Quantitative Surface Analysis Research Articles

Unveiling the adsorption mechanism of propanehydrazine derivatives on magnesium oxide surface: Insights from computational approach

The use of green and effective inhibitors for preventing metal oxide (MgO) corrosion in industrial applications is highly significant in promoting environmental protection and sustainable development. This study delves into the adsorption behavior and interfacial mechanism of environmentally friendly inhibitor derived from propane hydrazine (PH) on MgO surface. Specifically, PH1, PH2, PH3, and PH4 were explored for their effectiveness in preventing corrosion by using advanced theoretical simulations-based density functional theory (DFT) for assessing the reactivity and adsorption characteristics. The study considered a detailed exploration of local and global reactivity descriptors, providing insights into the inhibitors’ reactivity and adsorption abilities in both isolated and adsorbed states. These findings focus more in the mechanisms underlying organic-inorganic interactions and present promising prospects for further development and application. Using first-principles DFT calculations alongside quantitative molecular surface analyses, we examined the adsorption patterns of PHs on the MgO(100) surface. These investigations are boosted by the application of independent gradient model (IGM) framework, providing robust verification of PHs' adsorption behavior on MgO(100) surface. Our calculations reveal a substantial decrease in the energy gap following complex formation, suggesting that charge density changes occur upon interaction with MgO surfaces, thereby facilitating direct electron transfer in all the studied systems. Noreover, the results highlight the crucial role of intermolecular interactions in boosting the interaction between PHs and the [Mg(H2O)6]2+ cation. First-principles DFT calculations show that all PH molecules consistently display parallel adsorption on the MgO surface, where the oxygen atoms form bonds with adjacent magnesium atoms. The bond lengths vary from 2.18 to 2.35 Å when PHs bind to the Mg atoms in parallel orientations through the oxygen atom, suggesting a stable parallel arrangement for PH molecules on the MgO surface. The calculated adsorption energy (Eads) varies in the following order: MgO-PH3 (−815.14 Kcal mol−1) > MgO-PH2 (−803.85 Kcal mol−1)) > MgO-PH4 (−695.38 Kcal mol−1) > MgO-PH1 (−125.77 Kcal mol−1). This trend indicates that parallel interactions enhance the adsorption behavior and binding of PH compounds through inter- and intra-molecular interactions, resulting in the PHs being centered at specific sites on the MgO surface. The potential enhancement in electrochemical properties is believed to stem from the synergistic interaction between the PHs and the MgO surface, which theoretically allows for a precise adjustment of their adsorption and interaction within the composite structure. This understanding provides a fundamental framework for examining the complex interfacial dynamics between inhibitor structures and elucidating how these molecular interactions influence the selection of corrosion inhibitors and their adsorption behaviors on the corrosion layer's surface, rather than on metallic Mg.

Effect of herbal irrigants on surface roughness of intraradicular dentin using quantitative method of 3D surface texture analysis

Replacing the conventional endodontic irrigants with herbal agents could avoid complications associated with using sodium hypochlorite (NaOCl). Endodontic irrigants alter the surface roughness of the dentinal wall surface, which affects sealer mechanical retention. This study aimed to assess the effect of experimental herbal Moringa oleifera and orange peel extract irrigant on intraradicular dentin (IRD) surface roughness using quantitative 3D surface analysis by scanning electron microscopy (SEM) regarding the smear layer assessment. Sixty human root sections were divided into four groups (n = 15): NaOCl combined with 17% ethylenediaminetetraacetic acid (EDTA); negative control (saline); moringa extract (MO); and orange oil (OO). SEM images were assessed quantitatively for surface roughness (Ra) in the coronal, middle, and apical IRD. The data were analysed by Kruskal–Wallis, Friedman, and Dunn’s tests. All groups showed statistically significant differences (P = 0.007). MO exhibited significantly greater Ra values at the coronal, middle, and apical root levels than OO (P = 0.007, 0.009, and 0.046, respectively). There was no significant change in Ra values at various root levels within each group at P = 0.091, 0.819, 0.819, and 0.549 for the EDTA, saline, MO, and OO groups. Considerable (IRD) surface roughness analysis makes Moringa extract a promising herbal endodontic irrigant alternative to the NaOCl plus EDTA regimen.

