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1.
Sci Rep ; 12(1): 13425, 2022 Aug 04.
Article in English | MEDLINE | ID: mdl-35927566

ABSTRACT

Although Bioactive Glasses (BGs) have been progressively optimized, their preparation often still involves the use of toxic reagents and high calcination temperatures to remove organic solvents. In the present work, these synthesis related drawbacks were overcome by treating the ashes from the Equisetum hyemale plant in an ethanol/water solution to develop a bioactive composite [glass/carbon (BG-Carb)]. The BG-Carb was characterized by scanning electron microscopy, and transmission electron microscopy; and its chemical composition was assessed by inductively coupled plasma-optical emission spectroscopy. Brunauer-Emmett-Teller gas adsorption analysis showed a specific surface area of 121 m2 g-1. The formation of hydroxyapatite (HA) surface layer in vitro was confirmed by Fourier-transform infrared spectroscopy analysis before and after immersion in simulated body fluid (SBF) solution. The Rietveld refinement of the XRD patterns and selected area electron diffraction analyses confirmed HA in the sample even before immersing it in SBF solution. However, stronger evidences of the presence of HA were observed after immersion in SBF solution due to the surface mineralization. The BG-Carb samples showed no cytotoxicity on MC3T3-E1 cells and osteo-differentiation capacity similar to the positive control. Altogether, the BG-Carb material data reveals a promising plant waste-based candidate for hard and soft tissue engineering.


Subject(s)
Biocompatible Materials , Equisetum , Biocompatible Materials/chemistry , Durapatite/chemistry , Glass/chemistry , Microscopy, Electron, Scanning , Solutions , Spectroscopy, Fourier Transform Infrared , Tissue Engineering/methods , X-Ray Diffraction
2.
Water Sci Technol ; 86(1): 80-94, 2022 Jul.
Article in English | MEDLINE | ID: mdl-35838284

ABSTRACT

Cu(PABA) is a Cu-based MOF material assembled from Cu2+ and the organic ligand p-aminobenzoic acid (PABA). Cu (PABA) was synthesized by a solvothermal method, characterized and applied to the adsorption of direct red 31 dye (DR-31). The effects of pH, DR-31 concentration and temperature on the adsorption performance of Cu(PABA) were investigated. The adsorption kinetics were analyzed by pseudo-first-order, pseudo-second-order and intra-particle diffusion models, and the adsorption equilibrium data was fitted by Langmuir and Freundlich isotherm models. The pseudo-first-order kinetics and Langmuir model satisfactorily described the adsorption kinetics and adsorption equilibrium, respectively. The maximum adsorption capacity of Cu(PABA) for DR-31 dye at room temperature was 1,244.8 mg/g, as calculated using the Langmuir adsorption isotherm model. By response surface methodology (RSM), the optimal adsorption was found at pH value of 10.9, DR-31 dye concentration of 216.6 mg/L, and temperature of 27 °C, and the removal rate was as high as 99.4%. Therefore, Cu(PABA) can be used as an efficient adsorbent for removing DR-31 dye from aqueous solution.


Subject(s)
4-Aminobenzoic Acid , Acids , Adsorption , Azo Compounds , Hydrogen-Ion Concentration , Kinetics , Solutions
3.
J Chem Phys ; 156(24): 244903, 2022 Jun 28.
Article in English | MEDLINE | ID: mdl-35778071

ABSTRACT

Intermolecular interactions in protein solutions, in general, contain many contributions. If short-range attractions dominate, the state diagram exhibits liquid-liquid phase separation (LLPS) that is metastable with respect to crystallization. In this case, the extended law of corresponding states (ELCS) suggests that thermodynamic properties are insensitive to details of the underlying interaction potential. Using lysozyme solutions, we investigate the applicability of the ELCS to the static structure factor and how far effective colloidal interaction models can help to rationalize the phase behavior and interactions of protein solutions in the vicinity of the LLPS binodal. The (effective) structure factor has been determined by small-angle x-ray scattering. It can be described by Baxter's adhesive hard-sphere model, which implies a single fit parameter from which the normalized second virial coefficient b2 is inferred and found to quantitatively agree with previous results from static light scattering. The b2 values are independent of protein concentration but systematically vary with temperature and solution composition, i.e., salt and additive content. If plotted as a function of temperature normalized by the critical temperature, the values of b2 follow a universal behavior. These findings validate the applicability of the ELCS to globular protein solutions and indicate that the ELCS can also be reflected in the structure factor.


