Degree Of Substitution Research Articles

Impact of concentration and aging time of pea starch‐based polymeric solutions on the fabrication of electrospun nanofibers

AbstractPolymer concentration and aging time of polymeric solutions are crucial factors that can influence their viscosity, playing an essential role in the fabrication of electrospun nanofibers. Based on this, herein we evaluated the impact of aging time (24 and 48 h) and pea starch concentration (10%, 20%, and 30%, wt/vol) on the polymeric solutions to produce electrospun nanofibers. Solutions were evaluated by rheology, electrical conductivity, and degree of substitution. The nanofibers were analyzed by morphology, size distribution, chemical nature, and thermal properties. The degree of substitution of starches varied from 1.17 to 1.56. Overall, electrical conductivity decreased with increasing starch concentration and aging time of the polymeric solutions. The use of 10% starch displayed a transition from capsules to fibers, while 20% and 30% starch were able to manufacture homogenous, cylindrical, and random nanofibers with diameters varying from 89 to 373 nm. A significant impact of viscosity was not observed; on the other hand, aging time increased the average diameter of nanofibers. Besides, the fabricated nanofibers showed a lower decomposition temperature than raw starch. The fabricated nanofibers have great potential as wall materials for the encapsulation of different compounds and applications in the biomedical and food sectors.

High‐Cerium‐Content Fe–Ce–Nd–B Sintered Magnets with High Coercivity

Ce substitution of Nd in FeNdB sintered magnets is very interesting for reasons of resource efficiency, sustainability and costs. However, the magnetic properties of high Ce‐content magnets are poor. This is mainly due to the lower values of intrinsic magnetic properties of Fe14Ce2B compared to Fe14Nd2B as well as the Laves phase Fe2Ce, which is formed in the grain boundaries and forms flat aggregates for higher Ce‐content. In this article, sintered magnets with 75 at% degree of substitution of the composition Fe70.9–[(Ce1−xLax)0.75Nd0.25]18.8–B5.8–M4.5 (M = Co, Ti, Al, Ga, Cu, 0 ≤ x ≤ 0.3) are produced and analyzed. It is shown that a new rare earth rich grain boundary phase is formed adding La and that the Laves phase fraction can be reduced by up to 85%. With increasing La content, the remanence and Curie temperature increase and the temperature coefficient of Hc improves. A coercivity, remanence, and maximum energy density of up to μ0Hc = 0.74 T, Jr = 0.98 T, and (BH)max = 139.9 kJ m−3 have been achieved.

R&D investment and network effects: A dynamic model of the search engine market

ABSTRACT This paper considers R&D investment for quality improvement in a dynamic duopoly game in the search engine market. The aim is to determine the circumstances under which asymmetry between search engines (in terms of quality) tends to increase or decrease over time. I show that when the future sufficiently matters, the low-quality search engine can catch up with the high-quality engine by investing in quality. In contrast, when only the present matters, the high-quality search engine wins and the structure of the market transitions to a monopoly. I also show that a shift in asymmetry between firms can result in either an increase or decrease in consumer welfare, depending on the degree of substitutability between the two search engines.

Influence of Molar Mass and Degree of Substitution on Water Solubility of DEAE-Functionalized Apple Glycans

Influence of Molar Mass and Degree of Substitution on Water Solubility of DEAE-Functionalized Apple Glycans

Polyelectrolyte complexes of chitosan and hyaluronic acid or carboxymethylpullulan and their aminoguaiacol derivatives with biological activities as potential drug delivery systems

