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Supramolecular control of photoeliminations (IP-2014-09-6312)
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5 Research products, page 1 of 1

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  • Open Access Croatian
    Authors: 
    Katarina Zlatić; Ivana Antol; Lidija Uzelac; Ana-Matea Mikecin Dražić; Marijeta Kralj; Cornelia Bohne; Nikola Basarić;
    Publisher: American Chemical Society
    Country: Croatia
    Project: HRZZ | A multidisciplinary appro... (IP-2013-11-5660), NSERC , HRZZ | Supramolecular control of... (IP-2014-09-6312)

    A novel approach for the photolabeling of proteins by a BODIPY fluorophore is reported that is based on an anti-Kasha photochemi-cal reaction from an upper singlet excited state (Sn) leading to the deamination of the BODIPY quinone methide precursor. On the other hand, the high photochemical stability of the dye upon excita-tion by visible light to S1 allows for the selective fluorescence detection from the dye or dye-protein adduct, without concomitant bleaching or hydrolysis of the protein-dye adduct. Therefore, pho-tolabeling and fluorescence monitoring can be uncoupled by using different excitation wavelengths. Combined theoretical and experi-mental studies by preparative irradiations, fluorescence and laser flash photolysis fully disclose the photophysical properties of the dye and its anti- Kasha photochemical reactivity. The application of the dye was demonstrated on photolabeling of bovine serum albu-min.

  • Open Access
    Authors: 
    Đani Škalamera; Kata Mlinarić-Majerski; Irena Martin Kleiner; Marijeta Kralj; Jessy Oake; Peter Wan; Cornelia Bohne; Nikola Basarić;
    Publisher: American Chemical Society (ACS)
    Country: Croatia
    Project: HRZZ | Supramolecular control of... (IP-2014-09-6312)

    Anthrols 2-7 were synthesized and their photochemical reactivity investigated by irradiations in aq. CH3OH. Upon excitation with visible light (λ > 400 nm) in methanolic solutions they undergo photodehydration or photodeamination and deliver methyl ethers, most probably via quinone methides (QMs), with methanolysis quantum efficiencies ΦR = 0.02-0.3. Photophysical properties of 2-7 were determined by steady-state fluorescence and time-correlated single photon counting. Generally, anthrols 2-7 are highly fluorescent in aprotic solvents (ΦF = 0.5-0.9), whereas in aqueous solutions the fluorescence is quenched due to excited state proton transfer (ESPT) to solvent. The exception is amine 4 that undergoes excited state intramolecular proton transfer (ESIPT) in neat CH3CN where photodeamination is probably coupled to ESIPT. Photodehydration may take place via ESIPT (or ESPT) that is coupled to dehydration, or via a hitherto undisclosed pathway that involves photoionization and deprotonation of radical-cation, followed by homolytic cleavage of the alcohol OH group from the phenoxyl radical. QMs were detected by laser flash photolysis (LFP) and their reactivity with nucleophiles investigated. Biological investigation of 2-5 on human cancer cell lines showed enhancement of antiproliferative effect upon exposure of cells to irradiation by visible light, probably due to formation of electrophilic species such as QMs.

  • Open Access
    Authors: 
    Sermsiri Chaiwongwattana; Đani Škalamera; Nadja Doslic; Cornelia Bohne; Nikola Basarić;
    Publisher: Royal Society of Chemistry (RSC)
    Country: Croatia
    Project: NSERC , HRZZ | Supramolecular control of... (IP-2014-09-6312), HRZZ | Svjetlo na molekulama: is... (IP-2016-06-1142)

