The Structure of Liquid Tetrahydrofuran

Bulk Nanostructure of Mixtures of Choline Arginate, Choline Lysinate, and Water

Neutron diffraction with empirical potential structure refinement was used to investigate the bulk liquid nanostructure of mixtures of choline arginate (Ch[Arg]), choline lysinate (Ch[Lys]), and water at mole ratios of 1Ch[Arg]:1Ch[Lys]:6H2O (balanced), 1Ch[Arg]:1Ch[Lys]:20H2O (balanced dilute), 3Ch[Arg]:1Ch[Lys]:12H2O (Arg- rich), and 1Ch[Arg]:3Ch[Lys]:12H2O (Lys- rich). The Arg- and Lys- anions tend not to associate due to electrostatic repulsion between charge groups and weak anion-anion attractions. This means that the local ion structures around the anions in these mixtures resemble the parent single-component systems. The bulk liquid nanostructure varies with the Arg-:Lys- ratio. In the Lys--rich mixture (1Ch[Arg]:3Ch[Lys]:12H2O), Lys- side chains cluster into a continuous apolar domain separated from a charged domain of polar groups. In the balanced mixture (1Ch[Arg]:1Ch[Lys]:6H2O), Lys- side chains form discrete apolar aggregates within a continuous polar domain of Arg-, Ch+, and water, and in the Arg--rich mixture (3Ch[Arg]:1Ch[Lys]:12H2O), the distribution of Lys- and Arg- is nearly homogeneous. Finally, in the balance dilute system (1Ch[Arg]:1Ch[Lys]:20H2O), a percolating water domain forms.

Inelastic neutron scattering and spectroscopy methods to characterize dynamics in colloidal and soft matter systems

Colloidal systems and soft materials are well suited to neutron scattering, and the community has readily adopted elastic scattering techniques to investigate their structure. Due to their unique properties, neutrons may also be used to characterize the dynamics of soft materials over a wide range of length and time scales in situ. Both static structures and an understanding of how molecules move about their equilibrium positions is essential if we are to deliver on the promise of rationally designing soft materials. In this review we introduce the basics of neutron spectroscopy and explore the ways in which inelastic neutron scattering can be used to study colloidal and soft materials. Illustrative examples are chosen that highlight the phenomena suitable for investigation using this suite of techniques.

Stability and Reactivity of Aromatic Radical Anions in Solution with Relevance to Birch Reduction

We investigate the electronic structure of aromatic radical anions in the solution phase employing a combination of liquid-jet (LJ) photoelectron (PE) spectroscopy measurements and electronic structure calculations. By using recently developed protocols, we accurately determine the vertical ionization energies of valence electrons of both the solvent and the solute molecules. In particular, we first characterize the pure solvent of tetrahydrofuran (THF) by LJ-PE measurements in conjunction with ab initio molecular dynamics simulations and G0W0 calculations. Next, we determine the electronic structure of neutral naphthalene (Np) and benzophenone (Bp) as well as their radical anion counterparts Np- and Bp- in THF. Wherever feasible, we performed orbital assignments of the measured PE features of the aromatic radical anions, with comparisons to UV-vis absorption spectra of the corresponding neutral molecules being instrumental in rationalizing the assignments. Analysis of the electronic structure differences between the neutral species and their anionic counterparts provides understanding of the primarily electrostatic stabilization of the radical anions in solution. Finally, we obtain a very good agreement of the reduction potentials extracted from the present LJ-PES measurements of Np- and Bp- in THF with previous electrochemical data from cyclic voltammetry measurements. In this context, we discuss how the choice of solvent holds significant implications for optimizing conditions for the Birch reduction process, wherein aromatic radical anions play crucial roles as reactive intermediates.

