High Degree Of Substitution Research Articles

Click Cross-Linking Improves Retention and Targeting of Refillable Alginate Depots

Injectable alginate hydrogels have demonstrated utility in tissue engineering and drug delivery applications due in part to their mild gelation conditions, low immune responses and chemical versatility. Recently, the potential of these gels has expanded with the introduction of refillable hydrogel depots - alginate gels chemically decorated with chemistry groups to efficiently capture prodrug refills from the blood. Unfortunately, high degrees of click substitution on alginate gels lead to poor viscoelastic properties and loss of ionic cross-linking. In this work, we introduce tetrabicyclononyne (tBCN) agents that covalently cross-link azide-modified alginate hydrogels for tissue engineering and drug delivery application in vivo. Adjusting cross-linker concentration allowed tuning the hydrogel mechanical properties for tissue-specific mechanical strength. The bioorthogonal and specific reaction creates stable hydrogels with improved in vivo properties, including improved retention at injected sites. Azide-alginate hydrogels cross-linked with tBCN elicited minimal inflammation and maintained structural integrity over several months and efficiently captured therapeutics drug surrogates from the circulation. Taken together, azide-alginate hydrogels cross-linked with tBCN convey the benefits of alginate hydrogels for use in tissue engineering and drug delivery applications of refillable drug delivery depots.

Synthesis and structure of carboxymethylcellulose with a high degree of substitution derived from waste disposable paper cups

The cost of the cellulose derived from some raw materials was high. In addition, the dispersion of the cellulose with special shape and a low degree of substitution (DS) in water-soluble polymers was poor. To resolve this problem, cellulose was separated from waste disposable paper cups (WDPC) and then the carboxymethylcellulose (CMC) was synthesized by etherification. Under the optimized conditions (the etherification temperature of 70 ℃, the etherification time of 1.5 h, the monochloroacetic acid mass (C2H3ClO2) of 7 g), the DS of CMC was as high as 1.21. As-prepared CMC showed ribbon and rod-like shapes with a diameter of 25−50 μm. In addition, they exhibited an excellent thermal stability. Compared with other CMC, we could infer that as-prepared CMC in this paper will have potential applications in flexible composites and functional materials.

Composition of Individual Microspheres in a Finely Dispersed Fraction from Fly Ash after the Pulverized Combustion of Ekibastuz Coal

A systematic study of the compositions of individual microspheres with sizes of 90 wt % and FeO 90 wt % and FeO = 3–6 wt %. Mineral precursors of microspheres of group (3), SiO2 + Al2O3 < 90 wt % and FeO to 11 wt %, were mixed-layer illite–montmorillonites with a high degree of cationic substitution with iron and Fe3+ included into interlayer sites.

Sulfated and sialylated N-glycans in the echinoderm Holothuria atra reflect its marine habitat and phylogeny

Among the earliest deuterostomes, the echinoderms are an evolutionary important group of ancient marine animals. Within this phylum, the holothuroids (sea cucumbers) are known to produce a wide range of glycoconjugate biopolymers with apparent benefits to health; therefore, they are of economic and culinary interest throughout the world. Other than their highly modified glycosaminoglycans (e.g. fucosylated chondroitin sulfate and fucoidan), nothing is known about their protein-linked glycosylation. Here we used multistep N-glycan fractionation to efficiently separate anionic and neutral N-glycans before analyzing the N-glycans of the black sea cucumber (Holothuria atra) by MS in combination with enzymatic and chemical treatments. These analyses showed the presence of various fucosylated, phosphorylated, sialylated, and multiply sulfated moieties as modifications of oligomannosidic, hybrid, and complex-type N-glycans. The high degree of sulfation and fucosylation parallels the modifications observed previously on holothuroid glycosaminoglycans. Compatible with its phylogenetic position, H. atra not only expresses vertebrate motifs such as sulfo- and sialyl-Lewis A epitopes but displays a high degree of anionic substitution of its glycans, as observed in other marine invertebrates. Thus, as for other echinoderms, the phylum- and order-specific aspects of this species' N-glycosylation reveal both invertebrate- and vertebrate-like features.