Subject(s)
Proteins , Crystallization , Proteins/chemistry , Solutions/chemistry , Temperature , Thermodynamics
4.
Article in English | MEDLINE | ID: mdl-35805879

ABSTRACT

Forward osmosis (FO) is an evolving membrane separation technology for water treatment and reclamation. However, FO water treatment technology is limited by factors such as concentration polarization, membrane fouling, and reverse solute flux. Therefore, it is of a great importance to prepare an efficient high-density porous membrane and to select an appropriate draw solute to reduce concentration polarization, membrane fouling, and reverse solute flux. This review aims to present a thorough evaluation of the advancement of different draw solutes and membranes with their effects on FO performance. NaCl is still widely used in a large number of studies, and several general draw solutes, such as organic-based and inorganic-based, are selected based on their osmotic pressure and water solubility. The selection criteria for reusable solutes, such as heat-recovered gaseous draw, magnetic field-recovered MNPs, and electrically or thermally-responsive hydrogel are primarily based on their industrial efficiency and energy requirements. CA membranes are resistant to chlorine degradation and are hydrophilic, while TFC/TFN exhibit a high inhibition of bio-adhesion and hydrolysis. AQPs are emerging membranes, due to proteins with complete retention capacity. Moreover, the development of the hybrid system combining FO with other energy or water treatment technologies is crucial to the sustainability of FO.


Subject(s)
Membranes, Artificial , Water Purification , Osmosis , Sodium Chloride , Solutions , Waste Water
5.
JAMA ; 328(3): 251-258, 2022 07 19.
Article in English | MEDLINE | ID: mdl-35852528

ABSTRACT

Importance: In cardiac surgery, albumin solution may maintain hemodynamics better than crystalloids and reduce the decrease in platelet count and excessive fluid balance, but randomized trials are needed to compare the effectiveness of these approaches in reducing surgical complications. Objective: To assess whether 4% albumin solution compared with Ringer acetate as cardiopulmonary bypass prime and perioperative intravenous volume replacement solution reduces the incidence of major perioperative and postoperative complications in patients undergoing cardiac surgery. Design, Setting, and Participants: A randomized, double-blind, single-center clinical trial in a tertiary university hospital during 2017-2020 with 90-day follow-up postoperatively involving patients undergoing on-pump coronary artery bypass grafting; aortic, mitral, or tricuspid valve surgery; ascending aorta surgery without hypothermic circulatory arrest; and/or the maze procedure were randomly assigned to 2 study groups (last follow-up was April 13, 2020). Interventions: The patients received in a 1:1 ratio either 4% albumin solution (n = 693) or Ringer acetate solution (n = 693) as cardiopulmonary bypass priming and intravenous volume replacement intraoperatively and up to 24 hours postoperatively. Main Outcomes and Measures: The primary outcome was the number of patients with at least 1 major adverse event: death, myocardial injury, acute heart failure, resternotomy, stroke, arrhythmia, bleeding, infection, or acute kidney injury. Results: Among 1407 patients randomized, 1386 (99%; mean age, 65.4 [SD, 9.9] years; 1091 men [79%]; 295 women [21%]) completed the trial. Patients received a median of 2150 mL (IQR, 1598-2700 mL) of study fluid in the albumin group and 3298 mL (IQR, 2669-3500 mL) in the Ringer group. The number of patients with at least 1 major adverse event was 257 of 693 patients (37.1%) in the albumin group and 234 of 693 patients (33.8%) in the Ringer group (relative risk albumin/Ringer, 1.10; 95% CI, 0.95-1.27; P = .20), an absolute difference of 3.3 percentage points (95% CI, -1.7 to 8.4). The most common serious adverse events were pulmonary embolus (11 [1.6%] in the albumin group vs 8 [1.2%] in the Ringer group), postpericardiotomy syndrome (9 [1.3%] in both groups), and pleural effusion with intensive care unit or hospital readmission (7 [1.0%] in the albumin group vs 9 [1.3%] in the Ringer group). Conclusions and Relevance: Among patients undergoing cardiac surgery with cardiopulmonary bypass, treatment with 4% albumin solution for priming and perioperative intravenous volume replacement solution compared with Ringer acetate did not significantly reduce the risk of major adverse events over the following 90 days. These findings do not support the use of 4% albumin solution in this setting. Trial Registration: ClinicalTrials.gov Identifier: NCT02560519.


