Crystal plane-dependent gas-sensing properties of zinc oxide nanostructures: experimental and theoretical studies

Crystal plane-dependent gas-sensing performance of ZnO nanostructures toward ethanol has been investigated experimentally and theoretically through DFT simulation.

Abstract P2-09-22: Synthesis of nitroxyl radical-containing nanoparticles with pH-sensitive behavior and their application for cancer therapy

Extensive research has documented that redox dysregulation is a causative involvement in tumor progression, and reactive oxygen species (ROS) are involved in cancer initiation and progression. ROS are mutagenic and may promote cancer. Early studies observed that the increased ROS production was in response to oncogenic activity. It is now widely accepted that redox chemotherapeutics represents a novel class of promising anticancer agents. Small molecule nitroxides are stable free radicals which are able to scavenge radicals and act as radical chain reaction terminators. Nitroxyl radical, 2, 2, 6, 6-tetramethyl-piperidine-1-oxyl (TEMPO), is capable of reacting with ROS and shows chemotherapeutic efficacy in various cancer cell lines and xenograft models. However, low-molecular-weight TEMPO derivatives are hard to utilize in the clinic, owing to a preferential renal clearance and side effects such as antihypertensive effect.

To address these issues, we have designed and developed nitroxyl radical-containing nanoparticles with pH-sensitive behavior using the first generation PAMAM (G1 PAMAM) partially modified with 3,4,5,6-tetrahydrophthalic anhydride (THPA) and PROXYL. The synthesis of the modified PAMAM was carried out by a two-step reaction. Firstly, part of the primary amine end group of PAMAM dendrimers reacted with anhydride THPA to produce a THPA-modified PAMAM. The b-carboxylic acid amides between G1 PAMAM and THPA are acid-sensitive. Therefore, the THPA-modified PAMAM are stable and negatively charged at physiological pH, thus preventing blood serum aggregation. However, the THPA-modified PAMAM degrades at acidic pH, converting its surface to positive charge which is benefit for cellular uptake. Secondly, the THPA-modified PAMAM reacted subsequently with 3-carboxy-PROXYL whose carboxyl group was activated by N-hydroxysuccinimide. The EPR signal of the product was analyzed by EPR measurement and confirmed the PROXYL group covalently conjugated onto THPA-modified PAMAM. The obtained THPA-PROXYL-modified PAMAM was denoted as TP-PAMAM. Experimental results showed that TP-PAMAM was stable at pH 7.4, and hydrolyzed at pH 6.0. The rate of hydrolysis was increased with pH decreasing. In vitro studies indicated that cell proliferation of MDA-MB-231 was greatly inhibited by TP-PAMAM compared to low-molecular-weight TEMPO. This may due to the fact that cellular uptake is easy for nanoparticles with pH-sensitive behavior. Therefore, the nitroxyl radical conjugated onto the pH-sensitive nanoparticles scavenges ROS more effectively. As a result, these new nitroxyl radical-containing nanoparticles have a significantly high therapeutic efficacy in the application for cancer therapy. Hence, engineered nitroxyl radical-containing nanoparticles with pH-sensitive behavior may enable therapeutic selectivity and to overcome drug resistance and metastatic cancer.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-09-22.

Bioavailability of quercetin: problems and promises

Quercetin (QC) is a typical plant flavonoid, possesses diverse pharmacologic effects including antiinflammatory, antioxidant, anti-cancer, anti-anaphylaxis effects and against aging. However, the application of QC in pharmaceutical field is limited due to its poor solubility, low bioavailability, poor permeability and instability. To improve the bioavailability of QC, numerous approaches have been undertaken, involving the use of promising drug delivery systems such as inclusion complexes, liposomes, nanoparticles or micelles, which appear to provide higher solubility and bioavailability. Enhanced bioavailability of QC in the near future is likely to bring this product to the forefront of therapeutic agents for treatment of human disease.

Calculation of normal contact forces between silica nanospheres

In this work, interaction forces between two silica nanospheres after contact, including the van der Waals (vdW) attraction, Born repulsion, and mechanical contact forces are studied by molecular dynamics (MD) simulations. The effects of interaction path (approach or departure), initial relative velocity, and relative orientations of two nanospheres are first examined. The results show that the interparticle forces are, to a large degree, independent of these variables. Then, emphasis is given to other important variables. At a small contact deformation, the size dependence of the vdW attraction and Born repulsion qualitatively agrees with the prediction based on the conventional theories, but this becomes vague upon further deformation due to the gradually flattened shape of deformed particles. An alternative approach is provided to calculate the interparticle vdW attraction and Born repulsion forces. Moreover, the MD simulations show that the Hertz model still holds to describe the mechanical contact force at low compression, which is obtained by subtracting the vdW attraction and Born repulsion forces from the total normal force. Comparisons with the Johnson-Kendall-Roberts (JKR) and Derjaguin-Muller-Toporov (DMT) models, in terms of force-displacement relationships and contact radius, show that the two models can be used to provide the first approximation, but there is some deviation from the MD simulated results. The origins of the quantitative difference are analyzed. New equations are formulated to estimate the interaction forces between silica nanospheres, which should be useful in the dynamic simulation of silica nanoparticle systems.

