Solvent- and environment-dependent fluorescence of modified nucleobases

Fluorescent nucleosides with modified nucleobases are useful tools for detecting nucleic acids and probing their structures and functions. Nucleobases are suitable for modification because 1) intrinsically light-absorbing nucleobases can be converted to fluorescent chromophores by simple chemical modification, 2) attaching substituents to nucleobases at appropriately selected positions does not inhibit base pairing or duplex formation, and 3) duplex formation and protein interactions affect the environment of nucleobases, causing changes in their fluorescence intensities and/or wavelengths. This review summarizes recent fluorescent nucleosides and their photophysical properties, such as absorption wavelength, emission wavelength, and fluorescence quantum yield together with their solvent dependency.     

On the error term in the mean square formula for the Riemann zeta-function in the critical strip

For 1/2<<1 fixed, letE (T) denote the error term in the asymptotic formula for . We obtain some new bounds forE (T), and an _-result which is the analogue of the strongest _-result in the classical Dirichlet divisor problem.     

Synthesis and hybridization properties of oligodeoxynucleotides incorporating 2-N-carbamoylguanine derivatives as guanine analogs

2-N-Carbamoyldeoxyguanosine and its derivatives were synthesized and incorporated into ODNs. The T_m analyses revealed higher selective base recognition ability of 2-N-carbamoylguanine than that of guanine. The new guanine analog must be useful for the development of functional oligodeoxynucleotides capable of precise base recognition.     

Formation of Tetrahydrofuran Derivatives and Acetonylation of Alkenes Using Carbon Radicals Derived from Manganese(III) Oxidation of Diketene

Oxidation of a mixture of diketene and a 1,1-diarylethene 1 with manganese(III) acetate dihydrate gave an equilibrium mixture of 5-hydroxy-2-pentanone 2 and a tetrahydrofuran-2-ol, which was subsequently dehydrated in glacial acetic acid to yield 4-penten-2-one 4 in good yield. A similar reaction in the presence of alcohols or amines afforded 2-alkoxy-2-methyltetrahydrofurans 5 or 3-acetyl-2-aminodihydrofurans 9 in moderate yields. Diketene reacted with manganese(III) acetate in the presence of nucleophiles, such as water and alcohols, to give a mixture of unconjugated manganese(III) enolate A and conjugated manganese(III) enolate B. Major products 4 and 5 were formed by the oxidation of the conjugated manganese(III) enolate B. Tetrahydrofurylideneacetates 3 and 7 derived from the unstable unconjugated enolate A were also obtained as minor products. The reaction pathways are discussed.     

Chemically stabilized phenylboranylidene groups having a dimethoxytrityl group as a colorimetrically detectable protecting group designed for cis-1,2-diol functions of ribonucleosides in the solid-phase synthesis of m2(2,2)G5'ppT

To not only improve the inherently poor stability of the phenylboranylidene group as a protecting group of the 2',3'-cis-diol function of ribonucleosides but also introduce a colorimetrically detectable function into its mother structure, various 2-[(dialkylamino)methyl]phenylboronic acid derivatives having a [(4,4'-dimethoxytrityl)oxy]methyl group were synthesized. The reaction of uridine with these substituted phenylboronic acid derivatives gave the corresponding 2',3'-O-phenylboranylideneuridine derivatives. The stability of these phenylboranylidene groups was examined. As a result, it was shown that the steric hindrance around the amino group greatly influenced the stability of the 2-substituted phenylboranylidene groups. The 2-aminomethyl-5-[[(4,4'-dimethoxytrityl)oxy]methyl]phenylboranylidene group was the most stable. Its 2-dimethylamino counterpart, the 2-[(dimethylamino)methyl]-5-[[(4,4'-dimethoxytrityl)oxy]methyl]phenylboranylidene group, was the second most stable. When the most and second stable protecting groups were applied to the synthesis of m(2)(2,2)G(5)(')ppT on controlled pore glass, the second stable protecting group showed the best result. The use of this DMTr-containing protecting group enabled us to estimate colorimetrically the amount of the m(2)(2,2)G residue that was incorporated into the reactive site of the pT-loaded CPG resin.     

O‐Triorganosilyl Carbamoselenoates – Synthesis and Reactions

A series of O‐triorganosilyl carbamoselenoates were isolated in good yields from the reaction of sodium or potassium carbamoselenoates with triorganosilyl chlorides. The O‐silyl carbamoselenoates readily reacted with RbF and CsF and with organo‐germanium, ‐tin, and ‐lead halides and gave the corresponding heavy alkali metal and Se‐substituted Group 14 organometal and carbamoselenoates in moderate to good yields.     

