Ultraviolet Absorption Bands Research Articles

Spectroscopic properties of copper(H) complexes with quadridentate derivatives of L-proline amide and L-proline methyl amide

The copper(II) complexes with epaH 2, tpaH 2, epmaH 2, and tpmaH 2, potentially quadridentate derivatives of L-proline amide or methyl amide (see text), have been characterized by absorption, circular dichroism (CD), IR, and ESR spectroscopies. All of the spectral features of the complex with dianionic tpa indicated an ordinary planar geometry, whereas those of the tpma complex suggest an unusual ligand field containing a strong apical coordination. The epa and epma complexes appear to take a distorted geometry on the basis of the splitting of dd bands and the rhombic ESR. The ultraviolet absorption and CD bands associated with the coordinating amide group are also discussed.

UV absorption spectroscopy for monitoring hydride vapor-phase epitaxy of InGaAsP alloys

Ultraviolet (UV) absorption spectroscopy has been used to monitor the concentrations of gas-phase reactants participating in the growth of InGaAsP alloys by hydride vapor-phase epitaxy. Room-temperature absorption spectra for PH3, AsH3, and HCl as well as high-temperature (700°C) spectra of InCl, GaCl, PH3,P2, P4, As2, and As4 are presented. For the group V species, the UV absorption bands of the hydride, dimer, and tetramer exhibit considerable overlap, but can still be used to determine the approximate concentration of each species. GaCl and InCl exhibit extremely intense, sharp absorption bands at 248 and 267 nm, respectively. This technique has been used to study the effect of PH3 pyrolysis on InP growth, and to monitor In/Ga ratio for metal transport from an alloy source. This technique can be implemented on reactor systems without reactor design changes and without disturbing the thermal profile by using ‘‘light pipes’’ to probe concentrations of reactive species during growth.

The singlet states of styrene. Theoretical vibrational analysis of the ultraviolet spectrum

Vibrational analyses of the ground and lowest excited singlet states of styrene are performed using an extended PPP-CI model. Franck–Condon factors calculated from the model are used to analyze the intensity distribution of the ultraviolet absorption bands of the jet-cooled molecule from 34 000–46 000 cm−1. For the weak first absorption system (S1←S0) the small amount of vibrational excitation found experimentally is well described by the theoretical model. The relatively intense second absorption band shows more extended vibrational development. The model predicts that two electronic transitions S2←S0 and S3←S0 contribute to the absorption spectrum in this region and that a large number of vibrational excitations involving carbon–carbon stretching motions are active. For the S1←S0 and S2←S0 transitions a refinement of the theoretical model is performed to calculate the excited state equilibrium geometries from the measured spectra. Because of the large number of vibrations and the evidence for mixing among them in the excited states (Duschinsky effect), the full multimode treatment of the ground and excited state dynamics is required for an analysis of the spectrum.

Resonance Raman spectroscopy of alkyl nitroxyl radicals

AbstractResonance enhancement of the NO stretching Raman bands has been observed from dilute solutions (10−3‐10−2 mol dm−3) of some alkyl nitroxyl radicals by excitation into their ultraviolet absorption band (λmax ≈︁ 240 nm). Excitation at 248 nm was produced by a line‐narrowed, pulsed KrF excimer laser. Three overtone bands, which were observed for di‐tert‐butylnitroxyl, showed a small anharmonic contribution, xeνe = 8.8 cm−1.

Laser multiphoton processes in thin films: Non-linear photochemistry of organosilane polymers

Irradiation of organosilane polymers in the ultraviolet leads to photodegradation of the chain via a bond scission process. Here photodegradation by visible laser multi-quantum excitation is reported. The process is characterized by a sharp threshold at power densities of approximately 2.5 GW/cm 2. The photochemistry of the system beyond this power density proceeds non-linearly leading to vaporization of the absorbing film and 100% bleaching of the ultraviolet absorption bands. Utilization of laser wavelengths whose two-photon energies are insufficient to access the ultraviolet system, produced no measurable photodecomposition.

