Polar Solutes Research Articles

Star Days without Polar Stars Complete Solutions with Other Explanations

Star Days without Polar Stars Complete Solutions with Other Explanations

The kinetics of dissolution and cluster formation of fullerene in polar and low polar solutions

Fullerene and fullerene like nanostructures play a main role in various research areas. Theamount of investigations of fullerene C60 and C70 has grown up considerably due to their several unique properties [1-2, 6]. In this report we present theoretical models for cluster growth, the modeling of small angle neutron scattering curves, and the results of structural analysis (SANS) for polar solutions of these macromolecules. Investigation of kinetics of dissolution and complex formation are studied for C60/Benzene, C60/Toluene and C60/Nmethyl-2-pyrrolidone (NMP) solutions of various concentrations by UV-Vis spectrometry. We model the kinetics of simultaneously occurring processes in the solution via a system of basic kinetic equations and obtain the corresponding parameters dependence on preparation conditions. The investigation of structural properties of fullerene solution in CS2 was performed at the YuMO instrument of the IBR-2 reactor. The results are compared tomolecular dynamics simulations, and other research works

Can Urea and Trimethylamine-N-oxide Prevent the Pressure-Induced Phase Transition of Lipid Membrane?

Organisms dwelling in ocean trenches are exposed to the high hydrostatic pressure of ocean water. Increasing pressure can alter the membrane packing density and fluidity and trigger the fluid-to-gel phase transition. To combat environmental stress, the organisms synthesize small polar solutes, which are known as osmolytes. Urea and trimethylamine-N-oxide (TMAO) are two such solutes found in deep-sea creatures. While TMAO stabilizes protein, urea induces protein denaturation. These solutes strongly influence the packing density and membrane fluidity of the lipid bilayer at different conditions. But can these solutes affect the pressure-induced phase transition of the lipid membrane? In the present work, we have studied the effect of these two solutes on pressure-induced fluid-to-gel phase transition based on the all-atom molecular dynamics (MD) simulation approach. A high-pressure-stimulated fluid-to-gel phase transition of the membrane is seen at 800 bar, which is consistent with previous experiments. We have also observed that in the low-pressure region (1-400 bar), urea slightly increases the membrane fluidity where TMAO decreases the same. However, the phase transition pressure remains almost unchanged on the addition of urea while TMAO shifts the phase transition toward a lower pressure. We have found that the hydrogen (H)-bond interaction between lipid and urea plays an important role in preserving the fluidity of the membrane in the low-pressure zone. However, at a higher pressure, both water and urea are excluded from the membrane surface. TMAO is also excluded from the interfacial region of the membrane at all pressures. Exclusion from the membrane surface further triggers the phase transition of the lipid membrane from the fluid to gel phase at a high pressure.

The Improvement of the Performance of Sky-Blue OLEDs by Decreasing Interface Traps and Balancing Carriers with PSVA Treatment.

The mitigation of interfacial charge accumulation in solution-processed organic light-emitting diodes (s-OLEDs) is an effective method to improve device performance. In this study, the polar solvent vapor annealing (PSVA) method was used to treat two layers in s-OLED, PEDOT:PSS and mCP:DMAC-DPS emitting layers, separately, to optimize the carrier transmission and balance. After the double-layer PSVA treatment, the current efficiency increased, the lifetime of the device is improved, the efficiency roll-off alleviated from 33.3% to 26.6%, and the maximum brightness increased by 31.3%. It is worth mentioning that the work function of the EML interface reduced by 0.36 eV, and the initial injection voltage of the electrons also reduced. Simulating the solubility of the LUMO and HOMO molecule parts of the mCP and DMAC-DPS, it was found that the LUMO parts had stronger polarity and higher solubility in polar solution than the HOMO parts. By comparing the untreated luminescent layer films, it was found that the PSVA treatment improved the uniformity of the film morphology. We may infer that a more ordered molecular arrangement enhances carrier transport as the LUMO parts tend to be close to the surface and the reduced local state traps on the EML surface promote electron injection. According to the experimental results, the injection of holes and electrons is enhanced from both sides of the EML, respectively, and the charge accumulated at the interface of s-OLEDs is significantly reduced due to the improvement of carrier-transported characteristics.

Permeate Flux in Ultrafiltration Processes-Understandings and Misunderstandings.

