Nonlinear Concentration Dependence Research Articles

A new coaxial flow-through probe for electromembrane extraction of methadone from clinical samples on-line coupled to capillary electrophoresis

BackgroundA new design of a flow-through coaxial electromembrane extraction (EME) probe that can be on-line coupled with CE instrument is described and tested. The supporting base of the probe is a PDMS microchip with T-shaped channels into which two coaxially arranged capillaries for inlet and outlet solutions are inserted. The extraction part of the probe is a porous polypropylene hollow fiber, sealed at one end and modified with nitrophenyloctyl ether (NPOE) extraction fluid. The internal volume of the extraction probe is 1.1 μL. ResultsThe EME probe was tested on laboratory samples and methadone was extracted into 3.0 M AcOH as acceptor. The concentration dependence was linear in the range of 0.1–1.0 μg mL−1 at EME 300 s/150 V and in the range of 0.5–10.0 μg mL−1 at EME 100 s/150 V. The enrichment factor was greater than 30 and the LOD was 0.21 μg mL−1. The EME of methadone in clinical samples showed a linear concentration dependence in human urine and a nonlinear concentration dependence in serum. The distribution of methadone in each phase of the extraction system and the effect of extraction membrane thickness on the enrichment factor were studied. The EME probe can be applied repeatedly. SignificanceThe supporting base of EME probe and flow gating interface (FGI) are realized by a microfluidic PDMS microchips cast in the laboratory without the use of lithography. A supporting PDMS chip with coaxially arranged capillaries and extraction membrane forms a compact analytical instrument. The entire EME/CE analysis process is performed on a laboratory-made instrument and automated by LabView.

An innovative detection technique for capillary electrophoresis: Localized terahertz emission-time domain spectroscopy

Terahertz (THz) time-domain spectroscopy (TDS) is a recently emerging analysis method which can provide unique information on molecular vibration and rotation induced by inter/intra-molecular interactions. Although the application of THz-TDS to high-performance microscale separation methods like capillary electrophoresis (CE) has been anticipated, it has been hindered due to the diffraction limit of THz wave (typically, hundreds µm). In order to realize CE-THz-TDS, in this study, we placed a narrow open-tubular capillary on the surface of a GaAs semiconductor substrate as a “localized” THz-emitter. By focusing femtosecond pulsed laser beams at the surface of a gallium arsenide (GaAs) substrate closest to the capillary, THz waves were locally generated to pass through the capillary, so that THz absorbance spectra were obtained from the capillary which has narrower inner diameter than the diffraction limit. As a typical result from acetic acid analysis in the CE-THz-TDS platform, information on the refractive index and extinction coefficient was obtained, which showed non-linear and linear concentration dependence, respectively, similar to conventional THz-TDS using large liquid cells. Finally, CE-THz-TDS analysis of several carboxylic acids was demonstrated. Two acids were successfully separated and detected with THz-TDS, where their electrophoretic mobility values were estimated as close to those obtained with conventional contactless conductivity detection. Our proposed CE-THz-TDS showed the potential for the systematic analysis of inter/intra-molecular weak interactions like hydrogen bonds, which are unable to obtain with conventional detectors.

Nitrate detection at Pd-Cu-modified carbon screen printed electrodes

Carbon nanofibers (CNF) and single-walled carbon nanotubes (SWCNT) screen printed electrodes (SPEs) are used for bi-metal, Pd-Cu, modification. Pd nanoparticles (NPs) are deposited first on the pre-reduced carbon SPEs by means of a spontaneous electroless process in the absence of solute reductants. Copper is deposited in a next step under galavanostatic conditions. For both electrodes the Pd deposit consists of NPs with sizes in the 10-ths of nm range with a much denser population and larger amount of the metallic phase in the SWCNT case. The copper deposit on the Pd-modified SPEs differs markedly depending on the type of the underlying substrate with a three times larger mass ratio Pd/Cu of the deposited metals for the SWCNT electrode compared to the CNF one. Nitrate detection is studied on the Cu- and Pd-Cu-modified electrodes in slightly acidic sulfate solution by means of linear sweep voltammetry. The comparison of the mono- and bi-metal- modified electrodes shows a significant enhancement of the nitrate-related reductive currents at the Pd-Cu-modified carbon SPEs. Between the two bi-metal modified electrodes the SWCNT-based one has a higher sensitivity and a larger concentration range of reproducible electroanalytical signal. The non-linear concentration dependence of the nitrate reduction peak currents is modeled by means of a Langmuir type of equation and used for recovery measurements. The Pd-Cu-modified SWCNT-based SPE shows a good stability of the metallic phases over extended nitrate reduction measurements series.

