Conformational changes in serine on methylmercury complexation

1988 ◽  
Vol 66 (6) ◽  
pp. 1379-1385 ◽  
Author(s):  
Marie-Claude Corbeil ◽  
André L. Beauchamp
Keyword(s):  
Aqueous Solution ◽  
Conformational Changes ◽  
Hydroxyl Group ◽  
Side Chain ◽  
X Ray Diffraction ◽  
X Ray ◽  
Carboxylate Oxygen ◽  
Zwitterionic Complex ◽  
Ligand Conformation ◽  
C Nmr

The CH3Hg+ cation forms a zwitterionic complex CH3Hg[HOCH2CH(NH2)CO2—N,O,O] with serine in aqueous solution. X-ray diffraction (P212121, a = 5.821, b = 8.052, c = 14.307 Å, R = 0.021) shows that mercury is linearly bonded to the NH2 end of the amino acid, whereas one carboxylate oxygen and the side-chain hydroxyl group establish secondary Hg—O bonds. Coordination leads to characteristic changes in the infrared and Raman spectra of serine. From the 1H and 13C nmr spectra, N-coordination is found to be retained in aqueous solution, whereas the ligand conformation observed in the solid accounts for 76% of the conformer distribution.

Conformation of diastereoisomeric cyclo(neopentylglycyl-prolyls): NMR, X-ray, and CD studies

1987 ◽  
Vol 52 (9) ◽  
pp. 2295-2308 ◽  
Author(s):  
Karel Bláha ◽  
Miloš Buděšínský ◽  
Ivo Frič ◽  
Jan Pospíšek ◽  
Jindřich Symerský
Keyword(s):  
Chain Structure ◽  
Side Chain ◽  
Boat Conformation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Butyl Group ◽  
Boat Form ◽  
Cd Studies ◽  
Twisted Boat ◽  
C Nmr

Conformation of diastereoisomeric cyclo(L-neopentylglycyl-L-prolyl) (IV) and cyclo(D-neopentylglycyl-L-prolyl) (VIII) in solution was studied by 1H and 13C NMR spectroscopy. Both compounds have approximately the same conformation of the bicyclic moiety in which the 2,5-piperazinedione ring exists in the boat form with pseudoaxial proline H(α) atom, and the proline ring is in the C(γ)-exo conformation. Rotation of the neopentyl side chain is markedly hindered. In the trans-derivative VIII the side chain occupies a pseudoaxial position with staggered rotamer about the C(α)-C(β) bond, the tert-butyl group pointing from the ring in the direction of the nitrogen atom. The preferred rotamer of the cis-isomer markedly deviates from this staggered conformation in the exo-direction relative to the piperazine ring. X-Ray diffraction analysis shows that crystal conformation of the trans-isomer VIII is very similar to that in solution. According to CD measurements, steric interactions of the acyclic side chain with the dioxopiperazine ring lead to twisted boat conformations of this ring with non-planar amide groups. From comparison with other proline-containing cyclodipeptides it follows that the effect of these interactions depends on the side chain structure. The neopentyl side chain flattens the boat conformation and reduces the deviation of the amide groups from planarity.

scholarly journals Ligand binding remodels protein side chain conformational heterogeneity

2021 ◽  
Author(s):  
Stephanie A. Wankowicz ◽  
Saulo H.P. de Oliveira ◽  
Daniel W. Hogan ◽  
Henry van den Bedem ◽  
James S. Fraser
Keyword(s):  
Ligand Binding ◽  
Binding Site ◽  
Conformational Changes ◽  
Biological Function ◽  
Side Chain ◽  
Conformational Heterogeneity ◽  
X Ray Diffraction ◽  
Nmr Studies ◽  
Static Structure ◽  
X Ray

ABSTRACTWhile protein conformational heterogeneity plays an important role in many aspects of biological function, including ligand binding, its impact has been difficult to quantify. Macromolecular X-ray diffraction is commonly interpreted with a static structure, but it can provide information on both the anharmonic and harmonic contributions to conformational heterogeneity. Here, through multiconformer modeling of time- and space-averaged electron density, we measure conformational heterogeneity of 743 stringently matched pairs of crystallographic datasets that reflect unbound/apo and ligand-bound/holo states. When comparing the conformational heterogeneity of side chains, we observe that when binding site residues become more rigid upon ligand binding, distant residues tend to become more flexible, especially in non-solvent exposed regions. Among ligand properties, we observe increased protein flexibility as the number of hydrogen bonds decrease and relative hydrophobicity increases. Across a series of 13 inhibitor bound structures of CDK2, we find that conformational heterogeneity is correlated with inhibitor features and identify how conformational changes propagate differences in conformational heterogeneity away from the binding site. Collectively, our findings agree with models emerging from NMR studies suggesting that residual side chain entropy can modulate affinity and point to the need to integrate both static conformational changes and conformational heterogeneity in models of ligand binding.

