Влияние топологической структуры целлюлозы на процессы ацетилирования и нитрования

Эфиры целлюлозы активно используются при изготовлении новых полуфабрикатов, препаратов и материалов. Растительное сырье является основным источником для получения производных целлюлозы. Перспективным становится также производство целлюлозы путем микробиологического синтеза. Несмотря на одинаковые пути биосинтеза микрофибрилл, образцы целлюлозы растительного и бактериального происхождения отличаются по ряду структурных особенностей. Цель работы – оценка влияния топологической структуры целлюлозы растительного и бактериального происхождения на процессы ацетилирования и нитрования. В качестве образцов растительной целлюлозы использовали хлопковую и сульфатную целлюлозу. Бактериальную целлюлозу получали в лаборатории с применением смешанного сообщества микроорганизмов в статических условиях на синтетических глюкозных средах. Нитрование целлюлозы проводили смесью концентрированных H2SO4 и HNO3. Содержание азота в полученных образцах определяли ферросульфатным методом. ИК-спектры нитратов целлюлозы регистрировали на инфракрасном фурье-спектрометре Vertex-70 в диапазоне волновых чисел 4000…400 см–1. Ацетилирование целлюлозы осуществляли в среде сверхкритического диоксида углерода в системе сверхкритической флюидной экстракции SFE-5000, Thar Process. В ацетате целлюлозы титриметрически определяли содержание связанной уксусной кислоты, после чего рассчитывали степень замещения. Посредством электронной и атомно-силовой микроскопии визуализированы волокна растительной целлюлозы и фибриллы бактериальной целлюлозы. Выход нитрата из чистой хлопковой целлюлозы составил 160 %, т. е. степень замещения – 2,20. Нитрат целлюлозы, полученный из бактериальной целлюлозы в аналогичных условиях, имел степень замещения 1,96. Предложен новый метод прямого ацетилирования лиофильно высушенных препаратов бактериальной целлюлозы в среде сверхкритического диоксида углерода, что позволяет осуществлять процесс без кислотного катализатора и при пониженном расходе ацетилирующего агента. Ацетилирование растительной сульфатной целлюлозы показало степень замещения 2,40, для бактериальной целлюлозы – выход диацетилцеллюлозы с содержанием ацетильных групп 50 %, что соответствует степени замещения 2,10. Получение эфиров обусловлено как топохимическими особенностями микрофибрилл, так и кристалличностью материала. Для цитирования: Вашукова К.С., Терентьев К.Ю., Чухчин Д.Г., Ивахнов А.Д., Пошина Д.Н. Влияние топологической структуры целлюлозы на процессы ацетилирования и нитрования // Изв. вузов. Лесн. журн. 2023. № 6. С. 176–189. https://doi.org/10.37482/0536-1036-2023-6-176-18

Bordered Pit Formation in Cell Walls of Spruce Tracheids

The process of pit formation in plants still has various questions unaddressed and unknown, which opens up many interesting and new research opportunities. The aim of this work was elucidation of the mechanism for the formation of bordered pits of the spruce (Picea abies (L.) Karst.) tracheid with exosomes participation and mechanical deformation of the cell wall. Sample sections were prepared from spruce stem samples after cryomechanical destruction with liquid nitrogen. The study methods included scanning electron microscopy and enzymatic treatment. Enzymatic treatment of the elements of the bordered pit made it possible to clarify the localization of cellulose and pectin. SEM images of intermediate stages of bordered pit formation in the radial and tangential directions were obtained. An asynchronous mechanism of formation of bordered-pit pairs in tracheids is proposed. The formation of the pit pair begins from the side of the initiator cell and is associated with enzymatic hydrolysis of the secondary cell wall and subsequent mechanical deformation of the primary cell walls. Enzymatic hydrolysis of the S1 layer of the secondary cell wall is carried out by exosome-delivered endoglucanases

Features of the Chemical Composition and Structure of Birch Phloem Dioxane Lignin: A Comprehensive Study

Understanding the chemical structure of lignin in the plant phloem contributes to the systematics of lignins of various biological origins, as well as the development of plant biomass valorization. In this study, the structure of the lignin from birch phloem has been characterized using the combination of three analytical techniques, including 2D NMR, Py-GC/MS, and APPI-Orbitrap-HRMS. Due to the specifics of the phloem chemical composition, two lignin preparations were analyzed: a sample obtained as dioxane lignin (DL) by the Pepper’s method and DL obtained after preliminary alkaline hydrolysis of the phloem. The obtained results demonstrated that birch phloem lignin possesses a guaiacyl–syringyl (G-S) nature with a unit ratio of (S/G) 0.7–0.9 and a higher degree of condensation compared to xylem lignin. It was indicated that its macromolecules are constructed from β-aryl ethers followed by phenylcoumaran and resinol structures as well as terminal groups in the form of cinnamic aldehyde and dihydroconiferyl alcohol. The presence of fatty acids and flavonoids removed during alkaline treatment was established. Tandem mass spectrometry made it possible to demonstrate that the polyphenolic components are impurities and are not incorporated into the structure of lignin macromolecules. An important component of phloem lignin is lignin–carbohydrate complexes incorporating xylopyranose moieties