Mutual Diffusivities of Binary Mixtures of Water and Poly(ethylene) Glycol from Heterodyne Dynamic Light Scattering

In the present study, the mutual diffusivity D11 in binary mixtures of water with technical polydisperse poly(ethylene) glycol (PEG) blends with molar masses of (1000, 4000, or 6000) g⋅mol−1 as well as with a purified monodisperse PEG homolog with a polymerization number of 21 and a molar mass of 943 g⋅mol−1 was investigated by heterodyne dynamic light scattering (DLS) as a function of temperature and/or PEG concentration. The measured D11 for technical PEG 1000 and pure PEG 943 match within the experimental uncertainties and agree well with the available literature data. D11 decreases with increasing molar mass of the PEGs at constant temperature and weight fraction. For the technical PEG 4000, it could be shown that D11 increases with increasing temperature and exhibits a nonlinear concentration dependence. This study demonstrates that heterodyne DLS can be applied for the reliable determination of D11 of aqueous solutions of PEGs over a broad range of PEG weight fractions from 0.01 up to the solubility limit with an average expanded uncertainty (k = 2) of 5.5 %. Moreover, the results show that monodisperse PEGs are suitable model systems for studying the diffusion behavior of bimodal and also multimodal particulate systems.

Myosin II Adjusts Motility Properties and Regulates Force Production Based on Motor Environment.

Myosin II has been investigated with optical trapping, but single motor-filament assay arrangements are not reflective of the complex cellular environment. To understand how myosin interactions propagate up in scale to accomplish system force generation, we devised a novel actomyosin ensemble optical trapping assay that reflects the hierarchy and compliancy of a physiological environment and is modular for interrogating force effectors. Hierarchical actomyosin bundles were formed in vitro. Fluorescent template and cargo actin filaments (AF) were assembled in a flow cell and bundled by myosin. Beads were added in the presence of ATP to bind the cargo AF and activate myosin force generation to be measured by optical tweezers. Three force profiles resulted across a range of myosin concentrations: high force with a ramp-plateau, moderate force with sawtooth movement, and baseline. The three force profiles, as well as high force output, were recovered even at low solution concentration, suggesting that myosins self-optimize within AFs. Individual myosin steps were detected in the ensemble traces, indicating motors are taking one step at a time while others remain engaged in order to sustain productive force generation. Motor communication and system compliancy are significant contributors to force output. Environmental conditions, motors taking individual steps to sustain force, the ability to backslip, and non-linear concentration dependence of force indicate that the actomyosin system contains a force-feedback mechanism that senses the local cytoskeletal environment and communicates to the individual motors whether to be in a high or low duty ratio mode. The online version contains supplementary material available at 10.1007/s12195-022-00731-1.

Aqueous-phase reactive species formed by fine particulate matter from remote forests and polluted urban air

