Hydrophobic-hydrophilic Interactions Research Articles

Hedgehog-shaped {Mo368} cluster: unique electronic/structural properties, surfactant encapsulation and related self-assembly into vesicles and films.

The hedgehog-shaped {Mo368} cluster shows unique electronic (extremely high extinction coefficient) and structural features, especially regarding its size, the high number of delocalized electrons which allows to measure the surface enhanced Raman scattering (SERS) spectrum and the option for coordination chemistry inside the cavity. Its relative instability in aqueous solution can be overcome by embedment in a hydrophobic shell of dimethyldioctadecylammonium cations. The resulting hybrid self-assembles into spherical vesicles in acetone-water mixtures, according to a process directed by hydrophobic-hydrophilic interactions. It also forms rather stable Langmuir monolayers while a second layer evolves under higher surface pressure, in accordance with a rather low alkyl surface density.

Moving Macromolecular Surfaces under Hydrophobic/Hydrophilic Stress

Hydrophobic and hydrophilic interactions can be described as dispersive interactions throughout the molecules, interaction between permanent or induced dipoles and ionic interactions. Hydrophobic effect is synonymous with dispersive interactivity and hydrophilic one is synonymous with polar interactivity. Unification of all these interactions in one interaction is electromagnetic interaction's dependence on interacting body's geometries. Hydrogen bonding is direct implication of such geometric dependence. Given the uniqueness of the problem, which is obvious for two surfaces, we only focus on two-dimensional surfaces embedded in the higher four-dimensional Minkowskian ambient space. Though, the analysis can be easily extended to hypersurfaces of any dimension. Limitation by two surfaces, embedded in four space-time, which is necessary to describe electromagnetism, is consequence of specificity of processes that takes place on macromolecular surfaces. In the following paper we discuss equations for the dynamic of macromolecular surfaces under the influence of potential energy consisting from four-potential time four-current and contraction of electromagnetic tensor. The macromolecular surfaces are modeled as a two-dimensional surface with a variable surface mass density. Kinetic energy is calculated according to calculus of moving surfaces. Definition of Lagrangian by subtracting potential energy from kinetic energy and setting minimum action principal are yielding nonlinear equations for moving surfaces under hydrophobic-hydrophilic interactions. The equations can describe uniqueness and specific functionality of proteins and nucleic acids. Shape minimization problems as well as minimum surface problems are also discussed.

2014 AHA Late-Breaking Basic Science Abstracts

### 24178 ### MAVS Mediates Protection against Myocardial Ischemic Injury with Hydrogen Sulfide David Durrant, Adolfo G Mauro, Juan Valle Raleigh, Anindita Das, Jun He, Khoa Nguyen, Stefano Toldo, Antonio Abbate, Fadi N Salloum; Virginia Commonwealth Univ, Richmond, VA Background : Hydrogen sulfide (H2S) has been shown to protect against myocardial ischemic and inflammatory injury in part by preserving mitochondrial integrity. Since mitochondrial antiviral signaling (MAVS) protein has been implicated in attenuating Bax-mediated cytochrome c release from mitochondria caused by oxidative stress or ischemia, we sought to determine whether MAVS mediates the cardioprotective effects of H2S. Methods and Results : After baseline echocardiography, adult male wild type (WT) or MAVS KO mice underwent myocardial infarction (MI) by coronary artery ligation for 30 min. followed by 24 h reperfusion. Mice were pretreated with Na2S (100 μg/kg; ip ) or saline 1 h before MI. Infarct size, measured with TTC staining, was reduced and LV fractional shortening (FS) was preserved with Na2S at 24h post MI in WT mice as compared to saline-treated mice, but not in MAVS KO mice (Figs. A and B). The risk area was not different between the groups. Western blot analysis revealed a significant decline in myocardial MAVS expression at 24h post MI, which was preserved with Na2S (Fig. C). Another subset of mice was subjected to permanent coronary artery occlusion and treated with Na2S or saline daily for 28 days. LVFS decreased significantly at 28 days post-MI in the saline group, but was significantly preserved with Na2S (Fig. D). Moreover, LV infarct scar size, assessed by trichrome staining, was smaller in Na2S group (22.4 ± 2.7%) as compared to control (33.5 ± 2.1%, P<0.05). Survival rate was 2 fold higher with Na2S compared to saline (P<0.05). Western blot analysis confirmed a significant …

Effect of surface interactions on adhesion of electrospun meshes on substrates.

