1H-NMR-spektroskopische konformationsanalyse von halogenierten thymidinabkömmlingen: I. konformation von thymidin, 3',5'-didesoxy-3'-chlor-5'-fluor-thymidin und 3', 5'-didesoxy-3',5'-difluor-thymidin

An improved method is given for determining the conformation of furanoid nucleosides by ¹H-NMR-spectra analysis using halogen-substituted thymidines as examples. The state of the three equilibria - ring-puckering, rotation about the C₄-C₅- bond and about the glycosidic bond - are influenced by the halogen substituents. Compared with thymidine the 3'-chlorine substituent shifts the furanose conformation to conformers, where the 3'-chlorine substituent is equatorial. The 5'-fluorine substituent increases the contribution of the G-G-rotamer and the ratio of syn-conformation. The relationships between the conformers in the pseudo-rotatory cycle and the population of the C_4'-C_5' rotamers are discussed.     

Microbiological transformations—XII: Microbiological reduction of racemic 1-(2',2',3'-trimethyl-cyclopent-3'-en-1'-yl)propan-2-one and 1-(2',2',3'-trimethyl-cyclopent-3'-en-1'-yl)butan-2-one by rhodotorula mucilaginosa

The microbiological reduction of (±)-l-(2',2',3'-trimethylcyclopent-3'-en-l'-yl)-propan-2-one (4) and (±)-1-(2',2',3'-trimethylcyclopent-3'-en-l'-yl)-butan-2-one (5) by Rhodotorula mucilaginosa was investigated. Both enantiomers of 4 are reduced stereospecifically to corresponding alcohols; (+)-(2S, l'R)-(2',2',3'-trimethylcyclopent-3'-en-l'-yl)-propan-2-ol (6) and (-)-(2S,l'S)-(2',2',3'-trimethylcyclopent-3'-en-l'-yl)-propan-2-ol (7). p ]The substrate selectivity in the reduction of 5 was observed: R enantiomer of 5 yields stereospecifically (+)-(2S,1'R)-(2',2',3'-trimethylcyclopent-3'-en-l'-yl)-butan-2-ol (8) while S(-)5 remains unchanged.     

Spectrophotometric determination of cobalt(II) with 2,2'-dipyridyl-2-pyrimidylhydrazone

Some metallochromic indicators are examined for ion-pair formation with alkaloids, cationic surfactants and some pharmaceutical products. Eriochrome red B is recommended for the determination of quinine at pH 3.6 with extraction into chloroform and measurement at 475 nm.     

Spectrophotometric determination of zirconium with pyridoxal salicyloylhydrazone

The synthesis, characteristics and analytical applications of pyridoxal salicyloylhydrazone are described. The reaction between zirconium(IV) and this reagent was studied spectrophotometrically. A yellow 1:2 Zr:L complex (? = 2.4 × 10⁴ l mol^-1 cm^-1 at 395 nm) is formed from pH 3.5 to 5 M hydrochloric acid in an aqueous solution containing 2% dimethylformamide and 28% ethanol. The method is highly selective and is applied to the determination of zirconium in a steel and a nickel—chromium alloy.     

Spectrophotometric determination of zirconium using robinetin

Summary The complex formation between zirconium and robinetin has been spectrophotometrically investigated and made use of in the determination of zirconium. The complex has been found to contain zirconium and the flavonol in the molar ratio of 12. It obeys Beer's law up to 3.0 ppm of Zr and its stability constant has been calculated to be l.5×10⁹. The reaction is quite sensitive and selective at high concentrations of hydrochloric acid (sensitivity 0.0045 g/cm²).

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Zusammenfassung Zur spektrophotometrischen Bestimmung von Zirkonium wird als Reagens Robinetin empfohlen, das mit Zr einen Komplex im Verhältnis 12 (ZrRobinetin) bildet. Die Stabilitätskonstante wurde zu 1,5 · 10⁹ bestimmt. Das Beersche Gesetz wird bis zu 3,0 ppm Zr befolgt. In stark Salzsauren Lösungen ist die Reaktion empfindlich und selektiv (Empfindlichkeit: 0,0045 g Zr/cm²).

     

2'-deoxyribonucleoside 3'-aryl phosphoranilidates: Key intermediates in the stereospecific synthesis of 2'-deoxyribonucleoside cyclic 3',5'-phosphorothioates and dinucleoside(3'→5')-phosphoranilidates

Phosphorylation of the 5'-O-monomethoxytrityl-2'-deoxyribonucleosides by means of aryl phosphoranilidochloridates gives the diastereoisomers of 5'-O-monomethoxytrityl-2'-deoxyribonucleoside 3'-aryl phosphoranilidates. Their separation can be performed by means of chromatographic techniques. They can be further converted to the 2'-deoxyribonucleoside cyclic 3'-5' phosphoranilidates, which are intermediates in the stereospecific synthesis of 2'-deoxyribonucleoside cyclic (3'-5')phosphorothioates of known absolute configuration at phosphorus.     