    Photophysical properties and excited state intramolecular proton transfer (ESIPT) reactivity for anthrol carbaldehydes 1-5 have been investigated computationally and experimentally by steady-state and time-resolved fluorescence and laser flash photolysis (LFP). 1, 2-Disubstituted anthrol carbaldehydes 1 and 2 are not ESIPT reactive, contrary to naphthol analogues. The main deactivation channels from S1 for 1 and 2 are fluorescence (ΦF = 0.1-0.2) and intersystem crossing (ISC) to almost isoenergetic T2 states. The triplet states from 1 and 2 were detected by LFP (in N2-purged CH3CN, τ = 15 ± 2 μs for 1, and τ = 5.5 ± 0.1 μs for 2). In contrast, 2, 3-disubstituted anthrols 3-5 undergo efficient barrierless ultrafast ESIPT. However, the typical dual emission from locally excited states and ESIPT tautomers were not observed since ESIPT proceeds via a conical intersection with S0 delivering the keto-tautomer in the hot ground state. Therefore, anthrols 3-5 are about ten times less fluorescent compared to 1 and 2, and the emission for 3-5 originates from less-populated conformers that cannot undergo ESIPT. Keto-tautomers for 3-5 were detected in CH3CN by LFP (λmax = 370 nm, τ = 30-40 ns). The difference in ESIPT reactivity for 1-3 was fully disclosed by calculations at ADC(2)/aug-cc-pVDZ level of theory, and particularly, by calculation of charge redistribution upon excitation to S1. Only 2, 3-disubstituted anthrols exhibit polarization in S1 that increases the electron density on the carbonyl and decreases this density on the phenolic OH, setting the stage for ultrafast ESIPT.

  • Closed Access English
    Authors: 
    Nikola Cindro; Ivana Antol; Kata Mlinarić-Majerski; Ivan Halasz; Peter Wan; Nikola Basarić;
    Country: Croatia
    Project: HRZZ | Photochemistry of polycyc... (02.05/25), NSERC , HRZZ | Supramolecular control of... (IP-2014-09-6312)

    Three m-substituted phenol derivatives, each with a labile benzylic alcohol group and bearing either protoadamantyl 4, homoadamantyl 5, or a cyclohexyl group 6, were synthesized and their potential thermal acid-catalyzed and photochemical solvolytic reactivity studied, using preparative irradiations, fluorescence measurements, nanosecond laser flash photolysis, and quantum chemical calculations. The choice of m-hydroxy-substitution was driven by the potential for these phenolic systems to generate m-quinone methides on photolysis which could ultimately drive the excited state pathway, as opposed to forming simple benzylic carbocations in the corresponding thermal route. Indeed, thermal acid-catalyzed reactions gave the corresponding cations which undergo rearrangement and elimination from 4, only elimination from 5, and substitution and elimination from 6. On the other hand, photoexcitation of 4-6 to S1 in a polar protic solvent, proton dissociation from the phenol coupled by elimination of the benzylic OH (as hydroxide ion) gave zwitterions (formal m-quinone methides). The zwitterions exhibit different reactivity from the corresponding cations due to a difference in charge distribution, as shown by DFT calculations. Thus, protoadamantyl zwitterion has a less non-classical character than the corresponding cation so it does not undergo 1, 2-shift of the carbon atom, as observed in the acid-catalyzed reaction.

  • Open Access
    Authors: 
    Đani Škalamera; Cornelia Bohne; Stephan Landgraf; Nikola Basarić;
    Publisher: American Chemical Society (ACS)
    Country: Croatia
    Project: NSERC , HRZZ | Supramolecular control of... (IP-2014-09-6312)

    Derivatives of p-cresol 1-4 were synthesized and their photochemical reactivity, acid-base and photophysical properties were investigated. The photoreactivity of amines 1 and 3 is different from that for the corresponding ammonium salts 2 and 4. All compounds have low fluorescence quantum yields because the excited states undergo deamination reactions and for all cresols the formation of quinone methides (QMs) was observed by laser flash photolysis. The reactivity observed is a consequence of the higher acidity of the S1 states of these p-cresols and the ability for excited-state intramolecular proton transfer (ESIPT) to occur in the case of 1 and 3, but not for salts 2 and 4. In aqueous solvent deamination depends largely on the prototropic form of the molecule. The most efficient deamination takes place when monoamine is in the zwitterionic form (pH 9-11) or diamine is in the monocationic form (pH 7-9). QM1, QM3 and QM4 react with nucleophiles and QM1 exhibits shorter lifetime when formed from 1 (τ in CH3CN = 5 ms) then from 2 (τ in CH3CN = 200 ms) due to the reaction with eliminated dimethylamine, which acts as a nucleophile in the case of QM1. Bifunctional QM4 undergoes two types of reactions with nucleophiles, giving adducts or new QM species. The mechanistic diversity uncovered is of significance to biological systems, such as for the use of bifunctional QMs to achieve DNA cross-linking.