Study of Structural Morphology of Electrodeposited Ni Film

Structural morphology of thin electrodeposited metallic films plays a vital role in determining the properties of the films and their application. We prepared a range of Ni electrodeposited polycrystalline films using a BIOLOGIC potentiostat and investigated the effects of varying parameters such as the deposition rate and concentration of the solution to improve control over their properties. We conducted analysis of surface morphology of thin films of area 1cm2, as well as at microstructural level of area 50x50 um2, using ex-situ AFM and in-situ HS AFM. Ex-situ AFM data helps us to do quantitative surface analysis, including slope, scaling analysis [1] and grain area calculation as a function of time, concentration, and applied potential. HS AFM provides us with information about the grain structure evolution at microstructural level [2]. The texture of films was determined by XRD analysis. For the thin films, Ni[111] orientation was dominant, but for thick films, the dominant crystallographic orientations was Ni[200].We also performed EBSD analysis for Ni thin films after milling with focused ion beam. EBSD uses backscattered electron to obtain the information of structural morphology and crystallographic orientation of thin films layer by layer. The correlation between ex-situ AFM and EBSD data helps to gain a clear understanding of the structural features of the films. Liu, L., & Schwarzacher, W. (2013). Slope analysis and scaling analysis of electrodeposited thin films. Electrochemistry communications, 29, 52-54.Koorikkat, A., Payton, O., Picco, L., & Schwarzacher, W. (2020). Imaging the Surface of a Polycrystalline Electrodeposited Cu Film in Real Time Using In Situ High-Speed AFM. Journal of the Electrochemical Society, 167(16), 162510.

Cortical surface analysis for focal cortical dysplasia diagnosis by using PET images

Focal cortical dysplasia (FCD) is a neurological disorder distinguished by faulty brain cell structure and development. Repetitive and uncontrollable seizures may be linked to FCD's aberrant cortical thickness, gyrification, and sulcal depth. Quantitative cortical surface analysis is a crucial alternative to ineffective visual inspection. This study recruited 42 subjects including 22 FCD patients who underwent surgery and 20 healthy controls (HC). For the FCD patients, T1-weighted and PET images were obtained by a PET-MRI scanner, and the confirmed epileptogenic zone (EZ) was collected from postsurgical follow-up. For the HCs, CT and PET images were obtained by a PET-CT scanner. Cortical thickness, gyrification index, and sulcal depth were calculated using a computational anatomical toolbox (CAT12). A cluster-based analysis is carried out to determine each FCD patient's aberrant cortical surface. After parcellating the cerebral cortex into 68 regions by the Desikan-Killiany atlas, a region of interest (ROI) analysis was conducted to know whether the feature in the FCD group is significantly different from that in the HC group. Finally, the features of all ROIs were utilised to train a support vector machine classifier (SVM). The classification performance is evaluated by the leave-one-out cross-validation. The cluster-based analysis can localize the EZ cluster with the highest accuracy of 54.5 % (12/22) for cortical thickness, 40.9 % (9/22) and 13.6 % (3/22) for sulcal depth and gyrification, respectively. Moderate concordance (Kappa, 0.6) is observed between the confirmed EZs and identified clusters by using the cortical thickness. Fair concordance (Kappa, 0.3) and no concordance (Kappa, 0.1) is found by using sulcal depth and gyrification. Significant differences are found in 46 of 68 regions (67.7 %) for the three measures. The trained SVM classifier achieved a prediction accuracy of 95.5 % for the cortical thickness, while the sulcal depth and the gyrification obtained 86.0 % and 81.5 %. Cortical thickness, as determined by quantitative cortical surface analysis of PET data, has a greater ability than sulcal depth and gyrification to locate aberrant EZ clusters in FCD. Surface measures might be different in many regions for FCD and HC. By integrating machine learning and cortical morphologies features, individual prediction of FCD seems to be feasible.

Deep learning based initial crack size measurements utilizing macroscale fracture surface segmentation

