Magnetic anisotropy and GGG substrate stray field in YIG films down to millikelvin temperatures.

Quantum magnonics investigates the quantum-mechanical properties of magnons, such as quantum coherence or entanglement for solid-state quantum information technologies at the nanoscale. The most promising material for quantum magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons with the longest lifetimes. YIG films of the highest quality are grown on a paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at temperatures below 50 K despite the increase in YIG magnetization. We investigated a 97 nm-thick YIG film grown on 500 µm-thick GGG substrate through a series of experiments conducted at temperatures as low as 30 mK, and using both analytical and numerical methods. Our findings suggest that the primary factor contributing to the FMR frequency shift is the stray magnetic field created by the partially magnetized GGG substrate. This stray field is antiparallel to the applied external field and is highly inhomogeneous, reaching up to 40 mT in the center of the sample. At temperatures below 500 mK, the GGG field exhibits a saturation that cannot be described by the standard Brillouin function for a paramagnet. Including the calculated GGG field in the analysis of the FMR frequency versus temperature dependence allowed the determination of the cubic and uniaxial anisotropies. We find that the total crystallographic anisotropy increases more than three times with the decrease in temperature down to 2 K. Our findings enable accurate predictions of the YIG/GGG magnetic systems behavior at low and ultralow millikelvin temperatures, crucial for developing quantum magnonic devices.

Control of the Bose-Einstein Condensation of Magnons by the Spin Hall Effect.

Previously, it has been shown that rapid cooling of yttrium-iron-garnet-platinum nanostructures, preheated by an electric current sent through the Pt layer, leads to overpopulation of a magnon gas and to subsequent formation of a Bose-Einstein condensate (BEC) of magnons. The spin Hall effect (SHE), which creates a spin-polarized current in the Pt layer, can inject or annihilate magnons depending on the electric current and applied field orientations. Here we demonstrate that the injection or annihilation of magnons via the SHE can prevent or promote the formation of a rapid cooling-induced magnon BEC. Depending on the current polarity, a change in the BEC threshold of -8% and +6% was detected. These findings demonstrate a new method to control macroscopic quantum states, paving the way for their application in spintronic devices.

Polymer photonic microstructures for quantum applications and sensing.

We present modelling results for efficient coupling of nanodiamonds containing single colour centres to polymer structures on distributed Bragg reflectors. We explain how hemispherical and super-spherical structures redirect the emission of light into small numerical apertures. Coupling efficiencies of up to 68.5% within a numerical aperture of 0.34 are found. Further, we show how Purcell factors up to 4.5 can be achieved for wavelength scale hemispheres coated with distributed Bragg reflectors. We conclude with an experimental proposal for the realisation of these structures.

Solid immersion facilitates fluorescence microscopy with nanometer resolution and sub-ångström emitter localization.

Exploring the maximum spatial resolution achievable in far-field optical imaging, we show that applying solid immersion lenses (SIL) in stimulated emission depletion (STED) microscopy addresses single spins with a resolution down to 2.4 ± 0.3 nm and with a localization precision of 0.09 nm.

Synthesis, anticancer activity, and iron affinity of the Actinoplanes metabolite 7,8-dihydroxy-1-methylnaphtho[2,3-c]furan-4,9-dione.

The first synthesis of 7,8-dihydroxy-1-methylnaphtho[2,3-c]furan-4,9-dione (1), an isofuranonaphthoquinone produced by an Actinoplanes strain is described. Lactone ring opening of 6-methylfuro[3,4-c]furan-1(3H)-one (4) with ortho-lithiated veratrole (3), oxidation of product alcohol 5, and Friedel-Crafts acylation of the resulting aroylcarboxylic acid 7 afforded the mono methyl ether 2 of the target compound. The latter was obtained by demethylation of 2 with BBr(3) in 14% overall yield. While mono ether 2 was distinctly more cytotoxic than catechol 1 against a panel of five cancer cell lines, only the latter showed a siderophore-like binding affinity for Fe(III) with a complex dissociation constant K(D) of approximately 10(-29) M(3) (pM = 25.9).

4-(3-Halo/amino-4,5-dimethoxyphenyl)-5-aryloxazoles and -N-methylimidazoles that are cytotoxic against combretastatin A resistant tumor cells and vascular disrupting in a cisplatin resistant germ cell tumor model.

