https://www.cell.com/cell/pdf/0092-8674(93)90635-4.pdf

Seeding “one-dimensional crystallization” of amyloid: A pathogenic mechanism in Alzheimer's disease and scrapie?

It has become common to reference “pi-stacking” forces or “pi–pi interactions” when describing the interactions between neighbouring aromatic rings. Here, we review experimental and theoretical literature across several fields and conclude that the terms “pi-stacking” and “pi–pi interactions” do not accurately describe the forces that drive association between aromatic molecules of the types most commonly studied in chemistry or biology laboratories. We therefore propose that these terms are misleading and should no longer be used. Even without these terms, electrostatic considerations relating to polarized pi systems, as described by Hunter and Sanders, have provided a good qualitative starting place for predicting and understanding the interactions between aromatics for almost two decades. More recent work, however, is revealing that direct electrostatic interactions between polarized atoms of substituents as well as solvation/desolvation effects in strongly interacting solvents must also be considered and even dominate in many circumstances.

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Rethinking the term “pi-stacking”

The design of artificial catalysts able to compete with the catalytic proficiency of enzymes is an intense subject of research. Non-covalent interactions are thought to be involved in several properties of enzymatic catalysis, notably (i) the confinement of the substrates and the active site within a catalytic pocket, (ii) the creation of a hydrophobic pocket in water, (iii) self-replication properties and (iv) allosteric properties. The origins of the enhanced rates and high catalytic selectivities associated with these properties are still a matter of debate. Stabilisation of the transition state and favourable conformations of the active site and the product(s) are probably part of the answer. We present here artificial catalysts and biomacromolecule hybrid catalysts which constitute good models towards the development of truly competitive artificial enzymes.

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Supramolecular catalysis. Part 2: artificial enzyme mimics

Noncovalent intermolecular forces in polycrystalline and amorphous saccharides in the far infrared

The sequence of the Escherichia coli OsmB protein was found to resemble that of the C-terminal region of the beta amyloid protein of Alzheimer's disease, which seems to be the major determinant of its unusual structural and solubility properties. A peptide corresponding to residues 28-44 of the OsmB protein was synthesized, and its conformational properties and aggregation behavior were analyzed. The peptide OsmB(28-44) was shown to form amyloid fibrils, as did two sequence analogs designed to test the sequence specificity of fibril formation. These fibrils bound Congo red, and two of the peptides showed birefringence. The peptide fibrils were analyzed by electron microscopy and Fourier transform infrared spectroscopy. Subtle differences were observed which were not interpretable at the molecular level. The rate of fibril formation by each peptide was followed by monitoring the turbidity of supersaturated aqueous solutions. The kinetics of aggregation were characterized by a delay period during which the solution remained clear, followed by a nucleation event which led to a growth phase, during which the solution became viscous and turbid due to the presence of insoluble fibrils. The observation of a kinetic barrier to aggregation is typical of a crystallization event. The delay period could be eliminated by seeding the supersaturated solution with previously formed fibrils. Each peptide could be nucleated by fibrils formed from that same peptide, but not by fibrils from closely related sequences, suggesting that fibril growth requires specific hydrophobic interactions. It appears likely that this repeated sequence motif, which comprises most of the OsmB protein sequence, dictates the structure and possibly the function of that protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Amyloid fibril formation requires a chemically discriminating nucleation event: studies of an amyloidogenic sequence from the bacterial protein OsmB

The structure and binding properties of a series of receptor molecules based on the building block diphenylglycoluril are described. These receptors bind dihydroxy-substituted aromatic guests in chloroform solution by means of hydrogen bonding and π-π stacking interactions. IR difference spectroscopy shows that the hydrogen bonds are formed between the OH groups of the guest molecule and the π-electrons of the urea carbonyl groups present in the receptor. The structure of the complexes was further investigated by comparing the complexation-induced shifts in the 1 H NMR spectra with the calculated shifts for a number of geometries of the host-guest complexes. These data demonstrate that the guest molecules are clamped within the cavity of the receptor

/pdf/binding-features-of-molecular-clips-derived-from-3a6j3u4pbo.pdf

Binding features of molecular clips derived from diphenylglycoluril

Enhancement of amyloid induction by amyloid fibril fragments in hamster.

Determination of Acetone in Cow Milk by Fourier Transform Infrared Spectroscopy for the Detection of Subclinical Ketosis

/pdf/structural-information-from-oh-stretching-frequencies-51fr5wban0.pdf

Structural information from OH stretching frequencies monohydric saturated alcohols

The structure of the tetragonal NaBi(MoO4)2 crystal was determined. The space group is I4=S42 with cell dimensions a=5.267, c=11.565 A and Z=2. The molybdenum atoms occupy two different sites of 4 symmetry. The Na+ and Bi3+ cations are situated on two positions with different occupancy factors and are short-range ordered. The IR and Raman polarized spectra are discussed on the basis of the factor group analysis and phonon calculations. The modified Urey–Bradley force field and potential energy distribution were applied for three molecular models of local disorder. Polarization properties are explained and related to the crystal structure. © 1997 John Wiley & Sons, Ltd.

E.T.G. Lutz

Papers

Binding features of molecular clips derived from diphenylglycoluril

Enhancement of amyloid induction by amyloid fibril fragments in hamster.

Determination of Acetone in Cow Milk by Fourier Transform Infrared Spectroscopy for the Detection of Subclinical Ketosis

Structural information from OH stretching frequencies monohydric saturated alcohols

Structure and vibrational properties of tetragonal scheelite NaBi(MoO4)2