Recent Research Highlights

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https://sites.google.com/a/gauhati.ac.in/research/#ds19022019 Properties of PANI-SA composites

https://sites.google.com/a/gauhati.ac.in/research/#rt12022019 A perspective on π-π stacking

https://sites.google.com/a/gauhati.ac.in/research/#kb11022019 One more neutrino!

https://sites.google.com/a/gauhati.ac.in/research/#hc01022019 Schistura rebuw - a new species of fish

https://sites.google.com/a/gauhati.ac.in/research/#kt09012019 Modeling magnetospheric oscillations

https://sites.google.com/a/gauhati.ac.in/research/#tkg08122018 Killing cancer cells

https://sites.google.com/a/gauhati.ac.in/research/#sh30112018 Detection of arsenic in water

https://sites.google.com/a/gauhati.ac.in/research/#kt21112018 Funiculosone - an antimicrobial metabolites
Studying dielectric properties of PANI-SA composites

Deepali Sarkar and her graduate students study the dielectric properties of polyaniline (PANI) sulphonic acid (SA) composites. This work is published in the journal Synthetic Metals.


Authors
Mausumi Das, Ali Akbar, and D Sarkar

Abstract
Present work is primarily emphasised on the study of dielectric properties of sulphonic acids (SA) incorporated polyaniline (PANI). SA's function as dopants as well as surfactants for PANI. The PANI and PANI-SA samples are prepared by interfacial technique. The three composites prepared with three SA's [camphor sulphonic acid (CSA), dodecylbenzene sulphonic acid (DBSA) and polystyrene sulfonic acid (PSSA)] are characterised by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field effect scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA) and differential thermogram (DTG) prior to dielectric studies. The results of PANI not incorporated with SA are also shown for comparison. XRD shows enhancement of crystallinity on SA doping. FTIR confirms the molecular structure with enhanced oxidation states on SA doping. FESEM shows fibrillar morphology with reduced fibre diameter from 86 nm in pure PANI to minimum of 50 nm in one of the composites. TGA and DTG results show better thermal stability on SA doping. The dielectric and AC conductivity measurements of the undoped and dopedPANI are studied in the frequency range of 42 kHz - 2 MHz and in the temperature range of 300 K–330 K. The dielectric constant for all the PANI composites increases with increase in temperature which indicates increase in mobility of the electric dipoles in the polymers. The dielectric constant for DBSA doped PANI is nearly 5000 which is much higher in context to interfacially polymerised nanofibres compared to that of undoped PANI where this value is about 800. Electric modulus studies show relaxation peaks in imaginary modulus spectra which ascertains about the type of relaxation process. The AC conductivity of the composites is found to be much higher than that of undoped PANI. The electrical conductivity increases with increase of temperature. This is suggested to be caused due to the activated trapped charge carriers.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/#top 
 



Stacking - in the chemical way

Ranjit Thakuria and his collaborators elaborate on the nature and applications of π-π interactions. This work is published in the journal Crystal Growth & Design.


Authors
Ranjit Thakuria, Naba K Nath1, and Binoy K Saha1
1from other institutions

Abstract
This research article is a perspective published by the Guest Editors Ranjit Thakuria, Naba K Nath and Binoy K Saha for the Virtual Special Issue of Crystal Growth & Design on π−π Stacking in Crystal Engineering: Fundamentals and Applications. It highlights the nature of π−π interactions and their uses in various fields ranging from crystal engineering to material science to biochemistry and discusses about the articles published in the special issue.

https://sites.google.com/a/gauhati.ac.in/research/#top 
 



One more neutrino!

Kalpana Bora and her collaborators ask whether the sterile neutrino can fit into the existing neutrino hierarchy. Sterile neutrino is a possible dark matter candidate. This research is published in The European Physical Journal C.


