Isosbestic Research Articles

High Performance Thin Layer Chromatographic Method for Simultaneous Estimation of Vitamin C, Thymoquinone and Thymol in Plant Extracts

Background: Lack of an effective HPTLC simultaneous estimation method for vitamin C, thymoquinone and thymol in plant extracts. Aim: The present study involves the development of an accurate, precise, specific, and specific HPTLC method for the identification and quantification of three phytomarkers thymol and thymoquinone in Nigella sativa (kali jiri) seed extract and vitamin C in Hylocereus polyrhizus (dragon fruit) extract. Methods: Using an aluminum plate pre-coated with silica gel 60 F254 and methanol-n hexane-ammonia (15%) (8.5:1.5:0.2 v/v/v) as the mobile phase, thin layer chromatographic development was performed. Results: For each of the three markers, densitometric quantification was carried out at the isobestic point of 271 nm. Vitamin C, thymol, and thymoquinone bands were separated chromatographically at Rf values of 0.66, 0.35, and 0.19, respectively, by using developed mobile phase. For thymol, thymoquinone, and vitamin C, linearity range was 2000-8000 ng/band. The three markers showed 99.39%–99.91% recovery for thymol, 99.22%–99.89% recovery for thymoquinone, and 99.19%–99.69% recovery for vitamin C. Conclusion: The optimized method was used to quantify three thymol and thymoquinone in N. sativa (kali jiri) seed extract and vitamin C in H. polyrhizus (dragon fruit) extract.

Ultrafast dynamics of mCP and Br-mCP: Insights from transient absorption spectroscopy

Heavy atom activated organic room-temperature phosphorescence (RTP) has attracted considerable interest due to its high phosphorescence quantum yield and prolonged lifetime. This research provides a detailed analysis of the transient absorption spectroscopy of 1,3-Bis(N-carbazolyl)benzene (mCP) and 9,9'-(5-Bromo-1,3-phenylene)bis(9H-carbazole) (Br-mCP) in toluene solution. In the femtosecond transient absorption (fs-TA) spectroscopy of mCP, the excited state absorption (ESA) signal decreases at 630 nm while the triplet-triplet absorption (TTA) signal increases at 420 nm. Meanwhile, the isosbestic point observed at 455 nm indicates an intersystem crossing (ISC) lifetime of 15.4 ns. Moving on to the nanosecond transient absorption (ns-TA) spectroscopy, the TTA signal reaches its peak at 27.3 ns before decreasing, with the triplet lifetime of mCP measured at 2.8 μs. Br-mCP exhibits a similar dynamic evolution to mCP, but with a quicker ISC process (9.4 ns) and a longer triplet lifetime (3.9 μs). The quicker ISC process in Br-mCP is ascribed to the presence of heavy atom in the molecular structure, leading to an enhanced spin-orbit coupling constant (ξ(S1, T3)Br-mCP = 1.371 cm-1 > ξ(S1, T4)mCP = 0.060 cm-1). The prolonged triplet lifetime of Br-mCP (3.9 μs > 2.8 μs) results from its lower reorganization energy, effectively reducing non-radiative vibrational energy losses within the molecule. This work significantly enhances our understanding of RTP materials incorporating heavy atoms.

Development of Optical Sensors Based on Neutral Red Absorbance for Real-Time pH Measurements.

Measuring pH with an optical sensor requires the immobilization of a chemical recognition phase on a solid surface. Neutral red (NR), an acid base indicator was used to develop two different optical probe configurations. The chemistry of aryl diazonium salts was chosen for the elaboration of this chemical phase, as it enables strong covalent bonds to be established on the surface of metallized glass or metallic surfaces. It also allows the formation of a thick film required to obtain an exploitable spectral response. The surfaces of interest (metallized optical fiber and 316 L stainless-steel mirror) are modelized by flat surfaces (metallized glass plates and 316 L stainless-steel plates). The analytical characterizations carried out (IR, XPS, UV-Visible, and profilometry) show that NR was covalently grafted onto the model surfaces as well as on the surfaces of interest. The supports grafted with NR to develop optical pH probes exhibit spectral changes, particularly the values of pKa, the pH range, and the isosbestic point wavelength. The experimental results show that the optical probe can be used for pH measurements between 4 and 8.

