The Experts below are selected from a list of 147 Experts worldwide ranked by ideXlab platform
David J Aitken - One of the best experts on this subject based on the ideXlab platform.
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A solution to the component instability problem in the preparation of peptides containing C2 substituted cis-Cyclobutane b-aminoacids: synthesis of a stable rhodopeptin analogue.
Tetrahedron Letters, 2006Co-Authors: Olivier Roy, Sophie Faure, David J AitkenAbstract:Despite the inherent instability of C2-substituted cis-Cyclobutane β-aminoacids, incorporation of such residues into peptides is shown to be possible through use of a 1-amino-2-(hydroxymethyl)Cyclobutane Derivative as a stable β-aminoacid surrogate. This synthetic strategy was validated by the synthesis of a rhodopeptin analogue.
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A solution to the component instability problem in the preparation of peptides containing C2-substituted cis-Cyclobutane β-aminoacids: synthesis of a stable rhodopeptin analogue
Tetrahedron Letters, 2006Co-Authors: Olivier Roy, Sophie Faure, David J AitkenAbstract:Abstract Despite the inherent instability of C2-substituted cis-Cyclobutane β-aminoacids, incorporation of such residues into peptides is shown to be possible through use of a 1-amino-2-(hydroxymethyl)Cyclobutane Derivative as a stable β-aminoacid surrogate. This synthetic strategy was validated by the synthesis of a rhodopeptin analogue.
S. P. Gromov - One of the best experts on this subject based on the ideXlab platform.
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Features of cation packing in crystal forms of a 18-crown-6-containing styryl dye iodide and feasibility of the solid phase [2+2]-autophotocycloaddition reaction in it
Journal of Structural Chemistry, 2014Co-Authors: L. G. Kuz’mina, A. I. Vedernikov, M. V. Alfimov, J. A. K. Howard, E. Kh. Lermontova, A. V. Churakov, S. P. GromovAbstract:X-ray structure determinations of three crystal forms of a 18-crown-6-containing styryl dye of the pyridine series in iodide form ( 1 ), containing various solvate molecules, namely water ( 1a ), 2,6-dihydroxyoaphthalene ( 1b ), 1,4-hydroquinone ( 1c ), and analysis of crystal packings of these crystals, together with the previously investigated non-solvated form (crystal 1 ) and the solvates with benzene and water (crystal 1d ) has been carried out. Crystal packing in 1a , 1b , 1c , and 1d involves a stacking leading to dimers of the dye cations, structurally preorganized for the [2+2]-photocycloaddition (PCA) reaction. On irradiation of with visible light, the PCA reaction with the centrosymmetric rctt isomer leads to the Cyclobutane Derivative formation. In the case of 1a and 1b the PCA proceeds with the retention of crystallinity, while with other solvates crystals are transformed into a glass. The glasses keep the form and the shine of the initial crystals, nevertheless. In the cases of the non-solvated crystal form ( 1 ), translation-related stacks form, with the geometry inconsistent with that of the preorganized dimer. These crystals are stable in visible light.
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Supramolecular assembler based on cucurbit[8]uril: Photodimerization of a styryl dye in water
High Energy Chemistry, 2014Co-Authors: D. A. Ivanov, M. V. Alfimov, A. I. Vedernikov, N. Kh. Petrov, S. P. GromovAbstract:Photolysis of aqueous solutions of styryl dye 1 in the presence of cucurbit[8]uril (CB[8]) has been studied by optical spectroscopic methods for the molar ratios n = c _CB[8]/ c _ 1 in the range of 0 ≤ n ≤ 6. It has been found that the inclusion complexes ( 1 )_2@CB[8] dominate in the solution at n ≤ 0.5, whereas the complexes 1 @CB[8] dominate at n ≥ 1. The stability constants have been determined for the 1: 1 (log K _1 = 6.2 (L mol^−1)) and 2: 1 (log β = 11.9 (L^2 mol^−2)) complexes. The fluorescence decay kinetics of dye 1 in the presence of CB[8] is two-exponential, with the average lifetime increasing substantially at n ≥ 1. It has been shown that the system can operate in the cyclic mode as an assembler (or supramolecular catalyst) in the photodimerization reaction of dye 1 to form Cyclobutane Derivative 2 . The stability constant of the complex 2 @CB[8] (log K _3 = 5.9 (L mol^−1)) and the quantum yield of cycloaddition (⃜ ≈ 0.07 at n ≈ 0.5) have been determined.
