A significant color change and fluorescence enhancement can be ob

A significant color change and fluorescence enhancement can be observed in response to Cys (Figure 1). In the case of Hcy, because it has an additional methylene group in its side chain, a kinetically less favored 8-membered ring would form. As for GSH, selleck compound 1,4-addition of thiols to the ��,��-unsaturated carbonyl moieties of 4 can occur readily; however, the ensuing intramolecular cyclization similar to that of Cys cannot proceed without the presence of surfactant. No significant color formation or fluorescence response is seen in the case of Hcy or GSH under these conditions.Figure 1.Spectral response of 4 towards various thiols. (a) Absorption spectra of 4 (2.5 ��M) upon addition of thiols (2 equiv) in phosphate buffer (pH 7.4, 50 mM) at 20 min; (b) Fluorescence spectra of 4 (2.
5 ��M) upon addition of thiols (2 equiv) …Scheme 3.Proposed mechanism for the intrinsic response of 4 towards Cys.The time course of the fluorescence assay is shown in Figure 1(b). It can be seen that the fluorescence upon reaction with Cys increases with time and reaches a plateau after about 90 min, whereas for Hcy and GSH the reactions are significantly slower. The sensitivity and linearity of the response of 4 towards Cys was also investigated. Linear response with submicromolar sensitivity was observed (See Figure S5 in the Electronic Supplementary Information). The reaction products between 4 and thiols were further studied using HRMS (See Figures S6 and S7 in the Electronic Supplementary Information).3.2. Surfactant Mediated Modification of the Intrinsic SelectivityInclusion of surfactants (see Figure 2) dramatically alters the intrinsic selectivity of 4.
For example, solutions of GSH, Cys and Hcy (2 equiv) with the resorufin-acrylate probe 4 in pH 7.4 phosphate buffer generate the characteristic strong pink color immediately upon addition of CTAB only in the presence of GSH (Figure 3(a)). Other amino acids, such as Hcy and Cys, did not exhibit significant changes under the same conditions. This interesting feature indicates that 4-CTAB system can serve as a selective visual inspection dosimeter for GSH. Corresponding fluorescence increases were also observed (Figure 3(b)). Fluorescence upon reaction with GSH reaches a plateau in less than 2 min.Figure 2.Structures of surfactants employed.Figure 3.Surfactant-mediated responses of solutions Cilengitide containing 4-CTAB towards various thiols at pH 7.
4. (a) Absorption spectra of 4 (2.5 ��M) upon addition of thiols (2 equiv) in 2.0 mM CTAB media buffered at pH 7.4 (phosphate buffer, 50 mM). The inset …To study the effects of different surfactants, SDS, BC and Triton X-100 were evaluated. It was found that 4 serves as an outstanding indicator for GSH only SB203580 chemical structure in the presence of cationic surfactants such as BC and CTAB (Figure 4). Negatively charged SDS suppressed the response of
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