Asymmetric Peak Research Articles

Characterization of antibody surface properties and selection of a diverse subset for development of a generic size-exclusion chromatography method

Aggregates are an important quality attribute for biotherapeutics because they can affect the safety and efficacy of the drug and they are therefore routinely monitored, mainly with size-exclusion chromatography (SEC). However, there is often a need to tailor a SEC method to a specific molecule. This study describes the development of a generic SEC method tested on 138 antibodies with the variable domains taken from clinical stage antibodies. We report on the discovery of a subset of 12 antibodies that represents the full range of physiochemical properties found in the 138 antibodies. This subset is shown to be an efficient and reliable test set when developing chromatographic methods for antibodies. An understanding of the nature of the analyte-stationary phase interactions was gained when using this set with its wide range of physiochemical properties. Highly hydrophobic antibodies interact strongly with some modern silica hybrid materials causing the elution time to increase significantly, while a hydrophilically modified hybrid surface showed highly reduced interactions for the hydrophobic antibodies. Highly hydrophilic antibodies, on the other hand, exhibited asymmetric peaks to a certain extent on all stationary phases, while the elution time was not affected. The developed SEC method was shown to have satisfactory performance in terms of linearity, repeatability, range, and accuracy and exhibit very narrow distributions of elution time and peak symmetry when testing the 138 antibodies indicating its generic performance.

Appraising separation performance of MOF-808-based adsorbents for light olefins and paraffins

The development and design of efficient olefin/paraffin separation processes requires an understanding of the physicochemical properties of the adsorbent for target gas components. This paper presents experimental assessment of the adsorption characteristics of pristine and modified MOF-808s for ethane, ethene, propane and propene gases. The modification of MOF-808s was carried out using a post-synthesis approach, involving the use of two distinct types of ligands and subsequent addition of Cu metal. The pulse inverse gas chromatography technique at infinite dilution was employed to determine adsorption properties, including Henry's adsorption constants, adsorption enthalpies and entropies of the synthesized MOFs. The highest olefin/paraffin selectivity at 1 bar was identified in MOF-808-His-Cu, with selectivity values of 15.7 for ethene/ethane at 30 °C and 26.2 for propene/propane at 50 °C. This notable selectivity is probably attributable to the formation of π complexes between the olefin and Cu atoms present in the adsorbent. This is evidenced by the distinctive asymmetric chromatogram peak with a long tail, which aligns with their adsorption isotherm concavity. Depending on the molecule and the MOF-808 variant, different isotherm shapes and adsorption capacities were obtained.

A sensitive CsBr/Cs3Bi2Br3I6 heterostructure perovskite gas sensor for H2S detection at room temperature with high stability

In this paper, a new all inorganic lead-free perovskite gas sensor based on CsBr/Cs3Bi2Br3I6 composite was prepared to detect low concentrations H2S gas at room temperature (23 ℃). A two-step method of evaporation and subsequent spraying process was adopted, which makes the vertical growing Cs3Bi2Br3I6 nanoplates uniformly coating on the surface of the CsBr microspheres and forming a heterogeneous structure based conductive path way. The gas sensing test results indicate that the sensor shows good selectivity and reliable repeatability for H2S detection with long-term stability over 60 days, and the lowest concentration detected is 0.5 ppm. The sensor shows satisfactory stability in the range of relative humidity from 44 to 83 %. The in-situ diffuse reflectance infrared Fourier transformations spectroscopy (DRIFTs) results confirm the formation and enhancement process of SO asymmetric telescopic vibration peak due to the introduction of H2S gas, supporting the synergistic mechanism of adsorption-desorption and dynamic defect passivation.

Enhancing Vibration Control in Cable–Tip–Mass Systems Using Asymmetric Peak Detector Boundary Control

In this study, a boundary controller based on a peak detector system has been designed to reduce vibrations in the cable–tip–mass system. The control procedure is built upon a recent modification of the controller, incorporating a non-symmetric peak detector mechanism to enhance the robustness of the control design. The crucial element lies in the identification of peaks within the boundary input signal, which are then utilized to formulate the control law. Its mathematical representation relies on just two tunable parameters. Numerical experiments have been conducted to assess the performance of this novel approach, demonstrating superior efficacy compared to the boundary damper control, which has been included for comparative purposes.

