Tuning the metal-to-metal charge transfer energy of cyano-bridged dinuclear complexes

The metal-to-metal charge transfer (MMCT) transitions of a series of Class II mixed valence dinuclear complexes bearing cyano bridging ligands may be varied systematically by variations to either the hexacyanometallate(II) donor or Co-III acceptor moieties. Specifically, the new dinuclear species trans-[(LCoNCFe)-Co-14S(CN)(5)](-) (L-14S = 6-methyl-1,11-diaza-4,8-dithia- cyclotetradecane-6-amine) and trans-[(LCoNCRu)-Co-14(CN)(5)]-(L-14 = 6-methyl-1,4,8,11-tetraazacyclotetradecane-6-amine) have been prepared and their spectroscopic and electrochemical properties are compared with the relative trans-[(LCoNCFe)-Co-14(CN)(5)](-). The crystal structures of Na{trans-[(LCoNCFe)-Co-14S(CN)(5)]}.51/2H(2)O.1/2EtOH, Na{trans-[(LCoNCRu)-Co-14(CN)(5)]}.3H(2)O and Na{trans-[(LCoNCRu)-Co-14(CN)(5)]}.8H(2)O are also reported. The ensuing changes to the MMCT energy have been examined within the framework of Hush theory, and it was found that the free energy change between the redox isomers was the dominant effect in altering the energy of the MMCT transition.

Phenolic acids and abscisic acid in Australian Eucalyptus honeys and their potential for floral authentication

Seven phenolic acids related to the botanical origins of nine monofloral Eucalyptus honeys from Australia, along with two abscisic isomers, have been analyzed. The mean content of total phenolic acids ranges from 2.14 mg/100 g honey of black box (Eucalyptus largiflorens) honey to 10.3 mg/100 g honey of bloodwood (Eucalyptus intermedia) honey, confirming an early finding that species-specific differences of phytochemical compositions occur quantitatively among these Eucalyptus honeys. A common profile of phenolic acids, comprising gallic, chlorogenic, coumaric and caffeic acids, can be found in all the Eucalyptus honeys, which could be floral markers for Australian Eucalyptus honeys. Thus, the analysis of phenolic acids could also be used as an objective method for the authentication of botanical origin of Eucalyptus honeys. Moreover, all the honey samples analyzed in this study contain gallic acid as the main phenolic acid, except for stringybox (Eucalyptus globoidia) honey which has ellagic acid as the main phenolic acid. This result indicates that the species-specific differences can also be found in the honey profiles of phenolic acids. Further-more, the analysis of abscisic acid in honey shows that the content of abscisic acid varies from 0.55 mg/100 g honey of black box honey to 4.68 mg/ 100 g honey of bloodwood honey, corresponding to the contents of phenolic acids measured in these honeys. These results have further revealed that the HPLC analysis of honey phytochemical constituents could be used individually and/or jointly for the authentication of the botanical origins of Australian Eucalyptus honeys. (C) 2003 Elsevier Ltd. All rights reserved.

The rearrangements of naphthyinitrenes: UV/Vis and IR spectra of azirines, cyclic ketenimines, and cyclic nitrile ylides

Ar matrix photolysis of 1- and 2-naphthyl azides 3 and 4 at 313 nm initially affords the singlet naphthyl nitrenes, (1)1 and (1)2. Relaxation to the corresponding lower energy, persistent triplet nitrenes (3)1 and (3)2 competes with cyclization to the azirines 15 and 18, which can also be formed photochemically from the triplet nitrenes. On prolonged irradiation, the azirines can be converted to the seven-membered cyclic ketenimines 10 and 13, respectively, as described earlier by Dunkin and Thomson. However, instead of the o-quinoid ketenimines 16 and 19, which are the expected primary ring-opening products of azirines 15 and 18, respectively, we observed their novel bond-shift isomers 17 and 20, which may be formally regarded as cyclic nitrile ylides. The existence of such ylidic heterocumulenes has been predicted previously, but this work provides the first experimental observation of such species. The factors which are responsible for the special stability of the ylidic species 17 and 20 are discussed.

