The Ring Size Influence on 29Si N.M.R. Chemical Shifts of Some Spirocyclic Tetra- and Penta-coordinate Diolato Silicates

1995 ◽  
Vol 48 (1) ◽  
pp. 93 ◽  
Author(s):  
T Kemmitt ◽  
NB Milestone
Keyword(s):  
Chemical Shift ◽  
Coordination Number ◽  
Chemical Shifts ◽  
Membered Ring ◽  
Ring Size ◽  
Species Being

A series of tetracoordinate spirocyclic silicates has been prepared from the reaction of a range of diols with tetraethoxysilane, Si ( OEt )4. The silicates can be converted into anionic pentacoordinate silicates by reaction with KOBut/18-crown-6 in toluene. Alternatively, the pentacoordinate spirocycles can be prepared directly without prior preparation of a tetracoordinate spiro silicate. 29Si n.m.r. studies have demonstrated that the chemical shifts are sensitive to both coordination number and ring size. Ring contributions to the 29Si chemical shifts are apparent for the five- membered ring spiro silicates, those for the pentcoordinate species being less than those for the tetracoordinate species. Acyclic and six- membered ring spiro silicates are virtually indistinguishable by 29Si n.m.r. spectroscopy, which demonstrates that no ring contribution to the chemical shift is apparent for this ring size.

Connections Between 11B NMR Chemical Shifts and Electronic Structure in Metallaboranes. A Précis

1999 ◽  
Vol 64 (5) ◽  
pp. 767-782 ◽  
Author(s):  
Thomas P. Fehlner
Keyword(s):  
Electronic Structure ◽  
Chemical Shift ◽  
Transition Metal ◽  
Coordination Number ◽  
Chemical Shifts ◽  
Metal Cluster ◽  
Short Review ◽  
Electronic Charge ◽  
Chemical Shift Change ◽  
11B Nmr

An analysis of selected sets of metallaboranes in terms of a molecular orbital (MO) model of 11B chemical shift change is used to demonstrate the origin of transition metal effects on boron shifts for: (i) M-B edge protonation; (ii) replacement of direct B-B by M-B interactions; (iii) encapsulation of B in a metal cluster; (iv) change in metal identity; and (v) change in vertex coordination number. Metal effects on both filled and unfilled MO's are important but changes in the latter appear to dominate. Consequently, models based solely on filled orbital properties, e.g., electronic charge, are inadequate. A short review with 56 references.

scholarly journals Differentiation between 6- and 7-Membered Rings Based on Theoretical Calculation of NMR Parameters

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Karel D. Klika
Keyword(s):  
Dft Calculation ◽  
Chemical Shifts ◽  
Membered Ring ◽  
Coupling Constants ◽  
Scalar Coupling ◽  
Ring Size ◽  
Broad Application ◽  
Nmr Parameters ◽  
Difficult Cases

The determination of ring size can vary from simple to complex, but the process in difficult cases can be advantageously augmented by DFT calculation of NMR parameters such as the chemical shifts of (), (), and other nuclei as well as pertinent spin-spin (scalar) coupling constants, for example, those between protons (). Differentiation between 6- and 7-membered ring formation in the case of 3,4-dihydro-2H-3-hydroxymethyl-1,4-benzoxazine and 2,3,4,5-tetrahydro-1,5-benzoxazepine-3-ol was evaluated with a view to not only affecting 6- versus 7-membered ring differentiation generally for cases on hand, but also in the case of literature reports where the assigned structures may be in doubt. Thus, the main focus was on the usually reported NMR parameters of , , and and wherein the analysis was found to be highly successful, particularly for , and thus potentially amenable for broad application.

scholarly journals Structure of Nanobody Nb23

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3567
Author(s):  
Mathias Percipalle ◽  
Yamanappa Hunashal ◽  
Jan Steyaert ◽  
Federico Fogolari ◽  
Gennaro Esposito
Keyword(s):  
Nmr Spectroscopy ◽  
Chemical Shift ◽  
Solution Structure ◽  
Chemical Shifts ◽  
Molecular Size ◽  
Side Chain ◽  
3D Nmr ◽  
Target Antigen ◽  
Internuclear Distances ◽  
2D And 3D

