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.

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.

scholarly journals Robustness of surface activity electronic structure-based descriptors of transition metals

2018 ◽  
Vol 20 (31) ◽  
pp. 20548-20554 ◽  
Author(s):  
Lorena Vega ◽  
Biel Martínez ◽  
Francesc Viñes ◽  
Francesc Illas
Keyword(s):  
Electronic Structure ◽  
Transition Metal ◽  
Transition Metals ◽  
Coordination Number ◽  
Surface Activity ◽  
Metal Surfaces ◽  
Surface States ◽  
Density Functionals ◽  
Direct Relation ◽  
Transition Metal Surfaces

The d-band centre comes back from the dead being the most consistent of the main electronic descriptors, due to its excellent transferability between five density functionals. The robustness previously observed for bulk is here evaluated for transition metal surfaces and if large surface states are not involved, a direct relation with the coordination number is disclosed.

scholarly journals Demystifying fluorine chemical shifts: electronic structure calculations address origins of seemingly anomalous 19F-NMR spectra of fluorohistidine isomers and analogues

2015 ◽  
Vol 17 (45) ◽  
pp. 30606-30612 ◽  
Author(s):  
Chandana Kasireddy ◽  
James G. Bann ◽  
Katie R. Mitchell-Koch
Keyword(s):  
Electronic Structure ◽  
Chemical Shift ◽  
Electron Density ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Electronic Structure Calculations ◽  
19F Nmr ◽  
19F Nmr Spectra ◽  
Structure Calculations

Understanding localization/delocalization of fluorine electron density is shown to be critical for predicting and interpreting fluorine chemical shift.

Electronic structure and 11B-NMR spectra of nine-vertex heteroboranes: 4-CB8H14, 4-NB8H13, 4-SB8H12 and 4,6-C2B7H13

1981 ◽  
Vol 46 (10) ◽  
pp. 2479-2493 ◽  
Author(s):  
Jiří Dolanský ◽  
Stanislav Heřmánek ◽  
Rudolf Zahradník
Keyword(s):  
Electronic Structure ◽  
Density Matrix ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Nmr Chemical Shifts ◽  
Matrix Properties ◽  
11B Nmr

11B-NMR Spectra of 4-CB8H14, 4-NB8H13, 4-SB8H12 and 4,6-C2B7H13 are presented, together with a detailed assignment of individual signals. Correlations of 11B NMR chemical shifts with some STO-3G and CNDO/2 density matrix properties are evaluated. Similarities in the electronic structure and the nature of heteroatom bonding are discussed.

Darstellung und 11B-NMR-Spektren perhalogenierter closo-Hexaborate Β6ΧnY6-n2-, n=0-6; X ≠ Y= Cl, Br, I / Preparation and 11B NMR Spectra of the Perhalogenated closo-Hexaborates B6XnY6-n2-,n = 0-6; Χ ≠ Υ = Cl, Br, I

1990 ◽  
Vol 45 (8) ◽  
pp. 1113-1117 ◽  
Author(s):  
W. Preetz ◽  
M. Stallbaum
Keyword(s):  
Chemical Shift ◽  
Alkaline Solution ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Point Symmetry ◽  
Aqueous Alkaline Solution ◽  
11B Nmr ◽  
Characteristic Features ◽  
First Time

The mixed halogenohexaborates B6XnY6-n2-, n = 1-5; Χ ≠ Υ = Cl, Br, I, including most of the pure stereoisomers for n = 2—4, are prepared for the first time by treatment of the halohydrohexaborates B6XnH6-n2-, X = Cl, Br in aqueous alkaline solution with bromine and iodine or with halogenosuccinimides. The point symmetry is determined from the "B NMR spectra, which show characteristic features for homologous isostructural compounds. In the systems B6XnY6-n2- a considerable dispersion of the 11B signals is observed, for B(X) atoms to lower, for B(Y) atoms to higher field compared with B6X62- and B6Y62- (electronegativity X > Y), respectively. An additional chemical shift is caused by the mutual antipodal effect between pairs of opposite B atoms carrying different substituents. From the systematic influences on the chemical shifts the 11B NMR spectra of the missing species fac-B6X3Y32- are calculated.

Relation Between Local Structure, Electric Dipole and Charge Carrier Dynamics in DHICA Melanin, a Model for Biocompatible Semiconductors

2019 ◽  
Author(s):  
Micaela Matta ◽  
Alessandro Pezzella ◽  
Alessandro Troisi
Keyword(s):  
Electronic Structure ◽  
Degrees Of Freedom ◽  
Structural Model ◽  
Computational Study ◽  
Oxidative Polymerization ◽  
Radical Scavenging ◽  
Charge Carriers ◽  
Electronic Charge ◽  
Polymer Semiconductors ◽  
Synthetic Pigments

<div><div><div><p>Eumelanins are a family of natural and synthetic pigments obtained by oxidative polymerization of their natural precursors: 5,6 dihydroxyindole and its 2-carboxy derivative (DHICA). The simultaneous presence of ionic and electronic charge carriers makes these pigments promising materials for applications in bioelectronics. In this computational study we build a structural model of DHICA melanin considering the interplay between its many degrees of freedom, then we examine the electronic structure of representative oligomers. We find that a non-vanishing dipole along the polymer chain sets this system apart from conventional polymer semiconductors, determining its electronic structure, reactivity toward oxidation and localization of the charge carriers. Our work sheds light on previously unnoticed features of DHICA melanin that not only fit well with its radical scavenging and photoprotective properties, but open new perspectives towards understanding and tuning charge transport in this class of materials.<br></p></div></div></div>

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.

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