The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform
Paulo J Ferreira - One of the best experts on this subject based on the ideXlab platform.
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in situ transmission electron microscopy observations of Sublimation in silver nanoparticles
ACS Nano, 2013Co-Authors: M A Asoro, Desiderio Kovar, Paulo J FerreiraAbstract:In situ heating experiments were performed in a transmission electron microscope (TEM) to monitor the thermal stability of silver nanoparticles. The Sublimation kinetics from isothermal experiments on individual nanoparticles was used to assess the actual temperatures of the nanoparticles by considering the localized heating from the electron beam. For isolated nanoparticles, beam heating under normal TEM operating conditions was found to increase the temperature by tens of degrees. For nominally isothermal experiments, the observed Sublimation temperatures generally decreased with decreasing particle size, in agreement with the predictions from the Kelvin equation. However, Sublimation of smaller nanoparticles was often observed to occur in discrete steps, which led to faceting of the nanoparticles. This discrete behavior differs from that predicted by conventional theory as well as from experimental observations in larger nanoparticles where Sublimation was continuous. A hypothesis that explains the mec...
Henry R Costantino - One of the best experts on this subject based on the ideXlab platform.
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preparation of excipient free recombinant human tissue type plasminogen activator by lyophilization from ammonium bicarbonate solution an investigation of the two stage Sublimation phenomenon
Journal of Pharmaceutical Sciences, 1997Co-Authors: David E Overcashier, Dennis Brooks, Henry R CostantinoAbstract:Dry, excipient-free recombinant human tissue-type plasminogen activator (tPA) powder was prepared by lyophilization from ammonium bicarbonate solution. Ammonium bicarbonate sublimes into ammonia, water, and carbon dioxide upon lyophilization, without causing measurable harm to the protein. There were ∼4 mol of residual ammonium ion per mole of lyophilized tPA. Under certain lyophilization conditions, a large pressure increase in the lyophilizer chamber occurred, presenting a pressure control problem. Microscopy and Sublimation rate measurements on the frozen matrix revealed that ice Sublimation occurred first, followed by the Sublimation of ammonium bicarbonate. Analysis of the sectioned frozen matrix indicated that the bicarbonate salt was evenly distributed throughout the vial, suggesting that the delay of ammonium bicarbonate Sublimation was not due to hindrance by ice. In the two-stage process, ice Sublimation proceeded according to zero-order kinetics, whereas ammonium bicarbonate Sublimation followed a grain-burning (2/3-order) model and was governed by a higher activation enthalpy. In most cases, the Sublimation rate of ammonium bicarbonate in the presence of tPA was lower than that in the absence of the protein. Sublimation activation enthalpy for ammonium bicarbonate in the presence of tPA was 26.1 ± 3.8 kcal/mol, which was ∼10 kcal/mol greater than that for the tPA-free system. Consistent with a prediction from our kinetic modeling, a 6-h extension of primary drying enabled us to conduct lyophilization while maintaining pressure control.
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Preparation of excipient‐free recombinant human tissue‐type plasminogen activator by lyophilization from ammonium bicarbonate solution: An investigation of the two‐stage Sublimation phenomenon
Journal of Pharmaceutical Sciences, 1997Co-Authors: David E Overcashier, Dennis Brooks, Henry R CostantinoAbstract:Dry, excipient-free recombinant human tissue-type plasminogen activator (tPA) powder was prepared by lyophilization from ammonium bicarbonate solution. Ammonium bicarbonate sublimes into ammonia, water, and carbon dioxide upon lyophilization, without causing measurable harm to the protein. There were ∼4 mol of residual ammonium ion per mole of lyophilized tPA. Under certain lyophilization conditions, a large pressure increase in the lyophilizer chamber occurred, presenting a pressure control problem. Microscopy and Sublimation rate measurements on the frozen matrix revealed that ice Sublimation occurred first, followed by the Sublimation of ammonium bicarbonate. Analysis of the sectioned frozen matrix indicated that the bicarbonate salt was evenly distributed throughout the vial, suggesting that the delay of ammonium bicarbonate Sublimation was not due to hindrance by ice. In the two-stage process, ice Sublimation proceeded according to zero-order kinetics, whereas ammonium bicarbonate Sublimation followed a grain-burning (2/3-order) model and was governed by a higher activation enthalpy. In most cases, the Sublimation rate of ammonium bicarbonate in the presence of tPA was lower than that in the absence of the protein. Sublimation activation enthalpy for ammonium bicarbonate in the presence of tPA was 26.1 ± 3.8 kcal/mol, which was ∼10 kcal/mol greater than that for the tPA-free system. Consistent with a prediction from our kinetic modeling, a 6-h extension of primary drying enabled us to conduct lyophilization while maintaining pressure control.
M A Asoro - One of the best experts on this subject based on the ideXlab platform.
