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J D Correia

Publications and source records attributed to J D Correia.

8 recordsLinked to original sources
PubMed2001

Re tricarbonyl complexes with ligands containing P,N,N and P,N,O donor atom sets: synthesis and structural characterization.

The coordination chemistry of the heterofunctionalized phosphines HPN2 and H2PNO and of an analogue containing a relevant biomolecule, HPN-Pip (Pip = 4-(3-aminopropyl)-1-(2-methoxyphenyl)piperazine), was studied toward the synthon (NE4)2[ReBr3(CO)3]. The complexes isolated, [Re(CO)3(kappa(3)-PN2)], 3, [Re(CO)3Br(kappa(2)-H2PNO)], 4, and [Re(CO)3Br(kappa(2)-HPN-Pip)], 5, are the first examples of Re(I) compounds stabilized by such a combination of donor atoms. All of the compounds are neutral, but the phosphines, depending on the combination of atoms, act as monoanionic and tridentate (3) or as neutral and bidentate (4, 5). The characterization of 3-5 included IR, 1H NMR, and 31P NMR spectroscopy and X-ray crystallographic analysis. Colorless crystals of compounds 3 and 4 were obtained by slow evaporation of a methanolic solution of 3 and from a boiling acetonitrile solution of 4. Compound 3 crystallizes with two molecules of MeOH per asymmetric unit in the monoclinic space group P2(1)/c, a = 10.1237(8) A, b = 9.4959(4) A, c = 28.365(2) A, beta = 98.707(9) degrees, V = 2695.4(3) A(3), Z = 4; 4 crystallizes in the triclinic space group Ponebar, a = 10.0241(9) A, b = 11.2060(10) A, c = 13.0656(12) A, alpha = 84.883(11) degrees, beta = 71.163(10) degrees, gamma = 63.650(9) degrees, V = 1241.19(19) A(3), Z = 2.

Crystallography, X-Ray↗
PubMed2001

Statistical ensemble of scale-free random graphs.

A thorough discussion of the statistical ensemble of scale-free connected random tree graphs is presented. Methods borrowed from field theory are used to define the ensemble and to study analytically its properties. The ensemble is characterized by two global parameters, the fractal and the spectral dimensions, which are explicitly calculated. It is discussed in detail how the geometry of the graphs varies when the weights of the nodes are modified. The stability of the scale-free regime is also considered: when it breaks down, either a scale is spontaneously generated or else, a "singular" node appears and the graphs become crumpled. A new computer algorithm to generate these random graphs is proposed. Possible generalizations are also discussed. In particular, more general ensembles are defined along the same lines and the computer algorithm is extended to arbitrary (degenerate) scale-free random graphs.

Journal Article↗
PubMed2001

Virulence genes and P fimbriae PapA subunit diversity in canine and feline uropathogenic Escherichia coli.

In this study, a total of 118 Escherichia coli strains isolated from dogs (93) and cats (25) with urinary tract infection (UTI) were tested in a multiplex polymerase chain reaction for the presence of adhesin-encoding genes (pap, sfa, and afa), hemolysin encoding genes (hly), cytotoxic necrotizing factor 1 (cnf1) and aerobactin (aer) genes. Virulence gene frequencies detected in those isolates which had been randomly collected (68 canine strains) were: 43% pap, 57% sfa, 1% afa, 44% hly, 41% cnf1 and 34% aer. These frequencies were much higher in the remaining 50 hemolytic strains of either cat or dog origin. Virulence factor associations in the 80 hemolytic strains studied revealed that 50/80 simultaneously had two adhesin genes (pap and sfa) and two cytotoxin genes (hly and cnf1), and 15/80 in addition had the aer gene. The major structural subunit and antigenic determinant of P fimbriae of uropathogenic E. coli is PapA. Polymorphism in this subunit was studied by an F antigen-specific papA allele polymerase chain reaction in 51 canine and 22 feline pap positive E. coli strains. The most prevalent canine papA alleles were F10 (39%), F15 (37%) and F12 (35%). In feline strains F15 (50%) was more frequent, other allele frequencies were F12 (45%), F14 and F10 (27%) and F16 (23%). Only nine canine and two feline strains were negative for one of the 11 serologically defined F types of P fimbriae. Three copies of the pap operon were found in 16/51 canine and 9/22 feline UTI E. coli pap positive strains. In this study, we show that a particular combination of virulence genes appears with high frequency in dog and cat urinary tract E. coli strains (pap, sfa, hly, and cnf1). In spite of the more frequent presence of F10, F12 and F15 papA alleles in this virulence gene combination, the occurrence of different papA alleles in strains where up to three copies of the pap operon are present accounts for the observed P fimbriae diversity.

Alleles↗
PubMed2000

Posttranslational processing of Methanococcus voltae preflagellin by preflagellin peptidases of M. voltae and other methanogens.

Methanococcus voltae is a mesophilic archaeon with flagella composed of flagellins that are initially made with 11- or 12-amino-acid leader peptides that are cleaved prior to incorporation of the flagellin into the growing filament. Preflagellin peptidase activity was demonstrated in immunoblotting experiments with flagellin antibody to detect unprocessed and processed flagellin subunits. Escherichia coli membranes containing the expressed M. voltae preflagellin (as the substrate) were combined in vitro with methanogen membranes (as the enzyme source). Correct processing of the preflagellin to the mature flagellin was also shown directly by comparison of the N-terminal sequences of the two flagellin species. M. voltae preflagellin peptidase activity was optimal at 37 degrees C and pH 8.5 and in the presence of 0.4 M KCl with 0.25% (vol/vol) Triton X-100.

Electrophoresis, Polyacrylamide Gel↗