Chemistry


https://sites.google.com/a/gauhati.ac.in/research/chemistry/#nn06052019 Pigments from the deep sea

https://sites.google.com/a/gauhati.ac.in/research/instrumentation/#sg26042019 Synthesis of cobalt(II) complexes

https://sites.google.com/a/gauhati.ac.in/research/chemistry/#nn26042019 How plankton shaped our ecosystem

https://sites.google.com/a/gauhati.ac.in/research/chemistry/#rt08032019 Cocrystal dissociation - a case study

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

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

https://sites.google.com/a/gauhati.ac.in/research/chemistry/#rt06122018 Formation of eutectics vs cocrystals in PZA

https://sites.google.com/a/gauhati.ac.in/research/chemistry/#nn14092018 Enantiodiscrimination using NMR

https://sites.google.com/a/gauhati.ac.in/research/chemistry/#ps23052018 Synthesis of gold nanoparticles

https://sites.google.com/a/gauhati.ac.in/research/chemistry/#dm Photoluminescent quantum dots

https://sites.google.com/a/gauhati.ac.in/research/chemistry/#dm Freestanding polypyrrole film

https://sites.google.com/a/gauhati.ac.in/research/chemistry/#rt1 Synthesis of Olanzapine salts

https://sites.google.com/a/gauhati.ac.in/research/chemistry/#rt Drug-drug, drug-nutraceutical cocrystal

https://sites.google.com/a/gauhati.ac.in/research/chemistry/#pkb C-H functionalization in water
Scouring the deep sea to find pigments

Nilamoni Nath and coworkers find five new water soluble pigments from the deep sea off the coast of Japan. This work is published in the Journal of Natural Products.



Authors
Klaus Wolkenstein1, Juan Carlos Fuentes-Monteverde1, Nilamoni Nath, Tatsuo Oji1, and Christian Griesinger1
from other institutions

Abstract
Five new water-soluble amido- and aminoanthraquinone pigments, hypalocrinins A–E (1–5), the new amidoanthraquinone biaryls hypalocrinin F (6) and hypalocrinin G (7), and the known compounds 6-bromoemodic acid (8), crinemodin (9), and crinemodin sulfate (10) were isolated from the deep sea crinoid Hypalocrinus naresianus collected off Japan. The structures of the compounds were elucidated by NMR spectroscopy and mass spectrometry. Amido- and aminoquinones are quite unusual among natural products. The hypalocrinins are the first naturally occurring anthraquinones and anthraquinone biaryls conjugated with taurine.

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



Synthesis of cobalt complexes with anticancer potential

Sushobhan Ghosh and his collaborators report about synthesis of cobalt(II) complexes with anticancer potential. This research work is published in the journal Dalton Transactions.



Authors
Arvin Eskandari1, Arunangshu Kundu1, Chunxin Lu1, Sushobhan Ghosh, and Kogularamanan Suntharalingam1
1from other institutions

Abstract
The authors report the synthesis and characterisation of mono- and di-nuclear cobalt(II) complexes (1-3) containing L1, a polypridyl ligand with pyrazole moieties. DNA binding studies suggest that the mono-nuclear complex, 1 binds to DNA via the grooves prior to inducing oxidative DNA cleavage whereas the larger di-nuclear complexes, 2 and 3 bind to DNA via the grooves and intercalation prior to inducing oxidative DNA cleavage. The cobalt(II) complexes display micromolar potency towards U2OS (bone osteosarcoma), HepG2 (liver hepatocellular carcinoma), and GM05757 (normal human fibroblast) cells, comparable to clinically used platinum agents, cisplatin and carboplatin. Cellular mechanism of action studies shows that the most effective cobalt(II) complex, 2 enters U2OS cells, penetrates the nucleus, induces genomic DNA damage, and triggers caspase-dependent apoptosis in a p53-independent manner. This study highlights the potential of di-nuclear cobalt(II) complexes as artificial oxidative metallonucleases and tangible cancer cell-potent agents.

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



How predatory plankton created modern ecosystems!

Nilamoni Nath and his collaborators shed light on the great zigsaw puzzle involving intricacies how our modern ecosystem has come to this stage. This research work is published in Nature Communications.
This highlight is also featured in GU Homepage.


