DNA Binding and Chemistry of Dinuclear Platinum Complexes

Equilibrium Studies on Pd(II)-Amine Complexes with Bio-Relevant Ligands in Reference to Their Antitumor Activity

This review article presents an overview of the equilibrium studies on Pd-amine complexes with bio-relevant ligands in reference to their antitumor activity. Pd(II) complexes with amines of different functional groups, were synthesized and characterized in many studies. The complex formation equilibria of Pd(amine)²⁺ complexes with amino acids, peptides, dicarboxylic acids and DNA constituents, were extensively investigated. Such systems may be considered as one of the models for the possible reactions occurring with antitumor drugs in biological systems. The stability of the formed complexes depends on the structural parameters of the amines and the bio-relevant ligands. The evaluated speciation curves can help to provide a pictorial presentation of the reactions in solutions of different pH values. The stability data of complexes with sulfur donor ligands compared with those of DNA constituents, can reveal information regarding the deactivation caused by sulfur donors. The formation equilibria of binuclear complexes of Pd(II) with DNA constituents was investigated to support the biological significance of this class of complexes. Most of the Pd(amine)²⁺ complexes investigated were studied in a low dielectric constant medium, resembling that of a biological medium. Investigations of the thermodynamic parameters reveal that the formation of the Pd(amine)²⁺ complex species is exothermic.

Synthesis, characterization and biological evaluation of dipicolylamine sulfonamide derivatized platinum complexes as potential anticancer agents

Three new Pt complexes, [PtCl₂(N(SO₂(2-nap))dpa)], [PtCl₂(N(SO₂(1-nap))dpa)] and [PtCl₂(N(SO₂pip)dpa)], containing a rare 8-membered ring were synthesized in good yield and high purity by utilizing the ligands N(SO₂(2-nap))dpa, N(SO₂(1-nap))dpa and N(SO₂pip)dpa, which contain a dipicolylamine moiety. Structural studies of all three complexes confirmed that the ligands are bound in a bidentate mode via Pt–N_(pyridyl) bonds forming a rare 8-membered ring. The intense fluorescence displayed by the ligands is quenched upon coordination to Pt. According to time dependent density functional theory (TDDFT) calculations, the key excitations of N(SO₂(2-nap))dpa and [PtCl₂(N(SO₂(1-nap))dpa)] involve the 2-nap-ligand-centered π → π* excitations. While all six compounds have shown antiproliferative activity against human breast cancer cells (MCF-7), the N(SO₂pip)dpa and N(SO₂(2-nap))dpa ligands and [PtCl₂((NSO₂pip)dpa)] complex have shown significantly high cytotoxicity, directing them to be further investigated as potential anti-cancer drug leads.

Three new Pt complexes, [PtCl₂(N(SO₂(2-nap))dpa)], [PtCl₂(N(SO₂(1-nap))dpa)] and [PtCl₂(N(SO₂pip)dpa)], containing a rare 8-membered ring were synthesized in good yield and high purity by utilizing ligands which contain a dipicolylamine moiety.

Synthesis, cytotoxic activity and DNA interaction studies of new dinuclear platinum(ii) complexes with an aromatic 1,5-naphthyridine bridging ligand: DNA binding mode of polynuclear platinum(ii) complexes in relation to the complex structure

The synthesis, spectroscopic characterization, cytotoxic activity and DNA binding evaluation of seven new dinuclear platinum(ii) complexes Pt1-Pt7, with the general formula [{Pt(L)Cl}2(μ-1,5-nphe)](ClO4)2 (1,5-nphe is 1,5-naphthyridine; while L is two ammines (Pt1) or one bidentate coordinated diamine: ethylenediamine (Pt2), (±)-1,2-propylenediamine (Pt3), trans-(±)-1,2-diaminocyclohexane (Pt4), 1,3-propylenediamine (Pt5), 2,2-dimethyl-1,3-propylenediamine (Pt6), and 1,3-pentanediamine (Pt7)), were reported. In vitro cytotoxic activity of these complexes was evaluated against three tumor cell lines, murine colon carcinoma (CT26), murine mammary carcinoma (4T1) and murine lung cancer (LLC1) and two normal cell lines, murine mesenchymal stem cells (MSC) and human fibroblast (MRC-5) cells. The results of the MTT assay indicate that all investigated complexes have almost no cytotoxic effects on 4T1 and very low cytotoxicity toward LLC1 cell lines. In contrast to the effects on LLC1 and 4T1 cells, complexes Pt1 and Pt2 had significant cytotoxic activity toward CT26 cells. Complex Pt1 had a much lower IC50 value for activity on CT26 cells compared with cisplatin. In comparison with cisplatin, all dinuclear Pt1-Pt7 complexes showed lower cytotoxicity toward normal MSC and MRC-5 cells. In order to measure the amount of platinum(ii) complexes taken up by the cells, we quantified the cellular platinum content using inductively coupled plasma mass spectrometry (ICP-QMS). Molecular docking studies performed to evaluate the potential binding mode of dinuclear platinum(ii) complexes Pt1-Pt7 and their aqua derivatives W1-W7, respectively, at the double stranded DNA showed that groove spanning and backbone tracking are the most stable binding modes.

