Mid-IR spectra of different conformers of phenylalanine in the gas phase

The experimental mid- and far-IR spectra of six conformers of phenylalanine in the gas phase are presented. The experimental spectra are compared to spectra calculated at the B3LYP and at the MP2 level. The differences between B3LYP and MP2 IR spectra are found to be small. The agreement between experiment and theory is generally found to be very good, however strong discrepancies exist when -NH2 out-of-plane vibrations are involved. The relative energies of the minima as well as of some transition states connecting the minima are explored at the CCSD(T) level. Most transition states are found to be less than 2000 cm(-1) above the lowest energy structure. A simple model to describe the observed conformer abundances based on quasi-equilibria near the barriers is presented and it appears to describe the experimental observation reasonably well. In addition, the vibrations of one of the conformers are investigated using the correlation-corrected vibrational self-consistent field method.     

Photodynamic therapy in the treatment of actinic keratosis

The efficacy of photodynamic therapy (PDT) with 5-aminolevulinate and methyl aminolevulinate in the treatment of actinic keratosis has been demonstrated in a large number of clinical studies over the last several years. Here, we recapitulate the major findings, comparing the various photosensitizers, light sources and therapeutic regimens, and present a retrospective analysis of 142 own cases treated with 259 PDTs. In addition, we also discuss the value of PDT in comparison with cryotherapy or 5-fluorouracil. The efficacy and the low risk of side effects of PDT have resulted in a high patient preference in clinical trials.     

Solid phase synthesis of N-aminodipeptides in high optical purity

N-Aminodipeptide derivatives can be easily prepared with high optical purity on solid phase via a Mitsunobu protocol between a solid supported α-hydroxyacid and a free phthaloylated α-Z-N-aminohydrazide.     

Synthese und Metallierung des Diaminosiloxans O(SiiPr2NH2)2

Synthesis and Metalation of the Diaminosiloxane O(SiiPr₂NH₂)₂ The 1,3‐diaminoldisiloxane O(SiiPr₂NH₂)₂ ( 1 ) was obtained from the reaction of O(SiiPr₂Cl)₂ with NH₃. The reactions of 1 with AlEt₃ or GaEt₃ produced the compounds [O{SiiPr₂N(H)MEt₂}{SiiPr₂NMEt}]₂ ( 2 : M = Al; 3 : M = Ga). The crystal structures of 2 and 3 were determined by single crystal X‐ray diffraction, showing a polycyclic M₄N₄Si₄O₂ core structure of these molecules.     

Structure and conductance of aromatic and aliphatic dithioacetamide monolayers on Au(111)

The structure and electrical properties of self-assembled monolayers of cyclic aromatic and aliphatic dithioacetamides (1,4-bis(mercaptoacetamido)benzene and 1,4-bis(mercaptoacetamido)cyclohexane) and of mixed dithioacetamide/alkanethiol monolayers are characterized by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM) and contact angle goniometry. Both dithioacetamides are found to pack densely on Au(111), however the monolayers are poorly ordered as a result of hydrogen bond formation between the amide groups. The coassembly and the insertion method are compared for the formation of mixed dithioacetamide/alkanethiol monolayers. By coassembly, islands of dithioacetamides in a dodecanethiol matrix can only be obtained at a low dithioacetamide/dodecanethiol concentration ratio in solution (1/10) and by thermal annealing of the resulting monolayers. Small and well defined dithioacetamide domains are realized by insertion of dithioacetamides into defect sites of closely packed octanethiol monolayers. These domains are used to determine the molecular conductance by means of STM height profiles and molecular lengths resulting from density functional theory (DFT) calculations. The difference in the tunneling decay constant beta measured for aromatic dithioacetamides (beta = 0.74-0.76/A) and for aliphatic dithioacetamides (beta = 0.84-0.91/A) highlights the influence of the conjugation within the cyclic core on molecular conductance.     

Determination of polybrominated biphenyls in Tasmanian devils (Sarcophilus harrisii) by gas chromatography coupled to electron capture negative ion tandem mass spectrometry or electron ionization high‐resolution mass spectrometry

Two gas chromatography/mass spectrometry (GC/MS) methods for the determination of polybrominated biphenyls (PBBs) by isotope dilution analysis (IDA) using ¹³C₁₂‐PBB 153 in the presence of polybrominated diphenyl ethers (PBDEs) were compared. Recovery of ¹³C₁₂‐PBB 153 which was added to the extracted lipids before sample purification was commenced ranged from 88–117% (mean value 98.2 ± 8.9%). Nevertheless, IDA analysis of PBBs using ¹³C₁₂‐labelled congeners is limited by the potential co‐elution of PBBs with polybrominated diphenyl ethers (PBDEs). The pair PBB 153 and BDE 154 was inspected since M⁺ and [M–2Br]⁺ ions of ¹³C₁₂‐PBB 153 and BDE 154 were only separated by 4 u. Gas chromatography/electron ionization high‐resolution mass spectrometry with selected ion monitoring (GC/EI‐HRMS‐SIM) was suitable when m/z 475.7449 and m/z 477.7429 were used for ¹³C₁₂‐PBB 153 because they are below the monoisotopic peak of the [M–2Br]⁺ fragment ion of hexaBDEs at m/z 479.7. Gas chromatography/electron capture negative ion tandem mass spectrometry selected reaction monitoring (GC/ECNI‐MS/MS‐SRM) measurements could be applied because ¹³C₁₂‐PBB 153 and BDE 154 were separated by GC on a 25‐m Factor Four CP‐Sil 8MS column. Comparative measurements with GC/EI‐HRMS‐SIM and GC/ECNI‐MSMS‐SRM were carried out with samples of Tasmanian devils from Tasmania (Australia), an endangered species due to a virus epidemy which has already proved fatal for half of the population. Both techniques verified concentrations of PBB 153 in the range 0.3–11 ng/g lipids with excellent agreement of the levels in all but two samples. The PBB residue pattern demonstrated that PBB pollution originated from the previous discharge with technical hexabromobiphenyl which is dominated by PBB 153. Other congeners such as PBB 132 and PBB 138 were detected in the Tasmanian devils but the proportions relative to PBB 153 were lower than in the technical product. Samples of healthy and affected Tasmanian devils showed no significant difference in the PBB pollution level. The PBB concentrations in the Tasmanian devils were significantly below those causing toxic effects. On the other hand, PBB concentrations were one level or even higher than PBDEs. Copyright © 2008 John Wiley & Sons, Ltd.