梯度液相色谱保留时间公式在梯形梯度洗脱研究中的应用

根据前期得到的梯度液相色谱保留时间计算公式,在不指定溶剂强度模型形式的前提下,探讨了梯形梯度洗脱的一些特点。对于溶质在梯形梯度坡度上流出时的情形,推导得到溶质流出色谱柱所对应的流动相组成(φ_R)随梯度斜率(B)变化的表达式。该公式表明,在该情形中φ_R将会随着B值的增加而增加。对于溶质在梯形梯度最后一个等度区间流出时的情形,如果初始和终止流动相组成保持不变而仅有梯度的斜率发生变化时,从理论上证明了溶质保留时间(t_R)与梯度斜率的倒数(1/B)之间呈线性关系。实验中以C18色谱柱为固定相,甲醇-水为流动相,联苯为样品,测定了不同流动相组成以及梯形梯度条件下的保留时间,所得到的实验值与理论值吻合,从而验证了理论方法的正确性。     

Theoretical background of monolithic short layer ion-exchange chromatography for separation of charged large biomolecules or bioparticles

The retention and peak spreading in linear gradient elution of charged large biomolecules were investigated by using numerical simulations. Oligo-DNA separation by monolithic anion-exchange chromatography was chosen as a model system. The peak width and the retention were well predicted by using the parameters obtained by gradient elution experiments at different gradient slopes. As the distribution coefficient at the peak retention volume K_R decreases with increasing molecular size, the peak became sharper for larger DNAs. This is due to very large effective charge (binding site) values of large DNAs (20–60). The peak width was well correlated with K_R based on the model equation developed for linear gradient elution of proteins. It was shown that the monolithic disk is best suited for very large charged biomolecule separations at high flow velocities with shallow gradients slopes.     

Upturn effect in the Non-Newtonian intrinsic viscosity of polymer solutions. II. Polyisobutylene in polybutene oil

With an increasing gradient, the intrinsic viscosity of a high molecular weight polyisobutylene (M?_n = 7 × 10⁶) in polybutene oil L.100 (η_s = 5 poise) first drops to a minimum and then rises again. The minimum occurs at β = M[η]₀η_sG/NkT = 240, which is about ten times the value predicted by the dumbbell model. Such a shift to larger gradient is in good agreement with the more realistic necklace model of macromolecules in a good solvent. The increase of intrinsic viscosity after the minimum is nearly linear with the gradient and continues beyond the value at zero gradient. Experiments with capillaries of different length-to-diameter ratios yield identical flow curves so that one may exclude the possibility that the observed upturn is an artifact caused by end effects or time dependence of viscosity.     

Electric field gradient calculation in V2O5

The electric field gradient at the ⁵¹V nucleus in V₂O₅ has been calculated by the Mulliken–Wolfsberg–Helmholtz method. In contrast to the results obtained from crystal field theory, covalency effects in the MO method are shown to give rise to a valence contribution comparable with the lattice contribution. The total electric field gradient correlates with NMR experiments and confirms the adequacy of the method of calculation used.     

Tuning gradient property and initiating gradient photopolymerization of acrylamide aqueous solution of a hydrosoluble photocleavage polysiloxane‐based photoinitiator

A novel hydrosoluble photocleavage polysiloxane photoinitiator W‐Si‐HHMP₂ used for preparing a gradient polymer was synthesized on the basis of 2‐hydroxy‐1‐[4‐(2‐hydroxyethoxy)phenyl]‐2‐methyl propan‐1‐one (HHMP) and aminopolysiloxane. The water solubility of the photoinitiator, the kinetics of photopolymerization, and the self‐floating ability were investigated. This photoinitiator shows relatively good solubility in water and excellent photoinitiating efficiency, and has good floating capability due to lower surface tension and energy of polysiloxane. More importantly, it is proved that the gradient polymer with gradient molecular weight was obtained by controlling the concentration gradient of W‐Si‐HHMP₂ and presented an excellent yellowing resistance. The enrichment of W‐Si‐HHMP₂ on the surface caused by its good self‐floating ability can decrease the dispersion surface energy of gradient polymer film and generate a more hydrophobic surface. The W‐Si‐HHMP₂ can efficiently initiate gradient photopolymerization to prepare gradient materials and has a great potential application in gradient materials. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermosensitive Injectable Gradient Hydrogel-Induced Bidirectional Differentiation of BMSCs