The effect of alkyl chain tethers on the kinetics and mechanistic behaviour of bifunctional dinuclear platinum(ii) complexes bearing N,N′-dipyridylamine ligands

This study reports on non-classical dinuclear platinum(ii) complexes, with the ability to bind to DNA strands in a different manner from cisplatin and its analogues. This is an effort to design dinuclear Pt(ii) complexes that target DNA and are bifunctional.

Nanoparticle-mediated delivery of multinuclear platinum(IV) prodrugs with enhanced drug uptake and the activity of overcoming drug resistance

Here, a nanoparticle-mediated delivery of multinuclear platinum(IV) prodrugs [biodegradable polymer-di-cisPt(IV)] for overcoming cisplatin drug resistance is reported. From the MTT assays, lower IC50 values of polymer-di-cisPt(IV) on A2780DDP cells than A2780 were observed with the lowest resistance factor of 0.7. Inductively coupled plasma mass spectroscopy results showed that more drugs were delivered into cancer cells and greater number of Pt-DNA adducts were formed with the use of the polymer-di-cisPt(IV) conjugate nanoparticles. By a mechanistic study with endocytosis inhibitors to treat A2780 cells, we proved that polymer-di-cisPt(IV) conjugate nanoparticles were internalized by the cancer cells through endocytosis rather than through passive diffusion or copper transporter 1-mediated active transportation. This well illustrates the way how the polymer-di-cisPt(IV) micelles overcome cisplatin resistance.

The conformation effect of the diamine bridge on the stability of dinuclear platinum(II) complexes and their hydrolysis

In this paper, the hydrolysis process of a bisplatinum complex containing the flexible chain 1,6-hexanediamine between the two metal centers was investigated through the use of density functional theory (DFT) with the analysis of the role of the spacing group arrangement on the values of free energy activation barrier. All structures were fully optimized in aqueous solution using implicit model for solvent at DFT level. The energy profiles for the hydrolysis reaction were determined by using the supermolecule approach. Five transition states were proposed differing by the conformation of the bridge group, and the activation free energy calculated as a weighted average within the selected forms. The Gibbs population for reactant was used as a statistical weight leading to the predicted value of 23.1kcalmol(-1), in good accordance with experiment, 23.8kcalmol(-1). Our results suggests that for 1,6-hexanediamine bridge ligand, the extend forms with average torsional angle over the carbon chain larger than 130° have the greatest contribution to the hydrolysis kinetics. The results presented here point out that the hydrolysis mechanism might follow different paths for each conformation and each of these contributes to the observed energy barrier.

Palladium(II) Complexes Containing Mixed Nitrogen-Sulphur Donor Ligands: Interaction of [Pd(Methionine Methyl Ester)(H2O)2](2+) with Biorelevant Ligands

Pd(MME)Cl₂ complex (MME = methionine methyl ester) was synthesised and characterized by physicochemical measurements. The reaction of [Pd(MME)(H₂O)₂]²⁺ with amino acids, peptides, or dicarboxylic acids was investigated at 25°C and 0.1 M ionic strength. Amino acids and dicarboxylic acids form 1 : 1 complexes. Peptides form both 1 : 1 complexes and the corresponding deprotonated amide species. The stability of the complexes formed was determined and the binding centres of the ligands were assigned. Effect of solvent on the stability constant of Pd(MME)-CBDCA complex, taken as a representative example, shows that the complex is more favoured in a medium of low dielectric constant. The concentration distribution diagrams of the complexes were evaluated.