Mesoionic 1,3-oxazinium olates. Rearrangement to acylketenes and 3-azabicyclo[3.1.1]heptanetriones

Metastable but isolable mesoionic 1,3-oxazinium 4-olates 9d-f undergo ring opening to acylketenes 10 at or near room temperature. The ketenes undergo intramolecular criss-cross [2 + 2] cycloaddition to afford 3-azabicyclo[3.1.1]heptanetriones 12. The structure of 12d was established by X-ray crystallography.

Energy profiles for ketene cyclizations. interconversion of 1,3-oxazin-6-ones, mesoionic 1,3-oxazinium olates and acylketenes, imidoylketenes, oxoketenimines, and cyclization products

The energy surface connecting oxazinium olates 9, several possible conformers of ketenes 10 and 11, and the final cyclization products 12, 13 and 14, as well as the isomeric 1,3-oxazine-6-ones 15, ring opening of the latter to N-acylimidoylketenes 16, and subsequent rearrangement of 16 to oxoketenimines 17, azetinones 18, and the cyclization products 19 and 20 are evaluated computationally at the B3LYP/6-31G* and B3LYP/6-311+G*//B3LYP/6-31G* levels. The cyclizations of ketenes to oxazinium olates 9 and oxazines 15 have the characteristics of pseudopericyclic reactions. Plots of the energy vs internal reaction coordinate for the cyclization of transoid acylketenes such as 10 to 9 (via TS1) and 16 to 15 (via TS7) feature two inflection points and indicate that the part of the energy surface above the lower inflection points describe internal rotation of the acyl function in the ketene moiety, and the part below this point describes the cyclization of the cisoid ketene to the planar mesoionic oxazinium olate 9 or oxazinone 15. The 1,3-shifts of the OR group that interconvert ketenes 16 and ketenimines 17 via four-membered cyclic transition states TS8 behave similarly, the first portion (from the ketenimine side) of the activation barrier being due largely to internal rotation of substituents, and the top part being due to the 1,3-shift proper.

Phenolic acids in Australian Melaleuca, Guioa, Lophostemon, Banksia and Helianthus honeys and their potential for floral authentication

Eight phenolic acids and two abscisic acid isomers in Australian honeys from five botanical species (Melaleuca, Guioa, Lophostemon, Banksia and Helianthus) have been analyzed in relation to their botanical origins. Total phenolic acids present in these honeys range from 2.13 mg/100 g sunflower (Helianthus annuus) honey to 12.11 mg/100 g tea tree (Melaleuca quinquenervia) honey, with amounts of individual acids being various. Tea tree honey shows a phenolic profile of gallic, ellagic, chlorogenic and coumaric acids, which is similar to the phenolic profile of an Australian Eucalyptus honey (bloodwood or Eucalyptus intermedia honey). The main difference between tea tree and bloodwood honeys is the contribution of chlorogenic acid to their total phenolic profiles. In Australian crow ash (Guioa semiglauca) honey, a characteristic phenolic profile mainly consisting of gallic acid and abscisic acid could be used as the floral marker. In brush box (Lophostemon conferta) honey, the phenolic profile, comprising mainly gallic acid and ellagic acid, could be used to differentiate this honey not only from the other Australian non-Eucalyptus honeys but also from a Eucalyptus honey (yellow box or Eucalyptus melliodora honey). However, this Eucalyptus honey could not be differentiated from brush box honey based only on their flavonoid profiles. Similarly, the phenolic profile of heath (Banksia ericifolia) honey, comprising mainly gallic acid, an unknown phenolic acid (Phl) and coumaric acid, could also be used to differentiate this honey from tea tree and bloodwood honeys, which have similar flavonoid profiles. Coumaric acid is a principal phenolic acid in Australian sunflower honey and it could thus be used together with gallic acid for the authentication. These results show that the HPLC analysis of phenolic acids and abscisic acids in Australian floral honeys Could assist the differentiation and authentication of the honeys. © 2005 Elsevier Ltd. All rights reserved.

