Rigid-Rod β-Barrel Ion Channels with Internal “Cascade Blue” Cofactors − Catalysis of Amide, Carbonate, and Ester Hydrolysis

Synthesis and Activity of Histidine-Containing Catalytic Peptide Dendrimers

“…Since the rate constant k cat measures the reaction of bound substrate to bound transition state, the stabilizing effect of the protonated histidine would be expected in addition to a possible contribution to substrate binding (see below). A similar bifunctional mechanism has been suggested by other authors for similar ester hydrolysis reactions catalyzed by imidazole containing systems 3 Mechanistic Proposal for Dendrimer Catalyzed Ester Hydrolysis a a Reaction processes: (a) nucleophilic attack of histidine generated an acyl-dendrimer intermediate; (b) general base catalyzed nucleophilic attack of a water molecule 1 Calorimetric Titration of Nonreactive Substrate 4 and the Reaction Product 5 Added to A1 − A4 : Thermodynamic Parameters, Association Constants ( K a ), Number of Binding Sites ( n ) a N His n K a (×10 4 M -1 )Δ H a (kcal/mol)Δ G a (kcal/mol)Δ S a (cal/mol/K) A1 5 3 0.84(±0.22) 0.11(±0.02) −8.36(±2.46) −17.47(±0.45) 31(±10) A2 5 7 1.69(±0.09) 0.27(±0.03) −7.74(±0.59) −19.67(±0.28) 40(±3) A3 5 15 4.78(±0.43) 0.29(±0.05) −8.89(±1.07) −19.91(±0.43) 37(±5) A4 5 31 9.43(±1.5) 0.28(±0.07) −10.06(±1.92) −19.76(±0.62) 32(±8) A1 4 3 2.36(±0.07) 1.66(±0.51) −6.91(±0.33) −24.20(±0.77) 58(±4) A2 4 7 1.86(±0.04) 10.5(±3.2) −12.85(±0.38) −28.79(±0.76) 53(±4) A3 4 15 5.83(±0.03) 56.2(±12.0) −10.85(±0.11) −32.98(±0.53) 74(±2) A4 4 31 9.88(±0.04) 80.8(±15.0) −11.58(±0.10) −33.87(±0.46) 74(±2) a Conditions: A1 0.5 mM, A2 0.2 mM, A3 0.1 mM, A4 0.05 mM, 4 10 mM, 5 10 mM in citrate buffer pH 5.5 (5 mM), at 27 °C. …”

“…Other chemical synthetic strategies to artifical enzymes include the modification of macromolecules (e.g., cyclodextrins) and dendrimers (PAMAM, PPI), emphasizing the preparation of single macromolecular models without regards to enabling evolution and functional selection. Breslow and Schmuck reported a rate acceleration of k cat / k uncat = 120 for the hydrolysis of nitrophenyl phosphate catalyzed by a bis-imidazole substituted β-cyclodextrin 10j. A PPI-based polyimidazole catalyst showed only modest esterase activities with nitrophenyl acetate. 10e-i…”

“…Breslow and Schmuck reported a rate acceleration of k cat / k uncat = 120 for the hydrolysis of nitrophenyl phosphate catalyzed by a bis-imidazole substituted β-cyclodextrin 10j. A PPI-based polyimidazole catalyst showed only modest esterase activities with nitrophenyl acetate. 10e-i…”

