The battle over Syria's reconstruction

Reconstruction is becoming the new battleground in the Syrian conflict—its continuation by other means. It is instrumentalized by the regime as a way to reconsolidate its control over the country and by rival regional and international powers to shape the internal balance of power and establish spheres of influence in the country. The paper examines the Asad regime’s practices, including co-optation of militia leaders via reconstruction concessions and use of reconstruction to clear strategic areas of opposition-dominated urban settlements. The paper then surveys how the geopolitical struggle in Syria has produced an asymmetry as regards reconstruction: those powers that lost the geo-political contest on the ground seek to use geo-economic superiority to reverse the geo-political outcome. Then the impact of proxy wars and spheres of influence in the country on the security context for reconstruction is examined. Finally, the reconstruction initiatives of the various external parties are assessed, including Russia, Iran and Turkey as well as the spoiler role by which the US seeks to obstruct reconstruction that would spell victory in Syria for its Russian and Iranian rivals.PostprintPeer reviewe

Toxicity and cellular uptake of gold nanoparticles: what we have learned so far?

Gold nanoparticles have attracted enormous scientific and technological interest due to their ease of synthesis, chemical stability, and unique optical properties. Proof-of-concept studies demonstrate their biomedical applications in chemical sensing, biological imaging, drug delivery, and cancer treatment. Knowledge about their potential toxicity and health impact is essential before these nanomaterials can be used in real clinical settings. Furthermore, the underlying interactions of these nanomaterials with physiological fluids is a key feature of understanding their biological impact, and these interactions can perhaps be exploited to mitigate unwanted toxic effects. In this Perspective we discuss recent results that address the toxicity of gold nanoparticles both in vitro and in vivo, and we provide some experimental recommendations for future research at the interface of nanotechnology and biological systems

Synergistic antibacterial activity of silver nanoparticles and hydrogen peroxide.

The increasing challenge of antibiotic resistance requires not only the discovery of new antibiotics, but also the development of new alternative approaches. Herein, the synergistic antibacterial activity of silver nanoparticles and hydrogen peroxide combination is reported. Unlike the bacteriostatic or slightly bactericidal activity achieved by using each agent alone, using these two agents in combination, even at relatively low concentrations, resulted in complete eradication of both the Gram negative Escherichia coli and the Gram positive Staphylococcus aureus in short treatment times indicating a clear synergistic effect between them. Modifying the surface chemistry of silver nanoparticles and the accompanied change in their surface charge enabled a further enhancement of such synergistic effect implying the importance of this aspect. Mechanistically, a Fenton-like reaction between silver nanoparticles and hydrogen peroxide is discussed and hypothesized to be the basis of the observed synergy. Achieving such a significant antibacterial activity at low concentrations reduces the potential toxicity of these agents and hence enables their utilization as an alternative antibacterial approach in wider range of applications

Colloidal Stability of Citrate and Mercaptoacetic Acid Capped Gold Nanoparticles upon Lyophilization: Effect of Capping Ligand Attachment and Type of Cryoprotectants

For various applications of gold nanotechnology, long-term nanoparticle stability in solution is a major challenge. Lyophilization (freeze–drying) is a widely used process to convert labile protein and various colloidal systems into powder for improved long-term stability. However, the lyophilization process itself may induce various stresses resulting in nanoparticle aggregation. Despite a plethora of studies evaluating lyophilization of proteins, liposomes, and polymeric nanoparticles, little is known about the stability of gold nanoparticles (GNPs) upon lyophilization. Herein, the effects of lyophilization and freeze–thaw cycles on the stability of two types of GNPs: Citrate-capped GNPs (stabilized via weakly physisorbed citrate ions, Cit-GNPs) and mercaptoacetic acid-capped GNPs (stabilized via strongly chemisorbed mercaptoacetic acid, MAA-GNPs) are investigated. Both types of GNPs have similar core size and effective surface charge as evident from transmission electron microscopy and zeta potential measurements, respectively. Plasmon absorption of GNPs and its dependence on nanoparticle aggregation was employed to follow stability of GNPs in combination with dynamic light scattering analysis. Plasmon peak broadening index (PPBI) is proposed herein for the first time to quantify GNPs aggregation using nonlinear Gaussian fitting of GNPs UV–vis spectra. Our results indicate that Cit-GNPs aggregate irreversibly upon freeze–thaw cycles and lyophilization. In contrast, MAA-GNPs exhibits remarkable stability under the same conditions. Cit-GNPs exhibit no significant aggregation in the presence of cryoprotectants (molecules that are typically used to protect labile ingredients during lyophilization) upon freeze–thaw cycles and lyophilization. The effectiveness of the cyroprotectants evaluated was on the order of trehalose or sucrose > sorbitol > mannitol. The ability of cryoprotectants to prevent GNPs aggregation was dependent on their chemical structure and their ability to interact with the GNPs as assessed with zeta potential analysis

