Molecular Weight Measurements Research Articles

Mechanistic insights into controlled depolymerization of Chitosan using H-Mordenite

Kinetics of chitosan depolymerization were studied in dilute acetic acid solution, in presence of H-Mordenite (H-MOR). Rate constants for chitosan depolymerization were determined by measurement of molecular weight, using Gel permeation Chromatography (GPC). Depolymerization rate of chitosan was altered in presence of an acidic, porous material like H-MOR. Maximum concentration of H-MOR studied during process led to minimal increase in energy of activation, from 20.54 kJ/moL to 23.25 kJ/moL. Infra-red spectroscopy, adsorption studies and rheological assessment indicated adsorption /grafting of chitosan onto porous H-MOR surface as the possible mechanism for facilitation of the depolymerization process. Under extreme conditions investigated during process optimization, H-MOR resulted in a three-fold reduction in 5-Hydroxy Methyl Furfural (5-HMF) formation and over ten times decrease in glucosamine content, as compared to reactions conducted without H-MOR. Therefore, presence of H-MOR is imperative to cleave chitosan in controlled manner and obtain products of desired molecular weight, with fewer impurities.

Physicochemical characterization of Gleditsia triacanthos galactomannan during deposition and maturation

Gleditsia triacanthos polysaccharide, known as galactomannan, has not been exploited as a new functional material even though it possesses industrial potential in food and biomedicine. Galactomannans were recovered from the endosperm of seeds (15 weeks to 25 weeks after flowering) for deposition and maturation analysis. These galactomannans were characterized by using Nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and monosaccharide composition analysis (particularly the mannose to galactose ratio) and molecular weight, solubility, and rheological measurements. The ratio of the three parts in mature seeds was as follows: endosperm (36.67%), hull (34.41%), and embryo (28.92%). The M/G ratio increased from 2.53 to 3.24 between 15 and 23 weeks and then decreased to 3.16 in 25 weeks, consistent with the trends of rheology and solubility. The molecular weight (1.28 × 106 g/mol) and intrinsic viscosity (882.53 mL/g) reached the maximum at 23 weeks and then decreased. Additionally, NMR and XRD showed that the M/G ratio did not change the basic chemical structure but caused slight changes in crystallinity. The purpose of the study was to reveal the changes in galactomannan structure, rheology, and solubility during G. triacanthos galactomannan deposition and maturation to facilitate exploration of its potential industrial applications.

Synthesis and characterization of zn(ll),cd(Il) and Hg(II) complexes with thioether ligands and their adducts with 1,10 phenanthroline

New complexes of general formula [M(LXSBu'')2],[M(L)(SFur)z] and adducts [M(L)(SBu")2(phen)]. [M(L)(SFur)z(phen)l,where L:C is-bis- I .2-(phenylthio)ethylene. SBu'': 1 -butanethiol. SFur:2-furanmethanthiol.phen:1,10 phenanthroline, M:Zn(ll).cd(ll) and FIg(ll) have been prepared in basic medium. The complexes and adducts were ihaiacterized by atomic absorption, conductivity measurements,spectral (lR and electronic) and molecular weight measurements studies' ietrahedral environment around the metal ions in the complexes andoctahedral geometry in the adducts were suggested according to the above measurements.

Some Novel Dinuclear phenylboronates of biologically potent β‐enaminoesters: Synthesis, Spectroscopic characterization, antimicrobial activity and their antiandrogenic effect

Organoboron derivatives of biologically potent β‐enamino esters of the type [Where R = CH3(1a), C2H5 (1b), C3H7(1c) and C (CH3)3 (1d)] have been prepared by the reactions of β‐enamino esters and Phenyl boronic acid [PhB (OH)2] in 1:2 molar ratio in refluxing tetrahydrofuran (THF). All these derivatives have been characterized by physico‐chemical properties, elemental analyses and molecular weight measurements. The structures of these compounds have been proposed on the basis of IR, 1H, 13C, 11B NMR spectral data and GC‐mass spectrometry. Phenyl boronic acid, β‐enamino esters and their respective phenylboronates derivatives have been screened for the antibmicrobial activities against pathogenic bacteria (B. subtilis and E. coli) and fungi (A. niger and P. peniculosum) to access their growth inhibiting potential. In addition to this, antiandrogenic effect of Ligand, LaH2 and its boron derivative (1a) has also been tested in male albino rats.

