Capillary electrophoresis in N,N-dimethylformamide

N,N-Dimethylformamide (DMF) is a dipolar protophilic solvent with physicochemical properties that makes it suitable as solvent for capillary electrophoresis (CE). It is prerequisite for the proper application of CE to adjust and to change the pH of the background electrolyte (BGE) in a defined manner. This was done in the present work using benzoic acid-benzoate by selecting different concentration ratios of acid and salt, and calculating the theoretical pH from the activity-corrected Henderson-Hasselbalch equation. The mobilities of the analytes (chloro- and nitro-substituted phenolates) were found to follow reasonably well the typical sigmoid mobility versus pH curve as predicted by theory. The actual mobilities and pK(a) values (at 25 degrees C) of the analytes were derived from these curves. pK(a) values were in the range of 11.1-11.7, being thus 3-4.4 units higher than in water. This pK(a) shift is caused by the destabilization of the analyte anion and the better stability (solubility) of the molecular analyte acid in DMF, which overcome the higher basicity of DMF compared to water. Absolute mobilities were calculated from the actual mobilities; they were between 32x10(-9) and 42x10(-9) m(2)/Vxs. Slight deviations of the measured mobilities from the theoretical mobility versus pH curve were discussed on the bases of ion pairing and heteroconjugation and homoconjugation of either buffer components or buffer components and analytes. Heteroconjugation was used as a mechanism for the electrically driven separation of neutral analyte molecules in a BGE where salicylate acted as complex forming ion. Rough estimation of the complexation constants for the phenolic analytes gave values in the range of 100-200 L/mol. Addition of water to the solvent decreased the effect of heteroconjugation, but it was still present up to the surprisingly high concentration of 20% water. Electrophoretically relevant parameters like ionic mobilities and pK(a) values, and conjugation and ion pairing are dependent on the water content of the solvent. The water uptake of DMF was measured when exposed to humidity of ambient air. The resulted behavior of the water uptake was found rather similar to that for acetonitrile and methanol.     

Polymerization of α-amino acid N-carboxy anhydrides initiated by histamine in N,N-dimethylformamide

The polymerization of α-amino acid N-carboxy anhydrides (NCAs) initiated by 4-aminoethylimidazole (histamine) was studied in order to synthesize poly(amino acids) containing an imidazole nucleus at the end of polymer chain. On the basis of the kinetical measurements, it was found that the rate of polymerization is proportional to the first order in both NCA and initiator concentrations and that the initiation reaction is predominantly caused by the primary amine with the highest basicity in a histamine molecule. Binding of the histamine fragment to the end of polymer chain was confirmed by elementary analysis, nuclear magnetic resonance spectroscopy, and measuring the number-average molecular weight of the resulting polymers. It was thus possible to prepare poly(amino acids) with a pendant histamine. In addition, the lowering of the number-average degree of polymerization of the polymers prepared was observed under the condition that the initial molar ratio of NCA to histamine was larger. It was caused by the reinitiation of polymerization by the imidazole nucleus at the chain end.     

Volumetric properties of ammonium nitrate in N,N-dimethylformamide

The densities of the ammonium nitrate in N,N-dimethylformamide (DMF) mixtures were measured at T = (308.15 to 348.15) K for different ammonium nitrate molalities in the range from (0 to 6.8404) mol·kg⁻¹. From the obtained density data, volumetric properties (apparent molar volumes and partial molar volumes) have been evaluated and discussed in the term of respective ionic and dipole interactions. From the apparent molar volume, determined at various temperatures, the apparent molar expansibility and the coefficients of thermal expansion were also calculated.     

The electrochemical reaction of nitrate in N,N-dimethylformamide

Polarography, cyclic voltammetry and controlled-potential coulometry were used to study N,N-dimethylformamide solutions of nitrate. Nitrate is reversibly reduced in a one-electron step to NO(2). The diffusion coefficient of nitrate was polarographically estimated to be 4.6 x 10(-6) cm(2)/sec. Polarography in dimethylformamide was found to be a convenient method of analysis for nitrate in a solid fertilizer.     

Crystallization-driven self-assembly of isotactic polystyrene in N,N-dimethylformamide

Herein we demonstrate crystallization-driven self-assembly of isotactic polystyrene(i PS) with high isotacticity and narrow molecular weight distribution and crystallization-induced switching of the morphology of i PS aggregates in N, N-dimethylformamide(DMF). The formation and morphology switching of the self-assembled aggregates of i PS are investigated by means of dynamic light scattering(DLS), scanning electron microscopy(SEM), differential scanning calorimetry(DSC) and wide angle X-ray diffraction(WXRD). The results reveal that cooling DMF solution of i PS promotes i PS chains to self-assemble into spherical aggregates with a gelled core cross-linked by microcrystals, which is surrounded by solvent-swollen corona. Furthermore, crystallization induces the deformation of i PS aggregates from spherical to plate-like or nest-like.     