Synthesis and Activity of Histidine-Containing Catalytic Peptide Dendrimers

“…Since the rate constant k cat measures the reaction of bound substrate to bound transition state, the stabilizing effect of the protonated histidine would be expected in addition to a possible contribution to substrate binding (see below). A similar bifunctional mechanism has been suggested by other authors for similar ester hydrolysis reactions catalyzed by imidazole containing systems 3 Mechanistic Proposal for Dendrimer Catalyzed Ester Hydrolysis a a Reaction processes: (a) nucleophilic attack of histidine generated an acyl-dendrimer intermediate; (b) general base catalyzed nucleophilic attack of a water molecule 1 Calorimetric Titration of Nonreactive Substrate 4 and the Reaction Product 5 Added to A1 − A4 : Thermodynamic Parameters, Association Constants ( K a ), Number of Binding Sites ( n ) a N His n K a (×10 4 M -1 )Δ H a (kcal/mol)Δ G a (kcal/mol)Δ S a (cal/mol/K) A1 5 3 0.84(±0.22) 0.11(±0.02) −8.36(±2.46) −17.47(±0.45) 31(±10) A2 5 7 1.69(±0.09) 0.27(±0.03) −7.74(±0.59) −19.67(±0.28) 40(±3) A3 5 15 4.78(±0.43) 0.29(±0.05) −8.89(±1.07) −19.91(±0.43) 37(±5) A4 5 31 9.43(±1.5) 0.28(±0.07) −10.06(±1.92) −19.76(±0.62) 32(±8) A1 4 3 2.36(±0.07) 1.66(±0.51) −6.91(±0.33) −24.20(±0.77) 58(±4) A2 4 7 1.86(±0.04) 10.5(±3.2) −12.85(±0.38) −28.79(±0.76) 53(±4) A3 4 15 5.83(±0.03) 56.2(±12.0) −10.85(±0.11) −32.98(±0.53) 74(±2) A4 4 31 9.88(±0.04) 80.8(±15.0) −11.58(±0.10) −33.87(±0.46) 74(±2) a Conditions: A1 0.5 mM, A2 0.2 mM, A3 0.1 mM, A4 0.05 mM, 4 10 mM, 5 10 mM in citrate buffer pH 5.5 (5 mM), at 27 °C. …”

“…Other chemical synthetic strategies to artifical enzymes include the modification of macromolecules (e.g., cyclodextrins) and dendrimers (PAMAM, PPI), emphasizing the preparation of single macromolecular models without regards to enabling evolution and functional selection. Breslow and Schmuck reported a rate acceleration of k cat / k uncat = 120 for the hydrolysis of nitrophenyl phosphate catalyzed by a bis-imidazole substituted β-cyclodextrin 10j. A PPI-based polyimidazole catalyst showed only modest esterase activities with nitrophenyl acetate. 10e-i…”

“…Breslow and Schmuck reported a rate acceleration of k cat / k uncat = 120 for the hydrolysis of nitrophenyl phosphate catalyzed by a bis-imidazole substituted β-cyclodextrin 10j. A PPI-based polyimidazole catalyst showed only modest esterase activities with nitrophenyl acetate. 10e-i…”

Supported Catalytically Active Supramolecular Hydrogels for Continuous Flow Chemistry

“…In the literature, there are only few CASH‐enabled enantioselective processes, and the kinetic resolution of inactivated esters by CASH is still an unsolved challenge . We observed strong discrimination by the supported CASH between l ‐ and d ‐amino acid tert ‐butyl esters 6 : indeed, after a residence time of 30 min, we observed that almost 45 % of the natural enantiomer l ‐ 6 had been hydrolyzed whereas d ‐ 6 had not been yet affected (Figure a).…”

Receptor for Anionic Pyrene Derivatives Provides the Basis for New Biomembrane Assays

“…Interestingly, the K a value assessed for the pyranine−cyclen 1 complex in PBS from fluorometric titrations was very close to the K a value determined by ITC for the 1:1 complexation step in methanol. Although receptors for pyranine of lower or comparable affinity are known, 5d, to the best of our knowledge no fluorescence quenchers for pyranine, active at such low concentration, have been reported to date. The affinity of cyclen 1 to pyranine in aqueous medium compares favorably to that of the other artificial receptors for anionic substrates .…”

