The catalytic features of these conjoined aptamer-ribozyme constructs demonstrate that catalytic RNAs can also be subject to allosteric regulation-a key feature of certain protein enzymes. Moreover, by using simple rational design strategies, it is now possible to engineer new catalytic polynucleotides which have rates that can be tightly and specifically controlled by small effector molecules.
Strong exciton-photon coupling is the result of a reversible exchange of energy between an excited state and a confined optical field. This results in the formation of polariton states that have energies different from the exciton and photon. We demonstrate strong exciton-photon coupling between light-harvesting complexes and a confined optical mode within a metallic optical microcavity. The energetic anti-crossing between the exciton and photon dispersions characteristic of strong coupling is observed in reflectivity and transmission with a Rabi splitting energy on the order of 150 meV, which corresponds to about 1,000 chlorosomes coherently coupled to the cavity mode. We believe that the strong coupling regime presents an opportunity to modify the energy transfer pathways within photosynthetic organisms without modification of the molecular structure.
Deoxynucleoside phosphoramidites can be prepared in good yield from deoxynucleosides, bis-dialkylaminophosphines, and the corresponding dialkylamine hydrotetrazolide or tetrazole as catalysts. These phosphoramidites generated in situ lead to the direct synthesis of deoxyoligonucleotides on polymer supports.
INTRODUCTIONThe current phosphite triester methodology for deoxyoligonucleotide synthesis requires the condensation of deoxynucleoside phosphoramidites 7a-d or 8a-d, activated by tetrazole, with the 5'-hydroxyl group of a deoxynucleoside or deoxyoligonucleotide attached covalently to a polymer support (1-4). Although these phosphoramidites can be prepared by existing methods (5,6) from the appropriately protected deoxynucleosides la-d, the chlorophosphines 2 and 3 used in forming 7a-d and 8a-d, respectively, are difficult to prepare and easily react with trace amounts of water. Moreover, the high reactivity of 2 and 3 and the concomitant production of insoluble amine hydrochloride salts preclude their use for any strategy involving the in situ generation of deoxynucleoside phosphoramidites for deoxyoligonucleotide synthesis on solid supports (7). Because of our interest in the latter approach, we were prompted to investigate the relative stability and reactivity of the aminophosphines 4, 5, and 6 towards phosphodiester formation. We wish to report that the phosphoramidites 7a-d and 8a-d can be prepared in good yields by the reaction of suitably protected deoxynucleosides la-d and bis-dialkylaminophosphines 4 or 6 using amine salts 9 and 10, respectively, as catalysts. This method was applied to a
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