Using Fractionation and Diffusion Ordered Spectroscopy to Study Lignin Molecular Weight.

Recent reports demonstrate that applications of the biopolymer lignin can be helped by the use of a fraction of the lignin which has an optimal molecular weight range. Unfortunately, the current methods used to determine lignin's molecular weight are inconsistent or not widely accessible. Here, an approach that relies on 2D DOSY NMR analysis is described that provides a measure of lignin's molecular weight. Consistent results were obtained using this well‐established NMR technique across a range of lignins.

SiO2‐covered graphene oxide nanohybrids for in situ preparation of UHMWPE/GO(SiO2) nanocomposites with superior mechanical and tribological properties

ABSTRACTThe modified Hummer technique was used in the preparation of graphene oxide (GO) nanosheets, and then SiO2 decorated GO [GO(SiO2)] nanosheets were synthesized via the sol–gel method. Then, ultrahigh‐molecular‐weight polyethylene (UHMWPE) nanocomposites loaded with 0.5, 1, 1.5, and 2 wt % of GO(SiO2) were prepared using magnesium ethoxide/GO(SiO2)‐supported Ziegler–Natta catalysts via the in situ polymerization. Morphological study of the prepared polymer powders was assessed using field‐emission scanning electron microscopy, which showed that GO(SiO2) nanohybrids have been uniformly dispersed and distributed into the UHMWPE matrix. Also, the neat UHMWPE and its nanocomposites were evaluated with different analyses, including viscosity‐average molecular weight measurement, differential scanning calorimetry, thermogravimetric analysis, tensile test, scratch hardness, and pin‐on‐disk test. The characterization of the UHMWPE nanocomposites indicated that many characterizations, including the mechanical, thermal, and tribological properties of UHMWPE, were significantly improved by incorporation of these new nanosheets in spite of the molecular weight reduction of the polymeric matrix and the improved flowability and processability of the produced nanocomposite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47796.

Biodegradability study of polypropylene fibers blended with disposable recycledpoly(lactic acid) plastic flakes

Polymer blending as an efficient method for blending at least two~polymers is usually used to create new materials with desirable physical properties. This article focuses on the biodegradability evaluation of polypropylene (PP) fibers modified with disposable recycled poly(lactic acid) (r-PLA) plastic flakes. Biodegradable modified PP fibers containing 30% r-PLA were prepared by melt spinning process and evaluated with different methods of biodegradation assays. The soil burial test method, CO$_{2}$ evolution analysis, weight loss, mechanical properties, and average molecular weight measurements and analysis of surface morphological changes were performed for biodegradability evaluation of the modified PP fibers. Surface morphology of the blend fibers illustrated that by increasing the soil burial period cracks were formed on the surfaces of fibers. While different testing methods showed different values for the biodegradation process, the results obtained from the CO$_{2}$ evolution analysis, weight loss, and variation of mechanical properties confirmed a good agreement between different degradation methods. After incubation in soil for a long period of time, the initial moduli and tenacity of the modified fibers decreased up to 72% and 53%, respectively. In addition, the average molecular weight measurement showed a 28% decrease in average molecular weight after 80 days of soil burial.

Synthesis of Conjugated Polymers Containing Diketopyrrolopyrrole (DPP) Building Block and the Photophysical Study

Sonogashira coupling of two different diketopyrrolopyrrole (DPP)-containing dihaloarenes with the same aromatic bisalkyne resulted in two new conjugated polymers with the same backbone but different pendant groups on the DPP moiety. The polymers were found to have designed chemical structures via structural characterizations in comparison with three monomers. The molecular weight measurement further demonstrated the formation of polymers with polydispersity index around 2, consistent with the polycondensation nature of the polymerization based on Sonogashira coupling. Both polymers could dissolve in many organic solvents, and the one with long alkyl side group on DPP moiety had better solubility. Photophysical investigation showed that both polymers had typical absorption/emission of conjugated polymers, and varying the solvent did not have large influence. Compared with other polar solvents, toluene reduced the quantum yield of fluorescence of the polymers, especially for the one with long alkyl pedant group, accompanying with slight red-shift in absorption/emission. The difference in the absorption/emission wavelengths between the polymers was similar to that between the corresponding monomers. Adding water into the THF solution of polymers reduced the emission intensity but no redshift was observed. Discussion about the structure-property relationships was carried out in detail.

