Experimental study of dielectrophoresis and liquid dielectrophoresis mechanisms for particle capture in a droplet

This work presents a microfluidic system that can transport, concentrate, and capture particles in a controllable droplet. Dielectrophoresis (DEP), a phenomenon in which a force is exerted on a dielectric particle when it is subjected to a non-uniform electric field, is used to manipulate particles. Liquid dielectrophoresis (LDEP), a phenomenon in which a liquid moves toward regions of high electric field strength under a non-uniform electric field, is used to manipulate the fluid. In this study, a mechanism of droplet creation presented in a previous work that uses DEP and LDEP is improved. A driving electrode with a DEP gap is used to prevent beads from getting stuck at the interface between air and liquid, which is actuated with an AC signal of 200 V(pp) at a frequency of 100 kHz. DEP theory is used to calculate the DEP force in the liquid, and LDEP theory is used to analyze the influence of the DEP gap. The increment of the actuation voltage due to the electrode with a DEP gap is calculated. A set of microwell electrodes is used to capture a bead using DEP force, which is actuated with an AC signal of 20 V(pp) at a frequency of 5 MHz. A simulation is carried out to investigate the dimensions of the DEP gap and microwell electrodes. Experiments are performed to demonstrate the creation of a 100-nL droplet and the capture of individual 10-μm polystyrene latex beads in the droplet.     

N‐Linked Glycans of Chloroviruses Sharing a Core Architecture without Precedent

N‐glycosylation is a fundamental modification of proteins and exists in the three domains of life and in some viruses, including the chloroviruses, for which a new type of core N‐glycan is herein described. This N‐glycan core structure, common to all chloroviruses, is a pentasaccharide with a β‐glucose linked to an asparagine residue which is not located in the typical sequon N‐X‐T/S. The glucose is linked to a terminal xylose unit and a hyperbranched fucose, which is in turn substituted with a terminal galactose and a second xylose residue. The third position of the fucose unit is always linked to a rhamnose, which is a semiconserved element because its absolute configuration is virus‐dependent. Additional decorations occur on this core N‐glycan and represent a molecular signature for each chlorovirus.     

Hybrid genetic algorithm–tabu search approach for optimising multilayer optical coatings

Constructing multilayer optical coatings (MOCs) is a difficult large-scale optimisation problem due to the enormous size of the search space. In the present paper, a new approach for designing MOCs is presented using genetic algorithms (GAs) and tabu search (TS). In this approach, it is not necessary to specify how many layers will be present in a design, only a maximum needs to be defined. As it is generally recognised that the existence of specific repeating blocks is beneficial for a design, a specific GA representation of a design is used which promotes the occurrence of repeating blocks. Solutions found by GAs are improved by a new refinement method, based on TS, a global optimisation method which is loosely based on artificial intelligence. The improvements are demonstrated by creating a visible transmitting/infrared reflecting filter with a wide variety of materials.     

Enhancing detectability in CE by combining an isotachophoretic preconcentration with capillary zone electrophoresis in a single capillary

Summary This paper describes a strategy where a major part of a single capillary is filled with sample which when is isotachophoretically (ITP) preconcentrated while a hydrodynamic backpressure is applied to keep the analytes in the capillary. In the subsequent analysis of the test compounds, amitriptyline and metoprolol, capillary zone electrophoresis is used. The concentration limit of detection is lowered at least 170 times. Preliminary results where an ITP-preconcentration is combined with micellar electrokinetic chromatography with a neutral micellar agent is also presented.     

论化学反应动力学中的稳态假设

对单分子气相反应undemann机理提出了一个不用稳态假设的动力学新表述，并指出经典表述中的稳态假设是主观硬性加上的，缺少了一个条件。当反应气体压强变小时，经典表述中虽然应用稳态假设，但实际上是高活性中间产物的近似，并不真正存在稳态。稳态假设的适用性有两种不同的近似本质，一是平衡态近似或真稳态，另一是高活性中间产物近似，应予分辨。过去文献中往往把两者混在一起，这会导致得不到一般性结论，或所得一般性结论会有错误。文中也讨论了在复杂反应中真稳态的存在，而平衡态和真稳态的建立，都需经过一个初期瞬间过程，而高活性中间产物近似没有初期瞬间过程，因为不是一个形成稳态的过程。     

Facile Electrochemical Hydrogenation and Chlorination of Glassy Carbon to Produce Highly Reactive and Uniform Surfaces for Stable Anchoring of Thiolated Molecules

