Reactive intermediates formed upon irradiation of chromophoric dissolved organic matter (CDOM) co... more Reactive intermediates formed upon irradiation of chromophoric dissolved organic matter (CDOM) contribute to the degradation of various organic contaminants in surface waters. Besides well-studied "short-lived" photooxidants, such as triplet state CDOM (3CDOM*) or singlet oxygen, CDOM-derived "long-lived" photooxidants (LLPO) have been suggested as key players in the transformation of electron-rich contaminants. LLPO were hypothesized to mainly consist of phenoxyl radicals derived from phenolic moieties in the CDOM. To test this hypothesis and to better characterize LLPO, the transformation kinetics of selected target compounds (phenols and anilines) induced by a suite of electron-poor model phenoxyl radicals was studied in aerated aqueous solution at pH 8. The phenoxyl radicals were generated by photosensitized oxidation of the parent phenols using aromatic ketones as photosensitizers. Under steady-state irradiation, the presence of any of the electron-poor phenols lead to an enhanced abatement of the phenolic target compounds (at an initial concentration of 1.0 × 10-7 M) compared to solutions containing the photosensitizer but no electron-poor phenol. A trend of increasing reactivity with increasing one-electron reduction potential of the electron-poor phenoxyl radical (range: 0.85‒1.12 V vs. standard hydrogen electrode) was observed. Using the excited triplet state of 2-acetonaphthone as a selective oxidant for phenols, it was observed that the reactivity correlated with the concentration of electron-poor phenoxide present in solution. The rates of transformation of anilines induced by the 4-cyanophenoxyl radical were an order of magnitude smaller than for the phenolic target compounds. This was interpreted as a reduction of the radical intermediates back to the parent compound by the superoxide radical anion. Laser flash photolysis measurements confirmed the formation of the 4-cyanophenoxyl radical in solutions containing 2-acetonaphthone and 4-cyanophenol, and yielded values of (2.6 - 5.3) × 108 M-1 s-1 for the second-order rate constant for the reaction of this radical with 2,4,6-trimethylphenol. These and further results indicate that electron-poor model phenoxyl radicals generated through photosensitized oxidation are useful models to understand the photoreactivity of LLPO as part of the CDOM.
Vynalez se týka způsobu potlaceni mrazove denaturace bilkovin při mrazeni a/nebo lyofilizaci biol... more Vynalez se týka způsobu potlaceni mrazove denaturace bilkovin při mrazeni a/nebo lyofilizaci biologicky aktivnich latek ve formě vzorku
The paper discusses the real-time monitoring of the changing sample morphology during the entire ... more The paper discusses the real-time monitoring of the changing sample morphology during the entire lyophilization (freeze-drying) and vacuum-drying processes of model biopharmaceutical solutions by using an environmental scanning electron microscope (ESEM); the device's micromanipulators were used to study the interior of the samples in-situ without exposing the samples to atmospheric water vapor. The individual collapse temperatures (Tc) of the formulations, pure bovine serum albumin (BSA) and BSA/sucrose mixtures, ranged from -5 to -29 °C. We evaluated the impact of the freezing method (spontaneous freezing, controlled ice nucleation, and spray freezing) on the morphologies of the lyophiles at the constant drying temperature of -20 °C. The formulations with Tcabove-20 °C resulted in the lyophiles' morphologies significantly dependent on the freezing method. We interpret the observations as an interplay of the freezing rates and directionalities, both of which markedly influence the morphologies of the frozen formulations, and, subsequently, the drying process and the mechanical stability of the freeze-dried cake. The formulation with Tcbelow-20 °C yielded a collapsed cake with features independent of the freezing method. The vacuum-drying produced a material with a smooth and pore-free surface, where deep cracks developed at the end of the process.
Photochemical & Photobiological Sciences, 2018
The radical cation of DMABN was investigated as a model intermediate to understand the photodegra... more The radical cation of DMABN was investigated as a model intermediate to understand the photodegradation of anilines in surface waters.
