scholarly journals Study of the coordination of quinuclidine to a chiral zinc phthalocyanine dimer

2016 ◽  
Vol 20 (08n11) ◽  
pp. 1224-1232 ◽  
Author(s):  
Nelson Giménez-Agulló ◽  
Gemma Aragay ◽  
José Ramón Galán-Mascarós ◽  
Pablo Ballester
Keyword(s):  
Chemical Exchange ◽  
Variable Temperature ◽  
Exchange Process ◽  
Zinc Phthalocyanine ◽  
Hydrogen Atoms ◽  
Dimerization Constant ◽  
H Nmr ◽  
Dimerization Process ◽  
Nmr Titrations ◽  
Millimolar Concentration

We attempted the calculation of an accurate equilibrium constant for the dimerization process of enantiomerically pure Zn-1 using UV-vis dilution experiments. At millimolar concentration Zn-1 is involved in a chemical exchange process between its monomeric and dimeric state that is slow on the 1H NMR timescale. We performed variable-temperature 1H NMR experiments in CDCl3 solution to determine the dimerization constant value at different temperatures and performed a van’t Hoff plot to derive the thermodynamic parameters of the process. The calculated thermodynamic data revealed that the dimerization process is entropy-driven and enthalpically opposed. We also probed the coordination of quinuclidine, 1-azabicyclo[2.2.2]octane, 2, to the Zn-1 using UV-vis and 1H NMR titrations in CDCl3 solution. At micromolar concentration the Zn-1 exclusively exists in solution as a monomer and forms a simple 1:1, [Formula: see text], complex with quinuclidine having a stability constant of [Formula: see text]([Formula: see text]) [Formula: see text] 106 M[Formula: see text]. On the other hand, the 1H NMR titrations carried out at 298 K and at millimolar concentration showed that Zn-1 was present in solution as the dimer and formed 1:2, [Formula: see text], and 2:2, [Formula: see text] complexes by coordination to 2. In addition, the 1:1 complex, [Formula: see text] showed a reduced dimerization constant compared to the uncoordinated parent monomer Zn-1. At high quinuclidine concentration, the 1:1 complex, [Formula: see text], derived from the coordinated dimer dissociation was also detected. The 1H NMR spectra of the titrations displayed separate signals for some hydrogen atoms of the Zn-phthalocyanine in each one of the four species. Remarkably, the chemical exchange processes involving free and bound quinuclidine in the monomeric and dimeric complexes showed different kinetics on the NMR timescale.

scholarly journals Atropisomerism of a Podophyllotoxin Derivative: Experimental and Computational Study

2018 ◽  
Vol 13 (6) ◽  
pp. 1934578X1801300
Author(s):  
Shi-Wen Zhou ◽  
Fei Jiang ◽  
Yang Yu ◽  
Xiu-Yong Huang ◽  
Yong-Heng Wang ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Nmr Spectra ◽  
Computational Study ◽  
Variable Temperature ◽  
Exchange Process ◽  
Single Bond ◽  
H Nmr ◽  
Dysosma Versipellis ◽  
Dynamic Exchange ◽  
C Nmr

Diphyllin-7′- O-β-D-glucoside, a podophyllotoxin derivative, was isolated from the roots of Dysosma versipellis. The 1H and 13C NMR spectra acquired at 300 K exhibited doubling of signals, suggesting the existence of two rotamers in solution. Variable-temperature 1H NMR experiments indicated a dynamic exchange process between the two rotamers. DFT calculations verified nearly equal energies for the two rotamers about the single bond C7′-O7.

Shielding anisotropy in tin compounds: spectroscopic studies of alkyltin cations in strong acid solutions

1985 ◽  
Vol 63 (8) ◽  
pp. 2211-2216 ◽  
Author(s):  
Thomas Birchall ◽  
Veeragathy Manivannan
Keyword(s):  
Chemical Exchange ◽  
Variable Temperature ◽  
Exchange Process ◽  
Lattice Relaxation ◽  
Strong Acid ◽  
Relaxation Mechanism ◽  
Spectroscopic Studies ◽  
Spin Lattice Relaxation ◽  
System Variable ◽  
Tin Compounds

We have observed that the 119Sn nmr spectra of dialkyltin cationic species in highly acidic solutions are strongly field dependent. Relaxation time measurements at three different magnetic fields have established that the dominant spin-lattice relaxation mechanism for these species at high magnetic field is shielding anisotropy. A comparison of T1−1 and T2−1 values indicates that at room temperature a rapid chemical exchange process is occurring. In the case of the (CH3)2Sn(SO3F)2–HSO3F system variable temperature 119Sn nmr reveals the presence of three tin species which are involved in this exchange process.

