Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Isomalto/Malto-Polysaccharide, A Novel Soluble Dietary Fiber Made Via Enzymatic Conversion of Starch
    Leemhuis, H. ; Dobruchowska, J.M. ; Ebbelaar, M. ; Faber, F. ; Buwalda, P.L. ; Maarel, M.J.E.J. ; Kamerling, J.P. ; Dijkhuizen, L. - \ 2014
    Journal of Agricultural and Food Chemistry 62 (2014)49. - ISSN 0021-8561 - p. 12034 - 12044.
    including resistant starch - lactobacillus-reuteri 121 - structural-characterization - amylose content - chain-length - oligosaccharides - enzymes - 4,6-alpha-glucanotransferase - dextransucrase - dextranase
    Dietary fibers are at the forefront of nutritional research because they positively contribute to human health. Much of our processed foods contain, however, only small quantities of dietary fiber, because their addition often negatively affects the taste, texture, and mouth feel. There is thus an urge for novel types of dietary fibers that do not cause unwanted sensory effects when applied as ingredient, while still positively contributing to the health of consumers. Here, we report the generation and characterization of a novel type of soluble dietary fiber with prebiotic properties, derived from starch via enzymatic modification, yielding isomalto/malto-polysaccharides (IMMPs), which consist of linear (a1 ¿ 6)-glucan chains attached to the nonreducing ends of starch fragments. The applied Lactobacillus reuteri 121 GTFB 4,6-a-glucanotransferase enzyme synthesizes these molecules by transferring the nonreducing glucose moiety of an (a1 ¿ 4)-glucan chain to the nonreducing end of another (a1 ¿ 4)-a-glucan chain, forming an (a1 ¿ 6)-glycosidic linkage. Once elongated in this way, the molecule becomes a better acceptor substrate and is then further elongated with (a1 ¿ 6)-linked glucose residues in a linear way. Comparison of 30 starches, maltodextrins, and a-glucans of various botanical sources, demonstrated that substrates with long and linear (a1 ¿ 4)-glucan chains deliver products with the highest percentage of (a1 ¿ 6) linkages, up to 92%. In vitro experiments, serving as model of the digestive power of the gastrointestinal tract, revealed that the IMMPs, or more precisely the IMMP fraction rich in (a1 ¿ 6) linkages, will largely pass the small intestine undigested and therefore end up in the large intestine. IMMPs are a novel type of dietary fiber that may have health promoting activity.
    Characterisation of cell wall polysaccharides from rapeseed (Brassica napus) meal
    Pustjens, A.M. ; Schols, H.A. ; Kabel, M.A. ; Gruppen, H. - \ 2013
    Carbohydrate Polymers 98 (2013)2. - ISSN 0144-8617 - p. 1650 - 1656.
    campestris polysaccharides - nonstarch polysaccharides - structural-characterization - aspergillus-aculeatus - liquid-chromatography - rhamnogalacturonan-i - pectic substances - purification - xyloglucan - oligosaccharides
    To enable structural characteristics of individual cell wall polysaccharides from rapeseed (Brassica napus) meal (RSM) to be studied, polysaccharide fractions were sequentially extracted. Fractions were analysed for their carbohydrate (linkage) composition and polysaccharide structures were also studied by enzymatic fingerprinting. The RSM fractions analysed contained pectic polysaccharides: homogalacturonan in which 60% of the galacturonic acid residues are methyl-esterified, arabinan branched at the O-2 position and arabinogalactan mainly type II. This differs from characteristics previously reported for Brassica campestris meal, another rapeseed cultivar. Also, in the alkali extracts hemicelluloses were analysed as xyloglucan both of the XXGG- and XXXG-type decorated with galactosyl, fucosyl and arabinosyl residues, and as xylan with O-methyl-uronic acid attached. The final residue after extraction still contained xyloglucan and remaining (pectic) polysaccharides next to cellulose, showing that the cell wall matrix of RSM is very strongly interconnected
    Isolation and chemical characterization of a glucogalactomannan of the medicinal mushroom Cordyceps militaris
    Smiderle, F.R. ; Sassaki, G.L. ; Griensven, L.J.L.D. van; Iacomini, M. - \ 2013
    Carbohydrate Polymers 97 (2013)1. - ISSN 0144-8617 - p. 74 - 80.