Concentration polarization refers to the rapid emergence of concentration gradients at a membrane/solution interface resulting from selective transfer through the membrane. It is distinguishable from fouling in at least two ways: (1) the state of the molecules involved (in solution for concentration polarization, although no longer in solution for fouling); and (2) by the timescale, normally less than a minute for concentration polarization, although generally at least two or more orders of magnitude more for fouling. Thus the phenomenon of flux decline occurring over a timescale of tens of minutes should not be attributed to concentration polarization establishing itself. This distinction and a number of questions surrounding modelling are addressed and clarified. There are two paradigmatic approaches for modelling flux, one uses the overall driving force (in which case allowance for osmotic effects are expressed as additional resistances) and the other uses the net driving force across the separating layer or fouled separating layer, although often the two are unfortunately comingled. In the discussion of flux decline models’ robust approaches for the determination of flux-time relationships, including the integral method of fouling analysis, are discussed and various concepts clarified. The final section emphases that for design purposes, pilot plant data are vital.

Influence of hydrogen bond donor on zinc chloride in separation of binary mixtures: Activity coefficients at infinite dilution

Deep eutectic solvents are solvents similar to the ionic liquids (ILs) but less expensive and simple to prepare than ILs. The activity coefficients at infinite dilution of solutes in the deep eutectic solvents (DESs) plays an important role in designing of the separation processes. Gas liquid chromatography technique (GLC) was used to determine activity coefficients at infinite dilution for 34 polar and non-polar organic solutes: solutes include alkanes, alkenes, alcohols, ketones, thiophene, heterocyclics, cycloalkanes, acetonitrile, tetrahydrofuran, cycloalkenes, aromatic hydrocarbon and water in two zinc chloride based DESs [zinc chloride + acetic acid] (1:4) and [zinc chloride + phosphoric acid] (1:2.5) at temperatures (313.15, 323.15, 333.15, 343.15, 353.15) K. Excess thermodynamic parameters [partial molar excess enthalpies ΔG1E,∞,entropies(TrefΔS1E,∞) and Gibbs free energies (ΔG1E,∞)] were derived from activity coefficient at infinite dilution data. The selectivity and capacity values for separation of benzene/ethanol, cyclohexane/ethanol, n-octane/acetonitrile, ethylbenzene/butan-1-ol, n-heptane/butan-1-ol at T = 323.15 K were calculated and compared to literature values for DESs, ionic liquids (ILs), and sulfolane to assess the suitability of the DESs for possible use as an entrainers. Both DESs [zinc chloride + acetic acid] (1:4) and [zinc chloride + phosphoric acid] (1:2.5) have high selectivity values as compared to studied ionic liquids as well as conventional solvents in the literature for difficult separation system of benzene/ethanol, cyclohexane/ethanol, ethylbenzene/butanol and heptane/butanol which indicate that these DESs are an extraction solvent and has separation ability for difficult separation system of benzene/ethanol, cyclohexane/ethanol, ethylbenzene/butan-1-ol and n-heptane/butan-1-ol.

Water-soluble BODIPY-nido-carborane nanoparticles applied to biocompatibility tumor cell imaging.

In this article, o-carborane has a high boron content, high hydrophobicity, and goodchemicalstability. It has been widely used in the fields of biology and medicine, especially in the application of boron neutron capture therapy (BNCT). However, o-carborane is a fat-soluble compound, its hydrophobicity is too strong, and its bioavailability is poor. This project aims to improve the water solubility of o-carborane drugs, so that the drugs can reach specific sites. For this reason, this article provides a one-pot reaction for the synthesis of water-soluble boron-containing drugs. 2-Chloro-1-(difluoroboranyl)-5-((4-ethyl-3,5-dimethyl-2H-pyrrol-2-ylidene)(phenyl) methyl)-1H-pyrrole and ethylenediamine are used as raw materials to synthesize fluorescent molecular probe BODIPY-NH2, and the fluorescent molecular probe is reacted with P-CBMA (poly(carboxybetaine methacrylate)) to produce a water-soluble gel polymer. Water-soluble o-carborane polymers were synthesized by hydrogen bonding of the polymers with bis(4-azaspiro[3.4]octan-4-ium)-nido-ortho-carborane and bis(5-azaspiro[4.5]decan-5-ium)-nido-ortho-caborane. The two polymers were characterized and the results showed that the maximum UV absorption wavelength of the two boron polymers in different polar solutions was 530-540nm. In the fluorescence spectrum, the maximum emission wavelengths of the two boron polymers are concentrated between 550 and 560nm. Through electron microscopy imaging, the fluoroboron pyrrole polymers wrap the boron clusters to form a spherical stacked. Through fluorescent cell imaging, both boron polymers can enter target cells.