Irradiation of N-protected p-hydroxyphenacyl (pHP) ammonium caged derivatives at 313 nm releases ... more Irradiation of N-protected p-hydroxyphenacyl (pHP) ammonium caged derivatives at 313 nm releases primary and secondary amines or ammonia in nearly quantitative yields via the photo-Favorskii reaction when conducted in acidic or neutral aqueous buffered media. The reaction efficiencies are strongly dependent on the pH with the most efficient and highest yields obtained when the pH of the media maintains the ammonium and p-hydroxyl groups as their conjugate acids. For example, the overall quantum yields of simple secondary amines release are 0.5 at acidic pH from 3.9 to 6.6 dropping to 0.1 at neutral pH 7.0 and 0.01 at pH 8.4. Speciation studies provide an acid-base profile that helps define the scope and limitations of the reaction. When the pKa of the ammonium group is lower than that of the phenolic hydroxyl group, as is the case for the α-amino-protected amino acids, the more acidic ammonium ion deprotonates as the media pH is changed from acidic toward neutral or basic, thus dimi...
The primary photophysical processes of p-hydroxyacetophenone (HA) and the ensuing proton transfer... more The primary photophysical processes of p-hydroxyacetophenone (HA) and the ensuing proton transfer reactions in aqueous solution were investigated by picosecond pump-probe spectroscopy and nanosecond laser flash photolysis. Previous studies have led to mutually inconsistent conclusions. The combined data allow us to rationalize the excited-state proton transfer processes of HA in terms of a comprehensive, well-established reaction scheme. Following fast and quantitative ISC to the triplet state, (3)HA*, adiabatic proton transfer through solvent water simultaneously forms both the anion, (3)A(-)*, and the quinoid triplet enol tautomer, (3)Q*. The latter subsequently equilibrates with its anion (3)A(-)*. Ionization and tautomerization are likely to compete with the desired release reactions of p-hydroxyphenacyl photoremovable protecting groups.
Journal of Photochemistry and Photobiology A: Chemistry, 2007
Empirical solvent polarity parameters were used to evaluate the nature and magnitude of the inter... more Empirical solvent polarity parameters were used to evaluate the nature and magnitude of the intermolecular interactions of eight dipolar organic solvatochromic indicators in aqueous solutions frozen at 253 or 77K, using the concept that is generally employed to study the polarity of liquid solvents or solid surfaces. ET(30), ET(33), and ETN as well as α, acceptor number (AN) (hydrogen-bond donation
Collection of Czechoslovak Chemical Communications, 2004
Efficiencies of the intramolecular triplet-triplet energy transfer (ITET) in various bichromophor... more Efficiencies of the intramolecular triplet-triplet energy transfer (ITET) in various bichromophoric amino acids (glycine, valine, phenylalanine, and sarcosine), dipeptides (glycylglycine, phenylalanylphenylalanine), and a simple diester, with the benzoyl and naphthyl terminal groups serving as donor and acceptor, respectively, have been determined by the steady-state photokinetic measurements. The magnitude of the transfer rate constants (>108 s-1) and the number of bonds separating the chromophores (8 or 11 atoms) suggest a through-space exothermic exchange mechanism in all cases. The influence of interchromophore distance, the character of the connecting chain as well as of side chains, was evaluated. While the most efficient energy transfer was found in a flexible diester and in valine- and sarcosine-based molecules due to the steric effect of the side hydrocarbon groups, the benzyl groups in the phenylalanine and phenylalanylphenylalanine-based bichromophores had a suppressin...
A broadly based investigation of the effects of a diverse array of substituents on the photochemi... more A broadly based investigation of the effects of a diverse array of substituents on the photochemical rearrangement of p-hydroxyphenacyl esters has demonstrated that common substituents such as F, MeO, CN, CO2R, CONH2, and CH3have little effect on the rate and quantum efficiencies for the photo-Favorskii rearrangement and the release of the acid leaving group or on the lifetimes of the reactive triplet state. A decrease in the quantum yields across all substituents was observed for the release and rearrangement when the photolyses were carried out in buffered aqueous media at pHs that exceeded the ground-state pKaof the chromophore where the conjugate base is the predominant form. Otherwise, substituents have only a very modest effect on the photoreaction of these robust chromophores.
