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Dye-sensitized solar cells were fabricated using eight azo dyes which have different positions and/or numbers of carboxyl and hydroxyl groups. The short-circuit current density, photoabsorbance, absorptance and quantum yield for dyes-to-TiO 2 electron injection were measured by photons ranging from 380 to 800 nm. X-ray and ultraviolet photoelectron spectroscopy of the photovoltaic electrodes were also conducted. The photon-to-current conversion efficiency of the cells was found to depend mostly on the relative position of the lowest unoccupied molecular orbital of the adsorbed dyes and partly by their concentration on the TiO 2 nanoparticles.

Some difficulties on a sampling of gaseous glyoxal using DNPH-silica cartridge were discussed, and an alternative sampling procedure was proposed. When glyoxal was sampled using the cartridge, it partially formed mono-hydrazone with various degrees, whereas it was quantitatively converted into its bis-hydrazone when sample gas was directly bubbled into a DNPH acidic solution. Additionally, glyoxal polymerized on the inner wall of the system during trapping to the silica cartridge. We found that the polymerization of glyoxal was effectively suppressed by dissolving glyoxal into methanol under reduced pressure; glyoxal in methanol readily reacted with DNPH in a hydrochloric acid solution and gave bis-hydrazone derivative, without any interference of methanol and any formation of mono-hydrazone derivative. When glyoxal was sampled by the proposed method, 102% of recovery was obtained, whereas it was reduced to 92.7% when the trapped glyoxal was dissolved into methanol under atmosphere.

Variously substituted 7-deazaguanines are of interest as inhibitors of GTP cyclohydrolase I, the first enzyme in the biosynthetic pathway leading to dihydrofolate and tetrahydrobiopterin. Methods are described for the synthesis of 7-deazaguanines substituted at positions 2, 6 and 9 (purine numbering) such that a wide diversity of compounds can be prepared. These methods supplement our previous work that established routes for the synthesis of 7- and 8-substituted 7-deazaguanines. Emphasis is placed on the properties of 2-thioalkyl pyrimidines as intermediates because they provide the basis for a traceless solid-state synthesis of purines, pteridines, and their analogues. Compounds prepared have been assessed in a primary screen for their ability to inhibit GTPCH I and 8-methyldeazaguanine has been shown to be significantly more potent than any inhibitor yet described. Several compounds appeared to undergo transformation by GTPCH I; with the aid of a model reaction, their behaviour can be interpreted in the context of the mechanism of the hydrolytic phase of GTPCH I.

Change in the emission spectrum of diatomic sulphur molecule derived from a sulphur containing compounds in a hydrogen flame is measured with a multi-channel spectral analyser. The emission appears with introducing a cool body to the flame. The intensity decreases with time, while temperature of the body increases. It is expected that the introduction of a cool body to a flame suppresses the pre-dissociation of the excited diatomic sulphur molecules by collisional de-activation, and the possibility is discussed. Since the ratio of the number of molecule in the ν′=1 to that in the ν′=0 increases with increasing the ambient temperature near the body, it is concluded that the excited sulphur molecules are deactivated by collision with other molecules to the lower vibrational levels in the excited state. But, it is also noted that the collisional deactivation occurs even without the cool body and the S2 emission from a CS2 flame is not enhanced with the cool body. It is concluded that the enhancement effect observed in a hydrogen flame is not attributed to the suppression on the pre-dissociation of the excited molecules.

In order to provide access to highly functionalised pterins as potential inhibitors of enzymes in the folate biosynthesis pathway, the Wittig reaction has been applied to 6-formylpterin (1b) and 6-formyl-7,7-dihydro-7,7-dimethylpterin (6). Dimethylaminomethylene and pivaloyl moieties were found to be suitable protecting groups for the 2-amino group of the pterins compatible with reactions of phosphoranes with a variety of substituents including esters, ethers and amides. In contrast, attempts to prepare extended side chains at C-6 using aldol and Claisen chemistry were unsuccessful.

