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In this paper we describe the synthesis, the electrochemical behaviour as well as the linear and nonlinear optical (NLO) properties of two push-pull derivatives bearing pyranylidene electron donating fragment, pyrimidine/methyl pyrimidinium electron withdrawing moiety and a ferrocene part in the π-conjugated bridge. The properties of these two compounds were compared to their analogues without ferrocene or pyranylidene fragments. Experimental results were completed with DFT calculations to gain further insight into the intramolecular charge transfer (ICT). All the results indicate a significant charge transfer through the ferrocene unit. The ICT is however more limited than in all organic analogues.

A multiplexed solid-phase nucleic acid hybridization assay on a paper-based platform is presented using multicolor immobilized quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET). The surface of paper was modified with imidazole groups to immobilize two types of QD-probe oligonucleotide conjugates that were assembled in solution. Green-emitting QDs (gQDs) and red-emitting QDs (rQDs) served as donors with Cy3 and Alexa Fluor 647 (A647) acceptors. The gQD/Cy3 FRET pair served as an internal standard, while the rQD/A647 FRET pair served as a detection channel, combining the control and analytical test zones in one physical location. Hybridization of dye-labeled oligonucleotide targets provided the proximity for FRET sensitized emission from the acceptor dyes, which served as an analytical signal. Hybridization assays in the multicolor format provided a limit of detection of 90 fmol and an upper limit of dynamic range of 3.5 pmol. The use of an array of detection zones was designed to provide improved analytical figures of merit compared to that which could be achieved on one type of array design in terms of relative concentration of multicolor QDs. The hybridization assays showed excellent resistance to nonspecific adsorption of oligonucleotides. Selectivity of the two-plex hybridization assay was demonstrated by single nucleotide polymorphism (SNP) detection at a contrast ratio of 50:1. Additionally, it is shown that the use of preformed QD-probe oligonucleotide conjugates and consideration of the relative number density of the two types of QD-probe conjugates in the two-color assay format is advantageous to maximize assay sensitivity and the upper limit of dynamic range.

Transfer of the acetyl- l -leucine (AcLeu) residue from AcLeu-pentanucleotide to synthetic substrates under conditions of the fragment reaction was used to study the specificity of the acceptor site of ribosomal peptidyl transferase. 2′(3′)-O-Aminoacyl nucleosides are the simplest acceptor substrates. Their acceptor activity is dependent on the nature of the nucleoside to which the amino acid residue is bound. The acceptor activity decreased in the sequence 2′(3′)-O- l -phenylalanyladenosine (A-(Phe)) > I-(Phe) > C-(Phe); U-(Phe) was inactive. The presence of a free 2′-hydroxyl group in the ribose moiety of the aminoacyl adenosines was important for the acceptor activity, as shown by the low activity of dA-(Phe) in comparison with A-(Phe). Acceptor activity was influenced by the nature of the side chain of the amino acid residue bound to adenosine: A-(Phe) was a more active acceptor than puromycin, while the acceptor activity of 2′(3′)-O-glycyladenosine A-(Gly) was very low. Free phenylalanine, phenylalanine methyl ester, and adenosine did not act as acceptors. As terminal products of the reactions of AcLeu-pentanucleotide with puromycin, A-(Phe), I-(Phe) and C-(Phe), we isolated AcLeu-puromycin, 2′(3′)-O- acetyl- l -leucyl- l -phenylalanyladenosine (A-(AcLeu-Phe)), I-(AcLeu-Phe) and C-(AcLeu-Phe), respectively.

In vitro methylation of E. coli tRNAfMet fragments or their reconstituted molecule by rat liver methylase showed that (1) the whole tRNA molecule was not necessary for recognition by tRNA methylase, and (2) the extent and the site of methylation of fragments differed depending upon the type of fragment used. This indicates that the conformational structure of the methyl acceptor molecule is important for recognition by the tRNA methylase.