The formation mechanism and stability of konjac glucomannan (KGM) helical structure were investigated by molecular dynamic simulation and experimental method. The results indicate that the molecular conformation of KGM is a non-typical helical structure. In detail, helical structure of KGM is mainly sustained by acetyl group, whose size and stability are affected by the molecular polymerization degree of KGM. In vacuum among the non-bonding interactions, electrostatic force is the greatest factor affecting its helical structure, but in water solution, hydrogen bond affects the helical arrangement greatly. To our interest, temperature exhibits a reversible destroying effect to some extent; the helical structure will disappear completely and present a ruleless clew-like arrangement till 341 K. This work suggests that the method of combining molecular dynamic simulation and experiment tools can be effective in the study of KGM helical structure. 相似文献
In this paper we investigated the stability of konjac glucomnnan(KGM) chain hydrogen networks based on the quantum spin model. Dissipative particle dynamics method was applied in the structure simulation of KGM. The results reveled that acetyl residues of KGM were bonded with water molecules in aqueous solutions. Increasing the hydrogen bond formation decreases the energy in acetyl system. The expect-valuation of the thermal state with respect to the Hamiltonian is negative. Hence, the total energy of konjac glucomnnan chain with the acetyl groups decreases, which indicates the increasing stability of konjac glucomnnan chain. Our approach could provide a new insight into the investigation on the stability of konjac glucomnnan chain. 相似文献
To know the effects of irradiation on the konjac glucomannan (KGM) molecular chain membrane, KGM membrane solution was treated with the irradiation dose of 0-20 kGy in this study, and the structure and properties of KGM membrane were analyzed with Infrared spectrum, Raman spectrum, X-ray, SEM scanning and so on. The results revealed that the effects of different irradiation doses on the KGM molecular chain structure were different. Higher irradiation dose (20 kGy) resulted in partial damage against KGM membrane crystal structure, and there was no obvious change for the amorphous structure; with membrane property test, the tensile strength of KGM membrane gradually increased with the increase of irradiation dose and its elongation at break reduced, but these changes were not significant, WVP value reduced; with SEM, the membrane surface treated with irradiation was smoother even than the membrane without treatment. In addition, when increasing the irradiation dose, membrane surface became more even, and arrangement was more orderly and compact. Irradiation modification could effectively improve the KGM membrane properties, and it is an ideal modification method. 相似文献
The interactions between konjac glucomannan and carrageenan were studied with the method of molecular dynamics simulation. Part representative structure segments of KGM and two unit structures of κ-carrageenan (Fig. 2) were used as mode, and the force-field was AMBER2. The stability and sites of konjac glucomannan/carrageenan interactions in water were researched at 373 K with the following results: the potential energy (EPOT) of the mixed gel was dropped, while those of single-konjac glucomannan gel and single carrageenan were increased. The surface area (SA) of KGM in the mixed system was decreased to 1002.2A^°^2, and that of carrageenan to 800.9 A^°^2. The variations of two parameters showed that the stability of compound gel konjac glucomannan/carrageenan was improved, which is consistent with the previous studies. The sites of interactions in the mixed gel were the -OH groups on C(2), C(4) and C(6), the acetyl group in KGM mannose, and the -OH group on C(6) in carrageenan. The hydrogen bond was formed directly or indirectly by the bridge of waters. 相似文献
An ultra-light and high porosity nano microfibril aerogel was prepared from konjac glucomannan(KGM) by the electrospinning and freeze-drying. The structure of aerogel was analyzed by scanning electron microscopy(SEM) and X-ray diffraction(XRD) while the density and compressive strength of the samples were studied separately. Results reveal that porous network structure of the KGM nano microfibril aerogel is constructed by intermolecular hydrogen bonds in random and interpenetrate way. The nano microfibril structure presents in the KGM aerogel,which is an important reason of its high density and compressive strength. There is a potential application for this unique nano microfibril aerogel in the absorption of biodegradation bacteria to solve problems in marine oil spill pollution. 相似文献
1 INTRODUCTION gel using KGM and borax at 60 ℃, which can be used as slow-released reagent of theophylline and Generally, the mixture of Konjac Glucomanan dibucaine. And Hogi Tsuneo utilized KGM and tetra- (KGM) and salts that could be hydrolyzed to form valent boric acid to prepare artificial crystal[1]. This multi-hydroxyl hydrates leads to the generation of kind of crystal has good light transmission property, gelatum. Among the familiar salts, such as borate, elasticity, intensi… 相似文献
The early events in protein collapse and folding are guided by the protein's elasticity. The contributions of entropic coiling and poor solvent effects like hydrophobic forces to the elastic response of proteins are currently unknown. Using molecular simulations of stretched ubiquitin in comparison with models of proteins as entropic chains, we find a surprisingly high stiffness of the protein backbone, reflected by a persistence length of 1.2 nm, which is significantly reduced by hydrophobic forces acting between protein side chains to an apparent persistence length of 0.3-0.6 nm frequently observed in single-molecule stretching experiments. Thus, the poor solvent conditions of a protein in water lead to a protein compaction much beyond the coiling of an entropic chain and thereby allow a protein to appear softer than when using good solvents. 相似文献
A new method combining three-dimensional (3D) force measurements in an optical trap with the analysis of thermally induced (Brownian) position fluctuations of a trapped probe was used to investigate the mechanical properties of a single molecule, the molecular motor kinesin. One kinesin molecule attached to the probe was bound in a rigorlike state to one microtubule. The optical trap was kept weak to measure the thermal forces acting on the probe, which were mainly counterbalanced by the kinesin tether. The stiffness of kinesin during stretching and compression with respect to its backbone axis were measured. Our results indicate that a section of kinesin close to the motor domain is the dominating element in the flexibility of the motor structure. The experiments demonstrate the power of 3D thermal fluctuation analysis to characterize mechanical properties of individual motor proteins and indicate its usefulness to study single molecule in general 相似文献
Summary: The deconvolution of molecular weight distributions (MWDs) may be useful for obtaining information about the polymerization kinetics and properties of catalytic systems. However, deconvolution techniques are normally based on steady‐state assumptions and very little has been reported about the use of non‐stationary approaches for the deconvolution of MWDs. In spite of this, polymerization reactions are often performed in batch or semi‐batch modes. For this reason, dynamic solutions are proposed here for simple kinetic models and are then used for deconvolution of actual MWD data. Deconvolution results obtained with dynamic models are compared to deconvolution results obtained with the standard stationary Flory‐Schulz distributions. For coordination polymerizations, results show that dynamic MWD models are able to describe experimental data with fewer catalytic sites, which indicates that the proper interpretation of the reaction dynamics may be of fundamental importance for kinetic characterization. On the other hand, reaction dynamics induced by modification of chain transfer agent concentration seem to play a minor role in the shape of the MWD in free‐radical polymerizations.
