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A molecule containing an electron donor (pyrene, Py), an insulating tetramethylene bridge, an electron acceptor (perylenebisimide, PBI) and a bis-decyl swallowtail with two terminal thioesters was studied for its electrical rectification as a Langmuir–Blodgett (LB) monolayer between two Au electrodes at room temperature (over a 8 month period, the thioester terminations chemisorbed partially (about 15%) onto the bottom Au electrode). At lower bias (

The isomerization of tricyclo[3.1.0.02,6]hexane to 1,3-cyclohexadiene was studied using ab initio calculations at the multiconfiguration and single-configuration levels of theory. Single-point energy calculations were also performed using the MCQDPT2 and CCSD(T) methods. The isomerization process was found to proceed through an (E,Z)-1,3-cyclohexadiene intermediate following a concerted, asynchronous pathway characterized as a conrotatory ring opening of the bicyclobutane moiety. The second step involves rotation about the trans double bond resulting in the (Z,Z)-1,3-cyclohexadiene product. The rate determining step is the first one, with an activation barrier of about 43 kcal mol-1. The activation barrier of the second step was found to be only 3 kcal mol-1. A second concerted pathway was found leading directly to (Z,Z)-1,3-cyclohexadiene but with an activation barrier of 54 kcal mol-1. A multiconfiguration based wave function is necessary to properly describe the potential energy surface of the reaction.

Five unsymmetrical sulfides and one unsymmetrical disulfide were synthesized for self-assembled monolayer (SAM) formation on gold electrodes. Each compound contained a dinitrobenzyl ester group at the end of a primary alkyl chain as one sulfide arm, with an allyl, methyl, or cyanobenzyl group for the other arm. Cyclic voltammetry (CV) of the resulting SAMs showed no evidence for differential cleavage of allyl or cyanobenzyl sulfide groups relative to methyl, contrary to expectations if sulfide cleavage accompanied the self-assembly process.

Donor-σ-Acceptor (D-σ-A) molecules, arrayed in a monolayer between electrodes, can serve as molecular rectifiers. Using perylene-3,4,9,10-tetracarboxylic bisimide (PBI) as the acceptor allows the attachment of the donor group to one imide nitrogen and a solubilizing swallowtail, normally a long (e.g., C(19)) alkane connected at midchain, on the other. Such an alkyl tail facilitates the formation of Langmuir-Blodgett (LB) monolayers. We have employed several modified swallowtails to make new D-σ-A molecules: poly(ethylene glycol) (PEG) swallowtails with 6 ether oxygens or with 4 ether oxygens to promote hydrophilicity in orienting LB monolayers, and alkyl swallowtails ending with sulfur anchors (thioacetate, thiol, or methyl disulfide) to stabilize attachment of the D-σ-A molecules to gold electrodes. The preparation and characterization of D-σ-A molecules containing combinations of these swallowtails with pyrene, ferrocene, and tetramethylphenylenediamine donor groups is described.

We report spectroscopic characterization and unimolecular rectification (asymmetric electrical conduction) measurements of three donor-sigma-acceptor (D-sigma-A) compounds N-(10-nonadecyl)-N-(1-pyrenylmethyl)perylene-3,4,9,10-bis(dicarboximide) (1), N-(10-nonadecyl)-N-(4-[1-pyrenyl]butyl)perylene-3,4,9,10-bis(dicarboximide) (2), and N-(10-nonadecyl)-N-(2-ferrocenylethyl)perylene-3,4,9,10-bis(dicarboximide) (3). These molecules were arranged as one-molecule thick Langmuir-Blodgett monolayers between Au electrodes. In such an "Au | D-sigma-A | Au" sandwich, molecule 1 is a unimolecular rectifier, with rather small rectification ratios (between 2 and 3 at +/-1 V) that decrease upon cycling. Molecule 2 does not rectify. Molecule 3 rectifies, with a rectification ratio of between 14 and 28 at +/-1 V; the through-film rectification and currents persist, even with scans of +/-2 V, for up to 40 cycles of measurement. Qualitative arguments, based on a two-level rectification mechanism, are consistent with the current asymmetries observed in the monolayers of 1 and 3.

Donor-sigma-acceptor-lipid molecules were prepared by using perylenetetracarboxylic diimide as the acceptor, starting from perylenetetracarboxylic dianhydride. One imide nitrogen was attached to a "swallowtail" lipid (a long alkyl tail connected at midchain), which imparts enough solubility to make the system tractable and provides a lipophilic region suitable for promoting Langmuir-Blodgett monolayer formation. The other imide link was to a donor group (pyrene, ferrocene, tetramethylphenylenediamine, phenyl) through a short alkyl sigma bridge. Features of the 1H and 13C NMR spectra of swallowtailed perylenediimides are interpreted as resulting from restricted rotation about the imide C-N bond; the 13C NMR spectra and stereochemistry of these molecules are contrasted with the case of the related bis-(2,5-di-tert-butylphenyl)perylenetetracarboxylic diimide.

A diterpene hydrocarbon and diterpene ketone isolated from the paracloacal gland secretions of the Chinese alligator (alligator sinensis) were examined by GC-MS and 1H-NMR, 13C-NMR, and IR spectroscopy, and identified as 4,8,12-trimethyl-1-(1-methylethenyl)-3,7,11-cyclotetradecatrien e (cembrene A, 1) and its congeneric ketone, 4,8,12-trimethyl-1-(1-methylethenyl)-3,7-cyclotetradecadien- 10-one (2), respectively. This is the first report of cembrene A from a vertebrate; the ketone has not been described previously.

Periodation par l'acide periodique et l'iode dans H 2 SO 4 de benzene, nitro- et -chloro-benzenes, acide benzoique, anhydride phtalique et toluene

The fatty acids oleic, linoleic, and linolenic, each of which has a cis double bond at the delta 9 position, are known to lengthen the circadian period of conidiation (spore formation) of strains of Neurospora crassa carrying the cel mutation. cel confers a partial fatty acid requirement on the organism and has been used to promote incorporation of exogenous fatty acids. To test whether a physical effect imparted by the cis double bonds, such as increased membrane fluidity, is critical for the perturbation of the rhythm, various isomers of these fatty acids were supplemented to the bd csp cel strain. Positional isomers of oleic acid, such as petroselinic (delta 6) and vaccenic (delta 11) acids, and longer-chain isomers, such as eicosenoic (delta 11) and erucic (delta 13) acids, did not lengthen the rhythm. The shorter-chain palmitoleic (delta 9) acid did not give a consistent lengthening of the rhythm; it may be elongated to vaccenic acid. In contrast, gamma-linolenic acid (delta 6,9,12) dramatically lengthened the period. Linoelaidic acid (the trans,trans isomer of linoleic acid) lengthened the period at 22 degrees C, but elaidic acid (the trans isomer of oleic acid) did not. Elaidic acid was shown to exert a lengthening effect, but only at lower temperatures. The data do not support a direct physical action as the source of the fatty acids' "chronobiotic" ability.

Employing a fatty acid-requiring strain (bd csp cel) of Neurospora crassa, the 21.5-h period of the circadian spore-forming rhythm was manipulated by fatty acid supplementation. The addition to the medium of an unsaturated fatty acid (oleic, linoleic, or linolenic acid) lengthened the period to 26, 40, or 33 h, respectively. Ther period-lengthening effect of linoleic acid was proportional to its concentration up to 1.3 X 10(-4) M, and also was reversed by the addition to the medium of a saturated fatty acid, palmitic acid. None of these period-lengthening effects was observed in the prototrophic strain (bd csp cel+).