Spectrophotometric Study on Kinetics of Solvatochromism of Methyl Violet in Aqueous Methanol

The kinetics of the reaction of methyl violet with iodide in aqueous methanol system was studied by spectrophotometric method. The rate of reaction of methyl violet in different alcoholic composition in presence of potassium iodide was observed at pH 4 and 6 at various temperatures (298–318 K). Solvatochromic effect was studied in different percentages of methanol (0–50%). Bathochromic shift was observed with the decrease in polarity of solvent. The color change was attributed to molecule's structure, the delocalization of unit electrical charge causes deepening of color and decrease of delocalization causes fading of color due to reduction of dye. Increase in the rate of reaction was observed with increase in alcoholic content and also affected by potassium iodide salt and increased with increase in concentration of potassium iodide. Energy of activation (E_a) and transition energy (E_T) were calculated with the help of kinetic data. Thermodynamic parameters such as enthalpy change of activation (ΔH*), Gibbs free energy change of activation (ΔG*) and entropy change of activation (ΔS*) were evaluated as a function of concentration of solvent and salt.     

The photokinetics of phenothiazine dyes with titanium trichloride in different solvents

The kinetic parameters of photoinduced electron transfer reaction of two phenothiazine dyes, methylene blue and methylene green with titanium trichloride, were determined in water and different aqueous-alcoholic solvents at different acidities by using a specially designed optical system. The rate of photoinduced electron transfer reaction was measured by determining the quantum yield of the reaction. The methylene green had a higher reactivity as compared to methylene blue with titanium trichloride. The graphical analysis showed that the reaction of dye with titanium trichloride follows pseudo–first-order kinetics. A reaction mechanism was proposed by considering the different excited states of dye and their possible interaction with the solvent and titanium trichloride. The different steps in the reaction mechanism were taken into consideration for deriving rate equations, which were used to determine the different rate constants in the reaction mechanism in different solvents.     

The kinetics of electron transfer reaction of methylene green and titanium trichloride in different solvents

The kinetics of the electron transfer reaction of methylene green and titanium trichloride was investigated in different solvents by spectrophotometry at different temperatures. The the reaction rate was determined by monitoring the absorbance as a function of time at λ_max 655 nm. The reaction is pseudo-first order, dependent only on the concentration of titanium trichloride at a fixed concentration of methylene green.     

Oxidation kinetics of crystal violet by potassium permanganate in acidic medium

The oxidation kinetics of crystal violet (a triphenylmethane dye) by potassium permanganate was focused in an acidic medium by the spectrophotometric method at 584 nm. The oxidation reaction of crystal violet by potassium permanganate is carried out in an acidic medium at different temperatures ranging within 298–318 K. The kinetic study was carried out to investigate the effect of the concentration, ionic strength and temperature. The reaction followed first order kinetics with respect to potassium permanganate and crystal violet and the overall rate of the reaction was found to be second order. Thermodynamic activation parameters like the activation energy (E_a), enthalpy change (ΔH*), free energy change (ΔG*), and entropy change (ΔS*) have also been evaluated.     

Kinetics and thermodynamics of the blocking reaction of several aliphatic isocyanates

The oxime-blocking reaction of several aliphatic isocyanates, such as 1,6-Hexane diisocyanate (HDI), isophorone diisocyanate (IPDI), and dicyclohexylmethane-4,4′-diisocyanate (H₁₂MDI), is investigated. The reaction is carried on in various solvents that are divided into two categories: aromatic solvents and oxygen-contained solvents. In situ FT-IR is used to monitor the reaction and show the large difference of solvent and the structure of isocyanate. Kinetic studies indicate that the reaction rate appears faster in aromatic solvents although the polarity of aromatic solvents is lower. Then, thermodynamic parameters of the blocking reaction, such as activation energy (E_a), enthalpy (ΔH*) and entropy (ΔS*), are determined from the Arrhenius and Eyring equations. It is found that activation energy in aromatic solvents is higher, but the reaction rate is much faster, all of which are discussed corresponding to the reaction mechanism.     

