Ferrocene-modified bis(spiropyridopyran)s as synthetic signaling receptors for guanine-guanine dinucleoside derivatives

Synthesis, crystal structures and electrochemical properties of ferrocenyl imidazole derivatives

Six ferrocenyl imidazole derivatives substituted with -Cl, -NO₂ and -CH₃ on the 2-position of the 1H-imidazole ring have been synthesized. Of the six compounds, the di-substituted ferrocenes, i.e. compounds 4 (1,1′-ferrocenylmethyl(2-chloroimidazole)), 5 (1,1′-ferrocenyl(2-nitroimidazole)), and 6 (1,1′-ferrocenylmethyl(2-methylimidazole)) are reported for the first time. The structure-property relationships of compounds 4, 5 and 6 were investigated by means of UV-visible, FTIR, ¹H-NMR, ¹³C-NMR spectroscopy and electrochemical studies. UV-visible analysis in acetonitrile showed that the π -π* band of compounds 2 (1-ferrocenylmethyl(2-nitroimidazole)) and 5 appeared at longer wavelength compared to 1 (1-ferrocenylmethyl(2-chloroimidazole)), 3 (1-ferrocenylmethyl(2-methylimidazole)), 4 and 6. This phenomenon is due to the different electronics around the imidazole moieties. In cyclic voltammetry analysis, all compounds exhibited a quasi-reversible redox wave for the ferrocenyl and imidazole moieties. Density functional theoretical (DFT) calculations with the B3LYP/6-311+G(d) basis set were performed on compounds 1–6, and the calculated HUMO-LUMO band gap energies correlated with those obtained from electrochemical and spectroscopic data. The X-ray crystallographic analysis highlighted the effect of electron-withdrawing and electron-donating substituents on the conformation of the cyclopentadienyl rings attached to the ferrocenyl moiety.

Antioxidant Sensing by Spiropyrans: Substituent Effects and NMR Spectroscopic Studies

The development of stimuli-responsive small molecules for probing biologically active antioxidants such as glutathione (GSH) has important ramifications in the detection of oxidative stress. An ideal sensor for biological applications should exhibit sufficient sensitivity and selectivity for detection at physiological concentrations and be reversible to allow continuous and dynamic monitoring of antioxidant levels. Designing a suitable sensor thus requires a detailed understanding of activation properties and mechanism of action. In this work, we report a new set of GSH-responsive spiropyrans and demonstrate how changes in the electronic structure of spiropyrans influence GSH sensing with high specificity versus other structurally similar and biologically relevant redox-active molecules. The sensitivity, selectivity, kinetics, binding constant, and reversibility of GSH-responsive-substituted spiropyrans were investigated using UV-vis spectroscopy and laser irradiation experiments. Detailed studies of the mechanism of interaction between spiropyrans with GSH were investigated using NMR spectroscopy. Understanding how electronic effects impact the sensing ability of spiropyrans toward antioxidants and elucidating the mechanism of the spiropyran-GSH interaction will facilitate the design of more effective sensors for detection of antioxidants in vivo.

Molecular switches as photocontrollable "smart" receptors

This critical review focuses on the development of photochromic compounds as sensors for cations, anions, and biologically important molecules. The review commences with a brief description of photochromism and the strategies to exploit photochromic molecular switches' properties for sensing application. This is followed by a summary of photoswitchable receptors emerged to date and classified according to the photochromic structure they are based on. These include azobenzenes, fulgides, dithienylethenes, dihydroindolizines, chromenes and spiropyrans.

Single-nucleotide polymorphism detection with "wire-like" DNA probes that display quasi "on-off" digital action

Establishing a reliable genotyping protocol is a critical matter in post-sequence genetics. In this article, we describe a highly sensitive electrochemical detection of complementary DNAs (up to 43-mer) based on hole transport with molecular-scale, "wire-like" DNA probes. The presence of a single-base mismatch in the DNA duplexes caused a dramatic decrease in the electrochemical response. We applied this method to detect all of the possible transition and transversion SNPs and achieved "on-off"-type discrimination of fully complementary DNAs from their SNPs. Furthermore, naturally occurring polymorphisms, "hot spots" from the p53 gene, could clearly be distinguished from wild type by using our methodology.