Direct Ultraviolet Absorption Research Articles

Ballistic and delayed photodissociation channels in the B̃ 2A11 state of water studied with resonant inelastic x-ray scattering

Photodissociation is one of the most important photoinduced chemical reactions. It occurs when the potential energy curve along a chemical bond is repulsive in an excited state. Typically, “ballistic” ultrafast dissociation leads to the broadening of absorption resonances and the smearing out of vibrational fine-structure. We report on the photodissociation of H2O in the B̃ 2A11 electronic state, characterized by a |3a1−14a11〉 configuration, which can be reached via resonant inelastic x-ray scattering or direct ultraviolet absorption. In both cases the spectra show narrow vibrational resonances, in spite of the dissociative character of the state. We find that “delayed” dissociation pathways, caused by reflection of the nuclear wave packet, are responsible for this effect. In spite of the analogous topology of the potential energy surfaces of the core- and valence-excited states, the reflection of the wave packet takes place only in the latter. The two-dimensional wave packet of the O-H stretching coordinates becomes trapped in a “cavity” near the Franck-Condon region, resulting from a mismatch between the OH vibrational frequency in the cavity and the one at the dissociation limit. Published by the American Physical Society 2024

Salivary total protein levels among healthy controls, chronic gingivitis patients and chronic periodontitis patients

Background: Periodontal diseases are one of the most common chronic infectious and inflammatory diseases in the world that can be diagnosed by clinical, radiographic signs and some biomarkers. Saliva contains locally and systemically derived markers that can aid in the diagnosis of periodontal diseases. The aim of the present study was designed to evaluate salivary total protein levels in patients with chronic gingivitis and chronic periodontitis. Materials and Methods: Five milliliters of unstimulated whole saliva samples was collected from a total of 113 individuals; each of the healthy and chronic gingivitis groups was included 39 participants and 35 patients in the chronic periodontitis group. Salivary total protein levels, gingival index (GI), papillary bleeding index (PBI), probing pocket depth (PPD), and clinical attachment level were recorded in the respective groups. Salivary protein estimation was done by direct ultraviolet absorption method, and determination was based on biuret method. Results: The mean salivary total protein levels in the healthy, chronic gingivitis, and chronic periodontitis groups were 1.52, 2.58, and 6.30 g/dl, respectively. The salivary total protein levels of gingivitis and periodontitis patients were 1.6 and 4.2 times higher than healthy controls, which were statistically significant (P < 0.001). In addition, GI (r = 0.476) and PBI (r = 0.490) were significantly correlated with protein levels in gingivitis patients. However, PPD was significantly correlated with protein contents in only periodontitis patients (r = 0.387). Conclusions: Increased total protein levels are related to the severity of periodontal diseases, and it may serve as a biomarker in inflammation of the periodontium.

Sub-minute determination of rifampicin and isoniazid in fixed dose combination tablets by capillary zone electrophoresis with ultraviolet absorption detection.

A validated sub minute capillary zone electrophoresis method with direct ultraviolet absorption detection for simultaneous determination of isoniazid and rifampicin in fixed-dose combination tablets was developed. Background electrolyte was defined based on the analytes effective mobility curve and it was composed by 20mmol/L of sodium carbonate/sodium bicarbonate at pH 10.2. A careful validation procedure considering the main figures of merit was performed. Regression models were satisfactory for isoniazid and rifampicin, showing no lack of fit within 95% significance interval. Interday and intraday precision were evaluated in standard and sample and slight relative standard deviations were achieved for concentration, area, and migration time. Recovery values for accuracy in two levels were 99.97 and 90.08% for isoniazid and 95.45 and 95.12% for rifampicin. The limits of detection for isoniazid and rifampicin were 0.22 and 0.34mg/L, respectively, and the limits of quantification were 0.74 and 1.13mg/L, respectively. Method selectivity was verified by injecting diluent, background electrolyte, a standard mixture, and a sample, confirming no interferent peaks. The method proved to be simple, environmentally friendly, sensitive, and was successfully applied for simultaneous quantification of isoniazid and rifampicin in fixed-dose combination tablets.

