Reduction In Mw Research Articles

Structural and functional characterization of colonization factors AIBI-CS6 and AIIBII-CS6 of enterotoxigenic Escherichia coli

Over time, the structure and function of the broadly dispersed colonization factor (CF) CS6 of enterotoxigenic Escherichia coli (ETEC) have become more significant. CS6 is composed of tightly-associated subunits, CssA and CssB which due to presence of natural point mutation gave rise to CS6 subtypes. In contrast to the other ETEC CFs, CS6 is an afimbrial, spherical-shaped oligomers of (CssA-CssB)n complex where ‘n’ is concentration dependent. In this study, we have compared AIBI-CS6 and AIIBII-CS6 structurally and functionally. The Mw of CssAI was 18.5 kDa but Mw of CssAII was 15.1 kDa. Both CssBI and CssBII had Mw of 15.9 kDa. The substitution of Gly39 with Ala39 in CssAI leads to reduction in Mw from 18.5 to 15.1 kDa. Due to higher Mw of CssAI, the size of AIBI concentration-dependent oligomers should be higher. However, the Mw of AIIBII oligomers were higher and AIIBII also showed higher oligomeric forms compared to AIBI both in native PAGE and electron microscopy. The oligomers of both subtypes could withstand greater temperatures and denaturant concentrations. In terms of cellular response, the levels of inflammatory cytokines were significantly higher in case of AIBI-CS6 expressing ETEC as compared to AIIBII-CS6 expressing ETEC both in vitro and in vivo. When inflammatory cytokines were evaluated after infecting suckling mice with these ETEC strains, the results were consistent. In conclusion, even though there was subtle structural difference between AIBI-CS6 and AIIBII-CS6 due to natural point mutations but ETEC strains expressing these subtypes displayed great variability in pathogenicity.

Structure and functionality of cassava starch in different deep eutectic solvents/water mixtures: A comparative study

Starch, as one of the most abundant natural polysaccharides, is regarded as a sustainable material due to its renewability, biodegradability, and modifiability, and is widely used as an excellent industrial material. However, as a polyhydroxyl polymer, native starch has low solubility in most situations due to its network structure formed by intramolecular and intermolecular hydrogen bonds, which limits its industrial application. In this study, the solubility of cassava starch (CS) in a series of acidic, neutral, and alkaline deep eutectic solvents (DESs) was investigated. Relatively high solubilities of 52.8 wt%, 11.4 wt%, and 10.2 wt% were obtained in choline chloride/formic acid (CF), ethylammonium chloride/ethylene glycol (EE), and choline chloride/diethanolamine (CD), respectively. The dissolution behavior of CS in pure mixtures of these DESs and in DESs/water mixtures (2:8) was also compared. The results of gel permeation chromatography (GPC) analysis showed that the weight-average molecular weights (Mw) and number-average molecular weights (Mn) were ranked in the order CF > EE > CD. The same pattern was observed for the DESs/water mixtures (2:8), although the reduction in Mw and Mn was less distinct than in the pure DESs. The results of X-ray diffraction, small-angle X-ray scattering, and scanning electron microscope observations were consistent with the GPC data, i.e., the hydrolysis ability of CS was higher in the acidic DESs (CF) compared to the neutral (EE) and alkaline (CD) DESs. The dissolution behaviors of CS in the DESs/water mixtures were affected by the structure of the DESs and their water content. These results demonstrate that aqueous DESs serve as excellent media for starch dissolution. Moreover, this study provides a comprehensive understanding of the solubilization behavior of CS in different aqueous DESs and provides insights into the development of novel starch-based materials using DESs.

Production and Physicochemical Characterization of Gelatin and Collagen Hydrolysates from Turbot Skin Waste Generated by Aquaculture Activities.

Rising trends in fish filleting are increasing the amount of processing by-products, such as skins of turbot, a flatfish of high commercial value. In line with circular economy principles, we propose the valorization of turbot skins through a two-step process: initial gelatin extraction described for the first time in turbot, followed by hydrolysis of the remaining solids to produce collagen hydrolysates. We assayed several methods for gelatin extraction, finding differences in gelatin properties depending on chemical treatment and temperature. Of all methods, the application of NaOH, sulfuric, and citric acids at 22 °C results in the highest gel strength (177 g), storage and loss moduli, and gel stability. We found no relation between mechanical properties and content of pyrrolidine amino acids, but the best performing gelatin displays higher structural integrity, with less than 30% of the material below 100 kDa. Collagen hydrolysis was more efficient with papain than alcalase, leading to a greater reduction in Mw of the hydrolysates, which contain a higher proportion of essential amino acids than gelatin and show high in vitro anti-hypertensive activity. These results highlight the suitability of turbot skin by-products as a source of gelatin and the potential of collagen hydrolysates as a functional food and feed ingredient.

