The ubiquitous nature of helical structures in nature inspired scientists to reproduce the helix at the molecular level to understand more about helix structure and its function. After the pioneering work by Natta et al. in 1955, many different helical polymers have been developed and used in numerous applications, such as chiral recognition, asymmetric synthesis, and circularly polarized light-emitting materials. On the other hand, ways of providing helicity are limited and generally provided by exploiting non-covalent side-chain interactions. To demonstrate that backbone chirality of a polymer may also provide helicity to the polymers, we have designed (using MM), synthesized, and characterized two enantiomeric pairs of polymers having tartaric acid-derived backbone with incorporation of single benzene-based fluorophores (SBBFs). Synthesized polymers were shown to be helical in solution as CD studies indicate. Overall, this study presents a simple and efficient way of obtaining emissive chiral polymers having helical conformations.

Chirality is fundamental to biological systems and the pharmaceutical industry, yet efficient methods for determining the absolute configuration of chiral compounds remain a challenge. This study reports the synthesis and characterization of chiral diaminodicyanoquinodimethane (DADQ) compounds derived from tetracyanoquinodimethane (TCNQ) and primary amines. Using a combination of NMR, UV-Vis, circular dichroism (CD) spectroscopy, and EPR, we elucidated the formation mechanism of these compounds and explored their optical properties. Furthermore, CD spectra showed a pattern that correlates with their configurations: DADQs with R configuration showed negative CD signals in methanol and DMSO, whereas DADQs with S configuration showed positive CD signals. The DADQs with aromatic side chains reversed their CD signals in relatively nonpolar solvents. These findings indicate that chirality can be effectively transferred from primary amines to DADQ, offering a potential method for determining the absolute configurations of primary amines. The results highlight the promise of chiral DADQ compounds in chiroptical applications and their utility in elucidating the chirality of biologically relevant molecules.

We have developed a new scaffold that exhibits an efficient intramolecular through-space charge transfer (CT). In this design, electron-rich benzofuran and electron-deficient ynone groups are placed strategically in proximity via a naphthalene spacer. Charge transfer is supported by distinct CT bands in the visible region (>500 nm) in their UV-vis absorption and emission spectra.

Coumarins are multifaceted molecules with compelling fluorescence features. Along with biocompatible properties, they have recently been used in chiroptical studies. The chirality induction to benzo[f]coumarin moiety at the third position was investigated in this study. The chromophore derivatized with homochiral alanine and phenylalanine resulted in identical spectroscopic properties. When the chiroptical properties are concerned, the distinct CD spectra of both structures are also changed significantly by altering the organic solvent. Inter- and intra-molecular hydrogen bonding affects the CD spectra along with the chiroptical signal. The phenylalanine-benzo[f]coumarin structures were modified with TEG units to increase water solubility and enhance ordered aggregations. The chiroptical properties of the compounds were analyzed in organic solvents with spectroscopic techniques. It was found that coumarin is not only sensitive to the chiral unit attached but also that any conformational change on the side chain affects the chiroptical signal. Time-dependent DFT calculations in the gas phase supported these results.

Deviation of the H + concentration from optimum values within the organelles is closely associated with irregular cellular functions that cause the onset of various diseases. Therefore, determining subcellular pH values in live cells and tissues is valuable for diagnostic purposes. In this study, we report a novel ratiometric fluorescence probe 1H-pyrazole-3-carboxylic acid, 4-(benzo[d]thiazol-2-yl)-3-(2,4-dihydroxy-3-methylphenyl)-1H-pyrazole-5-carboxylicacid4-(2-benz othiazolyl)-5-(2,4-dihydroxy-3-methylphenyl), to which we will refer as ThiAKS Green (Thiazole AKyol shifting green), that is pH sensitive. The results presented here show that the probe can penetrate the cell membrane in less than 30 minutes and does not show any detectable toxicity. The measured color shifts up on pH change are linear and most significant around physiological pH (pKa=7.45), thus making this probe suitable for live-cell imaging and intracellular pH measurements. During the long-incubation periods following the application of the probe and the fluorescent microscopy measurements, it shows stable properties and is easy to detect in live cells. In conclusion, the results suggest that ThiAKS Green can be used to obtain precise information on the H + distribution at various compartments of the live cells.

