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Cycloaddition-Based Approaches to Bio-active Natural Products
Full text linkNatural products regime has been recognized as an invaluable source of compounds of
medicinal importance. While some natural products are directly used as drugs, some drugs are
derived from natural products by modification of structures. In some cases the pharmacophore is
placed in a new backbone that replaces the core skeleton present in the natural product. Thus
synthesis of natural products continues to be in the fore front of organic chemistry research.
Carbocyclic compounds having ring sizes four to six are found in a large number of natural
products with promising biological activities. Cycloaddition reactions such as [2 + 2] and [4 + 4] can
be employed to access directly compounds with four and six membered rings. Ring expansion of four
membered rings is one of the commonly employed approaches to construct five membered rings.
This proposed investigation will employ a combination of the above approaches for synthesis of
bioactive natural products containing four to six memebered rings.
Synthesis of optically active natural products using naturally occurring optically active materials is
the most efficient way when their availability and adaptability are fulfilled. However, such cases are
rare as great variety of natural products exist while adaptable chiral compounds are very limited.
Therefore, finding certain common chiral pools adaptable to versatile target molecules is one of the
most important tasks in organic synthesis. A programme has been initiated in July, 2010 under the
supervision of Professor Subrata Ghosh, F.A.Sc, F.N.A Department of Organic Chemistry, Indian
Association for the Cultivation of Science, Jadavpur, Kolkata – 700 032 for the synthesis of
enantiopure organic compounds starting from nature’s chiral pool starting material D-mannitol.
Investigation embodied in this dissertation entitled “Cycloaddition-Based Approaches to
Bio-active Natural Products” is directed towards the development of synthetic methodologies for
some fused carbocyclic system present in natural products.
The present thesis addresses the above mentioned themes of contemporary interest in organic
chemistry and is presented in three chapters. In Chapter 1, a brief review on construction of
cyclobutane ring system is described. Chapter 2 deals with synthetic studies toward kelsoene.
Approach to the asymmetric synthesis of a functionalized tricyclo[6.2.0.0
2,6
]decane ring system
present in kelsoene and poduran employing stereocontrolled copper (I)-catalyzed intramolecular
[2+2] photocycloaddition, and RCM reaction as the key steps. Chapter 3 deals with synthetic studies
on erythrodiene and spirojatamol. The key steps involve (i) pinacol-type rearrangement of a
cyclobutane derivative, (ii) copper(I)-catalyzed intramolecular [2 + 2] photocaycloaddition of a diene
prepared from (+) dihydrocarvone to form oxabicyclo[3.2.0]heptanes derivative.
ii
The subject matter of each part has been structured under following headings: Introduction,
Background, Results and Discussion, Conclusion, References, Experimental and NMR Spectra.
In keeping with the general practice of reporting scientific observations, due
acknowledgements have been made to the findings of other investigators.A Thesis
Submitted for the Degree of
Doctor of Philosophy (Science)
of Jadavpur University
by AMRITA GHOSHResearch had been conducted in the division of Organic chemistry under IACS fellowship under the supervision of Prof. Subrata Ghosh, O
Multi-reference coupled-cluster studies on the effect of dynamical and non-dynamical correlation on molecular energies and properties
No full textIn this thesis it has been formulated and implemented a suite of related multi-reference coupled cluster theories to describe open-shell molecular systems taking care to maintain spin-adaptation of the wave function and incorporate the effects of electron correlation and orbital relaxation to the greatest extent possible within the limits of computational and theoretical viability.Research was carried out under the supervision of Prof. Debasish Mukherjee and Dr. Ankan Paul of RCAMOS under SCS [School of Chemical Sciences]Research was conducted under grant of CSIR, India for the Shyama Prasad Mukherjee Fellowship, and DST, India. Also there are sponsorship from abroad , i.e. CEFIPRA/IFCPAR for
funding academic visits to Toulouse, France, CTCC, Oslo, Norway
