This study advances strategy and design in catalysts and reagents for fluorous and supercritical CO(2) chemistry by defining the structural requirements for insulating a typical active site from a perfluoroalkyl segment. The vertical ionization potentials of the phosphines P((CH(2))(m)R(f8))(3) (m = 2 (2) to 5 (5)) are measured by photoelectron spectroscopy, and the enthalpies of protonation by calorimetry (CF(3)SO(3)H, CF(3)C(6)H(5)). They undergo progressively more facile (energetically) ionization and protonation (P(CH(2)CH(3))(3) > 5 > 4 approximately equal to P(CH(3))(3) > 3 > 2), as expected from inductive effects. Equilibrations of trans-Rh(CO)(Cl)(L)(2) complexes (L = 2, 3) establish analogous Lewis basicities. Density functional theory is used to calculate the structures, energies, ionization potentials, and gas-phase proton affinities (PA) of the model phosphines P((CH(2))(m)()CF(3))(3) (2'-9'). The ionization potentials of 2'-5' are in good agreement with those of 2-5, and together with PA values and analyses of homodesmotic relationships are used to address the title question. Between 8 and 10 methylene groups are needed to effectively insulate a perfluoroalkyl segment from a phosphorus lone pair, depending upon the criterion employed. Computations also show that the first carbon of a perfluoroalkyl segment exhibits a much greater inductive effect than the second, and that ionization potentials of nonfluorinated phosphines P((CH(2))(m)CH(3))(3) reach a limit at approximately nine carbons (m = 8).

Molecular tweezers for lysine and arginine select a few residues on a protein surface and by their unique complexation mode disrupt a critical protein-protein interaction. Detailed structural information was gained by NMR experiments, strongly supported by QM/MM calculations and further substantiated by ITC, fluorescence anisotropy, ELISA and bio-layer-interference studies.

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The photoelectron spectra of substituted tetrazoles 1–3, 1,4‐dihydro‐5H‐tetrazol‐5‐ones 4–9, and 1,4‐dihydro‐5H‐tetrazole‐5‐thiones 10–15 have been recorded. Based on PM3 and some ab initio calculations, the ionization potentials have been assigned to molecular orbitals. Gas‐phase thermolyses of 1–15 have been studied by real‐time gas analysis controlled by photoelectron spectroscopy. Compounds 1 and 2 lose formaldehyde and thioformaldehyde, respectively, leaving unsubstituted tetrazole (16), which decomposes mainly through extrusion of a nitrogen molecule and formation of cyanamide. Thiirane is split off from 3, and the remaining molecule decomposes into smaller products. Compounds 4–9 are cleaved by [3+2] cycloreversion to isocyanates and azides. Some of the unsymmetrically substituted compounds exhibit a marked selectivity in this reaction. For thiones 10–15 [3+2] cycloreversion is the main way of decomposition affording isothiocyanates and azides. In addition, the sulfur atom can split off and dimerize or abstract hydrogen atoms to form hydrogen sulfide. Some products like thiirene, formaldehyde, thioformaldehyde and acetaldehyde are generated solely from substituents. Photoelectron spectroscopy proved to be an excellent method for such thermolysis studies.

Abstract:The relationship between electronic and geometrical structures in acceptor-substituted cyclopropanes has been investigated by B3LYP DFT calculations and photoelectron (PE) spectroscopy. The spectra of cyclopropanecarbaldehyde (2), cyclopropanecarboxylic acid (3), cyclopropanecarboxylic acid methyl ester (4), nitrocyclopropane (5), isothiocyanatocyclopropane (6), cyanocyclopropane (7), and 1,1-dicyanocyclopropane (8) have been analyzed. The first ionization potential (IP 1 ) of compounds 2 ± 5 was found to be 0.1 ± 0.4 eV higher than that of the analogous isopropyl derivatives indicating-contrary to expectation-that in these compounds the cyclopropyl group acts as a weaker electron donor than an isopropyl group. In the other compounds, IP 1 values are 0.4 ± 1.1 eV lower than in the open-chain congeners. The Walsh orbitals w S and w A of the three-membered ring are substantially stabilized to different extents by interactions with substituent orbitals, and this is reflected in shortened distal and elongated vicinal CÀC bonds. Although the nitro group in compound 5 causes large stabilizations of both w S and w A , their energy difference Dw remains rather small; this is in agreement with a relatively small difference Dr of the CÀC bond lengths. For the investigated monosubstituted cyclopropanes 2 ± 7, the largest effects with respect to Dw and Dr are caused by the formyl group in carboxaldehyde 2. Comparison of the results for nitriles 7 and 8 indicates that the effects of the cyano groups are additive. A linear relationship between Dw and Dr was established by B3LYP DFT calculations on geometrically distorted cyclopropane (1) and from the PE data of 2 ± 8.

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The Cu II solution chemistry of synthetic derivatives of naturally occurring pseudo-octapeptides (patellamides and ascidiacyclamide) is described. The complex stabilities [mono-and dicopper(II) complexes] of five different ligands were determined by isothermal microcalorimetry (ITC), and square wave voltammetry (SQW) was used to elucidate the electrochemical properties. In agreement with published spectroscopic data, there is cooperative binding of two Cu II ions and the overall stabilities are, in agreement with known stabilities of the natural ligands and expectations based on the donor sets (two N-based heterocycles and one amide per Cu II ), only moderate (K Յ 10 6 ). There is a slight dependence of the stabilities on the ligand struc-* Prof. Dr. P. Comba

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