Advanced search in
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Supramolecular control of photoeliminations (IP-2014-09-6312)
Include:
The following results are related to Canada. Are you interested to view more results? Visit OpenAIRE - Explore.
5 Research products, page 1 of 1
  • Open Access Croatian
    Authors: 
    Katarina Zlatić; Ivana Antol; Lidija Uzelac; Ana-Matea Mikecin Dražić; Marijeta Kralj; Cornelia Bohne; Nikola Basarić;
    Publisher: American Chemical Society
    Country: Croatia
    Project: HRZZ | A multidisciplinary appro... (IP-2013-11-5660), NSERC , HRZZ | Supramolecular control of... (IP-2014-09-6312)

    A novel approach for the photolabeling of proteins by a BODIPY fluorophore is reported that is based on an anti-Kasha photochemi-cal reaction from an upper singlet excited state (Sn) leading to the deamination of the BODIPY quinone methide precursor. On the other hand, the high photochemical stability of the dye upon excita-tion by visible light to S1 allows for the selective fluorescence detection from the dye or dye-protein adduct, without concomitant bleaching or hydrolysis of the protein-dye adduct. Therefore, pho-tolabeling and fluorescence monitoring can be uncoupled by using different excitation wavelengths. Combined theoretical and experi-mental studies by preparative irradiations, fluorescence and laser flash photolysis fully disclose the photophysical properties of the dye and its anti- Kasha photochemical reactivity. The application of the dye was demonstrated on photolabeling of bovine serum albu-min.

  • Open Access
    Authors: 
    Đani Škalamera; Kata Mlinarić-Majerski; Irena Martin Kleiner; Marijeta Kralj; Jessy Oake; Peter Wan; Cornelia Bohne; Nikola Basarić;
    Publisher: American Chemical Society (ACS)
    Country: Croatia
    Project: HRZZ | Supramolecular control of... (IP-2014-09-6312)

    Anthrols 2-7 were synthesized and their photochemical reactivity investigated by irradiations in aq. CH3OH. Upon excitation with visible light (λ > 400 nm) in methanolic solutions they undergo photodehydration or photodeamination and deliver methyl ethers, most probably via quinone methides (QMs), with methanolysis quantum efficiencies ΦR = 0.02-0.3. Photophysical properties of 2-7 were determined by steady-state fluorescence and time-correlated single photon counting. Generally, anthrols 2-7 are highly fluorescent in aprotic solvents (ΦF = 0.5-0.9), whereas in aqueous solutions the fluorescence is quenched due to excited state proton transfer (ESPT) to solvent. The exception is amine 4 that undergoes excited state intramolecular proton transfer (ESIPT) in neat CH3CN where photodeamination is probably coupled to ESIPT. Photodehydration may take place via ESIPT (or ESPT) that is coupled to dehydration, or via a hitherto undisclosed pathway that involves photoionization and deprotonation of radical-cation, followed by homolytic cleavage of the alcohol OH group from the phenoxyl radical. QMs were detected by laser flash photolysis (LFP) and their reactivity with nucleophiles investigated. Biological investigation of 2-5 on human cancer cell lines showed enhancement of antiproliferative effect upon exposure of cells to irradiation by visible light, probably due to formation of electrophilic species such as QMs.

  • Open Access
    Authors: 
    Sermsiri Chaiwongwattana; Đani Škalamera; Nadja Doslic; Cornelia Bohne; Nikola Basarić;
    Publisher: Royal Society of Chemistry (RSC)
    Country: Croatia
    Project: NSERC , HRZZ | Supramolecular control of... (IP-2014-09-6312), HRZZ | Svjetlo na molekulama: is... (IP-2016-06-1142)

