Establishment of Mark–Houwink–Sakurada Equations for Chitin in Multiple Solvent Systems and Their Implications for Solution Conformation

TL;DR

This study establishes new Mark–Houwink–Sakurada equations for chitin in various solvents, enabling better molecular weight estimation and revealing how chitin behaves in different solutions.

Contribution

New MHS equations for chitin in multiple solvents and insights into its solution conformation.

Findings

Intrinsic viscosity varied significantly across different solvent systems for chitin.

Chitin in LiCl/DMAc and NaOH/urea showed rod-like conformations, while in NaOH/tannic acid it showed random coil behavior.

Temperature increases led to higher intrinsic viscosity and conformation parameter values.

Abstract

Currently, only a limited number of Mark–Houwink–Sakurada (MHS) equations are available for chitin, and their applicability is constrained by the narrow range of suitable solvent systems. The Mark–Houwink–Sakurada (MHS) equation is a widely used and practical approach for estimating polymer molecular weight from intrinsic viscosity measurements, particularly when chromatographic techniques are not readily accessible. This study aimed to establish new MHS equations for chitin to facilitate reliable molecular weight determination across different solvents and temperatures. Chitin samples with varying molecular weights were prepared via H2O2 degradation, and their weight-average molecular weights (Mw) were determined by high-performance size-exclusion chromatography (HPSEC). Intrinsic viscosity ([η]) was measured using a capillary viscometer at 25 and 30 °C in three solvent systems: 5% LiCl/N,N-dimethylacetamide (LiCl/DMAc), 8% NaOH/4% urea, and 10% NaOH/0.3% tannic acid (w/w). Double-logarithmic plots of Mw versus [η] were constructed to derive the corresponding MHS equations. At identical molecular weights and temperatures, intrinsic viscosity followed the order: LiCl/DMAc > NaOH/urea > NaOH/tannic acid. Increasing temperature led to higher intrinsic viscosity and conformation parameter (a) values. Chitin dissolved in LiCl/DMAc and NaOH/urea exhibited rod-like conformations, with a values ranging from 0.79 to 0.97, whereas chitin in NaOH/tannic acid displayed random coil behavior (a = 0.56–0.69). These established MHS equations expand the solvent applicability for chitin molecular weight determination and provide insights into its solution conformation under different chemical environments.

Figures