Studies towards the synthesis of the benzodiazepine alkaloid auranthine

Different approaches towards the synthesis of auranthine have been investigated. A completed synthesis of 3‐[2‐(4‐oxo‐3,4‐dihydro‐quinazolin‐2‐yl)‐3,4‐dihydro‐1H‐benzo[e][1,4]‐diazepine‐2,5‐dione, an auranthine precursor, which after dehydration with 50% propylphophonic acid anhydride solution in ethl acetate and DMA gave a C‐acetyl derivative of aurnathine. Additionally studies towards the synthesis of fused quinazolinones yielded the C‐acetylated pyrido[2,1‐b]quinazolinones or butyric acid derivatives.     

Nanocrystalline ruthenium oxide and ruthenium in sensing applications – an experimental and theoretical study

In this project, we have explored RuO₂ and Ru nanoparticles (∼ ∼10 and ∼ ∼5 nm, respectively, estimated from XRD data) to be used as gate material in field effect sensor devices. The particles were synthesized by wet chemical procedure. The capacitance versus voltage characteristics of the studied capacitance shifts to a lower voltage while exposed to reducing gases. The main objectives are to improve the selectivity of the FET sensors by tailoring the dimension and surface chemistry of the nanoparticles and to improve the high temperature stability. The sensors were characterized using capacitance versus voltage measurements, at different frequencies, 500 Hz to 1 MHz, and temperatures at 100–400°C. The sensor response patterns have been found to depend on operating temperature. X-ray photoelectron spectroscopy (XPS) analyses were performed to investigate the oxidation state due to gas exposure. Quantum-chemical computations suggest that heterolytic dissociative adsorption is favored and preliminary computations regarding water formation from adsorbed hydrogen and oxygen was also performed.     

Unwinding of the C‐Terminal Residues of Neuropeptide Y is critical for Y2 Receptor Binding and Activation

Despite recent breakthroughs in the structural characterization of G‐protein‐coupled receptors (GPCRs), there is only sparse data on how GPCRs recognize larger peptide ligands. NMR spectroscopy, molecular modeling, and double‐cycle mutagenesis studies were integrated to obtain a structural model of the peptide hormone neuropeptide Y (NPY) bound to its human G‐protein‐coupled Y₂ receptor (Y₂R). Solid‐state NMR measurements of specific isotope‐labeled NPY in complex with in vitro folded Y₂R reconstituted into phospholipid bicelles provided the bioactive structure of the peptide. Guided by solution NMR experiments, it could be shown that the ligand is tethered to the second extracellular loop by hydrophobic contacts. The C‐terminal α‐helix of NPY, which is formed in a membrane environment in the absence of the receptor, is unwound starting at T³² to provide optimal contacts in a deep binding pocket within the transmembrane bundle of the Y₂R.     

Synthesis of cyclobutylideneacetic esters via aluminum chloride promoted [2+2] cycloadditions of ethyl 2,3-butadienoate to olefins

In the presence of AlCl₃, ethyl 2,3-butadiemoate reacts with a variety of olefins, including simple unactivated cycloalkenes, to give cyclobutylideneacetic esters at room temperature. The cycloaddition is regioselective and stereoselective.     

LaPt2Ge2 und EuPt2Ge2 – Neubestimmung der Kristallstrukturen

LaPt₂Ge₂ and EuPt₂Ge₂ – Revision of the Crystal Structures LaPt₂Ge₂ was rechecked by single crystal X‐ray methods resulting in space group P2₁/c (in place of P2₁) and the lattice constants a = 9.953(3), b = 4.439(1), c = 8.879Å, β = 90.62(4)°, and Z = 4. In contrast to previous reports the cell volume had to be doubled. The same is true for EuPt₂Ge₂ (a = 9.731(1), b = 4.446(1), c = 8.823(1) Å, β = 91.26(1)°). The crystal structures correspond to a monoclinic variant of the tetragonal CaBe₂Ge₂ type, whereas the distortion can be described as different rotations of the coordination polyhedra around the La and Eu atoms, respectively. It is most likely that the compounds APt₂Ge₂ with A = Ca, Y, La‐Dy undergo phase transitions at higher temperatures forming then the undistorted CaBe₂Ge₂ type, space group P4/nmm. This was confirmed for SmPt₂Ge₂ (a = 4.292(1), c = 9.980(1) Å; Z = 2) and might also be the case for APt₂Ge₂ with A = Ca, Nd, Sm, Eu, and Gd.     

