Klaus R. Koch

New chemistry with old ligands: N-alkyl- and N,N-dialkyl-N′-acyl(aroyl)thioureas in co-ordination, analytical and process chemistry of the platinum group metals

Abstract Recent developments in the fundamental co-ordination chemistry of N-alkyl-N′- (H2L) and N,N-alkyl-N′-acyl(aroyl)thioureas (HL) of Pt(II), Pd(II) and Rh(III) are reviewed. These studies show that the mode of co-ordination of H2L differs markedly from that of HL, the former ligand generally co-ordinating through the sulphur donor atom to Pt(II) and Pd(II), mimicking the co-ordination of simple thioureas, while HL tends to co-ordinate in a cis bidentate S,O manner to d8 metal ions, with loss of a proton. A series of new, relatively hydrophilic N-alkyl-N′- and N,N-alkyl-N′-acylthioureas have been prepared, and their co-ordination chemistry investigated. The new ligand, N-propyl-N′-butanoylthiourea (H2L8) shows an unprecedented N′,S mode of co-ordination of Pt(II) to yield trans-[Pt(HL8-N,S)2]. Moreover, the favourable physiochemical properties of Pt(II), Pd(II) and Rh(III) complexes makes these ligands useful for the reversed-phase HPLC determination of traces of these metal ions in real effluent streams, following complex formation in a homogeneous acetonitrile–hydrochloric acid phase and subsequent salt-induced phase separation. Complexes prepared in situ of Pt(II), Pd(II) and Rh(III) with N,N-di(2-hydroxylethyl)-N′-benzoyl-thiourea can quantitatively be pre-concentrated onto thin film C18-modified glass-fibre disks, followed by quantification using laser ablation inductively coupled mass spectroscopy at trace levels. Preliminary results show this method to be applicable to untreated PGM refinery process effluents.

Magnetic nanoparticles: Properties and potential applications

Magnetic particles may be used to selectively attach and manipulate or transport targeted species to a desired location under the influence of an external magnetic field. By virtue of their size, magnetic nanoparticles are superparamagnetic, offering great potential in a variety of applications in their bare form or through coating with a surface coating and functional group chosen for a specific application. In this paper, and in order to illustrate this concept, three applications for the use of magnetic nanoparticles will be discussed, namely, in magnetic liquids for densimetric separation, in therapeutic and diagnostic testing, and in effluent processing and metal ion removal.

Hydrophilic platinum complexes of N-2-hydroxyethyl- and N,N-di(2-hydroxyethyl)-N′-benzoylthiourea ligands. Crystal and molecular structure of N,N-di(2-hydroxyethyl)-N′-benzoythiourea

Abstract The crystal and molecular structure of hydrophilic N,N-di(2-hydroxyethyl)-N′-benzoylthiourea (H3L4) has been determined. This ligand coordinates to Pt(II), Pd(II) and Ni(II) in a bidentate manner yielding essentially neutral complexes of the type cis-[Pt(H2L4)2]. By contrast, N-(2-hydroexyethyl)-N′-benzoylthiourea (H3L5) behaves like a monodentate thiourea ligand and reacts with Pt(II) to yield a mixture of cis and trans complexes of [Pt(H3L5)2Cl2]. The ( + )FAB mass spectrum of the latter complexes is also discussed.

Self-assembly of 2:2 metallomacrocyclic complexes of NiII and PdII with 3,3,3′,3′-tetraalkyl-1,1′-isophthaloylbis(thioureas). Crystal and molecular structures of cis-[Pd(L2-S,O)]2 and the adducts of the corresponding NiII complexes: [Ni(L1-S,O)(pyridine)2]2 and [Ni(L1-S,O)(4-dimethylaminopyridine)2]2

Abstract The bipodal ligands 3,3,3′,3′-tetraethyl-1,1′-isophthaloylbis(thiourea), H 2 L 1 , and 3,3,3′,3′-tetra( n -butyl)-1,1′-isophthaloylbis(thiourea), H 2 L 2 , react with Ni(II) and Pd(II) to form exclusively 2:2 metallomacrocyclic cis -[Pd(L 2 - S , O )] 2 and cis -[Ni(L 1 - S , O )] 2 complexes in high yields. Purple-brown cis -[Ni(L 1 - S , O )] 2 readily form green adducts cis- [Ni(L 1 - S , O )(X) 2 ] 2 (X is pyridine or 4-dimethylaminopyridine), in which two X molecules are axially bound to each Ni(II) atom. Thermogravimetric analysis of these adducts shows that cis- [Ni(L 1 - S , O )(X) 2 ] 2 revert back to the planar cis -[Ni(L 1 - S , O )] 2 complexes on heating. The crystal structures of 3,3,3′,3′-tetraethyl-1,1′-isophthaloylbis(thiourea), cis -[Pd(L 2 - S , O )] 2 , cis- [Ni(L 1 - S , O )(pyridine) 2 ] 2 and cis- [Ni(L 1 - S , O )(4-dimethylamino-pyridine) 2 ] 2 are reported.