Versatile syntheses of 7- and 8-substituted 7-deazaguanines including N-alkyl derivatives have been developed by identifying selective annulation reactions with 2,6-diaminopyrimidin-4(3H)-one as substrate and β-halocarbonyl compounds as electrophiles. A new synthesis of 8-substituted 7-deazaguanines using nitrosoalkenes as electrophiles is described. With some combinations of reactants, furo[2,3-d]pyrimidines are significant products in place of or in addition to the required 7-deazaguanines [pyrrolo[2,3-d]-pyrimidin-4(3H)-ones]. When 2,4-diamino-6-chloropyrimidine was used as a substrate, imidazopyrimidines were produced.

Several factors which affect S2 emission response from sulphur-containing amino acids are investigated by molecular emission cavity analysis. It is found that multi-peaked responses observed from the amino acids result from heterogeneous gasification of the sample rather than formation of non-volatile compounds. A portion of the sample in a cavity is rapidly gasified by contact with flame gases and the others are slowly and thermally decomposed with temperature rise of the cavity. Thus, sample gasification processes are mainly discussed on the basis of several effects on the emission response, such as sample location within the cavity, addition of acids or bases, cavity temperature and flame composition. It is suggested that the amphoteric property of amino acids suppresses the rapid gasification process by contact with flame gases. Temporary condensed water on the cavity surface on introduction into a flame significantly affects the emission response from the amino acids and a mechanism for the effect is discussed.

Versatile syntheses of 7- and 8-substituted 7-deazaguanines including N-alkyl derivatives have been developed by identifying selective annulation reactions with 2,6-diaminopyrimidin-4(3H)-one as substrate and β-halocarbonyl compounds as electrophiles. A new synthesis of 8-substituted 7-deazaguanines using nitrosoalkenes as electrophiles is described. With some combinations of reactants, furo[2,3-d]pyrimidines are significant products in place of or in addition to the required 7-deazaguanines [pyrrolo[2,3-d]-pyrimidin-4(3H)-ones]. When 2,4-diamino-6-chloropyrimidine was used as a substrate, imidazopyrimidines were produced.

In order to provide access to highly functionalised pterins as potential inhibitors of enzymes in the folate biosynthesis pathway, the Wittig reaction has been applied to 6-formylpterin (1b) and 6-formyl-7,7-dihydro-7,7-dimethylpterin (6). Dimethylaminomethylene and pivaloyl moieties were found to be suitable protecting groups for the 2-amino group of the pterins compatible with reactions of phosphoranes with a variety of substituents including esters, ethers and amides. In contrast, attempts to prepare extended side chains at C-6 using aldol and Claisen chemistry were unsuccessful.

Alkali metal salts present in distilled water as impurities change the surface of a silica cavity from smooth to rough and groovy surface. The multi-peaked responses observed with a new cavity change into a single peak when the cavity is treated with alkali metal salts compounds. It is concluded that the effect of the alkali metal salt-treated cavity is mainly attributable to the roughness of the surface; the peak splitting is cuased by aggregate formation and the roughness of the cavity surface enhances good dispersion and volatility of samples and suppresses peak splitting.

The increasing appearance of drug resistant bacteria (1) and the need for more selective agrochemicals propagates the quest for new biologically active agents. Many successful antibacterial drugs and some herbicides interfere with folate metabolism either through inhibiting folate biosynthesis or dihydrofolate reductase and thymidylate synthase (2, 3). The enzymes involved in folate biosynthesis are particularly attractive targets because mammals lack the ability for de novo synthesis of pteridine cofactors. Consequently, the inhibition of the relevant biosynthetic enzymes is likely to be selective for the infective agent, weed or insect. Two such enzymes are GTP cyclohydrolase I (4) and 7,8-dihydroneopterin aldolase (5); the former catalyses the conversion of GTP into dihydroneopterin triphosphate, the latter catalyses the transformation of dihydroneopterin into 6-hydroxymethyl-7,8-dihydropterin.

The pKa values of unsubstituted and substituted alkylphosphonic acids in aqueous solution were found to have a good linear correlation with the electron densities of the phosphorus atom of the corresponding phosphonic acids, which are calculated using the PM3 method. This enabled us to predict the pKa values of this class of compounds.