This Figure illustrates that MWDs obtained at unsteady conditions should not be deconvoluted with standard steady‐state Flory‐Schulz distributions. 相似文献
The role of water as a chain-transfer agent in addition polymerization of methyl methacrylate and acrylamide in a mixed solvent system was studied. Water does not have any transfer with the growing polymer radical. The degree of polymerization is found to increase with increasing water concentration. This is probably due to a reduced termination rate resulting from coiling of the polymer chain in the presence of a nonsolvent like water. 相似文献
Structures of KGM treated in two high-voltage pulse electric fields were characterized by infrared spectroscopy,Raman spectroscopy,X-ray diffraction and so on.The results showed that intermolecular hydrogen bonding interactions of KGM were reduced after being treated with high-voltage pulse electric field,but there was no significant effect on its fiber chain form and thermal characteristics.Results of the study can provide a useful reference for further study on the structure and property of KGM,and especially can provide theoretical basis for the effect of physical field on the foodstuff deep processing related to KGM. 相似文献
A model for evaluating the instantaneous degree of polymerization distribution of homopolymers produced in emulsion, based on the mathematics of the Markov chains, is developed. The model accounts for any number of active chains per particle, as well as for the two fundamental mechanisms of chain termination: mono- and bi-molecular, both by combination and by disproportionation. The core of the model is the so called subprocessmain process treatment, which allows us to correctly evaluate the degree of polymerization of the chains growing in the polymer particles, by distinguishing between the events experienced by the polymer chain which imply a change of its degree of polymerization (subject transitions) and those which imply only a change in the particle state (environment transitions). This is obtained by properly defining the one-step transition probability matrix of the relevant Markov process. Once this is done, the evaluation of the distribution of the degrees of polymerization reduces to a few simple operations among matrices. Explicit expressions for the instantaneous probability density functions and the relative cumulative distributions are obtained. The application of such relationships is facilitated by the numerical procedures reported in the Appendices. The results of the model developed in this work are in agreement with those of earlier models in the range of parameter values of practical interest. In the limit of very low molecular weights, only the model developed in this work provides the correct answer. Moreover, a much more significant result is its applicability to the case of emulsion copolymerization, as it is shown in Part II. 相似文献
Polyimide is a potential material for high-performance printed circuit boards because of its chemical stability and excellent thermal and mechanical properties. Flexible printed circuit boards must have a low static dielectric constant and dielectric loss to reduce signal loss in high-speed communication devices. Engineering the molecular structure of polyimides with large pendant groups is a strategy to reduce their dielectric constant. However, there is no systematic study on how the large pendant groups influence electrical energy loss. We integrated all-atomic molecular dynamics and semi-empirical quantum mechanical calculations to examine the influence of pendant groups on polymer chain anisotropy and electrical energy loss at high frequencies. We analyzed the radius of gyration, relative shape anisotropy, dipole moment, and degree of polarization of the selected polyimides (TPAHF, TmBPHF, TpBPHF, MPDA, TriPMPDA, m-PDA, and m-TFPDA). The simulation results show that anisotropy perpendicular to chain direction and local chain rigidity correlate to electrical energy loss rather than dipole moment magnitudes. Polyimides with anisotropic pendant groups and significant local chain rigidity reduce electrical energy loss. The degree of polarization correlated well with the dielectric loss with a moderate computational cost, and difficulties in directly calculating the dielectric loss were circumvented. 相似文献
Polymethacrylonitrile (PMAN) was prepared by bulk, solution and precipitation polymerization. The thermal stability of the polymer, which is affected by the structure of the chain end groups, was studied by non-isothermal thermogravimetry (TG). On the basis of the differential TG curves of samples prepared by polymerization in the presence of chlorinated solvents, it may be concluded that, in addition to end-chain and random main chain scission initiated depolymerization, hydrogen chloride evolution also occurs during the thermal degradation of PMAN. 相似文献
In an earlier work it was shown that a random long-chain branching structure can be incorporated in polystyrene by copolymerizing styrene with a small amount of monomer that contains a chain transfer group. The use of vinylbenzylthiol as the chain transfer monomer produced a polystyrene with low number-average molecular weight and a degree of branching lower than expected. In this study polymerization kinetics were used to compute the theoretical molecular weight and degree of branching. The results show that if the chain-transfer constant of the chain transfer monomer is as high as that for vinylbenzylthiol the expected molecular weight and degree of branching will indeed be as low as those found experimentally. The theory also predicts that if the chain transfer constant is near one a highly branched bushy structure will result. 相似文献