Based on Davies' group contribution method, hydrophile-lipophile balance (HLB) values were calculated by effective chain length (ECL) instead of actual chain length of straight alkyl chain, polyoxyethylene (EO) chain, and polyoxypropylene (PO) chain. Linear equations were adopted for the effective chain length of straight alkyl chain and PO chain; a Gamma probability density function (PDF) was used to describe the contribution of each EO group to HLB and the effective chain length of EO chain could be obtained by integrating Gamma PDF. The HLB values of 224 nonionic surfactants were calculated and the average absolute error is less than 1.5, which is much better than the results obtained by Davies. 相似文献
Conformation of single polyelectrolytes in tetravalent salt solutions is investigated under the framework of a coarse-grained model, using Langevin dynamics simulations. The chain size, studied by the radius of gyration, shows three different variational behaviors with salt concentration, depending on the chain stiffness. According to the size variations, polyelectrolytes of fixed chain length are classified into three categories: (1) flexible chain, for which the variation shows a curve similar to a tilted L, (2) semiflexible chain, whose curve resembles U, and (3) rigid chain, for which the curve is a straight line. The wormlike chain model with persistence length predicted by the Odijk-Skolnick-Fixman theory is found to be able to qualitatively describe the end-to-end distance at low salt concentration not only for semiflexible and rigid chains but also for flexible chain. In a low salt region, a flexible polyelectrolyte extends more significantly than a semiflexible chain, in reference of the size of their uncharged counterparts, and in a high salt region, regardless of chain stiffness, a chain attains a dimension comparable to that of its neutral polymer. The chain stiffness influences both the local and the global chain structures. A flexible chain exhibits a zigzagged local structure in the presence of salt ions, and the condensed structure is a disordered, random globule. A semiflexible chain is locally smooth, and the condensed structure is orderly packed, taking a form such as hairpin or toroid. Moreover, the chain stiffness can also affect the nature of the coil-globule transition. The transition occurred in a discrete manner for semiflexible chain, whereas it occurred in a continuous way for flexible chain. This discrete feature happened not only at low salt concentration when a semiflexible chain collapsed but also at high salt concentration when the collapsed chain is reexpanded. At the end, the effects of chain stiffness and salt concentration on the conformation of single polyelectrolytes are summarized in a schematic state diagram. 相似文献
Size-exclusion chromatography (SEC) has been widely used to detect antibody aggregates, monomer, and fragments. SEC coupled
to mass spectrometry has been reported to measure the molecular weights of antibody; antibody conjugates, and antibody light
chain and heavy chain. In this study, separation of antibody light chain and heavy chain by SEC and direct coupling to a mass
spectrometer was further studied. It was determined that employing mobile phases containing acetonitrile, trifluoroacetic
acid, and formic acid allowed the separation of antibody light chain and heavy chain after reduction by SEC. In addition,
this mobile phase allowed the coupling of SEC to a mass spectrometer to obtain a direct molecular weight measurement. The
application of the SEC-MS method was demonstrated by the separation of the light chain and the heavy chain of multiple recombinant
monoclonal antibodies. In addition, separation of a thioether linked light chain and heavy chain from the free light chain
and the free heavy chain of a recombinant monoclonal antibody after reduction was also achieved. This optimized method provided
a separation of antibody light chain and heavy chain based on size and allowed a direct measurement of molecular weights by
mass spectrometry. In addition, this method may help to identify peaks eluting from SEC column directly. 相似文献
The spatial distribution function and second moments of circular freely jointed chain are derived based on an analytical method. The circular Gauss chain, which is simple for long chains, is compared with the circular freely jointed chain, which is exact for short chains. It is shown that the Gauss chain model predicts a more compact configurational distribution than the exact freely jointed chain. The two chain models, however, become closer to each other when the chain length increases. It is found that the difference of the mean square radius of gyration calculated with these two chain models is a constant, independent of the chain length. 相似文献
Finite difference equations can be used to study the responses of biochemical chain reactions at any step of the chain to
an external stimulus. In this study, we developed mathematical models for two hypothetical chain reactions involving loops
to study the responses in the chain as the length of the chain gets longer, so called transient and steady state responses.
