Peak Fitting Research Articles

Demixing and Analysis of Complex Biological Raman Hyperspectra Based on Peak Fitting, Amplitude Trend Clustering, and Spectrum Reconstruction.

To better interpret the Raman spectra from mammalian cells, it is often desirable to reduce their complexity by decomposing them into the spectral contributions from individual macromolecules or types of macromolecules. Diverse methods exist for demixing complex spectra, each with different benefits and drawbacks. However, some methods require a library of component spectra that might not be available, while others are hampered by noise and peak congestion that includes many proximal overlapping peaks. Through rapid fitting of individual peaks in every spectrum of a Raman hyperspectral data set, we have obtained individual peak parameters from which we determined the trends for all the peak amplitudes. We then grouped similar trends with k-means clustering. Then we used the peak parameters of all the peaks in a given cluster to reconstruct a spectrum representative of that cluster. This method produced spectra that were less distorted by unrelated overlapping peaks or noise, were less congested than those in the hyperspectral set, and thereby improved peak identification and macromolecule recognition. We have demonstrated the application of the method with Raman spectra from a perchlorate-polystyrene model system and extended it to complex spectra from methanol-fixed mammalian cells. We were able to recover independent spectra of perchlorate and polystyrene in the model system and spectra pertaining to individual macromolecular types (proteins, nucleic acids, lipids) from the mammalian cell data. We discuss how imperfections in spectral preprocessing and peak fitting can adversely affect the results. In summary, we have provided a proof-of-concept for a novel mixture resolution method with different attributes than extant ones.

Epistatic hotspots organize antibody fitness landscape and boost evolvability

The course of evolution is strongly shaped by interaction between mutations. Such epistasis can yield rugged sequence-function maps and constrain the availability of adaptive paths. While theoretical intuition is often built on global statistics of large, homogeneous model landscapes, mutagenesis measurements necessarily probe a limited neighborhood of a reference genotype. It is unclear to what extent local topography of a real epistatic landscape represents its global shape. Here, we demonstrate that epistatic landscapes can be heterogeneously rugged and this heterogeneity may render biomolecules more evolvable. By characterizing a multipeaked fitness landscape of a SARS-CoV-2 antibody mutant library, we show that heterogeneous ruggedness arises from sparse epistatic hotspots, whose mutation impacts the fitness effect of numerous sequence sites. Surprisingly, mutating an epistatic hotspot may enhance, rather than reduce, the accessibility of the fittest genotype, while increasing the overall ruggedness. Further, migratory constraints in real space alleviate mutational constraints in sequence space, which not only diversify direct paths taken but may also turn a road-blocking fitness peak into a stepping stone leading toward the global optimum. Our results suggest that a hierarchy of epistatic hotspots may organize the fitness landscape in such a way that path-orienting ruggedness confers global smoothness.

Multi-perspective kinetic analysis of plastic blends under thermogravimetric pyrolysis conditions.

Plastic blends were co-pyrolyzed under non-isothermal conditions in a thermogravimetric (TG) analyzer. The co-pyrolysis characteristics and kinetic triplet, i.e., apparent activation energies, reaction models, and preexponential factors, were investigated from different perspectives, including the overall, weight-loss stage, and overlapping complex reaction deconvolution perspective. Fraser Suzuki (FS) deconvolution was adopted for the peak fitting of the differential TG curves. A model-free method and the master plot theory were used to solve the kinetic equations and fit the reaction mechanism models, respectively. The results indicated that the co-pyrolysis of plastic blends (polyvinyl chloride (PVC)/polypropylene, PVC/polystyrene, PVC/acrylonitrile-butadiene-styrene) could not be adequately described using the overall approach or the weight-loss stage approach. The pyrolysis reaction exhibited a complex multistep overlapping reaction mechanism. FS deconvolution identified and separated four pseudo-reactions from the pyrolysis reaction. The kinetic triplet of the separated reactions was estimated and used to establish kinetic rate equations. Mathematical relations were established between the mass loss rate and pyrolysis temperature. The TG curves of the co-pyrolysis of plastic blends can be parameterized and predicted using the overlapping complex reaction deconvolution model. This study can act as a basis for the development of thermal conversion of mixed plastic waste.

