Effects of Shapes of Solute Molecules on Diffusion: A Study of Dependences on Solute Size, Solvent, and Temperature

Peptides Targeting HER2-Positive Breast Cancer Cells and Applications in Tumor Imaging and Delivery of Chemotherapeutics

Breast cancer represents the most common cancer type and one of the major leading causes of death in the female worldwide population. Overexpression of HER2, a transmembrane glycoprotein related to the epidermal growth factor receptor, results in a biologically and clinically aggressive breast cancer subtype. It is also the primary driver for tumor detection and progression and, in addition to being an important prognostic factor in women diagnosed with breast cancer, HER2 is a widely known therapeutic target for drug development. The aim of this review is to provide an updated overview of the main approaches for the diagnosis and treatment of HER2-positive breast cancer proposed in the literature over the past decade. We focused on the different targeting strategies involving antibodies and peptides that have been explored with their relative outcomes and current limitations that need to be improved. The review also encompasses a discussion on targeted peptides acting as probes for molecular imaging. By using different types of HER2-targeting strategies, nanotechnology promises to overcome some of the current clinical challenges by developing novel HER2-guided nanosystems suitable as powerful tools in breast cancer imaging, targeting, and therapy.

The chemical neighborhood of cells in a diffusion-limited system

Microorganisms follow us everywhere, and they will be essential to sustaining long-term human space exploration through applications such as vitamin synthesis, biomining, and more. Establishing a sustainable presence in space therefore requires that we better understand how stress due to the altered physical conditions of spaceflight affects our companion organisms. In microgravity environments such as orbital space stations, microorganisms likely experience the change in gravity primarily through changes in fluid mixing processes. Without sedimentation and density-driven convection, diffusion becomes the primary process governing the movement of growth substrates and wastes for microbial cells in suspension culture. Non-motile cells might therefore develop a substrate-deficient "zone of depletion" and experience stress due to starvation and/or waste build-up. This would in turn impact the concentration-dependent uptake rate of growth substrates and could be the cause of the altered growth rates previously observed in microorganisms in spaceflight and in ground-simulated microgravity. To better understand the extent of these concentration differences and their potential influence on substrate uptake rates, we used both an analytical solution and finite difference method to visualize concentration fields around individual cells. We modeled diffusion, using Fick's Second Law, and nutrient uptake, using Michaelis-Menten kinetics, and assessed how that distribution varies in systems with multiple cells and varied geometries. We determined the radius of the zone of depletion, within which cells had reduced the substrate concentration by 10%, to be 5.04 mm for an individual Escherichia coli cell in the conditions we simulated. However, we saw a synergistic effect with multiple cells near each other: multiple cells in close proximity decreased the surrounding concentration by almost 95% from the initial substrate concentration. Our calculations provide researchers an inside look at suspension culture behavior in the diffusion-limited environment of microgravity at the scale of individual cells.

Peel Diffusion and Antifungal Efficacy of Different Fungicides in Pear Fruit: Structure-Diffusion-Activity Relationships

Fungal pathogens can invade not only the fruit peel but also the outer part of the fruit mesocarp, limiting the efficacy of fungicides. In this study, the relationships between fungicide structure, diffusion capacity and in vivo efficacy were evaluated for the first time. The diffusion capacity from pear peel to mesocarp of 11 antifungal compounds, including p-aminobenzoic acid, carbendazim, difenoconazole, dipicolinic acid, flusilazole, gentamicin, kojic acid, prochloraz, quinolinic acid, thiophanate methyl and thiram was screened. The obtained results indicated that size and especially polarity were negatively correlated with the diffusion capacity. Although some antifungal compounds, such as prochloraz and carbendazim, were completely degraded after a few days in peel and mesocarp, other compounds, such as p-aminobenzoic acid and kojic acid, showed high stability. When applying the antifungal compounds at the EC₅₀ concentrations, it was observed that the compounds with high diffusion capacity showed higher in vivo antifungal activity against Alternaria alternata than compounds with low diffusion capacity. In contrast, there was no relationship between stability and in vivo efficacy. Collectively, the obtained results indicated that the diffusion capacity plays an important role in the efficacy of fungicides for the control of pear fruit diseases.

Atomistic Simulations of Dopamine Diffusion Dynamics on a Pristine Graphene Surface

Carbon microelectrodes enable in vivo detection of neurotransmitters, and new electrodes aim to optimize the carbon surface. However, atomistic detail on the diffusion and orientation of neurotransmitters near these surfaces is lacking. Here, we employ molecular dynamics simulations to investigate the surface diffusion of dopamine (DA), its oxidation product dopamine-o-quinone (DOQ), and their protonated forms on the pristine basal plane of flat graphene. We find that all DA species rapidly adsorb to the surface and remain adsorbed, even without a holding potential or graphene surface defects. We also find that the diffusivities of the adsorbed and the fully solvated DA are similar and that the protonated species diffuse more slowly on the surface than their corresponding neutral forms, while the oxidized species diffuse more rapidly. Structurally, we find that the underlying graphene lattice has little influence over the molecular adsorbate's lateral position, and the vertical placement of the amine group on dopamine is highly dependent upon its charge. Finally, we find that solvation has a large effect on surface diffusivities. These first results from molecular dynamics simulations of dopamine at the aqueous-graphene interface show that dopamine diffuses rapidly on the surface, even without an applied potential, and provide a basis for future simulations of neurotransmitter structure and dynamics on advanced carbon materials electrodes.

