Dynamic nuclear polarization of amyloidogenic peptide nanocrystals: GNNQQNY, a core segment of the yeast prion protein Sup35p

Dynamic nuclear polarization (DNP) permits a approximately 10(2)-10(3) enhancement of the nuclear spin polarization and therefore increases sensitivity in nuclear magnetic resonance (NMR) experiments. Here, we demonstrate the efficient transfer of DNP-enhanced (1)H polarization from an aqueous, radical-containing solvent matrix into peptide crystals via (1)H-(1)H spin diffusion across the matrix-crystal interface. The samples consist of nanocrystals of the amyloid-forming peptide GNNQQNY(7-13), derived from the yeast prion protein Sup35p, dispersed in a glycerol-water matrix containing a biradical polarizing agent, TOTAPOL. These crystals have an average width of 100-200 nm, and their known crystal structure suggests that the size of the biradical precludes its penetration into the crystal lattice; therefore, intimate contact of the molecules in the nanocrystal core with the polarizing agent is unlikely. This is supported by the observed differences between the time-dependent growth of the enhanced polarization in the solvent versus the nanocrystals. Nevertheless, DNP-enhanced magic-angle spinning (MAS) spectra recorded at 5 T and 90 K exhibit an average signal enhancement epsilon approximately 120. This is slightly lower than the DNP enhancement of the solvent mixture surrounding the crystals (epsilon approximately 160), and we show that it is consistent with spin diffusion across the solvent-matrix interface. In particular, we correlate the expected DNP enhancement to several properties of the sample, such as crystal size, the nuclear T(1), and the average (1)H-(1)H spin diffusion constant. The enhanced (1)H polarization was subsequently transferred to (13)C and (15)N via cross-polarization, and allowed rapid acquisition of two-dimensional (13)C-(13)C correlation data.     

Kinetic and galvanostatic studies of a polymer electrolyte for lithium-ion batteries

Quaternary polymer electrolyte (PE) based on poly(acrylonitrile) (PAN), 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (EMImBF₄), sulfolane (TMS) and lithium hexafluorophosphate salt (LiPF₆) (PAN-EMImBF₄-sulfolane-LIPF₆) was prepared by the casting technique. Obtained PE films of ca. 0.2–0.3 mm in thickness showed good mechanical properties. They were examined using scanning electron microscopy (SEM), thermogravimetry (TGA, DSC), the flammability test, electrochemical impedance spectroscopy (EIS) and galvanostatic charging/discharging. SEM images revealed a structure consisting of a polymer network (PAN) and space probably occupied by the liquid phase (LiPF₆ + EMImBF₄ + sulfolane). The polymer electrolyte in contact with an outer flame source did not ignite; it rather underwent decomposition without the formation of flammable products. Room temperature specific conductivity was ca. 2.5 mS cm^?1. The activation energy of the conding process was ca. 9.0 kJ mol^?1. Compatibility of the polymer electrolyte with metallic lithium and graphite anodes was tested applying the galvanostatic method. Charge transfer resistance for the C₆Li → Li⁺ + e^? anode processes, estimated from EIS curve, was ca. 48 Ω. The graphite anode capacity stabilizes at ca. 350 mAh g^?1 after the 30th cycle (20 mA g^?1).     

Preequilibrium α-emission in the Au(p,αx)-reaction at Ep = 72 MeV

Proton-induced α-spectra from ¹⁹⁷Au have been measured at E_p = 72.3 MeV and the angle-integrated cross section is compared to an exciton model Monte-Carlo calculation and to the spectral distribution of α-particles emitted after the absorption of negative pions at rest.     

External cavity diode lasers with E-beam written silicon diffraction gratings

Performance of external cavity diode lasers with silicon gratings produced by E-beam writing and subsequent reactive ion etching is described. Optical amplifiers used in the experiments were based on single quantum well heterostructures grown by molecular beam epitaxy. The lasers were set up in the Littrow configuration and have been designed to allow for wavelength tuning in the range centred at 960 nm.     

New157Lu isomer

The new low spin isomeric state of¹⁵⁷Lu (probably s_1/2) with T_1/2=9.6(8) s and E_±=4925(5) keV was found in experiments on YASNAPP-2 ISOL facility. The previously known isomer of¹⁵⁷Lu (T_1/2=4.75(10) s,_±=4998(5) keV) lies 32(2) keV higher than the new one.On leave from the M. Curie-Sklodowska University, Lublin, Poland     

1,3‐Dihydro‐1‐hydroxy‐3‐morpholin‐4‐yl‐2,1‐benzoxaborole: product of the reaction of o‐formylphenylboronic acid with morpholine

o‐Formylphenylboronic acid reacts with morpholine to form 1,3‐dihydro‐1‐hydroxy‐3‐morpholin‐4‐yl‐2,1‐benzoxaborole. The typical hydrogen‐bonded dimer motif with a planar benzoxaborole fragment has been obtained in the solid state. Copyright © 2005 John Wiley & Sons, Ltd.