2 research outputs found
Evolving Role of Ca<sup>2+</sup> on the Long-Term Phosphate Adsorption-Regeneration Performance of Nanoconfined Hydrated Lanthanum Oxides: Short-Term Enhancement and Long-Term Inhibition
Phosphorus (P) advanced treatment
by adsorption reduces the risk
of eutrophication in natural waters and reservoirs. The impact of
ubiquitous Ca2+ on long-term P removal is critical in assessing
the regeneration efficiency of one adsorbent, which is a vital indicator
for cost-effectiveness. Given the critical role of lanthanum (La)-based
composite materials in P removal, in this study, we unravel the long-term
evolving role of Ca2+ on phosphate removal by nanosized
hydrated lanthanum oxides (HLO) confined in cross-linked polystyrene
beads (HLO@201) over 20 adsorption-regeneration cycles and fixed-bed
column runs, with a combination of macroscopic adsorption experiments,
microscopic structural investigation, and theoretical calculations.
The role of Ca2+ gradually evolves from positive (5–70%
higher than Ca2+-free group) to negative (18–41%
lower than the Ca2+-free group) with ongoing cyclic runs
of HLO@201, which is distinctive from the bulky HLO. The presence
of Ca2+ enhances P uptake by HLO@201 possibly through La–P–Ca–P
multiple complexation and Ca–P precipitation (i.e., hydroxyapatite,
HAP) inside the polymeric host, which creates an antagonistic effect
with HLO over time. The formed Ca–P precipitates may accumulate
and encapsulate on the surface of HLO nanoparticles, which induce
the formation of irreversible LaPO4·xH2O under nanoconfinement that deplete the active adsorptive
sites. A two-step (acid wash + NaOH) regeneration method can partially
recover the P removal performance of HLO@201. We envision that this
study could be a cautionary tale for advanced treatment of P by adsorption,
to inspire re-evaluation on the long-term performance of adsorption
processes
Murgocil is a Highly Bioactive Staphylococcal-Specific Inhibitor of the Peptidoglycan Glycosyltransferase Enzyme MurG
Modern
medicine is founded on the discovery of penicillin and subsequent
small molecules that inhibit bacterial peptidoglycan (PG) and cell
wall synthesis. However, the discovery of new chemically and mechanistically
distinct classes of PG inhibitors has become exceedingly rare, prompting
speculation that intracellular enzymes involved in PG precursor synthesis
are not ‘druggable’ targets. Here, we describe a β-lactam
potentiation screen to identify small molecules that augment the activity
of β-lactams against methicillin-resistant Staphylococcus
aureus (MRSA) and mechanistically characterize a compound
resulting from this screen, which we have named murgocil. We provide
extensive genetic, biochemical, and structural modeling data demonstrating
both <i>in vitro</i> and in whole cells that murgocil specifically
inhibits the intracellular membrane-associated glycosyltransferase,
MurG, which synthesizes the lipid II PG substrate that penicillin
binding proteins (PBPs) polymerize and cross-link into the cell wall.
Further, we demonstrate that the chemical synergy and cidality achieved
between murgocil and the β-lactam imipenem is mediated through
MurG dependent localization of PBP2 to the division septum. Collectively,
these data validate our approach to rationally identify new target-specific
bioactive β-lactam potentiation agents and demonstrate that
murgocil now serves as a highly selective and potent chemical probe
to assist our understanding of PG biosynthesis and cell wall biogenesis
across Staphylococcal species