    alditol acetate standards - beta-d-glucan - structural-characterization - pleurotus-pulmonarius - agaricus-bisporus - nmr-spectroscopy - edible mushroom - rapid synthesis - cell-wall - d-mannan
    Cordyceps militaris dried fruiting bodies were extracted with 5% KOH solution. The extract was purified by freeze-thawing treatment, and dialysis (100 kDa), giving rise to a homogeneous polysaccharide (M-w 23,000 Da). Its monosaccharide composition was mannose (56.7%), galactose (34.5%), and glucose (8.8%). The anomeric configurations were determined by their coupling constants. A complex polysaccharide was identified by NMR and methylation analysis. The HSQC spectrum showed signals at delta 107.7/5.06 and 106.1/5.14; 105.9/5.12 relative to beta-D-Galf, and O-2-substituted beta-D-Galf units, respectively. The sign at delta 104.4/5.21 corresponded to alpha-D-Galf. Other signals corresponded to alpha-D-Manp O-6- and O-2-substituted (delta 100.2/4.94; 100.5/5.27; 100.6/5.23; 100.7/5.16), and alpha-D-Manp 2,6-di-O-substituted (from delta 99.3 to 99.9). The main linkages, confirmed by methylation analysis, showed the derivatives: 2,3,4-Me-3-Manp (11.9%) and 3,4,6-Me-3-Manp (28.6%). The branches were (1 -> 6)-linked-alpha-D-Manp or (1 -> 2)-linked-beta-D-Galf, terminating with beta-D-Galf, alpha-D-Galf, alpha-D-Galp, or alpha-D-Manp. 42.7% of the partially hydrolyzed product consisted of 3,4,6-Me-3-Manp, suggesting a (1 -> 2)-linked backbone. (C) 2013 Elsevier Ltd. All rights reserved.
    The ferulic acid esterases of Chrysosporium lucknowense C1: Purification, characterization and their potential application in biorefinery
    Kuhnel, S. ; Pouvreau, L.A.M. ; Appeldoorn, M.M. ; Hinz, S.W.A. ; Schols, H.A. ; Gruppen, H. - \ 2012
    Enzyme and Microbial Technology 50 (2012)1. - ISSN 0141-0229 - p. 77 - 85.
    sugar-beet pulp - plant-cell walls - aspergillus-niger - maize bran - feruloylated oligosaccharides - structural-characterization - wheat bran - degradation - classification - arabinoxylans
    Three ferulic acid esterases from the filamentous fungus Chrysosporium lucknowense C1 were purified and characterized. The enzymes were most active at neutral pH and temperatures up to 45 °C. All enzymes released ferulic acid and p-coumaric acid from a soluble corn fibre fraction. Ferulic acid esterases FaeA1 and FaeA2 could also release complex dehydrodiferulic acids and dehydrotriferulic acids from corn fibre oligomers, but released only 20% of all ferulic acid present in sugar beet pectin oligomers. Ferulic acid esterase FaeB2 released almost no complex ferulic acid oligomers from corn fibre oligomers, but 60% of all ferulic acid from sugar beet pectin oligomers. The ferulic acid esterases were classified based on both, sequence similarity and their activities toward synthetic substrates. The type A ferulic acid esterases FaeA1 and FaeA2 are the first members of the phylogenetic subfamily 5 to be biochemically characterized. Type B ferulic acid esterase FaeB2 is a member of subfamily 6.
    Self-Assembled Functional Organic Monolayers on Oxide-Free Copper
    Caipa Campos, M.A. ; Trilling, A.K. ; Yang, M. ; Giesbers, M. ; Beekwilder, J. ; Paulusse, J.M.J. ; Zuilhof, H. - \ 2011
    Langmuir 27 (2011)13. - ISSN 0743-7463 - p. 8126 - 8133.
    molecular-dynamics simulation - surface-plasmon resonance - alkanethiol monolayers - structural-characterization - infrared-spectroscopy - corrosion protection - wetting properties - oxygen-transport - carboxylic-acids - n-dodecanethiol
    The preparation and characterization of self-assembled monolayers on copper with n-alkyl and functional thiols was investigated. Well-ordered monolayers were obtained, while the copper remained oxide-free. Direct attachment of N-succinimidyl mercaptoundecanoate (NHS-MUA) onto the copper surface allowed for the successful attachment of biomolecules, such as ß-d-glucosamine, the tripeptide glutathione, and biotin. Notably, the copper surfaces remained oxide-free even after two reaction steps. All monolayers were characterized by static water contact angle measurements, X-ray photoelectron spectroscopy, and infrared reflection absorption spectroscopy. In addition, the biotinylated copper surfaces were employed in the immobilization of biomolecules such as streptavidin
    Polyphenol Identification Based on Systematic and Robust High-Resolution Accurate Mass Spectroscopy Fragmentation
    Hooft, J.J.J. van der; Vervoort, J.J.M. ; Bino, R.J. ; Beekwilder, M.J. ; Vos, R.C.H. de - \ 2011
    Analytical Chemistry 83 (2011)1. - ISSN 0003-2700 - p. 409 - 416.
