Chain Length Distribution Research Articles

Dimensions of Network Polymers

AbstractThe mean‐square radius of gyration Rg2 and the graph diameter D of the network polymers formed through the random crosslinking of predetermined primary chains with a fixed number of intermolecular and intramolecular crosslinks are investigated by the numerical calculation based on the graph theory. In the case of ring‐free polymers, D is the longest end‐to‐end path length, sometimes referred to as the maximum span length. The expected Rg2‐value for a given D is found to follow a linear relationship, Rg2 = a D + b, similarly as in the cases of the ring‐free polymers. The proportional coefficient, a decreases approximately linearly with the number of intramolecular crosslinks kc, or the cycle rank in the graph theory, essentially independent of the total number k of crosslinks and the primary chain length distribution. The contraction factor g of the average Rg2 of the whole network polymer system is also governed by kc, and decreases with kc. One may be able to design and control the Rg2‐values of crosslinked polymers through the magnitude of D, which is usually easier to imagine than the complex 3D architecture.

Loss of starch synthase IIIa changes starch molecular structure and granule morphology in grains of hexaploid bread wheat

Starch synthase III plays a key role in starch biosynthesis and is highly expressed in developing wheat grains. To understand the contribution of SSIII to starch and grain properties, we developed wheat ssIIIa mutants in the elite cultivar Cadenza using in silico TILLING in a mutagenized population. SSIIIa protein was undetectable by immunoblot analysis in triple ssIIIa mutants carrying mutations in each homoeologous copy of ssIIIa (A, B and D). Loss of SSIIIa in triple mutants led to significant changes in starch phenotype including smaller A-type granules and altered granule morphology. Starch chain-length distributions of double and triple mutants indicated greater levels of amylose than sibling controls (33.8% of starch in triple mutants, and 29.3% in double mutants vs. 25.5% in sibling controls) and fewer long amylopectin chains. Wholemeal flour of triple mutants had more resistant starch (6.0% vs. 2.9% in sibling controls) and greater levels of non-starch polysaccharides; the grains appeared shrunken and weighed ~ 11% less than the sibling control which was partially explained by loss in starch content. Interestingly, our study revealed gene dosage effects which could be useful for fine-tuning starch properties in wheat breeding applications while minimizing impact on grain weight and quality.

Living polymerization in nano-scale volumes. Impact of process conditions on polymerization kinetics and product characteristics

Living polymerization processes, irreversible and reversible, proceeding in a large number of isolated (no mass exchange) nano-scale reactors (droplets) were modeled using stochastic (Monte Carlo) and deterministic simulations and analytical solutions of derived mathematical equations. Monomer and living unimer used as initiator were redistributed in droplets uniformly or accordingly to the Poisson distribution, resulting in nanoreactors containing a small number of growing chains. Stochasticity of reactions involving low number of molecules affects the concentration of monomer and chain length distributions in individual droplets, both differing from ones accounted in macroscopic system. The developed mathematical description, based on values of rate constants of propagation (kp) and depropagation (kd) reactions and on initial monomer and living unimer concentrations, as well as numerical simulations, allow predicting kinetics of the process and of several characteristics of the products resulting therefrom, e.g. chain length distribution. Moreover, they allow also following evolution of droplet subpopulations that differ in composition. Moreover, for the reversible process the equilibrium monomer concentration in a droplets system [M]eq can be calculated. As living ionic and coordination polymerization and the controlled radical polymerization in nano-scale dispersions are rather little explored the theoretical predictions shown in this work could facilitate their further development.

On Elegant Solutions in PRE: Moment Equations for the Chain Length Distribution of Coordination Polyolefins

AbstractThe method of moments has been used for a long time to describe the chain length averages of polymers made via different mechanism. This article describes a mathematical analysis method to derive the simplest general expression for the moments of the chain length distribution of linear polyolefins made with single‐site‐type coordination catalysts. It also shows how to use this general solution for polyolefins made with multiple‐site‐type coordination catalysts. More importantly, this article advocates the use of elegant solutions in polymerization reaction engineering, which are deceivingly simple mathematical equations that capture the most essential information about complex polymerization systems. Elegant solutions shine more light on the phenomena they are modeling than more complex and computational demanding methods.

