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Artigos de revistas sobre o assunto "Collage covalent"
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DIAB, Mohammad, Jiann-Jiu WU, and David R. EYRE. "Collagen type IX from human cartilage: a structural profile of intermolecular cross-linking sites." Biochemical Journal 314, no. 1 (1996): 327–32. http://dx.doi.org/10.1042/bj3140327.
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Type IX collagen, a quantitatively minor collagenous component of cartilage, is known to be associated with and covalently cross-linked to type II collagen fibrils in chick and bovine cartilage. Type IX collagen molecules have also been shown to form covalent cross-links with each other in bovine cartilage. In the present study we demonstrate by structural analysis and location of cross-linking sites that, in human cartilage, type IX collagen is covalently cross-linked to type II collagen and to other molecules of type IX collagen. We also present evidence that, if the proteoglycan form of type IX collagen is present in human cartilage, it can only be a minor component of the matrix, similar to findings with bovine cartilage.
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Wu, J. J., D. R. Eyre, and H. S. Slayter. "Type VI collagen of the intervertebral disc. Biochemical and electron-microscopic characterization of the native protein." Biochemical Journal 248, no. 2 (1987): 373–81. http://dx.doi.org/10.1042/bj2480373.
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The collagen framework of the intervertebral disc contains two major fibril-forming collagens, types I and II. Smaller amounts of other types of collagen are also present. On examination of the nature and distribution of these minor collagens within bovine disc tissue, type VI collagen was found to be unusually abundant. It accounted for about 20% of the total collagen in calf nucleus pulposus, and about 5% in the annulus fibrosus. It was discovered by serially digesting disc tissue with chondroitin ABC lyase and Streptomyces hyaluronidase that native covalent polymers of type VI collagen could be extracted. Electron micrographs of this material prepared by rotary shadowing revealed the characteristic dimensions of tetramers and double tetramers of type VI molecules, with their central rods and terminal globular domains. Molecular-sieve column chromatography on agarose under non-reducing non-denaturing conditions gave a series of protein peaks with molecular sizes equivalent to the tetramer, double tetramer and higher multimers. On SDS/polyacrylamide-gel electrophoresis after disulphide cleavage, these fractions of type VI collagen all showed a main band at Mr 140,000 and four lesser bands between Mr 180,000 and 240,000. On electrophoresis without disulphide cleavage in agarose/2.4% polyacrylamide only dimeric (six chains) and tetrameric (12 chains) forms of type VI molecules were present. The ability to extract all the type VI collagen of the tissue in 4 M-guanidinium chloride, and absence of aldehyde-mediated cross-linking residues on direct analysis, showed that, in contrast with most matrix collagens, type VI collagen does not function as a covalently cross-linked structural polymer.
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Blumberg, B., L. I. Fessler, M. Kurkinen, and J. H. Fessler. "Biosynthesis and supramolecular assembly of procollagen IV in neonatal lung." Journal of Cell Biology 103, no. 5 (1986): 1711–19. http://dx.doi.org/10.1083/jcb.103.5.1711.
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The rate of biosynthesis of procollagen IV, the principal collagen of basement membranes, and the concentration of specific RNAs coding for procollagen IV were measured in neonatal rat lungs. Both decreased sharply at birth and then recovered again a few days later. The supramolecular assembly of procollagen IV was followed in neonatal rat, mouse, and chick lungs, which actively elaborate endothelial and alveolar basement membranes, and in chick embryo gizzard which is rich in smooth muscle. The tetramer of four procollagen IV molecules linked covalently through their amino ends was isolated as an assembly intermediate from all these tissues. While noncovalent association of the carboxyl ends of two procollagen IV molecules occurred readily, the subsequent establishment of covalent cross-links was substantially slower in the junctional complexes of the carboxyl ends than of the amino ends. Both disulfide bonds and other, unidentified covalent links formed. The six component carboxyl peptides of a junctional complex became progressively covalently linked into two kinds of carboxyl peptide pairs. We conclude that both amino-linked tetramers and carboxyl-linked dimers of procollagen IV molecules are intermediates in the biological assembly of the collagen networks of these basement membranes.
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Ao, Haiyong, Youtao Xie, Honglue Tan, et al. "Fabrication and in vitro evaluation of stable collagen/hyaluronic acid biomimetic multilayer on titanium coatings." Journal of The Royal Society Interface 10, no. 84 (2013): 20130070. http://dx.doi.org/10.1098/rsif.2013.0070.
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Layer-by-layer (LBL) self-assembly technique has been proved to be a highly effective method to immobilize the main components of the extracellular matrix such as collagen and hyaluronic acid on titanium-based implants and form a polyelectrolyte multilayer (PEM) film by electrostatic interaction. However, the formed PEM film is unstable in the physiological environment and affects the long-time effectiveness of PEM film. In this study, a modified LBL technology has been developed to fabricate a stable collagen/hyaluronic acid (Col/HA) PEM film on titanium coating (TC) by introducing covalent immobilization. Scanning electron microscopy, diffuse reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the PEM film. Results of Sirius red staining demonstrated that the chemical stability of PEM film was greatly improved by covalent cross-linking. Cell culture assays further illustrated that the functions of human mesenchymal stem cells, such as attachment, spreading, proliferation and differentiation, were obviously enhanced by the covalently immobilized Col/HA PEM on TCs compared with the absorbed Col/HA PEM. The improved stability and biological properties of the Col/HA PEM covalently immobilized TC may be beneficial to the early osseointegration of the implants.
