Assessment of Substituent Distribution of Derivatized Celluloses

In recent years, cellulose and cellulose-based polymers have gained great popularity in the pharmaceutical industry. Cellulose is a naturally occurring long-chain polymer that is often used as an excipient in the pharmaceutical industry. Cellulose has a very large number of semi-synthetic derivatives that are widely used in the pharmaceutical and cosmetic industries. The distribution of substituents on the dehydrated glucose units of cellulose (at the C2, C3 and C6 positions) is one of the important topics in the derivatization chemistry. The physical and chemical properties of cellulose derivatives are influenced not only by their molecular weight distribution, type of substituents and degree of substitution, but also by the distribution of the substituents within the monomer units and along the molecular backbone. BOC Sciences introduces advanced instrumentation and precise analytical methods for the analysis of starch and cellulose derivatives, as well as the use of specific hydrolysing enzymes to facilitate their analysis.

Figure 1. Distribution of Functional Groups in Cellulose Ethers by DNP-Enhanced Solid-State NMR Spectroscopy. (Berruyer, P.; et al. 2022)

Characteristic Methods of the Substituent Distribution

Gel Permeation Chromatography (GPC)

At BOC Sciences, we dissolve the polymer in a suitable solvent and the derivatized groups exhibit UV absorbance which can be used to detect their distribution along the polymer molecule. After enzymatic degradation with endoglucanase, the degradation pattern is analyzed by utilizing the GPC.

Nuclear Magnetic Resonance (NMR) Spectroscopy

The substitution distribution of ethylcellulose can be determined by ¹H and ¹³C NMR spectroscopy. Good agreement is obtained between the degree of substitution (DS) values obtained from the NMR spectroscopy analysis and those determined by the conventional nitrogen content method, indicating the validity of our well-established NMR method. Furthermore, the NMR method is also effective in determining the positional substituent distribution through the quantitative analysis of carbon signals.

Electrospray Ionization - Mass Spectrometry (ESI-MS)

The substituent distribution of the cellulose derivatives in the glucosyl units and along the polymer chain is analyzed by ESI-MS analysis of the labeled oligosaccharides. When the samples show similar regioselectivity of substitution and random distribution of ethyl and propyl groups, the distribution of all types of glucosyl residues identified by monomer analysis is also random over the cellulose molecules.

Fast Atom Bombardment - Mass Spectrometry (FAB-MS)

The substituent distribution along the cellulose backbone in methyl cellulose is determined by analyzing the composition of monomers and oligomers. The oligomers are obtained by partial acid hydrolysis of the polymers. The substituent distribution of the fibers is measured by fast atom bombardment mass spectrometry of the per-deuterated methylated partial hydrolysate

Figure 2. Substituent distribution of propyl cellulose studied by nuclear magnetic resonance. (Kono, H.; Numata, J. 2020)

Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF-MS)

We are able to analyze the methyl and hydroxypropyl patterns of hydroxypropyl methylcellulose (HPMC) and hydroxyethyl methyl cellulose (HEMC) in the glucosyl units and along the polymer chain. After the hydrolysis, reduction and acetylation process, the methyl pattern in the glucosyl unit is determined by GLC/MS, while the distribution of hydroxypropyl residues in the monomer could be analyzed with higher sensitivity. In order to determine the distribution of substituents along the polymer chain, we perform the hydrolysis process to obtain fully alkylated and permanently charged oligosaccharide derivatives. These compounds can be quantitatively analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS).

HPLC-NMR

The standards are separated by preparative HPLC, and our experts are able to perform quantitative analysis of the substituent distribution in carboxymethyl cellulose (CMC) using ¹³C-NMR spectroscopy. We perform the HPLC quantification of glucose and its carboxymethyl derivatives by employing the anion-exchange chromatography and pulsed amperometric detection.