The preparation of a polymer carrier for a boron delivery agent is presented through a combination of experimental and computational studies. A dodecahydro-closo-dodecaborate (B12H12)2- (B12) anion was used as a model boron-containing agent due to its high boron content. Quaternized poly(2-vinyl pyridine)-b-poly(ethylene oxide) (QP2VP-b-PEO) was chosen as a model neutral-cationic block copolymer to construct the carrier. The electrostatic association between QP2VP and B12 induced the self-assembly of QP2VP-b-PEO, resulting in micelles with (B12 + QP2VP)-core and PEO-corona. The mechanism of formation of (B12 + QP2VP)-b-PEO micelles was examined through density functional theory (DFT) calculations and classical simulations. (B12 + QP2VP)-b-PEO micelles were found to be undurable in biological medium. To enhance stability, micelles were utilized as building blocks together with poly(N-vinyl caprolactam) (PVCL) and tannic acid (TA) to construct layer-by-layer (LbL) microparticles. Cytotoxicity and cellular association of LbL particles were assessed using the HepG2 cell line. Multilayered particles were found to show no cellular cytotoxicity. Association studies and the boron content of treated cells through inductively coupled plasma optical emission spectroscopy (ICP-OES) showed that LbL microparticles were extensively associated with and successfully delivered boron to HepG2 cells. This study reveals the challenges and possible solutions to obtain stable self-assembled structures in a cell culture medium. These findings contribute to a fundamental understanding of the structure-property relationship in selfassembled micelles/LbL particles and provide a basis for further development of boron-containing polymer vehicles for boron neutron capture therapy.

Polyfunctional macrocycles have been studied extensively for their responsive properties. In this study, three electron- deficient novel azo-containing crown ethers were successfully synthesized. The synthesized macrocycles were characterized and their photophysical along with photoisomerization were studied. The results were compared with their acyclic derivative. It was found that these compounds did not convert to their cis-isomer completely due to the rigidity of the cycles. The fluorescence studies revealed that the macrocycles were fluorescent while the acyclic azo derivative was found not to show fluorescence. The macrocycles were also tested for alkali metal cation-binding abilities. It was shown with DFT calculations that not only the ring size of macrocycles but also the conformation places an important role in recognition of these cations.

Among photo-switchable compounds, spiropyrans have attracted significant attention owing to their multi-responsiveness towards a change in the pH, solvent polarity, and temperature, along with light. Upon exposure to the external stimulants, the merocyanine form is obtained due to bond cleavage between spiro carbon and oxygen, which transforms the optically active spiropyrans into an achiral form. The back conversion of the resulting achiral merocyanine form to the spiropyrans brings about a racemic mixture. In this study, D and L enantiomers of alanine and phenylalanine derivatives were incorporated onto a spiropyran bearing hydroxyl group to obtain optically active spiropyrans. Photochemical and photophysical properties of these compounds were studied in methanol, isopropanol, dichloromethane, and hexane. The effect of the benzyl and methyl units on the ring closure rate of the merocyanines was also investigated. For this purpose, ring closure kinetics of different merocyanines containing hydroxyl group, D-alanine, and D-phenylalanine derivatives were compared. The results reveal that the ring closure rate of the merocyanine with benzyl group attached is faster than the rate of the structures with methyl or hydroxyl groups.

