Gradual thermal spin-crossover mediated by a reentrant Z’ = 1 → Z’ = 6 → Z’ = 1 phase transition

The Fe[BF₄]₂ complex of the Schiff base podand tris[4-(thiazol-4-yl)-3-aza-3-butenyl]amine exhibits gradual thermal spin-crossover with T₁⁄₂ ≈ 208 K in the solid state. A weak discontinuity in the magnetic susceptibility curve at 190 K is associated with a reentrant symmetry-breaking transition involving a trebling of the unit cell volume (from P2₁/c, Z = 4, to P2₁, Z = 12). The intermediate phase contains six independent cations in puckered layers of low-spin, and high-spin or mixed-spin, molecules with an overall 30% high-spin population at 175 K

Non-collinear coupling between magnetic adatoms in carbon nanotubes

The long range character of the exchange coupling between localized magnetic moments indirectly mediated by the conduction electrons of metallic hosts often plays a significant role in determining the magnetic order of low-dimensional structures. In addition to this indirect coupling, here we show that the direct exchange interaction that arises when the moments are not too far apart may induce a non-collinear magnetic order that cannot be characterized by a Heisenberg-like interaction between the magnetic moments. We argue that this effect can be manipulated to control the magnetization alignment of magnetic dimers adsorbed to the walls of carbon nanotubes.Comment: 13 pages, 5 figures, submitted to PR

Spin States of Homochiral and Heterochiral Isomers of [Fe(PyBox)2]2+ Derivatives

The following iron(II) complexes of 2,6-bis(oxazolinyl)pyridine (PyBox; LH) derivatives are reported: [Fe(LH)2][ClO4]2 (1); [Fe((R)-LMe)2][ClO4]2 ((R)-2; LMe=2,6-bis{4-methyloxazolinyl}pyridine); [Fe((R)-LPh)2][ClO4]2 ((R)-3) and [Fe((R)-LPh)((S)-LPh)][ClO4]2 ((RS)-3; LPh=2,6-bis{4-phenyloxazolinyl}pyridine); and [Fe((R)-LiPr)2][ClO4]2 ((R)-4) and [Fe((R)-LiPr)((S)-LiPr)][ClO4]2 ((RS)-4; LiPr=2,6-bis{4-isopropyloxazolinyl}pyridine). Solid (R)-3⋅MeNO2 exhibits an unusual very gradual, but discontinuous thermal spin-crossover with an approximate Tmath formula of 350 K. The discontinuity around 240 K lies well below Tmath formula , and is unconnected to a crystallographic phase change occurring at 170 K. Rather, it can be correlated with a gradual ordering of the ligand conformation as the temperature is raised. The other solid compounds either exhibit spin-crossover above room temperature (1 and (RS)-3), or remain high-spin between 5–300 K [(R)-2, (R)-4 and (RS)-4]. Homochiral (R)-3 and (R)-4 exhibit more twisted ligand conformations and coordination geometries than their heterochiral isomers, which can be attributed to steric clashes between ligand substituents [(R)-3]; or, between the isopropyl substituents of one ligand and the backbone of the other ((R)-4). In solution, (RS)-3 retains its structural integrity but (RS)-4 undergoes significant racemization through ligand redistribution by 1H NMR. (R)-4 and (RS)-4 remain high-spin in solution, whereas the other compounds all undergo spin-crossover equilibria. Importantly, Tmath formula for (R)-3 (244 K) is 34 K lower than for (RS)-3 (278 K) in CD3CN, which is the first demonstration of chiral discrimination between metal ion spin states in a molecular complex

Novel and natural knockout lung cancer cell lines for the LKB1/STK11 tumor suppressor gene

Germline mutations of the LKB1 gene are responsible for Peutz-Jeghers syndrome (PJS), an autosomal dominant inherited disorder bestowing an increased risk of cancer. We have recently demonstrated that LKB1 inactivating mutations are not confined to PJS, but also appear in lung adenocarcinomas of sporadic origin, including primary tumors and lung cancer cell lines. To accurately determine the frequency of inactivating LKB1 gene mutations in lung tumors we have sequenced the complete coding region of LKB1 in 21 additional lung cancer cell lines. Here we describe the mutational status of LKB1 gene in 30 lung cancer cell lines from different histopathological types, including 11 lung adenocarcinomas (LADs) and 11 small cell lung cancers (SCLCs). LKB1 gene alterations were present in six (54%) of the LAD cell lines tested but in none of the other histological types. Similar to our previous observations in primary tumors, all point mutations were of the nonsense or frameshift type, leading to an abnormal, truncated protein. Moreover, 2 cell lines (A427 and H2126) harbored large gene deletions that spanned several exons. Hence, we have identified additional lung cancer cell lines carrying inactivating mutations of the LKB1 tumor suppressor gene, further attesting to the significance of this gene in the development of LADs and providing new natural LKB1 knockouts for studies of the biological function of the LKB1 protein

