N-alkylated Chitosan Research Articles

Synthesis and unambiguous NMR characterization of linear and branched N-alkyl chitosan derivatives

Chitosan, sourced from abundant chitin-rich waste streams, emerges as a promising candidate in the realm of future functional materials and chemicals. While showing numerous advantageous properties, chitosan sometimes falls short of competing with today's non-renewable alternatives. Chemical derivatization, particularly through N-alkylation, proves promising in enhancing hydrophobic functionalities. This study synthesizes fifteen chitosan derivatives (degree of substitution = 2–10 %) using an improved reductive amination method. Next, selective depolymerization through acid hydrolysis reduced the chain rigidity imposed by the polymer backbone. This facilitated unambiguous structural characterization of the synthesized compounds using a combination of common NMR techniques. Two potential side reactions are identified for the first time, emphasizing the need for detailed structural information to unlock the true potential of these derivatives in future applications. HypothesisThe increase in chain mobility induced by the selective depolymerization of aliphatic N-alkyl chitosan derivatives allows for an unambiguous NMR characterization.

Shaking up conjugates between chitosan and aldehydes via mechanochemistry

A solid-state mechanochemical protocol to synthesize Schiff base and N-alkyl chitosan derivatives is described. The transition from a liquid reaction medium to a solid-state reaction allowed for a more efficient...

Electrospun nanofiber membranes for rapid liver hemostasis via N-alkylated chitosan doped chitosan/PEO

The ideal hemostatic agents should be able to stop bleeding quickly and avoid secondary bleeding caused by adhesion with blood clots during dressing change. Herein, a hydrophobic electrospun nanofiber membrane was prepared for achieving hemostasis, rationally targeting both attributes, via doping N-alkylated chitosan (N-CS) grafted with octadecyl into chitosan/polyethylene oxide (PEO). In vitro and in vivo coagulation tests showed that CPNs doped with small amounts of N-CS (CPN31) could significantly shorten hemostasis time and promote the formation of more stable and stronger blood clots. In particular, the whole blood clotting time of CPN31 (58.8 ± 2.2 s) was significantly lower than that of chitosan/PEO (CPN0) nanofiber membrane (67 ± 3.5 s) and the medical sterile gauze (86.7 ± 0.6 s). Furthermore, due to the hemophobic nature of CPNs, blood wetting of the dressing was severely limited and blood can coagulated at the site of liver injury in rats, thus reducing blood loss and allowing rapid removal of the dressing without triggering secondary hemorrhage. The CPN31 exhibited excellent hemostasis properties, easy to remove, blood compatibility, biocompatibility and promoting fibroblast proliferation properties. This hydrophobic CPNs is a promising biological adhesive for hemorrhage control.

Comparative Study of the Removal Efficiency of Nalidixic Acid by Poly[(4-vinylbenzyl)trimethylammonium Chloride] and N-Alkylated Chitosan through the Ultrafiltration Technique and Its Approximation through Theoretical Calculations.

Emerging antibiotic contaminants in water is a global problem because bacterial strains resistant to these antibiotics arise, risking human health. This study describes the use of poly[(4-vinylbenzyl) trimethylammonium chloride] and N-alkylated chitosan, two cationic polymers with different natures and structures to remove nalidixic acid. Both contain ammonium salt as a functional group. One of them is a synthetic polymer, and the other is a modified artificial polymer. The removal of the antibiotic was investigated under various experimental conditions (pH, ionic strength, and antibiotic concentration) using the technique of liquid-phase polymer-based retention (LPR). In addition, a stochastic algorithm provided by Fukui's functions is used. It was shown that alkylated N-chitosan presents 65.0% removal at pH 7, while poly[(4-vinylbenzyl)trimethylammonium chloride] removes 75.0% at pH 9. The interaction mechanisms that predominate the removal processes are electrostatic interactions, π-π interactions, and hydrogen bonding. The polymers reached maximum retention capacities of 1605 mg g-1 for poly[(4-vinylbenzyl) trimethylammonium chloride] and 561 mg g-1 of antibiotic per gram for alkylated poly(N-chitosan). In conclusion, the presence of aromatic groups improves the capacity and polymer-antibiotic interactions.

Preparation, Characterization, and Bio Evaluation of Fatty N- Hexadecanyl Chitosan Derivatives for Biomedical Applications.

