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Institute
- Institut für Organische Chemie (48) (remove)
Sonstige beteiligte Institutionen
- Department of Cellular Biochemistry, University Medical Center Göttingen (1)
- Georg August University School of Science (1)
- Helmholtz Institute for RNA-based Infection Biology (HIRI), Josef-Schneider-Straße 2/D15, DE-97080 Wuerzburg, Germany (1)
- Institute of Cancer Research (ICR) London (1)
- Max Planck Institute for Biophysical Chemistry (1)
- Max Planck Institute for Biophysical Chemistry, Am Faßberg 11, DE-37077 Goetingen, Germany (1)
- Max Planck Institute for Biophysical Chemistry, Department of Molecular Biology, Göttingen (1)
- Max Planck Institute for Biophysical Chemistry, Research Group Structure and Function of Molecular Machines, Göttingen (1)
- Max-Planck Institute for Biophysical Chemistry, Department of Molecular Biology, Göttingen (1)
- Novartis Pharma AG, Lichtstrasse 35, CH-4056 Basel, Switzerland (1)
Interactions between proteins and carbohydrates with larger biomacromolecules, e.g., lectins, are usually examined using self-assembled monolayers on target gold surfaces as a simplified model measuring setup. However, most of those measuring setups are either limited to a single substrate or do not allow for control over ligand distance and spacing. Here, we develop a synthetic strategy, consisting of a cascade of a thioesterification, native chemical ligation (NCL) and thiol-ene reaction, in order to create three-component polymer conjugates with a defined double bioactivation at the chain end. The target architecture is the vicinal attachment of two biomolecule residues to the α telechelic end point of a polymer and a thioether group at the ω chain end for fixating the conjugate to a gold sensor chip surface. As proof-of-principle studies for affinity measurements, we demonstrate the interaction between covalently bound mannose and ConA in surface acoustic wave (SAW) and surface plasmon resonance (SPR) experiments.
Within this PhD thesis, chromophore-bridged biradicals were synthesised and their properties characterised. Therefore, it was necessary to develop novel synthetic procedures and implement several experimental characterisation methods. In summary, within this thesis the scope of pigment chromophore phenoxyl radical decoration was further explored and expanded to IIn as well as DPP colourants. HOMA analysis highlighted the importance of aromaticity in order to understand the spin crossover from heteroaromatic quinoidal to aromatic open shell DPPs. Finally, PBI, IIn and DPP biradicals were advanced towards stable materials by introduction of nitronyl nitroxide radical centres.
The most important stereodynamic feature of carbo[n]helicenes is the interconversion of their enantiomers. The Gibbs activation energy (ΔG≠(T)) of this process, which determines the rate of enantiomerization, dictates the configurational stability of [n]helicenes. High values of ΔG≠(T) are required for applications of functional chiral molecules incorporating [n]helicenes or helicene substructures. This minireview provides an overview of the mechanism, recent developments, and factors affecting the enantiomerization of [n]helicenes, which will accelerate the design process of configurationally stable functional chiral molecules based on helicene substructures. Additionally, this minireview addresses the misconception and irregularities in the recent literature on how the terms “racemization” and “enantiomerization” are used as well as how the activation parameters are calculated for [n]helicenes and related compounds.
Within this thesis the interactions between novel corannulene derivatives in solution as well as in the solid state by changing the imide residue of a literature known extended corannulene dicarboximide were investigated, in order to obtain a better understanding of the packing and possible charge transport in potential applications. Accordingly, the goal of the work was to synthesize and investigate an electron-poor corannulene bis(dicarboximide) based on previously published work but with higher solubility and less steric encumbrance in imide position to enable self-assembly in solution.
To obtain further insights into the conformational stability, structure and chiroptical properties of heavily twisted PBIs another aim of this thesis was the design, synthesis, and optoelectronic investigation of various fourfold directly arylated PBIs by substitution in bay position with smaller hydrocarbons with different steric demand, i.e., benzene, naphthalene and pyrene, which should be separable by chiral high performance liquid chromatography (HPLC).
As of yet, no concise study concerning the optical and electronic properties of differently core-substituted PBIs in the neutral as well as the mono- and dianionic state in solution is available, which also elucidates the origin of the different optical transitions observed in the absorption and emission spectra. Thus, in this thesis, the investigation of five PBI derivatives with different frontier energetic levels to produce a reference work of reduced PBIs was tackled.
