Sensing Remote Chirality: Stereochemical Determination of β‐, γ‐, and δ‐Chiral Carboxylic Acids

Determining the absolute stereochemisty of small molecules bearing remote nonfunctionalizable stereocenters is a challenging task. Presented is a solution in which appropriately substituted bis(porphyrin) tweezers are used. Complexation of a suitably derivatized β‐, γ‐, or δ‐chiral carboxylic acid to the tweezer induces a predictable helicity of the bis(porphyrin), which is detected as a bisignate Cotton Effect (ECCD). The sign of the ECCD curve is correlated with the absolute stereochemistry of the substrate based on the derived working mnemonics in a predictable manner.     

π‐Extended Indenofluorenes

A series of π‐extended aromatic indenofluorene (IF) analogues with naphthalene and anthracene cores have been synthesized through acid‐catalyzed intramolecular cyclization. The regioselectivity of the reaction is controlled by a combination of steric and electronic factors and in some cases several possible regioisomers have resulted from the same precursor. The effects of ring connectivity on the optoelectronic properties were investigated by DFT calculations, absorption/emission spectroscopy, cyclic voltammetry, and spectroelectrochemical studies. All regioisomers exhibited a redshift of their absorption/emission bands relative to the parent IF analogues, but the magnitude of this shift and other optoelectronic properties (luminescence quantum yield, etc.) depends on the ring connectivity in a less obvious manner.     

Nonplanar Butterfly‐Shaped π‐Expanded Pyrrolopyrroles

Large aza‐analogues of curved polycyclic aromatic hydrocarbons with a double‐helicene structure present unique features for molecular photonics. We present the preparation and characterization of three such structures. The synthesis of these heterocyclic nanographenes involves only a few high‐yield steps that use readily available starting materials. X‐ray analysis revealed that each of these new dyes has three conformational isomers: one diastereoisomer in a meso form and two enantiomers in twisted forms [(P,P)] and [(M,M)]. The low energy barriers between the conformers, however, prevent their separation by using chiral HPLC, and the NMR spectra show only one set of signals for each of these curved compounds. Density functional theory (DFT) calculations quantify the small energy difference and the small energy barriers between the chiral and meso forms, which fully supports the experimental results. Their optical absorption lacks any sensitivity to the solvent environment, whereas their fluorescence features exhibit pronounced solvatochromism. This rarely observed solvatofluorochromism of centrosymmetric molecules without either electron‐withdrawing groups or ‐donating substituents was probed by using time‐resolved spectroscopy. These studies suggest that, similar to 9,9′‐bianthryl, the nonpolar locally excited state shows negligible solvatochromism, whereas the charge‐transfer state is sensitive to solvent polarity.     

6‐TIPS‐β‐Cyclodextrin‐Modified Fe3O4 for Facile Enantioseparation of 1‐(1‐Naphthyl)ethylamine

A new type of chiral magnetic nanoparticle was prepared from covalently linked magnetic nanoparticles (Fe₃O₄) and heptakis‐(6‐O‐triisopropylsilyl)‐β‐cyclodextrin (6‐TIPS‐β‐CD). The resulting selectors (TIPS‐β‐CD‐MNPs) combined the good magnetic properties Fe₃O₄ and efficient chiral recognition ability of 6‐TIPS‐β‐CD. The enantioselectivity of TIPS‐β‐CD‐MNPs towards 1‐(1‐naphthyl)ethylamine was six times higher than that of the parent β‐CD modified Fe₃O₄ particles.     

Synthesis of linear and star‐like poly(ε‐caprolactone)‐b‐poly{γ‐2‐[2‐(2‐methoxy‐ethoxy)ethoxy]ethoxy‐ε‐caprolactone} amphiphilic block copolymers using zinc undecylenate