Experimental Investigation of the Effect of Microstructure on Coalbed Methane Adsorption Characteristics Affected by Chemical Solvents.

Coalbed methane (CBM) reservoir modification based on chemical solvent treatment could change the coal microstructure, which further affects the adsorption capacity and flow characteristics of this clean energy. Coal samples were extracted by tetrahydrofuran (THF), carbon disulfide (CS2), and hydrochloric acid (HCl). Low-pressure nitrogen adsorption, carbon dioxide adsorption, Fourier transform infrared spectroscopy, and methane isothermal adsorption test were adopted. The variations of pore structure and chemical composition in coal were evaluated by density functional theory, Barrett-Joyner-Halenda model, and peak fitting method, and their impacts on methane adsorption characteristics were studied. Results show that (1) the micropores less than 2 nm show a bimodal distribution. After acidification, micropore specific surface areas of coal samples I and II increase by 16.79% and 11.72%, respectively, while that of coal sample III-HCl decreases by 4.29% closely related to carbonate and silicate minerals in coal. Microporous specific surface areas of sample II-CS2 and III-CS2 affected by solvent rise by 4.28% and 4.17%, respectively. (2) Among the three original coal samples, the highest level of OH-OH hydrogen bonds content is observed. Solvents have a tendency to interact with -CH2 groups, which shorten the length of fat chains and increase the number of branched chains. THF tends to dissolve C-O-C groups and carbonyl C═O groups. Following CS2 treatment, samples II and III show 38.42% and 47.76% decrease in aromatic C═C area, respectively. (3) The methane adsorption capability in three coal samples is I > III > II. Except for sample I-HCl and sample III-THF, other coal samples have a lower methane adsorption capability than raw coal. Methane adsorption is reduced not just by a decrease in the number of micropores but also by aliphatic groups, aromatic structures, and oxygen-containing structures. Relevant results could deliver guiding significance for understanding methane adsorption and flow characteristics in coal after chemical solvent modification.

Optimisation strategies for directed evolution without sequencing.

Directed evolution can enable engineering of biological systems with minimal knowledge of their underlying sequence-to-function relationships. A typical directed evolution process consists of iterative rounds of mutagenesis and selection that are designed to steer changes in a biological system (e.g. a protein) towards some functional goal. Much work has been done, particularly leveraging advancements in machine learning, to optimise the process of directed evolution. Many of these methods, however, require DNA sequencing and synthesis, making them resource-intensive and incompatible with developments in targeted in vivo mutagenesis. Operating within the experimental constraints of established sorting-based directed evolution techniques (e.g. Fluorescence-Activated Cell Sorting, FACS), we explore approaches for optimisation of directed evolution that could in future be implemented without sequencing information. We then expand our methods to the context of emerging experimental techniques in directed evolution, which allow for single-cell selection based on fitness objectives defined from any combination of measurable traits. Finally, we explore these alternative strategies on the GB1 and TrpB empirical landscapes, demonstrating that they could lead to up to 19-fold and 7-fold increases respectively in the probability of attaining the global fitness peak.

Morphological optimization of CuO-Y2O3 BPMO composites for enhanced MIS diode performance

