Molecular Absorption Spectroscopy Research Articles

Thermodynamic and kinetic study of palladium(II) complexation with 1-methyl-2-mercaptoimidazole (methimazole) and their importance for structural design of metallodrugs

The acidobasic and complexing properties of 1-methyl-2-mercaptoimidazole (Methimazole, an anti-thyroid drug) were investigated. The pKa 11.49 ± 0.03 was estimated by molecular absorption spectroscopy (I = 0.10 M NaCl, t = 25.0 ± 0.1 °C). This value is in good agreement with the value 11.58 ± 0.05, obtained using the solvent-extraction technique. Theoretical (LFER and quantum chemical calculations) and experimental (1H/13C NMR spectroscopy) methods confirmed that the ligand prefers to be in the thion form, and the proton dissociation takes place on the nitrogen atom. Using glass electrode potentiometry, the complexation of the Pd(II) ion by the methimazole ligand occurs without the participation of protons. The best chemical model considers the [Pd(HL)]2+, [Pd(HL)2]2+ and [Pd(HL)3]2+ complex species, whose stability constants were also determined using spectroscopy and capillary zone electrophoretic (CZE) measurements. The metal complexes dissociate at –log [H+] > 7, where an uncharged palladium(II) hydroxide is formed. The formation kinetics of the palladium(II) complex with methimazole were studied in perchloric and hydrochloric acids (I = 1.00 M, t = 15–40 °C) and the determined rate constants and activation parameters are consistent with literature values determined for the reactions of the Pd(II) ion with thiourea derivatives. The rate constants decrease by two orders of magnitude in both media, which can be assigned to a lower tendency of the chloride ion to dissociate from the [PdCl4]2− complex species than the water molecule from the [Pd(H2O)4]2+ ion. The presented results can be utilized for the design of new Pd and Pt metallodrugs.

Molecular aggregates of merocyanine 540 with different surfactant systems

Merocyanine 540 (MC540) is a dye molecule that displays diverse photophysical features in varying environments. Micelle environments exert intriguing influences on the behavior of such molecules. This study’s primary objective is to examine the spectroscopic and thermodynamic consequences with different surfactants on the aggregation tendency of MC540. Interactions of MC540 with negatively charged sodium dodecyl sulphate (SDS), neutral triton X-100 (TX100) and positively charged hexadecyltrimethylammonium bromide (CTAB) surfactants were investigated by using molecular absorption spectroscopy. The interactions of MC540 with the SDS, CTAB, and TX100 under and above critical micelle concentration (CMC) were studied and H aggregate formation was observed under CMC. This H aggregate structure leaded to a shift towards monomer band above the CMC of SDS, TX100, CTAB according to the H aggregate-monomer equilibrium. Moreover, it was firstly observed that MC540 has trimer type aggregate structures as well with varying CTAB concentrations. In addition, by using temperature studies, thermodynamic function ΔH⁰dis values, dimer and trimer structures, were calculated as 6.10 kcal/mol, and 8.94 kcal/mol, respectively, and ΔS⁰dis values for dimer and trimer structures as −3.87 cal/Kmol, and −18.39 cal/Kmol, respectively. The calculated thermodynamic functions showed that disaggregation of aggregates is endothermic in nature and entropy is the driving force.

Characterization of TEMPO-Oxidized Cellulose Nanofiber From Biowaste and Its Influence on Molecular Behavior of Fluorescent Rhodamine B Dye in Aqueous Suspensions

