TY - JOUR A1 - Koetz, Joachim T1 - The Effect of Surface Modification of Gold Nanotriangles for Surface-Enhanced Raman Scattering Performance JF - Nanomaterials N2 - A surface modification of ultraflat gold nanotriangles (AuNTs) with different shaped nanoparticles is of special relevance for surface-enhanced Raman scattering (SERS) and the photo-catalytic activity of plasmonic substrates. Therefore, different approaches are used to verify the flat platelet morphology of the AuNTs by oriented overgrowth with metal nanoparticles. The most important part for the morphological transformation of the AuNTs is the coating layer, containing surfactants or polymers. By using well established AuNTs stabilized by a dioctyl sodium sulfosuccinate (AOT) bilayer, different strategies of surface modification with noble metal nanoparticles are possible. On the one hand undulated superstructures were synthesized by in situ growth of hemispherical gold nanoparticles in the polyethyleneimine (PEI)-coated AOT bilayer of the AuNTs. On the other hand spiked AuNTs were obtained by a direct reduction of Au³⁺ ions in the AOT double layer in presence of silver ions and ascorbic acid as reducing agent. Additionally, crumble topping of the smooth AuNTs can be realized after an exchange of the AOT bilayer by hyaluronic acid, followed by a silver-ion mediated reduction with ascorbic acid. Furthermore, a decoration with silver nanoparticles after coating the AOT bilayer with the cationic surfactant benzylhexadecyldimethylammonium chloride (BDAC) can be realized. In that case the ultraviolet (UV)-absorption of the undulated Au@Ag nanoplatelets can be tuned depending on the degree of decoration with silver nanoparticles. Comparing the Raman scattering data for the plasmon driven dimerization of 4-nitrothiophenol (4-NTP) to 4,4′-dimercaptoazobenzene (DMAB) one can conclude that the most important effect of surface modification with a 75 times higher enhancement factor in SERS experiments becomes available by decoration with gold spikes. KW - undulated KW - spiked and crumble gold nanotriangles KW - SERS enhancement factor KW - dimerization of 4-nitrothiophenol KW - AOT bilayer KW - PEI coating Y1 - 2020 U6 - https://doi.org/10.3390/nano10112187 SN - 2079-4991 VL - 10 IS - 11 PB - MDPI CY - Basel ER - TY - JOUR A1 - Haubitz, Toni A1 - Fudickar, Werner A1 - Linker, Torsten A1 - Kumke, Michael Uwe T1 - pH-sensitive fluorescence switching of pyridylanthracenes BT - the effect of the isomeric pattern JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - 9,10-substituted anthracenes are known for their useful optical properties like fluorescence, which makes them frequently used probes in sensing applications. In this article, we investigate the fundamental photophysical properties of three pyridyl-substituted variants. The nitrogen atoms in the pyridinium six-membered rings are located in the ortho-, meta-, and para-positions in relation to the anthracene core. Absorption, fluorescence, and transient absorption measurements were carried out and were complemented by theoretical calculations. We monitored the photophysics of the anthracene derivatives in chloroform and water investigating the protonated as well as their nonprotonated forms. We found that the optical properties of the nonprotonated forms are strongly determined by the anthracene chromophore, with only small differences to other 9,10-substituted anthracenes, for example diphenyl anthracene. In contrast, protonation leads to a strong decrease in fluorescence intensity and lifetime. Transient absorption measurements and theoretical calculations revealed the formation of a charge-transfer state in the protonated chromophores, where electron density is shifted from the anthracene moiety toward the protonated pyridyl substituents. While the para- and ortho-derivatives' charge transfer is still moderately fluorescent, the meta-derivative is affected much stronger and shows nearly no fluorescence. This nitrogen-atom-position-dependent sensitivity to hydronium activity makes a combination of these fluorophores very attractive for pH-sensing applications covering a broadened pH range. KW - Absorption KW - Aromatic compounds KW - Fluorescence KW - Hydrocarbons KW - Reaction mechanisms Y1 - 2020 U6 - https://doi.org/10.1021/acs.jpca.0c09911 SN - 1089-5639 SN - 1520-5215 VL - 124 IS - 52 SP - 11017 EP - 11024 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Wessig, Pablo A1 - Freyse, Daniel A1 - Schuster, David A1 - Kelling, Alexandra T1 - Fluorescent dyes with large stokes shifts based on Benzo[1,2-d:4,5-d']bis([1,3]dithiole) (“S4-DBD Dyes”) JF - Europan journal of organic chemistry N2 - We report on a further development of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes by replacement of the four oxygen atoms of the heterocyclic core by sulfur atoms. This variation causes striking changes of the photophysical properties. Whereas absorption and emission significantly shifted to longer wavelength, the fluorescence lifetimes and quantum yields are diminished compared to DBD dyes. The latter effect is presumably caused by an enhanced intersystem crossing to the triplet state due to the sulfur atoms. The very large Stokes shifts of the S-4-DBD dyes ranging from 3000 cm(-1) to 7400 cm(-1) (67 nm to 191 nm) should be especially emphasized. By analogy with DBD dyes a broad variation of absorption and