Background: Nanobodies, or VHHs, are derived from heavy chain-only antibodies (hcAbs) found in camelids. They overcome some of the inherent limitations of monoclonal antibodies (mAbs) and derivatives thereof, due to their smaller molecular size and higher stability, and thus present an alternative to mAbs for therapeutic use. Two nanobodies, Nb23 and Nb24, have been shown to similarly inhibit the self-aggregation of very amyloidogenic variants of β2-microglobulin. Here, the structure of Nb23 was modeled with the Chemical-Shift (CS)-Rosetta server using chemical shift assignments from nuclear magnetic resonance (NMR) spectroscopy experiments, and used as prior knowledge in PONDEROSA restrained modeling based on experimentally assessed internuclear distances. Further validation was comparatively obtained with the results of molecular dynamics trajectories calculated from the resulting best energy-minimized Nb23 conformers. Methods: 2D and 3D NMR spectroscopy experiments were carried out to determine the assignment of the backbone and side chain hydrogen, nitrogen and carbon resonances to extract chemical shifts and interproton separations for restrained modeling. Results: The solution structure of isolated Nb23 nanobody was determined. Conclusions: The structural analysis indicated that isolated Nb23 has a dynamic CDR3 loop distributed over different orientations with respect to Nb24, which could determine differences in target antigen affinity or complex lability.

Circular dichroism spectra of tetraamminecobalt(III) complexes of amino alcohols

1978 ◽  
Vol 31 (11) ◽  
pp. 2399 ◽  
Author(s):  
CJ Hawkins ◽  
GA Lawrance ◽  
JA Palmer
Keyword(s):  
Circular Dichroism ◽  
Chemical Shift ◽  
Chemical Shifts ◽  
Amino Alcohols ◽  
Circular Dichroism Spectra ◽  
Chemical Shift Difference ◽  
Solvent Dependence ◽  
Cotton Effects ◽  
Circular Dichroïsm ◽  
Chiral Amino Alcohols

The circular dichroism spectra are reported for tetraamminecobalt(III) complexes with the chiral amino alcohols 2-aminopropan-1-ol, 2- aminobutan-1-ol, 1-aminopropan-2-ol, 2-amino-1-phenyl-ethanol, ψ- ephedrine and ephedrine with the alcohol groups protonated (OH) and deprotonated (O-). The solvent dependence of the chemical shifts of the NH protons was investigated to determine the effects of stereoselective solvation on the circular dichroism, but, in contrast to some other related systems, the chemical shift difference between the two NH2 protons was relatively insensitive to solvent. Consistent with this, the circular dichroism spectra of the tetraphenylborate salts of the deprotonated complexes were found not to be markedly dependent on solvent. Tetraammine-{(-)-ψ-ephedrine)cobalt(III) and tetraammine{(-)- ephedrine}cobalt(III) were found to have the same signs of Cotton effects for the various d-d transitions, whereas bis{(-)-ψ- ephedrine}copper(II) and bis{(-)-ephedrine}copper(II) had opposite signs. This has been explained in terms of different conformer populations in the cobalt(III) and copper(II) systems.

NMR studies of tandem WW domains of Nedd4 in complex with a PY motif-containing region of the epithelial sodium channel

1998 ◽  
Vol 76 (2-3) ◽  
pp. 341-350 ◽  
Author(s):  
Voula Kanelis ◽  
Neil A Farrow ◽  
Lewis E Kay ◽  
Daniela Rotin ◽  
Julie D Forman-Kay
Keyword(s):  
Chemical Shift ◽  
Sodium Channel ◽  
Chemical Shifts ◽  
Epithelial Sodium Channel ◽  
Chemical Shift Assignment ◽  
Nmr Studies ◽  
Ww Domains ◽  
Ww Ii ◽  
Py Motif ◽  
Shift Assignment

Nedd4 (neuronal precursor cell-expressed developmentally down-regulated 4) is a ubiquitin-protein ligase containing multiple WW domains. We have previously demonstrated the association between the WW domains of Nedd4 and PPxY (PY) motifs of the epithelial sodium channel (ENaC). In this paper, we report the assignment of backbone 1Hα, 1HN, 15N, 13C', 13Cα, and aliphatic 13C resonances of a fragment of rat Nedd4 (rNedd4) containing the two C-terminal WW domains, WW(II+III), complexed to a PY motif-containing peptide derived from the β subunit of rat ENaC, the βP2 peptide. The secondary structures of these two WW domains, determined from chemical shifts of 13Cα and 13Cβ resonances, are virtually identical to those of the WW domains of the Yes-associated protein YAP65 and the peptidyl-prolyl isomerase Pin1. Triple resonance experiments that detect the 1Hα chemical shift were necessary to complete the chemical shift assignment, owing to the large number of proline residues in this fragment of rNedd4. A new experiment, which correlates sequential residues via their 15N nuclei and also detects 1Hα chemical shifts, is introduced and its utility for the chemical shift assignment of sequential proline residues is discussed. Data collected on the WW(II+III)-βP2 complex indicate that these WW domains have different affinities for the βP2 peptide.Key words: WW domain, PY motif, Nedd4, ENaC, NMR.