Facile preparation of CuO-Gd2Ti2O7 using Acmella uliginosa leaf extract for photocatalytic degradation of malachite green

CuO-Gd2Ti2O7 has been prepared in a two-phase system of polar precursor solution and non-polar hexane fraction of Acmella uliginosa leaf extract (AUE). The secondary metabolites in AUE have an essential role in the synthesis of CuO-Gd2Ti2O7. The optical bandgap value for CuO-Gd2Ti2O7 plummeted from 3.68 to 1.78 eV, compared to Gd2Ti2O7. The photocatalytic activity was investigated to degrade malachite green (MG) under visible light illumination. As a result, CuO-Gd2Ti2O7 showed the MG degradation percentage of 88.60% after 90 min of illumination, which was 1.9 times higher than the MG degradation percentage over Gd2Ti2O7. The improved photocatalytic activity could be ascribed to the narrower optical bandgap Gd2Ti2O7 after being decorated by CuO, which effectively works in the visible region. This research suggests a novel method to prepare CuO-Gd2Ti2O7 as a promising candidate with good photocatalytic activity for the degradation of malachite green under visible light illumination.

Numerical simulation of electrohydrodynamic convection induced by fast oscillating field emission

The paper presents a mathematical model of electrohydrodynamic convection in a mixture of benzene and chlorobenzene subjected to highly inhomogeneous alternating electric field. The field inhomogeneity is determined by the shape of the electrodes, of which one is a flat electrode, and the other is a tip oriented perpendicular to the plane of the first electrode. Recent experiments carried out with a field oscillating at a frequency of 50 Hz have shown that the excitation of an averaged convective flow at a given maximum voltage between the electrodes (8 kV) is observed only at a mole fraction of chlorobenzene of at least 0.4. The flow arises in a threshold manner and is a narrow intense jet directed from the sharp electrode towards the plane closed by an axisymmetric return flow. We propose a model that explains this phenomenon by analyzing the interaction between two fields of charged particles. The sharp electrode injects electrons every half period due to cold field emission. We assume that a chlorobenzene molecule has an uncompensated dipole moment, i.e., in a strong electric field, a chlorobenzene molecule gains an electron and forms a negative ion. However, an electron can exist in a polar dielectric solution for a long time due to the effect of its salvation by the medium. Therefore, the ionization process occurs both at the injector electrode and in the bulk of the medium. The mathematical model includes the Navier–Stokes equation, the transport equations for electrons and ionized chlorobenzene molecules, and the equation of alternating electric field. The sharp electrode boundary conditions are formulated to take into account the cold emission of electrons, which is described by a piecewise linear approximation of the Fowler–Nordheim law. The study of the performance of the proposed model was carried out by the method of direct numerical simulations of non-stationary physical fields. It is shown that if the presence of electrons in the volume of the medium is ignored, the averaged electrohydrodynamic convection does not occur, even if the sharp electrode continues to inject chlorobenzene molecules. The proposed model explains most of the experimental facts. As in the experiment, the excitation of convection critically depends on the mole fraction of chlorobenzene in the binary mixture. The calculated and experimentally observed structures of the convective flow are in good qualitative and quantitative agreement. The results of numerical experiments provide a good basis for the development of an averaged theory of electrohydrodynamic convection.

Supramolecular self-associating amphiphiles: determination of molecular self-association properties and calculation of critical micelle concentration using a high-throughput, optical density based methodology.

Supramolecular self-associating amphiphiles are a class of amphiphilic salt, the anionic component of which is 'frustrated' in nature, meaning multiple hydrogen bonding modes can be accessed simultaneously. Here we derive critical micelle concentration values for four supramolecular self-associating amphiphiles using the standard pendant drop approach and present a new high-throughput, optical density measurement based methodology, to enable the estimation of critical micelle concentrations over multiple temperatures. In addition, we characterise the low-level hydrogen bonded self-association events in the solid state, through single crystal X-ray diffraction, and in polar organic DMSO-d6 solutions using a combination of 1H NMR techniques. Moving into aqueous ethanol solutions (EtOH/H2O or EtOH/D2O (1 : 19 v/v)), we also show these amphiphilic compounds to form higher-order self-associated species through a combination of 1H NMR, dynamic light scattering and zeta potential studies.

The pervasive impact of critical fluctuations in liquid-liquid extraction organic phases.

