Ricardo Rojas - Academia.edu (original) (raw)

Papers by Ricardo Rojas

Microporous and Mesoporous Materials, 2008

Acetate-containing nickel zinc layered hydroxysalts LHS-[Ni-Zn-AcO] have been exchanged with M 2+... more Acetate-containing nickel zinc layered hydroxysalts LHS-[Ni-Zn-AcO] have been exchanged with M 2+ -edta complexes (M 2+ @Cu 2+ , Cd 2+ and Mn 2+ ) at different pHs. Upon a careful selection of the reaction conditions, a rather large concentration of metal chelate units in the interlayer space is achieved, as concluded from element chemical analyses, powder X-ray diffraction and FT-IR spectroscopy results.

Journal of Zoology, 2012

ABSTRACT

Journal of Solid State Chemistry, 2004

Interlayer acetate anions in layered double hydroxyacetates of Ni 2+ and Zn 2+ have been exchange... more Interlayer acetate anions in layered double hydroxyacetates of Ni 2+ and Zn 2+ have been exchanged by oxovanadates following three synthetic routes (at 60 C, under hydrothermal conditions and after preswelling with caprylate anions) and different pH; direct exchange at room temperature was not successful. Complete exchange was achieved under adequated conditions, and the precise nature of the interlayer anion depends on the pH during exchange: at low pH (4.5), the presence of a-VO 3 chains, with anchoring (grafting) of the species to the hydroxide layers, is proposed. At higher pH (9.5) V 2 O 7 4À species are present in the interlayer. Thermal decomposition of these vanadate-intercalated products leads to formation of orthorhombic Ni 2+ and Zn 2+ vanadates, together with NiO. r 2004 Elsevier Inc. All rights reserved.

Journal of Materials Chemistry, 2002

ABSTRACT First published as an Advance Article on the web 21st February 2002 Layered Ni,Zn hydrox... more ABSTRACT First published as an Advance Article on the web 21st February 2002 Layered Ni,Zn hydroxyacetates have been prepared by hydrothermal methods and have been used for anion exchange of the original acetate anions by chloride, bromide, carbonate, nitrate, sulfate, and phosphate. Exchange was complete in all cases. The solids have been characterised by elemental chemical analysis, powder X-ray diffraction, thermal analysis (thermogravimetric and differential), FT-IR spectroscopy and electron microscopy; XAS spectra were also recorded in some cases. Thermal decomposition in air leads to removal of interlayer water at 150–200 uC. Mixed NiO–ZnO oxides are formed at higher temperatures. Chloride, sulfate, and phosphate salts are also formed at intermediate calcination temperature, and phosphate remains even after calcination at 1000 uC.

The Journal of Infectious Diseases, 2006

Background. Failure of antimonial therapy has been increasingly reported in anthroponotic viscera... more Background. Failure of antimonial therapy has been increasingly reported in anthroponotic visceral leishmaniasis and in cutaneous disease. The role of drug resistance in treatment failure has been difficult to ascertain because therapeutic response is multifactorial, and the efficacy of antimonial drugs depends on an effective immune response. In this study, we sought to determine whether standard treatment selects for resistant organisms and whether drug resistance contributes to treatment failure.

The Journal of Infectious Diseases, 2010

Background. T cell differentiation determines susceptibility and resistance to experimental cutan... more Background. T cell differentiation determines susceptibility and resistance to experimental cutaneous leishmaniasis, yet mixed T1/Th2 responses characterize the clinical spectrum of human infection with Leishmania (Viannia) species.

Journal of Geophysical Research, 2004

Journal of Colloid and Interface Science, 2010

Layered double hydroxides (LDHs) weathering in acidic media is one of the main features that affe... more Layered double hydroxides (LDHs) weathering in acidic media is one of the main features that affects their applications in drug delivery systems. In this work, the dissolution kinetics of biocompatible Mg-Al LDHs was studied at different initial pH values and solid concentrations using a simple and fast experimental method that coupled flow injection analysis and amperometric detection. A carbonate intercalated sample was used to determine the controlling step of the process and the dissolution mechanism. Finally, the study was extended to an ibuprofen intercalated LDH. The obtained results showed that the weathering process was mainly controlled by the exposed area and surface reactivity of LDHs particles. The dissolution mechanism at the particle surface was described in two steps: fast formation of surface reactive sites by hydroxyl group protonation and slow detachment of metal ions from surface. At strongly acidic conditions, the reaction rate was pH dependent due to the equilibrium between protonated (active) and deprotonated (inactive) hydroxyl groups. On the other hand, at mildly acidic conditions, the dissolution behavior was also ruled by the equilibrium attained between the particle surface reactive sites and the dissolved species. LDHs solubility and dissolution rate presented strong dependence with the interlayer anion. The ibuprofen intercalated sample was more soluble and more rapidly dissolved than the carbonate intercalated one in acetic/acetate buffer. On the other hand, the dissolution mechanism was invariant with the interlayer anion.