Distribution of atomic chain lengths: Effect of local temperature profile

A challenging aim of current research in one-dimensional physics is the search for optimal conditions for the formation of well-ordered chains. The effect of local temperature profile was investigated using large-scale kinetic Monte Carlo simulations. It was found that well-ordered long chains are formed in the presence of a temperature gradient in the sample near the critical temperature. Furthermore, it was shown how the size distribution of chains changes during annealing and cooling. The observed change mechanism of the chain length during the annealing or cooling will be useful in industry for creating atomic chains with a given length.

Developing DHA microcapsules using linear dextrin aggregates of different chain length distributions

Linear dextrin aggregates (LDAs) were prepared in the current study as novel material for encapsulating docosahexaenoic acid (DHA). The high amylose corn starch was acid hydrolyzed and enzymically debranched into LDAs of varied chain length distributions (CLDs). Results showed that the encapsulation efficiency of microcapsules significantly increased from 68% to 81% correspondingly with the improved content of the intermediate linear dextrin (degree of polymerization, DP, ranges 10– 100). Meanwhile, the peroxide value was also showed a decrease of 2 mEq/kg during the storage. Molecular dynamic simulations further revealed that the linear dextrin with DP of 15 showed the highest interaction attraction while being encapsulated with DHA. The hypothesis is thus verified since the LDA with a specific CLD favors the formation of starch-based DHA microcapsules with better performance. When LDAs contained 22% intermediate linear dextrin, microcapsules showed the highest encapsulation efficiency (85%) and the lowest peroxide value (10 mEq/kg).

Effects of maltogenic α-amylase treatment on the proportion of slowly digestible starch and the structural properties of pea starch

In this study, pea starch was modified with maltogenic α-amylase and then its physicochemical properties, chain length distribution, and in vitro digestibility were examined. An analysis of the starch products resulting from the maltogenic α-amylase treatment revealed a decrease in the molecular weight, an increase in the proportion of short chains [degree of polymerization (DP) <13], a decrease in the proportion of long chains (DP > 13), and a decrease in viscosity, resulting in slower digestion. The results indicated that maltogenic α-amylase can selectively hydrolyze α-1,4- and α-1,6-glycosides to some extent. Cleaving the α-1,4 linkage of starch facilitated the transfer of the non-reducing D-glucosyl residues of maltose, thereby generating an α-1,6 branch linkage. The reaction between maltogenic α-amylase and pea starch was affected by the reaction time and enzyme concentration. The maximum slowly digestible starch content (38.5%) was obtained by digesting samples with 60.0 ppm maltogenic α-amylase for 4.0 h. These findings demonstrate that modifying pea starch using maltogenic α-amylase can generate starch products with new branching structures conducive to slow digestion.

Atomistic investigation of fracture mechanisms in phosphorus-functionalized epoxy resins

Modifying epoxy resin molecules using phosphorus-containing functional groups can enhance the liquid oxygen compatibility (LOC) of polymeric matrix composites, but will significantly change the mechanical and fracture properties of the functionalized thermosets due to the increased complexity of the molecular architecture. The underlying mechanisms responsible for these property changes are not well understood. In this work, we unveiled the molecular-scale fracture mechanisms of epoxy resins modified by 10-(2,5-dihydroxyphenyl) -10-hydrogen-9-oxa1-phenanthroline-10-oxide (ODOPB) using molecular dynamics (MD) simulations. We adopted a two-step reaction scheme to prepare the modified cross-linked networks of the epoxy thermosets. Then, a fracture simulation approach was developed based on hybrid use of non-reactive and reactive force field parameters, which enables accurate and efficient bond scission representation during tensile deformation. Efforts were made to explore the impact of varying the P content (proportional to ODOPB amount) on the molecular architectures and mechanical performance. It was found that the chain length distribution was a crucial determinant of the mechanical and fracture properties. More intriguingly, the simulation results showed that at a fixed P content, properties such as the fracture energy could be enhanced by regulating the chain length. This study offers valuable insights into the design and fabrication of high-performance aerospace composites with remarkable tolerance to harsh engineering environments.

