4 research outputs found
Development and Validation of a Qualitative Method for Target Screening of 448 Pesticide Residues in Fruits and Vegetables Using UHPLC/ESI Q‑Orbitrap Based on Data-Independent Acquisition and Compound Database
A semiautomated
qualitative method for target screening of 448
pesticide residues in fruits and vegetables was developed and validated
using ultrahigh-performance liquid chromatography coupled with electrospray
ionization quadrupole Orbitrap high-resolution mass spectrometry (UHPLC/ESI
Q-Orbitrap). The Q-Orbitrap Full MS/dd-MS<sup>2</sup> (data dependent
acquisition) was used to acquire product-ion spectra of individual
pesticides to build a compound database or an MS library, while its
Full MS/DIA (data independent acquisition) was utilized for sample
data acquisition from fruit and vegetable matrices fortified with
pesticides at 10 and 100 ÎĽg/kg for target screening purpose.
Accurate mass, retention time and response threshold were three key
parameters in a compound database that were used to detect incurred
pesticide residues in samples. The concepts and practical aspects
of in-spectrum mass correction or solvent background lock-mass correction,
retention time alignment and response threshold adjustment are discussed
while building a functional and working compound database for target
screening. The validated target screening method is capable of screening
at least 94% and 99% of 448 pesticides at 10 and 100 ÎĽg/kg,
respectively, in fruits and vegetables without having to evaluate
every compound manually during data processing, which significantly
reduced the workload in routine practice
Use of Recombinant Factor VII in Cardiac Surgery
The off-label use of recombinant human coagulation factor VIIa has been increasing to a number of different treatment areas since its original approval in 1999. Several US patents describe claims for FVIIa utilization in non-hemophilia patients, treatment of bleeding due to trauma, as a means to reverse major bleeding, including intracranial bleeding, induced from fibrinolytic therapy as well as a patent for using FVIIa in the treatment of bleeding for patients with bleeding disorders not caused by hemophilia, but rather bleeding disorders due to thrombocytopenia, platelet disorders, and von Willebrand’s disease. Bleeding after cardiac surgery remains a serious complication that can increase both morbidity and mortality. We review the off-label usage of recombinant factor VIIa as a hemostatic agent that may help control bleeding following cardiac surgery
The Carboxyl Terminus of Eremomycin Facilitates Binding to the Non‑d‑Ala‑d‑Ala Segment of the Peptidoglycan Pentapeptide Stem
Glycopeptide
antibiotics inhibit cell wall biosynthesis in Gram-positive
bacteria by targeting the peptidoglycan (PG) pentapeptide stem structure
(l-Ala-d-iso-Gln-l-Lys-d-Ala-d-Ala). Structures
of the glycopeptide complexed with a PG stem mimic have shown that
the d-Ala-d-Ala segment is the primary drug binding
site; however, biochemical evidence suggests that the glycopeptide–PG
interaction involves more than d-Ala-d-Ala binding.
Interactions of the glycopeptide with the non-d-Ala-d-Ala segment of the PG stem were investigated using solid-state nuclear
magnetic resonance (NMR). LCTA-1421, a double <sup>15</sup>N-enriched
eremomycin derivative with a C-terminal [<sup>15</sup>N]Âamide and
[<sup>15</sup>N]ÂAsn amide, was complexed with whole cells
of <i>Staphylococcus aureus</i> grown in a defined medium
containing l-[3-<sup>13</sup>C]ÂAla and d-[1-<sup>13</sup>C]ÂAla in the presence of alanine racemase inhibitor alaphosphin. <sup>13</sup>CÂ{<sup>15</sup>N} and <sup>15</sup>NÂ{<sup>13</sup>C} rotational-echo
double-resonance (REDOR) NMR measurements determined the <sup>13</sup>C–<sup>15</sup>N internuclear distances between the [<sup>15</sup>N]ÂAsn
amide of LCTA-1421 and the <sup>13</sup>C atoms of the bound d-[1-<sup>13</sup>C]ÂAla-d-[1-<sup>13</sup>C]ÂAla to be 5.1
and 4.8 Ă…, respectively. These measurements also determined the
distance from
the C-terminal [<sup>15</sup>N]Âamide of LCTA-1421 to the l-[3-<sup>13</sup>C]ÂAla of PG to be 3.5 Ă…. The measured REDOR
distance constraints position the C-terminus
of the glycopeptide in the proximity of the l-Ala
of the PG, suggesting that the C-terminus of the glycopeptide interacts
near the l-Ala segment of the PG stem. <i>In vivo</i> REDOR measurements provided structural insight into
how C-terminally modified glycopeptide antibiotics operate
Dual Mode of Action for Plusbacin A<sub>3</sub> in <i>Staphylococcus aureus</i>
We have used CÂ{F},
NÂ{F}, and NÂ{P} rotational-echo double resonance
NMR to determine the location and conformation of <sup>19</sup>F and <sup>15</sup>N double-labeled plusbacin A<sub>3</sub> and of double-labeled <i>deslipo</i>-plusbacin A<sub>3</sub>, each bound to the cell
walls of whole cells of <i>Staphyloccocus aureus</i> grown
in media containing [1-<sup>13</sup>C]Âglycine. The <sup>31</sup>P
is primarily in wall teichoic acid. Approximately 25% of plusbacin
headgroups (the cyclic depsipeptide backbone) are in a closed conformation
(N–F separation of 6 Å), while 75% are in a more open
conformation (N–F separation of 12 Å). The closed headgroups
have no contact with wall teichoic acid, whereas the open headgroups
have a strong contact. This places the closed headgroups in hydrophobic
regions of the cell wall and the open headgroups in hydrophilic regions.
None of the plusbacin tails have contact with the <sup>31</sup>P of
either wall teichoic acid or the cell membrane and thus are in hydrophobic
regions of the cell wall. In addition, both heads and tails of plusbacin
A<sub>3</sub> have contact with the glycyl <sup>13</sup>C incorporated
in cell-wall peptidoglycan pentaglycyl bridges <i>and</i> with <sup>13</sup>C-labeled purines near the membrane surface. We
interpret these results in terms of a dual mode of action for plusbacin
A<sub>3</sub>: <i>first</i>, disruption of the peptidoglycan
layer nearest to the membrane surface by closed-conformation plusbacin
A<sub>3</sub> leading to an inhibition of chain extension by transglycosylation; <i>second</i>, thinning and disruption of the membrane (possibly
including disruption of ATP-binding cassette transporters embedded
in the membrane) by open-conformation plusbacin A<sub>3</sub>, thereby
leading to release of ATP to the hydrophilic regions of the cell wall
and subsequent binding by plusbacin A<sub>3</sub>