•Xylanase Tx-xyn11 catalyses transxylosylation reactions with polyphenolic alcohols.•Modelling was developed to investigate Tx-xyn11-restricted specificity for acceptors.•Residue W126 from the ...aglycone subsite is involved in acceptor specificity.•Mutant W126A displayed improved transxylosylation with benzyl alcohol.
Xylanases Tx-xyn10 and Tx-xyn11 were compared for their transxylosylation abilities in the presence of various acceptors. Tx-xyn10 exhibited a broad specificity for various acceptors, whereas xylanase Tx-xyn11 catalysed transxylosylation reactions only in presence of polyphenolic acceptors. A modelling approach was developed to study the molecular bottlenecks into the active site of the enzyme that could be responsible for this restricted specificity. The glycosyl-enzyme intermediate of Tx-xyn11 was modelled, and a rotamer of the Y78 residue was integrated. In silico mutations of some residues from the (+1) and (+2) subsites were tested for the deglycosylation step in the presence of non-polyphenolic acceptors. The results indicated that the mutant W126A was able to use aliphatic alcohols and benzyl alcohol as acceptors for transxylosylation. Experimental validation was tested by mutating the xylanase Tx-xyn11 at position W126 into alanine. The specific activity and catalytic efficiency of the W126A mutant during the hydrolysis of xylans decreased by 2-fold and 4-fold, respectively, compared to wild-type xylanase. Among tested acceptors, transxylosylation catalysed by mutant W126A was improved with benzyl alcohol leading to a 2-fold higher concentration of benzyl xylobioside, as predicted by in silico mutation. This improved transxylosylation in the presence of benzyl alcohol leading to higher synthesis of benzyl xylobioside could likely be explained by lowest steric hindrance in the aglycone subsite of the mutated xylanase. No secondary hydrolysis of benzyl xylobioside occurred for both wild-type and mutant xylanases. Finally, our results demonstrated that the modelling approach was limited and that accounting for protein dynamics can lead to improved models.
Low gain avalanche detectors can measure charged particle fluences with high speed and spatial precision, and are a promising technology for radiation monitoring and dosimetry. A detector has been ...tested in a medical linac where single particles were observed with a time resolution of 50 ps. The integrated response is similar to a standard ionising chamber but with a spatial precision twenty times finer, and a temporal precision over 100 million times better, with the capability to measure the charge deposited by a single linac pulse. The unprecedented resolving power allows the structure of the ∼3 μs linac pulses to be viewed and the 350 ps sub-pulses in the train to be observed.
Lipase-catalyzed synthesis of xylo-oligosaccharides esters from pure xylobiose, xylotriose and xylotetraose in the presence of vinyl laurate was investigated. The influence of different experimental ...parameters such as the loading of lipase, the reaction duration or the use of a co-solvent was studied and the reaction conditions were optimized with xylobiose. Under the best conditions, a regioselective esterification occurred to yield a monoester with the acyl chain at the OH-4 of the xylose unit at the non-reducing end. Surface-active properties of these pure xylo-oligosaccharides fatty esters have been evaluated. They display interesting surfactant activities that differ according to the degree of polymerization (DP) of the glycone moiety.
Display omitted
•Lipase N435 can catalyze acylation of xylo-oligosaccharides with vinyl laurate.•Xylobiose, xylotriose and xylotetraose laurate monoesters are produced.•Regioselective acylation at the OH-4 position of the non-reducing end xylose unit.•Acylation yields decrease with the degree of polymerization of xylo-oligosaccharides.•Degree of polymerization of the glycone moiety impacts the surfactant activities.
A
bstract
This study focuses on hard diffractive events produced in proton-proton collision at LHC exhibiting one intact proton in the final state which can be tagged by forward detectors. We report ...prospective results on the W boson charge asymmetry measured for such events, which allow to constrain the quark diffractive density functions in the Pomeron.
Ultra Fast Silicon Detectors (UFSD) are sensors optimized for timing measurements employing a thin multiplication layer to increase the output signal. A multipurpose read-out board hosting a ...low-cost, low-power fast amplifier was designed at the University of Kansas and tested at the European Organization for Nuclear Research (CERN) using a 180 GeV pion beam. The amplifier has been designed to read out a wide range of detectors and it was optimized in this test for the UFSD output signal. In this paper we report the results of the experimental tests using 50 μm thick UFSD with a sensitive area of 1.4mm2. A timing precision below 30 ps wasachieved.
