The polymorphic nature of double-stranded DNA is well established. 1 A common feature of three major families of A-, B-, and Z-DNA duplexes is the antiparallel orientation of the constituent strands. Parallel-stranded DNA (ps-DNA) is a new family of DNA conformations experimentally confirmed in 1988, in which complementary strands have the same 5′-3′ orientation and form reverse Watson-Crick A-T base pairs. 2 Numerous thermodynamic studies revealed that the parallelstranded duplexes melt with considerably lower transition temperatures than the corresponding antiparallel duplexes. 2 Thus, 3′-p-3′-or 5′-p-5′-linked hairpins or relatively long oligomers such as 25-mers have been employed to investigate the thermodynamic behavior and reactivities of ps-DNA. 3 We reasoned that incorporation of 2′-deoxy-5-methylisocytosine (iC) or 2′-deoxyisoguanine (iG) as a new artificial base would stabilize parallel-stranded duplexes by forming three hydrogen bonds with guanine and cytosine, respectively. 4 We now report herein that iC-and iG-containing oligomers can form a parallelstranded duplex of a comparable stability with a normal antiparallel duplex even at a decamer level.PM3 semiempirical calculations in the gas phase suggested that both iC-G (-12.0 kcal) and iG-C (-13.7 kcal) base pairs are more stable than a reverse Watson-Crick A-T base pair (-4.6 kcal) and should possess stability comparable with a Watson-Crick G-C base pair (-11.9 kcal) ( Figure 1). 5 Thus, iG-and iC-containing deoxydecanucleotides (ODN I-III) were synthesized according to the standard -cyanoethyl phosphoramidite chemistry on a DNA synthesizer (Table 1). 6 The -cyanoethyl phosphoramidites of protected iC and iG were prepared according to the reported procedure. 7 After standard deprotection with concentrated ammonia, the oligomers were purified by reverse phase HPLC. Concentration and composition of oligomers were determined by complete digestion of oligomers with snake venom phosphodiesterase and bacterial alkaline phosphatase to mononucleosides.In order to investigate duplex formation, UV spectra of the mixture of ODN I and 5′-d(ACGTGCCTGA)-3′, which can form full-matched base pairs when aligned in a parallel orientation, were examined at various temperatures. As shown in Figure 2a, the mixture exhibited a thermally induced hyperchromicity. The 1:1 stoichiometry for complex formation of each strand was confirmed by UV mixing curve experiments. 8 Figure 2b shows a thermal denaturation profile of ODN I and 5′-d(ACGTGCCTGA)-3′ (p-1) together with p-2 and p-3, showing a cooperative UV melting behavior from base-stacked ps duplex to a single strand. A further indication for the ps-DNA duplex was obtained from CD spectrum of 1:1 mixture of ODN I and 5′-d(ACGTGCCTGA)-3′ as shown in Figure 2c. In accord with the previous observation, 2,3 the CD of p-1 showed a typical negative maximum dichroism near 260 nm, very similar to that observed for antiparallel duplexex.In order to investigate the recognition ability of iC-and iGcontaining oligomers toward single...

Three novel macrocyclic diterpepoids, 4,7-oxycyAbstract: The total synthesis of ethyl 3-carboline-1-propionate has been described and its ability to bind toward benzodiazepine and GABA receptors has been studied. It has been suggested that j3-carboline-1-propionic acid is the true natural product, its ester derivatives are only artefacts of the isolation procedure.

No abstract

No abstract

The system identification is regarded as the most basic technique for structural health monitoring to evaluate structural integrity. Although many system identification techniques that can extract mode information (e.g. mode frequency and mode shape) have been proposed so far, it is also desired to identify physical parameters (e.g. stiffness and damping). As for high-rise buildings subjected to long-period ground motions, the system identification for evaluating only the shear stiffness based on a shear model does not seem to be an appropriate solution to the system identification problem due to the influence of overall bending response. In this paper, a system identification algorithm using a shear-bending model is developed to identify both shear and bending stiffnesses. In this algorithm, an ARX (Auto-Regressive eXogenous) model corresponding to the transfer function for interstory accelerations is applied for identifying physical parameters. For the experimental verification of the proposed system identification framework, vibration tests for a 3-story steel mini-structure are conducted. The test structure is specifically designed to measure horizontal accelerations including both shear and bending responses. In order to obtain reliable results, system identification theories for two different inputs are investigated; (a) base input motion by a modal shaker, (b) unknown forced input on the top floor.