Journal of Colloid and Interface Science, 2009

EDTA modified layered double hydroxides (LDHs) were investigated as potential sorbents to remedia... more EDTA modified layered double hydroxides (LDHs) were investigated as potential sorbents to remediate heavy metals pollution. The polidentate ligand was introduced by an exchange method in a Zn-Al-LDH, which takes place with partial erosion of the layers, causing the intercalation of [Zn(EDTA)] 2− complex instead of the ligand. [Cu(H 2 O) 6 ] 2+ cation was selected as a model cation to study the uptake mechanism, exploring the elimination kinetics from the first minutes up to the steady state. A flow injection analysis system coupled to an amperometric detector (FIA-AM) was applied to perform fast and reliable [Cu(H 2 O) 6 ] 2+ determinations in monodisperse solid-aqueous solution systems. Furthermore, the sorbent stability was determined as a function of the pH and the nitrate concentration. The [Cu(H 2 O) 6 ] 2+ elimination is produced by an exchange reaction with [Zn(EDTA)] 2− anions placed either in the solid interlayer or in the aqueous solution, this last being released from the sorbent. Additional [Cu(H 2 O) 6 ] 2+ removal is produced by Cu(OH) 2 precipitation at high copper concentrations due to the LDHs high pH buffering capacity. The sorbent removes [Cu(H 2 O) 6 ] 2+ with high affinity in a wide concentration range. The elimination process reaches equilibrium in less than 30 min and leaves metal cation concentrations lower than 0.05 ppm in the supernatants.

Journal of Colloid and Interface Science, 2011

Layered double hydroxides (LDHs) reactivity and interfacial behavior are closely interconnected a... more Layered double hydroxides (LDHs) reactivity and interfacial behavior are closely interconnected and control particle properties relevant to the wide range of these solids' applications. Despite their importance, their relationship has been hardly described. In this work, chloride and dodecylsulfate (DDS(-)) intercalated LDHs are studied combining experimental data (electrophoretic mobility and contact angle measurements, hydroxyl and organic compounds uptake) and a simple mathematical model that includes anion-binding and acid-base reactions. This approach evidences the anion effect on LDHs interfacial behavior, reflected in the opposite particle charge and the different surface hydrophobic/hydrophilic character. LDHs reactivity are also determined by the interlayer composition, as demonstrated by the cation uptake capability of the DDS(-) intercalated sample. Consequently, the interlayer anion modifies the LDHs interfacial properties and reactivity, which in turn extends the customization capacity of these solids.

International Journal of Control, 1993

This paper proposes an iterative algorithm for achieving robust performance optimization for unce... more This paper proposes an iterative algorithm for achieving robust performance optimization for uncertain linear systems. The objective is to obtain a controller which minimizes the weighted infinity norm of sensitivity for the worst uncertainty scenario. The algorithm seeks ...

IEEE Control Systems, 2000

We propose that the logarithms of closed-loop poles be drawn instead of the plain poles in root l... more We propose that the logarithms of closed-loop poles be drawn instead of the plain poles in root loci for continuous-time linear loops, to help visualize significant closed-loop frequency responses simultaneously at specific values of the changing open-loop parameters. We also promote the splitting of the loci into pairs of graphs showing the imaginary and real parts of the logarithms of

Electrochimica Acta, 2009

Fast and simple quantitative determination in dispersed systems (layered double hydroxides -LDHss... more Fast and simple quantitative determination in dispersed systems (layered double hydroxides -LDHssuspensions in aqueous solutions) was performed by a procedure that couples flow injection and amperometric detection (FI-AM). LDH dispersions are injected in a continuous flow (1 mL min −1 ) of 0.05 mol L −1 KNO 3 solution and [Cu(H 2 O) 6 ] 2+ , used as a probe, is detected at a glassy carbon electrode housed in a flat electrochemical cell. The current intensity, recorded at the selected working potential (−0.25 V vs Ag/AgCl/NaCl (3 mol L −1 )), presents a linear relationship with [Cu(H 2 O) 6 ] 2+ concentration and the procedure offers high sensitivity (slope = 0.036 A/(mol L −1 )), a low detection limit (=0.7 mol L −1 ) and a wide quantification range (4-200 mol L −1 ).

