Solvents Of Low Polarity Research Articles

Cellulose Nanocrystal-in-Solvent Processing for Efficient One-Pot Upcycling of Commercial Polymeric PFAS.

Upcoming regulations aim to ban per- and polyfluoroalkyl substances (PFAS), including commercial polymeric PFAS, or fluoropolymers, such as poly(tetrafluoroethylene) (PTFE) and poly(vinylidene fluoride) (PVDF), due to their environmental and toxicological impacts. However, fluoropolymers also provide crucial properties for clean energy transitions, and their regulation may hinder further technological advancements. Therefore, a facile one-pot recycling-upcycling strategy for fluoropolymers using inexpensive biomass, such as cellulose nanocrystals (CNCs), as absorbents and cocomponents for fluoro-functionalized composites could align with global sustainability goals and technological demands. Herein, we present a closed-loop CNC-in-solvent (CiS) processing system, which involves stirring fluoropolymers and CNCs in only low-polarity solvents like toluene (CiS-T). Our study reveals that CiS-T is a two-step process where the CNC-solvent interaction exposes CNCs' reducing end aldehyde protons due to solvent polarity and promotes H-F bond formation. The solvent used was recollected and reused. Additionally, we demonstrate the practical application of PTFE- and PVDF-CNC hybrids, byproducts of the CiS-T process, as performance-enhancing agents in green-energy-harvesting devices such as triboelectric nanogenerators. Our findings not only offer a sustainable method to overcome challenges from regulations against commercial fluoropolymers but also offer insights into developing an efficient, solvent-mediated CNC functionalization process that addresses forthcoming challenges in key industries.

Calendula Flowers (Calendulae officinalis flos): Methods to Obtain Fractions of Biologically Active Substances

INTRODUCTION. The pharmaceutical industry aims at developing sustainable resource-saving technologies for manufacturing medicines. Approaches to the effective use of herbal drugs include applying technologies yielding compounds with various pharmacological effects in one production cycle. To date, no standardised herbal drug processing technology has been designed to produce calendula flower-based medicinal products with various pharmacological effects. The Member States of the Eurasian Economic Union (EAEU) process calendula flowers by extraction methods yielding one fraction of biologically active substances per cycle (either only flavonoids or only carotenoids).AIM. This article aimed to investigate the possibility of stepwise processing of calendula flowers to obtain biologically active substances with different polarities (carotenoids, flavonoids, and polysaccharides) per cycle.MATERIALS AND METHODS. The authors extracted carotenoids using hexane. The study included additional thermal pretreatment of the herbal drug. Carotenoids and flavonoids were quantified by spectrophotometry, and polysaccharides were quantified by gravimetric analysis. After hexane removal, the dry oily residue was dissolved in oil with mechanical stirring to obtain the oil extract. The study included a three-step processing method that comprised hexane extraction (extraction of carotenoids with a low-polarity organic solvent), extraction with a water–organic solvent system (extraction of flavonoids), and aqueous extraction (precipitation of polysaccharides).RESULTS. The lipophilic extracts obtained by single hexane extraction or by single hexane extraction and heat treatment had the maximum carotenoid content (~4%), which was 10 times the carotenoid content in the extracts obtained using a water– organic solvent system. Oil extracts were prepared from the dry residue left after removing hexane by distillation at its boiling point. The content of biologically active substances in the oil extracts was comparable to that in the intact herbal drug. Water–organic solvent extraction yielded 68.5% more flavonoids from the herbal drug extracted with hexane than from the intact herbal drug. In contrast, aqueous extraction applied to the intact herbal drug yielded 1.7 times the amount of flavonoids obtained by aqueous extraction preceded by hexane extraction. The water-soluble polysaccharide fraction extracted from the intact herbal drug had 10 times the flavonoid content observed in the fraction extracted from the processed herbal drug. Each subsequent processing step decreased the total polysaccharide content and the content of individual polysaccharide fractions and increased their purity. The ratio of polysaccharide fractions remained unchanged across all processing methods tested.CONCLUSIONS. Stepwise processing of calendula flowers ensured that one processing cycle provided three fractions containing increased amounts of carotenoids, flavonoids, and polysaccharides. Relative to the intact herbal drug, there was a 3.3-fold increase in the yield of carotenoids, and the yields of flavonoids and polysaccharides increased by 44.8 and 41.3%, respectively. The resulting product had a higher degree of purity than the products obtained by pretreatment and double hexane extraction or by using the intact herbal drug. The stepwise processing method is advisable for the production of medicines that are enriched with a specific group of biologically active substances or contain smaller amounts of impurities.