Bulk nanostructure of a deep eutectic solvent with an amphiphilic hydrogen bond donor

Neutron diffraction with empirical potential structure refinement (EPSR) show the deep eutectic solvent (DES) 1 : 4 choline chloride : butyric acid is amphiphilically nanostructured. Nanostructure results from solvophobic interactions between the alkyl chains of the butyric acid hydrogen bond donor (HBD) and is retained with addition of 10 wt% water. EPSR fits to the diffraction data is used to produce a three-dimensional model of the liquid which is interrogated to reveal the interactions leading to the solvophobic effect, and therefore nanostructure, in this DES at atomic resolution. The model shows electrostatic and hydrogen bond interactions cause the cation, anion and HBD acid group to cluster into a polar domain, from which the acid alkyl chains are solvophobically excluded into theapolar domain. The polar and apolar domains percolate through the liquid in a bicontinuous sponge-like structure. The effect of adding 10 wt% water is probed, revealing that water molecules are sequestered around the cation and anion within the polar domain, while the neat bulk structure is retained. Alkyl chain packing in the apolar domain becomes slightly better-defined indicating water marginally strengthens solvophobic segregation. These findings reveal bulk self-assembled nanostructure can be produced in DESs via an amphiphilic HBD.

Integrated effect of bulk cations on nano-confined reactivity of clay-intercalated subnanoscale zero-valent iron in water-tetrahydrofuran mixtures

Smectite clay-intercalated subnanoscale zero-valent iron (CSZVI) exhibits superior reactivity toward contaminants due to the small iron clusters (∼0.5 nm) under nano-confinement, which however is significantly influenced by the solution chemistry e.g., various cations, of polluted soil and water. This work was undertaken to elucidate the mechanisms of solution chemistry effects on dehalogenation ability of CSZVI in water-tetrahydrofuran solution using decabromodiphenyl ether as a model contaminant. By combined spectroscopic characterization and molecular dynamics simulation, it was revealed that bulk cations, i.e., Na⁺, K⁺, Mg²⁺ and Ca²⁺ collectively affected the interlayer distance, water content and Brønsted acidity of CSZVI and thus its degradation efficiency. Although causing inter-particle aggregation, Mg²⁺ induced optimal nano-confined interlayers at concentration of 20 mM, exhibiting a superior debromination efficiency with rate constant 9.84 times larger than that by the common nano-sized ZVI. Conversely, K⁺ rendered the interlayers less reactive, but protected CSZVI from corrosion loss with higher electron utilization efficiency, which was 1.7 times higher than CSZVI in presence of Mg²⁺. The findings provide new strategies to manipulate the reactivity of nano-confined CSZVI for effective wastewater and contaminated soil remediation.

Collective dynamics and self-motions in the van der Waals liquid tetrahydrofuran from meso- to inter-molecular scales disentangled by neutron spectroscopy with polarization analysis

By using time-of-flight neutron spectroscopy with polarization analysis, we have separated coherent and incoherent contributions to the scattering of deuterated tetrahydrofuran in a wide scattering vector (Q)-range from meso- to inter-molecular length scales. The results are compared with those recently reported for water to address the influence of the nature of inter-molecular interactions (van der Waals vs hydrogen bond) on the dynamics. The phenomenology found is qualitatively similar in both systems. Both collective and self-scattering functions are satisfactorily described in terms of a convolution model that considers vibrations, diffusion, and a Q-independent mode. We observe a crossover in the structural relaxation from being dominated by the Q-independent mode at the mesoscale to being dominated by diffusion at inter-molecular length scales. The characteristic time of the Q-independent mode is the same for collective and self-motions and, contrary to water, faster and with a lower activation energy (≈1.4 Kcal/mol) than the structural relaxation time at inter-molecular length scales. This follows the macroscopic viscosity behavior. The collective diffusive time is well described by the de Gennes narrowing relation proposed for simple monoatomic liquids in a wide Q-range entering the intermediate length scales, in contraposition to the case of water.

Atom-efficient synthesis of a benchmark electrolyte for magnesium battery applications

The benchmark magnesium electrolyte, [Mg₂Cl₃]⁺ [AlPh₄]^-, can be prepared in a 100% atom-economic fashion by a ligand exchange reaction between AlCl₃ and two molar equivalents of MgPh₂. NMR and vibrational spectroscopy indicate that the reported approach results in a simpler ionic composition than the more widely adopted synthesis route of combining PhMgCl with AlCl₃. Electrochemical performance has been validated by polarisation tests and cyclic voltammetry, which demonstrate excellent stability of electrolytes produced via this atom-efficient approach.