Functional Study of Nonmuscle Myosin II-C2 in Neuro-2a Cell Line
Full text linkNonmuscle myosin IIs (NM IIs) are ubiquitously expressed throughout the entire organism and play distinct roles in cell division, adhesion, migration etc. Till date, three types of nonmuscle myosin IIs, II-A, II-B and II-C are found in vertebrates. Recently, similar to NM II-B, it has been shown that splicing at loop 1 and loop 2 of NM heavy chain II-C can produce four different isoforms of NM II-C- NM II-C0, NM II-C1, NM II-C2 and NM II-C1C2. C2 insert containing isoforms are specifically expressed in mouse and human brain, and their activities are independent of myosin light chain phosphorylation. But it is unknown which type of cells in brain express C2 containing NM II-C isoforms, and also the functional role of these proteins. In this thesis, we have studied the function of C2 insert containing isoform of NM II-C, NM IIC1C2, in Neuro-2a cells. We have shown that expression of NM II-C1C2 both at mRNA and protein level during neuritogenesis of Neuro-2a cells is detectable by RT-PCR and immunoblot analysis. Inhibition of C2 insert containing isoform (NM II-C1C2) by siRNA decreases number of neurites and number of filopodia, reduces the length of neurites, and loosens neurite’s attachment with its substratum. NM II-C1C2 can colocalize and interact with 1 integrin at later stage of neuritogenesis. Ectopic expression of GFP - tagged C2 containing isoforms (NM II-C2 and NM II-C1C2) in Neuro-2a cells shows puncta localization in neurites. We further investigate what make C2 insert containing molecule so unique in binding with integrin and showing puncta pattern of localization in neurites. Fluorescence intensity versus time trajectories reveals that NM II-C2-GFP displays oscillation of fluorescence intensity in neurites. Deletion of N-terminal region of C2 insert abolishes the fluctuation nature of NM II-C2 in neurites of Neuro-2a cells. Our study provides the importance of Glutamine and Lysine residues of C2 insert in the neuritogenesis of Neuro-2a cells.Research was conducted under supervision of Prof. S S Jana of Biological Chemistry division under SBS [School of Biological Sciences]Research was conducted under DST fellowship and fundin
Time Resolved Spectroscopy and Microscopy: Application to Live Cells and Related Systems
Full text linkIn this thesis, we have applied time resolved confocal microscopy to five different processes, - intermittent oscillation of lipid droplets in live cells14, in situ imaging of cancer cell by fluorescent gold nanoclusters, selective killing of breast cancer cells, delivery of cytochrome c and hence imaging of live cell and effect of binary solvent
mixture on structure and dynamics of a protein. Intermittent oscillation in live lung cell is observed using time resolved confocal microscopy and we have observed significant differences between normal and cancer cell. Imaging of cancer cell was done using in situ generated gold nanoclusters. We have shown how doxorubicin loaded gold
nanoclusters (AuNC) selectively killed breast cancer cell. We have delivered
cytochrome c, inside a cell by gold nanoclusters. We have studied the structure and dynamics of cytochrome c in water-ethanol binary mixture using FCS.Research was conducted under the supervision of Prof. Kankan Bhattacharyya of the Physical Chemistry division under SCS [School of Chemical Sciences]Research was carried out under DST grant and CSIR fellowshi
Magnetic and Transport Properties of Bulk and Nano-structured Transition Metal Oxides
Full text linkThe transition-metal oxides (TMOs) have attracted considerable attention due to
their intriguing structural, magnetic, and electronic properties. The unusual physical
properties are correlated to the unique nature of outer most d-electrons. An electron
in a solid, that is, bound to or nearly localized on the specific atomic site, has three
attributes: charge, spin, and orbital degrees of freedom. The orbital represents the
shape of the electron cloud in solid. In transition-metal oxides with anisotropic-shaped
d-orbital electrons, the Coulomb interaction between the electrons (strong electron
correlation effect) is of important issue for understanding different exotic phenomena
viz., high-temperature superconductivity, metal-insulator transitions, colossal magnetoresistance,
etc. TMOs are not only associated with strong correlations but it often
manifests the interplay between charge, spin, orbital and lattice degrees of freedom.
