Isospectrality of spherical MHD dynamo operators: pseudo-Hermiticity and a no-go theorem

The isospectrality problem is studied for the operator of the spherical hydromagnetic alpha^2-dynamo. It is shown that this operator is formally pseudo-Hermitian (J-symmetric) and lives in a Krein space. Based on the J-symmetry, an operator intertwining Ansatz with first-order differential intertwining operators is tested for its compatibility with the structure of the alpha^2-dynamo operator matrix. An intrinsic structural inconsistency is obtained in the set of associated matrix Riccati equations. This inconsistency is interpreted as a no-go theorem which forbids the construction of isospectral alpha^2-dynamo operator classes with the help of first-order differential intertwining operators.Comment: 13 pages, LaTeX2e, improved references, to appear in J. Math. Phy

Total Synthesis of Epothilone D: The Nerol/Macroaldolization Approach

A highly convergent and stereocontrolled synthesis of epothilone D (<b>4</b>) is reported. Key features are a cheap and <i>Z</i>-selective synthesis of the northern half based on nerol and acetoacetate and chromium­(II)-mediated Reformatsky reactions as a powerful tool for chemoselective asymmetric carbon–carbon bond formations, including an unusual stereospecific macroaldolization

Peptide Coupling between Amino Acids and the Carboxylic Acid of a Functionalized Chlorido-gold(I)-phosphane

We have developed a protocol for the direct coupling between methyl ester protected amino acids and the chlorido-gold­(I)-phosphane (<i>p</i>-HOOC­(C₆H₄)­PPh₂)­AuCl. By applying the EDC·HCl/NHS strategy (EDC·HCl = <i>N</i>-ethyl-<i>N</i>′-(3-(dimethylamino)­propyl)­carbodiimide hydrochloride, NHS = <i>N</i>-hydroxysuccinimide), the methyl esters of l-phenylalanine, glycine, l-leucine, l-alanine, and l-methionine are coupled with the carboxylic acid of the gold complex in moderate to good yields (62–88%). All amino acid tagged gold complexes were characterized by ¹H and ¹³C NMR spectroscopy and high-resolution mass spectrometry. As corroborated by measurement of the angle of optical rotation, no racemization occurred during the reaction. The molecular structure of the leucine derivative was determined by single-crystal X-ray diffraction. In the course of developing an efficient coupling protocol, the acyl chlorides (<i>p</i>-Cl­(O)­C­(C₆H₄)­PPh₂)­AuX (X = Cl, Br) were also prepared and characterized

Lipid Monolayers and Adsorbed Polyelectrolytes with Different Degrees of Polymerization

Polystyrene sulfonate (PSS) of different molecular weight <i>M</i>_w is adsorbed to oppositely charged DODAB monolayers from dilute solutions (0.01 mmol/L). PSS adsorbs flatly in a lamellar manner, as is shown by X-ray reflectivity and grazing incidence diffraction (exception: PSS with <i>M</i>_w below 7 kDa adsorbs flatly disordered to the liquid expanded phase). The surface coverage and the separation of the PSS chains are independent of PSS <i>M</i>_w. On monolayer compression, the surface charge density increases by a factor of 2, and the separation of the PSS chains decreases by the same factor. Isotherms show that on increase of PSS <i>M</i>_w the transition pressure of the LE/LC (liquid expanded/liquid condensed) phase transition decreases. When the contour length exceeds the persistence length (21 nm), the transition pressure is low and constant. For low-<i>M</i>_w PSS (<7 kDa) the LE/LC transition of the lipids and the disordered/ordered transition of adsorbed PSS occur simultaneously, leading to a maximum in the contour length dependence of the transition enthalpy. These findings show that lipid monolayers at the air/water interface are a suitable model substrate with adjustable surface charge density to study the equilibrium conformation of adsorbed polyelectrolytes as well as their interactions with a model membrane

Molecular Doping of a High Mobility Diketopyrrolopyrrole–Dithienylthieno[3,2‑<i>b</i>]thiophene Donor–Acceptor Copolymer with F6TCNNQ

Herein we present a molecular doping of a high mobility diketopyrrolopyrrole–dithienylthieno­[3,2-<i>b</i>]­thiophene donor–acceptor copolymer poly­[3,6-(dithiophene-2-yl)-2,5-di­(6-dodecyl­octadecyl)­pyrrolo­[3,4-<i>c</i>]­pyrrole-1,4-dione-<i>alt</i>-thieno­[3,2-<i>b</i>]­thiophene], PDPP­(6-DO)₂TT, with the electron-deficient compound hexafluoro­tetracyano­naphthoquino­dimethane (F6TCNNQ). Despite a slightly negative HOMO_donor–LUMO_acceptor offset of −0.12 eV which may suggest a reduced driving force for the charge transfer (CT), a partial charge CT was experimentally observed in PDPP­(6-DO)₂TT:F6TCNNQ by absorption, vibrational, and electron paramagnetic resonance spectroscopies and predicted by density functional theory calculations. Despite the modest CT, PDPP­(6-DO)₂TT:F6TCNNQ films possess unexpectedly high conductivities up to 2 S/cm (comparable with the conductivities of the benchmark doped polymer system P3HT:F4TCNQ having a large positive offset). The observation of the high conductivity in doped PDPP­(6-DO)₂TT films can be explained by a high hole mobility in PDPP­(6-DO)₂TT blends which compensates a lowered (relatively to P3HT:F4TCNQ) concentration of free charge carriers. We also show that F6TCNNQ-doped P3HT, the system which has not been reported so far to the best of our knowledge, exhibits a conductivity up to 7 S/cm, which exceeds the conductivity of the benchmark P3HT:F4TCNQ system