Harold Boerrigter

Novel ligands for the separation of trivalent lanthanides and actinides-tetrakis(phosphane sulfide) and -(phosphinic acid) cavitands

Cavitands with phosphane sulfide moieties 4 and 8a,b were prepared in good yields from their phosphane oxide analogues, as more stable alternatives for the dithiophosphinic acids used at present. The cavitands 7a and 7b with flexible butoxyphosphane oxide ligating sites are more efficient than cavitand 3 having rigid methylphosphane oxide groups as was studied with EuIII picrate extractions. Due to the absence of an ionic functionality in the phosphane sulfides 4 and 8a,b AmIII and EuIII are not extracted, not even in the presence of synergents (e.g. TBP, TOPO, HDNNS). Cavitand 10 with phosphinic acid groups efficiently extracts EuIII in 1:1 or 2:1 complexes, depending on the metal-to-ligand concentration ratio (extraction constants Kex1 = 3.9·10-5M2 and Kex2 = 1.9·102M, respectively). Furthermore, in the case of 10 EuIII is preferentially extracted over AmIII with a separation factor SEu/Am up to 5.

Mechanistic study of trivalent europium transport through supported liquid membranes (SLMs) and a novel immobilized phase solvent extraction (IPSE) system

As a new method of membrane formation, we have investigated microcellular foaming of thin (100 μm) polysulfone films containing varying trace concentrations of tetrahydrofuran using carbon dioxide as a physical blowing agent. Membrane morphologies were obtained by first saturating the polymer with carbon dioxide at 5 MPa, and subsequently heating the sample above the glass transition temperature (Tg) of the polymer/gas mixture at atmospheric pressure. The presence of tetrahydrofuran in the polymer at concentrations above 0.04 wt.% led to a transition from a closed cellular structure into novel open-cellular morphologies. The open structure manifests itself by small spot-like openings (diameters between 10 and 100 nm) in the cell walls. The mass transport resistances of the porous films were quantified using gas permeation measurements, and a Knudsen-type separation mechanism was observed. Detailed investigation showed that the transport resistance can mainly be controlled by two variables: (1) the concentration of the residual solvent in the polymer film, and (2) the foaming temperature. At optimal foaming temperatures, thin cell walls are obtained, which break up when fluctuations in the wall thickness are amplified by plasticizing solvent molecules.

Proximally Functionalized Cavitands and Synthesis of a Flexible Hemicarcerand

A general study on the synthesis of partly bridged octols3a-d and4c-d is described. Tri-bridged diol3c can be prepared in 54% yield in DMSO at 70°C with excess CH2BrCl or in 52% yield in DMF at 70°C with only 4 equiv. of CH2BrCl. 1,3-Di-bridged tetrol4a, one of the two possible di-bridged isomers formed in preference to the other, was obtained in 30% yield. Tri-bridged diols3c andd can be selectively debrominated in one step by treatment with 5 equiv. ofn-BuLi in THF to afford the corresponding dibromo derivatives8a andb in 77% and 76% yields, respectively. After incorporation of the fourth bridge, the remaining two bromines can be replaced by C(O)OMe to give9c (60%), by OH to give9d (62%) or by CN to give9f (>95%). When the lithiated derivatives of3c andd are quenched with electrophiles other thanH+, a selectively functionalized tri-bridged diol with hydroxyl (8c, 47%) and selectively functionalized cavitands with thiomethyl (9g, 25%) or iodo (9h, 20%) groups can be synthesized. Two molecules of9d were coupled with CH2BrCl in DMSO/THF under high dilution conditions to give the flexible hemicarcerand10 in 71% yield.

Selective functionalization of resorcinarene cavitands; single crystal X-ray structure of a distally functionalized cavitand

A new method for the selective functionalization of resorcinarene cavitands is described starting from tetrakis(bromomethyl)cavitands.

A modular approach to potential synthetic receptors with large surfaces based on crown[n]cavitands

Crown[n]cavitands were synthesized by alkylation of tetrahydroxycavitands with polyethyleneglycol ditosylates. The bridging of two hydroxy groups at adjacent aromatic rings by a pentaethyleneglycol unit is favored over the bridging of two hydroxy groups at opposite aromatic rings. The presence of a sodium base enhances the formation of the 1,2-crown[n]cavitand and improves the yield. The combination of 1,2-crown[6]cavitands with calix[4]arenes or resorcin[4]arenes resulted in potential receptor molecules with large hydrophobic surfaces.

