1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

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3 Discussion and Results effects 128 . But also here, in most cases, it is dealt with achiral porphyrins adopting chiral supramolecular structures. To conclude, it can be stated, that chiral porphyrin systems without stereogenic centers existing in stable and resolvable conformations without any auxiliaries seem to be unknown up to now. 3.2.5.2 Inherent Chirality in Cycloketo-Porphyrin Systems Cycloketo-Porphyrin systems like 53 can be seen as analogs to chiral porphyrin 56 as their chirality also evolves from a distorted π-system due to reasons already discussed, but, based on the VT NMR data, their conformations are considered to be perfectly stable at room temperature in solution without additional stabilizers making a resolution possible. The enantiomers already shown in Scheme 32 can be assigned using the recommendations for axial chirality since the chirality arises from the positioning of substituents along a chiral axis which is represented by the elongation of the C meso -C α -bond. For the assignment of descriptors the substituent of lowest priority – in this case o-ArCH3 – is placed in front downwards while the opposite position is denoted priority 1 (Scheme 40). The neighbored pyrrolic positions are then to be 2 and 3 with the annulated position being higher in priority. If the rotation arising from those priorities is clockwise, the configuration is denoted Ra or P, else Sa or M (counter-clockwise). 72 2 N O 1 H 3 N H 1 O 3 2 N N S a or M R a or P N NH HN N O O N NH HN N Scheme 40. Assignment of stereochemical descriptors in 53. View along the C meso -C α -bond from the 5-phenyl substituent towards the porphyrin core. The corresponding enantiomeric structures are shown below. As cycloketo-porphyrin 53 is lacking functionalities an enantiomerically pure chiral auxiliary could be attached to, a chemical generation of diastereomers is not possible. For such a
Discussion and Results 3 purpose an additional functionality would have to be implemented (see paragraph 3.2.8). Also attempts to co-crystallize 53 with amino acids or other enantiomerically pure carboxylic acid derivatives failed. Thus, chiral chromatography was considered to resolve the mixture basing on diastereomeric interactions of the two present enantiomers with the enantiomerically pure stationary phase of the column leading to different retention times. Correspondingly, experiments were performed in the group of G. BRINGMANN utilizing a HPLC- CD coupling being able to directly identify the enantiomers present. The separation was achieved on a Lux column (Phenomenex®, Cellulose-1) at room temperature using an eluent mixture consistent of iso-propanol and hexanes in a 3 : 97 ratio on an analytical level. The experimental setup (see paragraph 6.1) allowed the detection via UV/Vis absorption and also by online CD measurements at 435 nm in a stopped-flow mode. 129 The results obtained for 53 are shown in Figure 29. The obtained elugrams clearly show two LC-UV peaks correspondent to two present enantiomers with retention times between 5 and 6 minutes in an approximate 1 : 1 ratio. While those species exhibit identical UV/Vis spectra, they show opposite CD effects. The fraction eluting first (peak A) thereby provides a negative CD signal and the second fraction a positive one at 435 nm. To determine the absolute configurations, full online CD spectra were recorded giving mirror-imaged CD curves with a negative first COTTON effect around 435 nm for peak A and a positive one for peak B. To provide a robust and reliable assignment of the absolute configuration to the two atropo- enantiomers, quantum chemical CD calculations 129b,130 were conducted starting with a conformational analysis of the P-enantiomer of 53 with RI-BP86/SV(P) 131 . The analysis delivered eight relevant conformers for which single CD and UV/Vis spectra were calculated with the semiempirical ZINDO/S-CIS method 132 . These were summed, energetically weighted according to the BOLTZMANN statistics, to give a theoretical CD curve for the P-enantiomer of 53. The corresponding CD curve for the M-enantiomer of 53 could be easily obtained by mirroring the spectrum calculated for P at the zero line. After UV/Vis correction 133 , both were compared to the experimentally obtained spectra. Thereby, the calculated CD curve for the M-enantiomer perfectly fits with the online CD curve of peak A while the one obtained for the P-enantiomer matches the CD curve measured for peak B. The absolute configurations hence are assigned like it has already been shown in Scheme 40. 73
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Semi-Natural and Synthetic Chiral C
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Die vorliegende Arbeit entstand in
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Table of Contents 1 Introduction 1
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n J j-coupling (constant) with n in
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1 Introduction characteristics. For
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1 Introduction 1.1 Porphyrins - A G
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1 Introduction Especially interesti
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1 Introduction 8 [H] 4 + 4 O H O H
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1 Introduction complexes are usuall
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1 Introduction transitions as it is
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1 Introduction 1.2 Photodynamic The
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1 Introduction Certainly, Photofrin
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1 Introduction intact membranes bei
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1 Introduction components, the limi
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Page 76 and 77: 3 Discussion and Results voltammogr
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3 Discussion and Results 3.2.8.2.7
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3 Discussion and Results 3.2.9 Pote
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3 Discussion and Results peak at m/
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3 Discussion and Results Table 25.
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3 Discussion and Results 130
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4 Summary As the characterization d
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5 Zusammenfassung 5 Zusammenfassung
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5 Zusammenfassung Da in guten Ausbe
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6 Experimental Section UV/Vis spect
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6 Experimental Section 6.2 Studied
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6 Experimental Section 13 C NMR (10
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6 Experimental Section (cyanomethyl
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6 Experimental Section 6.2.4 AB3-Ty
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6 Experimental Section 6.2.4.3 5 4
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6 Experimental Section 6.2.4.11 10
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6 Experimental Section EA: C57H56N4
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6 Experimental Section 6.2.4.15 10
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6 Experimental Section 6.2.5 A2B2-T
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6 Experimental Section 6.2.5.5 αβ
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6 Experimental Section 6.2.5.7 αβ
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6 Experimental Section 6.2.5.9 αα
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6 Experimental Section 6.2.5.11 α
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6 Experimental Section 6.2.5.13 α
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6 Experimental Section 6.2.6 AB2C-T
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6 Experimental Section UV/Vis (CH2C
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6 Experimental Section UV/Vis (CH2C
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6 Experimental Section broad signal
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7 References 16 H. Fischer, K. Zeil
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7 References 57 S. Schwartz, K. Abs
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7 References 89 (a) R. C. Fuson, J.
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7 References 131 (a) J. Perdew, Phy
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S. Jasinski, N. Jux, “Investigati
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Ein großer Dank gilt auch den Ange
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Cirruculum vitae Stefan Jasinski Ge
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1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

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