Linear and star‐like amphiphilic diblock copolymers were synthesized by the ring‐opening polymerization of ε‐caprolactone and γ‐2‐[2‐(2‐methoxyethoxy)ethoxy]ethoxy‐ε‐caprolactone monomers using zinc undecylenate as a catalyst. These polymers have potential applications as micellar drug delivery vehicles, therefore the properties of the linear and 4‐arm star‐like structures were examined in terms of their molecular weight, viscosity, thermodynamic stability, size, morphology, and drug loading capacity. Both the star‐like and linear block copolymers showed good thermodynamic stability and degradability. However, the star‐like polymers were shown to have increased stability at lower concentrations with a critical micelle concentration (CMC) of 5.62 × 10^?4 g L^?1, which is less than half the concentration of linear polymer needed to form micelles. The star‐like polymeric micelles showed smaller sizes when compared with their linear counterparts and a higher drug loading capacity of doxorubicin, making them better suited for drug delivery purposes. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3601–3608     

Synthesis of α‐Cyclodextrin‐Conjugated Poly(ε‐lysine)s and Their Inclusion Complexation Behavior

Novel functional polymers utilizing specific host/guest interactions were designed by introducing α‐CD host molecules into poly(ε‐lysine) chains as side groups. An interesting phase separation was observed as a result of the inclusion complexation between the polymeric host and 3‐(trimethylsilyl)propionic acid as a model guest in aqueous media. This water‐soluble polymeric host would be useful for various applications, particularly drug delivery, due to its biodegradability, low toxicity, and unique functionality represented as a complexation‐induced phase separation.     

Synthesis and Photovoltaic Properties of Boron β‐Ketoiminate Dyes Forming a Linear Donor‐π‐Acceptor Structure

Organoboron complexes are of interest as chromophores for dye sensitizers owing to their light‐harvesting and carrier‐transporting properties. In this study, compounds containing boron β‐ketoiminate (BKI) as a chromophore were synthesized and used as dye sensitizers in dye‐sensitized solar cells. The new dyes were orange or red crystals and showed maximum absorptions in the 410–450 nm wavelength region on titanium dioxide substrates. These electrodes exhibited maximum efficiencies of over 80% in incident photon‐to‐current conversion efficiency spectra, suggesting that the continuous process of light absorption‐excitation‐electron injection was effectively performed. Open‐circuit photovoltages were relatively high owing to the large dipole moments of the BKI dyes with a linear molecular structure. Thus, a maximum power conversion efficiency of 5.3% was successfully observed. Comparison of BKI dyes with boron β‐diketonate dyes revealed certain differences in solution stability, spectral properties, and photovoltaic characteristics.     

Improved Stability and Photodynamic Activity of Water‐Soluble 5,15‐Diazaporphyrins Incorporated in β‐(1,3‐1,6)‐d‐Glucan with On‐Off Switch

5,15‐Diazaporphyrins, which have a large absorption at wavelengths over 600 nm, were dissolved in water by complex formation with β‐(1,3‐1,6)‐d ‐glucans. Aqueous solutions of these complexes were relatively stable compared with their trimethyl‐β‐cyclodextrin‐complexed analogues. β‐Glucan‐complexed diazaporphyrins showed quenched fluorescence and had low singlet‐oxygen‐generation abilities owing to random self‐aggregation. However, external stimuli, such as the presence of liposomes or intracellular uptake, restored the fluorescence and singlet‐oxygen‐generation abilities of β‐glucan‐complexed diazaporphyrins. Consequently, β‐glucan‐complexed diazaporphyrins showed very high photodynamic activities toward HeLa cells.     

Effect of hexyl substituent groups on photophysical and electrochemical properties of the poly[(9,9‐Dioctyluorene)−2,7‐diyl‐alt‐(4,7‐bis (3‐Hexylthien‐5‐Yl)−2,1,3‐Benzothiadiazole)−2′,2″‐diyl]

The effect of the presence of hexyl group in thiophene on the photophysical and electrochemical properties of poly[(9,9‐dioctyluorene)?2,7‐diyl‐alt‐(4,7‐bis(3‐hexylthien‐5‐yl)?2,1,3‐benzothiadiazole)?2′,2″‐diyl] (F8TBT) is investigated. The copolymers present electron donor–acceptor architecture and are synthesized by Suzuki coupling reaction. The UV/Vis spectra show absorption maximum in the wavelength range of blue and orange, which are associated with different segments of the polymer backbone. Addition of hexyl substituent groups has a positive effect on the molar absorptivity and increases the emission and absorption intensities due to fluorene and thiophene‐benzothiadiazole‐thiophene (TBT) units, although an increment in the bandgap is observed. Cyclic voltammetry study of the polymer films reveal irreversible reduction and oxidation processes of the TBT units in the polymer chain and the HOMO and LUMO energy levels suggest ambipolar character for the polymers, while the electrochemical bandgaps are consistent with the absorbance measurements. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1975–1982     