Despite the importance of adhesion between electrospun meshes and substrates, the knowledge on adhesion mechanism and the method to improve the adhesion remain limited. Here, we precisely design the model system based on electrospun poly(ethylene oxide) (PEO) meshes and the substrate of styrene-b-(ethylene-co-butylene)-b-styrene elastomer (SEBS), and quantitatively measure the adhesion with a weight method. The surfaces of SEBS with different roughness are obtained by casting SEBS solution on the smooth and rough glass slides, respectively. Then, the surfaces of casted SEBS are respectively grafted with PEG oligomers and long PEG chains much larger than the entanglement molecular weight by surface-initiated atom transfer radical polymerization (SI-ATRP) of poly(ethylene glycol) methyl ether methacrylate (PEGMA). The detached surfaces of SEBS and electrospun fibers after adhesion measurements are analyzed by scanning electron microscopy (SEM). The adhesive force and adhesion energy are found to lie in the range from 68 to 220 mN and from 12 to 46 mJ/m(2), respectively, which are slightly affected by surface roughness of substrate but mainly determined by surface interactions. Just as the chemical cross-linking induces the strong adhesion, the chain entanglements on the interface lead to the higher adhesion than those generated by hydrophilic-hydrophobic interactions and hydrophilic interactions. The long grafted chains and the enhanced temperature facilitate the chain entanglements, resulting in the strong adhesive force. This work sheds new light on the adhesion mechanism at molecular level, which may be helpful to improve the adhesion between the electrospun fibers and substrates in an environmentally friendly manner.

Influence of Urea on Shifting Hydrophilic to Hydrophobic Interactions of Pr(NO3)3, Sm(NO3)3, and Gd(NO3)3 with BSA in Aqueous Citric Acid: A Volumetric, Viscometric, and Surface Tension Study

Density, surface tension, and viscosity for hexahydrate nitrate salts of praseodymium, samarium, and gadolinium from (0.023 to 0.150) mol·kg–1 in aqueous solutions of: (a) citric acid (1.11 mol·kg–1), (b) citric acid + urea, (c) citric acid + bovine serum albumin, and (d) citric acid + urea + bovine serum albumin at 298.15 K and atmospheric pressure are reported. By using densities and viscosities, the apparent molar volumes, limiting apparent molar volumes, apparent molar transfer volumes, and viscosity B-coefficients have been calculated. The varying trends of aforesaid physicochemical parameters have been interpreted in light of the solute–solvent and solute–solute interactions. An attempt has thus been made to investigate the influence of urea on the interacting activities of lanthanide nitrate with citric acid and the critical role being played by bovine serum albumin in decoding the dominance of hydrophilic–hydrophobic interactions.

Enhanced desalination via functionalized carbon nanotube immobilized membrane in direct contact membrane distillation

In this paper, for the first time we report the development of carbon nanotube immobilized membrane (CNIM) on porous polypropylene support for direct contact membrane distillation (DCMD) desalination application. We also describe the effect of specific interaction of functional group of carbon nanotubes (CNTs) with water moisture on the enhancement of water vapor flux in DCMD via alteration of polar–non polar nature of membrane surface. The incorporation of carboxylic acid (−COOH) functional group on carbon nanotubes alters the hydrophilic–hydrophobic interaction of water moistures with the membrane surface that provides additional pathway for enhanced water vapor transport. The water vapor flux was obtained 36.8kg/m2h at 70°C for CNT–COOH–PP, which is 51.5% higher than unmodified polypropylene membrane at salt concentration 10,000ppm in feed. The salt rejection was found greater than 99.9% at salt concentration 10,000ppm in feed solution. An increase in mass transfer coefficient about 1.5 times was also observed for CNT–COOH–PP membrane. The CNIM also exhibits higher thermal stability at elevated temperatures.