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2013

Agricultura Técnica, 2006

... PVY) on Solanaceus Crops Malezas del Género Datura como Factor Epidemiológico del Virus del m... more ... PVY) on Solanaceus Crops Malezas del Género Datura como Factor Epidemiológico del Virus del mosaico de la alfalfa (AMV), Virus del mosaico del pepino (CMV) y Virus Y de la papa (PVY) en Solanáceas Cultivadas Juan Ormeño 1 *,Paulina Sepúlveda 1 ,Ricardo Rojas 2 ...

Several approaches for structure estimation have been developed in recent years, which are mostly... more Several approaches for structure estimation have been developed in recent years, which are mostly based on exhaustive singularity tests of covariance matrices. This work intends to reduce the computational cost of the previous methods, by knowing the rank of (instrumental) finite-sampl e covariance matrices. I. I NTRODUCTION

Automatica, 2000

This paper is devoted to the problem of global (local) stabilization of a prescribed subset of th... more This paper is devoted to the problem of global (local) stabilization of a prescribed subset of the state space for a passive affine nonlinear system. It is assumed that the desired attractive set can be described as an inverse image of zero value of some smooth nonnegative function, and that this function does not increase along the solutions of the

Applied Clay Science, 2008

Zn–Al layered double hydroxides with different MII/MIII ratios were synthesized by the coprecipit... more Zn–Al layered double hydroxides with different MII/MIII ratios were synthesized by the coprecipitation method and the obtained solids were characterized by powder X-ray diffraction, infrared spectroscopy, acid–base potentiometric titrations, electrophoretic mobility and modeling of the electrical double layer. As general behavior, increasing hydroxyl adsorption with increasing pH and decreasing supporting electrolyte concentration takes place between pH 7 and 12. The

Applied Clay Science, 2010

ABSTRACT An acetate-intercalated Ni–Zn layered hydroxide salt (LHS) was exchanged with chromate a... more ABSTRACT An acetate-intercalated Ni–Zn layered hydroxide salt (LHS) was exchanged with chromate anions, achieving a rather large oxometalate concentration, which almost completely balanced the positive charges of the layers, as concluded from element chemical analysis, powder X-ray diffraction, and FT-IR spectroscopy results. Thermal decomposition of the solid led to dehydration and chromate anion grafting, followed by dehydroxylation of the host and reduction of the chromate anions. The solid then lost the layer structure, forming solids with large micro and mesoporosity, which corresponded to poorly crystallized (Zn, Ni)–Cr spinels, as well as nickel and zinc oxides.

Applied Clay Science, 2012

ABSTRACT Drug delivery by layered double hydroxides (LDHs) is extensively studied due to the capa... more ABSTRACT Drug delivery by layered double hydroxides (LDHs) is extensively studied due to the capacity of these solids to preserve the active agent and to modify its release rate and bioavailability. In this work, an ibuprofen–LDH complex was synthesized with high drug content (54% w/w), incorporated both in the interlayer and on the surface. The mechanisms involved in the ibuprofen release process were studied as a function of the anion type (chloride, acetate, and phosphate) and concentration, and the pH of the release media. The experimental conditions selected were based on the composition of pharmaceutically relevant fluids such as gastric, intes-tinal and lysosomal simulated media. Three release mechanisms accounted for the rate and extent of the drug release: ion exchange (highly dependent on the anions), desorption and weathering (dependent on the pH). These mechanisms, together with the different solubility of the anionic and non-ionic ibuprofen species, also explained the release behavior for particulate solid and hydrogel formulations. Anion exchange determined ibuprofen release in intestinal medium (phosphate anions pH 6.8) whereas surface reactions mediated by solid weathering or drug solubility ruled the release in acid media (gastric fluid and lysosomal medium).

