The photoisomerization of azobenzene has been known for almost 75 years but only recently has this process been widely applied to biological systems. The central challenge of how to productively couple the isomerization process to a large functional change in a biomolecule has been met in a number of instances and it appears that effective photocontrol of a large variety of biomolecules may be possible. This critical review summarizes key properties of azobenzene that enable its use as a photoswitch in biological systems and describes strategies for using azobenzene photoswitches to drive functional changes in peptides, proteins, nucleic acids, lipids, and carbohydrates (192 references).

Azobenzene photoswitches for biomolecules.

The charge transport mechanism of a wire can be revealed by how its electrical resistance varies with length. We have measured the resistance and current-voltage characteristics of conjugated molecular wires ranging in length from 1 to 7 nanometers, connected between metal electrodes. We observe the theoretically predicted change in direct-current transport from tunneling to hopping as a function of systematically controlled wire length. We also demonstrate that site-specific disruption of conjugation in the wires greatly increases resistance in the hopping regime but has only a small effect in the tunneling regime. These nanoscale transport measurements elucidate the role of molecular length and bond architecture on molecular conductivity and open opportunities for greater understanding of electrical transport in conjugated polymer films.

http://science.sciencemag.org/content/sci/320/5882/1482.full.pdf

Electrical Resistance of Long Conjugated Molecular Wires

Excited-state intramolecular proton transfer reactions are reviewed. Special emphasis is given to the intrinsic processes and to the mechanisms of proton transfers in relation to the nature of the intramolecular hydrogen bond ring.

Excited-state proton transfer reactions II. Intramolecular reactions

Cooperativity in Noncovalent Interactions.

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Water structure from scattering experiments and simulation.

Time-resolved and steady-state fluorescence studies of the excited-state proton transfer in 3-hydroxyflavone and 3-hydroxychromone

The molecular structure of trans-azobenzene (Ph−NN−Ph) has been determined by gas electron diffraction. Diffraction patterns were taken at 407 K and data analysis was made using the structural constraints obtained from MP2/6-31+G* calculations. Vibrational mean amplitudes and shrinkage corrections were calculated from the harmonic force constants given by a normal coordinate analysis. Vibrational mean amplitudes were refined as groups. The torsion of each phenyl ring was treated as a large amplitude vibration. The potential function for torsion was assumed to be V(φ1,φ2) = Σi=1,2{V2(1 − cos 2φi)/2 + V4(1 − cos 4φi)/2}, where φi denotes the torsional angle around each N−C bond. Quantum mechanical calculations were performed by taking account of two torsional motions to derive a probability distribution function, P(φ1,φ2). Because P(φ1,φ2) = N exp(−V(φ1,φ2)/kT) was found to be a good approximation at 407 K where N is a constant, it was adopted in the data analysis. The determined potential constants (V2 and...

Molecular Structure and Torsional Potential of trans-Azobenzene. A Gas Electron Diffraction Study

An unbiased algorithm for determining global minima of Lennard-Jones (LJ) clusters is proposed in the present study. In the algorithm, a global minimum is searched by using two operators:  one modi...

Clever and efficient method for searching optimal geometries of lennard-jones clusters.

A geometry optimization method for water clusters (H2O)n was developed in the present study. The method was applied to the TIP3P and TIP4P water clusters in the range of n ≤ 30, and the resulting structures were compared with the global-minimum structures in the literature (n ≤ 25 for the TIP3P potential and n ≤ 30 for the TIP4P potential). The method failed to reproduce the previously reported global minimum of the n = 24 TIP4P cluster. However, it was possible to find new global minima for the n = 24, 26−30 TIP3P cluster and the TIP4P clusters of 25, 28, 29, and 30 molecules.

Development of an Efficient Geometry Optimization Method for Water Clusters

Geometry optimization of carbon dioxide clusters (CO 2 ) n with the size of 4 ≤n < 40 is performed by a heuristic and unbiased method combined with geometrical perturbations. Comparison with the global minima reported in the literature shows that the present method reproduces the global minima for clusters with n = 6, 8, 13, 19, 28, 30, and 32 and yields new global minima for (CO 2 ) 23 , (CO 2 ) 25 , and (CO 2 ) 35 . For the other clusters under investigation, global minima are first reported in this article. Structural features of CO 2 clusters and efficiency of the optimization method are discussed.

Hiroshi Takeuchi

Papers

Time-resolved and steady-state fluorescence studies of the excited-state proton transfer in 3-hydroxyflavone and 3-hydroxychromone

Molecular Structure and Torsional Potential of trans-Azobenzene. A Gas Electron Diffraction Study

Clever and efficient method for searching optimal geometries of lennard-jones clusters.

Development of an Efficient Geometry Optimization Method for Water Clusters

Geometry optimization of carbon dioxide clusters (CO2)n for 4 < or = n < or = 40.