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Wu, Yuexin, and Gaoxiang Ge. "Complexity of type IV collagens: from network assembly to function." Biological Chemistry 400, no. 5 (2019): 565–74. http://dx.doi.org/10.1515/hsz-2018-0317.
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Abstract Collagens form complex networks in the extracellular space that provide structural support and signaling cues to cells. Network-forming type IV collagens are the key structural components of basement membranes. In this review, we discuss how the complexity of type IV collagen networks is established, focusing on collagen α chain selection in type IV collagen protomer and network formation; covalent crosslinking in type IV collagen network stabilization; and the differences between solid-state type IV collagen in the extracellular matrix and soluble type IV collagen fragments. We further discuss how complex type IV collagen networks exert their physiological and pathological functions through cell surface integrin and nonintegrin receptors.
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SEYER, JEROME M., and ANDREW H. KANG. "Covalent Structure of Collagen." Annals of the New York Academy of Sciences 460, no. 1 Biology, Chem (1985): 503–5. http://dx.doi.org/10.1111/j.1749-6632.1985.tb51223.x.
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Colman, RW, WR Figures, LM Scearce, AM Strimpler, FX Zhou, and AK Rao. "Inhibition of collagen-induced platelet activation by 5'-p- fluorosulfonylbenzoyl adenosine: evidence for an adenosine diphosphate requirement and synergistic influence of prostaglandin endoperoxides." Blood 68, no. 2 (1986): 565–70. http://dx.doi.org/10.1182/blood.v68.2.565.565.
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Abstract The relative roles of platelet autacoids such as adenosine diphosphate (ADP), prostaglandin endoperoxides, and thromboxane A2 (TXA2) in collagen-induced platelet activation are not fully understood. We reexamined this relationship using the ADP affinity analogue, 5'-p- fluorosulfonylbenzoyl adenosine (FSBA), which covalently modifies a receptor for ADP on the platelet surface, thereby inhibiting ADP- induced platelet activation. Collagen-induced shape change, aggregation, and fibrinogen binding were each fully inhibited under conditions in which FSBA is covalently incorporated and could not be overcome by raising the collagen used to supramaximal concentrations. In contrast, TXA2 synthesis stimulated by collagen under conditions that produced maximum aggregation was only minimally inhibited by FSBA. Since covalent incorporation of FSBA has been previously shown to specifically inhibit ADP-induced activation of platelets, the present study supports the contention that ADP is required for collagen-induced platelet activation. Under similar conditions, indomethacin, an inhibitor of cyclooxygenase, inhibited collagen-induced shape change, indicating that endoperoxides and/or TXA2 also play a role in this response. Shape change induced by low concentrations (10 nmol/L) of the stable prostaglandin endoperoxide, azo-PGH2, was also inhibited by FSBA. These observations indicate a role for ADP in responses elicited by low concentrations of endoperoxides. However, at higher concentrations of azo-PGH2 (100 nmol/L), inhibition by FSBA could be overcome. Thus, the effect of collagen apparently has an absolute requirement for ADP for aggregation and fibrinogen binding and for both ADP and prostaglandins for shape change. Aggregation and fibrinogen binding induced by prostaglandin endoperoxides also required ADP as a mediator, but ADP is not absolutely required at high endoperoxide concentration to induce shape change.
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Colman, RW, WR Figures, LM Scearce, AM Strimpler, FX Zhou, and AK Rao. "Inhibition of collagen-induced platelet activation by 5'-p- fluorosulfonylbenzoyl adenosine: evidence for an adenosine diphosphate requirement and synergistic influence of prostaglandin endoperoxides." Blood 68, no. 2 (1986): 565–70. http://dx.doi.org/10.1182/blood.v68.2.565.bloodjournal682565.
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The relative roles of platelet autacoids such as adenosine diphosphate (ADP), prostaglandin endoperoxides, and thromboxane A2 (TXA2) in collagen-induced platelet activation are not fully understood. We reexamined this relationship using the ADP affinity analogue, 5'-p- fluorosulfonylbenzoyl adenosine (FSBA), which covalently modifies a receptor for ADP on the platelet surface, thereby inhibiting ADP- induced platelet activation. Collagen-induced shape change, aggregation, and fibrinogen binding were each fully inhibited under conditions in which FSBA is covalently incorporated and could not be overcome by raising the collagen used to supramaximal concentrations. In contrast, TXA2 synthesis stimulated by collagen under conditions that produced maximum aggregation was only minimally inhibited by FSBA. Since covalent incorporation of FSBA has been previously shown to specifically inhibit ADP-induced activation of platelets, the present study supports the contention that ADP is required for collagen-induced platelet activation. Under similar conditions, indomethacin, an inhibitor of cyclooxygenase, inhibited collagen-induced shape change, indicating that endoperoxides and/or TXA2 also play a role in this response. Shape change induced by low concentrations (10 nmol/L) of the stable prostaglandin endoperoxide, azo-PGH2, was also inhibited by FSBA. These observations indicate a role for ADP in responses elicited by low concentrations of endoperoxides. However, at higher concentrations of azo-PGH2 (100 nmol/L), inhibition by FSBA could be overcome. Thus, the effect of collagen apparently has an absolute requirement for ADP for aggregation and fibrinogen binding and for both ADP and prostaglandins for shape change. Aggregation and fibrinogen binding induced by prostaglandin endoperoxides also required ADP as a mediator, but ADP is not absolutely required at high endoperoxide concentration to induce shape change.
