N-methylformamide Solutions Research Articles

Aqueous hydroxyl group as the vibrational probe to access the hydrophobicity of amide derivatives

First principles molecular dynamics (FPMD) simulations of relatively dilute aqueous solutions of N-methylformamide (NMF), N, N-dimethylacetamide (DMA), N-methylacetamide (NMA) were carried out to elucidate the effects of variation of hydrophobicity of amide molecules on structure, dynamics and spectral properties of solvating water molecules. A quantitative analysis of dangling OH groups of water molecules, one of the consequences of hydrophobicity, around the amide molecules was performed to explore the structure of surrounding water molecules. We observe that DMA has the most hydrophobic character among the three amide molecules; the lifetime of dangling OH mode of water molecules and the number of such modes are found to be more inside the solvation shell of DMA as compared to NMA and NMF molecules. Overall this lifetime is more inside the solvation shell of amides compared to the bulk water molecules for all aqueous solutions of amides. Rotational dynamics calculation suggests significant retardation of OH bonds of water near the amide oxygen atom (O) due to the OwHw⋯O strong hydrogen bonds. A moderate slowdown of reorientational dynamics is also observed for OH modes that are close to the hydrophobic surface of DMA in its aqueous solution. Vibrational density of states (VDOS) and frequency distribution calculations point out the higher average stretching frequency (~3600–3850 cm−1) of free OH groups. Hydrogen bond lifetime calculations conceive that DMA, having three methyl groups, makes stronger hydrogen bonds through the CO moiety. Vibrational spectral diffusion of bulk water and solvation shell water molecules were also calculated in combination with wavelet transform and frequency-frequency autocorrelation functions. The CO group affected OH stretching frequency bands for aqueous solutions of NMF and NMA molecules are more pronounced than that of DMA. However, NH affected OH frequency bands are less pronounced for NMA and DMA due to the presence of more number of hydrophobic methyl groups. Going from NMF to DMA, the OH frequency bands inside the amide solvation shells shift towards the higher value due to the enhancement of hydrophobicity. The vibrational spectral diffusion of OH modes around CO and NH (N for DMA) groups, as well as for bulk water molecules, is also investigated. Three time scales were found for these calculations for all the cases. The fast time scales in the range ~50–100 fs are due to the amide-water intact hydrogen bonding, and two slower time scales in the range ~0.6–3.90 ps and ~10–20 ps were found. The time scales in the range of ~0.6 to 3.90 ps can be attributed to carbonyl-water and N-H-water hydrogen bonding, and the very long time scales are due to the escape dynamics water molecules from the solvation shell of CO and NH (N for DMA) groups.

Catalytic activity of the Co(II)/Co(III) couple towards peptide bond cleavage and formation of molecular oxygen adducts in protic amide solutions

Formamide and N-methylformamide solutions containing variable amounts of Co(II) and Co(III) halide were employed as model systems to explain the catalytic potential of these ions towards amide bond cleavage reaction. The νCO downshifts in the IR spectra and the νCN upshifts in the Raman spectra are in agreement with the stabilization of a molecular structure near the dipolar amide form, which is considered the active species for catalysis. Quantitative analyses performed at the νCN and δOCN regions reveal the existence of four- and five-coordinate Co(II) complexes, but the addition of an oxidizing agent leads to the formation of five- and six-coordinate structures around Co(III) in 1:1 and 1:2 (O2/Co) type adducts. Attempt to correlate the electrostatic potential with the limiting canonical amide forms is also presented.