X-ray structural and nuclear magnetic resonance study of open chain and macrocyclic thioether complexes

1990 ◽  
Vol 68 (8) ◽  
pp. 1357-1363 ◽  
Author(s):  
C. Robert Lucas ◽  
Shuang Liu ◽  
Michael J. Newlands ◽  
Eric J. Gabe
Keyword(s):  
Nmr Spectra ◽  
Chemical Exchange ◽  
Variable Temperature ◽  
Low Frequency ◽  
Nuclear Magnetic Resonance Study ◽  
Conformational Exchange ◽  
Open Chain ◽  
H Nmr ◽  
Chain Complexes ◽  
C Nmr

Preparations of the thiophenophane and open chain thioether complexes MX2•BBTE(M = Pd; X = Cl, I)(M = Pt; X = Cl) (BBTE = 1,2-bis(benzylthio)ethane) and MX2•L (M = Pd; X = Cl, Br, I, SCN) (M = Pt; X = Cl) (L = 2,5,8-trithia[9](2,5)thiophenophane) are described. The molecular structure of PdBr2•L which contains a weak thiophene-sulfur-to-palladium interaction has been determined: space group P21/n, a = 8.3569(3), b = 16.3254(15), c = 11.1462(3) Å, β = 92.833(4)°, Z = 4, Rf = 0.060, Rw = 0.058. The electronic, low frequency ir, and 13C nmr spectra are described. Variable temperature 1H nmr spectra are discussed and it is concluded that the open chain complexes undergo rapid conformational exchange at room temperature but are configurationally rigid unless the temperature is increased. In contrast, the macrocyclic complexes undergo very limited conformational and no configurational exchange up to their decomposition temperatures. They are also nonfluxional in the same temperature range. Chemical exchange of acidic ligand hydrogens and a metal–ligand dissociative equilibrium were also detected when X = SCN. Keywords: thiophene, thioether, macrocyclic metal complexes.

H NMR Evidence for a Change in The Local Hydrogen Environment of Sites Associated with the Staebler-Wronski Effect in a-Si:H

2002 ◽  
Vol 715 ◽  
Author(s):  
T. Su ◽  
Robin Plachy ◽  
P. C. Taylor ◽  
S. Stone ◽  
G. Ganguly ◽  
...  
Keyword(s):  
Line Shape ◽  
Defect Density ◽  
Hydrogen Atoms ◽  
Hydrogen Environment ◽  
H Nmr ◽  
Line Shapes ◽  
Different Temperatures ◽  
Staebler Wronski Effect

AbstractWe study the H NMR line shapes of a sample of a-Si:H under several conditions: 1) as grown, 2) light-soaked for 600 hours, and 3) light-soaked followed by annealing at different temperatures. At T = 7 K, the NMR line shape of the sample after light soaking exhibits an additional doublet compared to that of the sample as-grown. This doublet is an indication of a closely separated hydrogen pair. The distance between the two hydrogen atoms is estimated to be about (2.3 ± 0.2) Å. The concentration of these hydrogen sites is estimated to be between 1017 and 1018 cm-3 consistent with ESR measurements of the defect density after light soaking. This doublet disappears after the sample is annealed at 200°C for 4 hours.

scholarly journals Protected Gold Nanoparticles with Thioethers and Amines As Surrogate Ligands

2013 ◽  
Vol 2013 ◽  
pp. 1-4 ◽  
Author(s):  
M. Rafiq H. Siddiqui
Keyword(s):  
Gold Nanoparticles ◽  
Variable Temperature ◽  
Size Control ◽  
Analytical Techniques ◽  
High Resolution Electron Microscopy ◽  
Phase Method ◽  
Two Phase ◽  
H Nmr ◽  
Resolution Electron ◽  
Vis Spectroscopy

Dodecyl sulfide, dodecyl amine, and hexylamine were shown to act as surrogate ligands (L) via metastable gold nanoparticles. By collating analytical and spectroscopic data obtained simultaneously, empirical formula Au24L was assigned. These impurity-free nanoparticles obtained in near quantitative yields showing exceptional gold assays (up to 98%Au) were prepared by a modification of the two-phase method. Replacement reactions on the Au24L showed that Au:L ratios may be increased (up to Au55:L (L= (H25C12)2S)) or decreased (Au12:L (L= H2NC12H25and H2NC6H13)) as desired. This work encompassing the role of analytical techniques used, that is, elemental analysis, variable temperature1H NMR, FAB mass spectrometry, UV-Vis spectroscopy, thin film X-ray diffraction, and high-resolution electron microscopy (HREM) has implications in the study of size control, purity, stability, and metal assays of gold nanoparticles.

