Toward the development of new photolabile protecting groups that can rapidly release bioactive compounds upon photolysis with visible light

The synthesis and characterization of a new photolabile protecting group (caging group) for carboxylic acids, the 2-(dimethylamino)-5-nitrophenyl (DANP) group, is described. This compound has a major absorption band in the visible wavelength region with a maximum near 400 nm (epsilon400 = 9077 M(-1) cm(-1) at pH 7.4 and 21 degrees C). The caging group is attached through an ester linkage to the carboxyl functionality of beta-alanine, which activates the inhibitory glycine receptor in the mammalian central nervous system. Such caged compounds play an important role in transient kinetic investigations of fast cellular processes. Upon photolysis of DANP-caged beta-alanine, the caging group is released within 5 micros. Quantum yields of 0.03 and 0.002 were obtained in the UV region (308 and 360 nm) and the visible region (450 nm), respectively. Laser-pulse photolysis experiments, using 337 or 360 nm light, were performed with the caged compound equilibrated with HEK 293 cells transiently transfected with cDNA encoding the alpha1 homomeric, wild-type glycine receptor. The experiments demonstrated that neither DANP-caged beta-alanine nor its byproducts inhibit or activate the glycine receptors on the cell surface. Under physiological conditions, the DANP-caged beta-alanine is water-soluble and stable and can be used for transient kinetic measurements.     

Synthesis of fluorescent oligonucleotide--EYFP conjugate: towards supramolecular construction of semisynthetic biomolecular antennae

A novel species of DNA--protein conjugate was synthesized by chemically linking DNA oligonucleotides to Aequorea victoria green fluorescent protein mutant EYFP. An additional cysteine was added to the C-terminus of the EYFP by genetic engineering and used to covalently attach amino-modified oligonucleotide with the aid of the heterobifunctional crosslinker sSMCC. EYFP maintained its fluorescence upon conjugation. The oligonucleotide provides an additional binding site to the fluorescent protein, and hence, the EYFP conjugate could be specifically hybridized with both complementary DNA-protein conjugates in-solution as well as immobilized at capture oligonucleotides attached to a solid substrate. These studies are paving the way for future applications in the self-assembly of photoactive supramolecular complexes, such as artificial light-harvesting systems.     

MS-Express: data-extracting and -processing software for high-throughput experimentation with mass spectrometry

High-throughput experiments (HTE) result in large amounts of raw data that have to be evaluated for sample classification. Especially mass spectrometry, a widely used detection method in catalytic HTE applications, produces enormous amounts of data. In the past few years, in catalysts research, several test rigs based on mass spectrometric detection have been independently reported by different groups. In a typical HTE, the catalysts are tested sequentially; the recording of the scans, however, occurs continuously. For this reason, the scans of interest have to be extracted from the raw data, and scans belonging to the same sample have to be averaged in a tedious procedure before further processing. In this publication, we present our custom-designed software MS-Express (mass spectrometry data-extracting and -processing software), an efficient tool for HTE MS data evaluation. MS-Express not only sorts the data, it also establishes statistical significance with the help of reference and blank data and provides concise information about abundance and intensity distributions of expected peaks. A special feature is that the program also reports unexpected MS signals, which potentially lead to unexpected discoveries.     

Polyampholytic Graft Copolymers as Matrix for TiO2/Eosin Y/[Mo3S13]2− Hybrid Materials and Light-Driven Catalysis

An effective strategy to enhance the performance of inorganic semiconductors is moving towards organic-inorganic hybrid materials. Here, we report the design of core–shell hybrid materials based on a TiO₂ core functionalized with a polyampholytic (poly(dehydroalanine)-graft-(n-propyl phosphonic acid acrylamide) shell (PDha-g-PAA@TiO₂). The PDha-g-PAA shell facilitates the efficient immobilization of the photosensitizer Eosin Y (EY) and enables electronic interactions between EY and the TiO₂ core. This resulted in high visible-light-driven H₂ generation. The enhanced light-driven catalytic activity is attributed to the unique core–shell design with the graft copolymer acting as bridge and facilitating electron and proton transfer, thereby also preventing the degradation of EY. Further catalytic enhancement of PDha-g-PAA@TiO₂ was possible by introducing [Mo₃S₁₃]²⁻ cluster anions as hydrogen-evolution cocatalyst. This novel design approach is an example for a multi-component system in which reactivity can in future be independently tuned by selection of the desired molecular or polymeric species.     

Bridging the Green Gap: Metal–Organic Framework Heteromultilayers Assembled from Porphyrinic Linkers Identified by Using Computational Screening

In organic photovoltaics, porphyrins (PPs) are among the most promising compounds owing to their large absorption cross-section, wide spectral range, and stability. Nevertheless, a precise adjustment of absorption band positions to reach a full coverage of the so-called green gap has not been achieved yet. We demonstrate that a tuning of the PP Q- and Soret bands can be carried out by using a computational approach for which substitution patterns are optimized in silico. The most promising candidate structures were then synthesized. The experimental UV/Vis data for the solvated compounds were in excellent agreement with the theoretical predictions. By attaching further functionalities, which allow the use of PP chromophores as linkers for the assembly of metal-organic frameworks (MOFs), we were able to exploit packing effects resulting in pronounced redshifts, which allowed further optimization of the photophysical properties of PP assemblies. Finally, we use a layer-by-layer method to assemble the PP linkers into surface-mounted MOFs (SURMOFs), thus obtaining high optical quality, homogeneous and crystalline multilayer films. Experimental results are in full accord with the calculations, demonstrating the huge potential of computational screening methods in tailoring MOF and SURMOF photophysical properties.