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Gwiazda, Marcin, Sheetal K. Bhardwaj, Ewa Kijeńska-Gawrońska, Wojciech Swieszkowski, Unni Sivasankaran, and Ajeet Kaushik. "Impedimetric and Plasmonic Sensing of Collagen I Using a Half-Antibody-Supported, Au-Modified, Self-Assembled Monolayer System." Biosensors 11, no. 7 (2021): 227. http://dx.doi.org/10.3390/bios11070227.
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This research presents an electrochemical immunosensor for collagen I detection using a self-assembled monolayer (SAM) of gold nanoparticles (AuNPs) and covalently immobilized half-reduced monoclonal antibody as a receptor; this allowed for the validation of the collagen I concentration through two different independent methods: electrochemically by Electrochemical Impedance Spectroscopy (EIS), and optically by Surface Plasmon Resonance (SPR). The high unique advantage of the proposed sensor is based on the performance of the stable covalent immobilization of the AuNPs and enzymatically reduced half-IgG collagen I antibodies, which ensured their appropriate orientation onto the sensor’s surface, good stability, and sensitivity properties. The detection of collagen type I was performed in a concentration range from 1 to 5 pg/mL. Moreover, SPR was utilized to confirm the immobilization of the monoclonal half-antibodies and sensing of collagen I versus time. Furthermore, EIS experiments revealed a limit of detection (LOD) of 0.38 pg/mL. The selectivity of the performed immunosensor was confirmed by negligible responses for BSA. The performed approach of the immunosensor is a novel, innovative attempt that enables the detection of collagen I with very high sensitivity in the range of pg/mL, which is significantly lower than the commonly used enzyme-linked immunosorbent assay (ELISA).
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Siverino, Claudia, Shorouk Fahmy-Garcia, Didem Mumcuoglu, et al. "Site-Directed Immobilization of an Engineered Bone Morphogenetic Protein 2 (BMP2) Variant to Collagen-Based Microspheres Induces Bone Formation In Vivo." International Journal of Molecular Sciences 23, no. 7 (2022): 3928. http://dx.doi.org/10.3390/ijms23073928.
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For the treatment of large bone defects, the commonly used technique of autologous bone grafting presents several drawbacks and limitations. With the discovery of the bone-inducing capabilities of bone morphogenetic protein 2 (BMP2), several delivery techniques were developed and translated to clinical applications. Implantation of scaffolds containing adsorbed BMP2 showed promising results. However, off-label use of this protein-scaffold combination caused severe complications due to an uncontrolled release of the growth factor, which has to be applied in supraphysiological doses in order to induce bone formation. Here, we propose an alternative strategy that focuses on the covalent immobilization of an engineered BMP2 variant to biocompatible scaffolds. The new BMP2 variant harbors an artificial amino acid with a specific functional group, allowing a site-directed covalent scaffold functionalization. The introduced artificial amino acid does not alter BMP2′s bioactivity in vitro. When applied in vivo, the covalently coupled BMP2 variant induces the formation of bone tissue characterized by a structurally different morphology compared to that induced by the same scaffold containing ab-/adsorbed wild-type BMP2. Our results clearly show that this innovative technique comprises translational potential for the development of novel osteoinductive materials, improving safety for patients and reducing costs.
Teses / dissertações sobre o assunto "Collage covalent"
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Lomonaco, Quentin. "Etude du collage SAB pour l'élaboration d'hétérostructure." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALY027.
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Les travaux de thèse présentés dans ce manuscrit sont consacrés à l'étude du collage SAB (de l'anglais « Surface Active Bonding ») appliqué à la fabrication d'hétérostructures. Il s’agit d’assemblages de plusieurs matériaux souvent utilisés dans l'optoélectronique et la photonique. Le collage SAB est une technique de collage direct sous ultravide permettant l'adhésion spontanée de deux surfaces sans l’utilisation de colle.Jusqu’à présent, les contraintes mécaniques, résultant des différences de coefficients de dilatation thermique entre les matériaux formant l’hétérostructure, représentent un défi majeur pour la fabrication d’hétérostructures ; mais contrôlées, elles peuvent également être avantageuses pour la fabrication et la qualité des produits finaux.L’approche technologique utilisée dans cette étude se concentre sur la fabrication d'hétérostructures en films minces monocristallins à partir de substrats épais, en utilisant le procédé Smart Cut™ et le collage SAB.Ce travail introduit pour la première fois la possibilité de réaliser des collages à chaud grâce à la technologie de collage SAB, en développant une nouvelle méthode appelée SAHB pour « Surface Active Hot Bonding ». Cette dernière offre la possibilité de contrôler la température lors de l’assemblage, permettant ainsi de gérer les contraintes mécaniques dues aux différences de coefficients d'expansion thermique dans l’hétérostructure. Une application remarquable de cette nouvelle méthode SAHB, mise en oeuvre dans le cadre de ces travaux, est la réalisation de reports de films contraints de germanium monocristallins de plusieurs centaines de nanomètres sur substrats de silicium. La modélisation par éléments finis est utilisée pour comprendre cette technologie de collage SAHB, car elle permet de visualiser les déformations des structures et d'estimer les niveaux de contrainte afin de limiter la casse de l’hétérostructure lors de sa fabrication, tout en maximisant la contrainte stockée dans le film reporté. De plus, l’étude du collage SAHB permet de mettre en évidence la nécessité d’une gestion précise de la température et d’une grande qualité de l'atmosphère de collage pour garantir son efficacité.Cette étude a mené à l’investigation des mécanismes du collage SAB, par des travaux sur l’impact de l’activation sur l’amorphisation l’interface de collage. Les résultats montrent que la seule présence de liaisons pendantes ne suffit pas à expliquer la très forte adhérence des collages SAB standards, mais qu’il est nécessaire que la surface soit suffisamment « malléable » pour permettre aux pointes