Low Dielectric Solvents Research Articles

Metal-Free Reversible Double Cyclization of Cyanuric Diazide to an Asymmetric Bitetrazolate via Cleavage of the Six-Membered Aromatic Ring.

Crystallization of the reaction mixture of 2-amino-4,6-diazido-1,3,5-triazine and excess tert-butylamine results in the isolation of tert-butylammonium N,N-[1'H-(1,5'-bitetrazol)-5-yl]cyanamidate, suggesting a complex decyclization/cyclization rearrangement involving breakage of the six-membered aromatic ring and the formation of two new five-membered azole rings mediated by deprotonation of the precursor by the amine. The addition of tert-butylamine to 2-amino-4,6-diazido-1,3,5-triazine gives spectroscopic indication of thermodynamically unfavorable reactivity in low-dielectric solvents, and high-level quantum chemical computations also suggest its formation to be unfavorable. A computed interconversion pathway describes the likely reaction mechanism and supports the general thermodynamic unfavorability of the reaction and the requirement for a high-dielectric environment to template formation of the ionic product and its trapping by crystallization.

An efficient method to establish electrostatic screening lengths of restricted primitive model electrolytes.

We present a novel, and computationally cheap, way to estimate electrostatic screening lengths from simulations of restricted primitive model (RPM) electrolytes. We demonstrate that the method is accurate by comparisons with simulated long-ranged parts of the charge density, at various Bjerrum lengths, salt concentrations and ion diameters. We find substantial underscreening in low dielectric solvent, but with an "aqueous" solvent, there is instead overscreening, the degree of which increases with ion size. Our method also offers a possible path to (future) more accurate classical density functional treatments of ionic fluids.

Exploiting the Steric Effect and Low Dielectric Constant of 1,2-Dimethoxypropane for 4.3 V Lithium Metal Batteries

1,2-Dimethoxyethane (DME) has been widely used as an electrolyte solvent for lithium metal batteries on account of its intrinsic reductive stability; however, its low oxidative stability presents a major challenge for use in high-voltage Li metal batteries (LMBs). In this direction, herein, we introduce a new low-dielectric solvent, 1,2-dimethoxypropane (DMP), as an electrolyte solvent. Compared to DME, DMP has decreased solvation power owing to its increased steric effects, thus promoting anion–Li+ interactions. This controlled solvation structure of the 2 M LiFSI-in-DMP electrolyte facilitated the formation of an anion-driven, stable interface at the lithium metal anode and oxidative stability for compatibility with widely adopted cathodes to afford Li|LiFePO4 and Li|LiNi0.8Co0.1Mn0.1O2 cells with decent cycling stability. These results imply the usefulness of steric control as an alternative strategy to commonly used fluorination to fine-tune the solvation power and, in general, the design of new solvents for practical lithium metal batteries.

A novel enzyme-less uric acid voltammetric sensor based on highly selective nano-imprinted polymer synthesized utilizing [tetrabutyl ammonium]+-[urate]− ion-pair complex as template

Uric acid is well known as a critical biological compound and its concentration level in biological fluids such as urine and plasma is correlated to some serious disorders. The preparation of imprinted polymer for this compound poses challenges because of its highly hydrophilic characteristic, disabling its dissolving in the rationally applied low dielectric solvents. Herein, the uric acid-selective nano-sized molecularly imprinted polymer (nano-MIP) was synthesized utilizing the aprotic solvent of chloroform. This was executed by introducing an ion pair complex compound of [tetrabutyl ammonium]+-[urate]− which was created in an aqueous media followed by its extraction in an immiscible solvent of chloroform. The extraction condition was optimized to maximize the efficiency of uric acid extraction. The polymeric nanoparticles were utilized as the modifying agent of a carbon paste electrode (CPE). The nano-MIP/CPE electrode response to uric acid was excellently higher than both the non-imprinted polymer-modified CPE (nano-NIP/CPE) and CPE, demonstrating the presence and well-functioning of selective sites within the MIP nanoparticles. The responses of the NIP/CPE and CPE electrodes to uric acid were found to be the same which is a good indication of the absence of non-selective uric acid up-taking by the MIP material. The optimized sensor response to uric acid was linear in the concentration range of 0.6 to 10.0 µM. The detection limit was estimated to be 0.03 µM (3S/N). The fabricated sensor showed excellent selectivity against uric acid’s similar compounds and it was successfully applied for uric acid determination in urine samples.

