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Bio-inspired cyclopeptidic heterodimers built on [beta]-sheet-like hydrogen-bonding networks and bearing photoactive and electroactive chromophores on the outer surface have been prepared. Different cross-strand pairwise relationships between the side chains of the cyclic [alpha],[gamma]-peptides afford the heterodimers as three nonequivalent dimeric species. Steady-state and time-resolved spectroscopies clearly show an electron transfer process from [PI]-extended tetrathiafulvalene, covalently attached to one of the cyclopeptides, to photoexcited [60]fullerene, located on the complementary cyclopeptide. The charge-separated state was stabilized for up to 1 [mu]s before recombining and repopulating the ground state. Our current example shows that cyclopeptidic templates can be successfully used to form light-harvesting/lightconverting hybrid ensembles with a distinctive organization of donor and acceptor units able to act as efficient artificial photosystems. cyclic peptide nanotubes | fullerenes | self-assembly

Efficient total syntheses of the marine hydrocarbon polyacetylenes callyberynes (A-C) are achieved using highly convergent routes, which involved metal-catalyzed cross-coupling reactions to sp centers as the key steps. The convergent approaches to the three polyacetylenes rely on bond disconnections at the end of central sp centers and employ transition-metal-catalyzed alkynylation reactions (sp-sp, sp(super 2)-sp, or sp(super 3)- sp).

The synthesis of several benzo[b]-, benzo[c]-, and dibenzo[b,g]fluorenones is achieved by the thermal cyclization of 1-[2-(arylethynyl)phenyl]-3-trimethylsilypropynones. The introduction of substituents with the right electronic and steric properties on the aryl rings can cause the ratio of the two isomers to vary between 100.0 and 0:100.

This correspondence addresses the problem of channel estimation and symbol detection in wireless direct-sequence code-division multiple-access (DS-CDMA) communication systems. We introduce a novel multiuser demodulation scheme that proceeds in two steps. First, the multiaccess channel parameters are estimated according to a suitable modification of the maximum-likelihood (ML) criterion using the expectation maximization (EM) algorithm. Subsequently, this estimate and other useful side information are employed to perform ML detection of the transmitted symbols with the Viterbi algorithm. Our main contribution is the development of a novel stochastic ML method for channel estimation that takes advantage of all the available statistical information referred to the transmitted signals and channel noise. Additionally, it can incorporate the knowledge of a fraction of the transmitted symbols; hence, the term semiblind. Computer simulation results are presented that show how close-to-optimum performance is achieved in time-dispersive fading channels using remarkably short training sequences. Index Terms--Channel estimation, code-division multiple access (CDMA), expectation maximization (EM) algorithm, maximum likelihood, multiuser detection, semiblind receivers.

The opening of the bridging ether of 8-oxabicyclo[3,2.1]oct-6-ene systems fused to a five-membered carbocycle is accomplished by choosing the five-membered ring witth a double bond conjugated to the oxabicycle. Data indicate that the double bond either mediates a 1,6-addition reaction or stabilizes the carbanion.