Flipping the light switch 'on'--the design of sensor molecules that show cation-induced fluorescence enhancement with heavy and transition metal ions.

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.

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Molecular switches as photocontrollable “smart” receptors

Despite considerable efforts toward the development of various sophisticated spiropyrans for metal ion sensing, less attention has been paid to organic molecule sensing One of the major difficulties for detection of organic molecules using a spiropyran is the weak and nonspecific interaction between the spiropyran and the target Here, we report the synthesis and molecular recognition characterization of two bis-spiropyrans for dipolar molecules and their application to in vivo glutathione (GSH) fluorescent probes Unlike the mono-spiropyrans, the newly designed bis-spiropyran molecules feature a rigidly maintained molecular cleft and two spiropyran units as binding modules The molecular recognition is based on multipoint electrostatic interactions and structure complementarity between the opened merocyanine form of the spiropyran and the analyte It was observed that the spiropyran 1a binds GSH in aqueous solution with high affinity (K = (752 +/- 183) x 10(4) M(-1)) and shows strong fluorescence emission upon binding Remarkably, fluorescence output of 1a is not significantly affected by other amino acids and peptides, especially, structurally similar compounds, such as cysteine and homocysteine Furthermore, fluorescence anisotropy and confocal fluorescent microscopy confirmed that spiropyran 1a is a comparatively good candidate for intracellular delivery and can be accumulated intensively into cells Thus, 1a can be utilized in vivo as a GSH probe or as a marker to show the level of intracellular GSH

Design of bis-spiropyran ligands as dipolar molecule receptors and application to in vivo glutathione fluorescent probes

A spiropyran-based ensemble for visual recognition and quantification of cysteine and homocysteine at physiological levels.

Chemists are now able to emulate the ideas and instruments of mathematics and computer science with molecules. The integration of molecular logic gates into small arrays has been a growth area during the last few years. The design principles underlying a collection of these cases are examined. Some of these computing molecules are applicable in medical- and biotechnologies. Cases of blood diagnostics, ‘lab-on-a-molecule’ systems, and molecular computational identification of small objects are included.

R.B. Davis

Papers

Photochromic chelating agents