Pressure and temperature effects on metal-to-metal charge transfer in cyano-bridged Co-III-Fe-II complexes

The effects of pressure and temperature on the energy (E-op) of the metal-to-metal charge transfer (MMCT, Fe-II --> Co-III) transition of the cyano-bridged complexes trans - [(LCoNCFe)-Co-14(CN)(5)](-) and cis-[(LCoNCFe)-Co-14(CN)(5)](-) (where L-14 = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) were examined. The changes in the redox potentials of the cobalt and iron metal centres with pressure and temperature were also examined and the results interpreted with Marcus Hush theory. The observed redox reaction volumes can mainly be accounted for in terms of localised electrostriction effects. The shifts in E-op due to both pressure and temperature were found to be less than the shifts in the energy difference (E degrees) between the Co-III-Fe-II and Co-II-Fe-III redox isomers. The pressure and temperature dependence of the reorganisational energy, as well as contributions arising from the different spin states of Co-II, are discussed in order to account for this trend. To study the effect of pressure on Co-III electronic absorption bands, a new cyano-bridged complex, trans - [(LCoNCCo)-Co-14(CN)(5)], was prepared and characterised spectroscopically and structurally. X-Ray crystallography revealed this complex to be isostructural with trans -[(LCoNCFe)-Co-14(CN)(5)] center dot 5H(2)O.

Visualizing levels of osteoblast differentiation by a two-color promoter-GFP strategy: Type I collagen-GFPcyan and osteocalcin-GFPtpz

A 3.9 kb DNA fragment of human osteocalcin promoter and 3.6 kb DNA fragment of the rat collagen type1a1 promoter linked with visually distinguishable GFP isomers, topaz and cyan, were used for multiplex analysis of osteoblast lineage progression. Three patterns of dual transgene, expression can be appreciated in primary bone cell cultures derived from the transgenic mice and by histology of their corresponding bones. Our data support the interpretation that strong pOBCol3.6GFPcyan alone is found in newly formed osteoblasts, while strong pOBCol3.6GFPcyan and hOC-GFPtpz are present in osteoblasts actively making a new matrix. Osteoblasts expressing strong hOC-GFPtpz and weak pOBCol3.6GF-Pcyan are also present and may or may not be producing mineralized matrix. This multiplex approach reveals the heterogeneity within the mature osteoblast population that cannot be appreciated by current histological methods. It should be useful to identify and isolate populations of cells within an osteoblast lineage as they progress through stages of differentiation.

Essential oil composition of diploid and tetraploid clones of ginger (Zingiber officinale roscoe) grown in Australia

Ginger oil, obtained by steam distillation of the rhizome of Zingiber officinale Roscoe, is used in the beverage and fragrance industries. Ginger oil displays considerable compositional diversity, but is typically characterized by a high content of sesquiterpene hydrocarbons, including zingiberene, arcurcumene, beta-bisabolene, and beta-sesquiphellandrene. Australian ginger oil has a reputation for possessing a particular lemony aroma, due to its high content of the isomers neral and geranial, often collectively referred to as citral. Fresh rhizomes of 17 clones of Australian ginger, including commercial cultivars and experimental tetraploid clones, were steam distilled 7 weeks post-harvest, and the resulting oils were analyzed by GC-MS. The essential oils of 16 of the 17 clones, including the tetraploid clones and their parent cultivar, were found to be of substantially similar composition. These oils were characterized by very high citral levels (51-71%) and relatively low levels of the sesquiterpene hydrocarbons typical of ginger oil. The citral levels of most of these oils exceeded those previously reported for ginger oils. The neral-to-geranial ratio was shown to be remarkably constant (0.61 +/- 0.01) across all 17 clones. One clone, the cultivar Jamaican, yielded oil with a substantially different composition, lower citral content and higher levels of sesquiterpene hydrocarbons. Because this cultivar also contains significantly higher concentrations of pungent gingerols, it possesses unique aroma and flavor characteristics, which should be of commercial interest.

