Khawla Qamhieh - Academia.edu (original) (raw)

Papers by Khawla Qamhieh

Research paper thumbnail of Effect of Dielectric Constant on the Zeta Potential of Spherical Electric Double Layers

Research paper thumbnail of Effect of discrete macroion charge distributions in solutions of like-charged macroions

Journal of Chemical Physics, Sep 8, 2005

The effect of replacing the conventional uniform macroion surface charge density with discrete ma... more The effect of replacing the conventional uniform macroion surface charge density with discrete macroion charge distributions on structural properties of aqueous solutions of like-charged macroions has been investigated by Monte Carlo simulations. Two discrete charge distributions have been considered: point charges localized on the macroion surface and finite-sized charges protruding into the solution. Both discrete charge distributions have been examined with fixed and mobile macroion charges. Different boundary conditions have been applied to examine various properties. With point charges localized on the macroion surface, counterions become stronger accumulated to the macroion and the effect increases with counterion valence. As a consequence, with mono- and divalent counterions the potential of mean force between two macroions becomes less repulsive and with trivalent counterions more attractive. With protruding charges, the excluded volume effect dominates over the increased correlation ability; hence the counterions are less accumulated near the macroions and the potential of mean force between two macroions becomes more repulsive/less attractive.

Research paper thumbnail of Electrostatic interactions between cationic dendrimers and anionic model biomembrane

Chemistry and Physics of Lipids, Aug 1, 2022

Research paper thumbnail of Effect of Discrete Macroion Charge Distributions on Electric Double Layer of a Spherical Macroion

Journal of Dispersion Science and Technology, Nov 2, 2013

ABSTRACT The effect of replacing the conventional uniform macroion surface charge density with di... more ABSTRACT The effect of replacing the conventional uniform macroion surface charge density with discrete macroion charge distributions on the structure of electric double layer (EDL) of a spherical macroion has been investigated by Monte Carlo (MC) simulations. Two discrete models have been investigated in addition to the central macroion charge: point charges localized on the macroion surface and finite-sized charges protruding into the solution. Both models have been studied with fixed and mobile macroion charges. The radial functions of local densities and electrostatic potential in EDL, are calculated and compared to the results obtained for the central macroion charge distribution. It is concluded that the model of charge distribution significantly affects the EDL structure close to the macroion, while the effect is much weaker at larger distances. With point charges localized on the macroion surface, counterions become stronger accumulated to the macroion, as a result the absolute values of surface potential Φ0 and zeta ξ potential are decreased. With protruding charges, the excluded volume effect dominates over the increased correlation ability; hence the counterions are less accumulated near the macroions and the absolute values of Φ0 and ξ potentials are increased.

Research paper thumbnail of Analytical model study of complexation of dendrimer as an ion penetrable sphere with DNA

Colloids and Surfaces A: Physicochemical and Engineering Aspects, Feb 1, 2014

ABSTRACT Poly (amidoamine) (PAMAM) dendrimers, being protonated under physiological conditions, h... more ABSTRACT Poly (amidoamine) (PAMAM) dendrimers, being protonated under physiological conditions, have great potential as nonviral vectors for gene transfection. Many experimental and simulation studies have been performed to study the effect of dendrimer size, charge, and salt concentration on the structure and transfection efficiency of condensed DNA aggregates. In this study a theoretical model describing a linear polyelectrolyte (LPE) and ion-penetrable spheres has been developed and applied to investigate the interaction between linearized DNA and positively charged dendrimer of different generations. Throughout the study, we emphasized on the effect of the medium’s environments on the complexation of LPE chain with one dendrimer. It is found that the wrapping degree of the chain around the dendrimer increases by increasing dendrimer’s charge (decreasing pH), Bjerum length, salt concentration, and decreases by increasing the rigidity of the chain. Also, the effect of 1:1 salt concentration on complexation of DNA plasmids with one dendrimer of different generations has been investigated, and found that the optimal wrapping length of the LPE chain around the dendrimer depends on dendrimer generation.