Breakdown of the Stokes-Einstein relation in supercooled water: the jump-diffusion perspective

Although water is the most ubiquitous liquid it shows many thermodynamic and dynamic anomalies. Some of the anomalies further intensify in the supercooled regime. While many experimental and theoretical studies have focused on the thermodynamic anomalies of supercooled water, fewer studies explored the dynamical anomalies very extensively. This is due to the intricacy of the experimental measurement of the dynamical properties of supercooled water. Violation of the Stokes-Einstein relation (SER), an important relation connecting the diffusion of particles with the viscosity of the medium, is one of the major dynamical anomalies. In absence of experimentally measured viscosity, researchers used to check the validity of SER indirectly using average translational relaxation time or α-relaxation time. Very recently, the viscosity of supercooled water was accurately measured at a wide range of temperatures and pressures. This allowed direct verification of the SER at different temperature-pressure thermodynamic state points. An increasing breakdown of the SER was observed with decreasing temperature. Increasing pressure reduces the extent of breakdown. Although some well-known theories explained the above breakdown, a detailed molecular mechanism was still elusive. Recently, a translational jump-diffusion (TJD) approach has been able to quantitatively explain the breakdown of the SER in pure supercooled water and an aqueous solution of methanol. The objective of this article is to present a detailed and state-of-the-art analysis of the past and present works on the breakdown of SER in supercooled water with a specific focus on the new TJD approach for explaining the breakdown of the SER.

Active food packaging of cellulose acetate: Storage stability, protective effect on oxidation of riboflavin and release in food simulants

In this work, cellulose acetate films were prepared with the incorporation of different carotenoids (lycopene, norbixin, and zeaxanthin). The effect of adding these natural antioxidants was evaluated through stability during storage under controlled conditions (temperature and light), degradation rate coefficient, release in food simulants and protective effect on oxidation of vitamin B₂. During storage at 25 °C or 40 °C the light showed a greater effect on the stability of the carotenoids, with significant increase in reaction constants (k) and decrease in half-life (t_1/2). The degradation of the carotenoids was followed by a variation in the color parameters and mechanical properties. The films with norbixin showed the highest barrier to the transmission of UV-Vis light, consequently preserving 72% of a vitamin B₂ stored under a photooxidative environment. Lycopene presented a higher release rate than norbixin and zeaxanthin to a fatty food simulant.

Composite Microgels Created by Complexation between Polyvinyl Alcohol and Graphene Oxide in Compressed Double-Emulsion Drops

Microgels, microparticles made of hydrogels, show fast diffusion kinetics and high reconfigurability while maintaining the advantages of hydrogels, being useful for various applications. Here, presented is a new microfluidic strategy for producing polymer-graphene oxide (GO) composite microgels without chemical cues or a temperature swing for gelation. As a main component of microgels, polymers that are able to form hydrogen bonds, such as polyvinyl alcohol (PVA), are used. In the mixture of PVA and GO, GO is tethered by PVA through hydrogen bonding. When the mixture is rapidly concentrated in the core of double-emulsion drops by osmotic-pressure-driven water pumping, PVA-tethered GO sheets form a nematic phase with a planar alignment. In addition, the GO sheets are linked by additional hydrogen bonds, leading to a sol-gel transition. Therefore, the PVA-GO composite remains undissolved when it is directly exposed to water by oil-shell rupture. These composite microgels can be also produced using poly(ethylene oxide) or poly(acrylic acid), instead of PVA. In addition, the microgels can be functionalized by incorporating other polymers in the presence of the hydrogel-forming polymers. It is shown that the multicomponent microgels made from a mixture of polyacrylamide, PVA, and GO show an excellent adsorption capacity for impurities.

Diffusivities in 1-Alcohols Containing Dissolved H2, He, N2, CO, or CO2 Close to Infinite Dilution

The influence of the strength of intermolecular interactions on mass diffusive processes remains poorly understood for mixtures of associative liquids with dissolved gases. For contributing to a fundamental understanding of the interplay between liquid structures and mass diffusivities in such systems, dynamic light scattering, Raman spectroscopy, and molecular dynamics simulations were used in this work. As model systems, binary mixtures consisting of the gases hydrogen, helium, nitrogen, carbon monoxide, or carbon dioxide dissolved in ethanol, 1-hexanol, or 1-decanol were selected. Experiments and simulations were performed at macroscopic thermodynamic equilibrium close to infinite dilution of solute for temperatures between 303 and 423 K. The Fick diffusion coefficients and self-diffusivities of the gas solutes increase with increasing temperature, decreasing alkyl chain length of the 1-alcohols, and decreasing molar mass of the solutes except for helium and hydrogen showing the opposite behavior. The analysis of the liquid structure of the mixtures showed that the fraction of hydrogen-bonded alcohol molecules decreases with increasing alkyl chain length and temperature. From the obtained structure-property relationships, a new correlation was developed to predict mass diffusivities in binary mixtures consisting of n-alkanes or 1-alcohols with dissolved gases close to infinite dilution within 10% on average.