Surface activity of ultrahigh methoxylated pectin of different size

Ultrahigh methoxylated pectin (UHMP), which is of moderate molecular weight (MW, ~150 kDa) and high methoxylation degree (DM, >90%), is a novel surface-active material. To investigate the effect of MW on the surface activity of UHMP, four small UHMPs (MW = 85.90, 67.01, 41.24 and 27.24 kDa) of low MW and DM values above 90% were prepared via enzymatic hydrolysis using commercial polygalacturonase. Low MW UMHPs can reduce the water surface tension to ~45 mN/m, which corresponds to a larger reduction than that of UHMP (~55 mN/m). Moreover, their critical micellization concentration was increased to 1–3 g/L. Surface excess and molecular area data suggested that a suitable reduction in MW enhanced the absorption of UHMP at the O/W interface. However, the analysis of interfacial rheology showed that an interfacial film could not be formed when the MW of UHMP was reduced to 20–40 kDa. In view of the improved surface activity, the grease-removing power (GRP) of each of the UHMPs was measured and compared with that of citrus pectin (CP). The GRP of CP was 79% at 1.0 g/L, and this value was decreased to ~20% when the CP concentration exceeded 4.0 g/L due to pectin aggregation. With reduced MWs, the UHMPs presented substantially higher GRP values (80–90%) than CP, especially at concentrations of 4.0–10.0 g/L. Increasing the temperature (45 °C) can effectively increase the GRP of each pectin. However, small UHMPs still reached larger GRPs (85–95%) than UHMP (75–90%) and CP (90% at <2.0 g/L, ~40% at >2.0 g/L). The experimental results suggested that MW can significantly affect the surface activity of UHMP. UHMPs of various sizes have diverse potential applications, for example, as edible films and surface-active materials in daily chemicals.

Molecular weight influence on shape memory effect of shape memory polymer blend (poly(caprolactone)/styrene‐butadiene‐styrene)

AbstractThe shape memory effect (SME) does not only concern the macroscopic structure. It concerns also the polymer structure at morphological, macromolecular, and molecular scales. This effect may depend on different physicochemical properties like morphology heterogeneity, chain rigidity, steric hindrance, chain polarity, free volume, cross‐linking or entanglement density, molecular shape and weight, and so on. Hence, finding the relationship between the SME and these properties is very important. This can help to obtain the knowledge about the phenomenon origin and mechanism. One of the basic polymer properties, which can have direct SME, may be the molecular weight (Mw). The question here is: If the Mw of a shape memory polymer (SMP) changes, for different reasons like degradation, what will be the effect of this change on its SME. In order to answer to this question, the investigation is focused on an SMP blend of 40% poly(ɛ‐caprolactone) (PCL) and 60% styrene‐butadiene‐styrene (SBS). Then, enzymatic hydrolysis is performed on this blend to change its Mw. It is shown that this change is only related to the variation in the Mw of PCL. After that, different samples with a distinct average Mw are prepared and characterized by various experimental methods. Shape memory tests are performed on these blends, and the recovery rate (Rr) for each of them is determined. It is found that when Mw of PCL decreases, its degree of crystallinity, its glass transition, and its melting temperatures, corresponding to the PCL phase, increase. However, the elongation at break of the blend declines with the reduction in Mw. The tests show that the alteration in the blend's Mw influences its SME. Indeed, Rr of the (PCL/SBS) mixture drops with the decrease in Mw of PCL.

Gamma-irradiation degraded sulfated polysaccharide from a new red algal strain Pyropia yezoensis Sookwawon 104 with in vitro antiproliferative activity.

