scholarly journals Assembly of synthetic Aβ miniamyloids on polyol templates

2015 ◽  
Vol 11 ◽  
pp. 2646-2653 ◽  
Author(s):  
Sebastian Nils Fischer ◽  
Armin Geyer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Solid Phase ◽  
Solid Phase Peptide Synthesis ◽  
Boronic Acids ◽  
Relative Orientation ◽  
Aβ Peptide ◽  
Aβ Peptides ◽  
Boronic Ester ◽  
Boronic Esters

Covalent dynamic chemistry is used to mimic the first steps of the highly cooperative fibril formation of Aβ peptides. For that purpose, Aβ peptide pentapeptide boronic acids 1 and 2 were synthesized by solid-phase peptide synthesis and studied in esterification experiments with polyhydroxylated templates. The bis-hydroxylated dipeptide Hot=Tap serves as a template of adjustable degree of oligomerization which spontaneously forms boronic esters with peptides of type 1 and 2. Nuclear magnetic resonance can differentiate between regioisomeric boronic esters and identifies preferred sites of esterification on the dimeric template 9. 2-Formylphenylboronic acid (14) is used to link the parent pentapeptide Leu-Val-Phe-Phe-Ala to the template 16 to obtain threefold boronic ester 17. The miniamyloid 17 assembles from seven components by imine and boronic ester bonds between the peptides and the template. The relative orientation and spacing of the peptides mimic the assembly of peptides in Alzheimer β-amyloids.

Studies of specifically fluorinated carbohydrates. Part I. Nuclear magnetic resonance studies of hexopyranosyl fluoride derivatives

1969 ◽  
Vol 47 (1) ◽  
pp. 1-17 ◽  
Author(s):  
L. D. Hall ◽  
J. F. Manville ◽  
N. S. Bhacca
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Angular Dependence ◽  
Chemical Shifts ◽  
Relative Orientation ◽  
Coupling Constants ◽  
Pyranose Ring ◽  
Spectral Parameters ◽  
Magnetic Resonance Studies ◽  
Nuclear Magnetic

A detailed study has been made of both the 1H and 19F nuclear magnetic resonance (n.m.r.) spectra of a series of hexopyranosyl fluoride derivatives. Some of the 1H spectra were measured at 220 MHz. The 1H spectral parameters define both the configuration and the conformation of each of these derivatives. Study of the 19F n.m.r. parameters revealed several stereospecific dependencies. The 19F chemical shifts depend upon, (a) the orientation of the fluorine substituent with respect to the pyranose ring and, (b) the relative orientation of other substituents attached to the ring; for acetoxy substituents, these configurational dependencies appear to be additive. The vicinal19F–1H coupling constants exhibit a marked angular dependence for which Jtrans = ca. 24 Hz whilst Jgauche = 1.0 to 1.5 Hz for [Formula: see text] and 7.5 to 12.6 Hz for [Formula: see text] The geminal19F–1H couplings depend on the orientation of the substituent at C-2; when this substituent is equatorial JF,H is ca. 53.5 Hz and when it is axial the value is ca. 49 Hz.

scholarly journals Diversity-oriented synthesis of peptide-boronic acids by a versatile building-block approach

2020 ◽  
Vol 11 (36) ◽  
pp. 9898-9903 ◽  
Author(s):  
Stefan P. A. Hinkes ◽  
Severin Kämmerer ◽  
Christian D. P. Klein
Keyword(s):  
Peptide Synthesis ◽  
Building Block ◽  
Solid Phase ◽  
Solid Phase Peptide Synthesis ◽  
Boronic Acids ◽  
Diversity Oriented Synthesis ◽  
Block Approach

Decarboxylative borylation and monophasic transesterification yields Fmoc-α-aminoboronates for solid-phase peptide synthesis.

scholarly journals Investigating the effect of internal gradients on static gradient nuclear magnetic resonance diffusion measurements

Geophysics ◽  
2017 ◽  
Vol 82 (5) ◽  
pp. D293-D301
Author(s):  
Emily L. Fay ◽  
Denys J. Grombacher ◽  
Rosemary J. Knight
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Susceptibility ◽  
Diffusion Coefficient ◽  
Magnetic Resonance ◽  
Pore Size ◽  
Solid Phase ◽  
Pore Fluid ◽  
Bulk Fluid ◽  
Nuclear Magnetic ◽  
Diffusion Editing

Nuclear magnetic resonance (NMR) methods can be used to measure the diffusion coefficient [Formula: see text] of fluids. In porous materials, diffusion of the pore fluid is restricted by pore boundaries, such that [Formula: see text] may be smaller than the diffusion coefficient of the bulk fluid. This reduction in [Formula: see text] provides information about the geometry of the pore space. Significant overestimates of [Formula: see text] can, however, occur due to internal gradients caused by magnetic susceptibility contrasts between the pore fluid and the solid phase. We have investigated the way in which internal gradients can impact the measured diffusion coefficient and obscure the link to pore geometry in unconsolidated sediments. We focus on measurements of [Formula: see text] obtained with a static gradient diffusion-editing sequence, which can be used with NMR logging tools to measure [Formula: see text] in subsurface sediments. Laboratory measurements of [Formula: see text] measured with a diffusion-editing [Formula: see text]-[Formula: see text] sequence indicate significant impacts from internal gradients, including [Formula: see text] values several orders of magnitude larger than [Formula: see text] of bulk water. The log-mean [Formula: see text] values were found to be highly correlated with estimated internal gradient magnitudes and indicate no clear relationship to pore size. Samples with heterogeneous magnetic susceptibility of the solid phase indicate [Formula: see text] distributions with multiple peaks, reflecting the nonuniform distribution of internal gradients in the sediment. We found evidence of high internal gradients impacting a majority of our samples, resulting in increased [Formula: see text] values that do not reflect pore size even in samples with low magnetic susceptibility.

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