Subject(s)
Albumins , Cardiac Surgical Procedures , Cardiopulmonary Bypass , Fluid Therapy , Heart Diseases , Isotonic Solutions , Aged , Albumins/administration & dosage , Albumins/adverse effects , Albumins/therapeutic use , Cardiac Surgical Procedures/adverse effects , Cardiac Surgical Procedures/methods , Cardiopulmonary Bypass/adverse effects , Cardiopulmonary Bypass/methods , Coronary Artery Bypass/adverse effects , Coronary Artery Bypass/methods , Double-Blind Method , Female , Fluid Therapy/adverse effects , Fluid Therapy/methods , Heart Diseases/surgery , Heart Diseases/therapy , Humans , Isotonic Solutions/administration & dosage , Isotonic Solutions/adverse effects , Isotonic Solutions/therapeutic use , Male , Middle Aged , Solutions/administration & dosage , Solutions/adverse effects , Solutions/therapeutic use
6.
Sensors (Basel) ; 22(14)2022 Jul 14.
Article in English | MEDLINE | ID: mdl-35890957

ABSTRACT

A cheap technique based on an open-ended coaxial probe together with a vector network analyzer was set up. The vector network analyzer NanoVNA, a very tiny handheld device, is the affordable component that gives the instrumental chain a cost-effective perspective. The open-ended coaxial probe is a cable with an SMA gold-plated termination. User-friendly programs can be used to calibrate the instrument, carry out the measurements, and save data on PC. Simple liquid solutions (sodium chloride, citric acids, and saccharose) and more complex liquid food (milk, egg products, and fruit juice) were investigated. In addition, the temperature on the electric measurement of milk was measured to evaluate a possible influence for refrigerated storage products. The reflection parameters, such as the real and imaginary parts of S11, were used to build univariate and multivariate models. The best results in terms of coefficient of determination and related error were 0.997 (RMSE 0.05%) for sodium chloride and 0.965 (RMSE 0.71 °Brix) for fruit juice considering the univariate model, and 0.997 (RMSE 0.04%) for sodium chloride and 0.981 (RMSE 4.44%) for yolk using multivariate analysis. The proposed solution is non-destructive, cheap, rapid, and very attractive for potential lab and industrial applications.


Subject(s)
Milk , Sodium Chloride , Animals , Cost-Benefit Analysis , Solutions , Temperature
7.
Molecules ; 27(14)2022 Jul 19.
Article in English | MEDLINE | ID: mdl-35889461

ABSTRACT

The supersaturation of a solution refers to a non-equilibrium phase in which the solution is trapped in a soluble state, even though the solute's concentration is greater than its thermodynamic solubility. Upon breaking supersaturation, crystals form and the concentration of the solute decreases to its thermodynamic solubility. Soon after the discovery of the prion phenomena, it was recognized that prion disease transmission and propagation share some similarities with the process of crystallization. Subsequent studies exploring the structural and functional association between amyloid fibrils and amyloidoses solidified this paradigm. However, recent studies have not necessarily focused on supersaturation, possibly because of marked advancements in structural studies clarifying the atomic structures of amyloid fibrils. On the other hand, there is increasing evidence that supersaturation plays a critical role in the formation of amyloid fibrils and the onset of amyloidosis. Here, we review the recent evidence that supersaturation plays a role in linking unfolding/folding and amyloid fibril formation. We also introduce the HANABI (HANdai Amyloid Burst Inducer) system, which enables high-throughput analysis of amyloid fibril formation by the ultrasonication-triggered breakdown of supersaturation. In addition to structural studies, studies based on solubility and supersaturation are essential both to developing a comprehensive understanding of amyloid fibrils and their roles in amyloidosis, and to developing therapeutic strategies.