AbstractCellulose nanofiber (CNFs) obtained through TEMPO oxidation was structurally characterized using FT-IR (Fourier Transformed Infrared) and SEM (Scanning Electron Microscopy) spectroscopy. The molecular aggregation and spectroscopic properties of Rhodamine B (Rh-B) in CNFs suspension were investigated using molecular absorption and steady-state fluorescence spectroscopy techniques. The interaction between CNFs particles in the aqueous suspension and the cationic dye compound was examined in comparison to its behavior in deionized water. This interaction led to significant changes in the spectral features of Rh-B, resulting in an increase in the presence of H-dimer and H-aggregate in CNFs suspension. The H-type aggregates of Rh-B in CNFs suspensions were defined by the observation of a blue-shifted absorption band compared to that of the monomer. Even at diluted dye concentrations, the formation of Rh-B’s H-aggregate was observed in CNFs suspension. The pronounced aggregation in suspensions originated from the strong interaction between negatively charged carboxylate ions and the dye. The aggregation behavior was discussed with deconvoluted absorption spectra. Fluorescence spectroscopy studies revealed a significant reduction in the fluorescence intensity of the dye in CNFs suspension due to H-aggregates. Furthermore, the presence of H-aggregates in the suspensions caused a decrease in the quantum yield of Rh-B compared to that in deionized water.

Efficient trihalomethane quantification in drinking water for minimally-equipped water treatment plants labs

Chlorine is a common disinfectant used in water treatment. However, its reaction with organic matter can lead to the formation of harmful byproducts, such as trihalomethanes (THMs), which are potentially carcinogenic. To address this issue, the aim of this work was to enhance a colorimetric method capable of quantifying THMs in drinking water through UV/Vis Spectrophotometry, using cost-effective equipment, and validate this methodology for the first time according to established validation protocols. The method’s innovation involved replacing the solvent pentane with the more common hexane, along with adjusting the heating ramp, elucidating the mechanisms involved in the process. This method involves the reaction between THMs, pyridine, and NaOH to produce a colored compound, which is then monitored through molecular absorption spectroscopy in the visible region. The method was thoroughly validated, achieving a limit of detection of 13.41 μg L−1 and a limit of quantification of 40.65 μg L−1. Recovery assays ranged from 86.1 % to 90.7 %, demonstrating high accuracy. The quality of the linear fit for the analytical curve exceeded R2 > 0.98. The method was applied to real samples, revealing concentrations ranging from 13.58 to 55.46 μg L−1, all way below the legal limit in Brazil (Maximum Contaminant Levels (MCL) = 100 μg L−1). This cost-effective and straightforward method is suitable for integration into water treatment plant laboratories.

Investigation of acute, sub-chronic toxicity, effects of mangiferin and mangiferin solid dispersion (HPTR) on Triton WR1339-induced hyperlipidemia on Swiss albino mice

Mangiferin is a xanthonoid found in Mango leaves in abundance with many effects as a hypoglycemic, antioxidant, and anti-inflammatory agent, plant metabolite, and so on. However, nowadays, mango leaves are merely a waste product in Vietnam. To take advantage of this valuable medicinal resource, extraction conditions of mangiferin using classical and ultrasound methods were researched, and mangiferin was purified from Cat Chu mango leaves (Mangifera indica L., Anacardiaceae) collected in Dong Thap. Ultrasound-assisted extraction method was conducted with the following conditions and mangiferin was extracted at a percentage of 6.728% with a purity of 91.11%. Purified mangiferin was evaluated using molecular absorption spectroscopy UV-Vis, scanning electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, simultaneous thermal analysis (STA: TGA/DSC), and dissolution measurement method. To optimize the solubility and permeability of mangiferin, the solid dispersion system (HPTR) was made by the combination of HPMC 6M:mangiferin at the ratio of 1:5. To investigate the acute, sub-chronic toxicity and hypolipidemia effect of HPTR as compared to purified mangiferin, we followed guidelines for preclinical and clinical trials of Traditional Medicine and Herbal Medicines by the Vietnam Ministry of Health and OECD, and used tyloxapol (Triton WR1339, 400 mg/kg, i.p.) to induce hyperlipidemia. Our results indicated that purified mangiferin and HPTR extract showed no acute toxicity and sub-chronic toxicity and has potential as an antihyperlipidemic agent. The HPTR brought about a significant decrease in total cholesterol, triglycerides and LDL-c when compared to mangiferin, however there was no significance between them.