Bimetallic Ag-Au nanowires: synthesis, growth mechanism, and catalytic properties

Silver-gold (Ag-Au) bimetallic nanowires were controllably synthesized by a newly developed wet-chemical method at room temperature. The Ag nanowires and Au nanoparticles were sequentially formed by reduction with vanadium oxide (V2O3) nanoparticles so as to form Ag-Au bimetal, in which the Ag nanowires show a diameter of ~20 nm and length up to 10 μm. A few unique features were noted in our new approach: it was rapid (within a few minutes), controllable in shape and size, reproducible, and there was no need for any surface modifiers. The formation and growth mechanisms of these Ag-Au bimetallic nanostructures driven by lattice match and a unique reducing agent (V2O3) have been proposed in this study. Moreover, the application of such bimetallic nanoparticles for catalytic reduction of 4-nitrophenol to 4-aminophenol was performed, and they exhibit catalytic properties superior to those of the Ag nanowires, Au nanoparticles, and Ag-Pd bimetallic nanostructures prepared under the reported conditions. These Ag-Au bimetallic nanoparticles have potential to be highly efficient catalysts for the reduction of 4-nitrophenol. This study may lead to new path for the generation of other bimetallic nanostructures with excellent catalytic efficiency.

2D and 3D anatomical analyses of hand dimensions for custom-made gloves

Measuring hand anthropometric data for the development of good-fitting gloves is crucial. In pursuing higher accuracy in hand anthropometric measurements, scanning of hand surfaces with the aids of image analysis system to acquire measurements is an alternative to the manual methods. This study proposes a new hand measuring approach by using 2D and 3D scanning which are evaluated through comparisons of manual measurements. Thirty-three dimensions are measured by using (1) tape and calliper measurement; (2) 2D image analysis; (3) 3D image analysis based on ten captures; and (4) 3D image analysis based on three captures, respectively. Repeated-measures ANOVA, correlation analysis and RMSE are used to examine the results. The hand dimensions obtained from the four methods are highly linearly correlated. Hand data taken from 3D image analysis has no significant difference compared with manual measurements on hand and wrist circumferences, length and breadth dimension, regardless of the number of captures.

Calculation of noncontact forces between silica nanospheres

Quantification of the interactions between nanoparticles is important in understanding their dynamic behaviors and many related phenomena. In this study, molecular dynamics simulation is used to calculate the interaction potentials (i.e., van der Waals attraction, Born repulsion, and electrostatic interaction) between two silica nanospheres of equal radius in the range of 0.975 to 5.137 nm. The results are compared with those obtained from the conventional Hamaker approach, leading to the development of modified formulas to calculate the van der Waals attraction and Born repulsion between nanospheres, respectively. Moreover, Coulomb's law is found to be valid for calculating the electrostatic potential between nanospheres. The developed formulas should be useful in the study of the dynamic behaviors of nanoparticle systems under different conditions.

[Mechanisms, clinical profile and role of prostaglandin and prostamide analogues in antiglaucomatous therapy]

Prostaglandin and prostamide analogues belong to a new substance group which came into the market in the 1990s. They have revolutionised antiglaucomatous therapy by their once-daily dosing regimen and fewer side effects. Today, prostaglandin and prostamide analogues are approved as first-line therapy for patients with primary open-angle glaucoma and ocular hypertension. They lower the intraocular pressure primarily by increasing the uveoscleral outflow. Recent investigations have shown that they also improve the trabecular outflow facility and thus the conventional outflow pathways. Prostaglandin and prostamide analogues are highly efficient in lowering the intraocular pressure, for which they are superior to other antiglaucomatous substance groups. In particular, they appear to have a good control of 24-hour intraocular pressure fluctuations by primarily improving the outflow pathways. Furthermore, they have less systemic side effects than β-blockers. However, their use is often associated with higher costs. In case of undesirable events, they mostly present with ocular symptoms. Based on their good clinical profile, prostaglandin and prostamide analogues play an important role in the primary and additive therapy for glaucoma.