Publications by authors named "Anupam Roy"

36 Publications

Intermediate Cu-O-Si Phase in the Cu-SiO/Si(111) System: Growth, Elemental, and Electrical Studies.

ACS Omega 2021 Sep 8;6(37):23826-23836. Epub 2021 Sep 8.

Institute of Physics, Sachivalaya Marg, Bhubaneswar, Odisha 751005, India.

We investigate here the strain-induced growth of Cu at 600 °C and its interactions with a thermally grown, 270 nm-thick SiO layer on the Si(111) substrate. Our results show clear evidence of triangular voids and formation of triangular islands on the surface via a void-filling mechanism upon Cu deposition, even on a 270 nm-thick dielectric. Different coordination states, oxidation numbers, and chemical compositions of the Cu-grown film are estimated from the core level X-ray photoelectron spectroscopy (XPS) measurements. We find evidence of different compound phases including an intermediate mixed-state of Cu-O-Si at the interface. Emergence of a mixed Cu-O-Si intermediate state is attributed to the new chemical states of Cu , O , and Si observed in the high-resolution XPS spectra. This intermediate state, which is supposed to be highly catalytic, is found in the sample with a concentration as high as ∼41%. Within the Cu-O-Si phase, the atomic percentages of Cu, O, and Si are ∼1, ∼86, and ∼13%, respectively. The electrical measurements carried out on the sample reveal different resistive channels across the film and an overall n-type semiconducting nature with a sheet resistance of the order of 10 Ω.
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http://dx.doi.org/10.1021/acsomega.1c02646DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8459365PMC
September 2021

Two-Step Growth of Uniform Monolayer MoS Nanosheets by Metal-Organic Chemical Vapor Deposition.

ACS Omega 2021 Apr 6;6(15):10343-10351. Epub 2021 Apr 6.

Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758, United States.

To achieve large area growth of transition metal dichalcogenides of uniform monolayer thickness, we demonstrate metal-organic chemical vapor deposition (MOCVD) growth under low pressure followed by a high-temperature sulfurization process under atmospheric pressure (AP). Following sulfurization, the MOCVD-grown continuous MoS film transforms into compact triangular crystals of uniform monolayer thickness as confirmed from the sharp distinct photoluminescence peak at 1.8 eV. Raman and X-ray photoelectron spectroscopies confirm that the structural disorders and chalcogen vacancies inherent to the as-grown MOCVD film are substantially healed and carbon/oxygen contaminations are heavily suppressed. The as-grown MOCVD film has a Mo/S ratio of 1:1.6 and an average defect length of ∼1.56 nm, which improve to 1:1.97 and ∼21 nm, respectively, upon sulfurization. The effect of temperature and duration of the sulfurization process on the morphology and stoichiometry of the grown film is investigated in detail. Compared to the APCVD growth, this two-step growth process shows more homogenous distribution of the triangular monolayer MoS domains across the entire substrate, while demonstrating comparable electrical performance.
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http://dx.doi.org/10.1021/acsomega.1c00727DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8153749PMC
April 2021

Considerations for improvising fortified extruded rice products.

J Food Sci 2021 Apr 8;86(4):1180-1200. Epub 2021 Mar 8.

Laboratory of Food Chemistry and Technology, Department of Chemical Engineering, Birla Institute of Technology Mesra, Ranchi, Jharkhand, 835215, India.

Micronutrient fortification of rice by extrusion is an effective strategy to enhance micronutrient levels within rice-consuming individuals. The success of extrusion-based fortification is associated with micronutrient retention, enhanced bioavailability, low postprocessing losses, prolonged storage stability, and minimal sensory changes. The success of an optimally fortified product is primarily reliant upon the compositional considerations, but many attributes of extrudates can be indebted to the processing parameters too. Hence, an exhaustive investigation of this technology has been taken-up here, emphasizing on the compositional parameters in association with process parameters, which influence the final quality attributes like nutrient stability, bioavailability, and sensory properties. Based on these attributes of the end product, a collected data have been presented here to bring out the optimal compositional requirements. These together with cooking processes, extrusion process parameters, and storage conditions will enable formulate a product with enhanced sensory acceptance, better retention during cooking and storage, improved texture, and acceptable color. This review will thus help to optimize a need-based product, its quality, and enhance benefits of fortified extruded rice products.
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http://dx.doi.org/10.1111/1750-3841.15656DOI Listing
April 2021

Hierarchical Assembly of Nanodimensional Silver-Silver Oxide Physical Gels Controlling Nosocomial Infections.

ACS Omega 2020 Dec 9;5(50):32617-32631. Epub 2020 Dec 9.

Chemical Biology Laboratory, Department of Sericulture, Raiganj University, Raiganj 733134, West Bengal, India.

Microbial infections originating from medical care facilities are raising serious concerns across the globe. Therefore, nanotechnology-derived nanostructures have been investigated and explored due to their promising characteristics. In view of this, silver-based antimicrobial hydrogels as an alternative to antibiotic-based creams could play a crucial role in combating such infections. Toward this goal, we report a simple method for the synthesis and assembly of silver nanoparticles in a biopolymer physical gel derived from plant in imparting antimicrobial properties against nosocomial pathogens. Synthesized silver nanoparticles (diameter, 30 ± 10 nm) were uniformly distributed inside the hydrogel. Such synthesized hydrogel assembly of silver nanoparticles dispersed in the biopolymer matrix exhibited hemocompatibility and antimicrobial and antibiofilm characteristics against nosocomial pathogens. The developed hydrogel as a surface coating offers reduced hardness and modulus value, thereby minimizing the brittleness tendency of the gel in the dried state. Hence, we believe that the hierarchical assembly of our hydrogel owing to its functional activity, host toxicity, and stability could possibly be used as an antimicrobial ointment for bacterial infection control.
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http://dx.doi.org/10.1021/acsomega.0c04957DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7758962PMC
December 2020

Deciphering the structural intricacy in virulence effectors for proton-motive force mediated unfolding in type-III protein secretion.

