Peak shape modeling by Haarhoff-Van der Linde function for the determination of correct migration times: a new insight into affinity capillary electrophoresis

Among the different experimental strategies available in capillary electrophoresis (CE) to determine binding parameters, affinity capillary electrophoresis (ACE) has been the most widely embraced due to its easiness of implementation and of data handling. Ligand-substrate binding constants are thus directly derived from the substrate migration time shifts resulting from the variation of ligand concentration introduced in a background electrolyte. Classically, the substrate migration time is measured on top of the electrophoretic peak, assuming symmetrical peak shape. Depending on both substrate and ligand concentrations that may be required to meet detection sensitivity or complexation conditions, zonal migrations in ACE may, however, produce triangular peak shape, most often due to pronounced electromigration dispersion (EMD), and this may result in positively or negatively erroneous migration time assessments. In this work, EMD distorted triangular peak shapes obtained in the course of host-guest complexation studies were fitted with the Haarhoff-Van der Linde function, allowing better estimation of migration time. The model systems studied were those of beta-cyclodextrin and naproxen, 2-naphthalenesulfonate, or 1-adamantanecarboxylate. The impact of this correction on binding isotherms and binding constant evaluation was exemplified. Furthermore, in situations where the substrate concentration injected by far overtakes that of the ligand in the electrolyte, the interest in this peak shape correction was discussed in connection with the question of whether the free ligand concentration can be still considered equal to the ligand concentration introduced, a question that still remains under debate nowadays.     

Discrete fluctuations and their influence on kinetics of reactions

We study the fluctuations arising from the discrete particle nature of the reactants in chemical processes, which we termdiscrete fluctuations. It is shown how the magnitude of discrete fluctuations is formally obtained from the Van Kampen-expansion of the master equation for the process in question. It is claimed that discrete fluctuations are, at times, an important factor in determining the anomalous kinetics of reaction systems. We specialize to diffusionlimited reactions in systems below their upper critical dimensionality. Some variations of the two-species annihilation process A + B inert, as well as some other examples, are presented and analyzed. Many of these examples prove our point about the dramatic influence of discrete fluctuations on the reaction kinetics. Our theoretical scaling predictions are backed by extensive Monte Carlo simulations.     

Rotational cooling of Li 2 ( 1 S g + ) molecules by ultracold collisions with a helium gas buffer

The very weak interaction of Li₂ with He atoms has been obtained from accurate ab initio calculations and is here analyzed in terms of its anisotropic features. Quantum scattering calculations of the rotational inelastic de-excitation cross sections are carried out using a recently proposed multichannel treatment, the modified variable phase method, implemented by the authors and applied here to ultralow collision energies. General conclusions on the low efficiency of a He buffer gas in cooling down molecular rotations in this system are presented and analyzed.Proceedings of the 11th International Congress of Quantum Chemistry satellite meeting in honor of Jean-Louis Rivail.This work is affectionately dedicated to Prof. Jean-Louis Rivail on the occasion of his university retirement. We wish our friend many more happy years of research and the continued opportunity of guiding young scientists.     

Tunneling motions in the Ar-CHF3 complex

The millimeter wave spectrum of the Ar-CHF₃ complex is measured. The microwave lines are split into two components due to tunneling between three equivalent minima. Aided by ab initio calculations, the bidimensional potential energy surface of the complex is investigated and the rotational dependence of the tunneling splitting is parameterized using an IAM-like approach. The analysis of the microwave data allows us to determine the parameters involved in this rotational dependence. The value obtained are consistent with a large amplitude motion involving a 2π/3 internal rotation of the CHF₃ moiety about its threefold axis of symmetry. Information about the geometry of the intermediate configuration of this large amplitude motions is obtained.     

范德华力对计算机磁头/磁盘超薄气膜承载性能的影响

在纳米间隙条件下,以楔型滑块和双轨式磁头为例,推导出楔型及双轨式磁头范德华力的计算公式,考察了范德华力对计算机磁头/磁盘超薄气膜承载性能的影响.结果表明,范德华力对计算机磁头/磁盘的承载性能影响很大,范德华力可以降低磁头的承载能力,尤其在最小空气间隙小于6 nm时;在相同尺寸的磁头中,双轨式磁头的范德华力小于楔型滑块的范德华力,而前者的承载力大于后者,双轨式磁头的范德华力对其承载性能影响较小.范德华力可以使飞行高度降低,为磁头设计和磁头/磁盘装配的重要依据.     