    performance liquid-chromatography - negative electrospray-ionization - collision-induced dissociation - nuclear-magnetic-resonance - flavonoid glycosides - phenolic-compounds - structural-characterization - plant metabolomics - o-glycosides - msn
    High-mass resolution multi-stage mass spectrometry (MSn) fragmentation was tested for differentiation and identification of metabolites, using a series of 121 polyphenolic molecules. The MSn fragmentation approach is based on the systematic breakdown of compounds, forming a so-called spectral tree. A chip-based nanoelectrospray ionization source was used combined with an ion-trap, providing reproducible fragmentation, and accurate mass read-out in an Orbitrap Fourier transform (FT) MS enabling rapid assignment of elemental formulas to the molecular ions and all fragment ions derived thereof. The used protocol resulted in reproducible MSn fragmentation trees up to MS5. Obtained results were stable over a 5 month time period, a concentration change of 100-fold, and small changes in normalized collision energy, which is key to metabolite annotation and helpful in structure and substructure elucidation. Differences in the hydroxylation and methoxylation patterns of polyphenolic core structures were found to be reflected by the differential fragmentation of the entire molecule, while variation in a glycosylation site displayed reproducible differences in the relative intensities of fragments originating from the same aglycone fragment ion. Accurate MSn-based spectral tree data are therefore a powerful tool to distinguish metabolites with similar elemental formula, thereby assisting compound identification in complex biological samples such as crude plant extracts.
    Okra pectin contains an unusual substitution of its rhamnosyl residues with acetyl and alpha-linked galactosyl groups
    Sengkhamparn, N. ; Bakx, E.J. ; Verhoef, R.P. ; Schols, H.A. ; Sajjaanantakul, T. ; Voragen, A.G.J. - \ 2009
    Carbohydrate Research : an international journal 344 (2009)14. - ISSN 0008-6215 - p. 1842 - 1851.
    hairy ramified regions - fat ingredient substitute - rhamnogalacturonan oligomers - structural-characterization - galacturonic acid - oligosaccharides - polysaccharides - degradation - substances - products
    The okra plant, Abelmoschus esculentus (L.) Moench, a native plant from Africa, is now cultivated in many other areas such as Asia, Africa, Middle East, and the southern states of the USA. Okra pods are used as vegetables and as traditional medicines. Sequential extraction showed that the Hot Buffer Soluble Solids (HBSS) extract of okra consists of highly branched rhamnogalacturonan (RG) I containing high levels of acetyl groups and short galactose side chains. In contrast, the CHelating agent Soluble Solids (CHSS) extract contained pectin with less RG I regions and slightly longer galactose side chains. Both pectic populations were incubated with homogeneous and well characterized rhamnogalacturonan hydrolase (RGH), endo-polygalacturonase (PG), and endo-galactanase (endo-Gal), monitoring both high and low molecular weight fragments. RGH is able to degrade saponified HBSS and, to some extent, also non-saponified HBSS, while PG and endo-Gal are hardly able to degrade either HBSS or saponified HBSS. In contrast, PG is successful in degrading CHSS, while RGH and endo-Gal are hardly able to degrade the CHSS structure. These results point to a much higher homogalacturonan (HG) ratio for CHSS when compared to HBSS. In addition, the CHSS contained slightly longer galactan side chains within its RG I region than HBSS. Matrix-assisted laser desorption ionization-time of flight mass spectrometry indicated the presence of acetylated RG oligomers in the HBSS and CHSS enzyme digests and electron spray ionization-ion trap-mass spectrum showed that not only galacturonosyl residues but also rhamnosyl residues in RG I oligomers were O-acetylated. NMR spectroscopy showed that all rhamnose residues in a 20 kDa HBSS population were O-acetylated at position O-3. Surprisingly, the NMR data also showed that terminal a-linked galactosyl groups were present as neutral side chain substituents. Taken together, these results demonstrate that okra contained RG I structures which have not been reported before for pectic RG I.