The objective of this study was to improve the antibacterial activities of chitosan via N-alkyl substitution using 1-bromohexadecane. Mono and di substitution (Mono-NHD-Ch and Di-NHD-Ch) were prepared and characterized using FT-IR, HNMR, TGA, DSC, and SEM. Elemental analysis shows an increase in the C/N ratio from 5.45 for chitosan to 8.63 for Mono-NHD-Ch and 10.46 for Di-NHD-Ch. The antibacterial properties were evaluated against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus cereus. In the examined microorganisms, the antibacterial properties of the novel alkyl derivatives increased substantially higher than chitosan. The minimum inhibitory concentration (MIC) of Mono-NHD-Ch and Di-NHD-Ch was perceived at 50 μg/mL against tested microorganisms, except for B. cereus. The MTT test was used to determine the cytotoxicity of the produced materials, which proved their safety to fibroblast cells. The findings suggest that the new N-Alkyl chitosan derivatives might be used as antibacterial alternatives to pure chitosan in wound infection treatments.

Synthesis of n‐alkylated quaternary ammonium chitosan and its long‐term antibacterial finish for rabbit hair fabric

AbstractIn this work, n‐alkyl chitosan (N‐CTS) was obtained by alkylation modification of chitosan with n‐butylaldehyde using Schiff alkali method. The etherifying agent 3‐chloro‐2‐hydroxypropyl triethylammonium chloride (CHPTAC‐ethyl) was synthesized from triethylamine and epichlorohydrin. The N‐CTS and CHPTAC‐ethyl were etherized to finally synthesize n‐alkyl quaternary ammonium chitosan (N‐CCTS). Scanning electron microscope, X‐ray diffractometer, Fourier transform infrared, X‐ray photoelectron spectroscopy, and 13CNMR were used to characterize the surface morphology and chemical structure. Viscosity method and spectrophotometry were used to determine its physical and chemical properties. The etherification reaction mechanism was studied systematically and the influence of reaction conditions on the degree of substitution and solubility of N‐CCTS was investigated. The minimum inhibitory concentration (MIC) of N‐CCTS against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was both 0.15 g/L, which was superior to the MIC value of natural chitosan. N‐CCTS was used to finish rabbit hair fabric with citric acid as cross‐linking agent and sodium hypophosphite as catalyst. The antibacterial and washing resistance of the product were investigated. After 25 times of washing, the antibacterial rate of N‐CCTS against E. coli and S. aureus remained stable at about 90%, and the antibacterial rate was higher than that of N‐CTS and natural chitosan, and it was a kind of natural polymer long‐acting antibacterial finishing agent for rabbit hair fabric.

Hydrophobic and self-recoverable cellulose nanofibrils/N-alkylated chitosan/poly(vinyl alcohol) sponge for selective and versatile oil/water separation

A highly hydrophobic and self-recoverable sponge was prepared with cellulose nanofibrils (CNFs), N-alkylated chitosan (NCS), and poly (vinyl alcohol) (PVA), which was then endowed with hydrophobic properties via simple thermal chemical vapor deposition (CVD). The three-dimensional (3D) interconnected microstructure of the prepared CNF/NCS/PVA sponge was found to have 96% porosity, ultra-low density (16.61–50.91 mg/cm3) and high hydrophobicity (water contact angle of 147°), which can absorb various organic solvents with an absorption capacity of 19.05–51.08 times of its original weight. Besides, the sponge could bear 80% strain and be cyclically compressed 50 times under the strain of 50%. The sponge can effectively separate oil/water mixtures and water-in-oil emulsions with high separation efficiency and fluxes. Moreover, the sponge could keep its good stability in various acidic, saline and mechanical abrasion conditions. The green preparation and good separation efficiency suggest a potential application of recyclable and versatile CNF/NCS/PVA sponges in oil/water separation.

Toxicity of chitosan derivatives to Varroa destructor (Anderson and Trueman) and their effects on immune gene expression in honey bees

Varroasisis caused by Varroa destrucor (Anderson and Trueman) is considered the most dangerous honey bee disease. V. destructor mites parasitize both brood and adults, causing considerable losses to the colony population. The control of Varroa mites is highly dependent on the application of synthetic acaricides, however, acaricide resistance can develop. To eliminate the risk of Varroa mite resistance and to reduce residues in hive products, organic-based substances for Varroa mite control are being applied. In the present study, the acaricidal activity of N-alkyl and O-acyl chitosan derivatives against Varroa mites and their side effects on honey bees have been evaluated. Chitosan has been extracted from the corpses of honey bees. The yield, degree of deacetylation, and molecular weight of chitosan from the chitin of honey bee corpses were determined as 89%, 90%, and 20 kDa, respectively. Varroa mite mortalities were observed between 6.28-84.38% and 0.00-90.47% by N-alkyl and O-acyl chitosan derivatives, respectively. The best derivatives against Varroa mite were N-(3-phenylbutyl)chitosan (NAC-5) and O-(heptanoyl)chitosan (OAC-4). The results showed that different lethal concentrations of NAC-5 and OAC-4 had side effects against honey bees less than 26%. No significant difference was found between honey bee mortalities at 24, 48, and 72 hours post-treatment, while mortalities significantly differed between 4, and 24 h post-treatment. Immune gene expression in honey bees exposed to a lethal concentration of NAC-5and OAC-4 showed that the expressions of AmHym, AmBask, and AmSpz were significantly lower compared with those of control honey bees.