Decomposition of Dissolved Methylene Blue in Water Using a Submerged Arc Between Titanium Electrodes

Low voltage, low energy submerged pulsed arcs between Ti electrodes with a pulse repetition rate of 100 Hz, energies of 2.6–192 mJ and durations of 10–40 μs, followed by aging in the dark, were used to decompose 10 mg/l methylene blue (MB) contamination in 40 ml aqueous solutions, with and without the addition of 0.5 % H₂O₂. The impact of the arc treatment on the MB removal ratio (C₀–C_ta)/C₀ was considered as a function of aging time t_a, where C₀ and C_ta are the MB concentrations initially and after t_a (the time needed to complete removal of MB after cessation of exposure of the arc). Particles eroded from the electrodes during the discharge enabled MB decomposition during aging. The particles were studied by XRD, XPS and Raman analysis, and titanium oxides and peroxides were found. MB decomposition during aging is explained by the formation of a surface layer of titanium peroxide that forms by the interaction of titanium dioxide with H₂O₂, which produce radicals which oxidize the MB. The 99.6 % MB removal yield (G_99.6 = 90 g/kWhr) of the submerged pulsed arc process with Ti electrodes and addition of 0.5 % H₂O₂ was more than 60 times larger than obtained at 50 % removal with other plasma methods.     

Polymerization of β-cyanopropionaldehyde. III. Polymerization by organoaluminum and by organoaluminum–titanium chloride complexes

The mechanism of formation and stereoregularity of poly(cyanoethyl)oxymethylene have been studied. The polymerization was carried out at ?78°C with use of aluminum compounds [Al(C₂H₅)₃, Al(C₂H₅)₂Cl, Al(C₂H₅)Cl₂, and AlCl₃] and complex catalysts [Al(C₂H₅)₃–TiCl₄, Al(C₂H₅)₃–TiCl₃, and Al(C₂H₅)₂Cl–TiCl₃] as initiators. The stereoregularity of poly(cyanoethyl)oxymethylene was estimated from the optical density ratio, D₁₂₅₈/D₁₂₇₀, in the infrared absorption spectrum. Polymer yields were observed to depend upon the aluminum compound used as initiators, while the stereoregularity of the polymer was nearly independent of the particular aluminum compound used. As the catalyst ratio of titanium chloride to aluminum compound increased, the polymer yield was found to increase to a maximum and then to decrease with further increase of the ratio. It is supposed that titanium chlorides themselves increase the acid strength of aluminum compounds through chlorination, resulting in the change of the polymer yield. The highest stereoregularity of poly(cyanoethyl)oxymethylene was attained by increasing the molar ratio of titanium trichloride to aluminum and by treating β-cyanopropionaldehyde (CPA) with titanium trichloride prior to the polymerization. Complex formation of the nitrile group of CPA with titanium is considered responsible for the increase in stereoregularity. A propagation mechanism is also proposed.     

Photo Decoloration of Methylene Blue with Ribose under Optimum Conditions by Visible Radiation

Photo decoloration of the methylene blue (MB) with reducing sugar, ribose (RH), was investigated on an especially designed optical processor using monochromatic radiation of 661 nm through a red filter. The dye molecule gets excited into triplet transient species (MBT) during flushing with lifetime of 10.1 ms into acetate buffered aqueous alcoholic medium, which later on reduces to protonated leuco dye (MBH). Photolysis of the aqueous alcholic medium generated highly reactive oxygen radical (O－•) with the production of 2e－, which led to probable oxidation of the ribose into respective acid while hydrogen abstraction and 2e－ reduced the dye (MB) into MBH by following reaction     

Reactivity Tracers of the Hydrolysis of Fe(II)‐Bis(salicylidene) Complexes: Initial–Transition States Analysis and Enhanced Impact of Tensides on the Kinetic Trends

The kinetics of the acid hydrolysis reaction of Fe(II)‐bis(salicylidene) complexes were followed under pseudo–first‐order conditions ([H⁺] >> [complex]) at 298 K. The ligands of the studied azomethine complexes were derived from the condensation of salicylaldehyde with different five α‐amino acids. The hydrolysis reactions were studied in acidic medium at different ratios (v/v) of aqua–organic mixtures. The decrease in the dielectric constant values of the reaction mixture enhances the reactivity of the reaction. The transfer chemical potentials of the initial and transition states (IS–TS) from water into mixed solvents were determined from the solubility measurements combined with the kinetic data. Nonlinear plots of logk_obs versus 1/D (the reciprocal of the dielectric constant) suggest the influence of the solvation of IS–TS on the reaction reactivity. Furthermore, the acid hydrolysis reactions were screened in the presence of different concentrations of cationic and anionic tensides. The addition of surfactants to the reaction mixture accelerates the reaction reactivity. The obtained kinetic data were used to determine the values of δ_mΔG^# (the change in the activation barrier) for the studied complexes when transferred from “water to various ratios (v/v) of water–co‐organic binary mixtures” and from “water to water containing different [surfactant].” It was found that the reactivity of the acid hydrolysis reaction was controlled by the hydrophobicity of the studied chelates.     