Incorporation of vinyl silane and epoxy silane oligomer into 2-EHA-based polyacrylate latexes via mini-emulsion polymerization and investigation of pressure-sensitive adhesive properties on polar and nonpolar surfaces

Pressure-sensitive adhesives (PSAs) form a bond to various surfaces when a light pressure is applied. PSAs combine the ability of being sticky with elasticity at definite proportions regarding the application area. The adhesion and cohesion mechanisms are well defined as peel adhesion, loop tack and shear strength in the literature and can be adjusted according to the specific requirements. On the purpose of having high peel adhesion and loop tack values without sacrificing the shear strength, 2-ethylhexyl acrylate-based latexes have been synthesized via mini-emulsion polymerization and latexes with high surface area were obtained enabling interactive relation with polar and nonpolar surfaces. Two types of silane selected among the mostly used species in industry were employed to increase the intermolecular interactions and proposed an approach for the incorporation of said compounds referring to the increasing demand of silane utilization in industry. N-dodecyl mercaptan was used as both chain regulator to adjust the molecular weight and cosurfactant to have colloidally stable hydrophobic particles in mini-emulsion polymerization. The incorporation of vinyl silane predominately led to an increase in shear strength owing to chemical cross-linking between chains. Epoxy silane oligomer, on the other hand, increased the peel adhesion and loop tack values considerably compared to the case of vinyl silane. The type of silane incisively affects the PSA properties and should be taken into consideration while constructing a polymer for a pre-specified application. The assumptions in question were strongly correlated with peel, shear and loop tack values, cross-linking density, molecular weight and gas chromatography measurements.

New approach on structure-property relationships of stabilized natural rubbers

The stabilization of natural rubber (NR) was studied using four NR samples, namely, whole natural rubber (WNR), deproteinized natural rubber (DPNR), acetone extracted natural rubber (ANR) and purified natural rubber (PNR). Proteins and lipids, which are non-rubber components in NR, significantly affect storage hardening via gel formation. The main function of the applied viscosity stabilizer was to perturb the dynamics of the NR structure, or alternatively, the formation of gel networks of the rubber chains with lipids and proteins, respectively. The Mooney viscosity and molecular weight of NR samples with the viscosity stabilizer added were found to be almost constant after 12 weeks. Moreover, the NR samples with the viscosity stabilizer required a longer curing time, presumably due to less gel network formation and the conventional packing of linear rubber chains. The results from crosslinking density and molecular weight measurements revealed that the viscosity stabilizer also had a role in stabilizing crosslinks between the chains and preventing the reversion to NR. The new approach of on structure-property relationships of stabilized natural rubbers has been proposed.

Grafted cyclodextrin as carrier for control drug delivery and efficient cell killing.

The presence of hydroxyl groups in cyclodextrin (CD) makes it highly hydrophilic and simultaneously allows its chemical modification to graft polyurethane to control the drug release for longer period of time by maintaining the hydrophobic-hydrophilic balance through varying extent of grafting. Grafting of polyurethane on CD is confirmed through 1 H NMR and molecular weight measurement while FTIR and UV visible studies further support grafting and emphasize the interaction among polymer chains as a whole. Degree of grafting is evaluated from the integrated peak area in NMR spectra. Thermal and mechanical measurements show improved stability and strength of the graft polymers with respect to pure CD. The conversion of particle nature of CD to strip-like morphology in graft copolymers is evident from atomic force microscopy. Sustained drug release has been achieved using graft copolymer against burst release from pure CD and specific interactions, as observed through spectroscopy and thermal measurements, are responsible for sustained release of drug. Biocompatibility of graft copolymers has been checked using cellular studies through MTT assay and cell adhesion. Importantly, the cell killing efficiency has been demonstrated by embedding anticancer drug in polymer matrices causing mortality rate of 75% using graft copolymer against scanty 25% using pure drug or drug embedded in CD and the result is understood from the sustained release of drug from the graft copolymer vis-à-vis burst release in other systems. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 434-444, 2019.

