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D J Williams

Publications and source records attributed to D J Williams.

At least 37 records · Page 2Linked to original sources
PubMed2001

Heterometallic network complexes of the ambidentate, extended-reach linear ligand 1-(4'-pyridyl)pyridin-4-one.

An investigation into the ability of the ambidentate, "extended-reach" ligand 1-(4'-pyridyl)pyridin-4-one (pypyd) to form polymeric network complexes has resulted in the X-ray characterization of the compounds [Cu(pypyd)(2)(H2O)(2)](ClO(4))(2).pypyd 1, [Co(2)Dy(2)(pypyd)(8)(H2O)(2)(NCS)(4)(NO(3))(4)][Co(NCS)(4)] 2, and [NiYb(pypyd)(4)(NCS)(2)(NO(3))(2)](NO(3)) 3. The homometallic copper complex, 1, forms a (4,4) sheet polymer with additional intrasheet cross-linking via hydrogen bonding of noncoordinated pypyd molecules to the aqua ligands on the Cu centers. The heterometallic Co/Dy complex, 2, also produces a contiguous (4,4) sheet but without the hydrogen bonded pypyd cross-link. The heterometallic Ni/Yb compound, 3, forms a more complex array comprised of mutually interpenetrating networks each of three-dimensional (6,4) topology. The crystal structure of an acetic acid adduct of pypyd, 4, is also reported.

Journal Article↗
PubMed2001

Synthesis and characterization of gallium silylamido complexes.

The reaction between GaCl(3) and 1 equiv of HN(SiMe(2)Ph)(2) in CH(2)Cl(2) solution affords colorless crystals of [Cl(2)Ga[mu-N(H)SiMe(2)Ph]](2) (1). The related reaction between GaCl(3) and 1 equiv of LiN(SiMe(2)Ph)(2) in hexane solution results in the isolation of colorless crystals of [PhGa[N(SiMe(2)Ph)(2)](mu-Cl)](2) (2). In contrast, treatment of GaCl(3) with 1 equiv of N(SiMe(3))(3) in CH(2)Cl(2) solutions affords colorless crystals of [MeGaCl(2)](2) (4). Compounds 2 and 4 are the result of monochloride substitution and transfer of a phenyl and methyl ligand, respectively, from the silyl group of the amine to the Ga center. All the complexes have been characterized by X-ray crystallography.

Journal Article↗
PubMed2001

Supramolecular daisy chains.

Two series of self-complementary daisy chain monomers, in which a secondary ammonium ion-containing arm is grafted onto a macrocycle with either a [24]- or [25]crown-8 constitution, have been synthesized. In the solid- and 'gas'-phases, the parent [24]crown-8-based monomer forms dimeric superstructures, as revealed by X-ray crystallography and mass spectrometry, respectively. Elucidation of the complicated solution-phase behavior of this compound was facilitated by the synthesis and study of both deuterated, and fluorinated, analogues. These investigations revealed that the cyclic dimeric superstructure also dominates in solution, except when extremes of either concentration (low), temperature (high), or solvent polarity (highly polar, e.g., dimethyl sulfoxide) are employed. Whereas, upon aggregation, the [24]crown-8-based daisy chain monomers have the capacity to form stereoisomeric superstructures further complicating the study of this series of compounds. The assembly of [25]crown-8-based monomers gives only achiral superstructures. The weaker association exhibited between secondary dialkylammonium ions and crown ethers with a [25]crown-8 constitution, however, resulted in limited oligomerization--only dimeric and trimeric superstructures were formed at experimentally attainable concentrations--of [25]crown-8-based daisy chain monomers.

Journal Article↗
PubMed2001

Relationships between non-occupational cadmium exposure and expression of nine cytochrome P450 forms in human liver and kidney cortex samples.

