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- ItemCurcuminoid–BF2 complexes: Synthesis, fluorescence and optimization of BF2 group cleavage(Frankfurt a.M. : Beilstein-Institut, 2017) Weiß, Henning; Reichel, Jeannine; Görls, Helmar; Schneider, Kilian R.A.; Micheel, Mathias; Pröhl, Michael; Gottschaldt, Michael; Dietzek, Benjamin; Weigand, WolfgangEight difluoroboron complexes of curcumin derivatives carrying alkyne groups containing substituents have been synthesized following an optimised reaction pathway. The complexes were received in yields up to 98% and high purities. Their properties as fluorescent dyes have been investigated. Furthermore, a strategy for the hydrolysis of the BF2 group has been established using aqueous methanol and sodium hydroxide or triethylamine.
- ItemCharacterization of Fluorescent Proteins with Intramolecular Photostabilization*(Weinheim : Wiley-VCH, 2021) Henrikus, Sarah S.; Tassis, Konstantinos; Zhang, Lei; van der Velde, Jasper H. M.; Gebhardt, Christian; Herrmann, Andreas; Jung, Gregor; Cordes, ThorbenGenetically encodable fluorescent proteins have revolutionized biological imaging in vivo and in vitro. Despite their importance, their photophysical properties, i. e., brightness, count-rate and photostability, are relatively poor compared to synthetic organic fluorophores or quantum dots. Intramolecular photostabilizers were recently rediscovered as an effective approach to improve photophysical properties of organic fluorophores. Here, direct conjugation of triplet-state quenchers or redox-active substances creates high local concentrations of photostabilizer around the fluorophore. In this paper, we screen for effects of covalently linked photostabilizers on fluorescent proteins. We produced a double cysteine mutant (A206C/L221C) of α-GFP for attachment of photostabilizer-maleimides on the β-barrel near the chromophore. Whereas labelling with photostabilizers such as trolox, a nitrophenyl group, and cyclooctatetraene, which are often used for organic fluorophores, had no effect on α-GFP-photostability, a substantial increase of photostability was found upon conjugation to azobenzene. Although the mechanism of the photostabilizing effects remains to be elucidated, we speculate that the higher triplet-energy of azobenzene might be crucial for triplet-quenching of fluorophores in the blue spectral range. Our study paves the way for the development of fluorescent proteins with photostabilizers in the protein barrel by methods such as unnatural amino acid incorporation. © 2021 The Authors. ChemBioChem published by Wiley-VCH GmbH
- ItemRole of electronic correlations in photoionization of NO2 in the vicinity of the 2A1/2B2 conical intersection(Cambridge : The Royal Soc. of Chemistry, 2017) Brambila, Danilo S.; Harvey, Alex G.; Houfek, Karel; Mašín, Zdeněk; Smirnova, OlgaWe present the first ab initio multi-channel photoionization calculations for NO2 in the vicinity of the 2A1/2B2 conical intersection, for a range of nuclear geometries, using our newly developed set of tools based on the ab initio multichannel R-matrix method. Electronic correlation is included in both the neutral and the scattering states of the molecule via configuration interaction. Configuration mixing is especially important around conical intersections and avoided crossings, both pertinent for NO2, and manifests itself via significant variations in photoelectron angular distributions. The method allows for a balanced and accurate description of the photoionization/photorecombination for a number of different ionic channels in a wide range of photoelectron energies up to 100 eV. Proper account of electron correlations is crucial for interpreting time-resolved signals in photoelectron spectroscopy and high harmonic generation (HHG) from polyatomic molecules.
- ItemAntioxidant and hydrophilic poly(lactic acid) fibers obtained through their modification with amines and ferulic acid(New York, NY [u.a.] : Wiley, 2017) Wojciechowska, Dorota; Herczyńska, Lucyna; Simon, Frank; Puchalski, Michał; Stawski, DawidThe ferulic acid (FA) is a natural antioxidant, abundantly present in plants, which acts as the plant's immune system. In order to take advantage of its properties, a method has been developed, which combines antioxidant FA with bio-based biodegradable poly(lactic acid) fibers and biocompatible hydrophilic polyallylamine, enabling the production of versatile base material that could be used for active anti-inflammatory wound dressings. The fibers are first subjected to aminolysis in order to obtain amino moieties on the surface, able to react with the molecules of FA. Next, the FA was attached to the aminolyzed fibers surface with use of 1-ethyl-3–(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide. The anti-inflammatory properties of the modified fibers were assessed using 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay. Presence of FA on the fibers’ surface was investigated through X-ray photoelectron spectroscopy analysis and Folin–Ciocalteu (total phenolic content) test.