A simple and efficient method for preparing covalent organic framework aerogels with ultra-light and super-elastic

In this paper, large-sized covalent organic framework (COF) aerogels were prepared using high-efficiency catalysis under room temperature combined with rapid gel and freeze-drying methods for the first time. Two kinds of COF aerogels with rigid and semi-rigid building blocks were prepared using this method, having good mechanical strength (126 and 106 kPa), elasticity (aerogels structure remains intact after 10 cycles), thermal insulation properties (low thermal conductivity of 0.03 wm −1 K −1 ), low dielectric constant (1 kHz of 1.21 and 1.51), thermal stability and solvent stability, and ultra-light characteristics (densities of 0.029 and 0.040 g cm −3 ). Compared to the traditional COF methods that generally result in small particles, the high-efficiency catalysis method developed in this paper can be used to prepare large-sized COF aerogels under mild reaction temperatures and within less time conducive to industrial production. This method is expected to greatly broaden the application field and application scope of COF materials. • Two COF aerogels were prepared combined with rapid gel and freeze-drying methods for the first time. • The COF aerogels behave good mechanical properties, thermal insulation properties, and ultra-light characteristics. • The method in this paper can be used to prepare large-sized COF aerogels under mild reaction temperatures and less time.

Identifying the Cellular Target of Cordyheptapeptide A and Synthetic Derivatives.

Cordyheptapeptide A is a lipophilic cyclic peptide from the prized Cordyceps fungal genus that shows potent cytotoxicity in multiple cancer cell lines. To better understand the bioactivity and physicochemical properties of cordyheptapeptide A with the ultimate goal of identifying its cellular target, we developed a solid-phase synthesis of this multiply N-methylated cyclic heptapeptide which enabled rapid access to both side chain- and backbone-modified derivatives. Removal of one of the backbone amide N-methyl (N-Me) groups maintained bioactivity, while membrane permeability was also preserved due to the formation of a new intramolecular hydrogen bond in a low dielectric solvent. Based on its cytotoxicity profile in the NCI-60 cell line panel, as well as its phenotype in a microscopy-based cytological assay, we hypothesized that cordyheptapeptide was acting on cells as a protein synthesis inhibitor. Further studies revealed the molecular target of cordyheptapeptide A to be the eukaryotic translation elongation factor 1A (eEF1A), a target shared by other lipophilic cyclic peptide natural products. This work offers a strategy to study and improve cyclic peptide natural products while highlighting the ability of these lipophilic compounds to effectively inhibit intracellular disease targets.

Temperature Tuning of Coherent Mixing between States Driving Singlet Fission in a Spiro-Fused Terrylenediimide Dimer.

The excited-state dynamics of a spiro-fused terrylene-3,4:11,12-bis(dicarboximide) (TDI) dimer (sTDI2) in toluene and 2-methyltetrahydrofuran (mTHF) were investigated as a function of temperature using femtosecond- and nanosecond-transient absorption spectroscopy, as well as two-dimensional electronic spectroscopy. The spiro conjugation and the corresponding geometry of this compound guarantee a short intermonomer distance along with a partial orbital overlap between the orthogonal TDI π-electron systems, providing electronic coupling between the TDIs. Photoexcitation of sTDI2 in toluene, a low dielectric solvent, at 295 K, results in the ultrafast formation of a state composed of a coherent mixture of singlet 1(S1S0), multiexciton 1(T1T1), and charge-transfer (CT) electronic characters. This mixed species decays to decorrelated triplet states on the nanosecond timescale, completing the process of intramolecular singlet fission (SF) in sTDI2. Upon decreasing the temperature from 295 to 200 K, the contribution of the 1(T1T1) state to the mixed species decreases concurrently with an increase in the CT state character. We attribute this behavior to the variation in the vibrational energy level alignment between the states comprising the mixture due to changes in the temperature and hence the local dielectric environment. In contrast, photoexcitation of sTDI2 in more polar mTHF at 295 K results in the formation of a mixed singlet and CT state before undergoing symmetry-breaking charge separation, owing to the increased stabilization of the CT state in the medium. However, in glassy mTHF at 85 K, photoexcited sTDI2 exhibits discernible multiexciton character, comparable to that observed in toluene at 200 K, which we rationalize by the similarity of the dielectric constants under these two sets of conditions. These observations of mixed states of varying diabatic contributions over the range of experimental conditions show that the temperature and the static dielectric constant can directly control the composition of the electronically mixed excited state of sTDI2 and thus the fate of the SF process.

