Search results for "nanotechnology"
showing 10 items of 9818 documents
On the tribology and rheology of polymer brushes in good solvent conditions: a molecular dynamics study
2003
Tribological and rheological properties of two polymer brushes in relative sliding motion and good solvent conditions are investigated by means of molecular dynamics (MD) simulations. The lateral forces between the brushes are found to decrease logarithmically with increasing relative sliding velocity v0 over a range of more than one decade in v0. We also observe an almost logarithmic relaxation of the end-to-end distance vector that occurs after sliding is stopped. The coincidence of these logarithmic dependencies support the picture that friction between polymer brushes is small due to the retraction of the polymers from the interpenetration zone. The shear stress relaxes almost instantly…
Can one detach a fully adsorbed flexible polymer chain by an ultra-small external force?
2013
Full adsorption of flexible chains onto typical solid substrates occurs at a surface interaction energy of (5–10) kBT. The corresponding detachment force is in the range 10–50 pN. In contrast to “bare” solid substrates common to non-living materials, surfaces coated with brush-like polymer layers are very common in biological soft matter. We employ a simple mean-field approach to describe the effects of weak attraction between a floating long macromolecule and the brush. We show that even for a moderately thick brush a very small effective attraction is enough to produce complete binding of the long chain. The detachment force scales as , where W is the brush thickness. Hence the force coul…
Inorganic Polymers: Morphogenic Inorganic Biopolymers for Rapid Prototyping Chain
2013
In recent years, considerable progress has been achieved towards the development of customized scaffold materials, in particular for bone tissue engineering and repair, by the introduction of rapid prototyping or solid freeform fabrication techniques. These new fabrication techniques allow to overcome many problems associated with conventional bone implants, such as inadequate external morphology and internal architecture, porosity and interconnectivity, and low reproducibility. However, the applicability of these new techniques is still hampered by the fact that high processing temperature or a postsintering is often required to increase the mechanical stability of the generated scaffold, …
Electrochemical monitoring of ROS generation by anticancer agents: the case of chartreusin
2017
Solution phase and solid-sate electrochemical techniques centered in the voltammetry of microparticles approach are applied for testing the cytotoxic activity of anticancer drugs. The possibility of electrochemical generation of reactive oxygen species (ROS) is exploited for evaluating their contribution to cellular damage. The described methodology is applied to the case of chartreusin (Ch) whose electrochemistry in non-aqueous solutions and in the solid state in contact with aqueous electrolytes is described in the absence (experimental data were confirmed by theoretical calculations) and in the presence of double-stranded DNA (dsDNA). In parallel, scanning electrochemical microscopy (SEC…
Electrochemical monitoring of ROS influence on seedlings and germination response to salinity stress of three species of the tribe Inuleae.
2019
Solid-state electrochemical methods have been applied to the establishment of patterns of plant growth and response to saline stress using seedlings of Inula helenium L., Dittrichia viscosa (L.) Greuter (Inula viscosa (L.) Aiton), Limbarda crithmoides (L.) Dumort (Inula crithmoides L.). Upon in situ electrochemical generation of reactive oxygen species (ROS) the reactivity with such species was monitored using voltammetric signals associated to the oxidation of polyphenolic components of the plants. A simple kinetic model based on second-order reaction between ROS and polyphenolic components is applied to electrochemical data yielding apparent rate constants which can be correlated with the…
Organic derivatives of mercury and tin as promoters of membrane lipid peroxidation.
2008
The toxicity mechanisms of mercury and tin organic derivatives are still under debate. Generally the presence of organic moieties in their molecules makes these compounds lipophilic and membrane active species. The recent results suggest that Hg and Sn compounds deplete HS-groups in proteins, glutathione and glutathione-dependent enzymatic systems; this process also results in the production of reactive oxygen species (ROS), the enhancement of membrane lipids peroxidation and damage of the antioxidative defence system. The goal of this review is to present recent results in the studies oriented towards the role of organomercury and organotin compounds in the xenobiotic-mediated enhancement …
Fundamentals and Applications of Cyclodextrins
2018
Cyclodextrins are natural oligosaccharides obtained from starch. They were discovered in 1891 by Villiers, and attracted major scientific and industrial interests from the late 1970s. Actually, cyclodextrins are among the most remarkable macrocyclic molecules with major theoretical and practical interest for chemistry and biology. Cyclodextrins belong to the family of cage molecules due to their structure, which is composed of a hydrophobic cavity that can encapsulate other molecules. Indeed, the most characteristic feature of cyclodextrins is their ability to form inclusion complexes with various molecules through host-guest interactions. Cyclodextrins and their derivatives have a wide var…
trans- andcis-Bicyclo[n.1.0]alk-2-ynes of Medium Ring Size
1997
Starting from cycloalkenes, the cis- or trans-cyclopropano anellated cycloalkynes 2–7 of medium ring size were synthesized. The triple bonds were introduced in the final reaction step either by the fragmentation of the corresponding 1,2,3-selenadiazoles or by direct dehydration of a ketone (Scheme 2). The cis-fused bicycles 2 and 3 and the trans-fused bicycles 5, 6 and 7 could be isolated in a pure state. The intermediary existence of the most strained system trans-bicyclo[7.1.0]dec-2-yne (4) was proven by trapping reactions.
Polysarcosine-containing copolymers: Synthesis, characterization, self-assembly, and applications
2018
Although the first polysarcosine (pSar) synthesis by Wesseley et al. was reported almost a century ago, it was only recently that pSar gained broader attention and is considered a potential alternative of poly(ethylene glycol) (PEG). In contrast to polyethers, such as PEG, pSar is a polypeptoid based on the amino acid sarcosine, i.e. N-methylated glycine. As a polymer, pSar combines PEG-like properties, e.g., excellent solubility in water, protein resistance, low cellular toxicity and a non-immunogenic character, while being based on endogenous material. Sarcosine can be obtained in a simple one-step reaction of bromoacetic acid and methylamine, easily transferred into the sarcosine N-(thio…
Synthesis and characterization of bisalkylated polysarcosine-based lipopolymers
2019
The use of PEGylated lipids for the synthesis of stealth liposomes and lipid formulations for nucleic acid delivery has promoted the development of nanoparticle based drugs for cancer therapy, and chronic diseases. Moreover, several other nanomedicines based on these materials have advanced into clinical trails. This enormous success, however, has recently been compromised by the occurrence of immune responses towards PEG, which render pharmacokinetics and can substantially reduce the therapeutic efficiency of drugs. Therefore, alternatives for PEGylated lipids with comparable or even identical solution properties are required. In this work, we report the synthesis of polysarcosine based li…