Int J Biol Macromol 2020 Sep 11;159:18-33. Epub 2020 May 11.

Department of Structural Biology and Bioinformatics, CSIR-Indian Institute of Chemical Biology (CSIR-IICB), India; Academy of Scientific and Innovative Research (AcSIR), India. Electronic address:

Given that the protein unfolding requisite for type-III secretion system (T3SS)-mediated secretion is an energetically unfavorable process, the question of how do pathogenic bacteria unfold and secrete hundreds of toxic proteins in seconds remain largely unknown. In this study, a systematic effort combining experimental and computational approaches has been employed to get some mechanistic insights on the unfolding of effectors in T3SS secretion. The in-depth analysis of pH-dependent folding and stability of a T3SS effector ExoY revealed that proton-concentration gradient (~pH 5.8-6.0) generated by proton-motive force (PMF) had significantly affected folding and structural stability of this protein without significant loss of the free energy of unfolding. Importantly, the lower energetic cost associated with the global unfolding of ExoY was mainly due to its inherent stereo-chemical frustrations embedded within its native-like structure as observed from its core structural analysis. These observations suggest that the cooperation between the evolved structural features of ExoY and pH-mediated unfolding is crucial for PMF-mediated T3SS secretion. From a comprehensive computational analysis of 371 T3SS effectors it was concluded that many of these effectors belong to the category of intrinsically disordered proteins (IDPs) and have similar conserved structural archetypes to facilitate early-stage unfolding process as observed in ExoY. We had also provided details of folding, stability, and molecular evolution in T3SS effectors and established the role of evolved structural archetypes in early-stage unfolding events of this effector for maintaining balance in secretion and function trade-off.
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http://dx.doi.org/10.1016/j.ijbiomac.2020.04.266DOI Listing
September 2020

Whole grain rice fortification as a solution to micronutrient deficiency: Technologies and need for more viable alternatives.

Food Chem 2020 Oct 12;326:127049. Epub 2020 May 12.

Laboratory of Food Chemistry and Technology, Department of Chemical Engineering, Birla Institute of Technology Mesra, Ranchi, Jharkhand 835215, India. Electronic address:

Rice fortification is an effective and economical strategy to increase micronutrient intakein countries where rice is a staple food. A successful fortification technology should deliver substantial micronutrient content, high bioavailability, stability during storage, and retention in sensory attributes. This article provides an extensive review of the available whole-grain fortification technologies conducted at the pre and post-harvest stages of rice processing. Soaking, parboiling, coating, germination, foliar spray, fertilization, dusting are some of the non-destructive techniques extensively employed for rice fortification with Fe, Zn, Ca, Se, I, vitamins and other micronutrients.An in-depth analysis has been taken-up on processing parameters,required facilities, and additives required. Conclusions have been drawn based upon physical property, chemical attributes, storage, washing and cooking stability, and bioavailability of fortified rice. The summarized dataon prospects and drawbackswould provide background information to carry out research-based developments in whole grain rice fortification and making further innovations.
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http://dx.doi.org/10.1016/j.foodchem.2020.127049DOI Listing
October 2020

Stacking-Order-Driven Optical Properties and Carrier Dynamics in ReS.

Adv Mater 2020 Jun 24;32(22):e1908311. Epub 2020 Apr 24.

Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX, 78712, USA.

Two distinct stacking orders in ReS are identified without ambiguity and their influence on vibrational, optical properties and carrier dynamics are investigated. With atomic resolution scanning transmission electron microscopy (STEM), two stacking orders are determined as AA stacking with negligible displacement across layers, and AB stacking with about a one-unit cell displacement along the a axis. First-principles calculations confirm that these two stacking orders correspond to two local energy minima. Raman spectra inform a consistent difference of modes I & III, about 13 cm for AA stacking, and 20 cm for AB stacking, making a simple tool for determining the stacking orders in ReS . Polarized photoluminescence (PL) reveals that AB stacking possesses blueshifted PL peak positions, and broader peak widths, compared with AA stacking, indicating stronger interlayer interaction. Transient transmission measured with femtosecond pump-probe spectroscopy suggests exciton dynamics being more anisotropic in AB stacking, where excited state absorption related to Exc. III mode disappears when probe polarization aligns perpendicular to b axis. The findings underscore the stacking-order driven optical properties and carrier dynamics of ReS , mediate many seemingly contradictory results in the literature, and open up an opportunity to engineer electronic devices with new functionalities by manipulating the stacking order.
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http://dx.doi.org/10.1002/adma.201908311DOI Listing
June 2020

Two-Dimensional to Three-Dimensional Growth of Transition Metal Diselenides by Chemical Vapor Deposition: Interplay between Fractal, Dendritic, and Compact Morphologies.

ACS Appl Mater Interfaces 2020 Apr 23;12(13):15885-15892. Epub 2020 Mar 23.

Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758, United States.

