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Introduction: Recent statistics have shown that there are hundreds of diseases caused by insects that have a significant impact on human health and they are often fatal. Mosquitoes cause about 10 diseases, most notably malaria, dengue fever and zika fever. N,N-diethyl-m-toluamide (1, DEET) or N,N-diethyl-m-methylbenzamide was globally approved under brand names m-Dephene, Detamide, Flypel as one of the most prominent agents for preparation of insect repellants. Objectives: To present an enhanced method for synthesis of N,N'-diethyl- m-toluamide which can be introduced to industrial scale. Method: The input materials: m-toluic acid has been activated with thionyl chloride to create the intermediate product, m-toluoyl chloride. This product then was reacted with diethylamine in order to produce DEET. This method has been improved the factors affecting the synthesis of DEET. Results: DEET was successfully synthesized using well known materials with high efficiency and purity. During research all the by-products and waste materials in the reaction are highly water-soluble, therefore the final product was obtained at pharmaceutical requirement without further purification. The analytical data has shown that DEET was collected at a very high yield in the range of 96-98%, purity (HPLC): 95.5-97.6%. The structure of DEET was determined by model spectroscopies MS, and NMR. Conclusions: An improved procedure for the synthesis of N,N-diethyl-m -toluamide (DEET) or N,N-diethyl-m-methylbenzamide is established where the use of all reagents was optimized in suitable amount to apply in industrial production.

Traditional antifouling coatings for metal substrates typically involve three layers including an anticorrosion primer, a midcoat, and an antifouling paint. However, the limited bonding capacity between these layers restricts their effectiveness in industrial metal corrosion protection. In this work, we developed a single coating by dipping method on steel substrate that combines the anticorrosion properties of zinc and the antifouling properties of copper, using an ethyl silicate binder. This pigment mixture, containing flake ZnAl (5 wt%) and Cu2O (10 wt%) with varying spherical Zn content (30, 40, and 50 wt%), was created and tested for its anticorrosion capabilities. Electrical properties were characterized using electrochemical impedance spectroscopy and the polarization curve method. Results showed that after 60 days of immersion in 3.5 wt% NaCl solution, the low-frequency impedance modulus of the coatings increased with higher Zn content, with the 40 wt% Zn content achieving the highest efficiency, showing an impedance modulus value of 56.43 kΩ cm2. Stability evaluations revealed an increased release of Zn and Cu content in samples with higher Zn content. Antifouling assessments in natural seawater demonstrated that the Zn40 integrated coating had the lowest fouling density among the tested samples, with hard fouling surface coverage (FR ≥ 40) at 9.31% after three months. These findings highlight the effectiveness of the integrated coating utilizing Zn and Cu in providing robust corrosion protection, preventing settlement, and inhibiting fouling marine growth. [ABSTRACT FROM AUTHOR]

This study investigates seasonal biomass variations in Betaphycus gelatinus, a red alga cultivated in the field in Ninh Thuan, Vietnam, along with the chemical composition, structural properties, and bioactivity of its carrageenan. Monthly measurements over a one-year period revealed peak growth (2.02% per day) and carrageenan yield (59.61%) in June, identifying it as the optimal harvest period. FTIR and NMR analyses of carrageenan extracted from field-cultivated B. gelatinus showed hybrid κ- and β-carrageenan forms and a unique pyruvylated β-carrageenan structure not previously reported for this species. Bioactivity assays indicated high antioxidant potential, with a total antioxidant capacity equivalent to 48.30 mg ascorbic acid/g carrageenan and an ABTS radical scavenging IC50 of 3.64 µg/mL. Additionally, antibacterial tests demonstrated strong inhibition of Listeria monocytogenes (12.00 mm inhibition zone). These findings suggest that field cultivation is a sustainable approach for carrageenan production, yielding bioactive compounds with promising applications in pharmaceuticals, cosmetics, and food preservation as a viable alternative to wild harvesting. [ABSTRACT FROM AUTHOR]