A Rule-Based Automated Chemical Recognition Algorithm for a Multi-Cell Multi-Detector Micro Gas Chromatograph

A chemical recognition algorithm is an integral part of any autonomous microscale gas chromatography (µGC) system for automated chemical analysis. For a multi-detector µGC system, the chemical analysis must account for the retention time of each chemical analyte as well as the relative response of each detector to each analyte, i.e., the detector response pattern (DRP). In contrast to the common approaches of heuristically using principal component analysis and machine learning, this paper reports a rule-based automated chemical recognition algorithm for a multi-cell, multi-detector µGC system, in which the DRP is related to theoretical principles; consequently, this algorithm only requires a small amount of calibration data but not extensive training data. For processing both the retention time and the raw DRP, the algorithm applies rules based on expert knowledge to compare the detected peaks; these rules are located in a customized software library. Additionally, the algorithm provides special handling for chromatogram peaks with a small signal-to-noise ratio. It also provides separate special handling for asymmetrical peaks that may result from surface adsorptive analytes. This work also describes an experimental evaluation in which the algorithm used the relative response of two complementary types of capacitive detectors as well as a photoionization detector that were incorporated into the µGC system of interest. In these tests, which were performed on chromatograms with 21–31 peaks for each detector, the true positive rate was 96.3%, the true negative rate was 94.1%, the false positive rate was 5.9%, and the false negative rate was 3.7%. The results demonstrated that the algorithm can support µGC systems for automated chemical screening and early warning applications.

Mass transport and thermal properties of liquid (melting to boiling point) tungsten: a molecular dynamics simulations

We present molecular dynamics simulation to obtain melting point, structural and atomic transport properties of liquid tungsten. We considered the second-neighbor extended Finnis-Sinclair (EFS) potential as an effective interaction. We find melting temperature (T M) and density in agreement with the reported values. EFS potential gives accurate information for structure factor S(q), pair correlation function g(r), and transport coefficients like self-diffusion coefficient and viscosity upto ∼1.5T M. Large viscosity proposes the rheological nature of liquid W. The self-diffusion coefficient follows the Arrhenius law giving the activation energy 1.22 eV. We find ’shoulder’ in the second peak of S(q), which disappears with temperatures. This characteristic is attributed to the high density and clustering of W-atoms at the near-neighbor distance. The asymmetric first peak in g(r) and shoulder in S(q) proposes that the liquid W exhibits non-normal metallic behaviour. Discrepancy observed in caloric properties for temperature >6000 K is also discussed. We propose that the ’softness’ and broad dip in EFS potential are responsible for these discrepancies, and necessitate the inclusion of angular forces. The single particle correlation is discussed in terms of the velocity autocorrelation function and the long-wavelength limit of S(q) is utilized to derive adiabatic sound velocity in confirmation with reported results.

Deconvolution of DSC peaks of high-temperature phases in an illite/smectite–CaCO3 mixture

Heat flow curves measured in differential scanning calorimetry (DSC) may contain overlapping peaks corresponding to multiple-step processes. To analyze the individual steps in such a process, a deconvolution of the overlapping peaks into the individual peaks is necessary. Using the Frazer-Suzuki function to describe asymmetric peaks, we apply a nonlinear least squares analysis to perform the decomposition of heat flow curves measured for a mixture of an illite/smectite clay with 19.6 wt.% of CaCO3. The curves contain two overlapping peaks associated with the crystallizations of gehlenite and anorthite in the temperature interval from 900 °C to 1050 °C. Several versions of the decomposition analysis may be used, depending on the number of optimized parameters. These may range from four to all eight parameters (four for either peak). We applied the versions with seven and eight fitting parameters, yielding results that are in very good agreement with the experimental data.

DFT-Based Calculation of Molecular Hyperpolarizability and SFG Intensity of Symmetric and Asymmetric Stretch Modes of Alkyl Groups.