Subject(s)
Amyloid , Amyloidosis , Amyloid/chemistry , Amyloidosis/metabolism , Humans , Solutions , Thermodynamics , beta 2-Microglobulin/chemistry
8.
J Chem Phys ; 157(3): 034109, 2022 Jul 21.
Article in English | MEDLINE | ID: mdl-35868919

ABSTRACT

Gibbs energies for reactions involving aqueous ions are challenging to predict due to the large solvation energies of such ions. A stringent test would be the ab initio reproduction of the aqueous-phase chelate effect, an entropic effect in reactions of very small enthalpy changes. This paper examines what is required to achieve such a reproduction for the paradigmatic reaction M(NH3)4 2+ + 2 en → M(en)2 2+ + 4 NH3 (en = 1,2-ethylenediamine), for which ΔrxnG* and ΔrxnH* are -2.3 and +1.6 kcal mol-1, respectively, if M = Zn. Explicit solvation via simulation was avoided in order to allow sufficiently accurate electronic structure models; this required the use of continuum solvation models (CSMs), and a great deal of effort was made in attempting to lower the relative errors of ΔsolvG*[M(NH3)4 2+] vs ΔsolvG*[M(en)2 2+] from the CSMs available in Gaussian software. CSMs in ADF and JDFTx software were also tested. A uniform 2.2 kcal mol-1 accuracy in ΔrxnG* for all three metal-atom choices M = {Zn, Cd, Hg} was eventually achieved, but not from any of the known CSMs tested, nor from cavity size reoptimization, nor from semicontinuum modeling: post facto solvation energy corrections [one per solute type, NH3, en, M(NH3)4 2+, M(en)2 2+] were needed. It is hoped that this study will aid (and encourage) further CSM development for coordination-complex ions.


Subject(s)
Metals , Water , Ions/chemistry , Solutions , Thermodynamics , Water/chemistry
9.
J Chem Phys ; 157(3): 034703, 2022 Jul 21.
Article in English | MEDLINE | ID: mdl-35868931

ABSTRACT

Recent studies suggest that cosolute mixtures may exert significant non-additive effects upon protein stability. The corresponding liquid-vapor interfaces may provide useful insight into these non-additive effects. Accordingly, in this work, we relate the interfacial properties of dilute multicomponent solutions to the interactions between solutes. We first derive a simple model for the surface excess of solutes in terms of thermodynamic observables. We then develop a lattice-based statistical mechanical perturbation theory to derive these observables from microscopic interactions. Rather than adopting a random mixing approximation, this dilute solution theory (DST) exactly treats solute-solute interactions to lowest order in perturbation theory. Although it cannot treat concentrated solutions, Monte Carlo (MC) simulations demonstrate that DST describes the interactions in dilute solutions with much greater accuracy than regular solution theory. Importantly, DST emphasizes a fundamental distinction between the "intrinsic" and "effective" preferences of solutes for interfaces. DST predicts that three classes of solutes can be distinguished by their intrinsic preference for interfaces. While the surface preference of strong depletants is relatively insensitive to interactions, the surface preference of strong surfactants can be modulated by interactions at the interface. Moreover, DST predicts that the surface preference of weak depletants and weak surfactants can be qualitatively inverted by interactions in the bulk. We also demonstrate that DST can be extended to treat surface polarization effects and to model experimental data. MC simulations validate the accuracy of DST predictions for lattice systems that correspond to molar concentrations.


Subject(s)
Surface-Active Agents , Monte Carlo Method , Solutions , Thermodynamics
10.
J Am Chem Soc ; 144(28): 12850-12860, 2022 Jul 20.
Article in English | MEDLINE | ID: mdl-35786922