We investigate the role of growth temperature and metal/chalcogen flux in atmospheric pressure chemical vapor deposition growth of MoSe and WSe on Si/SiO substrates. Using scanning electron microscopy and atomic force microscopy, we observe that the growth temperature and transition metal flux strongly influence the domain morphology, and the compact triangular or hexagonal domains ramify into branched structures as the growth temperature (metal flux) is decreased (increased). The competition between adatom attachment to the domain edges and diffusion of adatoms along the domain boundary determines the evolution of the observed growth morphology. Depending on the growth temperature and flux, two different branched structures-fractals and dendrites-grow. The fractals (with a dimension of ∼1.67) obey a diffusion-limited aggregation mechanism, whereas the dendrites with a higher fractal dimension of ∼1.80 exhibit preferential growth along the symmetry-governed directions. The effect of chalcogen environment is studied, where a Se-rich condition helps restrict Mo-rich nucleus formation, promoting lateral growth. For a Se-deficient environment, several multilayer islands cluster on two-dimensional domains, suggesting a transition from lateral to vertical growth because of insufficient Se passivation. X-ray photoelectron spectroscopy analysis shows a near perfect stoichiometry (Mo/Se = 1:1.98) of MoSe grown in a Se-rich environment, whereas in the Se-deficient condition, a ratio of Mo/Se = 1:1.68 is observed. This also supports the formation of metal-rich nuclei (MoSe) under Se-deficient conditions, leading to three-dimensional clustering. Tuning the growth temperature and metal/chalcogen flux, we propose an optimized CVD growth window for synthesizing large-area Mo(W) selenide.
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http://dx.doi.org/10.1021/acsami.9b23286DOI Listing
April 2020

Order, Disorder, and Reorder State of Lysozyme: Aggregation Mechanism by Raman Spectroscopy.

J Phys Chem B 2020 01 27;124(1):50-60. Epub 2019 Dec 27.

Structural Biology and Bioinformatics Division , Indian Institute of Chemical Biology, Council of Scientific and Industrial Research , 4, Raja S.C. Mullick Road , Kolkata 700032 , India.

Lysozyme, like many other well-folded globular proteins, under stressful conditions produces nanoscale oligomer assembly and amyloid-like fibrillar aggregates. With engaging Raman microscopy, we made a critical structural analysis of oligomer and other assembly structures of lysozyme obtained from hen egg white and provided a quantitative estimation of a protein secondary structure in different states of its fibrillation. A strong amide I Raman band at 1660 cm and a N-Cα-C stretching band at ∼930 cm clearly indicated the presence of a substantial amount of α-helical folds of the protein in its oligomeric assembly state. In addition, analysis of the amide III region and Raman difference spectra suggested an ample presence of a PPII-like secondary structure in these oligomers without causing major loss of α-helical folds, which is found in the case of monomeric samples. Circular dichroism study also revealed the presence of typical α-helical folds in the oligomeric state. Nonetheless, most of the Raman bands associated with aromatic residues and disulfide (-S-S-) linkages broadened in the oligomeric state and indicated a collapse in the tertiary structure. In the fibrillar state of assembly, the amide I band became much sharper and enriched with the β-sheet secondary structure. Also, the disulfide bond vibration in matured fibrils became much weaker compared to monomer and oligomers and thus confirmed certain loss/cleavage of this bond during fibrillation. The Raman band of tryptophan and tyrosine residues indicated that some of these residues experienced a greater hydrophobic microenvironment in the fibrillar state than the protein in the oligomeric state of the assembly structure.
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http://dx.doi.org/10.1021/acs.jpcb.9b09139DOI Listing
January 2020

Effect of feed supplementation with biosynthesized silver nanoparticles using leaf extract of Morus indica L. V1 on Bombyx mori L. (Lepidoptera: Bombycidae).

Sci Rep 2019 10 16;9(1):14839. Epub 2019 Oct 16.

Department of Analytical Chemistry, Faculty of Pharmacy, Erciyes University, Kayseri, 38039, Turkey.

Herein, we report the synthesis of silver nanoparticles (AgNPs) by a green route using the aqueous leaf extract of Morus indica L. V1. The synthesized AgNPs exhibited maximum UV-Vis absorbance at 460 nm due to surface plasmon resonance. The average diameter (~54 nm) of AgNPs was measured from HR-TEM analysis. EDX spectra also supported the formation of AgNPs, and negative zeta potential value (-14 mV) suggested its stability. Moreover, a shift in the carbonyl stretching (from 1639 cm to 1630 cm) was noted in the FT-IR spectra of leaf extract after AgNPs synthesis which confirm the role of natural products present in leaves for the conversion of silver ions to AgNPs. The four bright circular rings (111), (200), (220) and (311) observed in the selected area electron diffraction pattern are the characteristic reflections of face centered cubic crystalline silver. LC-MS/MS study revealed the presence of phytochemicals in the leaf extract which is responsible for the reduction of silver ions. MTT assay was performed to investigate the cytotoxicity of AgNPs against two human cell lines, namely HepG2 and WRL-68. The antibacterial study revealed that MIC value of the synthesized AgNPs was 80 µg/ml against Escherichia coli K12 and Staphylococcus aureus (MTCC 96). Finally, the synthesized AgNPs at 10 µg/ml dosages showed beneficial effects on the survivability, body weights of the Bombyx mori L. larvae, pupae, cocoons and shells weights via enhancing the feed efficacy.
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http://dx.doi.org/10.1038/s41598-019-50906-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6795853PMC
October 2019

Dependence of h-BN Film Thickness as Grown on Nickel Single-Crystal Substrates of Different Orientations.

ACS Appl Mater Interfaces 2018 Dec 11;10(51):44862-44870. Epub 2018 Dec 11.

