DNA Interaction with a Polyelectrolyte Monolayer at Solution—Air Interface

The formation of ordered 2D nanostructures of double stranded DNA molecules at various interfaces attracts more and more focus in medical and engineering research, but the underlying intermolecular interactions still require elucidation. Recently, it has been revealed that mixtures of DNA with a series of hydrophobic cationic polyelectrolytes including poly(N,N-diallyl-N-hexyl-N-methylammonium) chloride (PDAHMAC) form a network of ribbonlike or threadlike aggregates at the solution—air interface. In the present work, we adopt a novel approach to confine the same polyelectrolyte at the solution—air interface by spreading it on a subphase with elevated ionic strength. A suite of techniques–rheology, microscopy, ellipsometry, and spectroscopy–are applied to gain insight into main steps of the adsorption layer formation, which results in non-monotonic kinetic dependencies of various surface properties. A long induction period of the kinetic dependencies after DNA is exposed to the surface film results only if the initial surface pressure corresponds to a quasiplateau region of the compression isotherm of a PDAHMAC monolayer. Despite the different aggregation mechanisms, the micromorphology of the mixed PDAHMAC/DNA does not depend noticeably on the initial surface pressure. The results provide new perspective on nanostructure formation involving nucleic acids building blocks.

Characterization of Monoolein Langmuir Monolayers Spread at The Salt Solution/Air Interface

The Langmuir monolayer is commonly described at interfaces for an insoluble homogenous single molecular layer. Langmuir monolayers have demonstrated various issues regarding soft matters and complex fluids by forming ideal uniform two-dimensional structures over the air-water interface. This monolayer has advantages for evaluating physicochemical properties at interfaces and, for the insoluble molecules, can be applied simultaneously to the different interaction occurrences at interfaces. For this experiment, monoolein lipid was used as a spreading solvent to create a Langmuir monolayer, and five different types of salt sub-phases were applied for the physicochemical properties’ interaction studies. On the air-water interface, the surface properties of monoolein lipids were investigated for interfacial phase behaviors, using the Wilhelmy plate pressure sensor technique compression isotherm (π-A). Data and analysis were also contributed to the correspondent, precise verification of physical state behavior with the surface pressure measurements on the interfaces through the compressibility modulus and the elasticity modulus parameters on the surface. In the experiments, the interfacial activity of the monoolein lipids was found to be stable on the aqueous sub-phase, while the area per molecule over the interface did not have much impact as a sub-phase with a change in salts. The repeatability and reproducibility of tests were affirmed by the difference in the Langmuir monolayer’s particular phase transition orientation behavior and the stability of colloidal lipid dispersion. However, Langmuir monolayer formation contributes to several special groups being restructured and is found to be a more remarkable natural process for their attractive organic dynamic structural properties over the interface, but the interfacial molecular dynamics have proven to be difficult to calculate.

Characterization of Monoolein Langmuir Monolayers Spread at The Salt Solution/Air Interface

The Langmuir monolayer is commonly described at interfaces for an insoluble homogenous single molecular layer. Langmuir monolayers have demonstrated various issues regarding soft matters and complex fluids by forming ideal uniform two-dimensional structures over the air-water interface. This monolayer has advantages for evaluating physicochemical properties at interfaces and, for the insoluble molecules, can be applied simultaneously to the different interaction occurrences at interfaces. For this experiment, monoolein lipid was used as a spreading solvent to create a Langmuir monolayer, and five different types of salt sub-phases were applied for the physicochemical properties’ interaction studies. On the air-water interface, the surface properties of monoolein lipids were investigated for interfacial phase behaviors, using the Wilhelmy plate pressure sensor technique compression isotherm (π-A). Data and analysis were also contributed to the correspondent, precise verification of physical state behavior with the surface pressure measurements on the interfaces through the compressibility modulus and the elasticity modulus parameters on the surface. In the experiments, the interfacial activity of the monoolein lipids was found to be stable on the aqueous sub-phase, while the area per molecule over the interface did not have much impact as a sub-phase with a change in salts. The repeatability and reproducibility of tests were affirmed by the difference in the Langmuir monolayer’s particular phase transition orientation behavior and the stability of colloidal lipid dispersion. However, Langmuir monolayer formation contributes to several special groups being restructured and is found to be a more remarkable natural process for their attractive organic dynamic structural properties over the interface, but the interfacial molecular dynamics have proven to be difficult to calculate.

Characterization of Monoolein Langmuir Monolayers Spread at The Salt Solution/Air Interface

The Langmuir monolayer is commonly described at interfaces for an insoluble homogenous single molecular layer. Langmuir monolayers have demonstrated various issues regarding soft matters and complex fluids by forming ideal uniform two-dimensional structures over the air-water interface. This monolayer has advantages for evaluating physicochemical properties at interfaces and, for the insoluble molecules, can be applied simultaneously to the different interaction occurrences at interfaces. For this experiment, monoolein lipid was used as a spreading solvent to create a Langmuir monolayer, and five different types of salt sub-phases were applied for the physicochemical properties’ interaction studies. On the air-water interface, the surface properties of monoolein lipids were investigated for interfacial phase behaviors, using the Wilhelmy plate pressure sensor technique compression isotherm (π-A). Data and analysis were also contributed to the correspondent, precise verification of physical state behavior with the surface pressure measurements on the interfaces through the compressibility modulus and the elasticity modulus parameters on the surface. In the experiments, the interfacial activity of the monoolein lipids was found to be stable on the aqueous sub-phase, while the area per molecule over the interface did not have much impact as a sub-phase with a change in salts. The repeatability and reproducibility of tests were affirmed by the difference in the Langmuir monolayer’s particular phase transition orientation behavior and the stability of colloidal lipid dispersion. However, Langmuir monolayer formation contributes to several special groups being restructured and is found to be a more remarkable natural process for their attractive organic dynamic structural properties over the interface, but the interfacial molecular dynamics have proven to be difficult to calculate.