Authors
Neelakshi Sarma, Kalpana Bora, and Debasish Borah1
1from other institution

Abstract
Motivated by the recent resurrection of the evidence for an eV scale sterile neutrino from the MiniBooNE experiment, the authors revisit one of the most minimal seesaw model known as the minimal extended seesaw that gives rise to a 3 + 1 light neutrino mass matrix. The authors consider the presence of A4 flavour symmetry which plays a nontrivial role in generating the structure of the neutrino mass matrix. Considering a diagonal charged lepton mass matrix and generic vacuum alignments of A4 triplet flavons, we classify the resulting mass matrices based on their textures. Keeping aside the disallowed texture zeros based on earlier studies of 3 + 1 neutrino textures, we categorise the remaining ones based on texture zeros, μ-τ symmetry in the 3 × 3 block and hybrid textures. After pointing out the origin of such 3 + 1 neutrino textures to A4 vacuum alignments, the authors use the latest 3 + 1 neutrino oscillation data and numerically analyse the texture zeros and μ–τ symmetric cases. The authors find that a few of them are allowed from each category predicting interesting cor- relations between neutrino parameters. They also find that all of these allowed cases prefer normal hierarchical pattern of light neutrino masses over inverted hierarchy.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/#top 
 



Schistura rebuw - a new species of stone loach

Hrishikesh Choudhury and his colleagues have reported the finding of a new fish species from the Kameng River of lower Arunachal Pradesh. This finding is published in the journal Zootaxa


Authors
Hrishikesh Choudhury, Abhinit Dey, Ratul Ch Bharali1, Dandadhar Sarma, and Waikhom Vishwanath1
1 from other institutions

Abstract
Schistura rebuw, new species, is described from the Kameng River, a north-bank tributary of the Brahmaputra, Arunachal Pradesh, India. The new species is easily distinguished from all known congeners in the Brahmaputra basin by its unique sexual dimorphism, specifically a suborbital slit in adult females, and a suborbital flap in adult males; and a colour pattern of 10–11 blackish bars on a greyish-beige body, the pre-dorsal bars mostly broken or incomplete, coalescing dorsally in a more or less alternate fashion.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/#top 
 



Modeling aperiodic magnetospheric oscillations

Graduate Student Murchana Khusroo and Madhurjya P Bora explain why the magnetic oscillations in earth's magnetosphere are always almost aperiodic. This research work is published in Physical Review E


Authors

Abstract
The authors present an analysis of a Hall-magnetohydrodynamics model of the magnetospheric plasma with finite Larmor radius effect. Through a bifurcation analysis of the resultant nonlinear system, they show that this nonlinear model does not possess a limit cycle, which rules out regular periodic oscillations with constant amplitude. However, it does result in a train of magnetosonic solitons, localised in space, with amplitudes increasing in time, which are largely in agreement with what is usually observed in the magnetopause region. We call these oscillations aperiodic magnetospheric oscillations. The authors emphasise that most of the train of solitary oscillations observed by the Cluster fleet and other spacecrafts do not have constant amplitudes: they either continuously increase or decrease. These train of solitons with non-constant amplitudes is a primary solution of their mathematical model.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/#top 
 



What it takes to take on cancer

Tridib Kumar Goswami and his collaborators synthesise complexes which are found to kill cancer cells through generation of reactive oxygen species (ROS). This research work is published in Journal of Inorganic Biochemistry.


Authors
Atrayee Banaspati, Dhananjay Das, Chandan J Choudhury, Arnab Bhattacharyya1, and Tridib K Goswami
1 from other institution

Abstract
Four ternary copper(II) complexes of N-salicylyl-L-Tryptophan (Sal-TrpH) and phenanthroline bases of general formula [Cu(Sal-Trp)(L)], where L is 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 2), dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 3) and 2-(anthracen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (aip, 4), are synthesised and fully characterised. The complexes are evaluated for their affinity for biomolecules and photocytotoxic activities. Single crystal X-ray diffraction studies of complex 1 reveals that it has a square pyramidal CuN3O2 core with the phenolate oxygen of salicylaldehyde occupying the axial coordination site in the solid state. Complexes 1–4 display the Cu(II)-Cu(I) redox couples at ~ −0.3 V vs Ag/AgCl reference electrode in DMF-0.1 M [BunN4](ClO4). A Cu(II)-based weak d-d band ~650 nm and a moderately strong ligand to metal charge transfer band at ~430 nm are observed in DMF-Tris-HCl buffer (pH 7.2) (1:4 v/v). The complexes are efficient binders to calf thymus DNA and model proteins such as bovine serum albumin and lysozyme. They cleave supercoiled plasmid DNA efficiently when exposed to 446 and 660 nm laser radiation. They are cytotoxic to HeLa (human cervical cancer) and MCF-7 (human breast cancer) cells showing significant enhancement of cytotoxicity upon photo-excitation with low energy visible light. The complexes are found to kill cancer cells through generation of reactive oxygen species (ROS) as confirmed by DCFDA (2′,7′-dichlorofluorescin diacetate) assay. The apoptotic cell death induced by complex 4 is confirmed by Annexin V-Fluorescein isothiocyanate-Propidium iodide assay. Confocal microscopic images using 4 shows its primary cytosolic localisation in the HeLa and MCF-7 cells.