These materials show different characteristic features while size of the systems are
varied from nanoscale range to their bulk size. Typically the considerable differences
in physical properties are attributed to the particle size distribution, finite size effect,
shape of the particles, surface effect and interparticle interactions. Few strongly correlated TMO in both the nanoscale and bulk form will be investigated in this work. The perovskite oxides with general formula ABO3 (A= rare earth metals/Alkaline metals, B = Mn, Fe etc) such as manganites, ferrites etc are interesting to investigate because of many intrigue phenomena, such as ordering, colossal magnetoresistance, metal-insulator transition, magneto-caloric effect, multiferroics, etc. These interesting
series of compound will also be investigated in this study.Research was carried out under the supervision of Prof. Sourav Giri of the Solid State Physics division under SPS [School of Physical Sciences]Research was conducted under CSIR fellowship and research gran
Hybrid Core-Shell Nanoparticles: Fabrication and Characterization of Light-Emitting Diodes
Full text linkOrganic light-emitting diodes (LEDs) have limitations considering poor
charge carrier mobility and stability of the active materials. An effort has been
made to introduce inorganic quantum dots in LEDs. In LEDs based on the two
types of semiconductors, both inorganic nanocrystals and organic materials are
generally used as active materials. Inorganic nanocrystals have several advantages
in this direction.
Inorganic nanoparticles have higher charge carrier mobility than that in
organic thin films due to the crystalline nature of the quantum dots. The
nanocrystals are also very stable. By varying the diameter of the quantum dots,
color tuning of the devices can also be achieved. These nanoparticles have however
a limitation due to their insulating capping agent. An effort has been made to
remove these insulating stabilizers and replace them with dithiols so that the
interdot spacing will be improved and hence would render facile carrier
conduction.
The layers of a conventional light-emitting diode consists of (1)
transparent bottom electrode (indium tin oxide, ITO), (2) hole-transporting layer,
(3) light emitting layer, (4) electron-transporting layer, and (5) top electrode (Al,
Ca, Mg). We planned to substitute the organic layers by air stable semiconducting nanoparticles. The devices have been characterized by measuring external quantum efficiency (EQE), electroluminescence (EL) spectra and switching speed (time taken to emit light). The active light emitting quantum dots (QDs) along with II
organic or inorganic semiconductors as charge-transporting layers were used in
these LEDs. It is common to use N,N' bis(3-methylphenyl)-N,N'-diphenyl-benzidine
(TPD), nickel oxide (NiO), and graphene oxide (GO), as the hole-transporting
layers; poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)
and molybdenum oxide (MoO3) are used as hole-injecting layers; zinc oxide (ZnO)
is a common electron-transporting materials. An active layer of QDs as a emitting
material is sandwiched between the carrier transporting layers. All the devices
were fabricated on ITO coated glass substrates that were used as the bottom
electrode. The hole-transporting, active QD, and electron-transporting layers were
spun in succession followed by annealing in nitrogen environment. Finally
aluminum was thermally evaporated under vacuum to deposit the top electrode.
