Independent Mutation of Two Bridging Carboxylate Ligands Stabilizes Alternate Conformers of the Photosynthetic O2-Evolving Mn4CaO5 Cluster in Photosystem II.

The O2-evolving Mn4CaO5 cluster in photosystem II is ligated by six carboxylate residues. One of these is D170 of the D1 subunit. This carboxylate bridges between one Mn ion (Mn4) and the Ca ion. A second carboxylate ligand is D342 of the D1 subunit. This carboxylate bridges between two Mn ions (Mn1 and Mn2). D170 and D342 are located on opposite sides of the Mn4CaO5 cluster. Recently, it was shown that the D170E mutation perturbs both the intricate networks of H-bonds that surround the Mn4CaO5 cluster and the equilibrium between different conformers of the cluster in two of its lower oxidation states, S1 and S2, while still supporting O2 evolution at approximately 50% the rate of the wild type. In this study, we show that the D342E mutation produces much the same alterations to the cluster's FTIR and EPR spectra as D170E, while still supporting O2 evolution at approximately 20% the rate of the wild type. Furthermore, the double mutation, D170E + D342E, behaves similarly to the two single mutations. We conclude that D342E alters the equilibrium between different conformers of the cluster in its S1 and S2 states in the same manner as D170E and perturbs the H-bond networks in a similar fashion. This is the second identification of a Mn4CaO5 metal ligand whose mutation influences the equilibrium between the different conformers of the S1 and S2 states without eliminating O2 evolution. This finding has implications for our understanding of the mechanism of O2 formation in terms of catalytically active/inactive conformations of the Mn4CaO5 cluster in its lower oxidation states.

Site-specific mutagenesis on Mnemiopsin 2: Calcium coordination and substrate binding properties of new variants.

We used site-specific mutagenesis by targeting E179 and F190 on the structure of photoprotein Mnemiopsin 2 (Mn2) from Mnemiopsis leidyi. The tertiary structure of E179S and F190L mutants was made by the MODELLER program. Far-ultraviolet circular dichroism data showed that the overall secondary structural content of photoprotein is not changed upon mutation, however the helicity and stabilizing interactions in helical structure decreases in mutants as compared with the wild-type (WT) photoprotein. Fluorescence spectra data revealed that the tertiary structure of the mutants is more compact than that of WT Mn2. According to the heat-induced denaturation experiments data, the melting temperature (Tm ) for the unfolding of tertiary structure of the F190L variant increases by 3°C compared with that of the WT and E179S mutant. Interestingly, the conformational enthalpy of the F190L mutant (86 kcal mol-1 ) is considerably lower than those in the WT photoprotein (102 kcal mol-1 ) and E179S mutant (106 kcal mol-1 ). The significant difference in the enthalpy of the thermal unfolding process could be explained by considering that the thermally denatured state of the F190L mutant is structurally less expanded than the WT and E179S variants. Bioluminescence activity data showed that the maximum characteristic wavelengths of the mutants undergo blue shift as compared with the WT protein. Initial intensity of the F190L and E179S variants was recorded to be 137.5% and 55.9% of the WT protein, respectively.

Influence of Ultrasound on the Characteristics of CaP Coatings Generated Via the Micro-arc Oxidation Process in Relation to Biomedical Engineering.

Over the past decade, bone tissue engineering has been at the core of attention because of an increasing number of implant surgeries. The purpose of this study was to obtain coatings on titanium (Ti) implants with improved properties in terms of biomedical applications and to investigate the effect of ultrasound (US) on these properties during the micro-arc oxidation (MAO) process. The influence of various process parameters, such as time and current density, as well as US mode, on the properties of such coatings was evaluated. Novel porous calcium-phosphate-based coatings were obtained on commercially pure Ti. Their microstructure, chemical composition, topography, wettability, nanomechanical properties, thickness, adhesion to the substrate, and corrosion resistance were analyzed. In addition, cytocompatibility evaluation was checked with the human osteoblasts. The properties of the coatings varied significantly, depending on applied process parameters. The US application during the MAO process contributes to the increase of coating thickness, porosity, roughness, and skewness, as well as augmented calcium incorporation. The most advantageous coating was obtained at a current of 136 mA, time 450 s, and unipolar rectangular US, as it exhibits high porosity, adequate wettability, and beneficial skewness, which enabled increased adhesion and proliferation of osteoblasts during in vitro studies. Finally, the conducted research demonstrated the influence of various UMAO process parameters, which allowed for the selection of appropriate Ti implant modification for specific biomedical utilization.