Osteochondral defects threaten the quality of life of patients to a great extent. To simulate gradient changes in osteochondral tissue, a gradient-mixing injection device consisting of a controller and injection pumps is design. Bioactive glass (BG) and gellan gum (GG) are used to prepare thermosensitive injectable gradient hydrogels (B_0.5G, B₁G) with an upper critical solution temperature (UCST) range of 37.7–40.2 °C using this device for the first time. The mechanical properties of gradient hydrogels are significantly better than those of pure GG hydrogels. The gradients in the composition, structure, and morphology of gradient hydrogels are confirmed via physicochemical characterization. Cytocompatibility tests show that hydrogels, especially B_0.5G gradient hydrogels, promote the proliferation of bone marrow mesenchymal stem cells (BMSCs). Most importantly, qRT-PCR shows that the different components in B_0.5G gradient hydrogels simultaneously induce the osteogenic and chondrogenic differentiation of BMSCs. Experimental injection in porcine osteochondral defects indicates that the B_0.5G gradient hydrogel seamlessly fills irregular osteochondral defects in a less invasive manner by controlling the temperature to avoid cellular and tissue damage arising from crosslinkers or other conditions. These results show that thermosensitive injectable B_0.5G gradient hydrogels have the potential for less invasive integrated osteochondral repair.     

Aspects of the “Design Space” in high pressure liquid chromatography method development

The present paper describes a multifactorial optimization of 4 critical HPLC method parameters, i.e. gradient time (t_G), temperature (T), pH and ternary composition (B₁:B₂) based on 36 experiments. The effect of these experimental variables on critical resolution and selectivity was carried out in such a way as to systematically vary all four factors simultaneously. The basic element is a gradient time–temperature (t_G–T) plane, which is repeated at three different pH's of the eluent A and at three different ternary compositions of eluent B between methanol and acetonitrile. The so-defined volume enables the investigation of the critical resolution for a part of the Design Space of a given sample. Further improvement of the analysis time, with conservation of the previously optimized selectivity, was possible by reducing the gradient time and increasing the flow rate. Multidimensional robust regions were successfully defined and graphically depicted.     

Frequency dependence of intrinsic viscosity of macromolecules with finite internal viscosity

In order to explain the observed nonvanishing limiting value of dynamic intrinsic viscosity of polymer solutions at ω = ∞ one has considered the necklace model with finite resistance to the rate of coil deformation introduced long ago by Cerf for the study of gradient dependence of intrinsic viscosity and streaming birefringence. The calculation need not take into account change of hydrodynamic interaction as a consequence of coil deformation because the experimental data are always either obtained at very low gradient or extrapolated to zero gradient so that in the experiment the macromolecule has the same conformation as in the solution at rest. The model indeed yields a finite [η]′_{ω = ∞} in good agreement with experiments on polystyrene in Aroclor. According to the theory [η]′_{ω = ∞}/[η]₀ decreases with increasing molecular weight as M^?1 and M^?1/2 for the free-draining and impermeable coil, respectively. The absolute limiting value [η]_∞′, therefore turns out to be nearly independent of M, at least for small values of internal viscosity. From the observed value [η]_∞′/[η₀] one can obtain the coefficient of internal viscosity of the macromolecule. The value for polystyrene in Aroclor calculated from dynamic experiments on rather concentrated solutions is close to that derived by Cerf from streaming birefringence observations of polystyrene in a series of solvents of widely differing viscosity.     