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Design of crystal packings of styryl heterocycles and regularities of [2+2] photocycloaddition in their single crystals 8. Topochemical [2+2] autophotocycloaddition and back reaction in styryl dye of the benzothiazole series
Russian Chemical Bulletin, 2013Co-Authors: L. G. Kuz’mina, A. I. Vedernikov, M. V. Alfimov, J. A. K. Howard, E. Kh. Lermontova, S. P. GromovAbstract:New styryl dye of the 2-benzothiazole series was synthesized. The new dye contains two methoxy groups in the benzene ring and tosylate counterion. The [2+2] photocycloaddition (PCA) of the dye was studied in the polycrystalline film and in single crystal. Two modifications of the dye cocrystallizate with hydroquinone differed in the ratio of components were obtained, and their ability to enter PCA was studied. According to the X-ray diffraction data, molecular cations of the dye form stack packings either of syn -“head-to-tail” type or relatively isolated stacking dimers. In all cases, the ethylene bonds of the adjacent cations are brought together and antiparallel, favoring PCA to form the centrosymmetric rctt -isomer of 1,2,3,4-tetrasubstituted Cyclobutane. In two cases, the PCA reaction proceeded as the “single crystal-to-single crystal” transformation. Hydrogen bonds in crystals including hydroquinone molecules strengthen the crystal packing retarding the PCA. The back photoreaction (retro-PCA) was detected: it occurs without single crystal decomposition and results in the accumulation of the initial styryl dye in crystal consisting of the Cyclobutane Derivative. This is the first example of such a transformation in single crystals.
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Stereospecific [2+2] photocycloaddition in a pseudodimeric complex between N-ammoniopropylstyrylpyridine and 18-crown-6-containing styrylpyridine
Russian Chemical Bulletin, 2009Co-Authors: A. I. Vedernikov, L. G. Kuz’mina, M. V. Alfimov, S. K. Sazonov, J. A. K. Howard, S. P. GromovAbstract:A quaternary 4-styrylpyridinium salt having the N -ammoniopropyl substituent forms a pseudodimeric head-to-tail complex with neutral 18-crown-6-containing 4-styrylpyridine in MeCN through H-bonding. This complex undergoes stereospecific [2+2] photocycloaddition due to preorganization of the ethylene bonds in the syn -arranged chromophoric fragments of the components. The structure of the rctt -isomer of the Cyclobutane Derivative obtained was established by NMR spectroscopy and X-ray diffraction analysis.
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Stereospecific [2+2] autophotocycloaddition in the dimeric complex of 18-crown-6 ether styryl dye bearing N-(3-ammoniopropyl) substituent
Russian Chemical Bulletin, 2009Co-Authors: S. P. Gromov, A. I. Vedernikov, L. G. Kuz’mina, N. A. Lobova, J. A. K. Howard, M. V. AlfimovAbstract:New 18-crown-6 ether styryl dye of the 4-pyridine series bearing N -(3-ammoniopropyl) substituent has been synthesized. In MeCN, the dye forms a stable dimeric complex of the syn -head-to-tail type due to the complexation of the ammonium group of one molecule with the crown ether fragment of another. In the dimeric complex, the ethylene bonds of the molecules are close in space and antiparallel, which promotes an efficient stereospecific [2+2] autophotocycloaddition to yield the only rctt -isomer of 1,2,3,4-tetrasubstituted Cyclobutane. The Cyclobutane Derivative structure was confirmed by NMR spectroscopy and X-ray diffraction.
