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Host-Guest Interactions for Structural Analysis of Organic Molecules: Development of new Tools for Stereochemical Characterization
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.ORCID iD: 0000-0002-4871-0613
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The focus of this thesis is on the development of molecular tweezers as host-guest systems for stereochemical characterization of small organic molecules.

There are two central problems to stereochemical characterization of small molecules. The first is that there are few methods for the determination of absolute stereochemistry and the complexity of the task increases with the number of chiral centres in the molecule. The second is the flexibility of small molecules. The data received from NMR spectroscopy, the standard method for structural characterization is an average of all conformers present in solution, making exact determination of the structure challenging if stereocenters are involved.

This research group has previously developed two bis-porphyrin molecular tweezers that can be used as hosts for relative stereochemical determination by NMR (NAMFIS) by limiting the flexibility of the guest molecules and for absolute stereochemical determination Exciton-Coupled Circular Dichroism (ECCD) by providing suitable chromophores. However, the use of these tweezers was limited to diamine molecules.

To extend the application of both tweezer host systems, a range of metalloporphyrins have been investigated both computationally and experimentally to identify candidates binding strongly to oxygen containing functional groups (Paper I). One of the porphyrins identified has been used to synthesise a new system with the potential to be used for relative stereochemical determination by NMR (NAMFIS) of molecules with a wide variety of functional groups (Paper IV).

To further develop the systems, the photo-isomerization properties of the stiff stilbene linker of one of the tweezers has been investigated. Macrocyclic diether model compounds, incorporating the stiff stilbene linker have been used to show that the photo-isomerizability strongly is affected by molecular strain (Paper II). The results suggest that if paired with a suitable porphyrin (with no UV/Vis absorption overlap) a photo-switchable tweezer might be constructed.

To map the guest range of the stiff stilbene linked tweezer it was found that this tweezer gives strong to moderate signals for monoamines with a rigid structure (Paper III). As ditopic binding is usually a requirement for an ECCD signal when using bis-porphyrin molecular tweezers, this is a discovery that should be of general interest.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 63
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1810
Keywords [en]
metalloporphyrins, host-guest systems, bis-porphyrin tweezers, stiff stilbene macrocycles, organic synthesis, porphyrin binding studies, NMR, ECCD
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-382219ISBN: 978-91-513-0660-5 (print)OAI: oai:DiVA.org:uu-382219DiVA, id: diva2:1306284
Public defence
2019-06-14, Room A1:107, BMC, Husargatan 3, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-05-22 Created: 2019-04-23 Last updated: 2019-06-18
List of papers
1. Design of oxophilic metalloporphyrins: an experimental and DFT study of methanol binding
Open this publication in new window or tab >>Design of oxophilic metalloporphyrins: an experimental and DFT study of methanol binding
2018 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 47, no 33, p. 11572-11585Article in journal (Refereed) Published
Abstract [en]

By systematic measurements we have evaluated a series of tetraphenyl metalloporphyrins and halogenated tetraphenyl metalloporphyrin derivatives for binding to ligands with oxygen containing functional groups, using methanol, acetic acid and acetone as examples. Experimental binding constants identified three metalloporphyrins with good binding to all three ligands: MgTPFPP, MgTPPBr8 and ZnTPPBr8 as well as a range of porphyrins binding to select ligands. Based on these results the optimal porphyrins can be selected for the desired binding interactions. We also show how to use DFT calculations to evaluate the potential binding between a metalloporphyrin and a ligand, which is deduced from free energies of binding ΔG, charge transfer ΔQ, and change of metal spin state. Computations on unsubstituted porphyrins in lieu of tetraphenyl porphyrin systems yield reliable predictions of binding interactions with good correlation to the corresponding experimental data. The calculations have also yielded interesting insights into the effect of halogenation in the β-position on the binding to ligands with oxygen containing functional groups.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
Keywords
Porphyrins, DFT, host-guest
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-359830 (URN)10.1039/c8dt02432d (DOI)000442509700031 ()30087966 (PubMedID)
Funder
Swedish Research Council, 621-2012-3379Carl Tryggers foundation , 16:156Swedish National Infrastructure for Computing (SNIC), 2018/3-240National Supercomputer Centre (NSC), Sweden, SNIC 2018/3-240
Available from: 2018-09-06 Created: 2018-09-06 Last updated: 2019-04-23Bibliographically approved
2. Effect of Ring Size on Photoisomerization Properties of Stiff Stilbene macrocycles
Open this publication in new window or tab >>Effect of Ring Size on Photoisomerization Properties of Stiff Stilbene macrocycles
2019 (English)In: Beilstein Journal of Organic Chemistry, ISSN 2195-951X, E-ISSN 1860-5397, Vol. 15, p. 2408-2418Article in journal (Refereed) Published
Abstract [en]