Carbon is a highly adaptable family of materials and is one of the most chemically stable materials known, providing a remarkable platform for the development of tunable molecular interfaces. Herein, we report a two‐step process for the electrochemical hydrogenation of glassy carbon followed by either chemical or electrochemical chlorination to provide a highly reactive surface for further functionalization. The carbon surface at each stage of the process is characterized by AFM, SEM, Raman, attenuated total reflectance (ATR) FTIR, X‐ray photoelectron spectroscopy (XPS), and electroanalytical techniques. Electrochemical chlorination of hydrogen‐terminated surfaces is achieved in just 5 min at room temperature with hydrochloric acid, and chemical chlorination is performed with phosphorus pentachloride at 50 °C over a three‐hour period. A more controlled and uniform surface is obtained using the electrochemical approach, as chemical chlorination is observed to damage the glassy carbon surface. A ferrocene‐labeled alkylthiol is used as a model system to demonstrate the genericity and potential application of the highly reactive chlorinated surface formed, and the methodology is optimized. This process is then applied to thiolated DNA, and the functionality of the immobilized DNA probe is demonstrated. XPS reveals the covalent bond formed to be a C?S bond. The thermal stability of the thiolated molecules anchored on the glassy carbon is evaluated, and is found to be far superior to that on gold surfaces. This is the first report on the electrochemical hydrogenation and electrochemical chlorination of a glassy carbon surface, and this facile process can be applied to the highly stable functionalization of carbon surfaces with a plethora of diverse molecules, finding widespread applications.     

Design and fabrication of 2 kHz nematic liquid crystal variable retarder with reflection mode

ABSTRACT

This study proposes a simple method of designing a high-speed liquid crystal variable retarder (LCVR) with reflection mode. First, a series of simple formulas is provided for analysing the effects of tilt incidence and birefringence of the liquid crystal on the phase retardation and response time of the LCVR. Then, a reflective LCVR is fabricated to validate the theoretical analysis. Measured results show that the response speed can reach 2.7 kHz with a phase retardation of 1 λ. Furthermore, the theoretical curve is close to the measured curve while the incident angle is less than 10°. However, the theoretical and measured values show a considerable difference under a large incident angle. This problem is discussed, and a modified method is given. This work is helpful for the design and fabrication of high-speed LCVR.     

Single Quality Factor for Enthalpy-Entropy Compensation,Isoequilibrium and Isokinetic Relationships

Enthalpy-entropy compensation (EEC) is very often encountered in chemistry, biology and physics. Its origin is widely discussed since it would allow, for example, a very accurate tuning of the thermodynamic properties as a function of the reactants. However, EEC is often discarded as a statistical artefact, especially when only a limited temperature range is considered. We show that the likeliness of a statistical origin of an EEC can be established with a compensation quality factor (CQF) that depends only on the measured enthalpies and entropies and the experimental temperature range. This is directly derived from a comparison of the CQF with threshold values obtained from a large number of simulations with randomly generated Van ‘t Hoff plots. The value of CQF is furthermore a direct measure of the existence of a genuine isoequilibrium or isokinetic relationship.     

Optimization of asymmetric permeation in heterogeneous composite membranes

Asymmetric permeation in two-phase composite membranes with heterogeneous structures represented by a one-dimensional distribution of composition is treated theoretically on the basis of an irreversible thermodynamic transport equation. It is assumed that the permeability of one of the component phases is a monotone function of the activity of permeant while that of the other phase is constant, and that the permeability of the composite membrane is given by the volume average of the resistance coefficient, which is the inverse of permeability. Under these assumptions, it is shown that the optimal membrane which maximizes the degree of asymmetric permeation reduces to a binary laminate membrane. The condition for constructing the optimal laminate membrane is obtained explicitly. Conversely a condition on a desirable membrane component which realizes an arbitrary degree of asymmetric permeation is presented. These results can be applied to the optimal design of a membrane valve which is a chemical analog of a diode. © 1993 John Wiley & Sons, Inc.     

Laplacian of the Hamiltonian Kinetic Energy Density as an Indicator of Binding and Weak Interactions

The kinetic energy is the center of a controversy between two opposite points of view about its role in the formation of a chemical bond. One school states that a lowering of the kinetic energy associated with electron delocalization is the key stabilization mechanism of covalent bonding. In contrast, the opposite school holds that a chemical bond is formed by a decrease in the potential energy due to a concentration of electron density within the binding region. In this work, a topographic analysis of the Hamiltonian Kinetic Energy Density (KED) and its laplacian is presented to gain more insight into the role of the kinetic energy within chemical interactions. This study is focused on atoms, diatomic and organic molecules, along with their dimers. In addition, it is shown that the laplacian of the Hamiltonian KED exhibits a shell structure in atoms and that their outermost shell merge when a molecule is formed. A covalent bond is characterized by a concentration of kinetic energy, potential energy and electron densities along the internuclear axis, whereas a charge-shift bond is characterized by a fusion of external concentration shells and a depletion in the bonding region. In the case of weak intermolecular interactions, the external shell of the molecules merge into each other resulting in an intermolecular surface comparable to that obtained by the Non-covalent interaction (NCI) analysis.     