Impact of Coastal Sediments of the Northern Dvina River on Microplastics Inputs to the White and Barents Seas

The Northern Dvina River flowing into the White Sea may be one of the main sources of microplastic (MP) pollution in the Arctic region. The coastal sediments of the Northern Dvina River act as an intermediate link in the transport of microplastics to the areas of the White and Barents Seas. The µFT-IR and Py-GC/MS methods were used to determine that up to 200 particles or 120 mg of MP per kg could accumulate in the coastal sediments of the Northern Dvina River. Coastal sediments tend to accumulate ABS and PS plastic particles with a particle size of around 200 µm. The accumulated microplastics (218 particles or 117 mg per kg of sediment per year) are carried away by strong currents, especially during spring flooding, resulting in pollution of the Barents and White Seas. The obtained data play an important role in assessing the MP pollution of the Arctic region, especially the White and Barents Seas

Impact of Coastal Sediments of the Northern Dvina River on Microplastics Inputs to the White and Barents Seas

The Northern Dvina River flowing into the White Sea may be one of the main sources of microplastic (MP) pollution in the Arctic region. The coastal sediments of the Northern Dvina River act as an intermediate link in the transport of microplastics to the areas of the White and Barents Seas. The µFT-IR and Py-GC/MS methods were used to determine that up to 200 particles or 120 mg of MP per kg could accumulate in the coastal sediments of the Northern Dvina River. Coastal sediments tend to accumulate ABS and PS plastic particles with a particle size of around 200 µm. The accumulated microplastics (218 particles or 117 mg per kg of sediment per year) are carried away by strong currents, especially during spring flooding, resulting in pollution of the Barents and White Seas. The obtained data play an important role in assessing the MP pollution of the Arctic region, especially the White and Barents Seas

Chitin Cryogels Prepared by Regeneration from Phosphoric Acid Solutions

Cryogelation is a developing technique for the production of polysaccharide materials for biomedical applications. The formation of a macroporous structure during the freeze-drying of polysaccharide solutions creates biomaterials suitable for tissue engineering. Due to its availability, biocompatibility, biodegradability, and non-toxicity, chitin is a promising natural polysaccharide for the production of porous materials for tissue engineering; however, its use is limited due to the difficulty of dissolving it. This work describes the preparation of cryogels using phosphoric acid as the solvent. Compared to typical chitin solvents phosphoric acid can be easily removed from the product and recovered. The effects of chitin dissolution conditions on the structure and properties of cryogels were studied. Lightweight (ρ 0.025–0.059 g/cm3), highly porous (96–98%) chitin cryogels with various heterogeneous morphology were produced at a dissolution temperature of 20 ± 3 °C, a chitin concentration of 3–15%, and a dissolution time of 6–25 h. The crystallinity of the chitin and chitin cryogels was evaluated by 13C CP-MAS NMR spectroscopy and X-ray diffractometry. Using FTIR spectroscopy, no phosphoric acid esters were found in the chitin cryogels. The cryogels had compressive modulus E values from 118–345 kPa and specific surface areas of 0.3–0.7 m2/g. The results indicate that chitin cryogels can be promising biomaterials for tissue engineering

Biophysical Characterization and Cytocompatibility of Cellulose Cryogels Reinforced with Chitin Nanowhiskers

Polysaccharide-based cryogels are promising materials for producing scaffolds in tissue engineering. In this work, we obtained ultralight (0.046–0.162 g/cm3) and highly porous (88.2–96.7%) cryogels with a complex hierarchical morphology by dissolving cellulose in phosphoric acid, with subsequent regeneration and freeze-drying. The effect of the cellulose dissolution temperature on phosphoric acid and the effect of the freezing time of cellulose hydrogels on the structure and properties of the obtained cryogels were studied. It has been shown that prolonged freezing leads to the formation of denser and stronger cryogels with a network structure. The incorporation of chitin nanowhiskers led to a threefold increase in the strength of the cellulose cryogels. The X-ray diffraction method showed that the regenerated cellulose was mostly amorphous, with a crystallinity of 26.8–28.4% in the structure of cellulose II. Cellulose cryogels with chitin nanowhiskers demonstrated better biocompatibility with mesenchymal stem cells compared to the normal cellulose cryogels

Biocatalysis of Industrial Kraft Pulps: Similarities and Differences between Hardwood and Softwood Pulps in Hydrolysis by Enzyme Complex of Penicillium verruculosum