Enthalpies of β-Alanine Dissolution in Some Water + Organic Mixtures at 298.15 K

The enthalpies of solution (ΔsolHm) of β-alanine in aqueous solutions of acetonitrile (AN), 1,4-dioxane (1,4-DO), acetone (AC), formamide (FA), N-methylformamide (MFA), N,N-dimethylformamide (DMFA), N,N-dimethylacetamide (DMA), and dimethyl sulfoxide (DMSO) have been determined by calorimetric method as a function of organic solvent concentration at 298.15 K. Enthalpies of transfer (ΔtrH°) of β-alanine from water to aqueous organic mixtures as well as the enthalpy coefficients of pairwise interaction (hxy) were calculated from these data. The interrelation between enthalpy characteristics of β-alanine dissolution (transfer) and the composition of water–organic solvent binary mixtures has been ascertained. By means of a modified Kamlet–Taft equation the contributions of different physicochemical properties of organic cosolvents to the energy of β-alanine–cosolvent intermolecular interactions have been estimated quantitatively.

Liquid-phase synthesis of a Li3PS4 solid electrolyte using N-methylformamide for all-solid-state lithium batteries

A Li3PS4 solid electrolyte was directly synthesized from Li2S and P2S5 by a liquid-phase reaction using N-methylformamide (NMF) and n-hexane as reaction media. After the reaction of Li2S and P2S5, a yellow NMF solution was obtained. The NMF solution was dried at 180 °C for 3 hours under vacuum to remove NMF and to obtain a powder. A crystalline phase of the obtained powder from the NMF solution was attributed to Li3PS4 crystals, and the ionic conductivity of the obtained powder was 2.3 × 10−6 S cm−1 at 25 °C. Electrode–electrolyte composite materials for all-solid-state lithium batteries were prepared by coating the Li3PS4 solid electrolyte onto LiCoO2 particles using the NMF solution. SEM and EDX analysis showed that LiCoO2 particles were uniformly coated with the Li3PS4 solid electrolyte. An all-solid-state cell using the LiCoO2 particles coated with the Li3PS4 solid electrolyte as a positive electrode operated as a secondary battery.

Effect of metal nature on specific adsorption of Cl−, Br−, and I− ions from N-methylformamide solutions

The differential capacitance curves were measured with an ac bridge in the M/[N-MF+0.1m M KCl+0.1(1−m) M KClO4], M/[N-MF+0.1m M KBr+0.1(1−m) M KClO4], and M/[N-MF+0.1m MKI+0.1(1−m) M KClO4] systems (where M=In–Ga, Tl–Ga) at the following values of molar fraction m of the surface–active anion: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. The I−, Br− and Cl− (Hal−) anions specific adsorption in the above systems can be described quantitatively by the Frumkin isotherm. The main parameters of adsorption of the I−, Br−, and Cl− anions were determined for the studied interfaces. Unlike Ga/N-MF interface, where the adsorption energy (ΔGads) increased in the sequence Br−≈I−<Cl−, at the (In–Ga)/N-MF and (Tl–Ga)/N-MF interfaces, same as at the Hg/N-MF interface, it increased in the reverse sequence: Cl−<Br−<I−. It is found that the values of ΔGads, energy of metal–Hal− interaction (ΔGM-Hal-), and difference (ΔGM-Hal1--ΔGM-Hal2-) grow in the series of (Tl–Ga)<(In–Ga)<Ga. The metal–Hal− interaction energy increase in the sequence of ΔGM-Cl->ΔGM-Br->ΔGM-I-. The values of difference (ΔGM-Hal1--ΔGM-Hal2-) are higher for the Ga electrode and lower for the (In–Ga) and (Tl–Ga) electrodes than the values of difference between the Hal− solvation energies (ΔGS-Hal1--ΔGS-Hal2-), which determines the sequences of Hal− adsorption.

Preparation of Li2S–P2S5 solid electrolyte from N-methylformamide solution and application for all-solid-state lithium battery

Electrode–solid electrolyte composite materials for all-solid-state lithium batteries were prepared by coating of the Li2S–P2S5 solid electrolyte onto LiCoO2 particles using a N-methylformamide (NMF) solution of 80Li2S·20P2S5 (mol%) solid electrolyte. SEM and EDX analysis showed that the Li2S–P2S5 solid electrolyte was uniformly coated on LiCoO2 particles. The all-solid-state cell using the LiCoO2 particles coated with the solid electrolyte showed higher charge–discharge capacity than the cells using uncoated LiCoO2 particles.

