Franz L. Wimmer

Palladium(II) compounds with potential antitumour properties and their platinum analogues: a comparative study of the reaction of some orotic acid derivatives with DNA in vitro

Ethidium bromide was used to study perturbations induced in salmon sperm DNA complexed with a series of platinum and palladium compounds obtained from chloro and orotic acid derivatives as leaving ligands. The antitumoral activity of these compounds against Sarcoma 180 cells grafted intraperitoneally into mice is correlated with their capacity to interact with DNA in vitro and to perturb its secondary structure. Nevertheless, among these compounds, [Pt(Dach)(3-methyl-orot)] and [Pt(Dach)(5-fluoro-orot)] do not interact with DNA in vitro and are inactive against Sarcoma 180 cells. This lack of activity originates from the fact that strong chelating properties of the ligand prevent hydrolysis of the compounds which are unable to give rise to aquo species which are the reactive ones. On the other hand, the interaction with DNA is not the only prerequisite in order that a compound be active towards tumour cells. In fact, cis-[Pd(NH3)2Cl2] and cis[Pd(Dach)Cl2] are not antitumoral. It is well known that the former undergoes an inactive trans-conformation and that the two compounds hydrolyse very fast assuming that they interact in vivo with a lot of molecules particularly proteins preventing them to reach the DNA, their pharmacological target. By contrast, [Pd(Dach)(3-methyl-orot)] (T/C = 267%) and [Pd(Dach)(5-fluoro-orot)] (T/C = 270%) display significant antitumour activity.

Preparation and interconversion of dimeric di-µ-hydroxo and tri-µ-hydroxo complexes of platinum(II) and palladium(II) with 2,2′-bipyridine and 1,10-phenanthroline

Treatment of [Pt(L)I2][L = 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen)] with AgNO3 in acetone gives the nitrato complexes [PtL(ONO2)2]. The palladium analogues were prepared from [Pd(L)Cl2] in dilute nitric acid. Dissolution of [ML(ONO2)2](M = Pd or Pt) in water results in the formation of the hydroxo-bridged dimers [LM(µ-OH)2ML][NO3]2 plus nitric acid. Reaction of [M(L)Cl2] with AgNO3 in water gives [LM(µ-OH)2ML][NO3]2 directly as the sole product. The dimers are resistant to substitution, although prolonged heating in aqueous nitric acid reforms [ML(ONO2)2]. The dimers add 1 mol of OH– to form the very stable trihydroxo-bridged compounds [LM(µ-OH)3ML]+(M = Pt, deep red; M = Pd, deep yellow) where each metal is five-co-ordinate. These complexes are slowly cleaved by hydroxide to give [ML(OH)2], which was also prepared either by base hydrolysis or by reaction of [M(L)Cl2] with Ag2O. Addition of HX (X = NO3, or ClO4) to [PtL(OH)2] affords [LPt(µ-OH)3PtL]+, [LPt(µ-OH)2PtL]2+ or [PtL(ONO2)2] at pH 8, 4, and 1 respectively. The complexes have been characterised by i.r., u.v., and n.m.r. (195Pt, 13C, and 1H) spectroscopy.

Longevity, Lignin Content and Construction Cost of the Assimilatory Organs of Nepenthes Species

BACKGROUND AND AIMSnThis study examined level of causal relationships amongst functional traits in leaves and conjoint pitcher cups of the carnivorous Nepenthes species.nnnMETHODSnPhysico-chemical properties, especially lignin content, construction costs, and longevity of the assimilatory organs (leaf and pitcher) of a guild of lowland Nepenthes species inhabiting heath and/or peat swamp forests of Brunei, northern Borneo were determined.nnnKEY RESULTSnLongevity of these assimilatory organs was linked significantly to construction cost, lignin content and structural trait of tissue density, but these effects are non-additive. Nitrogen and phosphorus contents (indicators of Rubisco and other photosynthetic proteins), were poor predictors of organ longevity and construction cost, suggesting that a substantial allocation of biomass of the assimilatory organs in Nepenthes is to structural material optimized for prey capture, rigidity and escape from biotic and abiotic stresses rather than to light interception. Leaf payback time - a measure of net carbon revenue - was estimated to be 48-60 d. This is in line with the onset of substantial mortality by 2-3 months of tagged leaves in many of the Nepenthes species examined. However, this is a high ratio (i.e. a longer minimum payback time) compared with what is known for terrestrial, non-carnivorous plants in general (5-30 d).nnnCONCLUSIONSnIt is concluded that the leaf trait bivariate relationships within the Nepenthes genus, as in other carnivorous species (e.g. Sarraceniaceae), is substantially different from the global relationship documented in the Global Plant Trait Network.

