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1.
Bioresour Technol ; 393: 129939, 2024 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-37951553

RESUMO

The sulfate reagent plays a crucial role as an electron acceptor in the sulfidogenic biodegradation process of the BSP assay for assessing the anaerobic biodegradability of organic substrates. However, the specific role and influence of the monovalent cations (sodium or potassium) in the sulfate reagent remain unknown. To address this gap, a series of batch assays were conducted to investigate the mechanistic effects of Na+ and K+. The results demonstrated that sodium has inhibitory effects on BSP assay when the dosage exceeds 8500 mg/L, whereas no adverse effects were observed in the potassium tests (ranging from 1800 to 14400 mg/L). In fact, the presence of K+ even enhanced the anaerobic biodegradability of organic substrates, and the underlying mechanisms were explored. These findings confirm the influence of cations in the BSP assay for biodegradability assessment and also provide guidance on sulfate dosage strategies for BSP assay application in anaerobic biotechnologies.


Assuntos
Esgotos , Sulfetos , Cátions Monovalentes , Sulfetos/metabolismo , Sulfatos/metabolismo , Sódio , Potássio
2.
Int J Mol Sci ; 24(23)2023 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-38068884

RESUMO

Monovalent cation proton antiporters (CPAs) play crucial roles in ion and pH homeostasis, which is essential for plant development and environmental adaptation, including salt tolerance. Here, 68 CPA genes were identified in soybean, phylogenetically dividing into 11 Na+/H+ exchangers (NHXs), 12 K+ efflux antiporters (KEAs), and 45 cation/H+ exchangers (CHXs). The GmCPA genes are unevenly distributed across the 20 chromosomes and might expand largely due to segmental duplication in soybean. The GmCPA family underwent purifying selection rather than neutral or positive selections. The cis-element analysis and the publicly available transcriptome data indicated that GmCPAs are involved in development and various environmental adaptations, especially for salt tolerance. Based on the RNA-seq data, twelve of the chosen GmCPA genes were confirmed for their differentially expression under salt or osmotic stresses using qRT-PCR. Among them, GmCHX20a was selected due to its high induction under salt stress for the exploration of its biological function on salt responses by ectopic expressing in Arabidopsis. The results suggest that the overexpression of GmCHX20a increases the sensitivity to salt stress by altering the redox system. Overall, this study provides comprehensive insights into the CPA family in soybean and has the potential to supply new candidate genes to develop salt-tolerant soybean varieties.


Assuntos
Antiporters , Arabidopsis , Antiporters/genética , Antiporters/metabolismo , Prótons , Trocadores de Sódio-Hidrogênio/genética , Trocadores de Sódio-Hidrogênio/metabolismo , Cátions Monovalentes/metabolismo , Arabidopsis/genética , Regulação da Expressão Gênica de Plantas , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo
3.
Nat Commun ; 14(1): 8482, 2023 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-38123540

RESUMO

Cleavage and formation of phosphodiester bonds in nucleic acids is accomplished by large cellular machineries composed of both protein and RNA. Long thought to rely on a two-metal-ion mechanism for catalysis, structure comparisons revealed many contain highly spatially conserved second-shell monovalent cations, whose precise function remains elusive. A recent high-resolution structure of the spliceosome, essential for pre-mRNA splicing in eukaryotes, revealed a potassium ion in the active site. Here, we employ biased quantum mechanics/ molecular mechanics molecular dynamics to elucidate the function of this monovalent ion in splicing. We discover that the K+ ion regulates the kinetics and thermodynamics of the first splicing step by rigidifying the active site and stabilizing the substrate in the pre- and post-catalytic state via formation of key hydrogen bonds. Our work supports a direct role for the K+ ion during catalysis and provides a mechanistic hypothesis likely shared by other nucleic acid processing enzymes.