Synthesis and application of anthraquinone quaternary phosphonium salt electroplating copper leveler based on expanded electrostatic adsorption area strategy and physicochemical salt bridge mechanism

Four anthraquinone quaternary phosphate molecules (AQS-a, AQS-b, AQS-c, AQS-d) with different electrostatic adsorption areas were constructed as electroplating levelers based on the strategy of expanding the electrostatic adsorption area of the molecules. AQS-d with the largest electrostatic adsorption area was demonstrated to have the most excellent electrochemical performance by electrochemical tests. The physicochemical adsorption sites and interactions with copper ions of AQS levelers were proposed by theoretical calculations, molecular dynamics simulations, Raman spectroscopy and fluorescence absorption spectroscopy, and the electroplating salt bridge mechanism was proposed. Based on optical microscope, scanning electron microscope, atomic force microscope and X-ray diffractometer, it is proved that AQS-d has the ability to perfectly fill the microvia in actual plating by actual PCB blind hole filling experiment.

Validation of a small-scale method for determination of phosphorus in meat and meat products by molecular absorption spectroscopy

The purpose of this study was to evaluate the applicability of an alternative analytical technique to the reference method for phosphorus detection in meat and meat products established by ISO 2294:1974, revised by ISO 23776:2021. When an analytical method is modified or a new one is developed and implemented, it should be validated before being accepted for routine determinations. Furthermore, it is necessary to demonstrate that the new or alternative method has good performance characteristics in comparison with the reference method. Therefore, a comparison of the performance of the alternative and the reference method should be made. In the present study, a statistical evaluation of the calibration model of the alternative method was made with data from interlaboratory studies made in five consecutive years using fifty analyses of meat and meat products. The statistical parameters evaluated over time for the calibration curve were the y-intercept and slope; correlation and linearity; analytical limits: detection and quantification; working range; and accuracy (precision and trueness). In the interlaboratory tests, the results obtained by the alternative analytical method were compared with those obtained by the reference method, and their performance in these tests was also evaluated. The results obtained by the alternative method indicated better accuracy than the reference method due to lower relative errors, more precision, and a good trueness evaluation through lower absolute values of the z-score. The study demonstrated that the phosphorus alternative method is applicable for the determination of total phosphorus in the matrix of meat and meat products.

Silver Triangular Nanoplates as Analytical Reagents in Optical Molecular Absorption Spectroscopy: Possibilities and Prospects

Silver Triangular Nanoplates as Analytical Reagents in Optical Molecular Absorption Spectroscopy: Possibilities and Prospects

ONO-pincer Zn(II) & Cd(II) complexes: Synthesis, structural characterization, Hirshfeld surface analysis and CT-DNA interactions

Four new ONO pincer complexes of type Na2[Cd(L′)(OAc)2] (2a), Na2[Zn(L)(OAc)2] (3a), [Zn(LMe)(OAc)2] (4a) and [Cd(LMe)(OAc)2] (4b), where L′ = N,N'-bis(4-methylpyridin-2-yl)pyridine-2,6-dicarboximidate, L = N,N'-di(pyridin-2-yl)pyridine-2,6-dicarboximidate and LMe=N,N'-bis(1-methylpyridinium-2-yl)pyridine-2,6-dicarboximidate, were synthesized. The ligands were generated during complex formation reaction by the in situ deprotonation of their respective pro-ligands; H2L′ (2), H2L (3) and H2LMe (OTf)2 (4). The newly synthesized metal complexes were characterized by elemental analysis, FT-IR, NMR (1H and 13C), and single crystal X-ray diffraction techniques. The single crystal analysis of 4b disclosed that the central Cd(II) ion is adopting capped trigonal prism geometry. The nature of intermolecular interactions within the crystal structure, fingerprint plots, and molecular surface contours have been studied using Hirshfeld surface analysis. The DNA binding assay was conducted by molecular absorption spectroscopy, viscosity measurement and molecular modeling simulations. DNA-interaction measurements show that the compounds have a high propensity for binding with DNA as a groove binder.

