Synthese von Diterpenen als mögliche biogenetische Vorläufer des C20-Carotinoides Crocetin

Synthesis of Diterpenes as Possible Biogenetic Precursors of the C₂₀-Carotenoid Crocetin With regard to the investigation of the biosynthesis of the C₂₀-carotenoids in saffron the four diterpenes 6–9 were synthesized, who differ only in their degree of saturation. A detailed analysis of their ¹H- and ¹³C-NMR spectra has been achieved by their mutual comparison.     

Acoustic features of objects matched by an echolocating bottlenose dolphin

The focus of this study was to investigate how dolphins use acoustic features in returning echolocation signals to discriminate among objects. An echolocating dolphin performed a match-to-sample task with objects that varied in size, shape, material, and texture. After the task was completed, the features of the object echoes were measured (e.g., target strength, peak frequency). The dolphin's error patterns were examined in conjunction with the between-object variation in acoustic features to identify the acoustic features that the dolphin used to discriminate among the objects. The present study explored two hypotheses regarding the way dolphins use acoustic information in echoes: (1) use of a single feature, or (2) use of a linear combination of multiple features. The results suggested that dolphins do not use a single feature across all object sets or a linear combination of six echo features. Five features appeared to be important to the dolphin on four or more sets: the echo spectrum shape, the pattern of changes in target strength and number of highlights as a function of object orientation, and peak and center frequency. These data suggest that dolphins use multiple features and integrate information across echoes from a range of object orientations.     

Galvanic exchange platinization reveals laser-inscribed pattern in 3D-LAM-printed steel

Galvanic exchange involving dissolution of iron and the simultaneous growth of platinum onto 316 L stainless steel was investigated for specimens manufactured by 3D-printing, and the behavior was compared to conventional stainless steel. Novel phenomena associated with the 3D-printed steel, but not conventional steel, reacting in three distinct phases were observed: first, with low platinum loading, a bright etching pattern linked to the laser-manufacturing process is revealed at the steel surface; second, a nanostructured pore pattern with platinum nano-deposits forms; and third, a darker platinum film coating of typically 500-nm thickness forms and then peels off the steel surface with further platinum growth underneath. Unlike the conventional steel (and mainly due to residual porosity), 3D-printed steel supports well-adhered platinum films for potential application in electrocatalysis, as demonstrated for alkaline methanol oxidation.

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Rearrangement of 3-membered 1,1,2-trifluorobromonium and iodonium ions and comparison of trifluorochloronium to fluorocarbenium ions

Reactions of chlorine (Cl(2)) with 4-halo-1,1,2-trifluorobut-1-enes (1, 2, or 3) give open-ion intermediates A and E that are in equilibrium. The open-chloronium ions (E) rearrange to a five-membered-ring halonium ion during ionic chlorination of 3 when the number-4 halo-substituent is iodine. Three-membered-ring bromonium and iodonium ions from alkenes 1, 2, or 3 are rather symmetrical and similar in structure. Quantum chemical calculations show that five-membered-ring halonium ion intermediates are 11 to 27 kcal/mol more stable than the three-membered-ring halonium ions or the open-ions A and E. The five-membered-ring intermediates lead to rearranged products. Rearranged products increase as the number-4 halogen (Z) becomes more nucleophilic (Z: Cl < Br < I). Open chloronium ions from ionic chlorination of terminal fluorovinyl alkenes are compared to the open ions generated by protons to similar alkenes.     

Changes in the isotropic shielding of the 17O nucleus upon torsion in terminal oxygen systems: a computational study on their origin

We are presenting a computational study on the isotropic shielding, charge, and orbital contributions to the shielding of oxygen in benzaldehydes (Ar-CHO), nitrobenzenes (Ar-NO2), phenyl isocyanates (Ar-NCO), anilides (Ar-NHCOCH3), and N-sulfinylamines (Ar-NSO). In particular, changes upon ortho substitution of the aromatic ring and upon torsion of the unsubstituted parent molecules are examined. The experimentally observed changes in (17)O chemical shift, be they upfield or downfield, upon substitution by ortho-alkyl groups are reproduced well by the calculations. Relaxed torsional scans of the parent systems reveal that (a) charges change as expected from resonance arguments and (b) changes in isotropic shielding are monotonic and in line with changes upon substitution, with N-sulfinylaniline as an exception. In general, the changes in isotropic shieldings are explained in terms of changes in molecular orbitals, their energies, and relative alignments, whose mixing is magnetically active. Thus, for example, the observed deshielding of (17)O upon methyl substitution and upon torsion of benzaldehyde is mainly caused by a contribution from the pi-type oxygen lone pair, yet how these contributions change is fundamentally different. As a consequence, the experimentally observed downfield shift upon methyl substitution cannot be interpreted to imply a change in torsion angle between the phenyl ring and the aldehyde group. For N-sulfinylaniline, the consecutive downfield shifts upon methyl and tert-butyl substitution and the associated changes in torsion angle are in contrast to the 45 degrees maximum in isotropic shielding that is determined from a relaxed torsional scan.     