Research paper thumbnail of The Melting Mechanism of Dna Tethered to a Surface

PubMed, Mar 8, 2009

The details of melting of DNA immobilized on a chip or nanoparticle determines the sensitivity an... more The details of melting of DNA immobilized on a chip or nanoparticle determines the sensitivity and operating characteristics of many analytical and synthetic biotechnological devices. Yet, little is known about the differences in how the DNA melting occurs between a homogeneous solution and that on a chip. We used molecular dynamics simulations to explore possible pathways for DNA melting on a chip. Simulation conditions were chosen to ensure that melting occurred in a submicrosecond timescale. The temperature was set to 400 K and the NaCl concentration was set to 0.1 M. We found less symmetry than in the solution case where for oligomeric double-stranded nucleic acids both ends melted with roughly equal probability. On a prepared silica surface we found melting is dominated by fraying from the end away from the surface. Strand separation was hindered by nonspecific surface adsorption at this temperature. At elevated temperatures the melted DNA was attracted to even uncharged organically coated surfaces demonstrating surface fouling. While hybridization is not the simple reverse of melting, this simulation has implications for the kinetics of hybridization.

Research paper thumbnail of Microemulsion Phase Behavior of Aerosol-OT Combined with a Cationic Hydrotrope in the Dilute Region

Journal of Dispersion Science and Technology, Jan 21, 2010

The phase behavior of systems containing minimum amounts of sodium bis (2-ethylhexyl) sulfosuccin... more The phase behavior of systems containing minimum amounts of sodium bis (2-ethylhexyl) sulfosuccinate with equimolar ratio of tetra ethyl ammonium chloride were studied as a function of salt concentration and alkane carbon number at ambient temperature. Visual inspection as well as cross polarizers were used to detect anisotropy. Solubilization ratios for oil and brine in the middle phases were measured

Research paper thumbnail of Complexes formed between DNA and poly(amido amine) dendrimers of different generations – modelling DNA wrapping and penetration

Physical Chemistry Chemical Physics, 2014

Research paper thumbnail of Phase Behavior of Bicontinuous and Water/Diesel Fuel Microemulsions Using Nonionic Surfactants Combined with Hydrophilic Alcohol Ethoxylates

Journal of Dispersion Science and Technology, Feb 10, 2014

Research paper thumbnail of Analytical Model Study of Dendrimer/DNA Complexes

Biomacromolecules, May 13, 2009

Research paper thumbnail of Controlling microarray DNA hybridization efficiency by probe-surface distance and external surface electrostatics

Nucleation and Atmospheric Aerosols, 2015

DNA microarrays are analytical devices designed to determine the composition of multicomponent so... more DNA microarrays are analytical devices designed to determine the composition of multicomponent solutions of nucleic acids, DNA or RNA. These devices are promising technology for diverse applications, including sensing, diagnostics, and drug/gene delivery. Here, we modify a hybridization adsorption isotherm to study the effects of probe-surface distance and the external electrostatic fields, on the oligonucleotide hybridization in microarray and how these effects are varies depending on surface probe density and target concentration. This study helps in our understanding on-surface hybridization mechanisms, and from it we can observe a significant effect of the probe-surface distance, and the external electrostatic fields, on the hybridization yield. In addition we present a simple new criteria to control the oligonucleotide hybridization efficiency by providing a chart illustrating the effects of all factors on the DNA-hybridization efficiency.

Research paper thumbnail of Formulating Middle Phase Microemulsions Using Extended Anionic Surfactant Combined with Cationic Hydrotrope

Journal of Dispersion Science and Technology, Dec 21, 2010

The phase behavior of systems containing sodium alkyl polypropylene oxide sulfate with equimolar ... more The phase behavior of systems containing sodium alkyl polypropylene oxide sulfate with equimolar ratio of polypropylene oxide ammonium chloride was determined as a function of salt concentration and alkane carbon number at ambient temperature. Visual inspection as well as cross polarizers were used to detect anisotropy. Solubilization ratios for oil and brine in the middle phases were measured and used to calculate the interfacial tension (IFT) between the microemulsion and oil or brine. The fish diagram is presented showing a minimum amount of 0.20 wt% surfactant needed to form the middle phase. Swelling increases with decreasing the alkane carbon number of the oil. Ultra low IFT values were predicted for the systems investigated.

