Characteristics of the Watson-Crick type hydrogen-bonded DNA base pairs: An ab initio molecular orbital study

Characteristics of the Watson-Crick-type hydrogen-bonded base pairs, thymine-adenine and cytosineguanine, are presented. These were established using an ab initio molecular orbital method. Base–base interactions are revealed to have dominant roles in the structures of nucleic acids and also in their functions. The most stable conformations in Watson-Crick-type base pairs are almost in accord with the structure observed in fiber X-ray diffraction study. Explanations are given of the origin of the sequencedependent local structures which differ from one base pair to the next, as observed in single-crystal X-ray analyses. In the case of the thymine-adenine base pair, it is shown that various geometrical parameters having almost the same stability are available. According to the propeller twist, the instability is not large enough for a base pair to be twisted readily.     

Cooperativity in chiroptical sensing with dendritic zinc porphyrins

Zinc porphyrin-appended dendrimers, 12PZn, 18PZn, 24PZn, and 36PZn, containing 12, 18, 24, and 36 zinc porphyrin units, respectively, were synthesized using zinc porphyrin dyad (2PZn) and triad (3PZn) as precursors. Although these dye-functionalized dendrimers all serve as chiroptical sensors for an asymmetric bipyridine (RR- and SS-Py2), the sensing capability is highly dependent on the structure of the dendritic scaffold. 2PZn, which is chiroptically silent toward Py2, turns cooperative and displays a large ICD (induced circular dichroism) response in the visible region when incorporated into 12PZn. Judging from the extents of contribution of each zinc porphyrin unit to the CD amplitudes ([Deltaepsilonmax]), the cooperativity in 24PZn (112 M-1 cm-1) is lower than that in 12PZn (196 M-1 cm-1) and much lower in dendron 4PZn (59 M-1 cm-1). In contrast, 3PZn, which is ICD-active toward Py2, hardly shows such an enhanced cooperativity when incorporated into 18PZn and 36PZn and dendron 6PZn, as well. Absorption spectroscopy suggests some unique conformational characteristics of the zinc porphyrin units in highly cooperative 12PZn.     

Spin‐Crossover Physical Gels: A Quick Thermoreversible Response Assisted by Dynamic Self‐Organization

Iron(II) triazolate coordination polymers with lipophilic sulfonate counterions with alkyl chains of different lengths have been synthesized. In hydrocarbon solvents, these polymers formed a physical gel and showed a thermoreversible spin transition upon the sol–gel phase transition. The formation of a hydrogen‐bonding network between the triazolate moieties and sulfonate ions, bridged by water molecules, was found to play an important role in the spin‐crossover event. The spin‐transition temperature was tuned over a wide range by adding a small amount of 1‐octanol, a scavenger for hydrogen‐bonding interactions. This additive was essential for the iron(II) species to adopt a low‐spin state. Compared with nongelling references in aromatic solvents, the spin‐crossover physical gels are characterized by their quick thermal response, which is due to a rapid restoration of the hydrogen‐bonding network, possibly because of a dynamic structural ordering through an enhanced lipophilic interaction of the self‐assembling components in hydrocarbon solvents.     

Screening for genetic mutations. A review

A point mutation of a nucleotide within a single gene can have a profound effect on a specific organ and/or the entire human body. DNA sequences associated with human diseases may differ from the corresponding normal sequences by single nucleotide mutations or by large alterations such as deletions, insertions, duplications, or translocations of DNA segments or entire chromosomes. As a result of the heterogeneity of DNA alterations and genetic mutations, various screening approaches are required to detect these alterations. However, methods which facilitate the detection of large mutations in the genome are typically insensitive to point mutations, whereas methods which detect point mutations are not appropriate to detect large alterations within the genome. Since there is no single perfect method to screen for unknown mutations, combinations of these methods may be necessary for accurate genetic diagnosis. The applications of polymerase chain reaction (PCR) technology to genomic screening have made rapid and accurate genetical diagnosis possible. Furthermore, recent developments in the technology of DNA microarrays have opened the way for high throughput sequence analysis by hybridization, which shows great potential in both molecular biology and medicine in the near future.     

Isolation and stereostructures of neocitreoviridinol and epineocitreoviridinol

Both neocitreoviridinol and epineocitreoviridinol with a 2,5-dioxabicyclo[2.2.1]-heptane ring have been isolated as new metabolises of $\text{Penicillium citreo-viride}$ B., and their stereostructures have also been elucidated on the basis of their spectral data coupled with molecular mechanics calculations. In addition, a promising synthetic intermediate for neocitreoviridinol has been made.     

Chemical analysis of semiconducting and metallic SmS thin films by X-ray photoelectron spectroscopy

We studied the chemical state of semiconducting and metallic SmS thin films by X-ray photoelectron spectroscopy (XPS), which were fabricated using dual-target magnetron sputtering by controlling the power applied to both metal and chalcogenide targets. On the basis of the valence band spectra obtained, it was suggested that semiconducting SmS has the final state corresponding to the Sm²⁺(4f⁶) configuration below the Fermi level, and metallic SmS has mainly the Sm³⁺(4f⁵) final state and a virtual band state in the Sm 5d band, contributing to the delocalization of 4f electrons and the emergence of metallic conductivity (4f⁶d⁰-4f⁵d¹). Thus, the spectra of our fabricated SmS thin films correspond to the band structure obtained from the dielectric property. This is the first work performed on the intrinsically prepared metallic SmS while the former works done for the sample transformed from semiconductor to metal phase by hard polishing.     

Brittle fracture and spinnability of viscous materials

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