ABSTRACT

Reference states are useful as models for facilitating calculations of equilibrium constants, and they may also serve as standard states that are convenient for organizing and tabulating thermodynamic data; however, standard state conventions and appropriate reference states for adsorbed species have received less attention than those for pure substances and solutes. Here, we compare seven choices of reference states for calculations of equilibrium constants and transition state theory rate constants for flat surfaces, in particular (1) an ideal 2D harmonic oscillator, (2) an ideal rigid-molecule harmonic oscillator, (3) an ideal 2D harmonic oscillator with separable surface modes, (4) a 2D ideal gas, (5) an ideal 2D hindered translator, (6) an ideal 2D hindered translator with lowest-order barriers, and (7) a simple ideal 2D hindered translator proposed in this work. The advantage of models 5-7 is that they can treat both mobile and localized adsorbates in a consistent way, whereas models 1-3 are only appropriate for localized adsorbates, and model 4 is only appropriate for a freely translating adsorbate. Furthermore, models 6 and 7 reduce the computational cost without the user having to calculate barrier heights for diffusion. An advantage of the simple ideal 2D hindered translator is that it has a physical high-temperature limit. We also propose a reference state for nonflat surfaces. The user is encouraged to choose a reference state based on the appropriateness of the model and the practicality of the calculations.


Subject(s)
Gases , Diffusion , Entropy , Solutions , Thermodynamics
11.
J Phys Chem A ; 126(30): 4991-5010, 2022 Aug 04.
Article in English | MEDLINE | ID: mdl-35863113

ABSTRACT

Chemical transformations in aerosols impact the lifetime of particle phase species, the fate of atmospheric pollutants, and both climate- and health-relevant aerosol properties. Timescales for multiphase reactions of ozone in atmospheric aqueous phases are governed by coupled kinetic processes between the gas phase, the particle interface, and its bulk, which respond dynamically to reactive consumption of O3. However, models of atmospheric aerosol reactivity often do not account for the coupled nature of multiphase processes. To examine these dynamics, we use new and prior experimental observations of aqueous droplet reaction kinetics, including three systems with a range of surface affinities and ozonolysis rate coefficients (trans-aconitic acid (C6H6O6), maleic acid (C4H4O4), and sodium nitrite (NaNO2)). Using literature rate coefficients and thermodynamic properties, we constrain a simple two-compartment stochastic kinetic model which resolves the interface from the particle bulk and represents O3 partitioning, diffusion, and reaction as a coupled kinetic system. Our kinetic model accurately predicts decay kinetics across all three systems, demonstrating that both the thermodynamic properties of O3 and the coupled kinetic and diffusion processes are key to making accurate predictions. An enhanced concentration of adsorbed O3, compared to gas and bulk phases is rapidly maintained and remains constant even as O3 is consumed by reaction. Multiphase systems dynamically seek to achieve equilibrium in response to reactive O3 loss, but this is hampered at solute concentrations relevant to aqueous aerosol by the rate of O3 arrival in the bulk by diffusion. As a result, bulk-phase O3 becomes depleted from its Henry's law solubility. This bulk-phase O3 depletion limits reaction timescales for relatively slow-reacting organic solutes with low interfacial affinity (i.e., trans-aconitic and maleic acids, with krxn ≈ 103-104 M-1 s-1), which is in contrast to fast-reacting solutes with higher surface affinity (i.e., nitrite, with krxn ≈ 105 M-1 s-1) where surface reactions strongly impact the observed decay kinetics.


Subject(s)
Ozone , Aerosols/chemistry , Diffusion , Kinetics , Ozone/chemistry , Solutions , Water/chemistry
12.
Sci Rep ; 12(1): 9904, 2022 Jun 14.
Article in English | MEDLINE | ID: mdl-35701498

ABSTRACT

Due to the growing human tendency to treat with natural substances, fungi such as Ganoderma lucidum can be a good source to meet this need. Effectiveness, ease of use and a rich source of active ingredients such as ganoderic acids have caused G. lucidum to be considered in the pharmaceutical and food industries. In this project, G. lucidum was applied to extraction using supercritical carbon dioxide. Then expansion of supercritical fluid solution (ESS) was used as, novel, repeatable and green method to yield nanoparticles from G.lucidum extract. The response surface method was used to improve the Extraction efficiency, antioxidant activity, and improving the nanoparticles production status. Optimal conditions were observed at the extraction step by setting pressure at 27.5 MPa, dynamic time of 46 min, and modifier volume of 162 µL. The optimum point for the production of nanoparticles was obtained as follows: pressure drop at 25 MPa, 20 min for collection time, and 40° C for temperature. Under these conditions, the size and count were 86.13 nm, and 98, respectively. Nanoparticles were analyzed by FESM and, the DPPH was used for antioxidant activity evaluation. The LC-MS identified various ganoderic acids from G.lucidum that are famous to be highly oxygenated triterpenoids.