Assuntos
RNA , Spliceossomos , Spliceossomos/metabolismo , RNA/metabolismo , Splicing de RNA , Catálise , Metais/metabolismo , Potássio/metabolismo , Quelantes/metabolismo , Conformação de Ácido Nucleico , Sítios de Ligação , Cátions Monovalentes/metabolismo
4.
Phys Chem Chem Phys ; 25(40): 27744-27755, 2023 Oct 18.
Artigo em Inglês | MEDLINE | ID: mdl-37814577

RESUMO

Double-stranded DNA bears the highest linear negative charge density (2e- per base-pair) among all biopolymers, leading to strong interactions with cations and dipolar water, resulting in the formation of a dense 'condensation layer' around DNA. Interactions involving proteins and ligands binding to DNA are primarily governed by strong electrostatic forces. Increased salt concentrations impede such electrostatic interactions - a situation that prevails in oceanic species due to their cytoplasm being enriched with salts. Nevertheless, how these interactions' dynamics are affected in crowded hypersaline environments remains largely unexplored. Here, we employ steady-state and time-resolved fluorescence Stokes shifts (TRFSS) of a DNA-bound ligand (DAPI) to investigate the static and dynamic solvation properties of DNA in the presence of two divalent cations, magnesium (Mg2+), and calcium (Ca2+) at varying high to very-high concentrations of 0.15 M, 1 M and 2 M. We compare the results to those obtained in physiological concentrations (0.15 M) of monovalent Na+ ions. Combining data from fluorescence femtosecond optical gating (FOG) and time-correlated single photon counting (TCSPC) techniques, dynamic fluorescence Stokes shifts in DNA are analysed over a broad range of time-scales, from 100 fs to 10 ns. We find that while divalent cation crowding strongly influences the DNA stability and ligand binding affinity to DNA, the dynamics of DNA solvation remain remarkably similar across a broad range of five decades in time, even in a high-salinity crowded environment with divalent cations, as compared to the physiological concentration of the Na+ ion. Steady-state and time-resolved data of the DNA-groove-bound ligand are seemingly unaffected by ion-crowding in hypersaline solution, possibly due to ions being mostly displaced by the DNA-bound ligand. Furthermore, the dynamic coupling of cations with nearby water may possibly contribute to a net-neutral effect on the overall collective solvation dynamics in DNA, owing to the strong anti-correlation of their electrostatic interaction energy fluctuations. Such dynamic scenarios may persist within the cellular environment of marine life and other biological cells that experience hypersaline conditions.


Assuntos
DNA , Salinidade , Cátions Bivalentes , Ligantes , DNA/química , Íons , Sódio , Água/química , Cátions , Cátions Monovalentes
5.
Molecules ; 28(13)2023 Jun 29.
Artigo em Inglês | MEDLINE | ID: mdl-37446774

RESUMO

Two new esters of lasalocid, that are more hydrophilic, with glucose (LasGlu) and xylitol (LasX), have been synthesized, and their complexation of monovalent cations has been studied by various spectrometric and spectroscopic methods, such as ESI mass spectrometry, 1H, 13C NMR and FT-IR. Analyses of the results confirmed the synthesis of new esters with good yields. In order to carry out further studies, it was necessary to purify them using "flash" liquid chromatography. It was confirmed that the newly obtained molecules, as well as their complexes with lithium, sodium and potassium cations, were stabilized by a strong system of intramolecular hydrogen bonds. It was found that the hydroxyl groups of esters derived from xylitol and glucose were also involved in the complexation of cations. The results of the PM6 semiempirical calculations permitted determination of the heat of formation (HOF), and visualization of the structure of the new esters and their complexes with the cations studied. All computation results are in agreement with the spectroscopic data.


