Journal of Applied Spectroscopy最新文献

The influence of peripheral substitution and the nature of the macroheterocyclic heteroatoms on the basicity of hydrophilic 5,10,15,20-tetraarylporphyrins in the lowest excited singlet S₁ state was studied using absorption and fluorescence spectroscopies. The basicity of the porphyrins themselves in the lowest excited singlet S₁ state was found to decrease as compared to the ground S₀ state. The difference in basicity constants pK_a depended on the nature of electronic communication between the macrocycle and peripheral substituents. In the case of an inductive effect of the substituents, the difference in the basicity constants pK_a was small, while mesomeric effects led to significant differences in the pK_a values. The cooperative nature of protonation, leading to almost simultaneous addition of two protons, was shown to be preserved in both cases. Replacement of a pyrrole with a thiophene in the macroheterocycle led to a decrease in cooperativity in both the ground S₀ and the lowest excited singlet S₁ states. The basicity constants characterizing the addition of the second and third protons by thia-substituted porphyrin differed significantly in the S₁ state (pK_a2 – pK_a1 = 2), while they were close in the ground state. The activation entropy change ΔΔS^‡ upon protonation of the porphyrins in the lowest excited S₁ state was compared to that in the ground S₀ state.

The current study is focused on the ultraviolet spectrophotometric technique for the method development and validation of quercetin following the International Conference on Harmonisation guidelines for quantitative analysis. The developed and validated UV method is then applied to the solubility studies of quercetin in various solvents. The stock solution was prepared and further scanned to determine the wavelength at which the solution showed maximum absorbance (λ_max). The λ_max of quercetin was detected at 376 nm. Using various criteria such as precision, linearity, accuracy, the limit of quantification, the limit of detection, and ruggedness, the developed method was further validated. The sample solutions of the drug were made in the concentration having a range of linearity from 2 to 10μg/mL at a selected wavelength of 376 nm. The linear regression analysis data revealed a complementary linear relationship with the value of the correlation coefficient at 0.9997. The recovery experiment, which was carried out at three levels of 80, 100, and 120%, was used to examine the accuracy of the devised method utilizing percentage recovery (96.78– 99.18). The precision parameter for validation was carried out by performing intraday and interday variations. Two experts examined the ruggedness. Among all the solvents used, methanol was observed to show the highest solubility of quercetin (111.785 ± 0.263 μg/mL). The developed method was established to make it modest, safe, definite, sensitive, rapid, suitable, and economical for the quantitative evaluation of quercetin. However, the values observed for limit of detection (LOD) and the limit of quantitation (LOQ) were higher (i.e., 0.1805 and 0.5470, respectively) for the UV method than for the previously reported expensive and sophisticated RP-HPLC method (reported LOD and LOQ were 0.00488 and 0.03906 μg/mL, respectively) and HPLC method (reported LOD and LOQ were 0.05 and 0.1 μg/mL, respectively). However, we were able to develop an accurate, cost-effective, and precise method that can be utilized for routine quality control analysis of quercetin.

The spectral and luminescent properties of the styryl derivative of thioflavin T (ThT) 2-{(1E,3E)-4-[4-(dimethylamino)-2,6-dimethylphenyl]buta-1,3-dien-1-yl}-3-ethyl-1,3-benzothiazolium-3 tosylate (Th-C23) were studied. The fluorescence decay kinetics of Th-C23 incorporated into amyloid fibrils (AF) were not exponential and could be represented as a unimodal distribution of fluorophores over duration α(t). ThT and Th-C23 were shown to form an effective donor–acceptor (D–A) pair when incorporated into the AF structure. The degree of polarization of the acceptor fluorescence was high (~0.4) within the entire spectrum, despite the energy transfer, and was explained by the special orientation of D–A pairs, parallel and antiparallel. The measured fluorescence spectrum of the donor (ThT) and absorption spectrum of the acceptor (Th-C23) were used to calculate the critical energy-transfer radius R₀, which could take values from 54 to 68 Å depending on the mutual orientation and quantum yield of the donor and acceptor.

The characteristics of an Nd:YAG multistage optical amplifier of a laser beam, the spatial parameters of which were corrected by thermal lenses formed in the active elements of each amplifier stage, were studied. Nd:YAG crystals transverse-pumped by laser diode units were used as the amplifier active elements. Removal of lens-compensators was shown to reduce the total optical losses of the amplifier and enhance its compactness. The optical losses of an optical amplifier with five amplification stages and correction of the amplified beam characteristics by thermally induced lenses of active elements were 16%; its linear dimensions, 13% less than similar indicators for a five-stage amplification system with four two-lens compensators between amplification stages.