Crystallinity reduction and enhancement in the chemical reactivity of cellulose by non-dissolving pre-treatment with tetrabutylphosphonium acetate

Herein, we demonstrate the activation of commercial chemical cellulose pulps towards chemical modification by a pre-treatment step with tetrabutylphosphonium acetate ([P4444][OAc]). A heterogeneous (non-dissolving) pre-treatment was applied allowing for a significant reduction in crystallinity, without concomitant formation of the thermodynamically stable cellulose II. An increase in chemical reactivity was demonstrated using two model reactions; (1) acetylation (organic swelling conditions), where high degrees of substitution (DS) were obtained without the need for a catalyst, and (2) 4-acetamido-TEMPO oxidation (aqueous swelling conditions), where significant degrees of oxidation (DO) were obtained, beyond those for the untreated pulps. In both tests a notable improvement in cellulose reactivity was observed. Regioselectivity of acetylation was assessed using 2D NMR for one low and one high DS sample. The low DS showed a small degree of acetylation of the 6-OH, whereas, the high DS from the pre-treated sample showed mainly mixtures of triacetate and diacetates. Important mechanistic information is attained for future development of aqueous and organic-based reactions involving this ionic liquid pre-treatment.

Privatization of a multi-product public firm

ABSTRACT This study considers a public firm that provides a profitable service and an unprofitable service. In our model, only the public firm supplies the unprofitable service, while both the public firm and multiple private firms supply the profitable service. The two services may be substitutes, complements, or independent in demand, and the public firm has inferior technology. We examine whether the public firm should privatize either the profitable service or the service that faces competition from private firms. We obtain the following results. When the two services are complementary, the critical cost of the public firm such that privatizing the profitable service is socially preferable increases with the degree of complementarity. When the two services are substitutes, the critical cost decreases (increases) with the degree of substitution for a low (high) degree of substitution. For a sufficiently high degree of substitution, the critical cost becomes small.

Esterified cellulose nanofibres from saw dust using vegetable oil

In this work, cellulose nanofibres (CNFs) were extracted from sawdust, which is an underutilized by-product from the wood and timber industry. The extracted CNFs by chemical and mechanical treatments had a web-like structure with diameters ranging between 2 nm and 27 nm and lengths reaching a few microns. The obtained CNFs were further chemically modified with vegetable canola oil using two different esterification processes. In order to compare the effect of the surface modification of CNFs, the nanopapers were prepared from their prospective suspensions through solvent evaporation method, and then characterize with Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), UV–vis spectroscopy and tensile tester. FTIR results indicated that both methods led to a successful grafting of the long chain hydrocarbon structure onto the CNFs, and became more hydrophobic when compared to unmodified CNFs-based nanopapers. The crystallinity, mechanical, light transmittance and thermal properties were significantly affected primarily by the esterification method employed, thus the degree of substitution. It was found that high degree of substitution adversely affected the crystallinity, light transmittance, mechanical and thermal properties. The crystallinity decreased from 70% to <40% when the degree of substation was about 0.8.

Starch from two unripe plantains and esterified with octenyl succinic anhydride (OSA): Partial characterization

Chemical modification with octenyl succinic anhydride (OSA) helps to control the physicochemical and thermal properties of isolated starches. The main objective, herein, was to partially characterize modified starches from Dominico-Harton plantain and FHIA 21 planted in Colombia. The highest degree of substitution was found in FHIA 21 (0.020) starch with 3% OSA and 4-h reaction at room temperature. The grain morphology was not affected, but small changes on the surface were evident. Both modified starches reported absorption bands in the IR at 1566 and 1738 cm−1, proper for these types of starch derivatives. The hexagonal and monoclinic structures of starch were altered through chemical modification. In the bending curves, a drastic decrease in the viscosity of the modified starches was observed with respect to the native one. The gelatinization temperatures of the modified starches were similar to those of the isolated starches.

Recent Advances in the Preparation and Characterization of Intermediately to Highly Esterified and Etherified Starches: A Review

AbstractStarch can be derivatized with various functional groups to achieve different physicochemical properties. For decades, researchers have focused on lightly substituted starches since these starches can be prepared economically in aqueous slurries. In contrast, modified starches having high or intermediate degree of substitution have not been thoroughly investigated or extensively used, mainly because their conventional preparation involves harmful solvents that renders their purification uneconomical. Aiming to explore possible industrially feasible routes for producing medium and highly substituted starch derivatives, this review summarizes developments in synthetic methods, especially the influence of synthesis media and reaction conditions. In addition, crucial physicochemical properties of those highly substituted starches are discussed.