New combretastatin A analogues featuring oxazole or N-methylimidazole bridged Z-alkenes and halo- or amino-substituted A-rings were tested against various cancer cell lines and in testicular germ cell tumor xenografts in mice. Imidazoles with 3-halo-4,5-dimethoxy substituted A-rings and 3-amino-4-methoxy substituted B-rings (7b and 8b) were efficacious at nanomolar concentrations against cells of combretastatin A refractory HT-29 colon carcinoma, multidrug-resistant MCF-7/Topo breast carcinoma, and cisplatin-resistant 1411HP testicular germ cell tumor. They induced apoptosis and inhibited tubulin polymerization. While well tolerated by mice at high doses, these imidazoles initiated extensive intratumoral hemorrhage and regressions of highly vascularized 1411HP xenografts.

Ru(η6-arene) complexes of combretastatin-analogous oxazoles with enhanced anti-tumoral impact.

Oxazole-bridged combretastatin A-4 analogues bind to tubulin and exert anti-vascular and anti-angiogenic effects. When linked to Ru(η(6)-arene) complex fragments, conjugates with additional cytotoxic activity result which can ruthenate bionucleophiles such as DNA and proteins. For instance, the Ru(II)(p-cymene)(isonicotinate)Cl(2) complex 6a of the known 4-(3,4,5-trimethoxyphenyl)-5-(3-hydroxy-4-methoxyphenyl)-oxazole 4a was far more active than the latter against cells of the p53-competent wild-type form of HCT-116 colon carcinoma at low 0.01 µM concentrations. A fast reaction of 6a with nucleophilic N-acetyl-L-cysteine was observed in NMR studies. The Ru(arene) complexes 6a-c were also more efficacious against combretastatin-refractory p53(+) cells of human HT-29 colon carcinoma when compared to their parent 4-(3,4-dimethoxy-5-methoxy/halo-phenyl)-5-(3-hydroxy-4-methoxyphenyl)-oxazoles 4a-c. These cells are rich in ABC-transporters which are responsible for their multi-drug resistance and for which conjugates 6 are less good substrates than the phenols 4. Unlike 4a, its complex 6a also diminished the motility of human 518A2 melanoma cells in a wound-healing assay which is indicative of anti-metastatic activity in solid tumors. Overall, the Ru(arene) complex conjugates 6 broaden the anti-tumoral spectrum of the combretastatin A-4 analogues 4 considerably.

Melanoma-specific ferrocene esters of the fungal cytotoxin illudin M.

The unfavorable therapeutic index of the fungal cytotoxin illudin M was to be improved by covalent attachment of the redox modulator and phenyl isobiostere ferrocene. Esters of illudin M with ferrocenoic and 1,1'-ferrocenedioic acid were prepared, structurally characterised (X-ray), and tested for cytotoxicity [MTT assay, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide], induction of apoptosis (TUNEL assay; western blotting for caspase-9), and tumor specificity in cells of human HL-60 leukemia, human 518A2 melanoma, and in nonmalignant human foreskin fibroblasts. The diester of illudin M with 1,1'-ferrocenedioic acid was distinctly more antiproliferative and apoptosis inducing in the melanoma cells [half maximal inhibitory concentration, IC50(48 h) = 0.4+/-0.1 micromol/l] than in the HL-60 cells [IC50(48 h) = 3.0+/-1.6 micromol/l] and in the nonmalignant fibroblasts [IC50(48 h) = 3.7+/-1.9 micromol/l]. This corresponds to a doubling of the therapeutic index with respect to illudin M. The monoester of illudin M with ferrocenoic acid was nine times less efficacious in the cancer cells, when compared with the diester. In conclusion, the ferrocene diminishes the general toxicity of the illudin M moiety and increases its cell line specificity. The bis(illudinyl M) 1,1'-ferrocenedioate presumably operates by a synergistic, two-pronged attack on its molecular targets.

Pt(II) complexes of a combretastatin A-4 analogous chalcone: effects of conjugation on cytotoxicity, tumor specificity, and long-term tumor growth suppression.

Three dichlorido(6-aminomethylnicotinate)platinum complexes 6 comprising a combretastatin A-4 analogous chalcone were tested on a panel of 21 tumor cell lines from 9 entities. Parent chalcone 1a and the directly linked conjugate 6a exhibited excellent antiproliferative activities, similar in magnitude [average log(IC(50)) values of -7.3 (1a) and -7.0 (6a)] and cell line specificity but slightly different in the mechanism of apoptosis induction. While 1a and 6a caused an equally fast rise in caspase-9 in the tested cancer cell lines, the downstream effector caspase-3 built up faster in cells treated with 1a compared to 6a, yet reached an equal end level. They also had different long-term effects on the regrowth of cancer cells treated with a single dose. In contrast, conjugates 6b,c featuring longer spacers between the Pt complex and the chalcone moieties were less antiproliferative than 6a.

Conjugates of the fungal cytotoxin illudin M with improved tumour specificity.