    Characterisation of cell wall polysaccharides from okra (Abelmoschus esculentus (L.) Moench)
    Sengkhamparn, N. ; Verhoef, R.P. ; Schols, H.A. ; Sajjaanantakul, T. ; Voragen, A.G.J. - \ 2009
    Carbohydrate Research : an international journal 344 (2009)14. - ISSN 0008-6215 - p. 1824 - 1832.
    fat ingredient substitute - hairy ramified regions - europaea cv koroneiki - sugar-beet pectins - structural-characterization - oligosaccharides - acid - rhamnogalacturonan - xyloglucan - chromatography
    Okra pods are commonly used in Asia as a vegetable, food ingredient, as well as a traditional medicine for many different purposes; for example, as diuretic agent, for treatment of dental diseases and to reduce/prevent gastric irritations. The healthy properties are suggested to originate from the high polysaccharide content of okra pods, resulting in a highly viscous solution with a slimy appearance when okra is extracted with water. In this study, we present a structural characterisation of all major cell wall polysaccharides originating from okra pods. The sequential extraction of okra cell wall material yielded fractions of soluble solids extractable using hot buffer (HBSS), chelating agent (CHSS), dilute alkaline (DASS) and concentrated alkaline (CASS). The HBSS fraction was shown to be rich in galactose, rhamnose and galacturonic acid in the ratio 1.3:1:1.3. The degree of acetylation is relatively high (DA = 58) while the degree of methyl esterification is relatively low (DM = 24). The CHSS fraction contained much higher levels of methyl esterified galacturonic acid residues (63% galacturonic acid; DM = 48) in addition to minor amounts of rhamnose and galactose. The ratio of galactose to rhamnose to galacturonic acid was 1.3:1.0:1.3 and 4.5:1.0:1.2 for HBSS and CHSS, respectively. These results indicated that the HBSS and CHSS fractions contain rhamnogalacturonan type I next to homogalacturonan, while the latter is more prevailing in CHSS. Also the DASS fraction is characterised by high amounts of rhamnose, galactose, galacturonic acid and some arabinose, indicating that rhamnogalacturonan I elements with longer arabinose- and galactose-rich side chains were part of this fraction. Partial digestion of HBSS and CHSS by pectin methyl esterase and polygalacturonase resulted in a fraction with a lower Mw and lower viscosity in solution. These samples were subjected to NMR analysis, which indicated that, in contrast to known RG I structure, the acetyl groups in HBSS are not located on the galacturonic acid residues, while for CHSS only part of the acetyl groups are located on the RG I galacturonic acid residues. The CASS fraction consisted of XXXG-type xyloglucan and 4-methylglucuronoxylan as shown by their sugar (linkage) composition and enzymatic digestion.
    A Brief and Informationally Rich Naming System for Oligosaccharide Motifs of Heteroxylans Found in Plant Cell Walls
    Faure, R. ; Courtin, C.M. ; Delcour, J.A. ; Dumon, C. ; Faulds, C.B. ; Fincher, G.B. ; Fort, S. ; Fry, S.C. ; Halila, S. ; Kabel, M.A. ; Pouvreau, L.A.M. ; Quemener, B. ; Rivet, A. ; Saulnier, L. ; Schols, H.A. ; Driquez, H. ; O'Donohue, M.J. - \ 2009
    Australian Journal of Chemistry 62 (2009)6. - ISSN 0004-9425 - p. 533 - 537.
    structural-characterization - maize bran - arabinoxylans - nomenclature - library
    The one-letter code system proposed here is a simple method to accurately describe structurally diverse oligosaccharides derived from heteroxylans. Substitutions or ‘molecular decoration(s)’ of main-chain d-xylosyl moieties are designated by unique letters. Hence, an oligosaccharide is described by a series of single letters, beginning with the non-reducing d-xylosyl unit. Superscripted numbers are used to indicate the linkage position(s) of main-chain substitution(s) and, where necessary, superscripted lowercase letter(s) indicate the nature of non-glycosidic groups (e.g., methyl, acetyl, or phenolic derivative moieties) that can be present on the substituents. Although relatively simple and practical to use, this abbreviated system lends itself to the naming of a large number of different combinations of structural building blocks and substituents. In its present state, this system is, therefore, adequate to name and differentiate all currently known complex oligosaccharides derived from heteroxylans and is sufficiently flexible to accommodate new structures as they become available.