Mimicking Bubble Use in Nature: Propulsion of Janus Particles due to Hydrophobic‐Hydrophilic Interactions

Bubbles are widely used by animals in nature in order to fulfill important functions. They are used by animals in order to walk underwater or to stabilize themselves at the water/air interface. The main aim of this work is to imitate such phenomena, which is the essence of biomimetics. Here, bubbles are used to propel and to control the location of Janus particles in an aqueous medium. The synthesis of Janus SiO2-Ag and polystyrene-Ag (PS-Ag) particles through embedment in Parafilm is presented. The Janus particles, partially covered with catalytically active Ag nanoparticles, are redispersed in water and placed on a glass substrate. The active Ag sites are used for the splitting of H2O2 into water and oxygen. As a result, an oxygen bubble is formed on one side of the particle and promotes its propulsion. Once formed, the bubble-particle complex is stable and therefore, can be manipulated by tuning hydrophilic-hydrophobic interactions with the surface. In this way a transition between two- and three- dimensional motion is possible by changing the hydrophobicity of the substrate. Similar principles are used in nature.

Effects of concentration and temperature on interactions in (l-alanine/l-threonine/glycylglycine + aqueous d-glucose/aqueous sucrose) systems: Insights from viscosity measurements

Viscosities of (l-alanine/l-threonine/glycylglycine+1.13molkg−1 aqueous d-glucose/1.27molkg−1 aqueous sucrose) systems have been determined as a function of molal concentration of amino acid/peptide at different temperatures: (298.15, 303.15, 308.15, 313.15, 318.15, 323.15, and 328.15)K. Using the viscosity values of the solvent and solution, viscosity B-coefficients, activation free energy (Δμ2°#), activation enthalpy (ΔH2°#) and activation entropy (ΔS2°#) values have been computed. The computed Jones–Dole B-coefficients and activation free energy (Δμ2°#) values have been discussed in terms of ionic–hydrophilic, hydrophilic–hydrophilic and hydrophilic–hydrophobic interactions; and structure-making/structure-breaking tendency of amino acid/peptide molecules.

Asymmetric Electrostatic and Hydrophobic–Hydrophilic Interaction Forces between Mica Surfaces and Silicone Polymer Thin Films

We have synthesized model hydrophobic silicone thin films on gold surfaces by a two-step covalent grafting procedure. An amino-functionalized gold surface reacts with monoepoxy-terminated polydimethylsiloxane (PDMS) via a click reaction, resulting in a covalently attached nanoscale thin film of PDMS, and the click chemistry synthesis route provides great selectivity, reproducibility, and stability in the resulting model hydrophobic silicone thin films. The asymmetric interaction forces between the PDMS thin films and mica surfaces were measured with the surface forces apparatus in aqueous sodium chloride solutions. At an acidic pH of 3, attractive interactions are measured, resulting in instabilities during both approach (jump-in) and separation (jump-out from adhesive contact). Quantitative analysis of the results indicates that the Derjaguin-Landau-Verwey-Overbeek theory alone, i.e., the combination of electrostatic repulsion and van der Waals attraction, cannot fully describe the measured forces and that the additional measured adhesion is likely due to hydrophobic interactions. The surface interactions are highly pH-dependent, and a basic pH of 10 results in fully repulsive interactions at all distances, due to repulsive electrostatic and steric-hydration interactions, indicating that the PDMS is negatively charged at high pH. We describe an interaction potential with a parameter, known as the Hydra parameter, that can account for the extra attraction (low pH) due to hydrophobicity as well as the extra repulsion (high pH) due to hydrophilic (steric-hydration) interactions. The interaction potential is general and provides a quantitative measure of interfacial hydrophobicity/hydrophilicity for any set of interacting surfaces in aqueous solution.