Deposition behaviors and patterning of TiO2 thin films on different SAMs surfaces from titanium sulfate aqueous solution

Patterning of TiO₂ thin films was successfully obtained on different self-assembled monolayers (SAMs) in aqueous solution by micro-contact printing (μCP) method. The substrates were immersed in an aqueous solution containing titanium sulfate (Ti(SO₄)₂) and hydrogen peroxide for deposition at 80 °C. The growth rates on various surfaces were as follows: sulfonic (–SO₃H) > amino (–NH₂) > methyl (–CH₃) > hydroxyl (–OH). According to the XPS results, SAMs with the terminal groups of –SO₃H and –NH₂ were favorable for the deposition. The TiO₂ film deposited on the SAM with the terminal group of –CH₃ could be easily peeled off. Clearly, TiO₂ patterns were obtained on the prepatterned surfaces of –SO₃H/–CH₃ and –NH₂/–CH₃ SAMs. The deposition mechanism might be relevant to electrostatic interaction, Stern layer, lone pair electrons and Van der Vaals forces. The TiO₂ film was anatase after annealing at 500 °C and comprised particles with an average diameter of ca. 10 nm.     

Mass transfer mechanism in liquid chromatography columns packed with shell particles: Would there be an optimum shell structure?

The mass transfer mechanisms in columns packed with old (55 μm Zipax and 5 μm Poroshell) and recently commercialized shell particles (2.7 μm Halo-C(18) and Kinetex-C(18)) were investigated from a physico-chemical point of view. Combining a model of diffusion in heterogeneous packed beds (effective medium theory) with values of the heights equivalent to a theoretical plate (HETPs derived from the first and second central moments of the elution profiles) and of the peak variances provided by the peak parking method, we demonstrate that columns packed with current shell particles perform better than those packed with fully porous particles in resolving low molecular weight compounds because the eddy diffusion term of the van Deemter equation of the former is markedly smaller. The calculation of eddy diffusion in column beds suggests that the smaller A terms are due to smaller trans-column velocity bias in columns packed with shell particles. We also show that the mass transfer of large molecules (e.g., proteins) is faster when the internal volume accessible to the analyte increases. Therefore, it is suggested that shell particles made of concentric layers with average pore sizes increasing with increasing diameter would provide columns with higher efficiency.     

Hopf-pitchfork bifurcation in van der Pol's oscillator with nonlinear delayed feedback

First, we identify the critical values for Hopf-pitchfork bifurcation. Second, we derive the normal forms up to third order and their unfolding with original parameters in the system near the bifurcation point, by the normal form method and center manifold theory. Then we give a complete bifurcation diagram for original parameters of the system and obtain complete classifications of dynamics for the system. Furthermore, we find some interesting phenomena, such as the coexistence of two asymptotically stable states, two stable periodic orbits, and two attractive quasi-periodic motions, which are verified both theoretically and numerically.     

Crystal structures,antibacterial, antioxidant and nucleic acid interactions of mononuclear,and tetranuclear palladium(II) complexes containing Schiff base ligands

Two new palladium complexes, [Pd(dpbs)Cl] (1) and [Pd₄(dbbs)₄] (2) (where (dpbs)₂ = o,o′-(N,N′-dipicolinyldene)diazadiphenyl disulfide and (dbbs)₂ = N,N′-(1,1′-dithio-bis(phenylene))-bis(salicylideneimine)), have been synthesized and characterized by analytical and spectral (electronic, IR, ¹H, ¹³C spectroscopy) techniques. The structures of 1 and 2 have been solved by single-crystal X-ray diffraction experiments, which indicate distorted square planar coordination geometries around palladium(II) by O, N, and S donors. The metal chelates have been screened for their antibacterial and antioxidant activities, and compared with their respective ligands. The binding properties of the complexes have been studied by electronic absorption, emission spectroscopy, and viscosity measurements. The competitive fluorescence study with ethidium bromide and the effect of iodide concentration on ?uorescence of the complex-DNA system have been investigated. All these experimental results suggest that palladium complexes strongly bind to DNA, presumably via groove binding. The thermodynamic parameters, enthalpy change (ΔH°), and entropy change (ΔS°) were calculated by the Van’t Hoff equation, suggesting hydrogen bonds play a predominant role in the binding of complexes to DNA.