Sulfated polysaccharides SpvF1, SpvF2, SpvF3, and SpvF4 from the brown alga S. vietnamense collected north of Hon Do (Nha Trang Bay, Vietnam) were isolated and studied. The structure of the obtained polysaccharide was studied using chemical methods and NMR spectroscopy. Fucoidans were low-sulfated (SpvF1, SpvF2) and medium-sulfated (SpvF3, SpvF4) heterogeneous polysaccharides. The molecular weight of the polysaccharides obtained was in the range of 16 to 44 kDa. All investigated fucoidans until 400 µg/mL were not cytotoxic for human colon carcinoma cells DLD-1, HCT-116, and HT-29 in vitro. Fucoidans SpvF1 and SpvF2 have inhibited the colony formation and growth of investigated cells from 20 to 30%. Fucoidans SpvF3 and SpvF4 have the strongest inhibitory effect for investigated cancer cells: from 40 to 50%. [ABSTRACT FROM AUTHOR]

The artificial solar saltworks fields of Hon Khoi are important industrial and biodiversity resources in southern Vietnam. Most hypersaline environments in this area are characterized by saturated salinity, nearly neutral pH, intense ultraviolet radiation, elevated temperatures and fast desiccation processes. However, the extremely halophilic prokaryotic communities associated with these stressful environments remain uninvestigated. To fill this gap, a metabarcoding approach was conducted to characterize these communities by comparing them with solar salterns in northern Vietnam as well as with the Italian salterns of Motya and Trapani. Sequencing analyses revealed that the multiple reuses of crystallization ponds apparently create significant perturbations and structural instability in prokaryotic consortia. However, some interesting features were noticed when we examined the diversity of ultra-small prokaryotes belonging to Patescibacteria and DPANN Archaea. Surprisingly, we found at least five deeply branched clades, two from Patescibacteria and three from DPANN Archaea, which seem to be quite specific to the Hon Khoi saltworks field ecosystem and can be considered as a part of biogeographical connotation. Further studies are needed to characterize these uncultivated taxa, to isolate and cultivate them, which will allow us to elucidate their ecological role in these hypersaline habitats and to explore their biotechnological and biomedical potential. [ABSTRACT FROM AUTHOR]

Fucosylated chondroitin sulfate (FCS) was prepared from Bohadschia ocellata using protease hydrolysis. The structural characteristics of FCS were confirmed through chemical composition analysis using FTIR spectroscopy, 1H NMR, and 13C NMR. FCS from B. ocellata (FCS-Bo) exhibited an average molecular weight of approximately 122 kDa. The biological activities of FCS-Bo, including anticoagulant, anti-cancer, and Protein Tyrosine Phosphatase 1B (PTP1B) inhibition, were evaluated. FCS-Bo displayed potent anticoagulant properties, markedly extending activated partial thromboplastin time, prothrombin time, and thrombin time when compared to the heparin control. In anti-cancer bioactivity research, FCS-Bo efficiently inhibited colony formation in the colon cancer cell lines HCT-116, HT-29, and DLD-1, achieving inhibition rates of up to 65%. Additionally, FCS-Bo exhibited significant inhibition of PTP1B, with an IC50 as low as 0.0326 µg/mL, suggesting its potential for improving insulin sensitivity and managing conditions such as type 2 diabetes and obesity. [ABSTRACT FROM AUTHOR]