Olivier Roy - One of the best experts on this subject based on the ideXlab platform.
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A solution to the component instability problem in the preparation of peptides containing C2 substituted cis-Cyclobutane b-aminoacids: synthesis of a stable rhodopeptin analogue.
Tetrahedron Letters, 2006Co-Authors: Olivier Roy, Sophie Faure, David J AitkenAbstract:Despite the inherent instability of C2-substituted cis-Cyclobutane β-aminoacids, incorporation of such residues into peptides is shown to be possible through use of a 1-amino-2-(hydroxymethyl)Cyclobutane Derivative as a stable β-aminoacid surrogate. This synthetic strategy was validated by the synthesis of a rhodopeptin analogue.
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A solution to the component instability problem in the preparation of peptides containing C2-substituted cis-Cyclobutane β-aminoacids: synthesis of a stable rhodopeptin analogue
Tetrahedron Letters, 2006Co-Authors: Olivier Roy, Sophie Faure, David J AitkenAbstract:Abstract Despite the inherent instability of C2-substituted cis-Cyclobutane β-aminoacids, incorporation of such residues into peptides is shown to be possible through use of a 1-amino-2-(hydroxymethyl)Cyclobutane Derivative as a stable β-aminoacid surrogate. This synthetic strategy was validated by the synthesis of a rhodopeptin analogue.
M. V. Alfimov - One of the best experts on this subject based on the ideXlab platform.
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Features of cation packing in crystal forms of a 18-crown-6-containing styryl dye iodide and feasibility of the solid phase [2+2]-autophotocycloaddition reaction in it
Journal of Structural Chemistry, 2014Co-Authors: L. G. Kuz’mina, A. I. Vedernikov, M. V. Alfimov, J. A. K. Howard, E. Kh. Lermontova, A. V. Churakov, S. P. GromovAbstract:X-ray structure determinations of three crystal forms of a 18-crown-6-containing styryl dye of the pyridine series in iodide form ( 1 ), containing various solvate molecules, namely water ( 1a ), 2,6-dihydroxyoaphthalene ( 1b ), 1,4-hydroquinone ( 1c ), and analysis of crystal packings of these crystals, together with the previously investigated non-solvated form (crystal 1 ) and the solvates with benzene and water (crystal 1d ) has been carried out. Crystal packing in 1a , 1b , 1c , and 1d involves a stacking leading to dimers of the dye cations, structurally preorganized for the [2+2]-photocycloaddition (PCA) reaction. On irradiation of with visible light, the PCA reaction with the centrosymmetric rctt isomer leads to the Cyclobutane Derivative formation. In the case of 1a and 1b the PCA proceeds with the retention of crystallinity, while with other solvates crystals are transformed into a glass. The glasses keep the form and the shine of the initial crystals, nevertheless. In the cases of the non-solvated crystal form ( 1 ), translation-related stacks form, with the geometry inconsistent with that of the preorganized dimer. These crystals are stable in visible light.
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Supramolecular assembler based on cucurbit[8]uril: Photodimerization of a styryl dye in water
High Energy Chemistry, 2014Co-Authors: D. A. Ivanov, M. V. Alfimov, A. I. Vedernikov, N. Kh. Petrov, S. P. GromovAbstract:Photolysis of aqueous solutions of styryl dye 1 in the presence of cucurbit[8]uril (CB[8]) has been studied by optical spectroscopic methods for the molar ratios n = c _CB[8]/ c _ 1 in the range of 0 ≤ n ≤ 6. It has been found that the inclusion complexes ( 1 )_2@CB[8] dominate in the solution at n ≤ 0.5, whereas the complexes 1 @CB[8] dominate at n ≥ 1. The stability constants have been determined for the 1: 1 (log K _1 = 6.2 (L mol^−1)) and 2: 1 (log β = 11.9 (L^2 mol^−2)) complexes. The fluorescence decay kinetics of dye 1 in the presence of CB[8] is two-exponential, with the average lifetime increasing substantially at n ≥ 1. It has been shown that the system can operate in the cyclic mode as an assembler (or supramolecular catalyst) in the photodimerization reaction of dye 1 to form Cyclobutane Derivative 2 . The stability constant of the complex 2 @CB[8] (log K _3 = 5.9 (L mol^−1)) and the quantum yield of cycloaddition (⃜ ≈ 0.07 at n ≈ 0.5) have been determined.