Simultaneous spectrophotometric and chromatographic determination of Ketorolac and Dexamethasone: Overall assessment regarding environmental Impact, Practicality, and functionality principles

Determination of a drug combination that contains a minor component that is also a poorly UV absorbing analyte represents greet challenges in drug analysis. A fixed-dose ophthalmic combination of ketorolac tromethamine (KET) and dexamethasone sodium phosphate (DEX) (in the ratio of 5:1) is used to relieve post-surgical inflammation and seasonal allergic conjunctivitis due to their analgesic and anti-inflammatory activity. Five spectrophotometric methods and a reversed phase chromatographic separation method were developed and validated for simultaneous determination of both drugs in lab-prepared eye drops. Direct spectrophotometric determination of KET (the major, highly UV absorbing analyte) was achieved from the zero-order UV absorption spectra at 323 nm while DEX (which is the minor, poorly UV absorbing analyte) was quantified after applying several spectrophotometric methods. Either fundamental zero-order spectra or ratio spectra were used, and measurements were done at either single or dual wavelengths. The developed methods were: isosbestic point method, absorption factor method, dual wavelength method, ratio difference UV spectrophotometric method, and simultaneous equation method. The developed spectrophotometric methods determine KET in the linearity range of 2.0–12.0 μg/mL and DEX in the range of 5.0 – 35.0 μg/mL. For accurate spectrophotometric determination of DEX in the ratio of the dosage form, multiple standard addition method was applied. HPLC technique was also applied for separation and quantification of both drugs. Chromatographic separation was attained by using Hypersil ODS-C18 (150 x 4.6 mm, 5 μm) column. The mobile phase was composed of 50 % methanol: 50 % phosphate buffer (pH 2.5). The column compartment was maintained at 25 °C. Flow rate was adjusted at 1.2 mL/min and detection was performed by DAD at 254 nm. The linearity of HPLC method was 5.0–100.0 μg/mL, and 5.0–50.0 μg/mL for KET and DEX, respectively. Simultaneous determination of both drugs was applied to lab-prepared eye drops that contain also benzalkonium chloride as inactive ingredient. The developed methods determined the cited drugs with good and acceptable % recovery. The results of the developed methods and a reported HPLC method were compared using one-way ANOVA test, F-test and student’s t-test at confidence level 95 %, and they show no significant statistical difference. Assessment of greenness of the developed methods in comparison with reported HPLC method was performed using different tools, including analytical eco-scale, GAPI and AGREE. HPLC-EAT was also performed to ensure greenness of developed HPLC method. Moreover, assessment of practicality, applicability, and functionality of developed and reported methods was evaluated by BAGI metric tool and WAC calculator, respectively. The developed methods allow simple, rapid, and accurate analysis of quality control samples that contain KET and DEX.

Coupling several spectral manipulations with isosbestic approach to resolve overlapped spectra for concurrent analysis of lamivudine/tenofovir combination: Evaluating environmental sustainability

Acquired immunodeficiency syndrome (AIDS) is a chronic disease caused by the human immunodeficiency virus (HIV), which can severely damage the immune system. Recently, lamivudine (LAM) and tenofovir disoproxil fumarate (TDF) were co-formulated for the management of (AIDS). This work proposes three new UV spectrophotometric approaches based on the isosbestic point, namely: absorption subtraction method (AS), amplitude modulation method (AM) and amplitude summation method (A-Sum). The (AS) approach is based on the absorption factor method, and the two drugs can be determined at the isosbestic point in the range's zero order absorption spectra (224 nm). The (AM) method is utilizing normalized spectrum of LAM (1 μg/mL) as a divisor spectrum. After division, LAM and TDF can be determined at the isosbestic point that remained in the obtained ratio spectra at the same point even after division (224 nm). In (A-Sum) method, first order derivatization is done and the two drugs can be detected at the isosbestic point (276 nm) by using amplitude factor. The linear ranges for LAM and TDF were 5–30 μg/mL and 10–50 μg/mL, respectively. The limits of detection for LAM and TDF were 0.71–0.90 μg/mL and 0.56–1.09 μg/mL, respectively, indicating the sensitivity of these approaches. The two drugs were determined at the isospestic point without the requirement for a supplemental technique using the relevant unified regression equation. All methods were found to be accurate, repeatable, and selective based on ICH recommendations for linearity, accuracy, precision, and selectivity. The obtained results were statistically compared to the reported HPLC methods for LAM and TDF, which revealed no significant.