Photometric properties of powdered sulfur

The spectrophotometric (0.39 < λ < 0.7 λm) properties of three particle-size fractions (diameters <10 λm, <150 λm, and 420–850 λm) of sulfur have been investigated in the laboratory. Particle size, temperature, thermal history, and scattering geometry are all shown to influence the spectral reflectance of the normal (S 8) sulfur samples and an “orange-colored” S 8 sample produced by quenching molten sulfur. A scattering law consisting of a linear combination of lunar-like and Lambertian terms adequately describes the data for all particle sizes. Where sulfur is darkest (λ < 0.45 λm), the reflectance decreases with increasing particle size, whereas where sulfur is brightest (λ > 0.45 λm) the reflectance increases with decreasing particle size. In reflected light, the long wavelength edge of the strong ultraviolet absorption retreats smoothly to shorter wavelengths with decreasing temperature at ∼1.6Å/°K, a value lower than the 2.2Å/°K value previously reported for transmitted light. Near opposition, sulfur powders are found to follow closely a Minnaert limb darkening law except where the reflectance is low, i.e., in the strong ultraviolet absorption band of the larger particle size fractions. It is clear from our data that quantitative comparisons between disk-integrated observations of Io and laboratory measurements of flat samples of sulfur are not adequate unless temperature effects and changes in scattering geometry are included.

Cataracts and photochemical damage in the lens.

The possibility is considered that ultraviolet radiation, from sunlight and other ambient sources, is a major causative factor in certain human cataracts. Epidemiological and experimental data from the literature are reviewed and new experimental results on exposure of rat lenses to UV laser radiation in vitro are presented. This UV irradiation of lenses is shown to cause: (i) photochemical alteration of tryptophan residues in lens proteins, resulting in loss of tryptophan fluorescence, (ii) new ultraviolet absorption bands attributable to photo-oxidation products of lens proteins, and (iii) cross-linking of polypeptides in lens proteins, detected by sodium dodecylsulphate-polyacrylamide gel electrophoresis. It is noted that the UV radiation-induced lens changes reported are quite similar to the changes found when normal human lenses develop cataracts. In order to establish the degree to which UV-exposed lenses resemble naturally occurring cataracts, a comprehensive comparison of anatomical, histological and biochemical parameters for normal, cataractous and UV-exposed human lenses is proposed.

Chromatographic and spectroscopic analysis of phycoerythrin 545 and its subunits

Phycoerythrin 545 is a light-harvesting biliprotein isolated from the cryptomonad Rhodomonas lens. Although the absorption spectrum of the native protein suggests that this protein has only phycoerythrobilins for its chromophores, the denaturated protein shows a small near ultraviolet absorption band with a maximum at 333 nm which is not present in phycoerythrobilin. Two methods were employed to separate the α and β subunits of this protein: chromatography with Sephacryl S-200 in acidic urea or centrifugation in a sucrose density gradient at pH 3.0. The chromatography experiments yielded two bands, which were shown to be pure α or β subunits by sodium dodecyl sulfate gel electrophoresis. The absorption spectrum of β showed only phycoerythrobilins, but the spectrum of α was not like that of any known bilin chromophore. Its absorption spectrum could be constructed by a combination of phycoerythrobilin and cryptoviolin. The β subunit separated on the sucrose density gradient was highly aggregated. Circular dichroism and fluorescence polarization spectroscopy indicated that this aggregated β subunit has chromophores in atypical environments. Comparison of the absorption, spectra of native and denatured phycoerythrin 545 suggests that chromophores in the native state are held by the protein in a more linear confirmation.