A Novel Injectable pH/Temperature Sensitive CS-HLC/β-GP Hydrogel: The Gelation Mechanism and Its Properties

The chitosan-human-like collagen/β-sodium glycerophosphate (CS-HLC/β-GP) hydrogel, is sensitive to pH and temperature changes and has proved to be a potential candidate as an injectable filling biomaterial in plastic and reconstruction surgery. The formation and pH/temperature-sensitivity mechanism of the novel CS-HLC/β-GP hydrogel were explored by Fourier transform infrared spectroscopy (FTIR) and swelling tests. Our results showed that an amide bond (-CONH) is formed between the carbonyl (CO) of HLC and the amino of CS and -NRH2 + is formed between the amide bond and β-GP; the temperature sensitivity depended on the hydrophobic-hydrophilic interaction of molecular chains, and the pH sensitivity depended on the electrostatic interaction of ionic groups (-NRH2 + and -OPO3 2-). The properties of the novel CS-HLC/β-GP hydrogel were also examined using the tube inverting method, the swelling test, the liquid displacement method, and mechanical testing. The gelling time before and after addition of HLC is 30 min and 8 min, respectively, at 37°C. Compared with conventional CS/β-GP hydrogels, such as CS-AC (animal-derived collagen)/β-GP hydrogel, the CS-HLC/β-GP hydrogel showed a desirable porosity level, swelling ratio, pH/temperature sensitivity, a smooth surface, regular porous networks, and adequate mechanical strength and cross-linking densities. Therefore, the CS–HLC/β-GP hydrogels are excellent candidates for use in biomedical fields, such as in soft tissue defect filling and drug delivery.

Polyamidoamine dendrimer conjugated chitosan nanoparticles for the delivery of methotrexate

Encapsulating anticancer drugs to synthetic polymer is a promising approach to improve the efficiency and reduce the side effects of anticancer drugs. In this study, novel chitosan derivatives with polyamidoamine moieties (CS-PAMAM) were synthesized and characterized by morphology, particle size, and zeta potential. Then the anticancer drug–methotrexate-encapsulated CS-PAMAM was prepared by hydrophobic–hydrophilic interactions. The drug release assay showed that the amount of the methotrexate release from CS-PAMAM was pH depended. Meanwhile, the cell viability assay illustrated that CS-PAMAM was suitable for the drug delivery because of its low cytotoxicity on cells. Moreover, our results showed that the CS-PAMAM could significantly improve the cytotoxicity of free methotrexate on A549 cells. These results demonstrate that CS-PAMAM may provide a suitable platform for the water-insoluble drug delivery.

Molecular Hairpin: A Possible Model for Inhibition of Tau Aggregation by Tannic Acid

Inhibition of anomalous aggregation of tau protein would be an attractive therapeutic target for Alzheimer's disease (AD). In this study, tannic acid (TA), a polymeric plant polyphenol, and its monomer, gallic acid (GA), were introduced as the references to afford a molecular framework that integrates tau binding properties and inhibitory effects. Using a thioflavin S fluorescence assay and electron microscopy, we demonstrated that TA could competently inhibit the in vitro aggregation of tau peptide R3, corresponding to the third repeat unit of the microtubule-binding domain, with an IC50 of 3.5 μM, while GA's inhibition was comparatively piddling (with an IC50 of 92 μM). In the isothermal titration calorimetry experiment, we found that TA could strongly bind to R3 with a large amount of heat released. Circular dichroism spectra showed TA dose-dependently suppressed the conformational transition of R3 from a random coil structure to a β-sheet structure during the aggregation process. Finally, a structural model was built using molecular docking simulation to elucidate the possible binding sites for TA on the tau peptide surface. Our results suggest that TA recognizably interacts with tau peptide by forming a hairpin binding motif, a key framework required for inhibiting tau polymerization, in addition to hydrogen bonding, hydrophilic-hydrophobic interactions, and static electrical interactions, as reported previously. The inhibitory effect of TA on human full-length tau protein (tau441) was also verified by electron microscopy. This finding hints at the possibility of TA as a leading compound of anti-AD drugs and offers a new stratagem for the rational molecular design of a tau aggregation inhibitor.