N-Alkylated chitosan coupled to the liquid-phase polymer-based retention (LPR) technique to remove arsenic (V) from aqueous systems

Water-soluble polymer based on alkylated chitosan with a quaternary ammonium group (Ch-QAG) was prepared, characterized, and applied to remove arsenate ions from aqueous solution by LPR technique. The arsenic removal was performed by the washing method (WM) and enrichment method (EM). Through the WM, studies of the pH and variation in the concentrations of interferents and arsenate ions were carried out. The effect of the removal of arsenate ions in simulated water was determined from the Camarones River in northern Chile. Ch-QAG showed high affinity for binding arsenate species (99% of removal) at pH 11.0 at a molar ratio of 20:1 polymer: As(V). High selectivity was also observed in the presence of interfering ions such as Cl−, SO42-, and PO43-, resulting in a removal rate over 80% at percentages over 95% for a concentration of 100 mg L-1 of As (V). The maximum retention capacity obtained was 112, 105, and 98 mg g-1 for three load cycles. The retention percentage for simulated water was 46.3% at a concentration of 1300 μ g L-1. In conclusion, the results presented in this study show that using Ch-QAG with ultrafiltration membranes is a great alternative to remove As (V) at high removal rates.

Correction: A rapid hemostatic sponge based on large, mesoporous silica nanoparticles and N-alkylated chitosan.

Correction for 'A rapid hemostatic sponge based on large, mesoporous silica nanoparticles and N-alkylated chitosan' by Zihao Chen et al., Nanoscale, 2018, 10, 20234-20245, DOI: .

N-alkylated chitosan/graphene oxide porous sponge for rapid and effective hemostasis in emergency situations

N-alkylated chitosan (AC) sponges and graphene oxide (GO) sponges are promising candidates for emergency hemostat. However, AC sponges have weak mechanical strength and GO sponges may induce toxicity. To overcome these problems, a series of AC/GO composite spongs (ACGS) were prepared with various ratios (GO/AC, 0%, 5%, 10%, and 20%) using a dilute solution freeze phase separation and drying process. The sponges exhibit excellent absorption capacity, mechanical stability, and biocompatibility. In serial in vitro clotting tests, the higher the ratio of GO, the better the coagulation efficiency. ACGS with 20% ratio of GO (ACGS20) has shorter hemostatic time than Celox in a rabbit femoral injury test. Moreover, ACGS20 can accelerate erythrocyte and platelet adhesion. CD62p and intracellular Ca2+ measurements show that ACGS20 can promote the release of intracellular Ca2+ and stimulate platelet activation. These results suggest that ACGS20 is a good candidate composition for a safe and efficacious hemostatic dressing.

Immobilization of Carboxypeptidase A into Modified Chitosan Matrixes by Covalent Attachment.

Carboxypeptidase A (CPA) is a metalloexopeptidase that catalyzes the hydrolysis of the peptide bonds that are adjacent to the C-terminal end of a polypeptide chain. The enzyme preferentially cleaves over C-terminal L-amino acids with aromatic or branched side chains. This is of main importance for food industry because it can be employed for manufacturing functional foods from different protein sources with reduced hydrophobic amino acid content for patients with deficiencies in the absorption or digestion of the corresponding amino acids. In that way, strategies for effective multipoint covalent immobilization of CPA metalloenzyme on chitosan beads have been developed. The study of the ability to produce several chemical modifications on chitosan molecules before, during and after its coagulation to form carrier beads lead in a protective effect of the polymer matrix. The chemical modification of chitosan through the use of an N-alkylation strategy produced the best derivatives. N-alkyl chitosan derivative beads with D-fructose presented values of 0.86 for immobilization yield, 314.6IUg-1 bead for initial activity of biocatalyst and were 5675.64-fold more stable than the free enzyme at 55°C. Results have shown that these derivatives would present a potential technological application in hydrolytic processes due to both their physical properties, such as low swelling capacity, reduced metal chelation ability and bulk mesoporosity, and increased operational stability when compared with soluble enzyme.