New insights on cytotoxic activity of group 3 and lanthanide compounds: complexes with [N,N,N]-scorpionate ligands

Objectives

In this work was to evaluate the cytotoxic activity of a series of monomeric group 3 and lanthanide (N,N,N)-heteroscorpionate-triflate complexes (M (OTf) 2 (cybpamd) (THF)) (Ln = Sc (2), Y (3), La (4), Nd (5), Sm (6), Dy (7), Yb (8); OTf = SO3CF3; cybpamd = N, N′-dicyclohexyl-2,2-bis-(3,5-dimethyl-pyrazol-1-yl)-acetamidinate) having octahedral geometry around the metal atoms on the human epithelial lung adenocarcinoma (A549), human melanoma (A375), human cervical epithelial adenocarcinoma, human embryonic kidney (HEK-293) and murine macrophages (J774.A1) cell lines.

Methods

All the tested compounds were incubated with cells for 72 h and their growth inhibition assessed by using MTT assay.

Key findings

On the cell line HEK-293 complexes 5 and 7 show a reasonable activities, while the murine macrophage cell line (J774.A1), only the scandium 2 complex is not very active. All complexes tested are poorly active on human health adenocarcinoma lung epithelial (A549) and human melanoma (A375).

Conclusions

The group 3 and lanthanide (N,N,N)-heteroscorpionate triflate-complexes (M(OTf)2(cybpamd)(THF)) on murine macrophage (J774.A1) cell line, except that of scandium, show a reasonable activity. On human epithelial cervix adenocarcinoma (HeLa) complexes 3, 5 and 6 are significantly more active than cis-platinum, as well as complex 5 is more active on human embryonic kidney (HEK-293) cell line. All the tested complexes are poorly active on human epithelial lung adenocarcinoma (A549) and human melanoma (A375).

The different behaviour of the complexes examined (2–8) let us hypothesize that the cytotoxic activity is related to the molecule as a whole and not only to the ligand or the metal ion separately.

Platinum and Palladium Polyamine Complexes as Anticancer Agents: The Structural Factor

Since the introduction of cisplatin to oncology in 1978, Pt(II) and Pd(II) compounds have been intensively studied with a view to develop the improved anticancer agents. Polynuclear polyamine complexes, in particular, have attracted special attention, since they were found to yield DNA adducts not available to conventional drugs (through long-distance intra- and interstrand cross-links) and to often circumvent acquired cisplatin resistance. Moreover, the cytotoxic potency of these polyamine-bridged chelates is strictly regulated by their structural characteristics, which renders this series of compounds worth investigating and their synthesis being carefully tailored in order to develop third-generation drugs coupling an increased spectrum of activity to a lower toxicity. The present paper addresses the latest developments in the design of novel antitumor agents based on platinum and palladium, particularly polynuclear chelates with variable length aliphatic polyamines as bridging ligands, highlighting the close relationship between their structural preferences and cytotoxic ability. In particular, studies by vibrational spectroscopy techniques are emphasised, allowing to elucidate the structure-activity relationships (SARs) ruling anticancer activity.

The use of polymeric platinum(IV) prodrugs to deliver multinuclear platinum(II) drugs with reduced systemic toxicity and enhanced antitumor efficacy

Two dinuclear platinum(IV) prodrugs were prepared from cisplatin and oxaliplatin, and tethered to amphiphilic biodegradable block copolymers. The polymeric dinuclear platinum(IV) prodrugs were allowed to self-assemble into nanomicelles, which showed reduced systemic toxicity, relatively long blood circulation, and enhanced antitumor efficacy. In this way, the bottleneck of present multinuclear platinum drugs, especially their severe systemic toxicity, might be overcome.

Substitution behaviour of novel dinuclear Pt(II) complexes with bio-relevant nucleophiles

