Hyperpolarized xenon nuclear spins detected by optical atomic magnetometry

We report the use of an atomic magnetometer based on nonlinear magneto-optical rotation with frequency modulated light (FM NMOR) to detect nuclear magnetization of xenon gas. The magnetization of a spin-exchange-polarized xenon sample ($1.7$cm$^3$ at a pressure of $5$bar, natural isotopic abundance, polarization 1%), prepared remotely to the detection apparatus, is measured with an atomic sensor (which is insensitive to the leading field of 0.45 G applied to the sample; an independent bias field at the sensor is $140 \mu$G). An average magnetic field of $\sim 10$nG induced by the xenon sample on the 10-cm diameter atomic sensor is detected with signal-to-noise ratio $\sim 10$, limited by residual noise in the magnetic environment. The possibility of using modern atomic magnetometers as detectors of nuclear magnetic resonance and in magnetic resonance imaging is discussed. Atomic magnetometers appear to be ideally suited for emerging low-field and remote-detection magnetic resonance applications.Comment: 4 pages, 4 figure

Activation of the Arabidopsis thaliana Immune System by Combinations of Common ACD6 Alleles

A fundamental question in biology is how multicellular organisms distinguish self and non-self. The ability to make this distinction allows animals and plants to detect and respond to pathogens without triggering immune reactions directed against their own cells. In plants, inappropriate self-recognition results in the autonomous activation of the immune system, causing affected individuals to grow less well. These plants also suffer from spontaneous cell death, but are at the same time more resistant to pathogens. Known causes for such autonomous activation of the immune system are hyperactive alleles of immune regulators, or epistatic interactions between immune regulators and unlinked genes. We have discovered a third class, in which the Arabidopsis thaliana immune system is activated by interactions between natural alleles at a single locus, ACCELERATED CELL DEATH 6 (ACD6). There are two main types of these interacting alleles, one of which has evolved recently by partial resurrection of a pseudogene, and each type includes multiple functional variants. Most previously studies hybrid necrosis cases involve rare alleles found in geographically unrelated populations. These two types of ACD6 alleles instead occur at low frequency throughout the range of the species, and have risen to high frequency in the Northeast of Spain, suggesting a role in local adaptation. In addition, such hybrids occur in these populations in the wild. The extensive functional variation among ACD6 alleles points to a central role of this locus in fine-tuning pathogen defenses in natural populations

MeO-Biphep and Binap ligands as six-electron donors to ruthenium(II). X-ray and NMR studies on Cp-, pyrrole-, and indole-derived complexes

Ru(II) complexes of the chiral ligands Binap and MeO-Biphep containing six-electron hydrocarbon donors, such as Cp, a deprotonated pyrrole, or the benzene ring of indole, attain the 18-electron configuration by complexing a proximate biaryl double bond. The solid-state structures for two of these, [RuCp(2)]BF4 and [Ru(indole)(2)](BF4)(2) (2 = (6,6'-dimethoxybiphenyl-2,2'-diyl)bis(bis(3,5-di-tert-butylphenyl)phosphine)), have been determined by X-ray diffraction. They reveal that a biaryl double bond, immediately adjacent to one P-donor, coordinates to the ruthenium, thus making the chelating ligand a six-electron donor. The double bonds remain coordinated in solution as shown by HMBC C-13,H-1 long-range correlation spectroscopy. However, 2-D NMR exchange spectroscopy suggests that the biaryl double bond is weakly coordinated since the two halves of the C-2-symmetric Binap (or MeO-Biphep) Ligands are in slow exchange at ambient temperature