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The RNA genomes of a number of pathogenic RNA viruses, such as HIV-1, have extensive folded conformations with imperfect A-form duplexes that are essential for virus function and could serve as targets for structure-specific antiviral drugs. As an initial step in the discovery of such drugs, the interactions with RNA of a wide variety of compounds, which are known to bind to DNA in the minor groove, by classical or by threading intercalation, have been evaluated by thermal melting and viscometric analyses. The corresponding sequence RNA and DNA polymers, poly(A).poly(U) and poly(dA).poly(dT), were used as test systems for analysis of RNA binding strength and selectivity. Compounds that bind exclusively in the minor groove in AT sequences of DNA (e.g., netropsin, distamycin, and a zinc porphyrin derivative) do not have significant interactions with RNA. Compounds that bind in the minor grove in AT sequences of DNA but have other favorable interactions in GC sequences of DNA (e.q., Hoechst 33258, DAPI, and other aromatic diamidines) can have very strong RNA interactions. A group of classical intercalators and a group of intercalators with unfused aromatic ring systems contain compounds that intercalate and have strong interactions with RNA. At this time, no clear pattern of molecular structure that favors RNA over DNA interactions for intercalators has emerged. Compounds that bind to DNA by threading intercalation generally bind to RNA by the same mode, but none of the threading intercalators tested to date have shown selective interactions with RNA.

This paper reports both continuous and time-resolved spectroscopic studies of the emission properties of photoexcited pyrene labels covalently attached to uridine nucleosides and oligonucleotides. For all nucleic acid systems, uridine is substituted with pyrene at the 2'-oxygen position, 2'-0-[hexyl-/V-(l-pyrenepropylcarbonyl)amino]uridine, U(12)*. Three types of nucleic acid systems are investigated: the 5'-OH (1) and the S'-ODMT (2) substituted U(12)*-nucleosides; four pentameric oligonucleotides, X2U(12)*X2, where X is 2'-deoxyadenosine (A), 2'-deoxyguanosine (G), 2'-deoxythymidine (T), or 2'-deoxycytidine (C); and four duplexes with 18 base pairs each containing one strand with a central U(12)* label. The central U(12)* label in the duplexes has the following flanking base-sequences, 5'-• • •AX2U( 12)* 2 • • '-3', where X is A, G, T, or C. The 400-nm region emission kinetics for the four U(12)*-labeled pentamers establish the following order of pyrene*-quenching reactivities by flanking DNA bases: A < G < T < C. This ordering of reactivities is generally consistent with expected reactivites based on estimates of the free energies of pyrene* quenching by electron transfer, AG°(ET), to or from flanking DNA bases. Emission spectra and lifetimes in the 495nm region for both U(12)*-labeled pentamers and duplexes provide direct evidence for the formation and decay of the pyrene*+/U(12)'_ charge-transfer (CT) product. In general ca. 20% of the amplitude of the CT emission decays in the 1-7 ns time range and 70-80% of its amplitude decays in <0.2 ns. The C2U(12)*C2 pentamer has uniquely short , * emission decay with its longest emission-lifetime component lasting only 5.6 ns and its average emission lifetime <0.6 ns. (In contrast the longest , * emission components for pyrene butanoic acid (PBA) and U(12)*OH (1) in methanol last, respectively, 231 and 37 ns.) Finally, the longest , * emission lifetimes of U(12)*-labeled DNA duplexes exceed those of the corresponding pentamers.A measure of duplex-induced restricted access of pyrene* to base-paired nucleosides in double-strand (ds) versus single-strand (ss) DNA can be obtained by noting that the average , * emission lifetimes (for greater than 1 ns components) lengthen 3-fold on going from the T2U(12)*T2 pentamer to the corresponding •••AT2U(12)*T2A••• duplex and 9-fold on going from the C2U(12)*C2 pentamer to the •"AC2U(12)*C2A••• duplex.