The novel dinuclear Pt(II) complexes [{trans-Pt(NH(3))(2)Cl}(2)(μ-pyrazine)](ClO(4))(2) (Pt1), [{trans-Pt(NH(3))(2)Cl}(2)(μ-4,4'-bipyridyl)](ClO(4))(2)·DMF (Pt2), and [{trans-Pt(NH(3))(2)Cl}(2)(μ-1,2-bis(4-pyridyl)ethane)](ClO(4))(2) (Pt3), were synthesized. Acid-base titrations, and temperature and concentration dependent kinetic measurements of the reactions with biologically relevant ligands such as thiourea (Tu), glutathione (GSH) and guanosine-5'-monophosphate (5'-GMP) were studied at pH 2.5 and 7.2. The reactions were followed under pseudo-first-order conditions by stopped-flow and UV-vis spectrophotometry. (1)H NMR spectroscopy was used to follow the substitution of chloride in the complex [{trans-Pt(NH(3))(2)Cl}(2)(μ-4,4'-bipyridyl)](ClO(4))(2)·DMF by guanosine-5'-monophosphate (5'-GMP) under second-order conditions. The results indicate that the bridging ligand has an influence on the reactivity of the complexes towards nucleophiles. The order of reactivity of the investigated complexes is Pt1 > Pt2 > Pt3.

Stabilization of Triam(m)inechloridoplatinum Complexes by Oxidation to PtIV

PtIV analogues of the active end groups {PtClN3} of multinuclear Pt anticancer drugs have been investigated. The crystal structure of trans,mer-[PtCl(OH)2(dien)]Cl shows that the bond lengths are similar to those in the dihydroxidoplatinum(iv) analogue of cisplatin. The axial ligands are shown to be the predominant influence on reduction potentials with the dihydroxido complex trans,mer-[PtCl(OH)2(NH3)3]Cl being the most resistant to reduction. X-ray absorption near-edge spectroscopy is shown to be suitable for monitoring the oxidation state of these complexes and reveals that trans,mer-[PtCl(OH)2(NH3)3]+ survives for more than 2 h in cancer cells.

Effects of geometric isomerism and anions on the kinetics and mechanism of the stepwise formation of long-range DNA interstrand cross-links by dinuclear platinum antitumor complexes

Reported herein is a detailed study of the kinetics and mechanism of formation of a 1,4-GG interstrand cross-link by the dinuclear platinum anticancer compound [15N][{cis-PtCl(NH3)2}2{mu-NH2(CH2)6NH2}]2+ (1,1/c,c (1)). The reaction of [15N]1 with 5'-{d(ATATGTACATAT)2} (I) has been studied by [1H,15N] HSQC NMR spectroscopy in the presence of different concentrations of phosphate. In contrast with the geometric trans isomer (1,1/t,t), there was no evidence for an electrostatic preassociation of 1,1/c,c with the polyanionic DNA surface, and the pseudo-first-order rate constant for the aquation of [(15)N]1 was actually slightly higher (rather than lower) than that in the absence of DNA. When phosphate is absent, the overall rate of formation of the cross-link is quite similar for the two geometric isomers, occurring slightly faster for 1,1/t,t. A major difference in the DNA binding pathways is the observation of phosphate-bound intermediates only in the case of 1,1/c,c. 15 mM phosphate causes a dramatic slowing in the overall rate of formation of DNA interstrand cross-links due to both the slow formation and slow closure of the phosphate-bound monofunctional adduct. A comparison of the molecular models of the bifunctional adducts of the two isomers shows that helical distortion is minimal and globally the structures of the 1,4 interstrand cross-links are quite similar. The effect of carrier ligand was investigated by similar studies of the ethylenediamine derivative [15N]1-en. A pKa value of 5.43 was determined for the [15N]1,1/c,c-en diaquated species. The rate of reaction of [15N]1-en with duplex I is similar to that of 1,1/c,c and the overall conformation of the final adduct appears to be similar. The significance of these results to the development of "second-generation" polynuclear platinum clinical candidates based on the 1,1/c,c chelate (dach) series is discussed.

Influence of the bridging ligand on the substitution behaviour of dinuclear Pt(ii) complexes. An experimental and theoretical approach

A series of dinuclear Pt(II) complexes of the type [Pt2(N,N,N',N'-tetrakis(2-pyridylmethyl)diamine(H2O)2]4+ were synthesized. Acid-base titrations, and concentration and temperature dependent stopped-flow measurements of the reaction with chloride were performed to study the thermodynamic and kinetic behaviour of the dinuclear bridged complexes. The results indicate that there is a clear interaction between the two Pt(II) centres, which becomes weaker as the aliphatic chain increases in length. From a certain chain length onwards, the Pt(II) centres become independent of each other and exhibit identical thermodynamic and kinetic properties. The experimental results are discussed in reference to structures obtained by DFT (BP86/LACVP*) calculations.