Authors

Abstract
Eukaryotic algae rose to ecological relevance after the Neoproterozoic Snowball Earth glaciations, but the causes for this consequential evolutionary transition remain enigmatic. Cap carbonates were globally deposited directly after these glaciations, but they are usually organic barren or thermally overprinted. Here we show that uniquely-preserved cap dolos- tones of the Araras Group contain exceptional abundances of a newly identified biomarker: 25,28-bisnorgammacerane. Its secular occurrence, carbon isotope systematics and co- occurrence with other demethylated terpenoids suggest a mechanistic connection to extensive microbial degradation of ciliate-derived biomass in bacterially dominated ecosys- tems. Declining 25,28-bisnorgammacerane concentrations, and a parallel rise of steranes over hopanes, indicate the transition from a bacterial to eukaryotic dominated ecosystem after the Marinoan deglaciation. Nutrient levels already increased during the Cryogenian and were a prerequisite, but not the ultimate driver for the algal rise. Intense predatory pressure by bacterivorous protists may have irrevocably cleared self-sustaining cyanobacterial eco- systems, thereby creating the ecological opportunity that allowed for the persistent rise of eukaryotic algae to global importance.

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



Cocrystal dissociation under controlled humidity

Ranjit Thakuria and collaborators report a case study of cocrystal dissociation under a controlled environment. Cocrystals can be defined to be consisted of two or more components that form a unique crystalline structures having unique properties. This research work is published in Organic Process Research and Development.


Authors
Ranjit Thakuria1, Mihails Arhangelskis2, Mark D Eddleston2, Ernest H H Chow2, Kashyap Kumar Sarmah, Barry J Aldous2, Joseph F Krzyzaniak2, and William Jones2
1 Department of Chemistry, University of Cambridge
2 from other institutions

Abstract
Caffeine-glutaric acid cocrystal polymorphs, Form I and Form II, are presented as a model system to study cocrystal dissociation under controlled humidity. On the basis of relative humidity (RH) data, it is observed that Form I transforms to Form II at high RH and that the rate of the polymorphic phase transformation increases with increasing RH, with the relative stability of the cocrystal following a trend similar to that of the coformer deliquescence point for other caffeine dicarboxylic acid cocrystals. In addition, reduction in particle size, change in crystal morphology with greater number of crystal faces exposed to surrounding atmosphere, and internal arrangement of molecules in the crystal structure are shown to influence cocrystal instability and favour dissociation under increased humidity.

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/chemistry/#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/chemistry/#top 
 



Formation of eutectics vs cocrystals for antituberculosis drug pyrazinamide (PZA)

Ranjit Thakuria and his collaborators study formation of eutectics vs cocrystals for the antituberculosis drug pyrazinamide (PZA). This research work is published in the journal Crystal Growth and Design.


Authors
Trishna Rajbongshi, Kashyap Kumar Sarmah, Ankita Sarkar, Ramesh Ganduri1, Suryanarayan Cherukuvada1, Tejender S. Thakur1, and Ranjit Thakuria
1 from other institutions

Abstract
Cocrystallization of the antituberculosis drug pyrazinamide (PZA) with several substituted aromatic carboxylic acids as coformers is studied. The combinations are analyzed by X-ray diffraction and melting behavior to assess the formation of eutectic versus cocrystal. Benzoic acid, cinnamic acid, and N-heterocycle coformers gave eutectics, whereas the majority of their hydroxyl / methoxy substitutes formed cocrystals with PZA. X-ray crystal structures are obtained for some cocrystals, and binary phase diagrams are constructed to determine eutectic compositions. Differences in functional group position and variations in supramolecular growth are found to dictate the formation of eutectics versus cocrystals. Supramolecular synthon energy calculations on selected combinations validated the formation of eutectic versus cocrystal.

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



Insight into old and new pure shift NMR methods for enantiodiscrimination

Nilamoni Nath and his collaborators write a mini-review on enantiodiscrimination by using pure shift NMR methodologies. The article was published in Magnetic Resonance in Chemistry.



