多糖的酶法合成及其过程强化

多糖的酶法合成与过程调控是生物工程及药物开发领域的研究热点。以同多糖、杂多糖和多糖复合物等为代表的多糖类物质的酶法合成技术开发受到广泛关注,多糖的酶法合成以其高度区域选择性和立体选择性、酶可重复利用且环境友好无污染等优点,开始从实验室进入产业领域。酶法合成过程的强化是其产业化应用的关键,通过合成酶固定化、酶的定向变异、化学法与酶法结合等途径可以有效解决酶法合成目前存在的合成酶制备困难、合成反应复杂且产物相对分子质量分布难以控制等不足。酶法合成将成为功能性多糖及糖类聚合物研发与制备的有效途径。     

Understanding structure and composition of thermally rearranged polymers based on small‐molecule chemistry: a perspective

We provide a critical perspective of the burgeoning literature on microporous polymers prepared using thermal rearrangement (TR) processes based on the learning derived from analogous chemistry involving small‐molecular‐weight compounds. TR polymers have shown interesting permeability–selectivity relationships in gas separation and, thus, have generated wide interest as potential membrane materials for industrial applications. The intractable nature of the products obtained by TR processes has precluded rigorous structural elucidation of the polymers. Based on small‐molecule chemistry, we conclude that structures are likely to be more complex than generally depicted in the published literature. Interestingly, a simpler chemistry, namely thermal dehydrocyclization (TCD), leads to products identical to those derived from TR, but at significantly lower temperatures. However, TCD chemistry does not involve a skeletal rearrangement of the kind purported in TR during the conversion of imide to oxazole ring resulting in spatially confined heterocyclic ring polymers. Yet, they show similar fractional free‐volume elements as exhibited by TR polymers. This is intriguing and points to a need for more careful examination of the factors responsible for microporosity in such materials. TR chemistry as currently practiced appears limited to only benzoxazole‐type structures. The ability to precisely control and reproducibly produce materials with well‐defined structure and properties will be a key to large‐scale manufacture and industrial applications of such materials. Seen from this perspective, TR processes leave much to be desired and further improvements are clearly warranted. © 2019 Society of Chemical Industry     

The unique optical behaviour of bio‐related materials with organic chromophores

Molecularly designed materials based on macromolecules and organic dyes offer unique opportunities in connection with the possibility of preparing optically responsive ‘smart’ materials. Indeed macromolecules are able to transmit and amplify small signals reaching sites at interacting distance through the involvement of the whole chain. The corresponding materials can then acquire stimuli‐responsive properties in relation to specific features connected to primary structure and conformation. As a first approach to benefit from the above features for preparing eco‐compatible smart materials, bio‐related polypeptides, polysaccharides and polyesters can be used as the macromolecular partner in combination with a selected dye following different interaction methodologies. Two distinct routes were used to prepare optically responsive products from the above bio‐related polymers, respectively based either on the covalent bonding to the original macromolecules of photochromic molecular species, such as azobenzene and spiropyran, or on the morphology‐modulated dispersion of highly conjugated dyes in the polymer bulk. Examples related to the two different routes have been investigated in our laboratory and are presented and discussed also with reference to selected recent cases from the literature. Copyright © 2012 Society of Chemical Industry     

Post‐polymerization modification of bio‐based polymers: maximizing the high functionality of polymers derived from biomass

The renaissance of the bio‐based chemical industry over the last 20 years has seen an ever growing interest in the synthesis of new bio‐based polymers. The building blocks of these new polymers, so called platform molecules, contain significantly more chemical functionality than their petrochemical counterparts (such as ethene, propene and para‐xylene). As a result bio‐based polymers often contain greater residual chemical functionality in their chains, with groups such as alkenes and hydroxyls commonly observed. These functional groups can act as sites for post‐polymerization modification (PPM), thus further extending the range of applications for bio‐based polymers by tailoring the polymers' final properties. This mini‐review highlights some of the most recent and compelling examples of how to make use of bio‐based polymers with residual functional groups for PPM. It also looks at how the emerging interdisciplinary field of enzymatic polymer synthesis allows for increased functionality in polymers by avoiding side‐reactions as a result of milder reaction conditions, and additionally offers an alternative means of polymer surface modification. © 2018 Society of Chemical Industry     

Enzymatic ring‐opening polymerization (ROP) of polylactones: roles of non‐aqueous solvents

