Design, synthesis and characterization of fluorescent hyperbranched polyglycerols and organic nanoparticles with covalently bound anti-fading agents

The photobleaching of fluorophores is a major limitation in fluorescence microscopy. We sought to create a brighter and more stable fluorophore by covalently attaching fluorescein and anti-fading agent (AFA) moieties to hyperbranched polyglycerols (HPG). The use of HPGs as a scaffold to link fluorescein and anti-fading agents proved intractable, so a norbornyl based ROMP polymer was used instead. Through the iterative use of ROMP and RCM, organic nanoparticles (ONPs) were synthesized incorporating multiple fluorescein and AFA units. The ONPs were brighter and more photostable than fluorescein. The photostability of the ONPs without AFAs was found to loosely correlate to its brightness. Incorporation of AFAs in the ONPs led to increased stability in some cases

Effects of the Number and Placement of Positive Charges on Viologen–Cucurbit[n]uril Interactions

Recent developments in the synthesis and applications of the cucurbit[n]uril family of synthetic hosts has led to an increasing interest in the detailed studies of their interactions with a wide variety of guests. This paper describes a quantitative study of the effects of the number and placement of positive charges on the binding of viologen guests to cucurbit[7]uril and cucurbit[8]uril. A series of viologen derivatives with one to four charges was characterised by isothermal titration calorimetry, 1H NMR spectroscopy and mass spectrometry to determine the stoichiometry, affinity and mode of binding. These data show that stoichiometry can be controlled by the placement of charge, and that affinity can be increased by the addition of positive charges. This study should serve as a guide for the design of supramolecular structures built from viologens and cucurbit[n]urils

New guests for the cucurbit[8]uril host. Formation of G2H ternary complexes

On the basis of the highly stable G2H (2 : 1) ternary complex formed by two methyl viologen cation radicals inside the cavity of cucurbit[8]uril, we prepared three monocationic 4‐phenylpyridinium derivatives: 1‐(hydroxyethyl)‐4‐phenyl‐pyridinium (1+) bromide, 1‐(octaethyleneglycol)‐4‐phenyl‐pyridinium (2+) chloride, and 4‐[4‐(methoxymethoxy)phenyl]pyridinium (3+) iodide, as possible guests for 2 : 1 complexation inside cucurbit[8]uril. We also investigated a fourth monocationic guest (4+), in which a central vinylidene group is inserted to elongate the 4‐phenyl‐pyridinium residue. Using 1H NMR and UV–Vis spectroscopic data and mass spectrometric data, we obtained unequivocal evidence for the formation of G2H (2 : 1) ternary complexes in all cases. The stoichiometry of the complexes was further verified by continuous variation (Job) plots, and in some cases, high resolution ESI‐MS spectrometric data. Diffusion coefficient measurements, using 1H NMR pulse gradient spin echo techniques, yielded values consistent with the formation and expected structures of the ternary complexes. Copyright © 2012 John Wiley & Sons, Ltd. A set of 4‐phenyl‐pyridinium derivatives were prepared and characterized as guests for the cucurbit[8]uril molecular receptor. These guests were found to form stable ternary supramolecular complexes in which two identical guests share the space inside the host cavity

Patterning Three-Dimensional Hydrogel Microenvironments Using Hyperbranched Polyglycerols for Independent Control of Mesh Size and Stiffness

The extracellular matrix is an environment rich with structural, mechanical, and molecular signals that can impact cell biology. Traditional approaches in hydrogel biomaterial design often rely on modifying the concentration of cross-linking groups to adjust mechanical properties. However, this strategy provides limited capacity to control additional important parameters in 3D cell culture such as microstructure and molecular diffusivity. Here we describe the use of multifunctional hyperbranched polyglycerols (HPGs) to manipulate the mechanical properties of polyethylene glycol (PEG) hydrogels while not altering biomolecule diffusion. This strategy also provides the ability to separately regulate spatial and temporal distribution of biomolecules tethered within the hydrogel. The functionalized HPGs used here can also react through a copper-free click chemistry, allowing for the encapsulation of cells and covalently tethered biomolecules within the hydrogel. Because of the hyperbranched architecture and unique properties of HPGs, their addition into PEG hydrogels affords opportunities to locally alter hydrogel cross-linking density with minimal effects on global network architecture. Additionally, photocoupling chemistry allows micropatterning of bioactive cues within the three-dimensional gel structure. This approach therefore enables us to tailor mechanical and diffusive properties independently while further allowing for local modulation of biomolecular cues to create increasingly complex cell culture microenvironments

Bottom-Up Strategy To Prepare Nanoparticles with a Single DNA Strand

We describe the preparation of cross-linked, polymeric organic nanoparticles (ONPs) with a single, covalently linked DNA strand. The structure and functionalities of the ONPs are controlled by the synthesis of their parent linear block copolymers that provide monovalency, fluorescence and narrow size distribution. The ONP can also guide the deposition of chloroaurate ions allowing gold nanoparticles (AuNPs) to be prepared using the ONPs as templates. The DNA strand on AuNPs is shown to preserve its functions

Benzobis(imidazolium)-Cucurbit[8]uril Complexes for Binding and Sensing Aromatic Compounds in Aqueous Solution

The utilities of benzobis(imidazolium) salts (BBIs) as stable and fluorescent components of supramolecular assemblies involving the macrocyclic host, cucurbit[8]uril (CB[8]), are described. CB[8] has the unusual ability to bind tightly and selectively to two different guests in aqueous media, typically methyl viologen (MV) as the first guest, followed by an indole, naphthalene, or catechol-containing second guest. Based on similar size, shape, and charge, tetramethyl benzobis(imidazolium) (MBBI) was identified as a potential alternative to MV that would increase the repertoire of guests for cucurbit[8] uril. Isothermal titration calorimetry (ITC) studies showed that MBBI binds to CB[8] in a 1: 1 ratio with an equilibrium association constant (K-a) value of 5.7 x 10(5) M-1, and that the resulting MBBI.CB[8] complex binds to a series of aromatic second guests with K-a values ranging from 10(3) to 10(5) M-1. These complexation phenomena were supported by mass spectrometry, which confirmed complex formation, and a series of NMR studies that showed the expected upfield perturbation of aromatic peaks and of the MBBI methyl peaks. Surprisingly, the binding behavior of MBBI is strikingly similar to that of MV, and yet MBBI offers a number of substantial advantages for many applications, including intrinsic fluorescence, high chemical stability, and broad synthetic tunability. Indeed, the intense fluorescence emission of the MBBI.CB[8] complex was quenched upon binding to the second guests, thus demonstrating the utility of MBBI as a component for optical sensing. Building on these favorable properties, the MBBI.CB[8] system was successfully applied to the sequence-selective recognition of peptides as well as the controlled disassembly of polymer aggregates in water. These results broaden the available guests for the cucurbit[n]uril family and demonstrate potentially new applications