Liquid-liquid extraction is an essential chemical separation technique where polar solutes are extracted from an aqueous phase into a nonpolar organic solvent by amphiphilic extractant molecules. A fundamental limitation to the efficiency of this important technology is third phase formation, wherein the organic phase splits upon sufficient loading of polar solutes. The nanoscale drivers of phase splitting are challenging to understand in the complex hierarchically structured organic phases. In this study, we demonstrate that the organic phase structure and phase behavior are fundamentally connected in a way than can be understood with critical phenomena theory. For a series of binary mixtures of trialkyl phosphate extractants with linear alkane diluents, we combine small angle x-ray scattering and molecular dynamics simulations to demonstrate how the organic phase mesostructure over a wide range of compositions is dominated by critical concentration fluctuations associated with the critical point of the third phase formation phase transition. These findings reconcile many longstanding inconsistencies in the literature where small angle scattering features, also consistent with such critical fluctuations, were interpreted as reverse micellar-like particles. Overall, this study shows how the organic phase mesostructure and phase behavior are intrinsically linked, deepening our understanding of both and providing a new framework for using molecular structure and thermodynamic variables to control mesostructure and phase behavior in liquid-liquid extraction.

Synthesis of novel poly(arylene ether amide) containing aliphatic ring for optical property

In this work, the monomer N, N′-bis(4-fluorobenzamide)dicyclohexyl methane (BFDCM) was synthesized successfully by 4-fluorobenzoylchloride and 4,4′-diaminodicyclohexylmethane through interfacial reaction, and then the monomer BFDCM and 1,4-benzenediol (HQ) or 4.4′-biphenol (BH) were used to prepare the novel poly(arylene ether amide) (HQ-BFDCM and BH-BFDCM) containing an aliphatic ring in the main chain by nucleophilic substitution in NMP solution. These two polymers exhibited the inherent viscosities ranging from 0.828 to 1.044 dL g−1, high glass-transition temperatures (Tg) of 214.1–235.0 °C, and weight-loss temperature (T5%) of 425.2–441.3 °C. The polymers HQ-BFDCM and BH-BFDCM could completely or partly dissolve in some polar solutions, such as NMP, DMF, and so on, and they showed moderate corrosion resistance. Additionally, the obtained polymers HQ-BFDCM and BH-BFDCM exhibited good optical property, and the optical transmittances of HQ-BFDCM and BH-BFDCM were 74% and 80% at 450 nm, respectively, which showed that they could be applied to the heat-resistant optical films.

Propagation of axial and polar gravitational waves in Kantowski–Sachs universe

We apply the Regge-Wheeler formalism to study axial and polar gravitational waves in Kantowski-Sachs universe. The background field equations and the linearised perturbation equations for the modes are derived in presence of matter. To find analytical solutions, we analyze the propagation of waves in vacuum spacetime. The background field equations in absence of matter are solved by assuming the expansion scalar to be proportional to the shear scalar. Using the method of separation of variables, the axial perturbation parameter $ h_0(t, r) $ is obtained from its wave equation. The other perturbation $ h_1(t, r) $ is then determined from $ h_0(t, r) $. The anisotropy of the background spacetime is responsible for the damping of the axial waves. The polar perturbation equations are much more involved compared to their FLRW counterparts, as well as to the axial perturbations in Kantowski-Sachs background. In both the axial and polar cases, the radial and temporal solutions separate out as products. The temporal part of the polar perturbation solutions are plotted against time to obtain an order of magnitude estimate of the frequency of the propagating GWs and lies in the range 1000-2000 Hz. Using standard observational data for the GW strain we have placed constraints on the parameters in the polar perturbation solutions. The perturbation equations in presence of matter show that the axial waves can cause perturbations only in the azimuthal velocity of the fluid without deforming the matter field. But the polar waves must perturb the energy density, the pressure and also the non-azimuthal components of the fluid velocity.