Modeling the interactions of a peptide-major histocompatibility class I ligand with its receptors. II. Cross-reaction between a monoclonal antibody and two αβ T cell receptors

The recombinant antibody, pSAN13.4.1, has a unique T cell like specificity; it binds an Influenza Hemagglutinin octapeptide (Ha_255–262) in an MHC (H-2K^k)-restricted manner, and a detailed comparison of the fine specificity of pSAN13.4.1 with the fine specificity of two Ha_255–262-specific, H-2K^k-restricted T cell hybridomas has supported this contention. A three-dimensional model of pSAN13.4.1 has been derived by homology modeling techniques. Subsequently, the structure of the pSAN13.4.1 antibody in complex with the antigenic Ha-K^k ligand was derived after a flexible and automated docking of the MHC-peptide pair into the Fab combining site. Interestingly, the most energetically favored binding mode shows numerous analogies to the recently determined recognition of class I MHC-peptide complexes by T cell receptors (TCRs). The pSAN13.4.1 also binds diagonally across the MHC binding groove but is more deeply anchored to the peptide-MHC (pep/MHC) ligand than TCRs, notably through numerous interactions of its heavy chain. The present model accounts well for the experimentally determined binding affinity of a set of 144 single amino acid substituted Ha analogues and the observed shared specificity between the pSAN antibody and two different T cell receptors for the Ha-K^k antigenic ligand. Analogies and differences between Fab and TCR recognition are explained by dissecting the binding role of each chain of the immune receptors as well as the contribution of all peptide amino acids.     

Ein neuartiges Iod(III,V) Gemischtvalentes Iodoxopolykation in (IO2)3 HSO4

A Novel Iodine(III, V) Mixed Valent Iodinepolyoxocation in (IO₂)₃HSO₄ Previously unknown (IO₂)₃HSO₄ is formed by action of firstly conc. H₃PO₄ upon HIO₃ or H₅IO₆ at 310–330° C, and subsequently of conc. H₂SO₄ at room temperature. Its crystal structure (Pna2₁; a = 8.907(3), b = 20.464(6), c = 9.784(4) Å; Z = 8; 4354 diffractometer data; R = 0.087, R_w = 0.056) contain the novel polymeric cation (IO₂0_3nⁿ⁺. Iodine(III) is coordinated square-planar by oxygen, iodine(V trigonal- pyramidal. The HSO₄- anions are interconnected via hydrogen bonds. Raman and IR spectra are reported.     

Synthesis of the elusive (R3P)2MF2 (M = Pd, Pt) complexes

The synthesis and characterization of previously unknown palladium(II) and platinum(II) difluoro phosphine complexes are described. These complexes can be obtained either via a halide metathesis reaction with AgF in dichloromethane or by reacting the corresponding dimethyl complexes with XeF2. While the Pt(II) complexes can be prepared with both aryl- and alkyl-phosphine ligands, the stability of the Pd(II) complexes is limited to those having cis-oriented trialkyl phosphine ligands.     

Some Unusual Products from the Thermal Reaction of Azulenes with Dimethyl Acetylenedicarboxylate

The thermal reaction of azulene-1-carbaldehydes 5 and 6 with excess dimethyl acetylenedicarboxylate (ADM) in decalin leads mainly to the formation of (1 + 1) and (1 + 2) adducts arising from the addition of ADM at the seven-membered ring of the azulenes (cf. Schemes 2 and 4). The (1 + 2) adducts are formed in a homo-Diels-Alder reaction of ADM and isomeric tricyclic carbaldehydes which are derived from the primary tricyclic carbaldehydes by reversible [1s5s]-C shifts (cf. Schemes 3 and 5). The thus formed pentacyclic carbaldehydes seem to undergo deep-seated skeletal rearrangements (cf. Scheme 7) which result finally in the formation of the formyl-tetrahydrocyclopenta[bc]acenaphthylene-tetraesters 12 and 19 , respectively. In other cases, e.g., azulene-1-carbaldehydes 7 and 8 (cf. Scheme 8), the thermal reaction with excess ADM furnishes only the already known tetracycfic (1 + 2) adducts of type anti- 26 to ‘anti’- 29 . The thermal reaction of 1,3,4,8-tetramethylazulene ( 9 ) with excess ADM in decalin resulted in the formation of two (1 + 2) and one (1 + 3) adduct in low yields (cf. Scheme 9). The latter turned out to be the 2,6-bridged barrelene derivative 32 . There are structural evidences that 32 is formed by similar pathways as the formyl-tetrahydrocyclopenta[bc]acenaphthylene-tetraesters (cf. Schemes 7 and 11). [²H₃]Me-Labelling experiments are in agreement with the proposed mechanisms (cf. Scheme 13).     

Monitoring cell cultivation in microfluidic segments by optical pH sensing with a micro flow-through fluorometer using dye-doped polymer particles

Polymer microparticles containing an immobilized pH-sensitive dye are used for determination of pH inside microfluidic segments. The particles possess a hydrophilic surface in order to get a homogenous distribution inside the aqueous phase of microfluidic segments. The dye is coupled to the polymer matrix by a covalent bond. The pH can be determined by the read-out of fluorescence intensity. In contrast to dissolved indicator dyes, the chemical interference of the sensor particles with the surrounding solution is negligible. So, the particle-based sensing can easily be applied to the determination of pH changes during the cultivation of cells inside the microfluidic segments. The typical change of pH during cell cultivation can be used for monitoring the kinetic of cell cultivation inside single volumes in the nanoliter range, so that information about the metabolic activity of the organism can be obtained. An LED-based miniaturized flow-through fluorometer was developed to determine the fluorescence directly inside microtubes of an inner diameter of 0.5 mm. It allows measurement frequencies up to 60 Hz and is suited for characterization of fast moving large sequences of microfluidic segments.