The cost of living in the membrane: A case study of hydrophobic mismatch for the multi-segment protein LeuT

Many observations of the role of the membrane in the function and organization of transmembrane (TM) proteins have been explained in terms of hydrophobic mismatch between the membrane and the inserted protein. For a quantitative investigation of this mechanism in the lipid–protein interactions of functionally relevant conformations adopted by a multi-TM segment protein, the bacterial leucine transporter (LeuT), we employed a novel method, Continuum-Molecular Dynamics (CTMD), that quantifies the energetics of hydrophobic mismatch by combining the elastic continuum theory of membrane deformations with an atomistic level description of the radially asymmetric membrane–protein interface from MD simulations. LeuT has been serving as a model for structure–function studies of the mammalian neurotransmitter:sodium symporters (NSSs), such as the dopamine and serotonin transporters, which are the subject of intense research in the field of neurotransmission. The membrane models in which LeuT was embedded for these studies were composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid, or 3:1 mixture of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) lipids. The results show that deformation of the host membrane alone is not sufficient to alleviate the hydrophobic mismatch at specific residues of LeuT. The calculations reveal significant membrane thinning and water penetration due to the specific local polar environment produced by the charged K288 of TM7 in LeuT, that is membrane-facing deep inside the hydrophobic milieu of the membrane. This significant perturbation is shown to result in unfavorable polar–hydrophobic interactions at neighboring hydrophobic residues in TM1a and TM7. We show that all the effects attributed to the K288 residue (membrane thinning, water penetration, and the unfavorable polar–hydrophobic interactions at TM1a and TM7), are abolished in calculations with the K288A mutant. The involvement of hydrophobic mismatch is somewhat different in the functionally distinct conformations (outward-open, occluded, inward-open) of LeuT, and the differences are shown to connect to structural elements (e.g., TM1a) known to play key roles in transport. This finding suggests a mechanistic hypothesis for the enhanced transport activity observed for the K288A mutant, suggesting that the unfavorable hydrophobic–hydrophilic interactions hinder the motion of TM1a in the functionally relevant conformational transition to the inward-open state. Various extents of such unfavorable interactions, involving exposure to the lipid environment of adjacent hydrophobic and polar residues, are common in multi-segment transmembrane proteins, and must be considered to affect functionally relevant conformational transitions.

Why GPCRs behave differently in cubic and lamellar lipidic mesophases.

Recent successes in the crystallographic determination of structures of transmembrane proteins in the G protein-coupled receptor (GPCR) family have established the lipidic cubic phase (LCP) environment as the medium of choice for growing structure-grade crystals by the method termed “in meso”. The understanding of in meso crystallogenesis is currently at a descriptive level. To enable an eventual quantitative, energy-based description of the nucleation and crystallization mechanism, we have examined the properties of the lipidic cubic phase system and the dynamics of the GPCR rhodopsin reconstituted into the LCP with coarse-grained molecular dynamics simulations with the Martini force-field. Quantifying the differences in the hydrophobic/hydrophilic exposure of the GPCR to lipids in the cubic and lamellar phases, we found that the highly curved geometry of the cubic phase provides more efficient shielding of the protein from unfavorable hydrophobic exposure, which leads to a lesser hydrophobic mismatch and less unfavorable hydrophobic–hydrophilic interactions between the protein and lipid–water interface in the LCP, compared to the lamellar phase. Since hydrophobic mismatch is considered a driving force for oligomerization, the differences in exposure mismatch energies between the LCP and the lamellar structures suggest that the latter provide a more favorable setting in which GPCRs can oligomerize as a prelude to nucleation and crystal growth. These new findings lay the foundation for future investigations of in meso crystallization mechanisms related to the transition from the LCP to the lamellar phase and studies aimed at an improved rational approach for generating structure-quality crystals of membrane proteins.

