Wolfgang Kilian

A Xenon‐129 Biosensor for Monitoring MHC–Peptide Interactions

Caged in: The formation of a complex between a peptide ligand and a major histocompatibility complex (MHC) class II protein is detected by a (129)Xe biosensor. Cryptophane molecules that trap Xe atoms are modified with a hemagglutinin (HA) peptide, which binds to the MHC protein. The interaction can be monitored by an NMR chemical shift change of cage-HA bound (129)Xe.

Dynamic NMR spectroscopy of hyperpolarized 129Xe in human brain analyzed by an uptake model

Hyperpolarized 129Xe (HpXe) NMR not only holds promise for functional lung imaging, but for measurements of tissue perfusion as well. To investigate human brain perfusion, several time‐series of 129Xe MR spectra were recorded from one healthy volunteer after HpXe inhalation. The time‐dependent amplitudes of the MR spectra were analyzed by using a compartment model for xenon uptake modified to account for the loss of 129Xe polarization due to RF‐excitation and for the breathhold technique used in the experiments. This analysis suggests that the resonances detected at 196.5 ± 1 ppm and 193 ± 1 ppm originate from HpXe dissolved in gray and white matter, respectively, and that T1 relaxation times of HpXe are different in gray and white matter (T1g > T1w). Magn Reson Med 51:843–847, 2004.

New Limit on Lorentz-Invariance- and CPT-Violating Neutron Spin Interactions Using a Free-Spin-Precession

We report on the search for a CPT- and Lorentz-invariance-violating coupling of the He3 and Xe129 nuclear spins (each largely determined by a valence neutron) to posited background tensor fields that permeate the Universe. Our experimental approach is to measure the free precession of nuclear spin polarized He3 and Xe129 atoms in a homogeneous magnetic guiding field of about 400 nT using LTC SQUIDs as low-noise magnetic flux detectors. As the laboratory reference frame rotates with respect to distant stars, we look for a sidereal modulation of the Larmor frequencies of the colocated spin samples. As a result we obtain an upper limit on the equatorial component of the background field interacting with the spin of the bound neutron b(⊥)(n)<8.4 × 10(-34)u2009 GeV (68% C.L.). Our result improves our previous limit (data measured in 2009) by a factor of 30 and the worlds best limit by a factor of 4.

^3

We search for a spin-dependent P- and T-violating nucleon-nucleon interaction mediated by light pseudoscalar bosons such as axions or axionlike particles. We employ an ultrasensitive low-field magnetometer based on the detection of free precession of colocated 3He and 129Xe nuclear spins using SQUIDs as low-noise magnetic flux detectors. The precession frequency shift in the presence of an unpolarized mass was measured to determine the coupling of pseudoscalar particles to the spin of the bound neutron. For boson masses between 2 and 500u2009u2009μeV (force ranges between 3×1(-4)u2009u2009m and 10(-1)u2009u2009m) we improved the laboratory upper bounds by up to 4 orders of magnitude.

He -

We discuss the design and performance of a very sensitive low-field magnetometer based on the detection of free spin precession of gaseous, nuclear polarized 3He or 129Xe samples with a SQUID as magnetic flux detector. The device will be employed to control fluctuating magnetic fields and gradients in a new experiment searching for a permanent electric dipole moment of the neutron as well as in a new type of 3He/129Xe clock comparison experiment which should be sensitive to a sidereal variation of the relative spin precession frequency. Characteristic spin precession times T_2 of up to 60h could be measured. In combination with a signal-to-noise ratio of>5000:1, this leads to a sensitivity level of deltaB= 1fT after an integration time of 220s and to deltaB= 10^(-4)fT after one day. Even in that sensitivity range, the magnetometer performance is statistically limited, and noise sources inherent to the magnetometer are not limiting. The reason is that free precessing 3He (129Xe) nuclear spins are almost completely decoupled from the environment. That makes this type of magnetometer in particular attractive for precision field measurements where a long-term stability is required.