Harvesting the tuning mechanism of strategic polychrome and white light emission in NapH dye based on excited state intermolecular proton transfer

Organic white light emitting (WLE) materials have sparked a research boom due to their promising applications in display devices, artificial lighting, and molecular sensors. However, the complex luminescence mechanism of full-spectra emitting materials has limited the development of white light materials with high stability and reproducibility. In this study, building on the full-spectra luminescent naphthimide dye (NapH) introduced by Xu et al., (Chin. Chem. Lett. 35(2024), 108348), we report the solvent-sensitive excited state proton transfer (ESPT) properties and white light emission mechanism in NapH. Our theoretical research results show that the ESPT process of NapH molecule is hindered in the low-polar solvent tetrahydrofuran (THF), so only the blue fluorescence from the Enol* is observed in the experiment. In contrast, in polar solvents such as water (H2O) and methanol (MeOH), the formation of strong intermolecular hydrogen bonds successfully initiates the ESPT process, leading to the dual fluorescence observed in experiments, with blue emission from the Enol* and red emission from the Nap anion. In essence, different solvent environments can adjust several emission colors. Furthermore, we theoretically verify that the optimal white light emission can be achieved when the mixed solvent ratio of dimethyl sulfoxide (DMSO) and dioxane (DIOX) is 5:5, which aligns well with experimental results. More importantly, we elucidate the specific WLE mechanism from multiple perspectives, including potential energy curves and electron spectra. Our work not only displays the interaction models of NapH molecule in various solvents, but also reveals the underlying luminescence mechanism, thus providing a valuable theoretical reference for the development and advancement of new white light materials.

Copper and ZnO Dual-Catalyzed Photo-Assisted Depolymerization of Poly(Methyl Methacrylate) without Deoxygenation

Despite significant advancements in thermal and photothermal depolymerizations, the success of these techniques relies on tedious deoxygenation procedures. Herein, we report the development of the depolymerization technique efficient without prior deoxygenation, which was enabled by copper/ligand complexes and the inclusion (0.25 wt% relative to solvent) of zinc oxide (ZnO) nanocrystals activated by UV light. This approach was tested for poly(methyl methacrylate) (PMMA) prepared by atom transfer radical polymerization (ATRP); the effects of solvent polarity and the activity of ligands were investigated. Unexpectedly, a low-activity Cu-complex with 2,2‘-bipyridine ligand, in combination with a low-polarity solvent, 1,2,4-trichlorobenzene, enabled relatively high depolymerization yields in less than 1 h at 150 °C. Higher activity ATRP complexes with tris(2-pyridylmethyl)amine (TPMA) and N,N,N‘,N‘‘,N‘‘-pentamethyldiethylenetriamine (PMDETA) ligands, were less efficient, which was associated with their thermal decomposition and/or the excessive formation of radicals and premature termination of the chain ends. The presented facile approach was designed to be used even in partially aerated reactors, opening new avenues for efficient depolymerization.