Assuntos
Lasalocida , Xilitol , Espectroscopia de Infravermelho com Transformada de Fourier , Modelos Moleculares , Metais/química , Cátions/química , Cátions Monovalentes/química , Ésteres
6.
J Phys Chem B ; 127(31): 6842-6855, 2023 08 10.
Artigo em Inglês | MEDLINE | ID: mdl-37504511

RESUMO

G-Quadruplexes (G4s) are ubiquitous nucleic acid folding motifs that exhibit structural diversity that is dependent on cationic conditions. In this work, we exploit temperature-controlled single-molecule fluorescence resonance energy transfer (smFRET) to elucidate the kinetic and thermodynamic mechanisms by which monovalent cations (K+ and Na+) impact folding topologies for a simple G-quadruplex sequence (5'-GGG-(TAAGGG)3-3') with a three-state folding equilibrium. Kinetic measurements indicate that Na+ and K+ influence G4 formation in two distinctly different ways: the presence of Na+ modestly enhances an antiparallel G4 topology through an induced fit (IF) mechanism with a low affinity (Kd = 228 ± 26 mM), while K+ drives G4 into a parallel/hybrid topology via a conformational selection (CS) mechanism with much higher affinity (Kd = 1.9 ± 0.2 mM). Additionally, temperature-dependent studies of folding rate constants and equilibrium ratios reveal distinctly different thermodynamic driving forces behind G4 binding to K+ (ΔH°bind > 0, ΔS°bind > 0) versus Na+ (ΔH°bind < 0, ΔS°bind < 0), which further illuminates the diversity of the possible pathways for monovalent facilitation of G-quadruplex folding.


Assuntos
Quadruplex G , Termodinâmica , Polimorfismo Genético , Cinética , Cátions Monovalentes , Sódio/química , Potássio/química , Modelos Moleculares , Conformação de Ácido Nucleico , Temperatura
7.
Nature ; 618(7967): 1078-1084, 2023 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-37344591

RESUMO

Numerous studies have shown how RNA molecules can adopt elaborate three-dimensional (3D) architectures1-3. By contrast, whether DNA can self-assemble into complex 3D folds capable of sophisticated biochemistry, independent of protein or RNA partners, has remained mysterious. Lettuce is an in vitro-evolved DNA molecule that binds and activates4 conditional fluorophores derived from GFP. To extend previous structural studies5,6 of fluorogenic RNAs, GFP and other fluorescent proteins7 to DNA, we characterize Lettuce-fluorophore complexes by X-ray crystallography and cryogenic electron microscopy. The results reveal that the 53-nucleotide DNA adopts a four-way junction (4WJ) fold. Instead of the canonical L-shaped or H-shaped structures commonly seen8 in 4WJ RNAs, the four stems of Lettuce form two coaxial stacks that pack co-linearly to form a central G-quadruplex in which the fluorophore binds. This fold is stabilized by stacking, extensive nucleobase hydrogen bonding-including through unusual diagonally stacked bases that bridge successive tiers of the main coaxial stacks of the DNA-and coordination of monovalent and divalent cations. Overall, the structure is more compact than many RNAs of comparable size. Lettuce demonstrates how DNA can form elaborate 3D structures without using RNA-like tertiary interactions and suggests that new principles of nucleic acid organization will be forthcoming from the analysis of complex DNAs.


Assuntos
DNA , Proteínas de Fluorescência Verde , Mimetismo Molecular , Conformação de Ácido Nucleico , DNA/química , DNA/ultraestrutura , Quadruplex G , RNA/química , Proteínas de Fluorescência Verde/química , Proteínas de Fluorescência Verde/ultraestrutura , Cristalografia por Raios X , Microscopia Crioeletrônica , Ligação de Hidrogênio , Cátions Bivalentes/química , Cátions Monovalentes/química
8.
Electrophoresis ; 44(17-18): 1414-1422, 2023 09.
Artigo em Inglês | MEDLINE | ID: mdl-37354056