Isomeric distribution and catalyzed isomerization of cobalt(III) complexes with pentadentate macrocyclic ligands. Importance of hydrogen bonding

We have investigated the isomeric distribution and rearrangement of complexes of the type [CoXLn](2+,3+) (where X = Cl-, OH-, H2O, and L-n represents a pentadentate 13-, 14-, and 15-membered tetraaza or diaza-dithia (N-4 or N2S2) macrocycle bearing a pendant primary amine). The preparative procedures for chloro complexes produced almost exclusively kinetically preferred cis isomers (where the pendant primary amine is cis to the chloro ligand) that can be separated by careful cation-exchange chromatography. For L-13 and L-14 the so-called cis-V isomer is isolated as the kinetic product, and for L-15 the cis-VI form (an N-based diastereomer) is the preferred, while for the L-14(S) complex both cis-V and trans-I forms are obtained. All these complexes rearrange to form stable trans isomers in which the pendent primary amine is trans to the monodentate aqua or hydroxo ligand, depending on pH and the workup procedure. In total 11 different complexes have been studied. From these, two different trans isomers of [CoCIL14S](2+) have been characterized crystallographically for the first time in addition to a new structure of cis-V-[CoCIL14S](2+); all were isolated as their chloride perchlorate salts. Two additional isomers have been identified and characterized by NMR as reaction intermediates. The remaining seven forms correspond to the complexes already known, produced in preparative procedures. The kinetic, thermal, and baric activation parameters for all the isomerization reactions have been determined and involve large activation enthalpies and positive volumes of activation. Activation entropies indicate a very important degree of hydrogen bonding in the reactivity of the complexes, confirmed by density functional theory studies on the stability of the different isomeric forms. The isomerization processes are not simple and even some unstable intermediates have been detected and characterized as part of the above-mentioned 11 forms of the complexes. A common reaction mechanism for the isomerization reactions has been proposed for all the complexes derived from the observed kinetic and solution behavior.

Inositol polyphosphate-mediated iron transport in Pseudomonas aeruginosa

It has previously been shown that myo-inositol hexakisphosphate (myo- InsP6) mediates iron transport into Pseudomonas aeruginosa and overcomes iron-dependent growth inhibition. In this study, the iron transport properties of myo-inositol trisphosphate and tetrakisphosphate regio-isomers were studied. Pseudomonas aeruginosa accumulated iron (III) at similar rates whether complexed with myo-Ins(1,2,3)P3 or myo-InsP6. Iron accumulation from other compounds, notably D/L myo-Ins(1,2,4,5)P4 and another inositol trisphosphate regio-isomer, D-myo-Ins(1,4,5)P3, was dramatically increased. Iron transport profiles from myo-InsP6 into mutants lacking the outer membrane porins oprF, oprD and oprP were similar to the wild-type, indicating that these porins are not involved in the transport process. The rates of reduction of iron (III) to iron (II) complexed to any of the compounds by a Ps. aeruginosa cell lysate were similar, suggesting that a reductive mechanism is not the rate-determining step.

Inhibition of iron-catalysed hydroxyl radical formation by inositol polyphosphates: a possible physiological function for myo-inositol hexakisphosphate

1. The ability of myo-inositol polyphosphates to inhibit iron-catalysed hydroxyl radical formation was studied in a hypoxanthine/xanthine oxidase system [Graf, Empson and Eaton (1987) J. Biol. Chem. 262, 11647-11650]. Fe3+ present in the assay reagents supported some radical formation, and a standard assay, with 5 microM Fe3+ added, was used to investigate the specificity of compounds which could inhibit radical generation. 2. InsP6 (phytic acid) was able to inhibit radical formation in this assay completely. In this respect it was similar to the effects of the high affinity Fe3+ chelator Desferral, and dissimilar to the effects of EDTA which, even at high concentrations, still allowed detectable radical formation to take place. 3. The six isomers of InsP5 were purified from an alkaline hydrolysate of InsP6 (four of them as two enantiomeric mixtures) and they were compared with InsP6 in this assay. Ins(1,2,3,4,6)P5 and D/L-Ins(1,2,3,4,5)P5 were similar to InsP6 in that they caused a complete inhibition of iron-catalysed radical formation at > 30 microM. Ins(1,3,4,5,6)P5 and D/L-Ins(1,2,4,5,6)P5, however, were markedly less potent than InsP6, and did not inhibit radical formation completely; even when Ins(1,3,4,5,6)P5 was added up to 600 microM, significant radical formation was still detected. Thus InsP5s lacking 2 or 1/3 phosphates are in this respect qualitatively different from InsP6 and the other InsP5s. 4. scyllo-Inositol hexakisphosphate was also tested, and although it caused a greater inhibition than Ins(1,3,4,5,6)P5, it too still allowed detectable free radical formation even at 600 microM. 5. We conclude that the 1,2,3 (equatorial-axial-equatorial) phosphate grouping in InsP6 has a conformation that uniquely provides a specific interaction with iron to inhibit totally its ability to catalyse hydroxyl radical formation; we suggest that a physiological function of InsP6 might be to act as a 'safe' binding site for iron during its transport through the cytosol or cellular organelles