Polyelectrolyte complexes (PECs) were elaborated from chitosan as cationic polymer and carboxy-methylpullulan (CMP), hyaluronic acid (HA) and their derivatives grafted with aminoguaiacol (G) with different degrees of substitution (DSGA) with the aim of obtaining nanogels for drug delivery. For each couple of polysaccharides, the charge ratios giving the smaller size with the lower PDI were selected to produce PECs. CMP_CHIT and CMP-G_CHIT PECs had smaller sizes (220–280 nm) than HA_CHIT and HA-G_CHIT PECs (280–390 nm). PECs were stable at 4 °C during 28 days at pH 5. In phosphate buffer saline (PBS) at pH 7.4, at 4 °C, a better stability of PECs based on CMP-G derivatives was observed. The hydrophobic associations between aminoguaiacol groups (highlighted by measurements of pyrene fluorescence) led to a better PECs' stabilization in PBS. The PECs' antioxidant and antibacterial activities were demonstrated and related to the DSGA. Diclofenac and curcumin were used as drug models: their loading reached 260 and 53 μg/mg PEC, respectively. The release of diclofenac in PBS at 37 °C followed a quasi-Fickian diffusion mechanism with release constant between 0.88 and 1.04 h−1. The curcumin release followed a slow linear increase in PBS/EtOH (60/40 V/V) with an effect of DSGA.

Synthesis and characterization of cationic tamarind seed polysaccharide: An effective flocculating agent

A series of cationic tamarind seed polysaccharides (CTSPs) with different degrees of substitution were synthesized by etherification of tamarind seed polysaccharides (TSP) with 3-chloro-2-hydroxypropyl trimethylammonium chloride (CHPTAC). By elemental analysis, zeta potential and FTIR, the successful linking of cationic groups on the chain of TSPs were confirmed, and the substitution degrees were determined as 0.143, 0.197 and 0.346, respectively. NMR data indicated that the quaternary ammonium groups were linked to C6 of T-Gal. Subsequently, the flocculation behaviors of CTSPs in kaolin solution were investigated, and the results showed that both the degree of substitution and pH affected their flocculation properties. Charge neutralization and positional blocking effects caused flocculation to show an increasing and then decreasing trend with increasing substitution of CTSPs, whereas the lower the pH, the less flocculant was required to achieve the same flocculation effect. The presence of positive charges allowed CTSPs to effectively remove negatively charged waste water such as kaolin suspensions.

Synthesis and characterization of amino-functionalized guar gum based polyurea: Preparation of iodine complexes, structural investigation and release studies

Biobased materials are expanding dramatically in various industrial applications due to their unique intrinsic properties. In this study, various chemical functionalization procedures were used to synthesize guar gum, a naturally occurring polysaccharide-based polyurea, and its iodine complexes. Firstly, guar gum was subjected to tosylation reaction using p-toluene sulphonyl chloride to introduce tosyl moieties in the polymer chain with the degree of substitution (DS) ranging between 0.16 and 1.54. Sample having the highest degree of tosyl moiety was further reacted with tris(2-aminoethyl) amine to produce 6-deoxy-6-tris(2-aminoethyl) amine derivative via nucleophilic substitution reaction to impart amino functional groups. The degree of substitution in 6-deoxy-6-tris(2-aminoethyl) amine derivative was found to be 0.59. 6-deoxy-6-tris(2-aminoethyl) amine derivative was reacted with different diisocyanates (Toluene-2,4-diisocyanate (TDI), 1,6-diisocyanatohexane (HMDI)) to produce guar gum based polyurea. Iodine complexes of the resulting polyurea were prepared by reacting with different iodinating agents. Different chemical reactions, formation of polyurea and its iodine complexes were thoroughly analyzed by different analytical techniques such as FT-IR, NMR, elemental analysis, XRD, UV–Vis spectroscopy, and a reaction scheme has been proposed. Morphological and rheological characteristics were analyzed by SEM and viscosity measurement. Thermal analysis was carried out by TGA and DSC studies. Finally, by examining the complex's UV–Vis spectra, the iodine release characteristics from polyurea‑iodine complexes were investigated.