Low Band Gap Donor–Acceptor Conjugated Systems Based on 3‐Alkoxy or 3‐Pyrrolidino‐4‐cyanothiophene and Benzothiadiazole Units

3‐Hexyloxy‐4‐cyanothiophene, 3‐pyrrolidil‐4‐cyanothiophene, and 3,4‐ethylenedioxythiophene (EDOT) units are used with benzothiadiazole as building blocks for the development of three new conjugated donor–acceptor–donor (DAD) derivatives. The DAD molecules have the central acceptor part, which is formed by combining electron‐withdrawing cyano groups and the benzothiadiazole moiety, in common. Theoretical calculations and UV/Vis and electrochemical data reveal the key role of the end‐capped donor to tune the electronic properties of the derivatives. A study of the electropolymerization process of the three derivatives shows the strong influence of the donor parts on both the reactivity of the precursors and the electronic properties of the resulting polymers. Derivatives end‐capped with pyrrolidinocyano thiophene or EDOT units lead to films of polymers presenting low band gaps of around 0.9–1.4 eV. Upon oxidation, the two polymers present different behavior. In the presence of the pyrrolidinocyano thiophene moieties, oxidation leads to a blueshift of the absorption bands, whereas with EDOT units a classical redshift, giving high absorption in the near‐IR region, is observed for the oxidized states.     

Cyclodextrins in Polymer Synthesis: Photoinitiated Free‐Radical Polymerization of N‐Isopropylacrylamide in Water Initiated by a Methylated β‐Cyclodextrin/2‐Hydroxy‐2‐methyl‐1‐phenylpropan‐1‐one Host/Guest Complex

Methylated β‐cyclodextrin (Me‐β‐CD) was used to complex a free‐radical photoinitiator, 2‐hydroxy‐2‐methyl‐1‐phenylpropan‐1‐one ( 1 ), yielding the water‐soluble 1 : 1 host/guest complex 1 a . The structure of complex 1 a was verified by means of IR, UV/vis and ¹H NMR spectroscopy. The influence of Me‐β‐CD as the host on the photopolymerization kinetics of N‐isopropylacrylamide was studied. Compared to the photopolymerization carried out under nearly identical conditions but without cyclodextrin, an increase in the polymerization rate was registered in the presence of complex 1 a .     

Ladder π‐Conjugated Materials Containing Main‐Group Elements

Ladder π‐conjugated compounds, which have fully ring‐fused polycyclic skeletons, are an important class of materials possessing significant potentials for application in organic electronics. The incorporation of main‐group elements, such as B, Si, P, S, and Se, into the ladder skeletons as bridging moieties is a powerful strategy to endow unusual electronic structures as well as suitable molecular arrangements in the solid state, giving rise to attractive photophysical and electronic properties. Recent efforts have produced a number of fascinating ladder materials, some of which indeed showed high performance as light‐emitting materials and charge carrier transporting materials. This Focus Review is an overview of the progress in this chemistry, focusing on several important π‐conjugated skeletons.     

Cyclodextrins in Polymer Synthesis: Enzymatic Polymerization of a 2,6‐Dimethyl‐β‐Cyclodextrin/2,4‐Dihydroxyphenyl‐4′‐Hydroxybenzylketone Host‐Guest Complex Catalyzed by Horseradish Peroxidase (HRP)

This paper reports the enzymatic polymerization of the inclusion complex 2,4‐dihydroxyphenyl‐4′‐hydroxybenzylketone/2,6‐dimethyl‐β‐cyclodextrin by horseradish peroxidase (HRP) in aqueous media. The structure of the complex was determined by means of NOESY‐NMR and crystallographic analysis (indicating an orthorhombic structure). The enzymatic polymerization of the uncomplexed 2,4‐dihydroxyphenyl‐4′‐hydroxybenzylketone yields oligomers with molecular weights up to in organic‐aqueous media, but because of its poor solubility in aqueous systems, no polymerization is observed if water is used as solvent. An increase of the availability of the ketone in solution is achieved by complexing it with random‐methylated β‐cyclodextrin in water. We found that the use of methylated β‐cyclodextrin in equimolar concentration to the monomer increases the polymerization yield and the average molecular weight. The polymers formed were analyzed by GPC and ATR‐FTIR techniques.