Studies on the mode of action and beta-lactamase inhibitory properties of novel oxapenem compounds

Four novel oxapenem compounds were evaluated for their ß-lactamase inhibitory and antibacterial properties. Two (AM-112 and AM-113) displayed intrinsic antibacterial activity with MICs of between 2 to 16µg/ml and 0.5-2µg/ml against Escherichia coli and methicillin-sensitive and -resistant Staphylococcus aureus, respectively. The isomers of these compounds, AM-115 and AM-114 did not display significant antibacterial activity. Combination of the oxapenems with ceftazidime afforded protection against ß-lactamase-producing strains, including hyperproducers of class C enzymes and extended-spectrum ß-lactamase enzymes. A fixed 4µg/ml concentration of AM-112 protected a panel of eight cephalosporins against hydrolysis by class A and class C ß-lactamase producers. In vivo studies confirmed the protective effect of AM-112 for ceftazidime against ß-lactamase producing S. aureus, Enterobacter cloacae and E. coli strains in a murine intraperitoneal infection model. Each of the oxapenems inhibited class A, class C and class D ß-lactamases isolated from whole cells and purified by isoelectric focusing. AM-114 and AM-115 were as effective as clavulanic acid against class A enzymes. AM-112 and AM-113 were less potent against these enzymes. Class C and class D enzymes proved very susceptible to inhibition by the oxapenems. Molecular modelling of the oxapenems in the active site of the class A. TEM-1 and class C P99 enzymes identified a number of potential sites of interaction. The modelling suggested that Ser-130 in TEM-1 and Tyr-150 in P99 were likely candidates for cross-linking of the inhibitor, leading to inhibition of the enzyme. Morphology studies indicated that sub-inhibitory concentrations of the oxapenems caused the formation of round-shaped cells in E. coli DC0, indicating inhibition of penicillin-binding protein 2 (PBP2). The PBP affinity profile of AM-112 was examined in isolated cell membranes of E. coli DC0, S. aureus NCTC 6571, Enterococcus faecalis SFZ and E. faecalis ATCC 29213, in competition with a radiolabelled penicillin. PBP2 was identified as the primary target for AM-112 in E. coli DC0. Studies on S. aureus NCTC 6571 failed to identify a binding target. AM-112 bound to all the PBPs of both E. faecalis strains, and a concentration of 10µg/ml inhibited all the PBPs except PBP3.

Synthesis and cytotoxity of oxysterols:studies on the A,B ring polyoxygenated sterols