Dual-comb optomechanical spectroscopy

Optical cavities are essential for enhancing the sensitivity of molecular absorption spectroscopy, which finds widespread high-sensitivity gas sensing applications. However, the use of high-finesse cavities confines the wavelength range of operation and prevents broader applications. Here, we take a different approach to ultrasensitive molecular spectroscopy, namely dual-comb optomechanical spectroscopy (DCOS), by integrating the high-resolution multiplexing capabilities of dual-comb spectroscopy with cavity optomechanics through photoacoustic coupling. By exciting the molecules photoacoustically with dual-frequency combs and sensing the molecular-vibration-induced ultrasound waves with a cavity-coupled mechanical resonator, we measure high-resolution broadband ( > 2 THz) overtone spectra for acetylene gas and obtain a normalized noise equivalent absorption coefficient of 1.71 × 10−11 cm−1·W·Hz−1/2 with 30 GHz simultaneous spectral bandwidth. Importantly, the optomechanical resonator allows broadband dual-comb excitation. Our approach not only enriches the practical applications of the emerging cavity optomechanics technology but also offers intriguing possibilities for multi-species trace gas detection.

Simultaneous determination of paracetamol and codeine phosphate in pharmaceuticals using molecular absorption spectroscopy and classical least squares method

In this article, a combined method of molecular absorption spectroscopy and classical least squares is used to simultaneously determine paracetamol (PAR) and codeine phosphate (COP) in pharmaceutical samples without the need for prior separation or extraction steps. The absorption spectra of standard solutions and samples were measured in the wavelength range of 210 to 290 nm with a step size of 0.5 nm. The concentrations of PAR and COP in the sample solutions were calculated using a self-made program written in Microsoft Excel 2016 and Visual Basic for Applications (VBA). The reliability of the method was verified through the accuracy and reproducibility of the measurements when analyzing PAR and COP in Effer-Paralmax® Codeine tablets, and comparing the average values of their concentrations in the samples with the standard HPLC method.

Formation - Extraction of Ion Pair Complexes of [PdI4]-2 and[BiI4]-1 with Trifluoperazine Hydrochtoride (TFPri) Drug andDetermination by Molecular Absorption Spectroscopy

This Study includes the determination of (TFPH) drug via the formation of ion association pair with [pdly]? and with [Bily]" in aqueous phase . The analytical results obtained are as follow: the optimum pH is 5 and 4, reaction time is immediate and 5 minutes, mixing time 3 and 4 minutes for the two ion pair respectively. The statistical and other analytical results for the first ion pair in the concentration range (6- -40ppm) were as follow: the detection limit is 0.228 ppm, molar absorption coefficient is 2.3635x10* liter mole™ em™ at 297nm . For Bily — TFPH ion pair at 292 nm, the results in the concentration range (0.2-18ppm) ere as follow: detection limit is 0.0030 ppm , and molar absorption coefficient is 3.747 x 10° liter mole” cm™ . This method was applied to Salabid pharmaceutical preparation with percentage recovery of not less than 98.5%

Heterologous overexpression and characterization of homoserine dehydrogenase from Paracoccidioides brasiliensis

The enzyme Homoserine dehydrogenase from Paracoccidioides brasiliensis (PbHSD), an interesting enzyme in the search for new antifungal drugs against paracoccidioidomycosis, was expressed by E. coli. Thirty milligrams of PbHSD with 94% of purity were obtained per liter of culture medium. The analysis by CD spectroscopy indicates a composition of 45.5 ± 7.3% of α-helices and 10.5 ± 7.0% β-strands. Gel filtration chromatography indicates a homodimer as biological unity. Fluorescence emission spectroscopy has shown stability of PbHSD in the presence of urea until Cm of 4.13 ± 0.21 M, and a broad pH range in which there is no conformational change. The protein analysis by differential scanning calorimetry indicates high stability at room temperature, but low stability at high temperatures, suffering irreversible denaturation, with Tm = 58.65 ± 0.87 °C. Kinetic studies of PbHSD by molecular absorption spectroscopy in UV/Vis have shown an optimum pH between 9.35 and 9.50, with Michaelian behavior, presenting KM of 224 ± 15 μM and specific activity at optimum pH of 2.10 ± 0.07 μmol/min/mg for homoserine. Therefore, protein expression and purification were efficient, and the structural characterization has shown that PbHSD presents native conformation with enzymatic activity in kinetic assays.