Synthesis and characterization of a sulfur-containing phthalocyanine-gold nanoparticle hybrid

2015 ◽  
Vol 19 (01-03) ◽  
pp. 335-343 ◽  
Author(s):  
Vicente M. Blas-Ferrando ◽  
Javier Ortiz ◽  
Fernando Fernández-Lázaro ◽  
Ángela Sastre-Santos
Keyword(s):  
Gold Nanoparticle ◽  
Lipoic Acid ◽  
Zinc Phthalocyanine ◽  
Synthesis And Characterization ◽  
Ligand Exchange Reaction ◽  
H Nmr ◽  
Fluorescence Measurements ◽  
Transmission Electron ◽  
Yield Values

This work reports on the synthesis and characterization of a new gold nanoparticle-zinc phthalocyanine system, AuNP - S (t Bu )3 ZnPc , prepared by a ligand exchange reaction of tetraoctylammonium bromide with a novel unsymmetrically substituted zinc phthalocyanine which contains one thioester group in the peripheral position [ AcS (t Bu )3 ZnPc ]. The AuNP - S (t Bu )3 ZnPc hybrid was characterized using UV-vis and 1 H NMR spectroscopies. Transmission electron microscopy allowed the estimation of the size, which was calculated to be ~5 nm. AuNPs - S (t Bu )3 ZnPc conjugate showed much lower fluorescence quantum yield values than the AcS (t Bu )3 ZnPc demonstrating either an energy or electron transfer from the ZnPc to the AuNP . The AuNP - S (t Bu )3 ZnPc hybrid has been anchored to a TiO 2 semiconducting layer using lipoic acid. A solid configuration of TiO 2-lipoic acid- AuNP - S (t Bu )3 ZnPc has been prepared by anchoring lipoic acid to the TiO 2 ( TiO 2-LA) and introducing later the TiO 2-LA with free thiol groups in a toluene solution of AuNP - S (t Bu )3 ZnPc . We have also observed by UV-vis and fluorescence measurements the importance of the ZnPc in avoiding AuNP aggregation on the TiO 2 surface.

Chiral "basket handle" binaphthyl porphyrins: synthesis, catalytic epoxidation and NMR conformational studies

2010 ◽  
Vol 14 (07) ◽  
pp. 646-659 ◽  
Author(s):  
Eric Rose ◽  
Emma Gallo ◽  
Nicolas Raoul ◽  
Léa Bouché ◽  
Ariane Pille ◽  
...  
Keyword(s):  
Time Scale ◽  
Room Temperature ◽  
Conformational Equilibrium ◽  
Variable Temperature ◽  
Conformational Exchange ◽  
Iron Catalysts ◽  
Nmr Studies ◽  
Conformational Studies ◽  
H Nmr ◽  
Catalytic Epoxidation

Three "basket handle" porphyrins have been prepared by condensation of tetrakis-(α,β,α,β-2-aminophenyl)porphyrin atropoisomer with 1,1′-binaphthyl, 2,2′-dimethoxy, -3,3′-dicarbonylchloride, -3,3′-diacetylchloride and -3,3′-dipropanoylchloride. The epoxidation of styrene with the three iron catalysts, obtained after metalation of the free porphyrins, occurs with good yields and moderate ee up to 54%. These porphyrins showed unexpected conformational differences, as revealed by NMR spectroscopy. In particular, variable temperature NMR studies showed that the methoxy group in one of them undergoes intermediate conformational exchange on the 1H NMR time scale at room temperature. Lowering the temperature to -50 °C revealed the presence of four states in slow exchange on the NMR time scale. These results evidence a dynamic conformational equilibrium of the binaphthyl handles that adopt different, asymmetric positions with respect to the porphyrin plane.

scholarly journals Novel fluorescent probes for the fluoride anion based on hydroxy-substituted perylene tetra-(alkoxycarbonyl) derivatives

RSC Advances ◽  
2018 ◽  
Vol 8 (25) ◽  
pp. 14084-14091 ◽  
Author(s):  
Fengxia Zhang ◽  
Yunlong Zhao ◽  
Yanhui Chi ◽  
Yongshan Ma ◽  
Tianyi Jiang ◽  
...  
Keyword(s):  
Fluorescent Probes ◽  
Visual Detection ◽  
Fluoride Anion ◽  
Detection Experiment ◽  
H Nmr ◽  
Nmr Titrations

The fluoride anion (F−) sensing abilities of two fluorescent probes based on hydroxy-substituted perylene tetra-(alkoxycarbonyl) derivatives were studied through visual detection experiment, UV-Vis, fluorescence, and 1H NMR titrations.

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