To this date the safety assessment of materials, used for example in the nuclear power sector, commonly relies on a fracture mechanical analysis utilizing macroscopic concepts, where a global load quantity K or J is compared to the materials fracture toughness curve. Part of the experimental effort involved in these concepts is dedicated to the quantitative analysis of fracture surfaces, which is a cumbersome and time-consuming process. In addition, however, it is affected by subjective bias. Within the scope of our study, we have introduced a methodology that employs deep learning models for macroscopic fracture surface segmentation. To fight subjective bias and enable improved reproducibility, we set up three distinct and unique datasets labeled by different experts that correspond to typical isolated laboratory conditions and complex real-world (multi-laboratory) scenarios. To demonstrate the benefit of our approach for the fracture mechanics assessment, we employed the models for initial crack size measurements utilizing the area average method. Furthermore, the influence of structural similarity on the segmentation capability, differing due to the miscellaneous materials, specimen types, as well as imaging-induced variance has been analyzed. For semi-supervised learning a weak-to-strong consistency regularization was implemented. We were able to train robust and well-generalizing models that learned feature representations from images across different domains without observing a significant drop in prediction quality. Our approach reduced the number of labeled images required for training by a factor of 6. The deep learning assisted measurements proved to be as precise as manual measurements. For the multi-laboratory data, mean measurement deviations smaller 1 % could be achieved, showcasing the enormous potential of our approach.

Prediction of cosolvent effect on solvation free energies and analysis of intermolecular forces of tizanidine hydrochloride in ethyl acetate + methanol / ethanol mixtures

The solubility of small molecule drug in solvents can be dramatically affected by addition of a suitable cosolvent, which makes the screening of the best-suited cosolvent an important task for the purification and preparation. The present work aims to improve the fundamental understanding of tizanidine hydrochloride (TIZ HC) solvation by cosolvent. Solubility experimental data from TIZ HCl in mixtures of ethyl acetate + alcohols were obtained at different temperatures with the method of isothermal equilibrium. In the system of ethyl acetate + methanol, the solubility data increased firstly and then decreased with an increase in ethyl acetate content, however, the strictly monotonic decreasing of solubility in ethyl acetate + ethanol mixtures was observed. The solubility correlation fitting was performed with the Jouyban-Acree model and CNIBS/R-K model. The solvent effect analysis indicates that the hydrogen bond acidity, the polarity / polarizability and the cohesive forces of the solvent have a greater influence on the solubility, which was further validated by the local quantitative molecular surface analysis results of electrostatic potential (ESP). The dissolution process of TIZ HCl in systems with different solvent compositions was analyzed in the form of preferential solvation parameters, it was found that methanol is the preferred solvent in the solvation shell of TIZ HCl in methanol-rich and ethyl acetate-rich mixtures but the ethanol is preferred in intermediate compositions and ethyl acetate-rich mixtures. Moreover, the types of intermolecular solute–solvent interactions were discussed on the basis of the structural characteristics of TIZ HCl. The solvation free energy is a key parameter describing solvent effects, which is extremely important for understanding solution chemistry. For this part, with the aid of density functional theory (DFT) and molecular dynamics (MD) simulations, it was found that the cosolvent effect is consistent with the prediction trend of solvation free energy of TIZ HCl in each systems. The effect of the cavity formed by the solvent molecules and dipole moment of solute was calculated accordingly by the solvation model based on density (SMD) for explaining the former behavior.

Study on the microcosmic mechanism of inhibition of coal spontaneous combustion by antioxidant diphenylamine

Diphenylamine has been applied to suppress coal spontaneous combustion with good results, but its microscopic reaction mechanism is not clear. In this paper, the free radical reaction process of coal spontaneous combustion is calculated more systematically, and the quantum chemical method is applied to analyze in detail the process of diphenylamine depletion of reactive free radicals in coal from three perspectives: hydrogen atom transfer, direct radical capture, and regeneration cycle chain. By destroying the molecular structure of coal to generate free radicals as the initial condition of coal spontaneous combustion, the oxidation process of the free radical chain reaction was analyzed, the thermodynamic data of all reactions were calculated, the microscopic mechanism of free radical capture by diphenylamine was revealed, and the transition state structure model of the reaction process was given. The active sites of each reactant were determined by quantitative molecular surface analysis, the spontaneity of the reaction was measured by the free energy change, and the interaction relationship between different conformations was graphically represented by applying the IRI (interaction region indicator) method. The results show that most of the free radical reactions during the spontaneous combustion of coal are exothermic, and they provide heat for the spontaneous combustion of coal, which can react directly with oxygen when accumulated to a certain temperature. Diphenylamine can break the N-H bond, allowing hydroxyl radicals and carbon radicals to obtain hydrogen atoms to form stable compounds, and the generated diphenylamine radicals can reduce the content of free radicals in coal by direct capture. In addition, the process of diphenylamine inhibition of coal spontaneous combustion has a circular regeneration chain, which can indeed effectively reduce the content of reactive radicals and inhibit the spontaneous combustion of coal, which is reflected in the macroscopic level of reducing the generation of coal spontaneous combustion indicator gas, which is consistent with the experimental results.