Ion Solvation Engineering: How to Manipulate the Multiplicity of the Coordination Environment of Multivalent Ions.

Free energy analysis of solvation structures of free divalent cations, their ion pairs, and neutral aggregates in low dielectric solvents reveals the multiplicity of thermodynamically stable cation solvation configurations and identifies the micro- and macroscopic factors responsible for this phenomenon. Specifically, we show the role of ion-solvent interactions and solvent mixtures in determining the cation solvation free energy landscapes. We show that it is the entropic contribution of solvent degrees of freedom that is responsible for the solvation multiplicity, and the mutual balance between enthalpic and entropic forces or their concerted contributions is what ultimately defines the most stable ion solvation configuration and creates new ones. We show general consequences of ion solvation multiplicity on thermodynamics of complex electrolytes, specifically in the context of homogeneous or interfacial charge transfer. Identified factors and their interplay provide a pathway to formulation of solvation design rules that can be used to control bulk solvation, interfacial chemistry, and charge transfer. Our findings also suggest experimentally testable predictions.

Modulating Electrostatic Interactions in Ion Pair Intermediates To Alter Site Selectivity in the C-O Deoxygenation of Sugars.

Controlling which products one can access from the predefined biomass-derived sugars is challenging. Changing from CH2 Cl2 to the greener alternative toluene alters which C-O bonds in a sugar are cleaved by the tris(pentafluorophenyl)borane/HSiR3 catalyst system. This increases the diversity of high-value products that can be obtained through one-step, high-yielding, catalytic transformations of the mono-, di-, and oligosaccharides. Computational methods helped identify this non-intuitive outcome in low dielectric solvents to non-isotropic electrostatic enhancements in the key ion pair intermediates, which influence the reaction coordinate in the reactivity-/selectivity-determining step. Molecular-level models for these effects have far-reaching consequences in stereoselective ion pair catalysis.

Modulating Electrostatic Interactions in Ion Pair Intermediates To Alter Site Selectivity in the C−O Deoxygenation of Sugars

AbstractControlling which products one can access from the predefined biomass‐derived sugars is challenging. Changing from CH2Cl2 to the greener alternative toluene alters which C−O bonds in a sugar are cleaved by the tris(pentafluorophenyl)borane/HSiR3 catalyst system. This increases the diversity of high‐value products that can be obtained through one‐step, high‐yielding, catalytic transformations of the mono‐, di‐, and oligosaccharides. Computational methods helped identify this non‐intuitive outcome in low dielectric solvents to non‐isotropic electrostatic enhancements in the key ion pair intermediates, which influence the reaction coordinate in the reactivity‐/selectivity‐determining step. Molecular‐level models for these effects have far‐reaching consequences in stereoselective ion pair catalysis.

Free energy barriers for TMEA+, TMA+, and [formula omitted] ion diffusion through nanoporous carbon electrodes

The energy storage of supercapacitors can be enhanced by utilizing porous carbon electrodes with nanometer or even sub-nanometer sized pores that exhibit close match of the pore and ion size. In these highly confined regimes, ion diffusion barriers may be substantial, leading to a tradeoff between power output and energy storage. In this work, we utilize molecular dynamics simulations to quantify free energy barriers for ion diffusion through nanometer and sub-nanometer sized pores in carbon electrodes. We focus on prototypical electrolytes composed of trimethylethylammonium (TMEA+) and tetramethylammonium (TMA+) cations, and tetrafluoroborate (BF4-) anions, with both acetonitrile and 1,2-dichloroethane solvents. We quantify the dependence of diffusion barriers on nanopore width and pore length as a function of solvent and ion type. Our overarching conclusion is that sub-nanometer sized pores of 7.5–10 Å diameter, as previously demonstrated to be optimal for energy storage, lie exactly at the limit of diffusion accessibility at low voltage. We show that nanopore accessibility depends sensitively on the solvent dielectric strength, and that for low dielectric solvents, barriers are dictated by diffusion of ion pairs rather than single ions.

Conformational Preference of Macrocycles Investigated by Ion-Mobility Mass Spectrometry and Distance Geometry Modeling.