Aliphatic polyesters such as polylactides (PLAs) and other polylactones are thermoplastic, biodegradable and biocompatible polymers with the potential to replace petro‐chemical‐based synthetic polymers. A benign route for synthesizing these polyesters is through the enzyme‐catalyzed ring‐opening polymerization (ROP) reaction; this type of enzymatic process is very sensitive to reaction conditions such as solvents, water content and temperature. This review systematically evaluates the crucial roles of different solvents (such as solvent‐free/in bulk, organic solvents, supercritical fluids, ionic liquids, and aqueous biphasic systems) on the degree of polymerization and polydispersity. In general, many studies suggest that hydrophobic organic solvents with minimum water contents lead to efficient enzymatic polymerization and subsequently high molecular weights of polyesters; the selection of solvents is also limited by the reaction temperature, e.g. the ROP of lactide is often conducted at above 100 °C, therefore, the solvent typically needs to have its boiling point above this temperature. The use of supercritical fluids could be limited by its scaling‐up potential, while ionic liquids have exhibited many advantages including their low‐volatility, high thermal stability, controllable enzyme‐compatibility, and a wide range of choices. However, the fundamental and mechanistic understanding of the specific roles of ionic liquids in enzymatic ROP reactions is still lacking. Furthermore, the lipase specificity towards l ‐ and d ‐lactide is also surveyed, followed by the discussion of engineered lipases with improved enantioselectivity and thermal stability. In addition, the preparation of polyester‐derived materials such as polyester‐grafted cellulose by the enzymatic ROP method is briefly reviewed. © 2017 Society of Chemical Industry     

Chemical synthesis of polysaccharides and polysaccharide mimetics

Polysaccharides are ubiquitous in nature, and play many critical roles in biology. As such, the synthesis of polysaccharides and of polymers mimicking the structure or function of polysaccharides is of keen interest in order to reveal structure-function relationships and to prepare biocompatible and biodegradable materials for research and commercial applications. Recent developments in polymerization methodologies are enabling the synthesis of polysaccharides and polysaccharide mimetics with a variety of structures and architectures. While there have been significant advances in overcoming the difficulties in controlling the regioselectivity and stereospecificity of glycosidic bond formation during polymerization, the development of efficient synthetic routes with general applicability to stereoregular and structurally complex polysaccharides remains a challenge. This review comprehensively describes the chemical polymerization methods to synthesize polysaccharides with different compositions and architectures (linear, branched, and hyperbranched) and the synthetic procedures to polysaccharide mimetics possessing, for example, amine linkages, amide linkages, and carbonate linkages. It begins with a discussion of the challenges and strategies for the synthesis of polysaccharides. We highlight the complexity observed in theses macromolecules due to the number and variety of stereo- and regio-types of glycosidic linkages present between monosaccharide residues. With regards to polysaccharide mimetics, we focus on polymers displaying important structural features present in natural polysaccharides, such as a rigid polymer backbone containing heterocyclic ring structures, short linkages with less than three atoms, as well as multiple hydroxyl groups. Both condensation polymerization and ring-opening polymerization are used to prepare linear polysaccharides, branched polysaccharides, hyperbranched polysaccharides, non-O-glycosidic linked polysaccharide mimetics, and pseudopolysaccharides. The review concludes with reflections and suggestions for future directions of investigation.     

Recent Progress on the Design and Applications of Polysaccharide‐Based Graft Copolymer Hydrogels as Adsorbents for Wastewater Purification

Gum polysaccharides are one of the most abundant bio‐based polymers. They are generally derived from plants as exudates or from microorganisms and have diverse applications in many industries, especially in the food industries where they are used as emulsifiers and thickeners. In their natural form, gum polysaccharides have poor mechanical and physical properties; therefore, they are frequently modified with various synthetic monomers such as acrylamide and acrylic acid using graft copolymerization. Graft copolymerization is one of the most trusted and widely used synthetic methods for the modification of gum polysaccharides. Gum polysaccharides modified in this way have improved mechanical and physicochemical properties. Furthermore, gum polysaccharides contain a variety of functional groups, for example, carboxylic acid and hydroxyl groups; therefore, they have been used extensively as adsorbents for the removal of different impurities from wastewater such as toxic heavy metal cations and synthetic dyes. Here, the chemical and physical properties of gum polysaccharides, different methods of graft copolymerization, and the use of graft copolymer gum‐polysaccharide‐based hydrogels are reviewed in detail for the removal of toxic heavy metal cations and synthetic dyes from aqueous solutions.