Authors
Nilamoni Nath, Priyakshi Bordoloi1, Bhaskar Barman1, Bikash Baishya1, and Sachin R Chaudhari1
1 from other institutions

Abstract
Enantiodiscrimination and their quantification using nuclear magnetic resonance (NMR) spectroscopy has always been a subject of great interest. Proton is the nucleus of choice for enantiodiscrimination due to its high sensitivity and ubiquitous presence in nature. Despite its advantages, enantiodiscrimination suffers from extensive signal splitting by the proton‐ proton scalar couplings, which give complex multiplets that spread over a frequency range of some tens of hertz. These multiplets often overlap, further complicating interpretation of the spectra and quantifications. In this review, the authors discuss some of the recent developments in the pure shift 1H NMR based methods for enantiomer resolution and enantiodiscrimination. They also compare various pure shift methods used for enantiodiscrimination and measurement of enantiomeric excess, considering the fact that conventional 1H NMR fails to provide any detailed insight.

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



Surfactant free synthesis of gold nanoparticles

Dr Pranjal Saikia and his coworkers have developed methods to immobilise sub-3 nm gold nanoparticles within the mesoporous SBA-15 channels for catalytic applications. The work has been published in the journal Powder Technology.



Authors
Abu Taleb Miah, Saitanya K Bharadwaj, and Pranjal Saikia

Abstract
This work reports surfactant free synthesis of monodisperse gold (~ 2.3 nm) particles confined within the pore channels of ordered hexagonal mesoporous silica SBA-15 (Au/SBA-15) by a modified wetness impregnation method. The synthesized Au/SBA-15 composite showed excellent catalytic activity towards the reduction of different wastewater organic pollutants as well as their mixtures under ambient conditions. The composite was also investigated for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). XRD, UV-DR visible spectroscopy, N2 adsorption-desorption analysis, ICP-AES, FT-IR spectroscopy, and TEM were employed to characterize the catalyst samples. The wetness impregnation method followed by a washing step with dilute aqueous NH3 was found to be an effective route to synthesise stable and highly dispersed small gold nanoparticles (Au NPs) within the mesopore channels of SBA-15. All the catalytic reactions followed pseudo-first-order kinetics and catalytic efficiency of the composite was found almost constant up to five cycles.
https://sites.google.com/a/gauhati.ac.in/research/#top 
 



Facile synthesis of photoluminescent quantum dots

Dr Sonit Kumar Gogoi and his fellow researcher report about synthesis of photoluminescent graphitic carbon nitride quantum dots for Hg2+ detection, which is published in the American Chemical Society's journal, ACS Sustainable Chemical Engineering. The works is expected to enhance our knowledge on highly efficient optoelectronic devices.



Authors
Khemnath Patir and Sonit Kumar Gogoi

Abstract
Carbon nitride materials have become highly explored carbon based nanomaterials since their rediscovery in the 1990s due to their semiconductor like behaviour. In this research work, the authors report a facile one pot synthesis of sulfur and oxygen doped carbon nitride quantum dots (SCNQDs) from thiourea and ethylenediaminetetraacetic acid disodium salt by a thermal method. The SCNQDs prepared are characterized by UV− visible, FT-IR, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction, and transmission electron microscopy (TEM) imaging. The authors have demonstrated the Hg2+ sensing ability of SCNQDs in solution as well as in the solid phase, i.e. SCNQDs loaded onto filter paper. The Hg2+ sensing capability of the SCNQDs in the solution phase is the same for Hg2+ ion in double distilled water as well as in tap water, which gives the method a practical applicability in real conditions. The sensitivity of SCNQDs with Hg2+ follows a linear relationship in the range from 10 nM to 1 μM. The minimum detection limit is found to be 0.01 nM, which is lower than previous reports. Similarly the SCNQDs loaded onto filter paper also showed same sensing capability with Hg2+ spiked tap water as Hg2+ in double distilled water solutions. Through this work, the authors have devised a ready to use system for Hg2+ detection with SCNQDs loaded filter paper to be used in biological fluids as well as in environmental samples, which is not available now. Besides, the authors have also made a composite of SCNQDs with poly(vinyl alcohol) (PVA) to observe room temperature phosphorescence (RTP) in SCNQDs.
https://sites.google.com/a/gauhati.ac.in/research/chemistry/#top 




One-step preparation of freestanding polypyrrole films at air-water Interface

Dr Debajyoti Mahanta and Sibani Majumdar describe this one-step preparation method, which is published in Chemistry Select
, may be an effective pollutant removal!