Retracted: Synthesis, Characterization, and Surface Activities of Polymeric Cationic Thiol Surfactants in Aqueous Medium

AbstractA series of cationic polyurethane surfactants [PQ8‐18] were synthesized by the reaction of alkyl bromoacetate (namely: octyl‐, decyl‐, dodecyl‐, tetradecyl‐, hexadecyl‐, and octadecyl bromoacetate) as quaternizing agents and modified polyurethane contains tertiary amine species. Modified polyurethane was prepared by the reaction of toluene diisocyanate (TDI) and triethanol amine monomercaptoacetate. The chemical structures of the prepared surfactants were confirmed using elemental analysis, Fourier transform infrared spectroscopy (FTIR), and Proton nuclear magnetic resonance (1H NMR) spectroscopy. The molecular weight measurements of the prepared polymers showed that the segments of each polymer contain average 10 units of the urethane‐triethanol amine mercaptoacetate. The surface activities of the prepared surfactants including: surface tension (γ), effectiveness ( πcmc), concentration at micelle formation (CMC), efficiency (Pc20), maximum concentration at the interface (Γmax), and the average area occupied by each surfactant molecule at the interface at equilibrium ( A min) of surfactants solutions were established at 25°C. The surface tension and the critical micelle concentration values of the prepared surfactants were gradually decreased by the gradual increase of their alkyl chain length. The prepared cationic surfactants showed efficient activity as inhibitors for dissolution of carbon steel in an acidic medium and also as a biocide against the growth of bacteria, fungi, and yeast.

Formation and optical properties of pure nano-sized anatase titania by low-temperature aqueous sol-gel route

Nanocrystalline anatase titania particles were synthesized by low-temperature aqueous sol-gel transformations from new types of precursors [Ti{OPri}4] (A), [{acac}2Ti{OPri}{ONC9H6}] (1), and [{acac}2Ti{ONC9H6}2] (2) {where, ONC9H6 = 8-hydroxyquinoline}. Formation of all the precursors was confirmed by elemental analysis, molecular weight measurements, FTIR, and NMR (1H and 13C). Titania samples (a), (b), and (c) were formed by aqueous sol-gel transformations of (A), (1), and (2), respectively. The resulting nano-materials were characterized using XRD, TEM, SEM, EDX, SAED, FTIR, and UV-Visible spectroscopic techniques. From the X-ray pattern, the phase purity of the synthesized powders was confirmed as anatase TiO2. Crystallite size of all the oxide samples was measured by XRD and TEM, found to be 26 nm (a), 11 nm (b), and 8 nm (c). Surface morphologies of all the samples were evaluated by SEM. Selected area diffraction (SAED) of (b) and (c) are also corroborated the XRD results. The absorption spectra of oxide samples, (a), (b), and (c) show energy band gap of 2.9 eV, 3 eV, and 3.1 eV, respectively. SAED-EDX analysis confirmed the formation of pure anatase-phase titania nanoparticles.

Sol–Gel Synthesis of Pd@PdO Core–Shell Nanoparticles and Effect of Precursor Chemistry on Their Structural and Optical Properties

Nanocrystalline Pd@PdO core–shell (a) were synthesized by aqueous sol–gel transformations from precursor [Cl2PdL] (1) {where, L = 8-(2-pyridylmethoxy)quinoline}. Formation of the precursor (1) was confirmed by elemental analysis, molecular weight measurements, FT-IR, and NMR (1H and 13C). PdO nanoparticles (b) were obtained when unmodified PdCl2 (2) was used as precursor. XRD studies were done to determine crystal structure and phases of synthesized powders which was found to be cubic, tetragonal (Pd@PdO) and tetragonal (PdO), respectively. TEM studies were done to confirm the results obtained from XRD. HRTEM and SAED patterns confirmed the formation of core–shell nanoparticles. Crystallite size of both the samples as approximated by XRD and TEM were found to be in nanometer range. Raman spectroscopy confirmed the presence of PdO in both the samples. Surface morphologies of both the samples were evaluated by SEM. The absorption spectra of samples, (a) and (b) show the energy band gap of 1.43 and 1.89 eV, respectively.