Investigating the structure of the oxide on Ni‐Cr‐Mo alloys while presenting a method for analysis of complex oxides using QUASES

X‐ray photoelectron spectroscopy (XPS) is a technique that is widely used to study thin oxide films because of its extremely high surface sensitivity. Utilizing the QUASES (Quantitative Analysis of Surfaces by Electron Spectroscopy) software package developed by Sven Tougaard (University of Southern Denmark), a user can obtain additional information that is not extracted in conventional XPS analysis, specifically the composition as a function of depth. Presented here is the QUASES analysis of four Ni‐Cr‐Mo alloys performed while testing various inelastic mean free path (IMFP) determination methods in the context of providing a framework for the analysis of complex oxides in QUASES. Ni‐Cr‐Mo alloys are often used to replace conventional materials under aggressive conditions, because of their exceptional corrosion resistance. Their corrosion resistance is conferred by the formation of an inert surface oxide film that protects the underlying metal. Using the QUASES software, the thickness of the air‐formed oxide on four Ni‐Cr‐Mo alloys was found to lie within the range of 2.5–3.6 nm. They were found to be composed of an inner Cr2O3 layer and an outer Cr (OH)3 layer, with a transition zone where the two coexisted. Oxidized Mo species, MoO2 and MoO3, were found in trace amounts at the boundary between the Cr2O3‐only and mixed Cr2O3/Cr (OH)3 regions of the oxide. We also determined that using 20% reduced IMFP values gave results similar to those obtained using electron effective attenuation length (EAL) values. Auger depth profiles showed comparable trends to the QUASES models.

Revealing a notable interaction in the binding of type II statins to HMG‐CoA reductase: Stacked cation–π interaction

AbstractThis study has centered on potentially important enzyme‐ligand interaction currently not incorporated: stacked cation–π interaction between the guanidinium group of arginine 590 residues in the HMG‐CoA reductase active site and the 4‐fluorophenyl group of type II statins. The geometry of interaction between these planar groups has been considered based on the X‐ray crystallographic structures already available in the protein data bank (PDB) archive. Electronic interaction energies between this residue and statins have been acquired by M06 and MP2 methods. In addition, stacking interaction and hydrogen bonding as two important investigated interactions are verified through prominent analyses: (1) quantum theory of atoms in molecules (QTAIM) analysis; (2) plotting and quantitative molecular surface analyses such as electrostatic potential (ESP) analysis, Hirshfeld surface (HS) and Becke surface (BS) analyses; (3) visual study methods such as noncovalent interaction (NCI), independent gradient model (IGM) analyses; and (4) localized orbital locator integrated pi over plane (LOLIPOP) index.The results indicate the absolute binding energy for type II statins is overall more than for type I statins.

Interface engineering of LDH-based material as efficient anti-corrosive system via synergetic performance of host, interlayers, and morphological features of nature-mimic architectures

High-performance hybrid materials with special features are desired to meet the requirements of more complex cutting-edge applications. However, the self-assembly of layered double hydroxides (LDH) with organic frameworks is hampered by a lack of understanding of the formation mechanism and the effects of the self-assembled architecture on anticorrosion activity remain a major challenge. Herein, we put forward how the honeycomb-like network would architecturally upgraded on the pre-existing hierarchical floral structure with Trimesic acid (TMA) compound resulting in a promising layer-by-layer (LBL) material. This nature-inspired network is realized to offer an ideal approach not only endows with excellent properties but also exploits the power of layered coating materials as a bastion in the fields of nanotechnology, without limiting conditions, taking advantage of the synergy beneficial effects of the self-assembled honeycomb-like TMA and the anion-exchange ability of the layered coating material. In this work, a three-dimensional assembly with an architecture closely resembling interconnected micro-petals was successfully deposited on the defective surface obtained via plasma electrolytic oxidation (PEO) of Mg alloy, where TMA compound was used for supramolecular self-assembly. The MgO layer was first formed on AZ31Mg alloy via PEO treatment and the Mg-Al LDH micro-petals were synthesized on the MgO surface in the presence of a chelating agent [diethylenetriaminepentaacetic acid (DTPA)]. In a typical synthesis, TMA compound was used as an appropriate linker for the formation of well-organized multidimensional layered materials taking advantage of the synergy beneficial effects of the self-assembled honeycomb-like TMA and the anion-exchange ability of the Mg-Al LDH coating. The results indicate that Mg alloy coated with the self-assembled TMA@LDH-MgO materials presents excellent anti-corrosion performance as compared to the bare Mg. The use of such system would open a brand-new possibility to correct, in a targeted way, the inevitable defects of the layered coating morphology while retaining its exceptional potential. First-principles calculations, quantitative molecular surface analyses and independent gradient model framework further verify the self-assembly and adsorption behavior of TMA over the Mg-Al LDH layer. The improved performance of the TMA@Mg-Al LDH film is attributed to the synergistic effects of different interactions that occurred around active sites in the hierarchical network.

