Proton nuclear magnetic relaxation dispersion (NMRD) profiles were recorded between 0.24 mT and 1.4 T for lanthanum(III)- and gadolinium(III)-containing [15]metallacrown-5 complexes derived from alpha-aminohydroxamic acids and with copper(II) as the ring metal. The influence of the different R-groups on the proton relaxivity was investigated, and a linear relationship between the relaxivity and the molecular mass of the metallacrown complex was found. The selectivity of the metallacrown complexes was tested by transmetalation experiments with zinc(II) ions. The crystal structure of the copper [15]metallacrown-5 gadolinium complex with glycine hydroximate ligands is reported.

The conversion of 12-metallacrown-4 complexes with copper(II) in the central cavity to 15-metallacrown-5 complexes with lanthanide(III) ions in the central cavity upon addition of trivalent lanthanide ions was analysed in solution by electrospray ionisation mass spectrometry (ESI-MS), absorption spectrophotometry, circular dichroism and proton NMR spectroscopy. In all cases, copper(II) ions were the ring metals. The lanthanide-induced shifts of the proton resonances in the NMR spectra of different lanthanide(III)-containing 15-metallacrown-5 complexes with tyrosinehydroximate ligands

The coherence of state-of-the-art superconducting qubit devices is predominantly limited by two-level-system defects, found primarily at amorphous interface layers. Reducing microwave loss from these interfaces by proper surface treatments is key to push the device performance forward. Here, we study niobium resonators after removing the native oxides with a hydrofluoric acid etch. We investigate the reappearance of microwave losses introduced by surface oxides that grow after exposure to the ambient environment. We find that losses in quantum devices are reduced by an order of magnitude, with internal Qfactors reaching up to 7×10 6 in the single photon regime, when devices are exposed to ambient conditions for 16 min. Furthermore, we observe that Nb2O5 is the only surface oxide that grows significantly within the first 200 hours, following the extended Cabrera-Mott growth model. In this time, microwave losses scale linearly with the Nb2O5 thickness, with an extracted loss tangent tanδNb2O5 = 9.9×10 -3 . Our findings are of particular interest for devices spanning from superconducting qubits, quantum-limited amplifiers, microwave kinetic inductance detectors to single photon detectors.

Nanoparticle removal obtained without inflicting damage to fragile device elements remains a big challenge. The feasibility of physical cleans is assessed and boundary conditions are outlined. An overview of megasonic cleaning process improvements is given. In order to reduce damage without reducing particle removal frequencies during high frequency ultrasound cleaning processes, cavitation needs to be better controlled. This is partly achieved by (1) using pulsed acoustic fields which makes it possible to control the average bubble size and, at the same time, maximize the number of resonant bubbles, by (2) increasing the dissolved gas concentration and lowering the surface tension which facilitates bubble formation and, finally, by (3) introducing traveling waves to transport bubbles to the surface which needs to be cleaned.

Effects of uranyl on the pentacopper(II) complexes of alpha-leucinehydroxamic acid and alpha-tyrosinehydroxamic acid were studied in water and methanol by means of electrospray ionisation mass spectrometry (ES-MS), absorption spectrophotometry, circular dichroism spectroscopy and proton NMR spectroscopy. All the measurements were consistent with the complete conversion of a 12-metallacrown-4 to a 15-metallacrown-5 upon addition of one equivalent of the uranyl ion. The uranyl ion is accommodated in the cavity formed by five copper(II) ions and five alpha-aminohydroxamate ligands. The 15-metallacrown-5 inclusion complexes have a high affinity for the uranyl ion. Competition studies showed that even in the presence of a large excess of calcium(II), the 15-metallacrown-5 remained stable, and no exchange reactions between calcium(II) and uranyl were observed. Extraction of uranyl from the 15-metallacrown-5 was also not detected in the presence of a large excess of 18-crown-6. Trivalent lanthanide ions can be partially sequestered by the 15-metallacrown-5, however, even these trivalent ions are displaced by uranyl.