emission wavelength is possible by introducing different electron withdrawing substituents. Moreover, some derivatives for coupling with biomolecules were developed. KW - fluorescent dyes KW - sulfur KW - heterocycles KW - stokes shift KW - photophysics Y1 - 2020 U6 - https://doi.org/10.1002/ejoc.202000093 SN - 1434-193X SN - 1099-0690 VL - 2020 IS - 11 SP - 1732 EP - 1744 PB - Wiley CY - Weinheim ER - TY - JOUR A1 - Lood, Kajsa A1 - Schmidt, Bernd T1 - Stereoselective synthesis of conjugated polyenes based on tethered olefin metathesis and carbonyl olefination BT - application to the total synthesis of (+)-bretonin B JF - The journal of organic chemistry N2 - The combination of a highly stereoselective tethered olefin metathesis reaction and a Julia-Kocienski olefination is presented as a strategy for the synthesis of conjugated polyenes with at least one Z-configured C=C bond. The strategy is exemplified by the synthesis of the marine natural product (+)-bretonin B. KW - absolute-configuration KW - natural-products KW - formal synthesis KW - oxidation KW - derivatives KW - aldehydes KW - catalysts KW - alcohols KW - sponge KW - ethers Y1 - 2020 U6 - https://doi.org/10.1021/acs.joc.0c00446 SN - 0022-3263 SN - 1520-6904 VL - 85 IS - 7 SP - 5122 EP - 5130 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Mai-Linde, Yasemin A1 - Linker, Torsten T1 - Radical clock probes to determine carbohydrate radical stabilities JF - Organic letters N2 - Carbohydrate radical stabilities in the 1- and 2-position have been determined by a radical clock approach, starting from cyclopropanated sugars with xanthates as precursors. Various hexoses and pentoses afforded 1-deoxy sugars as main products, indicating that anomeric radicals are more stable than radicals in the 2-position. An additional influence of the configurations on radical stabilities has been observed. Our results should be interesting for the understanding of 1,2-radical rearrangements in carbohydrate chemistry and offer an easy access to deoxy-vinyl sugars. KW - stereoselective-synthesis KW - convenient synthesis KW - chemistry KW - cyclopropanation KW - mechanism KW - glycals KW - beta-(acyloxy)alkylrear KW - rangement KW - sugars Y1 - 2020 U6 - https://doi.org/10.1021/acs.orglett.0c00111 SN - 1523-7060 SN - 1523-7052 VL - 22 IS - 4 SP - 1525 EP - 1529 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schultze, Christiane A1 - Foß, Stefan A1 - Schmidt, Bernd T1 - 8-Prenylflavanones through microwave promoted tandem claisen rearrangement/6-endo-trig cyclization and cross metathesis JF - European journal of organic chemistry N2 - Prenylated flavanones were obtained from ortho-allyloxy chalcones through a one-pot sequence of Claisen rearrangement and 6-endo-trig cyclization, followed by olefin cross metathesis of the intermediate allyl flavanones with 2-methyl-2-butene. The synthetic utility of this route is illustrated for the synthesis of several naturally occurring prenyl flavanones. KW - tandem reactions KW - arenes KW - oxygen heterocycles KW - microwave chemistry KW - rearrangement Y1 - 2020 U6 - https://doi.org/10.1002/ejoc.202001378 SN - 1434-193X SN - 1099-0690 VL - 2020 IS - 47 SP - 7373 EP - 7384 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Schwarze, Thomas A1 - Riemer, Janine T1 - Highly K+ selective probes with fluorescence emission wavelengths higher than 500 nm in water JF - ChemistrySelect N2 - Herein, we report on the synthesis of highly K+/Na+ selective fluorescent probes in a feasible number of synthetic steps. These K+ selective fluorescent probes, so called fluoroionophores, 1 and 2 consists of different highly K+/Na+ selective building blocks the alkoxy-substituted N-phenylaza-18-crown-6 lariat ethers (ionophores) and "green" (cf. coumarin unit in 1) or "red" (cf. nile red unit in 2) fluorescent moieties (fluorophores). The fluorescent probes 1 and 2 show K+ induced fluorescence enhancement factors of 4.1 for 1 and 1.9 for 2 and dissociation constants for the corresponding K+ complexes of 43 mM (1+K+) and 18 mM (2+K+) in buffered aqueous solution. The fluorescence signal of 1 and 2 is changed by less than 5 % by pH values in the range of 6.8 to 8.8. Thus, 1 and 2 are capable fluorescent tools to determine extracellular K+ levels by fluorescence enhancements at wavelengths higher than 500 nm. KW - potassium KW - sodium KW - fluorescence KW - selectivity KW - probes Y1 - 2020 U6 - https://doi.org/10.1002/slct.202003785 SN - 2365-6549 VL - 5 IS - 42 SP - 13174 EP - 13178 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Hermanns, Jolanda A1 - Schmidt, Bernd A1 - Glowinski, Ingrid A1 - Keller, David T1 - Online teaching in the course "organic chemistry" for nonmajor chemistry students BT - from necessity to opportunity JF - Journal of chemical education N2 - In this communication the development of an online course on the topic organic chemistry for nonmajor chemistry students is described and discussed. For this online course, the existing classroom course was further developed. New elements such as podcasts, task navigators, and a forum for discussing the solving of tasks or problems with the content were added. This new online course was evaluated. Therefore, a questionnaire was developed. This consists of questions with regard to the longtime learning behavior of the students and to the online learning. The results of this evaluation show that a