Synthesis and Activity of Histidine-Containing Catalytic Peptide Dendrimers

“…Since the rate constant k cat measures the reaction of bound substrate to bound transition state, the stabilizing effect of the protonated histidine would be expected in addition to a possible contribution to substrate binding (see below). A similar bifunctional mechanism has been suggested by other authors for similar ester hydrolysis reactions catalyzed by imidazole containing systems 3 Mechanistic Proposal for Dendrimer Catalyzed Ester Hydrolysis a a Reaction processes: (a) nucleophilic attack of histidine generated an acyl-dendrimer intermediate; (b) general base catalyzed nucleophilic attack of a water molecule 1 Calorimetric Titration of Nonreactive Substrate 4 and the Reaction Product 5 Added to A1 − A4 : Thermodynamic Parameters, Association Constants ( K a ), Number of Binding Sites ( n ) a N His n K a (×10 4 M -1 )Δ H a (kcal/mol)Δ G a (kcal/mol)Δ S a (cal/mol/K) A1 5 3 0.84(±0.22) 0.11(±0.02) −8.36(±2.46) −17.47(±0.45) 31(±10) A2 5 7 1.69(±0.09) 0.27(±0.03) −7.74(±0.59) −19.67(±0.28) 40(±3) A3 5 15 4.78(±0.43) 0.29(±0.05) −8.89(±1.07) −19.91(±0.43) 37(±5) A4 5 31 9.43(±1.5) 0.28(±0.07) −10.06(±1.92) −19.76(±0.62) 32(±8) A1 4 3 2.36(±0.07) 1.66(±0.51) −6.91(±0.33) −24.20(±0.77) 58(±4) A2 4 7 1.86(±0.04) 10.5(±3.2) −12.85(±0.38) −28.79(±0.76) 53(±4) A3 4 15 5.83(±0.03) 56.2(±12.0) −10.85(±0.11) −32.98(±0.53) 74(±2) A4 4 31 9.88(±0.04) 80.8(±15.0) −11.58(±0.10) −33.87(±0.46) 74(±2) a Conditions: A1 0.5 mM, A2 0.2 mM, A3 0.1 mM, A4 0.05 mM, 4 10 mM, 5 10 mM in citrate buffer pH 5.5 (5 mM), at 27 °C. …”

“…Other chemical synthetic strategies to artifical enzymes include the modification of macromolecules (e.g., cyclodextrins) and dendrimers (PAMAM, PPI), emphasizing the preparation of single macromolecular models without regards to enabling evolution and functional selection. Breslow and Schmuck reported a rate acceleration of k cat / k uncat = 120 for the hydrolysis of nitrophenyl phosphate catalyzed by a bis-imidazole substituted β-cyclodextrin 10j. A PPI-based polyimidazole catalyst showed only modest esterase activities with nitrophenyl acetate. 10e-i…”

“…Breslow and Schmuck reported a rate acceleration of k cat / k uncat = 120 for the hydrolysis of nitrophenyl phosphate catalyzed by a bis-imidazole substituted β-cyclodextrin 10j. A PPI-based polyimidazole catalyst showed only modest esterase activities with nitrophenyl acetate. 10e-i…”

Supported Catalytically Active Supramolecular Hydrogels for Continuous Flow Chemistry

“…In the literature, there are only few CASH‐enabled enantioselective processes, and the kinetic resolution of inactivated esters by CASH is still an unsolved challenge . We observed strong discrimination by the supported CASH between l ‐ and d ‐amino acid tert ‐butyl esters 6 : indeed, after a residence time of 30 min, we observed that almost 45 % of the natural enantiomer l ‐ 6 had been hydrolyzed whereas d ‐ 6 had not been yet affected (Figure a).…”

Receptor for Anionic Pyrene Derivatives Provides the Basis for New Biomembrane Assays

“…Interestingly, the K a value assessed for the pyranine−cyclen 1 complex in PBS from fluorometric titrations was very close to the K a value determined by ITC for the 1:1 complexation step in methanol. Although receptors for pyranine of lower or comparable affinity are known, 5d, to the best of our knowledge no fluorescence quenchers for pyranine, active at such low concentration, have been reported to date. The affinity of cyclen 1 to pyranine in aqueous medium compares favorably to that of the other artificial receptors for anionic substrates .…”