Kinetic Studies on the Urethane Reaction of Propanediol with Isocyanate in Nitrogenous Solvents

The urethane reactions of 1,2-propanediol, 1,3-propanediol, and n-propanol with phenyl isocyanate were respectively carried out in nitrogenous solvents. In situ FT-IR was used to monitor the reactions, and rate constants were determined. It was shown that the reaction rate of 1,2-propanediol was fastest, followed by the reaction rates of 1,3-propanediol and n-propanol. After that, activation energy (E_a), activation enthalpy (ΔH), and activation entropy (ΔS) were calculated. It was found that these thermodynamic parameters for 1,2-propanediol and 1,3-propanediol are very similar, but they were very different from those of n-propanol, which is very useful to understand the urethane reaction mechanism.     

Effect of the Media on the Quantum Yield of Singlet Oxygen (O2(1Δg)) Production by 9H‐Fluoren‐9‐one: Solvents and Solvent Mixtures

We have investigated the effect of a series of 18 solvents and mixtures of solvents on the production of singlet molecular oxygen (O₂(¹Δ_g), denoted as ¹O₂) by 9H‐fluoren‐9‐one (FLU). The normalized empirical parameter E derived from E_T(30) has been chosen as a measure of solvent polarity using Reichardt's betaine dyes. Quantum yields of ¹O₂ production (Φ_Δ) decrease with increasing solvent polarity and protic character as a consequence of the decrease of the quantum yield of intersystem crossing (Φ_ISC). Values of Φ_Δ of unity have been found in alkanes. In nonprotic solvents of increasing polarity, Φ_ISC and, therefore, Φ_Δ decrease due to solvent‐induced changes in the energy levels of singlet and triplet excited states of FLU. This compound is a poor ¹O₂ sensitizer in protic solvents, because hydrogen bonding considerably increases the rate of internal conversion from the singlet excited state, thus diminishing Φ_Δ to values much lower than those in nonprotic solvents of similar polarity. In mixtures of cyclohexane and alcohols, preferential solvation of FLU by the protic solvent leads to a fast decrease of Φ_Δ upon addition of increasing amounts of the latter.     

Effect of the Media on the Quantum Yield of Singlet Oxygen (O2(1Δg)) Production by 9H‐Fluoren‐9‐one: Microheterogeneous Systems

The quantum yield (Φ_Δ) of singlet oxygen (O₂(¹Δ_g) production by 9H‐fluoren‐9‐one (FLU) is very sensitive to the nature of the solvent (0.02 in a highly polar and protic solvent, such as MeOH, to 1.0 in apolar solvents). This high sensitivity has been used for probing the interaction of FLU with micellar media and microemulsions based on anionic (sodium dodecyl sulfate, SDS; bis‐(2‐ethylhexyl)sodium sulfosuccinate, AOT), cationic (cetyltrimethylammonium chloride, CTAC) and nonionic (Triton X‐100, TX) surfactants. Values of Φ_Δ of FLU vary in a wide range (0.05–1.0) in both microheterogeneous media and neat solvent, and provide information on the microenvironment of FLU, i.e., on its localization within organized media. In ionic and nonionic micellar media, as well as in four‐component microemulsions, FLU is, to various extents, exposed to solvation by the polar and protic components of the microheterogeneous systems (water and/or butan‐1‐ol) in the micellar interfacial region (Φ_Δ=0.05–0.30). In contrast, in AOT reverse micelles (consisting of AOT as surfactant, cyclohexane as hydrophobic component, and water), FLU is located in the hydrophobic continuous pseudophase, and is totally separated from the micellar water pools (Φ_Δ≈1.0).     

The Synthesis of Pamidronic Derivatives in Different Solvents: An Optimization and a Mechanistic Study

The synthesis of pamidronic acid and sodium pamidronate dihydrate from β‐alanine and P‐reagents (phosphorus trichloride and phosphorous acid) was investigated at 75°C in different solvents, and the preparation was optimized. In sulfolane, the use of 2 equiv of phosphorus trichloride and phosphorous acid was found the optimum to lead to pamidronic acid in a yield of 63%. In methanesulfonic acid, 3.2 equiv of phosphorus trichloride was necessary without any phosphorous acid to give pamidronate dihydrate in the best yield (57%) after hydrolysis and pH adjustment. In the first case, the P‐nucleophile may be (HO)₂P–O–PCl–O–P(OH)₂ or (HO)₂P–O–PCl₂, whereas in the second case, the P‐reactant is probable Cl₂P–O–S(O)₂Me. It can be said that the mechanism proposed for the formation of pamidronic acid is highly influenced by the solvent used, as it determines the necessary P‐reagent(s). Our results promote the “on purpose” planning of the synthesis of dronates.     