Indication that starch and sucrose are biomarkers for oil yield in oil palm (Elaeis guineensis Jacq.)

Oil palm (Elaeis guineensis Jacq.) is the most productive oil-producing crop per hectare of land. The oil that accumulates in the mesocarp tissue of the fruit is the highest observed among fruit-producing plants. A comparative analysis between high-, medium-, and low-yielding oil palms, particularly during fruit development, revealed unique characteristics. Metabolomics analysis was able to distinguish accumulation patterns defining of the various developmental stages and oil yield. Interestingly, high- and medium-yielding oil palms exhibited substantially increased sucrose levels compared to low-yielding palms. In addition, parameters such as starch granule morphology, granule size, total starch content, and starch chain length distribution (CLD) differed significantly among the oil yield categories with a clear correlation between oil yield and various starch parameters. These results provide new insights into carbohydrate and starch metabolism for biosynthesis of oil palm fruits, indicating that starch and sucrose can be used as novel, easy-to-analyze, and reliable biomarker for oil yield.

Whole picture of human stratum corneum ceramides, including the chain-length diversity of long-chain bases

Ceramides are essential lipids for skin permeability barrier function, and a wide variety of ceramide species exist in the stratum corneum (SC). Although ceramides with long-chain bases (LCBs) of various lengths have been identified in the human SC, a quantitative analysis that distinguishes ceramide species with different LCB chain lengths has not been yet published. Therefore, the whole picture of human SC ceramides remains unclear. Here, we conducted LC/MS/MS analyses to detect individual ceramide species differing in both the LCB and FA chain lengths and quantified 1,327 unbound ceramides and 254 protein-bound ceramides: the largest number of ceramide species reported to date. Ceramides containing an LCB whose chain length was C16–26 were present in the human SC. Of these, C18 (28.6%) was the most abundant, followed by C20 (24.8%) and C22 (12.8%). Each ceramide class had a characteristic distribution of LCB chain lengths and was divided into five groups according to this distribution. There was almost no difference in FA composition between the ceramide species containing LCBs of different chain lengths. Furthermore, we demonstrated that one of the serine palmitoyltransferase (SPT) complexes, SPTLC1/SPTLC3/SPTSSB, was able to produce C16–24 LCBs. The expression levels of all subunits constituting the SPT complexes increased during keratinocyte differentiation, resulting in the observed chain-length diversity of LCBs in the human SC. This study provides a molecular basis for elucidating human SC ceramide diversity and the pathogenesis of skin disorders.

Beyond amylose content, selecting starch traits impacting in vitro α-amylase degradability in a wheat MAGIC population

A major challenge faced when studying the “structure-degradability” interaction of native starch is deciphering the interdependency between different structural levels, especially when experimental conditions limit the number of samples. To tackle this challenge, 224 wheat starches from a 4-way multiparent advanced generation inter-cross population were screened for structural features and degradation profiles by porcine pancreatic α-amylase. A hierarchical clustering on principal components (HCPC) were used as multifactorial analysis to explore the data structure. The degradation procedure was proved to be robust and sensible enough to screen a large collection of starches. The HCPC highlighted the combined effects of granule size distribution (GSD), amylopectin chain length distribution (CLD), amylose content and endogenous α-amylase activity on degradation kinetics. Especially the GSD and amylopectin CLD showed high co-occurrences with specific hydrolysis profiles. These findings provide an innovative screening method and structural factors to be primarily considered for wheat starch selection in breeding programs.