Nanomaterials Based on Polyanilines and MoSe2

Polyaniline, poly(N-methyl aniline), poly(2-ethyl aniline) and poly(2-propyl aniline) were intercalated into layered molybdenum diselenide by using the exfoliation/restacking property of LixMoSe2. MoSe2 was reacted with n-butyllithium to form LixMoSe2. The LixMoSe2 was exfoliated in N-methylformamide (NMF) with the help of ultrasonication which lead to the formation of single layers of MoSe2. Addition of NMF solutions of the polymers to the exfoliated layers resulted in their intercalation into MoSe2. The products were characterized by powder X-ray diffraction. Fourier transform infra-red spectroscopy, and four-probe van der Pauw technique electrical conductivity measurements are reported here for the first time.

Formation of Li2S–P2S5 Solid Electrolyte from N-Methylformamide Solution

Abstract Li2S–P2S5 solid electrolyte (SE) powders were successfully reprecipitated from a liquid phase. Powders of 80Li2S·20P2S5 (mol %) SE originally prepared by mechanical milling were dissolved in N-methylformamide (NMF) and a homogeneous solution was obtained. The NMF solution was dried at 150 °C for 3 h under vacuum to obtain precipitates. The main structural unit in the obtained powder was PS43−. The crystalline phase of the powders was confirmed to be Li3PS4, and ionic conductivity was 2.6 × 10−6 S cm−1.

Specific adsorption of bromide and iodide ions from N-methyl formamide solutions with constant ionic strength on liquid ga electrode

The differential capacitance curves were measured with an ac bridge in the Ga/[N-MF + 0.1 m M KBr + 0.1 (1 − m) M KClO4] and Ga/[N-MF + 0.1 m M KI + 0.1 (1 − m) M KClO4] systems at the following fractions m of surface-active anions: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. As compared with other solvents, N-methyl formamide (N-MF) enables one to realize the largest positive charges of Ga electrode, at which it remains ideally polarizable (up to 20 μ/cm2). The data on the specific adsorption of Br− and I− anions in the system can be quantitatively described by the Frumkin’s isotherm; to the first approximation, free energy of halide ion (Hal−) adsorption \(\Delta G_{adsHal^{ - 1} } \) is a linear function of electrode charge. It is found that, in contrast to the Hg/N-MF interface, \(\Delta G_{adsHal^{ - 1} } \) at the Ga/N-MF interface varies in the reverse order: Brt— ∼ I− \Delta G_{M - Br^ - } > \Delta G_{M - I^ - } \) and the difference \((\Delta G_{Ga - Hal_1^ - } - \Delta G_{Ga - Hal_2^ - } )\) is larger than the difference between the solvation energies of \(Hal^ - (\Delta G_{S - Hal_1^ - } - \Delta G_{S - Hal_2^ - } )\).

Specific adsorption of Cl−, Br−, and I− ions on liquid Ga electrode from N-methylformamide solutions

An ac bridge is used to measure the differential capacitance curves in the systems of Ga/[N-MF+0.1m M KCl+0.1(1−m) M KClO4], Ga/[N-MF+0.1m M KBr+0.1(1−m) M KClO4], and Ga/[N-MF+0.1m MKI+0.1(1−m) M KClO4] for the following values of fraction m of the surface-active anion: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. As compared to other solvents, N-methylformamide (N-MF) allows achieving much higher positive charges of the Ga electrode, at which it remains ideally polarizable (up to 20 and in some cases 30μC/cm2). The values of fraction m of the surface-active anion, 0.05, 0.1, 0.2, 0.5, and 1, are used to calculate adsorption parameters for model based on the Frumkin isotherm, in which free adsorption energy ΔGads is a function of the electrode charge. It is found that the ΔGads value at the Ga/N-MF interface changes inversely, Br−≈I−<Cl−, to the sequence observed on the Hg/N-MF interface. The obtained results can be used for the unique assessment of an increase in the metal–Hal− interaction energy in the series of ΔGM–Cl->ΔGM–Br->ΔGM–I- and of difference (ΔGGa–Hal1--ΔGGa–Hal2-) exceeding the difference of solvation energies of Hal− (ΔGS–Hal1--ΔGS–Hal2-).