Understanding the Liquid States of Cyclic Hydrocarbons Containing N, O, and S Atoms via the 3D-RISM-KH Molecular Solvation Theory

The 3D-reference interaction site model (3D-RISM) molecular solvation theory in combination with the Kovalenko-Hirata (KH) closure is extended to seven heterocyclic liquids to understand their liquid states and to test the performance of the theory in solvation free energy (SFE) calculations of solutes in select solvents. The computed solvent site distribution profiles were compared with the all-atom molecular dynamics (MD) simulations, showing comparable performances. The computational results were compared against the structural parameters for liquids, whenever available, as well as against the experimental SFEs. The liquids are found to have local ordered structures held together via weak interactions in both the RISM and MD simulations. The 3D-RISM-KH computed SFEs are in good agreement with the benchmark values for the tetrahydrothiophene-S,S-dioxide, and showed comparatively larger deviations in the case of the SFEs in the tetrahydrofuran continuum.

Carbene-enabled ether activation through the formation of oxonium: a theoretical view

Here, we report a theoretical investigation of the reactivity and chemoselectivity of carbene-enabled ether activation.

Conformational diversity of the THF molecule in N2 matrix by means of FTIR matrix isolation experiment and Car-Parrinello molecular dynamics simulations

Tetrahydrofuran (THF) is a widely used chemical compound, in particular as a solvent in organic and inorganic synthesis. The THF molecule has also an interesting property, namely, undergoes pseudorotation, similar to the case of the cyclopentane. Low energy difference between the envelope (C_s symmetry) and twisted (C₂ symmetry) conformations of the THF molecule leads to the interconversion between the two conformers. We study the influence of the molecular environment (N₂) on the C_s-C₂ equilibrium of tetrahydrofuran in the THF@N₂ system utilizing nitrogen matrix isolation infrared spectroscopy. We observe a different ratio between envelope (C_s) and twisted (C₂) conformations with respect to a change of the temperature. FTIR experimental studies are supported by the results of the static density functional theory calculations and Car-Parrinello molecular dynamics simulations. We focus on the dynamics of the pseudorotation process, in particular, the lifetime of the THF conformations and their mutual rearrangements. On the basis of the THF@N₂ matrix model, with explicit nitrogen molecules, the anharmonic infrared spectra are generated from the Fourier transformation of the dipole moment autocorrelation function.

Capturing Deuteration Effects in a Molecular Mechanics Force Field: Deuterated THF and the THF-Water Miscibility Gap

Deuteration is a common chemical modification used in conjunction with experiments such as neutron scattering, NMR, and Fourier-transform infrared for the study of molecular systems. Under the Born-Oppenheimer (BO) approximation, while the underlying potential energy surface remains unchanged by isotopic substitutions, isotopic substitution still alters intramolecular vibrations, which in turn may alter intermolecular interactions. Molecular mechanics (MM) force fields used in classical molecular dynamics simulations are assumed to represent local approximations of the BO potential energy surfaces, and hence, MD simulations using simple isotopic mass substitutions should capture BO-compatible isotope effects. However, standard MM force-field parameterizations do not directly fit to the local harmonic quantum mechanical (QM) Hessian that describes the BO surface, but rather to QM normal-modes and/or mass-dependent internal-coordinate derived distortion energies. Here, using tetrahydrofuran (THF)-water mixtures as our model system, we show that not only does a simple mass-substitution approach fail to capture an experimentally characterized deuteration effect (the loss of the closed-loop miscibility gap associated with the complete deuteration of THF) but also it is necessary to generate new MM force-field parameters that correctly describe isotopic dependent vibrations to capture the experimental deuteration effect. We show that the origin of this failure is a result of using mass-dependent features to fit the THF MM force field, which unintentionally biases the bonded terms of the force field to represent only the isotopologue used during the original force-field parameterization. In addition, we make use of our isotopologue-corrected force field for D₈THF to examine the molecular origins of the isotope-dependent loss of the THF-water miscibility gap.

