A review. This review describes the interfacial behavior of biomols., which were converted to more hydrophobic derivs. by covalent attachment of hydrophobic chains. The mols. presented are proteins (glucose oxidase, IgG, gelatin, ovalbumin) and polysaccharides (CM-cellulose, pullulan). In general, it was found that such hydrophobically modified biomols. have enhanced surface activity and ability to penetrate into phospholipid monolayers. In addn., it has been demonstrated, that such mols. can be used as efficient emulsifiers and foaming agents, and in unique biomedical application based on combining the surface activity and recognition ability. [on SciFinder(R)]
Logic circuits operating on different molecules or on different parts of the same molecule can be connected. As an example, a circuit known as a full adder is described. It is made up of two circuits, a half adder on a donor (rhodamine 6G) and another half adder on an acceptor (azulene). The signal, (an intermediate sum), is moved from donor to acceptor by electronic energy transfer. The concatenated logic arrangement is described, and potential applications using other bichromophoric molecules are outlined. Polychromophoric molecules will allow a fanout operation.
A rising blood titer of juvenile hormone (JH) in adult worker honey bees is associated with the shift from working in the hive to foraging. We determined whether the JH increase occurs in anticipation of foraging or whether it is a result of actual foraging experience and/or diurnal changes in exposure to sunlight. We recorded all foraging flights of tagged bees observed at a feeder in a large outdoor flight cage. We measured JH from bees that had taken 1, 3-5, or > 100 foraging flights and foragers of indeterminate experience leaving or entering the hive. To study diurnal variation in JH, we sampled foragers every 6 h over one day. Titers of JH in foragers were high relative to nurses as in previous studies, suggesting that conditions in the flight cage had no effect on the relationship between foraging behavior and JH. Titers of JH in foragers showed no significant effects of foraging experience, but did show significant diurnal variation. Our results indicate that the high titer of JH in foragers anticipates the onset of foraging and is not affected by foraging experience, but is modulated diurnally. (C) 2001 Elsevier Science Ltd. All rights reserved.
HHeF, a first predicted chemically-bound helium compound, is a metastable species that disintegrates by tunneling through energy barriers into He+HF and H+He+F. The reaction paths for these decomposition processes are calculated with single-configurational Moller-Plesset (MP2) and multiconfigurational quasidegenerate MCQDPT2/MCSCF(10,6) electronic structure methods. The lifetime of HHeF, estimated using a one-dimensional model along the minimum energy path and the semiclassical WKB approximation, is more than 120 ps, that of DHeF is 14 ns. The relatively long lifetimes are encouraging for the preparation prospects of this helium compound. (C) 2001 American Institute of Physics.
Diindeno[1,2,3,4-defg;1',2',3',4'-mnop]chrysene (DIC) (one of the smallest symmetrical bowl-shaped fragments of C60) and its tetra-tert-butyl derivative are reduced with lithium metal to yield dianions and tetraanions. Due to the high degree of symmetry (C2v) of DIC and its derivative, their NMR spectra cannot be assigned using the standard two-dimensional NMR techniques. A novel carbon-edited NOESY method was used to complete the assignments of the neutral and dianion species, whereas the tetraanions are aided by DFT calculations for their assignment. Experimental charge-distribution patterns were obtained and match those of the calculations. An extension of the empirical approach for estimating the charge distribution from the 13C-NMR spectra enables a direct comparison between experimentally derived charge-distribution data and the computed electron density in each of the lowest unoccupied molecular orbitals. The overall picture evolving from the orbital structure of DIC is presented and reflects the surface reactivity of C60.
The scanning electrochem. microscope was applied in the feedback mode to deposit Au microstructures on n-Si(111) and indium-tin oxide. This was accomplished by the anodic dissoln. of Au at the microelectrode followed by the subsequent redeposition of the Au on the substrate. The influence of pH, substrate potential, and deposition time on the cryst. nanometer structure of the micrometer Au deposits was studied. The effect of these parameters on deposition could be explained by the band structure of the silicon. Also, understanding the role played by the different parameters allows depositing predefined nanocryst. structures. [on SciFinder(R)]
F Remacle, EW Schlag, H Selzle, KL KOMPA, U Even, and RD LEVINE. 2001. “Logic gates using high Rydberg states.” PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 98, Pp. 2973-2978. Abstract
Connected logic gates can be operated on the levels of one molecule by making use of the special properties of high Rydberg states, Explicit experimental results for the NO molecule are provided as an example. A number of other options, including that of several gates concatenated so as to operate as a full adder, are discussed. Specific properties of high Rydberg states that are used are: their autoionization is delayed so that they can be distinguished from direct multiphoton ionization, during their long life such states also can decay by energy transfer to the molecular core in a way that can be controlled by the judicious application of very weak external electrical fields, and the Rydberg states can be detected by the application of an ionizing electrical field. The combination of two (or three) color photons with and without external weak fields allows the construction of quite elaborate logic circuit diagrams and shows that taking advantage of the different intramolecular dynamics of levels that differ by their excitation enables the compounding of logic operations on one molecular frame.