This study was undertaken to assess associations between age, gender, cigarette smoke and non-workplace cadmium exposure, and liver pathology and inter-individual variation in cytochrome P450 (CYP) expression in human tissues. Autopsy specimens of twenty-eight Queensland residents whose ages ranged from 3 to 89 years were analyzed for the presence of nine CYP protein isoforms by immunoblotting. All subjects were Caucasians and their liver cadmium contents ranged from 0.11 to 3.95 microg/g wet weight, while their kidney cadmium contents were in the range of 2 to 63 microg/g wet weight. CYP1A2, CYP2A6, CYP2D6, CYP3A4, and CYP3A5 were detected in liver but not in kidney, and CYP1A1 and CYP1B1 were not found in liver or kidney. Lowered liver CYP2C8/19 protein contents were found to be associated with liver pathology. Importantly, we show elevated levels of CYP2C9 protein to be associated with cadmium accumulation in liver. No mechanism that explains this association is apparent, but there are two possibilities that require further study. One is that variation in CYP2C9 protein levels may be, in part, attributed to an individual's non-workplace exposure to cadmium, or an individual's CYP2C9 genotype may be a risk factor for cadmium accumulation. A positive correlation was found between liver CYP3A4 protein and subject age. Levels of liver CYP1A2 protein, but not other CYP forms, were increased in people more exposed to cigarette smoke, but there was no association between CYP1A2 protein and cadmium. CYP2A6 protein was found in all liver samples and CYP2A6 gene typing indicated the absence of CYP2A6 null allele (CYP2A6(D)) in this sample group, confirming very low prevalence of homozygous CYP2A6(D) in Caucasians. CYP2A6 gene types W/W, W/C, and C/C were not associated with variations in liver microsomal CYP2A6 protein. CYP2D6 protein was absent in all twenty-five kidney samples tested but was detectable in liver samples of all but two subjects, indicating the prevalence of the CYP2D6 null allele (CYP2D6(D)) in this sample group to be about 7%, typical of Caucasian populations.

Adolescent↗
PubMed2001

Synthesis of dixanthones and poly(dixanthone)s by cyclization of 2-aryloxybenzonitriles in trifluoromethanesulfonic acid.

[reaction: see text] Condensation of 2-fluorobenzonitriles with phenoxides affords 2-aryloxybenzonitriles that cyclize cleanly in trifluoromethanesulfonic acid at room temperature to give xanthone-iminium triflates. The C=N bond in these compounds is remarkably resistant to hydrolysis, but prolonged reaction with strong aqueous acid under vigorous conditions affords xanthones in good yield. The synthesis is exemplified for a novel series of polynuclear dixanthones and for a high molar mass polyxanthone derived from the previously unreported monomer 3,3'-difluoro-4,4'-biphenyldicarbonitrile.

Journal Article↗
PubMed2001

Synthesis and characterization of coronanes: multicyclopropane-fused macrocyclic arrays.

Stepwise macrocyclization of the all syn-trans-1,15-quinquecyclopropanedimethanol (4) with iso- and terephthaloyl chlorides and 4,4'-methanediyl-dibenzoic acid (28) gave the corresponding coronanes 22, 23, and 32. The same protocol was used with all syn-trans-1,21-septecyclopropanedimethanol (5) and 2,3-naphthalenedicarboxylic acid to obtain the macrolide 27. Direct macrocyclization of diol 4 and 1,10-phenanthroline-2,9-dicarbonyl chloride (33) and 2,2'-bipyridine-4,4'-dicarbonyl chloride (35) gave the coronanes 34 and 36, respectively. Ring closing metathesis (RCM) of the diene 42 using Cl2(Cy3P)2Ru=CHPh (48) (Grubbs's catalyst) gave the macrocyclic lactone 45. The structures of coronanes 22, 23, 32, 34, 36, and 45 were confirmed by X-ray crystallographic studies which showed the cyclopropyl chain to adopt very differing conformations throughout the series. Several of the macrocycles have significant free pathways through their ring centers, and in the case of compound 34 there is a water molecule hydrogen bonded within the ring. This latter compound has the potential to act as a chiral ligand to metal centers.

Crystallography, X-Ray↗
PubMed2001

Synthesis of near-IR absorbing/emitting porphyrazine derivatives with tunable solubility.

