Aqueous Solutions Of Dimethylformamide Research Articles

Are Hansen solubility parameters relevant in predicting the post-treatment effect on polyamide-based TFC membranes?

This study investigates the impact of solvent post-treatment on polyamide-based thin film composite (TFC) membranes, specifically examining the effect on commercial nanofiltration (NF) and reverse osmosis (RO) membranes. Na2SO4 rejection and increase in pure water permeance (PWP) were considered as the output parameters. The disparity in Hansen solubility parameters (HSP) between the post-treatment solution and the polyamide layer of the TFC membrane, denoted by Ra, is well adapted to understand the enhancement in water permeance through the membranes upon treatment. Aqueous solutions of dimethylformamide with a Ra value of 4, acetonitrile with a Ra value of 8.3, and ethanol with a Ra value of 12.7 were used as the post-treatment solutions. Our experimental design, based on the Box-Behnken design of Response Surface Methodology, incorporates variables such as the concentration of the solvent in the solution (% v/v), Ra value, and treatment time (s). Our findings demonstrate that the effect of post-treatment on the TFC membranes is not governed by the Ra value. Notably, while the post-treatment with the aqueous solution of acetonitrile, 80% v/v for 30 s, had considerable effects on NF membranes (124.5% enhancement in PWP; reduction of 3.5% in Na2SO4 rejection), its impact on RO membranes was negligible. Several factors explain this discrepancy, including the limitations of the HSP model for composite polymers, the inaccuracy of the PWP or salt rejection as a swelling indicator, variations in the HSP values of the polyamide layers for different membranes, and possible modifications in the interface between the support membrane and the polyamide layer. In summary, our study provides insights into the complex interactions between solvents and composite membranes, indicating that HSP alone is not a decisive factor in predicting post-treatment effects on polyamide-based TFC membranes.

Hemin-utilizing G-quadruplex DNAzymes are strongly active in organic co-solvents

The widespread use of organic solvents in industrial processes has focused in recent years on the utility of “green” solvents – those with less harmful environmental, health, and safety properties – such as methanol and formamide. However, protein enzymes, regarded as green catalysts, are often incompatible with organic solvents. Herein, we have explored the oxidative properties of a Fe(III)-heme, or hemin, utilizing catalytic DNA (heme·DNAzyme) in different green solvent-water mixtures. We find that the peroxidase and peroxygenase activities of the heme·DNAzyme are strongly enhanced in 20–30% v/v methanol or formamide, relative to water alone. Protic solvent content of >30% v/v gradually diminishes heme·DNAzyme catalytic activity; however, the heme·DNAzyme is still active in as high as 80% v/v methanol. In contrast to protic solvents, aqueous dimethylformamide solutions largely inhibit heme·DNAzyme activity. In view of the strong catalytic activity of heme·DNAzyme in aqueous methanol, we were able to determine that a 60% v/v methanol-water mixture gives the most optimal yield of the dibenzothiophene sulfoxide (DBTO) oxidation product of petroleum-derived dibenzothiophene (DBT). The high product yield reflects both DNAzyme catalysis and a high substrate availability. Overall, these results emphasize the excellent promise of G-quadruplex forming DNA catalysts in application to “greener” industrial chemistry. This article is part of a Special Issue entitled “G-quadruplex” Guest Editor: Dr. Concetta Giancola and Dr. Daniela Montesarchio.

Surface activity of sodium chloride in aqueous solutions of dimethylformamide

The surface tensions of solutions of sodium chloride in water and aqueous solutions of dimethylformamide (DMF) were measured in the range of solute concentrations of up to 1 mol/kg at 298 and 303 K. It was found that the concentration dependence of the surface tension of the electrolyte solution has an extreme character regardless of the solvent nature. The dependences obtained are discussed from the standpoint of the effect of solute solvation processes on the adsorption, the composition of surface layers, and the surface activity of a solution.

Dependence of the solubility of Cr(III) and Co(III) trisacetylacetonates in mixed aqueous N,N-dimethylformamide solutions depending on solvent composition and temperature

Data on the solubility of cobalt(III) and chromium(III) trisacetylacetonates in water and aqueous-dimethylformamide solutions over a broad range of temperatures and concentrations are presented and the thermodynamic parameters of dissolution are calculated. The inversion point corresponding to the change in the hydration mechanism associated with the transition of the solvent’s structure from an aqueous solution to that of a mixed aqueous-organic solvent is found in dependences of solubility on the molar concentration of the organic component.