RESUMO

The free solution mobilities of 26-base pair (bp) DNA oligomers containing A-tracts with and without internal ApT steps have been measured by capillary electrophoresis, using the mobility of a 26-bp random-sequence oligomer as a reference. The background electrolytes (BGEs) contained mixtures of Li+ and tetrapropylammonium (TPA+ ) ions, keeping the total cation concentration constant at 0.3 M. The mobility ratios equaled 1.00 in 0.3 M TPA+ , indicating that the A-tract and reference oligomers had the same B-form conformation in this BGE. With increasing [Li+ ], the mobility ratio decreased as Li+ ions became localized in the A-tract minor groove, suggesting that the A-tract was now in the B* conformation. If the A-tract contained an internal ApT step and the oligomer contained less than ∼50% A + T, the mobility ratio reached a reduced plateau value that remained constant as the [Li+ ] increased to 0.3 M. However, for A-tracts without an internal ApT step and for A-tracts embedded in oligomers containing more than 50% A + T, the mobility ratios increased again at high [Li+ ], eventually reaching a plateau value of 1.00. Hence, DNA A-tracts in solution appear to exist as mixtures of the B and B* conformations, with the fractional concentration of each conformer depending on the [Li+ ], the A-tract sequence, and the total A + T content of the oligomer.


Assuntos
DNA , Lítio , Cátions Monovalentes , Sequência de Bases , Íons , Conformação de Ácido Nucleico
9.
Int J Mol Sci ; 24(11)2023 May 25.
Artigo em Inglês | MEDLINE | ID: mdl-37298189

RESUMO

The opening of the permeability transition pore (PTP) in mitochondria is a key event in the initiation of cell death in various pathologic states, including ischemia/reperfusion. The activation of K+ transport into mitochondria protects cells from ischemia/reperfusion. However, the role of K+ transport in PTP regulation is unclear. Here, we studied the role of K+ and other monovalent cations in the regulation of the PTP opening in an in vitro model. The registration of the PTP opening, membrane potential, Ca2+-retention capacity, matrix pH, and K+ transport was performed using standard spectral and electrode techniques. We found that the presence of all cations tested in the medium (K+, Na+, choline+, and Li+) strongly stimulated the PTP opening compared with sucrose. Several possible reasons for this were examined: the effect of ionic strength, the influx of cations through selective and non-selective channels and exchangers, the suppression of Ca2+/H+ exchange, and the influx of anions. The data obtained indicate that the mechanism of PTP stimulation by cations includes the suppression of K+/H+ exchange and acidification of the matrix, which facilitates the influx of phosphate. Thus, the K+/H+ exchanger and the phosphate carrier together with selective K+ channels compose a PTP regulatory triad, which might operate in vivo.


Assuntos
Mitocôndrias Hepáticas , Poro de Transição de Permeabilidade Mitocondrial , Humanos , Poro de Transição de Permeabilidade Mitocondrial/metabolismo , Mitocôndrias Hepáticas/metabolismo , Proteínas de Transporte da Membrana Mitocondrial/metabolismo , Cátions Monovalentes/metabolismo , Isquemia/metabolismo , Cálcio/metabolismo , Permeabilidade
10.
J Phys Chem B ; 127(9): 1932-1939, 2023 03 09.
Artigo em Inglês | MEDLINE | ID: mdl-36811958

RESUMO

At acidic pH, cytosine-rich single-stranded DNA can be folded into a tetraplex structure called i-motif (iM). In recent studies, the effect of monovalent cations on the stability of iM structure has been addressed, but a consensus about the issue has not been reached yet. Thus, we investigated the effects of various factors on the stability of iM structure using fluorescence resonance energy transfer (FRET)-based analysis for three types of iM derived from human telomere sequences. We confirmed that the protonated cytosine-cytosine (C:C+) base pair is destabilized as the concentration of monovalent cations (Li+, Na+, K+) increases and that Li+ has the greatest tendency of destabilization. Intriguingly, monovalent cations would play an ambivalent role in iM formation by making single-stranded DNA flexible and pliant for an iM structure. In particular, we found that Li+ has a notably greater flexibilizing effect than Na+ and K+. All taken together, we conclude that the stability of iM structure is controlled by the subtle balance of the two counteractive effects of monovalent cations: electrostatic screening and disruption of cytosine base pairing.