A new series of monomers in the donor-acceptor-donor array, namely 5-fluoro-4,7-di(furan-2-yl)benzo[c][1,2,5] thiadiazole (F2BT-F), and 5-fluoro-4,7-di(selenophen-2-yl)benzo[c][1,2,5] thiadiazole (S2BT-F), bearing 5-fluorobenzo[c][1,2,5]-thiadiazole as the acceptor moiety and furan and selenophene as the electron donating groups was synthesized and polymerized electrochemically. To compare heteroatom effect, thiophene analogue of newly synthesized (FBT)-B-2-F and S2BT-F namely, (5-fluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5] thiadiazole (T2BT-F)) and its corresponding polymer were also synthesized. Effect of donor units on the electrochemical and optical properties of fluorinated acceptor based systems was investigated in terms of the effect of different sized heteroatoms in five-membered rings on the dihedral angle and planarity. Theoretical calculations also suggested a deviation from planarity upon fluorination. Moreover, electrochemically obtained polymers possess low bandgap values (1.62 eV-1.68 eV for PF2BT-F and PS2BT-F, respectively) and exhibited electrochromic properties with relatively low switching times.

2,2,6,6-Tetramethylpiperidine 1-oxyl (TEMPO) is a versatile compound which is used mainly in organic oxidation reactions and organic battery applications. Incorporating TEMPO into a polymer could provide many applications into its repertoire. In this study, new polymeric TEMPO derivatives are synthesized and characterized to be used as catalysts in the presence of another polymer which constitutes N-halamine functionality. These polymeric mixtures were superior since the mixture could easily be separated from the reaction medium by simple filtration and reused in some other oxidation reactions numerous times. In turn, an all polymeric oxidation method was developed for oxidation of primary alcohols.

In recent years, the studies on artificial helical polymers have become an attractive field due to their impressive optical activity and functions. They have numerous potential applications in many areas such as chiral recognition, enantioselective crystallization, enantioselective release, asymmetric catalysis, and 3D displays.Two new urea containing polymers were synthesized in this study. P-1 synthesis was accomplished, starting from tartaric acid. Tartaric acid was successfully converted to diamine 4. The diamine was treated with a p-phenylene diisocyanate to get helical structures at the macroscopic level, as evidenced by SEM images. This was shown to be the case through interchain H-bonding between urea groups and microphase separation between the segments due to hydrophobicity difference along the chain. Limited conformational space in P-1 also assisted the helical structure formation. P-2 was synthesized by treating L-lysine with p-phenylene diisocyanate. Due to the ample conformational space and intersegmental mixing due to hydrogen bond between urea and L-lysine segments, P-2 was shown not to be in a helical conformation. Molecular dynamics simulations and first principle studies were used to explain observed structural behaviour for these polymers.

Weakly coordinating anions are extremely versatile species for capturing and characterizing cationic intermediates.Among these anions, carboranes and some boranes are known to be the most weakly coordinating anions.In this study, the carboranes and boranes were synthesized in order to use in different fields.B 11 H 14 -was synthesized from NaBH 4 and used to synthesize CB 11 H 12 -.CB 11 H 12 -was synthesized by carbene addition to undecaborate.B 11 H 14 -was converted to B 10 H 14 by oxidation and extrusion of one boron vertex.CB 11 H 12 -was methylated on boron vertex to get HCB 11 Me 11 -.The methylated carborane cages are more hydrophobic and weakly coordinating anions.

Using fluorescence to detect biologically relevant metals has been studied extensively due to its rapid and low detection limit ability. Sodium and potassium differentiation is significant in diagnosis of many medical conditions. For this, we designed coumarin dimers as flexible fluorescent probes using ethylene glycol units for differentiation of sodium and potassium. To our best knowledge, use of these easy-to-synthesize coumarin dimers linked through ethylene glycol units are first in the literature. In fluorescence titration experiments, diethylene glycol linked coumarin-3-carboxylate dimer is responsive for sodium ions but not for potassium ions. The driving force for the complexation of metal cation and fluorescence probes is thought to be size-matching. To further explain the phenomenon, we synthesized coumarin dimer using 1,8- octanediol as the linker, and methyl ester of coumarin-3-carboxylic acid to investigate the effect of structural changes on the fluorescence intensity. These two compounds could not differentiate the sodium and potassium. Flexible coumarin dimers as fluorophores are shown to be useful for sensing sodium cation in the presence of potassium cation.