https://sites.google.com/a/gauhati.ac.in/research/#top 
 



Detection of arsenic in water

Simanta Hazarika and graduate student Chiranjib Rajkonwar describe a method which has the potential for being an in-situ method for detection of groundwater arsenic. This research is published in the journal Laser Physics.





Authors

Abstract
Ingestion of arsenic by the human body through drinking water induces numerous diseases. Therefore, detection and estimation of arsenic concentration in water, especially in groundwater, is important to protect the human world from its toxicity. In this work we demonstrate a laser induced fluorescence resonance energy transfer (LIFRET) method for the determination of the arsenic concentration in water. The fluorescence resonance energy transfer (FRET) is observed in an aqueous solution of 1, 8-naphthalimide and rhodamine-B by exciting it with a laser radiation of wavelength 405 nm. It is observed that if arsenic contaminated water is added to the pure solution of 1, 8-naphthalimide and rhodamine-B the wavelength of the peak in its FRET spectrum shifts from its pure value at 632.45 nm (peak position of the FRET spectrum of a pure solution of 1, 8-naphthalimide and rhodamine-B). These shifts of wavelengths are towards the lower wavelength side, corresponding to an increase in the concentration of arsenic added to the solution. In the present work, based on the shifting of the peak wavelength value of the FRET spectra corresponding to different concentrations of arsenic, we have described a method for the estimation of arsenic in water up to a lowest limit of 0.00001 gm l−1 (the maximum permissible limit of arsenic in water according to the World Health Organisation). The LIFRET method described in this work is portable, relatively cost effective, more convenient and has the potential for any in situ measurement of arsenic in the ground water of arsenic contaminated areas.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/#top 
 



Funiculosone - a new antimicrobial metabolites

Kumanand Tayung and his collaborators have isolated a new antimicrobial metabolites which also shows anticandidal activity against Candida albicans Berkhout. This research is published in the journal Phytochemistry.



Authors
Srichanadan Padhi1, Marco Masi1, Alessio Cimmino1, Angela Tuzi1, Subhrakanta Jena1, Kumananda Tayung, and Antonio Evidente1
1 from other institutions

Abstract
An undescribed substituted dihydroxanthene-1,9-dione, named funiculosone, was isolated together with its two analogues identified as mangrovamide J and ravenelin, from the culture filtrates of Talaromyces funiculosus (Thom) Samson, Yilmaz, Frisvad & Seifert (Trichocomaceae), an endolichenic fungus isolated from lichen thallus of Diorygma hieroglyphicum (Pers.) Staiger & Kalb (Graphidaceae), in India. Funiculosone was characterised, essentially by spectroscopic methods, as 4,8,9a-trihydroxy-3,4a-dimethyl-4a,9a-dihydro-4H-xanthene-1,9-dione. Its relative stereochemistry was deduced by single crystal X-ray analysis while the absolute configuration was assigned as 4S,4aS,9aS by ECD spectra in comparison to that of the closely related mangrovamide J. This latter, to which, not being an amide, an inappropriate common name was given, was only recently isolated, together with undescribed and known prenylatedindole alkaloids and chromone derivatives from an unidentified Penicillium sp. X-ray structural analysis of the isolated mangrovamide J, for which no biological activity was previously reported, revealed polymorphism and a new crystalline phase is described. All the compounds displayed antibacterial activity with an IC50 range 23–104 μg/mL when assayed against Escherichia coli Escherich and Staphylococcus aureus Ogston. Funiculosone also showed anticandidal activity against Candida albicans Berkhout with an IC50 35 μg/mL.

Journal Reference
https://sites.google.com/a/gauhati.ac.in/research/#top