Assuntos
DNA de Cadeia Simples , Sódio , Humanos , Cátions Monovalentes/química , Sódio/química , Lítio/química , Citosina/química , Cátions
11.
Biophys Chem ; 294: 106949, 2023 03.
Artigo em Inglês | MEDLINE | ID: mdl-36706510

RESUMO

Monovalent and divalent cations play a crucial role in living cells and for molecular techniques such as PCR. Here we evaluate DNA melting temperatures in magnesium (Mg2+) and magnesium­potassium (Mg2++ K+) buffers with a mesoscopic model that allows us to estimate hydrogen bonds and stacking interaction potentials. The Mg2+ and Mg2++ K+ results are compared to previous calculations for sodium ions (Na+), in terms of equivalent sodium concentration and ionic strength. Morse potentials, related to hydrogen bonding, were found to be essentially constant and unaffected by cation conditions. However, for stacking interactions we find a clear dependence with ionic strength and cation valence. The highest ionic strength variations, for both hydrogen bonds and stacking interactions, was found at the sequence terminals. This suggests that end-to-end interactions in DNA will be strongly dependent on cation valence and ionic strength.


Assuntos
DNA , Magnésio , Ligação de Hidrogênio , Cátions , DNA/química , Sódio , Cátions Monovalentes/química
12.
Environ Technol ; 44(9): 1322-1333, 2023 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-34710003

RESUMO

Manganese is naturally present in water, but its increased concentration in potable water is undesirable for multiple reasons. This study investigates an alternative method of demanganization by a newly synthesized TiO2-based adsorbent prepared through the transformation of titanyl sulphate monohydrate to amorphous sodium titanate. Its adsorption capacity for Mn2+ was determined, while a range of influential factors, such as the effect of contact time, adsorbent dosage, pH value, and added ions was evaluated. The adsorbent appeared highly effective for Mn2+ removal owing to its unique characteristics. Besides adsorption via electrostatic interactions, ion-exchange was also involved in the Mn2+ removal. Although the Mn2+ removal occurred within the whole investigated pH range of 4-8, the maximum was achieved at pH 7, with qe = 73.83 mg g-1. Equilibrium data revealed a good correlation with Langmuir isotherm in the absence of any ions or in the presence of monovalent co-existing ions, while the results in the presence of divalent co-existing ions showed a better fit to Freundlich isotherm. Additionally, the presence of monovalent cations (Na+, K+) only slightly decreased the Mn2+ removal efficiency as compared to divalent cations (Ca2+, Mg2+) that caused a greater decrease; however, the effect of anions (Cl-, SO42-) was insignificant. To provide insight into the adsorbent safety, the toxicity assessment was performed and showed no harmful effect on cell activity. Furthermore, the residual concentration of titanium after adsorption was always below the detection limit. The results imply that the synthesized TiO2-based adsorbent is a safe promising alternative method for demanganization.Highlights The synthesis of amorphous TiO2-based adsorbent was presented.The TiO2-based adsorbent was found to be efficient for Mn2+ removal.The Mn2+ removal mechanisms were adsorption and ion-exchange.Increasing pH enhanced the efficiency of Mn2+ removal.Divalent cations decreased the Mn2+ removal efficiency more than monovalent cations.


Assuntos
Água Potável , Poluentes Químicos da Água , Purificação da Água , Manganês , Adsorção , Cátions Bivalentes , Íons , Cátions Monovalentes , Concentração de Íons de Hidrogênio , Cinética , Poluentes Químicos da Água/análise , Purificação da Água/métodos
13.
Biophys J ; 122(3): 565-576, 2023 02 07.
Artigo em Inglês | MEDLINE | ID: mdl-36540026