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Design of crystal packings of styryl heterocycles and regularities of [2+2] photocycloaddition in their single crystals 8. Topochemical [2+2] autophotocycloaddition and back reaction in styryl dye of the benzothiazole series
Russian Chemical Bulletin, 2013Co-Authors: L. G. Kuz’mina, A. I. Vedernikov, M. V. Alfimov, J. A. K. Howard, E. Kh. Lermontova, S. P. GromovAbstract:New styryl dye of the 2-benzothiazole series was synthesized. The new dye contains two methoxy groups in the benzene ring and tosylate counterion. The [2+2] photocycloaddition (PCA) of the dye was studied in the polycrystalline film and in single crystal. Two modifications of the dye cocrystallizate with hydroquinone differed in the ratio of components were obtained, and their ability to enter PCA was studied. According to the X-ray diffraction data, molecular cations of the dye form stack packings either of syn -“head-to-tail” type or relatively isolated stacking dimers. In all cases, the ethylene bonds of the adjacent cations are brought together and antiparallel, favoring PCA to form the centrosymmetric rctt -isomer of 1,2,3,4-tetrasubstituted Cyclobutane. In two cases, the PCA reaction proceeded as the “single crystal-to-single crystal” transformation. Hydrogen bonds in crystals including hydroquinone molecules strengthen the crystal packing retarding the PCA. The back photoreaction (retro-PCA) was detected: it occurs without single crystal decomposition and results in the accumulation of the initial styryl dye in crystal consisting of the Cyclobutane Derivative. This is the first example of such a transformation in single crystals.
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Stereospecific [2+2] photocycloaddition in a pseudodimeric complex between N-ammoniopropylstyrylpyridine and 18-crown-6-containing styrylpyridine
Russian Chemical Bulletin, 2009Co-Authors: A. I. Vedernikov, L. G. Kuz’mina, M. V. Alfimov, S. K. Sazonov, J. A. K. Howard, S. P. GromovAbstract:A quaternary 4-styrylpyridinium salt having the N -ammoniopropyl substituent forms a pseudodimeric head-to-tail complex with neutral 18-crown-6-containing 4-styrylpyridine in MeCN through H-bonding. This complex undergoes stereospecific [2+2] photocycloaddition due to preorganization of the ethylene bonds in the syn -arranged chromophoric fragments of the components. The structure of the rctt -isomer of the Cyclobutane Derivative obtained was established by NMR spectroscopy and X-ray diffraction analysis.
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Stereospecific [2+2] autophotocycloaddition in the dimeric complex of 18-crown-6 ether styryl dye bearing N-(3-ammoniopropyl) substituent
Russian Chemical Bulletin, 2009Co-Authors: S. P. Gromov, A. I. Vedernikov, L. G. Kuz’mina, N. A. Lobova, J. A. K. Howard, M. V. AlfimovAbstract:New 18-crown-6 ether styryl dye of the 4-pyridine series bearing N -(3-ammoniopropyl) substituent has been synthesized. In MeCN, the dye forms a stable dimeric complex of the syn -head-to-tail type due to the complexation of the ammonium group of one molecule with the crown ether fragment of another. In the dimeric complex, the ethylene bonds of the molecules are close in space and antiparallel, which promotes an efficient stereospecific [2+2] autophotocycloaddition to yield the only rctt -isomer of 1,2,3,4-tetrasubstituted Cyclobutane. The Cyclobutane Derivative structure was confirmed by NMR spectroscopy and X-ray diffraction.