The structure of water from hot to supercooled temperatures based on analysis of experimental X-ray scattering data

An increasing number of studies support the existence of a liquid–liquid critical point (LLCP) in water, implying that under ambient conditions, water is a supercritical mixture of low-density (LDL) and high-density liquid (HDL) structures. Here, we analyse X-ray scattering data in terms of this model. Small-angle X-ray scattering data shows that anomalies are seen at temperatures as high as 360 K. By assuming the local structure in LDL-domains resembles that of the corresponding amorphous solid, we estimate the population of LDL-domains at different temperatures from pair-correlation functions (PCFs). By subtracting the LDL contribution, we isolate the PCF of the HDL component. The temperature-dependent HDL-PCFs show a feature around 4 Å in the supercooled regime, interpreted as interstitials resulting from collapse of the second coordination shell. We define the first coordination shell as neighbours up to 3.3 Å, based on an isosbestic point in the running coordination number. Our analysis shows that the HDL-domains have on average two strongly and two weakly H-bonded neighbours. The LDL population in TIP4P/2005-water is less temperature dependent than in real water, and the HDL component contains more structures with three strongly H-bonded neighbours, leading to a slight overestimation of the first peak of the PCF.

Exploring the Te(II)/Te(IV) Redox Couple of a Tellurorosamine Chromophore: Photophysical, Photochemical, and Electrochemical Studies.

A tellurorosamine dye [Te(II)] undergoes aerobic photooxidation. Although Te(IV) species have been used in a number of oxidations, key Te(IV)-oxo and Te(IV)-bis(hydroxy) intermediates are challenging to study. Under aerobic irradiation with visible light, Te(II) (λmax = 600 nm) transforms into a Te(IV) species (λmax = 669 nm). The resultant Te(IV) species is not stable in the dark or at -20 °C, decomposing back to Te(II) and other byproducts over many hours. To eliminate the structural ambiguity of the Te(IV) photoproduct, we used spectroelectrochemistry, wherein the bis(hydroxy) Te(IV)-(OH)2 was electrochemically generated under anaerobic conditions. The absorption of Te(IV)-(OH)2 matches that of the Te(IV) photoproduct. Because isosbestic points are maintained both photochemically and electrochemically, the oxo core formed photochemically must rapidly equilibrate with Te(IV)-(OH)2. Calculations on the bis(hydroxy) versus oxo species further corroborate that the equilibration is rapid and the spectra of the two species are similar. To further explore Te(IV) cores, two novel compounds, Te(IV)-Cl2 and Te(IV)-Br2, were synthesized. Characterization of Te(IV)-X2 was simplified because these cores have no analogue to the Te(IV)-(O)/Te(IV)-(OH)2 equilibrium. This work provides insights into the photophysical and electrochemical behavior of Te analogues of chalcogenoxanthylium dyes, which are relevant for a broad range of photochemical applications.

Cation-Stacking Approach Enabling Interconversion between Bis(xanthylium) and its Reduced Species.

Cyclophane-type dications with two units of xanthylium were designed, with the expectation that intramolecular interaction between cation units could induce changes in absorption and redox behavior. The desired dications were synthesized via the macrocyclic diketone as a key intermediate, which was efficiently obtained by a stepwise etherification. X-ray and UV/Vis measurements revealed that the cyclophane-type dications adopt a stacking structure in both the crystal and solution. Due to the intramolecular interaction caused by π-π stacking of the xanthylium units, a considerable blue shift compared to the corresponding monocations and a two-stage one-electron reduction process were observed in the dications. Furthermore, upon electrochemical reduction of dications, the formation of biradicals via radical cation species was demonstrated by UV/Vis spectroscopy with several isosbestic points at both stages. Therefore, the cation-stacking approach is a promising way to provide novel properties due to perturbation of their molecular orbitals and to stabilize the reduced species even though they have open-shell characters.