A series of perylene bisimide (PBI) dyes bearing various aryl substituents in 1,6,7,12 bay positions has been synthesized by Suzuki cross-coupling reaction. These molecules exhibit an exceptionally large and conformationally fixed twist angle of the PBI π-core due to the high steric congestion imparted by the aryl substituents in bay positions. Single crystal X-ray analyses of phenyl-, naphthyl- and pyrenyl-functionalized PBIs reveal interlocked π-π-stacking motifs, leading to conformational chirality and the possibility for the isolation of enantiopure atropoisomers by semipreparative HPLC. The interlocked arrangement endows these molecules with substantial racemization barriers of about 120 kJ mol\(^{−1}\) for the tetraphenyl- and tetra-2-naphthyl-substituted derivatives, which is among the highest racemization barriers for axially chiral PBIs. Variable temperature NMR studies reveal the presence of a multitude of up to fourteen conformational isomers in solution that are interconverted via smaller activation barriers of about 65 kJ mol\(^{−1}\). The redox and optical properties of these core-twisted PBIs have been characterized by cyclic voltammetry, UV/Vis/NIR and fluorescence spectroscopy and their respective atropo-enantiomers were further characterized by circular dichroism (CD) and circular polarized luminescence (CPL) spectroscopy.
In the course of this work, a total of three photocatalytically active dyads for proton reduction could be synthesized together with the associated individual components. Two of them, D1 and D2, comprised a [Ru(bpy)3]2+ photosensitizer and D3 an [Ir(ppy)2bpy]+ photosensitizer. A Ppyr3-substituted propyldithiolate [FeFe] complex was used as catalyst in all systems. The absorption spectroscopic and electrochemical investigations showed that an inner-dyadic electronic coupling is effectively prevented in the dyads due to conjugation blockers within the bridging units used. The photocatalytic investigations exhibited that all dyad containing two-component systems (2CS) showed a significantly worse performance than the corresponding bimolecular three-component systems (3CS). Transient absorption spectroscopy showed that the 2CS behave very similarly to the associated multicomponent systems during photocatalysis. The electron that was intended for the intramolecular transfer from the photosensitizer unit to the catalyst unit within the dyads remains at the photosensitizer for a relatively long time, analogous to the 3CS and despite the covalently bound catalyst. It is therefore assumed that this intramolecular electron transfer is likely to be hindered as a result of the weak electronic coupling caused by the bridge units used. Instead, the system bypasses this through an intermolecular transfer to other dyad molecules in the immediate vicinity. In addition, with the help of emission quenching experiments and electrochemical investigations, it could be clearly concluded that all investigated systems proceed via the reductive quenching mechanism during photocatalysis.
Molecular functionality can be often directly attributed to given properties of the electronic wavefunction. Analogous to the potential energy surface, these properties can be represented as a function of the nuclear coordinates, giving rise to molecular “functional landscapes.” However, so far there has been no possibility for their systematic investigation. This perspective aims to discuss the development of new theoretical methods based on the multistate extension of the metadynamics approach, employing electronic collective variables. This emerging methodology allows to explore functional landscapes and to gain a deeper understanding of the structure–function relation in molecules and complex molecular systems in the ground and excited electronic state.
Two series of organic–inorganic composite materials were synthesized through solvothermal imine condensation between diketopyrrolopyrrole dialdehyde DPP-1 and 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) in the presence of varying amounts of either amino- or carboxy-functionalized superparamagnetic iron oxide nanoparticles (FeO). Whereas high FeO loading induced cross-linking of the inorganic nanoparticles by amorphous imine polymers, a lower FeO content resulted in the formation of crystalline covalent organic framework domains. All hybrid materials were analyzed by magnetization measurements, powder X-ray diffraction, electron microscopy, IR, and UV/Vis absorption spectroscopy. Crystallinity, chromophore stacking, and visible absorption features are directly correlated to the mass fraction of the components, thus allowing for a fine-tuning of materials properties.
