8071 research outputs found
Sort by
Design And Development Of Estrogen-Based Anticancer Therapeutics
Full text linkEstrogen and its receptor are classically involved in a majority of cancers of
gynecological origin. The estrogen receptor (ER), a nuclear hormone receptor, is
expressed in estrogen-responsive organs such as ovary, uterus and mammary glands.
Estrogen and estrogen-bound ER possess both genomic and non-genomic functions.
Since, the functional expression of the ER is confined to the initial stages of neoplastic
transformation; the design of compounds that interfere with ER function is expected to
be an effective strategy in preventing these types of cancer.
Cancer treatment needs multi-modal strategies to restrain its aggressive malignancy.
Strategies that include simultaneous detection/sensing and treatment should be
specific for cancer to avoid any unwanted side-effects. Among tumour-detecting
molecular probes, intrinsically fluorescent small molecules are preferably and widely
employed as they can enter live cells easily and offer screening through visual
detection.
Tumour-selective ligands have been used to construct novel drug conjugates. Vitamin
folic acid (FA), displays high affinity for the folate receptor (FR), a
glycosylphosphatidyinositol-linked membrane protein that captures its ligands from
the extracellular milieu and transports them inside the cell via a non-destructive, recycling, endosomal pathway. Owing to the fact that its expression is largely absent from normal tissues, FR is also a recognized tumor antigen/biomarker. Because of this, diagnostic and therapeutic methods which exploit the FR’s function have been developed to treat cancer.
The present work involves, therefore, the exploration of highly potent, ER-selective, anti-breast-cancer oxindole-conjugated bis-phenols. With intrinsic fluorescence, this bis-arylideneoxindole derivative upon conjugation with known ROS generator betulinic acid, is then further employed for selective detection and killing of cancer cells. The most potent derivative in the library, is further preceded towards folate receptor targeted chemotherapy. Biological evaluation of this conjugate is underway to expand our knowledge in optimizing the pharmacophore with improved potential.The research carried out under the supervision of Prof. S S Adhikari, Calcutta University and Prof. Amitava Sarkar of Organic Chemistry division under SCS [School of Chemical Sciences
O2 and H2: Activation and Reduction using Bio-inspired Small Molecules Thesis
Full text linkBio-inorganic chemistry is important in elucidating the implications of electron-transfer proteins, substrate binding and activtion as well as metal properties in biological chemistry. Many reactions in life process involve water and metal ions are often at the catalytic centers (active sites) of metalloenzymes. Aerobic life makes extensive use of metal ions such as iron, copper and manganese. Heme is utilized by red blood cells in the form of haemoglobin for oxygen transport. Oxidases and oxygenases are metal systems found throughout nature that take advantage of oxygen to carry out important reaction such as energy generation or small molecule oxidation in cytochrome P450. Some metalloprotein are designed in such a way they can protect a biological process from the potentially harmful effects of oxygen and other reactive oxygen-containig molecules such as H2O2. These systems include peroxodases, catalases and superoxide dismutases. This thesis entitled “O2 and H2: Activation and Reduction using Bio-inspired Small Molecules” mimicks the structural and functional properties of these metallo-enzyme active sites and understanding the geometric and electronic structural contribution to their reactivity.Research was conducted under the supervision of Dr. Avishek Dey, Inorganic Chemistry division under SCS [School of Chemical Sciences]Research was conducted under CSIR fellowshi
Magnetic properties of transition metal based intermetallic alloys