Simulation of growth and corrosion during the formation of a passive layer

From the analysis of experiments relative to the formation of a passive layer at the Li-solvent interface a model is proposed in order to describe the gross features concerning the growth of this layer. In this model the growth is initiated by chemical reactions partially counterbalanced by a poisoning process. The model which works at a mesoscopic scale is simulated on a two-dimensional lattice. A quantitative analysis of the results shows that this model appears as the superposition of the Eden model which describes the structure of the front and a similar percolation process which determines the properties of the bulk part of the layer as its porosity. A second model in which the corrosion is taken into account is introduced. It is analyzed in a very simple case in which there is no poisoning. The corrosion induces a restructuring in the layer and this gives rise to a porosity in the bulk part of the layer. Some unexpected results are interpreted.     

Fine Structure of Meniscus of a Wetting Liquid

Equilibrium of a capillary meniscus near a wetting film on a solid in a gravitational field is considered. Unlike previous studies, the present study proves that the fine meniscus structure in a gravitational field is a universal feature—it takes place in a wide variety of problems. In the general case, the capillary meniscus is at a certain distance from the wetting film and does not intersect it. The relation for the minimum distance from the arbitrary meniscus to the solid generalizes the Derjaguin formula for a flat slit. An equation that optimally approximates the meniscus with due account of the contribution of the meniscus/film transition region is derived. A refined solution to the problem of a meniscus on a vertical plate is derived within the perturbation theory. Both gravity and nonuniformity of the vertical static film above a capillary–gravitational meniscus do not affect the minimum distance (the influence is less than 0.0001). A general method for solving sophisticated problems of capillary equilibrium in gravitational field is proposed.     

Intrinsic field theory of chemical reactions

An intrinsic principle of least action is presented for the intrinsic dynamism of chemical reactions. Then, as the stationary trajectory, a meta-IRC (intrinsic reaction coordinate) draws a geodesic curve in a rigged Riemannian space. This establishes a geodesic law for the intrinsic dynamism. Moreover, a diagrammatic perturbation theory is formulated for the intrinsic dynamism, and a dynamical interaction between a chemically reacting system and a background system is investigated. Then, the structural stability of the system is discussed using a new concept of the dynamical potential field. An example is given in order to elucidate the present theory.Dedicated to Prof. Hermann Hartmann on the occasion of his 65th birthday.     

Microchip analysis of lithium in blood using moving boundary electrophoresis and zone electrophoresis

The determination of inorganic cations in blood plasma is demonstrated using a combination of moving boundary electrophoresis (MBE) and zone electrophoresis. The sample loading performed under MBE conditions is studied with the focus on the quantitative analysis of lithium. A concentration adjustment takes place when the sample components migrate into the chip during the sample loading step. Using a heart-cutting method, a diluted sample plug is subsequently separated with capillary zone electrophoresis. The excessive dispersion that is typical of the samples with a high ionic strength is thereby prevented. The method can be easily applied to commercially available capillary electrophoresis microchips under the condition that the electroosmotic flow is suppressed. For the first time the lithium concentration is determined in the blood plasma from a patient on lithium therapy without sample pretreatment. Using a microchip with conductivity detection, a detection limit of 0.1 mmol/L is obtained for lithium in a 140 mmol/L sodium matrix.     

Full enzymatic hydrolysis of commercial sucrose laurate by immobilized-stabilized derivatives of lipase from Thermomyces lanuginosa

Sucrose laurate is a detergent that is useful for various biochemical applications because it is a green compound and is easily degradable after hydrolysis with a lipase or esterase. One problem observed in the process of sucrose laurate degradation is that most commercial detergent preparations are impure, necessitating the hydrolysis of all of the sucrose esters present in the preparation, all of them with detergent properties. In this article, a highly active catalyst, which is able to perform the hydrolysis of commercial sucrose laurate, is presented. The use of glyoxyl agarose preparations of a previously aminated Thermomyces lanuginosa lipase (TLL) enabled complete hydrolysis, in less than 30 min, of all of the compounds that comprise the mixture. In addition, this derivative is stable in the presence of 20% ethanol, which is necessary to prevent microbial contamination.     