Vibrational sum frequency generation (SFG) spectroscopy has been extensively used for obtaining structural information of molecular functional groups at two-dimensional (2D) interfaces buried in the gas or liquid medium. Although the SFG experiment can be done elegantly, interpreting the measured intensity in terms of molecular orientation with respect to the lab coordinate is quite complicated. One of the main reasons is the difficulty of determining the hyperpolarizability tensors of even simple molecules that govern their SFG responses. The single-bond polarizability derivative model has been proposed to estimate the relative magnitude of SFG-active hyperpolarizability by assuming that the perturbation associated to each vibration is negligible. In this study, density functional theory was used to calculate the polarizability and dipole derivative tensors of the CH3 stretch mode of CH3I, CH3CH2I, CH3OH, and CH3CH2OH. Then, the hyperpolarizability tensors of symmetric and asymmetric vibration modes were calculated considering the Boltzmann distribution of representative conformers, which allowed us to theoretically calculate their SFG intensities at all polarization combinations as a function of the tilt angle of the CH3 group with respect to the surface normal direction. Then, the ratios of the calculated SFG intensities for the CH3 symmetric and asymmetric stretch peaks used in experimental studies for the CH3 tilt angle determination were compared. This comparison clearly showed that the effect of vibrational coupling among neighboring functional groups is significant and cannot be assumed to be negligible. This study presents new parameters that can be used in determining the average tilt angle of the CH3 group at the 2D interface with SFG measurements as well as limitations of the method.

Enhancing enantiomeric and diastereomeric separations: A single chromatograph approach for two-dimensional heart-cut methodology

A high-performance chromatograph was adapted and reconfigured to establish a two-dimensional methodology for separations that are not easily achievable using a single enantioselective column. Allethrin, a pyrethroid used widely as a pesticide in domestic environments, was chosen as the model analyte. With three chiral centers, it has eight stereoisomers and is considered one of the more difficult chiral separations. Diastereomeric separation was achieved in the first dimension using a shape-selective stationary phase based on ultrapure porous graphitic carbon (particle diameter, 3 μm) in the reversed phase mode. Advanced asymmetric bidirectional peak functions (half-Gaussian modified Gaussian and exponentially modified Gaussian) were employed to extract overlapping peak areas. The four diastereomeric peaks were heart-cut and sent to the second dimension online using a standard six-port 2-position rotary valve. Enantiomeric separation was attained in the second dimension using an immobilized-cellulose tris(3,5-dichlorophenylcarbamate) column (3 μm) with chromatographic resolutions >2.7 for all enantiomeric pairs. The second dimension method was developed using the information from circular dichroism detection. The baseline separation of seven peaks of allethrin in a single dimension was also demonstrated using (2-hydroxypropyl)-β-cyclodextrin. The enantiomeric purity of a purified formulation of allethrin in a commercial pesticide was validated using the developed 2D approach.

Impact of electroplating salt (AgNO3) concentration on the morphological, optical, electrical and thermoelectric properties of silver assisted electrochemically etched silicon nanowires (SINWs)

Silicon nanowires (SINWs) are fabricated through silver assisted electrochemical etching route at room temperature. Very high yield vertically aligned SINWs are obtained through this electrochemical etching route. The effect of electroplating salt concentration on the properties of SINWs is investigated. Surface morphology shows grass like structures with increase of length and decrease of diameter with increasing salt concentration. Atomic force microscopy reveals increased surface roughness. UV–Visible spectra show reduced reflectivity enabling the material to be efficient for antireflection coatings. Photoluminescence spectra exhibit multiband transitions. Raman spectra show asymmetric peak broadening with peak downshift. Electrical properties display enhancement of SINWs current with higher AgNO3 concentration due to increased surface mediated effects. Current - voltage characteristics follow thermionic emission model. Samples exhibit space charge limited conduction at higher bias voltages due to presence of traps or crystal imperfections. Prepared samples are also investigated for thermoelectric properties and the results show enhanced Seebeck coefficient with increasing AgNO3 concentration.