Primary structure and anticoagulant activity of fucoidan from the sea cucumber Holothuria polii

Sea cucumber fucoidan is recently endowed with a variety of biological activities. In the present study, we studied the structure and anticoagulant effect of fucoidan from the sea cucumber Holothuria polii (Fuc-Hp). The Fuc-Hp was purified by anion exchange chromatography and its structure was characterized by FT-IR and NMR spectroscopy. Molecular weight measurements were performed by HPSEC-MALLS-dRI. Fuc-Hp anticoagulant activity was measured by activated partial thromboplastin and thrombin times, and by in vitro thrombin inhibition in the presence of antithrombin and heparin cofactor II. The assessment of thrombin generation was investigated using calibrated automated thrombography. Fuc-Hp with a high sulfate content (34.6%) and an average molecular mass of 1376.3 kDa was isolated from H. polii in amount of ~2.7 mg/g dry body wall. Primary structural analysis indicated that Fuc-Hp was mainly composed of a tetrafucose repeating unit branched by glucuronic acid. Fuc-Hp exhibited a high anticoagulant effect mediated essentially by heparin cofactor II and to lesser extent by antithrombin with IC50 values of 0.16 μg/mL and 0.5 μg/mL, respectively. Overall results showed a high anticoagulant activity of Fuc-Hp, which was attributed to the high sulfate content and abundance of disulfated fucose residues of H. polii fucoidan.

Synthesis, characterizations and photo-physical properties of novel lanthanum(III) complexes

ABSTRACTA series of novel complexes of La(III) with substituted pyrazolines and mixed ligand complexes with these pyrazolines and thio-ligands have been synthesized and characterized by elemental analysis, molecular weight measurement, Fourier transform infra-red, 1H and 13C NMR spectroscopy. The particle/crystallite sizes were confirmed by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopic techniques. Optical characterizations have been performed by electronic absorption and fluorescence emission spectroscopies in order to investigate their luminescence behaviour, which reveals fairly good quantum yield and fluorescence life time for some of the complexes. Thermal analyses such as thermogravimetric and differential thermal analysis indicate that these complexes are thermally stable at high temperature. Investigations pertaining to solid-state optical absorption spectra and photoelectron yield spectroscopy reveal that upon thermal annealing beyond 300°C, these compounds form dark-brown to black semiconducting materials with an optical band gap between 1.9 and 2.3 eV.Abbreviations: La-PyH : La-HPY = [La(C15H12N2OH)2(H2O)Cl]; La-PyH-dtc = [La(C15H12N2OH)(C5H10NS2)(2H2O)Cl]; La-OCPy-xan: [La(C15H12N2OOCH3)(C2H5OCS2)(2H2O)Cl]

Degradation of carboxymethylcellulose using ultrasound and β-glucanase: Pathways, kinetics and hydrolysates’ properties

In order to provide an efficient way to degrade carboxymethylcellulose (CMC), three pathways were investigated: enzymolysis, combination of ultrasound pretreatment and enzymolysis, and sonoenzymolysis. Effects of these treatments on enzymatic kinetics, degradation kinetics and properties of degraded CMC were investigated. The degradation degree of CMC was increased by 18.90% and 35.73% with ultrasound pretreatment (at an intensity of 24 W/mL for 30 min) and sonoenzymolysis (at an intensity of 9 W/mL for 50 min), compared with that obtained under the traditional enzymolysis. Analysis of kinetics demonstrated that ultrasound, both pretreatment and combined with β-glucanase, could accelerate CMC degradation. Measurements of rheological properties, molecular weight and structures of CMC hydrolysates revealed that ultrasound broke the glycosidic bond of CMC chains without changing its primary structure. The sonoenzymolysis process was the most efficient method to degrade CMC, with potential to provide a way to obtain CMC with lowest molecular weight or viscosity.