Anionic species from multivalent metal salts are differentially retained during aqueous ionic gelation of sodium alginate and could fine-tune the hydrogel properties.

The role of anionic counterions of divalent metal salts in alginate gelation and hydrogel properties has been thoroughly investigated. Three anions were selected from the Hofmeister series, namely sulphate, acetate and chloride, paired in all permutations and combinations with divalent metal cations like calcium, zinc and copper. Spectroscopic analysis revealed the presence of anions and their interaction with the respective metal cations in the hydrogel. The data showed that the gelation time and other hydrogel properties were largely controlled by cations. However, subtle yet significant variations in viscoelasticity, water uptake, drug release and cytocompatibility properties were anion dependent in each cationic group. Computational modelling based study showed that metal-anion-alginate configurations were energetically more stable than the metal-alginate models. The in vitro and in silico studies concluded that acetate anions preceded chlorides in the drug release, swelling and cytocompatibility fronts, followed by sulphate anions in each cationic group. Overall, the data confirmed that anions are an integral part of the metal-alginate complex. Furthermore, anions offer a novel option to further fine-tune the properties of alginate hydrogels for myriads of applications. In addition, full exploration of this novel avenue would enhance the usability of alginate polymers in the pharmaceutical, environmental, biomedical and food industries.

Calcium complexation by steroids involved in the steroidogenesis.

Steroids that take part in the pathways of human steroidogenesis are involved in many biological mechanisms where they interact with calcium. In the present work, the binding selectivities and affinities for calcium of progestagens, mineralocorticoids, androstagens, and estrogens were studied by Electrospray Ionization-Mass Spectrometry (ESI-MS). The adduct profile of each steroid was characterized by high resolution and tandem mass spectrometry. The relative stability of the most important adducts was studied by threshold collision induced dissociation, E1/2. Doubly-charged steroid-calcium complexes [nM + Ca]2+ with n = 1-6 were predominant in the mass spectra. The adduct [5M + Ca]2+ was the base peak for most 3-keto-steroids, while ligands bearing hindered ketones or α-hydroxy-ketones also yielded [nM + Ca + mH2O]2+ with n = 3-4 and m = 0-1. Principal component analysis allowed us to spot the main differences and similarities in the binding behavior of these steroids. The isomers testosterone and dehydroepiandrosterone, androstanolone and epiandrosterone, and 17-α-hydroxyprogesterone and 11-deoxycorticosterone showed remarkable differences in their adduct profiles. Computational modeling of representative adducts was performed by density functional theory methods. The possible binding modes at low and high numbers of steroid ligands were determined by calcium Gas Phase Affinity, and through modeling of the complexes and comparison of their relative stabilities, in agreement with the experimental results.

Influence of acidification and re-neutralization on mineral equilibria and physicochemical properties of model cheese feed.

Cheese feed is used as spray-dryer feed in cheese powder production, where there is growing consumer demand to eliminate calcium-chelating salts (ES). To develop ES-free feed production processes, it is essential to investigate the relationship between pH, structural changes, and mineral solubilization. This study investigated the influence of acidification and pH re-neutralization on calcium equilibria and stability of ES-free model cheese feeds. The goal was to increase protein availability by solubilizing colloidal calcium phosphate (CCP) and to assess whether CCP solubilization is reversible upon re-neutralization. The extent of acidification (to pH 4.2 or pH 4.7) significantly affected the irreversibility of calcium solubilization upon re-neutralization. Moreover, re-neutralization treatment seemed to induce changes in protein-fat interactions. Feed viscosity was mainly influenced by the final pH, rather than the re-neutralization history. These results offer new insights into the complex interplay of pH, structural modifications, mineral solubilization, and stability in cheese feed production.

