Thalappil Pradeep

Bio: Thalappil Pradeep is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Cluster (physics) & Mass spectrometry. The author has an hindex of 76, co-authored 581 publications receiving 24664 citations. Previous affiliations of Thalappil Pradeep include DST Systems & Lawrence Berkeley National Laboratory.

Emergence of metallicity in silver clusters in the 150 atom regime: a study of differently sized silver clusters

Abstract: We report the systematic appearance of a plasmon-like optical absorption feature in silver clusters protected with 2-phenylethanethiol (PET), 4-flurothiophenol (4-FTP) and (4-(t-butyl)benzenethiol (BBS) as a function of cluster size. A wide range of clusters, namely, Ag44(4-FTP)30, Ag55(PET)31, ∼Ag75(PET)40, ∼Ag114(PET)46, Ag152(PET)60, ∼Ag202(BBS)70, ∼Ag423(PET)105, and ∼Ag530(PET)100 were prepared. The UV/Vis spectra show multiple features up to ∼Ag114; and thereafter, from Ag152 onwards, the plasmonic feature corresponding to a single peak at ∼460 nm evolves, which points to the emergence of metallicity in clusters composed of ∼150 metal atoms. A minor blue shift in the plasmonic peak was observed as cluster sizes increased and merged with the spectrum of plasmonic nanoparticles of 4.8 nm diameter protected with PET. Clusters with different ligands, such as 4-FTP and BBS, also show this behavior, which suggests that the ‘emergence of metallicity’ is independent of the functionality of the thiol ligand.

Percolation network dynamicity and sheet dynamics governed viscous behavior of polydispersed graphene nanosheet suspensions

Abstract: The viscosity of polydispersed graphene nanosheet (5 nm–1.5 μm) suspensions (GNS) and its behavior with temperature and concentration have been experimentally determined. A physical mechanism for the enhanced viscosity over the base fluids has been proposed for the polydispersed GNSs. Experimental data reveal that enhancement of viscosity for GNSs lies in between those of carbon nanotube suspensions (CNTSs) and nano-alumina suspensions, indicating the hybrid mechanism of percolation (like CNTs) and Brownian motion-assisted sheet dynamics (like alumina particles). Sheet dynamics and percolation, along with a proposed percolation network dynamicity factor, have been used to determine a dimensionally consistent analytic model to accurately determine and explain the viscosity of polydispersed GNSs. The model also provides insight into the mechanisms of viscous behavior of different dilute nanoparticle suspensions. The model has been found to be in agreement with the GNS experimental data, and even for CNT (diameter 20 nm, length 10 μm) and nano-alumina (45 nm) suspensions.

A Unified Framework for Understanding the Structure and Modifications of Atomically Precise Monolayer Protected Gold Clusters

Abstract: Atomically precise monolayer protected clusters are molecules comprising a few-atom cluster core of a noble metal, typically Au or Ag, surrounded by a protective layer of ligands, exhibiting many special optical, electrical, catalytic, and magnetic properties, and are emerging as important materials in biology, medicine, catalysis, energy conversion and storage, and sensing. The structural diversity of these clusters or aspicules, as we definitively term them, meaning shielded molecules, combining the Greek word aspis (shield) with molecule, is rapidly increasing due to new compositions and modification routes such as ligand-exchange, alloying, or supramolecular functionalization. We present a structural analysis of the most stable cluster of this kind, Au25(SR)18, and propose a Borromean rings diagram for the cluster, showing its topological configuration of three interlocked (Au8S6)-rings. This simplified two-dimensional diagram is used to represent its structure and modifications via ligand or metal at...

Sunlight mediated synthesis and antibacterial properties of monolayer protected silver clusters

Abstract: Glutathione protected, silver clusters were synthesized within gel cavities, using sunlight. Compared to the conventional chemical reduction process, this method is cheaper and environmentally friendly as it involves the use of natural resources. The as-synthesized silver quantum clusters in aqueous medium show a distinct step-like behavior in their absorption profile. They have been characterized with various spectroscopic and microscopic techniques such as UV/Vis Spectroscopy, Luminescence Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), High Resolution Transmission Electron Microscopy (HRTEM), and X-ray Photoelectron Spectroscopy (XPS). Polyacrylamide gel cavities seemingly control the growth of the particles. The cluster synthesis is scalable by increasing the amount of reagents yielding hundreds of milligrams in a single step. The antibacterial properties of the as-synthesized Ag clusters were studied against a Gram negative and Gram positive organism, Escherichia coli and Staphylococcus aureus, respectively.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Gold nanoparticles in chemical and biological sensing.

Abstract: Detection of chemical and biological agents plays a fundamental role in biomedical, forensic and environmental sciences1–4 as well as in anti bioterrorism applications.5–7 The development of highly sensitive, cost effective, miniature sensors is therefore in high demand which requires advanced technology coupled with fundamental knowledge in chemistry, biology and material sciences.8–13 In general, sensors feature two functional components: a recognition element to provide selective/specific binding with the target analytes and a transducer component for signaling the binding event. An efficient sensor relies heavily on these two essential components for the recognition process in terms of response time, signal to noise (S/N) ratio, selectivity and limits of detection (LOD).14,15 Therefore, designing sensors with higher efficacy depends on the development of novel materials to improve both the recognition and transduction processes. Nanomaterials feature unique physicochemical properties that can be of great utility in creating new recognition and transduction processes for chemical and biological sensors15–27 as well as improving the S/N ratio by miniaturization of the sensor elements.28 Gold nanoparticles (AuNPs) possess distinct physical and chemical attributes that make them excellent scaffolds for the fabrication of novel chemical and biological sensors (Figure 1).29–36 First, AuNPs can be synthesized in a straightforward manner and can be made highly stable. Second, they possess unique optoelectronic properties. Third, they provide high surface-to-volume ratio with excellent biocompatibility using appropriate ligands.30 Fourth, these properties of AuNPs can be readily tuned varying their size, shape and the surrounding chemical environment. For example, the binding event between recognition element and the analyte can alter physicochemical properties of transducer AuNPs, such as plasmon resonance absorption, conductivity, redox behavior, etc. that in turn can generate a detectable response signal. Finally, AuNPs offer a suitable platform for multi-functionalization with a wide range of organic or biological ligands for the selective binding and detection of small molecules and biological targets.30–32,36 Each of these attributes of AuNPs has allowed researchers to develop novel sensing strategies with improved sensitivity, stability and selectivity. In the last decade of research, the advent of AuNP as a sensory element provided us a broad spectrum of innovative approaches for the detection of metal ions, small molecules, proteins, nucleic acids, malignant cells, etc. in a rapid and efficient manner.37 Figure 1 Physical properties of AuNPs and schematic illustration of an AuNP-based detection system. In this current review, we have highlighted the several synthetic routes and properties of AuNPs that make them excellent probes for different sensing strategies. Furthermore, we will discuss various sensing strategies and major advances in the last two decades of research utilizing AuNPs in the detection of variety of target analytes including metal ions, organic molecules, proteins, nucleic acids, and microorganisms.