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

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

Synthesis and Selective Loading of Polyhydroxyethyl Methacrylate‑<i>l</i>‑Polysulfone Amphiphilic Polymer Conetworks

Polyhydroxyethyl methacrylate-<i>linked by</i>-polysulfone amphiphilic polymer conetworks of two types of segments with <i>T</i>_g above room temperature are presented. The conetworks are prepared by free radical copolymerization of methacryloyl-terminated PSU macromers with 2-ethyl methacrylate, followed by removal of the TMS protecting groups by acidic hydrolysis. Phase separation in the nanometer range due to the immiscibility of the two covalently linked segments is observed using transmission electron and scanning force microscopy. The swelling of the conetworks in water and methanol as polar solvents and chloroform as nonpolar solvent are studied gravimetrically and then in a more detailed fashion by solid-state NMR spectroscopy. Selective swelling and also targeted loading of a small organic model compound specifically to one of the two phases are demonstrated

Joining Two Natural Motifs: Catechol-Containing Poly(phosphoester)s

Numerous catechol-containing polymers, including biodegradable polymers, are currently heavily discussed for modern biomaterials. However, there is no report combining poly­(phosphoester)­s (PPEs) with catechols. Adhesive PPEs have been prepared via acyclic diene metathesis polymerization. A novel acetal-protected catechol phosphate monomer was homo- and copolymerized with phosphoester comonomers with molecular weights up to 42000 g/mol. Quantitative release of the catechols was achieved by careful hydrolysis of the acetal groups without backbone degradation. Degradation of the PPEs under basic conditions revealed complete and statistical degradation of the phosphotri- to phosphodiesters. In addition, a phosphodiester monomer with an adhesive P–OH group and no protective group chemistry was used to compare the binding to metal oxides with the multicatechol-PPEs. All PPEs can stabilize magnetite particles (NPs) in polar solvents, for example, methanol, due to the binding of the phosphoester groups in the backbone to the particles. ITC measurements reveal that multicatechol PPEs exhibit a higher binding affinity to magnetite NPs compared to PPEs bearing phosphodi- or phosphotriesters as repeating units. In addition, the catechol-containing PPEs were used to generate organo- and hydrogels by oxidative cross-linking, due to cohesive properties of catechol groups. This unique combination of two natural adhesive motives, catechols and phosphates, will allow the design of novel future gels for tissue engineering applications or novel degradable adhesives

Poly(ethylene glycol)-Functionalized Hexaphenylbenzenes as Unique Amphiphiles: Supramolecular Organization and Ion Conductivity

The synthesis of a series of propeller-shaped hexaphenylbenzenes (HPB) substituted with one (<b>3</b>), two (<b>1</b>) and four (<b>2</b>) poly­(ethylene glycol) (PEG) chains as well as of an ortho-connected trimer of HPBs bearing two PEG chains (<b>4</b>) result in remarkable amphiphiles with supramolecular organization and suppressed dynamics. The thermodynamic state and self-assembly are studied with DSC and X-ray diffraction whereas the dynamics of HPB core and PEG segments are elucidated via heteronuclear NMR and dielectric spectroscopy. The phase state is largely determined by the rod–coil nature and architecture of block copolymers comprising a HPB “mesogen’ and flexible PEG chains. In addition, the molecular shape of the ortho-connected trimer of HPBs (<b>4</b>) promotes π–π stacking and gives rise to a supramolecular columnar organization uncommon to most other HPBs. The emerging dynamic picture is that of practically frozen HPB cores that are surrounded by mobile PEG segments. The implications of this supramolecular organizationstacked/immobile HPB cores and flexible/fast moving PEG segments with suppressed crystallinityto ion transport are discussed with respect to the conductivity measurements in amphiphiles doped with LiCF₃SO₃ salt at different [EG]:[Li⁺] ratios. A unique feature of the doped amphiphiles is the Vogel–Fulcher–Tammann temperature dependence of ionic conductivity with values that are comparable to the archetypal polymer electrolyte (PEG)_<i>x</i>LiCF₃SO₃

Evaluation of quantum dot cytotoxicity: interpretation of nanoparticle concentrations versus intracellular nanoparticle numbers

<p>While substantial progress has been achieved in the design of more biocompatible nanoparticles (NP), detailed data are required on the precise interactions of NPs and their environment for more reliable interpretation of toxicity results. Therefore, this study aims to investigate the interaction of two quantum dots (QDs) of the same core material CdSe/ZnS coated with two different amphiphilic polymers, with two well-established mammalian cell lines representing possible sites of QD accumulation. Results are linked to either extracellular QD concentrations (given dose) or cellular QD levels (number of internalized particles). In this study, QD internalization, effects on cellular homeostasis, and consequent inflammatory and cytoskeletal alterations caused by these QDs were explored. Fluorescence imaging techniques, including; image-based flow cytometry, confocal microscopy and high-content imaging with the InCell analyzer were used in a multiparametric methodology to evaluate cell viability, induction of oxidative stress, mitochondrial health, cell cytoskeletal functionality and changes in cellular morphology. Gene expression arrays were also carried out on 168 key genes involved in the cytoskeletal architecture and inflammatory pathway accompanied with the analysis of focal adhesions as key markers for actin-mediated signaling. Our results show distinct differences between the PMA and PTMAEMA-<i>stat</i>-PLMA coated QDs, which could mainly be attributed to differences in their cellular uptake levels. The toxicity profiles of both QD types changed drastically depending on whether effects were expressed in terms of given dose or internalized particles. Both QDs triggered alterations to important but different genes, most remarkably the up-regulation of tumor suppression and necrosis genes and the down regulation of angiogenesis and metastasis genes at sub-cytotoxic concentrations of these QDs.</p