METHOD OF NATURAL HYDRATE METHANE PRODUCTION WITH SIMULTANEOUS CARBON ACID SEQUESTION

Background Methane hydrate is a combination of methane with water, resistant to low temperatures and high pressure, outwardly resembles compressed snow. According to investigations, the reserves of methane hydrates are considered the largest reserves of natural methane, exceeding the world's oil reserves. Since methane is also a valuable natural energy source, timely development of its reserves is important for the economy and ecology. At present, a search is underway for a promising method for extracting methane from its hydrates. Recent research into the exploitation of this energy resource is related to CO2 sequestration, so this energy source can be obtained through CO2 sequestration, which will help to reduce the threat of global warming. However, be aware that the threat of global warming in this case is itself produced methane which is a greenhouse gas, therefore, must strike a balance in this process. Aims and Objectives Consideration of a new version of the method of extraction of methane from natural hydrates with simultaneous sequestration of carbon dioxide. Results In this paper, we propose a promising method for extracting hydrated methane that allows increasing the rate and depth of dissociation of methane hydrate with a sufficiently high degree of substitution of methane hydrate for carbon dioxide hydrate in the reservoir.

Alkylation enhances biocompatibility and siRNA delivery efficiency of cationic curdlan nanoparticles

Cationic curdlan derivatives are a class of promising carriers for nucleic acid delivery including short interfering RNA (siRNA). While our previous studies demonstrated the siRNA delivery efficiency of aminated curdlan derivatives, the associated cytotoxicity issue remained unsolved. To investigate the effects of alkylation on the toxicity as well as the transfection efficiency, we conjugated short alkyl chains to 6-amino-6-deoxy-curdlan (6AC-100). The cytotoxicity of alkylated 6AC-100 derivatives (denote CuVa polymers) decreased with the increase of the degree of substitution (DS). CuVa3, with the highest DS, showed a 50% decreased cytotoxicity compared to 6AC-100 to 6AC-100 at a concentration of 140 μg/mL. The CuVa polymers readily complexed with siRNA to form nanoparticles, and induced significant knockdown of a disease related gene (STAT3) in mouse melanoma cell line B16. However, B16 cells transfected with siSTAT3 complexed to CuVa3 showed the highest phenotypic changes. These findings suggest that CuVa polymers have significantly enhanced biocompatibility and may be a promising delivery system for delivery of therapeutic siRNAs.

Ultrasound-assisted catalyst-free thiol-yne click reaction in chitosan chemistry: Antibacterial and transfection activity of novel cationic chitosan derivatives and their based nanoparticles

In this work, we demonstrate that the thiol-yne click reaction could be efficiently mediated by ultrasonic irradiation and implement the ultrasound-assisted thiol-yne click reaction to chitosan chemistry as a polymer-analogous transformation. We optimize power and frequency of ultrasound to preserve selectivity of the click reaction and avoid ultrasonic degradation of the chitosan polymer chain. Thus, we obtain a new water-soluble betaine. Using ionic gelation of the obtained betaine derivatives of chitosan, we prepare nanoparticles with a unimodal size distribution. Furthermore, we present results of antibacterial and transfection activity tests for the chitosan derivatives and their based nanoparticles. The derivative with a medium molecular weight and a high degree of substitution demonstrated the best antibacterial effect. It derived nanoparticles with a size of ca. 100 nm and ζ-potential of ca. +69 mV revealed even higher antibacterial activity, slightly superior to commercial antibiotics ampicillin and gentamicin. On the contrary, the obtained polymers possess a much more pronounced transfection activity as compared with their based nanoparticles and species with a low degree of substitution acts as the most efficient transfecting agent. Moreover, the obtained betaine chitosan derivatives as well as their derived nanoparticles are non-toxic.

Bacterial Nanocellulose and Its Surface Modification by Glycidyl Methacrylate and Ethylene Glycol Dimethacrylate. Incorporation of Vancomycin and Ciprofloxacin.

Among nanocelluloses, bacterial nanocellulose (BNC) has proven to be a promising candidate in a range of biomedical applications, from topical wound dressings to tissue-engineering scaffolds. Chemical modifications and incorporation of bioactive molecules have been obtained, further increasing the potential of BNC. This study describes the incorporation of vancomycin and ciprofloxacin in BNC and in modified BNC to afford bioactive BNCs suitable for topical wound dressings and tissue-engineering scaffolds. BNC was modified by grafting glycidylmethacrylate (GMA) and further cross-linking with ethylene glycol dimethacrylate (EGDMA) with the formation of stable C–C bonds through a radical Fenton-type process that involves generation of cellulose carbon centred radicals scavenged by methacrylate structures. The average molar substitution degree MS (MS = methacrylate residue per glucose unit, measured by Fourier transform infrared (FT–IR) analysis) can be modulated in a large range from 0.1 up to 3. BNC-GMA, BNC-EGDMA and BNC-GMA-EGDMA maintain the hydrogel status until MS reaches the value of 1. The mechanical stress resistance increase of BNC-GMA and BNC-GMA-EGDMA of MS around 0.8 with respect to BNC suggests that they can be preferred to BNC for tissue-engineering scaffolds in cases where the resistance plays a crucial role. BNC, BNC-GMA, BNC-EGDMA and BNC-GMA-EGDMA were loaded with vancomycin (VC) and ciprofloxacin (CP) and submitted to release experiments. BNC-GMA-EGDMA of high substitution degree (0.7–1) hold up to 50 percentage of the loaded vancomycin and ciprofloxacin amount, suggesting that they can be further investigated for long-term antimicrobial activity. Furthermore, they were not colonized by Staphylococcus aureus (S.A.) and Klebsiella pneumonia (K.P.). Grafting and cross-linking BNC modification emerges from our results as a good choice to improve the BNC potential in biomedical applications like topical wound dressings and tissue-engineering scaffolds.