Analyzing the quasi-oscillatory nature of electrical parameters with the concentration of sucrose in aqueous solution at room temperature

The impedance, capacitance and conductance of aqueous sucrose polar solution are measured by employing impedance spectroscopy method and the current passing through the system for different DC voltages are measured implementing I-V method. The variation of electrical parameters with sucrose content in such solution exhibits a quasi-oscillatory nature, which is attributed to the random orientation of water and sucrose dipoles in the solution and their mutual interactions at the molecular level, including water-water, water-sucrose and sucrose-sucrose dipole interactions. To justify the quasi-oscillatory nature from analytical point of view, a theoretical model is developed on the basis of multi-body dipolar interactions of randomly distributed molecular dipoles. The experimental data agrees well with those obtained from the analytical model. The measurement of electrical parameters is performed within a frequency window of 100 Hz to 4 MHz for volume fractions of sucrose with respect to water, ranging from 0.1 to 0.6. The impedance, capacitance and conductance are obtained to be in the range of 0.907 k – 281 k, 38 pF – 266 pF, and 3 µS – 55 µS respectively for the sucrose volume fraction range considered. Current voltage measurements for the same concentration range are performed for a voltage swing between ±5 V and the obtained values vary from +20 µA to -25 µA. The study represents a deterministic approach to analyze the effective nature of a sucrose solution in terms of dielectric polarization of the system which finds application in sucrose quality assessments.

Solitons and soliton interactions in repulsive spinor Bose–Einstein condensates with nonzero background

We characterize the soliton solutions and their interactions for a system of coupled evolution equations of nonlinear Schrödinger (NLS) type that models the dynamics in one-dimensional repulsive Bose–Einstein condensates with spin one, taking advantage of the representation of such model as a special reduction of a $$2\times 2$$ matrix NLS system. Specifically, we study in detail the case in which solutions tend to a nonzero background at space infinities. First we derive a compact representation for the multi-soliton solutions in the system using the Inverse Scattering Transform (IST). We introduce the notion of canonical form of a solution, corresponding to the case when the background as $$x\rightarrow \infty $$ is proportional to the identity. We show that solutions for which the asymptotic behavior at infinity is not proportional to the identity, referred to as being in non-canonical form, can be reduced to canonical form by unitary transformations that preserve the symmetric nature of the solution (physically corresponding to complex rotations of the quantization axes). Then we give a complete characterization of the two families of one-soliton solutions arising in this problem, corresponding to ferromagnetic and to polar states of the system, and we discuss how the physical parameters of the solitons for each family are related to the spectral data in the IST. We also show that any ferromagnetic one-soliton solution in canonical form can be reduced to a single dark soliton of the scalar NLS equation, and any polar one-soliton solution in canonical form is unitarily equivalent to a pair of oppositely polarized displaced scalar dark solitons up to a rotation of the quantization axes. Finally, we discuss two-soliton interactions and we present a complete classification of the possible scenarios that can arise depending on whether either soliton is of ferromagnetic or polar type.

Exploring the Assembly of Resorc[4]arenes for the Construction of Supramolecular Nano-Aggregates.

Many biologically active compounds feature low solubility in aqueous media and, thus, poor bioavailability. The formation of the host-guest complex by using calixarene-based macrocycles (i.e., resorcinol-derived cyclic oligomers) with a good solubility profile can improve solubilization of hydrophobic drugs. Herein, we explore the ability of resorc[4]arenes to self-assemble in polar solutions, to form supramolecular aggregates, and to promote water-solubility of an isoflavone endowed with anti-cancer activity, namely Glabrescione B (GlaB). Accordingly, we synthesized several architectures featuring a different pattern of substitution on the upper rim including functional groups able to undergo acid dissociation (i.e., carboxyl and hydroxyl groups). The aggregation phenomenon of the amphiphilic resorc[4]arenes has been investigated in a THF/water solution by UV–visible spectroscopy, at different pH values. Based on their ionization properties, we demonstrated that the supramolecular assembly of resorc[4]arene-based systems can be modulated at given pH values, and thus promoting the solubility of GlaB.

N‐Butanol: An Ecologically and Economically Viable Extraction Solvent for Isolating Polar Products from Aqueous Solutions

AbstractWater is the solvent of choice in terms of greenness and sustainability. However, it can be difficult to isolate very polar products from water. Here, we discuss the use of n‐butanol as a solvent to extract polar compounds from aqueous solution. n‐Butanol produces high yields and can also be sourced sustainably from biomass, which makes it attractive from a climate perspective. The reason for its high efficiency is that the wet n‐butanol phase is a nanomaterial that incorporates little pockets of water that can stabilize the polar solute. Thus, the environment remains very water‐like, and the presence of hydrophobic groups can tip the equilibrium towards the n‐butanol phase. We also discuss a simple estimate whether n‐butanol will be an efficient extraction solvent for the compound of interest based on common public databases. This should help to guide practicing organic chemists during the solvent selection process.