d'aspérités de s'écraser et aux liaisons pendantes de s'appairer.Les travaux présentés dans ce manuscrit introduisent une nouvelle méthode de collage, le SAHB, et développent la fabrication des premières hétérostructures par cette voie. Cette méthode ouvre de nouvelles perspectives pour la fabrication de structures complexes et la manipulation des contraintes dans les matériaux hétérogènes.Mots clés : Collage direct, collage covalent, collage SAB, collage d’hétérostructures, collage de silicium, collage SAHB, transfert de film, films minces monocristallins<br>These research work presented in this thesis are dedicated to the study of SAB, "Surface Active Bonding", for the fabrication of heterostructures. These are assemblies of several materials often used in optoelectronics and photonics. SAB bonding is a direct bonding technique under ultrahigh vacuum that enables the spontaneous covalent bonding of two surfaces without glue.To date, mechanical stresses, resulting from differences in thermal expansion coefficients between the materials forming the heterostructure, represent a major challenge for the manufacture of heterostructures; but controlled, they can also be advantageous for the manufacture process and the quality of the final products.The field of studies developed in this study focuses on the fabrication of single-crystal thin-film heterostructures from thick substrates, using the Smart Cut™ process and SAB bonding.This work introduces for the first time the possibility of producing hot bonds using SAB bonding technology, by developing a new method called SAHB for "Surface Active Hot Bonding". The latter offers the opportunity of controlling the temperature during bonding, enabling mechanical stresses due to differences in thermal expansion coefficients in the heterostructure to be managed. One of the main applications of this new SAHB method is that it can be used to transfer strained single-crystal germanium films of several hundred nanometers onto silicon substrates. Finite-element modeling is used to understand this SAHB bonding technology, as it enables structural deformations to be visualized and stress levels to be estimated in order to limit heterostructure breakage during fabrication, while maximizing the stress stored in the transferred film. In addition, the study of SAHB bonding highlights the need for precise temperature management and a high-quality bonding atmosphere to guarantee its effectiveness.This study led to the investigation of SAB bonding mechanisms, with work on the impact of activation on the amorphization of the bonding interface. The results show that the mere presence of dangling bonds is not sufficient to explain the very high adherence of standard SAB, but that it is necessary for the surface to be sufficiently "malleable" to allow asperity tips to crush and dangling bonds to pair.The work presented in this manuscript introduce a new bonding method, the SAHB, and develops the production of the first heterostructures by this route. This method opens up new perspectives for the fabrication of complex structures and the manipulation of stresses in heterogeneous materials.Keywords: Direct bonding, covalent bonding, SAB bonding, heterostructure bonding, silicon bonding, SAHB bonding, film transfer, thin monocrystalline films
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Chen, Jingsong [Verfasser]. "Covalent coupling of growth factors to collagen matrices : a novel development towards a tissue substitute with enhanced angiogenesis / vorgelegt von Jingsong Chen." 2001. http://d-nb.info/963958801/34.
Texto completo da fonteCapítulos de livros sobre o assunto "Collage covalent"
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Gautheron, Danièle C., Bruno G. Blanchy, and Pierre R. Coulet. "Enzymes Covalently Bound on Collagen Membranes Immobilization of Blood Clotting Factor XIII." In Advances in Experimental Medicine and Biology. Springer US, 1988. http://dx.doi.org/10.1007/978-1-4684-7908-9_26.
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"Collagen and Skin Structure." In Tanning Chemistry: The Science of Leather, 2nd ed. The Royal Society of Chemistry, 2019. http://dx.doi.org/10.1039/9781788012041-00001.
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In order to understand the principles that underpin the conversion of hide or skin to leather, it is necessary to know the fundamental structure of the raw material and how that structure might be modified chemically. The chemistry of collagen defines not only the sequencing of its amino acid constituents but also the physical nature of its structure and how it creates levels of structure or a hierarchy. This depends on the chains creating a triple helix as the basic unit of structure. The chemical properties of collagen are defined by the sidechains on the helices, which may be charged, depending on the pH; in this way, collagen can undergo a wide range of covalent or electrostatic reactions, which are the basis for tanning processes. At the heart of the chemistry of collagen is the relationship with water, which is an integral feature of structure: the supramolecular matrix of water around the triple helices provides the region for chemical modification, leading to tanning technology.
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Berg, Richard A. "Enzymes involved in the post-translational processing of collagen." In Extracellular Matrix. Oxford University PressOxford, 1995. http://dx.doi.org/10.1093/oso/9780199632213.003.0006.
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Abstract An affinity column technique for isolating enzymes or proteins bound to macromolecular substrates such as collagen was designed by covalently linking the macromolecule to a chromatography resin. This method has been developed for the purification of prolyl hydroxylase to homogeneity (1). The purified enzyme from a number of sources including chick embryos, human fibroblasts, and human liver was found to be a tetramer composed of two pairs of non-identical subunits α and β, (2). Recently it has been found that the pair of β, subunits of prolyl hydroxylase is identical to protein disulfide isomerase (3) which is non-covalently associated with the 2 α subunits of prolyl hydroxylase to produce an α2, β2 tetrameric structure.
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Atkins, Peter, Julio de Paula, and David Smith. "Interactions between molecules." In Elements of Physical Chemistry. Oxford University Press, 2016. http://dx.doi.org/10.1093/hesc/9780198727873.003.0062.
