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91.
92.
Tenni R Sonaggere M Viola M Bartolini B Tira ME Rossi A Orsini E Ruggeri A Ottani V 《Micron (Oxford, England : 1993)》2006,37(7):640-647
Several properties of fibrillar collagens depend on abundance and position of ionic amino acids. We recently demonstrated that N-methylation and N-acetylation of Lys/Hyl amino group did not significantly alter the thermal stability of the triple helical conformation and that the binding of modified collagens I and II to decorin is lost only on N-acetylation. The positive charge at physiological pH of Lys/Hyl side chains is preserved only by N-methylation. We report here the new aspect of the influence of the same modifications on collagen self-aggregation in neutral conditions. Three collagen preparations are very differently affected by N-methylation: acid-soluble type I collagen maintains the ability to form banded fibrils with 67-nm periodicity, whereas almost no structured aggregates were detected for pepsin-soluble type I collagen; pepsin-soluble type II collagen forms a very different supramolecular species, known as segment long spacing (SLS). N-acetylation blocks the formation of banded fibrils in neutral conditions (as did all other chemical modifications reported in the literature), demonstrating that the positive charge of Lys/Hyl amino groups is essential for self-aggregation. Kinetic measurements by turbidimetry showed a sizeable increase of absorbance only for the two N-methylated samples forming specific supramolecular aggregates; however, the derivatization affects aggregation kinetics by increasing lag time and decreasing maximum slope of absorbance variation, and lowers aggregation competency. We discuss that the effects of N-methylation on self-aggregation are caused by fewer or weaker salt bridges and by decrease of hydrogen bonding potential and conclude that protonated Lys side chains are involved in the fibril formation process. 相似文献
93.
Henning Lühmann Enrique Quiroga‐Gonzlez Lorenz Kienle Viola Duppel Gero Neubüser Wolfgang Bensch 《无机化学与普通化学杂志》2019,645(3):198-206
Solvothermal syntheses of copper‐indium‐sulfides performed with different Cu:In:S ratios afforded crystallization of nanocrystalline Cu‐In‐S phases with compositions close to CuInS2, CuIn3S5, and CuIn7S11. Each sample shows a different and distinguishable morphology. The minority component CuInS2 with wurtzite‐type structure crystallizes as thin plates, which are preferably stacked parallel to black stacks. The component with composition CuIn3S5 forms isolated few nm thin layers being arranged like the petals of a flower growing from a common point. Finally, red CuIn7S11 is obtained as nanobelts with individual diameters of about 20 nm and lengths up to more than 1 μm. According to electron diffraction patterns and X‐ray diffractometry the structures of CuIn3S5 and CuIn7S11 cannot be assigned to known bulk phases of the Cu‐In‐S system, however first structure models are proposed. 相似文献
94.
The aim of this paper is to study the dynamic behaviour of functionally graded parabolic and circular panels and shells of
revolution. The First-order Shear Deformation Theory (FSDT) is used to study these moderately thick structural elements. The
treatment is developed within the theory of linear elasticity, when the materials are assumed to be isotropic and inhomogeneous
through the thickness direction. The two-constituent functionally graded shell consists of ceramic and metal that are graded
through the thickness, from one surface of the shell to the other. Two different power-law distributions are considered for
the ceramic volume fraction. For the first power-law distribution, the bottom surface of the structure is ceramic rich, whereas
the top surface is metal rich and on the contrary for the second one.
The governing equations of motion are expressed as functions of five kinematic parameters, by using the constitutive and kinematic
relationships. The solution is given in terms of generalized displacement components of the points lying on the middle surface
of the shell. The discretization of the system equations by means of the Generalized Differential Quadrature (GDQ) method
leads to a standard linear eigenvalue problem, where two independent variables are involved without using the Fourier modal
expansion methodology. Numerical results concerning eight types of shell structures illustrate the influence of the power-law
exponent and of the power-law distribution choice on the mechanical behaviour of parabolic and circular shell structures.
Preliminary results were presented by the authors at the XVIII° National Conference of Italian Association of Theoretical
and Applied Mechanics (AIMETA 2007) (Tornabene and Viola 27). 相似文献
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98.
The problem of solving x6 + y6 + z6 = u6 + v6 + w6, subject to certain auxiliary conditions, is reduced to a single cubic. In this way some earlier known solutions are inserted into an infinite cyclic group lying on the cubic. 相似文献
99.
Cortese B D'Amone S Manca M Viola I Cingolani R Gigli G 《Langmuir : the ACS journal of surfaces and colloids》2008,24(6):2712-2718
Wettability control has been widely investigated in the last decades for technological applications such as microfluidic devices and self-cleaning surfaces by modifying both the chemical composition and the geometric structure of the surfaces. Inspired by the typical morphology of superhydrophobic leaves (such as lotus leaves), we have developed a dual-scale roughness, micro- and nanosized, on polydimethylsiloxane (PDMS) surfaces. By combining different geometric parameters and plasma treatment conditions, the structures were controlled hierarchically, at different independent length scales. Both the microsized replicated pillars and the nanosized etched posts tuned the wettability of the PDMS surfaces in a very simple way, up to contact angles of 170 degrees . Furthermore, changes in the influence of micro- and nanoscale geometrical structures were investigated. Hysteresis and contact angles of water droplets are evaluated as a combined effect of micropillars and a superimposed roughness, resulting in high advancing contact angles and low sliding angles. 相似文献
100.
Structural determination and DPPH radical-scavenging activity of two acylated flavonoid tetraglycosides in oolong tea (Camellia sinensis) 总被引:1,自引:0,他引:1
Two major acylated flavonoid tetraglycosides were isolated from the methanol extract of oolong tea. Their structures were elucidated by spectroscopic methods as quercetin 3-O-[2(G)-(E)-coumaroyl-3(G)-O-beta-D-glucosyl-3(R)-O-beta-D-glucosylrutinoside] (1) and kaempferol 3-O-[2(G)-(E)-coumaroyl-3(G)-O-beta-D-glucosyl-3(R)-O-beta-D-glucosylrutinoside] (2). Compounds 1 and 2 exhibited scavenging activity against DPPH radical with EC(50) values of 30.5 and 487.2 microM, respectively. 相似文献