Carbon-13 spin lattice relaxation in the neuraminic acids. Evidence for an unusual intramolecular hydrogen bonding network

1976 ◽  
Vol 98 (4) ◽  
pp. 1023-1025 ◽  
Author(s):  
Michael F. Czarniecki ◽  
Edward R. Thornton
Keyword(s):  
Hydrogen Bonding ◽  
Lattice Relaxation ◽  
Intramolecular Hydrogen Bonding ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Neuraminic Acids ◽  
Hydrogen Bonding Network ◽  
Intramolecular Hydrogen

Crystal structures of two polymorphic forms of DOTAM-mono-acid dihydrate

2018 ◽  
Vol 74 (5) ◽  
pp. 542-547
Author(s):  
Paul Jurek ◽  
Garry E. Kiefer ◽  
Frank R. Fronczek
Keyword(s):  
Hydrogen Bonding ◽  
Intramolecular Hydrogen Bonding ◽  
Temperature Structure ◽  
Intermolecular Hydrogen Bonding ◽  
Space Group ◽  
Pendant Arm ◽  
Polymorphic Forms ◽  
Higher Temperature ◽  
Hydrogen Bonding Network ◽  
Intramolecular Hydrogen

The structural chemistry of 2-[4,7,10-tris(carbamoylmethyl)-1,4,7,10-tetraazacyclododecan-1-yl]acetic acid dihydrate, C16H31N7O5·2H2O, is described. The macrocyclic compound, also known by the abbreviation DOTAM-mono-acid, crystallized at room temperature and was isolated concomitantly as two polymorphic forms. The structures of both polymorphs were determined at 90 K. The first polymorph crystallized as a zwitterionic dihydrate [systematic name: 4,7,10-tris(carbamoylmethyl)-1-(carboxylatomethyl)-1,4,7,10-tetraazacyclododecan-1-ium dihydrate] in the space group P21/n, with Z′ = 1. The second polymorph crystallized as a zwitterionic dihydrate in the space group P21 at 90 K, with Z′ = 2. The two independent molecules are related by a local center. In each polymorph, the zwitterion is formed between the negatively-charged carboxylate group and the ring N atom that bears the acetate pendant arm. Extensive inter- and intramolecular hydrogen bonding exists in both polymorphic structures. In polymorph 1, an intermolecular hydrogen-bonding network propagating parallel to the a direction creates an infinite chain. A second hydrogen-bonding network is observed through a water molecule of hydration in the b direction. Polymorph 2 also has two intermolecular hydrogen-bonding networks. One propagates parallel to the a direction, while the other propagates in the [\overline{1}10] direction. Increasing the temperature of polymorph 2 yields the same structure at T = 180 K, but the pseudocenter becomes exact at 299 K. The higher-temperature structure has Z′ = 1 in the space group P21/c.

Spin-lattice relaxation and hydrogen bonding in methanol-solvent mixtures

1975 ◽  
Vol 79 (21) ◽  
pp. 2307-2312 ◽  
Author(s):  
Rush O. Inlow ◽  
Melvin D. Joesten ◽  
John R. Van Wazer
Keyword(s):  
Hydrogen Bonding ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Solvent Mixtures ◽  
Spin Lattice

NH4+ Ion Motions in Some Ammonium Salts

1981 ◽  
Vol 36 (3) ◽  
pp. 205-209 ◽  
Author(s):  
Fevzi Köksal
Keyword(s):  
Hydrogen Bonding ◽  
Low Temperatures ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Experimental Results ◽  
Ammonium Salts ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Unit Cells ◽  
Good Agreement

Spin-lattice relaxation times of protons in polycrystalline (NH4)2SO4, (NH3OH)2SO4, (NH4)2HPO4, NH4VO3, (NH4)2CrO4, (NH4)2C2O4 • H2O and NH4HF2 salts were measured over the temperature range 100-430 K. The double minima in T1 for the first three compounds were attributed to the nonequivalent NH4+ ions in the unit cells. In NH4VO3, the double minima were attributed to the reorientations about two and three fold axes. However only one minimum in T1 was observed for (NH4)2CrO4, (NH4)2C2O4 • H2O and NH4HF2 and the relaxation mechanisms for the first three compounds were attributed to random reorientations of NH4+ ions. The experimental results are in good agreement with the calculated values by using the existing theoretical expressions. The discrepancies between experimental and calculated values for (NH4)2HPO4 and NH4HF2 at low temperatures were attributed to the tightness of the hydrogen bonding at those temperatures

A Study of Thermal Motion of Ammine Groups in Carbonatotetramminecobalt(III) Sulfate

1973 ◽  
Vol 51 (7) ◽  
pp. 1107-1108 ◽  
Author(s):  
B. A. Dunell ◽  
M. D. Pachal ◽  
S. E. Ulrich
Keyword(s):  
Hydrogen Bonding ◽  
Lattice Relaxation ◽  
Activation Energies ◽  
Thermal Motion ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Relaxation Measurements

The results of spin–lattice relaxation measurements are reported for carbonatotetramminecobalt(III) sulfate. The observed TI minima and activation energies, 1.9 and 4.3 kcal, for the reorientation of ammine groups are interpreted on the basis of hydrogen bonding effects.

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