Abstract. In the aqueous phase, fine particulate matter can form reactive species (RS) that influence the aging, properties, and health effects of atmospheric aerosols. In this study, we explore the RS yields of aerosol samples from a remote forest (Hyytiälä, Finland) and polluted urban locations (Mainz, Germany; Beijing, China), and we relate the RS yields to different chemical constituents and reaction mechanisms. Ultra-high-resolution mass spectrometry was used to characterize organic aerosol composition, electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping technique was applied to determine the concentrations of ⚫OH, O2⚫-, and carbon- or oxygen-centered organic radicals, and a fluorometric assay was used to quantify H2O2. The aqueous H2O2-forming potential per mass unit of ambient PM2.5 (particle diameter < 2.5 µm) was roughly the same for all investigated samples, whereas the mass-specific yields of radicals were lower for sampling sites with higher concentrations of PM2.5. The abundances of water-soluble transition metals and aromatics in ambient PM2.5 were positively correlated with the relative fraction of ⚫OH and negatively correlated with the relative fraction of carbon-centered radicals. In contrast, highly oxygenated organic molecules (HOM) were positively correlated with the relative fraction of carbon-centered radicals and negatively correlated with the relative fraction of ⚫OH. Moreover, we found that the relative fractions of different types of radicals formed by ambient PM2.5 were comparable to surrogate mixtures comprising transition metal ions, organic hydroperoxide, H2O2, and humic or fulvic acids. The interplay of transition metal ions (e.g., iron and copper ions), highly oxidized organic molecules (e.g., hydroperoxides), and complexing or scavenging agents (e.g., humic or fulvic acids) leads to nonlinear concentration dependencies in aqueous-phase RS production. A strong dependence on chemical composition was also observed for the aqueous-phase radical yields of laboratory-generated secondary organic aerosols (SOA) from precursor mixtures of naphthalene and β-pinene. Our findings show how the composition of PM2.5 can influence the amount and nature of aqueous-phase RS, which may explain differences in the chemical reactivity and health effects of particulate matter in clean and polluted air.

Purification and analysis of a protein cocktail capable of scavenging cell-free hemoglobin, heme, and iron.

Hemolysis releases toxic cell-free hemoglobin (Hb), heme, and iron, which overwhelm their natural scavenging mechanisms during acute or chronic hemolytic conditions. This study describes a novel strategy to purify a protein cocktail containing a comprehensive set of scavenger proteins for potential treatment of hemolysis byproducts. Tangential flow filtration was used to purify a protein cocktail from Human Cohn Fraction IV (FIV). A series of in vitro assays were performed to characterize composition and biocompatibility. The in vivo potential for hemolysis byproduct mitigation was assessed in a hamster exchange transfusion model using mechanically hemolyzed blood plasma mixed with the protein cocktail or a control colloid (dextran 70 kDa). A basis of 500 g of FIV yielded 62 ± 9g of a protein mixture at 170 g/L, which bound to approximately 0.6 mM Hb, 1.2 mM heme, and 1.2 mM iron. This protein cocktail was shown to be biocompatible in vitro with red blood cells and platelets and exhibits nonlinear concentration dependence with respect to viscosity and colloidal osmotic pressure. In vivo assessment of the protein cocktail demonstrated higher iron transport to the liver and spleen and less to the kidney and heart with significantly reduced renal and cardiac inflammation markers and lower kidney and hepatic damage compared to a control colloid. Taken together, this study provides an effective method for large-scale production of a protein cocktail suitable for comprehensive reduction of hemolysis-induced toxicity.

Effect of Co content on magnetic features and SPIN states IN Ni–Zn spinel ferrites

The manuscript contains data on the effect of the Co content on the magnetic properties of Zn0·3Ni0·7Fe2O4 spinels, in which Ni2+ ions are partially substituted by Co2+ ions. Ferrites were produced via solid-state reaction from a mixture of oxides. All samples are single-phase with a spinel-type structure (SG: Fd-3m). The linear increase in the lattice parameters with increasing cobalt content was explained by the difference in ionic radii Co2+/Ni2+. The effect of the Co2+ content on the magnetic characteristics of Ni–Zn ferrites was established. Curie temperature decreased from 419 °C to 326 °C with increasing Co content from x = 0.0 to 0.7, respectively. At the same time, an increase in Ms; Mr and Hc was observed due to the larger magnetic moment of the Co2+ ion in comparison with Ni2+. Non-linear concentration dependence of the magnetic characteristics was discussed in terms of the Co2+ spin states.