Effects of solvent extraction on the phytoconstituents and in vitro antioxidant activity properties of leaf extracts of the two selected medicinal plants from Malawi

This study evaluated and compared the phytochemical and antioxidant properties of the solvent extracts of Azadirachta indica A. Juss and Vernonia amygdalina Del leaves. Methanolic and aqueous extracts showed high (P ≤ 0.05) extract yields (in %), compared to chloroform and ethyl acetate extracts from both V. amygdalina and A. indica leaves. The study exhibited high phytochemical content in methanol and aqueous extracts compared to chloroform and ethyl acetate extracts, confirming the potential for medicinal use. V. amygdalina methanol and aqueous extracts had higher (P ≤ 0.05) total phenolic content (TPC), in mg GAE/gDW, (158.810±0.846 and 217.883±0.265, respectively) than chloroform (37.574±0.118) and ethyl acetate (104.758±0.236) but higher ethyl acetate content in A. indica extracts. Low polar solvents extracted high (P ≤ 0.05) total flavonoids, in mgQE/gDW, (367.051±0.858 and 149.808±0.009) compared to high polar solvents (14.863±0.071 and 54.226±0.014 ) in V. amygdalina while as in A. indica leaf extracts, low polar solvents showed high TFC ( 658.469±3.451 and 275.288±10.490) compared to high polar solvents (26.312±0.063 and 48.858±0.063) respectively. In vitro total antioxidant capacity, in mg/g, was higher in polar solvents than in low-polar solvents, ranging from 34.300±1.784 to 121.015±6.839 for A. indica ethyl acetate and methanolic extracts. A strong correlation between TPC and tannic acid content was observed, except in A. indica methanolic extracts of A. indica. Ferric reducing power was high, except for V. amygdalina chloroform and methanol leaf extracts, which were lower (P≤ 0.05) than that of the standard ascorbic acid. The study revealed that high polar solvents, such as methanol and water, are more efficient in the extraction of antioxidants from A. indica but lower in V. amygdalina extracts. High phytochemical content and antioxidative capacity could be significant in treating various diseases in humans.

Phenols, flavonoids and anthocyanins in Solanum lasiocarpum from Borneo: In vitro antioxidant activity and phytochemical profiling via LCMS Q-TOF

Phenols, flavonoids, and anthocyanins are compounds that reported play important roles in plant defence mechanism system. Antioxidant activity is mostly derived from these phytochemical groups, which have a wide range of pharmaceutical properties, including antimicrobial, antitumor, anti-inflammatory, antipyretic, anti-allergy, anti-fertility, hypoglycemic, anti-histamine, antioxidant, antiviral, analgesic, anti-ulcerogenic, nephroprotective, antidiabetic, immuno-secretory, cardiovascular, anti-platelet aggregation, antibacterial, anticancer, and hepatoprotective activities. However, these compounds in Solanum lasiocarpum from Borneo areas are remaining unclear. In this experiment, we performed comprehensive evaluation on effect of extraction solvents on phenols, flavonoids, and anthocyanin's contents and further on the scavenging activity (2,2-diphenyl-1-picrylhydrazyl-hydrate, DPPH; 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid), ABTS; and ferric-reducing antioxidant power, FRAP). High phenolic, flavonoid and anthocyanin contents be found in low polar solvent. Antioxidant assay showed acetone was higher activity with IC50 of 6.36 mg/mL compared to methanol (12.1 mg/mL) and hexane (17.8 mg/mL). Furthermore, liquid chromatography mass spectrometry quadrupole-time of flight (LCMS Q-TOF) mass spectrometer detected N-Acryloylglycine, butoctamide hydrogen succinate, eruberin B, emmotin A and N-Cyclohexanecarbonylpentadecylamine that important in natural polymers, serve as sleep disorders treatment agents, anti-fibrotic property, immunomodulatory activity, and act as differentiator between N-palmitoylethanolamine-hydrolyzing acid amidase (NPAA) compared to fatty acid amide hydrolase (FAAH), respectively. The limitation of this research is the assessment of antioxidant properties related to the polarity of the extraction solvent. Polar solvents may exhibit high scavenging activity, but phenolic compounds, flavonoids, and anthocyanins are found in higher concentrations in non-polar solvents. We encourage further investigation into phytochemical profiles due to the abundance from non-polar solvents.