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This chapter looks at liquids and solids which are bound together by one or more cohesive interactions, such as van der Waals interactions, hydrogen bonding, and hydrophobic effect. It describes the strengths of the various van der Waals interactions, which are related to dipole moments and polarizabilities. It also explains how van der Waals interactions exclude interactions which result from the formation of covalent or ionic bonds and are restricted to interactions for which the potential energy is inversely proportional to the sixth power of the separation of the molecules. The chapter discusses how attractive interactions result in cohesion, while repulsive interactions prevent the complete collapse of matter to nuclear densities. It looks at several types of molecular interactions responsible for the formation of condensed phases and large molecular assemblies.
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Wadman, Isobel A., Kanwar Virdee, Denise S. Fernandez, Christine L. Wasunna, and Richard W. Farndale. "Measurement of protein phosphorylation, kinase activity, and G protein function in intact platelets and membrane preparations." In Platelets. Oxford University PressOxford, 1996. http://dx.doi.org/10.1093/oso/9780199635382.003.0009.
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Abstract We have collated in this chapter methods for locating or determining the activity of platelet signalling proteins. SDS-PAGE provides a means of separating the proteins, their labelling is achieved either by covalent or affinity methods, and they are usually detected on film, either by autoradiography or Western blotting. The preparation of platelets and platelet membranes from Blood Transfusion Service concentrates, together with basic electrophoretic methods, are described in Section 1. Methods for protein phosphorylation and the determination of kinase activity are described in Section 2, and for GTP binding proteins in Section 3. We expect that the reader will modify the precise conditions of the methods to suit their particular need; the protocols below will provide a starting point from which these and other assays may be developed.
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Rodriguez-Pascual, Fernando. "The Evolutionary Origin of Elastin: Is Fibrillin the Lost Ancestor?" In Extracellular Matrix - Developments and Therapeutics [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.95411.
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Elastin is the extracellular matrix protein providing large arteries, lung parenchyma and skin with the properties of extensibility and elastic recoil. Within these tissues, elastin is found as a polymer formed by tropoelastin monomers assembled and cross-linked. In addition to specific protein regions supporting the covalent cross-links, tropoelastin is featured by the presence of highly repetitive sequences rich in proline and glycine making up the so-called hydrophobic domains. These protein segments promote structural flexibility and disordered protein properties, a fundamental aspect to explain its elastomeric behavior. Unlike other matrix proteins such as collagens or laminins, elastin emerged relatively late in evolution, appearing at the divergence of jawed and jawless fishes, therefore present in all species from sharks to humans, but absent in lampreys and other lower chordates and invertebrates. In spite of an intense interrogation of the key aspects in the evolution of elastin, its origin remains still elusive and an ancestral protein that could give rise to a primordial elastin is not known. In this chapter, I review the main molecular features of tropoelastin and the available knowledge on its evolutionary history as well as establish hypotheses for its origin. Considering the remarkable similarities between the hydrophobic domains of the first recognizable elastin gene from the elasmobranch Callorhinchus milii with certain fibrillin regions from related fish species, I raise the possibility that fibrillins might have provided protein domains to an ancestral elastin that thereafter underwent significant evolutionary changes to give the elastin forms found today.
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Lambert, Tristan H. "Asymmetric C–Heteroatom Bond Formation." In Organic Synthesis. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190200794.003.0036.
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Tomislav Rovis at Colorado State University developed (Angew. Chem. Int. Ed. 2012, 51, 5904) an enantioselective catalytic cross-aza-benzoin reaction of aldehydes 1 and N-Boc imines 2. The useful α-amido ketone products 4 were configurationally stable under the reaction conditions. In the realm of asymmetric synthesis, few technologies have been as widely employed as the Ellman chiral sulfonamide auxiliary. Francisco Foubelo and Miguel Yus at the Universidad de Alicante in Spain have adapted (Chem. Commun. 2012, 48, 2543) this approach for the indium-mediated asymmetric allylation of ketimines 5, which furnished amines 6 with high diastereoselectivity. There has been vigorous research in recent years into the use of NAD(P)H surrogates, especially Hantzsch esters, for biomimetic asymmetric hydrogenations. Yong-Gui Zhou at the Chinese Academy of Sciences showed (J. Am. Chem. Soc. 2012, 134, 2442) that 9,10-dihydrophenanthridine (10) can also serve as an effective “H2” donor for the asymmetric hydrogenation of imines, including 7. Notably, 10 is used catalytically, with regeneration occurring under mild conditions via Ru(II)-based hydrogenation of the phenanthridine 11. A unique approach for asymmetric catalysis has been developed (Nature Chem. 2012, 4, 473) by Takashi Ooi at Nagoya University, who found that ion-paired complexes 14 could serve as effective chiral ligands in the Pd(II)-catalyzed allylation of α-nitrocarboxylates 12. The resulting products 13 are easily reduced to furnish α-amino acid derivatives. Another novel catalytic platform has been employed (J. Am. Chem. Soc. 2012, 134, 7321) for the chiral resolution of 1,2-diols 15 by Kian L. Tan at Boston College. Using the concept of reversible covalent binding, the catalyst 16 was found to selectively silylate a secondary hydroxyl over a primary one, thus leading to the enantioenriched products 17 and 18. Scott E. Denmark at the University of Illinois has applied (Angew. Chem. Int. Ed. 2012, 51, 3236) his chiral Lewis base strategy to the enantioselective vinylogous aldol reaction of N-silyl vinylketene imines 19 to produce γ-hydroxy-α,β-unsaturated nitriles 22. For the preparation of enantioenriched homopropargylic alcohols 25, the asymmetric addition of allenyl metal nucleophiles (e.g., 24) to aldehydes 23 provides a straightforward approach.