Electromagnetic Properties of Composite Materials Based on Nd-Compound Modified Fe-Si-Al Alloy

The investigation of microstructure, optical and electromagnetic properties of powder prepared from Nd-compound doped Al6Si9Fe85 (Alsifer) alloy. The result of energy-dispersive X-ray spectroscopy is an evidence that the complementary Nd-containing Nd-Fe phase is on the surface of Alsifer particles. The magnetic particles distribution histogram in powder after mechanical treatment was plotted and analyzed. The electromagnetic properties (components magnetic permeability and dielectric permittivity) for produced composites with Nd-compound doped Alsifer powder with 50-90% (wt.) was studied. The nonlinear concentration dependence of magnetic and dielectric permittivity versus concentration Nd-compound doped Alsifer particles was observed. The magnetic resonance in composites was detected that shifted in low frequencies with increased magnetic filler concentration. The resonance field, absorption linewidth, g-factor and microwave absorption ability of Nd-compound doped Alsifer powder were determined from FMR experiment.

Acoustic Phonons in Periodical GeSiSn/Si Nanostructures

We apply Raman spectroscopy to study the phonon spectrum in periodical GeSiSn/Si nanostructures with Sn concentration varied from 0 to 20%. In the optical spectral region, an insignificant shift of the phonon mode positions with a variation of the Sn content prevents determination of Sn concentration relying only on the optical phonons behavior. In the acoustic region, we observe the doublets of the folded acoustic phonons, the spectral positions of which undergo the low-frequency shift with increasing the Sn content. The application of the elastic continuum model with the linear approximation of sound velocity via Sn content in GeSiSn layers fails to explain the experimental results. This indicates a nonlinear Sn concentration dependence of sound velocity in GeSiSn layers which describes well the positions of the folded acoustic phonons.

Producing Collagen Micro-stripes with Aligned Fibers for Cell Migration Assays.

The orientation of collagen fibers in native tissues plays an important role in cell signaling and mediates the progression of tumor cells in breast cancer by a contact guidance mechanism. Understanding how migration of epithelial cells is directed by the alignment of collagen fibers requires in vitro assays with standardized orientations of collagen fibers. To address this issue, we produced micro-stripes with aligned collagen fibers using an easy-to-use and versatile approach based on the aspiration of a collagen solution within a microchannel. Glass coverslips were functionalized with a (3-aminopropyl)triethoxysilane/glutaraldehyde linkage to covalently anchor micro-stripes of aligned collagen fibers, whereas microchannels were functionalized with a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO)nonionic triblock polymer to prevent adhesion of the collagen micro-stripes. Using this strategy, microchannels can be peeled off to expose micro-stripes of aligned collagen fibers without affecting their mechanical integrity. We used time-lapse confocal reflection microscopy to characterize the polymerization kinetics of collagen networks for different concentrations and the orientation of collagen fibers as a function of the microchannel width. Our results indicate a non-linear concentration dependence of the area of fluorescence, suggesting that the architecture of collagen networks is sensitive to small changes in concentration. We show the possibility to influence the collagen fibril coverage by adjusting the concentration of the collagen solution. We applied this novel approach to study the migration of epithelial cells, demonstrating that collagen micro-stripes with aligned fibers represent a valuable in-vitro assay for studying cell contact guidance mechanisms.

Increasing valence pushes DNA nanostar networks to the isostatic point

The classic picture of soft material mechanics is that of rubber elasticity, in which material modulus is related to the entropic elasticity of flexible polymeric linkers. The rubber model, however, largely ignores the role of valence (i.e., the number of network chains emanating from a junction). Recent work predicts that valence, and particularly the Maxwell isostatic point, plays a key role in determining the mechanics of semiflexible polymer networks. Here, we report a series of experiments confirming the prominent role of valence in determining the mechanics of a model system. The system is based on DNA nanostars (DNAns): multiarmed, self-assembled nanostructures that form thermoreversible equilibrium gels through base pair-controlled cross-linking. We measure the linear and nonlinear elastic properties of these gels as a function of DNAns arm number, f, and concentration [DNAns]. We find that, as f increases from three to six, the gel's high-frequency plateau modulus strongly increases, and its dependence on [DNAns] transitions from nonlinear to linear. Additionally, higher-valence gels exhibit less strain hardening, indicating that they have less configurational freedom. Minimal strain hardening and linear dependence of shear modulus on concentration at high f are consistent with predictions for isostatic systems. Evident strain hardening and nonlinear concentration dependence of shear modulus suggest that the low-f networks are subisostatic and have a transient, potentially fractal percolated structure. Overall, our observations indicate that network elasticity is sensitive both to entropic elasticity of network chains and to junction valence, with an apparent isostatic point [Formula: see text] in agreement with the Maxwell prediction.

