University of Siegen
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Publication Access status: Metadata only , Spectroscopic Investigation of the Quadruplex DNA‐Binding Properties of 9‐Aryl‐Substituted Isoquinolinium DerivativesThe spectroscopic investigation of the binding properties of berberine‐type 9‐aryl‐substituted isoquinolinium derivatives with G‐quadruplex DNA (G4‐DNA) are presented. Photometric titrations show that these ligands bind with high affinity to the telomeric G4‐DNA form 22AG ( K =1.0–44×10 5 M −2 ). Furthermore, fluorimetric analysis of thermal DNA denaturation (FRET melting) reveals a significant thermal stabilization of G4‐DNA 22AG upon association with the methoxy‐substituted derivatives. As an analytically useful property, the derivatives with a phenyl substituent or with additional electron‐donating groups show a very weak fluorescence intensity, which increased significantly upon G4‐DNA complexation (fluorescence light‐up effect). Additional time‐resolved fluorescence spectroscopy indicated increased fluorescence lifetimes of the DNA‐bound 9‐(4‐methoxyphenyl)‐substituted derivative, when interacting with the quadruplex‐forming strand 22AG . Notably, the changes of the steady‐state and time‐resolved emission properties of the ligand are more pronounced with G4‐DNA than with duplex DNA so that the combination of these complementary methods may be used for the selective G4‐DNA detection.Source Type:Article3 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Two-color four-wave mixing contribution to an electrostrictive laser-induced grating signal in CO<sub>2</sub>–N<sub>2</sub> mixtures and gas diagnostics(2023); ; Multiparameter determination in the gas phase using the versatile laser-induced grating (LIG) technique is a challenging task due to interdependence of observables on multiple thermodynamic parameters. In CO 2 -N 2 mixtures, simultaneous determination of species concentration and gas temperature can be achieved by using an additional CO 2 concentration-dependent contribution to the LIG signal, which appears if 1064 nm pump pulses are employed. This contribution can be attributed to a direct, quasi-resonant two-color four-wave mixing (TCFWM) of the pump and probe radiations in CO 2 . A detailed study of the laser power and beam polarization, as well as mixture composition, pressure, and temperature dependencies of the TCFWM intensity relative to that of the LIG signal, allowed for the formulation of analytical relations enabling simultaneous mixture composition and temperature determination.Source Type:Article4 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Effect of Sample Plates and Sample Matrix on the Quantification Capabilities of Surface-Assisted Flowing Atmospheric-Pressure Afterglow Mass Spectrometry (SA-FAPA-MS)(2023); Ambient desorption/ionization mass spectrometry (ADI-MS) has been broadly applied to accomplish direct analysis without sample preparation or separation. However, quantification capabilities and analytical performance are sometimes limited. Here, we report signal enhancement effects and improved quantification capabilities in plasma-based ADI-MS, when a flowing atmospheric-pressure afterglow (FAPA) source is used to probe analytes on tailored thin-layer chromatography (TLC) plates. It was found that quantitative results could be achieved when the TLC plate merely served as a sampling plate without a preceding separation step. Specifically, the dynamic response of caffeine, nicotine, acetaminophen, and progesterone was investigated with FAPA-MS on a variety of different TLC surfaces (normal-phase silica, reversed-phase-modified silica, cyano [CN]-modified silica, and dimethyl [RP2]-modified silica). All analytes were studied as single-analyte standards and in a multianalyte mixture to evaluate the effect of sample plates and sample matrix on analytical performance and competitive ionization processes. Overall, dimethyl (RP2)- and CN-modified silica resulted in superior performance compared to other TLC materials. After careful optimization and without the use of internal standards, linear ranges of five orders of magnitude were accessible for caffeine and nicotine. Limits of detection down to femtomole amounts of analyte were achieved. Quantitation limits using RP2-TLC and FAPA-MS were 0.062, 0.062l, 0.31, and 14 pmol for caffeine, nicotine, progesterone, and acetaminophen, respectively. Interestingly, the presence of nicotine at relatively high amounts reduced the signal of the other analytes, an observation that was found to correlate with the differences in the enthalpy of vaporization (Δ H vap ) and proton affinity. To prove the quantitative capabilities, nicotine quantification in a real matrix-heavy e-liquid sample was demonstrated using an isotopically labeled standard. The use of TLC-based surfaces with FAPA-MS can aid in the direct and quantitative mass spectrometric investigation of complex mixtures.Source Type:Article2 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Fluorescence and Phosphorescence Energy Transfer in Cucurbituril‐Based Supramolecular SystemsSupramolecular systems demonstrating resonance energy transfer have recently became a topical area on the borderline of supramolecular chemistry, photochemistry, photophysics and biology. The modularity of supramolecular interactions is a prerequisite for fine tuning of optical properties, which is difficult to achieve by other means. As a component of such systems, cucurbit[n]uril (CB[n]) macrocycles can play a wide spectrum of roles from anchoring of FRET pairs and modulation of the optical output to providing biocompatibility of FRET stains for cell imaging. The aim of this Review is to outline the development of the CB[n]‐based systems with fluorescence (FRET) and phosphorescence (TS‐FRET) energy transfer and to highlight achievements, challenges and perspectives of this fascinating combination of a