Exploration of Blood Coagulation of N-Alkyl Chitosan Nanofiber Membrane in Vitro.

N-Alkylated chitosan (NACS) may improve the blood clotting efficiency of chitosan (CS). To study its blood coagulation capability, a series of NACSs with various carbon chain lengths and degrees of substitution (DS) of alkyl groups were synthesized and characterized by FTIR, NMR, elemental analysis, and X-ray diffraction (XRD). The corresponding NACS nanofiber membranes (NACS-NM) were subsequently fabricated by electronic spinning technique. SEM, XRD, DSC, surface area, porosity, contact angle, blood absorption, and mechanical properties were used to characterize the CS-NM/NACS-NM. Moreover, cytotoxicity, coagulation, activated partial thromboplastin time, plasma prothrombin time, thrombin time, and platelet aggregation tests were performed to evaluate the biocompatibility and blood coagulation properties of NACS-NM. The results showed that NACS-NM was not cytotoxic. NACS-NM with DS of 19.25% for N-hexane CS (CS6b), 17.87% for N-dodecane CS (CS12b), and 8.97% for N-octadecane CS (CS18a) exhibited good blood clotting performance. Moreover, NACS-NMs favored the activation of coagulation factors and platelets. In addition, intracellular Ca2+ was not related to platelet activation. The above results suggested that NACS-NM would be an effective hemostatic agent.

Blood coagulation evaluation of N-alkylated chitosan

N-Alkylated chitosan (NACS) may improve the haemostatic efficiency of chitosan (CS). To study its coagulation capability and function, a series of NACS with various carbon chain lengths and substitution degrees (SD) of alkyl groups were synthesized and characterized by FTIR, NMR, and elemental analysis. Haemolysis and toxicity assays revealed that NACS showed good biocompatibility. In vitro blood clotting tests indicated that NACS had better haemostatic activity than CS, of which N-octadecyl CS with 3.85% SD showed the best results. Blood plasma coagulation tests showed that NACS was not favourable for activating coagulation factors. Platelet adhesion, intracellular Ca2+, and CD62p measurements demonstrated that the coagulation properties of NACS were not related to platelet activation. Erythrocyte adhesion examination indicated that blood coagulation of NACS may be attributable to its effects on erythrocytes. This study suggests that NACS is an ideal candidate for clotting.

Synthesis of N-alkylated chitosan and its interactions with blood

When hydrophobically modified chitosan (HM-CHI) comes into contact with red blood cells (RBCs), it can cause agglomeration. This property leads HM-CHI to be a potential agent to form a rapid haemostatic plug to stop bleeding at wound sites. In this study, we investigated the properties of the HM-CHI biopolymer to act as an agent that rapidly clots blood. We have examined the synthesis and structural characteristics of HM-CHI – blood substances using X-ray diffraction, infrared spectroscopy and elemental analysis. To understand the rheological behaviour of RBCs within HM-CHI, we have studied the effects of HM-CHI on RBC aggregation and morphology using a rheometer and scanning electron microscopy (SEM), respectively. When mixed with sodium citrate, HM-CHI rapidly transformed human blood into an elastic gel. In contrast, un-modified chitosan (i.e. without hydrophobes) was unable to clot blood. The hydrophobias within HM-CHI entered into the RBC membranes and connected to the cells by a sample-spanning network, which subsequently led to the formation of an elastic gel. The gelling ability of HM-CHI is similar to that of fibrin-based sealants, but at a much lower cost and greater availability.

Hemostasis mechanism and applications of N-alkylated chitosan sponge

Chitosan (CHI) is a versatile biological material that is well known for its hemostatic properties. This preliminary study evaluated several self-assembling hydrophobically modified chitosan (HM–CHI) sponges to determine their efficacy on hemostasis. Fourier transform infrared (FT-IR) spectroscopy was used to determine the successful graft of dodecyl groups onto the nitrogen atoms of CHI molecules. A platelet aggregation assay revealed that HM–CHI accelerated the platelet aggregation rate. Fluorescence spectroscopy showed that the HM–CHI changed the structure of fibrinogen in blood. Activated partial thromboplastin time, prothrombin time, fibrinogen time, and thromboelastographic assays were used to explore the effect of HM–CHI on the autologous blood coagulation pathway. Finally, a hemostatic sponge was made with HM–CHI and freeze-dried zeolite composite film and was applied to the rat femoral artery hemostasis model. A hemostasis time of 86 ± 5 sec was achieved, which was significantly better than the one composed with pure CHI. The experimental results of the HM–CHI hemostatic materials are inspiring and will encourage the research and development of such materials. HM–CHI may be a strong candidate as a safe and effective hemostatic material. Copyright © 2017 John Wiley & Sons, Ltd.