    Photophysical properties and excited state intramolecular proton transfer (ESIPT) reactivity for anthrol carbaldehydes 1-5 have been investigated computationally and experimentally by steady-state and time-resolved fluorescence and laser flash photolysis (LFP). 1, 2-Disubstituted anthrol carbaldehydes 1 and 2 are not ESIPT reactive, contrary to naphthol analogues. The main deactivation channels from S1 for 1 and 2 are fluorescence (ΦF = 0.1-0.2) and intersystem crossing (ISC) to almost isoenergetic T2 states. The triplet states from 1 and 2 were detected by LFP (in N2-purged CH3CN, τ = 15 ± 2 μs for 1, and τ = 5.5 ± 0.1 μs for 2). In contrast, 2, 3-disubstituted anthrols 3-5 undergo efficient barrierless ultrafast ESIPT. However, the typical dual emission from locally excited states and ESIPT tautomers were not observed since ESIPT proceeds via a conical intersection with S0 delivering the keto-tautomer in the hot ground state. Therefore, anthrols 3-5 are about ten times less fluorescent compared to 1 and 2, and the emission for 3-5 originates from less-populated conformers that cannot undergo ESIPT. Keto-tautomers for 3-5 were detected in CH3CN by LFP (λmax = 370 nm, τ = 30-40 ns). The difference in ESIPT reactivity for 1-3 was fully disclosed by calculations at ADC(2)/aug-cc-pVDZ level of theory, and particularly, by calculation of charge redistribution upon excitation to S1. Only 2, 3-disubstituted anthrols exhibit polarization in S1 that increases the electron density on the carbonyl and decreases this density on the phenolic OH, setting the stage for ultrafast ESIPT.

  • Closed Access English
    Authors: 
    Nikola Cindro; Ivana Antol; Kata Mlinarić-Majerski; Ivan Halasz; Peter Wan; Nikola Basarić;
    Country: Croatia
    Project: HRZZ | Photochemistry of polycyc... (02.05/25), NSERC , HRZZ | Supramolecular control of... (IP-2014-09-6312)

    Three m-substituted phenol derivatives, each with a labile benzylic alcohol group and bearing either protoadamantyl 4, homoadamantyl 5, or a cyclohexyl group 6, were synthesized and their potential thermal acid-catalyzed and photochemical solvolytic reactivity studied, using preparative irradiations, fluorescence measurements, nanosecond laser flash photolysis, and quantum chemical calculations. The choice of m-hydroxy-substitution was driven by the potential for these phenolic systems to generate m-quinone methides on photolysis which could ultimately drive the excited state pathway, as opposed to forming simple benzylic carbocations in the corresponding thermal route. Indeed, thermal acid-catalyzed reactions gave the corresponding cations which undergo rearrangement and elimination from 4, only elimination from 5, and substitution and elimination from 6. On the other hand, photoexcitation of 4-6 to S1 in a polar protic solvent, proton dissociation from the phenol coupled by elimination of the benzylic OH (as hydroxide ion) gave zwitterions (formal m-quinone methides). The zwitterions exhibit different reactivity from the corresponding cations due to a difference in charge distribution, as shown by DFT calculations. Thus, protoadamantyl zwitterion has a less non-classical character than the corresponding cation so it does not undergo 1, 2-shift of the carbon atom, as observed in the acid-catalyzed reaction.

  • Open Access
    Authors: 
    Đani Škalamera; Cornelia Bohne; Stephan Landgraf; Nikola Basarić;
    Publisher: American Chemical Society (ACS)
    Country: Croatia
    Project: NSERC , HRZZ | Supramolecular control of... (IP-2014-09-6312)

    Derivatives of p-cresol 1-4 were synthesized and their photochemical reactivity, acid-base and photophysical properties were investigated. The photoreactivity of amines 1 and 3 is different from that for the corresponding ammonium salts 2 and 4. All compounds have low fluorescence quantum yields because the excited states undergo deamination reactions and for all cresols the formation of quinone methides (QMs) was observed by laser flash photolysis. The reactivity observed is a consequence of the higher acidity of the S1 states of these p-cresols and the ability for excited-state intramolecular proton transfer (ESIPT) to occur in the case of 1 and 3, but not for salts 2 and 4. In aqueous solvent deamination depends largely on the prototropic form of the molecule. The most efficient deamination takes place when monoamine is in the zwitterionic form (pH 9-11) or diamine is in the monocationic form (pH 7-9). QM1, QM3 and QM4 react with nucleophiles and QM1 exhibits shorter lifetime when formed from 1 (τ in CH3CN = 5 ms) then from 2 (τ in CH3CN = 200 ms) due to the reaction with eliminated dimethylamine, which acts as a nucleophile in the case of QM1. Bifunctional QM4 undergoes two types of reactions with nucleophiles, giving adducts or new QM species. The mechanistic diversity uncovered is of significance to biological systems, such as for the use of bifunctional QMs to achieve DNA cross-linking.