Electro- and spectroelectrochemistry of platinum(II) bipyridine complexes and related species

Abstract The cyclic voltammetry of 2,4′-bipyridine ( I ), N ′-methyl-2,4′-bipyridinium ( II ), and 4,4′-diphenyl-2,2′-bipyridine ( III ), together with the platinum(II) complexes Pt(bipy)Cl 2 ( IV ), [Pt(bipy)(4-NCpy)Cl] + ( V ), Pt(Ph 2 -bipy)Cl 2 ( VI ), Pt(Me 2 -bipy)Cl 2 ( VII ), Pt(2,4′-bipyOct-H)Cl 2 ( VIII ), [Pt(2,4′-bipyOct)Cl 3 ] ( IX ), [Pt(2,4′-bipyMe-H)(bipy)] 2+ ( X ), [Pt(2,4′-bipyMe-H)(py) 2 ] + ( XI ), [Pt(terpy)Cl] + ( XII ), and Pt(DCMB)Cl 2 ( XIII ) (bipy = 2,2′-bipyridine; 4NCpy = 4-cyanopyridine; Me 2 -bipy = 4,4′-dimethyl-2,2′-bipyridine; Ph 2 -bipy = 4,4′-diphenyl-2,2′-bipyridine; 2,4′-bipyOct-H = N′-octyl-2,4′-bipyridin-3′-ylium; 2,4′-bipyOct = N′-octyl-2,4′-bipyridinium; 2,4′-bipyMe-H N′-methyl-2,4′-bipyridin-3′-ylium; terpy = 2,2′:6′,2″-terpyridine; DCMB = 3,3′-dicarboxymethyl-2,2′- bipyridine) was carried out in DMF. All the complexes show one (in some cases two) ligand-based reductions, and in many cases a platinum-based reduction at around −2V vs. FeCp 2 ue5f8FeCp 2 + . The difference in reduction potential of a given ligand in different coordination environments can be attributed to metal-ligand and ligand-metal-ligand interactions. Singly and, where possible, doubly reduced states were generated by controlled potential electrolysis, and their electronic absorption spectra taken in situ. Properties were compared with those of 2,2′-bipyridine and [Pt(bipy)py 2 ] 2+ . In all cases the spectra of the singly reduced complexes show the general features of ligand anion radicals, while the second reduction of VIII is metal-based.

Solid-state cyclometallation of the 1-methyl-2,4'-bipyridinium complexes of palladiumII and platinumII

Abstract The complexes [M(2,4′-bpyMe)X3] · nH2O (M = Pd, Pt; X = Cl, Br; 2,4′-bpyMe = 1-methyl-2,4′-bipyridinium, n = 0, 1, 2) cyclometallate with elimination of HX to give [M(2,4′bpyMe-H)X2] in the solid state on heating or upon microwave irradiation. Thermal analysis (TGA, DTA, DSC) in conjunction with infrared spectroscope indicates that these complexes cyclometallate in the temperature range 160–260°C. The ease of cyclometallation is Pd > Pt and Cl > Br. The time of cyclometallation with microwave irradiation depends on the mode of irradiation.

Influence of the length of the quaternisation group on the cyclometallation of [M(2,4′-R-bipy)Cl3](M = PtII or PdII; 2,4′-R-bipy = 1′-alkyl-2,4′-bipyridinium)

Solid-state thermolysis of the 1′-alkyl-2,4′-bipyridinium complexes [M(2,4′-R-bipy)Cl3](M = PdII or PtII; R = H, Me, Bu, C6H13, C8H17 or C10H21) gave the cyclometallated complexes [M(2,4′-R-bipy – H)Cl2] in quantitative yield. For M = Pd there is no clear variation of the cyclometallation temperature with the length of the alkyl chain, whereas the temperature of cycloplatination decreases steadily as the length of the alkyl chain increases. The extent of cyclometallation in aqueous solution depends on the solubility of the complex and decreases as the hydrophobicity of the chain increases.