classical photophysical process and a classical supramolecular host. Particular attention in this Review is given to the current and potential applications of the reviewed systems.Source Type:Article1 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Bis‐ and Tris‐norbornadienes with High Energy Densities for Efficient Molecular Solar Thermal Energy StorageMolecular solar thermal energy storage (MOST) systems can convert, store and release solar energy in chemical bonds, i.e., as chemical energy. In this work, phenyl‐ and naphthyl‐linked bis‐ and tris‐norbornadienes are presented as promising MOST systems with very high energy densities. The substrates were synthesized by Suzuki–Miyaura coupling reactions and their absorption properties and characteristic parameters for MOST applications were investigated. The norbornadiene derivatives showed absorption onsets of up to 386 nm and photoisomerization quantum yields of 56 % per photoisomerization event. The resulting quadricyclane products have half‐lifes up to 14 d and very high energy densities of up to 734 kJ/kg. Overall, these norbornadienes fulfill necessary criteria for an optimal MOST system and are, therefore, a highly promising basis for the development of materials for efficient solar energy conversion and storage.Source Type:Article3 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Policy rules and political polarization(2024); We develop a model to analyze policymakers' incentives to install policy rules, comparing the case of no rule with a binding and a contingent policy rule that allows policymakers to suspend the rule in response to a sufficiently large shock. First, abstracting from political polarization, we show that the choice of the policy rule depends on policymakers' policy targets. Depending on the policy target, there is an unambiguous ranking going from a no‐rule regime to a contingent rule to a binding rule. Next, allowing for political polarization, the incentive to install the different types of rules changes with political polarization between different policymakers and their probability of being elected into office. Increasing political polarization when there is a sufficiently high election probability for policymakers with a high policy target increases the preference for more binding policy rules. It also leads to stricter rules in a contingent rule regime.Source Type:Article - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Transition at a standstill: preschoolers’ motor development during the COVID-19 pandemic(2024)There is no other stage in life where physical growth and motor skills development undergo such rapid changes comprehensively impacting children's overall development than the early and preschool years. Motor skills proficiency contributes to cognitive, social-emotional and academic development and closely connects to positive transition experiences and school success. While research indicates that COVID-19 restrictions have negatively impacted young children's overall development, little is known about their motor skills development during this time. This longitudinal study investigates gross, fine, and visual motor performance during the 2020 shutdown. Due to challenges following-up all children after transition during the pandemic resulting 35% missing data, two analysis groups were used: Analysis 1 (n = 52) included children with complete pre- and post-test data, while Analysis 2 (n = 34) had varying data completeness. Results indicate declines in gross motor skills and visual motor quality during the shutdown, worsening throughout the pandemic. Fine motor and visual motor completion time deteriorated during the shutdown but improved post-transition to primary school, with fine motor quality unchanged. These findings offer insights into preschoolers' motor development during transition, guiding future research and educational practices.Source Type:Article2 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , 1 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Boosting the Cell Harvesting Performance of Poly(di(ethylene glycol)methyl ether methacrylate) Cell Release Layers via Copolymerization of Photo‐ and Thermoresponsive MonomersThe performance of the cell‐selective thermoresponsive poly(di(ethylene glycol)methyl ether methacrylate) (PDEGMA) cell harvest system is shown to be drastically enhanced by exploiting the combination of photoresponsive spiropyran derivates and PDEGMA in copolymerized brushes. The analysis of copolymerized 1′‐(2‐methacryloxyethyl)‐3′,3′‐dimethyl‐6‐nitrospiro(2 H ‐1‐benzopyran‐2,2′‐indoline) (SPMA) (DEMGA) di(ethylene glycol)methyl ether methacrylate brushes revealed that a minor adjustment of the SPMA/DEGMA ratios results in a significant alternation of wettability as well as protein adsorption, when switching the temperature from 37 to 22 °C and alternately irradiating using different light wavelengths (from 530 to 365 nm). Thin P(SPMA‐ co ‐DEGMA) layers supported pancreatic tumor PaTu 8988t cells with high cell viability. Copolymer layers with 2.5% SPMA/DEGMA led to the highest efficiency of enzyme‐free cell release with very good cell viability. The release is induced by cooling the cell culture medium to 22 °C and irradiating the surface with 365 nm light. Compared to neat PDEGMA, the P(SPMA‐ co ‐DEGMA) layers showed a threefold increase in the speed of the change of cell morphology of the attached cells and a >5 times increased fraction of detached cells, which underlines the potential of these dual responsive PDEGMA systems for optimized performance in the facile capture, culture, and release of different cell lines.Source Type:Article5 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Fast and slow walking driven by chemical fuelUsing a di Stefano fuel acid, the two-component walker-on-deck exhibits fast forward motion upon protonation and slow stepwise return to the starting point.Source Type:Article2
