Search results for "Absorption"
showing 10 items of 2701 documents
Nondestructive full-field imaging XANES-PEEM analysis of cosmic grains
2006
For chemical analysis of submicron particles, mass spectrometric methods have the disadvantage of being destructive. Thus, a nondestructive elemental and chemical mapping with a high spatial resolution prior to mass analysis is extremely valuable to precharacterize the sample. Here, first results are presented of combined XANES (x-ray absorption near-edge structure) and PEEM (photoemission electron microscopy) measurements on a cosmic grain fraction from the Murchison meteorite. This nondestructive full-field imaging method is well suited for a quantitative analysis and for a preselection prior to detailed mass spectrometric investigations with isotopic resolution/selectivity. A spectral un…
Activity–Bioavailability balance in Oral Drug Development for a Selected Group of 6‐Fluoroquinolones
2002
Abstract A nomogram is proposed to select the best candidate in drug development studies with quinolones and is intended to substitute other possible models. The nomogram is referred to as an activity–bioavailability balance (ABB) because it includes the following two criteria: ABB= 1 / gm MIC ( drug candidate ) 1 /gm MIC ( ciprofloxacin ) · F calc \( drug candidate \) F calc ( ciproflaxacin ) . The in vitro activity of a group of 4′ N ‐alkyl‐ciprofloxacin derivatives was determined together with that of ciprofloxacin, initially against some reference strains and subsequently against 159 clinical isolates of eight selected species. The inverse of the geometric mean of the lowest concentrati…
Electrochromic absorbance changes in the chlorophyll-c-containing alga Pleurochloris meiringensis (Xanthophyceae)
1994
Flash-induced absorbance changes were measured in the Chl-c-containing alga Pleurochloris meiringensis (Xanthophyceae) between 430 and 570 nm. In addition to the bands originating from redox changes of cytochromes, three major positive and tow negative transient bands were observed both 0.7 and 20 ms after the exciting flash. These transient bands peaking at 520, 480 and 451 nm and 497 and 465 nm, respectively, could be assigned to an almost homogeneous shift of the absorbance bands with maxima at 506, 473 and 444 nm, respectively. The shape of the absorbance transients elicited from PS I or PS II was identical, and the two photosystems contributed nearly equally to the absorbance changes. …
Experimental evidence of E’_gamma centers generation from oxygen vacancies in a-SiO2
2007
Abstract We report on the thermal treatment effects in a γ-ray irradiated oxygen deficient amorphous silicon dioxide (a-SiO2) containing Al impurities. We observed that by thermal treatments the intensity of the 7.6 eV optical absorption band, associated to an oxygen deficient center, and the EPR signal amplitude of irradiation induced [AlO4]0 centers gradually decrease. During these thermal treatments, the E γ ′ centers concentration is found to increase in a correlated way to the decrease of the 7.6 eV absorption amplitude. These results are interpreted assuming an hole-transfer process from the [AlO4]0 centers to the diamagnetic oxygen vacancies, resulting in the generation of E γ ′ cent…
Sodium nitrate and tungsten as matrix modifiers for the determination of arsenic in shotgun pellets by electrothermal atomic absorption spectrometry
2001
A method for the determination of arsenic in a complicated sample matrix by Zeeman effect electrothermal atomic absorption spectrometry using tungsten and sodium nitrate as matrix modifiers was developed. The determination of arsenic in SRM C2416 (Bullet Lead) and SRM 2710 (Montana Soil) by ETAAS using a mixture of palladium and magnesium nitrate as a matrix modifier failed to obtain the certified concentrations at the 95% level of confidence using the t-test. Both tungsten and sodium nitrate as matrix modifiers stabilized arsenic so that the certified concentrations of the SRMs were determined with high accuracy and precision (RSD 0.999), with low detection and quantification limits, wer…
ChemInform Abstract: Methylium Ions with OPV Chains - New NIR Dyes.
2010
Carbinols, which contain three OPV chains, were generated in convergent syntheses. The extension of the conjugation leads to a bathochromic effect that shifts the absorption from the UV into the visible region. The carbinol series has a convergence limit of the absorption at λmax = 415 nm. The corresponding carbenium ions exhibit a stronger bathochromic shift with the increasing number of repeating units in each chain. Thus, NIR dyes were obtained which show a convergence limit at λmax = 879 nm. The charge distribution in the ground state of the carbocations is discussed on the basis of 13C NMR spectroscopic data.
Thermal oxidative process in extra-virgin olive oils studied by FTIR, rheology and time-resolved luminescence
2011
Abstract With the aim to characterise the antioxidant properties of different extra-virgin olive oils and to understand in more detail the mechanisms of oil degradation, we have made an experimental study on thermal induced oxidative processes of extra-virgin olive oils by using different techniques: Fourier Transform Infrared (FTIR) spectroscopy, rheology and time-resolved luminescence. The oxidation process was followed at three different heating temperatures (30, 60 and 90 °C) as a function of time up to 35 days. Thermal treatment induced changes in the FTIR spectra in the wavenumbers region 3100–3600 cm −1 : in particular, the absorption profiles show an initial formation of hydroperoxi…
Alkyloxy modified pyrene fluorophores with tunable photophysical and crystalline properties
2019
Novel alkyloxy modified 2,7-di-tert-butyl-4,5,9,10-tetra(arylethynyl)pyrenes were prepared through a straightforward Sonogashira coupling approach. Optical properties such as quantum yields and absorption/emission spectra of the fluorophores were investigated by UV/Vis and fluorescence measurements. Aggregation induced excimer formation of the chromophores in polar solvents and in the solid state was proved by the presence of a characteristic bathochromically shifted emission band and a decrease of the emission capability. These results strongly indicate the unexpected observation that the excimer formation of adjacent pyrene rings is not prevented by the introduction of bulky tert-butyl su…
Dendrimers with peripheral stilbene chromophores
2006
Abstract Two types of dendritic nanoparticles were prepared, which contain ( E )-stilbene chromophores in the terminal positions of the dendrons. The compounds showed a highly efficient photoreactivity in the course of which statistical CC bond formations led to a crosslinking of the particles. Finally, all stilbene chromophores reacted and the typical ( E )-stilbene absorption and fluorescence disappeared completely.
Poly(propylene imine) dendrimers functionalized with stilbene or 1,4-distyrylbenzene chromophores
2007
Abstract Two generations of dendritic nanoparticles were prepared, which contain ( E )-stilbene or ( E , E )-1,4-distyrylbenzene chromophores in the 4 or 8 terminal positions of the propylene imine dendrons. The compounds show a highly efficient photoreactivity. On prolonged irradiation all stilbenoid chromophores were destroyed by oligomerization (crosslinking) and the typical absorption and fluorescence of the chromophores disappeared completely.