We report an investigation of structure and photophysics of thin layers of cibalackrot, a sturdy dye derived from indigo by double annulation at the central double bond. Evaporated layers contain up to three phases, two crystalline and one amorphous. Relative amounts of all three have been determined by a combination of X-ray diffraction and FT-IR reflectance spectroscopy. Initially, excited singlet state rapidly produces a high yield of a transient intermediate whose spectral properties are compatible with charge-transfer nature. This intermediate more slowly converts to a significant yield of triplet, which, however, does not exceed 100% and may well be produced by intersystem crossing rather than singlet fission. The yields were determined by transient absorption spectroscopy and corrected for effects of partial sample alignment by a simple generally applicable procedure. Formation of excimers was also observed. In order to obtain guidance for improving molecular packing by a minor structural modification, calculations by a simplified frontier orbital method were used to find all local maxima of singlet fission rate as a function of geometry of a molecular pair. The method was tested at 48 maxima by comparison with the ab initio Frenkel-Davydov exciton model.

Synthesis of two new pi-conjugated monomers containing fluorine substituted benzothiadiazoles as acceptor units and 3,4-ethylenedioxythiophene (EDOT) as donor unit was accomplished by facilitating Stille cross-coupling reactions (4,7-bis(2,3-dihydrothieno[3,4-b][1,4] dioxin-5-yl)-5-fluorobenzo[c][1,2,5] thiadiazole (E2BTD-F) and 4,7-bis(2,3-dihydrothieno [3,4-b][1,4] dioxin-5-yl)-5,6-difluorobenzo[c][1,2,5] thiadiazole (E2BTD-2F)). NMR and HRMS spectra of newly synthesized compounds are in agreement with the structures. To compare fluorine substitution effects, non-fluorinated analogue (4,7-bis(2,3-dihydrothieno[3,4-b][1,4] dioxin-5-yl) benzo[c][1,2,5] thiadiazole (E2BTD)) was also synthesized. Besides a blue shift in their absorption spectra, an anodic shift was also noted in the oxidation potentials of both monomers with fluorine atom substitution on the acceptor unit. This was further confirmed by DFT calculations such that upon fluorine substitution EDOT donor units deviate from planarity. Electropolymerization of the monomers were achieved successfully via potentiodynamic polymerization method. A similar trend in optoelectronic properties was also observed for the polymer films as for the monomers. (C) 2019 The Electrochemical Society.

In this study, novel porous three-dimensional (3D) scaffolds from silk fibroin (SF) and functionalized (amidated and oxidized) citrus pectin (PEC) were developed for skin tissue engineering applications. Crosslinking was achieved by Schiff's reaction in borax presence as crosslinking coordinating agent and CaCl2 addition. After freeze-drying and methanol treatment, plasma treatment (10 W, 3 min) was applied to remove surface skin layer formed on scaffolds. 3D matrices had high porosity (83%) and interconnectivity with pore size about 120 mu m that providing suitable microenvironment for cells. Modifications on PEC chain and crosslinking of scaffolds were verified by fourier-transform infrared spectroscopy (FTIR) analysis and spectrophotometric assay. Scaffolds showed low weight loss (21.3% in 40 days) and high water uptake ability in phosphate-buffered saline (800% in 24 h). Mechanical properties of 3D matrices satisfied the stability of scaffolds under compressive stress and supported adhesion, proliferation and penetration of fibroblast cells. Our results suggested that modified PEC-SF scaffolds would be proposed for use in tissue engineered skin dermal substitutes. (c) 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2625-2635, 2018.