Sol- gel synthesis of Ga2O3 nanorods and effect of precursor chemistry on their structural and morphological properties

Synthesis of mono-crystalline Ga2O3 Nanorods was done by sol-gel transformation of gallium(III) isopropoxide (Ga(OPri)3). XRD studies were done to determine the planes and crystal structure of synthesized nanorods that showed the synthesis of β-Ga2O3(a). TEM studies of synthesized Ga2O3 confirmed the synthesis of monocrystalline β-Ga2O3 nanorods. To study the effect of precursor chemistry and to determine role of precursor structures on the crystal structure, phase and morphology of the Ga2O3, a new modified precursor complex was synthesized. The reaction of Ga(OPri)3 with N-phenylsalicylaldimine, [C6H4(OH)CH=N(C6H5)] in 1:1 M ratio yielded [{(H5C6)N = CH-C6H4O}Ga(OPri)2]. The newly synthesized complex was characterized by elemental analyses, molecular weight measurement, FT-IR and NMR (1H and 13C) spectral studies. Spectral studies of the modified complex suggest the presence of bi-dentate mode of attachment of Schiff's base in the solution state. Sol-gel transformations of [{(H5C6)N = CH-C6H4O}Ga(OPri)2] in organic medium, yielded γ-Ga2O3(b), as found by XRD studies. TEM image of the sample (a) revealed the formation of nano-rods of oxide with average diameter of ~100 nm whereas the TEM image of sample (b) showed presence of nano-sized particles of oxide with average particle size of 10 nm. Morphological and compositional studies of synthesized samples (a) and (b) were carried out using SEM and EDX. The method provides a possibility of large scale synthesis of dissimilar shaped and pure Ga2O3 nanoparticles.

The Determination of Protease Specificity in Mouse Tissue Extracts by MALDI-TOF Mass Spectrometry: Manipulating PH to Cause Specificity Changes.

Proteases have several biological functions, including protein activation/inactivation and food digestion. Identifying protease specificity is important for revealing protease function. The method proposed in this study determines protease specificity by measuring the molecular weight of unique substrates using Matrix-assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) mass spectrometry. The substrates contain iminobiotin, while the cleaved site consists of amino acids, and the spacer consists of polyethylene glycol. The cleaved substrate will generate a unique molecular weight using a cleaved amino acid. One of the merits of this method is that it may be carried out in one pot using crude samples, and it is also suitable for assessing multiple samples. In this article, we describe a simple experimental method optimized with samples extracted from mouse lung tissue, including tissue extraction, placement of digestive substrates into samples, purification of digestive substrates under different pH conditions, and measurement of the substrates' molecular weight using MALDI-TOF mass spectrometry. In summary, this technique allows for the identification of protease specificity in crude samples derived from tissue extracts using MALDI-TOF mass spectrometry, which may easily be scaled up for multiple sample processing.

UV irradiation- $$\hbox {H}_{2} \hbox {O}_{2}$$ H 2 O 2 system as an effective combined depolymerization technique to produce oligosaccharides from chitosan

UV irradiation hydrogen peroxide ( $$\hbox {H}_{2} \hbox {O}_{2}$$ ) system is used as an effective, easy and low-cost combined depolymerization technique to produce oligosaccharides from chitosan. UV–Vis spectroscopic studies explained that with increasing treatment time, the absorption of the depolymerized chitosan solution has increased, indicating the increase in the carbonyl and amino groups in their structure. Fourier transform infrared spectroscopy and nuclear magnetic resonance (1H NMR) analysis showed that the 1,4- $$\beta $$ -d-glucoside linkages of chitosan are degraded without important changes in chemical structure of decomposed samples. X-ray diffraction patterns verified the polymerization of chitosan to produce oligomers, changing in structure from crystalline to amorphous. Viscosity-average molecular weight measurements of fragmented chitosan samples and Mark–Houwink equation are used to demonstrate the efficiency of this depolymerization method. Finally, the obtained results ascertained that this combined method could produce water soluble chitosan with significant efficiency and no essential change in its chemical structure.