Cucurbituril binding of trans-[{PtCl(NH3)2}2(µ-NH2(CH2)8NH2)]2+and the effect on the reaction with cysteine

The effect of encapsulation by cucurbiturils Q[7] and Q[8] on the rate of reaction of the anti-cancer dinuclear platinum complex trans-[{PtCl(NH3)2}2(micro-NH2(CH2)8NH2)]2+ with the model biological nucleophiles glutathione and cysteine has been examined by NMR spectroscopy. It was expected that the octamethylene linking chain would fold inside the cucurbituril host and hence position the reactive platinum centres close to the cucurbituril portals, and thereby, confer resistance to degradation by biological nucleophiles. The upfield shifts of the resonances from the methylene protons in the linking ligand observed in 1H NMR spectra of the platinum complex upon addition of either Q[7] or Q[8] indicate that the cucurbituril is positioned over the linking ligand, with the Pt(II) centres projecting out of the portal. Furthermore, the relative changes in chemical shift of the methylene resonances suggest that the octamethylene linking chain folds within the cucurbituril cavity, particularly in Q[8]. Simple molecular models, based on the observed relative changes in chemical shift, could be constructed that were consistent with the proposed folding of the linking ligand within the cucurbituril cavity. Encapsulation by Q[7] was found to reduce the rate of reaction of the platinum complex with glutathione. Encapsulation by Q[7] and Q[8] was also found to reduce the rate of reaction of the platinum complex with cysteine, with Q[8] slowing the reaction to a greater extent than Q[7], consistent with the inferred encapsulation geometries. Encapsulation of dinuclear platinum complexes within the cucurbituril cavity may provide a novel way of reducing the reactivity and degradation of these promising chemotherapeutic agents with blood plasma proteins.

A positively charged trinuclear 3N-chelated monofunctional platinum complex with high DNA affinity and potent cytotoxicity

A trinuclear 3N-chelated monofunctional platinum complex, [Pt3(HPTAB)Cl3](ClO4)3 (HPTAB = N,N,N',N',N'',N''-hexakis(2-pyridylmethyl)-1,3,5-tris(aminomethyl)benzene), has been structurally characterized, which binds to DNA and demonstrates much higher potency against the murine leukemia cell line (P-388) and the human nonsmall-cell lung cancer cell line (A-549) than cisplatin.

Cucurbit[n]uril binding of platinum anticancer complexes

The encapsulation of cisplatin by cucurbit[7]uril (Q[7]) and multinuclear platinum complexes linked via a 4,4'-dipyrazolylmethane (dpzm) ligand by Q[7] and cucurbit[8]uril (Q[8]) has been studied by NMR spectroscopy and molecular modelling. The NMR studies suggest that some cisplatin binds in the cucurbituril cavity, while cis-[PtCl(NH3)2(H2O)]+ only binds at the portals. Alternatively, the dpzm-linked multinuclear platinum complexes are quantitatively encapsulated within the cavities of both Q[7] and Q[8]. Upon encapsulation, the non-exchangeable proton resonances of the multinuclear platinum complexes show significant upfield shifts in 1H NMR spectra. The H3/H3* resonances shift upfield by 0.08 to 0.55 ppm, the H5/H5* shift by 0.9 to 1.6 ppm, while the methylene resonances shift by 0.74 to 0.88 ppm. The size of the resonance shift is dependent on the cavity size of the encapsulating cucurbituril, with Q[7] encapsulation producing larger shifts than Q[8]. The upfield shifts of the dpzm resonances observed upon cucurbituril encapsulation indicate that the Q[7] or Q[8] is positioned directly over the dpzm linking ligand. The terminal platinum groups of trans-[{PtCl(NH3)2}2 mu-dpzm]2+ (di-Pt) and trans-[trans-{PtCl(NH3)2}2-trans-{Pt(dpzm)2(NH3)2}]4+ (tri-Pt) provide a barrier to the on and off movement of cucurbituril, resulting in binding kinetics that are slow on the NMR timescale for the metal complex. Although the dpzm ligand has relatively few rotamers, encapsulation by the larger Q[8] resulted in a more compact di-Pt conformation with each platinum centre retracted further into each Q[8] portal. Encapsulation of the hydrolysed forms of di-Pt and tri-Pt is considerably slower than for the corresponding Cl forms, presumably due to the high-energy cost of passing the +2 platinum centres through the cucurbituril portals. The results of this study suggest that cucurbiturils could be suitable hosts for the pharmacological delivery of multinuclear platinum complexes.