Composition of the Cytochrome c Complex with Cardiolipin by Thermal Lens Spectrometry.

Thermal lens spectrometry along with spectrophotometric titration were used to assess the composition of the complex of oxidized cytochrome c (ferricytochrome c) with 1,1',2,2'-tetraoleyl cardiolipin, which plays a key role in the initiation of apoptosis. Spectrophotometric titration was carried out for micromolar concentrations at which the complex is mainly insoluble, to assess the residual concentration in the solution and to estimate the solubility of the complex. Thermal lens spectrometry was used as a method of molecular absorption spectroscopy, which has two advantages over conventional optical transmission spectroscopy: the higher sensitivity of absorbance measurements and the possibility of studying the light absorption by chromophores and heat transfer in complex systems, such as living cells or tissues. Thermal lens measurements were carried out at nanomolar concentrations, where the complex is mainly in solution, i.e., under the conditions of its direct measurements. From the thermal lens measurements, the ratios of cytochrome c and cardiolipin in the complex were 50 at pH 7.4; 30 at pH 6.8; and 10 at pH 5.5, which fit well to the spectrophotometric data. The molecular solubility of the complex at pH 6.8-7.4 was estimated as 30 µmol/L.

Molecular dynamics simulation and X-ray absorption spectroscopy to characterize the local structure and dynamics of calcium ion in sulfonated polystyrene

Molecular Dynamics (MD) Simulation and the Extended X-ray Absorption Fine Structure spectroscopy (EXAFS) were combined to characterize the “averaged” coordination structures and short-time dynamics of the calcium-doped sulfonated polystyrene (CaSPS) at the atomistic level. MD simulation of the CaSPS ionomer implies that there is evidence for the Ca...O coordination from both the sulfonate group and oxygen atoms. The EXAFS fitting procedure was compared between the conventional technique using the atomic coordinates from the standard CaO crystal and the method using selected snapshots from MD trajectories. The averaged Ca…O distance and the coordination number in the first solvation shell from the simulation are in good agreement with the EXAFS spectra (2.5, 2.4 Å and CN = 5.8, 5.7 from MD, EXAFS analysis, respectively). From MD simulation, the cases of 5–7 oxygen atoms from 4 to 5 sulfonated groups coordinating with calcium are the most frequently seen. The best fit of EXAFS data using the atomic coordinates from MD snapshot suggests that there is only one dominant shell for Ca…O coordination which is six oxygen atoms from five different sulfonated groups and the other one from a water molecule. The interaction between Ca2+ ion and sulfonate group strongly slows down the dynamics of these species in the cooperative manner whereas water molecules exhibit much faster dynamics.

Preliminary study on direct measurements and diagnostics for chemical reaction dynamics of NOx by using laser wavelength modulation spectroscopy

Studies on the kinetics of gas-phase chemical reactions currently rely on calculations or simulations and lack simple, fast, and accurate direct measurement methods. We developed a tunable laser molecular absorption spectroscopy measurement system to achieve direct measurements of such reactions by using wavelength modulated spectroscopy and performed online measurements and diagnostics of molecular concentration, reaction temperature, and pressure change during the redox reaction of ozone with nitrogen oxides (NOx) with 0.1 s temporal resolution. This study provides a promising diagnostic tool for studying gas-phase chemical reaction kinetics.

