1,2,3-Triazolo[4,5-d]-1,2,4-triazolo[4,3-b]pyridazines

Some new 1,2,3-triazolo[4,5-d]-1,2,4-triazolo[4,3-b]pyridazines were prepared starting from the corresponding 1,2,3-triazolo[4,5-d]pyridazines via the formation of the 1,2,4-triazole ring, by condensation of an appropriate monocarbon fragment with the 4-hydrazino substituent and the nitrogen atom in the 5 position of the heterocycle. Condensation of 4-phenylhydrazino substituted derivatives with formic acid gave zwitterionic compounds.     

C.I. Calculations on the lower transitions in the terphenyl and quaterphenyl di-valent ions

Energies and transition dipole moments for the lower electronic transitions in the terphenyl and quaterphenyl di-valent ions have been calculated starting from the Pople SCF MO's for the ground state ions. The configuration interaction included about one-hundred singly and doubly excited configurations. The results of the calculations for the lower allowed electronic transitions are in very satisfactory agreement with the experimental spectra.     

Multimodal open-tubular capillary electrochromatographic analysis of amines and peptides

This study describes a comparison of different modes of open-tubular electrochromatography (OTCEC) in bare and etched capillaries. To carry out the investigation, the separation of impurities of two synthetic peptides and the separation of a mixture of five heterocyclic aromatic amines were studied. Three different types of stationary phase were evaluated: (i) fluorosurfactants (anionic and zwitterionic) adsorbed in the inner wall of the capillary (electrochromatography with dynamically modified stationary phases (DMS)CEC); (ii) physically adsorbed polymers (DMA-SO(3-) and DMA-N(+)(CH(3))(3)) and (iii) chemically modified capillaries (C(18), cholesteryl 10-undecanoate and diol). The results confirm that electrochromatography can be a viable alternative to capillary electrophoresis (CE) and liquid chromatography, more established separation techniques. It is possible to differentiate some minor species for the synthetic peptides that cannot be resolved by CE or high-performance liquid chromatography (HPLC). Moreover the separation of the amine mixture depends strongly on the stationary phase used.     

"Exact" surface free energies of iron surfaces using a modified embedded atom method potential and lambda integration

Previously a new universal lambda-integration path and associated methodology was developed for the calculation of "exact" surface and interfacial free energies of solids. Such a method is in principle applicable to any intermolecular potential function, including those based on ab initio methods, but in previous work the method was only tested using a relatively simple embedded atom method iron potential. In this present work we apply the new methodology to the more sophisticated and more accurate modified embedded atom method (MEAM) iron potential, where application of other free- energy methods would be extremely difficult due to the complex many-body nature of the potential. We demonstrate that the new technique simplifies the process of obtaining "exact" surface free energies by calculating the complete set of these properties for the low index surface faces of bcc and fcc solid iron structures. By combining these data with further calculations of liquid surface tensions we obtain the first complete set of exact surface free energies for the solid and liquid phases of a realistic MEAM model system. We compare these predictions to various experimental and theoretical results.     

Improved coupled-column liquid chromatographic method for the determination of glyphosate and aminomethylphosphonic acid residues in environmental waters

An existing method for the determination of glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) in water has been improved. It is based on precolumn derivatization with the fluorescent reagent 9-fluorenylmethylcloroformate (FMOC) followed by large-volume injection in a coupled-column LC system using fluorescence detection (LC-LC-FD). The derivatization step was slightly modified by changing parameters such as volume and/or concentration of sample and reagents to decrease the limits of quantification (LOQ) of glyphosate and AMPA to 0.1 microg/l. Additionally, the use of Amberlite IRA-900 for preconcentration of glyphosate, prior to the derivatization step, was investigated; the LOQ of glyphosate was lowered to 0.02 microg/l. Drinking, surface and ground water spiked with glyphosate and AMPA at 0.1-10 microg/l concentrations were analysed by the improved LC-LC-FD method. Recoveries were 87-106% with relative standard deviations lower than 8%. Drinking and ground water spiked with glyphosate at 0.02 and 0.1 microg/l were analysed after preconcentration on the anion-exchange resin with satisfactory recoveries (94-105%) and precision (better than 8%).     

Studies towards the total synthesis of contignasterol

The (17R,20S,22S,24S) C₂₀-C₂₉ segment of contignasterol has been stereoselectively prepared in 8 steps and 40% overall yield from (S)-carvone. Synthetic studies towards contignasterol's C/D ring functionalization/isomerization are also reported.     