Biosurfactant-amphiphilized hyaluronic acid: A dual self-assembly anticancer nanoconjugate and drug vector for synergistic chemotherapy

Novel amphiphilic nanoconjugates of hyaluronic acid (HA), 50 kDa (HA50) and 100 kDa (HA100), and the lipopeptide biosurfactant surfactin (SF) were developed for potential anticancer applications. Physicochemical characterization indicated the formation of an ester conjugate (HA: SF molar ratio 1: 40) with the HA50-SF derivative exhibiting higher degree of substitution, hydrolytic stability, and surface activity. Self-assembly resulted in nanomicelles with smaller size and greater negative charge relative to SF micelles. Biological data demonstrated distinct anticancer activity of HA50-SF which displayed greater synergistic cytotoxicity and selectivity for MDA-MB 231 and MCF-7 breast cancer cells alongside greater modulation of apoptosis-related biomarkers leading to apoptosis. As bioactive vector for chemotherapeutic agents, the selected HA50-SF nanoconjugate efficiently (70 %) entrapped berberine (BER) producing a sustained release BER-HA50-SF synergistic anticancer nanoformulation. Lactoferrin (Lf) coating for dual HA/Lf targeting endowed Lf/BER-HA50-SF with significantly greater selectivity for both cell lines. A murine Ehrlich breast cancer model provided evidence for the efficacy and safety of Lf/BER-HA50-SF via tumoral, histological, immunohistochemical, molecular and systemic toxicity assessments. Thus, HA-SF nanoconjugates integrating the HA and SF properties and biofunctionalties present a novel biopolymer-biosurfactant platform of benefit to oncology nanomedicine and possibly other applications.

Structural characterization and bioactivities of maize bran feruloylated arabinoxylan and oligosaccharides obtained by a combined hydrothermal and enzymatic pre-treatment

Feruloylated arabinoxylans (F-AX) are gaining importance due to their immense health benefits as nutraceuticals. In the current study, we extracted F-AX from maize bran by a combination of hydrothermal pre-treatment and xylanase and cellulase double enzymatic digestion and studied them in detail. The F-AX composition included carbohydrate (533.74 ± 7.59 mg/g), and phenolic acid (153.71 ± 3.55 mg/g) with an arabinoxylan percentage of 74.17% and degree of substitution of 0.99. Ferulic acid was the major phenolic acid found esterified to arabinose. The GC, FTIR, UPLC, and methylation analysis revealed the typical structure of arabinoxylan with bound ferulic acid and a highly substituted xylopyranose backbone. The LC-MS/MS analysis revealed the structure of F-AXOS, which were the predominant oligosaccharides in the purified fraction. The F-AX showed potent antioxidant activity (DPPH, ABTS, and FRAP) and could effectively inhibit the formation of advanced glycation end products (argpyrimidine, pentosidine, and vesperlysine) and protein oxidation products (dityrosine and N′-formylkynurenine). F-AX also showed potent antiproliferative activity against the human colon cancer cells - Colo 205 and HCT 116. The current study revealed that the combined extraction method has yielded a unique blend of F-AX with bioactivities and these molecules have the potential to be used in the development of innovative functional foods.

Homogeneous films from amphiphilic hyaluronan and their characterization by confocal microscopy and nanoindentation

Self-supporting films from amphiphilic hyaluronan are suitable for medical applications like wound dressings or resorbable implants. These films are typically cast from water/alcohol solutions. However, when the mixed solvent evaporates in ambient air, convection flows develop in the solution and become imprinted in the film, potentially compromising its properties. Consequently, we developed a novel film manufacturing method: drying in a closed box under saturated vapour conditions. Using this approach, we prepared a series of optically clear lauroyl-hyaluronan (LHA) films with uniform thickness and compared them to their air-dried counterparts. We first evaluated swelling ratios and elastic moduli for LHA films with varying degrees of substitution. The box-dried films swelled significantly less and were 1–2 orders of magnitude stiffer than air-dried films from the same LHA sample. Confocal microscopy revealed that box-dried films exhibited a regular microstructure, while air-dried films displayed a pore-size gradient and strong microstructure modulation due to convection flows. Local elastic modulus variations arising from these microstructures were assessed using nanoindentation mapping. Importantly, achieving the desired film stiffness requires much lower polymer modification when box-drying is used, enhancing the biological response to the material. These findings have implications for all polysaccharide formulations that utilize mixed solvents.