Induction of a Proton Gradient across a Gold‐Supported Biomimetic Membrane by Electroenzymatic H2 Oxidation

Energy‐transduction mechanisms in living organisms, such as photosynthesis and respiration, store light and chemical energy in the form of an electrochemical gradient created across a lipid bilayer. Herein we show that the proton concentration at an electrode/phospholipid‐bilayer interface can be controlled and monitored electrochemically by immobilizing a membrane‐bound hydrogenase. Thus, the energy derived from the electroenzymatic oxidation of H₂ can be used to generate a proton gradient across the supported biomimetic membrane.     

Preparation and characterization of gradient distribution of silicon in emulsion blend films

In this work, a functional gradient polymeric material derived from silicon-containing acrylate blend emulsion film is prepared in two steps. Firstly, 3-[tris(trimethylsilyloxy)silyl] propyl methacrylate (TRIS)-modified acrylate latex is prepared using multiple emulsifiers by the two-stage semicontinuous emulsion copolymerization method. Next, blend latexes composed of TRIS-containing and TRIS-free acrylate latexes are obtained. Detailed studies on the effects of the film-formation temperature and the glass transition temperature (T _g) differences on the compositional gradient film are conducted. Surface energy analysis shows that silicon elements enriched at the film-air (F-A) interface and T _g differences facilitate the fabrication of silicon gradient in emulsion blend films. Scanning electron microscopy-energy dispersive X-ray further reveals that the concentration of silicon components varies in a gradient-like manner along the overall transaction of the film when the film-formation temperature is 55 °C. However, excessive temperature creates the formation of a segmental gradient distribution of silicon in the emulsion blend films.     

Synthesis of gradient copolymers with complexing groups by RAFT polymerization and their solubility in supercritical CO2

We report the synthesis of new gradient fluorinated copolymers with complexing groups and soluble in supercritical carbon dioxide (scCO₂). Poly(1,1,2,2‐tetrahydroperfluorodecyl acrylate‐co‐acetoacetoxyethyl methacrylate) (poly(FDA‐co‐AAEM)) and poly(1,1,2,2‐tetrahydroperfluorodecyl acrylate‐co‐vinylbenzylphosphonic acid diethylester) (poly(FDA‐co‐VBPDE)) gradient copolymers were synthesized by reversible addition fragmentation chain transfer polymerization in α,α,α‐trifluorotoluene. Poly(1,1,2,2‐tetrahydroperfluorodecyl acrylate‐co‐vinylbenzylphosphonic diacid) (poly(FDA‐co‐VBPDA)) gradient copolymer was efficiently obtained by cleavage of the phosphonic ester groups of poly(FDA‐co‐VBPDE). The cloud points of these gradient copolymers in dense CO₂ were measured in a variable volume view cell at temperatures between 25 and 65 °C. The gradient copolymers show very good solubility in compressed CO₂ with the decreasing order: poly(FDA‐co‐AAEM) ≈ poly(FDA‐co‐VBPDE) > poly(FDA‐co‐VBPDA). Following a green chemistry strategy, poly(FDA‐co‐AAEM) gradient copolymer was successfully synthesized in scCO₂ with a good control over number‐average molecular weight and composition. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5448–5460, 2009     

Analysis of Invertebrate Neuropeptides by RP-HPLC

Abstract

The application of reverse phase-high performance liquid chromatography to the analysis of four synthetic invertebrate neuropeptides is described. Proctolin (Arg-Try-Leu-Pro-Thr), locust adipokinetic hormone (p-Glu-Leu-Asn-Phe-Thr-Pro-Asn-Trp-Gly-Thr-NH₂), crustacean erythrophore concentrating hormone (p-Glu-Leu-Asn-Phe-Ser-Pro-Gly-Trp-NH₂) and mulluscan cardioexcitatory neuropeptide (Phe-Met-Arg-Phe-NH₂) were analyzed on several different reverse phase columns by means of gradient elution with 0.01M KH₂ PO₄, 0.1% H₃PO₄, 0.25N triethylammonium phosphate (TEAP), pH 2.20, or 0.1% trifluoroacetic acid (TFA) versus acetonitrile. Column effluents were monitored at both 254 and 195 nm except in the case of TFA where 254 and 210 nm were monitored. At the lower wavelength computerized background correction was sometimes necessary to correct excessive baseline drift during the course of the gradient run. Best results were obtained on the Supelcosil LC-18DB column with a concave gradient of 90° 40%B over 1 hr at 1.1 ml/min where B[dbnd]0.25N TEAP, pH 2.20, A[dbnd]acetonitrile. With this system less than 5 ng of peptide was detectable. The use of the volatile TFA buffer permitted recovery of peptides from the column effluent by lyophilization.     