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Kihlberg, Jan. "Glycopeptide synthesis." In Fmoc Solid Phase Peptide Synthesis. Oxford University Press, 1999. http://dx.doi.org/10.1093/oso/9780199637256.003.0012.
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Most eukaryotic proteins, some bacterial and many viral proteins carry structurally diverse carbohydrates that are covalently attached through N- or O-glycosidic bonds to the side chains of asparagine, serine, threonine, hydroxylysine, tyrosine, and hydroxyproline. In nature, N-linked glycoproteins are assembled by post-translational, enzymatic attachment of a common oligosaccharide having the composition Glc3Man9GlcNAc2 to the side chain of asparagine. This saccharide is then modified enzymatically, thereby giving structural variation to the part remote from the protein. However, N-linked glycoproteins have a common pentasaccharide core (Manα3(Manα6)Manβ4GlcNAcβ4GlcNAc) in which the chitobiose moiety (GlcNAcβ4GlcNAc) is bound to asparagine. By contrast, O-linked glycoproteins are built up by sequential attachment of monosaccharides by different enzymes to hydroxylated amino acids in the protein, and therefore no common core is formed. Thus, N-acetyl-α-D-galactosamine attached to serine and threonine is found in mucin secreted from epithelial cells. β-D-Xylosyl serine is found in many proteoglycans, whereas β-D-galactosyl hydroxylysine is common in collagen found in connective tissue. α-L-Fucosyl residues linked to serine and threonine are found in fibrinolytic and coagulation proteins. N-Acetyl-β-D-glucosamine attached to serine and threonine occurs frequently in glycoproteins located in the nucleus and cytoplasm, whereas glycoproteins produced by yeast have α-D-mannosyl residues linked to serine and threonine. Larger structures are usually formed by attachment of additional saccharides to the O-linked 2-4 when found in glycoproteins. Structures 5,10, and 11 can also carry additional monosaccharides. In recent years numerous glycoproteins have been isolated and characterized, but the roles for the protein-bound carbohydrates have only just begun to be unravelled. It is now well established that glycosylation affects both the physiochemical properties and the biological functions of a glycoprotein. For instance, glycosylation has been found to influence uptake, distribution, excretion, and proteolytic stability. It is also known to have important roles in communication between cells and in attachment of bacteria and viruses to the host. Efforts to understand the role of glycosylation of proteins, or to develop glycopeptides as tools in drug discovery and drug design, have led to substantial progress in development of methodology for the synthesis of glycopeptides during the last decades.
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Taber, Douglass F. "Carbon-Carbon Bond Formation." In Organic Synthesis. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780199965724.003.0025.
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Akiya Ogawa of Osaka Prefecture University found (Tetrahedron Lett. 2010, 51, 6580) that the Sm-mediated reductive coupling of a halide 1 with CO2 to give the carboxylic acid 2 was strongly promoted by visible light. Gregory C. Fu of MIT designed (Angew. Chem. Int. Ed. 2010, 49, 6676) a Ni catalyst for the coupling of a primary borane 4 with a secondary alkyl halide 3. James P. Morken of Boston College devised (Org. Lett. 2010, 12, 3760) conditions for the carbonylative conjugate addition of a dialkyl zinc to an enone 6 to give the 1,4-dicarbonyl product 7. Louis Fensterbank of the Institut Parisien de Chimie Moléculaire developed (Angew. Chem. Int. Ed. 2010, 49, 8721; not illustrated) a protocol for the conjugate addition of alkyl boranes to enones. Hyunik Shin of LG Life Science, Daejeon, and Sang-gi Lee of Ewha Womans University showed (Tetrahedron Lett. 2010, 51, 6893) that the intermediate from Blaise homologation of a nitrile 8 was a powerful nucleophile, smoothly opening an epoxide 10 to deliver 11. Sébastien Reymond and Janine Cossy of ESPCI ParisTech found (J. Org. Chem. 2010, 75, 5151) that FeCl3 smoothly catalyzed the coupling of an alkenyl Grignard 13 with the primary iodide 12. The Ti-mediated coupling of an alkyne 16 with an allylic alkoxide 15 (J. Am. Chem. Soc. 2010, 132, 9576) developed by Glenn C. Micalizio of Scripps/Florida was the key step in the total synthesis (J. Am. Chem. Soc. 2010, 132, 11422) of lehualide B. Huanfeng Jiang of the South China University of Technology observed (Chem. Commun. 2010, 46, 8049) that KI added to a bromoalkyne 18 to give the dihalide 19 with high geometric control. Haruhiko Fuwa of Tohoku University improved (Org. Lett. 2010, 12, 5354) the selective hydroiodination of a methyl alkyne 20 to 21. Takuya Kurahashi and Seijiro Matsubara of Kyoto University devised (Chem. Commun. 2010, 46, 8055) the Ni-catalyzed three-component coupling of an alkyne 22, methyl acrylate 23, and phenyl isocyanate to give the doubly homologated lactam 24. Patrick H. Toy of the University of Hong Kong showed (Synlett 2010, 1997; Org. Lett. 2010, 12, 4996 for a polymer with covalently attached base) that resin-bound triphenylphosphine participated efficiently in the Wittig coupling of 26 with an aldehyde 25.