Modulation of the Complex Spherical Packings through Rationally Doping a Discrete Homopolymer into a Discrete Block Copolymer: A Quantitative Study

The Frank–Kasper phase and quasicrystalline phase are an intriguing class of complex crystalline structures, which so far are sporadically observed only in a limited number of block copolymers. Incorporation of a homopolymer into a block copolymer has recently been demonstrated as an effective and robust approach to regulate the formation and evolution of these complex spherical phases. The experimental explorations, however, suffer from inherent chain length distribution of the blending stocks. In this study, we quantitatively assessed the phase behaviors of the block copolymer/homopolymer binary blends using discrete species with a precise chemical structure and uniform chain length, ruling out all interferences associated with chemical heterogeneities. Diverse spherical packings, including σ, A15, C15, and C14 phases, were captured by rationally tuning the chain length and loading content of the homopolymer. The short chains swell the spherical core and drive a transition toward the lattices with a lower interfacial curvature (i.e., σ → A15 → HEX), whereas the long chains localize in the center of the core and prompt the formation of the Frank–Kasper phases with the increasing particle volume asymmetry (C15 and C14). The experimental observation validates the recent theoretical advances, demonstrating that the blending strategy is a robust approach for structural engineering.

Amylose Inter-Chain Entanglement and Inter-Chain Overlap Impact Rice Quality.

Retrogradation of cooked rice happens in two ways: one is by the formation of ordered structures, and the other is through intra- and inter-chain entanglement and inter-chain overlap, which in turn are affected by the amylose chain-length distribution. Both entanglement and overlap could affect rice texture. Here, four amylose samples were isolated from starch by precipitation from a dimethyl sulfoxide solution with butan-1-ol and isoamyl alcohol. Following enzymatic debranching, they were then characterized using size-exclusion chromatography. Amylose solutions (10%, m/v) were made by dissolving amylose in 90% (v/v) DMSO. Amylose gels (10%, w/v) were made by dissolving amylose powders into hot water, followed by cooling. The rigidity of the amylose gels and the structural order were measured using a texture analyzer and X-ray diffractometer, respectively. In the amylose solution, for a given mass of polymer in a fixed amount of solvent, the total occupied volume was reduced when the polymer molecular weight was smaller, resulting in less inter-chain overlap and a lower viscosity of the amylose solution. The overall mobility and diffusion of the molecules were inversely related to the square of the molecular weight until the gelation concentration. Thus, amylose gels in which amylose had a lower molecular weight had a greater chance to permeate into other molecules, which counterintuitively led to more inter-chain entanglement and more rigid amylose gels during retrogradation. This information could help rice breeders improve rice quality by using the molecular structure of starch as a guide.

Paleoecological and paleohydrological changes during the Eocene/Oligocene transition in the Qaidam Basin, NE Tibetan Plateau

The Eocene/Oligocene transition (EOT) at ∼34 Ma has been considered the most prominent climatic cooling event in the Cenozoic Era. However, few organic biomarker studies have attempted to reconstruct relevant terrestrial ecological and hydrological responses to an age characterized by drastic temperature changes. This research aims to reconstruct the paleoecological and paleohydrological evolution of the Qaidam Basin (QB) on the northeastern Tibetan Plateau (NE TP) between 40.2 and 29.9 Ma, based on analyses of n-alkane chain length distributions as well as compound-specific hydrogen isotopic compositions (δ2Halk). Research showed the presence of a sequence of pronounced ecological and hydrological variations at 35.0–33.1 Ma, including: 1) a significantly decreased input of bacteria, algae and aquatic plants, allied with a markedly increased input of terrestrial plants, reflected in a significant increase in carbon preference index (CPI) and the average chain length (ACL) ratio, as well as an abrupt decline in the relative ratio of mid- to long-chain length homologue (Paq) values and the ratio of low- to high- molecular-weight n-alkanes (L/H); and 2) drier climatic conditions, reflected in an 18.1‰ increase in δ2H31 values, as well as more positive hydrogen isotopic precipitation values (δ2Hp). These features demonstrate significant paleoecological and paleohydrological changes in the QB in response to the drier and cooler climate during the EOT.