Microelectronics Research Center , The University of Texas at Austin , Austin , Texas 78758 , USA.

Chemical vapor deposition (CVD) of two-dimensional materials has been an active area of research in recent years because it is a scalable process for obtaining thin films that can be used to fabricate devices. The growth mechanism for hexagonal boron nitride (h-BN) on metal catalyst substrates has been described to be either surface energy-driven or diffusion-driven. In this work, h-BN is grown in a CVD system on Ni single-crystal substrates as a function of Ni crystallographic orientation to clarify the competing forces acting on the growth mechanism. We observed that the thickness of the h-BN film depends on the Ni substrate orientation, with the growth rate increasing from the (100) surface to the (111) surface and the highest on the (110) surface. We associate the observed results with surface reactivity and diffusivity differences for different Ni orientations. Boron and nitrogen diffuse and precipitate from the Ni bulk to form thin multilayer h-BN. Our results serve to clarify the h-BN CVD growth mechanism which has been previously ascribed to a surface energy-driven growth mechanism.
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http://dx.doi.org/10.1021/acsami.8b16816DOI Listing
December 2018

Growth of lateral graphene/h-BN heterostructure on copper foils by chemical vapor deposition.

Nanotechnology 2019 Jan 12;30(3):03LT01. Epub 2018 Nov 12.

Department of Physics, Key Laboratory of Low Dimensional Condensed Matter Physics (Department of Education of Fujian Province), Xiamen University, Xiamen, 361005, People's Republic of China. Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX 78757, United States of America.

The synthesis of lateral heterostructures assembled by atomically-thin materials with distinct intrinsic properties is important for future heterojunction-embedded two-dimensional (2D) devices. Here we report an etching-assisted chemical vapor deposition method to synthesize large-area continuous lateral graphene/hexagonal boron nitride (Gr/h-BN) heterostructures on carbon-containing copper foils. The h-BN film is first synthesized on the copper foil, followed by hydrogen etching, and then epitaxial graphene domains are grown to form continuous lateral heterostructures. Analyses, including Raman spectroscopy, atomic force microscopy, scanning electron microscopy, x-ray photoelectron spectroscopy, and ultraviolet-visible absorption spectroscopy, are used to characterize the coexistence of both materials and the highly continuous nature of this lateral heterostructure. This facile and scalable synthesizing method enables the potential usage of Gr/h-BN heterostructure in both fundamental studies and related 2D devices.
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http://dx.doi.org/10.1088/1361-6528/aaeb75DOI Listing
January 2019

Structural Insight of Amyloidogenic Intermediates of Human Insulin.

ACS Omega 2018 Feb;3(2):2452-2462

Structural Biology and Bioinformatics Division, Indian Institute of Chemical Biology, Council of Scientific and Industrial Research, 4, Raja S.C. Mullick Road, Kolkata 700032, India.

Engaging Raman spectroscopy as a primary tool, we investigated the early events of insulin fibrilization and determined the structural content present in oligomer and protofibrils that are formed as intermediates in the fibril formation pathway. Insulin oligomer, as obtained upon incubation of zinc-free insulin at 60 °C, was mostly spherical in shape, with a diameter of 3-5 nm. Longer incubation produced "necklace"-like beaded protofibrillar assembly species. These intermediates eventually transformed into 5-8 nm thick fibers with smooth surface texture. A broad amide I band in the Raman spectrum of insulin monomer appeared at 1659 cm, with a shoulder band at 1676 cm. This signature suggested the presence of major helical and extended secondary structure of the protein backbone. In the oligomeric state, the protein maintained its helical imprint (∼50%) and no substantial increment of the compact cross-β-sheet structure was observed. A nonamide helix signature band at 940 cm was present in the oligomeric state, and it was weakened in the fibrillar structure. The 1-anilino-8-naphthalene-sulfonate binding study strongly suggested that a collapse in the tertiary structure, not the major secondary structural realignment, was the dominant factor in the formation of oligomers. In the fibrillar state, the contents of helical and disordered secondary structures decreased significantly and the β-sheet amount increased to ∼62%. The narrow amide I Raman band at 1674 cm in the fibrillar state connoted the formation of vibrationally restricted highly organized β-sheet structure with quaternary realignment into steric-zipped species.
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http://dx.doi.org/10.1021/acsomega.7b01776DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6045404PMC
February 2018

High density nonmagnetic cobalt in thin films.

Nanotechnology 2018 May 20;29(19):195703. Epub 2018 Feb 20.

Department of Materials Science, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata-700032, India.

Recently high density (HD) nonmagnetic cobalt has been discovered in a nanoscale cobalt thin film, grown on Si(111) single crystal. This form of cobalt is not only nonmagnetic but also superconducting. These promising results have encouraged further investigations of the growth of the nonmagnetic (NM) phase of cobalt. In the original investigation, the cobalt film had a natural cobalt oxide at the top. We have investigated whether the growth of HD NM cobalt layers in the thin film depends on (i) a capping layer on the cobalt film, (ii) the thickness of the cobalt film and (iii) the nature of the substrate on which the cobalt film is grown. The results of such investigations indicate that for cobalt films capped with a thin gold layer, and for various film thicknesses, HD NM cobalt layers are formed. However, instead of a Si substrate, when the cobalt films are grown on oxide substrates, such as silicon oxide or cobalt oxide, HD NM cobalt layers are not formed. The difference is attributed to the nature-crystalline or amorphous-of the substrate.
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http://dx.doi.org/10.1088/1361-6528/aab0e9DOI Listing
May 2018

The Bumpy Face of Che Guevara: An Interesting Case.