Wavelength dependence of ultraviolet radiation‐induced DNA damage as determined by laser irradiation suggests that cyclobutane pyrimidine dimers are the principal DNA lesions produced by terrestrial sunlight

To elucidate the involvement of specific ultraviolet (UV) wavelengths in solar mutagenesis, we used a laser system to investigate the induction of DNA damage, both in the overall genome and at the nucleotide resolution level, in the genomic DNA of transgenic Big Blue mouse fibroblasts irradiated with a series of UV wavelengths, inclusive of UVC (λ<280 nm), UVB (λ=280-320 nm), and UVA (λ>320 nm). Subsequently, we sought correlation between the locations of UV-induced DNA lesions in the cII transgene of irradiated DNA samples and the frequency distribution and codon position of the induced cII mutations in counterpart mouse cells irradiated with simulated sunlight. Using a combination of enzymatic digestion assays coupled with gel electrophoresis, immunodot blot assays, and DNA footprinting assays, we demonstrated a unique wavelength-dependent formation of photodimeric lesions, i.e., cyclobutane pyrimidine dimers (CPDs) and (6-4) photoproducts [(6-4)PPs], based on direct UV absorption of DNA, in irradiated mouse genomic DNA, which could partially explain the induction of mutations in mouse cells irradiated with simulated sunlight. Most notably, there was a divergence of CPD and (6-4)PP formation at an irradiation wavelength of 296 nm in mouse genomic DNA. Whereas substantial formation of (6-4)PPs was detectable in samples irradiated at this wavelength, which intensified as the irradiation wavelength decreased, only small quantities of these lesions were found in samples irradiated at wavelengths of 300-305 nm, with no detectable level of (6-4)PPs in samples irradiated with longer wavelengths. Although CPD formation followed the same pattern of increase with decreasing wavelengths of irradiation, there were substantial levels of CPDs in samples irradiated with UVB wavelengths borderlined with UVA, and small but detectable levels of these lesions in samples irradiated with longer wavelengths. Because the terrestrial sunlight spectrum rolls off sharply at wavelengths ~300 nm, our findings suggest that CPDs are the principal lesion responsible for most DNA damage-dependent biological effects of sunlight.

Gradient elution isotachophoresis with direct ultraviolet absorption detection for sensitive amino acid analysis

This work demonstrates coupling of the newly described electrophoretic enrichment technique of gradient elution isotachophoresis (GEITP) to a low-cost, conventional ultraviolet absorbance detector to realize sensitive measurements with a universal detector, eliminating the need for fluorescent analytes or derivatization. The effects of various parameters on enrichment were studied, including current density varied by leading electrolyte concentration, current density varied by applied electric field, and counter-flow acceleration across varying capillary inner diameters. Optimized parameters were applied to the enrichment and separation of the amino acids tryptophan (Trp) and tyrosine (Tyr). Limits of detection for Trp and Tyr were 51 and 215 nM, respectively, reflecting sensitivity enhancements of 860- and 1900-fold. Analysis times were less than 6 min, and peak height RSDs were less than 4%. A demonstration of enrichment and separation of these amino acids from artificial cerebrospinal fluid is additionally shown as a first step to realizing biochemical monitoring by GEITP.

Photoreactivity of Molecular Aggregates

AbstractThe spectroscopy and photoreactivity of atmospheric trace gases embedded in clusters is examined in this work. Perturbations induced by intermolecular interactions are obtained in order to evaluate the role that the heterogeneous photochemistry of such species could play in the chemical balance of the atmosphere. – Spectroscopic effects are monitored using aggregates produced in supersonic jets and measured by high resolution Fourier Transform direct ultraviolet absorption techniques. These spectra are compared with those of the isolated molecule to extract shifts and intensity changes when the chromophore is clustered. Photochemical studies involve laser pump‐probe experiments with mass resolved multiphoton ionization detection. Changes in the isolated molecule photochemistry are monitored as a function of cluster formation. – This paper discusses the methodology developed as well as the specific example of clusters of ozone with atmospheric trace gases.

Various techniques for the routine evaluation of the degradation of glucose in parenteral solutions — a critical study

A practical approach is described for studying the influence of various physicochemical factors on the degradation of glucose in parenteral solutions sterilized by heating in an autoclave. Five routine analytical methods are discussed: pH determination; direct ultraviolet absorption measurement (BP) method; liquid chromatography of 5-HMF; thin-layer chromatography of sugars, carboxylic acids and carbonyl species; and enzymatic determination of glucose. The effects of various factors on the degradation of glucose were studied: glucose concentration (10%, 30%, 50%); pH of solution before sterilization (2-10); sterilization cycle (103 min at 110 degrees C, 20 min at 120 degrees C, 3 min at 134 degrees C; same Fo); time of heating at 120 degrees C (30, 40, 60 min); and the presence of salts (sodium acetate, sodium lactate, sodium chloride). The results demonstrate the importance of these factors in influencing the rate of glucose degradation during sterilization. In the presence of salts, 5-HMF is not the most important product of degradation and the BP assay is not suitable for evaluation of glucose breakdown. The authors propose two control procedures. For simple solutions of glucose, the BP method is suitable. In the presence of salts the glucose oxidase method should be used.