여러 가지 수용액에서의 폴리아크릴로니트릴 필름의 팽윤이 히드라진과의 반응에 미치는 영향

Abstract: Swelling behaviors of polyacrylonitrile (PAN) films in various aqueous solutions, such as N,N'-dimethylformamide(DMF)/water, N,N'-dimethylacetamide (DMAc)/water, dimethylsulfoxide (DMSO)/water, NaSCN or KSCN solution,the effects of the concentrations of these solutions, and the effects of swelling temperature and time on the degree ofswelling of PAN films were analyzed. Among the various aqueous solutions, DMF and NaSCN solution were found tobe effective for high swelling of PAN films. High swelling of PAN films in the hydrazine solutions wherein aqueous,organic solvents or salt solutions were used as solvents for hydrazine, resulted in higher absorption of hydrazine and ahigh degree of cross-linking. Analysis of the bands of FT-IR spectra and the cyclization peaks of DSC curves for var-ious hydrazine-treated PAN films showed that the effective cross-linking of PAN films at the same hydrazine concen-tration was obtained by using DMF/water or NaSCN/water solutions as solvents for hydrazine and treating medium forPAN films. Keywords: polyacrylonitrile (PAN) film, swelling, aqueous solution, DMF/water, NaSCN/water, hydrazine, cross-linking

Heteromolecular structures in aqueous solutions of dimethylformamide and tetrahydrofuran, according to molecular dynamics data

The complex dielectric permittivity of aqueous solutions of tetrahydrofuran and dimethylformamide in wide ranges of temperature (220–300 K) and pressure (0.1–12 MPa) is studied by means of molecular dynamics. The autocorrelation functions of the dipole moments of molecules are calculated. Dielectric permittivity spectra are obtained. The dielectric relaxation times are determined as functions of the tetrahydrofuran and dimethylformamide concentrations in the indicated binary mixtures. The dielectric relaxation frequency shifts toward low frequencies in the range of tetrahydrofuran and dimethylformamide concentrations x ≤ 0.5 molar fraction, due to the formation of heteromolecular structures with hydrogen bonds. This is confirmed by the negative values of the excess dielectric permittivities of binary solutions at x ∼ 0.3–0.4 molar fraction.

Phosphate salts facilitate the electrospinning of hyaluronic acid fiber mats

Electrospinning is a cost effective and facile method to manufacture fiber mats appropriate for biomedical applications. Due to its high molecular weight and charged backbone, hyaluronic acid (HA) fiber mats with consistent fiber morphology have been difficult to electrospin from neutral pH solutions. Here, we present that the electrospinning of HA fibers in aqueous dimethylformamide solutions is facilitated by the addition of three phosphate salts. The salts—glycerol phosphate (GP), sodium phosphate (SP), and tripolyphosphate (TPP)—facilitated electrospinning of the solutions as characterized by conductivity measurements and fiber morphology. From tensile experiments, HA mats electrospun with SP demonstrated improved Young’s modulus (12 MPa) over HA mats spun with either GP or TPP (5 and 3 MPa, respectively). This work demonstrates that a new neutral solvent system can be employed to spin HA fibers, which offers the potential for using the fibers for biomedical applications, such as a bone biomimetic.

Simultaneous determination of hydroquinone and catechol based on glassy carbon electrode modified with gold-graphene nanocomposite

We have synthesized a virtually monodisperse gold-graphene (Au-G) nanocomposite by a single-step chemical reduction method in aqueous dimethylformamide solution. The nanoparticles are homogenously distributed over graphene nanosheets. A glassy carbon electrode was modified with this nanocomposite and displayed high electrocatalytic activity and extraordinary electronic transport properties due to its large surface area. It enabled the simultaneous determination of hydroquinone (HQ) and catechol (CC) in acetate buffer solution of pH 4.5. Two pairs of well-defined, quasi-reversible redox peaks are obtained, one for HQ and its oxidized form, with a 43 mV separation of peak potentials (ΔEp), the other for CC and its oxidized form, with a ΔEp of 39 mV. Due to the large separation of oxidation peak potentials (102 mV), the concentrations of HQ and CC can be easily determined simultaneously. The oxidation peak currents for both HQ and CC increase linearly with the respective concentrations in the 1.0 μM to 0.1 mM concentration range, with the detection limits of 0.2 and 0.15 μM (S/N = 3), respectively. The modified electrode was successfully applied to the simultaneous determination of HQ and CC in spiked tap water, demonstrating that the Au-G nanocomposite may act as a high-performance sensing material in the selective detection of some environmental pollutants.

Copper(II), iron(III), and chromium(III) complexes with 5,10-dioxo-4,5,9,10-tetrahydro-4,9-diazapyrene derivatives

Six copper(II), iron(III), and chromium(III) complexes with 5,10-dioxo-4,5,9,10-tetrahydro-4,9-diazapyrene derivatives (H2L1-H2L3) have been synthesized and studied by physical methods (IR and electronic absorption spectroscopy, quantum-chemical calculations). The composition of the complexes has been determined and their stability constants in aqueous dimethylformamide solutions have been calculated. The energy characteristics, electronic structure and geometry of isolated diazapyrenes and their tautomeric forms have been calculated by the PM6 method, and their complexes have been modeled.