The development of techniques for synthesizing nanomaterials with convertible characteristics has resulted from the need to enhance photodiode performance. In this article, we presented the synthesis of CuO-Y2O3 nanocomposites for optoelectronic applications using feasible low-temperature co-precipitation technique. In A cubic phase structure for pure Y2O3 and a orthorhombic structure for CuO-Y2O3 composite have been proven to exist based on XRD patterns with predominant orientations along the directions (2 2 2) and (1 2 1), respectively. Dual phase polycrystalline structure with cubic and orthorhombic crystals is seen for samples of CuO with Y2O3 of various compositions. In the CuO composite with Y2O3, FESEM images reveal the existence of thorn-like, rectangular, irregular rectangular forms, and discrete shaped particles. The appearance of two predominant stretching vibrations of both CuO-Y2O3 and Y2O3 obtained from the FT-IR spectra at 555 cm−1 and 493 cm−1 respectively. The 75–25 composition of Cu-Y sample has the lowest band-gap energy (1.944 eV), according to UV-DRS spectra. Two significant peaks with binding energies 158.88 eV (for Y3d3/2) and 157.08 eV (for Y3d5/2) are evidenced in the Y3d XPS peak fit. According to the results of the I–V investigation, the p-Si/Al interface contains CuO-Y2O3 nanocomposites, which enhance the MIS diode’s performance. The developed photo-detectors are ideally suited for nano-electronic applications due to their superior optoelectronic characteristics.

Following the propagation of erroneous x-ray photoelectron spectroscopy peak fitting through the literature. A genealogical approach

This study considers how poor x-ray photoelectron spectroscopy (XPS) peak fitting in the scientific literature is both affected by previous precedent and affects future published work. It focuses on a highly cited paper (the “Subject” paper) from a respected journal that contains incorrect S 2p peak fits. This paper was studied in a genealogical fashion vis-à-vis the XPS peak fitting in its “child,” “parent,” “grandparent,” and “great-grandparent” papers. Interestingly, precedents were not followed to a high degree between parent and child papers. However, in many cases, even when the authors of a study did not follow the incorrect precedent that they cited, they still incorrectly fit their data. Thus, not necessarily for good reasons, the effects of poor XPS peak fits on future generations of papers may be less than some experts had expected or feared. In many cases, older papers appear to contain better XPS peak fitting than newer ones.

Reaction kinetics dominated by melt decomposition mechanism: Intrinsic pyrolysis of insensitive HTPE polyurethane and the efficient inter-reaction with AP

The novel insensitive HTPE (hydroxyl terminated polyether) adhesive holds a great potential application to develop the insensitive solid propellants. However, the pyrolysis kinetics and reaction mechanism of HTPE polyurethane are remained unclear. In this experimental investigation, the DTG curve of HTPE polyurethane was effectively deconvoluted into two main reaction stages via Gaussian peak fitting method, and the kinetic parameters for each pyrolysis stage were calculated. The calculation of the reaction mechanism functions indicated that both reaction stages follow an n-order reaction model with a very close n value. The overall pyrolysis process can be expressed as f(α) = (1 - α)ⁿ (n = 1.8 or 1.9). The TG-FTIR-GCMS results of online-collected gaseous products demonstrated that the pyrolysis of HTPE polyurethane is gradually decomposed from the outer layer to the inner layer, rather than being completely dominated by the kinetics of different functional groups. Localized melting of HTPE polyurethane was observed at 150 °C, moreover, it would almost completely transform into the liquid phase before the decomposition reaction occurred. Thus, it is suggested that the distinctive melt decomposition process of HTPE polyurethane alters the chemical environment even turns heat and mass transfer models of internal molecules, ultimately leading to its unique pyrolysis kinetics and reaction mechanisms. Furthermore, HTPE polyurethane could delay the first-stage pyrolysis of ammonium perchlorate (AP), but significantly promote its second-stage pyrolysis process. Therefore, HTPE polyurethane is beneficial in reducing the sensitivity of AP under thermal stimulation as well as promoting its concentrated heat release process.

Reevaluation of XPS Pt 4f peak fitting: Ti 3s plasmon peak interference and Pt metallic peak asymmetry in Pt@TiO2 system