Full text linkThe present thesis deals with unique magnetic behaviour of Heusler based metamagnetic shape memory alloys. Transition metal based alloys and compounds are formed by combining magnetically important d-block element with nonmagnetic metals (such as Al, Ga, Zn, In) or sp elements (such as Si, Ge). The alloys and compounds can be binary (containing two elements), ternary (containing three elements) or even quaternary (containing four elements). A major part of the present thesis work is devoted to Huesler based metamagnetic shape memory alloys of general formula Ni2Mn1+xZ1−x (where Z is a sp element such as In, Sn or Sb) via suitable doping at the different sites. A brief summary of all the chapters including the plan and procedure of this work, the results from the systems and control experiments, and discussion on the results have been put forward in eight chapters of this thesis. A general introductory view of the field of research is discussed in the introduction. Basic properties and application of Heusler based metamagnetic shape memory alloys, electrical resistivity and various magnetofunctional properties of metamagnetic shape memory alloys are also added in this chapter. Various experimental techniques which were followed during the investigation are the basic contents of the next chapter. It also includes sample synthesis and annealing procedure, characterization methods and various measurement techniques. Chapter 3 is based on studying the effect of Ga doping at the In site of Ni2Mn1.32In0.68 metamagnetic shape memory alloy by transport and dc magnetization measurements. The parent sample Ni2Mn1.32In0.68 does not show any structural instability, however small Ga substitution at the In site suddenly induces martensitic transition in it. The studied alloys are all found to be ferromagnetic below about room temperature and also undergo the martensitic phase transition at different temperature depending upon Ga doping. Samples showing thermally driven maretnsitic transition are also found to be susceptible to the applied magnetic field as they show large magnetoresistance and magnetocaloric effect. Clear indication of magnetic field induced transition and kinetically arrested state are also observed. A detailed investigation on the effect of excess Ni doping at the expense of Mn and Sn in Ni2Mn1.4Sn0.6 is presented by means of studying the magnetic and structural properties are present in Chapter 4. The parent alloy undergoes martensitic type structural transition below approximately 180 K. However, doping of Ni at the Mn site keeping Sn unaltered (Ni2+xMn1.4−xSn0.6) leads to non-monotonous variation of lattice parameter, martensitic transition temperature, magnetic moment, ferromagnetic Curie point, magnitude of magnetoresistance etc. Approximately up to the concentration x = 0.08, all the physical parameters vary more or less in a uniform manner. But beyond this concentration, there is a change in the trend of variation. Clear signatures of spin-glass like behaviour, large exchange bias effect and thermoremanent magnetization at low temperature are observed for the x = 0.04 sample. On the other hand, for doping of Ni at the Sn site keeping Mn unchanged (Ni2+xMn1.4Sn0.6−x) shifts the martensitic transition temperature close to 290 K for x = 0.04. Magnetization study reveals the presence of multiple magnetic transitions in the sample. Apart from that, the magnetofunctional properties also get enhanced as evident from the observation of large magnetoresistance and magnetocaloric effect around 290 K. Chapter 5 deals with the magnetic character of Ni1.84Mn1.64In0.52 and Ni2.048Mn1.312In0.64 alloys through transport and magnetization measurements. Both the samples undergo long range ferromagnetic ordering below Curie point followed by the martensitic transition. The second composition is also subjected to another transition from a paramagnetic- like state to a ferromagnetic state upon further cooling below martensitic transition. Large negative magnetoresistance and inverse magnetocaloric effect are observed across the region of martensitic instability for both the samples. However for the second composition, the martensitic transition temperature is very close to room temperature and the magnitude of magnetofunctionality is quite large. Almost 16.7 J/kg-K (for H0 = 50 kOe) of magnetocaloric effect and -45% of magnetoresistance at 300 K are observed. The sample also shows a maximum of 2.25 J/kg-K (for H0 = 50 kOe) conventional entropy change across the second magnetic transition in the martensite along with the observation of -4% magnetoresistace for H = 80 kOe around 195 K.
