Kinetic studies of glucose oxidase in polyelectrolyte multilayer films by means of scanning electrochemical microscopy (SECM)

Multilayer films of glucose oxidase (GOx) and poly(dimethyl diallyl ammonium chloride) (PDDA) prepared by layer-by-layer deposition were studied using scanning electrochemical microscopy (SECM). Aminated glass slides were coated with five bilayers of poly(styrene sulfonate) (PSS) and PDDA and used as substrates onto which GOx/PDDA multilayers were deposited. UV-Vis experiments confirmed multilayer growth, scanning force microscopic images provided morphological information about the films. SECM current-distance curves enabled the determination of kinetic information about GOx in GOx/PDDA multilayers as a function of layer number, film termination, inert covering layers, and enzyme substrate concentration after fitting to numerical models. The results indicate that only the topmost layers contributed significantly to the conversion. An odd-even pattern was observed for PDDA-terminated films or GOx-terminated films that correlated with morphological changes.     

Effective potentials for spectator groups in molecular systems I. Potential curves and binding energies

Summary A method for representing inactive groups, i.e. spectator groups, in a molecular system by an effective potential is presented. The matrix elements for the spectator's short-range Hartree-Fock potential is stored in an intermediate AO basis, from which it can be transferred into the user basis for the active part of the molecular system. The longer-range of the potential is transferred via a (distributed) multipole expansion. The method is illustrated for the NH₃·X (X=NH₃, H₂O, HF) complexes: binding energies could be reproduced to within 5% by employing the effective NH₃ potential (whereby the lone pair was included in the active system), the entire NH₃·HF potential curve with a depth of 50 kJ/mol is reproduced within 2 kJ/mol if various intermediate basis sets are chosen. Technical details are discussed; the effective potential can directly be introduced in CI calculations.     

Structural and Photosensitizing Features of Phthalocyanine—Zeolite Hybrid Nanomaterials

In this work, we have quantified for the first time the fluorescence and singlet oxygen quantum yields of a silicon(IV) phthalocyanine bound to the surface of zeolite L nanocrystals. The photophysical properties were correlated with the absorption spectra and the morphology of the nanoparticles, and most importantly, with the fraction of photoactive chromophores. By comparison with the fluorescence and singlet oxygen quantum yields of the free phthalocyaninate in dilute solution (Φ_F = 0.50 and Φ_? = 0.50, respectively), we conclude that for the most efficient nanoparticles nearly 80% of chromophores are active as monomeric units on the surface, as indicated by the corresponding quantum yields (Φ_F = 0.40 and Φ_? = 0.40). We further functionalized and raised the ζ‐potential of the best performing nanomaterial to improve its water dispersibility. The functionalization was monitored by thermogravimetric analysis and time‐of‐flight secondary‐ion mass spectrometry, and its influence on the photophysical properties was assessed. The resulting nanomaterials are capable of establishing stable suspensions in water while retaining the ability to form reactive oxygen species upon irradiation with red light. This provides a basis for the rational design of photoactive nanomaterials for photodynamic therapy or water decontamination.     

Diaryldichalcogenide radical cations

One-electron oxidation of two series of diaryldichalcogenides (C₆F₅E)₂ (13a–c) and (2,6-Mes₂C₆H₃E)₂ (16a–c) was studied (E = S, Se, Te). The reaction of 13a and 13b with AsF₅ and SbF₅ gave rise to the formation of thermally unstable radical cations [(C₆F₅S)₂]˙⁺ (14a) and [(C₆F₅Se)₂]˙⁺ (14b) that were isolated as [Sb₂F₁₁]^– and [As₂F₁₁]^– salts, respectively. The reaction of 13c with AsF₅ afforded only the product of a Te–C bond cleavage, namely the previously known dication [Te₄]²⁺ that was isolated as [AsF₆]^– salt. The reaction of (2,6-Mes₂C₆H₃E)₂ (16a–c) with [NO][SbF₆] provided the corresponding radical cations [(2,6-Mes₂C₆H₃E)₂]˙⁺ (17a–c; E = S, Se, Te) in the form of thermally stable [SbF₆]^– salts in nearly quantitative yields. The electronic and structural properties of these radical cations were probed by X-ray diffraction analysis, EPR spectroscopy, and density functional theory calculations and other methods.     

Microelectrochemical modulation of micropatterned cellular environments

Patterned cell cultures obtained by microcontact printing have been modified in situ by a microelectrochemical technique. It relies on lifting cell-repellent properties of oligo(ethylene glycol)-terminated self-assembled monolayers (SAMs) by Br2, which is produced locally by an ultramicroelectrode of a scanning electrochemical microscope (SECM). After Br2 treatment the SAM shows increased permeability and terminal hydrophobicity as characterized by SECM approach curves and contact angle measurements, respectively. Polarization-modulation Fourier transform infrared reflection-absorption spectroscopic (PM FTIRRAS) studies on macroscopic samples show that the Br2 treatment removes the oligo(ethelyene glycol) part of the monolayer within a second time scale while the alkyl part of the SAM degrades with a much slower rate. The lateral extension of the modification can be limited because heterogeneous electron transfer from the gold support destroys part of the electrogenerated Br2 once the monolayer is locally damaged in a SECM feedback configuration. This effect has been reproduced and analyzed by exposing SAM-modified samples to Br2 in the galvanic cell Au|SAM|5 microM Br2 + 0.1 M Na2SO4||10 microM KBr + 0.1 M Na2SO4|Au followed by an PM FTIRRAS characterization of the changes in the monolayer system.     

Mesogenic Groups Control the Emitter Orientation in Multi-Resonance TADF Emitter Films**

The use of thermally activated delayed fluorescence (TADF) emitters and emitters that show preferential horizontal orientation of their transition dipole moment (TDM) are two emerging strategies to enhance the efficiency of OLEDs. We present the first example of a liquid crystalline multi-resonance TADF (MR-TADF) emitter, DiKTa-LC . The compound possesses a nematic liquid crystalline phase between 80 °C and 110 °C. Importantly, the TDM of the spin-coated film shows preferential horizontal orientation, with an anisotropy factor, a, of 0.28, which is preserved in doped poly(vinylcarbazole) films. Green-emitting (λ_EL=492 nm) solution-processed OLEDs based on DiKTa-LC showed an EQE_max of 13.6 %. We thus demonstrate for the first time how self-assembly of a liquid crystalline TADF emitter can lead to the so-far elusive control of the orientation of the transition dipole in solution-processed films, which will be of relevance for high-performance solution-processed OLEDs.     

Early Stage UV-B Induced Molecular Modifications of Human Eye Lens γD-Crystallin

In the human eye lenses, the crystallin proteins facilitate transparency, light refraction, as well as UV light protection. A deregulated balanced interplay between α-, β-, and γ-crystallin can cause cataract. γD-crystallin (hγD) is involved in the energy dissipation of absorbed UV light by energy transfer between aromatic side chains. Early UV-B induced damage of hγD with molecular resolution is studied by solution NMR and fluorescence spectroscopy. hγD modifications are restricted to Tyr 17 and Tyr 29 in the N-terminal domain, where a local unfolding of the hydrophobic core is observed. None of the tryptophan residues assisting fluorescence energy transfer is modified and hγD is remained soluble over month. Investigating isotope-labeled hγD surrounded by eye lens extracts from cataract patients reveals very week interactions of solvent-exposed side chains in the C-terminal hγD domain and some remaining photoprotective properties of the extracts. Hereditary E107A hγD found in the eye lens core of infants developing cataract shows under the here used conditions a thermodynamic stability comparable to the wild type but an increased sensitivity toward UV-B irradiation.