Determination of chemical shifts in 6-condensed syringylic lignin model compounds

Holzforschung ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Lucas Lagerquist ◽  
Jani Rahkila ◽  
Patrik Eklund
Keyword(s):  
Chemical Shift ◽  
Methoxy Group ◽  
Chemical Shifts ◽  
Model Compounds ◽  
Correlation Peak ◽  
Lignin Model Compounds ◽  
Benzylic Alcohols ◽  
Lignin Model ◽  
C Nmr

Abstract A small library of 6-substituted syringyl model compounds with aliphatic, carboxylic, phenylic, benzylic alcohols and brominated substituents were prepared. The influence of the substituents on the chemical shifts of the compounds was analyzed. All of model compounds showed a characteristic increase in the 13C NMR chemical shift of the methoxy group vicinal to the substitution. This 13C NMR peak and its corresponding correlation peak in HSQC could potentially be used to identify 6-condensation in syringylic lignin samples.

scholarly journals XPS Investigations on Solid and Vacuum Deposited, Oxidized and Non-oxidized Palladium

1995 ◽  
Vol 50 (4-5) ◽  
pp. 381-387 ◽  
Author(s):  
Jürgen Kintrup ◽  
Harald Züchner
Keyword(s):  
Chemical Shift ◽  
Curve Fitting ◽  
Photoelectron Spectroscopy ◽  
Chemical Shifts ◽  
Atmospheric Oxygen ◽  
Hydrogen Permeability ◽  
Photoelectric Effect ◽  
High Accuracy ◽  
X Ray ◽  
Charging Effect

Abstract X-ray photoelectron spectroscopy (XPS) has been carried out to study the reaction of differently prepared palladium samples (solid and film Pd) with atmospheric oxygen. A careful curve fitting of the measured Pd-3d5/2 peak allows to separate the Pd-3d5/2 peak for Pd in surface PdO from the dominant Pd-3d5/2 peak of the non-oxidized bulk palladium and to determine the chemical shift of the "oxidized" Pa line with high accuracy. Differences in the chemical shifts for the surface PdO on solid and film palladium are explained by a different charging caused by the photoelectric effect in XPS measurements. The smaller charging effect observed for film palladium as compared to solid palladium indicates a stronger oxygen bonding to the (rougher) film palladium. The strong Pd-O bonding seems to be an essential reason for the reduced hydrogen-permeability of film palladium compared to solid palladium

Aluminum Siting in the ZSM-22 and Theta-1 Zeolites Revisited: A QM/MM Study

2008 ◽  
Vol 73 (6-7) ◽  
pp. 909-920 ◽  
Author(s):  
Stepan Sklenak ◽  
Jiří Dědeček ◽  
Chengbin Li ◽  
Fei Gao ◽  
Bavornpon Jansang ◽  
...  
Keyword(s):  
Experimental Data ◽  
Chemical Shift ◽  
Nearest Neighbor ◽  
Membered Ring ◽  
Mas Nmr ◽  
Isotropic Chemical Shift ◽  
Reaction Space ◽  
Ring Channel ◽  
T1 And T2 ◽  
Nmr Signals

The Al siting in the silicon rich ZSM-22 and Theta-1 zeolites of the TON structure was investigated analyzing already published 27Al 3Q MAS NMR experimental data using QM/MM calculations. The results of our computations show that Al atoms can be located in 6 framework T positions because the two eightfold sites (T1 and T2) split into four fourfold T sites after an Al/Si substitution. The observed resonance at 55.5 ppm corresponds to the T4 site which is predominantly occupied by Al. This site is not located on the surface of the TON ten-membered ring channel and thus the protonic sites related with the majority of Al atoms in the TON structure exhibit a significantly limited reaction space. The 27Al NMR signals centered at 57.6 and 58.7 ppm correspond to either the T2 and T3 sites, respectively, or only to T2. The T2 and T3 sites accommodate some 40% and up to 10%, respectively, of Al while the T1 site is unoccupied by Al. Isotropic shifts of 61.1 and 61.6 ppm were calculated for Al atoms located in the T1-1 and T1-2 sites, respectively. The effect of a silanol "nest" as a next-next-nearest neighbor on the 27Al isotropic chemical shift of Al located in the T4 site is calculated to be less than 1 ppm.

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