Subject(s)
Ganoderma , Nanoparticles , Reishi , Triterpenes , Antioxidants , Chromatography, Liquid , Humans , Reishi/chemistry , Solutions , Triterpenes/chemistry
13.
Int J Mol Sci ; 23(11)2022 Jun 04.
Article in English | MEDLINE | ID: mdl-35682979

ABSTRACT

The study of the formation of microstructures during the interaction of a protonated drug-like compound (API) with a maleic acid monoanion sheds light on the assembly processes in an aqueous solution at the molecular level. Molecular dynamics (MD) simulations coupled with density functional theory (DFT) calculations made it possible to find initial hydrogen bonding motifs during the assembly process, leading to the formation of heterodimers and trimers. The process of trimer formation [protonated API-maleic acid monoanion-protonated API] proceeds through the formation of three intermolecular H-bonds by the CO2- group of the maleic acid monoanion in both systems. The total enthalpy/energy of these H-bonds is more than 70 kJ/mol. Thus, the maleic acid monoanion plays a key role in the processes of association in aqueous solution, and the interaction of the maleic acid monoanion with API is more preferable than the interaction of API molecules with each other. DFT computations in the discrete continuum approximation reveal the spectral features of heterodimers and trimers, and the ATR-IR spectra confirmed these findings. MD simulations followed by DFT calculations made it possible to describe the initial stages of the formation of pharmaceutical cocrystals in an aqueous solution.


Subject(s)
Molecular Dynamics Simulation , Salts , Hydrogen Bonding , Maleates/chemistry , Solutions , Water/chemistry
14.
Molecules ; 27(11)2022 Jun 03.
Article in English | MEDLINE | ID: mdl-35684533

ABSTRACT

The micellar liquid chromatography technique and quantitative retention (structure)-activity relationships method were used to predict properties of carbamic and phenoxyacetic acids derivatives, newly synthesized in our laboratory and considered as potential pesticides. Important properties of the test substances characterizing their potential significance as pesticides as well as threats to humans were considered: the volume of distribution, the unbonded fractions, the blood-brain distribution, the rate of skin and cell permeation, the dermal absorption, the binding to human serum albumin, partitioning between water and plants' cuticles, and the lethal dose. Pharmacokinetic and toxicity parameters were predicted as functions of the solutes' lipophilicities and the number of hydrogen bond donors, the number of hydrogen bond acceptors, and the number of rotatable bonds. The equations that were derived were evaluated statistically and cross-validated. Important features of the molecular structure influencing the properties of the tested substances were indicated. The QSAR models that were developed had high predictive ability and high reliability in modeling the properties of the molecules that were tested. The investigations highlighted the applicability of combined chromatographic technique and QS(R)ARs in modeling the important properties of potential pesticides and reducing unethical animal testing.


Subject(s)
Pesticides , Animals , Chromatography, Liquid/methods , Pesticides/toxicity , Quantitative Structure-Activity Relationship , Reproducibility of Results , Solutions , Structure-Activity Relationship
15.
J Phys Chem B ; 126(25): 4711-4722, 2022 06 30.
Article in English | MEDLINE | ID: mdl-35729500