Thermodynamic and structural aspects of the interaction of l-histidine with urea and dimethylformamide in water

The solubility of l-histidine in water and aqueous solutions of dimethylformamide (DMF) at 25°C was determined. The thermal effects of solution of l-histidine in aqueous solutions of urea and DMF were measured. The standard enthalpies, free energies, and entropies of solution and transfer of the amino acid from water to aqueous solutions of amides were calculated. It was shown that the interaction of l-histidine with urea is attractive, and that with DMF, repulsive, with the change in the free energy determined by the enthalpy term in both cases. The enthalpy-entropy compensation taking place to a certain extent in the interaction of l-histidine and l-phenylalanine with amide was revealed. This effect is the most pronounced in the interaction of predominantly hydrophobic DMF and l-phenylalanine.

Thermodynamics of interaction of L-α-phenylalanine with urea and dimethylformamide in aqueous solution

The thermal effects of solution of L-phenylalanine in aqueous solutions of urea and dimethylformamide (DMF) at 25°C were determined. The solubility of L-phenylalanine in water and aqueous DMF solutions was measured. The standard enthalpies, free energies, and entropies of solution of the amino acid in aqueous solutions of amides were calculated. The parameters of pair and ternary amino acid-amide interactions were determined within the framework of the McMillan-Mayer theory. The amino acid-amide pair interaction is accompanied by a decrease in the Gibbs free energy, controlled by the entropy term with DMF and by the enthalpy term with urea. The interaction of L-phenylalanine with two amide molecules is repulsive, which in the case of DMF leads to an increase in the standard free energies of solution of the amino acid at the amide mole fraction X 2 > 0.05.

The heats of hydrogen adsorption on Raney nickel from aqueous-organic solvents with acid and base admixtures

The heats of hydrogen adsorption on porous nickel from aqueous solutions of dimethylformamide containing acetic acid and sodium hydroxide admixtures were measured by adsorption calorimetry. The introduction of acid or alkaline admixtures changed both the amount of hydrogen adsorbed on the surface of porous nickel and the character of the dependences of the heats of adsorption on this amount. The composition of solvents influenced adsorption because of the quantitative redistribution of adsorption values among various hydrogen adsorption forms bound by the active centers of the surface of nickel determined by changes in medium basicity.

Fluorescence of 4-dimethylaminochalcone and interaction in the system aromatic amines-surfactants

It is demonstrated that 4-dimethylaminochalcone (DMC) can be used as a fluorescent probe for studying the microenvironment in the arylamine-surfactant system. A molecular simulation of the location of DMC at the water-lipophilic medium phase boundary is performed. The fluorescence of DMC is studied in aqueous solutions of dimethylformamide and surfactants of different natures. The influence of the nature and concentration of arylamines on the characteristics of the fluorescence of DMC in micellar TX-100 solutions is revealed.

Thermodynamic parameters of intermolecular interaction in strongly associated solvents and their mixtures with dimethylformamide

The specific and nonspecific constituents of the total energy of intermolecular interasction in ethylene glycol, diethylene glycol, and formamide were determined for the range 288.15–323.15 K using a simulation approach. Diethylene glycol, like formamide and ethylene glycol, forms networks of hydrogen bonds. In ethylene glycol and formamide, the hydrogen bonds make a predominant contribution to the total interaction energy. The specific and nonspecific contributions in mixtures of the above solvents with dimethyl-formamide were calculated, and the results were discussed in combination with the data for aqueous dimethyl-formamide solutions.

Antiparallel Pleated β-Sheets Observed in Crystal Structures of N,N-Bis(trichloroacetyl) and N,N-Bis(m-bromobenzoyl) Gramicidin S