Insight into the hydrophobic functionalization of cellulose microfibrils using the Passerini three-component reaction

The aqueous catalyst-free one-pot Passerini 3-component reaction (P-3CR) was employed for the functionalization of dialdehyde cellulose (DAC) derived from the periodate oxidation of microfibrillated cellulose (MFC) with insights provided by 13C and 15N CP-MAS NMR and FTIR analyses. The kinetics of the P-3CR revealed rapid progress within the initial 2 h, reaching a plateau between 6 and 18 h. The reaction achieved a maximum degree of substitution (DS) with only 1 equivalent of carboxylic acid and isocyanide with respect to the number of aldehydes, therefore demonstrating the atom economy character of the P-3CR performed on MFC. Variable DS values (0.08 to 0.37) were achieved by altering the degree of oxidation of DAC (ranging from 0.48 to 1.1) when reacted with heptanoic acid and tert-butyl isocyanide. Additionally, aliphatic chain lengths of carboxylic acids from C4 to C11 were successfully used for the functionalization of DAC with distinct hydrophobic chains. Furthermore, while cosolvents negatively affected the DS when using heptanoic acid, a significant increase was observed in the case of undecanoic acid due to an improved solubility of the reagent. The aqueous medium P-3CR can thus be considered a versatile tool to tailor the functionalization of MFC and provide it with hydrophobicity.

Super soft poly(N-isopropylacrylamide) microgels using functionalized starch nanoparticles as crosslinker

A set of poly(N-isopropylacrylamide) p(NIPAM) microgels was successfully prepared through precipitation polymerization (PP) using acryloyl starch nanoparticles (ASNPs) as crosslinkers. Functionalized starch nanoparticles used in microgel preparation, with a degree of substitution (DS) of 0.78 (ASNP12) or 1.37 (ASNP24) were found to have different properties. Dynamic light scattering (DLS) revealed that microgels prepared with ASNP12 exhibit a higher swelling capacity compared to the microgels designed with ASNP24, which was also observed by atomic force microscopy (AFM), showing super soft microgels flattened into disk shape on the substrate. This may be related to softer and surface smoothed microgels. Turbidity analysis revealed a slight shift of the so-called volume phase transition temperature (VPTT) towards higher values for microgels synthesized with ASNP24, indicating its contribution as a hydrophilic comonomer. Considering their high swelling capacity, these bio-based crosslinked microgels are potential materials for adsorptive processes. They can also be considered as candidates for biomedical applications due to the presence of a biopolymer in their structure.

Analyzing Stabilities of Metal-Organic Frameworks: Correlation of Stability with Node Coordination to Linkers and Degree of Node Metal Hydrolysis.

Among the important properties of metal-organic frameworks (MOFs) is stability, which may limit applications, for example, in separations and catalysis. Many MOFs consist of metal oxo cluster nodes connected by carboxylate linkers. Addressing MOF stability, we highlight connections between metal oxo cluster chemistry and MOF node chemistry, including results characterizing Keggin ions and biological clusters. MOF syntheses yield diverse metal oxo cluster node structures, with varying numbers of metal atoms (3-13) and the tendency to form chains. MOF stabilities reflect a balance between the number of node-linker connections and the degree of node hydrolysis. We summarize literature results showing how MOF stability (the temperature of decomposition in air) depends on the degree of hydrolysis/condensation of the node metals, which is correlated to their degree of substitution with linkers. We suggest that this correlation may help guide the discovery of stable new MOFs, and we foresee opportunities for progress in MOF chemistry emerging from progress in metal oxo cluster chemistry.

Extraction of cellulose from halophytic plants for the synthesis of a novel biocomposite.