The influence of transfer distance and pace of work on foot positioning strategies and low back loading in a manual material handling task

Foot positioning strategies are a key parameter in manual materials handling. The objective of this study was to assess the effects of transfer distance, pace and foot positioning on low back loading. Sixteen handlers performed a free handling task with conditions of pace (self-selected and 25% faster), distance (1.5 m, 1.0 m and 0.5 m), height (near-ground and above-waist levels), and mass (10 kg and 20 kg). A linear mixed model was used to evaluate the effects of mass, distance, pace and height on foot positioning occurrences. A non-parametric test (nparLD) was used to evaluate the effects of Pace × Foot positioning and Distance × Foot positioning on L5/S1 sagittal and asymmetrical moments. Positioning the feet aside from the lifting pallet was more prevalent when transferring at shorter transfer distances, high lifting height, and faster pace. When the feet were oriented aside the lifting area, asymmetrical peak moments were slightly higher when transferring at short distance. Facing the lifting pallet may ensure load symmetry, but orienting the feet aside may help to adapt to fast pace or short transfer distance.

Theory of Photoluminescence Spectral Line Shapes of Semiconductor Nanocrystals.

Single-molecule photoluminescence (PL) spectroscopy of semiconductor nanocrystals (NCs) reveals the nature of exciton-phonon interactions in NCs. Understanding the homogeneous spectral line shapes and their temperature dependence remains an open problem. Here, we develop an atomistic model to describe the PL spectrum of NCs, accounting for excitonic effects, phonon dispersion relations, and exciton-phonon couplings. We validate our model using single-NC measurements on CdSe/CdS NCs from T = 4 to 290 K, and we find that the slightly asymmetric main peak at low temperatures is comprised of a narrow zero-phonon line (ZPL) and acoustic phonon sidebands. Furthermore, we identify the specific phonon modes that give rise to the optical phonon sidebands. At temperatures above 200 K, the spectral line width shows a stronger dependence upon the temperature, which we demonstrate to be correlated with higher order exciton-phonon couplings. We also identify the line width dependence upon reorganization energy, NC core sizes, and shell thicknesses.

4U 1626−67 returns to spin-down: timing features toe the line

ABSTRACT We present a comprehensive analysis of X-ray pulsar 4U 1626−67 during its current spin-down (2SD) state, following a recent torque reversal. Since its discovery, this ultra-compact binary has experienced multiple torque states, transitioning from spin-up (1SU) during 1977–1990 to spin-down (1SD) during 1990–2008, and again spin-up (2SU) until 2023. From Nuclear Spectroscopic Telescope ARray observation of May 2023, we have investigated the timing and spectral properties of this pulsar during its 2SD phase, while also comparing them with previous spin-up-down states. For energies up to 8 keV, a distinct bi-horned pulse profile was observed during the spin-up phase, while several substructures emerged during spin-down. Beyond 8 keV, a broad asymmetric peak was consistently observed across all torque states. The pulse fraction during the 2SD phase was higher than that during 2SU phase. A prominent ∼46.8 mHz quasi-periodic oscillation has been exclusively detected during the spin-down phase. The broad-band spectrum during the 2SD phase is described by empirical Negative and Positive power-law with Exponential cutoff model, cyclotron absorption feature and its first harmonic. The spectrum during 2SU phase requires an additional blackbody component and asymmetry in the cyclotron absorption line. A significant flux drop by a factor of ∼3 in the 2SD was observed.

High-Temperature Dielectric Relaxation and Electric Conduction Mechanisms in a LaCoO3-Modified Na0.5Bi0.5TiO3 System.

This research study examines the high-temperature dielectric relaxation and electric conduction mechanisms in (x)LaCoO3-(1 - x)Na0.5Bi0.5TiO3 samples, where x is 0.05, 0.10, and 0.15. The findings demonstrate that all the samples exhibit two dielectric transitions: first, a frequency-dispersive shoulder at a lower temperature (Ts) around 425-450 K, which is associated with polar nanoregions (PNRs), and second, from ferroelectric to paraelectric transition at the Curie temperature (Tc) approximately between 580 and 650 K. The impedance analysis reveals the negative temperature coefficient of resistance behavior of the specimens. The broad and asymmetric relaxation peaks obtained from modulus spectroscopy demonstrate a wide range of relaxations, suggesting non-Debye-type behavior. Furthermore, the conductivity studies provide insights into understanding the transport phenomena in the samples. The oxygen vacancies resulting from the addition of LaCoO3 into the Na0.5Bi0.5TiO3 ceramics are responsible for the relaxation and conduction processes, and the charge carrier is doubly ionized oxygen ion vacancies. All samples except for LCNBT10 at 1 kHz exhibit a negative magnetodielectric response.