Determination of Essential Element and Titanium Contents in Rocks using Flame Atomic and Molecular Absorption Spectrometry

Rocks contain a large number of elements such as Na, K, Ca, Mg, Fe, Mn, and Ti. The determination of those element contents is important in geological and geographical exploration as well as the original identification and classification of rocks. Currently, the analysis of the elemental composition of rocks can be carried out on equipments such as ICP-OES, ICP-MS,... However, in some laboratories with limited conditions, the analysis has many difficulties. In the present study, we analyzed rock samples after being treated by microwave using flame atomic and molecular absorption spectroscopy. The results showed that the content of elements in the range of Na (0.31 – 2.46%), K (1.38 – 3.71%), Ca (0.08 – 0.23%), Mg (0.16 – 0.69%), Fe (2.38 – 5.19) %), Mn(0.08 – 0.1%) and Ti(0.12 – 0.36%). The study provides a simple and cost-effective method for rock analysis.

Применение метода терагерцовой газовой спектроскопии высокого разрешения для исследования состава продуктов термического разложения биологической жидкости (урины) крыс с дисбактериозом

The trend towards diagnostic approach based on revealing the metabolic profile of disease is observed in current medicine. The metabolic profile of the disease is a set of metabolites – final or intermediate products of metabolism in the living body, specific for a given disease or pathology. The search for biomarkers is possible in exhaled breath, as well as in biological liquids, and last ones are often more informative, because the liquids respond fast to changes of biological organism state and substances may be present in higher concentrations than gas excretions of organism. Preclinical trials of approaches to the treatment of diseases, including socially significant ones, such as dysbacteriosis, are carries out on rodents. The thermal decomposition products content of the line of the urine samples of rats with artificially induced dysbacteriosis was studied in this work. A promising approach for studying multicomponent gas mixtures of various origins, including biological ones, is molecular absorption spectroscopy, in particular, nonstationary spectroscopy in the terahertz (THz) frequency range. When radiation that has passed through a gaseous sample is detected, absorption lines are recorded in the spectrum, which are an unambiguous characteristic of specific substances. By the presence of these absorption lines, the conclusion about the presence of these substances in the studied multicomponent gas mixture can be done, and, therefore, potential markers of pathologies, diseases and markers that characterize the effects of various effects on a living organism, can be identified. A set of metabolites appeared during thermal decomposition of urine samples of rodent (healthy, with artificially induced dysbacteriosis, with various treatment regimens) was revealed, and the compositions of gaseous products were compared. The presented approach is promising for the development of a non-invasive research method that allows to identify markers that reflect the presence of dysbacteriosis, as well as to assess the impact on the rat’s organism during the therapy.

Direct Observation of Contact Ion-Pair Formation in La3+ Methanol Solution.

An approach combining molecular dynamics (MD) simulations and X-ray absorption spectroscopy (XAS) has been used to carry out a comparative study about the solvation properties of dilute La(NO3)3 solutions in water and methanol, with the aim of elucidating the still elusive coordination of the La3+ ion in the latter medium. The comparison between these two systems enlightened a different behavior of the nitrate counterions in the two environments: while in water the La(NO3)3 salt is fully dissociated and the La3+ ion is coordinated by water molecules only, the nitrate anions are able to enter the metal first solvation shell to form inner-sphere complexes in methanol solution. The speciation of the formed complexes showed that the 10-fold coordination is preferential in methanol solution, where the nitrate anions coordinate the La3+ cations in a monodentate fashion and the methanol molecules complete the solvation shell to form an overall bicapped square antiprism geometry. This is at variance with the aqueous solution where a more balanced situation is observed between the 9- and 10-fold coordination. An experimental confirmation of the MD results was obtained by La K-edge XAS measurements carried out on 0.1 M La(NO3)3 solutions in the two solvents, showing the distinct presence of the nitrate counterions in the La3+ ion first solvation sphere of the methanol solution. The analysis of the extended X-ray absorption fine structure (EXAFS) part of the absorption spectrum collected on the methanol solution was carried out starting from the MD results and confirmed the structural arrangement observed by the simulations.

Mangiferin/β-cyclodextrin complex: determination of the Inclusion constant in aqueous solution by Higuchi–Connors method and molecular absorption and photoluminescence UV spectroscopies at pH 3.4

Mangiferin/β-cyclodextrin complex: determination of the Inclusion constant in aqueous solution by Higuchi–Connors method and molecular absorption and photoluminescence UV spectroscopies at pH 3.4