Inkjet printing of laminin gradient to investigate endothelial cellular alignment

To investigate the influence of the protein surface-density gradient on endothelial cell alignment, a novel approach for the fabrication of a laminin gradient on gold-coated substrates has been developed in this study. Our approach involves programmed inkjet printing of an alkanethiol (11-mercaptoundecanoic acid, C₁₀COOH, MUA) gradient onto gold-coated substrates, followed by backfilling with 11-mercapto-1-undecanol (C₁₁OH, MUD). The –COOH moieties were activated and then covalently linked with laminin. This treatment led to a surface-density gradient of laminin. Contact angle measurement, X-ray photoelectron spectroscopy (XPS) and fluorescence microscopy were employed to characterize the self-assembled monolayers (SAMs) and protein gradient, respectively. Results proved the feasibility of the fabrication of a protein gradient by using the inkjet printing technique. The self-assembled monolayer gradients displayed a high packing density, as indicated by dynamic contact angle measurement. More importantly, the gradient slope was easily tunable over a significant distance from 20 to 30 mm. The laminin gradient was clearly visible by fluorescence microscopy observation. Endothelial cells cultured on the surface-density gradient of laminin demonstrated a strong alignment tendency in parallel to the gradient. The higher the laminin density the more cells were observed. The result indicates that cell attachment is dependent on the surface density of laminin. This work broadens our methodology to investigate chemical stimuli-induced cell directional alignment. It is potentially important for understanding cell alignment/ingrowth behavior for angiogenesis and implant technology including tissue-engineered structures.     

Modeling of salt and pH gradient elution in ion‐exchange chromatography

The separation of proteins by internally and externally generated pH gradients in chromatofocusing on ion‐exchange columns is a well‐established analytical method with a large number of applications. In this work, a stoichiometric displacement model was used to describe the retention behavior of lysozyme on SP Sepharose FF and a monoclonal antibody on Fractogel SO₃ (S) in linear salt and pH gradient elution. The pH dependence of the binding charge B in the linear gradient elution model is introduced using a protein net charge model, while the pH dependence of the equilibrium constant is based on a thermodynamic approach. The model parameter and pH dependences are calculated from linear salt gradient elutions at different pH values as well as from linear pH gradient elutions at different fixed salt concentrations. The application of the model for the well‐characterized protein lysozyme resulted in almost identical model parameters based on either linear salt or pH gradient elution data. For the antibody, only the approach based on linear pH gradients is feasible because of the limited pH range useful for salt gradient elution. The application of the model for the separation of an acid variant of the antibody from the major monomeric form is discussed.     

Possibilities and Limitations of Computer-Assisted Method Development in HILIC: A Case Study

