Aggregation-free and high stability core–shell polymer nanoparticles with high fullerene loading capacity,variable fullerene type,and compatibility towards biological conditions

Fullerenes have unique structural and electronic properties that make them attractive candidates for diagnostic, therapeutic, and theranostic applications. However, their poor water solubility remains a limiting factor in realizing their full biomedical potential. Here, we present an approach based on a combination of supramolecular and covalent chemistry to access well-defined fullerene-containing polymer nanoparticles with a core–shell structure. In this approach, solvophobic forces and aromatic interactions first come into play to afford a micellar structure with a poly(ethylene glycol) shell and a corannulene-based fullerene-rich core. Covalent stabilization of the supramolecular assembly then affords core-crosslinked polymer nanoparticles. The shell makes these nanoparticles biocompatible and allows them to be dried to a solid and redispersed in water without inducing interparticle aggregation. The core allows a high content of different fullerene types to be encapsulated. Finally, covalent stabilization endows nanostructures with stability against changing environmental conditions.

A polymer nanoparticle approach to biorelevant and robust fullerene nanoparticles is presented.     

Synthesis of azahelicenes through Mallory reaction of imine precursors: corannulene substrates provide an exception to the rule in oxidative photocyclizations of diarylethenes

Typically, the synthesis of phenanthrene-based polycyclic aromatic hydrocarbons relies on the Mallory reaction. In this approach, stilbene (PhCH CHPh)-based precursors undergo an oxidative photocyclization reaction to join the two adjacent aromatic rings into an extended aromatic structure. However, if one C C carbon atom is replaced by a nitrogen atom (C N), the synthesis becomes practically infeasible. Here, we show the very first examples of a successful Mallory reaction on stilbene-like imine precursors involving the molecularly curved corannulene nucleus. The isolated yields exceed 90% and the resulting single and double aza[4]helicenes exhibit adjustable high affinity for electrons.

First azahelicene synthesis from corannulene-based imine precursors is presented.     

Bioactive Molecules for Discriminating Robinia and Helianthus Honey: High-Performance Liquid Chromatography–Electron Spray Ionization–Mass Spectrometry Polyphenolic Profile and Physicochemical Determinations

Bioactive molecules from the class of polyphenols are secondary metabolites from plants. They are present in honey from nectar and pollen of flowers from where honeybees collect the “raw material” to produce honey. Robinia pseudoacacia and Helianthus annuus are important sources of nectar for production of two monofloral honeys with specific characteristics and important biological activity. A high-performance liquid chromatography–electro spray ionization–mass spectrometry (HPLC–ESI–MS) separation method was used to determine polyphenolic profile from the two types of Romanian unifloral honeys. Robinia and Helianthus honey showed a common flavonoid profile, where pinobanksin (1.61 and 1.94 mg/kg), pinocembrin (0.97 and 1.78 mg/kg) and chrysin (0.96 and 1.08 mg/kg) were identified in both honey types; a characteristic flavonoid profile in which acacetin (1.20 mg/kg), specific only for Robinia honey, was shown; and quercetin (1.85 mg/kg), luteolin (21.03 mg/kg), kaempferol (0.96 mg/kg) and galangin (1.89 mg/kg), specific for Helianthus honey, were shown. In addition, different phenolic acids were found in Robinia and Helianthus honey, while abscisic acid was found only in Robinia honey. Abscisic acid was correlated with geographical location; the samples collected from the south part of Romania had higher amounts, due to climatic conditions. Acacetin was proposed as a biochemical marker for Romanian Robinia honey and quercetin for Helianthus honey.     

Double-stranded cycles: toward C84's belt region

The reactivity of the double-stranded hydrocarbon cycle with two ether bridges (1) toward iodotrimethylsilane (TMSI) was investigated in some detail. The carbon skeleton of cycle 1 resembles the belt region of a C84 fullerene which makes it a potential precursor to the long sought after fully aromatic derivative. Upon exposure to TMSI, cycle 1 undergoes a cascade of reactions which involve different states of iodination/reduction which ultimately lead to the hydrogenated cycle 5a, whose structure was proven by single-crystal X-ray analysis. A deeper insight into mechanistic aspects of this sequence of conversions was gained by performing the reaction under dry and wet conditions, whereby the latter involved both normal and deuterated water. With the help of detailed NMR correlation studies and DFT computations, all important aspects were clarified including an unexpected selective H/D exchange at the naphthalenic moieties.     

Syntheses,structures, and dynamic behavior of chiral racemic organoantimony and -bismuth compounds RR'SbCl,RR'BiCl,and RR'SbM [R = 2-(Me2NCH2)C6H4, R' = CH(Me3Si)2, M = H,Li, Na