Polymerization of styrene miniemulsions

Polymerization of styrene miniemulsions, prepared using a mixed emulsifier system comprising sodium lauryl sulfate and cetyl alcohol, was carried out using both water-soluble (potassium persulfate) and oil-soluble [2,2′-azobis-(2-methyl butyronitrile)] initiators. The effects of variation of initiator concentration, polymerization temperature, and added inhibitor on the kinetics and particle-size distributions were investigated to obtain more quantitative evidence concerning the locus of polymerization in miniemulsion systems. Experimental results for the kinetics and particle-size distributions clearly showed that monomer droplets became the main source of polymer particle formation. This was attributed to the fact that stable emulsions with droplet diameters in the range of 0.05 to 0.15 μm were produced using this mixed-emulsifier system. In this size range, droplet initiation could effectively compete with other mechanisms due to their large surface area. Their size was indeed similar to the corresponding latex particle size obtained after polymerization.     

N,N-dimethylformamide: a multipurpose building block

Often used as a common solvent for chemical reations and utilized widely in industry as a reagent, N,N-dimethylformamide (DMF) has played an important role in organic synthesis for a long time. Numerous highly useful articles and reviews discussing its utilizations have been published. With a focus on the performance of DMF as a multipurpose precursor for various units in numerous reactions, this Minireview summarizes recent developments in the employment of DMF in the fields of formylation, aminocarbonylation, amination, amidation, and cyanation, as well as its reaction with arynes.     

The acidity scale of HCl solutions in N,N-dimethylformamide

The scale of the thermodynamic acidity of HCl solutions in DMF has been measured at 25 and 39.5 °C up to 15 mol L^–1 acid concentration by the indicator method. It is shown that in the HCl-DMF system the ionization of the nitroaniline-derived indicators occurs by the ion pair mechanism. Within the temperature range studied acidity is independent of temperature. Indicators of the nitroaniline series are used.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1025–1028, June, 1994.     

Enthalpic interaction coefficients of formamides dissolved in N,N-dimethylformamide

Enthalpies of dilution of formamide, N-methylformamide, N-ethylformamide, N-propylformamide, N-butylformamide, N-pentylformamide, N,N-diethyl-formamide, N,N-dipropylformamide, N,N-dibutylformamide, and N,N-dipentyl-formamide dissolved in N,N-dimethylformamide as solvent have been measured calorimetrically at 25°C. The results are interpreted in terms of the McMillan-Mayer theory. Enthalpic interaction parameters are obtained for pairs, triplets, and in some cases, quadruplets of solute molecules. In general, the enthalpic pair interaction coefficients are negative, whereas the triplet coefficients are positive. The interaction enthalpies are positive only for N-methylformamide and formamide. The magnitudes of the enthalpic pair and triplet interaction coefficients increase with increasing number of C atoms in the N-alkyl groups. The results for the formamides presented in this paper are compared with those for corresponding acetamides published earlier. Although the trends are comparable, distinct differences are observed. The contribution of the -CH₃ group at the CO side of the dialkylacetamides to the enthalpic interaction coefficients appears to be negligible. The same is true for -CH₂ groups at the NH side of a number of amides and related compounds. The enthalpic pair interaction coefficients of the mono-N-alkylsubstituted formamides show a shift of about 100 J-kg-mol^–2 as compared with isomeric N-alkylacetamides. This is discussed in terms of the difference in proton donating and accepting ability of several types of amide molecules. It is concluded that substitution effects should be incorporated in additivity models for these type of systems.     

Electrogenerated chemiluminescence of triazole-modified deoxycytidine analogues in N,N-dimethylformamide

Triazole-modified deoxycytidines have been prepared for incorporation into single-stranded deoxyribonucleic acid (ssDNA). Electrochemical responses and electrogenerated chemiluminescence (ECL) of these deoxycytidine (dC) analogues, 1-4, were investigated as the monomers. Cyclic voltammetry and differential pulse voltammetry techniques were used to determine the oxidation and reduction potentials of 1-4, along with the reversibility of their electrochemical reactions. The dC analogues, in N,N-dimethylformamide containing 0.1 M tetra-n-butylammonium perchlorate as electrolyte, exhibited weak relative ECL efficiencies following the annihilation mechanism, while these efficiencies were enhanced with the use of benzoyl peroxide following the coreactant mechanism. It was shown that these nucleosides could generate excited monomers, and excimers as seen by the red-shifted ECL maxima relative to their corresponding photoluminescence peak wavelengths.     