We have fabricated different light-emitting diodes based on hybrid
materials or inorganic QDs and have characterized them. The past and recent
works, work plan, experimental procedure, results of all scientific investigation,
and discussion have been described in the first seven chapters of the thesis. The
eighth chapter consists of concluding remarks about all the systems and the results that we have studied. A brief review of all the chapters is given below.Research was conducted under Prof. A J Pal of the Solid State Physics division under SPS [School of Physical Sciences]Research was carried out under CSIR and DST gran
Synthesis and characterisation of Graphene based 2-dimensional systems
Full text linkThe present thesis deals with the graphene based 2-dimentional
systems. The synthesis, characterization and the study of different
aspects of these 2-dimentional systems are the principal objectives of
this thesis. Different graphene based 2-dimentional systems have been
synthesized using different techniques, e.g., sonochemical method,
hydrothermal reaction etc. One of the systems shows quantum
confinement effects, e.g. graphene quantum sheets. The materials
have been characterized by X-Ray diffractometry, transmission
electron microscopy, magnetization measurements under both zero
field-cooled and field-cooled conditions. Zero band gap graphite like structure has also been prepared by easy chemical method. Both magnetic and magnetodielectric properties have been investigated on graphene/ZnCo2O4 nanocomposites synthesized by hydrothermal
reaction. Superparamagnetic graphene/Mn3O4 nanocomposites and conducting graphene based polyaniline nanocomposites have been
synthesized by ultrasonic vibration. The synthesis, characterization
and the detailed analysis of the observed physical properties have been described in different chapters.Research was carried out under the supervision of Prof. S K Saha of Materials Science under SPS [School of Physical Sciences]Research was conducted under the CSIR research grant and fellowshi
FIRST-PRINCIPLES STUDY OF FUNCTIONALIZED GRAPHENE AND ITS DERIVATIVES
No full textIn this thesis work, it has been studied the electronic properties of graphene and graphene like planar nano-sheets. It has been specifically tried to address the problem of band gap engineering
in the native as well as functionalized derivatives of graphene and graphene-like
planar nanomaterials. In chapter-3, we have solved the tight binding Hamiltonian of graphene. It shows that
in a pristine graphene sheet, there is Dirac Cone like merging between the valence band
and the conduction band. As a result of which the electrons are highly mobile and shows
finite conductivity even at 0 K. Therefore, in order to validate the application of native
graphene sheet in transistor industry a small band gap must be introduced into the sheet.
On the other hand, h-BN sheet has a large band gap but having a close lattice matching
with graphene. Our first principle calculation show that H-passivation of graphene
opens up a large band gap into the material while H-passivation lowers the band gap of
a pristine h-BN sheet.
In chapter-4, we present here our first-principles DFT based calculations to propose a
different conformer of graphane, called stirrup. This structure has an intermediate stability
between the chair and boat conformers of graphane. The ground-state electronic
properties of this conformer have been compared to the other two conformers of graphane
and are found to be similar. It is an insulator with a direct energy-band gap of 3.1 eV
at the point. Any other alternative hydrogenation of the graphene sheet disrupts the
symmetric puckered geometry of the structure and turns out to be energetically less favorable.
In chapter-5, we report the ground state structure, stability and electronic properties
of hydrogenated BN sheet on the basis of our first principles DFT based calculations.
The three possible BHNH conformers are chair, boat and stirrup. All the conformers
have an insulating direct band gap varying between 3 - 4.5 eV. The stirrup conformer as
proposed in this work, turns out to be the most stable conformer. Any other alternative
hydrogenation of BN sheet disrupts its periodic puckered geometry and is found to be
energetically less stable.
Application of mechanical strain also leads to deformation in the crystal lattice and therefore
might lead to change in the effective potential faced by the electron which might result
in change of band gap of the sheet. In chapter-6 study the effect of biaxial homogeneous
v
mechanical strain applied within the harmonic limits on the electronic band structure
of H/F passivated graphene and h-BN sheet. Within the harmonic approximation, the
deformation is found to be higher for hydrogenated systems than for fluorinated systems.
