Three-junction SQUID-on-tip with tunable in-plane and out-of-plane magnetic field sensitivity.

Nanoscale superconducting quantum interference devices (SQUIDs) demonstrate record sensitivities to small magnetic moments but are typically sensitive only to the field component that is normal to the plane of the SQUID and out-of-plane with respect to the scanned surface. We report on a nanoscale three-junction Pb SQUID, which is fabricated on the apex of a sharp tip. Because of its three-dimensional structure, it exhibits a unique tunable sensitivity to both in-plane and out-of-plane fields. We analyze the two-dimensional interference pattern from both numerical and experimental points of view. This device is integrated into a scanning microscope, and its ability to independently measure the different components of the magnetic field with outstanding spin sensitivity better than 5 µB/Hz(1/2) is demonstrated. This highlights its potential as a local probe of nanoscale magnetic structures.

N-linked peptidocalix[4]arene bisureas as enantioselective receptors for amino acid derivatives.

Bisurea calix[4]arenes 1 and 2 possessing L-amino acid moieties at the lower rim were synthesized by reaction of the methyl esters of glycine, L-alanine, or L-isoleucine with the appropriate isocyanate (12 or 13), obtained with a safe and efficient Curtius rearrangement from the corresponding carboxylic acid derivatives. The conformational properties of the ligands 1 and 2 were investigated by means of a combined NMR and molecular modeling study which evidences that they are deeply influenced by strong intramolecular H-bonds between the urea NH groups and the vicinal phenolic oxygen atoms or the opposite urea C=O group. Complexation studies performed by ESI-MS and NMR spectroscopy in acetone solution show that the binding ability of these bisurea hosts decreases by increasing the side chain size of the amino acid. Host 2b has a remarkable binding ability for the N-acetyl-D-phenylalaninate anion with an interesting enantioselectivity (KDass/KLass=4.14), which is explained on the basis of a three-point interaction mode of binding.

Diastereoselective lower rim (1S)-camphorsulfonylation as the shortest way to the inherently chiral calix[4]arene.

[structure: see text]. A diastereomeric mixture of chiral 25-(1S)-camphorsulfonyloxy-26-isopropoxycalix[4]arene 2a (de 15%) and 25-isopropoxy-26-((1S)-10-camphorsulfonyl)calix[4]arene 2b has been obtained by asymmetrical lower rim (1S)-camphorsulfonylation of the monoisopropoxycalix[4]arene. Pure diastereomer 2a has been obtained by simple crystallization, and its absolute configuration has been determinated by X-ray analysis. Enantiomerically pure inherently chiral 5,11-dibromo-26-isopropoxycalix[4]arene 4 has been synthesized by the upper rim dibromination of the diastereomer 2a followed by hydrolytical removal of the auxiliary camphorsulfonyl group.

Selective mono-O-acylation of C2V-symmetrical calix[4]arenediols with acylisocyanates.

Calix[4]arenedialkyl ethers 3 react with an excess of acylisocyanates to give selectively monoacylated products 4. Intramolecular hydrogen bonds and steric effects of the acylcarbamate fragments are most likely responsible for the high selectivity of this monoprotection. [reaction: see text]