Gaspard Huber

Cell uptake of a biosensor detected by hyperpolarized 129Xe NMR: The transferrin case

For detection of biological events in vitro, sensors using hyperpolarized (129)Xe NMR can become a powerful tool, provided the approach can bridge the gap in sensitivity. Here we propose constructs based on the non-selective grafting of cryptophane precursors on holo-transferrin. This biological system was chosen because there are many receptors on the cell surface, and endocytosis further increases this density. The study of these biosensors with K562 cell suspensions via fluorescence microscopy and (129)Xe NMR indicates a strong interaction, as well as interesting features such as the capacity of xenon to enter the cryptophane even when the biosensor is endocytosed, while keeping a high level of polarization. Despite a lack of specificity for transferrin receptors, undoubtedly due to the hydrophobic character of the cryptophane moiety that attracts the biosensor into the cell membrane, these biosensors allow the first in-cell probing of biological events using hyperpolarized xenon.

A Water-Soluble Xe@cryptophane-111 Complex Exhibits Very High Thermodynamic Stability and a Peculiar 129Xe NMR Chemical Shift

The known xenon-binding (±)-cryptophane-111 (1) has been functionalized with six [(η(5)-C(5)Me(5))Ru(II)](+) ([Cp*Ru](+)) moieties to give, in 89% yield, the first water-soluble cryptophane-111 derivative, namely [(Cp*Ru)(6)1]Cl(6) ([2]Cl(6)). [2]Cl(6) exhibits a very high affinity for xenon in water, with a binding constant of 2.9(2) × 10(4) M(-1) as measured by hyperpolarized (129)Xe NMR spectroscopy. The (129)Xe NMR chemical shift of the aqueous Xe@[2](6+) species (308 ppm) resonates over 275 ppm downfield of the parent Xe@1 species in (CDCl(2))(2) and greatly broadens the practical (129)Xe NMR chemical shift range made available by xenon-binding molecular hosts. Single crystal structures of [2][CF(3)SO(3)](6)·xsolvent and 0.75H(2)O@1·2CHCl(3) reveal the ability of the cryptophane-111 core to adapt its conformation to guests.

Cryptophane-xenon complexes in organic solvents observed through NMR spectroscopy.

The interaction of xenon with cryptophane derivatives is analyzed by NMR by using either thermal or hyperpolarized noble gas. Twelve hosts differing by their stereochemistry, cavity size, and the nature and the number of the substituents on the aromatic rings have been included in the study, in the aim of extracting some clues for the optimization of (129)Xe-NMR based biosensors derived from these cage molecules. Four important properties have been examined: xenon-host binding constant, in-out exchange rate of the noble gas, chemical shift, and relaxation of caged xenon. This work aims at understanding the main characteristics of the host-guest interaction in order to choose the best candidate for the biosensing approach. Moreover, rationalizing xenon chemical shift as a function of structural parameters would also help for setting up multiplexing applications. Xenon exhibits the highest affinity for the smallest cryptophane, namely cryptophane-111, and a long relaxation time inside it, convenient for conservation of its hyperpolarization. However, very slow in-out xenon exchange could represent a limitation for its future applicability for the biosensing approach, because the replenishment of the cage in laser-polarized xenon, enabling a further gain in sensitivity, cannot be fully exploited.

Towards thrombosis-targeted zeolite nanoparticles for laser-polarized 129Xe MRI

The synthesis and functionalisation of zeolite nanoparticles designed for laser-polarized 129Xe NMR experiments in solution are described. These nanoparticles were functionalized by using original synthesis pathways through semicarbazide COCHO chemistry in order to ensure anchoring of a peptide for targeting biological receptors and attachment of PEG chains for in vivo experiments. Results demonstrated that accessibility of the dissolved noble gas to the micropores was maintained after functionalization. γ Scintigraphy with 111In linked to the zeolite particles has been investigated in order to follow the behaviour of the zeolite nanoparticles in mice. These preliminary 111In scintigraphy experiments showed the localization of the nanoparticles after injection in mice and their biodistribution, as a first proof-of-concept towards in vivo129Xe MRI.