Chitosan and N-Alkyl chitosan as a heterogeneous based catalyst in the transesterification reaction of used cooking oil

This paper explains the result of research on the use of chitosan and N-alkyl chitosan (N-methyl chitosan, N-isopropyl chitosan) as a heterogeneous base catalyst in the transesterification reaction of used cooking oil. N-methyl chitosan and N-isopropyl chitosan synthesized by reacting chitosan with formaldehyde and acetone successively forming Schiff bases were then reduced using NaBH4. Then chitosan, N-methyl chitosan, N-isopropyl chitosan are used as heterogeneous catalysts in the transesterification reaction of used cooking oil. The results show that inclusion of alkyl groups to the chitosan structure leads to increase the amount of base in which chitosan, N-methyl chitosan, and N-isopropyl chitosan are 0.066 mole.g-1, 0.0068 mole.g-1, 0.0070 mole.g-1 respectively. It is also evident from the increasing yield of methyl esters. N-isopropyl chitosan gives the greatest content of methyl esters yield.

Chitosan-based core-shell structured particles for in vivo sustainable gene transfection.

A core-shell structured chitosan (CS)-based gene vector with a sustainable gene transfection effect was designed and successfully prepared in this study. The pEGFP was first combined with the thiolated and N-alkylated chitosan (TACS). Then, hydroxybutyl chitosan grafted with poly(ethylene glycol) (EG-HBC) was coated on the pEGFP-loaded TACS particles. The prepared pEGFP-loaded TACS@EG-HBC particles have a size of about 200 nm and little cytotoxicity. The in vitro and in vivo gene transfection experiments indicate that the pEGFP-loaded TACS@EG-HBC particles possess a better sustainable gene transfection capacity and a high transfection efficiency, which should be attributed to the biodegradation of the CS-based shell, the thiolation and N-alkylation modification on CS cores, and the grafted PEG chains with better biocompatibility. The in vivo gene expression of the loaded pEGFP can persist up to 60 days. This novel gene vector has a theoretical and practical significance for gene therapy with sustained transfection effect.

The sustained-release behavior and in vitro and in vivo transfection of pEGFP-loaded core-shell-structured chitosan-based composite particles.

Novel submicron core-shell-structured chitosan-based composite particles encapsulated with enhanced green fluorescent protein plasmids (pEGFP) were prepared by complex coacervation method. The core was pEGFP-loaded thiolated N-alkylated chitosan (TACS) and the shell was pH- and temperature-responsive hydroxybutyl chitosan (HBC). pEGFP-loaded TACS-HBC composite particles were spherical, and had a mean diameter of approximately 120 nm, as measured by transmission electron microscopy and particle size analyzer. pEGFP showed sustained release in vitro for >15 days. Furthermore, in vitro transfection in human embryonic kidney 293T and human cervix epithelial cells, and in vivo transfection in mice skeletal muscle of loaded pEGFP, were investigated. Results showed that the expression of loaded pEGFP, both in vitro and in vivo, was slow but could be sustained over a long period. pEGFP expression in mice skeletal muscle was sustained for >60 days. This work indicates that these submicron core-shell-structured chitosan-based composite particles could potentially be used as a gene vector for in vivo controlled gene transfection.

Antioxidant and Free Radical Scavenging Activities of N-Modified Chitosans

Recently, the search for effective natural antioxidants use in food and medicinal fields to replace synthetic ones has attracted the most attention. Chitosan, a natural nontoxic biopolymer, is known to possess antioxidant property, which is attributed that NH2 and OH attached in the pyranose ring react with unstable free radicals to form stable macromolecule radicals. It has been observed that the antioxidant activity of chitosan is closely related to the form of nitrogen atom in the molecules. This review focuses on the antioxidant and free radical scavenging activities of various nitrogen atom of chitosan, including N-acylated chitosans, Schiff bases of chitosan, N-alkyl chitosan, and N-quaternized chitosan. The free radical scavenging mechanisms are summarized and the effects on free radical scavenging activity of N-modified chitosan are discussed. This work may provide more insights into the antioxidant ability of N-modified chitosans and potentially enable them to be used as natural antioxidants for application in food, agriculture, cosmetic and biomedical science. Keywords: N-modified chitosan, Sythesis, Antioxidant, Free radical scavenging