Effect of benzotriazole on the prevention of electroless nickel–immersion gold treated copper corrosion

The effect of benzotriazole on the corrosion prevention of electroless nickel–immersion gold (ENIG)-treated copper in 3.5 wt% sodium chloride solution was investigated using electrochemical tests, qualitative and quantitative surface analyses, and density functional theory calculations. Benzotriazole showed high corrosion inhibiting efficiency of approximately 90% or more for both copper and nickel, which are components of ENIG-treated copper. Furthermore, adding benzotriazole suppressed more than half of galvanic corrosion between nickel and gold, previously identified as the cause of corrosion of ENIG-treated copper. By chemisorption of its nitrogen atoms on the copper and nickel surfaces, benzotriazole effectively inhibited corrosion of ENIG-treated copper. The corrosion and corrosion inhibition mechanisms of ENIG-treated copper specimens were investigated using scanning electron microscopy with energy-dispersive X-ray spectroscopy after immersion testing of ENIG-treated copper specimens.

Nitazoxanide in aqueous co-solvent solutions of isopropanol/DMF/NMP: Solubility, solvation thermodynamics and intermolecular interactions

At the microscopic level, quantitative surface analysis was utilized to highlight the electrostatic features of acidity and basicity, respectively. The groups of –NO2 and > NH are the principal sites of electrophilic and nucleophilic attack, respectively, on the nitazoxanide (NTZ) molecule. The weak interaction regions between NTZ and solvent were visually examined through the IGMH method. The solubility of NTZ in three co-solvent blends, namely isopropanol + water, DMF + water, and NMP + water, was determined over a temperature range of 278.15 to 323.15 K. The isothermal saturation method was used to obtain the results, which were carried out under a pressure of 101.2 kPa. No evidence of crystal transition or solvate production was observed in the experiments conducted. Under the same investigational conditions, such as the same temperature and composition of isopropanol (DMF or NMP), the NTZ solubility in mole fraction was significantly greater in aprotic DMF/NMP + water blends than in protic isopropanol + water blends. Five models were used to relate solubility data: the Jouyban–Acree model, the extended Hildebrand solubility model, the modified Jouyban–Acree-van't Hoff model, the NRTL model and the UNIQUAC model. Under the conditions of 298.15 K, an investigation into the preferential solvation of NTZ was carried out using a technique based on inverse Kirkwood–Buff integrals. With isopropanol/DMF/NMP-medium and -rich composition areas, the preferential solvation parameters of NTZ showed positive values, indicating that the co-solvents were preferentially solvating the drug.