Advanced stability-indicating gradient elution reverse phase-high performance liquid chromatography method development and validation for simultaneous estimation of rutin and curcumin using an analytical quality by design approach

This research delves into a systematic Analytical Quality by Design (AQbD) approach to develop and validate a stability-indicating robust RP-HPLC method for the simultaneous determination of Rutin and Curcumin, compounds known for their anti-inflammatory, antioxidant, and wound-healing properties. Utilizing QbD principles, critical method parameters (CMPs) were identified and screened using design of experiments (DoE) and optimized via response surface methodology (RSM) with Central Composite Design (CCD). The optimized chromatographic separation used a Phenomenex Luna C18 column with gradient elution, using methanol and 0.1% formic acid, a flow rate of 1 ml/min, and detection at 345 nm (isosbestic point). The retention times were 5.63 mins for Rutin and 17.01 mins for Curcumin. The stability indication of the developed HPLC method was performed, and validation parameters were meticulously conducted following the ICH Q2(R1) guidelines, demonstrating linearity over 2-10 μg/ml for Rutin and 5-25 μg/ml for Curcumin, with correlation coefficients of 0.9999 and 0.9998, respectively. Precision studies showed %RSD within acceptable limits, and accuracies ranged between 97-100%. This validated HPLC method offers a reliable, sensitive approach for simultaneous quantifying Rutin and Curcumin, suitable for routine analysis in pharmaceutical laboratories and quality control.

Delineating a Tailor-Made Fluorescent Probe Designed for the Selective Detection of Tyrosinase.

A dicyanoisophorone based fluorescent probe (E)-2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-en-1-ylidene)malononitrile (DCIP-OH) was developed for the selective sensing of tyrosinase in apple extract and live cells. The probe was obtained by the condensation of 2-(3,5,5-trimethylcyclohex-2-en-1-ylidene)malononitrile with 4-hydroxybenzaldehyde. Upon interaction with tyrosinase, the probe exhibited absorbance switching from 417 nm to 357 nm, accompanied by a slight increase in absorption value and an isosbestic point observed at 373 nm. Additionally, a reduction in emission intensity at 592 nm was observed. Furthermore, we successfully employed the probe for sensing of tyrosinase in apple extract and conducted inhibition studies by using kojic acid. LOD was determined to be ~0.4 nM. Moreover, the biocompatible nature of DCIP-OH enabled its effective localization in epithelial-like melanoma cells, B16F10, where it demonstrated successful fluorescent probing of intracellular tyrosinase.

Possibilities of Skin Autofluorescence Reflecting the Characteristics of Diabetes Mellitus in Childhood

Objective: To measure skin autofluorescence in children and adolescents suffering from type 1 diabetes mellitus and evaluate its relationship with gender, age, experience and chronic complications of the disease. Materials and Methods: The study group included 47 children and adolescents with type 1 diabetes. Autofluorescence of the skin from the inner surface of the shoulder and nail of patients was measured using an original compact spectrofluorimeter based on the STS-VIS OCEAN OPTICS © USA microspectrometer with UVA excitation. Statistical analysis was carried out using StatsoftStatistica 12.0 software. The data is presented as a two-dimensional array. The UV LED signal was averaged and smoothed using the moving average method with a 10 nm window. Then the spectra were renormalized taking into account the found coefficients. The result of applying additional normalization is a decrease in the standard deviation. Results and Discussion: Significant differences were revealed in the skin fluorescence spectra of children of different ages. between age groups (5-7) and (8-12) is most significant in the region of the alpha band of oxyhemoglobin (540 nm) (p <0.005). When using I-normalization, the NADH peak region (p < 0.02) is significant with increasing disease duration. When studying the influence of gender factors on the level of skin autofluorescence, the most significant differences are found in the area of only the isosbestic points of deoxy and oxyhemoglobin 442 nm (p<10-7) and 491 nm (p<10-8). Significant differences in skin autofluorescence at the reference length were also obtained waves in the autofluorescence spectrum of 500 nm correspond to p<10-14, depending on the presence of complications. Conclusion: In Russia, as well as throughout the world, there is an increase in the incidence of type 1 diabetes mellitus. For early diagnosis of changes in carbohydrate metabolism and complications of the disease, a simple, accessible, non-invasive research method is needed. Taking into account the results of our study, when creating non-invasive methods for monitoring the state of carbohydrate metabolism, it is necessary to take into account gender and age characteristics, experience and the presence of complications of type 1 diabetes mellitus.

