1433-11-0Relevant articles and documents
Solid-state NMR investigations on urea inclusion compounds: Order and dynamics of 1,6-dibromohexane
Yang, Xiaorong,Müller, Klaus
, p. 75 - 89 (2007)
The molecular properties of 1,6-dibromohexane in its urea inclusion compound are investigated by means of a multinuclear solid-state NMR spectroscopy. 13C CP/MAS and 1H MAS NMR studies (line shapes, spin-lattice relaxation measurements) were performed for the first time to probe the guest dynamics and conformational order. Variable temperature 2H NMR studies comprising line shape analysis as well as spin-lattice relaxation (T1Z, T1Q) experiments were done on samples with guest molecules selectively deuterated at two different positions. A quantitative analysis of the experimental data proves that the guest dynamics are dominated by mutual exchange between two gauche conformers. It is shown that these guest motions unequivocally can be quantified (type and time-scale) by a comprehensive analysis of the T1Z and T1Q data. In addition, there is evidence that other motional contributions, such as overall molecular fluctuations and lateral motions, also contribute to spin relaxation. The molecular behaviour of 1,6-dibromohexane in urea is completely different from that reported for the long chain analogues or for n-alkanes where typically unhindered overall rotational motions of the guests in their all-trans conformation around the urea channel long axis are discussed. The differences in guest ordering and dynamics are a direct consequence of the differences of the urea lattice structures (monoclinic vs. hexagonal urea lattice).
The Neutron Structure at 116 K of the 1:1 Complex of Perdeuterated Parabanic Acid and Urea
Weber, H. P.,Ruble, J. R.,Craven, B. M.,McMullan, R. K.
, p. 1121 - 1126 (1980)
The perdeuterated 1:1 complex of parabanic acid (C3D2N2O3) and urea (CD4N2O) at 116 K is monoclinic, space group P21/c, with a=8.910 (3), b=5.597 (2), c=14.525 (6) Angstroem, β=108.39 (3) grad, and has four molecules of each kind per unit cell.The nuclear configuration has been determined from 2165 neutron intensities (sinθ/λ-1, λ=1.0450 Angstroem) to give e.s.d.'s in apparent bond lengths and angles of 0.001 Angstroem and 0.1 grad, or less.The configurations of the two molecules are similar to those found in their separate crystal structures, but there are small differences, which appear to be related to the different hydrogen bonding .There is an unusually short hydrogen bond (N...O, 2.66 Angstroem) between parabanic acid N-D and urea O atoms.There are also short C...O distances (2.81, 2.86 Angstroem) between carbonyl groups of different parabanic acid molecules.The polar molecular interactions of parabanic acid are similar to those of the drug-active barbiturates.
Structure of concentrated aqueous urea solutions involving alkali metal salts studied by neutron diffraction with 14n/15n, 6li/7li, and 35Cl/37Cl isotopic substitution methods
Miyazaki, Takuya,Kameda, Yasuo,Amo, Yuko,Usuki, Takeshi
, p. 104 - 111 (2013)
Neutron diffraction with 14N/15N, 35Cl/37Cl, and 6Li/7Li isotopic substitution methods have been applied to aqueous 10 mol% urea solutions involving 5mol% NaCl and 10mol% LiCl, in order to obtain information on the hydration structure around the amino group of urea which is affected by coexisting ions, Cl and Li+. Observed first-order difference functions, N inter(Q), Cl(Q), and Li(Q), were respectively analyzed using least-squares fitting. The nearest neighbor intermolecular NOw (Ow: oxygen atom in D2O) distance was determined to be 3.09(1) and 3.19(1), from the analyses for sample solutions involving NaCl and LiCl, respectively. These intermolecular NOw distances are slightly longer than those reported for aqueous urea solutions of similar concentrations. These results suggest that hydrogen bonds among amino groups of urea and neighboring water molecules are weakened by coexisting alkali metal salts. The structural parameters concerning the first hydration shell of Cl- and Li+, have been determined to be r(ClDw) = 2.27(1) (Dw: deuterium atom in D2O) and r(Li+Ow) = 1.95(1), respectively. The results indicate that the structure of the first hydration shell around Cl- and Li+ is not affected by the presence of urea molecules in the aqueous solution.
The guest ordering and dynamics in urea inclusion compounds studied by solid-state 1H and 13C MAS NMR spectroscopy
Yang, Xiaorong,Müller, Klaus
, p. 113 - 120 (2011)
Urea inclusion compounds with different guest species were studied by 13C CP MAS and 1H MAS NMR spectroscopy. It is possible to arrange the asymmetric guest species in three different ways: head-head, head-tail and tail-tail. 13C CP MAS NMR studies indicate that the preference arrangement is determined by the interaction strength of the end functional groups. 13C relaxation experiments are used to study the dynamic properties of urea inclusion compounds. 13C relaxation studies on urea inclusion compounds with n-alkane or decanoic acid show that the 13C T1 and 13C T1ρ values exhibit the position dependence towards the center of the chain, indicating internal chain mobility. The analysis of variable-temperature 13C T1ρ experiments on urea inclusion compounds with hexadecane and pentadecane, for the first time, suggests that chain fluctuations and lateral motion of n-alkane guests may contribute to the 13C T1ρ relaxation.
Fine Structures of 1H-Coupled 13C MAS NMR Spectra for Uniaxially Rotating Molecules in Deuterated Surroundings: Conformations of n-Alkane Molecules Enclathrated in Urea Channels
Kubo, Atsushi,Imashiro, Fumio,Terao, Takehiko
, p. 10854 - 10860 (1996)
It is theoretically shown that spectral fine structures due to the intramolecular 1H-1H dipolar couplings and the 13C-1H J-couplings can be observed in uniaxially rotating molecules magnetically isolated from the surroundings when the 13C spectrum is observed under magic-angle spinning without 1H-decoupling.Such fine structures were observed for decane molecules enclathrated in deuterated urea channels.
1H NMR spectra of ternary platinum(II) complexes with N-ethyl- or N- benzyl-1,2-ethanediamine and 2,2'-bipyridine or 1,10-phenanthroline: Intramolecular aromatic-aromatic interaction in coordination sphere, and it's solvent and temperature effects
Goto, Masafumi,Sumimoto, Masamitsu,Matsumoto, Takashi,Iwasaki, Maki,Tanaka, Yoshitomo,Kurosaki, Hiromasa,Yuto, Koji,Yoshikawa, Yuzo
, p. 1589 - 1598 (2007/10/03)
Square-planar complexes with the formula [Pt(L1) (L2)]X2, where L1 is di(ammine) or 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen) and L2 is N-ethyl-1,2-ethanediamine (Eten) or N-benzyl-1,2-ethanediamine (Been), and X = NO3- or Cl-, were prepared. NMR measurements of D2O solutions of these complexes showed that the N-ethyl and N-benzyl groups are forced to take a pseudo axial disposition due to an intramolecular repulsion from hydrogen atoms of aromatic diamines for complexes where L1 = bpy or phen and significant upfield shifts due to the ring current effect were observed for the Been complexes. An analysis of coupling with N-H and 195Pt showed that the major rotamer due to rotation around CH2-NH is (-)-syn for the Been with a significant intramolecular stacking between aromatic rings of L1 and L2, but anti-for the Eten complexes. The solvent and temperature dependency of the upfield shift of the Been complexes are described; the protein denaturants, guanidinium chloride, and urea, act to reduce stacking as dioxane.