Canonical structural-binding modes in the calmodulin–target protein complexes

Intracellular calcium sensor protein calmodulin (CaM) belongs to the large EF-hand protein superfamily. CaM shows a unique and not fully understood ability to bind to multiple targets, allows them to participate in a variety of regulatory processes. The protein has two approximately symmetrical globular domains (the N- and C-lobes). Analysis of the CaM-binding sites of target proteins showed that they have two hydrophobic ‘anchor’ amino acids separated by 10 to 17 residues. Consequently, several CaM-binding motifs: {1–10}, {1–11}, {1–13}, {1–14}, {1–16}, {1–17}, differing by the distance between the two anchor residues along the amino acid sequence, have been identified. Despite extensive structural information on the role of target–protein amino acid residues in the formation of complexes with CaM, much less is known about the role of amino acids from CaM contributing to these interactions. In this work, a quantitative analysis of the contact surfaces of CaM and target proteins has been carried out for 35 representative three-dimensional structures. It has been shown that, in addition to the two hydrophobic terminal residues of the target fragment, the interaction also involves residues that are 4 residues earlier in the sequence (binding mode {1–5}). It has also been found that the N- and C-lobes of CaM bind the {1–5} motif located at the ends of the target in a structurally identical manner. Methionine residues at positions 51 (corresponding to 124 in the C-lobe), 71 (144), and 72 (145) of the CaM amino acid sequence are key hydrophobic residues for this interaction. They are located at the N- and C-boundaries of the even EF-hand motifs. The hydrophobic core of CaM (‘Ф-quatrefoil’) consists of 10 amino acids in the N-lobe (and in the C-lobe): Phe16 (Phe89), Phe19 (Phe92), Ile27 (Ile100), Thr29 (Ala102), Leu32 (Leu105), Ile52 (Ile125), Val55 (Ala128), Ile63 (Val136), Phe65 (Tyr138), and Phe68 (Phe141) and do not intersect with the target-binding methionine residues. CaM belongs to the ‘dynamic’ group of EF-hand proteins, in which calcium and protein ligand binding causes only global conformational changes but does not alter the conservative ‘black’ and ‘grey’ clusters described in our earlier works (PLoS One. 2014; 9(10):e109287). The membership of CaM in the ‘dynamic’ group is determined by the triggering and protective methionine layer: Met51 (Met124), Met71 (Met144) and Met72 (Met145). HIGHLIGHTS Interchain interactions in the unique 35 CaM complex structures were analyzed. Methionine amino acids of the N- and C-lobes of CaM form triggering and protective layers. Interactions of the target terminal residues with these methionine layers are structurally identical. CaM belonging to the ‘dynamic’ group is determined by the triggering and protective methionine layer. Communicated by Ramaswamy H. Sarma

The more accurate determination of surface excitation parameters, the more accurate quantitative surface analysis

The accurate quantitative surface analysis for the study of nanostructures practically used for e.g. photocatalysis, electrocatalysis, energy storage and sensing applications is of high importance. Moreover, the accurate quantitative electron spectroscopy and analytical microscopy of semiconducting nanomaterials such as nano-photocatalysts relies on the accurate determination of surface excitation parameters (SEP). Reflection electron energy loss spectroscopy (REELS) as a surface sensitive technique could be applied for the determination of SEP. The chemical, mechanical, thermal stability, optical and dielectric properties of Ni6MnO8 as binary metal oxide makes such structure suitable for practical applications. Therefore, here Ni6MnO8 due to its great importance in its special applications was typically studied by REELS using the Yubero-Tougaard algorithm, which is based on dielectric response theory. After an extrapolation process applied to the obtained REELS spectrum, the energy gap (Eg) of this material was obtained to be 3 eV. The surface and bulk energy loss functions of the material were also determined. The values of inelastic mean free path (IMFP) of the electrons of different energies in the range of 500–4000 electron volts travelled in Ni6MnO8 were determined. In addition, from the obtained energy loss function (ELF), by using the Kramers-Kronig transformations of the real and imaginary parts of dielectric function (ε), the important optical parameters of Ni6MnO8 such as refractive index (n), attenuation coefficient (k) and absorption coefficient (μ) were determined. Finally, as a critical parameter in quantitative electron spectroscopy, the SEP and its angular distribution were determined. It was found that the Pauli-Tougaard model requires a modification to make it better descriptive to well fit the SEP data for a given material. Therefore, a more accurate model was obtained to make a better surface analysis and analytical microscopy.

Quantitative surface and Hirshfeld surface analysis of nicorandil molecule and further insight into its solubility in several aqueous protic and aprotic cosolvent solutions

The quantum-chemical quantities of highest negative surface electrostatic potential and lowest surface average local ionization energy as well as Hirshfeld surface were used herein to explain the electrostatic features of both basicity and acidity of nicorandil molecule. The primary electrophilic and nucleophilic sites are the -Nand > NH groups, respectively. According to the nicorandil solubility in solutions of isopropanol (1) + water (2), ethanol (1) + water (2), DMF (1) + water (2), and methanol (1) + water (2), preferential solvation of nicorandil was investigated using the famous inverse Kirkwood-Buff integrals approach. In poor water composition areas, nicorandil was surrounded preferentially by organic solvent, showing the selective solvation of nicorandil by methanol/DMF/ethanol/isopropanol. This performance was due to high basicity of organic solvents compared with water, which favors interactions with nicorandil's acidic groups. The Hansen solubility parameter was used to evaluate the performance of nicorandil solubility in depth. The derived dissolution Gibbs energy change, enthalpy and entropy indicated that the solubilization capacity improved with increasing methanol/DMF/ethanol/isopropanol compositions. As the proportions of methanol/DMF/ethanol/isopropanol rose, analysis of enthalpy–entropy compensation revealed a shift in main dissolving mechanism from enthalpy-driven to entropy-driven (alcohol solutions) or from entropy-driven to enthalpy-driven (DMF solutions).

