Measuring electronic coupling in the reaction center of purple photosynthetic bacteria by two-color, three-pulse photon echo peak shift spectroscopy

One- and two-color, three-pulse photon echo peak shift spectroscopy (1C and 2C3PEPS) was used to estimate the electronic coupling between the accessory bacteriochlorophyll (B) and the bacteriopheophytin (H) in the reaction center of the purple photosynthetic bacterium Rhodobacter sphaeroides as approximately 170 +/- 30 cm-1. This is the first direct experimental determination of this parameter; it is within the range of values found in previously published calculations. The 1C3PEPS signal of the Qy band of the bacteriochlorophyll B shows that it is weakly coupled to nuclear motions of the bath, whereas the 1C3PEPS signal of the Qy band of the bacteriopheophytin, H, shows that it is more strongly coupled to the bath, but has minimal inhomogeneous broadening. Our simulations capture the major features of the data with the theoretical framework developed in our group to separately calculate the response functions and population dynamics.     

Are hydroxyl-containing biomolecules important in biosilicification? A model study

To understand the roles of hydroxyl-containing biomolecules in biosilicification, theoretical and experimental studies of silica formation utilizing biological and model organic additives have been undertaken. However, the role of hydroxyl functionalized biomolecules in silica formation is still not fully understood. To address this problem, we performed a systematic in vitro study of silica formation in the presence of two proteins rich in hydroxyl-containing amino acids (native sericin proteins extracted from Bombyx mori and a recombinant sericin precursor peptide) and a range of small alkanediols. The data obtained suggest the following hypotheses for the role of hydroxyl-containing organic molecules in silica formation. In the first case, hydroxyl-containing organic molecules are not at all involved chemically in the formation of silica. Instead, they may be only assisting in rendering stability and solubility to the organic molecules found occluded in silica. The second possibility is that if we assume that hydroxyl-containing organic molecules affect silica formation, then the environments of silicic acid polymerization could be highly deficient in water to increase the effects of hydroxyl functional groups of proteins in silica formation. These results and their implications are discussed in the context of biosilicification and biomineralization.     

Unexpected phenyl group rearrangement during an intramolecular Scholl reaction leading to an alkoxy-substituted hexa-peri-hexabenzocoronene

A simple dimethoxy-substituted hexa-peri-hexabenzocoronene (m-dimethoxy HBC) was unexpectedly obtained along with a bis-spirocyclic dienone during an intramolecular Scholl reaction of its para isomer.     

Isolation and structural elucidation of a key aluminoaromatic intermediate and evidence for dismutation phenomena in TMP-alumination chemistry

Lithium TMP-aluminate "(i)Bu(3)Al(TMP)Li" undergoes dismutation in THF solution to precipitate the tetraalkylaluminate [{Li.(THF)(4)}(+){Al((i)Bu)(4)}(-)], but reacts kinetically as a TMP base towards N,N-diisopropylbenzamide to afford the crystalline ortho-aluminated species [(THF)(3).Li{O([=C)N((i)Pr)(2)(C(6)H(4))}Al((i)Bu)(3)] and TMPH.     

Information content in organic molecules: Brownian processing at low levels

The informatic properties of organic molecules have been the subject of our research during the past several years. In the present study, we investigate the lower levels wherein information is expressed via Brownian processing. Organic molecules are like other electronic devices in that their informatic details depend on the operating level in question. The low and high levels are distinguished (among other ways) by the amount of work they require for processing. In this work, a Brownian model is developed by which the low-level content of a chemical system can be quantified. The model is demonstrated for diverse organic molecules. In so doing, several scaling properties of low-level information are illustrated. In addition, the correspondence traits regarding the different levels are examined. Molecular information represents a capacity for work control such as during chemical reactions. Thus, the information expressed at low levels is examined in connection with the reaction pathway selectivity of organic compounds.     

pH-sensitive holograms for continuous monitoring in plasma

Conventional electrochemical methods of determining the pH of body fluids have drawbacks. Newer optical methods offer the promise of miniaturisation and continuous in vivo measurements without drift. This report examines the ability of a holographic sensor based on a thin-film, biocompatible hydrogel (approximately 10 μm) of poly(2-hydroxyethyl methacrylate) and ionisable 2-(dimethylaminoethyl) methacrylate to accurately measure the pH of blood plasma ex vivo. It is found that the sensors behave in a fully reversible manner. After an initial calibration with buffers, they can measure pH over extended periods (more than 40 h). Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Casimir forces between arbitrary compact objects

We develop an exact method for computing the Casimir energy between arbitrary compact objects, either dielectrics or perfect conductors. The energy is obtained as an interaction between multipoles, generated by quantum current fluctuations. The objects' shape and composition enter only through their scattering matrices. The result is exact when all multipoles are included, and converges rapidly. A low frequency expansion yields the energy as a series in the ratio of the objects' size to their separation. As an example, we obtain this series for two dielectric spheres and the full interaction at all separations for perfectly conducting spheres.