Carbohydrate metal ion complexes. Interaction of D-glucono-1,5-lactone with Zn(II), Cd(II), and Hg(II) ions in the solid and aqueous solution, studied by 13C-NMR, FT-IR, and X-ray powder diffraction measurements

1989 ◽  
Vol 67 (4) ◽  
pp. 651-654 ◽  
Author(s):  
H. A. Tajmir-Riahi
Keyword(s):  
Aqueous Solution ◽  
Metal Ions ◽  
Powder Diffraction ◽  
Metal Ion ◽  
Binding Mode ◽  
X Ray ◽  
Group Metal ◽  
Carboxylate Oxygen ◽  
Ft Ir ◽  
C Nmr

D-Glucono-1,5-lactone interaction with zinc group metal ions has been studied in aqueous solution and solid salts of the type Zn(D-gluconate)2.2H2O, Cd(D-gluconate)2 and Hg(D-gluconate)2 have been isolated. These metal sugar salts were characterized by elemental analysis, 13C-NMR, FT-IR spectroscopy, and X-ray powder diffraction measurements.X-ray powder diffraction diagrams and other spectroscopic evidence showed that Zn(D-gluconate)2.2H2O is isomorphous with the structurally identified Mn(D-gluconate)2.2H2O, suggesting a similar metal–sugar binding mode, through a carboxylate oxygen atom (O-1) and an OH group of the two sugars anions as well as to two H2O molecules, resulting in a six-coordinate Zn(II) ion. The Cd(II)- and Hg-D-gluconate salts are not similar and show dissimilarities to the Zn(II) compound. The Cd(II) ion binds to two D-gluconate anions possibly through the carboxylate O-1 and sugar O(2)—H, and O(3)—H groups of each anion, giving a six-coordinate Cd(II) ion. The Hg(II) ion is possibly four-coordinate, binding to two sugar anions via a carboxylate O-1 and O(2)—H groups of each D-gluconate anion. The zinc group metal-D-gluconate salts are aggregated through bridging sugar OCO− groups with sugar anion possibly having bent-chain conformation. Keywords: carbohydrate, metal ions, 13C-NMR, FT-IR, X-ray powder diffraction.

Structural Study of a new Compound Based on Acid 1,4-Cyclohexanedicarboxylic (1,4-CDC)

2010 ◽  
Vol 6 (1) ◽  
pp. 891-896
Author(s):  
Manel Halouani ◽  
M. Dammak ◽  
N. Audebrand ◽  
L. Ktari
Keyword(s):  
Aqueous Solution ◽  
Water Molecules ◽  
Carboxyl Group ◽  
X Ray Diffraction ◽  
Compound I ◽  
Unit Cell Parameters ◽  
Monoclinic System ◽  
X Ray ◽  
Cell Parameters ◽  
Cyclohexanedicarboxylic Acid

One nickel 1,4-cyclohexanedicarboxylate coordination polymers, Ni2 [(O10C6H4)(COO)2].2H2O  (I), was hydrothermally synthesized from an aqueous solution of Ni (NO3)2.6H2O, (1,4-CDC) (1,4-CDC = 1,4-cyclohexanedicarboxylic acid) and tetramethylammonium nitrate. Compound (I) crystallizes in the monoclinic system with the C2/m space group. The unit cell parameters are a = 20.1160 (16) Å, b = 9.9387 (10) Å, c = 6.3672 (6) Å, β = 97.007 (3) (°), V= 1263.5 (2) (Å3) and Dx= 1.751g/cm3. The refinement converged into R= 0.036 and RW = 0.092. The structure, determined by single crystal X-ray diffraction, consists of two nickel atoms Ni (1) and Ni (2). Lots of ways of which is surrounded by six oxygen atoms, a carboxyl group and two water molecules.

