Self-assembled monolayers (SAMs) obtained from Z-b-[N-(v-acetylsulfanylalkyl)-3-methyl-4-pyridinium]-acyano-4-styryldicyanomethanide (1), a pyridinium analogue of the extensively studied rectifying dyes,

2-Thiouracil-containing nucleosides are essential modified units of natural and synthetic nucleic acids. In particular, the 5-substituted-2-thiouridines (S2Us) present in tRNA play an important role in tuning the translation process through codon–anticodon interactions. The enhanced thermodynamic stability of S2U-containing RNA duplexes and the preferred S2U-A versus S2U-G base pairing are appreciated characteristics of S2U-modified molecular probes. Recently, we have demonstrated that 2-thiouridine (alone or within an RNA chain) is predominantly transformed under oxidative stress conditions to 4-pyrimidinone riboside (H2U) and not to uridine. Due to the important biological functions and various biotechnological applications for sulfur-containing nucleic acids, we compared the thermodynamic stabilities of duplexes containing desulfured products with those of 2-thiouracil-modified RNA and DNA duplexes. Differential scanning calorimetry experiments and theoretical calculations demonstrate that upon 2-thiouracil desulfuration to 4-pyrimidinone, the preferred base pairing of S2U with adenosine is lost, with preferred base pairing with guanosine observed instead. Therefore, biological processes and in vitro assays in which oxidative desulfuration of 2-thiouracil-containing components occurs may be altered. Moreover, we propose that the H2U-G base pair is a suitable model for investigation of the preferred recognition of 3′-G-ending versus A-ending codons by tRNA wobble nucleosides, which may adopt a 4-pyrimidinone-type structural motif.

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Alignment of cationic donor-(pi-bridge)-acceptor molecules via metathesis with a self-assembled monolayer formed from sodium 3-mercapto-1-propanesulfonate results in ultra-thin rectifying Au-S-(CH2)3SO3-/A+-pi-D structures which exhibit optimum current ratios of 450 at +/-1 V for N-methyl-5-(4-dibutylaminobenzylidene)-5,6,7,8-tetrahydroisoquinolinium.