Aqueous chemistry of platinum and palladium complexes. Part 2. Synthesis and crystal structure of a palladium hydroxo complex [Pd(terpy)(OH)]ClO4·H2O (terpy = 2,2′:6′,2″-terpyridine)

The complex [Pd(terpy)(ONO2)]NO3(terpy = 2,2′:6′,2″-terpyridine) can be prepared from the reaction of Pd(NO3)2 with terpy in dilute nitric acid or from metathesis of [Pd(terpy)Cl]Cl using AgNO3. It dissolves in water with hydrolysis of the co-ordinated nitrato group to form [Pd(terpy)(OH2)]2+. Attempts to isolate this complex were unsuccessful. Addition of sodium perchlorate to a solution of [Pd(terpy)(ONO2)]NO3 at pH 10.5 afforded orange needles of [Pd(terpy)(OH)]ClO4·H2O. The Pd–OH bond distance is 1.966(3)A, and the hydroxo group forms strong hydrogen bonds with the molecule of water of crystallisation.

The mode of co-ordination of the quaternised 2,4′-bipyridinium cation. Crystal structures of trichloro(1′-methyl-2,4′-bipyridinium-χN1)platinum(II) dihydrate and dichloro(1′-methyl-2,4′-bipyridin-3′-ylium-χC3′, N1)platinum(II)

The 1′-methyl-2,4′-bipyridinium ion (2,4′-mbipy+) reacts with K2[MX4](M = PtII or PdII; X = Cl or Br) to give the zwitterionic compounds [M(2,4′-mbipy)X3]. The crystal and molecular structure of [Pt(2,4′-mbipy)Cl3] has been determined by single-crystal X-ray analysis. The compound crystallizes in the monoclinic system, space group P21/c with a= 12.319(2), b= 9.359(1), c= 13.665(2)A, and β= 107.90(1)°. From [M(2,4′-mbipy)X3], cyclometallated [ML3X2](M = Pt or Pd, X = Cl or Br, L3= 1′-methyl-2,4′-bipyridin-3′-ylium) has been synthesized and spectroscopically characterized. The crystal and molecular structure of [PtL3Cl2] has been determined by single-crystal X-ray analysis. The compound crystallizes in the orthorhombic system, space group Pbca, a= 7.643(1), b= 17.726(2), and c= 17.142(2)A. 2,4′-Bipyridyl (2,4′-bipy) reacts with PdX2(X = Cl or O2CMe) to yield trans-[Pd(2,4′-bipy)2X2] and with K2[PtCl4] to give cis-[Pt(2,4′-bipy)2X2]. Heating trans-[Pd(2,4′-bipy)2X2] in acetic acid gives the cyclometallated dimer [{PdL2(µ-O2CMe)}2](L2= 2,4′-bipyridin-3-ylium).

Synthesis of aquanitrato(1-methyl-2,2′-bipyridin-3-yl-ium)-palladium(II) perchlorate hydrate

Abstract Treatment of [Pd(bpyMeue5f8H)Cl2]/(bpyMeue5f8H ue5fb 1-methyl-2,2′-bipyridin-3-yl-ium) with 2 mol of AgNO3 in water yields a solution of [Pd(bpyMeue5f8H)(H2O)2]2+ and NO3−, which on evaporation forms [Pd(bpyMeue5f8H)(ONO2)2]. Addition of NaClO4 to a solution of [Pd(bpyMeue5f8H)(H2O)2]2+ and NO3− yields [Pd(bpyMeue5f8H)(H2O)(ONO2)]ClO4 · H2O.

Leaf properties and construction costs of common, co-occurring plant species of disturbed heath forest in Borneo

The leaf properties and construction costs (CC) are reported for eight indigenous heath (kerangas) forest species and three invasive (exotic) species of Acacia. Both groups of species co-occur and colonise disturbed lowland tropical heath rainforest habitats in Brunei, Borneo Island. Across species, CC mass-based increased with nitrogen (N) and heat of combustion (H C ), and decreased with ash content. CC area-based showed similar trends (although weaker in strength) in addition to significant positive correlation with leaf mass per unit area (LMA). Within the native species, the CCs of the shrub and small tree species were lower and significantly different from those of medium-sized tree species. Given the invasive success of the three acacias, it is hypothesised that these species may require less energy for biomass construction than do the native species. Within similar life growth form, no difference in CC mass-based was detected between the native trees and the invasive acacias. For CC area-based, the invasive Acacia species had a higher value. These findings failed to uphold our hypothesis. LMA and leaf N and phosphorus (P), but not potassium (K), were higher in the invasive acacias. The higher N and LMA could have been the cause of higher CC area-based in the invasive acacias. From the ordination of 11 species on the basis of leaf properties, the invasive and native species are more likely to be found in different groupings—although some native species seem more affiliated with the invasive than with their own guild, especially Alphitonia and Macaranga. BT04 Lea io iv ic e O. O. Os et al