Chapter 6 is devoted to the study of the effect of external pressure on the magnetic character of
Ni2.04Mn1.4Sn0.56 and Ni2.048Mn1.312In0.64 samples via magnetization measurements. For the first alloy,
martensitic start temperature increases in presence of pressure and almost 2 K shift per 1 kBar pressure is
observed. The ferromagnetic Curie temperature in the austenite also moves towards higher temperature with a
rate of about 1 K increase per 1 kBar pressure. The ground state saturation moment and exchange bias effect
get enhanced with applied pressure. Magnitude of inverse magnetocaloric effect increases from 12.36 J/kg-K
to 16 J/kg-K for 0 to 8 kBar pressure change at 50 kOe magnetic field and the peak temperature moves to 300
K. However, for the second sample, effect of pressure is quite opposite to some extent. Though for this case
also the martensitic start temperature increases with pressure, but the ground state saturation moment and magnetocaloric effect get suppressed too. Magnitude of inverse magnetocaloric effect decreases from 16.7 J/kg-K to 14.06 J/kg-K for 7 kBar applied pressure at 50 kOe of field. Detailed investigation on the polycrystalline sample of Mn11Ge8 via magnetic, transport and heat capacity measurements is presented in chapter 7. The sample orders ferromagnetically below 274 K, which occurs only due to the ordering of small
atomic moment (∼ 0.05 μB/Mn) along the b direction of the crystallographic axis and on further cooling below 150 K, it undergoes a spin reorientation type transition to a non-collinear antiferromagnetic state. The
development of antiferromagnetic correlation below 150 K occurs through a first order structural instability,
where lattice parameters show discontinuous change keeping the overall crystal symmetry unchanged. Drastic
change in resistivity is observed below 150 K. Both the positive and negative magnetoresistance are obtained depending upon the measurement temperature and strength of applied field. The sample also shows large inverse magnetocaloric effect having the magnitude of 2.8 J/kg-K for H = 90 kOe around 140 K. Concluding remarks and summary of the whole work with the inference have been presented next. Some plans of future works are also included in chapter 8.Research was carried out under the supervision of Prof. Subham Majumdar of Solid State Physics division under SPS [School of Physical Sciences]Research was conducted under DST gran
Self Assembling Peptides and Amino Acids based Soft Materials: Functional Gels and Charge Transfer Complexes
Full text linkThis thesis describes the formation of supramolecular hydrogels and organogels from different synthetic amino acid based amphiphiles and semiconducting organic moiety named naphthalenediimide appended peptide based derivatives. Amino acid and peptide derivatives have been synthesized, purified, characterized and studied in details. Their gelation ability in different aqueous and organic (aromatic/aliphatic) solvents has been studied extensively. These gelator molecules self-associated using various non-covalent interactions including intermolecular hydrogen bonds, electrostatic interactions, - staking etc. to form fibrillar assembly that can encapsulate solvent molecules into their interstitial pores to form self-supported gels. These gel materials have been characterized morphologically, structurally and rheologically. Furthermore, different kinds of applications of these gel materials have been explored.Research was carried out under the supervision of Prof. Arindam Banerjee of the Biological Chemistry division under SBS [School of Biological Sciences]Research was conducted under CSIR fellowshi
Organic/Inorganic Hybrid Heterostructure Solar Cells
Full text linkIn photovoltaic devices, device operation involves (1) exciton generation, (2) charge separation, and (3)
carrier transport to the opposite electrodes. Since the three steps occur in sequence, efforts have been
made to enhance efficiency or output of each of the steps. Generation of excitons depends on the
electronic absorption spectrum of the active materials under solar illumination. Hence active materials
are chosen accordingly. Exciton dissociation or charge separation occurs at the interface between a donor
and an acceptor layer owing to the internal field that develops due to the difference of energy levels at the
interfaces. Carrier transport, the third step, is directed by the internal field generated by the difference in
work functions of the two electrodes. Apart from the electric field, mobility of charge carriers plays a
major role in determining short-circuits current of photovoltaic devices.
Organic semiconductors have suffered from low carrier mobility compared to inorganic ones. The solar
cells fabricated with organic semiconductors are advantageous due to their easy processibility on any
substrate. Apart from easy processibility, organic solar cells are disadvantageous regarding the stability.