以2,2′,4,4′-四羟基二苯甲酮为配体分光光度法测定痕量镍

以2,2′,4,4′-四羟基二苯甲酮(BP-2)为配体,采用分光光度法测定痕量Ni 2+。在pH9.80的硼酸-氯化钾-氢氧化钠缓冲溶液中,BP-2与Ni 2+在60℃下反应20min后,生成络合物,其最大吸收波长在434nm,摩尔吸光率为2.025×104L·mol-1·cm-1。Ni 2+的质量浓度在0.20~23.0mg·L-1范围内与吸光度呈线性关系,检出限(3S/N)为0.17 mg·L-1。加标回收率在99.3%~103%之间,测定值的相对标准偏差(n=6)在1.1%之内。采用此方法测定含Ni 2+废液中的Ni 2+,结果与原子吸收光谱法的测定结果的相对误差为-0.98%。     

Heterocyclic N-glycosyl derivatives—XIX : Glycal nucleosides. their relationship with 2',3'-unsaturated nucleosides and their utilization in the synthesis of 1',3'-two base nucleosides

The acid catalized reaction of tri-0-acetyl-D-glucal with benzotriazole or 6-methylthiopurine in acetonitrile gave a mixture of 1',2'- and 2',3'-unsaturated nucleosides, the former predominating. The relationship between these unsaturated nucleosides is studied and an allylic carbonium ion is proposed as an intermediate for these isomerizations. The acid catalized reaction of 1',2'-unsaturated nucleosides with more benzotriazole or 6-methylthiopurine gave 1',3'-two base nucleosides. The conformation and anomeric configuration of the N-glycosyl compounds obtained were assigned by NMR spectroscopy.     

An efficient synthesis of certain 5-substituted-2'-deoxyuridine 3',5'-cyclic monophosphate p-o-alkyl(aralkyl) esters. The crystal and molecular structure of 5-IODO-2'-deoxyuridine 3',5'-cyclic monophosphate p-o-methyl ester with axial methoxy group

Some 5-alkyl- and 5-halogeno-2'-deoxyuridine 3',5'-cyclic mono- phosphate P-O-alkyl(aralkyl) esters have been prepared from the silver salts of the parent cyclic monophosphates and alkyl(aralkyl) iodides. The diastereomeric phosphotriesters have been characterized by spectroscopic methods. The crystal and molecular structure of 5-iodo-2'-deoxyuridine 3',5'-cyclic monophosphate P-O-methyl ester with axial methoxy group has been determined. We failed to obtain the desired triesters from the reactions of the cAMP silver salt with alkyl iodides, contrary to previous claims in the literature.     

Spectrophotometric determination of zirconium in steels with xylenol orange

Zirconium (0.005–0.25%) is determined after acid dissolution of the steel, and fusion of insoluble matter with sodium carbonate and sodium hydrogensulphate. Niobium and other interfering ions are removed by mercury cathode electrolysis. Residual small amounts of iron(III) are masked with ascorbic acid.     

Spectrophotometric determination of niobium in zirconium with 4-(2-pyridylazo)resorcinol

The direct spectrophotometric determination of niobium in zirconium alloys with 4-(2-pyridylazo)resorcinol is described. Samples are dissolved in hydrofluoricsulphuric acid mixture and the colour developed without the removal of fluoride. In the presence of EDTA only Co²⁺, Ta⁵⁺ and V⁵⁺ cause serious interference. The molar absorptivity is 3.67 .10⁴ in the presence of 1 /smg of zirconium, and Beer's law is obeyed up to 1.0μg Nb/ml. The method can be applied to zirconium alloys containing as little as 0.005% niobium.     

Spectrophotometric determination of trace copper with a Cu-diethyldithiocarbamate-beta-cyclodextrin colour system

A simple, selective and accurate spectrophotometric method for determination of trace copper with diethyldithiocarbamate(DDTC) in the presence of beta-cyclodextrin(beta-CD) in ammonia media has been developed. The apparent molar absorptivity of Cu(II)-DDTC-beta-CD inclusion complex is 1.3 x 10(4) 1 . mole(-1) . cm(-1) at 436 nm, and Beer's law is obeyed for copper in the range 0-150 mug/25 ml. The detection limit is 4.38 x 10(-7)M(S/N = 3). The proposed method has been successfully applied to the determination of copper in aluminium alloys, soils, millet, wheat flour, herbs, vegetables and some traditional Chinese herbal medicines with satisfactory results.     

Spectrophotometric determination of total vicinal diketones with isoniazide and a zirconium salt

Summary A method has been worked out for the spectrophotometric determination of total vicinal diketones.It is based on the distillation of diacetyl and/or 2,3-pentanedione, the subsequent condensation with isoniazide (yielding the corresponding hydrazones), the complexation with zirconium(IV) and the photometric measurement of the resulting yellow complexes at 410 nm. The two reactions were studied separately. Variables such as pH, heating time, and excess reactives are discussed. The method may be used for the determination of these compounds in foods.     

Spectrophotometric determination of zirconium with 9-methyl-2,3,7-trihydroxy-6-fluorone

Summary 9-Methyl-2.3.7-trihydroxy-6-fluorone has been used as a new colorimetric reagent for zirconium. The rose-red complex shows maximum absorption, against the reagent blank, at 500 nm and obeys Beer's law from 0.1 to 2.5 ppm. The optimum concentration range is from 0.66 to 2.5 ppm, where the per cent relative analysis error is 2.96. The composition of the complex, obtained from Job's method, indicates that the complex in solution contains the metal and the reagent in a ratio of 11. The instability constant of the complex is 1.07 · 10^–6.