Pyropia yezoensis Sookwawon 104 is a newly cultivated strain of red marine algae. The present study aimed to investigate the in vitro antiproliferative activity of sulfated polysaccharide extracted from P. yezoensis Sookwawon 104 (PYSP), as well as that of its low molecular weight (Mw) derivatives. PYSP is a heterogeneous sulfated polysaccharide mainly composed of galactose, glucose and fucose. PYSP was degraded by gamma-irradiation at doses of 20 and 100 kGy to produce two derivatives, named as PYSP-20 and PYSP-100, respectively. Comparison of PYSP, PYSP-20 and PYSP-100 revealed clear differences in their molecular weight (Mw) distributions, and distinct in vitro antiproliferative activities against Hep3B, MDA-MB-231 and HeLa cancer cell lines. PYSP-20 and PYSP-100 exhibited stronger antiproliferative effects than PYSP, suggesting that the reduction in Mw may have increased the in vitro antiproliferative activity. Furthermore, the mRNA expression levels of the antitumor gene P53 and cell cycle-associated genes P21, Cyclin B1 and cyclin dependent kinase 1 (Cdk1) were further analyzed by reverse transcription-quantitative PCR in PYSP-20 and PYSP-100-treated cancer cells. PYSP and its derivatives were shown to inhibit the proliferation of tumor cells by regulating the expression of P53, P21, Cyclin B1 and Cdk1. In conclusion, low-Mw polysaccharide derivatives prepared from P. yezoensis Sookwawon 104 by gamma-irradiation exhibit significant inhibition effects on cancer cell proliferation in vitro and may be a novel source of potential anticancer therapeutic agents.

Understanding lignin depolymerization to phenols via microwave-assisted solvolysis process

In this study, microwave assisted degradation of lignin, a paper industry and biorefinery waste product, is investigated in presence of different organic solvents such as ethylene glycol (EG), dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF) at different temperatures (100–140°C) and treatment periods (20–80min). Experiments performed in batch microwave reactor revealed that, in all the solvents, a major reduction in weight average molecular weight (Mw) of lignin was observed in the time period of 20–40min. In a polar protic solvent with high loss tangent (EG), maximum reduction in Mw was observed at 120°C, while in polar aprotic solvents (DMSO and DMF), Mw decreased with increase in temperature. Significant yield of phenolics (20wt.%) containing acetosyringone, guaiacol, syringaldehyde, anisole and lignin dimers (m/z 306, 322Da) was obtained at 100°C in DMF and DMSO, while at 140°C, 11wt.% phenolics were obtained in EG. Plausible reactions for the formation of phenolic monomers and dimers include etheric CβO and CαCβ bond cleavages induced by solvent interactions. The shift of molecular weight distribution to higher molecular weights suggested the involvement of recombination reactions at long treatment periods. This study shows that solvent-assisted microwave processing is a promising technique to convert lignin to phenols.

Hydrolytic mechanism of α-maltotriohydrolase on waxy maize starch and retrogradation properties of the hydrolysates

In this study, we explored the hydrolytic mechanism of glucan 1,4-α-maltotiohydrolase (AMTS). Kinetic parameters analysis of AMTS were performed using the amylopectin with different external chain lengths (ECL). Then, the waxy maize starch was gelatinized and hydrolyzed by AMTS to various degrees; retrogradation of starch hydrolysates were determined. Michaelis constant (Km) of the β-dextrin-3 (ECL 2.3) was eight folds than the amylopectin (ECL 17.8), but its catalytic efficiency (kcat/Km) was only 6.5% of amylopectin. AMTS preferred the external chains to the internal chains for hydrolysis, and amylopectin was hydrolyzed by AMTS through combined exo- and endo-action. In the initial hydrolysis stage, the exo-action of AMTS was predominant with slow reduction in Mw and little changes in the internal chains of amylopection. The percentage of maltotriose in the soluble oligosaccharides (PM) was 90.5% at 2.1% degree of hydrolysis (DH), and gradually decreased from 90.5% to 71.2% at 35.4% DH. The PM decreased could be partially attributed to the increased transglycosylation reactions of AMTS. Complete inhibition of amylopectin retrogradation was observed with >15.9% hydrolysis for the increased shorter outer chains and low molecular weight dextrins. These results indicate that AMTS may be effective in retarding starch retrogradation in baked products.

Full, Reactive Solubilization of Humin Byproducts by Alkaline Treatment and Characterization of the Alkali-Treated Humins Formed

The valorization of the humin byproducts that are formed during hydrothermal, acid-catalyzed dehydration of carbohydrates is hampered by the insolubility of these byproducts. Here, we report on an alkaline pretreatment method that allows for the insolubility of this highly recalcitrant and structurally complex feed to be overcome. The reactive solubilization of glucose-derived humins was found to require a treatment at 200 degrees C in 0.5 M NaOH for 3.5 h. Fructose- and xylose-derived humins were found to be more recalcitrant, and complete dissolution required raising the temperature to 240 degrees C. Gel permeation chromatographic analyses show the relative average molecular weight of the now soluble humins to decrease with increasing temperature and reaction time. The alkali-treated humins are soluble in water of pH >= 7. Elemental analysis, IR, 2D PASS C-13 solid-state NMR and pyrolysis-GC MS (gas chromatography mass spectrometry) data indicate that the alkaline pretreatment leads to considerable changes in the molecular structure of the humins. Cleavage of C-O-C bonds and further aromatization of the originally highly furanic humins result in the formation of (polycyclic) aromatic structures decorated with carboxylic acids. The combination of the reduction in Mw and the formation of polar functional groups are thought to be the reasons behind the improved solubility.