They degrade very fast in presence of light and in ambient condition. To overcome the problems
inorganic semiconductors are often used with organic one to fabricate solar cells. The use of inorganic
nanomaterials not only improves the charge carrier lifetime as well as they provide the tunability in
optoelectronic devices. To improve the device performance by capturing the both advantages of organic
and inorganic semiconductor in a same device we have fabricated various solar cells with the
combination of both organic and inorganic semiconductors. Mainly bilayer hybrid heterojunction and
bulk-heterojunction device structures are studied in details in this thesis.As an effort to improve performance of organic photovoltaic devices, inorganic nanostructures can be
included. In this direction, we have introduced an organic/inorganic hybrid pn-junction for solar cell
applications. Layers of II-VI quantum dots and a metal-phthalocyanine in sequence have been used as nand p-type materials, respectively, to form a junction. With indium tin oxide and Au as electrodes, we have formed an inverted structure for solar cell applications. The film of quantum dots has been formed
on top of an ITO electrode followed by removal of long chain ligands with short chain ones to improve particle to particle charge transport. From the current-voltage characteristics of the hybrid heterostructure with indium tin oxide and Au as the electrodes, we have inferred formation of a depletion region at the pn-junction that played a key role in charge separation and correspondingly a photocurrent in the external circuit. The capacitance-voltage characteristics have shown that the width of the depletion
region was much higher as compared to that in devices based on the components.Research was conducted under the supervision of Prof. A. J. Pal of Solid State Physics division under the SPS [School of Physical Sciences]Research was carried out based on financial assistance from DST, SERIIUS & Deit
Tunneling and Electronic Properties of Shape Controlled Mono and Heterogeneous Semiconductor Nanocrystals
No full textSingle NC electrical measurements of semiconductor NCs provide the fundamental limits
for miniaturizing the semiconductor device thereby offering the ultimate control over the
real time advanced device applications. In this context, STM and STS provide several
advantages over conventional measurement techniques by performing the imaging and I-V
spectroscopy down to atomic resolution limit. The corresponding tunneling characteristics
are directly proportional to the density of states of the sample under characterization. Thus,
by using STM and STS one can essentially probe the density of states of a material/molecule
at the atomic resolution limit. This technique also surpasses the limitations imposed by
statistical averaged optical spectroscopy techniques. Investigating the electronic properties
of semiconductor monocomponent and heterogeneous NCs using STM and STS provides an
opportunity to lead the material to advanced device applications like photovoltaics,
optoelectronics and ultra high density memories.
Semiconductor NCs are tiny single crystalline particles, which have the size of the
order of few nanometers, exhibit size and shape dependent optical and electronic properties.
In particular, the spatial confinement of the charge carriers in a semiconductor NC occurs in
different directions depending on the shape of the NC and the extension of the electron and
hole wave functions. Because of these variable degrees of freedom for charge carriers, a wide variety of novel aspects can be realized from such shape controlled semiconductor NCs. For example, a crossover in the valence levels upon changing the NC shape from 0D QDs to 1D nanorods result in a change in the polarization properties of emitted light. Shape of NCs is also one of important factor for field emission applications. Controlling the semiconductor NC to a 2D configuration is also an important criterion in the present and future electronic industry as they relatively eases the fabrication of complex device structures needed for miniaturization of electronic devices. Moreover, the shape controlled semiconductor NCs has crucial impacts in a wide variety of applications such as photovoltaics, optoelectronics, LEDs, NC lasers and biological labels etc. In addition to the shape controlled NCs, coupling of two different semiconducting quantum materials of different sizes or shapes known as hetero-junctions is found to be an unique approach in recent years to improve the tuning of electronic properties beyond the quantum confinement phenomenon. The main advantage of nanoscale hetero-junctions owes its origin to the formation of interface with two different materials which can lead to realization of new properties which are entirely different from the individual constituent materials. These nanoscale hetero-junctions are currently in the spotlight of research for improved performance in wide variety of applications. In this thesis work, we preferred the single NC electrical spectroscopy techniques like STM/STS and four probe measurements to investigate the tunneling and transport properties of these unique mono and heterogeneous semiconductor NCs.Research was carried out under the supervision of Prof. Somobrata Acharya of CAM under SPS [School of Physical Sciences]Research was conducted under the CSIR & DST gran
Functional Noble Metal Nanoparticle for Biomedical Application
Full text linkThe work presented in this thesis entitled “Functional Noble Metal Nanoparticle for
Biomedical Application” was initiated by the author in January, 2011 in Centre for
Advanced Materials, Indian Association for the Cultivation of Science, Kolkata, under
the supervision of Dr. Nikhil Ranjan Jana.
