Kinetics and mechanism of base hydrolysis of tris(3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine)iron(II) in aqueous and micellar media

The kinetics of base hydrolysis of tris(3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine)iron(II), \( {\text{Fe(PDT)}}_{ 3}^{2 + } \) has been studied in aqueous, cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) media at 25, 35 and 45 °C under pseudo-first-order conditions, i.e. \( [ {\text{OH}}^{ - } ]\gg [{\text{Fe(PDT)}}_{ 3}^{2 + } ] \). The reactions are first order in both of substrate \( {\text{Fe(PDT)}}_{ 3}^{2 + } \) and hydroxide ion. The rates decrease with increasing ionic strength in aqueous and CTAB media, whereas SDS medium shows little ionic strength effect. The rate also increases with CTAB concentration but decreases with SDS. The specific rate constant, k and thermodynamic parameters (E _a, ΔH ^#, ΔS ^# and ΔG ^#) have also been evaluated. The near equal values of ΔG ^# obtained in aqueous and CTAB media suggest that these reactions occur essentially by the same mechanism such that \( {\text{Fe(PDT)}}_{ 3}^{2 + } \) reacts with OH^? in the rate-determining step. The ionic strength effect in SDS medium suggests that the rate-determining step involves an ion and a neutral species. The results in this study are compared with those obtained for other iron(II)-bipyridine complexes.     

Luminescent Gold Nanorods To Enhance the Near-Infrared Emission of a Photosensitizer for Targeted Cancer Imaging and Dual Therapy: Experimental and Theoretical Approach

Strong plasmon absorption in the near-infrared (NIR) region renders gold nanorods (GNRs) amenable for biomedical applications, particularly for photothermal therapy. However, these nanostructures have not been explored for their imaging potential because of their weak emission profile. In this study, the weak fluorescence emission of GNRs is tuned to match that of the absorption of a photosensitizer (PS) molecule, and energy transfer from the GNR to PS enhances the emission profile of the GNR–PS combination. GNR complexes generally quench the fluorescence emission of nearby chromophores. However, herein, the complex retains or rather enhances the fluorescence through competition in energy transfer. Excitation-dependent energy transfer has been explained experimentally and theoretically by using DFT calculations, the CIE chromaticity diagram, and power spectrum. The final GNR–PS complex modified for tumor specificity serves as an excellent organ-specific theranostic probe for bioimaging and dual therapy both in vitro and in vivo. Principal component analysis designates photodynamic therapy a better candidate than that of photothermal therapy for long-term efficacy in vivo.     

A study of some parameters relevant to the response of harwell PMMA dosimeters to gamma and electron irradiation

The effects on the radiation response of Harwell polymethylmethacrylate (PMMA) dosimeters of dose-rate, radiation type, temperature during irradiation and post-irradiation storage, and post-irradiation stability, are of importance to the operators of commercial irradiation facilities.

This paper describes recent studies of the effects of some of these parameters on the radiation response of Harwell Red 4034, Amber 3042, and Gammachrome YR Perspex dosimeters, and provides data on batch to batch variation and shelf-life.     

Changing the role of 2,2'-bipyridine from secondary ligand to protagonist in [Ru(bpy)2(N-N)]2+ complexes: low-energy, red emission from a ruthenium(II)-to-2,2'-bipyridine 3MLCT state

Two new bidentate ligands (1 and 2) with bicyclic guanidine moieties were synthesized and attached to a Ru(II)(bpy)(2) core (bpy = 2,2'-bipyridine) to afford complexes 3 and 4, which were characterized by spectroscopic and electrochemical methods. Complex 4 was further characterized by X-ray crystallography. In cyclic voltammetric studies, both complexes show a Ru(II/III) couple, which is 500 mV less positive than the Ru(II/III) couple of Ru(bpy)(3)(2+). The (1)MLCT and (3)MLCT states of 3 (560 nm/745 nm) and 4 (550 nm/740 nm) are significantly red-shifted with respect to Ru(bpy)(3)(2+) (440 nm/620 nm). Compounds 3 and 4 exhibit emission from a Ru(II)-to-bpy (3)MLCT state, which is rarely the emitting state at λ > 700 nm in [Ru(bpy)(2)(N-N)](2+) complexes.     

Advanced green analytical chemistry for environmental pesticide detection

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The effect of particle size on the thermal decomposition kinetics of potassium bromate

The thermal decomposition of potassium bromate (KBrO₃) has been studied as a function of particle size, in the range 53?C150???m, by isothermal thermogravimetry at different temperatures, viz. 668, 673, 678, and 683?K in static air atmosphere. The theoretical and experimental mass loss data are in good agreement for the thermal decomposition of all samples of KBrO₃ at all temperatures studied. The isothermal decomposition of all samples of KBrO₃ was subjected to both model fitting and model-free (isoconversional) kinetic methods of analysis. Isothermal model fitting analysis shows that the thermal decomposition kinetics of all the samples of KBrO₃ studied can be best described by the contracting square equation. Contrary to the expected increase in rate followed by a decrease with decrease in particle size, KBrO₃ shows a regular increase in rate with reduction in particle size, which, we suggest, is an impact of melting of this solid during decomposition.     

Synthesis of casein-G-poly(vinyl acetate). II

Poly(vinyl acetate) was graft-copolymerized onto casein in the presence of potassium peroxydisulfate-ascorbic acid. The effect of synthetic variables on the rates of conversion of monomer (R_p), graft copolymerization (R_g), and homopolymerization (R_h), percent grafting, and grafting efficiency were investigated and the results, compared with the system initiated by peroxydisulfate alone.     

Synthesis and characterization of liquid–crystalline polyesters with chiral and achiral twin spacers

A series of novel thermotropic main-chain chiral liquid–crystalline random copolyesters consisting of spacers of two different types—chiral and achiral—was synthesized. Polyesters (BmTa) with tartaric acid as the chiral spacer (Ta), aliphatic diols (with ‘m’ = 2–10 methylene groups) as the achiral spacers, and 4,4′-dihydroxy biphenyl (B) as the mesogen were synthesized via condensation polymerization in solution after duly protecting the 2,3-dihydroxy groups of tartaric acid by acetylation. The copolymers were characterized by Fourier transform infrared spectroscopy, ¹H and ¹³C NMR spectra, gel permeation chromatography, and thermogravimetric analysis. Transition temperatures for phase changes recorded by DSC were corroborated with the textures observed by a hot-stage optical polarizing microscope. The wide-angle X-ray diffraction (WAXD) profiles indicated a SmE phase at room temperature. The lower angle region at 2θ = 0.5–2.45 covered by WAXD indicated a layer of thickness of 161 Å, less than the molecular length for B0Ta. The [α_D] values were recorded on a digital polarimeter. The birefringence was lost at higher mesophase temperatures in lower members with m < 5, a behavior found in certain chiral systems, and the higher members with m > 5 showed a lesser number of phase transitions. On cooling, the polyesters produced a texture with the formation of transition bars. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1743–1752, 2001