CD44 is a widely-distributed type I transmembrane glycoprotein that binds hyaluronic acid (HA) in most cell types, including primary tumor cells and cancer-initiating cells and has roles in cell migration, cell-cell, and cell-matrix adhesion. HA-derived conjugates and nanoparticles that target the CD44 receptor on cells have been reported for targeted delivery of therapeutics and imaging agents. Altering crucial interactions of HA with CD44 active sites holds significant importance in modulating targeting ability of hyaluronic acid to other cancer types that do not express the CD44 receptor or minimizing the interaction with CD44+ cells that are not target cells. The approach adopted here was deacetylation of the N-acetyl group and selective sulfation on the C6-OH on the HA polymer, which form critical interactions with the CD44 active site. Major interactions identified by molecular modeling were confirmed to be hydrogen bonding of the C6-OH with Tyr109 and hydrophobic interaction of the N-acetyl group with Tyr46, 83 and Ile 92. Modified HA was synthesized and characterized and its interactions were assessed by in vitro and molecular modeling approaches. In vitro techniques included flow cytometry and fluorescence polarization, while in silico approaches included docking and binding calculations by a MM-PBSA approach. These studies indicated that while both deacetylation and sulfation of HA individually decrease CD44 interaction, both chemical modifications are required to minimize interaction with CD44+ cells. The results of this study represent the first step to effective retargeting of HA-derived NPs for imaging and drug delivery.

The nature of the electronic excited state of many symmetric multibranched donor-acceptor molecules varies from delocalized/multipolar to localized/dipolar depending on the environment. Solvent-driven localization breaks the symmetry and traps the exciton in one branch. Using a combination of ultrafast spectroscopies, we investigate how such excited-state symmetry breaking affects the photochemical reactivity of quadrupolar and octupolar A-(π-D) 2,3 molecules with photoisomerizable A-π-D branches. Excited-state symmetry breaking is identified by monitoring several spectroscopic signatures of the multipolar delocalized exciton, including the S 2 ← S 1 electronic transition, whose energy reflects interbranch coupling. It occurs in all but nonpolar solvents. In polar media, it is rapidly followed by an alkyne-allene isomerization of the excited branch. In nonpolar solvents, slow and reversible isomerization corresponding to chemically-driven symmetry breaking, is observed. These findings reveal that the photoreactivity of large conjugated molecules can be tuned by controlling the localization of the excitation.

The excited-state dynamics of an aniline-triazine electron donor-acceptor dyad with an alkyne spacer has been investigated using a combination of ultrafast broadband mid-IR and visible transient absorption and fluorescence spectroscopies. The transient IR data reveal the occurrence of an efficient alkyne to allene isomerization of the spacer with a time constant increasing from a few hundreds of femtoseconds to a few picoseconds with solvent viscosity. This process is faster than the vibrational cooling of the Franck-Condon excited state, indicative of nonequilibrium dynamics. The transient electronic absorption and fluorescence data evidence that this transformation is accompanied by a charge separation between the donor and the acceptor subunits. The allene character of the spacer implies an orthogonal orientation of the donor and acceptor moieties, similar to that proposed for twisted intramolecular charge-transfer states. Such states are often invoked in the excited-state dynamics of donor-acceptor dyads, but their involvement could never be unambiguously evidenced spectroscopically. The alkyne-allene isomerization involves not only a torsional motion but also a bending of the molecule due to the sp to sp rehybridization of one of the alkyne carbon atoms. This twisted and rehybridized intramolecular charge transfer ("TRICT") state decays back to the planar and linear alkyne ground state on a time scale decreasing from a few hundred to ten picoseconds upon going from weakly to highly polar solvents. The different solvent dependencies reveal that the dynamics of the allene buildup are controlled by the structural changes, whereas the decay is limited by the charge recombination step.

The advent of nanomedicine has rejuvenated the need for increased understanding of the fundamental physicochemical properties of polymeric amphiphiles. Hyaluronic acid (HA) is a hydrophilic polysaccharide that is frequently conjugated to hydrophobic moieties and then used to entrap dyes and therapeutics. Here, we develop computational models to examine the effects of the hydrophobic modification on supramolecular behavior among three systematically designed HA derivatives substituted with alkyl chains of increasing length. Our simulations coalesce with experimentally obtained results to demonstrate the dependence of supramolecular behavior on intramolecular forces. We show that the formation of clearly defined hydrophobic domains in samples of octadecylamine-modified HA compared to HA conjugates with shorter alkyl chains is a result of more favorable hydrophobic interactions. Trends in hydrodynamic radius and polydispersity are observed in experimental results that coalesce with theoretical calculations, suggesting that supramolecular properties are dependent on the physicochemical characteristics of individual polymer strands.