In situ sono-rheometric assessment of procaine-loaded calcium pectinate hydrogel for enhanced drug releasing under ultrasound stimulation.

Ultrasound (US) triggered alterations in the viscoelastic behavior of the procaine-loaded ionically gelatinized pectin hydrogel matrix, and drug release was observed using a sono-device rheometer. The gel softened immediately upon activation of the ultrasound operated at 43 kHz and remained in a softened state throughout the irradiation. Upon cessation of ultrasound, the gel promptly reverted to its original hardness. This cycle of softening was consistently observed in ionically crosslinked pectin hydrogels, resulting in the promotion of procaine release, particularly with higher US power and lower calcium concentration. As the amount of loaded procaine increased, the gel weakened due to ion exchange with the calcium crosslinker and procaine. The most substantial release efficiency, reaching 82 % with a concentration of 32 µg/ml, was achieved when the hydrogels contained 0.03 % procaine within the gelatinized hydrogel medicine at a calcium concentration of 0.9 M, representing a six-fold increase compared to that without US. Notably, US exposure affected the 3D porous structure and degradation rate, leading to hydrogel collapse and facilitating medicine release. Additionally, the procaine-loaded pectin hydrogels with 0.9 M calcium exhibited improved fibroblast cell viability, indicating non-toxicity compared to those hydrogels prepared at a higher Ca2+ concentration of 2.4 M.

Pectin Nanoporous Structures Prepared via Salt-Induced Phase Separation and Ambient Azeotropic Evaporation Processes.

Polysaccharide nanoporous structures are suitable for various applications, ranging from biomedical scaffolds to adsorption materials, owing to their biocompatibility and large surface areas. Pectin, in particular, can create 3D nanoporous structures in aqueous solutions by binding with calcium cations and creating nanopores by phase separation; this process involves forming hydrogen bonds between alcohols and pectin chains in water and alcohol mixtures and the resulting penetration of alcohols into calcium-bound pectin gels. However, owing to the dehydration and condensation of polysaccharide chains during drying, it has proven to be challenging to maintain the 3D nanoporous structure without using a freeze-drying process or supercritical fluid. Herein, we report a facile method for creating polysaccharide-based xerogels, involving the co-evaporation of water with a nonsolvent (e.g., a low-molecular-weight hydrophobic alcohol such as isopropyl or n-propyl alcohol) at ambient conditions. Experiments and coarse-grained molecular dynamics simulations confirmed that salt-induced phase separation and hydrogen bonding between hydrophobic alcohols and pectin chains were the dominant processes in mixtures of pectin, water, and hydrophobic alcohols. Furthermore, the azeotropic evaporation of water and alcohol mixed in approximately 1:1 molar ratios was maintained during the natural drying process under ambient conditions, preventing the hydration and aggregation of the hydrophilic pectin chains. These results introduce a simple and convenient process to produce 3D polysaccharide xerogels under ambient conditions.

Magnesium calcites for CO2 capture and thermochemical energy storage using the calcium-looping process.

