Molecular Weight Distribution Research Articles

The scope of alum coagulation-flocculation assisted by slaked lime for the treatment of industrial wastewater containing highly concentrated Acid Black 194 dye. Optimization, molecular weight distribution and toxicity analysis

This work evaluated the capacity of the alum coagulation-flocculation (C–F) process, assisted by slaked lime, for the treatment of industrial textile wastewater (ITWW) containing highly concentrated Acid Black 194 dye. By optimizing the operating conditions ([Alum] = 16.09 g/L, [Ca(OH)2] = 5.16 g/L) through experimental design, response surface methodology, and multi-objective optimization analysis, the C–F process removed 95 % of the dye, 63 % of the COD, 60 % of the TOC, and 94 % of the total Cr concentration, with a total operating cost of 5.99 USD/m3. This improved the biodegradability index (from 0.20 to 0.26), the COS parameter (from 0.14 to 2.46), and the toxicity of the effluent (LC50 for Artemia salina increased from 15.16 mg/L to 56.7 mg/L). The calcium hardness and total hardness were also reduced by 40 % and 44 %, respectively. The C–F supernatant was composed mainly of molecules with molecular weights less than and equal to 10 kDa. An LC-MS spectral analysis revealed the presence of four residual aromatic and recalcitrant compounds in the C–F supernatant, indicating that its further treatment is required before it can be safely discharged or recycled for industrial purposes. The alum C–F process, assisted by slaked lime, demonstrated greater performance, surpassing the individual processes in effectiveness and efficiency, and confirming their synergetic effect. The alum process alone (16.09 g/L) achieved a 37 % reduction COD and 91 % color removal, at a total cost of 4.49 USD/m3. The lime process alone (5.16 g/L) achieved a 37 % COD reduction and 64 % color removal, at a total cost of 1.36 USD/m3.

Structural characterization and physicochemical properties of grain amaranth starch

With potato starch (PS) and corn starch (CS) as the controls, the structure and physicochemical properties of grain amaranth starch (GAS) and its binding with dihydromyricetin were investigated in this study. The results indicated that GAS granules were small in size (3.21 ± 0.13 μm) and had a low amylose content (11.57 ± 0.91%). GAS exhibited low paste clarity, solubility, and swelling power, but demonstrated good freeze-thaw stability and resistance to retrogradation. Although the pasting temperature of GAS was high (75.88 ± 0.03 °C), its peak viscosity, breakdown viscosity, and setback viscosity were significantly lower than those of PS and CS. GAS was classified as A-type starch, with a high molecular weight and broad distribution (Mw, 3.96 × 107 g/mol; PDI, 2.67). For its chain length distribution, chain B1 had the highest proportion (50.09%), while chain B3 had the lowest proportion (13.50%). The complexation of GAS with dihydromyricetin effectively enhanced its ABTS and DPPH free radical scavenging capacities.

RAFT copolymerization of methyl methacrylate and di(ethylene glycol) methyl ether methacrylate in a hexylpyridinium ionic liquid

AbstractSmart polymers undergo significant physical or chemical changes in response to stimuli like temperature and pH. Achieving a narrow molecular weight distribution is crucial for their sensitivity. Reversible addition–fragmentation chain transfer (RAFT) in ionic liquids is an effective method for synthesizing such polymers due to its favorable kinetics and environmental benefits. Most studies use imidazolium ionic liquids, while pyridinium ionic liquids are less common despite their easy synthesis. This study reports the first successful RAFT copolymerization of di(ethylene glycol) methyl ether methacrylate (DEGMEMA) and methyl methacrylate in N‐hexylpyridinium hexafluorophosphate ([HPY][PF6]). Both linear and hyperbranched copolymers (Mn > 25,000) with narrow molecular weight distribution were synthesized, showing observable temperature responses and biocompatibility. The linear copolymers had a desirable dispersity (Ð) of less than 1.10, while the hyperbranched copolymer had a Ð of 2.034. The lower critical solution temperatures (LCSTs) of the copolymers were close to or below the LCST of PDEGMEMA (26°C). This study indicates that pyridinium ionic liquids can be explored as a suitable solvent for synthesizing methacrylate‐based smart polymers.