Indian J Dermatol 2017 Nov-Dec;62(6):675

Department of Dermatology, Calcutta School of Tropical Medicine, Kolkata, West Bengal, India.

Placement of decorative tattoo on the skin may lead to various immunological, infective, and coincidental complications. Inoculation of human papillomavirus leading to development of verruca is an uncommon complication of tattoos. The present report highlights the development of verruca vulgaris, developing after 2 years of tattooing in a young male.
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http://dx.doi.org/10.4103/ijd.IJD_1_17DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5724329PMC
December 2017

Cutaneous Cysts with Nail Dystrophy in a Young Female: A Classical Association.

Indian J Dermatol 2017 Nov-Dec;62(6):661-664

Department of Dermatology, Venereology and Leprosy, School of Tropical Medicine, Kolkata, West Bengal, India.

Pachyonychia Congenita (PC) refers to a group of autosomal dominant disorders with variable clinical presentations. While nail dystrophy and plantar keratoderma are the most consistent features in all the variants, a myriad of other manifestations has been observed. This report highlights a case of young female presenting with multiple asymptomatic cutaneous cysts associated with plantar kearatoderma and nail dystrophy. Similar nail changes were evident in her son also. Such clinical presentation, in corroboration with histopathological evaluation of the cutaneous cyst prompted us to make a diagnosis of Pachyonychia Congenita type II.
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http://dx.doi.org/10.4103/ijd.IJD_473_16DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5724318PMC
December 2017

Carrier Trapping by Oxygen Impurities in Molybdenum Diselenide.

ACS Appl Mater Interfaces 2018 Jan 19;10(1):1125-1131. Epub 2017 Dec 19.

Microelectronics Research Center and Department of Electrical and Computer Engineering, The University of Texas at Austin , Austin, Texas 78758, United States.

Understanding defect effect on carrier dynamics is essential for both fundamental physics and potential applications of transition metal dichalcogenides (TMDs). Here, the phenomenon of oxygen impurities trapping photoexcited carriers has been studied with ultrafast pump-probe spectroscopy. Oxygen impurities are intentionally created in exfoliated multilayer MoSe with Ar plasma irradiation and air exposure. After plasma treatment, the signal of transient absorption first increases and then decreases, which is a signature of defect-capturing carriers. With larger density of oxygen defects, the trapping effect becomes more prominent. The trapping defect densities are estimated from the transient absorption signal, and its increasing trend in the longer-irradiated sample agrees with the results from X-ray photoelectron spectroscopy. First-principle calculations with density functional theory reveal that oxygen atoms occupying Mo vacancies create mid-gap defect states, which are responsible for carrier trapping. Our findings shed light on the important role of oxygen defects as carrier trappers in TMDs, and facilitate defect engineering in relevant materials and device applications.
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http://dx.doi.org/10.1021/acsami.7b15478DOI Listing
January 2018

A Case of Inappropriate Self-Medication Compounded with Prescribing Dispensing Errors and the Hazardous Consequence.

Curr Drug Saf 2018 ;13(1):51-54

Department of Clinical & Experimental Pharmacology, Calcutta School of Tropical Medicine, Kolkata, India.

Introduction: Self-medication behavior appears to be a commonplace; and when it is ignorant it may prove dangerous. On the other hand, dispensing errors and consequent adverse outcomes, though not too uncommon, are seldom reported. We report here a case of methotrexateinduced acute vesico-bullous eruptions in a patient of psoriasis who indulged in self-medication and was wrongfully dispensed higher doses of methotrexate.

Case Description: A 50-year-old man was diagnosed with psoriasis two years back and advised tablet methotrexate 20 mg once weekly and folic acid supplementation. He experienced symptoms remission after 8 weeks of treatment and preferred to discontinue the medication. As the psoriatic lesions reappeared four weeks ago, he attended a retail pharmacy for refill of the two-year old prescription. He was obliged by the man in the counter who wrongfully dispensed the medicine and the patient consumed methotrexate 10 mg twice daily. On the 20th days, the patient experienced erythematous, vesico-bullous lesions spread all over the body including both limbs and scalp, with oral mucosal involvement without any history of fever, and with mildly deranged liver function, and presented to the dermatology OPD of a tertiary hospital. He was admitted and treated with injection glucocorticoid and leucovorin. He responded well and completely recovered in a week. A 'probable' causality was adjudged for this serious adverse event by both WHO-UMC scale and Naranjo's algorithm. The reaction was moderately severe (Hartwig's scale) and it was definitively preventable (modified Schumock-Thornton scale).

Conclusion: This case report highlights the hazard of uninformed Self-medication and irresponsible dispensing behavior resulting in serious drug-related injury.
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http://dx.doi.org/10.2174/1574886312666170919174925DOI Listing
September 2018

Envisaging the Structural Elevation in the Early Event of Oligomerization of Disordered Amyloid β Peptide.

ACS Omega 2017 Aug 8;2(8):4316-4327. Epub 2017 Aug 8.

Structural Biology and Bioinformatics Division, Indian Institute of Chemical Biology, Council of Scientific and Industrial Research, 4, Raja S.C. Mullick Road, Kolkata, West Bengal 700032, India.