Effects of geometric isomerism in dinuclear platinum antitumor complexes on aquation reactions in the presence of perchlorate, acetate and phosphate

The aquation and subsequent reactions of the dinuclear Pt antitumor complexes [{trans-PtCl(NH(3))(2)}(2)(mu-NH(2)(CH(2))(6)NH(2))](2+) (1,1/t,t) and [{cis-PtCl(NH(3))(2)}(2)(mu-NH(2)(CH(2))(6)NH(2))](2+) (1,1/c,c) in 15 mM perchlorate, acetate or phosphate solutions were followed at 298 K by [(1)H,(15)N] HSQC 2D NMR spectroscopy. Rate and equilibrium constants for the initial reversible aquation and the subsequent reversible reaction with phosphate or acetate are reported. The rate constant for the first aquation step is two-fold lower for 1,1/c,c than 1,1/t,t but the anation rate constants are similar so that the equilibrium lies further towards the chloro form for the 1,1/c,c compound. A pK (a) value of 6.01+/-0.03 was determined for the diaquated species [{cis-Pt(NH(3))(2)(H(2)O)}(2)(mu-NH(2)(CH(2))(6)NH(2))](4+) (1,1/c,c-3) which is 0.4 units higher than that of the 1,1/t,t compound. The rate constants for the binding of acetate and phosphate to 1,1/t,t are similar, but the rate constant for the reverse reaction is close to ten-fold higher in the case of phosphate so that equilibrium conditions are attained more rapidly (12 h compared with 64 h). On the other hand, for 1,1/c,c the rate constants for the forward and reverse reactions with acetate and phosphate are quite similar so that equilibrium conditions are reached very slowly (80-100 h) and a greater proportion of phosphate-bound species are present. The reduced lability of the bound phosphate for 1,1/c,c is attributed to the formation of a macrochelate phosphate-bridged species which was characterized by (31)P NMR and ESI-MS. The speciation profiles of 1,1/t,t and 1,1/c,c under physiological conditions are explored.

Effects of geometric isomerism in dinuclear antitumor platinum complexes on their interactions with N-acetyl-L-methionine

In this study, the reactions of N-acetyl-L-methionine (AcMet) with [{trans-PtCl(NH(3))(2)}(2)-mu-H(2)N(CH(2))(6)NH(2)](NO(3))(2) (BBR3005: 1,1/t,t 1) and its cis analog [{cis-PtCl(NH(3))(2)}(2)-mu-{H(2)N(CH(2))(6)NH(2)}]Cl(2) (1,1/c,c 2) were analyzed to determine the rate and reaction profile of chloride substitution by methionine sulfur. The reactions were studied in PBS buffer at 37 degrees C by a combination of multinuclear ((195)Pt, {(1)H-(15)N} HSQC) magnetic resonance (NMR) spectroscopy and electrospray ionization time of flight mass spectrometry (ESITOFMS). The diamine linker of the 1,1/t,t trans complex was released as a result of the trans influence of the coordinated sulfur atom, producing trans-[PtCl(AcMet)(NH(3))(2)](+) (III) and trans-[Pt(AcMet)(2)(NH(3))(2)](2+) (IV). In contrast the cis geometry of the dinuclear compound maintained the diamine bridge intact and a number of novel dinuclear platinum compounds obtained by stepwise substitution of sulfur on both platinum centers were identified. These include (charges omitted for clarity): [{cis-PtCl(NH(3))(2)}-mu-NH(2)(CH(2))(6)NH(2)-{cis-Pt(AcMet)(NH(3))(2)}] (V); [{cis-Pt(AcMet)(NH(3))(2)}(2)-mu-NH(2)(CH(2))(6)NH(2)] (VI); [{cis-PtCl(NH(3))(2)}-mu-NH(2)(CH(2))(6)NH(2)-{PtCl(AcMet)NH(3)] (VII); [{PtCl(AcMet)(NH(3))}(2)-mu-NH(2)(CH(2))(6)NH(2)] (VIII); [{trans-Pt(AcMet)(2)(NH(3))}-mu-NH(2)(CH(2))(6)NH(2)-{PtCl(AcMet)(NH(3))] (IX) and the fully substituted [{trans-Pt(AcMet)(2)(NH(3))}(2)-mu-{NH(2)(CH(2))(6)NH(2)] (X). For both compounds the reactions with methionine were slower than those with glutathione (Inorg Chem 2003, 42:5498-5506). Further, the 1,1/c,c geometry resulted in slower reaction than the trans isomer, because of steric hindrance of the bridge, as observed previously in reactions with DNA and model nucleotides.