Macrocycles provide intricate shape manifolds that leverage the depth of the modern organic chemistry toolbox. Novel chemistry can be introduced via new bond types and unique torsional angles inaccessible by traditional small molecules and biomolecules. In this work, we investigate the conformational space of a class of biscationic macrocycles in protic and aprotic solvents using a combination of ion-mobility spectrometry mass spectrometry, distance geometry modeling, and quantum mechanical calculations. We identify at least three major conformations of the macrocycles. Two of the conformations are rotational isomers in which the amide (carbonyl amide) N-C bond of the acyl hydrazine can adopt either E- or Z-configuration. The E- and Z-rotational isomers were separately observed in previous X-ray crystallography studies on the same set of macrocycles, but both isomers were never proved to exist for the same molecule. We show that low-dielectric solvents and counterions, such as Cl- or PF6-, appear to stabilize the Z-conformation. Lastly, desolvation of the macrocycles in the absence of bound counterions yields a gas-phase "flat" Z-conformation. Our results suggest that the macrocycles are flexible and behave much like short polypeptides. The combination of ion-mobility spectrometry mass spectrometry and distance geometry modeling provides a versatile and robust approach to unravel fundamental information on the flexible chemical space of macrocycles.

Cyclic Peptide Design Guided by Residual Dipolar Couplings, J-Couplings, and Intramolecular Hydrogen Bond Analysis.

Cyclic peptides have long tantalized drug designers with their potential ability to combine the best attributes of antibodies and small molecules. An ideal cyclic peptide drug candidate would be able to recognize a protein surface like an antibody while achieving the oral bioavailability of a small molecule. It has been hypothesized that such cyclic peptides balance permeability and solubility using their solvent-dependent conformational flexibility. Herein we report a conformational deconvolution NMR methodology that combines residual dipolar couplings, J-couplings, and intramolecular hydrogen bond analysis along with conformational analysis using molecular dynamics simulations and density functional theory calculations for studying cyclic peptide conformations in both low-dielectric solvent (chloroform) and high-dielectric solvent (DMSO) to experimentally study the solvent-dependent conformational change hypothesis. Taken together, the combined experimental and computational approaches can illuminate conformational ensembles of cyclic peptides in solution and help identify design opportunities for better permeability.

Ion Correlation and Collective Dynamics in BMIM/BF4-Based Organic Electrolytes: From Dilute Solutions to the Ionic Liquid Limit.

Quantifying ion association and collective dynamical processes in organic electrolytes is essential for fundamental property interpretation and optimization for electrochemical applications. The extent of ion correlation depends on both the ion concentration and dielectric strength of the solvent; ions may be largely uncorrelated in sufficiently high-dielectric solvents at low concentration, but properties of concentrated electrolytes are dictated by correlated and collective ion processes. In this work, we utilize molecular dynamics simulations to characterize ion association and collective ion dynamics in organic electrolytes composed of binary mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM+][BF4-] and 1,2-dichloroethane, acetone, acetonitrile, and water solvents. We illustrate different physical regimes of characteristically distinct ion correlations for the systematic range of electrolyte concentrations and solvent dielectric strengths. Dilute electrolytes composed of low-dielectric solvents exhibit significant counterion correlation in the form of ion pairing and clustering driven by both weak screening and relatively low solvation energies. This regime is characterized by enhanced ion coordination numbers and near equality of cation and anion diffusion coefficients, despite the significantly different ion sizes. In contrast, ion correlation in highly concentrated electrolytes is dominated by the anti-correlated motion of both like-charge and opposite-charge ions, approaching neat ionic liquid behavior. We show that the cross-over of these correlation regimes is clearly illuminated by quantifying the fractional self and distinct contributions to the net ionic conductivity. For organic electrolytes composed of low-dielectric solvents, we conclude that significant ion correlation exists at all concentrations but the nature of the correlation changes markedly from the dilute electrolyte to the pure ionic liquid limit.

Polarization Effects in Binary [BMIM+][BF4-]/1,2-Dichloroethane, Acetone, Acetonitrile, and Water Electrolytes.

Organic electrolytes are unique in that their constituent solvents may be of much lower dielectric strength than water. This is because the ions of organic electrolytes are often those that comprise room-temperature ionic liquids, which are surprisingly miscible with many different organic solvents of low dielectric strength. Strong ion correlation results from the relatively low dielectric screening of the solvent, resulting in properties that can substantially deviate from Debye-Huckel descriptions; in addition remains the fundamental question of why the ionic liquids and low dielectric solvents are even miscible in the first place. In this work, we study electrolyte mixtures composed of the room-temperature ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM+][BF4-] mixed with four solvents of systematically varying dielectric strength, 1,2-dichloroethane, acetone, acetonitrile, and water. We show that miscibility with the lowest dielectric solvent, dichloroethane, is directly attributed to ion solvation enhancement mediated by both electronic and conformational polarization of the solvent molecules. A strong dielectric enhancement results from the ∼70-80% increase in solvent dipole moments at high ion content, providing significantly better solvation than predicted by the bulk solvent dielectric strength. This implies a general mechanism for miscibility of ionic liquids with low dielectric solvents, through which ions effectly create their own solvation dipoles by polarizing the local environment. From a purely computational perspective, our results imply that explicitly polarizable force fields are essential for modeling many of the organic electrolytes that are used in electrochemical applications.

