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Palladium(0) phosphine complexes are of great importance as catalysts in numerous bond formation reactions that involve oxidative addition of substrates. Highly active catalysts with labile ligands are of particular interest but can be challenging to isolate and structurally characterize. We investigate here the synthesis and chemical reactivity of Pd 0 complexes that contain geometrically adaptable diferrocenylmercury-bridged diphosphine chelate ligands (L) in combination with a labile dibenzylideneacetone (dba) ligand. The diastereomeric diphosphines 1a (p S p R , meso -isomer) and 1b (p S p S -isomer) differ in the orientation of the ferrocene moieties relative to the central Ph 2 PC 5 H 3 –Hg–C 5 H 3 PPh 2 bridging entity. The structurally distinct trigonal LPd 0 (dba) complexes 2a ( meso ) and 2b (p S p S ) are obtained upon treatment with Pd(dba) 2 . A competition reaction reveals that 1b reacts faster than 1a with Pd(dba) 2 . Unexpectedly, catalytic interconversion of 1a ( meso ) into 1b ( rac ) is observed at room temperature in the presence of only catalytic amounts of Pd(dba) 2 . Both Pd 0 complexes, 2a and 2b , readily undergo oxidative addition into the C–Cl bond of CH 2 Cl 2 at moderate temperatures with formation of the square-planar trans -chelate complexes LPd II Cl(CH 2 Cl) ( 3a , 3b ). Kinetic studies reveal a significantly higher reaction rate for the meso -isomer 2a in comparison to (p S p S )- 2b .
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This content will become publicly available on January 14, 2027
The transitional kinetics between open and closed Rep structures can be tuned by salt via two intermediate states
Abstract DNA helicases undergo conformational changes; however, their structural dynamics are poorly understood. Here, we study single molecules of the superfamily 1A DNA helicase Rep, which undergoes conformational transitions during bacterial DNA replication, repair, and recombination. We use time-correlated single-photon counting (TCSPC), fluorescence correlation spectroscopy (FCS), rapid single-molecule Förster resonance energy transfer (smFRET), Anti-Brownian ELectrokinetic (ABEL) trapping, and molecular dynamics simulations (MDS) to provide unparalleled temporal and spatial resolution of Rep’s domain movements. We detect four states revealing two hitherto hidden intermediates (S2, S3), between the open (S1) and closed (S4) structures, whose stability is salt dependent. Rep’s open-to-closed switch involves multiple changes to all four subdomains 1A, 1B, 2A, and 2B along the S1→S2→S3→S4 transitional pathway comprising an initial truncated swing of 2B, which then rolls across the 1B surface, followed by combined rotations of 1B, 2A, and 2B. High forward and reverse rates for S1→S2 suggest that 1B may act to frustrate 2B movement to prevent premature Rep closure in the absence of DNA. These observations support a more general binding model for accessory DNA helicases that utilises conformational plasticity to explore a multiplicity of structures whose landscape can be tuned by salt prior to locking in upon DNA binding.
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- Award ID(s):
- 2121044
- PAR ID:
- 10679742
- Publisher / Repository:
- Oxford
- Date Published:
- Journal Name:
- Nucleic Acids Research
- Volume:
- 54
- Issue:
- 2
- ISSN:
- 0305-1048
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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