Ian Riddlestone

Methylation of DNA nucleobases is a naturally occurring process in living organisms. Usually, it functions as a gene regulation marker and is connected to inheritable epigenetic effects. However, the methylation of guanine in the O6 position due to external agents disrupts the hydrogen bonding between pairing bases and may have mutagenic effects. In this paper, we use density functional theory (DFT) to investigate the Double Proton Transfer (DPT) between methyl-guanine (mG) and cytosine. We compare the DPT dynamics between mG-C and unmethylated G-C using ab initio nuclear quantum dynamics as implemented in the Nuclear-Electronic Orbital (NEO-DFT) approach, where the protons involved in the transfer are described at the same quantum-mechanical level as the electrons of the system. We find that nuclear quantum effects facilitate the DPT for both systems but increase the rate of point mutations for the canonical base pair G-C more significantly. Noteworthy, when similar calculations are performed in the presence of explicit solvent and strand separation, the DPT mechanism becomes assisted by water, lowering the energy barrier of the reaction.

[Ni(IMes) 2 ] reacts with chloroboranes via oxidative addition to form rare unsupported Ni-boryls. In contrast, the oxidative addition of hydridoboranes is not observed and products from competing reaction pathways are identified. Computational studies relate these differences to the mechanism of oxidative addition: B–Cl activation proceeds via nucleophilic displacement of Cl − , while B–H activation would entail high energy concerted bond cleavage.

The use of a sterically demanding pincer ligand to prepare an unusual square planar aluminium complex is reported. Due to the constrained geometry imposed by the ligand scaffold, this four-coordinate aluminium centre remains Lewis acidic and reacts via differing metal-ligand cooperative pathways for activating ketones and CO2. It is also a rare example of a single-component aluminium system for the catalytic reduction of CO2 to a methanol equivalent at room temperature.

Polymers with tailored architectures and degradability were prepared through thiocarbonyl addition ring-opening (TARO) atom-transfer radical polymerization (ATRP) using dibenzo[c,e]oxepin-5(7H)-thione (DOT), Cu(I)Br, and tris[2-(dimethylamino)ethyl]amine (Me6TREN) as the thionolactone, catalyst, and ligand, respectively, in combination with a selection of acrylic comonomers. Although copolymers with selectively degradable backbone thioesters and low dispersities (1.10 ≤ D̵ ≤ 1.26) were achieved using DMSO, acetonitrile, or toluene as the solvent, the Cu(I)-catalyzed dethionation of DOT to its (oxo)lactone analogue limited the achievable copolymer DOT content. Using anhydrous polymerization conditions minimized the side reaction and provided degradable copolymers with a higher (≤32 mol %) thioester content. Water-soluble molecular brushes were prepared by grafting poly(ethylene glycol) methyl ether acrylate–DOT copolymers from a pre-made multi-ATRP initiator. Due to copolymerization kinetics, the thioesters were installed close to the junctions and enabled the fast (<1 min) cleavage of the arms from the core to give water-soluble products using 10 mM oxone.

The complexes Ag(L)(n)[WCA] (L=P₄S₃, P₄Se₃, As₄S₃, and As₄S₄; [WCA]=[Al(OR^F)(4)](-) and [F{Al(OR^F)(3)}(2)](-); R-F=C(CF3)(3); WCA=weakly coordinating anion) were tested for their performance as ligand-transfer reagents to transfer the poorly soluble nortricyclane cages P₄S₃, P₄Se₃, and As₄S₃ as well as realgar As₄S₄ to different transition-metal fragments. As₄S₄ and As₄S₃ with the poorest solubility did not yield complexes. However, the more soluble silver-coordinated P₄S₃ and P₄Se₃ cages were transferred to the electron-poor Fp(+) moiety ([CpFe(CO)(2)](+)). Thus, reaction of the silver salt in the presence of the ligand with Fp-Br yielded [Fp-P₄S₃][Al(OR^F)(4)] (1 a), [Fp-P₄S₃][F(Al(OR^F)(3))(2)] (1 b), and [Fp-P₄Se₃][Al(OR^F)(4)] (2). Reactions with P₄S₃ also yielded [FpPPh(3)-P₄S₃][Al(OR^F)(4)] (3), a complex with the more electron-rich monophosphine-substituted Fp(+) analogue [FpPPh(3)](+) ([CpFe(PPh3)(CO)](+)). All complex salts were characterized by single-crystal XRD, NMR, Raman, and IR spectroscopy. Interestingly, they show characteristic blueshifts of the vibrational modes of the cage, as well as structural contractions of the cages upon coordination to the Fp/FpPPh(3) moieties, which oppose the typically observed cage expansions that lead to redshifts in the spectra. Structure, bonding, and thermodynamics were investigated by DFT calculations, which support the observed cage contractions. Its reason is assigned to sigma and pi donation from the slightly P-P and P-E antibonding P₄E₃-cage HOMO (e symmetry) to the metal acceptor fragment.

Upon coordinating P₄ to electron poor cyclopentadienyl-

iron cations, the average P-P bond distances

shrink and the respective P₄ breathing mode in the

Raman spectra (600 cm-¹, P₄, free) is blueshifted by

>40 cm-¹ in [CpFe(CO)(L)(h¹-P₄)]⁺ cations (L=CO or

PPh₃). Analysis suggests that this corresponds to an umpolung

of the bonding from more phosphidic in the

known, electron-rich systems to more phosphonium-like

in the reported electron-poor versions. This may open

new functionalization pathways for white phosphorus P₄.

The ruthenium–zinc heterobimetallic complexes, [Ru(IPr)₂(CO)ZnMe][BAr^F₄] (7), [Ru(IBiox6)₂(CO)(THF)ZnMe][BAr^F₄] (12) and [Ru(IMes)′(PPh₃)(CO)ZnMe] (15), have been prepared by reaction of ZnMe₂ with the ruthenium N-heterocyclic carbene complexes [Ru(IPr)₂(CO)H][BAr^F₄] (1), [Ru(IBiox6)₂(CO)(THF)H][BAr^F₄] (11) and [Ru(IMes)(PPh₃)(CO)HCl] respectively. 7 shows clean reactivity towards H₂, yielding [Ru(IPr)₂(CO)(η²-H₂)(H)₂ZnMe][BAr^F₄] (8), which undergoes loss of the coordinated dihydrogen ligand upon application of vacuum to form [Ru(IPr)₂(CO)(H)₂ZnMe][BAr^F₄] (9). In contrast, addition of H₂ to 12 gave only a mixture of products. The tetramethyl IBiox complex [Ru(IBioxMe₄)₂(CO)(THF)H][BAr^F₄] (14) failed to give any isolable Ru–Zn containing species upon reaction with ZnMe₂. The cyclometallated NHC complex [Ru(IMes)′(PPh₃)(CO)ZnMe] (15) added H₂ across the Ru–Zn bond both in solution and in the solid-state to afford [Ru(IMes)′(PPh₃)(CO)(H)₂ZnMe] (17), with retention of the cyclometallation.