RESUMO

The prediction of RNA secondary structure and thermodynamics from sequence relies on free energy minimization and nearest neighbor parameters. Currently, algorithms used to make these predictions are based on parameters from optical melting studies performed in 1 M NaCl. However, many physiological and biochemical buffers containing RNA include much lower concentrations of monovalent cations and the presence of divalent cations. In order to improve these algorithms, thermodynamic data was previously collected for RNA duplexes in solutions containing 71, 121, 221, and 621 mM Na+. From this data, correction factors for free energy (ΔG°37) and melting temperature (Tm) were derived. Despite these newly derived correction factors for sodium, the stabilizing effects of magnesium have been ignored. Here, the same RNA duplexes were melted in solutions containing 0.5, 1.5, 3.0, and 10.0 mM Mg2+ in the absence of monovalent cations. Correction factors for Tm and ΔG°37 were derived to scale the current parameters to a range of magnesium concentrations. The Tm correction factor predicts the melting temperature within 1.2°C, and the ΔG°37 correction factor predicts the free energy within 0.30 kcalmol. These newly derived magnesium correction factors can be incorporated into algorithms that predict RNA secondary structure and stability from sequence.


Assuntos
Magnésio , Sódio , Magnésio/química , Termodinâmica , Temperatura , Sódio/química , Cátions Monovalentes/farmacologia , RNA/química , Conformação de Ácido Nucleico , Estabilidade de RNA
14.
J Biol Chem ; 299(2): 102811, 2023 02.
Artigo em Inglês | MEDLINE | ID: mdl-36539036

RESUMO

The Na+/K+-ATPase is an integral plasma membrane glycoprotein of all animal cells that couples the exchange of intracellular Na+ for extracellular K+ to the hydrolysis of ATP. The asymmetric distribution of Na+ and K+ is essential for cellular life and constitutes the physical basis of a series of fundamental biological phenomena. The pumping mechanism is explained by the Albers-Post model. It involves the presence of gates alternatively exposing Na+/K+-ATPase transport sites to the intracellular and extracellular sides and includes occluded states in which both gates are simultaneously closed. Unlike for K+, information is lacking about Na+-occluded intermediates, as occluded Na+ was only detected in states incapable of performing a catalytic cycle, including two Na+-containing crystallographic structures. The current knowledge is that intracellular Na+ must bind to the transport sites and become occluded upon phosphorylation by ATP to be transported to the extracellular medium. Here, taking advantage of epigallocatechin-3-gallate to instantaneously stabilize native Na+-occluded intermediates, we isolated species with tightly bound Na+ in an enzyme able to perform a catalytic cycle, consistent with a genuine occluded state. We found that Na+ becomes spontaneously occluded in the E1 dephosphorylated form of the Na+/K+-ATPase, exhibiting positive interactions between binding sites. In fact, the addition of ATP does not produce an increase in Na+ occlusion as it would have been expected; on the contrary, occluded Na+ transiently decreases, whereas ATP lasts. These results reveal new properties of E1 intermediates of the Albers-Post model for explaining the Na+ transport pathway.


Assuntos
Biocatálise , ATPase Trocadora de Sódio-Potássio , Sódio , Animais , Trifosfato de Adenosina/metabolismo , Membrana Celular/metabolismo , Cinética , Potássio/metabolismo , Sódio/metabolismo , ATPase Trocadora de Sódio-Potássio/química , ATPase Trocadora de Sódio-Potássio/metabolismo , Transporte de Íons , Fosforilação , Cátions Monovalentes/metabolismo
15.
Adv Biol (Weinh) ; 7(3): e2200164, 2023 03.
Artigo em Inglês | MEDLINE | ID: mdl-36328593

RESUMO

The effect of monovalent cations on a cell-free transcription-translation (TX-TL) system is examined using a luciferase assay. It is found that the potency for all ions analyzed here is in the order Rb+  > K+  > Cs+  > Na+  ≈ Li+  > (CH3 )4 N+ , where Rb+ is most efficient at promoting TX-TL and the ions of Li+ , Na+ , and (CH3 )4 N+ exhibit an inhibitory effect. Similar promotion/inhibition effects are observed for cell-free TL alone with an mRNA template.


