26 research outputs found
Formation of racemic compound crystals by mixing of two enantiomeric crystals in the solid state. Liquid transport of molecules from crystal to crystal
Mixing of powdered (-)- and (+)-enantiomer crystals in the solid state gives crystals of the racemic compound. This racemic crystal formation was followed by IR spectral measurement of a 1 :1 mixture of (-)- and (+)-enantiomer crystals as a Nujol mull. As the formation of racemic crystals proceeds, the OH absorptions of the enantiomer disappear gradually and new OH absorptions due to the racemic compound appear. The formation of racemic crystals from enantiomer crystals has been studied for various kinds of chiral compounds: 2,29-dihydroxy-1,19-binaphthyl (1) and its derivatives, 10,109-dihydroxy-9,99-biphenanthryl (4), 2,29-dihydroxy-4,49,6,69-tetramethylbiphenyl (5) and its derivatives, 4,49-dihydroxy-2,29,3,39,6,69- hexamethylbiphenyl (8), 1,6-di(o-chlorophenyl)-1,6-diphenylhexa-2,4-diyne-1,6-diol (11) and its derivatives, trans-4,5-bis[hydroxy(diphenyl)methyl]-2,2-dimethyl-1,3-dioxacyclopentane (17) and itsderivatives, tartaric acid (20) dimethyl tartrate (21), malic acid (22), mandelic acid (23), and norephedrine (24). These molecular movements and blending occur rapidly in the presence of liquids such as liquid paraffin (Nujol), seed oils such as olive, coconut, rapeseed and soybean oil, artificial oil such as silicone oil and water, although the same movement also occurs in the absence of the liquid. For example, keeping a mixture of powdered (-)-1 (1a) and (+)-1 (1b) at room temperature for 48 h gives racemic crystals (1c). However, molecular aggregation sometimes occurs in solution but not in the solid state. Forexample, recrystallization of (-)-16 (16a) and (+)-16 (16b) from solvent gives racemic crystals of 16c, although mixing of these two components as powders in the presence of liquid does not give 16c. In order to determine the mechanism of the molecular movement in the solid state, X-ray crystal structures of optically active and racemic compounds and also the molecular movements from optically active crystal to racemic crystal have been studied
Crystal Structures of Branched-Chain Amino Acid Aminotransferase Complexed with Glutamate and Glutarate: True Reaction Intermediate and Double Substrate Recognition of the Enzyme †
Formation of racemic compound crystals by mixing of two enantiomeric crystals in the solid state. Liquid transport of molecules from crystal to crystal
Formation of racemic compound crystals by mixing of two enantiomeric crystals in the solid state. Liquid transport of molecules from crystal to crystal
ADP-Ribose Pyrophosphatase Reaction in Crystalline State Conducted by Consecutive Binding of Two Manganese(II) Ions as Cofactors
Adenosine
diphosphate ribose pyrophosphatase (ADPRase), a member
of the Nudix family proteins, catalyzes the metal-induced and concerted
general acid–base hydrolysis of ADP ribose (ADPR) into AMP
and ribose-5′-phosphate (R5P). The ADPR-hydrolysis reaction
of ADPRase from <i>Thermus thermophilus</i> HB8 (<i>Tt</i>ADPRase) requires divalent metal cations such as Mn<sup>2+</sup>, Zn<sup>2+</sup>, or Mg<sup>2+</sup> as cofactors. Here,
we report the reaction pathway observed in the catalytic center of <i>Tt</i>ADPRase, based on cryo-trapping X-ray crystallography
at atomic resolutions around 1.0 Å using Mn<sup>2+</sup> as the
reaction trigger, which was soaked into <i>Tt</i>ADPRase-ADPR
binary complex crystals. Integrating 11 structures along the reaction
timeline, five reaction states of <i>Tt</i>ADPRase were
assigned, which were ADPRase alone (E), the ADPRase-ADPR binary complex
(ES), two ADPRase-ADPR-Mn<sup>2+</sup> reaction intermediates (ESM,
ESMM), and the postreaction state (E′). Two Mn<sup>2+</sup> ions were inserted consecutively into the catalytic center of the
ES-state and ligated by Glu86 and Glu82, which are highly conserved
among the Nudix family, in the ESM- and ESMM-states. The ADPR-hydrolysis
reaction was characterized by electrostatic, proximity, and orientation
effects, and by preferential binding for the transition state. A new
reaction mechanism is proposed, which differs from previous ones suggested
from structure analyses with nonhydrolyzable substrate analogues or
point-mutated ADPRases