Photoinduced Spontaneous Free-Carrier Generation of (7,5)-Chirality-Enriched Single-Walled Carbon Nanotubes in a Low Dielectric Solvent

We demonstrate photoinduced spontaneous free-carrier generation in highly individualized (7,5)- chirality-enriched SWCNT samples ((7,5)-SWCNTs) suspended in a non-polar organic solvent. Frequency-resolved solution-phase flash photolysis time-resolved microwave conductivity (fp- TRMC), provides a contactless and quantitative measurement of the real and imaginary photoconductance of these individually suspended nanotubes. We use substantially lower excitation fluences than have been possible in previous studies, corresponding to absorbed photon densities of ~0.05 photons per micron length of (7,5)-SWCNTs, allowing us to avoid complications from dielectric screening by nearby excitons or exciton-exciton collisions. Even under these mild conditions, we unambiguously measure a photoconductance due to free carriers that are generated following excitation of both the first and second exciton transitions (S11 and S22, respectively). The low-fluence carrier generation quantum yield (Φ) with S22 excitation appears c.a. 2.4 times higher than that with S11 excitation, suggesting that the autoionization of S22 excitons clearly enhances the carrier generation efficiency. In contrast, the transient decay dynamics are independent of excitation wavelength, suggesting that the mobile carriers generated from either S11 or S22 excitation undergo identical decay pathways (i.e. trapping, recombination, etc.).

Photoinduced spontaneous free-carrier generation in semiconducting single-walled carbon nanotubes.

Strong quantum confinement and low dielectric screening impart single-walled carbon nanotubes with exciton-binding energies substantially exceeding kBT at room temperature. Despite these large binding energies, reported photoluminescence quantum yields are typically low and some studies suggest that photoexcitation of carbon nanotube excitonic transitions can produce free charge carriers. Here we report the direct measurement of long-lived free-carrier generation in chirality-pure, single-walled carbon nanotubes in a low dielectric solvent. Time-resolved microwave conductivity enables contactless and quantitative measurement of the real and imaginary photoconductance of individually suspended nanotubes. The conditions of the microwave conductivity measurement allow us to avoid the complications of most previous measurements of nanotube free-carrier generation, including tube–tube/tube–electrode contact, dielectric screening by nearby excitons and many-body interactions. Even at low photon fluence (approximately 0.05 excitons per μm length of tubes), we directly observe free carriers on excitation of the first and second carbon nanotube exciton transitions.

Enhancement of ionization efficiency of mass spectrometric analysis from non-electrospray ionization friendly solvents with conventional and novel ionization techniques

Electrospray ionization mass spectrometry (ESI-MS) has significantly impacted the analysis of complex biological and petroleum samples. However ESI-MS has limited ionization efficiency for samples in low dielectric and low polarity solvents. Addition of a make-up solvent through a T union or electrospray solvent through continuous flow extractive desorption electrospray ionization (CF-EDESI) enable ionization of analytes in non-ESI friendly solvents. A conventional make-up solvent addition setup was used and a CF-EDESI source was built for ionization of nitrogen-containing standards in hexane or hexane/isopropanol. Factors affecting the performance of both sources have been investigated and optimized. Both the make-up solvent addition and CF-EDESI improve the ionization efficiency for heteroatom compounds in non-ESI friendly solvents. Make-up solvent addition provides higher ionization efficiency than CF-EDESI. Neither the make-up solvent addition nor the CF-EDESI eliminates ionization suppression of nitrogen-containing compounds caused by compounds of the same chemical class.

Probing the Physicochemical Boundaries of Cell Permeability and Oral Bioavailability in Lipophilic Macrocycles Inspired by Natural Products.

