Showing papers by "Amit Singh published in 2006"

Role of halide ions and temperature on the morphology of biologically synthesized gold nanotriangles.

Abstract: In this paper, we demonstrate the effect of halide ions on the formation of biogenically prepared gold nanotriangles using the leaf extract of lemongrass (Cymbopogon flexuosus) plant. We have also studied the effect of halide ions on the morphology of biogenic nanotriangles. It has been shown that iodide ions have a greater propensity to transform flat gold nanotriangles into circular disk-like structures as compared to other halide ions. The study also suggests that the presence of Cl- ions during the synthesis promotes the growth of nanotriangles, whereas the presence of I- ions distorts the nanotriangle morphology and induces the formation of aggregated spherical nanoparticles. The change in the morphology of gold nanotriangles has been explained in terms of the ability of the halide ions to stabilize or inhibit the formation of (111) faces to form [111] oriented gold nanotriangles. Last, we have also shown that the temperature is an important parameter for controlling the aspect ratio and the relative amounts of gold nanotriangles and spherical particles. The results show that, by varying the temperature of reaction condition, the shape, size, and optical properties of anisotropic nanoparticles can be fine-tuned.

Dissecting virulence pathways of Mycobacterium tuberculosis through protein–protein association

Abstract: The sudden increase in information derived from the completed Mycobacterium tuberculosis (Mtb) genome sequences has revealed the need for approaches capable of converting raw genome sequence data into functional information. To date, an experimental system for studying protein–protein association in mycobacteria is not available. We have developed a simple system, termed mycobacterial protein fragment complementation (M-PFC), that is based upon the functional reconstitution of two small murine dihydrofolate reductase domains independently fused to two interacting proteins. Using M-PFC, we have successfully demonstrated dimerization of yeast GCN4, interaction between Mtb KdpD and KdpE, and association between Esat-6 and Cfp-10. We established the association between the sensor kinase, DevS, and response regulator, DevR, thereby demonstrating the potential of M-PFC to study protein associations in the mycobacterial membrane. To validate our system, we screened an Mtb library for proteins that associate with the secreted antigen Cfp-10 and consistently identified Esat-6 in our screens. Additional proteins that specifically associate with Cfp-10 include Rv0686 and Rv2151c (FtsQ), a component and substrate, respectively, of the evolutionary conserved signal recognition pathway; and Rv3596c (ClpC1), an AAA-ATPase chaperone involved in protein translocation and quality control. Our results provide empirical evidence that directly links the Mtb specialized secretion pathway with the evolutionary conserved signal recognition and SecA/SecYEG pathways, suggesting they share secretory components. We anticipate that M-PFC will be a major contributor to the systematic assembly of mycobacterial protein interaction maps that will lead to the development of better strategies for the control of tuberculosis.

Construction of conductive multilayer films of biogenic triangular gold nanoparticles and their application in chemical vapour sensing

Abstract: Metal nanoparticles are interesting building blocks for realizing films for a number of applications that include bio- and chemical sensing To date, spherical metal nanoparticles have been used to generate functional electrical coatings In this paper we demonstrate the synthesis of electrically conductive coatings using biologically prepared gold nanotriangles as the building blocks The gold nanotriangles are prepared by the reduction of aqueous chloroaurate ions using an extract of the lemongrass plant (Cymbopogon flexuosus) which are thereafter assembled onto a variety of substrates by simple solution casting The conductivity of the film shows a drastic fall upon mild heat treatment, leading to the formation of electrically conductive thin films of nanoparticles We have also investigated the possibility of using the gold nanotriangle films in vapour sensing A large fall in film resistance is observed upon exposure to polar molecules such as methanol, while little change occurs upon exposure to weakly polar molecules such as chloroform

Ruptured sinus of valsalva into right ventricle: a unique case with prolonged survival.

Abstract: A 51 years male motor mechanic turned shopkeeper presented to us with complaints of progressive exertional breathlessness and pitting pedal edema for last one year. On examination, a wide pulse pressure (160/40 → 0) was found and a continuous murmur (with thrill) was heard over his left parasternal region, best in the 3rd and 4th intercostals spaces, that was more prominent during diastole. A clinical diagnosis of ruptured sinus of Valsalva into right ventricular was made. Upon reviewing his records it was found that he was first diagnosed as having this illness in 1979 when he presented as a 26 year old man with sudden onset chest pain with severe breathlessness. Although advised surgery then, he did not comply. Eleven years later (in 1991) he again came to this institute and was referred to cardiology as a case of Pyrexia of Unknown Origin (PUO). Echocardiography and blood cultures done then established the diagnosis of infective endocarditis. With appropriate antibiotics he improved and was cured of infective endocarditis. Even after this episode of infective endocarditis he refused surgery. By judicious curtailment of his activities involving strain, and with medical therapy he had so far led a productive life. This time he presented with the dyspnea on exertion (NYHA class II) and over these years began to perceive his murmur (complains he hears it). We performed his ECHO (Figs. 1, 2, 3) and wish to report this case since a limited number of patients have been reported with as long productive lives after rupture of sinus of valsalva into right ventricle. Whereas, in most cases this illness is known to proceed quickly to decompensated failure, there are a very few reports of prolonged survival. Chojnacki1 reported a case who underwent surgery after 15 years of detection. Another patient survived 17 years.2 An interesting case report of aneurysm of all three sinus of valsalva was published in 19403, and the subject survived 30 years. Our patient has survived 25 years now since rupture and is amongst the longest reported survivors.