Structure Of DMF Research Articles

Solvent Dependent Folding of an Amphiphilic Polyaramid.

A series of synthetic alternating and amphiphilic aromatic amide polymers were synthesized by a step growth polymerization. Alternating meta- and para-linkages were introduced to force the polymer chain into a helical shape in the highly polar solvent water. The polymers were analyzed by 1H NMR spectroscopy and SEC in polar aprotic solvents such as DMSO and DMF. However, the polymers also showed good solubility in water. 1H NMR spectroscopy, small-angle X-ray scattering, and dynamic light scattering provided clear evidence of polymer folding in water but not DMF. We employed parallel tempering metadynamics in the well-tempered ensemble (PTMetaD-WTE) to simulate the free energy surfaces of an analogous model polymer in DMF and water. The simulations gave a molecular model of an unfolded structure in DMF and a helically folded tubular structure in water.

Exploring the dynamic changes in hydrogen bond structure of water and heavy water under external perturbation of DMF

The Raman spectra of DMF-water/heavy water binary solutions at different volume ratios are measured to investigate the hydrogen bond structure between N, N-dimethylformamide (DMF) and water/heavy water. It was observed that when VDMF below 40 %, DMF reinforces the hydrogen bond among water molecules through the substitution of a small amount of water molecules within the tetrahedral structure. However, a similar enhancement phenomenon is not observed in heavy water. When VDMF is less than 60 %, the hydrogen bonds among DMF and heavy water molecules affect the symmetry of OD covalent bond. Furthermore, as VDMF exceeds 40 %/60 %, the tetrahedral structures of water and heavy water are gradually replaced by DMF·3H2O/3D2O, DMF·2H2O/2D2O, and DMF·H2O/D2O clusters. The transition point of hydrogen bond structure in DMF- aqueous solution moved to VDMF = 15 % under the influence of under the influence of dynamic high pressure caused by pulsed laser beam. This study provides valuable insights into the microstructure of water/heavy water clusters.

Single-molecule mechanics of synthetic aromatic amide helices: Ultrafast and robust non-dissipative winding

Summary Because of proteins’ many degrees of conformational freedom, programming protein folding dynamics, overall elasticity, and motor functions remains an elusive objective. Instead, smaller and simpler objects, such as synthetic foldamers, may be amenable to design. However, little is known about their mechanical performance. Here, we show that reducing molecular size may not compromise mechanical properties. We report that helical aromatic oligoamides as small as 1 nm possess outstanding elasticity and outperform most natural helices. Using single-molecule force spectroscopy, we characterize their folding trajectories and intermediate states. We show that they cooperatively and reversibly unwind at high forces. They extend up to 3.8 times their original length and rewind against considerable forces on a timescale of 10 μs. Pulling and relaxing cycles follow the same trace up to a very high loading rate, indicating that the mechanical energy accumulated during the stretching does not dissipate and is immediately reusable.

Basic Information on Nonsubstituted Polyphenylene and Polythiophene Obtained via Solubilization of Polymers

Basic information on the molecular weights and structures of poly(p-phenylene) PPP, poly(m-phenylene) PMP, poly(thiophene-2,5-diyl) PTh, and related copolymers has been obtained. PPPs prepared by a Ni-catalyzed dehalogenative polycondensation of p-C6H4Br2 with Mg (PPP(Ni)) and an oxidative polymerization of benzene using CuCl2 (PPP(Cu)) became soluble in DMF after nitration. The nitration proceeded essentially without crosslinking, and GPC analysis gave Mn values of 8300 and 6100 for nitrated PPP(Ni) and PPP(Cu), respectively. Light scattering analysis indicated that nitrated PPP(Ni) and PPP(Cu) assumed a rather stiff structure in DMF with ρv (degree of depolarization) in the range of 0.12−0.13. PMP and PTh also became soluble in DMF after nitration, and GPC analysis of nitrated PMP and PTh gave Mn values of 5500 and 8500, respectively. Light scattering analysis of nitrated PTh gave a ρv of 0.33, which indicated that the polymer had a stiff structure in DMF. Copolymers of p-phenylene (PP) and m-phenylene (MP) were soluble in organic solvents when the content of the PP unit was about 20%, and a soluble fraction with an Mn of 12 100 was obtained. Light scattering analysis indicated that the copolymer assumed an essentially random coil-like structure in THF. To the contrary, copolymers of 2,5-thienylene (2,5-Th) and 2,4-thienylene (2,4-Th) were insoluble in organic solvents presumably due to their essentially linear and stiff structure.