Biocompatible Polylactide-<i>block</i>-Polypeptide-<i>block</i>-Polylactide Nanocarrier

Polypeptides are successfully incorporated into poly­(l-lactide) (PLLA) chains in a ring-opening polymerization (ROP) of l-lactide by using them as initiators. The resulting ABA triblock copolymers possess molecular weights up to 11000 g·mol^–1 and polydispersities as low as 1.13, indicating the living character of the polymerization process. In a nonaqueous emulsion, peptide-initiated polymerization of l-lactide leads to well-defined nanoparticles, consisting of PLLA-<i>block</i>-peptide-<i>block</i>-PLLA copolymer. These nanoparticles are easily loaded by dye-encapsulation and transferred into aqueous media without aggregation (average diameter of 100 nm) or significant dye leakage. Finally, internalization of PLLA-<i>block</i>-peptide-<i>block</i>-PLLA nanoparticles by HeLa cells is demonstrated by a combination of coherent anti-Stokes Raman spectroscopy (CARS) and fluorescence microscopy. This demonstrates the promise of their utilization as cargo delivery vehicles

Supramolecular Linear‑<i>g</i>‑Hyperbranched Graft Polymers: Topology and Binding Strength of Hyperbranched Side Chains

Complex, reversible hyperbranched graft polymer topologies have been obtained by spontaneous self-assembly. Well-defined adamantyl- and β-cyclodextrin-functionalized polymers were employed to generate linear-<i>g</i>-(linear–hyperbranched) supramolecular graft terpolymers. For this purpose the synthesis of monoadamantyl-functionalized linear polyglycerols (Ada-<i>lin</i>PG) and hyperbranched polyglycerols (Ada-<i>hb</i>PG) as well as poly­(ethylene glycol)-<i>block</i>-linear polyglycerol (Ada-PEG-<i>b</i>-<i>lin</i>PG) and poly­(ethylene glycol)-<i>block</i>-hyperbranched poly­(glycerol) (Ada-PEG-<i>b</i>-<i>hb</i>PG) block copolymers was established. Isothermal titration calorimetry (ITC) with β-cyclodextrin revealed a shielding effect of hyperbranched polyglycerol for the adamantyl functionality, which was significantly less pronounced when using a linear spacer chain between the adamantyl residue and the hyperbranched polyglycerol block. Additionally, well-defined poly­(2-hydroxypropylamide) (PHPMA) with pendant β-cyclodextrin moieties was synthesized via RAFT polymerization and sequential postpolymerization modification. Upon mixing of the β-cyclodextrin-functionalized PHPMA with Ada-PEG-<i>b</i>-<i>hb</i>PG, a supramolecular linear-<i>g</i>-(linear–hyperbranched) graft terpolymer was formed. The self-assembly was proven by ITC, diffusion-ordered NMR spectroscopy (DOSY), and fluorescence correlation spectroscopy (FCS)

Poly(Methyl Vinyl Ketone) as a Potential Carbon Fiber Precursor

Given their increasing importance in a variety of applications, the preparation of carbon fibers with well-defined chemical structures and innocuous byproducts has garnered a growing interest over the past decade. We report the preparation of medium molecular weight poly­(methyl vinyl ketone) (PMVK) as a potential carbon fiber precursor material which can easily undergo carbonization via the well-known, acid-catalyzed aldol condensation with water as a sole byproduct. Rheological studies further show that PMVK (MW ∼ 50 kg/mol) exhibits excellent physical and thermal properties for the spinning of single and multifilament fibers and easily produces carbon yields of 25% at temperatures as low as 250 °C. Analysis of the carbonized product also suggests a more defect-free structure than commercially available carbon fibers

Polymer-Coated Nanoparticles Interacting with Proteins and Cells: Focusing on the Sign of the Net Charge

To study charge-dependent interactions of nanoparticles (NPs) with biological media and NP uptake by cells, colloidal gold nanoparticles were modified with amphiphilic polymers to obtain NPs with identical physical properties except for the sign of the charge (negative/positive). This strategy enabled us to solely assess the influence of charge on the interactions of the NPs with proteins and cells, without interference by other effects such as different size and colloidal stability. Our study shows that the number of adsorbed human serum albumin molecules per NP was not influenced by their surface charge. Positively charged NPs were incorporated by cells to a larger extent than negatively charged ones, both in serum-free and serum-containing media. Consequently, with and without protein corona (<i>i.e.</i>, in serum-free medium) present, NP internalization depends on the sign of charge. The uptake rate of NPs by cells was higher for positively than for negatively charged NPs. Furthermore, cytotoxicity assays revealed a higher cytotoxicity for positively charged NPs, associated with their enhanced uptake

A Universal Scheme to Convert Aromatic Molecular Monolayers into Functional Carbon Nanomembranes

Free-standing nanomembranes with molecular or atomic thickness are currently explored for separation technologies, electronics, and sensing. Their engineering with well-defined structural and functional properties is a challenge for materials research. Here we present a broadly applicable scheme to create mechanically stable carbon nanomembranes (CNMs) with a thickness of ∼0.5 to ∼3 nm. Monolayers of polyaromatic molecules (oligophenyls, hexaphenylbenzene, and polycyclic aromatic hydrocarbons) were assembled and exposed to electrons that cross-link them into CNMs; subsequent pyrolysis converts the CNMs into graphene sheets. In this transformation the thickness, porosity, and surface functionality of the nanomembranes are determined by the monolayers, and structural and functional features are passed on from the molecules through their monolayers to the CNMs and finally on to the graphene. Our procedure is scalable to large areas and allows the engineering of ultrathin nanomembranes by controlling the composition and structure of precursor molecules and their monolayers