A simplified procedure for the isolation of gram quantities of illudin M from culture broths of basidiomycete Omphalotus olearius is described. Esters of illudin M with docosahexaenoic acid, chlorambucil, demethylcantharidinic acid (endothall) and 2,2'-bipyridyl-5,5'-dicarboxylic acid were synthesised and tested for cytotoxicity and induction of apoptosis in two clinically relevant tumour cell lines (Panc-1 pancreas carcinoma and HT-29 colon carcinoma) and in non-malignant human foreskin fibroblasts. The demethylcantharidin and the bipyridine conjugates retained the cytotoxicity of the parent illudin M while displaying an improved specificity for the tumour cells over the fibroblasts.

Monoterpenes as drug shuttles: cytotoxic (6-aminomethylnicotinate)dichloridoplatinum(II) complexes with potential to overcome cisplatin resistance.

(6-Aminomethylnicotinate)dichloridoplatinum(II) complexes 4 esterified with terpene alcohols were tested on a panel of five human tumor cell lines. While they were accumulated in all cell lines more readily than cisplatin (CDDP), their cytotoxicities were tumor-specific and structure-dependent. Cell lines known to feature elevated levels of antiapoptotic, ion-channel-affecting proteins or otherwise impaired caspase-9 activation responded better to 4 than to CDDP, e.g., the HL-60 leukemia to the fenchyl and bornyl derivatives 4a,b at an IC90 < or = 10 microM. The (-)-menthyl complex 4g was far better accumulated and more efficacious in CDDP-resistant 1411HP male germ cell tumor cells than in the congenerous CDDP-sensitive H12.1 cell line. 4g also broke the CDDP resistance of 518A2 melanoma cells. Cell decay in each case was apoptotic as to TUNEL and Annexin V fluorescence assays. Some complexes 4 seem to positively modulate the permeability of the cell membrane and of blocked mitochondrial anion channels.

ARF6-dependent interaction of the TWIK1 K+ channel with EFA6, a GDP/GTP exchange factor for ARF6.

TWIK1 belongs to a family of K(+) channels involved in neuronal excitability and cell volume regulation. Its tissue distribution suggests a role in epithelial potassium transport. Here we show that TWIK1 is expressed in a subapical compartment in renal proximal tubules and in polarized MDCK cells. In nonpolarized cells, this compartment corresponds to pericentriolar recycling endosomes. We identified EFA6, an exchange factor for the small G protein ADP-ribosylation factor 6 (ARF6), as a protein binding to TWIK1. EFA6 interacts with TWIK1 only when it is bound to ARF6. Because ARF6 modulates endocytosis at the apical surface of epithelial cells, the ARF6/EFA6/TWIK1 association is probably important for channel internalization and recycling.

Regulation of vascular tone in animals overexpressing the sarcolemmal calcium pump.

The mechanisms governing vascular smooth muscle tone are incompletely understood. In particular, the role of the sarcolemmal calcium pump PMCA (plasma membrane calmodulin-dependent calcium ATPase), which extrudes Ca2+ from the cytosol, and its importance compared with the sodium/calcium exchanger remain speculative. To test whether the PMCA is a regulator of vascular tone, we generated transgenic mice overexpressing the human PMCA4b under control of the arterial smooth muscle-specific SM22alpha promoter. This resulted in an elevated systolic blood pressure compared with littermate controls. In PMCA-overexpressing mice, endothelium-dependent relaxation of norepinephrine-preconstricted aortic rings to acetylcholine did not differ from wild type controls (76 +/- 8% versus 79 +/- 8% of maximum relaxation; n = 12, n.s.). De-endothelialized aortas of transgenic mice exhibited stronger maximum contraction to KCl (100 mmol/liter) compared with controls (86 +/- 6% versus 68 +/- 7% of reference KCl contraction at the beginning of the experiment; p <0.05). Preincubation of de-endothelialized vessels with the nitric oxide synthase (NOS) inhibitor l-NAME (l-N(G)-nitroarginine methyl ester) (10-5 mol/liter) resulted in a stronger contraction to KCl (p <0.05 versus without l-NAME), thus unmasking vasodilatory effects of inherent NO production. Maximum contraction to KCl after preincubation with l-NAME did not differ between PMCA mice and controls. In analogy to the results in PMCA-overexpressing mice, contractions of de-endothelialized aortas of neuronal NOS-deficient mice to KCl were significantly increased compared with controls (151 +/- 5% versus 131 +/- 6% of reference KCl contraction; p <0.05). In conclusion, our data suggest a model in which the sarcolemmal Ca2+ pump down-regulates activity of the vascular smooth muscle Ca2+/calmodulin-dependent neuronal NOS by a functionally relevant interaction. Therefore, the PMCA represents a novel regulator of vascular tone.