Principle and mechanism of direct porphyrin metalation: joint experimental and theoretical investigation

The direct metalation of tetraphenylporphyrin with bare metal atoms (Co and Zn) was studied with X-ray photoelectron spectroscopy, scanning tunneling microscopy, and temperature-programmed reaction measurements on ordered monolayer films of the molecules adsorbed on a Ag(111) surface. The mechanism of this novel type of surface reaction was investigated using density functional theory (DFT) calculations for the related gas-phase reactions of the unsubstituted porphyrin with the metals Fe, Co, Ni, Cu, and Zn. The reaction starts with the formation of an initial complex, in which the metal atom is coordinated by the intact unreduced porphyrin. This complex resembles the sitting-atop complex proposed for porphyrin metalation with metal ions in solution. In two subsequent steps, the pyrrolic hydrogen atoms are transferred to the metal atom, forming H2, which is eventually released. The activation barriers of the H-transfer steps vary for the different metal atoms. DFT calculations suggest that metalations with Fe, Co, and Ni show two-state reactivity, while those with Cu and Zn proceed on a single potential energy surface. For metalation with Zn, we calculated a barrier of the first hydrogen transfer step of 32.6 kcal mol(-1), in good agreement with the overall experimental activation energy of 31 kcal mol(-1).     

«Push-Pull»-Acetylene als Hilfsmittel zur Synthese von Peptiden

Peptide synthesis by Means of ‘Push-Pull’-Acetylenes ‘Push-pull’-acetylenes 1 are excellent reagents for peptide synthesis: Addition of ‘push-pull’-acetylenes to solutions of N-protected amino acids (or vice versa) gives enol esters 5 , which react selectively with the amino function of a second amino acid. In this way serine, tyrosine, 4-hydroxyproline, cysteine as well as histidine are linked to form dipeptide esters without protection of the second functional group (OH, SH or NH). The amount of racemization is very low. Similarly tri- as well as tetrapeptides are available. The versatility of the reaction is discussed.     

Selection properties of uniform and related structures

In this paper we present some results on selection properties in asymmetric generalized metric and uniform spaces. We demonstrate differences between selection properties of these spaces and selection properties of metric and uniform spaces.     

Cycloaddition von benzothiet an oxime,oximether und oximester

Benzothiete 1 generates by thermal ring opening an 8π electron system 2 which undergoes [8π + 2π] cycloaddition reactions with the oxime systems 3a-g . In accordance with the FMO theory the 1,3-thiazine derivatives 4a-g are formed in a regiospecific and 4f additionally in a stereospecific manner. The O-acylated adducts 4h-j enter the same cycloaddition; however, an elimination reaction 4 ← 5, 6 can provoke the addition of a second benzothiete, yielding the tetracyclic compounds 7j , and 8i,j .     

Distributions invariant under a group of diffeomorphisms

We consider a transformation group G of an open set A in Rⁿ such that the orbits of G are the fibers of a fiber bundle. For distributions in A, a natural notion of “constancy on the fibers” is defined, and for certain wide classes of groups G it is proved that the G-invariant distributions are constant on the fibers.     

The VSFASSQQ motif confers calcium sensitivity to the intracellular apyrase LALP70

Background  

Apyrases are divalent ion dependent tri- and dinucleotide phosphatases with different substrate specificity. The intracellular lysosomal apyrase LALP70 is also expressed as a splice variant (LALP70v) lacking a VSFASSQQ motif in the center of the molecule (aminoacids 287–294). However, the functional significance of this motif is unknown. In this report we used a thin layer chromatography approach to study separately the UTPase and UDPase activity of the two LALP-enzymes.     

Time-resolved photoacoustic spectroscopy using fiber Bragg grating acoustic transducers

An acoustic transducer based on a fiber Bragg grating (FBG) is presented and characterized for use in time-resolved laser-induced photoacoustic spectroscopy (PAS) on solid samples. The photoacoustic wave was generated by pulsed laser excitation of immobilized carbon black or erbium oxide powder, and detected by recording either the transmission or reflection spectrum of a clamped fiber Bragg grating (FBG). The characterization of the FBGs photoacoustic response is based on the experimental comparison with a static lateral strain source and on theoretical analysis using the piecewise-uniform approach to photoelastic theory. The temporal resolution of the response is determined by the arrangement of the FBG with respect to the source of the acoustic wave and is better than 150 ns, as was verified in a deconvolution analysis.The method has not only a fast time response but also is simple, inexpensive, and accurate as indicated by the good agreement of the experimental photoacoustic spectrum with previous measurements.     

Aqua Ions. 2. Structural manifestations of the Jahn-Teller effect in the beta-alums

Variable-temperature single-crystal neutron diffraction structures of the alums CsM(III)(SO(4))(2).12D(2)O, where M(III) = Ti, V, Mn, and Ga, are reported. Structural differences are highlighted by the titanium and manganese alums, which undergo cubic (Pathremacr;) to orthorhombic (Pbca) phase transitions at approximately 13 and approximately 156 K, respectively. The structural instability exhibited by these salts is interpreted as arising from cooperative Jahn-Teller interactions, and these measurements characterize the structural changes that result from the coupling between the electronic and vibrational states. Although the symmetry changes associated with the phase transformations are analogous for the Ti and Mn alums, the low-temperature geometries of the tervalent hexaaqua cations are markedly different. Whereas the MnO(6) framework is subject to a pronounced tetragonal elongation, changes in the Ti-O bond lengths are very modest; but significant changes in the O-Ti-O bond angles and in the disposition of the coordinated water molecules are identified. The large differences in the transition temperatures and in the low-temperature stereochemistries of the [Ti(OD(2))(6)](3+) and [Mn(OD(2))(6)](3+) cations are related to the sensitivity of the energies of the t(2g) (O(h)) and e(g) (O(h)) orbitals to the various asymmetric vibrations of the hexaaqua complex.