Cellulose nanofibers, a sustainable and promising material with widespread applications, exhibit appreciable strength and excellent mechanical and physicochemical properties. The preparation of cellulosic nanofibers from food or agricultural residue is not sustainable. Therefore, this study was designed to use three halophytic plants (Cressa cretica, Phragmites karka, and Suaeda fruticosa) to extract cellulose for the subsequent conversion to cellulosic nanofibers composites. The other extracted biomass components including lignin, hemicellulose, and pectin were also utilized to obtain industrially valuable enzymes. The maximum pectinase (31.56 IU mL-1), xylanase (35.21 IU mL-1), and laccase (15.89 IU mL-1) were produced after the fermentation of extracted pectin, hemicellulose, and lignin from S. fruticosa, P. karka, and C. cretica, respectively. Cellulose was methylated (with a degree of substitution of 2.4) and subsequently converted into a composite using polyvinyl alcohol. Scanning electron microscopy and Fourier-transform infrared spectroscopy confirmed the successful synthesis of the composites. The composites made up of cellulose from C. cretica and S. fruticosa had a high tensile strength (21.5 and 15.2 MPa) and low biodegradability (47.58% and 44.56%, respectively) after dumping for 3 months in soil, as compared with the composite from P. karka (98.79% biodegradability and 4.9 MPa tensile strength). Moreover, all the composites exhibited antibacterial activity against gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae) and gram-positive bacteria (Staphylococcus aureus). Hence, this study emphasizes the possibility for various industrial applications of biomass from halophytic plants.

Optimal taxation of nonrenewable resources during clean energy transition: A general equilibrium approach

In this paper we study clean energy transition in a modified version of the Ramsey growth model by including nonrenewable and renewable resources as well as pollution externalities. The main difference from previous works is that we consider imperfect substitution between nonrenewable and renewable resources. We characterize the social optimum and show that the economy converges to a clean state in the long run. We then study the decentralized equilibrium and show that the economy converges to the same state even without regulation, but with higher environmental damage. Further, we investigate the properties of the taxation trajectory that drives the laissez-faire economy to follow the optimal path and show that it can be either increasing or decreasing over time. We identify different channels that influence the path of optimal taxation and show that it depends, among other things, on the level of capital, the cost of renewable energy and the degree of substitution between renewable and nonrenewable resources.

A New Concept for Interpretation of the Viscoelastic Behavior of Aqueous Sodium Carboxymethyl Cellulose Systems.

Viscoelastic behaviors of aqueous systems of commercially available sodium carboxymethyl cellulose (NaCMC) samples with the degrees of substitution (DS) of approximately 0.68 and 1.3, and the weight-average molar masses (Mw) higher than 200 kg mol-1 dissolved in pure water and aqueous sodium chloride solutions were investigated over a wide concentration (c) range of NaCMC samples. The dependencies of the specific viscosity (ηsp), the average relaxation time (τw), and the reciprocal of the steady-state compliance (Je-1) on c were discussed. The relationships ηsp ∝ c3, τw ∝ c2, and Je-1 ∝ c, characteristic of the rod particle suspensions, were clearly observed in a range lower than the c where the critical gel behavior was observed. Thus, a new concept based on the rheology of rod particle suspensions was employed to interpret the viscoelastic behaviors obtained in the c range. In this context, NaCMC polymer molecules are assumed to behave as extended rod particles with length (L) and diameter (d), including effective electrostatic repulsive distances, due to the dissociation of Na+ in aqueous systems. Thus, the number density of polymer molecules is given to be ν = c/Mw, and viscoelastic parameters such as ηsp, τw, and Je-1 are calculated using the theoretical model for rod particle suspensions proposed by Doi and Edwards. This concept reasonably described not only the viscoelastic data obtained in this study but also those from other groups using NaCMC samples with different DS and Mw values.