Cyclic peptide natural products contain a variety of conserved, nonproteinogenic structural elements such as d-amino acids and amide N-methylation. In addition, many cyclic peptides incorporate γ-amino acids and other elements derived from polyketide synthases. We hypothesized that the position and orientation of these extended backbone elements impact the ADME properties of these hybrid molecules, especially their ability to cross cell membranes and avoid metabolic degradation. Here we report the synthesis of cyclic hexapeptide diastereomers containing γ-amino acids (e.g., statines) and systematically investigate their structure-permeability relationships. These compounds were much more water-soluble and, in many cases, were both more membrane permeable and more stable to liver microsomes than a similar non-statine-containing derivative. Permeability correlated well with the extent of intramolecular hydrogen bonding observed in the solution structures determined in the low-dielectric solvent CDCl3, and one compound showed an oral bioavailability of 21% in rat. Thus, the incorporation of γ-amino acids offers a route to increase backbone diversity and improve ADME properties in cyclic peptide scaffolds.

Influence of Solvent on Lithium-Sulfur Redox Reactions: A Rotating Ring-Disk Electrode Study

Introduction Detailed mechanistic understanding of Li−S redox reactions is critical for realizing efficient and long-lasting rechargeable Li−S batteries.1-4 Recently, we exploited rotating ring-disk electrode (RRDE) technique and specially-designed Li-S catholyte cell to examine sulfur charge/discharge behavior in 1,3-dioxolane:1,2-dimethoxyethane (DOL:DME) and dimethyl sulfoxide (DMSO).5 We show that only part of the sulfur reduction capacity is obtained through direct electrochemical steps, and that the rest of the capacity is achieved via various subsequent chain-growth and disproportionation reactions that generate reducible species. The rates of these chain-growth/disproportionation reactions are higher in low-dielectric solvents such as DOL:DME (εDOL = 7.13; εDME = 7.075)6 compared to high-dielectric solvents such as DMSO (εDMSO = 46.5)6 due to its poor stabilization of polysulfides, which leads to a higher rate capability in the Li-S batteries. In this study, we investigate the influence of various solvent properties including dielectric constant and donor number on the Li-S redox and disproportionation behaviors. Results and Discussion To investigate the influence of dielectric constant on the Li-S behaviors, we first replaced DOL with 1,4-Dioxane (Diox), which has a lower dielectric constant (εDiox = 2.21)6 than DOL. Decreasing solvent’s dielectric constant from DOL to Diox is expected to further de-stabilize polysulfides. Figure 1a-c show the cyclic voltammograms (CVs) and RRDE results of a glassy carbon (GC) electrode in 4 mM S8 in 1.0 M LiTFSI Diox:DME(1:1) and DOL:DME(1:1). First, the onset potential of S-reduction in DOL:DME is ~150 mV higher than that in Diox:DME. This observation is in line with our hypothesis that the S-reduction kinetics decreases with decreasing solvent dielectric constant (i.e. decreasing polysulfide stability),5 which is consistent with the fact that S-reduction activity in DMSO is ~100 mV higher than that in DOL:DME.5 Second, the second reduction wave diminishes in Diox:DME, which indicates that there is only one direct electrochemical step in Diox:DME. The numbers of electron transferred in Diox:DME is determined to be 2.2 e–/S8 via Levich Koutecky relationship, which is significantly lower than that measured in DOL:DME (ave. 5 e–/S8).5 The single reduction wave observed in Diox:DME with 2.2 e–/S8 could be attributed to: S8 + 2e– -> S8 2– Interestingly, further electrochemical reduction from S8 2– to S8 4– (or 2S4 2–) is significantly discouraged upon replacing DOL with Diox. We believe that the drastic decrease in solvent’s dielectric constant from DOL to Diox prohibits further electrochemical and/or disproportionation reactions of S8 2– to other polysulfide species such as S4 2– and/or S6 2– and/or S3 –∙ due to the extremely poor stabilization ability of Diox. Therefore, it is critical to identify optimum solvent dielectric constant and potential secondary descriptor to optimize the S-reduction kinetics and the polysulfide disproportionation rates. Further investigation using RRDE, UV-VIS spectroscopy, Li-S catholyte cells and its implication in rechargeable Li-S batteries will be presented. Acknowledgments The authors are grateful to Dr. Juan Herranz-Salaner for RRDE cell design and scientific discussion, Dr. Himendra Jha for experimental assistance and scientific discussion, and Johannes Hattendorff for the measurement of solvent viscosity. Financial support of this research by the Bavarian Ministry of Economic Affairs and Media, Energy and Technology performed under the auspices of the EEBatt project. Y.C. Lu is grateful to the funding support from project RNEp1-13 of the Shun Hing Institute of Advanced Engineering, The Chinese University of Hong Kong.