Semi-Automated Optimization of the CHARMM36 Lipid Force Field to Include Explicit Treatment of Long-Range Dispersion

The development of the CHARMM lipid force field (FF) can be traced back to the early 1990s with its current version denoted CHARMM36 (C36). The parametrization of C36 utilized high-level quantum mechanical data and free energy calculations of model compounds before parameters were manually adjusted to yield agreement with experimental properties of lipid bilayers. While such manual fine-tuning of FF parameters is based on intuition and trial-and-error, automated methods can identify beneficial modifications of the parameters via their sensitivities and thereby guide the optimization process. This paper introduces a semi-automated approach to reparametrize the CHARMM lipid FF with consistent inclusion of long-range dispersion through the LennardJones particle-mesh Ewald (LJ-PME) approach. The optimization method is based on thermodynamic reweighting with regularization with respect to the C36 set. Two independent optimizations with different topology restrictions are presented. Targets of the optimizations are primarily liquid crystalline phase properties of lipid bilayers and the compression isotherm of monolayers. Pair correlation functions between water and lipid functional groups in aqueous solution are also included to address headgroup hydration. While the physics of the reweighting strategy itself is well understood, applying it to heterogeneous, complex anisotropic systems poses additional challenges. These were overcome through careful selection of target properties and reweighting settings allowing for the successful incorporation of the explicit treatment of long-range dispersion, and we denote the newly optimized lipid force field as C36/LJ-PME. The current implementation of the optimization protocol will facilitate the future development of the CHARMM and related lipid force fields.<br>

Semi-Automated Optimization of the CHARMM36 Lipid Force Field to Include Explicit Treatment of Long-Range Dispersion

The development of the CHARMM lipid force field (FF) can be traced back to the early 1990s with its current version denoted CHARMM36 (C36). The parametrization of C36 utilized high-level quantum mechanical data and free energy calculations of model compounds before parameters were manually adjusted to yield agreement with experimental properties of lipid bilayers. While such manual fine-tuning of FF parameters is based on intuition and trial-and-error, automated methods can identify beneficial modifications of the parameters via their sensitivities and thereby guide the optimization process. This paper introduces a semi-automated approach to reparametrize the CHARMM lipid FF with consistent inclusion of long-range dispersion through the LennardJones particle-mesh Ewald (LJ-PME) approach. The optimization method is based on thermodynamic reweighting with regularization with respect to the C36 set. Two independent optimizations with different topology restrictions are presented. Targets of the optimizations are primarily liquid crystalline phase properties of lipid bilayers and the compression isotherm of monolayers. Pair correlation functions between water and lipid functional groups in aqueous solution are also included to address headgroup hydration. While the physics of the reweighting strategy itself is well understood, applying it to heterogeneous, complex anisotropic systems poses additional challenges. These were overcome through careful selection of target properties and reweighting settings allowing for the successful incorporation of the explicit treatment of long-range dispersion, and we denote the newly optimized lipid force field as C36/LJ-PME. The current implementation of the optimization protocol will facilitate the future development of the CHARMM and related lipid force fields.<br>

Molecular-level insight into the binding of arginine to a zwitterionic Langmuir monolayer

Arginine molecules bind to a DPPC monolayer, altering the interfacial electrostatic potential and the lateral mobility of the lipids, while having little effect on the compression isotherm of the monolayer.

Synthesis and Self-assembly of DMPC-conjugated Gold Nanoparticles

ABSTRACTBio-conjugated nanomaterials play a promising role in the development of novelsupramolecular structures, molecular machines, and biosensing devices. In this study, lipid-capped gold nanoparticles were synthesized and allowed to form a self-assembled monolayer structure. The nanoparticles were prepared by a phase transfer method, which involved the reduction of potassium tetrachloroaurate(III) by sodium citrate in an aqueous solution and the simultaneous transfer of the reduced species to an organic medium containing DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine). The gold nanoparticles were characterized using Uv-vis spectroscopy and dynamic light scattering (DLS) particle-size analysis. In addition, the resulting nanoparticles were examined using transmission electron microscopy (TEM). The Langmuir-Blodgett (LB) technique was used to assemble the DMPC-capped nanoparticles onto a water subphase at room temperature. The measurement of the compression isotherm confirmed the assemblage of lipid capped gold nanoparticles. This method of synthesis of ordered structures utilizing molecular interactions of lipids will be useful in developing novel metamaterials and nanocircuits.