Authors
Sibani Majumdar and Debajyoti Mahanta

Abstract
A simple one-step method of preparing freestanding polypyrrole (PPy) and p-toluenesulfonic acid doped PPy (PTSA-PPy) films has been developed. This novel method provides a simple and general route for preparing rough surfaced hydrophobic PPy films having many potential applications. It has been shown the effective removal of pollutant by these films from aqueous medium.
https://sites.google.com/a/gauhati.ac.in/research/chemistry/#top 




Mechanochemical synthesis of Olanzapine salts and their hydration stability

Dr Ranjit Thakuria and his collaborators study mechanochemical properties of Olanzapine salts using X-ray diffraction. This work is published in Crystal Growth & Design.



Authors
Kashyap Kumar Sarmah, Pranamika Sarma, Dharmaraj R Rao, Poonam Gupta, Naba K Nath, Mihails Arhangelskis, and Ranjit Thakuria

Abstract
A series of olanzapine (OLN) dicarboxylic acid salts including earlier reports on olanzapinium malonate (1:1) and maleate (1:1 and 1:2) were prepared mechanochemically using liquid assisted grinding (LAG) in order to study their hydration stability. Powder X-ray diffraction was used as a characterization tool during the investigation. On the basis of the single crystal structures of respective OLN salts, a negative correlation between the dicarboxylic acid chain length and the hydration stability of the corresponding OLN salt was found. Our observations suggest that the overall crystal packing, beyond the stronger hydrogen bond synthon (N+–H···O– in OLN salts compared to O–H···N in OLN hydrates) plays an important role in designing OLN salts with better hydration stability. In addition, melting point analysis showed that OLN dicarboxylic acid salts follow melting point alteration behavior similar to the pure diacids.

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





A review on drug-drug and drug-nutraceutical cocrystal/salt

Dr Ranjit Thakuria and his collaborator write about drug-drug and drug-nutraceutical cocrystal/salt in a review article published in the journal Crystals.



Authors
Ranjit Thakuria and Bipul Sarma

Abstract
The pre-formulation of pharmaceutical cocrystals and salts is a concept of crystal engineering that has emerged as a promising technique for drug development in pharmaceutical industry. Recent introduction of pharmaceutical cocrystals in regulatory guidelines of US Food and Drug Administration (FDA) made them one of the potential alternatives when salt preparation is not feasible. Apart from generally regarded as safe (GRAS) coformers, drug‑drug and drug‑nutraceutical cocrystals are recent additions to pharmaceutical cocrystal family that have additional health benefits. Indeed, preparation of salt forms is a routine practice to deal with inadequacies associated with the active pharmaceutical ingredient (API) and happens to be a potentially reliable method. Amongst them, drug-drug and drug-nutraceutical cocrystals have drawn significant importance in the recent past as they reduce drug load and cost effects during multiple disease diagnosis. However, one has to be prudent in the selection of drug molecules, the presence of complementary hydrogen bond synthon, disease management during multiple disease therapy, etc. that play important roles in their preparation. That is the reason why drug–drug cocrystals are scarce in the literature compared to pharmaceutical cocrystals containing GRAS coformers and salt forms. Herein, we discuss case studies preferably the reported drug‑drug, drug‑nutraceutical cocrystals, and a few salts with an emphasis on their role in physicochemical property modulation.

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




C-H functionalization in water in presence of only molecular oxygen

Dr Pranjal K Baruah and his collaborators demonstrate what is believed to be the first example of C-H functionalization in water in presence of only molecular oxygen without any catalyst. The related article is published in journal Green Chemistry.




Authors
Mohit L Deb, Choitanya D Pegu, Paran J Borpatra, Prakash J Saikia, and Pranjal K Baruah
Department of Applied Sciences (Chemical Science Division), GUIST, GU


Abstract
Recently, C-H functionalization has been in the centre of attraction for being atom and step economical, directive, and environment-friendly than cross-coupling reactions which require prefunctionalization of substrates. Multi-component C-H functionalization gained much interest in synthetic chemistry due to their atom economy, easy mode of operation, and energy savings. We have reported catalyst-free 3-component reaction of naphthols, aldehydes and tetrahydroisoquinolines to synthesize 1,3-oxazines. It is one-pot multi-component C-H functionalization reaction carried out in water using only molecular oxygen as the sole oxidant. No catalyst or chemically synthesized oxidant is required for the reaction. We believe, this is the first example of C-H functionalization taking place in water in presence of only molecular oxygen. 


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