Transition metal catalysis has traditionally relied on organometallic complexes that can cycle through a series of ground-state oxidation levels to achieve a series of discrete yet fundamental ...fragment-coupling steps. The viability of excited-state organometallic catalysis via direct photoexcitation has been demonstrated. Although the utility of triplet sensitization by energy transfer has long been known as a powerful activation mode in organic photochemistry, it is surprising to recognize that photosensitization mechanisms to access excited-state organometallic catalysts have lagged far behind. Here, we demonstrate excited-state organometallic catalysis via such an activation pathway: Energy transfer from an iridium sensitizer produces an excited-state nickel complex that couples aryl halides with carboxylic acids. Detailed mechanistic studies confirm the role of photosensitization via energy transfer.
Challenges in semileptonic B decays Gambino, P.; Kronfeld, A. S.; Rotondo, M. ...
The European physical journal. C, Particles and fields,
10/2020, Letnik:
80, Številka:
10
Journal Article
Recenzirano
Odprti dostop
Two of the elements of the Cabibbo–Kobayashi–Maskawa quark mixing matrix,
|
V
ub
|
and
|
V
cb
|
, are extracted from semileptonic
B
decays. The results of the
B
factories, analysed in the light of ...the most recent theoretical calculations, remain puzzling, because for both
|
V
ub
|
and
|
V
cb
|
the exclusive and inclusive determinations are in clear tension. Further, measurements in the
τ
channels at Belle, Babar, and LHCb show discrepancies with the Standard Model predictions, pointing to a possible violation of lepton flavor universality. LHCb and Belle II have the potential to resolve these issues in the next few years. This article summarizes the discussions and results obtained at the MITP workshop held on April 9–13, 2018, in Mainz, Germany, with the goal to develop a medium-term strategy of analyses and calculations aimed at solving the puzzles. Lattice and continuum theorists working together with experimentalists have discussed how to reshape the semileptonic analyses in view of the much higher luminosity expected at Belle II, searching for ways to systematically validate the theoretical predictions in both exclusive and inclusive
B
decays, and to exploit the rich possibilities at LHCb.
This article reports world averages of measurements of
b
-hadron,
c
-hadron, and
τ
-lepton properties obtained by the Heavy Flavor Averaging Group using results available through summer 2016. For the ...averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters,
C
P
violation parameters, parameters of semileptonic decays, and Cabbibo–Kobayashi–Maskawa matrix elements.
A
bstract
It is well known that in
b
-hadron decays with a single unreconstructible final state particle, the decay kinematics can be solved up to a quadratic ambiguity, without any knowledge of the
...b
-hadron momentum. We present a method to infer the momenta of
b
-hadrons produced in hadron collider experiments using information from their reconstructed flight vectors. Our method is strictly agnostic to the decay itself, which implies that it can be validated with control samples of topologically similar decays to fully reconstructible final states. A multivariate regression algorithm based on the flight information provides a
b
-hadron momentum estimate with a resolution of around 60% which is sufficient to select the correct solution to the quadratic equation in around 70% of cases. This will improve the ability of hadron collider experiments to make differential decay rate measurements with semileptonic
b
-hadron decays.
A
bstract
We propose an approach for measuring the moments of the hadronic invariant mass distribution in semileptonic
B
s
0
meson decays using a sum-of-exclusive technique. Using the present and ...foreseen knowledge about exclusive semileptonic
B
s
0
decays, we estimate the uncertainties on moments of the kinematic distribution. Semileptonic
B
s
0
decays can be described, as their
B
0
counterpart, using the Heavy Quark Expansion (HQE), with the only difference between the
B
s
0
and
B
0
mesons being the SU(3)
F
breaking effects that change the numerical values of the non-perturbative HQE parameters. We extract the HQE parameters for the
B
s
0
decays from our estimates of the moments, showing the potential of the proposed method. We identify a set of required measurements for a future precision measurement.
Inhibitors of metallo-β-lactamases Rotondo, Caitlyn M; Wright, Gerard D
Current opinion in microbiology,
October 2017, 2017-Oct, 2017-10-00, 20171001, Letnik:
39
Journal Article
Recenzirano
•β-Lactams are among the most effective and commonly used antibiotics.•Resistance to β-lactams is mainly caused by β-lactamases.•No metallo-β-lactamase (MBL) inhibitors are yet approved for human ...clinical use.•MBL inhibition can be achieved through Zn-dependent or Zn-independent modes.•Most prevalent MBL inhibitors act by direct chelation or by removal of the active site Zn2+ ions.