Kinetics of Active Oxygen Species with Implications for Atmospheric Ozone Chemistry

Photochemical processes involving singlet oxygen (O₂(a¹Δ)), oxygen atoms_, and ozone are critical in determining atmospheric ozone concentrations. Here we report on kinetic measurements and modeling that examine the importance of the reactions of vibrationally excited ozone. Oxygen atoms and O₂(a¹Δ) were produced by UV laser photolysis of ozone. Time‐resolved absorption spectroscopy was used for O₃ concentration measurements. It was found that vibrationally excited ozone formed by O + O₂ + M → O₃(ν) + M recombination reacts effectively with O₂(a¹Δ) and O atoms. The reaction O₃(υ) + O₂(a¹Δ) → O + 2O₂ results in a reduction of the ozone recovery rate due to O atom regeneration, whereas the reaction O₃(υ) + O → 2O₂ removes two odd oxygen species, resulting in incomplete ozone recovery. The possible impact of these reactions on the atmospheric O₂(a¹Δ) and O₃ budgets at altitudes in the range of 80–100 km is considered.     

Rational Design of Emissive NIR‐Absorbing Chromophores: RhIII Porphyrin‐Aza‐BODIPY Conjugates with Orthogonal Metal–Carbon Bonds

The facile synthesis of Group 9 Rh^III porphyrin‐aza‐BODIPY conjugates that are linked through an orthogonal Rh?C(aryl) bond is reported. The conjugates combine the advantages of the near‐IR (NIR) absorption and intense fluorescence of aza‐BODIPY dyes with the long‐lived triplet states of transition metal rhodium porphyrins. Only one emission peak centered at about 720 nm is observed, irrespective of the excitation wavelength, demonstrating that the conjugates act as unique molecules rather than as dyads. The generation of a locally excited (LE) state with intramolecular charge‐transfer (ICT) character has been demonstrated by solvatochromic effects in the photophysical properties, singlet oxygen quantum yields in polar solvents, and by the results of density functional theory (DFT) calculations. In nonpolar solvents, the Rh^III conjugates exhibit strong aza‐BODIPY‐centered fluorescence at around 720 nm (Φ_F=17–34 %), and negligible singlet oxygen generation. In polar solvents, enhancements of the singlet‐oxygen quantum yield (Φ_Δ=19–27 %, λ_ex=690 nm) have been observed. Nanosecond pulsed time‐resolved absorption spectroscopy confirms that relatively long‐lived triplet excited states are formed. The synthetic methodology outlined herein provides a useful strategy for the assembly of functional materials that are highly desirable for a wide range of applications in material science and biomedical fields.     

Photoinduced Degradation of the Herbicide Clomazone Model Reactions for Natural and Technical Systems

The photodegradation of the herbicide clomazone in the presence of S₂O₈^2? or of humic substances of different origin was investigated. A value of (9.4 ± 0.4) × 10⁸ m ^?1 s^?1 was measured for the bimolecular rate constant for the reaction of sulfate radicals with clomazone in flash‐photolysis experiments. Steady state photolysis of peroxydisulfate, leading to the formation of the sulfate radicals, in the presence of clomazone was shown to be an efficient photodegradation method of the herbicide. This is a relevant result regarding the in situ chemical oxidation procedures involving peroxydisulfate as the oxidant. The main reaction products are 2‐chlorobenzylalcohol and 2‐chlorobenzaldehyde. The degradation kinetics of clomazone was also studied under steady state conditions induced by photolysis of Aldrich humic acid or a vermicompost extract (VCE). The results indicate that singlet oxygen is the main species responsible for clomazone degradation. The quantum yield of O₂(a¹Δ_g) generation (λ = 400 nm) for the VCE in D₂O, Φ_Δ = (1.3 ± 0.1) × 10^?3, was determined by measuring the O₂(a¹Δ_g) phosphorescence at 1270 nm. The value of the overall quenching constant of O₂(a¹Δ_g) by clomazone was found to be (5.7 ± 0.3) × 10⁷ m ^?1 s^?1 in D₂O. The bimolecular rate constant for the reaction of clomazone with singlet oxygen was k_r = (5.4 ± 0.1) × 10⁷ m ^?1 s^?1, which means that the quenching process is mainly reactive.     