Flow synthesis, characterization, anticoagulant activity of xylan sulfate from sugarcane bagasse

High-value utilization of hemicellulose is critical to improve the append value of integrated biorefineries. In this research, the alkali-soluble sugarcane bagasse hemicellulose was sulfated using chlorosulfonic acid and N,N-dimethylformamide/LiCl under homogeneous conditions. With the aid of flow technique, a rapid, mild, and efficient method for the synthesis of xylan sulfate with high molecular weight and controllable degree of substitution was achieved. The results showed that the reaction time and the degradation of xylan chain were drastically reduced compared to the “in flask” batch conditions. High molecular weight of the product (Mw = 148,217) with a reasonable degree of substitution (DS = 1.49) could be obtained even at room temperature in 10 min under the present flow system. Anticoagulant experiments showed good anticoagulant activity of the resultant xylan sulfate, which could significantly prolong the activated partial thromboplastin time and thrombin time. This work not only provides a novel method for the synthesis of xylan sulfate, but also offers new opportunities for the production of other functional polysaccharide derivatives under the flow reaction conditions.

Hydrophobic agave fructans for sustained drug delivery to the human colon

Given their glycosidic β 2−1 and β 2−6 linkages, fructans from Agave tequilana Weber var. azul (AtF) may be employed for the design of drug carriers targeting the human colon. However, the high water solubility of AtF prevents their use for such a purpose. In this work, AtF were esterified with acetyl, lauroyl and palmitoyl groups with the aim to encapsulate ibuprofen as a model drug and characterize its enzymatic release in simulated colon conditions. It was found that efficiency of encapsulation increased from 0.8% (unmodified fructan) to 17 or 21.5% when AtF was esterified with acetyl groups at high degree of substitution (2.75 DS) or with a long acyl chain such as palmitoyl at low DS (0.18) respectively. Hydrophilic fructan based microspheres (AtF, and lauroyl fructan, 46 and 61.3° contact angle respectively) had poor encapsulation efficiency (0.8–1.5%) and lost most of their cargo (85%) at gastric conditions. In contrast, hydrophobic fructan based microspheres (acetyl and palmytoyl, 91–98° contact angle) showed high stability at gastric pH and were able to release the drug for long periods. These characteristics make hydrophobic fructans appropriate vehicles that show great potential for the delivery of drugs to the colon, allowing long drug bioavailability during its delivery and release.

Thermoanalytical studies (TG\u2013DTG\u2013DSC, Py\u2013GC/MS) of sodium carboxymethyl starch with different degrees of substitution

The paper presents the results of thermal analysis of polymer material in the form of starch derivatives in the form of sodium carboxymethyl starch (CMS–Na) with degree of substitution (DS) in the range 0.2–0.9 for the preparation of foundry binder. In this work, the thermal behavior of the modified starch and qualitative assessment of degradation products released during pyrolysis were determined and comprised. The analysis of the course of progressive decomposition of the starch material under controlled heating in the range of 25–1000 °C in anaerobic atmosphere was based on the results of thermal analysis methods (TG–DTG–DSC) in combination with the results of pyrolysis–gas chromatography–mass spectrometry (Py–GC/MS). The detailed TG–DTG–DSC analysis allowed to determine and compare the temperature at which the process of decomposition of carboxymethyl starches sodium salts with different degrees of substitution begins and to determine the course of its degradation under conditions corresponding to the contact of the foundry binder in the form of starch material with liquid metal (conditions like in foundry mold). Thermogravimetric analysis shows that decomposition processes are multistage, and dehydration is the first step of decomposition. Moreover, TG–DTG–DSC analyses indicate that the thermal stability and the decomposition path of tested compounds depend on the DS. Results of Py–GC/MS studies showed that the formation of decomposition products (including cyclic and aromatic hydrocarbons) in a predetermined temperature range is lower in the case of CMS–Na with high DS.