In the present study, we investigated the possibilities and limitations of computer-assisted method development (CAMD) for the HILIC separation optimization of a mixture of 13 isomeric hydroxy- and aminobenzoic acids on a ZIC-HILIC column. The isocratically obtained Neue and Kuss retention parameters enabled the accurate gradient retention modeling for peaks eluting well within the gradient (mean error of 2.7 %). The prediction errors for peaks eluting at the end of the gradient could be reduced from 8.8 to 6.1 % by implementing the isocratic regime after the gradient into the expression for the gradient retention factor. The prediction of the corresponding peak widths improved significantly for certain compounds and gradient profiles using individual gradient N values for each compound compared to employing a single N value for all compounds and gradient profiles. Two gradient optimization strategies (constructing the R _s map based on individual retention modeling and predictive elution stretching and shifting, PEWS²) resulted in a reasonable separation of the challenging mixture of 13 isomeric hydroxy- and aminobenzoic acids on the ZIC-HILIC column. Overall, the optimization was limited by the steep decrease in N (dropping to the isocratic N value) and corresponding increase in peak width when increasing the gradient time. The discrimination factors d ₀ were used to assess the resolution between peaks varying widely in height. The best separation was found to be obtained via the PEWS² approach. Both the individual retention modeling and PEWS² strategies corresponded to a total instrument time less than 12 h (including equilibration). Finally, it was found that the salt concentration had a significant effect on both the retention and the peak shape of the compounds, resulting in a small “solution domain” at 10 mM. Coupled columns with higher efficiencies are suggested to improve the resolution and robustness of the separation.     

Alternating,gradient, block,and block–gradient copolymers of ethylene and norbornene by Pd–Diimine‐Catalyzed “living” copolymerization

We demonstrate, in this article, the facile synthesis of a broad class of low‐polydispersity ethylene–norbornene (E–NB) copolymers having various controllable comonomer composition distributions, including gradient, alternating, diblock, triblock, and block–gradient, through “living”/quasiliving E–NB copolymerization facilitated with a single Pd – diimine catalyst ( 1 ). This synthesis benefits from two remarkable features of catalyst 1 , its high capability in NB incorporation and high versatility in rendering E–NB “living” copolymerization at various NB feed concentrations ([NB]₀) while under an ethylene pressure of 1 atm and at 15 °C. At higher [NB]₀ values between 0.42 and 0.64 M, E–NB copolymerization with 1 renders nearly perfect alternating copolymers. At lower [NB]₀ values (0.11–0.22 M), gradient copolymers yield due to gradual reduction in NB concentration, with the starting chain end containing primarily alternating segments and the finishing end being hyperbranched polyethylene segments. Through two‐stage or three‐stage “living” copolymerization with sequential NB feeding, diblock or triblock copolymers containing gradient block(s) have been designed. This work thus greatly expands the family of E–NB copolymers. All the copolymers have controllable molecular weight and relatively low polydispersity (with polydispersity index below 1.20). Most notably, some of the gradient and block–gradient copolymers have been found to exhibit the characteristic broad glass transitions as a result of their possession of broad composition distribution. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Direct LC analysis of selected priority pollutants in water at ppb levels

Thirty-two priority pollutants can be analyzed in water with detection limits of 10 ppb by direct liquid chromatography. High sensitivity is obtained by use of an ultra-violet detector at 202 nm and a reverse phase C₁₈ column with a water-acetonitrile gradient that is compatible with two milliliter water samples.     

Deshydratation de l'alun d'ammonium

The formation of the two kinds of partially dehydrated amorphous alum can be explained by the water vapour gradient which appears within the sample during dehydration and by existence of a critical water pressureP _c at the reaction interface. The mechanisms of dehydration at “low” and “high” pressure are described.     

ChemInform Abstract: Structure and Reactivity of Binary Au12Pt Cluster.

An all‐electron scalar relativistic calculation on the geometrical structure and reactivity of Au₁₂Pt cluster is performed by DFT with the generalized gradient approximation at PW91 level.     

Electric field gradients in EuScFe garnets

The electric quadrupole interactions at the octahedral, tetrahedral, and dodecahedral sites in the Eu_3?ySc_2+yFe₃O₁₂ (0 ≤ y ≤ 0.5) garnet system were studied with ⁵⁷Fe and ¹⁵¹Eu Mössbauer spectroscopy. The electric field gradient tensor at the three sites was calculated using a monopole-point-dipole model. It is shown that the dipole contribution to the electric field gradient tensor is not negligible even for very small values of the oxygen dipole polarizability. The importance of the overlap and second-order 4f contributions is discussed.