Switching of Self-Assembly to Solvent-Assisted Assembly of Molecular Motor: Unveiling the Mechanisms of Dynamic Control on Solvent Exchange

Natural biological molecular motors are capable of performing several biological functions, such as fuel production, mobility, transport, and many other dynamic features. Inspired by these biological motors, scientists effectively synthesized artificial molecular motors to mimic several biological functionalities. Several molecular systems, from sensitive materials to molecular motors, are essential for controlling dynamic processes in larger assemblies. In this work, we discuss the self-assembly of molecular motors in water and how this self-assembly switches to the solvent-assisted assembly as solvent changes to a water-THF (tetrahydrofuran) mixture. We present an elaborate description of the morphological changes of molecular motor assemblies from pure water to a water-THF mixture to pure THF. Under the influence of THF solvent, molecular motors form an assembled structure by taking a sufficient number of THF molecules in between themselves, resulting in an assembled molecular motor with a softened core. So, molecular motor assembly swells in the water-THF mixture, and in pure water, it shrinks. This solvent-assisted assembled structure has a specific shape. We have confirmed this assembly as a solvent-assisted assembly with the help of molecular dynamics simulation and quantum chemical analysis. Molecular motor-THF and THF-THF interactions are the main responsible interactions for solvent-assisted assembly over self-assembly. This work is a perfect example of conversion between self-assembly (shrinking) and solvent-assisted assembly (swelling) of molecular motors by adding THF into water or vice versa. A spectacular check on the shrinking and swelling by merely altering solvents illustrates so many intriguing possibilities for an alteration of dynamic processes at the nanoscale.

On the supramolecular properties of neutral, anionic and cationic cadmium complexes harvested from dithiolate–polyamine binary ligand systems

Three Cd(ii) complexes [Cd(i-mnt)(DMSO)₂]_n (1), {[Cd(i-mnt)pn]·2H₂O} (2), and [Cd(i-mnt)₃][Cd(tren)₂]₂ (3) harvested from 1,1-dicyanoethylene-2,2-dithiolate (i-mnt²⁻) and polyamine ligand systems have been designed, synthesized and structurally characterized.

Single-walled carbon nanotubes in tetrahydrofuran solution: microsolvation from first-principles calculations

The molecular interactions between the commonly used solvent tetrahydrofuran (THF) and single-walled carbon nanotubes (SWCNT) are studied using density functional theory calculations and Car-Parrinello molecular dynamics simulations. The competitive interplay between THF-THF and THF-SWCNT interactions via C-H⋯O and C-H⋯π hydrogen bonds is analyzed in detail. The binding energies for different global and local energy minima configurations of THF monomers, dimers, trimers, and tetramers on SWCNT(10,0) were determined. The adsorbed species are analyzed in terms of their coordination to the surface via weak hydrogen bonds of the C-H⋯π type and in terms of their ability to form intermolecular C-H⋯O hydrogen bonds, which are responsible for the self-aggregation of THF molecules and a possible dimerization or tetramerization process. A special focus is put on the pseudorotation of the THF molecules at finite temperatures and on the formation of blue-shifting hydrogen bonds.

Structures of a Clathrate Hydrate Former, Inhibitor, and Synergist in Water

SANS studies are reported for aqueous THF at the 1:17 clathrate hydrate-forming composition and on aqueous solutions of the synergist 2-butoxyethanol. Addition of the clathrate hydrate inhibitor polyvinylcaprolactam and a dimeric model compound, 1,3-bis(caprolactamyl)butane, show that the inhibitors do not significantly affect the solution structures of these two important species in clathrate hydrate formation and inhibition. The SANS studies show that 1,3-bis(caprolactamyl)butane is a good model for polyvinylcaprolactam, and both the polymer and model compound exhibit hydrogen bonding interactions with water but do not interact significantly with 2-butoxyethanol in aqueous solution.