In this study, a precipitation-based synthesis method has been employed to prepare magnesium calcites with the general formula Ca1-xMgxCO3, with the objective of use them in the calcium looping (CaL) process for CO2 capture (CaL-CCS) and thermochemical energy storage (CaL-CSP). The structure and microstructure of the samples have been characterized. It has been found by X-ray diffraction that the samples with a Ca:Mg molar ratio of 0.5:0.5 and 0.55:0.45 are phase pure, while the samples with molar ratios of 0.7:0.3 and 0.8:0.2 are composed by two phases with different stoichiometry. In addition, the sample prepared with calcium alone shows the aragonite phase. The microstructure of the magnesium-containing samples is composed of nanocrystals, which are aggregated in spherical particles whereas the aragonite sample presents a typical rod-like morphology. The multicycle tests carried out under CaL-CCS conditions show that an increase on the MgO content in the calcined samples results in a reduced value of effective conversion when compared to aragonite. On the other hand, under CaL-CSP conditions, the samples with the higher MgO content exhibit nearly stable effective conversion values around 0.5 after 20 cycles, which improve the results obtained for aragonite and those reported for natural dolomite tested under the same conditions.

Physicochemical properties of AH plus bioceramic sealer, Bio-C Sealer, and ADseal root canal sealer.

BACKGROUND: The aim of this study was to evaluate the physicochemical properties of two newly introduced premixed calcium silicate-based root canal sealers (AH Plus Bioceramic Sealer and Bio-C Sealer) compared to a resin-based root canal sealer (ADseal root canal sealer). METHODS: Solubility, pH analysis, calcium ion release, and film thickness of each sealer were evaluated following ISO guidelines. The data were examined using the two-way ANOVA test. Furthermore, X-ray diffraction (XRD) examination was performed to investigate the crystalline phase of each type of sealer. X-ray fluorescence (XRF) analysis was done for the chemical elemental analysis of each sealer. RESULTS: The least film thickness, highest alkalinity, and highest calcium ion release were all displayed by AH Plus Bioceramic Sealer. High solubility, high alkalinity, intermediate calcium ion release, and intermediate film thickness were all displayed by Bio-C Sealer. While ADseal root canal sealer displayed the greatest film thickness, least solubility, alkalinity, and calcium ion release. CONCLUSIONS: Both AH Plus Bioceramic Sealer and Bio-C Sealer represented adequate properties to be considered a good sealer that could be used as a potential alternative to resin-based root canal sealers.

The reversible activation of norovirus by metal ions.

Murine norovirus (MNV) undergoes extremely large conformational changes in response to the environment. The T = 3 icosahedral capsid is composed of 180 copies of ~58-kDa VP1 comprised of N-terminus (N), shell (S), and C-terminal protruding (P) domains. At neutral pH, the P domains are loosely tethered to the shell and float ~15 Å above the surface. At low pH or in the presence of bile salts, the P domain drops onto the shell and this movement is accompanied by conformational changes within the P domain that enhance receptor interactions while blocking antibody binding. While previous crystallographic studies identified metal binding sites in the isolated P domain, the ~2.7-Å cryo-electron microscopy structures of MNV in the presence of Mg2+ or Ca2+ presented here show that metal ions can recapitulate the contraction observed at low pH or in the presence of bile. Further, we show that these conformational changes are reversed by dialysis against EDTA. As observed in the P domain crystal structures, metal ions bind to and contract the G'H' loop. This movement is correlated with the lifting of the C'D' loop and rotation of the P domain dimers about each other, exposing the bile salt binding pocket. Isothermal titration calorimetry experiments presented here demonstrate that the activation signals (bile salts, low pH, and metal ions) act in a synergistic manner that, individually, all result in the same activated structure. We present a model whereby these reversible conformational changes represent a uniquely dynamic and tissue-specific structural adaptation to the in vivo environment.IMPORTANCEThe highly mobile protruding domains on the calicivirus capsids are recognized by cell receptor(s) and antibodies. At neutral pH, they float ~15 Å above the shell but at low pH or in the presence of bile salts, they contract onto the surface. Concomitantly, changes within the P domain block antibody binding while enhancing receptor binding. While we previously demonstrated that metals also block antibody binding, it was unknown whether they might also cause similar conformational changes in the virion. Here, we present the near atomic cryo-electron microscopy structures of infectious murine norovirus (MNV) in the presence of calcium or magnesium ions. The metal ions reversibly induce the same P domain contraction as low pH and bile salts and act in a synergistic manner with the other stimuli. We propose that, unlike most other viruses, MNV facilely changes conformations as a unique means to escape immune surveillance as it moves through various tissues.