1H-Phenalen-1-one: Photophysical Properties and Singlet-Oxygen Production

The efficiency of aromatic ketones as singlet-oxygen (¹O₂(¹Δ_g)) sensitizers can vary considerably with the electronic configuration of their lowest triplet state and the solvent used. Near-infrared measurements of tie luminescence of singlet oxygen have shown that the quantum yield of singlet-oxygen production (Φ_Δ) by 1H-phenalen-1-one ( 1 ) is close to unity in both polar (Φ_Δ = 0.97±0.03 in methanol) and non-polar solvents (Φ_Δ = 0.93±0.04 in benzene). Analysis of the absorption spectra of the ground state and phosphorescence measurements show that the lowest singlet and triplet states have dominant π, π* electronic configurations. The quantum yield of intersystem crossing (Φ_ISC) of 1 , determined by laser flash photolysis (partial-saturation method), is equal to unity. In comparison with other aromatic ketones, these parameters are important for the discussion of the surprisingly high Φ_ISC of 1 and the efficient energy transfer from its triplet state to molecular oxygen. The 1H-phenalen-1-one ( 1 ), being one of the most efficient singlet-oxygen sensitizers in both polar and non-polar media, could be used as a reference sensitizer, in particular in the area of relatively high energies of excitation.     

Synthesis,Photophysical and Electrochemical Properties of Amide‐Linked Phthalocyanine‐Fullerene Dyad

A new amide‐linked phthalocyanine‐fullerene dyad ZnPc‐C₆₀ was synthesized and characterized. The photophysical and electrochemical properties of the ZnPc‐C₆₀ dyad were investigated. The fluorescence spectrum and quantum yield in different solvents showed the occurrence of photoinduced electron transfer (PET) from the singlet excited ZnPc to C₆₀, which was further confirmed by nanosecond transient absorption spectra and cyclic voltammetry data. The free energy change for charge separation (ΔG_CS) was estimated to be exothermic with ?0.51 eV, which favored the formation of charge‐separation state. The PET from ZnPc to C₆₀ in ZnPc‐C₆₀ made the dyad exhibit stronger reverse saturable absorption performance compared with C₆₀ and the control sample in the Z‐scan experiments, which indicated the synergistic effect of two active moieties in the dyad.     

光谱法研究噻菁染料与血清蛋白的相互作用

本文通过吸收和荧光光谱法研究了一种噻菁染料与人血清蛋白及牛血清蛋白的相互作用。吸收光谱数据表明,与血清蛋白结合后,噻菁染料单体的吸收峰发生红移,同时强度也有很大变化;还通过吸收光谱计算确定了噻菁染料与血清蛋白的结合位点数（ n ）。与人血清蛋白或牛血清蛋白结合后,噻菁染料的荧光量子产率增加。分析噻菁染料的荧光强度随溶液中血清蛋白浓度的变化得到了二者反应的表观结合常数（ K _a）和自由能变化（ ΔG ）。根据表观结合常数（ K _a）可以判断,人血清蛋白比牛血清蛋白与噻菁染料的结合更强。     

Adsorption of Methylene Blue from Aqueous Solution on High Lime Fly Ash: Kinetic,Equilibrium, and Thermodynamic Studies

Kinetic, equilibrium, and thermodynamic studies were performed for the batch adsorption of methylene blue (MB) on the high lime fly ash as a low cost adsorbent material. The studied operating variables were adsorbent amount, contact time, dye concentration, and temperature. The kinetic data were analyzed using the pseudo-first order and pseudo-second order kinetic models and the adsorption kinetic was followed well by the pseudo-second order kinetic model. The equilibrium data were fitted with the Freundlich, Langmuir, and Dubinin Radushkevich (D–R) isotherms and the equilibrium data were found to be well represented by the Freundlich and D–R isotherms. Based on these two isotherms MB is taken by chemical ion exchange and active sites on the high lime fly ash have different affinities to MB molecules. Various thermodynamic parameters such as enthalpy of adsorption (ΔH°), free energy change (ΔG°), and entropy change (ΔS°) were investigated. The positive value of ΔH° and negative value of ΔG° indicate that the adsorption is endothermic and spontaneous. The positive value of ΔS° shows the increased randomness at the solid–liquid interface during the adsorption. A single-stage batch adsorber was also designed based on the Freundlich isotherm for the removal of MB by the high lime fly ash.