Mechanistic Insights into the Inhibition of Endo-β 1,4 Xyloglucan Hydrolase by a Classical Aspartic Protease Inhibitor

This is the first report of inactivation of xyloglucanase from Thermomonospora sp by pepstatin A, a specific inhibitor towards aspartic proteases. The steady state kinetics revealed a reversible, competitive, two-step inhibition mechanism with IC ₅₀ and K _i values of 3.5?±?0.5 μM and 1.25?±?0.5 μM respectively. The rate constants determined for the isomerization of EI to EI^* and the dissociation of EI* were 14.5?±?1.5?×?10^?5?s^?1 and 2.85?±?1.2?×?10^?8?s^?1 respectively, whereas the overall inhibition constant K _i ^* was 27?±?1 nM. The conformational changes induced upon inhibitor binding to xyloglucanase were monitored by fluorescence analysis and the rate constants derived were in agreement with the kinetic data. The abolished isoindole fluorescence of o-phthalaldehyde (OPTA)-labeled xyloglucanase and far UV analysis suggested that pepstatin binds to the active site of the enzyme. Our results revealed that the inactivation of xyloglucanase is due to the interference in the electronic microenvironment and disruption of the hydrogen-bonding network between the essential histidine and other residues involved in catalysis.     

X-ray spectroscopy in the EC nucleus

The probabilities P_KK of double K-shell vacancy production per K electron capture decay and per K internal conversion of ¹⁰⁹Cd and ²⁰⁷Bi have been determined by means of the double- and triple-coincidence experiments using Kα X-ray and K internal conversion. For ¹⁰⁹Cd we find P_KK(EC) = (4.2 ± 0.5) × 10⁻⁵ and P_KK(IC) = (4.32 ± 0.46) × 10⁻⁵, and for ²⁰⁷Bi, P_KK(EC) = (2.54 ± 0.50) × 10⁻⁵. The observed X-ray energy shifts of the hypersatellite Ag (Kα₁^H) X-ray and the hypersatellite Pb (Kα₁^H) X-ray lines are 545±15 eV and 1238±45 eV, respectively.     

Evidence for a newK * \bar K state at a mass of 1,530 MeV withIJ PC=01++ observed inK − p interactions at 4.2 GeV/c

Evidence is presented for a newK ^* \(\bar K\) +c.c. resonance with a mass of (1,526±6) MeV, a width of (107±15) MeV and quantum numbersIJ ^PC=01⁺⁺. We call itD′ meson. Initially it is observed as aK ^* \(\bar K\) +c.c. enhancement in the reactionsK ^? p→(K _s ⁰ K ^±π^?)Λ at 4.2 GeV/c. The isospin assignmentI=0 comes from its further observation in the reactionsK ^? p→(K _s ⁰ K ^±π^?)Σ ⁰ andK ^? p→(K _s ⁰ K ^±π^?)Σ(1,385)⁰ but not inK ^? p→(K ⁺ K ^?π^?)Σ⁺ orK ^? p→(K _s ⁰ K ^±π^?)Σ(1,385)⁺. A maximum likelihood analysis of the (K \(\bar K\) π) decay Dalitz plots in the reactionsK ^? p→(K _s ⁰ K ^±π^?) determines theJ ^PC of theD′ meson to be 1⁺⁺. A satisfactorySU(3) fit is obtained to a 1⁺⁺ nonet composed of theI-1A ₁, theI=1/2Q _A with theD(1,285) and theD′(1,526) as theI=0 members having a mixing angle close to the magic one.     

Luminescence and decay times of CsI:In+

Luminescence spectra of single crystals of CsI:In⁺ excited in the A(304 nm), B(288 nm), C(268 nm) and D(257 nm) absorption bands have been studied in the temperature range 4.2–300 K. Excitation in the A band at 4.2 K gives rise to the principal emission at 2.22 eV accompanied by a partly-overlapping weak band at 2.49 eV. An additional emission band at about 2.96 eV is observed on excitation in the B, C or D bands. Yet another emission band located at 2.67 eV is excited only in the D band. The relative intensities of the bands are very sensitive to excitation wavelength as well as to temperature. The origin of all these bands is assigned in terms of a model for the relaxed excited states (RES). All the luminescence spectra were resolved into an appropriate number of skew-Gaussian components. Moments analysis leads to a value of (1.35 ± 0.02) × 10¹³ rad s^-1 for the effective frequency (ω_eff) of lattice vibrations coupled to the RES. At the lowest temperature, the radiative decay times of each of the intracenter emission bands (2.22, 2.49 and 2.96 eV) show a slow decay ( ～ 10–100 μs) and a fast decay ( ～ 10–100 ns). The 2.96 eV band, which is assigned to an emission process which is the inverse of the D-band absorption, exhibits a single decay mode ( ～ 10 μs). The intrinsic radiative decay rates (k₁, k₂), the one-phonon transition rate (K) and the second-order spin-orbit splitting (D) for the RES responsible for the principal emission are: k₁ = (6.0±-0.3)×10³ s^-1, k₂ = (1.33±-0.06)×10⁵ s^-1, K = (2.4±-0.4)×10⁷ s^-1 and D = (13.8±-0.5) cm^-1.     