Kraft pulp enzymatic hydrolysis is a promising method of woody biomass bioconversion. The influence of composition and structure of kraft fibers on their hydrolysis efficiency was evaluated while using four substrates, unbleached hardwood pulp (UHP), unbleached softwood pulp (USP), bleached hardwood pulp (BHP), and bleached softwood pulp (BSP). Hydrolysis was carried out with Penicillium verruculosum enzyme complex at a dosage of 10 filter paper units (FPU)/g pulp. The changes in fiber morphology and structure were visualized while using optical and electron microscopy. Fiber cutting and swelling and quick xylan destruction were the main processes at the beginning of hydrolysis. The negative effect of lignin content was more pronounced for USP. Drying decreased the sugar yield of dissolved hydrolysis products for all kraft pulps. Fiber morphology, different xylan and mannan content, and hemicelluloses localization in kraft fibers deeply affected the hydrolyzability of bleached pulps. The introduction of additional xylobiase, mannanase, and cellobiohydrolase activities to enzyme mixture will further improve the hydrolysis of bleached pulps. A high efficiency of never-dried bleached pulp bioconversion was shown. At 10% substrate concentration, hydrolysates with more than 50 g/L sugar concentration were obtained. The bioconversion of never-dried BHP and BSP could be integrated into working kraft pulp mills

Production of Biomodified Bleached Kraft Pulp by Catalytic Conversion Using <i>Penicillium verruculosum</i> Enzymes: Composition, Properties, Structure, and Application

The global development of the bioeconomy is impossible without technologies for comprehensive processing of plant renewable resources. The use of proven pretreatment technologies raises the possibility of the industrial implementation of the enzymatic conversion of polysaccharides from lignocellulose considering the process’s complexity. For instance, a well-tuned kraft pulping produces a substrate easily degraded by cellulases and hemicelulases. Enzymatic hydrolysis of bleached hardwood kraft pulp was carried out using an enzyme complex of endoglucanases, cellobiohydrolases, β-glucosidases, and xylanases produced by recombinant strains of Penicillium verruculosum at a 10 FPU/g mixture rate and a 10% substrate concentration. As a result of biocatalysis, the following products were obtained: sugar solution, mainly glucose, xylobiose, xylose, as well as other minor reducing sugars; a modified complex based on cellulose and xylan. The composition of the biomodified kraft pulp was determined by HPLC. The method for determining the crystallinity on an X-ray diffractometer was used to characterize the properties. The article shows the possibility of producing biomodified cellulose cryogels by amorphization with concentrated 85% H3PO4 followed by precipitation with water and supercritical drying. The analysis of the enzymatic hydrolysate composition revealed the predominance of glucose (55–67%) among the reducing sugars with a maximum content in the solution up to 6% after 72 h. The properties and structure of the modified kraft pulp were shown to change during biocatalysis; in particular, the crystallinity increased by 5% after 3 h of enzymatic hydrolysis. We obtained cryogels based on the initial and biomodified kraft pulp with conversion rates of 35, 50, and 70%. The properties of these cryogels are not inferior to those of cryogels based on industrial microcrystalline cellulose, as confirmed by the specific surface area, degree of swelling, porosity, and SEM images. Thus, kraft pulp enzymatic hydrolysis offers prospects not only for producing sugar-rich hydrolysates for microbiological synthesis, but also cellulose powders and cryogels with specified properties

Enzymatic Hydrolysis of Kraft and Sulfite Pulps: What Is the Best Cellulosic Substrate for Industrial Saccharification?

Sulfite and kraft pulping are two principal methods of industrial delignification of wood. In recent decades, those have been considered as possibilities to pretreat recalcitrant wood lignocellulosics for the enzymatic hydrolysis of polysaccharides and the subsequent fermentation of obtained sugars to valuable bioproducts. Current work compares chemistry and technological features of two different cooking processes in the preparation of polysaccharide substrates for deep saccharification with P. verruculosum glycosyl hydrolases. Bleached kraft and sulfite pulps were subjected to hydrolysis with enzyme mixture of high xylanase, cellobiohydrolase, and β-glucosidase activities at a dosage of 10 FPU/g of dry pulp and fiber concentration of 2.5, 5, and 10%. HPLC was used to analyze soluble sugars after hydrolysis and additional acid inversion of oligomers to monosaccharides. Kraft pulp demonstrated higher pulp conversion after 48 h (74–99%), which mostly resulted from deep xylan hydrolysis. Sulfite-pulp hydrolysates, obtained in similar conditions due to higher hexose concentration (more than 50 g/L), had higher fermentability for industrial strains producing alcohols, microbial protein, or organic acids. Along with saccharification, enzymatic modification of non-hydrolyzed residues occurred, which led to decreased degree of polymerization and composition changes in two industrial pulps. As a result, crystallinity of kraft pulp increased by 1.3%, which opens possibilities for obtaining new types of cellulosic products in the pulp and paper industry. The high adaptability and controllability of enzymatic and fermentation processes creates prospects for the modernization of existing factories