An unusual reaction of a bridged triterpenoid α-diketone with acetic anhydride

1991 ◽  
Vol 56 (12) ◽  
pp. 2917-2935 ◽  
Author(s):  
Eva Klinotová ◽  
Václav Křeček ◽  
Jiří Klinot ◽  
Miloš Buděšínský ◽  
Jaroslav Podlaha ◽  
...  
Keyword(s):  
Acetic Acid ◽  
Nmr Spectroscopy ◽  
Acetic Anhydride ◽  
Spectral Methods ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mild Conditions ◽  
Condensation Products ◽  
Unsaturated Lactones ◽  
C Nmr

3β-Acetoxy-21,22-dioxo-18α,19βH-ursan-28,20β-olide (IIIa) reacts with acetic anhydride in pyridine under very mild conditions affording β-lactone IVa and γ-lactones Va and VIIa as condensation products. On reaction with pyridine, lactones Va and VIIa undergo elimination of acetic acid to give unsaturated lactones VIIIa and IXa, respectively. Similarly, the condensation of 20β,28-epoxy-21,22-dioxo-18α,19βH-ursan-3β-yl acetate (IIIb) with acetic anhydride leads to β-lactone IVb and γ-lactone Vb; the latter on heating with pyridine affords unsaturated lactone VIIIb and 21-methylene-22-ketone Xb. The structure of the obtained compounds was derived using spectral methods, particularly 1H and 13C NMR spectroscopy; structure of lactone IVa was confirmed by X-ray diffraction.

Darstellung, 11B-, 13C-, 29Si-NMR- und Schwingungsspektren von Trimethylsilylmethyl-hexahydro-closo-hexaborat, [B6H6(CH2Si(CH3)3)]- sowie Kristallstruktur von [P(C6H5)4][B6H6(CH2Si(CH3)3)] / Preparation, 11B, 13C, 29Si NMR and Vibrational Spectra of Trimethylsilylmethyl-hexahydro-clo-hexaborate, [B6H6(CH2Si(CH 3)3)]-and the Crystal Structure of [P(C6H5)4] [B6H6(CH2Si(CH3)3)]

1995 ◽  
Vol 50 (7) ◽  
pp. 1025-1029 ◽  
Author(s):  
J. Baurmeister ◽  
A. Franken ◽  
W. Preetz
Keyword(s):  
Crystal Structure ◽  
Monoclinic Space Group ◽  
29Si Nmr ◽  
X Ray Diffraction ◽  
Nmr Spectrum ◽  
X Ray ◽  
Quadrupole Coupling ◽  
Stretching Vibration ◽  
Ir And Raman ◽  
C Nmr

By reaction of [N(C4H9 )4]2 [B6H6] with iodomethyl-trimethylsilane in acetonitrile a solution with trimethylsilylm ethyl-closo-hexaborate(1-)anions, [B6H6 (CH2Si(CH3)3)]-, is formed. The crystal structure of [P(C6H5 )4][B6H6(CH2Si(CH3)3)] has been determined by single crystal X-ray diffraction analysis; monoclinic, space group P21/n with a = 16.140(2), b = 11.646(8), c = 16.731(3) Å, β 109.664(11)°. The 11B NMR spectrum reveals features of a mono hetero substituted octahedral B6 cage. The 13C NMR spectrum exhibits a quartet at +0.18 ppm with 1J(C,H) = 118 Hz for the three methyl groups and a weak multiplet at -0.65 ppm for the methylene bridge due to quadrupole coupling with the boron atoms. In the 29Si NMR spectrum a decet at +2.25 ppm with 2J(C,H ) = 6.9 Hz is observed. The B -C stretching vibration is observed at 1155 cm-1 in the IR and Raman spectrum.

scholarly journals Leaching Titaniferous Magnetite Concentrate by Alkaline Aqueous Solution

2021 ◽  
Author(s):  
Ke Guo ◽  
Shaoyan Wang ◽  
Renfeng Song ◽  
Zhiqiang Zhang
Keyword(s):  
Aqueous Solution ◽  
Alkali Concentration ◽  
Water Usage ◽  
X Ray Diffraction ◽  
High Concentration ◽  
X Ray ◽  
Iron Concentrate ◽  
Titaniferous Magnetite ◽  
Magnetite Concentrate ◽  
Kinetics Of