Inter-/intra-molecular interactions, preferential solvation, and dissolution and transfer property for tirofiban in aqueous co-solvent mixtures

Using Hirshfeld surface, interaction region indicator and quantitative molecular surface analysis, the microscopic electrostatic features of basicity and acidity of the tirofiban molecule were clearly demonstrated. Both the O atoms in >SO2 and H atom in –COOH serve as primary electrophilic site and nucleophilic site, respectively. Utilizing solubility data for tirofiban in four different water-based co-solvent mixtures {isopropanol/ethylene glycol (EG)/methanol/ethanol (1) + water (2)}, the inverse Kirkwood–Buff integral method was utilized to determine the preferred solvent for the tirofiban solvation according to the results of preferential solvation analysis. In water-rich composition ranges, the drug is surrounded by water, whereas in isopropanol/methanol/ethanol-intermediate and -rich composition ranges, the drug is surrounded by ethanol/methanol/isopropanol. Isopropanol solutions had the largest magnitude of preferential solvation. Alcohols may have a greater basicity that enhances interactions with the Lewis acidic function groups of tirofiban, giving rise to selective solvation of this drug. The linear solvation energy relationships were used to determine the relative impact of solvent-solvent and solvent-solute interactions in determining the variation of solubility magnitudes. The properties of dissolution and transfer, such as entropy, enthalpy and Gibbs energy change were computed. Entropy-driven and enthalpy-driven mechanisms were shown to be responsible for the change in tirofiban solubility in the four aqueous solutions, according to the enthalpy–entropy compensation analysis.

Corrosion of orthodontic brackets: qualitative and quantitative surface analysis.

To determine and compare surface characteristics and presence of corrosion in new and used brackets with optical light microscopy (OLM) and scanning electron microscopy (SEM), and with elemental chemical analysis with energy-dispersive X-ray spectroscopy (EDS). OLM and SEM were used to analyze 24 new and 24 used conventional premolar brackets. EDS analysis was performed in six used brackets and four new brackets with corrosion-suspected spots. OLM and SEM images showed wear/abfraction signs, striations, pits/crevices, and adherent material. Used brackets showed more deterioration than new brackets. SEM images disclosed more morphological features than OLM images. EDS analysis revealed a significantly higher phosphorus (P = .001) and sodium (P < .005) weight fraction and significantly lower amounts of chromium (P < .001) in used brackets. The iron, chromium, and nickel weight fractions did not differ significantly between the clean and corrosion-suspected spots. Of the corrosion-suspected spots analyzed by combined SEM and EDS, 44.14% and 6.90% remained corrosion-suspected on used and new brackets, respectively. Used brackets showed more signs of corrosion than new ones. Combined assessment of SEM and EDS indicates that the bracket surface is affected during orthodontic treatment as a result of corrosion.

Quantitative molecular surface analysis of doxofylline and its thermodynamic solubility behavior in aqueous solutions

The Hirshfeld surface, molecular surface electrostatic potential together with molecular surface average local ionization energy, were employed in this work to analyze the electrostatic characteristics of acidity and basicity of doxofylline at a microscopic level. H···H and O···H contacts present predomination among all contact interactions and doxofylline molecule can behave as a hydrogen-bonding donor with powerful ability. The nitrogen of -N = group and oxygen of >C=O group of doxofylline molecule are primary sites of electrophilic attack. The mole-fraction solubility of doxofylline in four blends of isopropanol + water, ethanol + water, acetone + water and methanol + water covering the temperature from 278.15 to 323.15 K was acquired by the use of saturation shake-flask method under atmospheric pressure of 101.2 kPa. For each aqueous solution, the solubility data firstly presented a peak at isopropanol (ethanol, acetone or methanol) composition of 0.7 and then decreased with the increasing mass fraction of organic solvents at a fixed temperature. No existence of crystaltransition and solvation was recorded in all experiments as indicated by X-ray power diffraction patterns. Solubility data were mathematically correlated by Jouyban-Acree, modified Wilson model, Apelblat and modified van’t Hoff-Jouyban–Acree models. Investigation on preferential solvation of crystalline doxofylline was performed by the inverse Kirkwood–Buff integrals over temperatures from 293.15 to 313.15 K. The preferential solvation parameters of isopropanol, acetone or acetonitrile presented positive values in blends with middle isopropanol/acetone/acetonitrile composition regions, demonstrating the preferential solvation of doxofylline by isopropanol/acetone/acetonitrile. In addition, the extended Hildebrand solubility approach was employed to quantitatively describe the solubility behavior at 298.15 K in isopropanol/ethanol/acetone/methanol + water blends studied in this paper and in acetonitrile + water blends previously reported, attaining the average relative deviations of < 7.80 %.