preference for online learning and a preference for classroom teaching can be measured separately in two scales. Students values on the scale representing a preference for online learning correlate positively and significantly with confidence in the choice of the study subject, enthusiasm about the subject, and the ability to organize their learning, learning environment, and time management. They correlate also with the satisfaction concerning the materials provided. Students values for one of those teaching methods also correlate with their rating with regard to their exam preparation. Values representing a preference for online teaching correlate positively with students better feeling of exam preparation. Values representing a preference for classroom teaching show negative correlations with the values representing students similar or even better preparation for the exams as a result of online teaching. It is therefore not surprising that the ratings for the two scales correlate with the wish for a combination of online teaching and classroom teaching in the future. As a solution, a new course concept for the time after the corona virus crisis that suits all students is outlined in the outlook. KW - first-year undergraduate/general KW - organic chenlistry KW - computer-based KW - learning KW - distance learning/self instruction Y1 - 2020 U6 - https://doi.org/10.1021/acs.jchemed.0c00658 SN - 0021-9584 SN - 1938-1328 VL - 97 IS - 9 SP - 3140 EP - 3146 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Fudickar, Werner A1 - Linker, Torsten T1 - Structural motives controlling the binding affinity of 9,10-bis(methylpyridinium)anthracenes towards DNA JF - Bioorganic & medicinal chemistry : a Tetrahedron publication for the rapid dissemination of full original research papers and critical reviews on biomolecular chemistry, medicinal chemistry and related disciplines N2 - In the search of new DNA groove binding agents a series of substituted 9,10-methylpyridiniumanthracenes have been synthesized and their interactions with DNA have been studied by UV/vis absorption, CD and fluorescence spectroscopy. A minor groove binding mode is confirmed by DNA melting studies, strong CD effects, the dependence of the binding affinity on ionic strength, and the differentiation between AT and GC base pairs. No binding occurs to GC sequences. Binding constants to calf thymus DNA (ct-DNA) and poly(dA:dT) in the range between 1 x 10(4) and 3 x 10(5) M-1 have been determined. The binding strength decreases with the size of substituents attached at the anthracene site. Variation of the substitution pattern of the charged groups shows that methyl groups in meta position cause slightly stronger binding than methyl groups in para position. In contrast, with these groups in ortho position, no binding interaction has been observed. The strongest binding is achieved with an expansion of the peripheral heterocycle from pyridine to quinoline. Molecular modeling reveals the pivotal role of the substitution pattern: Anthracenes with para and meta pyridines align along the minor grooves. On the other hand, the ortho derivative adopts no groove-alignment. KW - groove binding KW - anthracenes KW - ct-DNA KW - fluorescence enhancement KW - docking Y1 - 2020 U6 - https://doi.org/10.1016/j.bmc.2020.115432 SN - 0968-0896 SN - 1464-3391 VL - 28 IS - 8 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Perovic, Milena A1 - Qin, Qing A1 - Oschatz, Martin T1 - From molecular precursors to nanoparticles BT - tailoring the adsorption properties of porous carbon materials by controlled chemical functionalization JF - Advanced functional materials N2 - Nanoporous carbon materials (NCMs) provide the "function" of high specific surface area and thus have large interface area for interactions with surrounding species, which is of particular importance in applications related to adsorption processes. The strength and mechanism of adsorption depend on the pore architecture of the NCMs. In addition, chemical functionalization can be used to induce changes of electron density and/or electron density distribution in the pore walls, thus further modifying the interactions between carbons and guest species. Typical approaches for functionalization of nanoporous materials with regular atomic construction like porous silica, metal-organic frameworks, or zeolites, cannot be applied to NCMs due to their less defined local atomic construction and abundant defects. Therefore, synthetic strategies that offer a higher degree of control over the process of functionalization are needed. Synthetic approaches for covalent functionalization of NCMs, that is, for the incorporation of heteroatoms into the carbon backbone, are critically reviewed with a special focus on strategies following the concept "from molecules to materials." Approaches for coordinative functionalization with metallic species, and the functionalization by nanocomposite formation between pristine carbon materials and heteroatom-containing carbons, are introduced as well. Particular focus is given to the influences of these functionalizations in adsorption-related applications. KW - composites KW - heteroatoms KW - metal species KW - porous carbon materials KW - surface KW - functionalization Y1 - 2020 U6 - https://doi.org/10.1002/adfm.201908371 SN - 1616-301X SN - 1616-3028 VL - 30 IS - 41 PB - Wiley-VCH CY - Weinheim ER -