AbstractLeaching titaniferous magnetite concentrate with alkali solution of high concentration under high temperature and high pressure was utilized to improve the grade of iron in iron concentrate and the grade of TiO2 in titanium tailings. The titaniferous magnetite concentrate in use contained 12.67% TiO2 and 54.01% Fe. The thermodynamics of the possible reactions and the kinetics of leaching process were analyzed. It was found that decomposing FeTiO3 with NaOH aqueous solution could be carried out spontaneously and the reaction rate was mainly controlled by internal diffusion. The effects of water usage, alkali concentration, reaction time, and temperature on the leaching procedure were inspected, and the products were characterized by X-ray diffraction, scanning electron microscope, and energy dispersive spectroscopy, respectively. After NaOH leaching and magnetic separation, the concentrate, with Fe purity of 65.98% and Fe recovery of 82.46%, and the tailings, with TiO2 purity of 32.09% and TiO2 recovery of 80.79%, were obtained, respectively.

scholarly journals Base-enhanced catalytic water oxidation by a carboxylate–bipyridine Ru(II) complex

2015 ◽  
Vol 112 (16) ◽  
pp. 4935-4940 ◽  
Author(s):  
Na Song ◽  
Javier J. Concepcion ◽  
Robert A. Binstead ◽  
Jennifer A. Rudd ◽  
Aaron K. Vannucci ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Proton Transfer ◽  
Water Oxidation ◽  
Proton Acceptor ◽  
Half Time ◽  
X Ray ◽  
X Ray Crystallography ◽  
Buffer Base ◽  
Electron Proton Transfer ◽  
C Nmr

In aqueous solution above pH 2.4 with 4% (vol/vol) CH3CN, the complex [RuII(bda)(isoq)2] (bda is 2,2′-bipyridine-6,6′-dicarboxylate; isoq is isoquinoline) exists as the open-arm chelate, [RuII(CO2-bpy-CO2−)(isoq)2(NCCH3)], as shown by 1H and 13C-NMR, X-ray crystallography, and pH titrations. Rates of water oxidation with the open-arm chelate are remarkably enhanced by added proton acceptor bases, as measured by cyclic voltammetry (CV). In 1.0 M PO43–, the calculated half-time for water oxidation is ∼7 μs. The key to the rate accelerations with added bases is direct involvement of the buffer base in either atom–proton transfer (APT) or concerted electron–proton transfer (EPT) pathways.

Removal of Heavy Metals from Aqueous Solution by Hydroxyapatite/Chitosan Composite

2013 ◽  
Vol 789 ◽  
pp. 176-179 ◽  
Author(s):  
Eny Kusrini ◽  
Nofrijon Sofyan ◽  
Dwi Marta Nurjaya ◽  
Santoso Santoso ◽  
Dewi Tristantini
Keyword(s):  
Heavy Metals ◽  
Aqueous Solution ◽  
Metal Ions ◽  
Precipitation Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
Removal Of Heavy Metals ◽  
Sem Micrograph ◽  
Pseudo Second Order ◽  
Chitosan Composite

Hydroxyapatite/chitosan (HApC) composite has been prepared by precipitation method and used for removal of heavy metals (Cr6+, Zn2+and Cd2+) from aqueous solution. The HAp and 3H7C composite with HAp:chitosan ratio of 3:7 (wt%) were characterized by Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy-energy dispersive X-ray spectroscopy. The SEM results showed that HAp is spherical-shaped and crystalline, while chitosan has a flat structure. SEM micrograph of 3H7C composite reveals crystalline of HAp uniformly spread over the surface of chitosan. The crystal structure of HAp is maintained in 3H7C composite. Chitosan affects the adsorption capacity of HAp for heavy metal ions; it binds the metal ions as well as HAp. The kinetic data was best described by the pseudo-second order. Surface adsorption and intraparticle diffusion take place in the mechanism of adsorption process. The binding of HAp powder with chitosan made the capability of composite to removal of Cr6+, Zn2+and Cd2+from aqueous solution effective. The order of removal efficiency (Cr6+> Cd2+> Zn2+) was observed.

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