Trabalhos de conferências sobre o assunto "Collage covalent"
1
Bourne, Jonathan W., Jared M. Lippell, and Peter A. Torzilli. "Covalent Cross-Linking Accelerates Collagen Enzyme Mechano-Kinetic Cleavage: Nanomechanics Predicts Microscale Behavior." In ASME 2012 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/sbc2012-80392.
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Fibrillar collagens are an integral structural element of tissues throughout the body and help provide tensile strength. These collagens are highly resistant to degradation other than by a small number of collagenolytic enzymes. Examples of tensile mechanical forces in vivo include expansion and contraction of blood vessels, tension on tendons and ligaments, and compression and swelling of cartilage.
2
Balguid, Angelique, Anita Mol, Niels Driessen, Carlijn Bouten, and Frank Baaijens. "Stress Dependent Collagen Fibril Diameter Distribution in Human Aortic Valves." In ASME 2007 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2007. http://dx.doi.org/10.1115/sbc2007-175644.
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The mechanical properties of collagenous tissues are known to depend on a wide variety of factors, such as the type of tissue and the composition of its extracellular matrix. Relating mechanical roles to individual matrix components in such a complex system is difficult, if not impossible. However, as collagen is the main load bearing component in connective tissues, the relation between collagen and tissue biomechanics has been studied extensively in various types of tissues. The type of collagen, the amount and type of inter- and intramolecular covalent cross-links and collagen fibril morphology are involved in the tissues mechanical behavior (Beekman et al., 1997; Parry et al., 1978; Avery and Bailey, 2005). From literature it is known that the the collagen fibril diameter distribution can be directly related to the mechanical properties of the tissue. In particular, the diameter distribution of collagen fibrils is largely determined by the tissues requirement for tensile strength and elasticity (Parry et al., 1978).
3
Hatami-Marbini, Hamed, and Ebitimi Etebu. "Influence of Ionic Concentration on Swelling Behavior and Shear Properties of the Bovine Cornea." In ASME 2012 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/sbc2012-80896.
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The mechanical properties and structure of connective tissues such as the cornea and the cartilage are derived from the functions and properties of their extracellular matrix, a polyelectrolyte gel composed of collagenous fibers embedded in an aqueous matrix. The collagen fibers in the extracellular matrix of the corneal stroma are arranged in regular lattice structures, which is necessary for corneal transparency and transmitting the incident light to the back of the eye. This regular pseudo hexagonal arrangement is attributed to the interaction of collagen fibers with the proteoglycans as these regularities are lost in knock-out mice [i]. Proteoglycans (PGs) are heavily glycosylated glycoproteins. They consist of a core protein to which is glycosaminoglycan chains are covalently attached. The main PG in the corneal stroma is the proteoglycan decorin. Decorin is the simplest small leucine-rich PG and only has a single glycosaminoglycan side chain. It has a horse shape core protein and binds collagen fibrils at regular sites. Chondroitin sulfate (CS), dermatan sulfate (DS), keratan sulfate (KS) are among the prevalent glycosaminoglycans found in the cornea. Under physiological conditions, these linear carbohydrate polymers are ionized and carry negative charges due to the presence of negatively charged carboxylate and sulfate groups. Therefore, a hydrated gel is formed in the empty space between collagen fibrils by attracting water. The interaction of negatively charged glycosaminoglycans with themselves and their interaction with the free ions contribute to the corneal swelling pressure and subsequently to its compressive stiffness. From structural view point, the corneal stroma is a composite polyelectrolyte system in which the observed regular spacings of the collagens are suggested to exist because of the structural interaction of collagens, negatively charged glycosaminoglycans, and the free ions in the interfibrillar space.
4
Twomey, John R., Vivek Sundaram, Krishna Madhavan, and Wei Tan. "Characterization of Carbon Nanotube-Conjugated Collagen Composite Matrix Mechanics." In ASME 2007 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2007. http://dx.doi.org/10.1115/sbc2007-176643.
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In the case of vascular grafts, enhanced mechanical properties of engineered tissue constructs are required in order to function properly in mechanically-active physiologic conditions. It is proposed that a composite matrix constructed of type I collagen, fibronectin, and covalently-functionalized single-walled carbon nanotubes (SWNTs) will provide the desired mechanical properties required for the development of implantable tissues capable of withstanding high-stress environments.
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Drzewiecki, Kathryn, Ian Gaudet, Douglas Pike, Jonathan Branch, Vikas Nanda, and David Shreiber. "Temperature Dependent Reversible Self Assembly of Methacrylated Collagen Gels." In ASME 2013 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/sbc2013-14705.
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Hydrogel-based tissue engineering scaffolds can allow tissues to repair and regenerate by providing a 3D environment similar to soft tissue. Type I collagen has the ability to assemble into a fibrillar gel at physiological temperature and pH, while promoting cell adhesion and growth. Our lab has modified type I collagen by covalently adding methacrylate groups to lysine residues to create collagen methacrylamide (CMA). This biomaterial, like collagen, maintains the ability to self-assemble, and can then be photocrosslinked with long-wave UV light and a water-soluble photoinitiator, which allows extensive spatiotemporal control of mechanical and biochemical properties [1]. In characterizing CMA and developing it for other applications, we discovered an interesting property. Unlike type I collagen hydrogels, which maintain a stable fibrillar network during cooling and freezing, CMA will spontaneously disassemble at temperatures less than 10°C. In this paper, we discuss the temperature-dependent rheological properties of CMA as well as the nature of its molecular and supramolecular structure in comparison to collagen.