The structural, electronic, and electrochemical properties of noble metals supported on transition metal oxides, such as Pt nanoparticles (NPs) supported on TiO2 (Pt@TiO2), have been extensively studied for their relevance to energy technologies, including photocatalysis, electrocatalysis, and electrochemical energy conversion. As the need to lower the amount of Pt and other noble metals used in energy conversion systems becomes urgent, it is essential to accurately quantify the loading of these metals and electronic density redistribution between them and their supports. X-ray photoelectron spectroscopy (XPS) is widely used for the identification and quantification of chemical species. In particular, fitting of the Pt 4f spectra for Pt@TiO2 is frequently performed to determine the chemical environment and oxidation state of Pt, which strongly affect the physical behavior and catalytic performance of this system. Here, we show that neglecting contributions due to the Pt surroundings and the asymmetry of the Pt metal peak in the line shape fitting can lead to severe mischaracterization of the oxidation state of Pt. We quantify the effects of background contributions that stem from the TiO2 support and discuss how factoring in the strong asymmetry of Pt 4f doublets, which stems from the shake-up type processes, affects the interpretation of Pt 4f XPS line shape.

Microstructural characteristics of aluminosilicate minerals in cement clinker prepared from coal gangue, carbide slag, and desulfurization gypsum

Utilizing solid waste to prepare cement clinker with low-calcium minerals is crucial for the low-carbon evolution of cementitious materials. In this study, a belite-ye’elimite-ternesite cement clinker was prepared using coal gangue, carbide slag, and desulfurization gypsum instead of non-renewable resources. The evolution law of the silica-alumina mineral phase in cement clinker under different calcining temperatures was tested and analysed. The results show that the predominant mineral phases in cement clinker consist of belite, ye’elimite, and ternesite at 1200 °C to 1250 °C. The composition of cement clinker transforms into belite and ye’elimite as the calcination temperature increases to 1300–1400 °C. At 1400 ℃, the content of belite in cement clinker reaches a remarkable 85 %. The results of XPS and NMR spectra showed that the chemical binding energy and chemical shift of Al in the cement clinker changed after calcination, representing the transformation of the aluminate in kaolinite, with [AlO6], to ye’elimite, with [AlO4]. The peak fitting results of 29Si NMR spectra semi-quantitatively describe the transition process of the silicate mineral phase from kaolinite to ternesite and then to belite. Morphologically, the increase in calcination temperature leads to a significant enlargement of the grain size of belite in cement clinker. This study can provide a basis for research on the phase regulation of cement clinker composed mainly of low-calcium minerals.

Production cross sections of 102mRh and 108mAg in proton bombed natPb target with 400 MeV energy

The accelerator-driven subcritical system (ADS) is a competitive option for next-generation nuclear energy systems. Production cross sections of long-lived residual radioactive nuclides in a proton-nuclide reaction are basic quantities for the calculation of accumulated radioactivity in the use of ADS systems. This work presents the production cross sections of 102mRh and 108mAg in a natural lead (natPb) target activated by 400 MeV protons. The natPb target was irradiated by a 400 MeV proton beam in NRC “Kurchatov Institute” and measured two decades later by a low background gamma spectrometer in China Jinping Underground Laboratory (CJPL). A spectrum analysis method based on simulated single-isotope spectrum and Bayesian peak fitting was employed to compute the activities and production cross sections of the residual nuclides. The experimentally measured cross-sections for 102mRh and 108mAg were 0.72 ± 0.05 mb and 0.76 ± 0.09 mb respectively. These values are approximately twice as high as those predicted by the QGSP_INCLXX_HP model and fall within the range predicted by the INCL4+ABLA and LAQGSM+GEM2 models for mass numbers A=102 and A=108. These findings offer new experimental insights for ADS research and provide a practical benchmark for theoretical models concerning proton-lead interactions.

Autonomic Dysfunction Among Adult Survivors of Childhood Cancer in the St. Jude Lifetime Cohort Study