Inspired by the fact that sufficient solubility in aqueous media can be achieved by functional substitution of perylene bisimides (PBIs) with polar groups, one of the essential aims of this thesis was the design and successful synthesis of the new water-soluble PBI cyclophanes [2PBI]-1m and [2PBI]-1p, which are appended with branched, hydrophilic oligoethylene glycol (OEG) chains. Subsequently, the focus was set on the elucidation of properties of PBI cyclophane hosts which are also of relevance for recognition processes in biological systems. The performance of the new amphiphilic PBI cyclophane [2PBI]-1p as synthetic receptors for various natural aromatic alkaloids in aqueous media was thoroughly investigated. Alkaloids represent a prominent class of ubiquitous nitrogen containing natural compounds with a great structural variety and diverse biological activity. As of yet, no chromophore host acting as a molecular probe for a range of alkaloids such as harmine or harmaline is known. In addition, the self-association behavior of cyclophane host [2PBI]-1m and its reference monomer in water was studied in order to gain insights into the thermodynamic driving forces affecting the self-assembly process of these two PBI systems in aqueous environment. Moreover, the chirality transfer upon guest binding previously observed for a PBI cyclophane was investigated further. The assignment of the underlying mechanism of guest recognition to either the induced fit or conformational selection model was of particular interest.
Two dipolar merocyanines consisting of the same π‐conjugated chromophore but different alkyl substituents adopt very different packing arrangements in their respective solid state with either H‐ or J‐type exciton coupling, leading to ultranarrow absorption bands at 477 and 750 nm, respectively, due to exchange narrowing. The social self‐sorting behavior of these push‐pull chromophores in their mixed thin films is evaluated and the impact on morphology as well as opto‐electronical properties is determined. The implementation of this well‐tuned two‐component material with tailored optical features allows to optimize planar heterojunction organic photodiodes with fullerene (C\(_{60}\)) with either dual or single wavelength selectivity in the blue and NIR spectral range with ultranarrow bandwidths of only 11 nm (200 cm\(^{-1}\)) and an external quantum efficiency of up to 18% at 754 nm under 0 V bias. The application of these photodiodes as low‐power consuming heart rate monitors is demonstrated by a reflectance‐mode photoplethysmography (PPG) sensor.
Two di- and tetranuclear Ru(bda) (bda: 2,2′-bipyridine-6,6′-dicarboxylate) macrocyclic complexes were synthesized and their catalytic activities in chemical and photochemical water oxidation investigated in a comparative manner to our previously reported trinuclear congener. Our studies have shown that the catalytic activities of this homologous series of multinuclear Ru(bda) macrocycles in homogeneous water oxidation are dependent on their size, exhibiting highest efficiencies for the largest tetranuclear catalyst. The turnover frequencies (TOFs) have increased from di- to tetranuclear macrocycles not only per catalyst molecule but more importantly also per Ru unit with TOF of 6 \(^{-1}\) to 8.7 \(^{-1}\) and 10.5 s\(^{-1}\) in chemical and 0.6 s\(^{-1}\) to 3.3 \(^{-1}\) and 5.8 \(^{-1}\) in photochemical water oxidation per Ru unit, respectively. Thus, for the first time, a clear structure–activity relationship could be established for this novel class of macrocyclic water oxidation catalysts.
Poorly water-soluble drugs frequently solubilize into bile colloids and this natural mechanism is key for efficient bioavailability. We tested the impact of pharmaceutical polymers on this solubilization interplay using proton nuclear magnetic resonance spectroscopy, dynamic light scattering, and by assessing the flux across model membranes. Eudragit E, Soluplus, and a therapeutically used model polymer, Colesevelam, impacted the bile-colloidal geometry and molecular interaction. These polymer-induced changes reduced the flux of poorly water-soluble and bile interacting drugs (Perphenazine, Imatinib) but did not impact the flux of bile non-interacting Metoprolol. Non-bile interacting polymers (Kollidon VA 64, HPMC-AS) neither impacted the flux of colloid-interacting nor colloid-non-interacting drugs. These insights into the drug substance/polymer/bile colloid interplay potentially point towards a practical optimization parameter steering formulations to efficient bile-solubilization by rational polymer selection.