Theoretical Study of an Authentic Hydrocarbon Ion Pair.

For many years researchers believed that hydrocarbons only contain covalent bonds. However, since 1985 Okamoto et al. demonstrated the formation of hydrocarbon salts in several systems, demolishing the structural principle that hydrocarbons only contain covalent bonds. Despite the great importance of this outcome to the study of chemical bonds, quantum chemical calculations on these systems are essentially nonexistent. The stability of the hydrocarbon ions along with the steric hindrance associated with the formation of the covalent bond contribute to their occurrence either in solution (dissociated) or in the solid state. These facts along with the common formation of ion pairs in solvents of low polarity motivated us to search for hydrocarbon ion pairs in the gas phase. Its energetics has also been studied in four nonprotic solvents, through a continuum solvation model (CPCM). DFT and CASSCF calculations indicate a metastable and highly polar ion pair between the tricyclopropylcyclopropenylium cation and a simplified Kuhn's anion. The barrier to the covalent structure varies from ∼4.8 to 14.4 kcal/mol, while the energy difference between the ion pair and the covalent form varies from ∼4.3 to 25.4 kcal/mol. The obtained theoretical results along with previous experimental results suggest the following strategy to obtain kinetically and thermodynamically stable hydrocarbon ion pairs: choose very stable hydrocarbon ions and systematically increase the steric hindrance between them.

Solvatochromic fluorescent ethynyl naphthalimide derivatives for detection of water in organic solvents

Three new derivatives of (4-methoxyphenyl) ethynyl-naphthalimide were synthesized by Sonogashira coupling reaction. These compounds showed robust and strong fluorescent signals, which shift from blue to orange as the solvent polarity increases. Computational calculations revealed that in low-polarity solvents, the molecules preferred a 90° rotation between the naphthalimide and ethynyl benzene fragments. In high-polarity solvents, where the energy barrier for rotation of the alkyne bond was higher, the molecules favored the 0° conformer, leading to longer emission wavelengths. The compound with a 2-methoxyethyl group tethered to the naphthalimide nitrogen demonstrated sensitivity to water presence in the ranges of 0–30 % (v/v) in THF, 0–15 % (v/v) in DMSO, 0–30 % (v/v) in MeCN, 0–15 % (v/v) in acetone, and 0–40 % (v/v) in EtOH. The detection limits for water were determined to be 0.0523 %, 0.1365 %, 0.0337 %, 0.0570 %, and 0.1170 % (v/v) in THF, DMSO, MeCN, acetone, and EtOH, respectively. The effectiveness of this compound in quantifying ethanol content in spirit samples was successfully demonstrated.

Radiolytic degradation of 1,2,4-trichlorobenzene (TCB) in some organic solvents by gamma rays: The kinetic properties of complete dechlorination of TCB and its pathway

This study investigates the degradation of TCB in methanol, ethanol, hexane, and benzene solutions using gamma radiolysis. Kinetic properties of TCB dechlorination and its pathway are examined, with TCB selected as a representative chlorinated organic compound. Chromatograms of irradiated samples and mass spectra of liquid-phase products are presented. The change in concentration of TCB, dichlorobenzenes (DCB), chlorobenzene (MCB), and benzene with absorbed doses are observed. The radiation-chemical yield (G values) of TCB in the solvents are calculated as 1.83, 2.56, 1.93, and 1.84 100eV−1 in methanol, ethanol, hexane, and benzene solutions, respectively. 100 % degradation of TCB by gamma irradiation is found to be efficient in polar solvents but leads to a wide variety of byproducts in low polar solvents, particularly the formation of polychlorinated biphenyls in TCB + benzene solutions, making benzene an incompatible medium. The main dechlorination pathway of TCB involves the formation of 1,4-DCB, MCB, and benzene.Environmental Implication.The gamma irradiation of chlorinated organic compounds, focusing on TCB as a model compound, was investigated due to its status as a hazardous material for the environment and living organisms. TCB is a byproduct of the dechlorination of certain chlorinated pesticides listed under the Stockholm Convention's Persistent Organic Pollutants (POPs) list, which prohibits their production and use. Gamma irradiation was found to be an effective method for the degradation of chlorinated compounds, achieving 100 % degradation during irradiation. The study underscores the potential of gamma irradiation as a viable approach for the treatment of chlorinated compounds, particularly in addressing environmental and health concerns associated with TCB and related compounds.