Research paper thumbnail of Osmotic pressure in polyelectrolyte solutions: cell-model and bulk simulations

Research paper thumbnail of Transport properties of alternative fuel microemulsions based on sugar surfactant

Journal of Dispersion Science and Technology, Jul 29, 2016

Research paper thumbnail of Effective Macroion Charge and Stability of Highly Asymmetric Electrolytes at Various Salt Conditions

Journal of Physical Chemistry B, Jun 28, 2003

Research paper thumbnail of Water-Diesel Microemulsions Stabilized by an Anionic Extended Surfactant and a Cationic Hydrotrope

Journal of Dispersion Science and Technology, Apr 1, 2012

Research paper thumbnail of Effect of Type of Fragrance Compounds on Their Location in Hexagonal Liquid Crystal

Journal of Dispersion Science and Technology, Dec 1, 2006

... Three fragrances, limonene, benzaldehyde, and phenethylalcohol (that differ in their polariti... more ... Three fragrances, limonene, benzaldehyde, and phenethylalcohol (that differ in their polarities), were solubilized in hexagonal liquid crystal using the polyethylene oxide‐polypropylene oxide‐polyethylene oxide, (EO 27 PO 61 EO 27 ), P 104 triblock copolymer, and water. ...

Research paper thumbnail of The retention of multivalent pollutants in mineral layers

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2022

Research paper thumbnail of Complexes formed between polyelectrolyte and acetylated cationic dendrimers

Journal of Analytical & Pharmaceutical Research

Gene therapies are receiving a revival, especially because of the potential for use in cancer and... more Gene therapies are receiving a revival, especially because of the potential for use in cancer and infectious disease vaccination. However, effectively condensing and maintaining deoxyribonucleic acid (DNA) carriers for gene therapy are used, such as dendrimers. The penetrable sphere model developed by Qamhieh et al., explain the interaction between linear polyelectrolyte (LPE) and an ion-penetrable sphere was employed to study the complexation of negatively charged DNA and acetylated dendrimer. Throughout the study, we emphasized the effect of acetylation on two types of complexations: single dendrimer-DNA chain complex and multiple dendrimers-DNA chain complex. The interaction between three different DNA lengths: L = 90 nm of 265; L = 184 nm of 541 bp; and L = 680 nm of 2000 bp individually with the poly (amido amine) (PAMAM) dendrimer of generation 5 was studied. For a single dendrimer-DNA complex, the number of condensed monomers around the dendrimer and the fraction of optimal l...

Research paper thumbnail of DNA compaction by poly (amido amine) dendrimers of ammonia cored and ethylene diamine cored

Journal of Physics: Conference Series, 2017

Research paper thumbnail of Effect of Dielectric Constant on the Zeta Potential of Spherical Electric Double Layers

Research paper thumbnail of Effect of discrete macroion charge distributions in solutions of like-charged macroions

Journal of Chemical Physics, Sep 8, 2005

The effect of replacing the conventional uniform macroion surface charge density with discrete ma... more The effect of replacing the conventional uniform macroion surface charge density with discrete macroion charge distributions on structural properties of aqueous solutions of like-charged macroions has been investigated by Monte Carlo simulations. Two discrete charge distributions have been considered: point charges localized on the macroion surface and finite-sized charges protruding into the solution. Both discrete charge distributions have been examined with fixed and mobile macroion charges. Different boundary conditions have been applied to examine various properties. With point charges localized on the macroion surface, counterions become stronger accumulated to the macroion and the effect increases with counterion valence. As a consequence, with mono- and divalent counterions the potential of mean force between two macroions becomes less repulsive and with trivalent counterions more attractive. With protruding charges, the excluded volume effect dominates over the increased correlation ability; hence the counterions are less accumulated near the macroions and the potential of mean force between two macroions becomes more repulsive/less attractive.

Research paper thumbnail of Electrostatic interactions between cationic dendrimers and anionic model biomembrane

Chemistry and Physics of Lipids, Aug 1, 2022

Research paper thumbnail of Effect of Discrete Macroion Charge Distributions on Electric Double Layer of a Spherical Macroion

Journal of Dispersion Science and Technology, Nov 2, 2013

ABSTRACT The effect of replacing the conventional uniform macroion surface charge density with di... more ABSTRACT The effect of replacing the conventional uniform macroion surface charge density with discrete macroion charge distributions on the structure of electric double layer (EDL) of a spherical macroion has been investigated by Monte Carlo (MC) simulations. Two discrete models have been investigated in addition to the central macroion charge: point charges localized on the macroion surface and finite-sized charges protruding into the solution. Both models have been studied with fixed and mobile macroion charges. The radial functions of local densities and electrostatic potential in EDL, are calculated and compared to the results obtained for the central macroion charge distribution. It is concluded that the model of charge distribution significantly affects the EDL structure close to the macroion, while the effect is much weaker at larger distances. With point charges localized on the macroion surface, counterions become stronger accumulated to the macroion, as a result the absolute values of surface potential Φ0 and zeta ξ potential are decreased. With protruding charges, the excluded volume effect dominates over the increased correlation ability; hence the counterions are less accumulated near the macroions and the absolute values of Φ0 and ξ potentials are increased.

