title: Characterization of water in hydrated Bombyx mori silk fibroin fiber and films by2H NMR relaxation and13C solid state NMR.
abstract: The mechanical properties of Bombyx mori silk fibroin (SF), such as elasticity and tensile strength, change remarkably upon hydration. However, the microscopic interaction with water is not currently well understood on a molecular level. In this work, the dynamics of water molecules interacting with SF was studied by2H solution NMR relaxation and exchange measurements. Additionally, the conformations of hydrated [3-13C]Ala-, [3-13C]Ser-, and [3-13C]Tyr-SF fibers and films were investigated by13C DD/MAS NMR. Using an inverse Laplace transform algorithm, we were able to identify four distinct components in the relaxation times for water in SF fiber. Namely, A: bulk water outside the fiber, B: water molecules trapped weakly on the surface of the fiber, C: bound water molecules located in the inner surface of the fiber, and D: bound water molecules located in the inner part of the fiber were distinguishable. In addition, four components were also observed for water in the SF film immersed in methanol for 30s, while only two components for the film immersed in methanol for 24h. The effects of hydration on the conformation of Ser and Tyr residues in the site-specific crystalline and non-crystalline domains of13C selectively labeled SF, respectively, could be determined independently. Our measurements provide new insight relating the characteristics of water and the hydration structure of silk, which are relevant in light of current interest in the design of novel silk-based biomaterials.
  
  
  
  The mechanical properties of Bombyx mori silk fibroin (SF) change remarkably upon hydration. However, the microscopic interaction between SF and water is not currently well understood on a molecular level. We were able to identify four distinct components in the relaxation times for water in SF fiber by2H solution NMR relaxation and exchange measurements. In addition, the effects of hydration on the conformation of Ser and Tyr residues in the site-specific crystalline and non-crystalline domains of13C selectively labeled SF, respectively, could be determined independently. Thus, our measurements provide new insight relating the characteristics of water and the hydration structure of silk, which are relevant in light of current interest in the design of novel silk-based biomaterials.
authors.affiliation: Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan. Electronic address: asakura@cc.tuat.ac.jp.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Asakura
authors.affiliation: Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
authors.forename: Kotaro
authors.initials: K
authors.lastname: Isobe
authors.affiliation: Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Kametani
authors.affiliation: Department of Physics, Hunter College of The City University of New York, 695 Park Avenue, NY 10065, USA.
authors.forename: Obehi T
authors.initials: OT
authors.lastname: Ukpebor
authors.affiliation: Department of Physics, Hunter College of The City University of New York, 695 Park Avenue, NY 10065, USA.
authors.forename: Moshe C
authors.initials: MC
authors.lastname: Silverstein
authors.affiliation: Department of Physics, Brooklyn College of The City University of New York, 2900 Bedford Avenue, Brooklyn, NY 11210, USA; Department of Physics, The Graduate Center of The City University of New York, 365 5th Avenue, New York, NY 10016, USA. Electronic address: gboutis@brooklyn.cuny.edu.
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Boutis
mesh_terms: D000818:Animals; D012831:Bombyx / Q000737:chemistry*; D066241:Carbon-13 Magnetic Resonance Spectroscopy; D005349:Fibroins / Q000737:chemistry*; D011487:Protein Conformation; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D005349:Fibroins
keywords: (13)C DD/MAS NMR; (2)H NMR relaxation; Bombyx mori silk fibroin; Fiber; Film