Noble metal nanoparticles have versatile application potential in biomedical field
as they are highly biocompatible, posses plasmon-based strong optical properties suitable for detection/imaging and their synthetic method and surface chemistry are well advanced. Thus they have been successfully applied in cell labeling/subcellular targeting,
site-specific drug/gene delivery, photothermal therapy, selective and sensitive detection of biomolecules and extended to in vivo clinical studies. In recent years, fluorescent gold
nanoclusters have gained increased research focus particularly in biolabeling and sensing application due to their low cytotoxicity, small hydrodynamic diameter and superior photostability. These attracted features make them promising cellular imaging probes and as a replacement of toxic semiconductor nanocrystals.Research was conducted under the supervision of Prof. N R Jana of CAM under SMS [School of Materials Sciences]Research was carried out under CSIR fellowship and gran
Stochastic Simulation Quantifying Cell Mechanics and Division
Full text linkThis thesis is devoted to study the mechanical aspects of mitotic cell divisions in
mammalian and yeast cells through computational modeling. The organization of
the thesis is as follows:
Chapter 1 of this thesis describes the literature review of the mitotic process. A
brief introduction to mammalian and yeast systems are presented and their exotic
features are discussed.
In chapter 2 we study the chromosomal oscillation during the prometaphase and
metaphase in mitosis of a mammalian cell.We present a robust computational model
that incorporates stochastic dynamics of various molecular motors and microtubule
dynamics to demonstrate the oscillation. Our analysis supports a tug-of-war like
mechanism between opposing molecular motors is the main reason of chromosomal
oscillation.
Chapter 3 deals with spontaneous achievement of a stable bipolar spindle during
metaphase which eventually ensures proper segregation of the DNA into the daughter
cells. Employing a robust three dimensional mechanistic model to investigate the
formation and maintenance of a bipolar mitotic spindle in mammalian cells under
different physiological constraints. The model predicts a novel feature of the spindle
instability arising from the insufficient inter-centrosomal angular separation and
impaired sliding of the inter-polar microtubules. In addition, our model successfully reproduces different chromosomal configurations observed in mammalian cells.
In chapter 4 we study the centromeres clustering near the spindle pole bodies
(SPBs).We observed that in G1 and in late anaphase, SPB-centromere proximity was
disturbed in mutant cells lacking Ctf19 complex members, Chl4p and/or Ctf19p,
whose centromeres lay further away from their SPBs than those of the wild-type
cells. We show that the SPB-centromere proximity and distances are not dependent
on physical interactions between SPB and kinetochore components, but involve
microtubule-dependent forces only. Further insight on the positional difference between wild-type and mutant kinetochores was gained by generating our computational
model.
In chapter 5 we compare chromosome segregation process in two yeast phyla;
Ascomycetes and Basidiomycetes.We use mechanistic computational model that
reproduces experimental observations related to spindle alignment, nuclear migration,
and microtubule dynamics during cell division in these yeasts. Two distinct
pathways, based on the population of cytoplasmic microtubules and cortical
dyneins, differentiate nuclear migration and spindle orientation in these two phyla. In addition, the model accurately predicts the contribution of specific classes of microtubules in chromosome segregation.
In Chapter 6 the summary of the thesis is presented. The possible future research in
continuation of this work is also highlighted.Research was conducted under the supervision of Dr. Raja Paul of Solid State Physics division under SPS [School of Physical Sciences]Research was carried out under CSIR and DST gran
Ab-initio Study of Novel Nano-structures
Full text linkIn the present thesis, we have employed first principles electronic structure calculations
based on density functional theory to understand various properties of novel nanostructures.