Reactive intermediates formed upon irradiation of chromophoric dissolved organic matter (CDOM) co... more Reactive intermediates formed upon irradiation of chromophoric dissolved organic matter (CDOM) contribute to the degradation of various organic contaminants in surface waters. Besides well-studied "short-lived" photooxidants, such as triplet state CDOM (3CDOM*) or singlet oxygen, CDOM-derived "long-lived" photooxidants (LLPO) have been suggested as key players in the transformation of electron-rich contaminants. LLPO were hypothesized to mainly consist of phenoxyl radicals derived from phenolic moieties in the CDOM. To test this hypothesis and to better characterize LLPO, the transformation kinetics of selected target compounds (phenols and anilines) induced by a suite of electron-poor model phenoxyl radicals was studied in aerated aqueous solution at pH 8. The phenoxyl radicals were generated by photosensitized oxidation of the parent phenols using aromatic ketones as photosensitizers. Under steady-state irradiation, the presence of any of the electron-poor phenols lead to an enhanced abatement of the phenolic target compounds (at an initial concentration of 1.0 × 10-7 M) compared to solutions containing the photosensitizer but no electron-poor phenol. A trend of increasing reactivity with increasing one-electron reduction potential of the electron-poor phenoxyl radical (range: 0.85‒1.12 V vs. standard hydrogen electrode) was observed. Using the excited triplet state of 2-acetonaphthone as a selective oxidant for phenols, it was observed that the reactivity correlated with the concentration of electron-poor phenoxide present in solution. The rates of transformation of anilines induced by the 4-cyanophenoxyl radical were an order of magnitude smaller than for the phenolic target compounds. This was interpreted as a reduction of the radical intermediates back to the parent compound by the superoxide radical anion. Laser flash photolysis measurements confirmed the formation of the 4-cyanophenoxyl radical in solutions containing 2-acetonaphthone and 4-cyanophenol, and yielded values of (2.6 - 5.3) × 108 M-1 s-1 for the second-order rate constant for the reaction of this radical with 2,4,6-trimethylphenol. These and further results indicate that electron-poor model phenoxyl radicals generated through photosensitized oxidation are useful models to understand the photoreactivity of LLPO as part of the CDOM.
Vynalez se týka způsobu potlaceni mrazove denaturace bilkovin při mrazeni a/nebo lyofilizaci biol... more Vynalez se týka způsobu potlaceni mrazove denaturace bilkovin při mrazeni a/nebo lyofilizaci biologicky aktivnich latek ve formě vzorku
The paper discusses the real-time monitoring of the changing sample morphology during the entire ... more The paper discusses the real-time monitoring of the changing sample morphology during the entire lyophilization (freeze-drying) and vacuum-drying processes of model biopharmaceutical solutions by using an environmental scanning electron microscope (ESEM); the device's micromanipulators were used to study the interior of the samples in-situ without exposing the samples to atmospheric water vapor. The individual collapse temperatures (Tc) of the formulations, pure bovine serum albumin (BSA) and BSA/sucrose mixtures, ranged from -5 to -29 °C. We evaluated the impact of the freezing method (spontaneous freezing, controlled ice nucleation, and spray freezing) on the morphologies of the lyophiles at the constant drying temperature of -20 °C. The formulations with Tcabove-20 °C resulted in the lyophiles' morphologies significantly dependent on the freezing method. We interpret the observations as an interplay of the freezing rates and directionalities, both of which markedly influence the morphologies of the frozen formulations, and, subsequently, the drying process and the mechanical stability of the freeze-dried cake. The formulation with Tcbelow-20 °C yielded a collapsed cake with features independent of the freezing method. The vacuum-drying produced a material with a smooth and pore-free surface, where deep cracks developed at the end of the process.
Photochemical & Photobiological Sciences, 2018
The radical cation of DMABN was investigated as a model intermediate to understand the photodegra... more The radical cation of DMABN was investigated as a model intermediate to understand the photodegradation of anilines in surface waters.
