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Biomedical subjects

Peter G Jones

Publications and source records attributed to Peter G Jones.

53 records · Page 3Linked to original sources
PubMed2002

Secondary interactions in N-(chloromethyl)pyridinium chlorides (n = 2, 3, 4).

In the isomeric title compounds, viz. 2-, 3- and 4-(chloromethyl)pyridinium chloride, C(6)H(7)ClN(+).Cl(-), the secondary interactions have been established as follows. Classical N-H.Cl(-) hydrogen bonds are observed in the 2- and 3-isomers, whereas the 4-isomer forms inversion-symmetric N-H(.Cl(-).)(2)H-N dimers involving three-centre hydrogen bonds. Short Cl.Cl contacts are formed in both the 2-isomer (C-Cl.Cl(-), approximately linear at the central Cl) and the 4-isomer (C-Cl.Cl-C, angles at Cl of ca 75 degrees ). Additionally, each compound displays contacts of the form C-H.Cl, mainly to the Cl(-) anion. The net effect is to create either a layer structure (3-isomer) or a three-dimensional packing with easily identifiable layer substructures (2- and 4-isomers).

Journal Article↗
PubMed2002

Do aurophilic interactions compete against hydrogen bonds? Experimental evidence and rationalization based on ab initio calculations.

[M(C6F5)(N(H)=CPh2)] (M = Ag (1) and Au (2)) complexes have been synthesized and characterized by X-ray diffraction analysis. Complex 1 shows a ladder-type structure in which two [Ag(C6F5)(N(H)=CPh2)] units are linked by a Ag(I)-Ag(I) interaction in an antiparallel disposition. The dimeric units are associated through hydrogen bonds of the type N-H...F(ortho). On the other hand, gold(I) complex 2 displays discrete dimers also in an antiparallel conformation in which both Au(I)-Au(I) interactions and N-H.F(ortho) hydrogen bonds appear within the dimeric units. The features of these coexisting interactions have been theoretically studied by ab initio calculations based on four different model systems in order to analyze them separately. The interactions have been analyzed at HF and MP2 levels of theory showing that, in this case, even at larger distances. The Au(I)-Au(I) interaction is stronger than Ag(I)-Ag(I) and that N-H.F hydrogen bonding and Au(I)-Au(I) contacts have a similar strength in the same molecule, which permits a competition between these two structural motifs giving rise to different structural arrangements.

Journal Article↗
PubMed2002

Three ruthenocene derivatives: (eta(5)-4,7-dimethylindenyl)(eta(5)-pentamethylcyclopentadienyl)ruthenium(II), [eta(5)-[2](4,7)indeno[2]paracyclophanyl](eta(5)-pentamethylcyclopentadienyl)ruthenium(II) and bis[eta(5)-[2](4,7)indeno[2]paracyclophanyl]ruthenium(II).

In the title compounds, [Ru(C(10)H(15))(C(11)H(11))], (III), [Ru(C(10)H(15))(C(19)H(17))], (IV), and [Ru(C(19)H(17))(2)], (V), respectively, the coordinating ring systems are planar and parallel, with the Ru atoms lying at perpendicular distances of Ru-Cp* 1.790 (1) A and Ru-indenyl 1.836 (1) A in (III), Ru-Cp* 1.791 (1) A and Ru-indenyl 1.837 (1) A in (IV), and Ru-indenyl 1.812 (1) A and 1.809 (1) A in (V) (Cp* is pentamethylcyclopentadienyl). The ring conformations are eclipsed for (III), staggered for (IV) and intermediate for (V). All three compounds show short intermolecular contacts from C-H groups to some ring centroids; these could be regarded as C-H.pi hydrogen bonds. The molecules of each compound are thus connected via the 2(1) screw axis to form layers parallel to the xy plane.

Journal Article↗
PubMed2002

Polymeric methylenebis(diphenylphosphine oxide) hydrogen triiodide.

The conformation of the cationic part of the title compound, [[(C(6)H(5))(2)POH(0.5)](2)CH(2)]I(3) or dppmO(2)H(+) x I(3)(-) (dppm is diphenylphosphinomethane), is determined by hydrogen bonds between cations of monoprotonated [(C(6)H(5))(2)P([double bond]O)](2)CH(2) (dppmO(2)). Symmetric P[double bond]O...H...O[bond]P bridging, with H atoms lying on centres of inversion, leads to chain-like polymeric cations, (dppmO(2)H(+))(x), made up of H...OP(C(6)H(5))(2)[bond]CH(2)[bond](C(6)H(5))(2)PO... moieties. These are, in turn, cross-connected by non-classical C[bond]H...I contacts between the (dppmO(2)H(+))(x) methylene-group H atoms and the terminal I atoms of the triiodide anions, which display crystallographic inversion symmetry.

Journal Article↗
PubMed2002

Biomimetic studies on iodothyronine deiodinase intermediates: modeling the reduction of selenenyl iodide by thiols.