Jeffamine-based diblock copolymer nanoparticles via reverse sequence polymerization-induced self-assembly in aqueous media

Jeffamines® are commercially available amine-capped poly (alkylene oxides) that have been used for various applications. In this study, a weakly hydrophobic monoamine-capped propylene oxide-rich Jeffamine® (M2005) is derivatized to introduce a trithiocarbonate end-group via amidation. This precursor is then dissolved using N,N′-dimethylacrylamide (DMAC), 2-(N-acryloyloxy)ethyl pyrrolidone (NAEP) or N-acryloylmorpholine (NAM) as a co-solvent to produce a concentrated aqueous reaction mixture containing 20 % w/w water. Subsequently, reversible addition-fragmentation chain transfer (RAFT) polymerization is used to prepare Jeffamine®-core diblock copolymer nanoparticles by reverse sequence polymerization-induced self-assembly (PISA). At intermediate conversion, additional degassed water is added and each polymerization continues to almost full conversion (>99 %) within 4 h at 60 °C, resulting in a 10–20 % w/w aqueous dispersion of sterically-stabilized Jeffamine®-core nanoparticles. Efficient chain extension of the Jeffamine® precursor is achieved in most cases and relatively narrow molecular weight distributions are obtained (Mw/Mn < 1.30) as judged by GPC analysis. Transmission electron microscopy studies confirm a polydisperse spherical morphology and dynamic light scattering studies report hydrodynamic diameters ranging from 145 to 312 nm. Finally, aqueous electrophoresis studies indicate essentially neutral nanoparticles over a wide range of solution pH, as expected for the three types of non-ionic steric stabilizer chains selected for this study.

Polysaccharides from Seedless Chestnut Rose (Rosa sterilis) Fruits: Insights into Innovative Drying Technologies and Their Structural Characteristics, Antioxidant, Antiglycation, and α-Glucosidase Inhibitory Activities.

The selection of an optimal drying method is essential for extending the shelf life and enhancing the quality of Rosa sterilis fruits. This study investigated the effects of both innovative (microwave vacuum drying and infrared drying) and traditional (freeze-drying and hot air drying) techniques on the structural characteristics and bioactivities of polysaccharides from R. sterilis fruits (RSPs). Four different RSPs were obtained from fruits dried using these methods. Results demonstrated that the structural characteristics and bioactivities of RSPs varied significantly with the drying method. Notable differences were observed in extraction yield, total sugar, uronic acid content, monosaccharide molar ratios, molecular weight distribution, particle size, thermal stability, and microstructures of RSPs. Despite these variations, the types of constituent monosaccharides and major glycosidic linkages remained consistent across all methods. Notably, RSPs obtained via microwave vacuum drying (RSPs-MVD) showed a higher uronic acid content and lower molecular weight, and exhibited stronger in vitro antioxidant, α-glucosidase inhibitory, and antiglycation activities. These findings suggest that microwave vacuum drying is an effective pre-drying technique for extracting RSPs, making them suitable as bioactive ingredients in functional foods and pharmaceuticals for managing diabetes mellitus and its complications.

Fabrication of flat and sizeable nanocellular polymethyl methacrylate (PMMA) foam with tunable thermal conductivity

AbstractPolymeric nanocell foam is a promising material that faces manufacturing challenges. Producing sizable and thick foams for properties testing has been challenging. This study aims to scale up and understand the foaming mechanism of nanocellular foams by controlling the saturation temperature, pressure, and molecular weight distribution of the matrix to fine‐tune the glass transition temperature of the polymer/gas mixture. The hot‐press foamed samples possess a 100 × 70 × 6 ~ 8 mm3 dimension and a cell size of less than 200 nm. Bimodal structures can also be created by controlling the critical processing parameters. Introducing 37% microcells into unimodal nanocellular foam reduced the relative density from 0.29 to 0.19. The thermal conductivity of the foams was tuned by controlling the cell size distribution. Unimodal nanofoams have the lowest thermal conductivity for foams of the same density due to the Knudsen effect and tortuosity. The measured thermal conductivity is in agreement with theoretical models.Highlights PMMA nanofoam with a dimension of 100 × 70 × 6–8 mm3 and cell size below 200 nm. The morphology of nanofoams was tuned to be unimodal and bimodal. The foam density of the bimodal nanofoams was lowered below 0.238 g/cm3. The thermal conductivity of foams was tuned by controlling the cell structure.