Measurement of Ar(I) and Ar(II) transition probabilities in LTE ARC plasmas

The transition probabilities of two Ar(I) lines and one Ar(II) line have been measured in emission on wall-stabilized argon arc plasmas (0·5×10⁵?p, Nm^-2?3×10⁵; 10,000?T, K?20,000; 10²²?N_e, m^-3?5×10²³) using the “method of best fit (MBF)”. The results (without line-wing correction) are for Ar(I) at 714·7 nm, A_nm=5·66×10⁵ s^-1±5%; for Ar(I) at 430·0 nm, A_nm=3·40×10⁵ s^-1±5%; for Ar(II) at 480·6 nm, A_nm=8·82×10⁷ s^-1±7%. These values were not influenced by deviations from LTE, which have been observed at electron number densities n_e?10²³ m^-3. The small uncertainties were achieved after careful corrections of different sources of error.     

Magnetic anisotropy in multilayers

Magnetic anisotropy between in-plane and out of plane magnetic alignments is studied in a variety of multilayer systems using Mössbauer spectrosopy to observe the (Fe) magnetic orientation. The surface anisotropy in Fe/Au (1 1 1) multilayers is measured as K _s = 0.9 × 10^?3 Jm^?2. In Fe/Ni multilayers the dependence of magnetic orientation on external field applied normal to the layers enables volume and interface anisotropies K _v = (?5 ± 1) × 10⁴ Jm^?3 and K _s = (?0.6 ± 0.4)× 10^?3 Jm^?2 to be evaluated. In similar applied field experiments coherent rotation of the magnetic Fe and NiFe layers in Fe/Cu/NiFe/Cu multilayers was observed for intervening Cu layer thickness x = 5 Å but independent rotation for x = 50 Å. Out of plane magnetic components are observed for DyFe₂, YFe₂ thin films and DyFe₂/YFe₂ multilayers. In fields of up to 0.25 T applied inplane only the moments of the YFe₂ film showed significant rotation.     

Observation of a narrowK s 0 K s 0 π+π− state at 1.97 GeV produced inK + p interactions at 32 GeV/c

Evidence is provided for a new resonance in theK _s ⁰ K _s ⁰ π⁺π^? system with a mass of 1.97±0.01 GeV and width 40±20 MeV. It is produced with an inclusive cross section of ～6μb in the beam fragmentation process of 4-prongK ⁺ p interactions with at least 2 associatedV ⁰'s at 32 GeV/c and decays dominantly into theK ^{* ±} (892)K _s ⁰ π^? mode.     

Magnetic hyperfine interaction in muonic indium,osmium and mercury

The magnetic hyperfine interaction in several muonic atoms has been measured. The magnetic splittings of the 1s _1/2, 2s _1/2 and 2p _1/2 muon states in the 9/2⁺ ground state of¹¹⁵In, determined by measuring muonic X rays areΔE _mag(1s _1/2,¹¹⁵In 9/2⁺)=3580±70 eVΔE _mag(2s _1/2,¹¹⁵In 9/2⁺)=525±120 eVΔE _mag(2p _1/2,¹¹⁵In 9/2⁺)=850±180 eV. The magnetic splitting of nuclearγ rays in the presence of a muon in the 1s _1/2 state yields for the 1/2^? ground state in¹⁹⁹HgΔE _mag(1s _1/2,¹⁹⁹Hg 1/2^?)=468±115 eV and the following values for the first excited 2⁺ states in the nuclei^190,192Os and²⁰⁰Hg:ΔE _mag(1s _1/2,¹⁹⁰Os 2⁺)=665± ₄₀ ⁸⁰ eVΔE _mag(1s _1/2,¹⁹²Os 2⁺)=800±80 eVΔE _mag(1s _1/2,²⁰⁰Hg 2⁺)=655± ₇₅ ¹⁰⁵ eV. These data are compared with calculations using different nuclear models.     