The direct ultraviolet absorption spectrum of the 1Σg+ → 1B2(1Σu+) transition of jet-cooled 13C32S2 and 12C34S2

The absorption spectra of isotopically substituted carbon disulfide, i.e., 13C32S2 and 12C34S2, cooled in supersonic expansion are reported here and compared with the spectrum of the natural isotope. Cooling these samples eliminated spectral congestion due to inhomogeneous factors and yielded measurements of frequencies and isotopic shifts of bands of 13C32S2 and 12C34S2 relative to 12C32S2. The spectrum obtained is interpreted to reflect a transition from a linear ground state to a bent excited state up to ∼49 000 cm−1 and to a quasilinear excited state above this energy.

The direct ultraviolet absorption spectrum of the A'~A2" .rarw. ~X'A1 transition of jet-cooled ammonia

The A tilde formed from X tilde transition in ammonia is investigated by direct ultraviolet absorption spectroscopy of samples cooled in supersonic jet expansions. Franck-Condon factors are reported here for this transition of NH/sub 3/ and ND/sub 3/: they are considerably different from those available from room-temperature data. The spectra are discussed in light of models available for the A state ammonia.

A chromatographic quality control procedure based on HPLC for 5-hydroxymethylfurfural in autoclaved D-glucose infusion fluids.

A specific qualitative chromatographic assay method is described for 5-hydroxymethylfurfuraldehyde (5HMF) in degraded D-glucose solutions incorporating an internal standard. Comparison is made between the chromatographic method and the official direct ultraviolet absorption measurements at 284 nm for solutions of D-glucose degraded to different extents. Hospital samples of autoclaved Dextrose Injection, 5% w/v, are also examined by both methods and it is demonstrated that quite different results can be obtained depending upon the conditions of measurement. It is demonstrated that the direct absorption method does not provide an adequate limit test for compounds related to 5HMF.

ChemInform Abstract: DIRECT ABSORPTION SPECTRA OF HIGHER EXCITED STATES OF JET‐COOLED MONOSUBSTITUTED BENZENES: PHENYLACETYLENE, STYRENE, BENZALDEHYDE, AND ACETOPHENONE

The second π→π* absorption bands of phenylacetylene, styrene, benzaldehyde, and acetophenone cooled in supersonic molecular jets are investigated by direct ultraviolet absorption spectroscopy. New vibronic structure is observed and vibrational assignments are discussed. The most prominent vibronic bands arise from motions centered in the substituent and from substituent‐sensitive benzene modes. This contrasts with the spectra of the first π→π* transitions of these molecules, which exhibit structure involving ring‐localized motions primarily. The spectra presented here demonstrate the utility of the direct absorption technique in the investigation of higher electronic transitions of jet‐cooled molecules.

Direct absorption spectra of higher excited states of jet-cooled monosubstituted benzenes: Phenylacetylene, styrene, benzaldehyde, and acetophenone

The second π→π* absorption bands of phenylacetylene, styrene, benzaldehyde, and acetophenone cooled in supersonic molecular jets are investigated by direct ultraviolet absorption spectroscopy. New vibronic structure is observed and vibrational assignments are discussed. The most prominent vibronic bands arise from motions centered in the substituent and from substituent-sensitive benzene modes. This contrasts with the spectra of the first π→π* transitions of these molecules, which exhibit structure involving ring-localized motions primarily. The spectra presented here demonstrate the utility of the direct absorption technique in the investigation of higher electronic transitions of jet-cooled molecules.

Analysis on Heat Coagulated Blood and Serum

Abstract A direct ultraviolet absorption method that does not require uricase for the determination of serum urate is presented. Serum (0.3 ml.) is placed in the bottom of a 25 X 95-mm. shell vial and coagulated by immersion of the vial in boiling water for 2 min. The clot is overlaid with 3.0 ml. of water and the serum urate extracted for 60 min. at 37°. The absorbance of the extract is measured at 295 mµ, and the serum urate determined by comparison with the known absorption of pure urate at the same wavelength. The agreement between the direct ultraviolet method and a standard phosphotungstate reduction method is excellent in cases in which no medication is being administered. Some drugs absorb ultraviolet light, and in certain instances may be responsible for a discrepancy up to 1.5 mg./100 ml. between the two procedures. The method is extremely simple and requires no reagents.

A Spectrophotometric Method for Residual Styrene in SBR Latex

Abstract The spectrophotometric method of analysis for residual styrene monomer in SBR latex has several advantages. No standardization of reagents is required. The method is rapid, accurate, and precise. The direct ultraviolet absorption method is applicable only in absence of interferences. The alternate distillation-ultraviolet method is applicable even in the presence of most interferences.