Potential of Benchtop NMR for the Determination of Polymer Molar Masses, Molar Mass Distributions, and Chemical Composition Profiles by Means of Diffusion-Ordered Spectroscopy, DOSY.

The determination of molar masses and their distributions is crucial in polymer synthesis and design. This work presents the current performance and limitations of diffusion-ordered spectroscopy (DOSY) on a low-field (benchtop) NMR spectrometer (at 90MHz) as an alternative to size exclusion chromatography (SEC) for determining diffusion coefficient distributions (DCDs) and molar mass distributions (MMDs). After optimization for narrowly distributed homopolymers, MMDs obtained with inverse Laplace transformation (ILT) and log-normal distribution are compared with average molar masses obtained with mono- and bi-exponential fits, as well as MMDs obtained from SEC. This approach enables ILT to determine DCDs and MMDs even for bimodal homopolymers with fully spectrally overlapping signals and block copolymers with various chemical compositions, for which chemical composition profiles are determined. The feasibility of low-field diffusion NMR with samples dissolved in non-deuterated solvents is further demonstrated and methods for solvent suppression are discussed.

What Is the Molecular Weight of "High" Molecular Weight Dissolved Organic Matter?

The use of ultrafiltration to isolate high molecular weight dissolved organic matter (HMWDOM) from seawater is a fundamental tool in the environmental organic chemist's toolbox. Yet, important characteristics of HMWDOM relevant to its origin and cycling, such as its molecular weight distribution, remain poorly defined. We used diffusion-ordered NMR spectroscopy coupled with mixed-mode chromatography to separate and characterize two major components of marine HMWDOM: acylpolysaccharides (APS) and high molecular weight humic substances (HS). The molecular weights (MWs) of APS and HS both fell within distinct, narrow envelopes; 2.0-16 kDa for APS and 0.9-6.5 kDa for HS. In water samples from the North Pacific Ocean the average MW of both components decreased with depth through the mesopelagic. However, the minimum MW of APS was >2 kDa, well above the molecular weight cutoff of the ultrafilter, suggesting APS removal processes below 2 kDa are highly efficient. The MW distribution of APS shows only small variations with depth, while the MW distribution of HS narrowed due to removal of HMW components. Despite the narrowing of the MW distribution, the concentration of HS did not decrease with depth between 15 and 915 m. This suggests that HMW HS produced in surface waters was either degraded into lower MW compounds without significant remineralization, or that HMW HS was remineralized but replaced by an additional source of HS in the mesopelagic ocean. Based on these results, we propose potential pathways for the production and removal of these major components of HMWDOM.

Well-Defined Homopolymer Nanoparticles with Uniaxial Molecular Orientation by Synchronized Polymerization and Self-Assembly.

Synthesizing anisotropic polymeric nanoparticles (NPs) with well-defined shapes, dimensions, and molecular orientations is a very challenging task. Herein, we report the synthesis of surprisingly highly uniform shape-anisotropic polymer NPs with uniaxial internal molecular orientation. Keys to our method are synchronized polymerization and self-assembly (SPSA), which can even be realized by regular dispersion polymerization. This is demonstrated using a monomer containing a rigid 4-nitroazobenzene (NAB) side group. The short nucleation period, the completion of microphase separation before molecular motion is frozen, and sufficient low particle/solvent interfacial tension are shown to be the origins of the highly uniform dimensions, single liquid crystal domains, and well-defined anisotropic shape of particles. The liquid crystallization ability of the polymers, control of molecular weight distribution, and the polymerization kinetics are identified as three key factors controlling the NP formation. The uniformity of these NPs facilitates their SA formation into colloidal crystals. The particles exhibit optically anisotropic properties depending on orientations and, in particular, show intriguing photoswitchable LC-glass (order-disorder) transition, which can be used for the detection of ultraviolet (UV) light and allows the fabrication of photoreversible colloidal films.