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in situ transmission electron microscopy observations of Sublimation in silver nanoparticles
ACS Nano, 2013Co-Authors: M A Asoro, Desiderio Kovar, Paulo J FerreiraAbstract:In situ heating experiments were performed in a transmission electron microscope (TEM) to monitor the thermal stability of silver nanoparticles. The Sublimation kinetics from isothermal experiments on individual nanoparticles was used to assess the actual temperatures of the nanoparticles by considering the localized heating from the electron beam. For isolated nanoparticles, beam heating under normal TEM operating conditions was found to increase the temperature by tens of degrees. For nominally isothermal experiments, the observed Sublimation temperatures generally decreased with decreasing particle size, in agreement with the predictions from the Kelvin equation. However, Sublimation of smaller nanoparticles was often observed to occur in discrete steps, which led to faceting of the nanoparticles. This discrete behavior differs from that predicted by conventional theory as well as from experimental observations in larger nanoparticles where Sublimation was continuous. A hypothesis that explains the mec...
David E Overcashier - One of the best experts on this subject based on the ideXlab platform.
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preparation of excipient free recombinant human tissue type plasminogen activator by lyophilization from ammonium bicarbonate solution an investigation of the two stage Sublimation phenomenon
Journal of Pharmaceutical Sciences, 1997Co-Authors: David E Overcashier, Dennis Brooks, Henry R CostantinoAbstract:Dry, excipient-free recombinant human tissue-type plasminogen activator (tPA) powder was prepared by lyophilization from ammonium bicarbonate solution. Ammonium bicarbonate sublimes into ammonia, water, and carbon dioxide upon lyophilization, without causing measurable harm to the protein. There were ∼4 mol of residual ammonium ion per mole of lyophilized tPA. Under certain lyophilization conditions, a large pressure increase in the lyophilizer chamber occurred, presenting a pressure control problem. Microscopy and Sublimation rate measurements on the frozen matrix revealed that ice Sublimation occurred first, followed by the Sublimation of ammonium bicarbonate. Analysis of the sectioned frozen matrix indicated that the bicarbonate salt was evenly distributed throughout the vial, suggesting that the delay of ammonium bicarbonate Sublimation was not due to hindrance by ice. In the two-stage process, ice Sublimation proceeded according to zero-order kinetics, whereas ammonium bicarbonate Sublimation followed a grain-burning (2/3-order) model and was governed by a higher activation enthalpy. In most cases, the Sublimation rate of ammonium bicarbonate in the presence of tPA was lower than that in the absence of the protein. Sublimation activation enthalpy for ammonium bicarbonate in the presence of tPA was 26.1 ± 3.8 kcal/mol, which was ∼10 kcal/mol greater than that for the tPA-free system. Consistent with a prediction from our kinetic modeling, a 6-h extension of primary drying enabled us to conduct lyophilization while maintaining pressure control.
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Preparation of excipient‐free recombinant human tissue‐type plasminogen activator by lyophilization from ammonium bicarbonate solution: An investigation of the two‐stage Sublimation phenomenon
Journal of Pharmaceutical Sciences, 1997Co-Authors: David E Overcashier, Dennis Brooks, Henry R CostantinoAbstract:Dry, excipient-free recombinant human tissue-type plasminogen activator (tPA) powder was prepared by lyophilization from ammonium bicarbonate solution. Ammonium bicarbonate sublimes into ammonia, water, and carbon dioxide upon lyophilization, without causing measurable harm to the protein. There were ∼4 mol of residual ammonium ion per mole of lyophilized tPA. Under certain lyophilization conditions, a large pressure increase in the lyophilizer chamber occurred, presenting a pressure control problem. Microscopy and Sublimation rate measurements on the frozen matrix revealed that ice Sublimation occurred first, followed by the Sublimation of ammonium bicarbonate. Analysis of the sectioned frozen matrix indicated that the bicarbonate salt was evenly distributed throughout the vial, suggesting that the delay of ammonium bicarbonate Sublimation was not due to hindrance by ice. In the two-stage process, ice Sublimation proceeded according to zero-order kinetics, whereas ammonium bicarbonate Sublimation followed a grain-burning (2/3-order) model and was governed by a higher activation enthalpy. In most cases, the Sublimation rate of ammonium bicarbonate in the presence of tPA was lower than that in the absence of the protein. Sublimation activation enthalpy for ammonium bicarbonate in the presence of tPA was 26.1 ± 3.8 kcal/mol, which was ∼10 kcal/mol greater than that for the tPA-free system. Consistent with a prediction from our kinetic modeling, a 6-h extension of primary drying enabled us to conduct lyophilization while maintaining pressure control.
Desiderio Kovar - One of the best experts on this subject based on the ideXlab platform.
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in situ transmission electron microscopy observations of Sublimation in silver nanoparticles
ACS Nano, 2013Co-Authors: M A Asoro, Desiderio Kovar, Paulo J FerreiraAbstract:In situ heating experiments were performed in a transmission electron microscope (TEM) to monitor the thermal stability of silver nanoparticles. The Sublimation kinetics from isothermal experiments on individual nanoparticles was used to assess the actual temperatures of the nanoparticles by considering the localized heating from the electron beam. For isolated nanoparticles, beam heating under normal TEM operating conditions was found to increase the temperature by tens of degrees. For nominally isothermal experiments, the observed Sublimation temperatures generally decreased with decreasing particle size, in agreement with the predictions from the Kelvin equation. However, Sublimation of smaller nanoparticles was often observed to occur in discrete steps, which led to faceting of the nanoparticles. This discrete behavior differs from that predicted by conventional theory as well as from experimental observations in larger nanoparticles where Sublimation was continuous. A hypothesis that explains the mec...