Contribution of the inelastic channels K − p → Yπ to the shift of the ground-state energy level of kaonic hydrogen

The contribution of the inelastic channels K ^? p → Yπ, where Yπ = Σ^? π ⁺, Σ ⁺ π ^?, Σ ⁰ π ⁰, or λ⁰ π ⁰, kinematically allowed at the K ^? p threshold to the S-wave scattering length of elastic K ^? p scattering, as well as the shift of the ground-state energy of kaonic hydrogen, is calculated. The result, δa ₀ ^K?p = ?0.037 ± 0.010 fm and δε _1s = 15 ± 4 eV, will be important for the theoretical analysis of the expected data from the experiments scheduled by the DEAR and SIDDHARTA Collaborations at the end of 2006.     

Observation of kaonic hydrogen atom X-ray

We successfully observed clear K-series kaonic hydrogen X-rays for the first time taking advantage of two charged pions tagging technique and a gaseous hydrogen target. The strong-interaction energy shift and width of 1s state of K ⁻p atom were determined to be ΔE _1s = -323 ± 63 (statistical) ± 11 (systematic) eV and Г_1s = 407 ± 208 ± 100 eV. Our result means that the K ⁻p strong interaction near threshold is repulsive and the long-standing kaonic hydrogen puzzle is solved. This revised version was published online in August 2006 with corrections to the Cover Date.     

Line strengths,spin-splittings,and forbidden transitions in the (101) band of 14N16O2

Measurements of line strengths in the (101) and (111)-(010) bands of ¹⁴N¹⁶O₂ have been made at a resolution of 0.02 cm^?1 in the region 2863 to 2934 cm^?1. The strength data in the (101) band were analyzed to determine a vibrational band strength and coefficients of the F factor. Each subband for K_?1 ≤ 9 was analyzed separately and all the F-factor coefficients in terms of the rotational quantum number, N, were found to be too small to be of significance. However, F was found to be dependent on K_?1 and the experimentally determined subband strengths were least-squares fitted to the expression S_v⁰·F, where S_v⁰ = 68.3 cm^?2 atm^?1 at 296 K and F = 1 + (2.899 × 10^?3)K_?1 + (4.08 × 10^?3)K_?1² ? (2.34 × 10^?4)K_?1³. The integrated strengths for the (101) and (111)-(010) bands were found to be 70.9 ± 2.3 and 2.7 ± 0.3 cm^?2 atm^?1 at 296 K, respectively. Also included in this study are measurements of line center positions in the two bands and spin-splittings in the (101) band. Recent frequency measurements of lines with K_?1 ≤ 8 in the (101) band have been made at a resolution of 0.0033 cm^?1 by V. Dana and J. P. Maillard (J. Mol. Spectrosc.71, 1–4) (1978)) for the region above 2889 cm^?1 and our values are in excellent agreement with theirs. Separations of the split lines measured in this work (K_?1 ≤ 10) agree well with calculated values using expressions which include the η_aaaaK_?1⁴ term with η′_aaaa = ?1.70 ± 0.15 × 10^?4 cm^?1 as derived for the (101) state. Three forbidden (ΔN ≠ ΔJ, ΔK_?1 = 0) transitions in the (101) band were observed with their identifications based on the agreement between measured and calculated line positions and strengths.     

Pressure dependent optical absorption edge shift and compressibility of CdCr2Se4 single crystals

The pressure shift of the optical absorption edge (dE_g/dp = (1.1 ± 0.1) × 10^?6 eV bar^?1) and the compressibility (κ = (1.3 ± 0.) × 10^?6 bar^?1) of single crystalline CdCr₂Se₄ have been measured at ambient temperature. These data suggest an interpretation of the fundamental absorption in terms of either p → p interband or p → localized d charge transfer transitions, but exclude excitations involving s-band states.     

An influence of deposition temperature on structural,optical and electrical properties of sprayed ZnO thin films of identical thickness

Nanocrystalline ZnO thin films were deposited at different temperatures (T_s = 325 °C–500 °C) by intermittent spray pyrolysis technique. The thickness (300 ± 10 nm) independent effect of T_s on physical properties was explored. X-Ray diffraction analysis revealed the growth of wurtzite type polycrystalline ZnO films with dominant c-axis orientation along [002] direction. The crystallite size increased (31 nm–60 nm) and optical band-gap energy decreased (3.272 eV–3.242 eV) due to rise in T_s. Scanning electron microscopic analysis of films deposited at 450 °C confirmed uniform growth of vertically aligned ZnO nanorods. The films deposited at higher T_s demonstrated increased hydrophobic behavior. These films exhibited high transmittance (>91%), low dark resistivity (～10^?2 Ω-cm), superior figure of merit (～10^?3 Ω^?1) and low sheet resistance (～10² Ω/□). The charge carrier concentration (η -/cm³) and mobility (μ – cm²V^?1s^?1) are primarily governed by crystallinity, grain boundary passivation and oxygen desorption effects.     