Assuntos
Lítio , Sódio , Cátions Monovalentes/farmacologia , Lítio/farmacologia , Sódio/farmacologia , Expressão Gênica
16.
Food Chem ; 404(Pt A): 134519, 2023 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-36252377

RESUMO

The present study aimed to investigate effects of pH and monovalent (Na+ and K+)/divalent (Ca2+ and Mg2+) cations on the structural and physicochemical properties of myofibrillar protein (MP) from silver carp. MP treated with divalent cation had lesser change for the structure than that treated with monovalent cation. Ca2+-ATPase activity of MP treated with monovalent cation was increased firstly and then decreased, while that treated with divalent cation was decreased with increasing ionic strength. Surface hydrophobicity and Z-average of MP treated with divalent cations was lower than that with monovalent cations, while they decreased and then increased with the pH shifting from 3.0 to 9.0. Zeta potential of MP was increased and then decreased with increasing the pH but decreased and then increased with increasing ionic strength. In general, the pH and monovalent/divalent cations could cause various hydrophobic and electrostatic interactions, resulting in changes of the physicochemical properties of MP.


Assuntos
Carpas , Animais , Cátions Monovalentes/química , Cátions Bivalentes/química , Carpas/metabolismo , Sódio/metabolismo , Concentração de Íons de Hidrogênio , Cátions
17.
J Phys Chem B ; 126(49): 10471-10480, 2022 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-36451081

RESUMO

The accurate description of the structures of water and hydrated ions is important in electrochemical desalination, ion separation, and supercapacitors. In this work, we present an ab initio atomistic simulation-based study to explore the structure of water and hydrated monovalent ions (Li+, Na+, K+, Rb+, F-, and Cl-) at ambient conditions using generalized gradient approximation (GGA)-based methods with and without van der Waals correction (PBE, PBE + D3, and revPBE + D3) and recently developed strongly constrained and appropriately normed (SCAN) meta-GGA. We find that both revPBE + D3 and SCAN can well capture the structure of bulk water with +30 K artificial high temperature in contrast to overstructuring water using PBE and PBE + D3. However, being the same as PBE + D3, revPBE + D3 overestimates the structure of the hydration shell, especially for monovalent cations. Surprisingly, SCAN can well match the experimental results of hydrated monovalent ions. Detailed structure analyzes of entropy reveal that the hydration shell under the level of PBE + D3 and revPBE + D3 is more disordered and looser than SCAN. The successful prediction of the flexible SCAN functional could facilitate the exploration of complex ionic processes in the aqueous phase, the interactions of hydrated ions with surfaces, and solvation states in nanopores at an accurate, efficient, predictive, and ab initio level.


Assuntos
Simulação de Dinâmica Molecular , Água , Água/química , Teoria da Densidade Funcional , Íons/química , Cátions Monovalentes
18.
Sci Rep ; 12(1): 16496, 2022 10 03.
Artigo em Inglês | MEDLINE | ID: mdl-36192436

RESUMO

Swelling of epidermal cell walls decreases cell-to-cell adhesion and increases cracking susceptibility in sweet cherry. Ca is suggested to decrease cracking susceptibility by crosslinking of cell wall components and, possibly, by decreasing swelling. The objective is to test this hypothesis. The effect of Ca on swelling of anticlinal epidermal cell walls was quantified microscopically in vivo using excised skin sections and in vitro using extracted cell walls. After removal of turgor, cell wall thickness increased. Incubation in CaCl2 decreased cell wall thickness up to 3 mM CaCl2. At higher concentrations thickness remained constant. Decreased cell wall swelling in vivo also occurred with other salts of divalent and trivalent cations, but not with those of monovalent cations. Decreased swelling was due to the Ca cation, the anions had no effect. Ca also decreased swelling of cell walls that were already swollen. CaCl2 also decreased swelling of extracted cell walls in vitro. There was no effect on swelling pressure. The effect on swelling increased as the CaCl2 concentration increased. Chlorides of divalent and trivalent cations, but not those of monovalent cations decreased swelling in vitro. The decrease in swelling among the divalent cations was linearly related to the radius of the cation. The results indicate that Ca decreases cracking susceptibility by decreasing swelling.


