Physicochemical study of spiropyran-terthiophene derivatives: photochemistry and thermodynamics

The photochemistry and thermodynamics of two terthiophene (TTh) derivatives bearing benzospiropyran (BSP) moieties, 1-(3,3’’-dimethylindoline-6’-nitrobenzospiropyranyl)-2-ethyl 4,4’’-didecyloxy-2,2’:5’,2’’-terthiophene-3’-acetate (BSP-2) and 1-(3,3’’-dimethylindoline-6’-nitrobenzospiropyranyl)-2-10 ethyl 4,4’’-didecyloxy-2,2’:5’,2’’-terthiophene-3’-carboxylate (BSP-3), differing only by a single methylene spacer unit, have been studied. The kinetics of photogeneration of the equivalent merocyanine (MC) isomers (MC-2 and MC-3, respectively), the isomerisation properties of MC-2 and MC-3, and the thermodynamic parameters have been studied in cetonitrile, and compared to the parent, non-TThfunctionalised, benzospiropyran derivative, BSP-1. Despite the close structural similarity of BSP-2 and 15 BSP-3, their physicochemical properties were found to differ significantly; examples include activation energies (Ea(MC-2) = 75.05 KJ mol-1, Ea(MC-3) = 100.39 kJ mol-1) and entropies of activation (S‡ MC-2 = - 43.38 J K-1 mol-1, S‡ MC-3 = 37.78 J K-1 mol-1) for the thermal relaxation from MC to BSP, with the MC-3 value much closer to the unmodified MC-1 value (46.48 J K -1 mol-1) for this latter quantity. The thermal relaxation kinetics and solvatochromic behaviour of the derivatives in a range of solvents of 20 differing polarity (ethanol, dichloromethane, acetone, toluene and diethyl ether) are also presented. Differences in the estimated values of these thermodynamic and kinetic parameters are discussed with reference to the molecular structure of the derivatives

Novel synthesis and characterisation of 3,3-dimethyl-50-(2-benzothiazolyl)- spironaphth(indoline-2,30-[3H]naphth[2,1-b] [1,4]oxazine) derivatives

Novel modified spirooxazines (SOs) with additional chelating groups were synthesised and the crystal structure of one of these was determined. UV–vis spectroscopic characterization of the photoisomerization of the SO derivatives shows that the photochromic behaviour is altered with Zn2+ coordination. In particular, addition of a group as in carboxylic acid 5 to the indole section of the SO increases the lifetime of the merocyanine Zn 2+ complex by 20-fold compared to the methylated indole 6

Characterization of the thermal and photoinduced reactions of photochromic spiropyrans in aqueous solution

Six water-soluble spiropyran derivatives have been characterized with respect to the thermal and photoinduced reactions over a broad pH-interval. A comprehensive kinetic model was formulated including the spiro- and the merocyanine isomers, the respective protonated forms, and the hydrolysis products. The experimental studies on the hydrolysis reaction mechanism were supplemented by calculations using quantum mechanical (QM) models employing density functional theory. The results show that (1) the substitution pattern dramatically influences the pKa-values of the protonated forms as well as the rates of the thermal isomerization reactions, (2) water is the nucleophile in the hydrolysis reaction around neutral pH, (3) the phenolate oxygen of the merocyanine form plays a key role in the hydrolysis reaction. Hence, the nonprotonated merocyanine isomer is susceptible to hydrolysis, whereas the corresponding protonated form is stable toward hydrolytic degradation

Using Charge to Control the Functional Properties of Self‐Assembled Nanopores in Membranes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86890/1/smll_201100394_sm_suppl.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/86890/2/2016_ftp.pd

Peptide immobilisation on porous silicon surface for metal ions detection

In this work, a Glycyl-Histidyl-Glycyl-Histidine (GlyHisGlyHis) peptide is covalently anchored to the porous silicon PSi surface using a multi-step reaction scheme compatible with the mild conditions required for preserving the probe activity. In a first step, alkene precursors are grafted onto the hydrogenated PSi surface using the hydrosilylation route, allowing for the formation of a carboxyl-terminated monolayer which is activated by reaction with N-hydroxysuccinimide in the presence of a peptide-coupling carbodiimide N-ethyl-N'-(3-dimethylaminopropyl)-carbodiimide and subsequently reacted with the amino linker of the peptide to form a covalent amide bond. Infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy are used to investigate the different steps of functionalization

The fidelity of in vitro protein synthesis and its implications for the aging of human cells

To test the error catastrophe theory of cell senescence, we have developed a cell-free protein synthetic system from human diploid fibroblasts capable of translating both the synthetic mRNA, poly (u), and endogenous cellular mRNA in vitro. We have measured the fidelity of poly(U)-directed protein synthesis in extracts from a variety of cells. The results contradict the error catastrophe in several ways: - cells from subjects suffering maladies of premature aging, progeria and Werner Syndrome, exhibited error frequencies within the normal range. - cells from an old donor did not have elevated error frequency of protein synthesis. - early-passage (young) normal cells had error frequencies higher than those of late-passage (old) cells. The error frequency in one normal strain of fibroblasts declined throughout its tissue culture lifespan. Cells maintained in the post-mitotic (terminal) state, in which there was no cell selection, exhibited a constant error frequency over 16 weeks. In a series of experiments using clonal populations of cells, it became evident that the decline in error frequency as a function of passage was dependent on the clonal heterogeneity of the mass culture. In no experiment, however, could any correlation between the error frequency of protein synthesis and cellular growth parameters be made. Overall, the senescence characteristic of human diploid fibroblasts was independent of the measured fidelity of protein synthesis in vitro.Doctor of Philosophy (PhD

Quantitative investigations of the aggregation behaviour of hydrophobic anilino squaraine dyes through UV/vis spectroscopy and dynamic light scattering

In continuing studies of the aggregation behaviour of squaraine dyes in DMSO-water mixtures, we have examined a series of symmetrical anilino-based squaraines with increasing N-alkyl chain length (n-butyl, n-octyl, and n-dodecyl). The aggregation behaviour was assessed through UV/vis spectroscopic and Dynamic Light Scattering (DLS) studies with quantitative interpretation based on exciton theory. This class of N-alkyl squaraines forms two distinct solution aggregates, Type J and Type H, depending on the composition of the DMSO-water medium. DLS measurement of the aggregates in the Type J and Type H morphologies showed that (i) the particle diameter increased with increasing hydrophobicity; (ii) DMSO has a large effect on the aggregate size; (iii) Type J aggregates are of equal dimensions with Type H aggregates. Moreover, even though as the DMSO-water solvent composition is varied the UV/vis spectra of Type H and Type J aggregates remained unchanged, the number of molecules comprising each aggregate varies widely. It is proposed that the dynamic conversion (J →&gt; H) results from intramolecular reorganization of individual molecules within the aggregate. Quantification of aggregation through DLS has further developed the "kinetic" versus "thermodynamic" control model of dye aggregation.Key words: squaraine, dynamic light scattering, DMSO-water mixtures, self-assembly, kinetic/thermodynamic control. </jats:p