Influence of heavy modes on perturbations in multiple field inflation

We investigate linear cosmological perturbations in multiple field inflationary models where some of the directions are light while others are heavy (with respect to the Hubble parameter). By integrating out the massive degrees of freedom, we determine the multi-dimensional effective theory for the light degrees of freedom and give explicitly the propagation matrix that replaces the effective sound speed of the one-dimensional case. We then examine in detail the consequences of a sudden turn along the inflationary trajectory, in particular the possible breakdown of the low energy effective theory in case the heavy modes are excited. Resorting to a new basis in field space, instead of the usual adiabatic/entropic basis, we study the evolution of the perturbations during the turn. In particular, we compute the power spectrum and compare with the result obtained from the low energy effective theory.Comment: 24 pages, 13 figures; v2 substantial changes in sec.V; v3 matching the published version on JCA

Synthetic Lethality of Chk1 Inhibition Combined with p53 and/or p21 Loss During a DNA Damage Response in Normal and Tumor Cells

Cell cycle checkpoints ensure genome integrity and are frequently compromised in human cancers. A therapeutic strategy being explored takes advantage of checkpoint defects in p53-deficient tumors in order to sensitize them to DNA-damaging agents by eliminating Chk1-mediated checkpoint responses. Using mouse models, we demonstrated that p21 is a key determinant of how cells respond to the combination of DNA damage and Chk1 inhibition (combination therapy) in normal cells as well as in tumors. Loss of p21 sensitized normal cells to the combination therapy much more than did p53 loss and the enhanced lethality was partially blocked by CDK inhibition. In addition, basal pools of p21 (p53 independent) provided p53 null cells with protection from the combination therapy. Our results uncover a novel p53-independent function for p21 in protecting cells from the lethal effects of DNA damage followed by Chk1 inhibition. As p21 levels are low in a significant fraction of colorectal tumors, they are predicted to be particularly sensitive to the combination therapy. Results reported in this study support this prediction

Phosphorylation by Akt within the ST loop of AMPK-α1 down-regulates its activation in tumour cells

The insulin/IGF-1 (insulin-like growth factor 1)-activated protein kinase Akt (also known as protein kinase B) phosphorylates Ser(487) in the ‘ST loop’ (serine/threonine-rich loop) within the C-terminal domain of AMPK-α1 (AMP-activated protein kinase-α1), leading to inhibition of phosphorylation by upstream kinases at the activating site, Thr(172). Surprisingly, the equivalent site on AMPK-α2, Ser(491), is not an Akt target and is modified instead by autophosphorylation. Stimulation of HEK (human embryonic kidney)-293 cells with IGF-1 caused reduced subsequent Thr(172) phosphorylation and activation of AMPK-α1 in response to the activator A769662 and the Ca(2+) ionophore A23187, effects we show to be dependent on Akt activation and Ser(487) phosphorylation. Consistent with this, in three PTEN (phosphatase and tensin homologue deleted on chromosome 10)-null tumour cell lines (in which the lipid phosphatase PTEN that normally restrains the Akt pathway is absent and Akt is thus hyperactivated), AMPK was resistant to activation by A769662. However, full AMPK activation could be restored by pharmacological inhibition of Akt, or by re-expression of active PTEN. We also show that inhibition of Thr(172) phosphorylation is due to interaction of the phosphorylated ST loop with basic side chains within the αC-helix of the kinase domain. Our findings reveal that a previously unrecognized effect of hyperactivation of Akt in tumour cells is to restrain activation of the LKB1 (liver kinase B1)–AMPK pathway, which would otherwise inhibit cell growth and proliferation

Magnetic properties of spin waves in thin yttrium iron garnet films

We report spin wave propagation experiments in thin yttrium iron garnet (YIG) films. Using time-resolved scanning Kerr microscopy we extract the mode structure of the spin waves. For quasi-single-mode excitation, the spin wave decay can be fitted with a damped harmonic oscillator function providing us with information about the attenuation length. We measure values of about 2.7 and 3.6 μm for the spin wave decay length of 38- and 49-nm-thick YIG samples, respectively. Micromagnetic simulations are performed to compare experimental and simulated modes. The data are in very good agreement with these simulations

Large non-Gaussian Halo Bias from Single Field Inflation

We calculate Large Scale Structure observables for non-Gaussianity arising from non-Bunch-Davies initial states in single field inflation. These scenarios can have substantial primordial non-Gaussianity from squeezed (but observable) momentum configurations. They generate a term in the halo bias that may be more strongly scale-dependent than the contribution from the local ansatz. We also discuss theoretical considerations required to generate an observable signature.Comment: 30 pages, 14 figures, typos corrected and minor changes to match published version JCAP09(2012)00

Optical conversion of pure spin currents in hybrid molecular devices

Carbon-based molecules offer unparalleled potential for THz and optical devices controlled by pure spin currents: a low-dissipation flow of electronic spins with no net charge displacement. However, the research so far has been focused on the electrical conversion of the spin imbalance, where molecular materials are used to mimic their crystalline counterparts. Here, we use spin currents to access the molecular dynamics and optical properties of a fullerene layer. The spin mixing conductance across Py/C60 interfaces is increased by 10% (5 × 1018 m−2) under optical irradiation. Measurements show up to a 30% higher light absorbance and a factor of 2 larger photoemission during spin pumping. We also observe a 0.15 THz slowdown and a narrowing of the vibrational peaks. The effects are attributed to changes in the non-radiative damping and energy transfer. This opens new research paths in hybrid magneto-molecular optoelectronics, and the optical detection of spin physics in these materials