As viruses are obligatory intracellular parasites, any step during their life cycle strictly depends on successful interaction with their particular host cells. In particular, their interaction with cellular membranes is of crucial importance for most steps in the viral replication cycle. Such interactions are initiated by uptake of viral particles and subsequent trafficking to intracellular compartments to access their replication compartments which provide a spatially confined environment concentrating viral and cellular components, and subsequently, employ cellular membranes for assembly and exit of viral progeny. The ability of viruses to actively modulate lipid composition such as sphingolipids (SLs) is essential for successful completion of the viral life cycle. In addition to their structural and biophysical properties of cellular membranes, some sphingolipid (SL) species are bioactive and as such, take part in cellular signaling processes involved in regulating viral replication. It is especially due to the progress made in tools to study accumulation and dynamics of SLs, which visualize their compartmentalization and identify interaction partners at a cellular level, as well as the availability of genetic knockout systems, that the role of particular SL species in the viral replication process can be analyzed and, most importantly, be explored as targets for therapeutic intervention.
The ongoing transition from fossil to renewable feedstocks demands new efficient processes for an economically viable production of biomass‐derived commodities and fine chemicals. Novel energy‐ and material‐efficient product purification and separation will play a crucial role due to altered product and feed composition. The present study comprises the synthesis and tests of cross‐linked p‐vinylphenylboronate polymers for the separation of 18 diols, sugar alcohols, and saccharides, which can be obtained during biomass processing. The separation was based on molecular recognition, that is, esterification of the phenylboronate with vicinal diols. A correlation of the molecular complexation constant, the polymer swelling, and the maximum adsorption capacity was found. The adsorption curves over time were recorded. Preliminary results on competitive adsorption of binary mixtures showed a high potential for the separation of substrates with significantly different complexation constants. Desorption tests implied easier desorption of substrates that only adsorb on the outer polymer shell.
A highly strained covalent organic cage compound was synthesized from hexahydroxy tribenzotriquinacene (TBTQ) and a meta-terphenyl-based diboronic acid with an additional benzoic acid substituent in 2’-position. Usually, a 120° bite angle in the unsubstituted ditopic linker favors the formation of a [4+6] cage assembly. Here, the introduction of the benzoic acid group is shown to lead to a perfectly preorganized circular hydrogen-bonding array in the cavity of a trigonal-bipyramidal [2+3] cage, which energetically overcompensates the additional strain energy caused by the larger mismatch in bite angles for the smaller assembly. The strained cage compound was analyzed by mass spectrometry and \(^{1}\)H, \(^{13}\)C and DOSY NMR spectroscopy. DFT calculations revealed the energetic contribution of the hydrogen-bonding template to the cage stability. Furthermore, molecular dynamics simulations on early intermediates indicate an additional kinetic effect, as hydrogen bonding also preorganizes and rigidifies small oligomers to facilitate the exclusive formation of smaller and more strained macrocycles and cages.
Our research group focusses on the isolation, structural elucidation, and synthesis of bioactive natural products, among others, the naphthylisoquinoline alkaloids from tropical lianas. This intriguing class of compounds comprises representatives with activities against, e.g. P. falciparum, the cause of Malaria tropica, against the neglected disease leishmaniasis, and, as discovered more recently, against different types of cancer cells. Based on the high potency of theses extraordinary secondary metabolites, this thesis was devoted to the total synthesis of bioactive natural products and closely related analogs.
Squaraine dyes have attracted more attention in the past decade due to their strong and narrow absorption and fluorescence along with the easily functionalized molecular structure. One successful approach of core functionalization is to replace one oxygen of the squaric carbonyl group with a dicyanomethylene group, which shifts the absorption and emission into the near infrared (NIR) region and at the same time leads to a rigid, planar structure with C2v symmetry. However, such squaraines tend to aggregate cofacially in solution due to dispersion forces and dipole-dipole interactions, usually leading to H-type exciton coupling with undesired blue-shifted spectrum and quenched fluorescence. Therefore, the goal of my research was the design of dicyanomethylene-substituted squaraine dyes that self-assemble into extended aggregates in solution with J-type coupling, in order to retain or even enhance their outstanding optical properties. Toward this goal, bis(squaraine) dyes were envisioned with two squaraine units covalently linked to trigger a slip-stacked packing motif within the aggregates to enable J-type coupling.
In my first project, bis(squaraine) dye BisSQ1 was synthesized, in which two dicyanomethylene squaraine chromophores are covalently linked. Concentration and temperature-dependent UV/Vis/NIR spectroscopy experiments reveal that BisSQ1 undergoes cooperative self-assembly resulting in J-type aggregates in a solvent mixture of toluene/1,1,2,2-tetrachloroethane (TCE) (98:2, v/v). The J type exciton coupling is evident from the significantly red shifted absorption maximum at 886 nm and the fluorescence peak at 904 nm. In conclusion, this was a first example to direct squaraine dye aggregation in solution to the more desired slip-stacked packing leading to J-type exciton coupling by simply connecting two dyes in a head-to-tail bis chromophore structure.