Deceptively simple Pt complexes of N, N-dialkyl-N′-benzoylthiourea: a 1H, 13C and 195Pt NMR study of their acid-base chemistry in solution and the molecular structure of cis-bis(N, N′-di(n-butyl)-N′-benzoylthioureato)platinum(II)

N,N-Di(n-butyl)-N′-benzoylthiourea readily reacts with PtX42− to yield neutral cis-[PtL2] complexes for X = Cl− and Br−, while for X = I−, the protonated cis-[Pt(LH)2]I2 complex is isolated. The crystal structure of cis-[PtL2] is reported. In chloroform solution, the neutral cis-[PtL2] complexes may readily be protonated to yield a distribution of cis-[Pt(LH)L]+ and cis-[Pt(LH)2]2+ species which have been characterized by means of high resolution multinuclear NMR. Remarkably the 195Pt chemical shift of the cationic species is strongly dependent on the nature of the uncoordinated anion (Cl−, Br−, I−) present, suggesting tight ion-pair formation in solution.

Membrane fluidity of platelets and erythrocytes in patients with Alzheimer's disease and the effect of small amounts of aluminium on platelet and erythrocyte membranes

The membrane fluidity of platelet and erythrocyte membranes in 10 Alzheimers disease patients and 9 age-matched controls was studied. The platelet membranes of patients with Alzheimers disease were found to be significantly more fluid than those of controls (p<0.02). However, erythrocyte membranes of Alzheimer patients were less fluid (more viscous) than those of controls (p<0.05). On further investigation of platelet and erythrocyte membranes obtained from healthy volunteers, the fluidity was found to change with increasing aluminium concentrations. When aluminium ammonium sulphate (0.01–10 μM) was added to membrane suspensions, the fluidity of platelet membranes was increased, whereas the fluidity of erythrocyte membranes was decreased (i.e. the microviscosity was increased).

Identification of indigo-related pigments produced by Escherichia coli containing a cloned Rhodococcus gene

Pigments produced by Escherichia coli containing a cloned piece of DNA from Rhodococcus sp. ATCC 21145 were extracted in chloroform and separated into blue and pink components. Evidence from TLC, NMR spectroscopy, absorption spectrum analysis and solubility behaviour suggested that the blue pigment was indigo and the pink pigment was indirubin, a structural isomer of indigo. The proposed pathway for pigment production on LB agar involves the conversion of tryptophan to indole by tryptophanase of E. coli and the oxidation of indole to indigo by the product of the cloned Rhodococcus DNA insert.

Highly selective extraction of platinum group metals with silica-based (poly)amine ion exchangers applied to industrial metal refinery effluents

Batches of authentic industrial base metal refinery (BMR) and precious metal refinery (PMR) effluents containing large amounts of Ni, Cu and Fe ions and relatively small amounts of the valuable Pt, Pd and Rh metal ions have been treated with silica-based (poly)amine anion exchangers. In most cases, notably with the PMR effluents, the extraction of Pt and Pd appeared to be very effective, with recuperation of more than 95% from some of the effluents, while an increase in temperature was not necessary to obtain maximum metal ion uptake. Successive Rh extraction from the BMR effluents resulted in a maximum removal of 22% of the metal ions initially present. A higher percentage could not be reached apparently due to the presence of large amounts of competing sulphate and chloride counter ions. The removal of Rh from PMR effluents containing smaller amounts of other transition metal ions was somewhat more effective. Despite the large amounts of Ni, Cu and Fe in many of the tested effluents, no uptake of any of these metal ions has been observed. The platinum group metal (PGM) selectivity of these ion exchangers over the other transition metals has thus proven to be very high.

Highly Selective and Efficient Recovery of Pd, Pt, and Rh from Precious Metal‐Containing Industrial Effluents with Silica‐Based (Poly)Amine Ion Exchangers

Abstract The recovery of Pd, Pt, and Rh from batches of authentic industrial precious metal refinery (PMR) effluents containing large amounts of Ni, Cu, and Fe ions and relatively small amounts of the expensive Pt, Pd, and Rh ions was investigated with silica‐based anion exchangers containing monoamine, ethylenediamine, and diethylenetriamine functionalities. All platinum group metal (PGM) recoveries have proven to be highly selective over various base metal ions, such as Cu2+. Quantitative recovery of Pd and Pt from some of the PMR effluents was effected by these ion exchangers, whereby HCl appears to be a powerful desorbent. Moreover, in most cases, Pd and Pt have been completely stripped from the ion exchangers with thiourea or with a combination of thiourea and HCl. Rh recovery from a base metal refinery (BMR) effluent was found to be less efficient, with maximum adsorption values of just over 20% and with a maximum desorption of about 50%. Rh stripping after extraction from one of the PMR effluents appeared to be much more successful. The well‐known difficulties in Rh recovery can be largely attributed to the occurrence of several kinetically inert species in hydrometallurgical effluents.

Metallamacrocyclic complexes of Ni(II) with 3,3,3′,3′-tetraalkyl-1,1′-aroylbis(thioureas): crystal and molecular structures of a 2 : 2 metallamacrocycle and a pyridine adduct of the analogous 3 : 3 complex

The crystal and molecular structure of a square planar 2 : 2 metallamacrocyclic Ni(II) complex of 3,3,3′,3′-tetraethyl-1,1′-isophthaloylbis(thiourea) is reported together with that of the octahedral Ni(II) pyridine adduct of the corresponding 3 : 3 metallamacrocycle synthesised from 3,3,3′,3′-tetraethyl-1,1′-terephthaloylbis(thiourea). The former complex is a nearly planar molecule which packs in a manner dictated by strong π–π interactions. The latter is found to possess an unusually large unit cell containing two adduct molecules, with significantly dissimilar conformations, and five pyridine guests. Most of the guest molecules are located in close proximity to the adduct molecules, in contrast with the mode of host–guest interactions observed for pyridine adducts of analogous 2 : 2 metallamacrocycles.