Revisited UV- spectra of chlorohydroxoaurate anions

The most important ionic precursor of gold, [AuCl4]-, is used in aqueous solution leading to chlorohydroxoaurates species, [AuCl4-x(OH)x]- (x = 1–4) due to partial hydrolysis. Their UV spectral signatures are still relatively unknown though very useful in many domains of application. Individual spectra of each of them are determined for the first time thanks to a thorough experimental investigation comprising the range 200–250 nm, surpringly ignored up to now. New isosbestic points useful for species partition analysis are evidenced. Electronic transition attribution is obtained from quantum chemical calculations based on TD-DFT. The prediction of the experimental blueshifted bands of the [AuCl4-x(OH)x]-1 anions was possible only after applying energy corrections calibrated on the full UV range two-band spectrum of the [AuCl4]- complex.

Chromogenic recognition of Cr(III) and Cu(II) using a novel Schiff base and “turn-on” fluorescent detection of CO32− by its reduced scaffold in aqueous media

An upsurge of severe toxic inorganic ionic species in water arising due to anthropogenic activities, has caused global concern and detection of such harmful contaminants is a matter of supreme importance. In this regard, a novel trans-1,2-diaminocyclohexane containing Schiff base N,N′-di(4-acetamidophenylmethylene)-1,2-cyclohexanediamine (1) and its reduced scaffold N,N’-di(4-acetamidophenylmethyl)-1,2-cyclohexanediamine (2) have been synthesized and characterized by FT-IR and 1H & 13C NMR while the structures of both 1 and 2 have been determined by X-ray single crystal diffraction analysis. The detection response of 1 and 2 have been investigated toward same set of analytes and found to be entirely different both in absorption and emission studies. Compound 1 selectively and very sensitively detects Cr3+ and Cu2+via hydrolytic rupture of >C = N- bond as indicated by ratiometric change and emergence of an isosbestic point in UV–vis analysis. Further, the kinetic studies clearly suggested rapid hydrolysis of 1 (< 3.0 mins) in the presence of Cr3+ whereas it requires ∼1.0 h for complete hydrolysis with Cu2+. In contrast, the recognition of Cr3+ and Cu2+ not be observed through fluorescence technique. Moreover, 2 remains silent toward Cr3+/Cu2+in UV–vis analysis, however, it selectively recognizes CO32− through ‘turn-on’ fluorescence output in the background presence of several tested cations and anions. Job's plot and mass analysis suggested 1:2 (CO32−: 2) binding stoichiometry between CO32− and 2. Remarkably, the present findings demonstrate entirely different functionality of a Schiff base and its reduced form in presence of same analytes. The main objective of this report is to illustrate that how a subtle structural change of a molecule governs the analyte detection ability.

Stochastic density functional theory combined with Langevin dynamics for warm dense matter.

This study overviews and extends a recently developed stochastic finite-temperature Kohn-Sham density functional theory to study warm dense matter using Langevin dynamics, specifically under periodic boundary conditions. The method's algorithmic complexity exhibits nearly linear scaling with system size and is inversely proportional to the temperature. Additionally, a linear-scaling stochastic approach is introduced to assess the Kubo-Greenwood conductivity, demonstrating exceptional stability for dc conductivity. Utilizing the developed tools, we investigate the equationof state, radial distribution, and electronic conductivity of hydrogen at a temperature of 30000K. As for the radial distribution functions, we reveal a transition of hydrogen from gaslike to liquidlike behavior as its density exceeds 4g/cm^{3}. As for the electronic conductivity as a function of the density, we identified a remarkable isosbestic point at frequencies around 7eV, which may be an additional signature of a gas-liquid transition in hydrogen at 30000K.