Specific adsorption of chloride ions on liquid Ga electrode from N-methylformamide solutions with constant ionic strength

Differential capacitance curves are measured by mans of an ac-bridge in the system Ga/[N-MF + 0.1m M KCl + 0.1(1 − m) M KClO4] with the surface-active anion taken in the following molar fractions m: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. As compared with the other solvents, N-methylformamide (N-MF) makes it possible to realize the highest positive charges of the Ga electrode at which the electrode remains ideally polarizable (up to 20 μC/cm2). The data on the specific adsorption of Cl− ions in the mentioned system can be described qualitatively by the Frumkin isotherm in which the free energy is considered as a linear function of the electrode charge.

Volumetric Properties of Amino Acids in Aqueous N-Methylformamide Solutions at T = 298.15 K

Densities of glycine, l-alanine, and l-serine in aqueous solutions of N-methylformamide (NMF) were measured at 298.15 K. The standard partial molar volumes (Vϕ°), standard partial molar volumes of ...

Testing if the Interstitial Atom,X, of the Nitrogenase Molybdenum−Iron Cofactor Is N or C: ENDOR, ESEEM, and DFT Studies of theS=3/2Resting State in Multiple Environments

A high-resolution (1.16 A) X-ray structure of the nitrogenase molybdenum-iron (MoFe) protein revealed electron density from a single N, O, or C atom (denoted X) inside the central iron prismane ([6Fe]) of the [MoFe7S9:homocitrate] FeMo-cofactor (FeMo-co). We here extend earlier efforts to determine the identity of X through detailed tests of whether X = N or C by interlocking and mutually supportive 9 GHz electron spin echo envelope modulation (ESEEM) and 35 GHz electron-nuclear double resonance (ENDOR) measurements on 14/15N and 12/13C isotopomers of FeMo-co in three environments: (i) incorporated into the native MoFe protein environment; (ii) extracted into N-methyl formamide solution; and (iii) incorporated into the NifX protein, which acts as a chaperone during FeMo-co biosynthesis. These measurements provide powerful evidence that X not equal N/C, unless X in effect is magnetically decoupled from the S = 3/2 electron spin system of resting FeMo-co. They reveal no signals from FeMo-co in any of the three environments that can be assigned to X from either 14/15N or 13C: If X were either element, its maximum observed hyperfine coupling at all fields of measurement is estimated to be A(14/15NX) < 0.07/0.1 MHz, A(13CX) < 0.1 MHz, corresponding to intrinsic couplings of about half these values. In parallel, we have explicitly calculated the hyperfine tensors for X = 14/15N/13C/17O, nuclear quadrupole coupling constant e2qQ for X = 14N, and hyperfine constants for the Fe sites of S = 3/2 FeMo-co using density functional theory (DFT) in conjunction with the broken-symmetry (BS) approach for spin coupling. If X = C/N, then the decoupling required by experiment strongly supports the "BS7" spin coupling of the FeMo-co iron sites, in which a small X hyperfine coupling is the result of a precise balance of spin density contributions from three spin-up and three spin-down (3 upward arrow:3 downward arrow) iron atoms of the [6Fe] prismane "waist" of FeMo-co; this would rule out the "BS6" assignment (4 upward arrow:2 downward arrow for [6Fe]) suggested in earlier calculations. However, even with the BS7 scheme, the hyperfine couplings that would be observed for X near g2 are sufficiently large that they should have been detected: we suggest that the experimental results are compatible with X = N only if aiso(14/15NX) < 0.03-0.07/0.05-0.1 MHz and aiso(13CX) < 0.05-0.1 MHz, compared with calculated values of aiso(14/15NX) = 0.3/0.4 MHz and aiso(13CX) = 1 MHz. However, the DFT uncertainties are large enough that the very small hyperfine couplings required by experiment do not necessarily rule out X = N/C.