We report the synthesis of porphyrazines (pzs), or tetraazaporphyrins, of the form H2[pz(An;B4-n)], where A is [S(CH2)3COOR]2 (R = n-Pr,H) and B is a fused beta,beta'-diisopropyloxybenzo group, including the compounds with n = 4 (6), n = 3 (7) and the trans compound with n = 2 (8) (Scheme 1). The synthesis employs Linstead crossover macrocyclization of dimethyl 6,7-dicyano-5,8-dithia-6(Z)-dodecenedioate, MNT(C4O2Me)2 (2), with 1-imino-4,7-bis(1-methylethoxy)-1H-isoindole-3-amine (4). These pigments were characterized by 1H NMR, 13C NMR, absorbance/fluorescence spectroscopy, mass spectrometry, and microanalysis. An X-ray crystal structure of 8 is presented. Of particular note, 6-8 display intense near-IR absorbance and dual UV-visible/near-IR emission which are very important in potential biomedical applications, both for cancer therapy (photodynamic therapy, PDT) and cancer diagnosis (optical tumor imaging). For example, the trans-porphyrazine 8 has an intense long-wavelength absorption at ca. 800 nm (log epsilon = 4.18) and S1 fluorescence at approximately 820 nm, where mammalian tissue is effectively penetrated by light. Transformation of the ester group permits a wide range of functionality and solubility to be generated without change in optical properties. As an example, hydrolysis of these compounds by LiOH in THF/H2O gives the corresponding carboxylato-functionalized pigments 9-11, which are described. The last of these dissolves without aggregation in fetal calf serum.

Journal Article↗
PubMed2001

Influence of the counteranion on the formation of polymeric networks by metal complexes of hexamethylenebis(acetamide).

An investigation into the anion dependence of the network-forming ability of metal complexes of hexamethylenebis(acetamide), CH3CONH(CH2)6NHCOCH3 (HMBA), has resulted in the X-ray characterization of the compounds [Co(HMBA)3][Co(NCS)4], 1, [Nd(HMBA)3][Nd(NO3)6].2CHCl3, 2, [Co(HMBA)3][HgCl4], 3, and [Mn(HMBA)3][HgBr4].3CHCl3, 4. The structures of compounds 1, 3, and 4 each comprise cationic frameworks formed by the bridging action of HMBA ligands binding octahedrally to the cobalt or manganese centers and, in the cases of 3 and 4, the formation of tetrahedral HgX4(2-) anions by transfer of the respective halide ions from Co or Mn to Hg. Complete anion (NO3-) transfer between Nd centers is also a key factor in the structure of 2, which forms a cationic 3-D network of HMBA-bridged octahedrally coordinated Nd centers with occluded [Nd(NO3)6]3- anions. These types of inter-metal-anion transfer, with consequent complex counteranion formation, appear to facilitate the network-forming ability of the metal-HMBA cationic arrays.

Journal Article↗
PubMed2001

Thermodynamics of 2'-ribose substitutions in UUCG tetraloops.

The ribose 2'-hydroxyl group confers upon RNA many unique molecular properties. To better appreciate its contribution to structure and stability and to monitor how substitutions of the 2' hydroxyl can alter an RNA molecule, each loop pyrimidine ribonucleotide in the UUCG tetraloop was substituted with a nucleotide containing either a fluorine (2'-F), hydrogen (2'-H), amino (2'-NH2), or methoxy (2'-OCH3) group, in the context of both the C:G and G:C loop-closing base pair. The thermodynamic parameters of these tetraloop variants have been determined and NMR experiments used to monitor the structural changes resulting from the substitutions. The modified riboses are better tolerated in the G[UUCG]C tetraloop, which may be due to its increased loop flexibility relative to the C[UUCG]G loop. Even for these simple substitutions, the free-energy change reflects a complex interplay of hydrogen bonding, solvation effects, and intrinsic pucker preferences of the nucleotides.

Base Sequence↗
PubMed2001

Increased cerebral blood flow and cardiac output following cerebral arterial air embolism in sheep.

1. The effects of cerebral arterial gas embolism on cerebral blood flow and systemic cardiovascular parameters were assessed in anaesthetized sheep. 2. Six sheep received a 2.5 mL injection of air simultaneously into each common carotid artery over 5 s. Mean arterial blood pressure, heart rate, end-tidal carbon dioxide and an ultrasonic Doppler index of cerebral blood flow were monitored continuously. Cardiac output was determined by periodic thermodilution. 3. Intracarotid injection of air produced an immediate drop in mean cerebral blood flow. This drop was transient and mean cerebral blood flow subsequently increased to 151% before declining slowly to baseline. Coincident with the increased cerebral blood flow was a sustained increase in mean cardiac output to 161% of baseline. Mean arterial blood pressure, heart rate and end-tidal carbon dioxide were not significantly altered by the intracarotid injection of air. 4. The increased cardiac output is a pathological response to impact of arterial air bubbles on the brain, possibly the brainstem. The increased cerebral blood flow is probably the result of the increased cardiac output and dilation of cerebral resistance vessels caused by the passage of air bubbles.