The capabilities of spectroscopy with spatial resolution when determining the optical properties and parameters of the microvasculature of the circulatory system of surface tissues are demonstrated using specific examples of recording and processing the spectral-spatial profiles of local diffuse reflection of light by tissues of the human hand. The heterogeneity of tissue properties caused by individual distribution of vessels and chromophore concentration gradients at the investigated point of the body in addition to inadequacies of the used calculation model due to poorly studied absorption indices of the main chromophores of exsanguinated and dehydrated subcutaneous tissue are shown to contribute most to the scatter of the obtained results. A technique for recording spectral-spatial profiles and their two-stage processing is presented. Its capabilities and disadvantages are discussed. Prospective application of diffuse reflectance spectroscopy with spatial resolution to controlling the hydration of surface tissues during treatment of their inflammation and edema is shown.

The greater transparency of the polymer obtained by adding a small amount of molecular iodine to the liquid photopolymerizing composition is satisfactorily explained by the formation of a π,σ-type charge transfer (CT) complex of oligocarbonate dimethacrylate with molecular iodine. The CT band at 360 nm absorbs a significant part of the actinic radiation such that the rate of the photolytic decomposition of the photoinitiator in the initial polymerization stage permits release of free volume from the polymer into the liquid part of the photopolymerizing composite. Layer-by-layer photopolymerization occurs at advanced stages due to the thin upper layers exposed to UV irradiation becoming steadily more transparent.

Valbenazine tosylate, a benzoquinolizidine derivative, is a highly selective vesicular monoamine transporter 2 inhibitor. The drug has been approved by the FDA as the first and only approved treatment for tardive dyskinesia. To our knowledge, this is the first report on the development and validation of simple, rapid, sensitive, and cost-effective spectrofluorimetric methods based on the native fluorescence of the drug in acidic, basic, and neutral media. The stability-indicating potential of the method was assessed by recovery studies in the forced degraded solutions of the drug. The method was validated in accordance with the International Council for Harmonisation guidelines with respect to linearity, accuracy, precision, limit of detection, limit of quantification, and robustness. Excellent linearity was noted within the concentration range 2.0–30.0 μg/mL (0.1 N hydrochloric acid), 0.5–15.0 μg/mL (0.1 N sodium hydroxide), 0.1–20.0 μg/mL (water) with corresponding correlation coefficients of 0.9963, 0.9989, and 0.9998. Limits of detection and quantitation for the proposed methods were found to range from 0.025 to 0.044 and from 0.077 to 0.1357 μg/mL, respectively, for the three methods. The proposed methods were used to quantify the drug in its marketed capsule formulation, with good recoveries suggesting their applicability to routine analysis of the drug in bulk as well as in formulation.

The chemical deposition method was used to synthesize light-accumulating HfO₂–ZrO₂ oxide systems with afterglow duration up to 10 min and their spectral-luminescent properties were studied. The HfO₂:ZrO₂ ratio was found to have a significant effect on the intensity and decay kinetics of the visible luminescence of such systems as well as on the weighting coefficients and positions of individual components of the luminescence and luminescence excitation spectra. The results were explained by the contribution of complex titanium impurity optical centers in ZrO₂ to the intracenter luminescence of oxygen vacancies in HfO₂ and the competitive quenching of the luminescence by nonradiative recombination sites;

A study was carried out on the luminescence excitation spectra and photoluminescence (PL) spectra as well as the luminescence kinetics of low-density polyethylene composites with different contents of CaGa₂S₄:Eu²⁺ phosphor filler. The phospholuminescence was attributed to the 4f⁶5d → 4f⁷ transition of the Eu³⁺ ion and was greatest when the filler concentration was 7 vol.%. The dependence of the PL intensity on the excitation power density up to 0.3 W/cm² was found to be linear, indicating that these phosphors can be used as visible radiation sources in various lighting systems.

Current challenges in the field of luminescent materials are concerned with designing efficient material to meet the rapidly rising demands of industry. Luminescent material excitation and emission are highly complex phenomena driven by the combination of atomic-level properties such as valence electron, inter-atomic radius, ionic radius, etc., and physical properties such as crystal structure, symmetry, etc. The current research paper focuses on the development of a machine-learning algorithm based on simple luminescent materials to predict the excitation to the closest possible accuracy using easily accessible key attributes by the CatBoost regressor, multiple linear regression (MLR), and an artificial neural network (ANN) approach. These selected features likely correlate with the excitation of the material. In comparison, the ANN and MLR algorithms have higher mean absolute error values in both the training and test datasets. The CatBoost algorithm outperforms the other algorithms in terms of mean of the absolute percentage difference, achieving a value of 0.302136% in the training dataset. The CatBoost algorithm exhibits the lowest root mean squared error value of 1.680768 nm in the training dataset, indicating that its predictions have a smaller average deviation from the actual values. The style for studying the material property has the potential to reduce the cost and time involved in an Edisonian approach to the lengthy laboratory experiment to identify excitation.