Microporous and Mesoporous Materials, 2008

Acetate-containing nickel zinc layered hydroxysalts LHS-[Ni-Zn-AcO] have been exchanged with M 2+... more Acetate-containing nickel zinc layered hydroxysalts LHS-[Ni-Zn-AcO] have been exchanged with M 2+ -edta complexes (M 2+ @Cu 2+ , Cd 2+ and Mn 2+ ) at different pHs. Upon a careful selection of the reaction conditions, a rather large concentration of metal chelate units in the interlayer space is achieved, as concluded from element chemical analyses, powder X-ray diffraction and FT-IR spectroscopy results.

Journal of Zoology, 2012

ABSTRACT

Journal of Solid State Chemistry, 2004

Interlayer acetate anions in layered double hydroxyacetates of Ni 2+ and Zn 2+ have been exchange... more Interlayer acetate anions in layered double hydroxyacetates of Ni 2+ and Zn 2+ have been exchanged by oxovanadates following three synthetic routes (at 60 C, under hydrothermal conditions and after preswelling with caprylate anions) and different pH; direct exchange at room temperature was not successful. Complete exchange was achieved under adequated conditions, and the precise nature of the interlayer anion depends on the pH during exchange: at low pH (4.5), the presence of a-VO 3 chains, with anchoring (grafting) of the species to the hydroxide layers, is proposed. At higher pH (9.5) V 2 O 7 4À species are present in the interlayer. Thermal decomposition of these vanadate-intercalated products leads to formation of orthorhombic Ni 2+ and Zn 2+ vanadates, together with NiO. r 2004 Elsevier Inc. All rights reserved.

Journal of Materials Chemistry, 2002

ABSTRACT First published as an Advance Article on the web 21st February 2002 Layered Ni,Zn hydrox... more ABSTRACT First published as an Advance Article on the web 21st February 2002 Layered Ni,Zn hydroxyacetates have been prepared by hydrothermal methods and have been used for anion exchange of the original acetate anions by chloride, bromide, carbonate, nitrate, sulfate, and phosphate. Exchange was complete in all cases. The solids have been characterised by elemental chemical analysis, powder X-ray diffraction, thermal analysis (thermogravimetric and differential), FT-IR spectroscopy and electron microscopy; XAS spectra were also recorded in some cases. Thermal decomposition in air leads to removal of interlayer water at 150–200 uC. Mixed NiO–ZnO oxides are formed at higher temperatures. Chloride, sulfate, and phosphate salts are also formed at intermediate calcination temperature, and phosphate remains even after calcination at 1000 uC.

The Journal of Infectious Diseases, 2006

Background. Failure of antimonial therapy has been increasingly reported in anthroponotic viscera... more Background. Failure of antimonial therapy has been increasingly reported in anthroponotic visceral leishmaniasis and in cutaneous disease. The role of drug resistance in treatment failure has been difficult to ascertain because therapeutic response is multifactorial, and the efficacy of antimonial drugs depends on an effective immune response. In this study, we sought to determine whether standard treatment selects for resistant organisms and whether drug resistance contributes to treatment failure.

The Journal of Infectious Diseases, 2010

Background. T cell differentiation determines susceptibility and resistance to experimental cutan... more Background. T cell differentiation determines susceptibility and resistance to experimental cutaneous leishmaniasis, yet mixed T1/Th2 responses characterize the clinical spectrum of human infection with Leishmania (Viannia) species.

Journal of Geophysical Research, 2004

Journal of Colloid and Interface Science, 2010

Layered double hydroxides (LDHs) weathering in acidic media is one of the main features that affe... more Layered double hydroxides (LDHs) weathering in acidic media is one of the main features that affects their applications in drug delivery systems. In this work, the dissolution kinetics of biocompatible Mg-Al LDHs was studied at different initial pH values and solid concentrations using a simple and fast experimental method that coupled flow injection analysis and amperometric detection. A carbonate intercalated sample was used to determine the controlling step of the process and the dissolution mechanism. Finally, the study was extended to an ibuprofen intercalated LDH. The obtained results showed that the weathering process was mainly controlled by the exposed area and surface reactivity of LDHs particles. The dissolution mechanism at the particle surface was described in two steps: fast formation of surface reactive sites by hydroxyl group protonation and slow detachment of metal ions from surface. At strongly acidic conditions, the reaction rate was pH dependent due to the equilibrium between protonated (active) and deprotonated (inactive) hydroxyl groups. On the other hand, at mildly acidic conditions, the dissolution behavior was also ruled by the equilibrium attained between the particle surface reactive sites and the dissolved species. LDHs solubility and dissolution rate presented strong dependence with the interlayer anion. The ibuprofen intercalated sample was more soluble and more rapidly dissolved than the carbonate intercalated one in acetic/acetate buffer. On the other hand, the dissolution mechanism was invariant with the interlayer anion.