    Topological switching between an a-ß parallel protein and a remarkably helical molten globule.
    Nabuurs, S.M. ; Westphal, A.H. ; Toorn, M. aan den; Lindhoud, S. ; Mierlo, C.P.M. van - \ 2009
    Journal of the American Chemical Society 131 (2009)23. - ISSN 0002-7863 - p. 8290 - 8295.
    azotobacter-vinelandii apoflavodoxin - pathway folding intermediate - structural-characterization - on-pathway - unfolded molecules - hydrogen-exchange - energy landscape - flavodoxin-ii - state - apomyoglobin
    Partially folded protein species transiently exist during folding of most proteins. Often these species are molten globules, which may be on- or off-pathway to native protein. Molten globules have a substantial amount of secondary structure but lack virtually all the tertiary side-chain packing characteristic of natively folded proteins. These ensembles of interconverting conformers are prone to aggregation and potentially play a role in numerous devastating pathologies, and thus attract considerable attention. The molten globule that is observed during folding of apoflavodoxin from Azotobacter vinelandii is off-pathway, as it has to unfold before native protein can be formed. Here we report that this species can be trapped under nativelike conditions by substituting amino acid residue F44 by Y44, allowing spectroscopic characterization of its conformation. Whereas native apoflavodoxin contains a parallel ß-sheet surrounded by a-helices (i.e., the flavodoxin-like or a-ß parallel topology), it is shown that the molten globule has a totally different topology: it is helical and contains no ß-sheet. The presence of this remarkably nonnative species shows that single polypeptide sequences can code for distinct folds that swap upon changing conditions. Topological switching between unrelated protein structures is likely a general phenomenon in the protein structure universe
    "Noncooperative formation of the off-pathway molten globule during folding of the a-ß parallel protein apoflavodoxin"
    Nabuurs, S.M. ; Westphal, A.H. ; Mierlo, C.P.M. van - \ 2009
    Journal of the American Chemical Society 131 (2009)7. - ISSN 0002-7863 - p. 2739 - 2746.
    azotobacter-vinelandii apoflavodoxin - nmr-spectroscopy - structural-characterization - different denaturants - unfolded molecules - hydrogen-exchange - energy landscape - transition-state - on-pathway - intermediate
    During folding of many proteins, molten globules are formed. These partially folded forms of proteins have a substantial amount of secondary structure but lack virtually all tertiary side-chain packing characteristic of native structures. Molten globules are ensembles of interconverting conformers and are prone to aggregation, which can have detrimental effects on organisms. Consequently, molten globules attract considerable attention. The molten globule that is observed during folding of flavodoxin from Azotobacter vinelandii is a kinetically off-pathway species, as it has to unfold before the native state of the protein can be formed. This intermediate contains helices and can be populated at equilibrium using guanidinium hydrochloride as denaturant, allowing the use of NMR spectroscopy to follow molten globule formation at the residue level. Here, we track changes in chemical shifts of backbone amides, as well as disappearance of resonances of unfolded apoflavodoxin, upon decreasing denaturant concentration. Analysis of the data shows that structure formation within virtually all parts of the unfolded protein precedes folding to the molten globule state. This folding transition is noncooperative and involves a series of distinct transitions. Four structured elements in unfolded apoflavodoxin transiently interact and subsequently form the ordered core of the molten globule. Although hydrophobic, tryptophan side chains are not involved in the latter process. This ordered core is gradually extended upon decreasing denaturant concentration, but part of apoflavodoxin's molten globule remains random coil in the denaturant range investigated. The results presented here, together with those reported on the molten globule of alpha-lactalbumin, show that helical molten globules apparently fold in a noncooperative manner
    The pectic polysaccharide rhamnogalacturonan II is present as a dimer in pectic populations of bilberries and black currants in muro and in juice
    Hilz, H. ; Williams, P. ; Doco, T. ; Schols, H.A. ; Voragen, A.G.J. - \ 2006
    Carbohydrate Polymers 65 (2006)4. - ISSN 0144-8617 - p. 521 - 528.
    plant-cell-walls - structural-characterization - suspension-cultures - borate ester - acid - oligosaccharides - component - phenols - complex - roots
    Rhamnogalacturonan II (RG II) can play an important role during processing of berries due to its enzyme resistance and its possible role as a pectic cross-linker. This article describes the presence of RG II in cell walls, in juice and in press cake of bilberries and black currants. RG II was identified and quantified via its diagnostic sugar residues. RG II, which was released from homogalacturonan, was probably present in its dimeric form in muro. Juice contained the free RG II dimer, while from press cake dimeric RG II was released by enzymatic degradation of homogalacturonan. A higher amount of RG II was present in juice than in press cake. During juice processing a cross-linker RG II might improve gel formation, which hinders the processability of berries. In addition, enzymes used during juice processing release dimeric RG II from pectin molecules and accumulate RG II in the juice.