Synthesis and Activity of Histidine-Containing Catalytic Peptide Dendrimers

“…Since the rate constant k cat measures the reaction of bound substrate to bound transition state, the stabilizing effect of the protonated histidine would be expected in addition to a possible contribution to substrate binding (see below). A similar bifunctional mechanism has been suggested by other authors for similar ester hydrolysis reactions catalyzed by imidazole containing systems 3 Mechanistic Proposal for Dendrimer Catalyzed Ester Hydrolysis a a Reaction processes: (a) nucleophilic attack of histidine generated an acyl-dendrimer intermediate; (b) general base catalyzed nucleophilic attack of a water molecule 1 Calorimetric Titration of Nonreactive Substrate 4 and the Reaction Product 5 Added to A1 − A4 : Thermodynamic Parameters, Association Constants ( K a ), Number of Binding Sites ( n ) a N His n K a (×10 4 M -1 )Δ H a (kcal/mol)Δ G a (kcal/mol)Δ S a (cal/mol/K) A1 5 3 0.84(±0.22) 0.11(±0.02) −8.36(±2.46) −17.47(±0.45) 31(±10) A2 5 7 1.69(±0.09) 0.27(±0.03) −7.74(±0.59) −19.67(±0.28) 40(±3) A3 5 15 4.78(±0.43) 0.29(±0.05) −8.89(±1.07) −19.91(±0.43) 37(±5) A4 5 31 9.43(±1.5) 0.28(±0.07) −10.06(±1.92) −19.76(±0.62) 32(±8) A1 4 3 2.36(±0.07) 1.66(±0.51) −6.91(±0.33) −24.20(±0.77) 58(±4) A2 4 7 1.86(±0.04) 10.5(±3.2) −12.85(±0.38) −28.79(±0.76) 53(±4) A3 4 15 5.83(±0.03) 56.2(±12.0) −10.85(±0.11) −32.98(±0.53) 74(±2) A4 4 31 9.88(±0.04) 80.8(±15.0) −11.58(±0.10) −33.87(±0.46) 74(±2) a Conditions: A1 0.5 mM, A2 0.2 mM, A3 0.1 mM, A4 0.05 mM, 4 10 mM, 5 10 mM in citrate buffer pH 5.5 (5 mM), at 27 °C. …”

“…Other chemical synthetic strategies to artifical enzymes include the modification of macromolecules (e.g., cyclodextrins) and dendrimers (PAMAM, PPI), emphasizing the preparation of single macromolecular models without regards to enabling evolution and functional selection. Breslow and Schmuck reported a rate acceleration of k cat / k uncat = 120 for the hydrolysis of nitrophenyl phosphate catalyzed by a bis-imidazole substituted β-cyclodextrin 10j. A PPI-based polyimidazole catalyst showed only modest esterase activities with nitrophenyl acetate. 10e-i…”

“…Breslow and Schmuck reported a rate acceleration of k cat / k uncat = 120 for the hydrolysis of nitrophenyl phosphate catalyzed by a bis-imidazole substituted β-cyclodextrin 10j. A PPI-based polyimidazole catalyst showed only modest esterase activities with nitrophenyl acetate. 10e-i…”

Supported Catalytically Active Supramolecular Hydrogels for Continuous Flow Chemistry

“…In the literature, there are only few CASH‐enabled enantioselective processes, and the kinetic resolution of inactivated esters by CASH is still an unsolved challenge . We observed strong discrimination by the supported CASH between l ‐ and d ‐amino acid tert ‐butyl esters 6 : indeed, after a residence time of 30 min, we observed that almost 45 % of the natural enantiomer l ‐ 6 had been hydrolyzed whereas d ‐ 6 had not been yet affected (Figure a).…”

Receptor for Anionic Pyrene Derivatives Provides the Basis for New Biomembrane Assays

“…Interestingly, the K a value assessed for the pyranine−cyclen 1 complex in PBS from fluorometric titrations was very close to the K a value determined by ITC for the 1:1 complexation step in methanol. Although receptors for pyranine of lower or comparable affinity are known, 5d, to the best of our knowledge no fluorescence quenchers for pyranine, active at such low concentration, have been reported to date. The affinity of cyclen 1 to pyranine in aqueous medium compares favorably to that of the other artificial receptors for anionic substrates .…”