Journal of Colloid and Interface Science, 2009

EDTA modified layered double hydroxides (LDHs) were investigated as potential sorbents to remedia... more EDTA modified layered double hydroxides (LDHs) were investigated as potential sorbents to remediate heavy metals pollution. The polidentate ligand was introduced by an exchange method in a Zn-Al-LDH, which takes place with partial erosion of the layers, causing the intercalation of [Zn(EDTA)] 2− complex instead of the ligand. [Cu(H 2 O) 6 ] 2+ cation was selected as a model cation to study the uptake mechanism, exploring the elimination kinetics from the first minutes up to the steady state. A flow injection analysis system coupled to an amperometric detector (FIA-AM) was applied to perform fast and reliable [Cu(H 2 O) 6 ] 2+ determinations in monodisperse solid-aqueous solution systems. Furthermore, the sorbent stability was determined as a function of the pH and the nitrate concentration. The [Cu(H 2 O) 6 ] 2+ elimination is produced by an exchange reaction with [Zn(EDTA)] 2− anions placed either in the solid interlayer or in the aqueous solution, this last being released from the sorbent. Additional [Cu(H 2 O) 6 ] 2+ removal is produced by Cu(OH) 2 precipitation at high copper concentrations due to the LDHs high pH buffering capacity. The sorbent removes [Cu(H 2 O) 6 ] 2+ with high affinity in a wide concentration range. The elimination process reaches equilibrium in less than 30 min and leaves metal cation concentrations lower than 0.05 ppm in the supernatants.

Journal of Colloid and Interface Science, 2011

Layered double hydroxides (LDHs) reactivity and interfacial behavior are closely interconnected a... more Layered double hydroxides (LDHs) reactivity and interfacial behavior are closely interconnected and control particle properties relevant to the wide range of these solids' applications. Despite their importance, their relationship has been hardly described. In this work, chloride and dodecylsulfate (DDS(-)) intercalated LDHs are studied combining experimental data (electrophoretic mobility and contact angle measurements, hydroxyl and organic compounds uptake) and a simple mathematical model that includes anion-binding and acid-base reactions. This approach evidences the anion effect on LDHs interfacial behavior, reflected in the opposite particle charge and the different surface hydrophobic/hydrophilic character. LDHs reactivity are also determined by the interlayer composition, as demonstrated by the cation uptake capability of the DDS(-) intercalated sample. Consequently, the interlayer anion modifies the LDHs interfacial properties and reactivity, which in turn extends the customization capacity of these solids.

International Journal of Control, 1993

This paper proposes an iterative algorithm for achieving robust performance optimization for unce... more This paper proposes an iterative algorithm for achieving robust performance optimization for uncertain linear systems. The objective is to obtain a controller which minimizes the weighted infinity norm of sensitivity for the worst uncertainty scenario. The algorithm seeks ...

IEEE Control Systems, 2000

We propose that the logarithms of closed-loop poles be drawn instead of the plain poles in root l... more We propose that the logarithms of closed-loop poles be drawn instead of the plain poles in root loci for continuous-time linear loops, to help visualize significant closed-loop frequency responses simultaneously at specific values of the changing open-loop parameters. We also promote the splitting of the loci into pairs of graphs showing the imaginary and real parts of the logarithms of

Electrochimica Acta, 2009

Fast and simple quantitative determination in dispersed systems (layered double hydroxides -LDHss... more Fast and simple quantitative determination in dispersed systems (layered double hydroxides -LDHssuspensions in aqueous solutions) was performed by a procedure that couples flow injection and amperometric detection (FI-AM). LDH dispersions are injected in a continuous flow (1 mL min −1 ) of 0.05 mol L −1 KNO 3 solution and [Cu(H 2 O) 6 ] 2+ , used as a probe, is detected at a glassy carbon electrode housed in a flat electrochemical cell. The current intensity, recorded at the selected working potential (−0.25 V vs Ag/AgCl/NaCl (3 mol L −1 )), presents a linear relationship with [Cu(H 2 O) 6 ] 2+ concentration and the procedure offers high sensitivity (slope = 0.036 A/(mol L −1 )), a low detection limit (=0.7 mol L −1 ) and a wide quantification range (4-200 mol L −1 ).