Enthalpies of transfer of amino acids from water to aqueous solutions of N-methylformamide and N, N-dimethylformamide at T = 298.15 K

Enthalpies of solution of glycine, l-alanine and l-serine in aqueous solutions of N-methylformamide and N, N-dimethylformamide were measured at 298.15 K. Enthalpies of transfer (Δ tr H) of amino acids from water to aqueous solutions of amides were derived and interpreted in terms of structural interaction. The results were compared with those in aqueous formamide solutions.

Thermodynamic characteristics of and intermolecular interactions in aqueous solutions of N-methylformamide

The thermodynamic characteristics of aqueous solutions of N-methylformamide were calculated over the whole range of mixture compositions. Intermolecular interaction parameters were determined, and the boundaries of concentration regions with different types of intercomponent association and solution structural organization were established.

Cooperativity and intermediates in the equilibrium reactions of Fe(II,III) with ethanethiolate in N-methylformamide solution

The reaction of FeCl(2) or FeCl(3) with sodium ethanethiolate (SEt) in N-methylformamide (NMF) has been reevaluated to rectify a previous Fe(II) oxidation artifact. On titrating Fe(II) with EtS(-) concentrations up to 12 mol Eq, new features in the UV/vis spectrum (epsilon(344)=(3.1+/-0.2)x10(3) M(-1) cm(-1); epsilon(486)=(4.5+/-0.1)x10(2) M(-1) cm(-1)) indicated that the first observable step was the formation of a single complex different from the known tetrahedral tetrathiolate, [Fe(SEt)(4)](2-) . As the EtS(-) concentration increased past 12.5 mol Eq the UV/vis spectrum gradually transformed to that of [Fe(SEt)(4)](2-) (lambda(max)=314 nm). A Hill-formalism fit to the titration data of the initially formed complex indicated cooperative ligation by three ethanethiolate ions, with K(coop)=(1.7+/-0.1)x10(3) M(-3) and Hill "n"=2.4+/-0.1 (r=0.997). The 3:1 EtS(-)-Fe(II) complex is proposed to be [Fe(2)(SEt)(6)](2-). Titration of Fe(III) with EtS(-) showed direct cooperative formation of [Fe(SEt)(4)](-) [epsilon(340)=(3.4+/-0.5)x10(3) M(-1) cm(-1)] with a Hill-formalism K(coop)=(4.3+/-0.1)x10(2) M(-4) and a Hill coefficient "n"=3.7+/-0.2 (r=0.996). Further ligation past [Fe(SEt)(4)](-) was observed at EtS(-) concentrations above 35 mol Eq. The Fe(III) Hill constants are at variance with our previous report. However, the UV/vis spectrum of Fe(III) in NMF solution was found to change systematically over time, consistent with a slow progressive deprotonation of [Fe(nmf)](3+). The observed time-to-time differences in the equilibrium chemistry of Fe(III) with ethanethiolate in NMF thus reflect variation in the microscopic solution composition of FeCl(3) in alkaline NMF solvent. These results are related to the chemistry of nitrogenase FeMo cofactor in alkaline NMF solution.

Volumetric and Viscometric Properties of Aqueous Solutions of N-Methylformamide, 1,2-Diaminopropane and 2-Methylpropane-2-ol

Density and viscosity of aqueous solutions of N-methylformamide (NMF), 1,2-diaminopropane (DAP) and 2-methylpropane-2-ol (MPL) have been measured precisely over the entire composition range (i.e., 1 ≥ x 2 ≥ 0) at five equidistant temperatures ranging from 298.15 to 318.15 K. Excess molar volume (VE m ) and excess viscosity (η E ) have been calculated from measured density and viscosity data, respectively. Excess molar volume and excess viscosity have been fitted by the least squares method to the four parameters Redlich-Kister equation. The results have been interpreted on the basis of (i) interstitial incorporation, (ii) breakdown of the structure of pure liquids, (iii) hydrophobic hydration, (iv) hydrophobic interaction and (v) association between dissimilar liquids.