Multinuclear platinum(ii)–amine complexes containing bis(aminopropyl)dicarba-closo-dodecaborane(12) ligands

Treatment of the bridging bidentate 1,Z-bis(aminopropyl)-1,Z-dicarba-closo-dodecaborane(12)(1,Z-bis(aminopropyl)-1,Z-carborane) ligands of the type 1,Z-[H(2)N(CH(2))(3)](2)-1,Z-C(2)B(10)H(10)(L(1), Z= 7, 5) or (L(2), Z= 12, 6) with two equivalents of trans-[PtClI(2)(NH(3))](-), followed by halogen ligand metathesis with AgOTf and HCl((aq)) afforded the novel diplatinum(II)-amine species cis-[[PtCl(2)(NH(3))](2)L(n)](7(n= 1) or 8(n= 2), respectively). Similarly, the reaction of L(1) or L(2) with the labile trans-[PtCl(dmf)(NH(3))(2)](+) afforded trans-[[PtCl(NH(3))(2)](2)L(n)](OTf)(2)(9(n= 1) or 10(n= 2), respectively) in good yield and purity. However, isolation of the analogous 1,2-carborane complexes was not possible owing to decomposition reactions that led to extensive degradation of the carborane cage and reduction of the metal centre. The mixed dinuclear complex [cis-[PtCl(2)(NH(3))]-L(1)-trans-[PtCl(NH(3))(2)]]OTf (19) was prepared by treatment of the Boc-protected amine ligand 1-[(Boc)(2)N(CH(2))(3)]-7-[H(2)N(CH(2))(3)]-1,7-C(2)B(10)H(10)(L(3), 15) with trans-[PtCl(dmf)(NH(3))(2)](+) to yield trans-[PtCl(NH(3))(2)L(3)]OTf (16), followed by acid deprotection of the pendant amine group, complexation with trans-[PtClI(2)(NH(3))](-), and halogen ligand metathesis using AgOTf and HCl((aq)). A novel trinuclear species containing 5 was prepared by the addition of two equivalents of 15 to the labile precursor cis-[Pt(dmf)(2)(NH(3))(2)](2+) followed by acid deprotection of the pendant amine groups. Further complexation with two equivalents of trans-[PtClI(2)(NH(3))](-) followed by halogen ligand metathesis using AgOTf and HCl((aq)) afforded the triplatinum(II)-amine species [cis-[Pt(NH(3))(2)(L(1))(2)]-cis-[PtCl(2)(NH(3))](2)](OTf)(2)(23). Complexes 7-10, 19 and 23 represent the first examples of multinuclear platinum(ii)-amine derivatives containing carborane cages. Preliminary in vitro cytotoxicity studies for selected complexes are also reported.

Photoelectron spectroscopy and density functional theory of puckered ring structures of Group 13 metal-ethylenediamine

The ethylenediamine (en) complexes of Al, Ga, and In atoms were prepared in laser-vaporization supersonic molecular beams and studied with pulsed field ionization zero electron kinetic energy photoelectron spectroscopy and density functional theory. Several conformers of each metal complex are obtained by B3LYP calculations, and a five-membered cyclic structure is identified by combining the experimental measurements and theoretical calculations. Adiabatic ionization potentials, vibrational frequencies, and bond dissociation energies are determined for the ring structure. The ionization potentials of the Al, Ga, and In species are measured to be 32 784 (5), 33 324 (5), and 33 637 (7) cm(-1), respectively, and metal-ligand dissociation energies of the ionic and neutral complexes are calculated to be 60.2/16.2 (Al(+)/Al), 55.5/13.0 (Ga(+)/Ga), and 50.0/11.4 (In(+)/In) kcal mol(-1). Metal-ligand stretch and bend as well as a number of ligand-based vibrations are measured. Harmonic frequencies and anharmonicities of the M(+)-N (M=Al,Ga,In) stretch are determined for all three M(+)-en ions and the C-C-N bend of Ga(+)-en and In(+)-en. In comparison to monodentate methylamine, the bidentate binding of ethylenediamine leads to a significantly lower ionization potential and higher metal-ligand bond strength of the metal complexes.