Judith A. K. Howard - One of the best experts on this subject based on the ideXlab platform.
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Synthesis, structure, and stereospecific cross-[2+2] photocycloaddition of pseudodimeric complexes based on ammonioalkyl Derivatives of styryl dyes
New Journal of Chemistry, 2016Co-Authors: Sergey P. Gromov, S. K. Sazonov, Artem I. Vedernikov, Lyudmila G. Kuzmina, Natalia A. Lobova, Yuri A. Strelenko, Judith A. K. HowardAbstract:New 4-pyridine-derived styryl dyes having an ammonioalkyl N-substituent in the pyridine moiety and various substituents in the benzene moiety were synthesized. The formation of pseudodimeric complexes of ammonioalkyl styryl dye Derivatives with 18-crown-6-containing styryl dyes of the 4-pyridine, 4-quinoline, and 2-benzothiazole series was studied by 1H NMR in MeCN-d3. It was found that the stability of supramolecular complexes is mainly determined by the monotopic interaction of the ammonioalkyl group with the crown ether moiety via hydrogen bonding. The components of pseudodimeric complexes undergo stereospecific cross-[2+2] photocycloaddition reaction to give unsymmetrical rctt isomers of Cyclobutane Derivatives owing to the syn-head-to-tail arrangement of components in the initial complex. The efficiency of photoreaction is affected by the N-substituent length, the nature of the substituent in the benzene ring of the ammonioalkyl component, and the nature of the heterocyclic residue of the crown-containing component. The structures of dyes, pseudodimeric complexes, and the Cyclobutane Derivative were studied by X-ray diffraction.
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4-Styrylquinolines: synthesis and study of [2 + 2]-photocycloaddition reactions in thin films and single crystals
New J. Chem., 2007Co-Authors: Lyudmila G. Kuz’mina, Artem I. Vedernikov, Natalia A. Lobova, Judith A. K. Howard, Andrei V. Churakov, Michael V. Alfimov, Sergey P. GromovAbstract:Four new (E)-4-styrylquinoline compounds containing two methoxy substituents or an 18-crown-6-ether fragment were synthesized in order to investigate the [2 + 2]-photocycloaddition (PCA) reaction in the solid state. These compounds reveal different abilities to undergo the photoreaction depending on the packing of the quinoline molecules in thin polycrystalline films and single crystals. The only products from the irradiation of (E)-4-styrylquinolines were an rctt isomer of 1,2,3,4-tetrasubstituted Cyclobutane and, rarely, a Z isomer of the styrylquinoline. The rctt Cyclobutane Derivative was formed as a result of the PCA of centrosymmetric syn-‘head-to-tail’ dimeric pairs of the reactant species that are preorganized in such a way as to promote this reaction. Peculiarities in the crystal packing motifs that are typical for single crystals of 4-styrylquinoline compounds are discussed. The solvate molecules can affect significantly the packing of styrylquinolines. Benzene solvate molecules create a soft, flexible, shell about the dimeric pairs that facilitates the PCA in the single crystal without causing degradation of the crystal. In crystal packing that contains CH2Cl2 and H2O solvate molecules, they are prone to form complicated systems of hydrogen bonds with crown-ether oxygen atoms and each other. This results in distorting the organic molecule geometry toward non-planarity and accomplishing a new type of crystal packing uncommon for styrylheterocycles, in which the PCA is impossible. The topochemical single-crystal-to-single-crystal PCA reaction was monitored for one of the species. Two Cyclobutane Derivatives obtained in single crystals were subjected to recrystallization from a solution. The new single crystals formed belong to different crystal systems, with different unit cell parameters as compared with initial single crystals; significant differences in the geometry of the Cyclobutane molecules were also found. This implies that the Cyclobutane Derivatives obtained in the solid phase have a molecular geometry that is somewhat stressed.