     

Soybean oil‐based shape‐memory polyurethanes: Synthesis and characterization

Shape‐memory polymers (SMPs) have wide range of applications due to their ability to sense environmental stimuli and reshape from a temporary shape to a permanent shape. Plant oil‐based polymeric materials are highly concerned in recent years in consideration of petroleum depletion and environmental pollution. However, plant oil‐based polymers are rarely investigated regarding their shape‐memory characteristics though bio‐based SMPs are highly desired nowadays. In this study, a series of soybean oil‐based shape‐memory polyurethanes (SSMPUs) are prepared through a mild chemo‐enzymatic synthetic route, and their properties are fully characterized with tensile testing, DSC, dynamic mechanical analysis (DMA), and shape‐memory testing. Results show that SSMPUs are soft rubbers with tensile strength in the range of 1.9–2.2 MPa and glass transition temperature in the range of 2–5°C, and possess good shape recoveries at RT when stretching ratio is 10, 20, and 30%, respectively. This work would promote the development of high‐value‐added plant oil‐based shape‐memory polyurethanes. Practical applications: Using annual renewable plant oil as feedstock, the synthesized SSMPUs show good shape recovery properties, which will make them applicable as potential alternatives to petroleum‐based shape‐memory materials. The simple and mild preparation process also contributes to the further exploration of plant oil to value‐added functional materials.     

Chemical and structural characterization of alkaline‐extractable hemicelluloses from various eucalyptus species

Eucalyptus species are currently one of the main feedstock for pulping and papermaking industry in China. In the present study, alkali‐extractable hemicelluloses were isolated from different eucalyptus species (Eucalyptus camaldulensis, E. urophylla × grandis, and E. urophylla × E. tereticornis) at mild conditions prior to pulping. Structural characterization of these hemicellulosic polymers based on monosaccharide, molecular weight, Fourier transform infrared, ¹H, ¹³C, and two‐dimensional heteronuclear single quantum coherence nuclear magnetic resonance analysis revealed that these alkali‐extractable polysaccharides shared the common structure composed of the (1→4)‐linked‐β‐D‐xylopyranosyl backbone with 4‐O‐methyl‐α‐D‐glucuronic acid attached to O‐2 of the xylose residues. The potential structures of the alkali‐extractable hemicelluloses were proposed based on the comprehensive analysis. The well‐characterized structures of these hemicelluloses could enlarge the industrial application of these hemicelluloses from the Eucalyptus species in a biorefinery process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2390–2398, 2013     

Main properties and current applications of some polysaccharides as biomaterials

This review concerns the applications of some polysaccharides in the domain of biomaterials and bioactive polymers. Natural polysaccharides from different sources have been studied for a long time, and their main properties are summarized in this paper; some of their derivatives obtained by chemical modification are also described. The main polysaccharides currently used in the biomedical and pharmaceutical domains are chitin and its derivative chitosan, hyaluronan and alginates. Alginates are well known for their property of forming a physical gel in the presence of divalent counterions (Ca, Ba, Sr) whereas carrageenans form a thermoreversible gel; these seaweed polysaccharides are mainly used to encapsulate different materials (cells, bacteria, fungi). Other promising systems are the electrostatic complexes formed when an anionic polysaccharide is mixed with a cationic polysaccharide (e.g. alginate/chitosan or hyaluronan/chitosan). An important development of the applications of polysaccharides can be predicted for the next few years in relation to their intrinsic properties such as biocompatibility and biodegradability in the human body for some of them; they are also renewable and have interesting physical properties (film‐forming, gelling and thickening properties). In addition, they are easily processed in different forms such as beads, films, capsules and fibres. Copyright © 2007 Society of Chemical Industry     

Transformation of complex internal structures of poly(ethylene oxide)/chitosan oligosaccharide electrospun nanofibers