Animals↗
PubMed2001

Experimental studies on the transmission of Neospora caninum between cattle.

Three studies were conducted to investigate the transmission of Neospora caninum between cattle by the oral route. In the first study, six calves were dosed with 10(7)N caninum tachyzoites (NC LivB1) in colostrum and/or milk replacer on four occasions. In the second study, two calves and two cows were fed placental tissues from N caninum -infected cows, and, in the third study, seven uninfected calves were fostered onto N caninum -infected dams. In the first study, all six calves developed antibody responses and five calves developed antigen-specific lymphoproliferation responses, including two calves initially challenged at 1 week of age. No evidence of N caninum infection was found in the brain or heart of these calves by histology or polymerase chain reaction (PCR). In the second and third studies, there was no evidence of N caninum infection in any of the calves and cows. The results confirm that calves up to 1 week of age can be experimentally infected via the oral route, but suggest that this is not an important natural route of transmission for N caninum between cattle.

Animals↗
PubMed2001

Changes in zinc and copper homeostasis in human livers and kidneys associated with exposure to environmental cadmium.

This study was undertaken to assess changes in zinc and copper homeostasis in human tissues that could be attributed to human exposure to environmental cadmium, using samples of lung, liver and kidney cortex of 61 Queensland residents, aged 2 to 89 years, who had died of accidental causes. None of the subjects were exposed to cadmium in the workplace. Levels of zinc in liver and kidney cortex samples showed inverse associations with donor age whereas zinc in lung only showed inverse association with gender. Lung zinc levels in females were 14% lower than in males. Zinc in liver and kidney cortex samples were found to exist in at least two pools; one was associated with cadmium that bound to metallothionein (MT) and the other was associated with non-MT bound copper. In liver, the amounts of zinc in the MT pool were smaller compared to those in non-MT pool given that only 7% of zinc variations were explained by cadmium whereas 22% of the liver zinc variations were accounted for by non-MT bound copper. In sharp contrast, larger amounts of zinc in kidney cortex samples were in the MT pool, compared to those in the non-MT pool given that cadmium was found to explain 69% of total zinc variation whereas copper explained only 17% of kidney zinc variations. The levels of copper in liver were found to be increased by 45-50% in subjects with high cadmium exposure level, compared to subjects of similar ages with medium exposure level. The levels of zinc and copper in kidney cortex samples in the subjects with high cadmium exposure were both found to be significantly elevated compared to those found in the medium-exposure group whereas copper contents were about 19-23% greater than in medium- as well as low-exposure groups. Taken together these results indicate increased sequestration of zinc and copper in liver and kidney cortex samples. The increases in metal sequestrations were observed in liver samples having cadmium contents of greater than 1 microg/g wet weight and in kidney cortex having cadmium contents of greater than 26 microg/g wet weight. Zinc and copper contents in lung of this sample group, however, were not associated with cadmium due probably to lower exposure levels compared to those of liver and kidney.

Adolescent↗
PubMed2000

Sulfone-linked paracyclophanes via macrocyclic aromatic thioethers: synthetic and structural investigations.

Reaction of 4,4'-sulfonylbis(benzenethiol) with 4,4'-dichlorodiphenylsulfone under pseudo-high-dilution conditions leads to macrocyclic thioethersulfones [-S-Ar-SO2-Ar-]n (Ar = 1,4-phenylene). These include a highly strained [1+1] cyclodimer (n = 2), a cyclotrimer resulting from thioetherexchange reactions, and a [2+2] cyclotetramer which can adopt two entirely different conformations in the crystalline state, one having molecular D2d ("tennis-ball-seam") symmetry. The same type of reaction is successful using 4,4'-thiobis(benzenethiol) instead of 4,4'-sulfonylbis(benzenethiol) and affords macrocycles with a higher ratio of thioether to sulfone linkages. Exhaustive oxidation of macrocyclic thioethersulfones with hydrogen peroxide affords a series of sulfone-linked paracyclophanes, [-Ar-SO2-]4, [-Ar-SO2-]6, [-Ar-SO2-]8 and [-Ar-SO2-]12. Single crystal X-ray analysis reveals [Ar-SO2-]4 to be a near-perfect square box, whilst the cyclic hexamer [-Ar-SO2-]6 adopts a much more irregular conformation. and [-Ar-SO2-]8 displays a "double-box" structure clearly related to that of [Ar-SO2-]4.

Journal Article↗