Research paper thumbnail of Analytical model study of complexation of dendrimer as an ion penetrable sphere with DNA

Colloids and Surfaces A: Physicochemical and Engineering Aspects, Feb 1, 2014

ABSTRACT Poly (amidoamine) (PAMAM) dendrimers, being protonated under physiological conditions, h... more ABSTRACT Poly (amidoamine) (PAMAM) dendrimers, being protonated under physiological conditions, have great potential as nonviral vectors for gene transfection. Many experimental and simulation studies have been performed to study the effect of dendrimer size, charge, and salt concentration on the structure and transfection efficiency of condensed DNA aggregates. In this study a theoretical model describing a linear polyelectrolyte (LPE) and ion-penetrable spheres has been developed and applied to investigate the interaction between linearized DNA and positively charged dendrimer of different generations. Throughout the study, we emphasized on the effect of the medium’s environments on the complexation of LPE chain with one dendrimer. It is found that the wrapping degree of the chain around the dendrimer increases by increasing dendrimer’s charge (decreasing pH), Bjerum length, salt concentration, and decreases by increasing the rigidity of the chain. Also, the effect of 1:1 salt concentration on complexation of DNA plasmids with one dendrimer of different generations has been investigated, and found that the optimal wrapping length of the LPE chain around the dendrimer depends on dendrimer generation.

Research paper thumbnail of The Melting Mechanism of Dna Tethered to a Surface

PubMed, Mar 8, 2009

The details of melting of DNA immobilized on a chip or nanoparticle determines the sensitivity an... more The details of melting of DNA immobilized on a chip or nanoparticle determines the sensitivity and operating characteristics of many analytical and synthetic biotechnological devices. Yet, little is known about the differences in how the DNA melting occurs between a homogeneous solution and that on a chip. We used molecular dynamics simulations to explore possible pathways for DNA melting on a chip. Simulation conditions were chosen to ensure that melting occurred in a submicrosecond timescale. The temperature was set to 400 K and the NaCl concentration was set to 0.1 M. We found less symmetry than in the solution case where for oligomeric double-stranded nucleic acids both ends melted with roughly equal probability. On a prepared silica surface we found melting is dominated by fraying from the end away from the surface. Strand separation was hindered by nonspecific surface adsorption at this temperature. At elevated temperatures the melted DNA was attracted to even uncharged organically coated surfaces demonstrating surface fouling. While hybridization is not the simple reverse of melting, this simulation has implications for the kinetics of hybridization.

Research paper thumbnail of Microemulsion Phase Behavior of Aerosol-OT Combined with a Cationic Hydrotrope in the Dilute Region

Journal of Dispersion Science and Technology, Jan 21, 2010

The phase behavior of systems containing minimum amounts of sodium bis (2-ethylhexyl) sulfosuccin... more The phase behavior of systems containing minimum amounts of sodium bis (2-ethylhexyl) sulfosuccinate with equimolar ratio of tetra ethyl ammonium chloride were studied as a function of salt concentration and alkane carbon number at ambient temperature. Visual inspection as well as cross polarizers were used to detect anisotropy. Solubilization ratios for oil and brine in the middle phases were measured

Research paper thumbnail of Complexes formed between DNA and poly(amido amine) dendrimers of different generations – modelling DNA wrapping and penetration

Physical Chemistry Chemical Physics, 2014

Research paper thumbnail of Phase Behavior of Bicontinuous and Water/Diesel Fuel Microemulsions Using Nonionic Surfactants Combined with Hydrophilic Alcohol Ethoxylates

Journal of Dispersion Science and Technology, Feb 10, 2014

Research paper thumbnail of Analytical Model Study of Dendrimer/DNA Complexes

Biomacromolecules, May 13, 2009

Research paper thumbnail of Controlling microarray DNA hybridization efficiency by probe-surface distance and external surface electrostatics