Assuntos
Prunus avium , Cálcio/metabolismo , Cloreto de Cálcio/metabolismo , Cloreto de Cálcio/farmacologia , Cálcio da Dieta/metabolismo , Cátions Bivalentes/metabolismo , Cátions Monovalentes/metabolismo , Parede Celular , Frutas/metabolismo , Sais/farmacologia
19.
J Chem Phys ; 157(15): 154902, 2022 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-36272789

RESUMO

Lipopolysaccharides (LPSs) are negatively charged molecules covering the surface of Gram-negative bacteria (GNB). Adding divalent cations (DCs) is important to stabilize the LPS bilayer. Thus, DCs are always only considered as membrane stabilizing ions. Here, on the basis of a coarse-grained (CG) Martini force field, we conduct molecular dynamic (MD) simulations to study the divalent cation mediated LPS interaction and the stability of the LPS membrane in a wide range of DC concentrations. By measuring the LPS binding free energy and the LPS-LPS aggregate from the association course between two LPS molecules, we find that the initial addition of DCs may significantly facilitate the aggregation of LPSs into a compact structure, while sequentially adding more DCs only unpacks the LPS aggregate and drives the dissolution of LPSs. With an increasing concentration of DCs, we find a gradual replacement of DCs to monovalent cations as condensed counterions on the LPS, which follows a sign change from negative to positive in terms of the LPS effective charge and a switch of LPSs in solution from undergoing precipitation to resolubilization on adding DCs. This interaction change in the level of two LPSs accounts for the structure variation of the LPS assembly on a larger scale, where the LPS packing rigidity in the assembly bilayer is found with a similar nonmonotonic dependence with the DC concentration. Thus, our results demonstrate for the first time the presence of a re-entrant condensation behavior for LPS molecules, which can be exploited for developing novel membrane-perturbing agents based on multivalent ions as efficient GNB antibiotics.


Assuntos
Bactérias Gram-Negativas , Lipopolissacarídeos , Cátions Bivalentes/química , Lipopolissacarídeos/química , Bactérias Gram-Negativas/química , Cátions Monovalentes , Antibacterianos
20.
Environ Sci Technol ; 56(19): 14069-14079, 2022 10 04.
Artigo em Inglês | MEDLINE | ID: mdl-36126287

RESUMO

Nanofiltration (NF) membranes are playing increasingly crucial roles in addressing emerging environmental challenges by precise separation, yet understanding of the selective transport mechanism is still limited. In this work, the underlying mechanisms governing precise selectivity of the polyamide NF membrane were elucidated using a series of monovalent cations with minor hydrated radius difference. The observed selectivity of a single cation was neither correlated with the hydrated radius nor hydration energy, which could not be explained by the widely accepted NF model or ion dehydration theory. Herein, we employed an Arrhenius approach combined with Monte Carlo simulation to unravel that the transmembrane process of the cation would be dominated by its pairing anion, if the anion has a greater transmembrane energy barrier, due to the constraint of anion-cation coupling transport. Molecular dynamics simulations further revealed that the distinct hydration structure was the primary origin of the energy barrier difference of cations. The cation having a larger incompressible structure after partial dehydration through subnanopores would induce a more significant ion-membrane interaction and consequently a higher energy barrier. Moreover, to validate our proposed mechanisms, a membrane grafting modification toward enlarging the energy barrier difference of dominant ions achieved a 3-fold enhancement in ion separation efficiency. Our work provides insights into the precise separation of ionic species by NF membranes.


Assuntos
Desidratação , Nylons , Ânions/química , Cátions Monovalentes , Humanos , Simulação de Dinâmica Molecular
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