G1 dendrimers-mediated evolution of silver nanostructures from nanoparticles to solid spheres.
With the control of G1 poly(amidoamine) (PAMAM), an evolutionary course of stable colloidal silver from discrete nanoparticles to solid spheres through ultraviolet irradiation reduction of silver nitrate solutions was observed by transmission electron microscopy (TEM). The morphologies of the products depend on the Ag+ concentration. A mechanism of globular assembly was put forward to interpret the evolution of the nanostructures. Powder X-ray diffraction (XRD), electron diffraction (ED) patterns, and X-ray photoelectron spectroscopy (XPS) indicate the presence of cubic symmetry silver. XPS and Fourier transform infrared (FT-IR) spectroscopy confirm that dendrimers have participated in the stabilization and control of Ag nanostructures. In the UV-vis spectra, the intense surface plasmons are centered at 425 and 430 nm corresponding to the shapes of dots and solid spheres, respectively. The solid spheres exhibit excellent catalytic efficiency on the reduction of 2,7-dicholoroflurescein (DCF).
Synthesis of Dendrimer-Passivated Noble Metal Nanoparticles in a Polar Medium: Comparison of Size between Silver and Gold Particles
The synthesis of silver and gold metal nanospherical particles stabilized by the fourth-generation poly(amido amine) (G4 PAMAM) dendrimer is reported. The reduction of silver nitrate and sodium tetrachloroaurate in the presence of the PAMAM dendrimer having terminal amine groups results in the formation of stable, water-soluble nanoparticles. The formation and size of the particles have been determined from the UV−vis plasmon absorption band and transmission electron microscopic (TEM) analyses. The average particle sizes are (6.2 ± 1.7)−(12.2 ± 2.9) nm for silver and are (3.2 ± 0.7)−(7.3 ± 1.5) nm for gold, depending on the metal ion-to-dendrimer terminal amine ratio (M:D) used. Thus, dendrimer-protected silver particles are substantially larger than the gold particles synthesized in similar systems. Nanoparticles prepared at 0.25:1 and lower M:D ratios are stable for a long period of time. A TEM study of the morphology also shows a short-ranged hexagonal arrangement of particles in a monolayer onto the c...
A comment on thyrotoxic pericarditis.
We read with great pleasure the work by Inami et al. published in a recent issue of the International Journal of Cardiology [1]. The authors have described an interesting case of acute pericarditis triggered by thyrotoxic crisis in Graves' disease. The authors attribute the causation of acute pericarditis to likely an autoimmune mechanism. This has been supported by a comprehensive review of the existing literature (mostly case reports). Autoimmune forms of pericarditis are often recurrent [2]. Non-recurrent forms of acute pericarditis (as previously described by several reports) occurring only during acute thyrotoxic phase may potentially need another causative explanation. In addition to the possible autoimmune or viral causes as authors have described, we believe that a direct metabolic impact exerted by acute thyrotoxicosis possibly also plays an independent contributory role by leading to an alteration in the pericardial fat metabolism. The hypothesis is supported by the fact as the role of cholesterol-laden effusions in hypothyroidism/myxedema is previously well described [3]. In addition to the described ECG findings, we would also like to highlight yet another valuable ECG finding on the provided ECG illustration i.e. a concave JT-segment elevation with a slightly downsloping TP-segment, also now referred to as the Spodick's sign [4–6]. Spodick's sign is present in about 80% of the patients affected with acute pericarditis and is often a give-away to the diagnosis [5,6]. This finding is best visualized in the lead II and sometimes lateral precordial leads. When used along with PR-segment depression, it often serves as an important electrocardiographic tool for distinguishing the acute pericarditis from acute coronary syndrome.