57Fe NMR spectroscopy of ferrocenes derived from aminoferrocene and 1,1'-diaminoferrocene

Three series of ferrocenes, derived from aminoferrocene Fc-NH2 and 1,1'-diaminoferrocene fc(NH2)2, were studied by 57Fe NMR spectroscopy. A marked decrease in 57Fe magnetic nuclear shielding with respect to ferrocene is observed if the nitrogen atom becomes part of a pi-acceptor linked to one or both cyclopentadienyl rings. In contrast, pi-donor properties of the amino group(s) affect delta57Fe to a much smaller extent. In the case of the fairly rigid structures of 1,3-diaza-2-element-[3]ferrocenophanes, a significant increase of 57Fe nuclear magnetic shielding is observed, in contrast to the corresponding [n]ferrocenophanes with n > 3. Structures of numerous of the ferrocene derivatives have been optimized for the gas phase by calculations (B3LYP/6-311 + G(d,p) level of theory), and 57Fe nuclear magnetic shieldings were calculated using these geometries. There is reasonable agreement in the trends for experimental and calculated data.     

An in vitro comparison of microdialysis relative recovery of Met- and Leu-enkephalin using cyclodextrins and antibodies as affinity agents

Cyclodextrins and antibodies have been used as affinity agents to improve relative recovery during microdialysis sampling. Two neuropeptides, methionine-enkephalin (ME) and leucine-enkephalin (LE), were chosen to compare the use of cyclodextrins and antibodies as possible affinity agents for improving their relative recovery across polycarbonate and polyethersulfone membranes during in vitro sampling. Cyclodextrins (CD) including β-CD, 2-hydroxypropyl-β-cyclodextrin (2HPβ-CD), and γ-CD gave improvements of relative recovery for both peptides of less than 2-fold as compared to controls. Comparisons of relative recovery between tyrosine–glycine–glycine, tyrosine, and phenylalanine using different cyclodextrins in the perfusion fluid were also obtained. Inclusion of an antibody against met-enkephalin in the microdialysis perfusion fluid resulted in relative recovery increases of up to 2.5-fold. These results show that using antibodies as affinity agents during microdialysis sampling may be more effective agents to improve the relative recovery of these opioid neuropeptides.     

Relationships between equilibrium spreading pressure and phase equilibria of phospholipid bilayers and monolayers at the air-water interface

The intricate interplay between the bilayer and monolayer properties of phosphatidylcholine (PC), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE) phospholipids, in relation to their polar headgroup properties, and the effects of chain permutations on those polar headgroup properties have been demonstrated for the first time with a set of time-independent bilayer-monolayer equilibria studies. Bilayer and monolayer phase behavior for PE is quite different than that observed for PC and PG. This difference is attributed to the characteristic biophysical PE polar headgroup property of favorable intermolecular hydrogen-bonding and electrostatic interactions in both the bilayer and monolayer states. This characteristic hydrogen-bonding ability of the PE polar headgroup is reflected in the condensed nature of PE monolayers and a decrease in equilibrium monolayer collapse pressure at temperatures below the monolayer critical temperature, T(c) (whether above or below the monolayer triple point temperature, T(t)). This interesting phenomena is compared to equilibrated PC and PG monolayers which collapse to form bilayers at 45 mN/m at temperatures both above and below monolayer T(c). Additionally, it has been demonstrated by measurements of the equilibrium spreading pressure, pie, that at temperatures above the bilayer main gel-to-liquid-crystalline phase-transition temperature, T(m), all liquid-crystalline phospholipid bilayers spread to form monolayers with pie around 45 mN/m, and spread liquid-expanded equilibrated monolayers collapse at 45 mN/m to form their respective thermodynamically stable liquid-crystalline bilayers. At temperatures below bilayer T(m), PC and PG gel bilayers exhibit a drop in bilayer pi(e) values < or =0.2 mN/m forming gaseous monolayers, whereas the value of pic of spread monolayers remains around 45 mN/m. This suggests that spread equilibrated PC and PG monolayers collapse to a metastable liquid-crystalline bilayer structure at temperatures below bilayer T(m) (where the thermodynamically stable bilayer liquid-crystalline phase does not exist) and with a surface pressure of 45 mN/m, a surface chemical property characteristically observed at temperatures above bilayer T(m) (monolayer T(c)). In contrast, PE gel bilayers, which exist at temperatures below bilayer T(m) but above bilayer T(s) (bilayer crystal-to-gel phase-transition temperature), exhibit gel bilayer spreading to form equilibrated monolayers with intermediate pie values in the range of 30-40 mN/m; however, bilayer pie and monolayer pic values remain equal in value to one another. Contrastingly, at temperatures below bilayer T(s), PE crystalline bilayers exhibit bilayer pie values < or =0.2 mN/m forming equilibrated gaseous monolayers, whereas spread monolayers collapse at a value of pic remaining around 30 mN/m, indicative of metastable gel bilayer formation.