Silver Dendritic Gels with Luminescence and Aggregation-Induced Emission Effect.

This work reports on a novel family of silver metallogels based on discrete coordination complexes. Structurally, they consist of dendrimers containing a trinuclear silver metallacycle at the core, with the general formula [M(μ-pz)]3, and poly(benzyl)ether branched structures with different numbers or terminal alkoxy chains at the periphery. These silver metallodendrimers are able to gel low-polarity solvents such as dodecane or cyclohexane, giving rise to luminescent organogels at room temperature with the property of aggregation-induced emission (AIE). This property means that in solution or the sol state, they are weak emitters, but in the gel state, luminescence is considerably increased. In this particular case, they exhibit blue luminescence. Two different dendritic scaffolds have been studied, finding significant differences in solubility, gel formation and dependence of luminescence on temperature. The results show that properly tailored silver gelators can show luminescence in the gel state.

Characteristics of the existing methods for obtaining carotenes from carotenoid concentrates

Carotenes, which simultaneously have the properties of natural dyes and biologically active substances that have a positive effect on human health and life expectancy, are becoming increasingly widespread in the food, pharmacological and cosmetic industries. This necessitates an increase in the production of carotenes on an industrial scale. For use in food technologies, an encapsulated form of carotenes is recommended, which requires their high purity. The purpose of this study is to analyze domestic and foreign scientific, technical and patent information on existing methods for obtaining carotenes from carotenoid concentrates to determine the direction of research for the development of technology for the production of carotenes, in particular lycopene, ensuring the production of high purity lycopene from carotenoid concentrates, as well as increasing release of lycopene. The issues of using chromatographic methods for isolating lycopene, their advantages and disadvantages, as well as the use of non-polar and low-polar organic solvents for isolating lycopene from carotenoid concentrate are considered. The promising direction of research on the use of adsorption resins in the isolation of lycopene from carotenoid concentrates is noted.It has been concluded that the currently existing methods for obtaining carotenes from carotenoid concentrates, in particular lycopene, are quite technically complex and time-consuming. Some of the mallow the production of high purity lycopene, but the yield of lycopene is so low that their industrial scaling seems impractical. Taking this into account, research is being updated in the field of developing a technology for producing lycopene from a carotenoid concentrate, providing a high yield of high purity lycopene, with the possibility of its implementation on an industrial scale.

Tuning the Electrolyte and Interphasial Chemistry for All-Climate Sodium-ion Batteries.

Sodium-ion batteries (SIBs) present a promising avenue for next-generation grid-scale energy storage. However, realizing all-climate SIBs operating across a wide temperature range remains a challenge due to the poor electrolyte conductivity and instable electrode interphases at extreme temperatures. Here, we propose a comprehensively balanced electrolyte by pairing carbonates with a low-freezing-point and low-polarity ethyl propionate solvent which enhances ion diffusion and Na+-desolvation kinetics at sub-zero temperatures. Furthermore, the electrolyte leverages a combinatorial borate- and nitrile-based additive strategy to facilitate uniform and inorganic-rich electrode interphases, ensuring excellent rate performance and cycle stability over a wide temperature range from -45 °C to 60 °C. Notably, the Na||sodium vanadyl phosphate cell delivers a remarkable capacity of 105 mAh g-1 with a high rate of 2 C at -25 °C. In addition, the cells exhibit excellent cycling stability over a wide temperature range, maintaining a high capacity retention of 84.7 % over 3,000 cycles at 60 °C and of 95.1 % at -25 °C over 500 cycles. The full cell also exhibits impressive cycling performance over a wide temperature range. This study highlights the critical role of electrolyte and interphase engineering for enabling SIBs that function optimally under diverse and extreme climatic environments.