Simultaneous Analysis of Flumethasone Pivalate and Clioquinol in the Presence of Phenoxyethanol Preservative in Their Pharmaceuticals Using TLC and UHPLC Methods

Two novel separation methods have been presented for the concurrent assessment of flumethasone pivalate (FP) and clioquinol (CL) in their combinations in ear drop formulations or in the presence of phenoxyethanol preservative (PEP) in their cream formulations. The first method is an innovative thin-layer chromatographic (TLC) method. The optimal separation was accomplished via silica gel aluminum plates F254, with a mixture of benzene, ethyl acetate and formic acid (5:5:0.2, in volumes) as the mobile system. In Method II, a new ultra-high-performance liquid chromatographic method (UHPLC) with a photodiode array detector (PDA) was presented. A reversed-phase inertsil ODS 5 µm C 18 packed column (100 Å, 4.6 mm internal diameter (I.D.) × 50 mm) at 30 °C was employed. Elution was completed in 3 min. Unfortunately, greener solvents were tested as a mobile phase, but an asymmetric peak for CL was noted. In addition, the new UHPLC method has a priority over the old HPLC one by Sayed et al., 2014, in terms of quickness and avoiding interference from the PEP preservative. Concerning the TLC method, the novel TLC method has the advantage of preventing the interference of PEP. This paper represents the first analytical approach for the concurrent assay of FP and CL in the presence of the preservative phenoxyethanol in the cream formulation.

Double Lorentzian lineshape for asymmetric peaks in photoelectron spectroscopy

This paper addresses the challenges of fitting asymmetric photoelectron peaks by showing that the use of the double Lorentzian (DL) line shape usually leads to high-quality, reliable, and reproducible fits. In contrast to the Doniach-Sunjic (DS) line shape, used to fit asymmetric peaks, the DL distribution is integrable and produces higher-quality fits. The functional form of the DL is described in detail; examples of the application of the DS line shape to fit transition metals and one transition metal oxide are shown. The transition from symmetric Voigt functions, used to fit many photoelectron peaks, to asymmetric DL functions is smooth and easy. The DL is encompassed in the freely available AAnalyzer software (https://xpsoasis.org/download). By using the DL, the number of free peak parameters reduces notably, thereby improving the stability of the fitting process, reducing the uncertainties of peak parameters, and improving the reproducibility of results from different operators.

Insight note: X‐ray photoelectron spectroscopy (XPS) peak fitting of the Al 2p peak from electrically isolated aluminum foil with an oxide layer

X‐ray photoelectron spectroscopy (XPS) is the most widely used and important method for chemically analyzing and speciating surfaces. XPS has surface sensitivity (5–10 nm), is quantitative, and is able to probe the oxidation states of the elements at surfaces. However, during the past few years, a great deal of incorrect XPS data analysis has entered the scientific literature. Accordingly, efforts, including this Insight Note, are being made to provide tutorial information to the scientific community. Aluminum is a scientifically and technologically important element. Here we discuss approaches for fitting the Al 2p peak envelope from a sample of aluminum foil with a thin layer of oxide on it. Signals from the metal and oxide are present. We discuss methods for electrically isolating (or not isolating) the sample during data acquisition, the choice of the baseline, fitting the oxide peak with one or two synthetic peaks, and fitting the metal signal with two symmetric or two asymmetric peaks. The thickness of the oxide is calculated based on the areas of the oxide and metal signals.