Rapid and reliable identification of pathogenic microorganisms is of great importance for human and animal health. Most conventional approaches are time-consuming and require expensive reagents, sophisticated equipment, trained personnel, and special storage and handling conditions. Sensor arrays based on small molecules offer a chemically stable and cost-effective alternative. Here we present a ratiometric fluorescent sensor array based on the derivatives of 2-(4′-N,N-dimethylamino)-3-hydroxyflavone, and investigate its ability to provide a dual-channel ratiometric response. We demonstrate that by using discriminant analysis of the sensor array responses, it is possible to effectively distinguish between eight bacterial species and recognize their Gram status. Thus, multiple parameters can be derived from the same dataset. Moreover, the predictive potential of this sensor array is discussed, and its ability to analyze unknown samples beyond the list of species used for the training matrix is demonstrated. The proposed sensor array and analysis strategies open new avenues for the development of advanced ratiometric sensors for multiparametric analysis.

Understanding the interaction of fluorescent dyes with monolayer-protected gold nanoparticles (AuNPs) is of fundamental importance in designing new fluorescent nanomaterials. Among a variety of molecular sensors and reporters, fluorescent probes based on a 3-hydroxychromone (3HC) skeleton appear to be very promising. They exhibit the phenomenon of dual band emission, resulting from excitedstate intramolecular proton transfer (ESIPT), known to be highly sensitive to a nature of microenvironment surrounding a fluorophore. In this study, dodecanethiol-protected gold nanoparticles were synthesized, and, owing to the transmission electron micrograph imaging, their average diameter was found to be ∼1.4 nm. Fluorescence titrations of the 3HC ESIPT probes with AuNPs in toluene solutions demonstrate significant changes in the intensity ratio of their normal and tautomeric emission bands, suggesting that the probe molecules become noncovalently bound to a dodecanethiol layer of AuNPs. Despite expected fluorescence quenching induced by close proximity to the metal surface, no fluorescence lifetime decrease was observed, indicating that a bound-fluorophore is shielded from a nanoparticle core. Further spectral analysis revealed that the ratiometric fluorescence changes could be interpreted as a consequence of intermolecular hydrogen bonding between a probe and residual ethanol molecules, trapped into the dodecanethiol shell of AuNPs during the synthesis. Evidences for residual traces of ethanol in the ligand shell of the nanoparticles were also observed in NMR spectra, suggesting that alkylthiol-coated gold nanoparticles may not be as hydrophobic as one could expect. To elucidate structural features of dodecanethiol-stabilized gold nanoparticles at the supramolecular level, a molecular dynamics (MD) model of AuNP was developed. The model was based on the all-atom CHARMM27 force field parameters and parametrized according to available experimental data of the synthesized AuNPs. Our MD simulations show that in bulk toluene the 3HC probe molecule becomes weakly bound to a dodecanethiol monolayer, so that a fluorophore favors residence in an outer shell of AuNP. In addition, MD simulations of transfer of AuNP from bulk ethanol to toluene demonstrate that a small population of ethanol molecules are able to penetrate deeply into the dodecanethiol layer and may indeed be trapped into the ligand shell of alkylthiolfunctionalized gold nanoparticles. The results of our fluorescence experiments and molecular dynamics simulation suggest that 3hydroxychromones can be used as a noncovalent fluorescent labeling agent for alkylthiol-stabilized noble metal nanoparticles.

Self-assembled fluorescent nanomaterials based on small-molecule organic dyes are gaining increasing popularity in imaging and sensing applications over the past decade. This is primarily due to their ability to combine spectral property tunability and biocompatibility of small molecule organic fluorophores with brightness, chemical, and colloidal stability of inorganic materials. Such a unique combination of features comes with rich versatility of dye-based nanomaterials: from aggregates of small molecules to sophisticated core-shell nanoarchitectures involving hyperbranched polymers. Along with the ongoing discovery of new materials and better ways of their synthesis, it is very important to continue systematic studies of fundamental factors that regulate the key properties of fluorescent nanomaterials: their size, polydispersity, colloidal stability, chemical stability, absorption and emission maxima, biocompatibility, and interactions with biological interfaces. In this review, we focus on the systematic description of various types of organic fluorescent nanomaterials, approaches to their synthesis, and ways to optimize and control their characteristics. The discussion is built on examples from reports on recent advances in design and applications of such materials. Conclusions made from this analysis allow a perspective on future development of fluorescent nanomaterials design for biomedical and related applications.

Three2-(benzimidazol-2-yl)-3-hydroxychromonederivativesweresynthesized.Theirspectroscopicandfluorescentproperties,due to excited state intramolecular proton transfer (ESIPT) from OH to carbonyl, were studied. Theoretical possibility of an alternative intramolecularH-bondingandexperimentalevidenceforsuchbehaviorarediscussed. © Versita Warsaw and Springer-Verlag Berlin Heidelberg.