Oxysterols (OS), the polyoxygenated sterols, represent a class of potent regulatory molecules for important biological actions. Cytotoxicity of OS is one of the most important aspects in studies of OS bioactivities. However, studies, the structure-activity relationship (SAR) study in particular, have been hampered by the limited availability of structurally diverse OS in numbers and amounts. The aim of this project was to develop robust synthetic methods for the preparation of polyhydroxyl sterols, thereof, evaluate their cytotoxicity and establish structure-activity relationship. First, we found hydrophobicity of the side chain is essential for 7-HC's cytotoxicity, and a limited number of hydroxyl groups and a desired configuration on the A, B ring are required for a potent cytotoxicity of an OS, after syntheses and tests of a number of 7-HC's analogues against cancer cell lines. Then polyoxygenation of cholesterol A, B rings was explored. A preparative method for the synthesis of four diastereomerically pure cholest-4-en-3,6-diols was developed. Epoxidation on these cholest-4-en-3,6-diols showed that an allyl group exerts an auxiliary role in producing products with desired configuration in syntheses of the eight diastereomerically pure 45-epoxycholestane-3,6-diols. Reduction of the eight 45-epoxycholestane-3,6-diols produced all eight isomers of the cytotoxic 5α-acholestane 3β,5,6β-triol (CT) for the first time. Epoxide ring opening with protic or Lewis acids on the eight 45-epoxycholestane-3,6-diols are carefully studied. The results demonstrated a combination of an acid and a solvent affected the outcomes of a reaction dramatically. Acyl group participation and migration play an important role with numbers of substrates under certain conditions. All the eight 4,5-trans cholestane- 3,4,5,6-tetrols were synthesised through manipulation of acyl participation. Furthermore these reaction conditions were tested when a number of cholestane-3,4, 5,6,7-pentols and other C3-C7 oxygenated sterols were synthesised for the first time. Introduction of an oxygenated functional group through cholest-2-ene derivatives was studied. The elimination of 3-(4-toluenesulfonate) esters showed the interaction between the existing hydroxyls or acyls with the reaction centre often resulted in different products. The allyl oxidation, epoxidation and Epoxide ring opening reactions are investigated with these cholest-2-enes.

Base modified peptidic nucleic acids: synthesis and crystallographic analysis of intermediates

Peptidic Nucleic Acids (PNAs) are achiral, uncharged nucleic add mimetics, with a novel backbone composed of N-(2-aminoethyl)glycine units attached to the DNA bases through carboxymethylene linkers. With the aim of extending and improving upon the molecular recognition properties of PNAs, the aim of this work was to synthesjse PNA building block intermediates containing a series of substituted purine bases for subsequent use in automated PNA synthesis. Four purine bases: 2,6~diaminopurine (D), isoGuanine (isoG), xanthine (X) and hypoxanthine (H) were identified for incorporation into PNAs targeted to DNA, with the promise of increased hybrid stability over extended pH ranges together with improvements over the use of adenine (A) in duplex formation, and cytosine (C) in triplex formation. A reliable, high-yielding synthesis of the PNA backbone component N -('2- butyloxycarbonyl-aminoethyl)glycinate ethyl ester was establishecl. The precursor N~(2-butyloxycarbonyl)amino acetonitrile was crystallised and analysed by X-ray crystallography for the first time. An excellent refinement (R = 0.0276) was attained for this structure, allowing comparisons with known analogues. Although chemical synthesis of pure, fully-characterised PNA monomers was not achieved, chemical synthesis of PNA building blocks composed of diaminopurine, xanthine and hypoxanthine was completely successful. In parallel, a second objective of this work was to characterise and evaluate novel crystalline intermediates, which formed a new series of substituted purine bases, generated by attaching alkyl substituents at the N9 or N7 sites of purine bases. Crystallographic analysis was undertaken to probe the regiochemistry of isomers, and to reveal interesting structural features of the new series of similarly-substituted purine bases. The attainment of the versatile synthetic intermediate 2,6-dichloro~9- (carboxymethyl)purine ethyl ester, and its homologous regioisomers 6-chloro~9- (carboxymethyl)purine ethyl ester and 6-chloro-7-(carboxymethyl)purine ethyl ester, necessitated the use of X-ray crystallographic analysis for unambiguous structural assignment. Successful refinement of the disordered 2,6-diamino-9-(carboxymethyl) purine ethyl ester allowed comparison with the reported structure of the adenine analogue, ethyl adenin-9-yl acetate. Replacement of the chloro moieties with amino, azido and methoxy groups expanded the internal angles at their point of attachment to the purine ring. Crystallographic analysis played a pivotal role towards confirming the identity of the peralkylated hypoxanthine derivative diethyl 6-oxo-6,7-dihydro-3H-purlne~3,7~djacetate, where two ethyl side chains were found to attach at N3 and N7,