RR'SbCl (1) and RR'BiCl (2) [R = 2-(Me(2)NCH(2))C(6)H(4), R' = CH(Me(3)Si)(2)] form by the reaction of R'ECl(2) (E = Sb, Bi) with RLi. The reaction of 1 with LiAlH(4) and metalation with n-BuLi gives RR'SbH (3) and RR'SbLi.2THF (4) (THF = tetrahydrofuran). Transmetalation of 4 with sodium tert-butoxide in the presence of TMEDA (TMEDA = tetramethylethylenediamine) leads to RR'SbNa.TMEDA (5). Structural analyses by (1)H NMR in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO with a variation of the temperature (1, 2, 4, and 5) and by single-crystal X-ray diffraction (1, 2, 4, and 5) revealed the intramolecular coordination of the pendant Me(2)N group on the pnicogen centers in 1 and 2 and on Li or Na in 4 or 5. The variable-temperature (1)H NMR spectra of the hydride 3 in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO show that the pyramidal configuration on antimony is stable up to 100 degrees C, whereas inversion at the nitrogen is not prevented by internal coordination even at -80 degrees C. The crystals of 1, 2, 4, and 5 consist of discrete molecules with the Sb and Bi atoms in an approximately Psi-trigonal-bipyramidal environment in the cases of 1 and 2 and in a pyramidal environment in the cases of 4 and 5. Crystal data for 1: triclinic, space group Ponemacr;, a = 7.243(4) A, b = 10.373(3) A, c = 15.396(5) A, alpha = 79.88 degrees, beta = 78.27 degrees, gamma = 71.480(10) degrees, V = 1066.2(7) A(3), Z = 2, R = 0.0614. 2: monoclinic, space group P2(1)/n, a = 10.665(2) A, b = 14.241(2) A, c = 14.058(2) A, beta = 90.100(10) degrees, V = 2135.1(6) A(3), Z = 4, R = 0.049. 4: monoclinic, space group P2(1)/n, a = 11.552(2) A, b = 16.518(3) A, c = 15.971(5) A, beta = 96.11(2) degrees, V = 3030.2(12) A(3), Z = 4, R = 0.0595. 5: monoclinic, space group P2(1)/n, a = 9.797(2) A, b = 24.991(5) A, c = 14.348(3) A, beta = 94.98(3) degrees, V = 3499.66(12) A(3), Z = 4, R = 0.0571. The dissociation of the intramolecular N-pnicogen bond and inversion at the nitrogen occurs when solutions of 1 or 2 in C(6)D(6) or C(6)D(5)CD(3) are heated above 25 or 30 degrees C. 1 and 3-5 are stable with respect to inversion of the configuration at the antimony in C(6)D(6), C(6)D(5)CD(3), or (CD(3))(2)SO up to 160 degrees C. Bismuth inversion, probably via the edge mechanism, is observed in solutions of 2 in (CD(3))(2)SO at 45 degrees C but not in C(6)D(5)CD(3) below 125 degrees C.     

Supramolecular star polymers with compositional heterogeneity

We present the synthesis of supramolecular star polymers with heterogeneous chemical compositions through potassium cation‐templated assembly of guanosine end‐functionalized random, diblock, and Y‐shaped copolymers. The assembly and disassembly processes of the synthesized star polymers have been systematically examined on changing the concentration, the temperature, the solvent, and the amount of cation using ¹H NMR, UV/vis, and CD spectroscopy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and Stereochemistry of Some New 1,3-Oxathiane Derivatives

Summary. The synthesis and stereochemistry of some new 2,5-substituted 1,3-oxathiane derivatives are reported. The anancomeric or flexible structure of the derivatives and some peculiar cases of prochirality are revealed by NMR investigations.     

Aza‐Michael addition reaction: Post‐polymerization modification and preparation of PEI/PEG‐based polyester hydrogels from enzymatically synthesized reactive polymers

The utility of aza‐Michael addition chemistry for post‐polymerization functionalization of enzymatically prepared polyesters is established. For this, itaconate ester and oligoethylene glycol are selected as monomers. A Candida Antarctica lipase B catalyzed polycondensation reaction between the two monomers provides the polyesters, which carry an activated carbon‐carbon double bond in the polymer backbone. These electron deficient alkenes represent suitable aza‐Michael acceptors and can be engaged in a nucleophilic addition reaction with small molecular mono‐amines (aza‐Michael donors) to yield functionalized linear polyesters. Employing a poly‐amine as the aza‐Michael donor, on the other hand, results in the formation of hydrophilic polymer networks. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 745–749     

A Three‐Photon Active Organic Fluorophore for Deep Tissue Ratiometric Imaging of Intracellular Divalent Zinc

Deep tissue bioimaging with three‐photon (3P) excitation using near‐infrared (NIR) light in the second IR window (1.0–1.4 μm) could provide high resolution images with an improved signal‐to‐noise ratio. Herein, we report a photostable and nontoxic 3P excitable donor‐π‐acceptor system (GMP) having 3P cross‐section (σ₃) of 1.78×10^?80 cm⁶ s² photon^?2 and action cross‐section (σ₃η₃) of 2.31×10^?81 cm⁶ s² photon^?2, which provides ratiometric fluorescence response with divalent zinc ions in aqueous conditions. The probe signals the Zn²⁺ binding at 530 and 600 nm, respectively, upon 1150 nm excitation with enhanced σ₃ of 1.85×10^?80 cm⁶ s² photon^?2 and σ₃η₃ of 3.33×10^?81 cm⁶ s² photon^?2. The application of this probe is demonstrated for ratiometric 3P imaging of Zn²⁺ in vitro using HuH‐7 cell lines. Furthermore, the Zn²⁺ concentration in rat hippocampal slices was imaged at 1150 nm excitation after incubation with GMP, illustrating its potential as a 3P ratiometric probe for deep tissue Zn²⁺ ion imaging.     

Thiol‐epoxy “click” chemistry: Application in preparation and postpolymerization modification of polymers

Base‐catalyzed reaction between a thiol and an epoxide group is a simple fusion process that leads to the formation of a β‐hydroxythio‐ether linkage. This reaction is efficient, regio‐selective, and fast. In addition, it produces a reactive hydroxyl group upon completion. Therefore, it is of considerable potential in synthesis of reactive and functional soft materials. Here, we discuss the fundamental aspects of this process, the so‐called thiol‐epoxy “click” reaction, and its utility in the preparation and post‐polymerization functionalization of polymers and crosslinked networks. Furthermore, its application in surface modification of solid substrates is also considered. Finally, utility of multifunctional materials created using the thiol‐epoxy reaction is discussed in the biomedical arena. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3057–3070