Conformational study of a collagen peptide by ¹H NMR spectroscopy: observation of the ¹⁴N‐¹H spin‐spin coupling of the Arg guanidinium moiety in the triple‐helix structure

Abstract

CB2, a CNBr peptide of 36 residues from type I collagen K K1(I) chain has been studied by NMR spectroscopy as a function of temperature. At low temperature, the guanidinium protons of Arg W showed sharp 1:1:1 NMR triplets around 6.95 ppm, characteristic of IR N coupled protons ( I J xr =52 Hz) when the quadrupolar relaxation rate is drastically reduced. These spectral characteristics and the low temperature coefficient of the 1:1:1 triplets (v vN N/v vT of 33.6 ppb/³C) suggest that the H atoms of the protonated guanidinium moiety of Arg W in the triple helix are slowly exchanging with bulk water, most likely involved in hydrogen bonds. On the basis of conformational energy computations on a model segment of type I collagen (Vitagliano, L., Ne èmethy, G., Zagari, A. and Scheraga, H.A. (1993) Biochemistry 32, 7354^7359), similar to CB2, our data could indicate that the guanidinium group of Arg W form hydrogen bonds with a backbone carbonyl of an adjacent chain probably by using the N O hydrogen, leaving the four N R hydrogens bound to water molecules that must be in slow exchange with bulk water and that could therefore be considered structural elements of the trimeric K K1(I) CB2 triple helix. The behaviour of Arg W has been investigated also in terms of equilibrium between random monomer and helical trimer conformations controlled by temperature. The thermal unfolding process was found to be reversible and the melting point resulted to be 17³C.z 1998 Federation of European Biochemical Societies.

Elucidation of the Chemical and Morphological Structure of Double‐Network (DN) Hydrogels by High‐Resolution Magic Angle Spinning (HRMAS) NMR Spectroscopy

“…[35][36][37] The same triplet pattern with exactly the same splitting value is also observed when using a 250 and 600 MHz spectrometer, instead of 500 MHz spectrometer, confirming unambiguously that it originates from a 1:1:1 scalar coupling involving a spin one nucleus. The high value of the scalar coupling splitting excludes the latter to be due to deuterium.…”

Chitosan-graft-Polyaniline-Based Hydrogels: Elaboration and Properties

“…On the other hand, the reaction of aniline on chitosan amino groups is favored compared to its homopolymerization. This phenomenon has already been described when grafting ANI onto poly(aminostyrene) . On the contrary, a mixture of chitosan and PANI would be observed.…”

“…This phenomenon has already been described when grafting ANI onto poly(aminostyrene). 46 On the contrary, a mixture of chitosan and PANI would be observed.…”

Orchestration of Structural, Stereoelectronic, and Hydrogen-Bonding Effects in Stabilizing Triplexes from Engineered Chimeric Collagen Peptides (ProX-ProY-Gly)6 Incorporating 4(R/S)-Aminoproline

“…Increasing pH enhances the neutral forms at both X/Y-sites, synergistically driving prolines to unfavorable puckered states resulting in a lower triplex stability at higher pH. Such pH-dependent triplex stabilities have been observed in case of collagen peptides having other charged side chains (e.g., lysine, arginine). , Theoretical calculations on 4­( R/S )-NH 2 -proline at monomer and dipeptide levels have suggested a possible switch of axial/equatorial orientation of the 4-substituent through pucker change upon protonation . Differential solvation of the axial/equatorial substituents may distinctly stabilize the relevant exo / endo puckered states ordained by the nature of the 4-NH 2 /NH 3 + substituent…”