A quality by design approach to optimise disulfide-linked hyaluronic acid hydrogels

In this study, the disulfide-linked hyaluronic acid (HA) hydrogels were optimised for potential application as a scaffold in tissue engineering through the Quality by Design (QbD) approach. For this purpose, HA was first modified by incorporating the cysteine moiety into the HA backbone, which promoted the formation of disulfide cross-linked HA hydrogel at physiological pH. Utilising a Design of Experiments (DoE) methodology, the critical factors to achieve stable biomaterials, i.e. the degree of HA substitution, HA molecular weight, and coupling agent ratio, were explored. To establish a design space, the DoE was performed with 65 kDa, 138 kDa and 200 kDa HA and variable concentrations of coupling agent to optimise conditions to obtain HA hydrogel with improved rheological properties. Thus, HA hydrogel with a 12 % degree of modification, storage modulus of ≈2321 Pa and loss modulus of ≈15 Pa, was achieved with the optimum ratio of coupling agent. Furthermore, biocompatibility assessments in C28/I2 chondrocyte cells demonstrated the non-toxic nature of the hydrogel, underscoring its potential for tissue regeneration. Our findings highlight the efficacy of the QbD approach in designing HA hydrogels with tailored properties for biomedical applications.

Sulfated Polysaccharides with Anticoagulant Potential: A Review Focusing on Structure-Activity Relationship and Action Mechanism.

Thromboembolism is the culprit of cardiovascular diseases, leading to the highest global mortality rate. Anticoagulation emerges as the primary approach for managing thrombotic conditions. Notably, sulfated polysaccharides exhibit favorable anticoagulant efficacy with reduced side effects. This review focuses on the structure-anticoagulant activity relationship of sulfated polysaccharides and the underlying action mechanisms. It is concluded that chlorosulfonicacid-pyridine method serves as the preferred technique to synthesize sulfated polysaccharides. The anticoagulant activity of sulfated polysaccharides is linked to the substitution site of sulfate groups, degree of substitution, molecular weight, main side chain structure, and glycosidic bond conformation. Moreover, sulfated polysaccharides exert anticoagulant activity via various pathways, including the inhibition of blood coagulation factors, activation of antithrombin III and heparin cofactor II, antiplatelet aggregation, and promotion of the fibrinolytic system.

Sulfonamide modified chitosan oligosaccharide with high nematicidal activity against Meloidogyne incognita

Chitosan oligosaccharide (COS) modification is a feasible way to develop novel green nematicides. This study involved the synthesis of various COS sulfonamide derivatives via hydroxylated protection and deprotection, which were then characterized using NMR, FTIR, MS, elemental analysis, XRD, and TG/DTG. In vitro experiments found that COS-alkyl sulfonamide derivatives (S6 and S11–S13) exhibited high mortality (>98 % at 1 mg/mL) against Meloidogyne incognita second-instar larvaes (J2s) among the derivatives. S6 can cause vacuole-like structures in the middle and tail regions of the nematode body and effectively inhibit egg hatching. In vivo tests have found that S6 has well control effects and low plant toxicity. Additionally, the structure-activity studies revealed that S6 with a high degree of substitution, a low molecular weight, and a sulfonyl bond on the amino group of the COS backbone exhibited increased nematicidal activity. The sulfonamide group is a potential active group for developing COS-based nematicides.

FTIR determination of the degree of molar substitution for hydroxypropyl chitosan

We developed and validated a novel Fourier transform infrared (FTIR) method to determine the degree of molar substitution (MS) for hydroxypropyl chitosan (HPCS) using nuclear magnetic resonance (1H NMR) as a reference, and investigated the factors influencing the MS assay. Through extensive screening of integration methods for candidate bands in the FTIR spectrum of HPCS using 20 HPCS samples with degrees of acetylation (DA) ranging from 0.003 to 0.139, we found that when using band area at 2970 cm−1 as a probe integral, the MS values obtained via the 1H NMR method exhibited linear correlations (R2 > 0.98) with at least 16 integral ratios derived from their FTIR spectra. The optimal reference bands with high reliability are located at 3440 cm−1 and 1415 cm−1, with R2 exceeding 0.99 and a MS range of 0.17–1.92. The band at 2875 cm−1 is less affected by the trace moisture present in HPCS samples than the others. The results of the method validation demonstrated a mean recovery of 98.9 ± 2.8 % and an RSD below 10 %, suggesting a simple, robust, and highly accurate and precise method. This method could be extendable for the determination of the MS of insoluble HPCS derivatives and other hydroxypropylated polysaccharides.