M.C. Rath

Effects of organised media on the excited-state proton transfer in 2-(2′-pyridyl)benzimidazole

Absorption and fluorescence characteristics of 2-(2′-pyridyl)benzimidazole (2-PBI) are studied in the presence of α- and β-cyclodextrins (CD) in aqueous solution at two different pHs. Steady-state and time-resolved fluorescence measurements are used for the investigation of the effect of organised media on the excited-state proton transfer reaction in 2-PBI. Semi-empirical CI calculation for the geometry of the molecule reveals that the 2-PBI molecule may be involved in host–guest complex formation with α-CD and β-CD in different configurations. NMR measurements corroborate this, providing information about the orientation of the 2-PBI molecule inside the cavity of the CDs. No complex formation was evident in γ-CD owing to its larger cavity dimension compared to the size of the 2-PBI molecule.

A novel method for ranitidine hydrochloride determination in aqueous solution based on fluorescence quenching of functionalised CdS QDs through photoinduced charge transfer process: Spectroscopic approach

A novel method for the quantitative determination of ranitidine hydrochloride (RNH) based on the fluorescence quenching of functionalised CdS quantum dots (QDs) by RNH in aqueous solution was proposed. The method is simple, rapid, specific and highly sensitive with good precision. The thioglycolic acid (TGA)-capped CdS QDs were synthesized from cadmium nitrate and sodium sulfide in alkaline solution. Under the optimal conditions, the Stern-Volmer calibration plot of F(0)/F against concentration of RNH was linear in the range of 0.50-15.0 μg mL(-1) with a correlation coefficient of 0.996. The limit of detection (LOD) was 0.38 μg mL(-1). The method was satisfactorily applied to the direct determination of RNH in pharmaceutical formulations with no significant interference from excipients. The results were found to be in good agreement with those obtained by the reference method and the claimed value. The accuracy and reliability of the method were further ascertained by recovery studies via the standard-addition method, with percentage recoveries in the range of 98.47 to 102.30%. The possible fluorescence quenching mechanism for the reaction was also discussed.

Photoelectrochemical cell studies of Fe2+ doped ZnSe nanorods using the potentiostatic mode of electrodeposition

The Fe(2+) doped ZnSe nanorods are synthesized using simple potentiostatic mode of electrodeposition on the ITO substrate. In order to study the doping effect of Fe(2+) in ZnSe, varied the doing percent such as 0.5%, 1%, 1.5%. These films are characterized for structural, compositional, morphological, optical and electrochemical properties using the X-ray diffraction study (XRD), X-ray photoelectron spectroscopy, field emission scanning electron microscopy, UV-vis spectroscopy and electrochemical spectroscopy. Along with these Raman spectroscopy and photoluminescence spectroscopy have been studied for understanding the characteristics vibrations of ZnSe and luminescence of ZnSe nanorods. FE-SEM shows the nanorods like morphology. Photoelectrochemical cell performance studied using the J-V measurement and it shows the maximum efficiency at 1% Fe(2+) doped ZnSe nanorods. The observed maximum efficiency of Fe(2+) doped ZnSe nanorods is 0.32%.

Evaluation of interparticle interaction between colloidal Ag nanoparticles coated with trisodium citrate and safranine by using FRET: Spectroscopic and mechanistic approach

Current study employs fluorescence spectroscopy, UV-Vis absorbance spectroscopy, dynamic light scattering (DLS) and cyclic voltammetry (CV) to investigate the interaction of safranine dye with spherical shaped silver nanoparticles (AgNPs) coated with trisodium citrate. In fluorescence spectroscopic study we used the AgNPs and safranine dye as component molecules for the construction of FRET, whereas AgNPs serve as donor fluorophore and safranine as acceptor. The fluorescence quenching of AgNPs followed by sensitization of safranine occurs almost simultaneously by addition of safranine dye with different concentrations, indicating fluorescence energy transfer observed between them. Interaction between safranine and AgNPs is also confirmed by using UV-Vis absorption spectroscopy. Addition of safranine results in the significant decrease in the absorbance of AgNPs at 423 nm and simultaneous increase in the absorbance of safranine at 518, 276 and 248 nm which is indication of rapid binding of safranine molecules with AgNPs. However CV measurements reveals that the safranine molecule does not alter the redox properties of the AgNPs but the safranine molecule lose their redox properties upon getting bonded with AgNPs. This clearly confirms that the safranine molecules get attached on the surface of AgNPs which was also supported by the DLS as well as zeta potential measurement.