    DFT normal coordinate analysis of the vibrational spectra of iron and germanium corroles
    Zakharieva, O. ; Veeger, C. - \ 2005
    Journal of Molecular Structure : THEOCHEM 723 (2005)1-3. - ISSN 0166-1280 - p. 171 - 182.
    transition-metal centers - resonance raman-spectra - noninnocent ligands - structural-characterization - electronic absorption - oxidation-states - force-field - compound-i - complexes - density
    DFT calculations on the vibrational modes of [FeCl(OECorr)], [FeCl(TPCorr)], [FeC6H5(OECorr)] and the corresponding germanium systems, [GeCl(OECorr)], [GeCl(TPCorr)] and [GeC6H 5(OECorr)] are for the first time presented. In addition DFT calculations on the electronic structure of the germanium corroles are given (OECorr, octaethylcorrole; TPCorr, triphenylcorrole). B3LYP functional and the 6-311G basis are used for the H, C and N atoms while for iron and germanium the Wachters-Hay double-¿ basis as implemented in the program package Gaussian 98 is applied. The normal modes of vibrations are calculated for geometries, obtained by optimizations on the theoretical potential energy surfaces. The formation of a ¿-cation corrole radical in the cases of [FeCl(OECorr)] and [FeCl(TPCorr)] is confirmed by the downshift of some C-C corrole skeletal modes compared to [GeCl(OECorr)] or [GeCl(TPCorr)], respectively. The largest shifts are derived for vibrations with high C¿-Cmeso, C¿-C¿ as well as C¿-C ß eigenvectors. Also the Cß-Cß valence frequencies show a downshift in cases when the Cß-C ß bonds stretch and contract in phase. The downshifts of some C-C stretchings in the phenyl axial ligand of the [FeC6H 5(OECorr)] provide evidence for an electron flow from the axial ligand to iron. Simulated nuclear inelastic scattering (NIS) spectra are generated by using the calculated normal modes. High intensity of the bands, connected with substantial contributions to the mean square displacements of the iron nucleus, is associated with in-plane equatorial iron modes, namely the Fe-N stretchings
    The photophysical and metal coordination properties of the N-CH3 substituted porphyrins: H(N-CH3)TPP vs H(CH3)OEP
    Sazanovich, I.V. ; Berezin, D.B. ; Hoek, A. van; Panarin, A.Yu. ; Bolotin, V.L. ; Semeykin, A.S. ; Chirvony, V.S. - \ 2005
    Journal of Porphyrins and Phthalocyanines 9 (2005). - ISSN 1088-4246 - p. 59 - 67.
    free-base porphyrins - structural-characterization - complexes - deactivation - diacids - state
    The effect of N-methyl substitution on photophysical and metal coordination properties of the respective derivatives of octaethylporphyrin (H2OEP) and tetraphenylporphyrin (H2TPP) was studied by means of steady-state and time-resolved optical spectroscopies combined with semi-empirical quantum-chemical calculations and coordination chemistry methods. In case of H2TPP, the insertion of the methyl substituent into the center of the porphyrin macrocycle leads to noticeable nonplanar distortions of the molecule and is accompanied by changes of its photophysical and physicochemical properties towards those manifested by "classical" nonplanar porphyrins. Contrasting to that, N-methyl substituted H2OEP does not undergo significant nonplanar distortions and possesses photophysical characteristics mainly similar to unsubstituted H2OEP, except for the long-wavelength shift of the absorption and emission bands. The Zn coordination/Zn complex dissociation and macrocycle thermal stability parameters were also determined for both N-methyl substituted and parent unsubstituted macrocycles, which correlate well with a higher degree of nonplanarity of the N-methyl substituted H2TPP as compared to H2OEP. Basing on the results of this study the conclusion postulated is that N-methyl substitution has a different effect on the photophysical and coordination properties of H2TPP vs. H2OER Copyright (c) 2005 Society of Porphyrins & Phthalocyanines.
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