Physicochemical properties of calcium silicate cement based endodontic sealers.

AIM: To mensure the physicochemical properties of three ceramic cement endodontic sealers AH Plus Bioceramic, Bio-C Sealer and Bio-C Sealer Ion+ with an epoxy resin sealer, AH Plus. MATERIAL AND METHODS: These properties were measured: hardening time (HT), dimensional change (DC), solubility (SL), flow (FL) and radiopacity (RD). The distilled water obtained from the SL test was analyzed with atomic absorption spectrometry. A sample calculation was made considering n = 5 repetitions for each experimental sealer evaluated. Statistical analysis was performed using one-way ANOVA and post hoc Tukey tests (p < 0.05). RESULTS: For the HT, AH Plus (484 ± 2.76 min) and AH Plus Bioceramic (424 ± 1.23 min) set more slowly than of Bio-C Sealer (370 ± 4.50 min) and Bio-C Sealer Ion+ (380 ± 1.42 min) (p < 0.05). AH Plus Bioceramic (12.56 ± 2.71 %) was more soluble than Bio-C Sealer (6.69 ± 1.67 %), Bio-C Sealer Ion+ (5.67 ± 2.16 %) and AH Plus (0.15 ± 0.01 %) (p < 0.05). AH Plus (0.03 ± 0.01 %) had slight expansion while the cement-based sealers had shrinkage: AH Plus Bioceramic (-1.60 ± 0.63 %) and Bio-C Sealer (-1.38 ± 0.69 %), Bio-C Sealer Ion+ (-5.19 ± 1.23 %) (p < 0.05). Bio-C Sealer Ion+ (59.80 ± 0.86 mm) and Bio-C Sealer (58.60 ± 0.98 mm) had the highest flow compared with AH Plus (56.90 ± 0.56 mm) and AH Plus Bioceramic (49.50 ± 0.63 mm) (p < 0.05). AH Plus (9.17 ± 0.06 mmAl) and AH Plus Bioceramic (8.27 ± 0.84 mmAl) showed radiopacity values when compared with those of Bio-C Sealer (4.90 ± 0.08 mmAl) and Bio-C Sealer Ion+ (4.14 ± 0.05 mmAl) (p > 0.05). CONCLUSION: Ion release is inhered to these cement-based sealers and this result in calcium ion release.

Uncovering allostery and regulation in SORCIN through molecular dynamics simulations.

Soluble resistance-related calcium-binding protein or Sorcin is an allosteric, calcium-binding Penta-EF hand (PEF) family protein implicated in multi-drug resistant cancers. Sorcin is known to bind chemotherapeutic molecules such as Doxorubicin. This study uses in-silico molecular dynamics simulations to explore the dynamics and allosteric behavior of Sorcin in the context of Ca2+ uptake and Doxorubicin binding. The results show that Ca2+ binding induces large, but reversible conformational changes in the Sorcin structure which manifest as rigid body reorientations that preserve the local secondary structure. A reciprocal allosteric handshake centered around the EF5 hand is found to be key in Sorcin dimer formation and stabilization. Binding of Doxorubicin results in rearrangement of allosteric communities which disrupts long-range allosteric information transfer from the N-terminal domain to the middle lobe. However, this binding does not result in secondary structure destabilization. Sorcin does not appear to have a distinct Ca2+ activated mode of Doxorubicin binding.Communicated by Ramaswamy H. Sarma.

Optimization of enzymatic saccharification of industrial wastes using a thermostable and halotolerant endoglucanase through Box-Behnken experimental design.