Redox investigations of the type 3 site in type 2 copper depleted rhus laccase

We report the results of experiments designed to characterize the Type 1 and Type 3 copper sites in Rhus laccase depleted of Type 2 copper (T2D). Use of the Lowry method for determining protein concentration, with native laccase as a standard, established the value 5680 ± 710 M −1 cm −1 for the extinction at 615 nm FOR T2D laccase. Anaerobic reductive titrations of T2D laccase have been performed using Cr(II)aq ions, Ru(NH 3 ) 2+ 6 and hydroquinone as reductants. For five independent titrations on three independent T2D laccase preparations, 3.1 ± 0.25 reduction equivalents were required to reduce the protein completely, as judged by the absorption at 615 nm. Thus the fact that the Type 3 copper ions are in the +2 oxidation state in fresh T2D laccase is unequivocal. The data from equilibrium reductive titrations with hydroquinone fit a model in which the Type 1 site copper in T2D laccase is 35 mv more oxidizing than those of the Type 3 site, and the Type 3 site coppers are reduced in equipotential single electron steps. Both these findings contrast with the case for the native enzyme. In addition theoretical considerations governing the electron distribution in multinuclear equivalent site species during reduction imply that reduction of the Type 3 site coppers is accompanied by a protonation or conformational transition within the site itself in T2D laccase. Treatment of T2D laccase with a 70-fold excess of H 2 O 2 induced a new shoulder at 330 nm (Δϵ = 660 M −1 cm −1 ), minor intensity enhancement of the ultraviolet absorption band and a decreased absorption at 615 nm (Δϵ=−900 M −1 cm −1 ). The following difference spectra were constructed from experimental data: (native laccase minus T2D laccase) and (peroxy native laccase minus peroxy T2D laccase). Both were found to exhibit maxima at 325 nm, (Δϵ ∼ 1200 M −1 cm −1 ) and shoulders near 370 nm ((Δϵ ∼ 500 M −1 cm −1 ). The similarity of these spectra throughout the near violet region confirms previous CD results that peroxide is bound to the Type 3 copper site of T2D laccase in a fashion similar to that of the native protein, despite the diminished binding constant (10 4 M −1 vs > 10 8 M −1 , respectively). The lack of any other new near-UV feature on treatment with peroxide corroborates the reductive titrations in demonstrating the oxidized state of the Type 3 copper ions in resting T2D laccase. Dioxygen reoxidation of ascorbate reduced T2D laccase produced new difference bands at 330 nm (Δϵ = 700 M −1 cm −1 ) and 270 nm (Δϵ = 13000 M −1 cm −1 ), the former assigned to a bound peroxide dioxygen reduction intermediate. In the corresponding epr spectrum of this material new low intensity Cu(II)g ∥ features (A ∥ ∼ 130 G) indicative of a magnetically isolated copper ion, as well as a new triplet signal near 3400 Gauss were observed. Reoxidation by dioxygen as mediated by iron hexacyanide, or by ferricyanide alone, produced a reoxidized protein having the original spectral determinants. Thus not only does reduced T2D laccase react directly with dioxygen, but the magnetism of the reoxidized Type 3 site may occasionally be perturbed during turnover. Conformational transitions occurring in T2D laccase during turnover may therefore diminish and perhaps obviate the binuclear coupling of the Type 3 copper ions. In summary, removal of the Type 2 copper from Rhus laccase has produced an altered Type 3 site. It appears that T2D laccase is conformationally labile around the Type 3 site, and therefore that direct analogies relating the chemistry or spectroscopy of native and T2D laccase should be drawn with caution.

Characterization of Lignin in Situ by Photoacoustic Spectroscopy

Photoacoustic spectroscopy is a recently developed nondestructive analytical technique that provides ultraviolet, visible, and infrared absorption spectra from intensely light scattering, solid, and/or optically opaque materials not suitable for conventional spectrophotometric analysis. In wood and other lignocellulosics, the principal ultraviolet absorption bands, in the absence of photosynthetic pigments, arise from the aromatic lignin component of the cell walls. Photoacoustic spectra of extracted lignin fragments (milled wood lignin) and synthetic lignin-like polymers contain a single major absorption band at 280 nanometers with an absorption tail extending beyond 400 nanometers. Photoacoustic spectra of pine, maple, and oak lignin in situ contain a broad primary absorption band at 300 nanometers and a longer wavelength shoulder around 370 nanometers. Wheat lignin in situ, on the other hand, exhibits two principle absorption peaks, at 280 nanometers and 320 nanometers. The presence of absorption bands at wavelengths greater than 300 nanometers in intact lignin could result from (a) interacting, nonconjugated chromophores, or (b) the presence of more highly conjugated structural components formed as the result of oxidation of the polymer. Evidence for the latter comes from the observation that, on the outer surface of senescent, field-dried wheat culms (stems), new absorption bands in the 350 to 400 nanometer region predominate. These new bands are less apparent on the outer surface of presenescent wheat culms and are virtually absent on the inner surface of either senescent or presenescent culms, suggesting that the appearance of longer wavelength absorption bands in senescent wheat is the result of accumulated photochemical modifications of the ligin polymer. These studies also demonstrate photoacoustic spectroscopy to be an important new tool for the investigation of insoluble plant components.

