Guest Uptake by Rigid Polyphenylene Dendrimers Acting As a Unique Dendritic Box in Solution Proven by Isothermal Calorimetry

Abstract

The existence of a dendritic box in polyphenylene dendrimers is demonstrated by isothermal titration calorimetry (ITC). The thermodynamic parameters of the uptake process of a variety of small guest molecules into the dendrimers are measured. ITC revealed that for dendrimers with an unpolar interior this process is mainly entropically driven. Two processes have been elucidated for the entropy gain: (i) the release of solvent molecules which solvate the guests and (ii) solvent molecules in the voids of the dendrimers which are replaced by the guests. For dendrimers which are substituted with polar functionalities in the core, enthalpic effects become more dominant as some hydrogen bonds and π–π-interaction come into play. Because of the rigidity of the dendrimer host, these less specific interactions can only occur in the core of the differently functionalized interior of the dendrimers since the surface is the same all over. Thereby, it is evidenced that guest molecules can be selectively trapped inside the dendrimer and not on the surface. For different host–guest pairs ITC resulted in characteristic thermodynamic parameters for the uptake. These values might give guidelines to estimate and model the binding strength and the release properties between a drug and dendritic carrier.

Importance of the Anchor Group Position (Para versus Meta) in Tetraphenylmethane Tripods: Synthesis and Self‐Assembly Features

“…Very similar1Dc onductance histograms of log(G/G 0 )w ere obtained for both molecules, showingabroad conductance feature, which can be fitted by two peaks (see Figure 9). For the para derivative ( 7), these two peaks give high and low conductance valuese qual to G H = 10 À3.16 AE 0.46 G 0 and G L = 10 À4.07 AE 0.59 G 0 ,a nd for the meta derivative( 21)v alues of G H = 10 À3.32 AE 0.54 G 0 and G L = 10 À4.05 AE 0.40 G 0 ,r espectively.T he low conductance values are almosti denticalf or both molecules,w hereas the high conductance value is slightly higherf or the para derivative (7). It was proposed recently that al ow conductance value G L may be caused by aw eakly conducting cofacial p-p stacked dimer formation, whereas G H represents true single-molecule conductance.…”

“…Functional group transformation chemistry subsequently allows both the establishment of the acetyl-protected thiol anchor groups and the transformation of the phenolic hydroxy group Figure 1. Structure of molecular tripods (7,21), and proposed arrangement of 21 on ag old substrate. Chem.…”

“…The SAMs for the STM characterization at 77 Kw ere prepared on freshly annealed gold-coated (300 nm) mica substrates (typically 55mm), which were purchased from Georg-Albert-PVD, Germany.T he substrates were immersed in as olution (0.25 mm)o fmeta (21)o rpara (7)t ripodal molecules in am ixture of methanol/THF (3:1, v/v) containing 30 %o fa1m solution of ammonia in methanol as cleaving agent, at room temperature for 48 h. The samples were rinsed thoroughly with methanol, DI water,a nd THF,d ried under as tream of argon, and placed into the UHV-STM chamber.…”

“…Te trahedral molecules based on tetraphenylmethane have been studied extensively in recent decades. In particular, they have been used as shape-providing core motives of covalent organic frameworks (COFs), [1][2][3] porous organic polymers (POPs), [4,5] hyperbranched polymers and dendrimers, [6,7] molecular gyroscopes, [8,9] ando rganic light-emittingd iodes (OLEDs). [10,11] In addition, the potential of the tetrahedral synthon to act as at ripodalf oot, [12] organizing and controlling the spatialarrangement of molecules in self-assembledm onolayers (SAMs) on flat substrates, has been investigated.…”

“…The concept was pioneered by Tour and co-workers with their carbazole and oligophenylenethylene-fullerene hybrids. [34][35][36][37] In this paper,w ec ompare two regioisomers of tetraphenylmethanef ooting architectures, namely the derivativew ith the three acetyl-protected thiol anchor groups in para positions (7), and the analogue with the anchor groups in meta positions (21) ( Figure 1). As the active tail group facilitating their spectroscopic investigations,b oth model compounds expose an itrile group in the para position, decorating the fourth remaining phenyls ubunit.…”