Interestingly, our calculated band-gap deformations for hydrogenated/fluorinated
graphene and BN sheets are positive, while that for a pristine BN sheet is found to be
negative. This is due to the strong overlap between nearest-neighbor π orbitals in the
pristine BN sheet, which is absent in the passivated systems. We also estimate the intrinsic
strength of these materials under a harmonic uniaxial strain, and find that the in-plane
stiffnesses of fluorinated and hydrogenated graphene are close, but larger in magnitude compared to those of a fluorinated and hydrogenated BN sheet. In chapter-7, we have performed first principles calculations to estimate the stability and ground-state properties of the h-BN sheet chemically functionalized by various groups, viz. H, F, OH, CH3 , CHO, CN, NH2, etc. Using these dopants, the band gap of these chemically modified sheets can be tuned from 3.2 eV to 0.3 eV. Most of these functional groups, excepting CHO and CN, results in direct band gap semiconductors. Functionalization by the CHO group in particular leads to a sharp decrease in the electronic band
gap of the pristine BN sheet to 0.3 eV, which is congenial for its usage in transistor-based devices. We have also carried out phonon calculations on these functionalized sheets to show that the frequencies corresponding to all their vibrational modes are real (positive), suggesting their inherent stability. The chemisorption energy of these groups to the B and N atoms of the sheet are found to lie in the range of 1.5-6 eV.
In chapter-8, we report from our first principles based calculations, the bonding, stability and electronic structure of silicene monolayer, when epitaxially grown on various Group II-VI, Group III-V and Group IV semiconductor substrates viz. AlAs(111), AlP(111), GaAs(111), GaP(111), ZnS(111), ZnSe(111) and Ge(111). We find that the relative stability and other properties of the silicene overlayer depends sensitively on whether the interacting top layer of the substrate is metal or non-metal terminated. The binding energy of silicene monolayer to the metal terminated surfaces of these substrates are estimated to be range in the 0.56 ± 0.12 eV/atom. We compare these binding energies with that of silicene on Ag(111) substrate, and find that all the MT semiconductor substrates bind silicene with close or comparable binding energy, while this binding is even lower for GaAs(111) and ZnSe(111) substrate. The introduction of silicene monolayer on the NMT surface of all these semiconductor substrates, leads to enhancement in the magnetic moment of the composite system. The behavior of silicene on MT surface of semiconductor substrates can be metallic, magnetic or semi-metallic depending on the
choice of substrate. The silicene monolayer undergoes substrate induced p-type doping on NMT substrates while p-/ n-type doping on MT substrates depending upon its charge transfer with the substrates.The research was conducted under Prof. G P Das of the Materials Science division under SMS (School of Materials Science)The research was carried out under IACS fellowshi
Design of Core Shell Nanomaterials and their Characteriaztion
No full textCore-shell nanomaterials have been attracting a great deal of interest to improve luminescence efficiency by reducing the surface defects of the nanocrystals. A significant enhancement of the quantum yield to core shell nanocrystals is obtained due to suppressing energy-loss processes at the nanoparticle surface. The association of core and shell materials in the same core shell heterostructure allows for design of nanocrystals combining different physical properties, i.e. fluorescence, magnetism, different decay life lifetimes etc. In such a manner, novel functional building blocks can be generated for applications in fields ranging from optoelectronics, solid state lasers, catalysis, display devices, medical imaging etc. In this thesis, it has been described general synthetic methodologies to design different core-shell nanostructures.The research was conducted under the supervision of Prof. Amitava Patra of the Materials Science division under SMS [School of Materials Sciences]The research was carried out under CSIR fellowshi
Functional Porous Nanocomposite: Synthesis and Application
No full textPorous nanomaterials have received great attention in different research field of nanoscience and nanotechnology such as drug delivery, bio-imaging, detection, catalysis, optics energy and environmental application. This is due to their high surface area, tunable pore size and structure. Chemical stability and versatile chemistry for functionalization. Most widely used porous materials of pore size less than 2mm, mesoporous materials of pore size 2 to 50 mm and macroporous materials of pore size larger than 50 mm. Among these microporous materials have limited application due to small pore size but other two porous materials have wide range of applications. Recent sudy shows that nanoparticle incorporated porous materials can be used for multifunctional application. Various nanoparticles have their unique chemical and physical properties.Research was carried out under the supervision of Prof. N R Jana of SMS [School of Materials Science]Research was conducted under CSIR fellowshi