Single‐Scan Multidimensional NMR Analysis of Mixtures at Sub‐Millimolar Concentrations by using SABRE Hyperpolarization

Signal amplification by reversible exchange (SABRE) is a promising method to increase the sensitivity of nuclear magnetic resonance (NMR) experiments. However, SABRE-enhanced (1)H NMR signals are short lived, and SABRE is often used to record 1D NMR spectra only. When the sample of interest is a complex mixture, this results in severe overlaps for (1)H spectra. In addition, the use of a co-substrate, whose signals may obscure the (1) H spectra, is currently the most efficient way to lower the detection limit of SABRE experiments. Here, we describe an approach to obtain clean, SABRE-hyperpolarized 2D (1)H NMR spectra of mixtures of small molecules at sub-millimolar concentrations in a single scan. The method relies on the use of para-hydrogen together with a deuterated co-substrate for hyperpolarization and ultrafast 2D NMR for acquisition. It is applicable to all substrates that can be polarized with SABRE.

Interaction of xenon with cucurbit[5]uril in water.

There is growing interest in the development of molecular containers dedicated to gas trapping in water. Cucurbit[5]uril (CB[5]), the smallest member of a glycoluril macrocycles family (Figure 1), is able to interact with a large array of guest molecules, among which noble gases. The interaction of cucurbit[6]uril (CB[6]) with xenon, a promising noble gas for molecular imaging applications, was investigated in aqueous solution containing acids or salts designed to increase the solubility of the host molecule. However, it was shown that cations interact with the partial charges on oxygen atoms, while apolar molecules are encapsulated in the hydrophobic cavity of cucurbiturils. We already evidenced that the presence of these acids or salts alters the xenon in/out exchange for CB[6] (Figure S1 of the Supporting Information), confirming results obtained with CB*[6] (Figure 1a). In the literature, observation of xenon binding by cucurbituril derivatives in pure water was previously rendered possible only by grafting substituents, giving MeCB[5] and CB*[6] (Figure 1a). In order to understand the thermodynamics and kinetics of xenon binding in CB[5] , it seemed thus useful to study samples in deionized water. Although xenon binding in a crystalline form of native CB[5] was observed, no quantitative kinetics and thermodynamics data were reported for CB[5] or a derivative in aqueous solution. Herein, taking advantage of a solubility not so low in pure water, we show that CB[5] spontaneously incorporates xenon at 316 K with a quite high binding constant and a low in/out exchange rate. This exchange rate is even measurable at 293 K. In the presence of xenon, the H NMR spectrum of a D2O solution of CB[5] exhibits two series of signals characteristic of a slow exchange between two environments, one with and the other without xenon (Figure 1c). The Xe spectrum shows two signals (Figure 1d) also denoting a slow exchange. The signal at 196 ppm is assigned to free xenon in water and the signal at 225 ppm to xenon encapsulated in CB[5] (Xe@CB[5]), at a chemical shift close to that already observed in a crystal form of the molecule. The second signal exhibits a linear dependence of chemical shift with temperature between 277 and 334 K, with a slope of 117 3 ppbK 1 (Figure S2, Supporting Information). This may easily be explained by a deeper exploration of the CB[5] cavity by xenon in areas affected by the magnetic anisotropy effect of the carbonyl groups at higher temperatures. The xenon in/out exchange is also slow on the xenon longitudinal relaxation (T1) timescale. The T1 value of trapped Xe increases from 15 3 s to 28 5 s when temperature varies from 277 K to 315 K. The rather long T1 confirms previous results on CB*[6] and reflects the weakness of the proton– xenon dipolar interaction in a system where protons point outwards. The observed T1 value cannot be entirely explained by this mechanism, and other relaxation mechanisms such as chemical shift modulation must also be efficient. To our knowledge, CB[5] is the first example of a host molecule with which the xenon in/out exchange is slow on the relaxation timescale. This kinetics was characterized in more detail through gas-release experiments. Proton NMR spectra were recorded at repeated time intervals, in a situation where dissolved xenon tends to equilibrate with gaseous xenon. Figure 1. a) General formula of the cucurbiturils cited in the text. CB[5]: n=5, R=R’=H; CB[6]: n=6, R=R’=H. MeCB[5]: n=5, R=R’=CH3; CB*[6]: n=6, RR’= (CH2)4. b) Space-fill representation of a crystal structure of CB[5] , with both facing glycoluril units and attached methylene groups removed for clarity. A xenon atom is superimposed in the center of the molecule showing the geometry of the complex. c) H NMR spectrum of a 5.4 mm solution in D2O of CB[5] under 2.5 atm of xenon at 316 K. Signals assigned to CB[5] entrapping a xenon atom are denoted by *, while those standing for xenon-free cages are denoted by *. d) Xe NMR spectrum of a 0.25 mm D2O solution of CB[5] under 6 atm of xenon at 316 K at thermodynamic equilibrium, 20500 scans with a repetition rate of 3.8 s, Fourier transformed with a 6 Hz line broadening.