Nucleation and Atmospheric Aerosols, 2015

DNA microarrays are analytical devices designed to determine the composition of multicomponent so... more DNA microarrays are analytical devices designed to determine the composition of multicomponent solutions of nucleic acids, DNA or RNA. These devices are promising technology for diverse applications, including sensing, diagnostics, and drug/gene delivery. Here, we modify a hybridization adsorption isotherm to study the effects of probe-surface distance and the external electrostatic fields, on the oligonucleotide hybridization in microarray and how these effects are varies depending on surface probe density and target concentration. This study helps in our understanding on-surface hybridization mechanisms, and from it we can observe a significant effect of the probe-surface distance, and the external electrostatic fields, on the hybridization yield. In addition we present a simple new criteria to control the oligonucleotide hybridization efficiency by providing a chart illustrating the effects of all factors on the DNA-hybridization efficiency.

Research paper thumbnail of Formulating Middle Phase Microemulsions Using Extended Anionic Surfactant Combined with Cationic Hydrotrope

Journal of Dispersion Science and Technology, Dec 21, 2010

The phase behavior of systems containing sodium alkyl polypropylene oxide sulfate with equimolar ... more The phase behavior of systems containing sodium alkyl polypropylene oxide sulfate with equimolar ratio of polypropylene oxide ammonium chloride was determined as a function of salt concentration and alkane carbon number at ambient temperature. Visual inspection as well as cross polarizers were used to detect anisotropy. Solubilization ratios for oil and brine in the middle phases were measured and used to calculate the interfacial tension (IFT) between the microemulsion and oil or brine. The fish diagram is presented showing a minimum amount of 0.20 wt% surfactant needed to form the middle phase. Swelling increases with decreasing the alkane carbon number of the oil. Ultra low IFT values were predicted for the systems investigated.

Research paper thumbnail of Osmotic pressure in polyelectrolyte solutions: cell-model and bulk simulations

Research paper thumbnail of Transport properties of alternative fuel microemulsions based on sugar surfactant

Journal of Dispersion Science and Technology, Jul 29, 2016

Research paper thumbnail of Effective Macroion Charge and Stability of Highly Asymmetric Electrolytes at Various Salt Conditions

Journal of Physical Chemistry B, Jun 28, 2003

Research paper thumbnail of Water-Diesel Microemulsions Stabilized by an Anionic Extended Surfactant and a Cationic Hydrotrope

Journal of Dispersion Science and Technology, Apr 1, 2012

Research paper thumbnail of Effect of Type of Fragrance Compounds on Their Location in Hexagonal Liquid Crystal

Journal of Dispersion Science and Technology, Dec 1, 2006

... Three fragrances, limonene, benzaldehyde, and phenethylalcohol (that differ in their polariti... more ... Three fragrances, limonene, benzaldehyde, and phenethylalcohol (that differ in their polarities), were solubilized in hexagonal liquid crystal using the polyethylene oxide‐polypropylene oxide‐polyethylene oxide, (EO 27 PO 61 EO 27 ), P 104 triblock copolymer, and water. ...

Research paper thumbnail of The retention of multivalent pollutants in mineral layers

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2022

Research paper thumbnail of Complexes formed between polyelectrolyte and acetylated cationic dendrimers

Journal of Analytical & Pharmaceutical Research

Gene therapies are receiving a revival, especially because of the potential for use in cancer and... more Gene therapies are receiving a revival, especially because of the potential for use in cancer and infectious disease vaccination. However, effectively condensing and maintaining deoxyribonucleic acid (DNA) carriers for gene therapy are used, such as dendrimers. The penetrable sphere model developed by Qamhieh et al., explain the interaction between linear polyelectrolyte (LPE) and an ion-penetrable sphere was employed to study the complexation of negatively charged DNA and acetylated dendrimer. Throughout the study, we emphasized the effect of acetylation on two types of complexations: single dendrimer-DNA chain complex and multiple dendrimers-DNA chain complex. The interaction between three different DNA lengths: L = 90 nm of 265; L = 184 nm of 541 bp; and L = 680 nm of 2000 bp individually with the poly (amido amine) (PAMAM) dendrimer of generation 5 was studied. For a single dendrimer-DNA complex, the number of condensed monomers around the dendrimer and the fraction of optimal l...

Research paper thumbnail of DNA compaction by poly (amido amine) dendrimers of ammonia cored and ethylene diamine cored

Journal of Physics: Conference Series, 2017