Electrospun nanofibers with a core–shell structure or an internal microphase‐separated structure were obtained from a homogeneous solution using a conventional single‐nozzle electrospinning setup. Because of the poor miscibility of poly(ethylene oxide) (PEO) and chitosan oligosaccharide (CS), the two polymers will separate into a core–shell structure (PEO as core, CS as shell) or an internal microphase‐separated structure (PEO as discrete phase, CS as continuous phase) depending on the fraction of each component in the solution. Moreover, the core–shell structure transforms to the internal microphase‐separated structure with a continuous decrease of the PEO fraction. The reason for the transition of these internal structures can be attributed to the different phase separation mechanisms. For the core–shell structure, phase separation proceeds in a mechanism of nucleation and growth; however, the internal microphase‐separated structure results from spinodal decomposition. Therefore, wide‐angle X‐ray diffraction and differential scanning calorimetry were employed to investigate PEO crystallization. Since both PEO and CS are biocompatible polymers, together with being able to control the fiber internal structure (core–shell or microphase separation), these electrospun nanofibers will have a great future in the biomedical field. Copyright © 2011 Society of Chemical Industry     

Triptycene‐based fluorescent polymers with pendant alkyl chains: interaction with fullerenes and morphology of thin films

We report unique triptycene‐based alternating copolymers bearing long alkyl chains as pendants. Syntheses utilized 2,6‐diethynyltriptycene and appropriate alkyloxyarene monomers polymerized via Sonogashira cross‐coupling reaction to yield triptycene‐based poly(phenylene ethynylene)s. Resulting polymers are soluble in organic solvents and were characterized using various techniques. Experimental results suggest the polymers are thermally stable and fluorescent. The fluorescence emission is quenched in the presence of fullerenes (C₆₀ and C₇₀) suggesting strong host–guest interactions. The magnitude of the binding constant between the polymers and these fullerenes was determined to be of the order of 10⁵ mol L^?1. The effects of chain length on the morphology and wettability of the polymers on silicon substrates were studied using atomic force microscopy. Three distinct dewetting patterns, i.e. spherical domains, fractal structures and ring structures, were observed with variation in the pendant chain length. This ability to control the thin‐film morphology of the polymers may have potential technological applications, which include but are not limited to sensors, fluorescent coatings and organic electronics. © 2018 Society of Chemical Industry     

Characterization and strain‐energy‐function‐based modeling of the thermomechanical response of shape‐memory polymers

Shape‐memory polymers (SMPs) are an emerging class of active polymers that can be used on a wide range of reconfigurable structures and actuation devices. In this study, an epoxy‐based SMP was synthesized, and its thermomechanical behaviors were comprehensively characterized. The stress–strain behavior of the SMP was determined to be nonlinear, finite deformation in all regions. Strain‐energy‐based models were used to capture the complicated stress–strain behavior and shape‐recovery response of the SMP. Among various strain energy functions, the stretch‐based Ogden model provided the best fit to the experimental observations. Compared to the sophisticated models developed for SMPs, the strain‐energy‐based model was found to be reliable and much easier to use for practical SMP designs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41861.     

互穿网络聚合物水凝胶的制备及其吸附研究进展

互穿网络聚合物(IPN)水凝胶在分离技术领域具有广泛的应用前景,这些年受到人们广泛关注.本文介绍了聚多糖基(壳聚糖、海藻酸、淀粉和其他聚多糖)、蛋白质基(明胶、胶原蛋白、丝纤蛋白和大豆蛋白)和合成聚合物基(非离子型和离子型)IPN水凝胶的制备方法,主要包括同步-IPN、分步-IPN和半-IPN的制备方法.为了提高聚合物水凝胶的生物相容性、溶胀率和机械强度,采用天然高分子与合成高分子共混制备IPN水凝胶.与单网络水凝胶相比,IPN水凝胶对染料和重金属离子的吸附速率快、吸附容量大.为了达到选择性吸附和提高水凝胶的比表面积,制备离子印迹IPN水凝胶和多孔IPN复合冷冻凝胶,是未来研究高效吸附IPN水凝胶的发展方向之一.     

Bacterial polymers as materials for the development of micro/nanoparticles

Bacterial polysaccharides and polyhydroxyalkanoates present physical and chemical characteristics that impart them diverse functional properties, including the ability to produce structures from nano- to macroscale (e.g., spheres, capsules, beads). Such structures may be specially designed to fulfill the requirements of specific applications in different areas, either alone or conjugated with other polymers by means of ionic interactions, hydrogen bonding, or chemical reactions. The interest on using such biomaterials has been increasing due to their unique functional properties, nontoxicity, biodegradability, and biocompatibility. The fields of application of bacterial polymers-based structures include drug delivery, biomedicine, food products, environment, and agriculture, among others.     