Connecting two squaraine dyes with an additional phenylene spacer (BisSQ2) leads to two different polymorphs with very distinct absorption spectra upon cooling down a solution of BisSQ2 in a solvent mixture of toluene/TCE (98:2, v/v) with different rates. Accordingly, rapid cooling resulted in rigid helical nanorods with an absorption spectrum showing a panchromatic feature, while slow cooling led to a sheet-like structure with a significant bathochromic shift in the absorption spectrum.
It was discovered that the conventional molecular exciton model failed to explain the panchromatic absorption features of the nanorods for the given packing arrangement, therefore more profound theoretical investigations based on the Essential States Model (ESM) were applied to unveil the importance of intermolecular charge transfer (ICT) to adequately describe the panchromatic absorption spectrum. Moreover, the red-shift observed in the spectrum for the sheet-like structure can be assigned to the interplay of Coulomb coupling and ICT-mediated coupling.
Furthermore, the same bis-chromophore strategy was adopted for constructing an NIR-II emitter with a bathochromically-shifted spectrum. In chloroform, BisSQ3 exhibits an absorption maximum at 961 nm with a significant bathochromic shift (1020 cm−1) compared to the reference mono-squaraine SQ, indicating intramolecular J-type coupling via head-to-tail arrangement of two squaraine dyes. Moreover, BisSQ3 shows a fluorescence peak at 971 nm with a decent quantum yield of 0.33%. In less polar toluene, BisSQ3 self-assembles into nanofibers with additional intermolecular J-type coupling, causing a pronounced bathochromic shift with absorption maximum at 1095 nm and a fluorescence peak at 1116 nm. Thus, connecting two quinoline-based squaraines in a head-to-tail fashion leads to not only intra-, but also intermolecular J-type exciton coupling, which serves as a promising strategy to shift the absorption and emission of organic fluorophores into the NIR-II window while retaining decent quantum yields.
In conclusion, my research illustrates based on squaraine dyes how a simple modification of the molecular structure can significantly affect the aggregation behavior and further alter the optical properties of dye aggregates. Elongated supramolecular structures based on dicyanomethylene substituted squaraine dyes were successfully established by covalently linking two squaraine units to form a bis-chromophore structure. Then, a simple but efficient general approach was established to direct squaraine dye aggregation in solution to the more desired slip-stacked packing leading to J-type exciton coupling by directly connecting two squaraine dyes in a head-to-tail fashion without spacer units. Moreover, the additional spacer between the squaraine dyes in BisSQ2 allowed different molecular conformations, which leads to two different morphologies depending on the cooling rates for a hot solution. Hence, this is a promising strategy to realize supramolecular polymorphism.
In general, it is expected that the concept of constructing J-aggregates by the bis-chromophore approach can be extended to entirely different classes of dyes since J-aggregates possess a variety of features such as spectral shifts into the NIR window, fluorescence enhancement, and light harvesting, which are commonly observed and utilized for numerous fundamental studies and applications. Moreover, the insights on short-range charge transfer coupling for squaraine dyes is considered of relevance for all materials based on alternating donor-acceptor π-systems. The panchromatic spectral feature is in particular crucial for acceptor-donor-acceptor (ADA) dyes, which are currently considered as very promising materials for the development of bulk heterojunction solar cells.