No abstract

An alternative "signal on" immunosensor for ultrasensitive detection of apurinic/apyrimidinic endonuclease 1 (APE-1) was designed utilizing the self-enhanced electrochemiluminescence (ECL) of a novel Ru(II) complex functionalized coil-like nanocomposite as signal labels. The desirable self-enhanced ECL luminophore was achieved by combining the coreactant of poly(ethylenimine) (PEI) and the luminophor of bis(2,2'-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II) [Ru(bpy)2(5-NH2-1,10-phen)(2+)] to form one novel Ru(II) complex, which exhibited significantly enhanced ECL efficiency and stability. Moreover, the carbon nanotubes (CNTs) were employed as nanocarriers for self-enhanced Ru(II) complex loading via π-π stacking to obtain the coil-like nanocomposite to act as signal probe. Compared with traditional ECL immunoassay, our proposed strategy is simple and sensitive, avoiding the adding of any coreactant into testing solution for signal amplification, and shows a detection limit down to subfemtogram per milliliter level under the optimized experimental condition.

In this paper, a novel electrochemiluminescence resonance energy transfer (ECL-RET) system from O2/S2O8(2-) to a kind of amino-terminated perylene derivative (PTC-NH2) was demonstrated for the first time, which was then applied to construct a ratiometric aptasensor for lead ion (Pb(2+)) detection. First, gold-nanoparticles-functionalized fullerene nanocomposites (AuNPs@nano-C60) were coated on a glassy carbon electrode (GCE), and then thiol-modified assistant probes (APs) were attached on AuNPs@nano-C60/GCE. Then the resultant electrode was hybridized with capture probes (the aptamer of the Pb(2+), abbreviated as CPs) to generate DNA duplexes, which could induce PTC-NH2 to be intercalated into the dsDNA grooves by the electrostatic adsorption. Herein, ECL dual peaks at -0.7 V (vs Ag/AgCl) and -2.0 V (vs Ag/AgCl) were obtained when the prepared aptasensor was detected in air-saturated S2O8(2-) solution, which could be attributed to the emission of excited dimmers (π-excimers) ((1)(NH2-PTC)2*) and (1)(O2)2*, respectively. In the presence of Pb(2+), the dsDNA was unwound, and Pb(2+) G-quadruplex structure was generated because of the highly specific affinity between Pb(2+) and CPs, which made the PTC-NH2 release from the electrode surface. As a result, the ECL signal at -0.7 V was decreased, and the ECL signal around -2.0 V was increased. By measuring the ratio of ECL intensities at two excitation potentials, the developed aptasensor exhibited the linear response range from 1.0 × 10(-12) M to 1.0 × 10(-7) M with a detection limit of 3.5 × 10(-13) M (S/N = 3) for Pb(2+), which could offer an alternative analytical method with excellent properties of high selectivity, accuracy, and sensitivity.

Cu nanoclusters (Cu NCs), which emerged as a new class of nontoxic, economic, and excellent phosphors and catalysts, have attracted increasing interest for a wide variety of promising applications in biolabeling and biocatalysis. However, the electrochemiluminescence (ECL) behavior of Cu NCs has never been reported in previous works. Here, anodic and blue ECL emission of Cu NCs was observed for the first time with the efficient coreactant of hydrazine (HZ), and the possible luminescence mechanism of Cu NCs/HZ ECL system was studied in detail. Briefly, HZ was oxidized, and Cu NCs got the energy to generate excited state Cu NCs* for light radiation. Furthermore, a highly sensitive "signal-off" sensing platform for the determination of dopamine has been developed upon effectively quenching of dopamine toward the Cu NCs/HZ-based ECL system. As a result, this proposed method for dopamine detection possesses high selectivity, good stability, and excellent sensitivity with a detection limit down to 3.5 × 10 M. This indicates that Cu NCs show potential for applications in ECL bioanalysis as a new type of low-cost and superior luminophore candidates.

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