- ItemLike-likes-Like: Cooperative Hydrogen Bonding Overcomes Coulomb Repulsion in Cationic Clusters with Net Charges up to Q=+6e(Weinheim : Wiley-VCH Verl., 2018-4-26) Niemann, Thomas; Stange, Peter; Strate, Anne; Ludwig, RalfQuantum chemical calculations have been employed to study kinetically stable cationic clusters, wherein the monovalent cations are trapped by hydrogen bonding despite strongly repulsive electrostatic forces. We calculated linear and cyclic clusters of the hydroxy-functionalized cation N-(3-hydroxypropyl) pyridinium, commonly used as cation in ionic liquids. The largest kinetically stable cluster was a cyclic hexamer that very much resembles the structural motifs of molecular clusters, as known for water and alcohols. Surprisingly, strong cooperative hydrogen bonds overcome electrostatic repulsion and result in cationic clusters with a high net charge up to Q=+6e. The structural, spectroscopic, and electronic signatures of the cationic and related molecular clusters of 3-phenyl-1-propanol could be correlated to NBO parameters, supporting the existence of “anti-electrostatic” hydrogen bonds (AEHB), as recently suggested by Weinhold. We also showed that dispersion forces enhance the cationic cluster formation and compensate the electrostatic repulsion of one additional positive charge.
- ItemSynthesis, Characterization, and Physicochemical Performance of Nonionic Surfactants via PEG Modification of Epoxides of Alkyl Oleate Esters(Washington, DC : ACS Publ., 2023) Ogunjobi, Joseph K.; Farmer, Thomas J.; Clark, James H.; McElroy, Con RobertThe synthesis of surfactants from fatty acid esters via epoxide chemistry has been known for its accompanying challenges, which usually involve the use of toxic homogeneous catalysts in the ring-opening reaction step and generation of many side reaction products. This paper presents environmentally benign routes to a library of nonionic surfactants via a three-step synthesis involving transesterification of methyl oleate to alkyl oleates, epoxidation of the oleate alkene, and solventless heterogeneously catalyzed ring opening of the epoxides with poly(ethylene glycols) of varying chain length under a short reaction time (60 min). The processes were highly atom efficient and afforded a minimum surfactant yield of 80% with limited or negligible side reaction products. The intermediate molecules and synthesized surfactants were purified and comprehensively characterized, including physicochemical measurements: dynamic surface tension and equilibrium surface tension. Additionally, the hydrophilic-lipophilic balance (HLB) concept was used to comprehensively scan through the polarity behaviors of the surfactants’ head and tail in solution as a prediction of their end use. The results showed that surfactants have a critical micelle concentration (CMC) lower than 0.1 mg/ml as the alkyl oleate increases in length from ethyl to decyl and that the lower-molecular-weight surfactants reached equilibrium faster than the higher-molecular-weight surfactants. HLB results showed that the surfactants can be applied as oil-in-water emulsifiers, detergents, solubilizers, and wetting agents. In general, the synthesized surfactants potentially possess switchable properties for use in industrial formulations, as the alkyl chain length and the ethylene oxide number in the surfactant’s structure are varied.
- ItemThe interaction of chondroitin sulfate with a lipid monolayer observed by using nonlinear vibrational spectroscopy(Cambridge : RSC Publ., 2021) Szekeres, Gergo Peter; Krekic, Szilvia; Miller, Rebecca L.; Mero, Mark; Pagel, Kevin; Heiner, ZsuzsannaThe first vibrational sum-frequency generation (VSFG) spectra of chondroitin sulfate (CS) interacting with dipalmitoyl phosphatidylcholine (DPPC) at air–liquid interface are reported here, collected at a laser repetition rate of 100 kHz. By studying the VSFG spectra in the regions of 1050–1450 cm−1, 2750–3180 cm−1, and 3200–3825 cm−1, it was concluded that in the presence of Ca2+ ions, the head groups together with the head-group-bound water molecules in the DPPC monolayer are strongly influenced by the interaction with CS, while the organization of the phospholipid tails remains mostly unchanged. The interactions were observed at a CS concentration below 200 nM, which exemplifies the potential of VSFG in studying biomolecular interactions at low physiological concentrations. The VSFG spectra recorded in the O–H stretching region at chiral polarization combination imply that CS molecules are organized into ordered macromolecular superstructures with a chiral secondary structure.