Self-diffusion of water and poly(amidoamine) dendrimers in dilute aqueous solutions

Abstract

Medium generation PAMAM dendrimers are extensively researched as drug delivery vehicles therefore detailed knowledge of their physico-chemical properties in solution is vital. We have selected ethylenediamine core, generation five poly(amidoamine) (PAMAM_E5) dendrimers (amine terminated PAMAM_E5.NH 2 and its succinamic acid derivative PAMAM_E5.SAH, respectively) as model compounds to study their dynamic behavior in water as a function of pH and concentration. Diffusion coefficients of water and the dendrimers were determined in deuterium oxide using pulse-field gradient stimulated echo (PGSE) NMR. The diffusion rate for PAMAM_E5.NH 2 increased monotonously with increasing pH values while for PAMAM_E5.SAH a maximum was found at an isoelectric value of pH ¼ 5.7. The apparent diffusion coefficients of dendrimers decreased linearly with increasing concentration measured at their self-pH (pH ¼ 9.4 for PAMAM_E5.NH 2 and pH ¼ 5.7 for PAMAM_E5.SAH) in the absence of added salts. The observations could be explained by considering hard sphere interactions between strongly hydrated dendrimer molecules. The average hydrodynamic radii of dendrimers were determined by extrapolating the measured diffusion coefficients to zero dendrimer concentration and applying the Stokes-Einstein equation. The calculated values were R H ¼ 3.05 AE 0.04 nm for PAMAM_E5.NH 2 and R H ¼ 3.37 AE 0.08 nm for PAMAM_E5.SAH respectively. Measured diffusion coefficients of water (D 2 O) also decreased linearly with increasing dendrimer concentration. From the concentration dependence, the average number of water molecules that form one dynamic unit with one macromolecule could be calculated on the basis of three different obstruction models. It has been concluded that hydrated PAMAM dendrimers in aqueous solutions behave as soft colloids against solvent molecules but as hard-sphere colloids against each other. Their equivalent hard-sphere radii were found to be equal to the measured hydrodynamic radii.

The pore network and the adsorption characteristics of mesoporous silica aerogel: adsorption kinetics on a timescale of seconds

“…33 The cryoporometric constant for water is 30 K nm. 42 The pore size distribution of the aerogel was reconstructed both from the melting and the freezing curves by using Eqs. 2a and 2b (n m = 2, n f = 3), respectively.…”

Spectroscopic and calorimetric studies of formation of the supramolecular complexes of PAMAM G5-NH2 and G5-OH dendrimers with 5-fluorouracil in aqueous solution

“…S1) as well as the mixtures of this drug and PAMAM G5-OH (Fig. S2) in heavy water as in previous 1 H NMR studies of PAMAM-NH 2 (Bányai et al, 2013;Barra et al, 2014a,b;Buczkowski et al, 2012bBuczkowski et al, , 2013Cao et al, 2013;Giri et al, 2011;Hu et al, 2010Hu et al, , 2012Keri et al, 2015) and PAMAM-OH dendrimers (Choi et al, 2012;Giri et al, 2011;Gomez et al, 2009a,b;Hu et al, 2012;Pellechia et al, 2004;Wang et al, 2013). With increasing the concentration of 5-fluorouracil in the mixture of drug and dendrimer one can observe that peak at 2.6 ppm corresponding to the protons of methylene groups present at tertiary amine groups is not clearly shifted during the drug bonding by cationic PAMAM G5-NH 2 dendrimer (Fig.…”

Development of a disposable paper-based potentiometric immunosensor for real-time detection of a foodborne pathogen

“…This observation can be attributed to changes in IMS structure, caused by the repulsion operated by non-connected dendrimer amine groups (that stays protonated at pH 7), that may transform the dendrimer in a flatter and dislike shape over the analysis time. As PAMAM(NH 2 ) 64 dendrimer presents a relative flexibility "container properties", this setback is usually overcome simply by the use of a phosphate ionic background that gone into dendrimer pores creating an inert and stable conformation (Banyai et al, 2013;Scott et al, 2005;Taghavi Pourianazar et al, 2014). Although, should be noted that in this work was used a low concentration of ions in PB (0.01 mol L −1 ) in that may not be sufficient to block the positive charge (Lee et al, 2005).…”