Amphiphile conformation impacts aggregate morphology and solution structure across multiple lengthscales

Although the self-assembly of amphiphiles is well-studied in aqueous solutions, much less is understood about the fundamental driving forces and structure property relationships in non-polar media. In recent work [Journal of Physical Chemistry B, 2020, 124, 10822.] the authors have studied a series of malonomide-based amphiphiles that are relevant to liquid-liquid extraction. That work demonstrated that aggregation is largely driven by local dipole-dipole interactions between molecules. Here, we build upon this observation to develop a more detailed understanding of how the balance of dipole-dipole interactions (controlled by conformation) and molecular architecture influences the morphology of the aggregates across lengthscales. Using constrained molecular dynamics about key degrees of freedom, we demonstrate that the conformation of N,N-dimethyl,N,N-dioctylhexylethoxy malonamide (DMDOHEMA) and N,N-dimethyl,N,N-dibutyltetradecyl malonamide (DMDBTDMA) has a significant impact upon self-association - where appropriate conformational sampling is essential. To quantify the aggregate morphology, several graph theoretic and persistent homology based properties are determined. The former examines the patterns of intermolecular interactions within clusters, while the latter examines the 3-dimensional spatial distribution. Based upon these analyses, we find that the morphology of aggregates, particularly at higher malonamide concentration, depends on a balance of dipole alignment and alkyl tail sterics. Dipole alignment encourages linear patterns of the intermolecular interactions within aggregates, while the alkyl tail steric interactions between the malonamide result in noticeably less linear aggregates for DMDOHEMA than DMDBTDMA. This is reflected in the spatial distribution, where more holes or voids exist between extractants within the DMDOHEMA that distribute within the solution in more of a “swiss cheese” arrangement as opposed to the more filamentous distribution of DMBDTDMA. This study links conformation and molecular structure to the morphology of amphiphile assemblies, and serves as a basis for ongoing study of multicomponent amphiphile solutions with polar and other solutes, and how these impact aggregation phenomena.

On the behavior of quercetin + organic solvent solutions and their role for C60 fullerene solubilization

The nature of flavonoids in polar organic solvents solutions is studied using classical molecular dynamics simulations considering quercetin as an archetypical flavonoid and acetone, dimethylformamide and dimethyl sulfoxide as representatives of solvents with different polarity. The solvation, intermolecular forces (hydrogen bonding) and interactions of the flavonoid with the solvents are analyzed. Likewise, the role of quercetin on changing the solvent properties and the possibility of acting as a solubility enhancer for fullerenes (C60) are studied by considering the properties of C60 fullerene in quercetin plus polar solvents solutions. The reported results provide information on the nature of the considered complex liquid mixtures and analyze the possibility of using flavonoids as natural, non-toxic, modifiers of traditional polar organic solvents and to improve the solubility of complex solutes such as fullerene nanoparticles.

NMR Relaxation Rates of Quadrupolar Aqueous Ions from Classical Molecular Dynamics Using Force-Field Specific Sternheimer Factors.

The nuclear magnetic resonance (NMR) relaxation of quadrupolar nuclei is governed by the electric field gradient (EFG) fluctuations at their position. In classical molecular dynamics (MD), the electron cloud contribution to the EFG can be included via the Sternheimer approximation, in which the full EFG at the nucleus that can be computed using quantum density functional theory (DFT) is considered to be proportional to that arising from the external, classical charge distribution. In this work, we systematically assess the quality of the Sternheimer approximation as well as the impact of the classical force field (FF) on the NMR relaxation rates of aqueous quadrupolar ions at infinite dilution. In particular, we compare the rates obtained using an ab initio parametrized polarizable FF, a recently developed empirical FF with scaled ionic charges and a simple empirical nonpolarizable FF with formal ionic charges. Surprisingly, all three FFs considered yield good values for the rates of smaller and less polarizable solutes (Li+, Na+, K+, Cl-), provided that a model-specific Sternheimer parametrization is employed. Yet, the polarizable and scaled charge FFs yield better estimates for divalent and more polarizable species (Mg2+, Ca2+, Cs+). We find that a linear relationship between the quantum and classical EFGs holds well in all of the cases considered; however, such an approximation often leads to quite large errors in the resulting EFG variance, which is directly proportional to the computed rate. We attempted to reduce the errors by including first order nonlinear corrections to the EFG, yet no clear improvement for the resulting variance has been found. The latter result indicates that more refined methods for determining the EFG at the ion position, in particular those that take into account the instantaneous atomic environment around an ion, might be necessary to systematically improve the NMR relaxation rate estimates in classical MD.