Pyruvate aldolases from Pfam family PF03328, recently described to be able to use hydroxypyruvic acid as nucleophile substrate, were shown to also catalyse aldol adducts formation from 2‐oxobutyric ...acid. A 1H NMR‐based assay was used to screen 21 aldolases for their activity towards 2‐oxobutyric acid and to predict their stereoselectivity at position 3 of the aldol adducts. The best biocatalysts were then proved to be strictly (3S)‐selective. Contrary to known enzymes from this family that are seldom stereoselective at position 4, three aldolases were highlighted as allowing a selective access to (3S,4R) or (3S,4S) aldols. Seven 3‐deoxy‐3‐methylulosonic acids never described before were finally prepared and isolated with good yields and stereoselectivities.
The neutron Electric Dipole Moment (nEDM) is a probe for physics beyond the Standard Model. A report on the nEDM measurement performed at the Paul Scherrer Institute (Switzerland) is given. A neutron ...spin analyzer designed to simultaneously detect both neutron spin states is presented.
Efficient, biocompatible, stereospecific strategies were developed to prepare eight probes to assay transketolase (TK) variants with new substrate specificities. The structure of these probes ...combines a sugar moiety (D‐threo or L‐erythro ketose, or D‐threo aldose) with the side chain of an amino acid (Ala, Leu, Val, Met, Thr) for in vivo detection of new TK activities using amino acid auxotrophs. To obtain D‐threo ketose probes, biocatalysts, such as transketolase and fructose‐6‐phosphate aldolase Ala129Ser, were used whereas L‐erythro ketoses and D‐threo aldose probes were synthesized by the way of organocatalysis or Sharpless dihydroxylation as sustainable alternative key steps to biocatalysis.
The right combination: Catalytic, biocatalytic, and pure synthetic methods are implemented for the preparation of eight probes. These compounds consist of a sugar moiety (D‐threo ketose, L‐erythro ketose, or D‐threo aldose) bound to an amino acid side chain (Ala, Leu, Val, Met, or Thr). They could be used for in vivo assaying new transketolases using amino acid auxotrophs.
The reactor antineutrino anomaly might be explained by the oscillation of reactor antineutrinos toward a sterile neutrino of eV mass. In order to explore this hypothesis, the STEREO experiment ...measures the antineutrino energy spectrum in six different detector cells covering baselines between 9 and 11 m from the compact core of the ILL research reactor. In this Letter, results from 66 days of reactor turned on and 138 days of reactor turned off are reported. A novel method to extract the antineutrino rates has been developed based on the distribution of the pulse shape discrimination parameter. The test of a new oscillation toward a sterile neutrino is performed by comparing ratios of cells, independent of absolute normalization and of the prediction of the reactor spectrum. The results are found to be compatible with the null oscillation hypothesis and the best fit of the reactor antineutrino anomaly is excluded at 97.5% C.L.
We present a magnetometer based on optically pumped Cs atoms that measures the magnitude and direction of a 1 μT magnetic field. Multiple circularly polarized laser beams were used to probe the free ...spin precession of the Cs atoms. The design was optimized for long-time stability and achieves a scalar resolution better than 300 fT for integration times ranging from 80 ms to 1000 s. The best scalar resolution of less than 80 fT was reached with integration times of 1.6 to 6 s. We were able to measure the magnetic field direction with a resolution better than 10 μrad for integration times from 10 s up to 2000 s.
We report a new limit on a possible short range spin-dependent interaction from the precise measurement of the ratio of Larmor precession frequencies of stored ultracold neutrons and Hg199 atoms ...confined in the same volume. The measurement was performed in a ∼1μT vertical magnetic holding field with the apparatus searching for a permanent electric dipole moment of the neutron at the Paul Scherrer Institute. A possible coupling between freely precessing polarized neutron spins and unpolarized nucleons of the wall material can be investigated by searching for a tiny change of the precession frequencies of neutron and mercury spins. Such a frequency change can be interpreted as a consequence of a short range spin-dependent interaction that could possibly be mediated by axions or axion-like particles. The interaction strength is proportional to the CP violating product of scalar and pseudoscalar coupling constants gSgP. Our result confirms limits from complementary experiments with spin-polarized nuclei in a model-independent way. Limits from other neutron experiments are improved by up to two orders of magnitude in the interaction range of 10−6<λ<10−4m.
We describe a spin-echo method for ultracold neutrons (UCNs) confined in a precession chamber and exposed to a |B0|=1 μT magnetic field. We have demonstrated that the analysis of UCN spin-echo ...resonance signals in combination with knowledge of the ambient magnetic field provides an excellent method by which to reconstruct the energy spectrum of a confined ensemble of neutrons. The method takes advantage of the relative dephasing of spins arising from a gravitationally induced striation of stored UCNs of different energies, and also permits an improved determination of the vertical magnetic-field gradient with an exceptional accuracy of 1.1 pT/cm. This novel combination of a well-known nuclear resonance method and gravitationally induced vertical striation is unique in the realm of nuclear and particle physics and should prove to be invaluable for the assessment of systematic effects in precision experiments such as searches for an electric dipole moment of the neutron or the measurement of the neutron lifetime.
5-
O-Coumarinyl-
d-xylulose was studied as a fluorogenic substrate for the stereospecific assay of transketolase enzyme. Enzymatic C2–C3 cleavage released an α-hydroxyl, β-coumarinyl substituted ...aldehyde. Although the subsequent β-elimination step was rate limiting under chemical or enzymatic catalysis, we detected a TK activity as low as 0.7
mIU. To improve the fluorescence signal release, kinetic and product distribution analyses of this reaction were performed by LC/UV/MS coupling.
PDF