This study describes the production, characterization and application of an endoglucanase from Penicillium roqueforti using lignocellulosic agro-industrial wastes as the substrate during solid-state fermentation. The endoglucanase was generated after culturing with different agro-industrial wastes for 96 h without any pretreatment. The highest activity was obtained at 50 °C and pH 4.0. Additionally, the enzyme showed stability in the temperature and pH ranges of 40-80 °C and 4.0-5.0, respectively. The addition of Ca2+, Zn2+, Mg2+, and Cu2+ increased enzymatic activity. Halotolerance as a characteristic of the enzyme was confirmed when its activity increased by 35% on addition of 2 M NaCl. The endoglucanase saccharified sugarcane bagasse, coconut shell, wheat bran, cocoa fruit shell, and cocoa seed husk. The Box-Behnken design was employed to optimize fermentable sugar production by evaluating the following parameters: time, substrate, and enzyme concentration. Under ideal conditions, 253.19 mg/g of fermentable sugars were obtained following the saccharification of wheat bran, which is 41.5 times higher than that obtained without optimizing. This study presents a thermostable, halotolerant endoglucanase that is resistant to metal ions and organic solvents with the potential to be applied in producing fermentable sugars for manufacturing biofuels from agro-industrial wastes.

Assessment of calcium alginate gels as wall materials for encapsulation systems.

BACKGROUND: Calcium alginate gels are widely used to encapsulate active compounds. Some characteristic parameters of these gels are necessary to describe the release of active compounds through mechanistic mathematical models. In this work, transport and kinetics properties of calcium alginate gels were determined through simple experimental techniques. RESULTS: The weight-average molecular weight ( M ¯ w = 192 × 103 Da) and the fraction of residues of α-l-guluronic acid ( F G = 0.356) of sodium alginate were determined by capillary viscometry and 1 H-nuclear magnetic resonance at 25 °C, respectively. Considering the half egg-box model, both values were used to estimate the molecular weight of calcium alginate as M g = 2.02 × 105 Da. An effective diffusion coefficient of water ( D eff , w = 2.256 × 10-9 m2 s-1 ) in calcium alginate was determined using a diffusion cell at 37 °C. Finally, a kinetics constant of depolymerization ( k m = 9.72 × 10-9 m3 mol-1 s-1 ) of calcium alginate was obtained considering dissolution of calcium to a medium under intestinal conditions. CONCLUSION: The experimental techniques used are simple and easily reproducible. The obtained values may be useful in the design, production, and optimization of the alginate-based delivery systems that require specific release kinetics of the encapsulated active compounds. © 2023 Society of Chemical Industry.

Mapping interactions of calmodulin and neuronal NO synthase by crosslinking and mass spectrometry.

Neuronal nitric oxide synthase (nNOS) is a homodimeric cytochrome P450-like enzyme that catalyzes the conversion of L-arginine to nitric oxide in the presence of NADPH and molecular oxygen. The binding of calmodulin (CaM) to a linker region between the FAD/FMN-containing reductase domain, and the heme-containing oxygenase domain is needed for electron transfer reactions, reduction of the heme, and NO synthesis. Due to the dynamic nature of the reductase domain and low resolution of available full-length structures, the exact conformation of the CaM-bound active complex during heme reduction is still unresolved. Interestingly, hydrogen-deuterium exchange and mass spectrometry studies revealed interactions of the FMN domain and CaM with the oxygenase domain for iNOS, but not nNOS. This finding prompted us to utilize covalent crosslinking and mass spectrometry to clarify interactions of CaM with nNOS. Specifically, MS-cleavable bifunctional crosslinker disuccinimidyl dibutyric urea was used to identify thirteen unique crosslinks between CaM and nNOS as well as 61 crosslinks within the nNOS. The crosslinks provided evidence for CaM interaction with the oxygenase and reductase domain residues as well as interactions of the FMN domain with the oxygenase dimer. Cryo-EM studies, which gave a high-resolution model of the oxygenase domain, along with crosslink-guided docking provided a model of nNOS that brings the FMN within 15 Å of the heme in support for a more compact conformation than previously observed. These studies also point to the utility of covalent crosslinking and mass spectrometry in capturing transient dynamic conformations that may not be captured by hydrogen-deuterium exchange and mass spectrometry experiments.