BackgroundThe burden and functional significance of autonomic dysfunction among survivors of childhood cancer is unknown. ObjectivesWe evaluated the prevalence, risk factors, and functional relevance of autonomic dysfunction in survivors. MethodsWe conducted a cross-sectional prospective evaluation of 1,041 adult survivors of childhood cancer treated with anthracyclines (31.1%), chest-directed radiation (13.5%), both (19.5%), or neither (35.9%), and 286 community control subjects enrolled in the SJLIFE (St Jude Lifetime Cohort Study). Four measures of autonomic dysfunction were evaluated: elevated resting heart rate, decreased heart rate reserve, decreased systolic blood pressure response to exercise, and delayed heart rate recovery. Logistic regression tested associations with impaired cardiorespiratory fitness (peak Vo2 < 80% predicted). ResultsSurvivors (50.7% female) were 9.0 ± 5.8 years at cancer diagnosis and 35.5 ± 8.9 years at evaluation. Prevalence (survivors vs control subjects) of elevated resting heart rate (17.9% vs 7.0%), decreased heart rate reserve (21.7% vs 9.1%), decreased systolic blood pressure response to exercise (25.3% vs 12.6%), and delayed heart rate recovery (24.3% vs 10.6%) was more than 2-fold higher among survivors (P < 0.001 for all). Carboplatin (adjusted OR: 2.50; 95% CI: 1.42-4.40; P = 0.001), chest-directed radiation therapy (adjusted OR: 2.06; 95% CI: 1.52-2.75; P < 0.001), and cranial radiation (adjusted OR: 1.49; 95% CI: 1.08-2.05; P = 0.015) were associated with an increased likelihood of having ≥2 measures of autonomic dysfunction. Survivors with ≥2 measures of autonomic dysfunction were at increased risk for impaired cardiorespiratory fitness (adjusted OR: 2.71; 95% CI: 1.82-4.02; P < 0.001). ConclusionsSurvivors of childhood cancer manifest a higher prevalence of autonomic dysfunction associated with impaired cardiorespiratory fitness.

Synergistic release of Cd(II) and As(V) from ternary sorption systems containing ferrihydrite nanoparticles: The role of binary and ternary surface complexes

Cadmium (Cd) and arsenic (As) generally exhibit mutually beneficial co-sorption behavior on iron oxyhydroxides through multiple mechanisms, including surface precipitation, ternary surface complexes, and electrostatic interactions. However, the numerous factors that control the immobilization of Cd and As in turn complicated the processes and mechanisms involved in their co-desorption from iron minerals, which hindered the full understanding of their geochemical behaviors. Here, the simultaneous release of Cd(II) and As(V) from newly precipitated ferrihydrite nanoparticles by either Ca or P was investigated through kinetics and isothermal desorption experiments. We showed that the Cd(II) and As(V) present two-phase desorption processes (rapid desorption and slow desorption) in both binary (Fe–Cd or Fe–As alone) and ternary systems (Fe–Cd–As co-presence). Compared to their binary counterparts, Cd(II) and As(V) in the ternary systems are more prone to detachment from ferrihydrite. Further desorption of Cd(II) and As(V) at different co-presence scenarios (different initial concentrations) demonstrated mutual promotion behaviour towards their counterparts; the co-presence of Cd(II) facilitates the desorption of As(V), while the co-presence of As(V) also promotes the desorption of Cd(II). XPS and FTIR results demonstrated that either Ca or P showed minor effects on the binding environment of Cd and As. Further results from the in-situ ATR-FTIR experiment and second derivative peak fitting analysis indicate that the enhanced detachment of Cd(II) and As(V) from the ternary system may be due to the synergistic desorption of the ternary surface complexes and other surface complex species. Our results provide new insights into the prediction of the environmental behaviour of the coexistence of Cd(II) and As(V) in iron-rich geological settings. The potential environmental risks of iron-based remediation methods should be considered due to the enhanced bioavailability of Cd(II) and As(V) in co-presence circumstances.

A Novel Accurate Peak Extraction Algorithm of Mass Spectrometry Based on Iterative Adaptive Curve Fitting.

