Nanosecond fluctuations of the molecular backbone of collagen in hard and soft tissues: a carbon-13 nuclear magnetic resonance relaxation study

We have determined the amplitude of nanosecond fluctuations of the collagen azimuthal orientation in intact tissues and reconstituted fibers from an analysis of 13C NMR relaxation data. We have labeled intact rat calvaria and tibia collagen (mineralized and cross-linked), intact rat tail tendon and demineralized bone collagen (cross-linked), and reconstituted lathyritic (non-cross-linked) chick calvaria collagen with [2-13C]glycine. This label was chosen because one-third of the amino acid residues in collagen are glycine and because the 1H-13C dipolar coupling is the dominant relaxation mechanism. Spin-lattice relaxation times (T1) and nuclear Overhauser enhancements were measured at 15.09 and 62.98 MHz at 22 and -35 degrees C. The measured NMR parameters have been analyzed by using a dynamic model in which the azimuthal orientation of the molecule fluctuates as a consequence of reorientation about the axis of the triple helix. We have shown that if root mean square fluctuations in the azimuthal orientations are small, gamma rms much less than 1 rad, the correlation function decays with a single correlation time tau and T1 depends only upon tau and gamma rms and not the detailed model of motion. Our analysis shows that, at 22 degrees C, tau is in the 1-5-ns range for all samples and gamma rms is 10 degrees, 9 degrees, and 5.5 degrees for the non-cross-linked, cross-linked, and mineralized samples, respectively. At -35 degrees C, gamma rms is less than 3 degrees for all samples. These results show that mineral and low temperature significantly restrict the amplitude of nanosecond motions of the collagen backbone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Q fever urban cases in Romania

Q fever urban sporadic cases in Romania in the 1981-87 period are reviewed as concerns their incidence, seasonality and epidemiological data. Urban cases represented 76.8% as against 23.2% rural cases from the 134 Q fever sporadic cases detected in this period. Cases were distributed throughout all months with peaks during April (18.4% of cases) and June (19.4%). Infections were not related to contact with livestock or domestic birds or with raw milk drinking. Cases could not be identified as Q fever occupational ones. 36.7% of patients were working in nonalimentary industry and only 12.6% were involved in meat industry, veterinary or human medical practices. New studies concerning unusual sources of urban infection such as dogs, cats or urban street pigeons are emphasized.     

Synthesis of N-carboxyalkyl and N-aminoalkyl functionalized dipeptide building units for the assembly of backbone cyclic peptides.

To improve the assembly of backbone cyclic peptides, N-functionalized dipeptide building units were synthesized. The corresponding N-aminoalkyl or N-carboxyalkyl amino acids were formed by alkylation or reductive alkylation of amino acid benzyl or tert-butyl esters. In the case of N-aminoalkyl amino acid derivatives the aldehydes for reductive alkylation were obtained from N,O-dimethyl hydroxamates of N-protected amino acids by reduction with LiAlH4. N-carboxymethyl amino acids were synthesized by alkylation using bromoacetic acid ester and the N-carboxyethyl amino acids via reductive alkylation using aldehydes derived from formyl Meldrums acid. Removal of the carboxy protecting group leads to free N-alkyl amino acids of very low solubility in organic solvents, allowing efficient purification by extraction of the crude product. These N-alkyl amino acids were converted to their tetramethylsilane-esters by silylation with N,O-bis-(trimethylsilyl)acetamide and could thus be used for the coupling with Fmoc-protected amino acid chlorides or fluorides. To avoid racemization the tert-butyl esters of N-alkyl amino acids were coupled with the Fmoc-amino acid halides in the presence of the weak base collidine. Both the N-aminoalkyl and N-carboxyalkyl functionalized dipeptide building units could be obtained in good yield and purity. For peptide assembly on the solid support, the allyl type protection of the branching moiety turned out to be most suitable. The Fmoc-protected N-functionalized dipeptide units can be used like any amino acid derivative under the standard conditions for Fmoc-solid phase synthesis.     

The effect of substrate modification on binding of porcine pancreatic alpha amylase: hydrolysis of modified amylose containing D-allose residues

A modified amylose containing 10% of tritiated D-allose residues has been hydrolyzed by porcine pancreatic alpha amylase (PPA). This reaction produced a number of radioactive oligosaccharides of low molecular weight, including modified mono-, di-, and tri-saccharides, as well as larger products. Analysis of these products by chemical and enzymic methods identified D-allose, two isomers of modified maltose, and isomers of modified maltotriose. These results may be interpreted in terms of current PPA models to indicate that D-allose residues may be productively bound at all five subsites of the active site of the enzyme. The distribution of modified residues in these products, however, further suggests that productive binding of D-allose at the subsite where catalytic attack occurs (subsite 3) is less favorable than binding of D-glucose. These results are compared with results of a series of PPA substrates having modifications at C-3 and at other positions. Trends observed in enzyme hydrolysis of these modified substrates reflect factors that contribute to PPA catalysis, with respect to steric, electronic, and hydrogen-bonding interactions between enzyme and substrate.     

Effect of microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin

doi:10.1111/j.1741‐2358.2009.00333.x
Effect of microwave treatment on the shear bond strength of different types of commercial teeth to acrylic resin Objective: The purpose of this study was to verify the effect of microwave treatment on the shear bond strength of commercial types of teeth to acrylic resin, when the glossy ridge laps were unmodified (groups 1 and 5), bur abraded (groups 2 and 6), bur grooved (groups 3 and 7) or etched by monomer (groups 4 and 8). Background: Controversial findings have shown that mechanical or chemical changes in ridge‐lap surface of the tooth increase or decrease the bond strength between tooth and acrylic resin, and the microwave disinfection may cause different changes on this bond strength. Materials and methods: Eighty specimens (n = 10) were made with the acrylic resin bonded to tooth glossy ridge lap, polymerised in water at 74°C for 9 h, and deflasked after flask cooling. Specimens of the groups 5, 6, 7 and 8 were individually immersed in 150 ml of water and submitted to microwave treatment in an oven at 650 W for 3 min. Control specimens (groups 1, 2, 3 and 4) were not microwave treated. Shear bond strength test was performed in an Instron machine with a cross‐speed of 1 mm/min. Collected data were submitted to anova and Tukey’s test (α = 0.05). Results: Microwave treatment decreased the shear bond strength values of the tooth/resin bond. In the microwaved and non‐microwaved procedures, mechanical retention improved the shear bond strength when compared with the control and monomer treatments. Conclusion: Shear bond strength of the tooth/resin bond was influenced by the microwave treatment and different commercial teeth association, and was lower for the Biotone tooth.