The TOTEM experiment at the LHC has performed the first measurement at
s
=
13
TeV
of the
ρ
parameter, the real to imaginary ratio of the nuclear elastic scattering amplitude at
t
=
0
, obtaining the ...following results:
ρ
=
0.09
±
0.01
and
ρ
=
0.10
±
0.01
, depending on different physics assumptions and mathematical modelling. The unprecedented precision of the
ρ
measurement, combined with the TOTEM total cross-section measurements in an energy range larger than
10
TeV
(from 2.76 to
13
TeV
), has implied the exclusion of all the models classified and published by COMPETE. The
ρ
results obtained by TOTEM are compatible with the predictions, from other theoretical models both in the Regge-like framework and in the QCD framework, of a crossing-odd colourless 3-gluon compound state exchange in the
t
-channel of the proton–proton elastic scattering. On the contrary, if shown that the crossing-odd 3-gluon compound state
t
-channel exchange is not of importance for the description of elastic scattering, the
ρ
value determined by TOTEM would represent a first evidence of a slowing down of the total cross-section growth at higher energies. The very low-|
t
| reach allowed also to determine the absolute normalisation using the Coulomb amplitude for the first time at the LHC and obtain a new total proton–proton cross-section measurement
σ
tot
=
(
110.3
±
3.5
)
mb
, completely independent from the previous TOTEM determination. Combining the two TOTEM results yields
σ
tot
=
(
110.5
±
2.4
)
mb
.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Several tetraalkylphosphonium and tetraalkylammonium salts containing xyloside- and xylobioside-based anionic moieties have been prepared. Two stereoselective routes have been developed: i) a ...chemical pathway in four steps from D-xylose, and ii) a chemoenzymatic pathway directly from biomass-derived xylans. These salts displayed interesting properties as ionic liquids. Their structures have been correlated to their thermal properties (melting, glass transition and decomposition temperatures).
Display omitted
•ILs were synthesized through chemical and/or enzymatic reactions from D-xylose or directly from biomass-derived xylan.•Various salts containing phosphonium or ammonium cations and xyloside- and xylobioside-based anionic moieties are proposed.•The physicochemical properties of ILs are studied as a function of the different anion/cation associations.•The hydrophilic lipophilic balance (HLB) of the anionic part seems to influence partially their physicochemical properties.
The TOTEM collaboration has measured the proton–proton total cross section at
s
=
13
TeV
with a luminosity-independent method. Using dedicated
β
∗
=
90
m
beam optics, the Roman Pots were inserted ...very close to the beam. The inelastic scattering rate has been measured by the T1 and T2 telescopes during the same LHC fill. After applying the optical theorem the total proton–proton cross section is
σ
tot
=
(
110.6
±
3.4
) mb, well in agreement with the extrapolation from lower energies. This method also allows one to derive the luminosity-independent elastic and inelastic cross sections:
σ
el
=
(
31.0
±
1.7
)
mb
and
σ
inel
=
(
79.5
±
1.8
)
mb
.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The TOTEM collaboration at the CERN LHC has measured the differential cross-section of elastic proton–proton scattering at
s
=
8
TeV
in the squared four-momentum transfer range
0.2
GeV
2
<
|
t
|
<
...1.9
GeV
2
. This interval includes the structure with a diffractive minimum (“dip”) and a secondary maximum (“bump”) that has also been observed at all other LHC energies, where measurements were made. A detailed characterisation of this structure for
s
=
8
TeV
yields the positions,
|
t
|
dip
=
(
0.521
±
0.007
)
GeV
2
and
|
t
|
bump
=
(
0.695
±
0.026
)
GeV
2
, as well as the cross-section values,
d
σ
/
d
t
dip
=
(
15.1
±
2.5
)
μ
b
/
GeV
2
and
d
σ
/
d
t
bump
=
(
29.7
±
1.8
)
μ
b
/
GeV
2
, for the dip and the bump, respectively.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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