Azizbek Anvarjon ugli Boydedaev, Dilnoza Muhtarovna Amonova, Muhiddin Shokirjon ugli Karimov, Muhabbat Okilkhan kizi Kalonova, Bahtiyor Ikromovich Muhitdinov, Abbaskhan Sabirkhanovich Turaev

HETEROGENEOUS SULFATION REACTIONS OF LOW MOLECULAR WEIGHT CHITOSAN

Introduction

Heterogeneous sulfation reactions of low molecular weight chitosan. Systematic study on heterogeneous sulfation of low molecular weight chitosan. Optimal conditions yield highly substituted, water-soluble derivatives with promise for biomedical applications.

Abstract

In this study, the heterogeneous sulfation of low molecular weight chitosan (LMWC, Mw = 12.2 kDa, DP = 73, PDI = 1.25) using sulfuric acid in isopropanol medium was systematically investigated. A series of sulfated chitosan derivatives were synthesized under varying reaction parameters, including temperature (-30 to +5 °C), time (1–24 h), and H₂SO₄ molar ratios (1.0–8.0 mmol/mmol GlcNU). The molecular characteristics of the obtained products varied within a wide range: DP = 58-73, DS = 0.026–1.289, sulfur content = 0.51–14.16%, SO3Na = 1.64–45.58%, with yields ranging from 10.12% to 80.12%. FTIR spectroscopy confirmed successful sulfation through characteristic -SO3- absorption bands at 1220, 1060, 987, and 814 cm-1, indicating that sulfation predominantly occurred at the C-6 position of glucosamine residues via hydroxyl and amino groups. The optimal reaction conditions were determined to be 4.0 mmol/mmol H2SO4 per glucosamine unit at -20 °C for 12 hours, ensuring high DS values and minimal depolymerization. Elemental analysis supported FTIR findings and showed high correlation between reaction variables and functional group incorporation. These results demonstrate that controlled heterogeneous sulfation of LMWC in isopropanol is an effective method to produce water-soluble, highly substituted chitosan derivatives with preserved backbone integrity. The obtained derivatives are promising for further biomedical applications such as drug delivery, anticoagulant formulations, and bioactive coatings. This study provides a clear understanding of how reaction parameters influence structural and functional outcomes in chitosan sulfation chemistry.

Review

This study presents a systematic investigation into the heterogeneous sulfation of low molecular weight chitosan (LMWC), an important biopolymer, using sulfuric acid in an isopropanol medium. The work addresses a critical area in biomaterial science, focusing on the chemical modification of chitosan to enhance its biological properties and solubility, which are crucial for various biomedical applications. By precisely controlling the reaction parameters, the authors aim to achieve high degrees of sulfation while minimizing backbone degradation, a common challenge in polysaccharide modification. The clear objective and methodical approach laid out in the abstract indicate a strong foundation for exploring the complex chemistry involved in chitosan functionalization. The methodology involved varying key reaction parameters: temperature (-30 to +5 °C), reaction time (1–24 h), and H₂SO₄ molar ratios (1.0–8.0 mmol/mmol GlcNU). This comprehensive exploration allowed for the synthesis of sulfated chitosan derivatives with a broad spectrum of molecular characteristics, including diverse degrees of polymerization (DP = 58-73) and sulfation (DS = 0.026–1.289), alongside varying sulfur content and yields. The success of sulfation was rigorously confirmed using FTIR spectroscopy, which identified characteristic absorption bands for -SO₃⁻ groups, specifically indicating predominant sulfation at the C-6 position via hydroxyl and amino groups. Crucially, the study successfully determined optimal reaction conditions (4.0 mmol/mmol H₂SO₄ per glucosamine unit at -20 °C for 12 hours) that yielded highly substituted products with minimal depolymerization, a significant achievement for maintaining the structural integrity essential for functional materials. The findings from this research clearly demonstrate that controlled heterogeneous sulfation of LMWC in isopropanol is an effective strategy for producing water-soluble and highly substituted chitosan derivatives with preserved backbone integrity. The ability to precisely tailor the degree of sulfation and maintain molecular weight makes these derivatives highly promising for a range of biomedical applications, including drug delivery systems, anticoagulant formulations, and bioactive coatings, where specific charge densities and molecular dimensions are often critical. By providing a detailed understanding of how reaction parameters influence the structural and functional outcomes, this study not only contributes valuable insights to chitosan chemistry but also lays a robust groundwork for the rational design and development of advanced chitosan-based biomaterials for therapeutic and diagnostic purposes.

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