An infrared study of host-guest association in solution by substituted resorcinarene cavitands. Part II. Comparison of halide complexation by tetrathiourea cavitands and a simple thiourea

Binding of halide has been studied for two thioureido-substituted resorcin[4]arenes and a model compound, with special attention to the NH stretching region and the bonding behaviour. Mathematical techniques such as curve fitting, Fourier self-deconvolution and Partial Least Squares analysis have been applied to investigate the characteristics of bonding, and the results are correlated with information obtained from a steric analysis.It is shown that association of the halide guest takes place via hydrogen bonding between halide ions and thioureido moieties solely for all ligands. Compared to a simple thiourea compound, pre-organisation of the thioureide side-chains on the upper rim by intramolecular bonding enhances the capability of association by a factor of 10 to 100.An analogy is found between complexation of a halide anion in the cavitands and complexation of an iodide anion by the model compound. This suggests that within the cavitand, chloride, bromide and iodide are all complexed by at least two thioureido moieties, whereas a simple thiourea binds chloride and bromide in a 1-to-1 fashion, and iodide in a 2-to-1 fashion.

Determination of the association constant of strongly bonded host–guest systems by multivariate regression of infrared spectroscopic data

A new method applying infrared spectroscopy in combination with multivariate regression for the determination of association constants has been developed to overcome the sensitivity problems arising when strongly associating complexes are investigated by NMR or UV–VIS methods. A concentration profile for the complex is derived by correction of multivariate regression data. Subsequent iterative fitting of the corrected data yields the association constant.The regression part is not integrated in the process of the association constant determination itself. Separating data treatment from the actual fitting procedure offers a means of evaluating the quality of the data set and the order of association before the actual calculation of the association constant. Furthermore, the method of regression can be varied and the applicability of the selected method can be assessed from the data-regression output.From simulated data, it is estimated that an association constant range of 102–106M–1 can be determined when measuring at millimolar concentration levels.Examples are shown for halide complexation of a thiourea compound and a urea-substituted resorcinarene cavitand.

An infrared study of host–guest association in solution by substituted resorcinarene cavitands. Part I. Structural aspects of halide complexation by a tetraurea cavitand

Complexation of chloride, bromide and iodide ion was investigated for a resorcinarene cavitand substituted on its upper rim with four N-(o-nitrophenoxy-n-octyl)ureido groups. Association in chloroform takes place solely via hydrogen bonding by the urea moieties, and is monitored well by infrared spectroscopy. Association constants are high, about 104 M–1, and a small preference for chloride over bromide and iodide is observed.Upon binding of the anion, the array of weak intramolecular bonds is disrupted and replaced by hydrogen bonds towards the halide lone pairs. No significant reorganisation of the urea o-nitrophenoxy-n-octyl substituents was found, which suggests a re-ordering of the urea groups only upon binding. Co-operation of the bonding moieties is observed in the complexation of halide ions as a result of pre-organisation of the urea groups on the upper rim of the resorcinarene cavitand by weak hydrogen bonding interactions.

Study of conformational behavior of CMP(O)-cavitands by NMR spectroscopy and X-ray analysis in relation to the extraction properties

Tetra-CMP(O)-functionalized cavitands are very effective europium(III) extractants. Cavitand 1b is the strongest ligand and has the highest extraction constant for 1:1 complexation with Eu(picrate)3 (viz. Kex 1 = 2.7 × 1012M−4). The conformational behavior of the CMP(O) cavitands 1a,b and 2a,b was studied by means of NMR spectroscopy. The introduction of an N-propyl substituent imposes large conformational differences due to inhibition of the free rotation around the amide N-C(O) bond. The Gibbs free energy of activation is about 75 kJ/mol for a rotation around the amide moiety (inwardoutward motion). The N-propyl-substituted cavitands form clusters; this aggregation originates from the association of propyl and pentyl chains of the cavitand molecules. The ability of bromomethylcavitand 3 to complex solvent molecules (e.g. CH2C12 or toluene) in the cavity is illustrated by a single crystal X-ray structure (with CH2C12).