Chemically Selective Transport in a Cross-Linked HII Phase Lyotropic Liquid Crystal Membrane

The uniform size and complex chemical topology of the pores formed by self-assembled amphiphilic molecules such as liquid crystals make them promising candidates for selective separations. In this work, we observe the transport of water, sodium ions, and 20 small polar solutes within the pores of a lyotropic liquid crystal (LLC) membrane using atomistic molecular simulations. We find that the transport of a species is dependent not only on molecular size but also on chemical functionality. The membrane's inhomogeneous composition gives rise to radially dependent transport mechanisms with respect to the pore centers. We observe that all solutes perform intermittent hops between lengthy periods of entrapment. Three different trapping mechanisms are responsible for this behavior. First, solutes that drift out of the pore can become entangled among the dense monomer tails. Second, solutes can donate hydrogen bonds to the monomer head groups. Third, solutes can coordinate with sodium counterions. The degree to which a solute is affected by each mechanism is dependent on the chemical functionality of the solute. Using the insights developed in this study, we can begin to think about how to redesign existing LLC membranes to perform solute-specific separations.

Demonstrating the Influence of Physical Aging on the Functional Properties of Shape-Memory Polymers

Polymers that allow the adjustment of Shape-Memory properties by the variation of physical parameters during programming are advantageous compared with their counterparts requiring synthesis of new material. Here, we explored the influence of hydrolytic (physical) aging on the Shape-Memory properties of the polyetherurethane system Estane, programmed in repeated thermomechanical cycles under torsional load. We were able to demonstrate that physical aging occurred through water adsorption influencing the existing free volume of the samples as well as the functional properties of Estane. Dynamic Mechanical Thermal Analysis determined the glass transition temperatures of dry and hydrolytically aged samples. According to our results, Estane takes up to 3 wt % water for two weeks (at an ambient temperature of θ = 20 °C). The glass transition temperatures of dry samples decreased within this period from 55 to 48 °C as a consequence of a plasticization effect. Next, for both samples, six subsequent thermomechanical cycles under torsional loading conditions were performed. We were able to confirm that hydrolytically aged samples showed higher shape recovery ratios of R_r ≥ 97%, although dry samples revealed better shape fixity values of about 98%. Moreover, it was observed that the shape fixity ratio of both dry and hydrolytically (physically) aged samples remained almost unchanged even after six successive cycles. Besides this, the shape recovery ratio values of the aged samples were nearly unaltered, although the shape recovery values of the dry samples increased from R_r = 81% in the first cycle to 96% at the end of six repeated cycles. Further, the evolution of the free volume as a function of temperature was studied using Positron Annihilation Lifetime Spectroscopy. It was shown that the uptake of two other organic solvents (acetone and ethanol) resulted in much higher specific free volume inside the samples and, consequently, a softening effect was observed. We anticipate that the presented approach will assist in defining design criteria for self-sufficiently moving scaffolds within a knowledge-based development process.

Food-packaging migration models: A critical discussion

The widely accepted and used migration models that describe the mass transport from polymeric packaging material to food and food simulants are confirmed here. A critical review of the most accepted models is presented in detail. Their main advantages and weak points, regarding their predictive accuracy, are discussed and weighted toward their usage extensiveness. By identifying the specific areas where using such models may not provide a strong correlation between theoretical and actual results, this work also aims in outlining some particular directions regarding further research on food - packaging interactions.

Molecular insight into the microstructure and microscopic dynamics of pyridinium ionic liquids with different alkyl chains based on temperature response

High temperature is advantageous to the aggregation of the polar regions as well as the nonpolar regions of pyridinium ionic liquids.

HER2-positive breast cancer targeting and treatment by a peptide-conjugated mini nanodrug

HER2+ breast cancer is one of the most aggressive forms of breast cancer. The new polymalic acid-based mini nanodrug copolymers are synthesized and specifically characterized to inhibit growth of HER2+ breast cancer. These mini nanodrugs are highly effective and in the clinic may substitute for trastuzumab (the marketed therapeutic antibody) and antibody-targeted nanobioconjugates. Novel mini nanodrugs are designed to have slender shape and small size. HER2+ cells were recognized by the polymer-attached trastuzumab-mimetic 12-mer peptide. Synthesis of the nascent cell-transmembrane HER2/neu receptors by HER2+ cells was inhibited by antisense oligonucleotides that prevented cancer cell proliferation and significantly reduced tumor size by more than 15 times vs. untreated control or PBS-treated group. We emphasize that the shape and size of mini nanodrugs can enhance penetration of multiple bio-barriers to facilitate highly effective treatment. Replacement of trastuzumab by the mimetic peptide favors reduced production costs and technical efforts, and a negligible immune response.