Optoelectronic properties of CaxBa1−xX (X=S, Se and Te) alloys: A first principles investigation employing modified Becke–Johnson (mBJ) functional

Optoelectronic properties of alkaline-earth calcium-barium chalcogenide ternary alloys Ca[Formula: see text]Ba[Formula: see text]S, Ca[Formula: see text]Ba[Formula: see text]Se and Ca[Formula: see text]Ba[Formula: see text]Te have been calculated using first principle-based FP-LAPW methodology employing modified Becke–Johnson (mBJ) exchange-correlation functional. Both the lattice parameter and the bulk modulus vary nonlinearly with dopant concentration in each of these alloy systems. The evolution of a series of thermodynamically stable wide-direct-bandgap ternary alloys as a result of amalgamation of indirect-bandgap homo-chalcogen CaX and BaX at Ca-concentrations [Formula: see text] = 0.25, 0.50 and 0.75 is observed. Bonding between calcium and chalcogen is ionic, while that between barium and chalcogen is covalent in nature. Each of the alloy systems show substantial nonlinearity in the concentration dependence of bandgap and the dominant role is played by the volume deformation effect in total bandgap bowing. It is observed that the chalcogen-p of valence band as initial states and Ca-3d as well as Ba-5d states of conduction band as final states play the dominant role in optical transitions. Nature of nonlinear concentration dependence of each of the static optical constants is opposite and critical point is similar to that of bandgap in each of the alloy systems. Several calculated properties are found to agree well with the corresponding experimental findings.

Charge transport in confined concentrated solutions: A minireview

Abstract This Minireview summarizes several recent experiments clouding over prevailing theoretical understanding of charge transport behaviors in electrochemical systems; they are nonlinear concentration dependence of ionic conductivity, ultra-long Debye length in ionic liquids, nonmonotonic double layer charging behavior, and anomalous increase in area specific capacitance with decreasing nanopore size. Theoretical activities reveal that nanoconfinement and high concentration exert strong influence on charge distribution and transport via strong ion-ion correlations and ion-wall interactions. By exemplifying where and why classical theories of charge transport fail, we defy the popular point of view that theoretical electrochemistry is well-established and we are left with applications of these theories only.

Electroanalytical determination of caffeic acid – Factors controlling the oxidation reaction in the case of PEDOT-modified electrodes

The present studies focus on the intrinsic role of poly(3,4-ethylenedioxythiophene) (PEDOT) in electrooxidation of caffeic acid (CA) in view of the application of this electrode material in electroanalytical sensing. Electrosynthesized PEDOT layers with different thickness and different doping counterions are investigated. Based on the scan rate dependence of the voltammetric peak currents it is found that depending on the thickness of the polymer layer different factors, i.e. adsorption for thin layers and diffusion for thick layers, are rate determining. In terms of electroanalytical characteristics it is established that adsorption control provides the opportunity to obtain higher electroanalytical sensitivity in a narrow concentration range of linear response. Diffusion control results in markedly lower sensitivity values but extended range of linearity in the concentration dependence. In the case of adsorption control a hyperbolic equation of the Langmuir/Michaelis–Menten type is suggested to model the experimentally obtained non-linear concentration dependence of the peak currents. The use of a non-linear calibration curve provides an extended concentration range for electroanalytical work under the established adsorption controlled conditions. Doping counterions (polysterene sulfonate and dodecyl sulfate) are found to have no effect on the electroanalytical performance of PEDOT for CA oxidation.

Acquisition of nonlinear kinetics from linear relations: Application on homogeneous transesterification reactions

This paper proposes a fast method to determine kinetic parameters in systems with nonlinear concentration dependencies in equilibrium reactions. Without the use of complicated software, the corresponding parameters can be obtained from linear relations, with a minimum number of experimental data, acquired by semi-batch operation. The underlying theory is given for a general equilibrium reaction A + B ↔ C + D and it is successfully applied for the real case of typical transesterification reactions.The proposed procedure opens the door for easy, i.e., linear, parameter estimation procedures using commercial software as Excel® without the tedious and nerve-racking nonlinear parameter estimation procedures.The presented methodology gives an easy access to forward as well as backward transesterification rate coefficients, which can be used for simulation purpose for non-steady reactor operation and corresponding optimization.

