Resorcinarene Cavitand Research Articles

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 II.1 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.

Ligands for EuIII, FeIII, SrII, and UO Based on CMPO‐Functionalized Resorcinarene Cavitands; Synthesis and Extraction

AbstractPartially functionalized cavitands (7a–d) have been synthesized starting from the tetrakis(bromomethyl)cavitand 6. New cavitand‐based cation ligands, with one to three carbamoylmethylphosphane oxide (CMPO) moieties (11a–d), were prepared in good (66–90%) yields. The ligands 11a–d extract EuIII, but do so less effectively than the tetra‐CMPO cavitand 1. The decreasing number of CMPO groups which result in decreasing extraction percentages for EuIII, also decrease the selectivity of EuIII over that of FeIII, SrII, and UO. There is a difference in extraction behavior, determined by radio‐tracer experiments, between the distal and proximal disubstituted ligands, 11b and 11c, respectively. The extraction constants for the 1:1 complex of 11b and 11c with Eu(picrate)3 are Kex = 6.7 · 108 M−4 and 3.7 · 109 M−4, respectively.

Novel Resorcinarene Cavitand-Based CMP(O) Cation Ligands: Synthesis and Extraction Properties.

Tetrafunctionalized resorcinarene cavitands (4-6) have been synthesized starting from tetrakis(bromomethyl)cavitand 3. New cavitand-based cation ligands with (carbamoylmethyl)phosphonate (CMP) and -phosphine oxide (CMPO) moieties (8a,b and 9a,b) were prepared via two different routes in good (45-86%) overall yields. The ligands (8a,b and 9b) are very effective europium extractants. Ph(2)CMPON(Pr)-cavitand 8b has the highest extraction constant, determined with radiotracer experiments, for 1:1 complexation with Eu(picrate)(3) (K(ex)(1) = 2.7 x 10(12) M(-)(4)). The steric preorganization of the four CMP(O) moieties on the resorcinarene cavitand improves the efficiency and selectivity [of Eu(III) over UO(2)(II) and Fe(III)] of the metal extraction processes, compared to simple CMP(O) extractants.

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.