A bis(squaraine) dye equipped with alkyl and oligoethyleneglycol chains was synthesized by connecting two dicyanomethylene substituted squaraine dyes with a phenylene spacer unit. The aggregation behavior of this bis(squaraine) was investigated in non-polar toluene/tetrachloroethane (98:2) solvent mixture, which revealed competing cooperative self-assembly pathways into two supramolecular polymorphs with entirely different packing structures and UV/Vis/NIR absorption properties. The self-assembly pathway can be controlled by the cooling rate from a heated solution of the monomers. For both polymorphs, quasi-equilibrium conditions between monomers and the respective aggregates can be established to derive thermodynamic parameters and insights into the self-assembly mechanisms. AFM measurements revealed a nanosheet structure with a height of 2 nm for the thermodynamically more stable polymorph and a tubular nanorod structure with a helical pitch of 13 nm and a diameter of 5 nm for the kinetically favored polymorph. Together with wide angle X-ray scattering measurements, packing models were derived: the thermodynamic polymorph consists of brick-work type nanosheets that exhibit red-shifted absorption bands as typical for J-aggregates, while the nanorod polymorph consists of eight supramolecular polymer strands of the bis(squaraine) intertwined to form a chimney-type tubular structure. The absorption of this aggregate covers a large spectral range from 550 to 875 nm, which cannot be rationalized by the conventional exciton theory. By applying the Essential States Model and considering intermolecular charge transfer, the aggregate spectrum was adequately reproduced, revealing that the broad absorption spectrum is due to pronounced donor-acceptor overlap within the bis(squaraine) nanorods. The latter is also responsible for the pronounced bathochromic shift observed for the nanosheet structure as a result of the slip-stacked arranged squaraine chromophores.
Nucleic acids are one of the important classes of biomolecules together with carbohydrates, proteins and lipids. Both deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are most well known for their respective roles in the storage and expression of genetic information.
Over the course of the last decades, nucleic acids with a variety of other functions have been discovered in biological organisms or created artificially. Examples of these functional nucleic acids are riboswitches, aptamers and ribozymes. In order to gain information regarding their function, several analytical methods can be used.
Electron paramagnetic resonance (EPR) spectroscopy is one of several techniques which can be used to study nucleic acid structure and dynamics. However, EPR spectroscopy requires unpaired electrons and because nucleic acids themselves are not paramagnetic, the incorporation of spin labels which carry a radical is necessary.
Here, three new spin labels for the analysis of nucleic acids by EPR spectroscopy are presented. All of them share two important design features. First, the paramagnetic center is located at a nitroxide, flanked by ethyl groups to prevent nitroxide degradation, for example during solid phase synthesis. Furthermore, they were designed with rigidity as an important quality, in order to be useful for applications like pulsed electron double resonance (PELDOR) spectroscopy, where independent motion of the spin labels relative to the macromolecule has a noticeable negative effect on the precision of the measurements.
Benzi-spin is a spin label which differs from most previous examples of rigid spin labels in that rather than being based on a canonical nucleoside, with a specific base pairing partner, it is supposed to be a universal nucleoside which is sufficiently rigid for EPR measurements when placed opposite to a number of different nucleosides. Benzi-spin was successfully incorporated into a 20 nt oligonucleotide and its base pairing behavior with seven different nucleosides was examined by UV/VIS thermal denaturation and continuous wave (CW) EPR experiments. The results show only minor differences between the different nucleosides, thus confirming the ability of benzi-spin to act as a universally applicable spin label.
Lumi-spin is derived from lumichrome. It features a rigid scaffold, as well as a free 2'-hydroxy group, which should make it well suited for PELDOR experiments once it is incorporated into RNA oligonucleotides.
EÇr is based on the Ç family of spin labels, which contains the most well known rigid spin labels for nucleic acids to this day. It is essentially a version of EÇm with a free 2'-hydroxy group. It was converted to triphosphate EÇrTP and used for primer extension experiments to test the viability of enzymatic incorporation of rigid spin labels into oligonucleotides as an alternative to solid-phase synthesis. Incorporation into DNA by Therminator III DNA polymerase in both single-nucleotide and full-length primer extensions was achieved.
All three of these spin labels represent further additions to the expanding toolbox of EPR spectroscopy on nucleic acids and might prove valuable for future research.
A protecting group strategy was employed to synthesise a series of indolenine squaraine dye oligomers up to the nonamer. The longer oligomers show a distinct solvent dependence of the absorption spectra, that is, either a strong blue shift or a strong red shift of the lowest energy bands in the near infrared spectral region. This behaviour is explained by exciton coupling theory as being due to H- or J-type coupling of transition moments. The H-type coupling is a consequence of a helix folding in solvents with a small Hansen dispersity index. DOSY NMR, small angle neutron scattering (SANS), quantum chemical and force field calculations agree upon a helix structure with an unusually large pitch and open voids that are filled with solvent molecules, thereby forming a kind of clathrate. The thermodynamic parameters of the folding process were determined by temperature dependent optical absorption spectra.