Diurnal changes in starch molecular structures and expression profiles of starch biosynthesis enzymes in rice developing seeds

The diurnal changes in the expression profiles of starch synthesis related enzymes (SSREs) has been previously studied in transitory starches, while its influences on storage starch molecular structures in the rice endosperm during seed development have not been elucidated. In this study, the changes in the transcript levels of starch synthesis related genes (SSRGs), the protein abundances and enzyme activities of SSREs as well as starch molecular structures in rice endosperm at 10 days after flowering (DAF) over the diurnal cycle were analyzed. It was found that the expression profiles of SSRG and the protein contents of SSREs displayed different diurnal patterns between two indica rice varieties with medium- and high-amylose content (AC), respectively. The expression levels of SSRGs were higher in the light time, and most SSREs also accumulated during this period except debranching enzymes. Amylose synthesis displayed distinct diurnal patterns in two rice varieties, which is attributed to the diurnal changes in the protein content of granule-bound starch synthase I (GBSSI), but amylopectin chain-length distributions (CLDs) remained unaltered due to its vast numbers of branches. The results provide the first step to understand the roles of each enzyme isoform involved in starch synthesis in response to diurnal regulation in rice endosperm.

Chain Assembly Kinetics from Magnetic Colloidal Spheres.

Magnetic colloidal chains are a microrobotic system with promising applications due to their versatility, biocompatibility, and ease of manipulation under magnetic fields. Their synthesis involves kinetic pathways that control chain quality, length, and flexibility, a process performed by first aligning superparamagnetic particles under a one-dimensional magnetic field and then chemically linking them using a four-armed maleimide-functionalized poly(ethylene glycol). Here, we systematically vary the concentration of the poly(ethylene glycol) linkers, the reaction temperature, and the magnetic field strength to study their impact on the physical properties of synthesized chains, including the chain length distribution, reaction temperature, and bending modulus. We find that this chain fabrication process resembles step-growth polymerization and can be accurately described by the Flory-Schulz model. Under optimized experimental conditions, we have successfully synthesized long flexible colloidal chains with a bending modulus, which is 4 orders of magnitude smaller than previous studies. Such flexible and long chains can be folded entirely into concentric rings and helices with multiple turns, demonstrating the potential for investigating the actuation, assembly, and folding behaviors of these colloidal polymer analogues.

Effect of Fermentation Time on Molecular Structure and Physicochemical Properties of Corn Ballast Starch.

The effect of fermentation treatment on the surface morphology, crystal structure, molecular weight, chain length distribution, and physicochemical properties of corn starch was investigated using natural fermentation of corn ballast. The amylose content in corn ballast starch reduced at first after natural fermentation, then grew, following the same trend as solubility. There were certain erosion marks on the surfaces of fermented corn ballast starch granules. The crystalline structure of corn ballast starch remained the same, i.e., a typical A-type crystalline structure, at different fermentation times; however, the intensities of diffraction peaks were different. The weight-average molecular weight of starch first increased and then decreased after fermentation. The content of low-molecular-weight starch (peak 3) decreased from 25.59 to 24.7% and then increased to 25.76%, while the content of high-molecular-weight starch (peak 1) increased from 51.45 to 53.26%, and then decreased to 52.52%. The fermentation time showed a negative correlation with the viscosity of starch, and the pasting temperature first increased, and then decreased. Natural fermentation can be used as a technical means to produce corn starch products as a result of the experiments' findings, and future experiments will detect and analyze the bacterial structure of corn fermentation broth in order to better understand the molecular mechanism of natural fermentation affecting the structure and physicochemical properties of corn starch.

How Does Starch Structure Impact Amylolysis? Review of Current Strategies for Starch Digestibility Study.