Assessment of skin autofluorescence in children with diabetes mellitus type

Objective: To measure skin autofluorescence in children and adolescents suffering from type 1 diabetes mellitus and evaluate its relationship with gender, age, experience, and chronic complications of the disease. Materials and methods: The study group included 47 children and adolescents with type 1 diabetes. Autofluorescence of the skin from the inner surface of the shoulder and nail of patients was measured using an original compact spectrofluorimeter based on the STS-VIS OCEAN OPTICS © USA microspectrometer with UVA excitation. Statistical analysis was carried out using StatsoftStatistica 12.0 software. The data is presented as a two-dimensional array. The UV LED signal was averaged and smoothed using the moving average method with a 10 nm window. Then the spectra were renormalized taking into account the found coefficients. The result of applying additional normalization is a decrease in the standard deviation. Results and discussion: Significant differences were revealed in the skin fluorescence spectra of children of different ages. Between age groups (5-7) and (8-12) is most significant in the region of the alpha band of oxyhemoglobin (540 nm) (p &lt; 0.005). When using I-normalization, the NADH peak region (p &lt; 0.02) is significant with increasing disease duration. When studying the influence of gender factors on the level of skin autofluorescence, the most significant differences are found in the area of only the isosbestic points of deoxy and oxyhemoglobin 442 nm (p &lt; 10-7) and 491 nm (p &lt; 10-8). Significant differences in skin autofluorescence at the reference length were also obtained waves in the autofluorescence spectrum of 500 nm correspond to p &lt; 10-14, depending on the presence of complications. Conclusion: In Russia, as well as throughout the world, there is an increase in the incidence of type 1 diabetes mellitus. For early diagnosis of changes in carbohydrate metabolism and complications of the disease, a simple, accessible, non-invasive research method is needed. Taking into account the results of our study, when creating non-invasive methods for monitoring the state of carbohydrate metabolism, it is necessary to take into account gender and age characteristics, experience, and the presence of complications of type 1 diabetes mellitus.

The behaviour and properties of some acid-base indicators: a review

This review focuses on Seven Acid-Base Indicators from the azo class and from the second type: Methyl Orange; Methyl Red; Methyl Yellow; Alizarin Yellow R; Alizarin Yellow GG; Tropaeolin O and Magneson I. These indicators show different colors involving the chemical reaction in aqueous solutions as results as change the acidity of solution causing the formation two different structure forms one in acid form and another in basic forms with possibility formation of resonance structures. Different variables such as temperature; ionic strength; solvents; concentrations; pressure; substituent’s; position of function group and surfactant that influence on the behavior of Acid-Base indicators were explained. The electronic absorption spectral, equilibrium, terminological aspects and characteristics as well as the possible schemes of formation two compounds at isosbestic point are discussed. The contributions of different methods using to estimate the dissociation constant for it is discussed.

Synthesis, characterization and analytical study of new azo ligand driven from benzocaine and its metal complexes

The synthesis and spectrum of of a new azo ligand derived from acetylacetone and benzocaine (Ethyl p-aminobenzoate)). Spectral investigations such as 1H NMR,FT.IR, 13C-NMR and Mass spectra were performed to investigate the azo dye ligand's structure. Several physiochemical approaches, FT-IR, electronic spectra, molar conductivity, atom absorption, and magnetic susceptibility were used to identify new complexes with CO(II), and Zn(II) ions Complexes that are all 1:2 [M:L] were formed using the procedures described, and an tetrahedral geometry with sp3 hybridization. At several pH ranges (2–12), the electronic spectra of these azo dyes have been examined in terms of their acid–base properties, which included determining their isosbestic points and protonation and ionization constants. In the other study, azodye were used as an inductor for acid-base titration.