The first model is for a chain with a negative feedforward loop, and the second one is for a chain that has a negative feedback
loop. Although both of the models have the same steady state equations and values, we showed that the chain with negative
feedforward and negative feedback loops can produce significantly different behaviors. The former can bring the chain into
oscillations with various periods and eventually chaos when the feedback is strong enough as the length of the reaction chain
increases, whereas the latter is not capable of producing oscillations and more complicated dynamics. 相似文献
1INTRODUCTION The single chain structure of KGM is the ele-mentary acting unit of its biological function and viscoelasticity of mechanical properties.The re-search method of saccharide chain and the com-plexity of its structure have restricted the study on structure-activity relationship.Therefore,the studies concerning KGM both at home and abroad mainly focus on its application,whereas less on its structure.Previous researches were only related to the determination and distribution as… 相似文献
Two-dimensional dynamic Monte Carlo simulations are applied to the protein-like HP chain model to investigate the influence of lateral confinement of the adsorbed chain on adsorption thermodynamics and the ensemble of accessible chain conformations. The structure of the model makes it possible to enumerate all possible chain conformations and thereby define with precision the relation between adsorption thermodynamics and changes in accessible chain conformations resulting from the adsorption process. Lateral confinement of the adsorbed chain is shown to dramatically reduce the number of accessible energy states and unique chain conformations such that, under certain conditions, adsorption is predicted to actually stabilize the chain against denaturation. Lateral confinement preferentially eliminates expanded conformations of the adsorbed chain, shifting the equilibrium from the unfolded state toward the native state. As a result, the conformational entropy of the adsorbed chain is predicted to be lower than that of the chain free in solution. The protein-like HP chain responds to an increase in the hydrophobicity of the sorbent surface by strongly favoring those conformations that minimize the overall internal energy of the system. As a result, adsorption severely destabilizes the native-state conformation. The ability of our simulation results to provide insights into underlying mechanisms for nonspecific protein adsorption is illustrated through qualitative comparison with activity data for hen egg-white lysozyme adsorbed on silica at different surface concentrations. 相似文献
The diMarzio theory has been extended to elucidate the intermolecular and intramolecular phase segregations of a single flexible chain polyelectrolyte in dilute salt-free solutions. At the long chain limit, this theory yields the formalism obtained from the more sophisticated Edward Hamiltonian for polyelectrolyte problems. The calculated phase diagram exhibits the features of a first-order phase transition, with continuous and discontinuous transitions separated by a critical point. Under the discontinuous transition, the polyelectrolyte chain exhibits coexistent expanded and collapsed conformational states, same as intermolecular phase segregation. For a limiting long chain, the mean chain size at critical point is roughly 90% of the size of an ideal chain. Such a result implies that partial contraction within a chain molecule is required to collapse a flexible polyelectrolyte chain. Moreover, the theory predicts that for a longer chain, intramolecular segregated conformations differ significantly from intermolecular segregated conformations, but the difference becomes small for shorter chains. Besides, the charge needed to induce intramolecular segregation is smaller than that of intermolecular segregation for a given chain length. These findings are consistent with previous literature results. 相似文献
The competition between chain propagation and chain termination reactions was shown to play an important role in gas-phase combustion. Conditions under which this competition to a substantial extent determined the critical ignition conditions and the rate of the process were analyzed. Examples that showed that ignoring the role played by chain propagation, chain termination, and chain branching reactions in branched-chain processes led to conclusions that contradicted experimental data were considered. 相似文献
Summary: Procedures are developed to estimate kinetic rate coefficients from available rate data for the free radical solution polymerization of butyl acrylate at 50 °C. The analysis is based upon a complete mechanistic set that includes the formation of mid‐chain radicals through backbiting and their subsequent reaction, and contains no assumptions on how the rate coefficient for cross‐termination of mid‐chain and end‐chain radicals is related to the two homo‐termination rate coefficients. After a thorough statistical analysis, the results of the fitting are combined with other recent literature data to provide a complete set of individual rate coefficients for the butyl acrylate system. Monomer addition to a mid‐chain radical is estimated to be slower than addition to a chain‐end radical by a factor of more than 400. The termination of two mid‐chain radicals is estimated to be two orders of magnitude slower than termination of two end‐chain radicals, with the cross‐termination rate coefficient close to the geometric mean.
Formation of a mid‐chain radical by intramolecular chain transfer to polymer by a chain‐end radical. 相似文献