Enhancing the photovoltaic responses of MAPbI3 poly-crystalline perovskite films via adjusting the properties of PEDOT:PSS hole transport material with a low-polarity solvent treatment process

The surface and electrical characteristics of the poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) materials are manipulated using a low-polarity solvent treatment process, which influences the formation and nucleation/crystal growth process of the CH3NH3PbI3 (MAPbI3) perovskite films and thereby determining the crystal orientation and grain size. The hydrophilicity of the PEDOT:PSS composite material fabricated on the ITO/glass sample is reduced with the xylenes solvent treatment or a hexamethyldisilazane:xylenes solvent mixture treatment, which can be used to form the photo-active perovskite crystals and thereby reducing the photocurrent hysteresis of the fabricated perovskite based photovoltaic devices. It is worthwhile to mention that the non-perfectness of closed-loop in the photocurrent density-voltage curves under the forward and backward scans can be used as an indicator to assess the properties of the MAPbI3 films. Our findings can facilitate the development of perovskite based optoelectronic devices.

Cooperativity of ESPT and Aggregation-Induced Emission Effects-An Experimental and Theoretical Analysis of a 1,3,4-Thiadiazole Derivative.

4-[5-(Naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl]benzene-1,3-diol (NTBD) was extensively studied through stationary UV-vis absorption and fluorescence measurements in various solvents and solvent mixtures and by first-principles quantum chemical calculations. It was observed that while in polar solvents (e.g., methanol) only a single emission band emerged; the analyzed 1,3,4-thiadiazole derivative was capable of producing dual fluorescence signals in low polarity solvents (e.g., n-hexane) and certain solvent mixtures (e.g., methanol/water). As clearly follows from the experimental spectroscopic studies and theoretical modeling, the specific emission characteristic of NTBD is triggered by the effect of enol → keto excited-state intramolecular proton transfer (ESIPT) that in the case of solvent mixture is reinforced by aggregation of thiadiazole molecules. Specifically, the restriction of intramolecular rotation (RIR) due to environmental hindrance suppresses the formation of non-emissive twisted intramolecular charge transfer (TICT) excited keto* states. As a result, this particular thiadiazole derivative is capable of simultaneously producing both ESIPT and aggregation-induced emission (AIE).

Structural design of a supergelator: Influence of the alkyl chain isomers on gelation behaviors, thermal stabilities, and supramolecular structures

Supramolecular gels have received a lot of attention due to their unique properties and potential applications. However, it is difficult to determine the relationship between the molecular structures of gelators and the influencing factors. To understand how the different alkyl chain isomers govern the gelation behaviors, benzene-1,3,5-tricarboxamide (BTA) derivatives have been designed and synthesized. Although these derivatives have the same molecular formula, the alkyl chain configurations are different on the amide bonds. The gelation behaviors indicated that BTA derivatives had obviously different gelation properties. Specifically, BTA–3C8 could only form organogels in cyclohexane, and it exhibited poor gelation properties. BTA–3MeC7 formed stable organogels in low-polar solvents. BTA–3EtC6 possessed excellent gelation properties, and it formed organogels in almost all the tested solvents. BTA–3BuC4 exhibited gelation abilities in a limited number of solvents. The thermal stabilities and the morphologies of organogels were determined. The results indicated that the alkyl chain groups of gelators significantly affected the thermal stabilities and the supramolecular structures of organogels. Using the FT–IR technique and XRD characterization, we investigated the main driving force and the molecular stacking patterns of the gelators. The results indicated that hydrogen bonds acted as the main driving force for the formation of gels. Moreover, the gelator molecules were self-assembled to form ordered and layered structures. Finally, the mechanism of the organogel formation was proposed. This study provides a useful idea for the preparation of soft materials with controllable supramolecular structures or special properties.