Cobalt(II) chloro complexation in N-methylformamide–N, N-dimethylformamide mixtures

Cobalt(II) chloro complexation has been studied by titration calorimetry and spectrophotometry in solvent mixtures of N-methylformamide (NMF) and N,N-dimethylformamide (DMF). It revealed that a series of mononuclear CoClnn (2–n)+ (n=1–4) complexes are formed in the mixtures of NMF mole fraction x NMF=0.05 and 0.25, and the CoCl+, CoCl3 – and CoCl4 2– complexes in the mixture of x NMF=0.5, and their formation constants, enthalpies and entropies were obtained. As compared with DMF, the complexation is markedly suppressed in the mixtures, as well as in NMF. The decreasing formation constant of CoCl+ with the NMF content is mainly ascribed to the decreasing formation entropy. DMF is aprotic and thus less-structured, whereas NMF is protic to form hydrogen- bonded clusters. In DMF-NMF mixtures, solvent clusters in neat NMF are ruptured to yield new clusters involving DMF, the structure of which depends on the solvent composition. The entropy of formation of CoCl+ will be discussed in relation to the liquid structure of DMF, NMF and their mixtures.

Synthesis and helical conformation of poly(N‐propargylamides) carrying L‐aspartic acid in the side chain

AbstractAspartic acid‐based novel poly(N‐propargylamides), i.e., poly[N‐(α‐tert‐butoxycarbonyl)‐L‐aspartic acid β‐benzyl ester N′‐propargylamide] [poly(1)] and poly[N‐(α‐tert‐butoxycarbonyl)‐L‐aspartic acid α‐benzyl ester N′‐propargylamide] [poly(2)] with moderate molecular weights were synthesized by the polymerization of the corresponding monomers 1 and 2 catalyzed with (nbd)Rh+[η6‐C6H5B−(C6H5)3] in CHCl3 at 30 °C for 2 h in high yields. The chiroptical studies revealed that poly(1) took a helical structure in DMF, while poly(2) did not in DMF but did in CH2Cl2, CHCl3, and toluene. The helicity of poly(1) and poly(2) could be tuned by temperature and solvents. Poly(2) underwent solvent‐driven switch of helical sense, accompanying the change of the tightness. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5168–5176, 2005

Short peptide alpha helices induced by multiple metal clips

Alpha helices are key structural components of proteins and important recognition motifs in biology. New techniques for stabilizing short peptide helices could be valuable for studying protein folding, modeling proteins, creating artificial proteins, and may aid the design of inhibitors or mimics of protein function. We previously reported* that 5-15 residue peptides, corresponding to the Zn-binding domain of thermolysin, react with [Pd(en)(ONO,),]in DMF-d’ and 90% H,O 10% DzO to form a 22-membered [Pd(en)(H*ELTH*)]2+ macrocycle that is helical in solution and acts as a template in nucleating helicity in both Cand N- terminal directions within the longer sequences in DMF. ~f~~g,J~p?:~~q&~+~~ ’ w w the difficulty of fixing intramolecular amide NH...OC H-bonds in 6,“;;” ( k.$ U”C.a , p d$. competition with the H-bond donor solvent water. To expand the utility of [Pd(en)(H*XXXH*)]*+ as a helix- @r4”8 & oJ#:& &G& @-qd ,‘d@-gyp promoting module in solution, we now report the result that Ac- ‘$4: %$yyy + H*ELTH*H*VTDH*-NH,(l), AC-H*ELTH*AVTDYH*ELTH*- NH, (2) and AC-H*AAAH*H*ELTH*H*VTDH*-NH* (3) react with multiple equivalents of [Pd(en)(ONO,),] to produce exclusively 4-6 respectively in both DMF-d7 and water (90% Hz0 10% D,O). Mass spectrometry, 15N- and 2D ‘H- NMR spectroscopy, and CD spectra were used to characterise the structures 4-6, and their three dimensional structures were calculated from NOE restraints using simulated annealing protocols. Results demonstrate (a) selective coordination of metal ions at (i, i+4) histidine positions in water and DMF, (b) incorporation of 2 and 3 a turn-mimicking modules [Pd(en)(HELTH)]2+ in lo-15 residue peptides, and (c) facile conversion of unstructured peptides into 3- and 4- turn helices of macrocycles, with well defined a-helicity throughout and more structure in DMF than in water.