A series of stiff stilbene macrocycles have been studied to investigate the possible impact of the macrocycle ring size on their photodynamic properties. The results show that reducing the ring size counteracts the photoisomerization ability of the macrocycles. However, even the smallest macrocycle studied (stiff stilbene subunits linked by a six carbon chain) showed some degree of isomerization when irradiated. DFT calculations of the energy differences between the E- and Z-isomers show the same trend as the experimental results. Interestingly the DFT study highlights that the energy difference between the E- and Z-isomers of even the largest macrocycle (linked by a twelve carbon chain) is significantly higher than that of the stiff stilbene unit itself. In general, it is indicated that addition of even a flexible chain to the stiff stilbene unit may significantly affect its photochemical properties and increase the photostability of the resulting macrocycle.

Keywords
Stiff stilbene cyclic photoisomerization
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-382215 (URN)10.3762/bjoc.15.233 (DOI)000489716300001 ()31666875 (PubMedID)
Funder
Swedish Research Council, 621-2012-3379Carl Tryggers foundation , CTS 16:156Swedish National Infrastructure for Computing (SNIC)
Available from: 2019-04-23 Created: 2019-04-23 Last updated: 2019-11-08Bibliographically approved
3. Exciton-Coupled Circular Dichroism Characterization of Monotopically Binding Guests in Host-Guest Complexes with a Bis(zinc porphyrin) Tweezer
Open this publication in new window or tab >>Exciton-Coupled Circular Dichroism Characterization of Monotopically Binding Guests in Host-Guest Complexes with a Bis(zinc porphyrin) Tweezer
2018 (English)In: ChemPlusChem, ISSN 2192-6506, Vol. 83, p. 1169-1178Article in journal (Refereed) Published
Abstract [en]

A stiff-stilbene-linked bisporphyrin tweezer with inherent helicity was used for exciton-coupled circular dichroism (ECCD) characterization of a series of monotopically binding amine guest molecules. CD signals were observed for a variety of monoamines at relatively low tweezer/amine (host/guest) ratios between 1 :10 to 1: 70. For the amines producing the most intense CD signals, a binding stoichiometry of 1:2 was found. A likely explanation is the presence of guest-guest interactions in the complexes. This is supported by the correlation observed between CD signal intensity and magnitude of possible noncovalent binding between the guests, which can be divided into three groups showing no, moderate and strong response, respectively. Further support for this rationalization comes from molecular modelling.

Place, publisher, year, edition, pages
Weinheim: Wiley-VCH Verlagsgesellschaft, 2018
Keywords
bis-porphyrin tweezers, conformation analysis, exciton-coupled circular dichroism, host-guest systems, molecular modeling
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-371629 (URN)10.1002/cplu.201800564 (DOI)000454527200013 ()
Funder
Swedish Research Council, 621-2012-3379Carl Tryggers foundation , CTS 16 : 156
Available from: 2018-12-21 Created: 2018-12-21 Last updated: 2019-04-23Bibliographically approved
4. Synthesis of a novel bis-Mg-porphyrin tweezer
Open this publication in new window or tab >>Synthesis of a novel bis-Mg-porphyrin tweezer
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We have synthesised a novel semi-rigid bis-(magnesium-porphyrin) tweezer with a glycoluril backbone. meso-Tetrakis(pentafluorophenyl)porphyrin constitutes the two porphyrin units, each holding a magnesium(II) ion, and being connected to the glycoluril backbone via two -positions. This connection prevents any porphyrin rotation, leaving changes in gap size as sole conformational variation. Magnesium(II) tetrakis(pentafluorophenyl)porphyrin has in previous studies shown to bind well to both nitrogen-containing and oxygen-containing functional groups. The tweezer has the potential to retain this binding ability, which would be useful in the stereochemical characterization of small flexible molecules with multiple stereocentra and a wide variety of functional groups.

Keywords
magnesium-porphyrin tweezer synthesis
National Category
Organic Chemistry
Research subject
Chemistry with specialization in Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-382217 (URN)
Funder
Swedish Research Council, 621-2012-3379Carl Tryggers foundation , CTS 16:156
Available from: 2019-04-23 Created: 2019-04-23 Last updated: 2019-04-23

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