Temperature-dependent chlorosomal self-aggregation of bacteriochlorophyll-d analogs with a branched alkyl chain in a single 1-chlorooctane solvent

Abstract Recently, the supramolecular polymerization of chlorophyll pigments mimicking a natural light-harvesting apparatus (chlorosome) was demonstrated in low-polar organic solvents or aqueous solutions. To obtain the most aggregation models, a concentrated solution of the pigments in a polar organic solvent was diluted with a large amount of a nonpolar organic solvent or water. Here, bacteriochlorophyll-d analogs possessing branched alkyl chains of different lengths at the peripheral 17-propionate residue on the core chlorin π-system were prepared and their highly soluble chlorosomal supramolecules were produced in single 1-chlorooctane as a low-polar solvent. Temperature-dependent electronic absorption and circular dichroism spectroscopies were employed to analyze their self-aggregation and disaggregation mechanisms. The synthetic analogs were monomeric at high temperatures and self-aggregated during cooling of the hot solution through a non-sigmoidal pathway. The obtained chlorosomal self-aggregates were reversibly monomerized by heating the homogeneous solution. The disaggregation pathway was fitted to an isodesmic model whose melting points depended on the alkyl-chain lengths.

Solvent-Dependent Emissions Properties of a Model Aurone Enable Use in Biological Applications.

Fluorophores are powerful visualization tools and the development of novel small organic fluorophores are in great demand. Small organic fluorophores have been derived from the aurone skeleton, 2-benzylidenebenzofuran-3(2H)-one. In this study, we have utilized a model aurone derivative with a methoxy group at the 3' position and a hydroxyl group at the 4' position, termed vanillin aurone, to develop a foundational understanding of structural factors impacting aurone fluorescence properties. The fluorescent behaviors of the model aurone were characterized in solvent environments differing in relative polarity and dielectric constant. These data suggested that hydrogen bonding or electrostatic interactions between excited state aurone and solvent directly impact emissions properties such as peak emission wavelength, emission intensity, and Stokes shift. Time-dependent Density Functional Theory (TD-DFT) model calculations suggest that quenched aurone emissions observed in water are a consequence of stabilization of a twisted excited state conformation that disrupts conjugation. In contrast, the calculations indicate that low polarity solvents such as toluene or acetone stabilize a brightly fluorescent planar state. Based on this, additional experiments were performed to demonstrate use as a turn-on probe in an aqueous environment in response to conditions leading to planar excited state stabilization. Vanillin aurone was observed to bind to a model ATP binding protein, YME1L, leading to enhanced emissions intensities with a dissociation equilibrium constant equal to ~ 30 µM. Separately, the aurone was observed to be cell permeable with significant toxicity at doses exceeding 6.25 µM. Taken together, these results suggest that aurones may be broadly useful as turn-on probes in aqueous environments that promote either a change in relative solvent polarity or through direct stabilization of a planar excited state through macromolecular binding.

Symmetry-Breaking Charge Transfer in Metal-Organic Frameworks.