The geometry and spectral properties of Ne+3, Ar+3, Kr+3, and Xe+3

A b initio polarization configuration interaction (POL-CI) calculations show that Ne+3 and Ar+3 are both linear, in agreement with indirect experimental evidence on Ar+3 and in contradiction to earlier approximate theoretical calculations on Ar+3, which predicted an equilateral triangular geometry. The experimentally unknown Ne+3 dissociation energy is predicted to be 0.15±0.01 eV. Simple diatomics-in-molecules (DIM) calculations were shown to be in very good agreement with the ab initio results. DIM calculations predict that Kr+3 and Xe+3 are also linear. All the rare-gas–trimer ions possess at least one very strong absorption band in the visible, even stronger than the near ultraviolet absorption band of the rare-gas–dimer ions.

Initial Reaction Intermediates in the Oxidation of Ascorbic Acid by Nitrous Acid

Nitrite and ascorbate react to form nitric oxide at pH 5.5. In the initial stages of the reaction, seven intermediates can be identified spectrally and chromatographically; these include two colorless nitroso derivatives which contain 30–60% of the initial nitrite, two nitroso reductant derivatives absorbing at 345 and 412 nm, diketogulonic acid and two further decomposition products. None of the intermediates was paramagnetic; except for diketogulonic acid, all decomposed rapidly during or after isolation. Based on the order of appearance of the ultraviolet and visible absorption bands in the reaction mixtures, the observed characteristics of the intermediates, and the lack of organic radicals, a sequence is proposed for the initial steps in the oxidation of ascorbic acid by nitrous acid.

Fluorescence‐free resonance Raman spectra of reduced nicotinamide adenine dinucleotide via ultraviolet excitation

AbstractExcitation of reduced nicotinamide adenine dinucleotide (NADH) on the high‐energy side (333.6 nm) of its ultraviolet absorption band shifts the Raman scattering away from the fluorescence band and produces a good quality resonance Raman spectrum. It is dominated by the amide I (CO stretch) mode, at 1687 cm−1, but several weaker bands are observed, and are tentatively assigned to amide II and III, and ring modes, consistent with N2H2 and 4‐2H isotope shifts. An identical spectrum is observed for nicotinamide mononucleotide (NMNH), indicating that the adenine and nicotinamide portions of NADH do not interact.

High-resolution spectroscopy of SO 2 using a frequency-doubled, continuous-wave dye laser

The SO 2 molecule is of considerable interest in the context of atmospheric pollution, and in many laser monitoring techniques the ultraviolet absorption band at 300 nm is used to determine SO 2 concentrations in the atmosphere. Recent laboratory experiments with a resolution of 2 × 10 -3 nm showed that variations could occur in absorption cross-section measurements made with different laser bandwidths due to unresolved fine structure. We have investigated absorption spectra with a line width of 3 × 10 -6 nm, using a frequency-doubled continuous-wave dye laser, and have confirmed the existence of fine structure in the absorption even when collisionally broadened with an atmosphere of nitrogen. These measurements provide a data base from which valid absorption cross sections may be calculated for all monitoring laser bandwidths. We estimate the pressure broadening coefficient for nitrogen in this wavelength region as 83 ± 38 kHz Pa -1 (11 ± 5 MHz torr -1). The temperature dependence of the absorption cross-section was also investigated.

