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.
A numerical method is given for effecting nonlinear local density functional evolution. Within a given time interval, Chebyshev quadrature points are used to sample the evolving orbitals. An implicit equation coupling wave functions at the different time points is then set up. The equation is solved iteratively using the ‘‘direct inversion in iterative space’’ acceleration technique. Spatially, the orbitals are represented on a Fourier grid combined with soft pseudopotentials. The method is first applied to the computation of the 3Pg adiabatic potential energy curves of Al2 . Next, the electronic dynamics of a toy molecular wire is studied. The wire consists of a C2H4 molecule connected via sulfur atoms to two gold atoms, the ‘‘electrodes.’’ The molecule is placed in a homogeneous electric field and a dynamical process of charge transfer is observed. By comparing the transient with that of a resistance-capacitance circuit, an effective Ohmic resistance and capacitance is estimated for the system.
A review is given on scanning electrochem. microscopy (SECM) as a tool for surface modification. It is distinguished between the direct mode and the feedback mode of the SECM. In the direct mode, the substrate serves as the auxiliary electrode, while, in the feedback mode, the substrate is unibiased, and a mediator is used that shuttles between the ultramicroelectrode and the surface. The etching of semiconductors, the metal deposition and etching, the deposition of conducting polymers, and the patterning of org. and biomols. are treated for both the direct- and the feedback mode technique of the SECM. The achievable resoln. and the patterning rate are addressed. [on SciFinder(R)]
KL KOMPA and RD LEVINE. 2001. “A molecular logic gate.” PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 98, Pp. 410-414. Abstract
We propose a scheme for molecule-based information processing by combining well-studied spectroscopic techniques and recent results from chemical dynamics. Specifically it is discussed how optical transitions in single molecules can be used to rapidly perform classical (Boolean) logical operations. In the proposed way, a restricted number of states in a single molecule can act as a logical gate equivalent to at least two switches. it is argued that the four-level scheme can also be used to produce gain, because it allows an inversion, and not only a switching ability. The proposed scheme is quantum mechanical in that it takes advantage of the discrete nature of the energy revers but we here discuss the temporal evolution, with the use of the populations only. On a longer time range we suggest that the same scheme could be extended to perform quantum logic, and a tentative suggestion, based on an available experiment, is discussed. We believe that the pumping can provide a partial proof of principle, although this and similar experiments were not interpreted thus far in our terms.
We present a molecular-level theory for amphiphile packing in linear micelles, focusing on the early stages of micellar elongation, i.e., on small and ``intermediate-size'' micelles, whose endcaps are not yet molded into a final shape. The internal free energy of a micelle of given size and shape is expressed as an integral over local molecular packing free energies in different regions of the micelle. The free energy per molecule is expressed as a sum of interfacial (''opposing forces'') and chain conformational contributions, both depending on the local geometry. The equilibrium shape and energy of the micelle is determined by functional minimization of the total free energy. For amphiphiles exhibiting strong preference for packing in the cylindrical geometry, we show that the early stages of growth involve an energetic barrier, resulting in a ``gap'' in the micellar size distribution. That is, at low total amphiphile concentrations only small (globular) micelles appear in solution. Their concentration reaches a well-defined saturation value, beyond which, all added amphiphiles are incorporated in long micelles, whose ``non-interacting'' endcaps are well separated by the cylindrical middle part. This, ``second CMC'' behavior is demonstrated by numerical calculations of micellar size distributions and average aggregation numbers as a function of the total concentration. The conditions necessary for the appearance of a second CMC are analyzed theoretically, with explicit reference to the underlying molecular packing characteristics. In particular, it is shown that a necessary condition for the appearance of a sharply defined second CMC is that the endcap energies (of at least some) of the small or intermediate-size micelles must be considerably lower than the asymptotic (long micelle) value of this quantity. The diameter of the minimal, spherical micelles, as well as that of the final endcaps, is found to be larger than the diameter of the cylindrical body of the very long micelles. Our results are in good qualitative agreement with recent cryo-TEM imaging studies of micellar shape and growth, as well as with previous (less direct) experiments revealing second CMC behavior.