High quantum-yield charge carrier generation from the initially prepared excitons defines a key step in the light-harvesting and conversion scheme. Photoinduced charge transfer in molecular electron donor-acceptor assemblies is driven by a sizable ΔG0, which compromises the potential of the generated carriers. Reminiscent of the special pair at the reaction center of the natural light-harvesting complex, symmetry-breaking charge transfer (SBCT) within a pair of identical struts of metal-organic framework (MOF) will facilitate the efficient generation of long-lived charge carriers with maximized potentials without incorporating any foreign redox species. We report SBCT in pyrene-based zirconium metal-organic framework (MOF) NU-1000 that leads to efficient generation of radical ions in a polar solvent and bound CT states in a low-polar solvent. The probe unveils the role of the low-lying non-Franck-Condon excitonic states as intermediates in the formation of the SBCT state from the initially prepared Franck-Condon S1 states. Ultrafast and transient spectroscopy─probed over 200 fs-30 μs time scale─evinces a kSBCT = (110 ps)-1 in polar media (εs = 37.5) forming solvated radical ions with recombination rate kCR = (∼45 ns)-1. A slower rate with kSBCT = (203 ps)-1 was recorded in low-polar (εs = 7.0) solvent manifesting a bound [TBAPy•+ TBAPy•-] state with kCR ≈ (17 μs)-1. This discovery, along with other unique photophysical features relevant to light harvesting, should define a MOF-based platform for developing heterogeneous artificial photon energy conversion systems.

Solvent-Dependent Folding Behavior of a Helix-Forming Aryl-Triazole Foldamer.

Aromatic foldamers make up a novel class of bioinspired molecules that display helical conformations and have functions that rely on control over their coil-helix folding preferences. While the folding has been extensively examined by experiment, it has rarely been paired with the types of atomic level insights offered by theory. We present the results of all-atom molecular dynamics (MD) simulations to examine the role of solvent polarity on driving the helical folding behavior of the aryl-triazole foldamer. The temperature-dependent enhanced sampling technique, replica-exchange MD simulations, was employed to understand the folding phenomena. The simulation results show that in a low polarity solvent (dichloromethane), the foldamer prefers to stay in the unfolded state. The unfolded state has four dipolar triazoles (5 D) in their favored all-anti geometries and favoring anti-parallel geometries. However, an increase in solvent polarity using acetonitrile resulted in solvophobic collapse, yielding the helically folded form as the predominant state. The folded helix has an all-syn geometry, with triazoles in parallel arrangements. Intermediate conformations with a mixture of syn and anti arrangements of the triazoles are of lower abundance in both the DCM and MeCN solvents. The chiral handedness of the helix observed experimentally is assigned as left-handed by correlation with computed electronic circular dichroism spectra using time-dependent density functional theory.

Organic-soluble cytosine derivatives for studying base-pair interactions in nonaqueous solution

The presence of higher order G-quadruplex-DNA (G4) structures in human cells in guanine-rich DNA sequences has been well established. In cases of G4 helicase impairment or G4 stabilization via association with G4 ligands, it has been determined that arrest and/or termination of DNA transcription/replication occurs because these structures act as physical barriers to both helicase and polymerase mobility along the DNA. Truncation of transcription or replication may result in the loss of genetic material expression leading to disorders. To ameliorate G4-induced barriers, agents that destabilize or “unwind” the quadraplex structures are sought. Earlier work has shown that the cytosine analogue phenylpyrrolocytosine has potential G4-destabilizing ability. It was hypothesized that the unwinding activity was related to its ability to base pair with guanosine. To facilitate the design and evaluation of the hydrogen bonding ability of cytosine analogues, solubility in aprotic, and low-polarity solvents, e.g., deutero-chloroform (CDCl3), is needed; then, determination of association constants ( Ka) with guanine via 1H nuclear magnetic resonance (NMR) spectroscopy or isothermal titration calorimetry (ITC) will be possible. Herein, we report on the synthesis of three new chloroform-soluble, cytosine analogues: N1-cyclohexylmethyl-7-phenylimidazolocytosine, N1-cyclohexylmethyl-7-(6-(methoxycarbonyl)pyridin-2-yl)imidazolocytosine, and N1-cyclohexylmethyl-7-(6-carbamoylpyridin-2-yl)imidazolocytosine. We further report the binding interactions of each of these analogues with the guanosine derivative 2′,3′,5′- O-tris( tert-butyldimethylsilyl)guanosine through the use of both ITC and 1H NMR titration experiments in chloroform and compare the binding to persilyated ribo-cytidine.