Platinum(II) and palladium(II) metallomacrocycles derived from cationic 4,4′-bipyridinium, 3-aminopyrazinium and 2-aminopyrimidinium ligands

Abstract

A series of cationic, ditopic N-donor ligands based on 4,4¢-bipyridine (4,4¢-bipy), 3-aminopyrazine (apyz) and 2-aminopyrimidine (apym), each incorporating two positively-charged N-heterocycles linked by a conformationally-flexible spacer unit, have been synthesised and treated with palladium(II) or platinum(II) precursors [M(2,2¢-bipy) 4 . When the cationic apyz or apym ligands were used in aqueous solution, the analogous metallomacrocycles did not form. Instead, deprotonation of the exocyclic amino group occurred upon coordination of the ligand to afford a tetranuclear [4+2] species in the case of platinum(II), with Pt(II) ◊ ◊ ◊ Pt(II) bonding supported by strong UV-vis absorption at l = 428 nm which was assigned to a metal-metal-to-ligand charge transfer (MMLCT) band. Thus, treatment of 1,6-bis(3-aminopyrazinium)hexane nitrate with [Pt(2,2¢-bipy)(NO 3 ) 2 ], followed by the addition of KPF 6 , led to the formation of the red species [Pt 4 (2,2¢-bipy) 4 {apyz(CH 2 ) 6 apyz-2H} 2 ](PF 6 ) 8 . No related products could be identified with palladium(II), consistent with the low propensity for this metal ion to form strong Pd(II) ◊ ◊ ◊ Pd(II) bonding interactions.

Self‐Assembled Supramolecular Hetero‐Bimetallacycles for Anticancer Potency by Intracellular Release

“…[5] More recently, the biological properties of these metallacyclic structures have also begun to emerge. Metallacycles [6] and helicates [7] have been found to interact with DNA, while other architectures have been shown to be cytotoxic to cancer cells and bacteria. [8] …”

Directional Self‐Sorting with Cucurbit[8]uril Controlled by Allosteric π–π and Metal–Metal Interactions

“…Extensive stacking may also result in emission at lower energies (typically > 800 nm) corresponding to 3 MMLCT excited states. [52,56,57,[62][63][64][65][66][67][68][69][70][71] The impact of CB[n]e ncapsulationo nt ransition energies varies greatly, with bathochromic shifts being typically more common than hypsochromic ones. [72][73][74][75][76][77] Shifts result from a combination of competitive factors:( 1) as shown by Nau and co-workersi nt he case of 2,3-diazabicyclo-[2.2.2]oct-2-ene and its n!p*transitions, [78] adecrease in the environment polarizability from the solvent to the cavity of CB [7] causes hypsochromic shifts; [79] (2) as shown by Biczóka nd co-workersint he case of berberine (1), [77] ad ecrease in the orientation polarizability parameter of the environment (that has both ap olarity and a polarizability term) causesb athochromic shifts from water to CB [7].O ne shoulda lso note that while the CB [7] cavityh as low polarities and polarizabilities, Kaifer and co-workers recently showed that the polarity of the environment surrounding the carbonyl rims of CB [7] is in fact more polar than water; [80] the impact of this specific environmento nt he optical properties of chromophores is not known.…”

“…Emissions typically originate from the 3 [π(C≡CR)→π*(tpy)] and 3 [dπ(Pt)→π*(tpy)] transitions. Extensive stacking may also result in emission at lower energies (typically >800 nm) corresponding to 3 MMLCT excited states …”

ESI-MS and thermal melting studies of nanoscale platinum(ii) metallomacrocycles with DNA

“…Complexes 8·8NO 3 and 9·8NO 3 were prepared as described previously. 14 The 16-mers D2a, D2b (Geneworks, HPLC grade) were purified using HPLC (aqueous NH 4 OAc→MeCN gradient) as reported previously. 35 In each case, equimolar quantities 36 of the appropriate strands (both dissolved in 0.1 M NH 4 OAc, pH 7.4) were combined to give a mixture in which the concentration of each of these constituents was 1 mM (values for [ssDNA] were estimated by measurement of UV absorbance at 260 nm using e 260 values for A, G, C and T of 15200, 12010, 7050 and 8400 M -1 cm -1 , respectively).…”

“…8 8+ and 9 8+ , containing ligands that incorporate two positivelycharged N-heterocycles linked by a conformationally-flexible spacer unit. 14 These metallomacrocycles possess high aqueous solubility and charge and contain cavities which are semi-rigid and of nanoscale dimensions. The DNA-binding characteristics of both these classes of complexes with double-and single-stranded DNA (dsDNA and ssDNA, respectively) were investigated using ESI-MS and thermal denaturation experiments.…”