Enthalpic interaction coefficients of amides dissolved in N,N-dimethylformamide

Enthalpies of dilution of propionamide, butyramide, pentanamide, hexanamide, N-pentylacetamide, N,N-dipentylacetamide, N-ethylhexanamide and N,N-diethylhexanamide dissolved in N,N-dimethylformamide as solvent have been measured calorimetrically at 25°C. The results are interpreted in terms of the McMillan-Mayer theory. Enthalpic interaction parameters are obtained for pairs, triplets and some quadruplets of solute molecules. All enthalpic pair interaction coefficients are negative, whereas those for triplets are positive. For unsubstituted amides the change of the enthalpic coefficients with the number of C-atoms differs considerably from that of the substituted compounds. The concept of polarophobic interaction is used for the interpretation of the results in connection with the assumption of formation of solute-solvent associates. For solutes with longer alkyl chains the results cannot be described satisfactorily in terms of the additivity approach of Savage and Wood. Probably the pair interactions of these compounds are not the result of interaction in a random way. Also the linear dependence of the pair interaction coefficients of the larger molecules with the number of C-atoms and the results for the unsubstituted amides support the occurrence of preferential orientations for these compounds.     

Thermodynamics of solution of proto- and mezoporphyrins in N,N-dimethylformamide

This paper describes the results of thermodynamic study of dissolution of proto- and mesoporphyrins in liquid N,N-dimethylformamide (DMF) at different temperatures. Enthalpies of solution and solubility of protoporphyrin dimethylester (PDE) and mesoporphyrin dimethylester (MDE) in DMF have been obtained from T = (298 to 318) K. Free energies, enthalpies, entropies and heat capacities of solution have been computed from the combination of enthalpic and solubility data via the Gibbs–Helmholtz equation. We have shown that for all blood porphyrins this approach reproduces both free energies of solution and solubility values for the physiological temperature range.     

One-pot alpha-glycosylation method using Appel agents in N,N-dimethylformamide

[reaction: see text] A concept for the development of practical glycosylation is presented and demonstrated by one-pot alpha-glycosylation applying Appel agents for 2-O-benzyl-1-OH hexoses in DMF. The reaction, in situ giving the equilibrium of glycosyl bromides and more reactive O-glycoside intermediates, accomplishes a near-quantitative alpha-glycosylation removing the water molecules.     

Rotating-disc electrode determination of nitrogen dioxide concentrated in N,N-dimethylformamide

Nitrogen dioxide at ppm levels in air is concentrated in N,N-dimethylformamide and determined by voltammetry at a rotating-disc electrode. The oxidation currents for nitrite are measured under the same conditions as the nitrogen dioxide reduction and are used as standards. The results are in good accordance with the values calculated from the absorption measurements.     

Superior dispersion of highly reduced graphene oxide in N,N-dimethylformamide

Here, we report the effect of temperature on the extent of hydrazine reduction of graphene oxide in N,N-dimethylformamide (DMF)/water (80/20 v/v) and the dispersibility of the resultant graphene in DMF. The highly reduced graphene oxide (HRG) had a high C/O ratio and good dispersibility in DMF. The good dispersibility of HRGs is due to the solvation effect of DMF on graphene sheets during the hydrazine reduction, which diminishes the formation of irreversible graphene sheet aggregates. The dispersibility of the HRGs was varied from 1.66 to 0.38 mg/mL when the reduction temperature increased from 25 °C to 80 °C. The dispersibility of the HRGs was inversely proportional to the electrical conductivity of the HRGs, which varied from 17,400 to 25,500 S/m. The relationships between the C/O ratio, electrical conductivity, and dispersibility of the HRGs were determined and these properties were found to be easily controlled by manipulating the reduction temperature.     

Electrochemical behavior of the N-nosyl-protected amino acids in N,N-dimethylformamide

The electrochemical reduction of serine, glycine, and leucine protected by the 4-nitrobenzenesulfonyl group in N,N-dimethylformamide at mercury cathode occurs at two steps. The first one at −0.8 V vs. SCE, after a one-electron transfer, leads the anion radical formation that dimerizes and adsorbs at electrode. In the second step at −1.4 V, an instable dianion forms which then cleaves. The mechanism is discussed. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 4, pp. 377–381. The text was submitted by the authors in English.     

Reaction paths of the water-assisted solvolysis of N,N-dimethylformamide

Density functional theory calculations were conducted on the title reactions with explicit inclusion of a variety of water molecules, H-CO-NMe2+MeOH+(H2O)n-->H-CO-OMe+HNMe2+(H2O)n. Geometries of transition states, reactant-like complexes and product-like ones were determined by the use of RB3LYP/6-31G(d) SCRF=dipole. Concerted paths were examined with n=0-3. Their Gibbs activation energies are larger than the experimental value. Stepwise paths were also investigated with n=2-4. The n=4 model has the energy close to the experimental value. However, when the catalytic water molecules were added to the n=4 one, the stepwise path was switched to the concerted one. A systematic comparison of the concerted path with n=2+1, 2+2, 2+3, 2+4, 2+5, 2+4+4, and 2+5+5 models was made, and the water-dimer based reaction path was found to be most favorable. The contrast between the concerted path of the amide solvolysis (and hydrolysis) and the stepwise one of the ester hydrolysis was discussed in terms of the frontier-orbital theory.