ABSTRACT

Recent experiments with undersaturated aqueous glycine solutions have repeatedly exhibited the presence of giant liquid-like clusters or nanodroplets around 100 nm in diameter. These nanodroplets re-appear even after careful efforts for their removal and purification of the glycine solution. The composition of these clusters is not clear, although it has been suggested that they are mainly composed of glycine, a small and very soluble amino acid. To gain insights into this phenomenon, we study the aggregation of glycine in aqueous solutions at concentrations below the experimental solubility limit using large-scale molecular dynamics simulations under ambient conditions. Three protonation states of glycine (zwitterion = GLZ, anion = GLA, and cation = GLC) are simulated using molecular force fields based on the 1.14*CM1A partial charge scheme, which incorporates the OPLS all-atom force field and TIP3P water. When initiated from dispersed states, we find that giant clusters do not form in our simulations unless salt impurities are present. Moreover, if simulations are initiated from giant cluster states, we find that they tend to dissolve in the absence of salt impurities. Therefore, the simulation results provide little support for the possibility that the giant clusters seen in experiments are composed purely of glycine (and water). Considering that strenuous efforts are made in experiments to remove impurities such as salt, we propose that the giant clusters observed might instead result from the aggregation of reaction products of aqueous glycine, such as diketopiperazine or other oligoglycines which may be difficult to separate from glycine using conventional methods, or their co-aggregation with glycine.


Subject(s)
Molecular Dynamics Simulation , Water , Amino Acids , Cluster Analysis , Glycine/chemistry , Sodium Chloride , Solutions , Water/chemistry
16.
J Phys Chem B ; 126(24): 4520-4530, 2022 06 23.
Article in English | MEDLINE | ID: mdl-35675630

ABSTRACT

Water dynamics is essential to biochemical processes by mediating all such reactions, including biomolecular degeneration in solutions. To disentangle the molecular-scale distribution of water dynamics around a solute biomolecule, we investigated here the rotational dynamics of water around lysozyme by combining molecular dynamics (MD) simulations and broadband dielectric spectroscopy (BDS). A statistical analysis using the relaxation times and trajectories of every single water molecule was proposed, and the two-dimensional probability distribution of water at a distance from the lysozyme surface with a rotational relaxation time was given. For the observed lysozyme solutions of 34-284 mg/mL, we discovered that the dielectric relaxation time obtained from this distribution agrees well with the measured γ relaxation time, which suggests that rotational self-correlation of water molecules underlies the gigahertz domain of the dielectric spectra. Regardless of protein concentration, water rotational relaxation time versus the distance from the lysozyme surface revealed that the water rotation is severely retarded within 3 Å from the lysozyme surface and is nearly comparable to pure water when farther than 10 Å. The dimension of the first hydration layer was subsequently identified in terms of the relationship between the acceleration of water rotation and the distance from the protein surface.


Subject(s)
Molecular Dynamics Simulation , Muramidase , Water , Muramidase/chemistry , Rotation , Solutions/chemistry , Stochastic Processes , Water/chemistry
17.
J Chem Theory Comput ; 18(6): 3805-3813, 2022 Jun 14.
Article in English | MEDLINE | ID: mdl-35648114

ABSTRACT

Length-scale dependence of the hydrophobic effect is well understood for apolar spherical solutes: for small solutes (diameter, d ≲ 0.8 nm), the hydration free energy is entropically driven, while for larger solutes (d ≳ 2 nm), it is enthalpically driven. The nature of the hydrophobic effect in the case of anisotropic molecules such as linear alkanes is not understood yet. In this work, we have calculated the hydration free energy of linear alkanes going from methane to octadecane and of a spherical decane droplet of d ≈ 3 nm using molecular simulations. We show that the hydration free energies of alkanes, irrespective of their size, are governed by the small length-scale hydrophobic effect. That is, unlike the case of large spherical solutes, the hydration free energies of linear alkanes are entropically driven.


Subject(s)
Alkanes , Water , Alkanes/chemistry , Hydrophobic and Hydrophilic Interactions , Solutions , Thermodynamics , Water/chemistry
18.
Phys Chem Chem Phys ; 24(23): 14452-14471, 2022 Jun 15.
Article in English | MEDLINE | ID: mdl-35661176