Energetics of mixing and transport phenomena in Cd-X (X=Pb, Sn) melts

We report a quasi-chemical study of the thermodynamic and transport properties of mixing of liquid Cd-Pb and Cd-Sn alloys at 773K. The interaction energy in the alloys is found to be positive which suggests homo-coordination of atoms in the alloys. The viscosities of the alloys at 773K computed from two different approaches exhibit non-linear concentration dependence with the results for Cd-Sn alloy being in very good agreement and satisfactory agreement for Cd-Pb alloy. In lower concentrations of Cd-component, Cd-Pb alloy has larger viscosity and on the other side of concentration, Cd-Sn alloy has larger value. The calculations of inter-diffusion coefficients result in concave diffusion isotherms for the alloys. The higher values of inter-diffusion coefficients for Cd-Sn suggest that Cd and Sn metals tend to mix more readily than Cd and Pb metals do in Cd-Pb alloy. The correlation between viscosity and diffusion implies that the inter-diffusion coefficient is large for low viscous liquid alloy and vice-versa.BIBECHANA 15 (2018) 113-120

Spatially resolved electronic structure of an isovalent nitrogen center in GaAs

Small numbers of nitrogen dopants dramatically modify the electronic properties of GaAs, generating very large shifts in the conduction-band energies with nonlinear concentration dependence, and impurity-associated spatially-localized resonant states within the conduction band. Cross-sectional scanning tunneling microscopy provides the local electronic structure of single nitrogen dopants at the (110) GaAs surface, yielding highly anisotropic spatial shapes when the empty states are imaged. Measurements of the resonant states relative to the GaAs surface states and their spatial extent allow an unambiguous assignment of specific features to nitrogen atoms at different depths below the cleaved (110) surface. Multiband tight binding calculations around the resonance energy of nitrogen in the conduction band match the imaged features. The spatial anisotropy is attributed to the tetrahedral symmetry of the bulk lattice. Additionally, the voltage dependence of the electronic contrast for two features in the filled state imaging suggest these features could be related to a locally modified surface state.

A new mathematical approach to predict the actual drug release from hydrogels

In the present study, we have developed a mathematical model of drug release from a film of highly swellable gelatin based hydrogel mixed with graphene. The model considers the hydrogel volume expansion because of the swelling as well as the non-linear concentration dependence of the diffusion coefficients for the solvent and the drug. An additionl term is considered for the drug diffusion coefficient enabling the model to predict the drug maximum release from the hydrogel. The model parameters are estimated by genetic algorithem and the model resutls are validated using data sets obtained from experiments on Zoledronic acid, the model drug, loaded hydrogel samples made from several weigth ratios of gelatin to graphene crosslinked with different amounts of glutaraldehyde. The model is further developed to mathematically predict the drug conrolled release into in vivo environment and the impact of several factors influencing the release rate into the surrounding environment is investigated.

The Viscosity and Intermolecular Interaction of Organic and Inorganic Hybrid Systems Composed of Chiral Schiff Base Ni(II), Cu(II), and Zn(II) Complexes with Long Ligands, Azobenzene, and PMMA

We have here synthesized new chiral Schiff base Ni(II), Cu(II), Zn(II) complexes (Ni, Cu, Zn) and hybrid materials with azobenzene (AZ) in polymethyl methacrylate (PMMA). Linearly polarized UV light irradiation of these hybrid materials slightly increased their optical anisotropy of AZ as well as the complexes, which were measured with polarized IR and UV-Vis spectra and discussed based on TD-DFT calculations. Non-linear concentration (viscosity) dependence of PMMA solutions about artifact peaks suggested weak intermolecular interactions due to the flexibility of complexes by inserted methylene chains. Molecular modeling indicated that large spaces around complexes in PMMA resulted in easy molecular orientation (Ni > Cu > Zn) as short-term saturation of the UV light irradiation.