Simultaneously Estimation of Multicomponent Containing Formulation by using UV-Spectroscopy [Aspirin-Atorvastatin

The market is currently offering a wide range of combination dose forms, and the quantity is growing daily. Due to their improved potency, various actions, speedier relief, fewer side effects, and higher patient acceptability, these multicomponent formulations are becoming more and more popular. It is therefore intended that these formulations satisfy all requirements for their efficacy, safety, and quality. This is only feasible if many analytical methods are available to determine them. When doing a simultaneous multicomponent analysis, various UV spectrophotometric techniques are applied.These techniques rely on logging and processing absorption spectra computationally. The various techniques covered in this review include the use of simultaneous equations, derivative spectrophotometry, mean centring of the ratio spectra, absorption factor method, double divisor ratio spectra derivative method, successive ratio derivative spectra, Q-absorbance ratio method, isosbestic point method, absorpitivity factor method, dual wavelength method, mean centring of the ratio spectra, and multivariate methods. A synopsis of the theories and a few uses for these techniques are given.

Reductive Dynamic and Static Excited State Quenching of a Homoleptic Ruthenium Complex Bearing Aldehyde Groups.

A new homoleptic Ru polypyridyl complex bearing two aldehyde groups on each bipyridine ligand, [Ru(dab)3](PF6)2, where dab is 4,4'-dicarbaldehyde-2,2'-bipyridine, was synthesized, characterized, and utilized for iodide photo-oxidation studies. In acetonitrile (CH3CN) solution, the complex displayed an intense metal-to-ligand charge transfer (MLCT) absorbance maximum at 475 nm (ε = 22,000 M-1 cm-1) and an infrared (IR) band at 1712 cm-1 assigned to the pendent aldehyde groups. Visible light excitation in air-saturated solution resulted in room temperature photoluminescence (PL) with a maximum at 675 nm, a quantum yield, ϕPL = 0.048, and an excited state lifetime, το = 440 ns, from which radiative and nonradiative relaxation rate constants were extracted, kr = 9.1 × 104 s-1 and knr = 1.8 × 106 s-1. Pulsed visible light excitation yielded transient UV-vis and IR absorption spectra consistent with an MLCT excited state; relaxation occurred with the maintenance of two isosbestic points in the visible region, and a lifetime that agreed with that measured by time-resolved PL. Cyclic voltammetry studies in a CH3CN solution with 0.1 M TBAPF6 electrolyte revealed a quasi-reversible oxidation, E°(RuIII/II) = +1.25 V vs. Fc+/0, and three sequential one-electron reductions at -1.10, -1.25, and -1.54 V vs. Fc+/0. An excited state reduction potential of E°(Ru*2+/+) = +0.89 V vs. Fc+/0 was estimated with the Rehm-Weller expression. Titration of tetrabutylammonium iodide, TBAI, into a CD3CN solution of [Ru(dab)3](PF6)2 resulted in significant shifts in the aldehyde H atom and 3,3'-biypridyl resonances that were analyzed with a 1:1 equilibrium model, from which Keq = 460 M-1 was extracted, increasing to 5800 M-1 when the solvent was changed to acetone-d6. Iodide titrations resulted in a significant quenching of the [Ru(dab)3]*2+ lifetime and quantum yield in both CH3CN and acetone solvents. In CH3CN, the quenching was mainly dynamic and well described by the Stern-Volmer model, from which a quenching rate constant, kq, of 4.5 × 1010 M-1 s-1 and an equilibrium constant, Keq, of 8.3 × 103 M-1 were obtained. In acetone, the static quenching pathway by iodide was greatly enhanced, with a Keq of 1.2 × 104 M-1 and a higher kq of 9.2 × 1010 M-1 s-1.

The isosbestic point in the Raman spectra of the hydration shell

Isosbestic point is often observed in a series of spectra, but their interpretation is still controversial, such as whether the continuum model can produce an isosbestic point. In order to answer this question, the Raman spectra of hydration shell with continuous distribution structure in different ionic aqueous solutions were separated by Raman ratio spectra, and an isosbestic point was successfully observed. Our experimental results show that the continuum model can indeed produce the isosbestic point. In order to deepen the understanding of the isosbestic point, we calculate the first moment of the Raman spectra and conduct molecular dynamics (MD) simulations. Both experimental and theoretical findings indicate that elevated temperatures lead to increased disorder among water molecules within the hydration shell.