One-electron transfer reactions of some hydroxynaphthoquinones. Solvent and substitution effect as studied by pulse radiolysis

The properties of one-electron reduced species of 1,4-naphthoquinone (NQ), 2-hydroxynaphthoquinone (2HNQ), 5-hydroxynaphthoquinone (5HNQ) and 5,8-dihydroxynaphthoquionone (58DHNQ) in water–isopropanol (PriOH)(5 mol dm–3)–acetone (1 mol dm–3) mixed solvent (MS), PriOH and water have been investigated by a pulse radiolysis technique. Semiquinones of 2HNQ produced at acidic pH resemble those produced in pure PriOH and have no absorption beyond 500 nm. These were assigned as neutral semiquinones. The semiquinones produced at higher pH (>11) were assigned as dianionic semi-quinones. Both the dianionic semiquinones and the one-electron oxidised species of 2 HNQ have absorption beyond 600 nm, but to a different extent since the difference of two electrons between the species leads to a difference in the extent of conjugation of the aromatic ring with the oxygen atom of the OH group. The pKs of the parent molecules and the semiquinones were determined in MS. The one-electron reduction potentials (E1) of the quinones were calculated and compared with those of other related quinones. The kinetics of formation and decay of both the one-electron reduced and the one-electron oxidised species have been calculated. The kf values for the reduced and the oxidised species were of the order of 109 dm3 mol–1 s–1. The corresponding kd values were of the order of 108 dm3 mol–1 s–1 for the oxidised species, but the decay of the semiquinones was very slow. The effect of the position of the OH groups in NQ on the semiquinone characteristics has been discussed for 2HNQ, 5HNQ and 58DHNQ in MS and aqueous solutions.

Investigation of Dynamics of Radiolytic Formation of CdSe Nanoparticles in Aqueous Solutions

The formation of cadmium selenide, CdSe, nanoparticles in aqueous solutions containing equimolar ammoniated cadmium sulfate, [Cd(NH(3))](4)SO(4) and sodium selenosulfate, Na(2)SeSO(3) as the starting materials, has been investigated by electron pulse radiolysis coupled with kinetic spectrometry. The formation of CdSe nanoparticles was found to proceed through the generation of short-lived transient intermediate species having an absorption peak at 520 nm, which is formed only upon the reaction of hydrated electrons, e(aq) with the precursor ions under deaerated conditions. The transient intermediate species decays with a weighted average rate constant, 1.2 × 10(7) s(-1). The transient intermediate species formed in the case of individual precursors did not match with the transients formed when both the precursors are taken together in the solutions under the present experimental conditions. The reaction rate constants between the precursor ions, [Cd(NH(3))(4)](2+) and the transient intermediate species formed from [SeSO(3)](2-) was 1.9 × 10(10) M(-1) s(-1). Similarly, the reaction rate constants between the precursor ions, [SeSO(3)](2-) and the transient intermediate species formed from [Cd(NH(3))(4)](2+) was 5.5 × 10(10) M(-1) s(-1). This clearly indicates that the formation of CdSe nanoparticles occurs through both reaction channels. However, the major reaction channel is through the reaction of e(aq) with the [Cd(NH(3))(4)](2+) ions (k = 3.1 × 10 (10) M(-1) s(-1)), as its rate constant is one order higher than that of the reaction of e(aq) with the [SeSO(3)](2-) ions (k = 2.3 × 10(9) M(-1) s(-1)).

Tuning of the electrical parameters of a twisted-nematic display material by using electron beam irradiation

Electron beam irradiation studies on 4′-pentyl-4-cyanobiphenyl (5CB) have been carried out. Dielectric measurements demonstrate that even a low level of irradiation (beyond a critical dose of ∼6kGy) results in a dramatic increase in the transverse component of the dielectric permittivity, and a corresponding decrease in the dielectric anisotropy. It is shown that the changes in dielectric parameters due to the irradiation can be fruitfully utilized to control the display performance of the device to a certain extent. The observed change in the dielectric parameters is attributed to the formation of a donor-acceptor type charge-transfer complex due to the irradiation.

Pulse-radiolytic one-electron reduction of anthraquinone and chloro-anthraquinones in aqueous-isopropanol-acetone mixed solvent

Abstract One-electron reduction of 9,10-anthraquinone and some chloro-anthraquinones and the characteristics of the semiquinones thus formed have been investigated in aqueous-isopropanol-acetone mixed solvent using electron pulse radiolysis technique. Spectroscopic characteristics, kinetic parameters of formation and decay, and the acid/base behaviour of the semiquinones have been investigated. The one-electron reduction potential of the quinones have been measured following electron transfer equilibria with a reference redox system (methyl viologen) and the values thus obtained have been compared with those of some other anthrasemiquinone systems. An analysis of the characteristics of the semiquinones shows that α-chloro substituents adjacent to the CO group act as electron withdrawing groups.

A comparative study of pulse radiolytic one-electron reduction of different unsubstituted quinones in aqueous-organic mixed solvent

Abstract The one-electron reduction of different unsubstituted paraquinones are studied by the pulse radiolysis technique in aqueous-organic mixed solvent and in pure isopropanol. The effect of additional benzene ring(s) in the higher analogue of benzoquinone is discussed with reference to their semiquinone characteristics. A qualitative interpretation based on their electron affinities (E.A.) is given for the one-electron reduction potential ( E 1 ) values.

The effects of electron irradiation on the optical properties of the organic semiconductor polypyrrole

The optical properties of polypyrrole (Ppy) thin films upon 2 MeV electron beam irradiation changes with different doses. The induced changes in the optical properties for Ppy thin films were studied in the visible range 300 to 800 nm at room temperature. The optical band gap of the pristine Ppy was found to be 2.19 eV and it decreases up to 1.97 eV for a 50 kGy dose of 2 MeV electron beam. The refractive index dispersion of the samples obeys the single oscillator model. The obtained results suggest that electron beam irradiation changes the optical parameters of Ppy thin films.