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Hatami-Marbini, Hamed, and Peter M. Pinsky. "Electrostatic Contribution of the Proteoglycans to the In-Plane Shear and Compressive Stiffness of Corneal Stroma." In ASME 2010 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2010. http://dx.doi.org/10.1115/sbc2010-19191.
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The extracellular matrix (ECM) is a fibrous structure embedded in an aqueous gel. The mechanical and electrostatic interactions of the ECM constituents, i.e. collagen fibers and proteoglycans (PGs), define the structure and mechanical response of connective tissues (CTs) such as cornea and articular cartilage. Proteoglycans are complex macromolecules consisting of linear chains of repeating gylcosaminoglycans (GAGs) which are covalently attached to a core protein. PGs can be as simple as decorin with a single GAG side chain or as complex as aggrecan with many GAGs. Decorin is the simplest small leucine-rich PG and is the main PG inside the corneal stroma. It has an arch shape and links non-covalently at its concave surface to the collagen fibrils. It has been shown that while collagen fibers inside the extracellular matrix resist the tensile forces, the negatively charged glycosaminoglycans and their interaction with water give compressive stiffness to the tissue. The role of PGs in biomechanical properties of the connective tissues has mainly been studied in order to explore the behavior of articular cartilage [1], which is a CT with large and highly negatively charged PGs, aggrecans. In order to explain the role of PGs in this tissue, it is commonly assumed that their contribution to the CT elasticity is because of both the repulsive forces between negatively charged GAGs and GAG interactions with free mobile charges in the ionic bath. The electrostatic contribution to the shear and compressive stiffness of cartilage is modeled by approximating GAGs as charged rods [1]. The Poisson-Boltzmann equation is used to compute the change in electrical potential and mobile ion distributions which are caused by the macroscopic deformation.
7
Ni, Qingwen, and Naniel P. Nicolella. "Assessment of Bone Quality Associated With Loosely and Tightly Bound Water." In ASME 2010 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2010. http://dx.doi.org/10.1115/sbc2010-19300.
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Previous studies have shown that the age-related increase in bone porosity results a decrease in bone strength, and porosity is related to the volume of mobile water in the pores. In addition, since water is also bound to collagen and mineral, changes in the amount of bound water will potentially affect the bone strength. It is known that the removal of the loosely bound water (via hydrogen bonding) requires less energy than the water molecules trapped inside collagen molecules, which in turn requires similar or less energy than water molecules bound to the surface charges of mineral apatite (more ionic in nature). Also, water that is imbedded in the lattice of hydroxyapatite (more covalent in nature) requires the highest energy to dislodge. However, there is no traditional method that can determine mobile and bound water, further for loosely and tightly bound ware accurately, non-destructively and non-invasively. Here, we propose that by using NMR Car-Purcell-Meiboom-Gill (CPMG) spin-spin relaxation measurement to determine the mobile water, and the NMR inversion T2-FID spectrum derived from NMR free induction decay (FID) measurements for estimating the bound and free water distribution. Furthermore, after comparison of the total water lost (weighing method) within tissue by using drying (free dry) on the air to the total mobile water lost measured by NMR CPMG method, then, the total loosely bound water lost can be estimated. Following this, the mechanical test will be used to evaluate the bone quality related to the tightly and loosely bound water within bone. This information can be used to further assessment of bone quality.
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Hatami-Marbini, Hamed, Ebitimi Etebu, and Abdolrasol Rahimi. "Characterizing Swelling Pressure and Hydration Relationship for Porcine Corneal Stroma." In ASME 2013 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/sbc2013-14759.
Texto completo da fonteResumo:
The mechanical properties and structure of connective tissues such as the cornea and articular cartilage are derived from the functions and properties of their extracellular matrix, which is a polyelectrolyte gel composed of collagenous fibers embedded in an aqueous matrix. The collagen fibrils in the extracellular matrix of the corneal stroma are arranged in a regular lattice structure, which is necessary for corneal transparency and transmitting the incident light to the back of the eye. This regular pseudo hexagonal arrangement is attributed to the interaction of collagen fibrils with the proteoglycans; these regularities are lost in proteoglycan knock-out mice [1]. Proteoglycans are heavily glycosylated glycoproteins consisting of a core protein to which glycosaminoglycan chains are covalently attached. The main proteoglycan in the corneal stroma is decorin. Decorin is the simplest small leucine-rich proteoglycan with only a single glycosaminoglycan side chain. It has a horse shape core protein and binds collagen fibrils at regular sites. Under normal physiological conditions, these linear carbohydrate polymers are ionized and carry negative charges due to the presence of negatively charged carboxylate and sulfate groups. The presence of these fixed charges creates an imbalance of charge density within the stroma and its surrounding aqueous domain. Therefore, the tissue has a tendency to swell when immersed in a bathing solution. In order to create mathematical models for the corneal mechanics, a proper experimental characterization of the swelling properties of the tissue is necessary.
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Wunder, A., EH Stelzer, H. Sinn, J. Funk, AD Ho, and C. Fiehn. "THU0107 Methotrexate covalently coupled to human serum albumin (mtx-hsa) targets to inflamed joints and is superior to methotrexate inhibiting the development of murine collagen-induced arthritis (cia)." In Annual European Congress of Rheumatology, Annals of the rheumatic diseases ARD July 2001. BMJ Publishing Group Ltd and European League Against Rheumatism, 2001. http://dx.doi.org/10.1136/annrheumdis-2001.984.
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