In Alzheimer's disease (AD), amyloid β (Aβ) protein plays a detrimental role in neuronal injury and death. Recent in vitro and in vivo studies suggest that soluble oligomers of the Aβ peptide are neurotoxic. Structural properties of the oligomeric assembly, however, are largely unknown. Our present investigation established that the 40-residue-long Aβ peptide (Aβ40) became more helical, ordered, and compact in the oligomeric state, and both the helical and β-sheet components were found to increase significantly in the early event of oligomerization. The band-selective two-dimensional NMR analysis suggested that majority of the residues from sequence 12 to 22 gained a higher-ordered secondary structure in the oligomeric condition. The presence of a significant amount of helical conformation was confirmed by Raman bands at 1650 and 1336 cm. Other residues remained mostly in the extended polyproline II (PPII) and less compact β-conformation space. In the event of maturation of the oligomers into an amyloid fiber, both the helical content and the PPII-like structural components declined and ∼72% residues attained a compact β-sheet structure. Interestingly, however, some residues remained in the collagen triple helix/extended 2.5-helix conformation as evidenced by the amide III Raman signature band at 1272 cm. Molecular dynamics analysis using an optimized potential for liquid simulation force field with the peptide monomer indicated that some of the residues may have preferences for helical conformation and this possibly contributed in the event of oligomer formation, which eventually became a β-sheet-rich amyloid fiber.
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http://dx.doi.org/10.1021/acsomega.7b00522DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6641910PMC
August 2017

Versatile Large-Area Custom-Feature van der Waals Epitaxy of Topological Insulators.

ACS Nano 2017 07 14;11(7):7457-7467. Epub 2017 Jul 14.

Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin , Austin, Texas 78758, United States.

As the focus of applied research in topological insulators (TI) evolves, the need to synthesize large-area TI films for practical device applications takes center stage. However, constructing scalable and adaptable processes for high-quality TI compounds remains a challenge. To this end, a versatile van der Waals epitaxy (vdWE) process for custom-feature bismuth telluro-sulfide TI growth and fabrication is presented, achieved through selective-area fluorination and modification of surface free-energy on mica. The TI features grow epitaxially in large single-crystal trigonal domains, exhibiting armchair or zigzag crystalline edges highly oriented with the underlying mica lattice and only two preferred domain orientations mirrored at 180°. As-grown feature thickness dependence on lateral dimensions and denuded zones at boundaries are observed, as explained by a semiempirical two-species surface migration model with robust estimates of growth parameters and elucidating the role of selective-area surface modification. Topological surface states contribute up to 60% of device conductance at room temperature, indicating excellent electronic quality. High-yield microfabrication and the adaptable vdWE growth mechanism with readily alterable precursor and substrate combinations lend the process versatility to realize crystalline TI synthesis in arbitrary shapes and arrays suitable for facile integration with processes ranging from rapid prototyping to scalable manufacturing.
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http://dx.doi.org/10.1021/acsnano.7b03894DOI Listing
July 2017

Morpho-physiological analysis of tolerance to aluminum toxicity in rice varieties of North East India.

PLoS One 2017 27;12(4):e0176357. Epub 2017 Apr 27.

Plant Molecular Biotechnology Laboratory, Department of Life Science and Bioinformatics, Assam University, Silchar, INDIA.

Aluminum (Al) is the third most abundant metal in earth crust, whose chemical form is mainly dependent on soil pH. The most toxic form of Al with respect to plants is Al3+, which exists in soil pH <5. Acidic soil significantly limits crop production mainly due to Al3+ toxicity worldwide, impacting approximately 50% of the world's arable land (in North-Eastern India 80% soil are acidic). Al3+ toxicity in plants ensues root growth inhibition leading to less nutrient and water uptake impacting crop productivity as a whole. Rice is one of the chief grains which constitutes the staple food of two-third of the world population including India and is not untouched by Al3+ toxicity. Al contamination is a critical constraint to plant production in agricultural soils of North East India. 24 indigenous Indica rice varieties (including Badshahbhog as tolerant check and Mashuri as sensitive check) were screened for Al stress tolerance in hydroponic plant growth system. Results show marked difference in growth parameters (relative growth rate, Root tolerance index, fresh and dry weight of root) of rice seedlings due to Al (100 μM) toxicity. Al3+ uptake and lipid peroxidation level also increased concomitantly under Al treatment. Histochemical assay were also performed to elucidate uptake of aluminum, loss of membrane integrity and lipid peroxidation, which were found to be more in sensitive genotypes at higher Al concentration. This study revealed that aluminum toxicity is a serious harmful problem for rice crop productivity in acid soil. Based on various parameters studied it's concluded that Disang is a comparatively tolerant variety whereas Joymati a sensitive variety. Western blot hybridization further strengthened the claim, as it demonstrated more accumulation of Glutathione reductase (GR) protein in Disang rice variety than Joymati under stressed condition. This study also observed that the emergence of lethal toxic symptoms occurs only after 48h irrespective of the dose used in the study.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0176357PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5407633PMC
September 2017

Orientation of tyrosine side chain in neurotoxic Aβ differs in two different secondary structures of the peptide.

R Soc Open Sci 2016 Oct 5;3(10):160112. Epub 2016 Oct 5.

Structural Biology and Bioinformatics Division , Indian Institute of Chemical Biology, Council of Scientific and Industrial Research , 4, Raja S.c. Mullick Road, Kolkata 700032 , India.