Reaction of ammonium sulphate with aluminium oxide

The reaction between ammonium sulphate with aluminium oxide was studied. It was confirmed by X-ray diffraction and chemical analysis that three intermediate reaction products, (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ and Al₂(SO₄)₃, are formed. The thermal decompositions of these three compounds were carried out. It has been shown that the same rate law is valid for them. The activation energies for (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ and Al₂(SO₄)₃ are 95.9, 177.9 and 291.0 kj/mol, respectively.

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Zusammenfassung Die Reaktion von Ammoniumsulfat mit Aluminiumoxid wurde untersucht. Durch Röntgendiffraktion und chemische Analyse wurde bestätigt, daß drei Zwischenprodukte (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ und Al₂(SO₄)₃ gebildet werden. Die thermische Zersetzung der drei Verbindungen wurde durchgeführt. Es wurde gezeigt, daß für alle drei dasselbe Geschwindigkeitsgesetz Gültigkeit hat. Die Aktivierungsenergien für (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ und Al₂(SO₄)₃ sind 95.9, 177.9 und 291.0 kJ/Mol.

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. - : (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ Al₂(SO₄)₃. , , . (NH₄)₃Al(SO₄)₃, NH₄Al(SO₄)₂ Al₂(SO₄)₃, , 95.9; 177.9 291.0 . ^–1.

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The authors are grateful to Dr. H. Osada and Mr. H. Nakamura, Department of Environmental Engineering, Kyushu Institute of Technology, for their helpful discussions.     

Electro-optic effects of colloidal crystals of polymer-modified silica spheres immobilized with gelator

Electro-optic responses of colloidal crystals consist of poly(maleic anhydride-co-styrene)-modified silica spheres (P(MA-ST)/SiO₂) in acetonitrile and the crystals immobilized with a gelator, N-benzyloxycarbonyl-L-isoleucilaminooctadecane (Z-L-Ile-C-18), are studied by reflected-light intensity measurements and time-resolved reflection spectroscopy. Application of an alternating electric field deforms P(MA-ST)/SiO₂ crystal lattices reversibly. The response waveforms from the crystals are dependent on the frequency and strength of the applied electric field; similar dependencies have been qualitatively observed for the colloidal crystals consisting of polystyrene or silica spheres in aqueous media in our previous studies. Both gelated and ungelated P(MA-ST)/SiO₂ crystals change the reflection intensity, however, the amplitude is larger for the latter. The small response for the gelated P(MA-ST)/SiO₂ crystals is attributed to the higher elastic modulus (G). The G value of the gelated P(MA-ST)/SiO₂ crystals in acetonitrile is estimated from the change in the inter-sphere distance to be 8.0 Pa, which is about 2.3 and 2.4 times larger than that for ungelated P(MA-ST)/SiO₂ crystals in acetonitrile and colloidal silica crystals in aqueous media, respectively.     

STRUCTURAL PHASE TRANSITION OF ALIPHATIC NYLONS VIEWED FROM THE WAXD/SAXS AND VIBRATIONAL SPECTRAL MEASUREMENTS AND MOLECULAR DYNAMICS CALCULATION

The crystalline phase transition of aliphatic nylon 10/10 has been investigated on the basis of the simultaneous measurement of wide-angle and small-angle X-ray scatterings, the infrared spectral measurement and the molecular dynamics calculation. An interpretation of infrared spectra taken for a series of nylon samples and the corresponding model compounds was successfully made, allowing us to assign the infrared bands of the planar-zigzag methylene segments reasonably. As a result the methylene segmental parts of molecular chains were found to experience an order-to-disorder transition in the Brill transition region, where the intermolecular hydrogen bonds are kept alive although the bond strength becomes weaker at higher temperature. The small-angle X-ray scattering data revealed a slight change in lamellar stacking mode in the transition region. The crystal structure has been found to change more remarkably in the temperature region immediately below the melting point, where the conformationally disordered chains experienced drastic rotational and translational motions without any constraints by hydrogen bonds, and the lamellar thickness increased largely along the chain axis. These experimental results were reasonably reproduced by the molecular dynamics calculation performed at the various temperatures.     

A new strategy for the synthesis of oligodeoxynucleotides directed towards perfect O-selective internucleotidic bond formation without base protection

Deoxyadenosine and deoxycytidine have nucleophilic amino groups so that the undesired N-phosphitylation of these amino groups occurred in the previous phosphoramidite methods without base protection. We report that the N-phosphitylation could be considerably suppressed in our new HOBt-mediated coupling strategy via phosphite intermediates as reactive species. Thus, 99.7-99.9% O-selective internucleotidic bond formation was achieved.