The β-lactams are the most successful class of antibiotic drugs but they are vulnerable to inactivation by a growing cadre of β-lactamases that now number more than a thousand variants. β-Lactamases operate by one of two general chemical mechanisms either catalyzing β-lactam ring hydrolysis via a covalent enzyme intermediate through the aegis of an active site serine residue or through a noncovalent Zn-dependent mechanism. The Ser-β-lactamases are currently dominant in the clinic and consequently, there has been great effort to identify inhibitors and to co-formulate these with β-lactam antibiotics. Four such inhibitors are approved for human clinical use and several more are in clinical trials. Metallo-β-lactamases (MBLs), on the other hand, are only now emerging as a global threat and consequently, inhibitor discovery has lagged behind their Ser counterparts. There are now several examples of MBL inhibitors that operate either in a Zn-dependent or Zn-independent mode. The Zn-dependent compounds are more prevalent and some show efficacy in animal models of infection. These compounds function by either acting as an alternate metal ligand, usually displacing a jointly held hydroxide ion shared by enzymes with two Zn2+ ions, or alternately by striping Zn from the active site. The increase in the number of candidate MBL inhibitors over recent years reflects the growing clinical challenge of pathogens expressing these enzymes that result in a carbapenem resistance phenotype. While none of these inhibitors are yet in human clinical trials, the increasing importance of these enzymes in drug failure is a strong incentive to continue identifying and characterizing such molecules.
The fruit fly of photophysics Arias-Rotondo, Daniela M
Nature chemistry,
2022-Jun-06, Letnik:
14, Številka:
6
Journal Article
Recenzirano
The tris(2,2′-bipyridine)ruthenium(II) cation, or ‘rubipy’ to its friends, has had a significant influence on our understanding of the photophysics of transition metal complexes, and has also helped ...revolutionize organic photochemistry, explains Daniela M. Arias-Rotondo.
•A new SL damper is experimentally investigated, analyzing its competitiveness due to changeable mechanical properties with geometry.•SL device has already been applied for new constructions and ...retrofit of existing buildings in South America.•A fully bolted connection is proposed to make easier installation without welding.•A properly designed set up system is proposed for monotonic and cyclic application of force up to 1000 kN.•Simple analytical formula are proposed to estimate mechanical properties.
This paper describes the experimental investigation on a newly designed steel shear link (SL) for seismic protection of civil structures. It is a low-cost hysteretic device, realized from a single steel plate where variable thickness is given through milling. It has been already adopted for several applications in South America, both for new constructions and seismic retrofit of existing buildings. Even small variation of device’s geometry can significantly modify its mechanical behavior, both in terms of strength and stiffness, making such devices very appealing for the flexibility in terms of design solutions.
SL device is conceived to be connected to the main frame through bolted connections and mounted on a supporting brace. In particular, slotted holes on one edge of the damper prevent the device from transmitting shear to the upper beam during the seismic excitation. A couple of specimens for each of 5 different geometries has been tested, for a total of 10 tests. Two different boundary configurations have been considered, analyzing results of fully-tightened or not fully-tightened bolts in correspondence of slotted holes. The set-up system has been properly designed to apply forces up to 1000 kN, to be able to accommodate and test the largest specimens of the set. The paper presents the experimental results and data processing concerning analysis of deformation process, hardening behavior and collapse. The main features of the control devices are highlighted, above all, the high dissipative capability that is mainly due to the particular shape of the steel damper, which leads to a high buckling resistance.
Abstract Objective Intrathecal baclofen therapy (ITB) is a well-known treatment for spasticity. Despite this fact, several topics have to be still discussed: new indications and screening tools, ...appropriate surgical timing and complicance avoidance. Methods A total of 112 consecutive patients all with a severe, progressive and refractory to medical therapy spasticity from different causes were treated using ITB, after a bolus test. Every patient was assessed by means of Modified Ashworth Scale (MAS), Penn spasm frequency scale (SFS) and Visual Analog Scale for pain. Since available, a Gait analysis was also performed. Results There were 63 males (56%) and 49 females (44%). Seventy-four (66%) had a quadriparesis, 34 (30.4%) had a paraparesis and 4 (3.6%) were hemiplegic. Among these patients 77 (68.7%) were non ambulatory, while 35 (31.3%) were ambulatory. These patients suffered from spasticity due to many different diseases. Mean follow-up was 55 months. The mean Modified Ashworth score decreased from 4.5 ± 0.5 preoperatively to 1.2 ± 0.4 on chronic intrathecal baclofen. Daily baclofen dose varied between 23 and 500 mcg. Drug-induced complications and catheter related problems occurred, respectively in 7 (6.3%) and 10 patients (8.9%). Conclusions Although ITB is a well known and good treatment option in the management of severe spasticity, because of the different goals and subgroups of patients treated, a variety of techniques are needed to evaluate the benefits of this therapy. New indications, effects of ITB on central nervous system and cognitive functions needs yet to be fully clarified.
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