Ernst Cleve

Complex Formation between Cucurbit[n]urils and Alkali, Alkaline Earth and Ammonium Ions in Aqueous Solution

The complex formation between cucurbit[5]uril, decamethylcucurbit[5]uril and cucurbit[6]uril and alkali, alkaline earth and ammonium cations is examined. The solubility of these ligands is rather small in aqueous solution. In the presence of salts the solubility normally increases due to the formation of complexes. The total concentration of the ligands can be easily measured from the total organic carbon content of the salt solutions saturated with the ligand. From these results it is possible to calculate the stability constants of the complexes formed even without the knowledge of the exact solubility of the ligand.

The determination of complex stabilities between different cyclodextrins and dibenzo-18-crown-6, cucurbit[6]uril, decamethylcucurbit[5]uril, cucurbit[5]uril, p-tert-butylcalix[4]arene and p-tert-butylcalix[6]arene in aqueous solutions using a spectrophotometric method

Abstract The solubility of dibenzo-18-crown-6, cucurbit[6]uril, decamethylcucurbit[5]uril, cucurbit[5]uril, p - tert -butylcalix[4]arene and p - tert -butylcalix[6]arene in aqueous solution increases in the presence of α-, β- and γ-cyclodextrin due to complex formation. The stability constants of the complexes formed are determined from UV-spectrophotometric measurements. Even without the knowledge of the molar absorptivities and of the solubilities of the guest molecules, the calculation of the stability constants is possible. The cavity size of the cyclodextrins used has only a minor influence upon the stability constants of the complexes formed in solution. The different guest molecules do not fit completely into the cavities of the cyclodextrin molecules. Obviously, supramolecular hosts like, e.g. dibenzo-18-crown-6 or calixarenes form complexes with cyclodextrins.

The Interactions Between Nonionic Surfactants and Cyclodextrins Studied by Fluorescence Measurements

The complex formation between some nonionic surfactants and α-, β- and γ-cyclodextrin was studied by fluorescence measurements. The relative fluorescence intensity of a solute containing a nonionic surfactant at a constant concentration far below the critical micelle concentration (CMC) are enhanced by the addition of cyclodextrins. Non linear type equations were derived to obtain stability constants by fluorescence measurements for inclusion complexes formed between cyclodextrins and the nonionic surfactants. In most cases 1 : 1- and 2 : 1-complexes (ratio of cyclodextrin to surfactant) are formed.

Determination of complex stabilities with nearly insoluble host molecules. Part II. Complexation of alkali and alkaline earth metal cations with dibenzo crown ethers in aqueous solution

An experimental method was developed to determine the stability constants with nearly insoluble ligands in homogeneous solution. This method was tested using dibenzo crown ethers, which have a very low solubility in aqueous solution. The stability constants for the complexation of alkali and alkaline earth metal cations with different dibenzo crown ethers were determined in aqueous solution. Owing to the complex formation the total concentration of the ligand in solution increases. Dibenzo crown ethers absorb in the ultraviolet spectral range, hence the increase in the ligand concentration can be easily detected. Without the knowledge of the molar absorptivities of the ligands and of the corresponding complexes and of the solubilities, the stabilities of the complexes formed can be calculated under certain assumptions. To verify these assumptions, the solubilities of the dibenzo crown ethers and the molar absorptivities were determined. The kinetics of the solubilization process of the ligands was followed by spectrophotometric measurements.

Untersuchungen zum Schmelz- und Strukturverhalten von Polyethylenterephthalatfasern in Luft bei 1 bar und in überkritischem CO2 bis 280 bar

A comparative study was carried out as to the influence of CO 2 on changes of the fibre structure of thermofixed and unfixed PETP multifilament and monofilament fibres in relation to pressure and temperature. To this aim measurements were carried out on the glass transition-, the pre-melting- and the melting temperature with a dynamic heat flow difference calorimeter (DDC) in air at I bar, as well as in CO 2 at pressures up to 280 bar. In the thermograms taken under high pressure the melting point was clearly visible, in contrast to the glass transition- and pre-melting temperatures. Owing to its hydrophobic properties, the CO 2 is capable of diffusing into the fibre where it can act as a virtual contamination to the effect that the melting point at 280 bar is lowered by 13-14 C for all PETP fibres. Measurements of the pre-melting temperature, stress-strain behaviour and shrinkage after treatment of the PETP fibres at temperatures between 80 and 200 C in air and CO 2 show that particularly in the case of non-thermofixed PETP yarns at 280 bar structural changes are brought about from temperatures as low as 80 C upwards which are attributable to partial crystallite growth in the imperfect areas of the fibre polymers. In CO 2 at 280 bar. this results in higher pre-melting temperatures, increased shrinkage and higher elasticity of the fibres in contrast to air at I bar at comparable treatment temperatures. In the case of thermofixed fibres these effects are, as a rule, considerably less marked.

Oberflächenstrukturierung polymerer Fasern durch UV‐Laserbestrahlung, 15. Beschreibung des Temperaturfeldes in PETP‐Polymeren während und nach der Laserbestrahlung mit einem gepulsten UV‐Laser

For understanding the generation of UV laser induced surface structures of PETP polymers the temperature field within the irradiated surface is calculated in dependence on the laser irradiation wavelength (193 nm, 248 nm, 308 nm), pulse time, pulse form, the irradiation intensity and depth, using temperature-independent material data of PETP polymers known from literature. For this purpose the solution function of the one-dimensional heat differential equation is used. Depending on the order of magnitude of the absorption coefficient of the polymer for UV light of different wavelengths, surface temperatures of approx. 16 000°C (193 nm), 11 000°C (248 nm) and 500°C (308 nm) are calculated at the end of the laser pulse. The temperature input within the polymer layer is limited to only a very small penetration depth. For the irradiation with the two laser wavelengths of 193 nm and 248 nm this is less then 0.4 μm. The cooling process is considerably slower, reaching the initial temperature after approx. 4 μs.

Anion Complexation by Meso-Octamethylcalix[4]pyrrole in Aqueous Solution

The ligand calix[4]pyrrole is quite insoluble in aqueous solution. In the presence of NaCl, KCl, CsCl, NH4Cl, CaCl2, and CdCl2, the solubility of calix[4]pyrrole linearly increases with the salt concentration. The ligand calix[4]pyrrole forms stable complexes with the chloride anion. All other halogen anions do not form complexes. The measurement of the amount of dissolved ligand allows the determination of the complex stabilities in aqueous solution. This experimental method is discussed in detail due to its general suitability to study the complexation reactions with nearly insoluble ligands.

Surface structuring of synthetic fibers by UV laser irradiation simulation of the temperature profile at the polymer surface

Abstract An investigation of the mechanism of the UV laser induced temperature field in a PETP-polymer is presented. We discuss a specific mathematical solution of the heat equation for large-area (uniform) irradiation on the PETP-substrate in relation to laser and substrate parameters. Depending on the order of magnitude of the absorption coefficient of the polymer for different UV-light surface temperatures of approx. 16,000°C (193 nm), 11,000°C (248 nm) and 520°C (308 nm) are calculated by simulation at the end of the laser pulse. The temperature input within the polymer layer is limited to only a very small penetration depth (< 0.4 μm at 193 nm, 248 nm and<8 μm for 308 nm). Besides the effect of surface structuring, material ablation processes also occur simultaneously during laser irradiation. Theoretically calculated results of the material removal depth on the PETP-polymer agree largely with the experiments.