Catalysts for low-temperature methanol synthesis. I. A study of the reduction process

A study of the reduction of CuO in a ternary oxide system (Cu:Zn:Al, atomic ratio 62:14:24) demonstrated that at lower temperatures it occurred in two stages, whereas at higher temperatures it was no longer possible to display the formation of Cu₂O. The rate of reduction of CuO was strongly reduced on decreasing the partial pressure of hydrogen, while the presence of CO₂ stabilized the Cu₂O, delaying the reduction to copper. On the basis of simpler systems it was possible to demonstrate the activating effect of Al₂O₃ and the delaying effect of ZnO on the reduction of CuO.     

New N6‐substituted 8‐alkyl‐2‐phenylmethylsulfanyl‐adenines. II

Title compounds bearing substituents on C(2), C(6) and C(8) were prepared from a newly synthesized pyrimidine derivative 11. The new pyrimidine 11 was generated from compound 2 through two different synthetic schemes. In one pathway, compound 2 was nitrosated, reduced and alkylated to produce com pounds 9 , 10 and 11 respectively (Scheme). In an alternate route using compound 2 as the starting material, a coupling reaction using the diazonium salt derived from p‐methylaniline afforded the azo derivative 7 , which was subsequently alkylated and reductively cleaved to form compounds 8 and 11 respectively (See Scheme). Compound 11 was annulated to the corresponding hypoxanthine derivatives 12–14 ; compounds 12 and 13 were chlorinated with phosphorus oxychloride, then reacted with amines to yield compound 17 and 20 respectively. Compounds 21 , 22 and 23 were obtained by oxidation of the corresponding sulfide as depicted in Scheme. Alkylation of the thiol function of 1 gave a mixture of 3 and 4. Compound 3 was chlo rinated to 5. Nitration of 5 resulted in electrophilic aromatic substitution of the aryl ring and concomitant oxidation of the sulfide to the sulfoxide, producing 6.     

Tele-substitution reactions in the naphthalene series : The behaviour of 1,4 - dimethyl - 2 - nitro - 3 - phenylsulphonyl - and 2,3 - bisphenylsulphonyl - 1,4 - dimethyl - naphthalene towards sodium arenethiolates and secondary aliphatic amines

1,4 - Dimethyl - 2 - nitro - 3 - phenylsulphonylnaphthalene (2) reacts with sodium benzenethiolate in DMSO at 120° to give 1 - methyl - 2 - nitro - 4 - phenylthiomethylnaphthalene (4) [tele-substitution product (TSP) of the phenylsulphonyl group] and 1,4 - dimethyl - 3 - phenylsulphonyl - 2 - phenylthionaphthalene (5) [normal substitution product (NSP) of the nitro group]. The analogous reactions of 2 with sodium 2,4,6- trimethylbenzenethiolate and of 2,3 - bisphenylsulphonyl -1,4 - dimethylnaphthalene (3) with sodium benzenethiolate or aliphatic amines give only TSPs of the phenylsulphonyl group. In the case of the reaction of 2 with aliphatic amines both the possible TSPs (tele-substitution of the phenylsulphonyl or of the nitro group) were isolated in 9:1 relative yield. All the data show that the phenylsulphonyl is a leaving group far better than the nitro in such tele-substitution processes. The mechanism previously proposed to account for the formation of TSPs from 1,4-dimethyl - 2,3 - dinitronaphthalene is strongly supported by the obtained results.     

2,4‐Diamino‐5‐(1‐naphthyl)‐3,5‐diaza‐1‐azoniaspiro[5.5]undeca‐1,3‐diene chloride

The title salt, C₁₈H₂₂N₅⁺·Cl^?, is a member of a new series of lipophilic 4,6‐di­amino spiro‐s‐triazines which are potent in­hib­itors of di­hydro­folate reductase. The protonated triazine ring deviates from planarity, whereas the cyclo­hexane ring adopts a chair conformation. A rather unusual hydrogen‐bonding scheme exists in the crystal. There is a centrosymmetric arrangement involving two amino groups and two triazine ring N atoms, with graph‐set R(8) and an N?N distance of 3.098 (3) Å, flanked by two additional R(8) systems, involving two amino groups, a triazine ring N atom and a Cl^? anion, with N?Cl distances in the range 3.179 (2)–3.278 (2) Å. Furthermore, the Cl^? anion, the protonated triazine ring N atom and an amino group form a hydrogen‐bonding system with graph‐set R(6).