Fucoidanases (EC 3.2.1.–) catalyze the hydrolysis of glycosidic bonds between fucose residues in fucoidans. Fucoidans are a compositionally and structurally diverse class of fucose‐containing sulfated polysaccharides that are primarily found in brown seaweeds. Here, the structural characterization of a novel endo‐α(1,4)‐fucoidanase, Mef1, from the marine bacterium Muricauda eckloniae is presented, showing sequence similarity to members of glycoside hydrolase family 107. Using carbohydrate polyacrylamide gel electrophoresis and nuclear magnetic resonance analyses, it is shown that the fucoidanase Mef1 catalyzes the cleavage of α(1,4)‐linkages between fucose residues sulfated on C2 in the structure [‐3)‐α‐l‐Fucp2S‐(1,4)‐α‐l‐Fucp2S‐(1‐]n in fucoidan from Fucus evanescens. Kinetic analysis of Mef1 activity by Fourier transform infrared spectroscopy revealed that the specific Mef1 fucoidanase activity (Uf) on F. evanescens fucoidan was 0.1 × 10−3 Uf µM−1. By crystal structure determination of Mef1 at 1.8 Å resolution, a single‐domain organization comprising a (β/α)8‐barrel domain was determined. The active site was in an extended, positively charged groove that is likely to be designed to accommodate the binding of the negatively charged, sulfated fucoidan substrate. The active site of Mef1 comprises the amino acids His270 and Asp187, providing acid/base and nucleophile groups, respectively, for the hydrolysis of glycosidic bonds in the fucoidan backbone. Electron densities were identified for two possible Ca2+ ions in the enzyme, one of which is partially exposed to the active‐site groove, while the other is very tightly coordinated. A water wire was discovered leading from the exterior of the Mef1 enzyme into the active site, passing the tightly coordinated Ca2+ site. [ABSTRACT FROM AUTHOR]

Fucosylated chondroitin sulfate FCS-Hf and preparations of fucan sulfates Hf-Fuc1 and Hf-Fuc2 were isolated from the Vietnamese sea cucumber Holothuria (Stauropora) fuscocinerea. Separation of the polysaccharides was carried out using anion-exchange chromatography on DEAE-Sephacel. The structure of polysaccharides was established by determinations of the content of monosaccharides and sulfate, as well as by NMR spectra. It was shown that FCS-Hf was built of the repeating trisaccharide fragments, with alternating 3-linked N-acetyl-β-D-galactosamine and 4-linked β-D-glucuronic acid residues forming the main polymer chain, which carries α-L-fucose residues as side branches attached to O3 of glucuronic acid. The regular structure of the polymer is masked by an uneven distribution of sulfate groups attached to fucose residues (2,4-disulfate, 3,4-disulfate and 4-monosulfate in a ratio of 2 : 2 : 1) and galactosamine residues (4,6-disulfate and 4-monosulfate in a ratio of 3 : 1). It was also shown that fucan sulfate Hf-Fuc1 contained predominantly linear molecules built of 4-linked α-L-fucose 3-sulfate residues, while Hf-Fuc2 appeared to be a mixture of several related linear and branched fucan sulfates containing 3-linked and 4-linked α-L-Fuc residues sulfated at different positions. [ABSTRACT FROM AUTHOR]

Three different fucoidan fractions were isolated and purified from the brown alga, Sargassum mcclurei. The SmF1 and SmF2 fucoidans are sulfated heteropolysaccharides that contain fucose, galactose, mannose, xylose and glucose. The SmF3 fucoidan is highly sulfated (35%) galactofucan, and the main chain of the polysaccharide contains a ?3)-a-L-Fucp(2,4SO3-)-(1?3)-a-L-Fucp(2,4SO3-)-(1? motif with 1,4-linked 3-sulfated a-L-Fucp inserts and 6-linked galactose on reducing end. Possible branching points include the 1,2,6- or 1,3,6-linked galactose and/or 1,3,4-linked fucose residues that could be glycosylated with terminal ß-D-Galp residues or chains of alternating sulfated 1,3-linked a-L-Fucp and 1,4-linked ß-D-Galp residues, which have been identified in galactofucans for the first time. Both a-L-Fucp and ß-D-Galp residues are sulfated at C-2 and/or C-4 (and some C-6 of ß-D-Galp) and potentially the C-3 of terminal ß-D-Galp, 1,4-linked ß-D-Galp and 1,4-linked a-L-Fucp residues. All fucoidans fractions were less cytotoxic and displayed colony formation inhibition in colon cancer DLD-1 cells. Therefore, these fucoidan fractions are potential antitumor agents. [ABSTRACT FROM AUTHOR]