Representation from X‐ray diffraction analysis of the 2,6‐dimethyl‐β‐cyclodextrin/2,4‐dihydroxyphenyl‐4′‐hydroxybenzylketone host‐guest complex ( 3 ).     

Allosteric Binding of Capsaicin by a Bis(β‐cyclodextrin)‐2,2′‐bipyridine Receptor

A new β‐cyclodextrin‐based receptor that showed allosteric binding behavior towards capsaicin in aqueous solution was prepared. By NMR titration and nonlinear regression, we obtained binding constants, which increased more than fivefold when an effector (Zn²⁺) was bound to a central 2,2′‐bipyridine that acts as the allosteric center.     

Discriminating Influence of α‐ and Methylated β‐Cyclodextrins on Complexation and Polymerization of Diacrylate and Dimethacrylate Monomers

Summary: Host‐guest complexes of α‐cyclodextrin (α‐CD) and methylated β‐cyclodextrin (Me‐β‐CD) with diacrylates and dimethacrylates of butan‐1,4‐diol and hexan‐1,6‐diol at varying stoichiometries were studied. The complexes were analyzed by means of ¹H NMR, two‐dimensional ROESY spectroscopy and Job's curves, which clearly revealed the discriminating influence of the two hosts towards complex formation. The corresponding polymers were obtained using a redox initiator system in water. Thermal analysis and IR measurements of the polymers provided evidence for the existence of a polyrotaxane architecture.

Proposed structure of the cross‐linked polymers obtained by the redox polymerization of the Me‐β‐CD complexed monomers.     

Concise Synthesis of α‐Methylene‐β‐hydroxy‐γ‐carboxy‐γ‐lactams

A concise protocol for the synthesis of α‐methylene‐β‐hydroxy‐γ‐carboxy‐γ‐lactams has been described via alkylation of amino acid derived iminoesters with α‐bromomethylmethacrylate, followed by allylic hydroxylation. All the synthesized compounds have been evaluated for their cytotoxicity on multiple myeloma cancer cell lines.     

Co‐crystals of 3‐deoxy‐3‐fluoro‐α‐d‐glucopyranose and 3‐deoxy‐3‐fluoro‐β‐d‐glucopyranose

3‐Deoxy‐3‐fluoro‐d ‐glucopyranose crystallizes from acetone to give a unit cell containing two crystallographically independent molecules. One of these molecules (at site A) is structurally homogeneous and corresponds to 3‐deoxy‐3‐fluoro‐β‐d ‐glucopyranose, C₆H₁₁FO₅, (I). The second molecule (at site B) is structurally heterogeneous and corresponds to a mixture of (I) and 3‐deoxy‐3‐fluoro‐α‐d ‐glucopyranose, (II); treatment of the diffraction data using partial‐occupancy oxygen at the anomeric center gave a high‐quality packing model with an occupancy ratio of 0.84:0.16 for (II):(I) at site B. The mixture of α‐ and β‐anomers at site B appears to be accommodated in the lattice because hydrogen‐bonding partners are present to hydrogen bond to the anomeric OH group in either an axial or equatorial orientation. Cremer–Pople analysis of (I) and (II) shows the pyranosyl ring of (II) to be slightly more distorted than that of (I) [θ_(I) = 3.85 (15)° and θ_(II) = 6.35 (16)°], but the general direction of distortion is similar in both structures [ϕ_(I) = 67 (2)° (B_C1,C4) and ϕ_(II) = 26.0 (15)° (^C3TB_C1); B = boat conformation and TB = twist‐boat conformation]. The exocyclic hydroxymethyl (–CH₂OH) conformation is gg (gauche–gauche) (H5 anti to O6) in both (I) and (II). Structural comparisons of (I) and (II) to related unsubstituted, deoxy and fluorine‐substituted monosaccharides show that the gluco ring can assume a wide range of distorted chair structures in the crystalline state depending on ring substitution patterns.