Determination of ligand binding constants for the iron-molybdenum cofactor of nitrogenase: monomers, multimers, and cooperative behavior.

Equilibrium titrations in N-methylformamide (NMF) of G-25 gel filtered (ox)-state FeMo cofactor [FeMoco(ox)] from Azotobacter vinelandii nitrogenase were carried out using sodium ethanethiolate and followed using UV/Vis absorption spectroscopy. For Fe-Moco(ox), a non-linear least squares (NLLSQ) fit to the data indicated a strong equilibrium thiolate-binding step with Keq = 1.3+/-0.2x10(6) M(-1). With 245 molar excess imidazole, cooperative binding of three ethanethiolates was observed. The best NLLSQ fit gave Keq=2.0+/-0.1x10(5) M(-2) and a Hill coefficient n=2.0+/-0.3. A Scatchard plot of these data was concave upward, indicating positive cooperativity. The fit to previously published data involving benzenethiol titration of the one-electron reduced (semi-reduced) cofactor, FeMoco(sr), as followed by EPR required a model that included both a sub-stoichiometric ratio of thiol to FeMoco(sr) and about five cooperative ligand binding sites. These constraints were met by modeling FeMoco(sr) as an aggregate, with fewer thiol binding sites than FeMoco(sr) units. The best fit model was that of FeMoco(sr) as a dodecamer with five cooperative benzenethiol binding sites, yielding a thiol binding constant of 3.32+/-0.09x10(4) M(-4.8) and a Hill coefficient n=4.8+/-0.6. The results of all the other published ligand titrations of FeMoco(sr) were similarly analyzed successfully in terms of equilibrium models that include both cooperative ligand binding and dimer-level aggregation. A possible structural model for FeMoco aggregation in NMF solution is proposed.

Interfacial Rearrangements at the Mercury Electrode in Nonaqueous Solvents of High Dielectric Constant. Reorientation of Triphenylbismouth and Triphenylantimony

Capacitance−potential curves of unusual form were obtained during the adsorption of triphenylbismouth and triphenylantimony at mercury electrodes from N-methylformamide, N,N-dimethylformamide, dimethyl sulfoxide, propylene carbonate, and methanol solutions. Most of these systems present nonadsorption−desorption capacitance peaks at intermediate negative potentials. The nature of those peaks was investigated by phase-selective ac (alternating current) polarographic measurements at the dropping and hanging Hg electrodes. The application of phenomenological criteria relative to the form of the curves of the electrode charge density and the surface pressure against potential and calculation of the projection area of the adsorbate molecules on the electrode surface make it possible to identify the observed effect with the reorientation of triphenylbismouth and triphenylantimony.

Exploring the reactivity of the isolated iron-molybdenum cofactor of nitrogenase

There is strong evidence that the iron-molybdenum cofactor (FeMoco) of nitrogenase forms part of the enzyme’s active site. FeMoco, a MoFe 7S 9·homocitrate cluster, can be extracted intact from the enzyme into N-methylformamide solution but is reported to be inactive in substrate reduction unless powerful reductants are used and then only acetylene and cyclopropene reductions have been observed. The literature on the catalytic and substrate binding reactivities of extracted FeMoco is reviewed and new data on electrocatalytic hydrogen evolution presented. A comparison of the ligand binding properties of FeMoco from the wild-type and a NifV − mutant enzyme, which has citrate in place of R-homocitrate, is presented. These data are interpreted in terms of their significance for enzyme turnover and of the obligate requirement for R-homocitrate for dinitrogen reduction.