Enzyme mimetic studies on the crucial intermediate (E-SeI) of the iodothyronine deiodinase cycle have been carried out by using an areneselenenyl iodide stabilized by intramolecular Se.N interactions. Treatment of this compound with aromatic thiols and thiobenzoxazole in the presence of NEt(3) affords areneselenenyl sulfides that are stable towards disproportionation reactions. The structures of three of the areneselenenyl sulfides were determined by X-ray crystallography. In one case, in the absence of NEt(3), a diselenide can be formed rather than the selenenyl sulfide. The areneselenenyl iodide also reacts with a related selenol to produce the corresponding diselenide, and this reaction is found to be much faster than that with thiols. The high reactivity of the selenenyl iodide with the selenol suggests that a reduced selenol group (R'-SeH) may react with the E-SeI intermediate to produce a diselenide (E-Se-Se-R') without any thiol cosubstrate. The intermediacy of selenenyl sulfides during the reduction of selenenyl iodide by thiols and its possible relevance to the iodothyronine deiodinase catalytic cycle is also described.

Binding Sites↗
PubMed2002

Three isomeric bis(methoxycarbonyl)[2.2]paracyclophanes.

The title isomers 4,16- (pseudo-ortho), 4,15- (pseudo-gem) and 4,12-bis(methoxycarbonyl)[2.2]paracyclophane (pseudo-para), C(20)H(20)O(4), all show the typical structural features of [2.2]paracyclophanes (flattened boat conformation of the rings, lengthened single bonds in the bridges and narrow ring angles at the bridgehead atoms). The 4,12-isomer displays crystallographic inversion symmetry. The carbonyl groups adopt a conformation in which they are directed away from the ring systems towards the nearest bridge; the corresponding angle at the ring substituent atom is widened. Crystal packing involves C-H.pi interactions for the 4,15-isomer and weak C-H.O hydrogen bonds for the other two isomers.

Journal Article↗
PubMed2002

Secondary interactions in 4-bromo-N,N-dimethylanilinium bromide.

The crystal packing of the title compound, C(8)H(11)BrN(+).Br(-), involves three types of secondary interaction: a classical N-H.Br(-) hydrogen bond, a 'weak' but short C-H.Br(-) interaction (normalized H.Br distance of 2.66 A) and a cation-anion Br.Br contact of 3.6331 (4) A. The hydrogen bonds connect two cations and two anions to form rings of graph set R(4)(2)(14). The Br.Br contacts link these rings to form layers parallel to the bc plane.

Journal Article↗
PubMed2002

An unusual palladium complex involved in an unusual rearrangement of ortho-palladated aryldithioacetals.

The reaction of 1 with Pd(dba)(2), Tl(TfO) and PPh(3) in 1:1:1:2 molar ratios to give 3 implicates (i) an oxidative addition reaction, (ii) a rearrangement involving the cleavage of one HC-S bond and formation of an aryl-S bonds, and (iii) coordination of the Pd(PR(3))(2) group with a ligand intermediate between eta(2)-[ArCH=S((+))To] and kappa(2)-C,S-ArCH((-))STo, which requires the consideration of 3 as intermediate between a Pd(0) and a Pd(II) complex. The coordination of the ligand as a chelating three-membered ring, instead of the expected five-membered ring involving C(10) and S(1), and the partial intramolecular redox process are explained as a consequence of the transphobia of the pair of ligands Ph(3)P/CH(STo)Ar.

Journal Article↗
PubMed2002

Synthesis, structure, and photophysical studies of luminescent two- and three-dimensional gold-thallium supramolecular arrays.

The reactions of tetrahydrofuran solutions of NBu(4)[AuR(2)] (R = C(6)F(5), C(6)Cl(5)) with TlPF(6) and 4,4'-bipyridine lead to the synthesis of the luminescent materials [Tl(bipy)](2)[Au(C(6)F(5))(2)](2) 1 and [Tl(bipy)][Tl(bipy)(0.5)(thf)][Au(C(6)Cl(5))(2)](2) 2 in high yield. The structures of these complexes, as analyzed by X-ray diffraction, consist of planar polymers formed by repetition of Tl-Au-Au-Tl (1) or Tl-Au-Tl'-Au (2) moieties linked through bidentate bridging bipy ligands. In complex 1 these layers are associated via Tl...F contacts between atoms of adjacent planes, whereas in complex 2 each two polymeric layers are linked through additional bridging bipy molecules. Both complexes are strongly luminescent at room temperature and at 77 K in the solid state, losing this characteristic in solution even at high concentrations. The luminescence is attributed to interactions between metal atoms which are strongly affected by their structural dispositions. DFT calculations are in accord with the observed experimental behavior, showing the nature of the orbitals involved in each transition. Detailed analyses reveal a substantial participation of the metals in the transition giving rise to the emission maxima, and also other more energetic bands in which the ligands are involved and which also give rise to these emissions. The obtained theoretical excitation spectra clearly match the experimental results.

Journal Article↗
PubMed2002

Synthesis of the first 1,2,3,4-azatriphospholene complex.

