Studies in werner clathrates. Part 2. Structures of bis (isothiocyanato) tetra (4-phenylpyridine) nickel (II)· 4-dimethylsulphoxide,bis (isothiocyanato) tetra (3-methylpyridine) nickel (II)· chloroform and bis (isothiocyanato) tetra (3,5-dimethylpyridine) nickel (II)

The structures of Ni(NCS)₂(4-PhPy)₄·4DMSO and Ni(NCS)₂(3-MePy)₄·CHCl₃ have been elucidated. Movement of guest molecules through channels in the host structure was simulated by potential energy calculations. Ni(NCS)₂(3,5-diMePy)₄ does not form inclusion compounds. An intra-molecular potential energy study shows that theortho-hydrogens on the 3,5-dimethylpyridine ligands control the conformation of the molecule. The same result is obtained with the 4-methylpyridine ligand, which suggests that the extent of rotation of substituted pyridines about the Ni–N bounds is not a factor governing clathrate formation. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82030 (43 pages).     

Eptastigmine,nicotinamide and nicotinic acid determination using an inhibition enzyme sensor; application to pharmaceutical analysis

An enzyme inhibition biosensor, developed in our laboratory and previously used for the analysis of compounds with anticholinesterase activity (e.g. physostigmine, neostigmine, pyridostigmine nicotine and organophosphorus compounds) has now been tested for the analysis of another recently synthesized cholinesterase inhibitor, i.e. eptastigmine. In addition nicotinic acid and nicotinamide, although displaying weaker inhibition properties, were also tested in pharmaceutical products using the same inhibition enzyme sensor. The biosensor consisted of a hydrogen peroxide amperometric electrode coupled to a functionalised nylon membrane chemically bonding both the enzymes butyrylcholinesterase and choline oxidase; a butyrylcholine standard solution in glycine buffer acted as substrate. The response of the system to all the inhibitors considered was characterised completely and the analysis of several pharmaceutical formulations containing nicotinamide or nicotinic acid was also performed.     

Unusual nitration of substituted 7-amino-1,8-naphthyridine in the synthesis of compounds with antiplatelet activity

Several 1,8-naphthyridine derivatives have been diazotizated to obtain the corresponding hydroxy derivatives or mixture of hydroxy and hydroxy nitro derivatives. The respective amounts of hydroxy and hydroxy nitro derivatives depends on the nature of the substituents, on their position on the naphthyridine nucleus, on the amount of sodium nitrite and on the reaction temperature. A study of the electronic density of some molecules suggests a possible explanation of the effects induced by the nature of the substituents and of their position. Some of the compounds were tested for their ability to inhibit human platelet aggregation in vitro induced by arachidonic acid. Only compound 26 showed interesting antiplatelet activity.     

Molecular switches of fluorescence operating through metal centred redox couples

Three-component molecular systems (redox active subunit)-spacer-(light-emitting fragment) can operate as fluorescence switches, following the alternate addition of an oxidizing agent and a reducing agent (or the adjustment of the potential of the working electrode in an electrolysis experiment). The redox active subunit typically consists of a metal centred redox couple (M⁽ⁿ⁺¹⁾⁺/Mⁿ⁺), encircled by a macrocyclic receptor, and switching efficiency requires that one of the two oxidation states quenches the proximate fluorophore and the other does not. Four ON/OFF systems, based on either the Cu^II/Cu^I or Ni^III/Ni^II couple, will be discussed. The nature of the quenching process responsible for the OFF state, either electron transfer or energy transfer, is related to the length and to the flexibility-rigidity of the spacer.     

Adsorption of 3-pyrroline on Si(100) from first principles

The chemisorption of 3-pyrroline (C(4)H(7)N) on Si(100) is studied from first principles. Three different structures can be realized for which, depending on the temperature, the chemisorption process is facile (for two of them it is essentially barrierless); among these configurations the most favored one, from a thermodynamical point of view, is a dissociated structure obtained through an exothermic reaction characterized by the formation of a N-Si bond and a H-Si bond in which the H atom is detached from the molecule. Several other chemisorption structures are possible which, however, require overcoming a significant energy barrier and often breaking multiple bonds. A number of reaction paths going from one stable structure to another have been investigated. We have also generated, for the two basic adsorption structures, theoretical scanning tunneling microscopy images which could facilitate the interpretation of experimental measurements, and we propose a possible reaction mechanism for nitrogen incorporation.     

Recent applications of sample preparation techniques in food analysis

Even with the emergence of advanced techniques of separation and identification, it is rarely possible to analyse food without manipulation. The traditional techniques for sample preparation are time consuming and require large amount of reagents, which are expensive, generate considerable waste, contaminate the sample and can enrich it for analytes. The more analytical techniques have become highly developed, the more has sample clean-up become important in order to fully take advantage of them. Due to the multiplicity of food matrices, it is not possible to use one sample preparation technique, so many methods have been proposed for meeting all the requirements. The newest variations of wet digestion, solvent and sorbent extraction and membrane separation are summarised and their most recent applications to food analysis are provided.     