Line Shape of the Chromium (VI) Absorption Band in Sodium Borate and Sodium Silicate Glasses

The effect of temperature on the line shape of the ultraviolet absorption bands of chromium (VI) in different (1-x) Na2O, xB2O3 (where x varied from 0.1 to 0.33), and in a 0.3Na2O, 0.7SiO2 glass was studied. The ultraviolet absorption of chromium (VI) in these glasses is characterised by two charge transfer bands centred around 250–270 nm and 350–370 nm, the location of the centre of absorption and relative intensities of the two bands depending on the borochromate/chromate ratio in the glass which in turn is dependent on the chemical composition of the glass. The 350–370 nm band has been found to be Gaussian at the top half of absorption, and exponential with wave-number at the low-energy tail of the band obeying Urbach's Rule. In all the glasses, the energy of absorption maximum decreased linearly with increasing temperature, and the bands became broader. The change in intensity of chromium (VI) absorption in different glasses with varying temperature has a satisfactory correlation with thermal expansion coefficient of these glasses strongly indicating a photon-phonon interaction in these cases.

Iue detection of sulfur dioxide in the atmosphere of Venus

Ultraviolet absorption bands of sulfur dioxide have been detected in the reflectance spectrum of Venus using the high resolution spectrometer of the International Ultraviolet Explorer (IUE). The identification of these bands in the 2080 to 2180 A range has been verified by comparison with laboratory absorption spectra. An estimate of the SO2 vertical column density using a reflecting layer model is 4 × 1016 cm−2.

ChemInform Abstract: SPECTROSCOPIC STUDY OF MICHLER′S KETONE. PART 1. ABSORPTION

It is shown that the near ultraviolet absorption band of Michler's ketone covers three electronic transitions. There are two ππ* transitions, an intense one polarized perpendicular to the dipole moment and a weaker one at higher energy polarized parallel to the dipole moment, and an nπ* transition polarized parallel to the dipole moment. For the ππ* transitions the change of dipole moment upon excitation has been determined as 5.8 ± 0.5 and 3 ± 1 Debye, respectively. Whereas the nπ* state appears to be the first excited singlet state in non-polar media, it becomes the third excited singlet state in ethanol. The change of the absorption spectrum with temperature is discussed.

Thermal variation of attenuation for optical fibers

Thermal variation of attenuation for multi-component and high-silica glass fibers has been measured at 0.63 μm wavelength in a temperature range from 20°C to 600°C. The multicomponent glass fibers have shown no increase in loss below 400°C, whereas the high-silica glass fibers have shown a drastic, exponential increase in loss with increasing temperature. The observed change of attenuation has been explained on the basis of the shift of the ultra-violet absorption band calculated from temperature change of refractive index. The increase in optical loss, calculated from the obtained data of refractive index and dispersion parameters at each temperature, shows good agreement with the observed increase in loss.

Spectroscopic study of Michler's ketone. Part 1.—Absorption

It is shown that the near ultraviolet absorption band of Michler's ketone covers three electronic transitions. There are two ππ* transitions, an intense one polarized perpendicular to the dipole moment and a weaker one at higher energy polarized parallel to the dipole moment, and an nπ* transition polarized parallel to the dipole moment. For the ππ* transitions the change of dipole moment upon excitation has been determined as 5.8 ± 0.5 and 3 ± 1 Debye, respectively. Whereas the nπ* state appears to be the first excited singlet state in non-polar media, it becomes the third excited singlet state in ethanol. The change of the absorption spectrum with temperature is discussed.

Optical studies on the structure of hemoglobin messenger ribonucleic acid

The secondary structure of hemoglobin mRNA (HbmRNA has been investigated by optical rotatory dispersion (ORD), circular dichroism (CD) and ultraviolet absorbance spectrophotometry. The dependence on temperature or reaction with formaldehyde of the CD and absorbance are characteristic of a structure with substantial base pairings at 20°C. The presence of Cotton effects in one of the major ultraviolet absorption bands indicates a highly ordered secondary structure. The UV hyperchromism on thermal denaturation is consistent with a value of 58% double helical content.