Synthesis of the first 1,2,3,4-azatriphospholene complex was achieved by heating a solution of a P-phenyl-substituted 7-phosphanorbornadiene tungsten complex and triphenylphosphonio cyanomethylide, whereby CH-insertion products were formed in a competing reaction; these results also provide first evidence for the ability of electrophilic terminal phosphanediyl complexes to react at the ylide carbon atom and at the carbonitrile nitrogen atom of Wittig-ylides having a nitrile functional group; the structures of both complexes were established through X-ray single-crystal diffraction studies.

Journal Article↗
PubMed2002

'Self-organization' processes in proton and deuteron mixtures in open-chain hydrogen bond systems: polarization IR spectra of 4-mercaptopyridine crystals.

This paper is devoted to IR spectroscopic studies in polarized light of 4-mercaptopyridine (4-MPD) hydrogen-bonded crystals. These studies were preceded by determination of the 4-mercaptopyridine X-ray structure. Polarization spectra of 4-mercaptopyridine crystals were measured in the frequency ranges of V(N-H) and V(N-D) bands at room temperature, and also at the temperature of liquid nitrogen, for the two different crystalline faces: 'bc' and 'ac'. When investigating 'residual' v(N-H) band shapes for crystals that were diluted by deuterium, strong dichroic effects in the spectra were still observed, providing evidence for the existence in the hydrogen bond chains of domains containing exclusively protons or deuterons. This phenomenon proves the existence of a new kind of H/D isotopic effects in open chain hydrogen bond systems, namely 'self-organization' effects. Such effects, however, were not observed for other open chain hydrogen bond systems, e.g. alcohol crystals. Solid-state spectra of 4-mercaptopyridine were quantitatively interpreted, along with the strong polarization and the isotopic effects, when based on the 'strong-coupling' theory for linearly arranged hydrogen bond dimers.

Deuterium↗
PubMed2002

Polarization IR spectra of model crystals containing cyclic N-H...S bonded dimers: 2-mercaptothiazoline and 2-mercapto-1-methylimidazole.

This paper deals with experimental studies on the polarization IR spectra of hydrogen bonds in 2-mercaptothiazoline and 2-mercapto-1-methylimidazole crystals. The crystal structure of 2-mercaptothiazoline was determined by X-ray diffraction. The polarization spectra of the two compounds were measured in the frequency ranges of the V(N-H) and V(N-D) bands at 77 and 298 K. The spectra were attributed to cyclic N-H...S hydrogen-bond dimers, which are present as structural units in the lattices. Variation of the Davydov-splitting energy magnitude from sample to sample suggests statistical disorder in the crystals. The influence of the electronic properties of the associating small-ring molecules on the spectral properties of the hydrogen bonds is also discussed.

Hydrogen Bonding↗
PubMed2002

New antioxidant hydroquinone derivatives from the algicolous marine fungus Acremonium sp.

A marine fungal isolate, identified as Acremonium sp., was mass cultivated and found to produce two novel hydroquinone derivatives, 7-isopropenylbicyclo[4.2.0]octa-1,3,5-triene-2,5-diol (1) and 7-isopropenylbicyclo[4.2.0]octa-1,3,5-triene-2,5-diol-5-beta-D-glucopyranoside (2). Compound 1 and its glucoside 2 possess a most unusual ring system. The new natural products (3R,4S)-3,4-dihydroxy-7-methyl-3,4-dihydro-1(2H)naphthalenone (3) and (3S,4S)-3,4-dihydroxy-7-methyl-3,4-dihydro-1(2H)-naphthalenone (4) were obtained as a 1:0.8 mixture. 2-(1-Methylethylidene)pentanedioic acid (5) was isolated for the first time as a natural product and its structure proven by X-ray analysis. In addition to these compounds an inseparable mixture of three new isomeric compounds, pentanedioic acid 2-(1-methylethylidene)-5-methyl ester (6), pentanedioic acid 2-(1-methylethylidene)-1-methyl ester (7), and pentanedioic acid 2-(1-methylethenyl)-5-methyl ester (8), was also obtained. Isolated together with the new compounds were three known hydroquinone derivatives, 9, 10, and 11. The structures of all compounds were determined by interpretation of their spectroscopic data (1D and 2D NMR, MS, UV, and IR). Each isolate was tested for its antioxidant properties, and compounds 1 and 9-11 were found to have significant activity.

Acremonium↗
PubMed2002

5-hydroxyramulosin, a new natural product produced by Phoma tropica, a marine-derived fungus isolated from the alga Fucus spiralis.

The fungus Phoma tropica was isolated from the inner tissue of the marine brown alga Fucus spiralis. After large-scale cultivation the fungus was investigated for its secondary metabolite content and found to contain the new natural product 5-hydroxyramulosin ( 1) together with 7-methoxycoumarin. Both structures were elucidated using spectroscopic methods, mainly 1D and 2D NMR, and in the case of 1, a single crystal X-ray diffraction analysis.

Ascomycota↗