Pteridines unsubstituted in the 4-position have been prepared from pyrazine intermediates by a new, general method that permits synthesis of several pteridines which could not be made from pyrimidine intermediates.

3-Aminopyrazine-2-carboxamide was converted into 3-(dimethylaminomethyleneamino)pyrazine-2-carbonitrile (1b) with dimethylformamide and phosphoryl chloride. This amidine (1b) was produced by the same reagents also from 3-aminopyrazine-2-carbonitrile (1a), and by the action of dimethylamine on 3-ethoxymethyleneamino-pyrazine-2-carbonitrile (1c). Compound (1c) was made from 3-aminopyrazine-2-carbonitrile with triethyl orthoformate and acetic anhydride.Compounds (1a—c) were used in several new pteridine syntheses. The amidine (1b) gave 4-amino- and 4-methyl-amino-pteridine (2a and b) with ammonium and methylammonium acetate, respectively. Use of the 6-chloro-derivative of amidine (1b) similarly led to 6-chloro-4-amino- and -4-methylamino-pteridine. Pteridine-4-thione was obtained from the amidine (1b) and sodium hydrosulphide. The ethoxymethylene compound (1c) gave 4-aminopteridine with ammonia but 3,4-dihydro-4-imino-3-methylpteridine (3) with cold methylamine; this imine was easily isomerized to 4-methylaminopteridine by a Dimroth reaction, but proved stable as a solid. 3-Aminopyrazine-2-carbonitrile (1a) gave 4-aminopteridine with formamidine acetate at 140°.Some unusual pyrazine reactions were encountered. The ethoxymethylene compound (1c), after brief contact with ammonium acetate solution, gave 3-(aminomethyleneamino)pyrazine-2-carbonitrile (1e). The ethoxy-methylene compound (1c) was hydrolysed by the water in cold 95% ethanol to 3-formamidopyrazine-2-carbonitrile (1d), and condensed with hydrazine hydrate to give 3-hydrazinomethyleneaminopyrazine-2-carboxamidrazone (4b). 3-Aminopyrazine-2-carbonitrile (1a) similarly gave 3-aminopyrazine-2-carboxamidrazone (4a). 3-Aminopyrazine-2-carboxamide was quantitatively brominated to give 3-amino-6-bromopyrazine-2-carboxamide.

3-Aminopyrazine-2-carbaldehyde (Ia) could be prepared by oxidizing 2-amino-3-hydroxymethylpyrazine (Ib) but not by reducing 3-aminopyrazine-2-carbonitrile (Ic), N-(3-aminopyrazine-2-carbonyl)piperidine (Id), or S-methyl 3-aminopyrazine-2-thiocarboxylate (Ie)(the latter was made by hydrolysing methyl 3-aminopyrazine-2-thiocarboximidate). The aldehyde (Ia) was converted into 2-amino-3-dimethoxymethylpyrazine (IIIa), which was acylated to give the N-acetyl, ethoxycarbonyl, formyl, ethoxalyl, and trifluoroacetyl derivatives. These acetals were hydrolysed to 3-acetamido-, 3-ethoxycarbonylamino-, 3-formamido-, and 3-ethoxalylamino-pyrazine-2-carbaldehyde. These aldehydes were cyclized with ammonia to 2-methylpteridine (IVc), pteridin-2-one, pteridine, and ethyl pteridine-2-carboxylate. Pteridine was shown to form a double-bond adduct with ammonia. The analogous methylamine adduct (Vb)(5,6,7,8-tetrahydro-6,7-bismethylaminopteridine) was isolated and characterized. The electronic patterns influencing these reactions are discussed.Both mild acetylation of 2-amino-3-hydroxymethylpyrazine (Ib) and acid hydrolysis of 2-acetamido-3-acetoxymethylpyrazine gave 2-acetoxymethyl-3-aminopyrazine.Ionization constants and u.v., i.r., and n.m.r. spectra are recorded and discussed.