Spin wave dispersion of ultra-low damping hematite ( α−Fe2O3 ) at GHz frequencies

Low magnetic damping and high group velocity of spin waves (SWs) or magnons are two crucial parameters for functional magnonic devices. Magnonics research on signal processing and wave-based computation at GHz frequencies focused on the artificial ferrimagnetic garnet ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ (YIG) so far. We report on spin wave spectroscopy studies performed on the natural mineral hematite ($\ensuremath{\alpha}{\text{-Fe}}_{2}{\text{O}}_{3}$), which is a canted antiferromagnet. By means of broadband GHz spectroscopy and inelastic light scattering, we determine a damping coefficient of $1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and magnon group velocities of a few 10 km/s, respectively, at room temperature. Covering a large regime of wave vectors up to $k\ensuremath{\approx}24\phantom{\rule{0.16em}{0ex}}\mathrm{rad}/\textmu{}\mathrm{m}$, we find the exchange stiffness length to be relatively short and only about 1 \AA{}. In a small magnetic field of 30 mT, the decay length of SWs is estimated to be 1.1 cm similar to the best YIG. Still, inelastic light scattering provides surprisingly broad and partly asymmetric resonance peaks. Their characteristic shape is induced by the large group velocities, low damping, and distribution of incident angles inside the laser beam. Our results promote hematite as an alternative and sustainable basis for magnonic devices with fast speeds and low losses based on a stable natural mineral.

Impact of stress induced anisotropic modifications on magneto-impedance behaviour of rapidly quenched CoFe based microwires

The investigation addresses the role of Al in devitrification stage of a series of (Co94Fe6)72.5Si12.5−xAlxB13Cr2 (X = 0, 2, 4, 6 at%) rapidly quenched microwires. The incorporation of Al displayed reduction in primary onset and activation energy (A.E) while it facilitated widening of span between primary and secondary crystallization onsets. The Giant Magneto-Impedance (GMI) behaviour was influenced by Al concentration as well as applied uniaxial stress. Optimal Al containing alloy (x ∼ 2 at%) displayed signature of asymmetric dual peak at the operating frequency of 1 MHz and its prospective application as a very low magnetic field sensor in pre-stressed condition. However, with increasing stress, the asymmetric character transformed to symmetric dual peak which is attributed to the transition of transverse anisotropy to circular anisotropy via helical anisotropy. High stress sensitivity has been attributed to either dominant transverse or circular anisotropy. The transition of stress induced anisotropies in the microwires has been portrayed schematically to elucidate the transitions.

Unveiling a hidden multiferroic state under magnetic fields in BaHoFeO4

In this paper, we report field-induced ferroelectricity in ${\mathrm{BaHoFeO}}_{4}$ in a narrow range of applied magnetic fields ($1.5\phantom{\rule{4.pt}{0ex}}\text{T}\ensuremath{\le}H\ensuremath{\le}5\phantom{\rule{4.pt}{0ex}}\text{T}$). Magnetization measurements reveal three magnetic anomalies, the first one at ${T}_{N}^{\text{Fe}}\ensuremath{\sim}52.8$ K, the second one at ${T}_{{N}_{2}}\ensuremath{\sim}36.4$ K, and the third one at ${T}_{N}^{\text{Ho}}\ensuremath{\sim}6.8$ K, corresponding to the antiferromagnetic ordering of ${\mathrm{Fe}}^{3+}$, a possible spin structure change of ${\mathrm{Fe}}^{3+}$, and the antiferromagnetic ordering of ${\mathrm{Ho}}^{3+}$ sublattices, respectively. Surprisingly, the heat capacity data did not show any anomaly at ${T}_{N}^{\text{Fe}}$ but exhibited a broad maximum at ${T}_{N}^{\text{Ho}}$. Below 40 K, isothermal magnetization measurements indicate a metamagnetic transition at 1.5 T. The temperature-dependent dielectric measurements performed below 1 T reveal two anomalies, around 6 and 36 K, corresponding to ${\mathrm{Ho}}^{3+}$ ordering and a possible change in the magnetic phase of the Fe sublattice. These anomalies disappear at higher magnetic fields, and a different dielectric anomaly appears above the metamagnetic transition with a broad asymmetric peak around 13 K (${T}_{P}$), which shifts to higher temperatures, reaches a maximum under 2 T, and then is suppressed further on increasing the magnetic field up to 9 T. A switchable electric polarization appears below 25 K and above the metamagnetic transition field ($H\ensuremath{\ge}1.5$ T). Intriguingly, the polarization disappears above 5 T. The presence of electric polarization in intermediate magnetic fields and its strong magnetic field dependence are interesting and make this material unique.