In the analysis of mass spectrometry, the peak identification from the overlapped region is necessary yet difficult. Although various methods have been developed to identify these peaks, especially the continuous wavelet transformation, their applications are still limited and it is hard to deal with the complex overlapped peaks. In this study, a novel peak extraction algorithm of mass spectrometry based on iterative adaptive curve fitting is proposed to address these challenges. It fully utilizes the global optimization characteristics of adaptive curve fitting. Initial peak parameters are obtained using a window searching method, and the residuals between the adaptive fitting peak and the original data indicate the fit's effectiveness and provide information about the peaks in overlap. Using this information, we performed iterative adaptive fitting, continuously updating the overlapped peaks until the residuals met the completion criteria. All of the peaks within the overlapped region can be successfully extracted by the final fitting. The proposed method is evaluated by the simulated data, the real signal from a public data set, and the spectra of two different mass spectrometry instruments. The results demonstrate that this method can more effectively extract peaks with severe overlap and multiple overlapped peaks, resist noise interference, and offer the potential to process peaks with a high dynamic range. More importantly, the proposed method accurately identifies overlapped peaks in the actual spectra from various mass spectrometry instruments, which helps the qualitative and quantitative analyses to a great extent.

Study on the interstitial oxygen diffusion to understand the reduction of cryogenic RF loss for the superconducting radio-frequency niobium cavities

Abstract Medium-temperature baking (Mid-T baking) is an innovative method employed to enhance the unloaded quality factor Q0 of superconducting radio-frequency (SRF) niobium (Nb) cavities at cryogenic temperatures. This study presents an interstitial oxygen diffusion model based on the decomposition of the natural oxide to clarify the improved performance of the Nb cavities after undergoing Mid-T baking. Additionally, the correlation between the interstitial oxygen within the RF penetration depth and the surface resistance of the Nb cavities has been explored. The parameter for the oxide decomposition was determined using in-situ X-ray photoelectron spectroscopy (XPS), where the thickness of the oxide/carbide layer was calculated from the peak fitting of Nb 3d spectra and the attenuation law of the photoelectron beam. The interstitial oxygen diffusion model, validated by the semi-quantitative distribution along the depth determined by Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS), quantifies the oxygen atomic concentration within the RF penetration depth in Mid-T baked Nb material. In the baking temperature range of 300~400 ℃, the calculated oxygen concentration from the interstitial oxygen diffusion model demonstrates a more pronounced dependence on the baking temperature than the baking time. This suggests that more precise control of the interstitial oxygen concentration can be achieved by adjusting the baking temperature. Furthermore, it has been observed that maintaining a uniform and moderate oxygen concentration throughout the depth is essential for optimal BCS resistance. This study paves the way for more efficient processing optimization and enhancing understanding of the mechanism behind RF loss in Nb cavities.

Interpretation of complex x-ray photoelectron peak shapes. II. Case study of Fe 2p3/2 fitting applied to austenitic stainless steels 316 and 304

In this paper, a review of the analysis of Fe 2p3/2 peak and other transition metals in the austenitic stainless steel literature is presented. It reveals the significant shortcomings of the most widely used approaches, based on the principle of “chemistry fitting,” where single symmetric peaks are used to represent either individual oxidation states or specific compounds. No meaningful conclusions can be drawn from these commonly employed two- or three-component peak fitting (2C and 3C) approaches; the implication being that a large portion of the literature that relies on this approach is flawed. As a significantly more accurate and reliable alternative to “chemistry fitting,” we also assess “envelope fitting” (using empirical multiplet structures) and examine its limitations when applying the approach to austenitic stainless steel data. A detailed comparison of these two fitting approaches is described in Part I. For other elements such as Cr 2p, the problems associated with using single components to represent oxidation states or compounds are not as severe. It was found that it does not impact binding energy measurements, but does influence relative intensities, which will have a flow-on effect for oxide thickness calculations and obtaining a correct understanding of the surface more broadly.