Pairwise interaction enthalpies of enantiomers of β-amino alcohols in DMSO + H2O mixtures at 298.15 K

The dilution enthalpies of enantiomers of six β-amino alcohols, namely (R)-(-)-2-amino-1-propanol versus (S)-(+)-2-amino-1-propanol, (R)-(-)-2-amino-1-butanol versus (S)-(+)-2-amino-1-butanol, and (R)-(-)-2-amino-1-pentanol versus (S)-(+)-2-amino-1-pentanol in dimethylsulfoxide (DMSO) + H(2)O mixtures (mass fractions of DMSO w = 0 to 0.3) have been determined respectively using an isothermal titration calorimeter (MicroCal ITC200, Northampton, MA, USA) at 298.15 K. According to the McMillan-Mayer theory, the corresponding homochiral enthalpic pairwise interaction coefficients (h(XX)) of the six amino alcohols have been calculated. It is found that across the whole studied composition range of mixed solvent, values of h(XX) for S-enantiomer are almost universally higher than those of R-enantiomer for each amino alcohol and that the variations of h(XX) depend largely on the composition of mixed solvent. The results were interpreted from the point of view of solute-solute interaction mediated by cosolvent DMSO, as well as competition equilibrium between hydrophobic-hydrophobic, hydrophilic-hydrophilic, and hydrophobic-hydrophilic interactions.

Enthalpic pairwise interactions of isomers of 2,4-pentanediol and 2,5-hexanediol in dimethylsulfoxide + water mixtures at 298.15 K

The dilution enthalpies of four chiral diols, namely (2S,4S)-(+)-2,4-pentanediol vs (2R,4R)-(−)-2,4-pentanediol and (2S,5S)-(+)-2,5-hexanediol vs (2R,5R)-(−)-2,5-hexanediol in dimethylsulfoxide (DMSO)+water mixtures at 298.15K have been determined respectively, using isothermal titration calorimeter (ITC). On the basis of the McMillan–Mayer theory, homochiral enthalpic pairwise interaction coefficients (hxx) of the four diols in the mixed solvents of various mass fractions (w=0–0.3) have been calculated. It is found amazedly that across the whole studied composition range of mixed solvent values of hxx for S-enantiomer are almost higher than R-enantiomer for each diol. The results are discussed from the point of view of solute–solute interaction and solute–solvent interaction accompanied by chiral discrimination effect. The variations of hxx with w for the four chiral diols depend largely on the competition equilibrium between hydrophobic–hydrophobic, hydrophilic–hydrophilic and hydrophobic–hydrophilic interactions in the ternary solution systems.

Quantitative Comparison of GPCR Interactions with the Lipid Bilayer of the Cubic and Lamellar Mesophases

Recent successes in the crystallographic determination of structures of transmembrane (TM) proteins in the G protein-coupled receptor (GPCR) family have established the lipidic cubic phase (LCP or “in meso”) environment as useful for growing diffraction quality crystals. The mechanism underlying in meso crystallogenesis is currently at a descriptive level. To begin developing a quantitative, energy-based nucleation and crystallization mechanism we are conducting molecular dynamics studies of the GPCR, rhodopsin, reconstituted into the LCP using the coarse-grained representations of the Martini force-field. The first aim is to quantify differences in the hydrophobic/hydrophilic exposure of the GPCR to lipids in the cubic and lamellar phases. Simulations of a single rhodopsin molecule in these monoolein-based mesophases showed more energetically unfavorable hydrophobic-hydrophilic interactions between the protein and lipid in planar bilayers of the lamellar phase. The reduced level of hydrophobic mismatch in the LCP, by contrast, is attributable to the highly curved geometry of the cubic phase that provides for more efficient shielding of the protein from unfavorable hydrophobic exposure. Since hydrophobic mismatch can drive oligomerization (Mondal et al., BJ 2011 - in press), these differences suggest that compared to the LCP, lamellar structures provide a more favorable setting in which GPCRs can oligomerize as a prelude to nucleation and crystal growth. These new findings lay the foundation for future studies of in meso crystallization mechanisms and for a rational approach to the generation of structure-quality crystals of membrane proteins.