Amyloid β (Aβ) peptide is present as a major component in amyloid plaque that is one of the hallmarks of Alzheimer's disease. The peptide contains a single tyrosine residue and Aβ has a major implication in the pathology of the disease progression. Current investigation revealed that the tyrosine side chain attained two different critical stereo orientations in two dissimilar conformational states of the peptide. The extended α-helical structure of the peptide observed in an apolar solvent or methanol/water mixture became disordered in aqueous medium and the radius of gyration decreased. In aqueous medium, the torsional angle around C-C of tyrosine group became -60°. However, in its α-helical conformation in an apolar system, the measured angle was 180° and this rotameric state may be reasoned behind stronger tyrosine fluorescence compared with the disordered state of the peptide. Molecular dynamics simulation analyses and spectroscopic studies have helped us to understand the major structural changes in the secondary structure of the peptide in the two conformational states. A conformational clustering indicated that the compact state is more stable with tyrosine residue attaining the torsion angle value of -60°, whereas the native state (in HFIP/water mixture) is prevalent at a torsion angle value of -180°. High solvent accessibility has possibly stabilized the particular rotameric state (-60°) of the tyrosine residue and could be the reason behind decrease in fluorescence of the sole tyrosine residue in an aqueous buffer solution (pH 7.4) compared with its fluorescence in the α-helical structure in the micellar environment.
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http://dx.doi.org/10.1098/rsos.160112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5098961PMC
October 2016

Comparison of a microsliced modified chondroperichondrium shield graft and a temporalis fascia graft in primary type I tympanoplasty: A prospective randomized controlled trial.

Ear Nose Throat J 2016 Jul;95(7):274-83

Corresponding author: Dr. Sudipta Pal, Department of ENT, Calcutta National Medical College, 32 Gora Chand St., Kolkata 700014, India. Email: From the Department of ENT, Murshidabad Medical College, Berhampur, Murshidabad, West Bengal, India (Dr. Bhattacharya); the Department of ENT, Calcutta National Medical College, Kolkata, India (Dr. Pal); the Department of ENT, NRS Medical College, Kolkata (Dr. Saha and Dr. Roy); and the Department of ENT, North Bengal Medical College, Siliguri, West Bengal (Dr. Gure). The study described in this article was conducted when all the authors were in the Department of ENT, R.G. Kar Medical College and Hospitals, Kolkata.

We conducted a prospective, randomized, controlled trial to compare outcomes in type I tympanoplasty patients who received an autologous microsliced modified cartilage perichondrium shield graft (cartilage group) and those who received an autologous temporalis muscle fascia graft (fascia group). Our three outcomes measures were (1) anatomic success rates at 3 months, (2) hearing results at 6 months, and (3) rates of morphologic success (i.e., the absence of reperforation, retraction, and graft displacement) at 2 years among those in each group who had an intact graft at 3 months. Of 56 patients who were initially enrolled and who underwent one of these type I tympanoplasty procedures, 51 completed the study-28 in the cartilage group and 23 in the fascia group. The former was made up of 11 males and 17 females, aged 15 to 48 years (mean: 27.4), and the latter included 9 males and 14 females, aged 15 to 52 years (mean: 31.7). The overall graft take rate at 3 months with respect to perforation closure (anatomic success) was 93.3% in the cartilage group and 91.7% in the fascia group, which was not a statistically significant difference. The mean hearing gain at 6 months was 11.7 ± 7.6 dB in the cartilage group and 12.6 ± 6.0 dB in the fascia group-again, not statistically significant. At 2 years, morphologic success rates were 92.3 and 81.0%, respectively-again, not statistically significant. We conclude that autologous microsliced modified cartilage perichondrium shield graft tympanoplasty is as effective as conventional temporalis fascia tympanoplasty in terms of graft take rates and functional results. Indeed, medium-term outcomes (2-yr follow-up) revealed that sustainable morphologic success was actually better with the cartilage technique than with the fascia technique because it was associated with fewer revision surgeries.
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July 2016

Mesoporous polyacrylic acid supported silver nanoparticles as an efficient catalyst for reductive coupling of nitrobenzenes and alcohols using glycerol as hydrogen source.

J Colloid Interface Sci 2016 Jun 17;472:202-9. Epub 2016 Mar 17.

Department of Chemistry, University of Kalyani, Kalyani, Nadia, 741235 W.B., India. Electronic address:

Silver nanoparticle immobilized mesoporous cross-linked polyacrylic acid (Ag-MCP-1) has been synthesized via aqueous-phase polymerization of acrylic acid followed by the surface immobilization with silver nanoparticles. The nanocomposite material has been characterized by different spectroscopic techniques. Powder X-ray diffraction patterns revealed the formation of silver nanoparticles, while transmission electron microscope image showed that Ag nanoparticles are formed and uniformly dispersed in the mesoporous polyacrylic acid. The Ag-MCP-1 nanocomposite can be used as an efficient heterogeneous catalyst in the reductive coupling of nitrobenzenes and alcohols using glycerol as hydrogen source. This nanocomposite can be reused more than five times without any significant decrease in its catalytic activity.
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http://dx.doi.org/10.1016/j.jcis.2016.03.037DOI Listing
June 2016

Structural and Electrical Properties of MoTe2 and MoSe2 Grown by Molecular Beam Epitaxy.

ACS Appl Mater Interfaces 2016 Mar 11;8(11):7396-402. Epub 2016 Mar 11.

Microelectronics Research Center, The University of Texas at Austin , Austin, Texas 78758, United States.