Tailoring the Morphology of Responsive Bioinspired Bicomponent Fibers

Nature is an intriguing inspiration for designing a myriad of functional materials. However, artificial mimicking of bioinspired structures usually requires different specialized procedures and setups. In this study, a new upscalable concept is presented that allows to produce two bioinspired, bicomponent fiber morphologies (side‐by‐side and coaxial bead‐on‐string) using the same electrospinning setup, just by changing the employed spinning solvent. The generated fiber morphologies are highly attractive for thermoresponsive actuation and water harvesting. Another challenge solved in this work is the compositional characterization of complex fiber morphologies. Raman imaging and atomic force microscopy is introduced as a powerful method for the unambiguous characterization of complex bicomponent fiber morphologies. The work opens the way for the construction of heterostructured fiber morphologies based on different polymers combinations, offering high potential for applications as actuators, smart textiles, water management, drug release, and catalysis.     

Experimental and Numerical Analysis of the Viscous Fingering Instability of Shear‐Thinning Fluids

Miscible flow displacements in a rectilinear Hele‐Shaw cell of Newtonian as well as rheologically well‐characterized shear‐thinning fluids are examined through experimental measurements and numerical modelling. Water is used as a displacing fluid while the displaced fluid consists of either a reference Newtonian glycerol solution or shear‐thinning solutions of Alcoflood? polymers of different molecular weights. The experimental measurements revealed that the shear‐thinning behaviour of the non‐Newtonian solutions resulted in more complex instability patterns and new finger structures not previously observed in the case of Newtonian displacements are identified and characterized. An analysis of the effects of the rheological behaviour of the shear‐thinning fluids on instability characteristics such as the finger width and finger tip velocity is presented. Numerical simulations using a pseudo‐spectral method are conducted and allowed to compare the predictions of the mathematical model based on an effective Darcy's law with the experimental measurements.     

Microbial polysaccharide‐based membranes: Current and future applications

Microbial polysaccharides are characterized by high molecular structure variability which translates into a wide range of different properties offering interesting opportunities for application in many different areas, including membrane‐based products and processes. Due to their new or improved properties, microbial polysaccharides can replace plant, algae, and animal products, either in their traditional or in new applications. The main constraint to their wider use is the production costs that are still higher than that of other natural and synthetic polymers. The current applications of microbial polysaccharide membranes in medical, food, and industrial processes are outlined. The limitations still faced by these membranes and the requirements for obtaining innovative products and processes are also addressed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40047.     

Semi-solid materials for controlled release drug formulation: current status and future prospects

Semi-solid materials represent an important category of inactive ingredients (excipients) of pharmaceutical products. Here we review several common semisolid polymers currently used in the controlled release formulations of many drugs. These polymers are selected based on their importance and broad scope of application in FDA-approved drug products and include several polysaccharides (cellulose, starch, chitosan, alginate) and carbomers, a group of mucoadhesive synthetic polymers. Glyceride-based polymers used in self-emulsifying drug delivery systems (SEDDS) will also be discussed for its importance in formulating poorly water-soluble drugs. Unique features and advantages of each type of semi-solid materials are discussed and examples of their use in oral delivery of drugs are provided. Finally, future prospects of developing new and better semi-solid excipients are discussed with the objective of facilitating clinical translation.     

On the stereochemical composition of poly(vinyl chloride) (PVC) and polypropylene (PP): a phenomenological study

The number of mmr‐ and rrm‐based structures which occur necessarily whenever an isotactic or a syndiotactic sequence breaks off respectively; the extent to which they are isolated or are extended to atactic sequences, and the fact that the mmr repeating sequence, especially when it takes the GTTG^?TT conformation, is shorter and exhibits greater local free volume than rrm, mmm and rrr sequences, are shown to be the stereochemical composition determining structures in poly(vinyl chloride) (PVC) and polypropylene (PP) polymers. These structures, as analyzed by ¹³C NMR spectroscopy and probability calculations, have been determined as a function of the overall tacticity for one series of samples prepared by bulk polymerization at temperatures varying from ?50 °C to 70 °C, and one series of samples prepared by polarity‐based fractionation of a commercial polymer. Using this approach, the stereochemical composition of the samples could be identified. The results are of interest to understand the changes in the physical properties as shown in earlier and current work for both series of polymers. © 2003 Society of Chemical Industry