Hydrophilic Interfacing for Thermal Micro Assembly of Polymers (HITMAP)

This paper presents a simple approach to create microchannels in polydimethylsiloxane (PDMS) using basic hydrophobic–hydrophilic interactions of polymers. During polymerization, low molecular weight hydrophobic chains of PDMS expel hydrophilic moieties. This phenomenon has been used to create microchannels in PDMS. The process is simple, systematic, flexible in design, easy to implement, rapid, inexpensive and does not require lithography. Fabrication of microchannels in PDMS can be carried out using bench-top tools without the aid of any special facilities or equipment. With directed thermal polymerization over the hot plate, the expulsion of hydrophilic materials creates microchannels along the path traveled by particles. The approach is sensitive to the polymer viscosity, temperature profile and the surface chemistry of the particles. This work can have important implications in reducing the cost and time for prototyping polymer based applications in separation science, cell behavior studies, catalytic membranes and hydrogen storage. The membranes are characterized for electrical continuity and charge effects on conductivity.

Interactions in ( l-alanine/ l-threonine + aqueous glucose/aqueous sucrose) systems at (298.15–323.15) K

Densities and speeds of sound of ( l-alanine + 1 mol L −1 aqueous glucose/1 mol L −1 aqueous sucrose) and ( l-threonine + 1 mol L −1 aqueous glucose/1 mol L −1aqueous sucrose) systems have been measured as a function of molal concentration of l-alanine and l-threonine at temperatures: (298.15, 303.15, 308.15, 313.15, 318.15, and 323.15) K. The partial molar volumes, transfer partial molar volumes, partial molar isentropic compressibilities and transfer partial molar isentropic compressibilities have been evaluated using the experimentally measured values of density and speed of sound. The trends of variations of experimental and computed parameters have been discussed in terms of ionic–hydrophilic, hydrophilic–hydrophilic and hydrophilic–hydrophobic interactions operative in the systems.

Formulation of Diblock Polymeric Nanoparticles through Nanoprecipitation Technique

Nanotechnology is a relatively new branch of science that involves harnessing the unique properties of particles that are nanometers in scale (nanoparticles). Nanoparticles can be engineered in a precise fashion where their size, composition and surface chemistry can be carefully controlled. This enables unprecedented freedom to modify some of the fundamental properties of their cargo, such as solubility, diffusivity, biodistribution, release characteristics and immunogenicity. Since their inception, nanoparticles have been utilized in many areas of science and medicine, including drug delivery, imaging, and cell biology(1-4). However, it has not been fully utilized outside of "nanotechnology laboratories" due to perceived technical barrier. In this article, we describe a simple method to synthesize a polymer based nanoparticle platform that has a wide range of potential applications. The first step is to synthesize a diblock co-polymer that has both a hydrophobic domain and hydrophilic domain. Using PLGA and PEG as model polymers, we described a conjugation reaction using EDC/NHS chemistry(5) (Fig 1). We also discuss the polymer purification process. The synthesized diblock co-polymer can self-assemble into nanoparticles in the nanoprecipitation process through hydrophobic-hydrophilic interactions. The described polymer nanoparticle is very versatile. The hydrophobic core of the nanoparticle can be utilized to carry poorly soluble drugs for drug delivery experiments6. Furthermore, the nanoparticles can overcome the problem of toxic solvents for poorly soluble molecular biology reagents, such as wortmannin, which requires a solvent like DMSO. However, DMSO can be toxic to cells and interfere with the experiment. These poorly soluble drugs and reagents can be effectively delivered using polymer nanoparticles with minimal toxicity. Polymer nanoparticles can also be loaded with fluorescent dye and utilized for intracellular trafficking studies. Lastly, these polymer nanoparticles can be conjugated to targeting ligands through surface PEG. Such targeted nanoparticles can be utilized to label specific epitopes on or in cells(7-10).