ABSTRACT

Molecular tweezers feature the first class of artificial receptors to pique the interest of researchers and emerge as an effective therapeutic candidate. The exceptional structure and exquisite binding specificity of tweezers establish this overall class of receptors as a promising tool, with abundant applications. However, their inclination to self-aggregate by mutual π-π stacking interactions of their aromatic arms diminishes their efficacy as a therapeutic candidate. Therefore, following up on sporadic studies, since the discovery of the Hofmeister series, on the ability of ions to either solvate (salting-in) or induce aggregation (salting-out) of hydrophobic solutes, the notions of ion-specificity effects are utilized on tweezer moieties. The impacts of three different aluminum salts bearing anions Cl-, ClO4- and SCN- on the self-association propensity of Whitlock's caffeine-pincered molecular tweezers are investigated, with a specific emphasis placed on elucidating the varied behavior of the ions on the hydration ability of tweezers. The comparative investigation is conducted employing a series of all-atom molecular dynamics simulations of five tweezer molecules in pure water and three salt solutions, at two different concentrations each, maintaining a temperature of 300 K and a pressure of 1 atm, respectively. Radial distribution functions, coordination numbers, and SASA calculations display a steady reduction in the aggregation proclivity of the receptor molecules with an increase in salt concentration, as progressed along the Hofmeister series. Orientational preferences between the tweezer arms reveal a disruptive effect in the regular π-π stacking interactions, in the presence of high concentrations of ClO4- and SCN- ions, while preferential interactions and tetrahedral order parameters unveil the underlying mechanism, by which the anions alter the solubility of the hydrophobic molecules. Overall, it is observed that SCN- exhibits the highest salting-in effect, followed by ClO4-, with both anions inhibiting tweezer aggregation through different mechanisms. ClO4- ions impart an effect by moderately interacting with the solute molecules as well as modifying the water structure of the bulk solution promoting solvation, whereas, SCN- ions engage entirely in interaction with specific tweezer sites. Cl- being the most charge-dense of the three anionic species experiences stronger hydration and therefore, imparts a very negligible salting-in effect.


Subject(s)
Sodium Chloride , Water , Anions/chemistry , Hydrophobic and Hydrophilic Interactions , Ions/chemistry , Sodium Chloride/chemistry , Solutions/chemistry , Water/chemistry
19.
Phys Chem Chem Phys ; 24(23): 14498-14510, 2022 Jun 15.
Article in English | MEDLINE | ID: mdl-35665790

ABSTRACT

Aiming to reduce the computational cost in the current explicit solvent molecular dynamics (MD) simulation, this paper proposes a fast-slow method for the fast MD simulation of biomolecules in explicit solvent. This fast-slow method divides the entire system into two parts: a core layer (typically solute or biomolecule) and a peripheral layer (typically solvent molecules). The core layer is treated using standard MD method but the peripheral layer is treated by a slower dynamics method to reduce the computational cost. We compared four different simulation models in testing calculations for several small proteins. These include gas-phase, implicit solvent, fast-slow explicit solvent and standard explicit solvent MD simulations. Our study shows that gas-phase and implicit solvent models do not provide a realistic solvent environment and fail to correctly produce reliable dynamic structures of proteins. On the other hand, the fast-slow method can essentially reproduce the same solvent effect as the standard explicit solvent model while gaining an order of magnitude in efficiency. This fast-slow method thus provides an efficient approach for accelerating the MD simulation of biomolecules in explicit solvent.


Subject(s)
Molecular Dynamics Simulation , Proteins , Proteins/chemistry , Solutions , Solvents/chemistry
20.
J Chem Phys ; 156(22): 221104, 2022 Jun 14.
Article in English | MEDLINE | ID: mdl-35705398

ABSTRACT

To gain quantitative insight into how the overall strength of the hydrophobic interaction varies with the molecular size, we calculate osmotic second virial coefficients B for hydrophobic spherical molecules of different diameters σ in water based on molecular simulation with corrections to the finite-size and finite-concentration effects. It is shown that B (<0) changes by two orders of magnitude greater as σ increases twofold and its solute-size dependence is best fit by a power law B ∝ σα with the exponent α ≃ 6, which contrasts with the cubic power law that the second virial coefficients of gases obey. It is also found that values of B for the solutes in a nonpolar solvent are positive but they obey the same power law as in water. A thermodynamic identity for B derived earlier [K. Koga, V. Holten, and B. Widom, J. Phys. Chem. B 119, 13391 (2015)] indicates that if B is asymptotically proportional to a power of σ, the exponent α must be equal to or greater than 6.


Subject(s)
Water , Hydrophobic and Hydrophilic Interactions , Osmosis , Solutions/chemistry , Thermodynamics , Water/chemistry
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