Study of Electron Ionization and Fragmentation of Non-hydrated and Hydrated Tetrahydrofuran Clusters

Mass spectroscopic investigations on tetrahydrofuran (THF, C₄H₈O), a common model molecule of the DNA-backbone, have been carried out. We irradiated isolated THF and (hydrated) THF clusters with low energy electrons (electron energy ~70 eV) in order to study electron ionization and ionic fragmentation. For elucidation of fragmentation pathways, deuterated TDF (C₄D₈O) was investigated as well. One major observation is that the cluster environment shows overall a protective behavior on THF. However, also new fragmentation channels open in the cluster. In this context, we were able to solve a discrepancy in the literature about the fragment ion peak at mass 55 u in the electron ionization mass spectrum of THF. We ascribe this ion yield to the fragmentation of ionized THF clusters. Graphical Abstract ᅟ.

Induced polarization restricts the conformational distribution of a light-harvesting molecular triad in the ground state

Free energy surface of the light-harvesting triad employing a non-polarizable force field (NFF) and a polarizable force field (PFF) shows that induced polarization limits the motion of rotation about chemical bonds as well as bending at the porphyrin, which are prominent using the NFF, thus limiting the conformational space of the triad.

Insights into the solvation of glucose in water, dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) and its possible implications on the conversion of glucose to platform chemicals

The presence of co-solvents, like DMSO, DMF and THF, significantly alters (i) the interaction of glucose with water, (ii) the mobility of glucose and (iii) its bonding with the solvent environment. This may have implications on glucose conversion reactions.

Polar stacking of molecules in liquid chloroform

‘Super-dipole’ aggregates in liquid chloroform may explain its outstanding solvent properties and highlight a route to designing new high-performance solvents.

Critical analysis of the accuracy of models predicting or extracting liquid structure information

This work aims at a critical assessment of properties predicting or extracting information on the density and structure of liquids. State-of-the-art NVT and NpT molecular dynamics (MD) simulations have been performed on five liquids: methanol, chloroform, acetonitrile, tetrahydrofuran, and ethanol. These simulations allow the computation of properties based on first principles, including the equilibrium density and radial distribution functions (RDFs), characterizing the liquid structure. Refinements have been incorporated in the MD simulations by taking into account basis set superposition errors (BSSE). An extended BSSE model for an instantaneous evaluation of the BSSE corrections has been proposed, and their impact on the liquid properties has been assessed. If available, the theoretical RDFs have been compared with the experimentally derived RDFs. For some liquids, significant discrepancies have been observed, and a profound but critical investigation is presented to unravel the origin of these deficiencies. This discussion is focused on tetrahydrofuran where the experiment reveals some prominent peaks completely missing in any MD simulation. Experiments providing information on liquid structure consist mainly of neutron diffraction measurements offering total structure factors as the primary observables. The splitting of these factors in reciprocal space into intra- and intermolecular contributions is extensively discussed, together with their sensitivity in reproducing correct RDFs in coordinate space.

Gas-phase energy of the S2←S0 transition and electrostatic properties of the S2 state of carotenoid peridinin via a solvatochromic shift and orientation broadening of the absorption spectrum

The solvent effect on the position and the shape of the absorption spectrum of peridinin for 12 protic and aprotic solvents as well as the temperature effect for methanol were studied using a solvatochromic theory based on the Onsager sphere cavity model.

On the hydration of the phosphocholine headgroup in aqueous solution

The hydration of the phosphocholine headgroup in 1,2-dipropionyl-sn-glycero-3-phosphocholine (C(3)-PC) in solution has been determined by using neutron diffraction enhanced with isotopic substitution in combination with computer simulation techniques. The atomic scale hydration structure around this head group shows that both the -N(CH(3))(3) and -CH(2) portions of the choline headgroup are strongly associated with water, through a unique hydrogen bonding regime, where specifically a hydrogen bond from the C-H group to water and a strong association between the water oxygen and N(+) atom in solution have both been observed. In addition, both PO(4) oxygens (P=O) and C=O oxygens are oversaturated when compared to bulk water in that the average number of hydrogen bonds from water to both X=O oxygens is about 2.5 for each group. That water binds strongly to the glycerol groups and is suggestive that water may bind to these groups when phosophotidylcholine is embedded in a membrane bilayer.