Quantitative surface analysis of paclobutrazol molecule and comprehensive insight into its solubility in aqueous co-solvent solutions

As powerful tools, the minimum negative surface electrostatic potential together with minimum surface average local ionization energy, were used herein to illustrate the electrostatic characteristics of acidity and basicity at a microscopic level, correspondingly. The groups of -N = and –OH of the paclobutrazol molecule are primary sites of electrophilic and nucleophilic attack. The mole-fraction solubility of paclobutrazol in three co-solvent blends of isopropanol + water, acetone + water and acetonitrile + water covering the temperature range from 278.15 to 318.15 K was experimentally acquired by the use of isothermal saturation method under 101.2 kPa. Under the identical experimental conditions, e.g. same temperature and mass composition of isopropanol (acetone or acetonitrile), the solubility of paclobutrazol in mole fraction was much larger in acetone + water blends than in isopropanol/acetonitrile + water blends. The minimal solubility was recorded in neat water solvent at 278.15 K; and the maximal one, in acetone/acetonitrile/isopropanol at T = 318.15 K. No appearance of crystaltransition as well as solvate formation was observed in experiments as indicated by X-ray power diffraction patterns. Solubility data were mathematically correlated by three models including Jouyban-Acree, Apelblat and modified van’t Hoff-Jouyban–Acree. Investigation on preferential solvation of crystalline paclobutrazol was performed by the powerful approach of inverse Kirkwood–Buff integrals at 298.15 K. The preferential solvation parameters of isopropanol, acetone or acetonitrile presented positive values in blends with middle and isopropanol/acetone/acetonitrile-rich composition regions, which indicated the preferential solvation of paclobutrazol by the co-solvents. In addition, the extended Hildebrand solubility approach was employed to quantitatively describe the solubility behavior at 298.15 K in isopropanol/acetone/acetonitrile + water blends studied in this paper and in ethanol/n-propanol/1,4-dioxane + water blends previously reported by us, attaining the average relative deviations < 7.61 %.

Equilibrium solubility of amrinone in aqueous co-solvent solutions reconsidered: Quantitative molecular surface, inter/intra-molecular interactions and solvation thermodynamics analysis

Two powerful tools of quantum-chemical parameters, minimum negative surface electrostatic potential together with minimum surface average local ionization energy, were employed in this communication to illustrate the electrostatic characteristics of acidity and basicity from a microscopic point of view, correspondingly. The -N = and > NH groups of amrinone molecule are primary sites of electrophilic and nucleophilic attacks. With the help of the famous method of inverse Kirkwood–Buff integrals, preferential solvation analysis was executed based on the reported amrinone solubility in four solution systems of EG (1) + water (2), ethanol (1) + water (2), DMF (1) + water (2) and methanol (1) + water (2). In rich water concentrations, amrinone was surrounded preferentially by water; while in intermediate and rich EG/ethanol/DMF/methanol compositions, EG/ethanol/DMF/methanol solvated preferentially amrinone. High basicity of EG/ethanol/DMF/methanol that favored interactions with the acidic groups of amrinone resulted in selective solvation of amrinone by the co-solvent. Deep investigation on the amrinone solubility behavior was done by the partial Hansen solubility parameters. The inspection of molecular interactions on amrinone solubility variation was made in the light of the well-known linear solvation energy relationships, identifying the solubility parameter, hydrogen-bond acidity and dipolarity-polarizability of solutions presented dominant contributions to the solubility variation. The transfer and thermodynamic dissolution properties including entropy, enthalpy and Gibbs free energy change were also derived and deeply discussed. Thermodynamic enthalpy–entropy compensation analysis validated a shift of prevailing mechanism of dissolution from entropy-driven (in rich water compositions) to enthalpy-driven (in rich co-solvent compositions).