Structural Composition and Molecular Weight Distribution of Dissolved Organic Matter in Bituminous Oil Sand from Okitipupa, Southern Nigeria

Structural Composition and Molecular Weight Distribution of Dissolved Organic Matter in Bituminous Oil Sand from Okitipupa, Southern Nigeria

Contribution of yeast freezing to the quality of frozen dough: Rheological properties, protein depolymerization, gluten conformation and water state

The present study has comparatively investigated the variation in yeast leachates in frozen suspension and dough systems and assessed the effects of leachate released from frozen yeast cells on dough rheology, protein molecular weight distribution, gluten conformation, and water state. The results revealed that yeast in the dough was more susceptible to freezing than that in the suspension and released more low-molecular-weight metabolites (e.g., trehalose, glutathione, and amino acids) into the dough matrix. Dynamic rheological measurements showed that frozen yeasted dough had weaker viscoelastic properties than non-yeasted dough. Fourier transform infrared spectroscopy revealed a high fraction of β-turns and random coils at the expense of α-helices and β-sheets, demonstrating a flexible protein secondary structure and increase in weakened hydrogen bonds in the gluten network. The presence of yeast in the frozen dough facilitated dough depolymerization via the cleavage of interchain disulfide bonds of gluten protein and softened the gluten network structure. Yeast leachates released from frozen yeast cells caused water redistribution in the dough and increased water release from the weakened gluten network, increasing freezable water content. This study has revealed the essential role of yeast freezing in gluten depolymerization and the deterioration of dough quality.

Artificial humic acid produced from wet distillers grains in a microwave-assisted hydrothermal process: Physicochemical characteristics and stimulation to plant growth

Wet distillers grains, as a waste biomass with a large annual output, pose a threat to the environment and food industry. Herein, artificial humic acid (AHA) was first produced from wet distillers grains in a dual-stage microwave-assisted hydrothermal process. The influence of temperature on AHA's characteristics was investigated and compared with natural humic acid (NHA) and standard humic acid (SHA). A high yield of AHA at 20.6% was obtained at 200 °C with a total reaction time of 1 h, which is 1.8–3.1 times that obtained in traditional single-stage hydrothermal process. Increasing the reaction temperature induced the formation of phenolic hydroxyl in AHA. AHA was rich in aromaticity and carboxylic acid structure, showing similar spectral characteristics to NHA. The distribution of molecular weight of AHA was mostly 5797 Da, which decreased by 15% compared to SHA. The optimal concentration of AHA to promote seedling growth was 0.2 g/L, and the root length was 2.0 times that of the control. The microwave hydrothermal process is a facile and efficient approach to preparing AHA from waste biomass with high moisture content.

Development of a comprehensive normal-phase liquid chromatography × size-exclusion chromatography platform with ultraviolet spectroscopy and high-resolution mass spectrometry detection for the chemical characterization of complex polyesters

BackgroundPolyesters are applied in high-end products in many industrial applications, including resins and powder-coating applications. The characterization of the chemical heterogeneities within a polyester is of utmost interest to develop new products or improve existing applications. Unfortunately, characterization is a difficult task, as polyesters may feature distributions in end-group functionality, molecular weight, chemical composition, and degree of branching. Currently, no analytical method can characterize all these interdependent distributions in a single analysis. ResultsWe report the use of comprehensive normal-phase liquid chromatography × size-exclusion chromatography hyphenated with ultraviolet-light spectroscopy and high-resolution mass spectrometry in parallel (NPLC × SEC–UV/HRMS) to characterize polyesters according to their end-group-functionality and molecular-weight distributions. The chemical composition can be measured with HRMS, while relative quantitation can be performed with UV detection. A supercharging agent was used during ionization allowing to extend the molecular-weight range of the detected chemical species. SignificanceThe presented platform allows characterization of polyesters with varying fractions of carboxyl or hydroxyl end-group functionalities and varying distributions of molecular weight, degree of branching, and chemical compositions. The number-average and weight-average molar masses are obtained in the same analysis. This information cannot be obtained by any one-dimensional technique. The developed NPLC × SEC–UV/HRMS platform is a valuable tool for characterizing polyesters in an industrial setting.

