Data and signal processing using photochromic molecules

Photochromes are chromophores that are reversibly isomerized between two metastable forms using light, or light and heat. When photochromes are covalently linked to other chromophores, they can act as molecular photonic analogues of electronic transistors. As bistable switches, they can be incorporated into the design of molecules capable of binary arithmetic and both combinatorial and sequential digital logic operations. Small ensembles of such molecules can perform analogue signal modulation similar to that carried out by transistor amplifiers. Examples of molecules that perform multiple logic functions, act as control elements for fluorescent reporters, and mimic natural photoregulatory functions are presented.     

A Fluorescent Kinase Inhibitor that Exhibits Diagnostic Changes in Emission upon Binding

The development of a fluorescent LCK inhibitor that exhibits favourable solvatochromic properties upon binding the kinase is described. Fluorescent properties were realised through the inclusion of a prodan‐derived fluorophore into the pharmacophore of an ATP‐competitive kinase inhibitor. Fluorescence titration experiments demonstrate the solvatochromic properties of the inhibitor, in which dramatic increase in emission intensity and hypsochromic shift in emission maxima are clearly observed upon binding LCK. Microscopy experiments in cellular contexts together with flow cytometry show that the fluorescence intensity of the inhibitor correlates with the LCK concentration. Furthermore, multiphoton microscopy experiments demonstrate both the rapid cellular uptake of the inhibitor and that the two‐photon cross section of the inhibitor is amenable for excitation at 700 nm.     

Self-assembled InAs island formation on GaAs (1 1 0) by metalorganic vapor phase epitaxy

Formation of self-assembled InAs 3D islands on GaAs (1 1 0) substrate by metal organic vapor phase epitaxy has been investigated. Relatively uniform InAs islands with an average areal density of 10⁹ cm⁻²are formed at 400 ° C using a thin InGaAs strain reducing (SR) layer. No island formation is observed without the SR layer. Island growth on GaAs (1 1 0) is found to require a significantly lower growth temperature compared to the more conventional growth on GaAs (1 0 0) substrates. In addition, the island height is observed to depend only weakly on the growth temperature and to be almost independent of the V/III ratio and growth rate. Low-temperature photoluminescence at 1.22 eV is obtained from the overgrown islands.     

Goldfish Geodesics and Hamiltonian Reduction of Matrix Dynamics

We describe the Hamiltonian reduction of a time-dependent real-symmetric N×N matrix system to free vector dynamics, and also provide a geodesic interpretation of Ruijsenaars–Schneider systems. The simplest of the latter, the goldfish equation, is found to represent a flat-space geodesic in curvilinear coordinates.      

Photonic switching of photoinduced electron transfer in a dihydropyrene-porphyrin-fullerene molecular triad

Photonic control of photoinduced electron transfer has been demonstrated in a dimethyldihydropyrene (DHP) porphyrin (P) fullerene (C(60)) molecular triad. In the DHP-P-C(60) form of the triad, excitation of the porphyrin moiety is followed by photoinduced electron transfer to give a DHP-P(*)(+)-C(60)(*)(-) charge-separated state, which evolves by a charge shift reaction to DHP(*)(+)-P-C(60)(*)(-). This final state has a lifetime of 2 micros and is formed in an overall yield of 94%. Visible (>or=300 nm) irradiation of the triad leads to photoisomerization of the DHP moiety to the cyclophanediene (CPD). Excitation of the porphyrin moiety of CPD-P-C(60) produces a short-lived (<10 ns) CPD-P(*)(+)-C(60)(*)(-) state, but charge shift to the CPD moiety does not occur, due to the relatively high oxidation potential of the CPD group. Long-lived charge separation is not observed. Irradiation of CPD-P-C(60) with UV (254 nm) light converts the triad back to the DHP form. Thermal interconversion of the DHP and CPD forms is very slow, photochemical cycling is facile, and in the absence of oxygen, many cycles may be performed without substantial degradation. Thus, light is used to switch long-lived photoinduced charge separation on or off. The principles demonstrated by the triad may be useful for the design of molecule-based optoelectronic systems.     

Allenes as carbon nucleophiles in intramolecular attack on (pi-1,3-diene)palladium complexes: evidence for trans carbopalladation of the 1,3-diene

Reaction of allene-substituted cyclohexa- and cyclohepta-1,3-dienes with [PdCl(2)(PhCN)(2)] gave eta(3)-(1,2,3)-cyclohexenyl- and eta(3)-(1,2,3)-cycloheptenylpalladium complexes, respectively, in which C-C bond formation between the allene and the 1,3-diene has occurred. Analysis of the (pi-allyl)palladium complexes by NMR spectroscopy, using reporter ligands, shows that the C-C bond formation has occurred by a trans carbopalladation involving nucleophilic attack by the middle carbon atom of the allene on a (pi-diene)palladium(II) complex. The stereochemistry of the (pi-allyl)palladium complexes was confirmed by benzoquinone-induced stereoselective transformations to allylic acetates.     

Stereoselective palladium-catalyzed carbocyclization of allenic allylic carboxylates

Palladium(0)-catalyzed reaction of allene-substituted allylic carboxylates 3-8 employing 2-5 mol % of Pd(dba)(2) in refluxing toluene leads to the carbocyclization and elimination of carboxylic acid to give bicyclo[4.3.0]nonadiene and bicyclo[5.3.0]decadiene derivatives (12-17). The carbon-carbon bond formation is stereospecific, occurring syn with respect to the leaving group. Addition of maleic anhydride as a ligand to the above-mentioned procedures changed the outcome of the reaction, and under these conditions 3-5 afforded cycloisomerized products 21-23. The experimental results are consistent with a mechanism involving oxidative addition of the allylic carboxylate to Pd(0) to give an electron-deficient (pi-allyl)palladium intermediate, followed by nucleophilic attack by the allene on the face of the pi-allyl opposite to that of the palladium atom. Furthermore, it was found that the Pd(dba)(2)-catalyzed cyclization of the trans-cycloheptene derivative (trans-8) can be directed to give either the trans-fused (trans-17) or the cis-fused (cis-17) ring system by altering the solvent. The former reaction proceeds via a nucleophilic trans-allene attack on the (pi-allyl)palladium intermediate, whereas the latter involves a syn-allene insertion into the allyl-Pd bond of the same intermediate. The products from the carbocylization undergo stereoselective Diels-Alder reactions to give stereodefined polycyclic systems in high yields.     

Visual DNA as a diagnostic tool

We report on the incorporation of the Visual DNA concept in a genotyping assay as a simple and straightforward detection tool. The principle of trapping streptavidin‐coated superparamagnetic beads of micrometer size for visualization of genetic variances is used for PrASE‐based detection of a panel of mutations in the severe and common genetic disorder of cystic fibrosis. The method allows a final investigation of genotypes by the naked eye and the output is easily documented using a regular hand‐held device with an integrated digital camera. A number of samples were run through the assay, showing rapid and accurate detection using superparamagnetic beads and an off‐the‐shelf neodymium magnet. The assay emphasizes the power of Visual DNA and demonstrates the potential value of the method in future point‐of‐care tests.