We demonstrate the growth of thin films of molybdenum ditelluride and molybdenum diselenide on sapphire substrates by molecular beam epitaxy. In situ structural and chemical analyses reveal stoichiometric layered film growth with atomically smooth surface morphologies. Film growth along the (001) direction is confirmed by X-ray diffraction, and the crystalline nature of growth in the 2H phase is evident from Raman spectroscopy. Transmission electron microscopy is used to confirm the layered film structure and hexagonal arrangement of surface atoms. Temperature-dependent electrical measurements show an insulating behavior that agrees well with a two-dimensional variable-range hopping model, suggesting that transport in these films is dominated by localized charge-carrier states.
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http://dx.doi.org/10.1021/acsami.6b00961DOI Listing
March 2016

Air Stable Doping and Intrinsic Mobility Enhancement in Monolayer Molybdenum Disulfide by Amorphous Titanium Suboxide Encapsulation.

Nano Lett 2015 Jul 26;15(7):4329-36. Epub 2015 Jun 26.

†Microelectronics Research Center and Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, United States.

To reduce Schottky-barrier-induced contact and access resistance, and the impact of charged impurity and phonon scattering on mobility in devices based on 2D transition metal dichalcogenides (TMDs), considerable effort has been put into exploring various doping techniques and dielectric engineering using high-κ oxides, respectively. The goal of this work is to demonstrate a high-κ dielectric that serves as an effective n-type charge transfer dopant on monolayer (ML) molybdenum disulfide (MoS2). Utilizing amorphous titanium suboxide (ATO) as the "high-κ dopant", we achieved a contact resistance of ∼180 Ω·μm that is the lowest reported value for ML MoS2. An ON current as high as 240 μA/μm and field effect mobility as high as 83 cm(2)/V-s were realized using this doping technique. Moreover, intrinsic mobility as high as 102 cm(2)/V-s at 300 K and 501 cm(2)/V-s at 77 K were achieved after ATO encapsulation that are among the highest mobility values reported on ML MoS2. We also analyzed the doping effect of ATO films on ML MoS2, a phenomenon that is absent when stoichiometric TiO2 is used, using ab initio density functional theory (DFT) calculations that shows excellent agreement with our experimental findings. On the basis of the interfacial-oxygen-vacancy mediated doping as seen in the case of high-κ ATO-ML MoS2, we propose a mechanism for the mobility enhancement effect observed in TMD-based devices after encapsulation in a high-κ dielectric environment.
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http://dx.doi.org/10.1021/acs.nanolett.5b00314DOI Listing
July 2015

Perpendicular Magnetic Anisotropy and Spin Glass-like Behavior in Molecular Beam Epitaxy Grown Chromium Telluride Thin Films.

ACS Nano 2015 Apr 13;9(4):3772-9. Epub 2015 Apr 13.

Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758, United States.

Reflection high-energy electron diffraction (RHEED), scanning tunneling microscopy (STM), vibrating sample magnetometry, and other physical property measurements are used to investigate the structure, morphology, magnetic, and magnetotransport properties of (001)-oriented Cr2Te3 thin films grown on Al2O3(0001) and Si(111)-(7×7) surfaces by molecular beam epitaxy. Streaky RHEED patterns indicate flat smooth film growth on both substrates. STM studies show the hexagonal arrangements of surface atoms. Determination of the lattice parameter from the atomically resolved STM image is consistent with the bulk crystal structures. Magnetic measurements show the film is ferromagnetic, having a Curie temperature of about 180 K, and a spin glass-like behavior was observed below 35 K. Magnetotransport measurements show the metallic nature of the film with a perpendicular magnetic anisotropy along the c-axis.
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http://dx.doi.org/10.1021/nn5065716DOI Listing
April 2015

Functional and structural insights on self-assembled nanofiber-based novel antibacterial ointment from antimicrobial peptides, bacitracin and gramicidin S.

J Antibiot (Tokyo) 2014 Nov 4;67(11):771-5. Epub 2014 Jun 4.

Centro de Análises Proteômicas e Bioquímicas, Programa de Pós-Graduação em Ciências Genômicas e Biotecnologia, UCB, Brasília, Brazil.

A novel antibacterial ointment using bacitracin, specific for Gram-positive bacteria, and gramicidin S, a highly toxic antibacterial peptide, was here developed showing broad-spectrum antibacterial activities against pathogenic strains with less toxicity after self-assembly into nanofiber structures. Such structures were confirmed with scanning electron microscopy and CD analyses. In addition, in silico studies using docking associated with molecular dynamics were carried out to obtain information about fiber structural oligomerization. Thus, the bacitracin and gramicidin S-based self-assembled nanopeptide ribbon may be a successful ointment formulation for bacterial infection control.
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http://dx.doi.org/10.1038/ja.2014.70DOI Listing
November 2014

Challenges and future prospects of antibiotic therapy: from peptides to phages utilization.

Front Pharmacol 2014 13;5:105. Epub 2014 May 13.

Centro de Análises Proteômicas e Bioquímicas, Pós-Graduação em Ciências Genômicas e Biotecnologia, Universidade Católica de Brasília Brasilia, Brazil.

Bacterial infections are raising serious concern across the globe. The effectiveness of conventional antibiotics is decreasing due to global emergence of multi-drug-resistant (MDR) bacterial pathogens. This process seems to be primarily caused by an indiscriminate and inappropriate use of antibiotics in non-infected patients and in the food industry. New classes of antibiotics with different actions against MDR pathogens need to be developed urgently. In this context, this review focuses on several ways and future directions to search for the next generation of safe and effective antibiotics compounds including antimicrobial peptides, phage therapy, phytochemicals, metalloantibiotics, lipopolysaccharide, and efflux pump inhibitors to control the infections caused by MDR pathogens.
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http://dx.doi.org/10.3389/fphar.2014.00105DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4027024PMC
June 2014
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