Effect of ultrasonic pretreatment on antifreeze activity of gluten antifreeze polypeptide

In this study, the effects of thermal hysteresis activity, ice recrystallization inhibition, amino acid composition and surface hydrophobicity of different ultrasonic pretreatments on gluten antifreeze polypeptide was studied.The results of the thermal hysteresis activity showed that the collaborative (flat-panel combined probe) ultrasonic working mode was superior to the single-frequence ultrasound mode. In the optimal working mode (15 min, 100 W/L), the results of polarized light microscope and gel chromatography column showed that ultrasonic pretreatment could effectively inhibit the growth of ice crystals, reduced the size of ice crystals, and to a certain extent, transfer the molecular weight distribution of peptides to small molecular peptides. The molecular weight was mainly concentrated at about 200–1000 u. The contents of Valine, Methionine, Leucine, Proline and Glutamic acid residues in the gluten antifreeze polypeptide pretreated by ultrasonic wave were relatively high and more hydrophobic groups were exposed. The secondary structure results showed that the molecular conformation of the polypeptide was mainly α-helix and β-sheet conformations.This paper systematically revealed the intrinsic correlation mechanism between the changes of key domains of substrate proteins and the antifreeze activity of enzymatic hydrolysis products assisted by ultrasoud, providing a theoretical basis for the preparation of antifreeze polypeptide.

Radial basis function neural network and overlay sampling uniform design toward polylactic acid molecular weight prediction

Polylactic acid (PLA) is a potential polymer material as a substitute for traditional plastics, and the accurate molecular weight distribution range of PLA is strictly required in practical applications. Therefore, exploring the relationship between synthetic conditions and PLA molecular weight is crucially important. In this work, direct polycondensation combined with overlay sampling uniform design (OSUD) was applied to synthesize the low molecular weight PLA. Then a multiple regression model and two artificial neural network models on PLA molecular weight versus reaction temperature, reaction time, and catalyst dosage were developed for PLA molecular weight prediction. The characterization results indicated that the low molecular weight PLA was efficiently synthesized under this method. Meanwhile, the experimental dataset acquired from OSUD successfully established three predictive models for PLA molecular weight. Among them, both artificial neural network models had significantly better predictive performance than the regression model. Notably, the radial basis function neural network model had the best predictive accuracy with only 11.9% of mean relative error on the validation dataset, which improved by 67.7% compared with the traditional multiple regression model. This work successfully predicted PLA molecular weight in a direct polycondensation process using artificial neural network models combined with OSUD, which provided guidance for the future implementation of molecular weight-controlled polymer’ synthesis.

Temporal graph convolutional network soft sensor for molecular weight distribution prediction

In chemical processes with distributed outputs, characteristics of products are influenced by their distributions and significantly correlated with process variables. It is crucial for an accurate distribution characteristic prediction to adequately describe variable relationships and their temporal variations. For this purpose, a temporal graph convolutional network (TGCN) soft sensor is developed to describe the distribution of outputs. First, the variable relationships are represented in a topology subgraph based on prior knowledge. Then, the graph is supplemented based on variable screening results with the maximal information coefficient (MIC) as standard. Finally, the graph convolutional mechanism is used to model variable relationships, the gated recurrent unit to capture temporal dependencies, and GNNexplainer to provide a comprehensive explanation for the prediction. Results suggest that prediction accuracy and explainability is improved by the proposed TGCN soft sensor on the basis of prior knowledge, and verified in the case of molecular weight distribution (MWD) modeling.