Nuclear Spin-Noise Spectra of Hyperpolarized Systems†

Spin-noise appeal: Detection of NMR spin-noise is very appealing when dilute hyperpolarized species are considered. Continuous monitoring of the noise absorption at the Larmor frequency enables determination of T(1) and T(2)*, independently of the static magnetic field. An inductively coupled microcoil located inside the NMR tube (see picture) allows acquisition of (129)Xe spin-noise spectra without radio-frequency excitation.

Observation of Noise‐Triggered Chaotic Emissions in an NMR‐Maser

We report a new phenomenon observed when the magnetization of dissolved hyperpolarized (129)Xe is intense and opposite to the Boltzmann magnetization. Without radio-frequency (rf) excitation, the system spontaneously emits a series of rf bursts characterized by very narrow bandwidths (0.03 Hz at 138 MHz). This chaotic NMR-maser illustrates the increase in the complexity of spin dynamics at high magnetization levels by unveiling an inhomogeneous spatial organization of the xenon magnetization and an apparent dependence of the xenon transverse relaxation time on its polarization and/or on time.

On the tuning of high-resolution NMR probes.

Three optimum conditions for the tuning of NMR probes are compared: the conventional tuning optimum, which is based on radio-frequency pulse efficiency, the spin noise tuning optimum based on the line shape of the spin noise signal, and the newly introduced frequency shift tuning optimum, which minimizes the frequency pushing effect on strong signals. The latter results if the radiation damping feedback field is not in perfect quadrature to the precessing magnetization. According to the conventional RLC (resistor–inductor–capacitor) resonant circuit model, the optima should be identical, but significant deviations are found experimentally at low temperatures, in particular on cryogenically cooled probes. The existence of different optima with respect to frequency pushing and spin noise line shape has important consequences on the nonlinearity of spin dynamics at high polarization levels and the implementation of experiments on cold probes.

The GC-MS Analysis of Organic Intermediates from the TiO2 Photocatalytic Treatment of Water Contaminated by Lindane (1α,2α,3/3,4α,5α,6β- hexachlorocyclohexane)+

Abstract Elimination from water of lindane, a common soil insecticide whose occurrence in groundwaters used as sources of drinking water is of great concern, was shown to be achieved by the TiO2-UV system. Gas chromatography-mass spectrometry analyses of a photocatalytically treated aqueous solution initially containing 3.44 mmol/L (=1g/L) lindane indicated that several specified or unspecified isomers were formed as intermediate products and pertained to the following chemical categories: chlorocyclohexanes, chlorocyclohexenes, chlorobenzenes, chlorophenols, chloropropanes and chloropropanones, as well as a pentachlorocyclohexenone isomer and 3,4dichloro-2,5-furandione (presumably produced by dehydration of dichlorobutenedioic acid during the analysis). Compared to lindane, these intermediates were generally oxidized and most of them contained a smaller number of xenobiotic C-Cl bonds. However, their nature showed that chlorine and hydrogen atoms were not only abstracted from the CHCl groups constituting lindane but also added to them. Accordingly, this proved that the reduction of the organics occurred in addition to their oxidation. Some conclusions concerning the lindane degradation pathways are also presented.