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2013

Agricultura Técnica, 2006

... PVY) on Solanaceus Crops Malezas del Género Datura como Factor Epidemiológico del Virus del m... more ... PVY) on Solanaceus Crops Malezas del Género Datura como Factor Epidemiológico del Virus del mosaico de la alfalfa (AMV), Virus del mosaico del pepino (CMV) y Virus Y de la papa (PVY) en Solanáceas Cultivadas Juan Ormeño 1 *,Paulina Sepúlveda 1 ,Ricardo Rojas 2 ...

Several approaches for structure estimation have been developed in recent years, which are mostly... more Several approaches for structure estimation have been developed in recent years, which are mostly based on exhaustive singularity tests of covariance matrices. This work intends to reduce the computational cost of the previous methods, by knowing the rank of (instrumental) finite-sampl e covariance matrices. I. I NTRODUCTION

Automatica, 2000

This paper is devoted to the problem of global (local) stabilization of a prescribed subset of th... more This paper is devoted to the problem of global (local) stabilization of a prescribed subset of the state space for a passive affine nonlinear system. It is assumed that the desired attractive set can be described as an inverse image of zero value of some smooth nonnegative function, and that this function does not increase along the solutions of the

Applied Clay Science, 2008

Zn–Al layered double hydroxides with different MII/MIII ratios were synthesized by the coprecipit... more Zn–Al layered double hydroxides with different MII/MIII ratios were synthesized by the coprecipitation method and the obtained solids were characterized by powder X-ray diffraction, infrared spectroscopy, acid–base potentiometric titrations, electrophoretic mobility and modeling of the electrical double layer. As general behavior, increasing hydroxyl adsorption with increasing pH and decreasing supporting electrolyte concentration takes place between pH 7 and 12. The

Applied Clay Science, 2010

ABSTRACT An acetate-intercalated Ni–Zn layered hydroxide salt (LHS) was exchanged with chromate a... more ABSTRACT An acetate-intercalated Ni–Zn layered hydroxide salt (LHS) was exchanged with chromate anions, achieving a rather large oxometalate concentration, which almost completely balanced the positive charges of the layers, as concluded from element chemical analysis, powder X-ray diffraction, and FT-IR spectroscopy results. Thermal decomposition of the solid led to dehydration and chromate anion grafting, followed by dehydroxylation of the host and reduction of the chromate anions. The solid then lost the layer structure, forming solids with large micro and mesoporosity, which corresponded to poorly crystallized (Zn, Ni)–Cr spinels, as well as nickel and zinc oxides.

Applied Clay Science, 2012

ABSTRACT Drug delivery by layered double hydroxides (LDHs) is extensively studied due to the capa... more ABSTRACT Drug delivery by layered double hydroxides (LDHs) is extensively studied due to the capacity of these solids to preserve the active agent and to modify its release rate and bioavailability. In this work, an ibuprofen–LDH complex was synthesized with high drug content (54% w/w), incorporated both in the interlayer and on the surface. The mechanisms involved in the ibuprofen release process were studied as a function of the anion type (chloride, acetate, and phosphate) and concentration, and the pH of the release media. The experimental conditions selected were based on the composition of pharmaceutically relevant fluids such as gastric, intes-tinal and lysosomal simulated media. Three release mechanisms accounted for the rate and extent of the drug release: ion exchange (highly dependent on the anions), desorption and weathering (dependent on the pH). These mechanisms, together with the different solubility of the anionic and non-ionic ibuprofen species, also explained the release behavior for particulate solid and hydrogel formulations. Anion exchange determined ibuprofen release in intestinal medium (phosphate anions pH 6.8) whereas surface reactions mediated by solid weathering or drug solubility ruled the release in acid media (gastric fluid and lysosomal medium).