Transformation of sedimentary dissolved organic matter in electrokinetic remediation catalogued by FT-ICR mass spectrometry

In electrokinetic remediation (EKR), the sedimentary dissolved organic matter (DOM) could impede remediation by scavenging reactive species and generating unintended byproducts. Yet its transformation and mechanisms remained largely unknown. This study conducted molecular-level characterization of the water-extractable DOM (WEOM) in EKR using negative-ion electrospray ionization coupled to 21 tesla Fourier transform ion cyclotron resonance mass spectrometry (21 T FT-ICR MS). The results suggested that ∼55 % of the ∼7,000 WEOM compounds identified were reactive, and EKR lowered their diversity, molecular weight distribution, and double-bond equivalent (DBE) through a combination of electrochemical and microbial redox reactions. Heteroatom-containing WEOM (CHON and CHOS) were abundant (∼ 35% of the total WEOM), with CHOS generally being more reactive than CHON. Low electric potential (1 V/cm) promoted the growth of dealkylation and desulfurization bacteria, and led to anodic CO2 mineralization, anodic cleavage of -SO and -SO3, and cathodic cleavage of -SH2; high electric potential (2 V/cm) only enriched desulfurization bacteria, and differently, led to anodic oxygenation and cathodic hydrogenation of unsaturated and phenolic compounds, in addition to cathodic cleavage of -SH2. The long-term impact of these changes on soil quality and nitrogen-sulfur-carbon flux may be need to studied to identify unknown risks and new applications of EKR.

Isolation of Polyethylene Glycol with Larger Molecular Weights via Metal-Organic Frameworks.

Polymer products typically present as mixtures with a range of molecular weights, which notably influence the expression of their properties. In this study, a technique is proposed to separate polyethylene glycol (PEG) mixtures of varying molecular weights using metal-organic frameworks (MOFs), thereby narrowing down their molecular weight distribution. Due to the hydrogen bond interactions between PEG and -OH groups in the pores of NU-1000, NU-1000 can selectively adsorb PEG with larger molecular weights from PEG mixture. This separation method consistently yields with narrower molecular weight distribution across multiple cycles. This is the first application of MOFs in regulating the dispersity (Ð) of polymers in solution, providing a novel approach for separating and purifying mixed molecular weight polymers.

2‐Azetine Derivatives as a Class of New Monomers for Controlled Ring‐Opening Metathesis Polymerization towards Polyenamides†

Comprehensive SummaryNitrogen‐containing polymers have found a wide myriad of applications in materials science and other different areas, and have attracted much attention towards the development of new synthetic methods. Ring‐opening metathesis polymerization represents an area of great versatility and potential for the synthesis of highly functionalized polymers with low dispersity and control over molecular weight and architecture complexity. Expanding the scope of monomers through the incorporation of nitrogen atoms would further expand their utilities. In this work, a controlled synthesis of polymers with in‐chain enamide moiety through ring‐opening metathesis polymerization was developed by utilizing azetine derivatives as the monomers. Relatively short synthetic routes were designed and generated a panel of five monomers. The polymerization exhibited living characteristics, as linear relationship between molecular weights and degrees of polymerization and relatively narrow molar mass distributions were observed, which was further confirmed by successful diblock copolymers formation through sequential addition of two monomers. The resulting polymers that contain the enamide moiety within the backbone exhibited good stability and underwent facile degradation under acidic conditions.

Advanced Synthesis, Structural Characterization, and Functional Applications of Precision Polymers.

In the realm of biological macromolecules, entities such as nucleic acids and proteins are distinguished by their homochirality, consistently defined chain lengths, and integral sequence-dependent functionalities. Historically, these refined attributes have eluded traditional synthetic polymers, which often exhibit wide variabilities in chain lengths, limited batch-to-batch reproducibility, and stochastic monomer arrangements. Bridging this divide represents a pivotal challenge within the domain of polymer science - a challenge that the burgeoning discipline of precision polymer chemistry is poised to address. Recent advancements have yielded precision polymers that boast prescribed monomer sequences and narrow molecular weight distributions, heralding a new era for developing model systems to decipher structure-property correlations within functional polymers, analogous to those within biological matrices. This review discusses the innovative liquid-phase and solid-phase synthesis techniques for creating precision polymers and the advanced characterization tools essential for dissecting their structure and properties. We highlight potential applications in self-assembly, catalysis, data storage, imaging, and therapy, and provide insights into the future challenges and directions of precision polymers.