^{129}

We report on the search for a CPT- and Lorentz-invariance-violating coupling of the He3 and Xe129 nuclear spins (each largely determined by a valence neutron) to posited background tensor fields that permeate the Universe. Our experimental approach is to measure the free precession of nuclear spin polarized He3 and Xe129 atoms in a homogeneous magnetic guiding field of about 400 nT using LTC SQUIDs as low-noise magnetic flux detectors. As the laboratory reference frame rotates with respect to distant stars, we look for a sidereal modulation of the Larmor frequencies of the colocated spin samples. As a result we obtain an upper limit on the equatorial component of the background field interacting with the spin of the bound neutron b(⊥)(n)<8.4 × 10(-34)u2009 GeV (68% C.L.). Our result improves our previous limit (data measured in 2009) by a factor of 30 and the worlds best limit by a factor of 4.

Xe Comagnetometer

We report on the search for Lorentz-violating sidereal variations of the frequency difference of colocated spin species while the Earth and hence the laboratory reference frame rotates with respect to a relic background field. The comagnetometer used is based on the detection of freely precessing nuclear spins from polarized 3 He and 129 Xe gas samples using SQUIDs as low-noise magnetic flux detectors. As result we can determine the limit for the equatorial component of the background field interacting with the spin of the bound neutron to be b n ⊥ < 3.7 · 10- 32 GeV (95% C.L.).

Constraints on spin-dependent short-range interaction between nucleons.

A stand-alone, self-contained and transportable system for the polarization of 129Xe by spin exchange optical pumping with Rb is described. This mobile polarizer may be operated in batch or continuous flow modes with medium amounts of hyperpolarized 129Xe for spectroscopic or small animal applications. A key element is an online nuclear magnetic resonance module which facilitates continuous monitoring of polarization generation in the pumping cell as well as the calculation of the absolute 129Xe polarization. The performance of the polarizer with respect to the crucial parameters temperature, xenon and nitrogen partial pressures, and the total gas flow is discussed. In batch mode the highest 129Xe polarization of PXexa0=xa040xa0% was achieved using 0.1xa0mbar xenon partial pressure. For a xenon flow of 6.5 and 26xa0mln/min, PXexa0=xa025xa0% and PXexa0=xa013xa0% were reached, respectively. The mobile polarizer may be a practical and efficient means to make the applicability of hyperpolarized 129Xe more widespread.

Ultra-sensitive magnetometry based on free precession of nuclear spins

Polarization of 3He gas by means of optical pumping is well known since the early 1960s with first applications in fundamental physics. Some thirty years later it was discovered, that one can use hyperpolarized 3He as contrast agent for magnetic resonance imaging of the lung. The wide interest in this new method made it necessary to find ways of polarizing 3He in large quantities with high polarization degrees. A high performance polarizing facility has been developed at the University of Mainz, designed for centralized production of hyperpolarized 3He gas. We present the Mainz concept as well as some examples of numerous applications of spin polarized 3He in fundamental research and medical applications.

New limit on Lorentz and CPT violating neutron spin interactions using a free precession 3 He- 129 Xe co-magnetometer

Exchange spectroscopy is used in combination with a variation of xenon concentration to disentangle the kinetics of the reversible binding of xenon to cryptophane-A. The signal intensity of either free or crytophane-bound xenon decays in a manner characteristic of the underlying exchange reactions when the spins in the other pool are perturbed. Three experimental approaches, including the well-known Hyper-CEST method, are shown to effectively entail a simple linear dependence of the signal depletion rate, or of a related quantity, on free xenon concentration. This occurs when using spin pool saturation or inversion followed by free exchange. The identification and quantification of contributions to the binding kinetics is then straightforward: in the depletion rate plot, the intercept at the vanishing free xenon concentration represents the kinetic rate coefficient for xenon detachment from the host by dissociative processes while the slope is indicative of the kinetic rate coefficient for degenerate exchange reactions. Comparing quantified kinetic rates for hyperpolarized xenon in aqueous solution reveals the high accuracy of each approach but also shows differences in the precision of the numerical results and in the requirements for prior knowledge. Because of their broad range of applicability the proposed exchange spectroscopy experiments can be readily used to unravel the kinetics of complex formation of xenon with host molecules in the various situations appearing in practice.