A method to obtain a near-minimal-volume molecular simulation of a macromolecule, using periodic boundary conditions and rotational constraints

If the rotational motion of a single macromolecule is constrained during a molecular dynamics simulation with periodic boundary conditions it is possible to perform such simulations in a computational box with a minimal amount of solvent. In this article we describe a method to construct such a box, and test the approach on a number of macromolecules, randomly chosen from the protein databank. The essence of the method is that the molecule is first dilated with a layer of at least half the cut-off radius. For the enlarged molecule a near-densest lattice packing is calculated. From this packing the simulation box is derived. On average, the volume of the resulting box proves to be about 50% of the volume of standard boxes. In test simulations this yields on average a factor of about two in simulation speed.     

Induction of Motion in a Synthetic Molecular Machine: Effect of Tuning the Driving Force

Rotaxane molecular shuttles were studied in which a tetralactam macrocyclic ring moves between a succinamide station and a second station in which the structure is varied. Station 2 in all cases is an aromatic imide, which is a poor hydrogen‐bond acceptor in the neutral form, but a strong one when reduced with one or two electrons. When the charge density on the hydrogen‐bond‐accepting carbonyl groups in station 2 is reduced by changing a naphthalimide into a naphthalene diimide radical anion, the shuttling rate changes only slightly. When station 2 is a pyromellitimide radical anion, however, the shuttling rate is significantly reduced. This implies that the shuttling rate is not only determined by the initial unbinding of the ring from the first station, as previously supposed. An alternative reaction mechanism is proposed in which the ring binds to both stations in the transition state.     

Theoretical Definition of a Functional Group and the Molecular Orbital Paradigm

It is the purpose of this review to demonstrate that the empirical classification of the observations of chemistry in terms of the properties assigned to functional groups is a consequence of and is predicted by physics. This is accomplished by showing that the atoms and functional groups of chemistry can be identified with bounded space-filling objects whose properties are defined by quantum mechanics. The quantum mechanical definition of a group is combined with a new pictorial representation of its form to obtain a unified picture which should make it eminently recognizable to chemists. This picture, when combined with the demonstrated ability of these groups to recover the measured properties of atoms in molecules, is offered as one which meets the expectations a chemist associates with the concept of a functional group. The manner in which this physical definition of a group differs fundamentally from models of functional groups based upon molecular orbital theory is discussed.     

A Water-Soluble Polymer-Lumefantrine Conjugate for the Intravenous Treatment of Severe Malaria

Uncomplicated malaria is effectively treated with oral artemisinin-based combination therapy (ACT). Yet, there is an unmet clinical need for the intravenous treatment of the more fatal severe malaria. There is no combination intravenous therapy for uncomplicated due to the nonavailability of a water-soluble partner drug for the artemisinin, artesunate. The currently available treatment is a two-part regimen split into an intravenous artesunate followed by the conventional oral ACT . In a novel application of polymer therapeutics, the aqueous insoluble antimalarial lumefantrine is conjugated to a carrier polymer to create a new water-soluble chemical entity suitable for intravenous administration in a clinically relevant formulation . The conjugate is characterized by spectroscopic and analytical techniques, and the aqueous solubility of lumefantrine is determined to have increased by three orders of magnitude. Pharmacokinetic studies in mice indicate that there is a significant plasma release of lumefantrine and production its metabolite desbutyl-lumefantrine (area under the curve of metabolite is ≈10% that of the parent). In a Plasmodium falciparum malaria mouse model, parasitemia clearance is 50% higher than that of reference unconjugated lumefantrine. The polymer-lumefantrine shows potential for entering the clinic to meet the need for a one-course combination treatment for severe malaria.     

A wall-jet disc electrode for simultaneous and continuous on-line measurement of sodium dithionite, sulfite and indigo concentrations by means of multistep chronoamperometry

In this paper, a multistep chronoamperometric method is presented to measure continuously and simultaneously the concentrations of indigo, sodium dithionite and sulfite for application in textile dyeing processes. The method is based on the oxidation of sodium dithionite and the reduced form of indigo at a platinum disc electrode. Sodium dithionite is oxidized at a potential of 0.3 V versus Ag/AgCl and shows transport controlled steady state currents at a rotating disc electrode and a wall-jet electrode. The latter has been developed for the purpose of the application. Implementation of a wall-jet instead of a rotating disc electrode is much easier and cost-effective. Indigo is oxidized at −0.55 V versus Ag/AgCl to a virtually water insoluble product, which precipitates at the electrode surface. Indigo behaves quasi-reversibly, and is reduced at a potential of −0.9 V versus Ag/AgCl. In order to clean the electrode surface this reduction is used as a step in the multistep sequence. Finally, sulfite is oxidized at a potential of 0.8 V versus Ag/AgCl but did not give rise to well defined transport controlled limiting currents. However, determination of its concentration is still possible within error margins of 5%.