K1±(890) production in 205 GeV/c pp interactions

Using data obtained from an exposure of the Fermilab 30-inch hydrogen bubble chamber to a 205 GeVc proton beam, we have studied K⁰π^± correlations and the inclusive production of K¹(890). Based on an analysis of the K_S⁰π^± effective mass distribution, we find a 95% confidence level upper limit of 0.22 K^1±(890) per inelastic event. Possible systematic effects in the experimental determination of the ?⁰ production rate due to the Kπ correlation are discussed. Our result for K¹ production at √s = 19.7 GeV is incompatible with that obtained in a recent ISR experiment at √s = 53 GeV.     

Isomer shift in BaSnO3 under a pressure up to 15 GPa

The dependence of the unit cell volume of BaSnO₃ on the pressure up to 15 GPa has been investigated and the constants of the Murnaghan equation of state B ₀ = 178.39 ± 4.09 GPa and B′₀ = 4.68 ± 0.56 have been obtained using the X-ray diffraction method. The change of the isomer shift (IS) in BaSnO₃ with a variation in the pressure P has been examined using the gamma resonance method. This quantity is ?IS(P)/?P = ?(0.00474 ± 0.0002) mm s^?1 GPa^?1 or, taking into account the measurements of the unit cell parameter under pressure, ?IS/?L = 1.42 mm s^?1Å^?1, where L is the tin-oxygen distance.     

X-rays from pionic 3He

Pionic X-ray energies, lorentzian widths, and relative intensities have been measured for the transitions in liquid ³He. The pion-nucleus interaction is found to result in an attractive shift of the 1s level of 27 ± 5 eV and in a lorentzian width of 65 ±12 eV. The measured K_β to K_α intensity ratio is 1.05±0.07.     

A measurement of the KL-KS mass difference from the charge asymmetry in semi-leptonic kaon decays

The change asymmetry in semi-leptonic kaon decays has been measured as a function of the kaon lifetime. High statistics data of K_e3⁰ and K_μ3⁰ decay modes agree with each other and with the general expectation of the CP violation phenomenology together with the ΔS?ΔQ rule. The K_L-K_S mass difference obtained is Δm = (0.533 ± 0.004) × 10¹⁰ s^?1.     

Temperature dependence of the energy gap of MgxZn1−xTe semiconductors alloys

Wavelength-modulation spectroscopy is used to obtain the temperature dependence of the near band gap reflectivity spectrum E_o of Mg_xZn_1?xTe ternary semiconducting alloys. Results are given in the range 80–100 K for the cubic materials: 0〈x〈0.5. The analysis of the line shapes as a function of x and T confirms the hypothesis of an exciton bound to the complex defect associated with zinc vacancy, as ZnTe. The E_o(x) curve is parabolic. The bowing parameter is C=0.45 ± 0.1 eV at 80 K, C=0.6 ± 0.1 eV at 300 K. Within experimental scattering the temperature coefficient dE₀dT is nearly constant with x:-4.5±0.3 × 10^?4eVK^?1. This data is smaller than the value calculated in the literature for ZnTe from pseudo potential method.     

Simulation of the thermal decomposition of the C9H10 methylcubane molecule

The thermal stability of the C₉H₁₀ methylcubane molecule was studied over the temperature range 1100–2100 K by molecular dynamics simulation with the tight binding potential. The temperature dependence of its lifetime to the decomposition moment was determined. The activation energy E _a = 1.7 ± 0.2 eV and frequency factor A = 10^{15.63 ± 0.53} s^?1 of the Arrhenius equation were found. Possible channels and final products of molecule decomposition were studied.     

On the natural width of the hypersatellite lines

The natural width of a hypersatellite line (K ^?2→K ^?1 L ^?1 transition) has been measured for the first time. In the case of Cu (Z=29) this width has been found equal toΓ = 5 eV, i.e. much larger than that of the diagram (K ^?1→L ^?1) line. This result follows a proposed empirical law assuming this width to be equal to 3Γ _K+Γ_L.