Interpretation of complex x-ray photoelectron peak shapes. I. Case study of Fe 2p3/2 spectra

Analyzing transition metal XPS peaks is widely used to determine surface composition and chemistry. However, these peaks have a complex structure, which is still the subject of investigation. Fe 2p analysis is a case in point where the multiplet structure and many-electron-effects lead to peak shapes that cannot be analyzed using standard approaches. Examination of the literature reveals that one of the most widely used approaches to data reduction when processing Fe 2p3/2 spectra involves using symmetric two- or three-component peak fitting with each peak effectively acting to capture a single chemical species (chemistry fit) in the complex spectra. Herein, this approach is compared to an envelope fit approach using Biesinger multiplet components of known iron oxides to determine how effective these methods are in reproducing iron oxide composition. Mixed oxide and metal XPS Fe 2p spectra were synthesized using reference spectra collected experimentally. For the first time, the accuracy and differences between the two approaches are reported. It is demonstrated that no meaningful conclusions can be drawn using single symmetric peaks to analyze complex Fe 2p3/2 spectra, implying that a large portion of the literature is flawed. The envelope fit approach, however, is shown to provide useful information regarding oxide ratios in mixed iron oxide materials, though limitations do exist. A methodology for evaluating the quality of XPS analysis of Fe 2p3/2 spectra is proposed for benchmarking new submissions so that reviewers, authors, and editors can assess these submissions.

Quantitative Analysis of Chondroitin Sulfate and Dermatan Sulfate Using Capillary Electrophoresis With Gaussian Distribution‐Based Peak Fitting for Improved Peak Resolution

ABSTRACTIn this work, capillary electrophoresis with Gaussian distribution‐based peak fitting for improved peak resolution for simultaneous quantitative analysis of chondroitin sulfate (CS) and dermatan sulfate (DS) was developed for the first time. The effects of different pH, voltage, and peak shapes on the peak fitting were investigated. The results indicate that separation conditions that affect peak shape have a significant impact on peak fitting. Under optimized separation conditions, the peak fitting achieves high accuracy and precision, the relative standard deviation (n = 5) of peak area and migration time of CS and DS were 1.1%, 1.8% and 0.94%, 0.84%, respectively. Furthermore, the results obtained by peak fitting were close to real values. The developed method was used to analyze the purity of CS. The results had a high consistency with the labeled value; furthermore, the peak fitting could point out the number of possible impurities. The developed method has good potential for the analysis of other glycosaminoglycans with peak overlap.

Effect of concentration and wavelength of excitation on the photophysics of salicylate anion in acetonitrile and water

Sodium salicylate (NaSA) molecule exists as salicylate anion in acetonitrile (ACN) and water solvents, and exhibits large Stokes shifted fluorescence due to excited state intramolecular proton transfer (ESIPT), with decay times of ∼5 ns in ACN and ∼3.9 ns in water by 300 nm (absorption maxima) excitation. Previous studies report both ground and excited state enol-keto tautomerization in ACN, but only excited state tautomerization in water at 10−4 M. However, the current work explores the effect of concentration and excitation wavelengths on the photoinduced dynamics of ESIPT in the salicylate anion. On increasing the concentration of NaSA, no change in absorption spectra appears in both the solvents, and emission spectra of NaSA in water remain unaffected by changes in concentration or excitation wavelength, whereas, a slight red shift and decrease in FWHM appears in ACN. Time-domain fluorescence measurements show predominantly single-exponential decay throughout the emission profile by 300 nm excitation above the 10−5 M concentration in both the solvents, while by 375 nm excitation, multi-exponential fluorescence decay is observed at low concentrations, and as the concentration of NaSA increases, this decay behaviour tends to converge towards a single exponential decay. These results suggest that solute–solvent interactions stabilize the ground-state intermolecular hydrogen-bonded species at low concentrations, while higher concentrations weaken these interactions, leading to emission solely from the salicylate anion. Peak fit analysis of excitation spectra confirms enol-keto tautomerization in both the solvents, with the keto form being more stabilized in ACN. These findings underscore that in ACN, behaviour of NaSA is influenced by both concentration and excitation wavelength and contrary to previous reports, the keto form of the molecule is also present in water, though at a very low concentration and an increase in non-radiative transitions in water cause fluorescence quenching.

Maximum a posteriori estimation for high-throughput peak fitting in X-ray photoelectron spectroscopy

Maximum a posteriori estimation for high-throughput peak fitting in X-ray photoelectron spectroscopy