A closer look at calcium-induced interactions between phosphatidylserine-(PS) doped liposomes and the structural effects caused by inclusion of gangliosides or polyethylene glycol- (PEG) modified lipids.

The effects of polyethylene glycol- (PEG) modified lipids and gangliosides on the Ca2+ induced interaction between liposomes composed of palmitoyl-oleoyl phosphatidylethanolamine (POPE) and palmitoyl-oleoyl phosphatidylserine (POPS) was investigated at physiological ionic strength. Förster resonance energy transfer (FRET) studies complemented with dynamic light scattering (DLS) and cryo-transmission electron microscopy (Cryo-EM) show that naked liposomes tend to adhere, rupture, and collapse on each other's surfaces upon addition of Ca2+, eventually resulting in the formation of large multilamellar aggregates and bilayer sheets. Noteworthy, the presence of gangliosides or PEGylated lipids does not prevent the adhesion-rupture process, but leads to the formation of small, long-lived bilayer fragments/disks. PEGylated lipids seem to be more effective than gangliosides at stabilizing these structures. Attractive interactions arising from ion correlation are proposed to be a driving force for the liposome-liposome adhesion and rupture processes. The results suggest that, in contrast with the conclusions drawn from previous solely FRET-based studies, direct liposome-liposome fusion is not the dominating process triggered by Ca2+ in the systems studied.

Transformations in crystals of DNA-functionalized nanoparticles by electrolytes.

Colloidal crystals have applications in water treatments, including water purification and desalination technologies. It is, therefore, important to understand the interactions between colloids as a function of electrolyte concentration. We study the assembly of DNA-grafted gold nanoparticles immersed in concentrated electrolyte solutions. Increasing the concentration of divalent Ca2+ ions leads to the condensation of nanoparticles into face-centered-cubic (FCC) crystals at low electrolyte concentrations. As the electrolyte concentration increases, the system undergoes a phase change to body-centered-cubic (BCC) crystals. This phase change occurs as the interparticle distance decreases. Molecular dynamics analysis suggests that the interparticle interactions change from strongly repulsive to short-range attractive as the divalent-electrolyte concentration increases. A thermodynamic analysis suggests that increasing the salt concentration leads to significant dehydration of the nanoparticle environment. We conjecture that the intercolloid attractive interactions and dehydrated states favour the BCC structure. Our results gain insight into salting out of colloids such as proteins as the concentration of salt increases in the solution.

Direct Determination of Ca, K, and Mg in Soy Leaf Samples Using Laser-Induced Breakdown Spectroscopy.

This study was dedicated to developing analytical methods for determining macronutrients (Ca, K, and Mg) in soy leaf samples with and without petioles. The study's primary purpose was to present Laser-induced breakdown spectroscopy (LIBS) as a viable alternative for directly analyzing leaf samples using chemometric tools to interpret the data obtained. The instrumental condition chosen for LIBS was 70 mJ of laser pulse energy, 1.0 µs of delay time, and 100 µm of spot size, which was applied to 896 samples: 305 of soy without petioles and 591 of soy with petioles. The reference values of the analytes for the proposition of calibration models were obtained using inductively coupled plasma optical emission spectroscopy (ICP-OES) technique. Twelve normalization modes and two calibration strategies were tested to minimize signal variations and sample matrix microheterogeneity. The following were studied: multivariate calibration using partial least squares and univariate calibration using the area and height of several selected emission lines. The notable normalization mode for most models was the Euclidean norm. No analyte showed promising results for univariate calibrations. Micronutrients, P and S, were also tested, and no multivariate models presented satisfactory results. The models obtained for Ca, K, and Mg showed good results. The standard error of calibration ranged from 2.3 g/kg for Ca in soy leaves without petioles with two latent variables to 5.0 g/kg for K in soy leaves with petioles with two latent variables.