Study of ruthenium(II) complexes with anticancer drugs as ligands. Design of metal-based phototherapeutic agents

The reaction of trans-[RuCl(2)(PPh(3))(3)] (Ph = C(6)H(5)) with 2-thio-1,3-pyrimidine (HTPYM) and 6-thiopurines (TPs) produced mainly crystalline solids that consist of cis,cis,trans-[Ru(PPh(3))(2)(N,S-TPYM)(2)] (1) and cis,cis,trans-[Ru(PPh(3))(2)(N(7),S-TPs)(2)]X(2) (X = Cl(-), CF(3)SO(3)(-)). In the case of TPs, other coordination isomers have never been isolated and reported. Instead, the mother liquor obtained after filtration of 1 produced red single crystals of trans,cis,cis-[Ru(PPh(3))(2)(N,S-TPYM)(2)].2H(3)O(+).2Cl(-) (2.2H(3)O(+).2Cl(-)). Selected ruthenium(II)-thiobase complexes were studied for their structural, reactivity, spectroscopic, redox, and cytotoxic properties. Single crystals of 1 contain thiopyrimidinato anions chelated to the metal center via N and S. The Ru[bond]N bonds are significantly elongated for 1 [2.122(2) and 2.167(2) A] with respect to 2 [2.063(3) A] because of the trans influence from PPh(3). The coordination pseudo-octahedron for 2 is significantly elongated at the apical sites (PPh(3) ligands). Solutions of cis,cis,trans isomers in air are stable for weeks, whereas those of 2 turn green within 24 h, in agreement with the respective redox potentials. cis,cis,trans- and trans,cis,cis-[Ru(PH(3))(2)(N,S-TPYM)(2)], as optimized through the DFT methods at the Becke3LYP level are in good agreement with experimental geometrical parameters (1 and 2), with cis,cis,trans being more stable than trans,cis,cis by 3.88 kcal. The trend is confirmed by molecular modeling based on semiempirical (ZINDO/1) and molecular mechanics (MM) methods. Cytotoxic activity measurements for cis,cis,trans-[Ru(PPh(3))(N-THZ)(N(7),S -H(2)TP)(2)]Cl(2) (4) (THZ = thiazole, H(2)TP = 6-thiopurine) and cis,cis,trans-[Ru(PPh(3))(2)(N(7),S-HTPR)2]Cl(2) (5) (HTPR = 6-thiopurine riboside) against ovarian cancer cells A2780/S gave IC(50) values of 17 +/- 1 and 29 +/- 9 microM, respectively. Furthermore, the spectral analysis of HTPYM, TPs, and their Ru(II) complexes in solution shows that intense absorptions occur in the UVA/vis region of light, whereas standard nucleobases absorb in the UVB region.     

Synthesis of new 1,2,3-triazolo[1,2-a]benzotriazole derivatives or substituted 2,3-benzo-1,3a,6,6a-tetraazapentalenes. II

This paper continues the synthesis of new 1,2,3-triazolo[1,2-a]benzotriazoles or 2,3-benzo-1,3a,6,6a-tetrazapentalenes to submit to biological assays. The derivatives were obtained by deoxycyclization reactions of appropriate nitrophenyl-1,2,3-triazole derivatives and by thermal decomposition of appropriate azidophenyl-1,2,3-triazoles (Schemes 1 and 2). Some attempts to extend these synthetic routes to the preparation of 1,2,4-triazolo[1,2-a]benzotriazoles (Scheme 3) and 1,2,3-triazolo[1,2-b]-4H-1,2,3-benzo-triazines (Scheme 4) completely failed.     

Synthesis of new pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidines and related heterocycles

The reaction between 5-amino-4-imino-1(2)-substituted-1(2)H-4,5-dihydropyrazolo[3,4-d]pyrimidines and several commercially available reactants afforded new heterocycles with a conserved pyrazolo[3,4-d]pyrimidine nucleus. The key intermediates employed proved to be suitable compounds by virtue of their two vicinal amino and imino groups that were used to obtain five, six and seven-membered rings.     

Use of solid-phase micro-extraction as a sampling technique in the determination of volatiles emitted by flowers,isolated flower parts and pollen

The volatiles emitted by fresh whole flowers or isolated flower parts of mandarin, Citrus deliciosa Ten. (Rutaceae), were sampled using solid-phase micro-extraction (SPME). This technique offers several advantages over dynamic headspace sampling techniques used in previous investigations. In particular, SPME requires smaller sample sizes and very short sampling times, which can minimize the formation of artifacts due to damage to the plant, and contaminations or loss of compounds. This was especially applicable to the collection of volatiles from pollen.