Irradiation of N-protected p-hydroxyphenacyl (pHP) ammonium caged derivatives at 313 nm releases ... more Irradiation of N-protected p-hydroxyphenacyl (pHP) ammonium caged derivatives at 313 nm releases primary and secondary amines or ammonia in nearly quantitative yields via the photo-Favorskii reaction when conducted in acidic or neutral aqueous buffered media. The reaction efficiencies are strongly dependent on the pH with the most efficient and highest yields obtained when the pH of the media maintains the ammonium and p-hydroxyl groups as their conjugate acids. For example, the overall quantum yields of simple secondary amines release are 0.5 at acidic pH from 3.9 to 6.6 dropping to 0.1 at neutral pH 7.0 and 0.01 at pH 8.4. Speciation studies provide an acid-base profile that helps define the scope and limitations of the reaction. When the pKa of the ammonium group is lower than that of the phenolic hydroxyl group, as is the case for the α-amino-protected amino acids, the more acidic ammonium ion deprotonates as the media pH is changed from acidic toward neutral or basic, thus dimi...
The primary photophysical processes of p-hydroxyacetophenone (HA) and the ensuing proton transfer... more The primary photophysical processes of p-hydroxyacetophenone (HA) and the ensuing proton transfer reactions in aqueous solution were investigated by picosecond pump-probe spectroscopy and nanosecond laser flash photolysis. Previous studies have led to mutually inconsistent conclusions. The combined data allow us to rationalize the excited-state proton transfer processes of HA in terms of a comprehensive, well-established reaction scheme. Following fast and quantitative ISC to the triplet state, (3)HA*, adiabatic proton transfer through solvent water simultaneously forms both the anion, (3)A(-)*, and the quinoid triplet enol tautomer, (3)Q*. The latter subsequently equilibrates with its anion (3)A(-)*. Ionization and tautomerization are likely to compete with the desired release reactions of p-hydroxyphenacyl photoremovable protecting groups.
Journal of Photochemistry and Photobiology A: Chemistry, 2007
Empirical solvent polarity parameters were used to evaluate the nature and magnitude of the inter... more Empirical solvent polarity parameters were used to evaluate the nature and magnitude of the intermolecular interactions of eight dipolar organic solvatochromic indicators in aqueous solutions frozen at 253 or 77K, using the concept that is generally employed to study the polarity of liquid solvents or solid surfaces. ET(30), ET(33), and ETN as well as α, acceptor number (AN) (hydrogen-bond donation
Collection of Czechoslovak Chemical Communications, 2004
Efficiencies of the intramolecular triplet-triplet energy transfer (ITET) in various bichromophor... more Efficiencies of the intramolecular triplet-triplet energy transfer (ITET) in various bichromophoric amino acids (glycine, valine, phenylalanine, and sarcosine), dipeptides (glycylglycine, phenylalanylphenylalanine), and a simple diester, with the benzoyl and naphthyl terminal groups serving as donor and acceptor, respectively, have been determined by the steady-state photokinetic measurements. The magnitude of the transfer rate constants (>108 s-1) and the number of bonds separating the chromophores (8 or 11 atoms) suggest a through-space exothermic exchange mechanism in all cases. The influence of interchromophore distance, the character of the connecting chain as well as of side chains, was evaluated. While the most efficient energy transfer was found in a flexible diester and in valine- and sarcosine-based molecules due to the steric effect of the side hydrocarbon groups, the benzyl groups in the phenylalanine and phenylalanylphenylalanine-based bichromophores had a suppressin...
A broadly based investigation of the effects of a diverse array of substituents on the photochemi... more A broadly based investigation of the effects of a diverse array of substituents on the photochemical rearrangement of p-hydroxyphenacyl esters has demonstrated that common substituents such as F, MeO, CN, CO2R, CONH2, and CH3have little effect on the rate and quantum efficiencies for the photo-Favorskii rearrangement and the release of the acid leaving group or on the lifetimes of the reactive triplet state. A decrease in the quantum yields across all substituents was observed for the release and rearrangement when the photolyses were carried out in buffered aqueous media at pHs that exceeded the ground-state pKaof the chromophore where the conjugate base is the predominant form. Otherwise, substituents have only a very modest effect on the photoreaction of these robust chromophores.
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