Colloidal Stability of Citrate and Mercaptoacetic Acid Capped Gold Nanoparticles upon Lyophilization: Effect of Capping Ligand Attachment and Type of Cryoprotectants

For various applications of gold nanotechnology, long-term nanoparticle stability in solution is a major challenge. Lyophilization (freeze–drying) is a widely used process to convert labile protein and various colloidal systems into powder for improved long-term stability. However, the lyophilization process itself may induce various stresses resulting in nanoparticle aggregation. Despite a plethora of studies evaluating lyophilization of proteins, liposomes, and polymeric nanoparticles, little is known about the stability of gold nanoparticles (GNPs) upon lyophilization. Herein, the effects of lyophilization and freeze–thaw cycles on the stability of two types of GNPs: Citrate-capped GNPs (stabilized via weakly physisorbed citrate ions, Cit-GNPs) and mercaptoacetic acid-capped GNPs (stabilized via strongly chemisorbed mercaptoacetic acid, MAA-GNPs) are investigated. Both types of GNPs have similar core size and effective surface charge as evident from transmission electron microscopy and zeta potential measurements, respectively. Plasmon absorption of GNPs and its dependence on nanoparticle aggregation was employed to follow stability of GNPs in combination with dynamic light scattering analysis. Plasmon peak broadening index (PPBI) is proposed herein for the first time to quantify GNPs aggregation using nonlinear Gaussian fitting of GNPs UV–vis spectra. Our results indicate that Cit-GNPs aggregate irreversibly upon freeze–thaw cycles and lyophilization. In contrast, MAA-GNPs exhibits remarkable stability under the same conditions. Cit-GNPs exhibit no significant aggregation in the presence of cryoprotectants (molecules that are typically used to protect labile ingredients during lyophilization) upon freeze–thaw cycles and lyophilization. The effectiveness of the cyroprotectants evaluated was on the order of trehalose or sucrose > sorbitol > mannitol. The ability of cryoprotectants to prevent GNPs aggregation was dependent on their chemical structure and their ability to interact with the GNPs as assessed with zeta potential analysis

Intracellular speciation of gold nanorods alters the conformational dynamics of genomic DNA

Gold nanorods are one of the most widely explored inorganic materials in nanomedicine for diagnostics, therapeutics and sensing1. It has been shown that gold nanorods are not cytotoxic and localize within cytoplasmic vesicles following endocytosis, with no nuclear localization2,3, but other studies have reported alterations in gene expression profiles in cells following exposure to gold nanorods, via unknown mechanisms4. In this work we describe a pathway that can contribute to this phenomenon. By mapping the intracellular chemical speciation process of gold nanorods, we show that the commonly used Au–thiol conjugation, which is important for maintaining the noble (inert) properties of gold nanostructures, is altered following endocytosis, resulting in the formation of Au(i)–thiolates that localize in the nucleus5. Furthermore, we show that nuclear localization of the gold species perturbs the dynamic microenvironment within the nucleus and triggers alteration of gene expression in human cells. We demonstrate this using quantitative visualization of ubiquitous DNA G-quadruplex structures, which are sensitive to ionic imbalances, as an indicator of the formation of structural alterations in genomic DNA