Despite intensive efforts, the structures of gramicidin S (GS) [cyclo(-Val-Orn-Leu-d-Phe-Pro-)2] and its analogues have not been elucidated by the X-ray diffraction method, except for the GS-urea complex (Hull et al., Nature 275, 206–207, 1978; Tishchenko et al., Acta Cryst. D53, 151–159, 1997). We focused on the acetylation of GS to obtain suitable crystals for X-ray diffraction. The amino groups of Orn residues were capped with trichloroacetic and m-bromobenzoic acids. Both trichloroacetyl and m-bromobenzoyl GSs (TcGS and BzGS, respectively) are hydrophobic and their properties are similar to those of acetyl-GS (AcGS). Although it is well known that AcGS yields hexagonal crystals, TcGS and BzGS yield monoclinic and orthorhombic crystals in aqueous dimethylformamide solution, respectively. Their cell volumes were approximately one-fourth or one-eighth of the hexagonal cell volume. The crystal structures of TcGS and BzGS were determined as the first examples of acetylated GS analogues: TcGS, C64H90N12O12Cl6 · 3(C3H7NO), Mr = 1651.47, monoclinic, P21, a = 15.4366(6) Å, b = 18.5312(4) Å, c = 16.4774(6) Å, β = 14.160(2)°, V = 4300.6(2) Å3, Z = 2; and BzGS, C64H98N12O12Br2 · 1.54(H2O), Mr = 1535.21, orthorhombic, P212121, a = 16.748(10) Å, b = 18.834(5) Å, c = 28.558(10) Å, V = 9008(7) Å3, Z = 4. Both these peptide molecules formed an antiparallel pleated β-sheet, and pseudo twofold symmetries existed in the repeated sequence. β-Turns formed at the fragments of d-Phe-Pro were classified into type II' based on their characteristics. The peptide conformations of TcGS and BzGS were similar to each other, and these structural features agreed with those of structures proposed by the previous studies.

A β-turn retro-enantiomeric analogue of achatin-I, H–D-Asp-[γCONH]-D-Ala–L-Phe–Gly–OH

A retro-enantiomeric analogue of achatin-I, β-D-aspartyl-D-alanyl-L-phenylalanylglycine, H-D-Asp-[γCONH]-D-Ala-L-Phe-Gly-OH (C 18 H 24 N 4 O 7 ), was crystallized from an aqueous dimethylformamide solution. The γ-amide bond at the D-Asp 1 residue imparts β-amino acid characteristics on this residue. The peptide adopts a β-turn conformation and its loop shape is similar to that of achatin-I.

Structural properties of dilute aqueous solutions of dimethylformamide and acetone based on computer simulation

The Monte Carlo simulation of molecular configurations for aqueous solutions ofN,N-dimethylformamide and acetone was carried out. The atom-atom radial distribution functions were determined. The topological properties of the H-bond system were investigated. The concentrations of closed H-bond cycles and the radial distribution functions of their geometric centers were found. It was shown that the local arrangement of molecules and supermolecular assemblies typical of the H-bond network in neat water is retained in the solutions studied.

Thermodynamic activity of some aqueous-organic solutions

It has been found that the concentration dependences of the thermodynamic activity of water in aqueous-dimethylacetamide and aqueous-dimethylformamide solutions have breaks in the concentration regions of organic component of 40, 60, and 85% by wt.

Physicochemical and Structural Studies of Triamterene

It has been shown by several physicochemical techniques that the existence of different crystal forms of triamterene, as well as the crystalline products from different solvents with distinct differences in melting points, does not necessarily imply polymorphic crystal forms. The crystalline structure for triamterene is reported herein, revealing a N,N-dimethylformamide molecule and a water molecule within the crystal lattice. Triamterene crystallizes in a face-centered orthorhombic space group, Fdd2 (#43), when grown from aqueous solutions of dimethylformamide (N,N-DMF). In addition, the asymmetric unit contains a partially occupied molecule which is situated on a crystallographic twofold axis. Weak hydrogen bonding occurs between atoms O(1) and N(7), with a distance of 2.66 Å, O(1) and N(5) with a distance of 2.96 Å, 0(2) and N(1), at two different symmetry sites of 2.99 Å, and N(2) and N(7), with a distance of 2.91 Å. The different solvated crystalline triamterene specimens have different melting points depending on organic solvation, water, or both.

Substitution Reactions of α-Alkyl 4- and 5-Nitropyrrol-2-ylmethyl Derivatives

The α-t-butyl 4- and 5-nitropyrrol-2-yl chlorides (5b) and (6b) react with azide, thiocyanate and p- toluenethiolate ions in dimethylformamide through cationic species in an SN 1-type process, rather than by the SRNl or SN(AEAE) processes, by which their analogues in the benzene, furan or thiophen systems react. These reactions are so facile that they take place in the aqueous dimethylformamide solutions produced during the workup of reaction mixtures. Solvolysis of (5b) or (6b) in methanol produces high yields of the corresponding methyl ethers (5f) and (6f) The chloride (6b) reacts with methoxide ion to produce the diene (33), which reacts reversibly with excess methoxide to give polymethoxylated derivatives. The mesitoic ester (3d) and the acetic ester (3c) are sufficiently unreactive by the cationic pathway, unlike the highly reactive chlorides (3b) and (4c), to allow reaction with the lithium salt (16) and the tetrabutylammonium salt (17) of 2-nitropropane to occur by an SRNl mechanism to give the C- alkylate (3e).