Studies on new highly phosphonated poly (ether ether ketone) based promising proton conducting membranes for high temperature fuel cell

The present study deals with the development of poly ether ether ketone (PEEK) based proton exchange membrane (PEM) having phosphonic acid as protogenic moiety. The synthesis of phosphonated PEEK was carried out in two simpler steps i.e. chloromethylation followed by phosphonation through Michaelis-Arbuzov reaction. The product was further investigated for structural property through FTIR, 1H NMR, 13C NMR, 31P NMR and XRD while thermal properties were analysed by TGA. Other physical properties such as ion exchange capacity, water uptake and proton conductivity were determined for the prepared membranes to execute their suitability as PEM. The presence of phosphonic acid group provides good thermal and chemical stability to the membranes. The high substitution degree (1.11–1.56) achieved in present case was favourable for providing significant proton conductivity of 0.047 S/cm at 120 °C under hydrated conditions to the corresponding membranes which entitle them as potential candidate for PEMs in fuel cells at high temperature.

Preparation and characterization of cassava starch acetate with high substitution degree

In this work, cassava starch (CS) was acetylated by a simple and scalable method to produce a highly hydrophobic polymeric material with potential use in coating and food packaging. The chemical structure, thermal stability and morphological properties of cassava starch acetate (CSA) were determined. Their formation was confirmed using FTIR by the presence of the carbonyl signal around 1749 cm−1. Degrees of substitution (DS) obtained by titration were between 1.9 and 2.9.Thermogravimetric analysis showed an increase in thermal stability with acetylation, the DS = 2.9 sample behaving as a homopolymer. SEM micrographs showed the loss of the structure of the starch granule and the appearance of a beehive-shaped new structures.CS and CSA were structurally characterized by NMR. The CS branching percentage obtained by 1H NMR was 4.76. Using quantitative 13C{1H}-NMR the DS was calculated, confirming the values already obtained and the regioselective substitution pattern was determined, demonstrating that the favorite position of acetylation is that of C6.

Controlled biodegradability of functionalized thermoplastic starch based materials

The present work focuses on the preparation and characterization of biodegradable materials based on plasticized and chemically modified starch. During the experiments, the morphology, properties and biodegradability of the starch materials were influenced by the functionalization (acetylation, propionation) of the starch, different processing procedures and the use of plasticizers. The starch materials were prepared by either solution casting or melt mixing or by the combination of the two procedures, which strongly affected the degree of the material plasticization, its homogeneity, and the final morphology. FTIR spectroscopy qualitatively proved the esterification of starch by the intensity of signals associated with esters groups. The thermogravimetric analysis confirmed a gradual reduction in the water content proportional to the acetylation of starches, as well as noticeable changes in their thermal properties at the higher degree of substitution (DS). Signal intensities and weight losses derived from FTIR and TGA, respectively, were well correlated with DS. The morphological changes of the polysaccharide materials were visualized by microscopy techniques. The biodegradation rate of prepared materials was expressed as the percentage of carbon mineralization and was significantly retarded as a function of the starch acetylation. A remarkable effect of the material processing, the presence of plasticizers, and the propionation of the starch on biodegradation has been found.

Physicochemical Properties and AAEM Retention of Copyrolysis Char from Coal Blended with Corn Stalks

Physicochemical properties (i.e., morphological variation, functional groups, and carbon structure change) and alkali and alkaline earth metal retention of chars during coal and corn stalks (CS) copyrolysis were investigated in this research. The copyrolysis char samples were obtained at the temperature ranging from 400 to 1000 °C at intervals of 100 °C under argon atmosphere by a horizontal furnace. The results indicate that the synergistic effects on char yields are slight or even negligible. The presence of CS promotes the formation of plastic mass during copyrolysis because of the interactions between volatiles and chars of coal and CS. As the pyrolysis temperature increases from 400 to 1000 °C, the aromatic C–H functional groups first increase and then decrease, and the char structure changes from a small aromatic ring system to a large aromatic ring system containing six or more fused benzene rings. The average number of hydrogen atoms per aromatic ring and the number of the aromatic ring structure with high substitution degree are highest at 500 °C. In addition, the C═O and aliphatic C–H functional groups in the char samples disappear when the pyrolysis temperature ranges from 600 to 700 °C. The release of K and Mg is inhibited during copyrolysis, while the release of Ca is promoted.