged Porphyrin EstersCHEMISTRY & BIODIVERSITY, Issue 1 2008Lin Wu Abstract A series of systematically modified porphyrin esters, compounds 1,6, with multiple, permanent positive charges introduced at the meso -positions via N -methylated 4-, 3-, or 2-pyridyl moieties, were prepared and characterized. Their singlet-oxygen production, CT-DNA-binding properties, and plasmid-DNA photocleavage propensities were determined spectroscopically and by gel electrophoresis, and compared to those of the known, fourfold-charged parent porphyrin 4,4,,4,,4,,,-porphyrin-5,10,15,20-tetrayltetrakis(1-methylpyridinium) (TMPyP4). Some interesting structure,activity relationships could be established to rationalize effects affecting DNA binding mode and cleavage ability. [source] | ||||||||||