In vitro digestibility of starch is a common analysis in human nutrition research, and generally consists of performing the hydrolysis of starch by α-amylase in specific conditions. Similar in vitro assays are also used in other research fields, where different methods can be used. Overall, the in vitro hydrolysis of native starch is a bridge between all of these methods. In this literature review, we examine the use of amylolysis assays in recent publications investigating the complex starch structure-amylolysis relation. This review is divided in two parts: (1) a brief review of the factors influencing the hydrolysis of starch and (2) a systematic review of the experimental designs and methods used in publications for the period 2016–2020. The latter reports on starch materials, factors investigated, characterization of the starch hydrolysis kinetics and data analysis techniques. This review shows that the dominant research strategy favors the comparison between a few starch samples most frequently described through crystallinity, granule type, amylose and chain length distribution with marked characteristics. This strategy aims at circumventing the multifactorial aspect of the starch digestion mechanism by focusing on specific features. An alternative strategy relies on computational approaches such as multivariate statistical analysis and machine learning techniques to decipher the role of each factor on amylolysis. While promising to address complexity, the limited use of a computational approach can be explained by the small size of the experimental datasets in most publications. This review shows that key steps towards the production of larger datasets are already available, in particular the generalization of rapid hydrolysis assays and the development of quantification approaches for most analytical results.

Exogenous Melatonin Improves the Quality Performance of Rice under High Temperature during Grain Filling

With the increasing greenhouse effect, high temperature has become the most unfavorable environmental factor for the rice grain filling process, affecting rice yield and quality mainly through changing the composition and structure of starch in rice grains. Research has focused on the rational management of water and fertilizer, and spraying of exogenous chemicals, which have become important measures to alleviate high temperature stress of rice. As a multifunctional molecule, melatonin has the potential to improve plant stress resistance by enhancing the scavenging efficiency of reactive oxygen species (ROS), thus protecting plants from the adverse effects of abiotic stress. The present study used a typical japonica rice variety Nipponbare (NPB) as the experimental material, which was treated with high temperature and melatonin during grain-filling stages. The effects of exogenous melatonin on the rice growth and quality traits, as well as starch synthesis, in response to high temperature were analyzed systematically. Exogenous melatonin significantly increased the rice leaf photosynthetic and heat-resistance properties. Melatonin could alleviate the effects of high temperature on the key physicochemical properties related to rice quality. Furthermore, milled rice from NPB plants treated with melatonin had better endosperm appearance under high temperature. Further study found that exogenous melatonin could stabilize the chain length distribution of starch in NPB (especially amylopectin), which implied that melatonin could be used in rice cultivation to alleviate the effect of high temperature on quality, optimization of amylopectin synthesis can also improve rice quality. The results of the present study provide a new idea and research direction to alleviate high temperature stress of rice in the context of global warming.

Molecular structure and architectural characteristics of outer shells and inner blocklets of normal and waxy wheat A- and B- starch granules

Outer shells and inner blocklets were isolated from normal and waxy wheat A- and B- starch granules. Microstructural, molecular, and architectural characteristics of the isolated shells and blocklets were investigated using different methods and techniques. The results revealed that the outer shells were flake and net pocket shaped, with a compact surface and mass fractal. On the other hand, inner blocklets exhibited spherical, beaded, and rod shapes with a typical V-type crystalline structure. Crystallinity, degree of short-range order, amylopectin and amylose molecular weight, amount of intramolecular hydrogen bonds, and the average of shorter semicrystalline lamellae repetition distance varied between outer shells and inner blocklets, as well as depending on the type of wheat starch granules, i.e. normal and waxy wheat A- and B- starch granules. The branch chain length distribution of amylopectin affected the thickness of amorphous and crystalline regions, and the crystal order degree influenced the fractal and morphological characteristics of outer shells and inner blocklets. Additionally, amylose and amylopectin of inner blocklets were polymerized to form larger amylose and amylopectin molecules and develop the outer shells. The obtained findings give a theoretical basis for understanding the relationship between molecular structure and architectural characteristics of starch.