Structural and physicochemical characterization of RS prepared using hydrolysis and heat treatments of chickpea starch

AbstractThe aim of this study was to evaluate the production and the structural and physicochemical properties of RS obtained by molecular mass reduction (enzyme or acid) and hydrothermal treatment of chickpea starch. Native and gelatinized starch were submitted to acid (2 M HCl for 2.5 h) or enzymatic hydrolysis (pullulanase, 40 U/g per 10 h), autoclaved (121°C/30 min), stored under refrigeration (4°C/24 h), and lyophilized. The hydrolysis of starch increased the RS content from 16% to values between 20 and 32%, and the enzymatic treatment of the gelatinized starch was the most efficient. RS showed an increase in water absorption and water solubility indexes due to hydrolytic and thermal process. The processes for obtaining RS changed the crystallinity pattern from C to B. Hydrolysis treatments caused an increase in relative crystallinity due to the greater retrogradation caused by the reduction in MW. RS obtained from hydrolysis showed a reduction in viscosity, indicating the rupture of molecules. The viscosity seemed to be inversely proportional to the RS content in the sample.

Deterioration in mechanical properties of glass fiber‐reinforced nylon 6,6 composites by aqueous calcium chloride mixture solutions

AbstractIn this article, nylon 6,6 (NY66) and glass fiber‐(30 wt%) reinforced NY66 (GFNY66) specimens were immersed in various aqueous calcium chloride (aq. CaCl2) mixture solutions at different thermal conditions for varying intervals of time, and analyzed using attenuated total reflection‐infrared (ATR‐IR) spectroscopy, inductively coupled plasma (ICP), energy dispersive X‐ray (EDX), gel permeation chromatography (GPC), and mechanical studies. ICP data revealed increasing concentration of absorbed Ca2+ ions with increasing immersion time resulting in disruption of intra‐ and intermolecular H‐bonding as confirmed using ATR‐IR results. From EDX data, the ratio of Ca2+ and Cl− ions absorbed by NY66 was calculated and found to follow its stoichiometric equivalence. GPC data exhibited less reduction in Mn and Mw for aq. CaCl2‐treated NY66 specimens suggesting the absence of any significant chemical degradation, but the occurrence of only physical changes involving H‐bond breakage and the formation of new CO···Ca2+ dative bond in NY66 matrix. The mechanical properties of GFNY66 samples treated with various types of aq. CaCl2 solutions exhibited pronounced deterioration, possibly due to the interfacial failure between glass fiber and NY66 matrix. The results obtained from this study were quite useful toward understanding the degradation mechanism in NY66 and GFNY66 caused by various aq. CaCl2 mixture solutions, and will be helpful in improving the mechanical properties of recycled NY66. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

On the mechanism of initiation of butyl methacrylate polymerization by silicon monoperoxide

Kinetic parameters have been determined for butyl methacrylate polymerization initiated by Me 3SiOOCMe 3 in the range 353–373 K. It has been proved by PMR analysis that the rate of formation of a donor-acceptor complex of monomer with silicon monoperoxide, decomposing to radicals, is higher than for the pure peroxide. Catalytic amounts of Lewis acids activate decomposition of Me 3SiOOCM 3. As regards their influence on the polymerization rate Lewis acids may be placed in the following order: Bu 3SnCl<R 2SnCl 2, where R=Me, Et, n-Pr, n-BU, <ZnCl 2⪡SnCl 4. An increase in the rate of polymerization initiated by Me 3SiOOCMe 3 in presence of Lewis acids is accompanied by a reduction in the activation energy of the process from 74·6 to 46·9 kJ/mole, and by a reduction in MW of the polymer. The polymerization rate is lower in the case of a marked excess of Lewis acid with respect to the peroxide. The activation effect stems from an increase in the rate of initiation of polymerization owing to the formation of a complex between components of the initiating system.