An X-ray diffraction study on the structure of solvated manganese(II) ion and manganese(II) complexes with pyridine, 3-methylpyridine and 4-methylpyridine in N,N-dimethylformamide

The structure of the solvated manganese(II) ion and the manganese(II) complexes with pyridine (py), 3-methylpyridine (3Me-py) and 4-methylpyridine (4Me-py) in N,N-dimethylformamide (DMF) has been studied by means of X-ray diffraction at 23°C. It was revealed that the manganese(II) ion binds with six DMF molecules and has an octahedral structure in DMF. The MnO (DMF) bond length within [Mn(dmf) 6] 2+ is 221(1) pm, practically the same as that (220 pm) within [Mn(H 2O) 6] 2+ in water. The non-bonding Mn … C (DMF) distance is 315(2) pm and the MnOC bond angle is thus 130°. It was also shown that the structure of [Mn(L)] 2+ (L = py, 3Me-py, 4Me-py) is octahedral in DMF. The MnO and MnN bond lengths are 222(1) pm for [Mn(py)(dmf) 5] 2+, 223(1) pm for [Mn(3Me-py)(dmf) 5] 2+ and 222(1) pm for [Mn(4Me-py)(dmf) 5] 2+, and are virtually the same as the MnO one within [Mn(dmf) 6] 2+. However, the non-bonding Mn … C (DMF) distances within [Mn(L)(dmf) 5] 2+ are longer (321–322 pm) and the corresponding MnOC bond angles (134–135°) are wider than those within [Mn(dmf) 6] 2+. Thus, in DMF the steric interaction between DMF molecules and pyridines in the first coordination sphere of the manganese(II) ion is quite large.

A Calorimetric Study of Ternary Zinc(II) Complexes with Chloride Ions and 2,2′-Bipyridyl in N,N-Dimethylformamide

Abstract Formation equilibria of ternary zinc(II) complexes with chloride ions and 2,2′-bipyridyl (bpy) have been calorimetrically studied in N,N-dimethylformamide (DMF) containing 0.4 mol dm−3 (C2H5)4NClO4 as a constant ionic medium at 25 °C. Formation of binary (2,2′-bipyridyl)zinc(II) complexes has also been explored. The calorimetric data were satisfactorily explained in terms of formation of the ternary [ZnCl(bpy)]+ and [ZnCl2(bpy)] complexes together with the binary [Zn(bpy)n]2+ (n=1–3) ones, and their formation constants and enthalpies were determined. The formation of the ternary [ZnCl(bpy)]+ and [ZnCl2(bpy)] complexes is not so favorable in DMF. It is suggested that both [ZnCl(bpy)]+ and [ZnCl2(bpy)] complexes have the four-coordinate tetrahedral structure in DMF.

The Proton Magnetic Resonance Spectrum of N,N-Dimethylformamide in a Nematic Solvent

Abstract The proton magnetic resonance spectrum of N,N-dimethylformamide (DMF) oriented in a nematic solvent is analyzed. From the derived dipolar coupling constants and using the best available structure of DMF it is shown that the NMR results are consistent only with rapidly inverting nonplanar conformers.