Nicole Werner

Gaussian effective interaction between flexible dendrimers of fourth generation: A theoretical and experimental study

We propose a theory for the effective interaction between soft dendritic molecules that is based on the shape of the monomer density profile of the macromolecules at infinite dilutions. By applying Flory-type arguments and making use of the experimentally measured density profiles, we derive a Gaussian effective interaction whose parameters are determined by the size and monomer number of the dendrimers that are derived from small-angle neutron scattering (SANS) measurements. By applying this theory to concentrated dendrimer solutions we calculate theoretical structure factors and compare them with experimental ones, derived from a detailed analysis of SANS-data. We find very good agreement between theory and experiment below the overlap concentration, where drastic shape deformations of the dendrimers are absent.

Determination of the structure factor of polymeric systems in solution by small-angle scattering: A SANS-study of a dendrimer of fourth generation

The analysis of concentrated solutions of a dendrimer G4 of fourth generation by small-angle neutron scattering (SANS) is presented. The determination of the structure factor S(q) (q = (4π/λ)sin(0/2); λ: wavelength of radiation; 0: scattering angle) from experimental data is discussed in detail. It is shown that the incoherent contribution I incoh to the measured scattering intensity may profoundly disturb the determination of S(q), in particular at high concentrations of the solute molecules. Contrast variation is used to determine I incoh which is subtracted subsequently from the measured intensities. Moreover, a general method for the check of the data of S(q) for internal consistency is presented. It is based on the expansion of S(q) into powers of q 2 . The structure factor S(q) obtained from the corrected data is shown to be consistent except at the highest concentration of the dendrimer G4 under consideration here. This finding is explained by a change of the form factor of the dendrimers due to overlap of the particles. The method of analysis presented here is general and can be applied to SANS-data of other structures as well.

Hydrophilic oxybathophenanthroline ligands: synthesis and copper(II) complexation

Hydrophilic oxybathophenanthroline dendrons (generation 1–3) have been synthesized by treatment of 4,7-bis(4′-hydroxyphenyl)-1,10-phenanthroline with the corresponding bromo-functionalized etheraryl branching units containing triethylene glycol monomethyl end groups. Radiotracer experiments using 64Cu prove the rapid formation of stable copper(II) complexes in aqueous solution. These 64Cu complexes remain unchanged even upon addition of a high excess of glutathione as competing ligand, thus demonstrating the high stability of the formed copper(II) complexes. Electronic and EPR spectroscopy indicate the formation of [Cu(L)2(OH2)2]2+ (L = ligand) complexes in aqueous solution, confirmed by time-resolved laser fluorescence spectroscopy and supported by molecular mechanics modeling.

Segmental contrast of dendrimers: a small-angle neutron scattering study including contrast variation

We present an analysis of the distribution of endgroups within a urea-functionalized poly(propyleneamine)-dendrimer of 4th generation by small-angle neutron scattering (SANS). The contrast between the solute and the solvent is varied in a systematic fashion (contrast variation). The analysis of the scattering intensity corrected for incoherent contributions gives three partial scattering functions that depend differently on contrast. It is demonstrated that difference in contrast of the different segments of the molecules give an additional scattering contribution not related to the overall structure. From these data the scattering length density distribution within the dendritic structure can be derived. All results obtained for the fully protonated dendrimer under consideration here agree with the deductions obtained previously for a partially deuterated dendrimer having the same chemical structure.