We have studied trends in band gap and band offsets for a series of small coupled dots
made of II-VI semiconductors using hybrid functional method. Our calculations reveal
absence of offset for the highest occupied molecular orbitals (HOMO) for coupled dots
with common anions while there is substantial HOMO offset for common cation systems.
The absorption peaks for these series of coupled dots are in the ultraviolet (UV) region
with the edges located in the visible region. The transport properties for a representative
type-II, CdS-ZnSe coupled dot displays asymmetric I-V characteristics with high rectification
ratio.
We have shown that experimentally synthesized zinc-blende (ZB) CdS-ZnSe coupled dot
is a type-II heterostructure where it is possible to engineer the band-offsets by varying
size of the CdS component due to the effect of quantum confinement and our results are
consistent with experimental observations. We have investigated and explained the origin
of oriented attachment of ZB ZnSe coupled dots into wurtzite nanorods. We have also
investigated the metal-semiconductors heterojunctions of Au/Pt and CdSe in two different
architectures (bulk interfaces and metal tipped dots). Our calculations reveal for both
the architectures there are metal induced gap states close to the Fermi level. Our estimated
Schottky barrier height (SBH) for bulk interfaces are smaller in comparison to metal tipped
CdSe dots due to quantum confinement induced relatively large band gap of the CdSe dots.
We have also shown that SBH can be tuned by changing the size of CdSe quantum dots.We have studied the electronic structure and the effect of strain on the band alignment of InAs polytye (WZ(2H), 4H, 6H, ZB(3C)) nanowire heterostructures. We have shown that the absence of valance band-offset at the interface of WZ-ZB, WZ-4H and WZ-6H
nanowire heterostructures with different WZ fraction is due to the presence of strain which is consistent with resonance Raman studies. Further we have explored the electronic structure of InAs nanosheets which has direct band gap and our study reveals that zigzag InAs
nanoribbons are metallic as well as ferromagnetic.
We have carried out a comparative study of magnetic and optical properties of Mn-, Gdand Nd-doped ultrathin ZnO nanowires (NWs) and find that antiferromagnetism is stabilized in case of Mn- and Gd- doped ZnO NWs, whereas Nd doped ZnO NWs stabilizes ferromagnetism (FM). Oxygen vacancies further stabilize FM in Nd doped ZnO NW. We have shown that Nd doped ZnO NWs exhibit giant magnetic anisotropy. We also find that Mn, Gd and Nd doped ZnO NWs primarily absorb light in the UV region.
Finally we have explored the electronic structure, optical and topological properties of [100] and [110] monolayer of rock-salt PbS. We have shown that [100] PbS monolayer may be a topological crystalline insulator in the presence of strong spin-orbit coupling. We have also shown that the absorption spectra of PbS nanosheets display step like behavior in agreement with experiment.Research was conducted under the supervision of Prof. Indra Dasgupta of the Solid State Physics division under SPS [school of Physical Sciences]Research was carried out under DST research grant and IACS fellowshi
STUDIES ON MAGNETIC AND DIELECTRIC PROPERTIES OF OXIDES AND NANOCOMPOSITES WITH MESOPOROUS STRUCTURE
No full textThe present thesis deals with the study of dielectric, ferroelectric and magnetic
property of oxides and nanocomposites with mesoporous structure. The synthesis,
characterization and the study of different physical properties of the mesoporous oxides and nanocomposites are the principal objectives of this thesis. To explore the field is not only of immense interest to the scientists, but also has potential for wide applicability. The materials have been synthesized using the soft chemical route. The characterization and detailed analysis of the observed physical properties have been discussed in the different chapters.The research was carried out under the supervision of Prof. Dipankar Chakraborty of MLS and Prof. A. Bhaumik of Materials Science division under SMS [School of Materials Science]The research was conducted under CSIR research fellowship and also grant from Indo-Australian project supported by
Department of Science and Technology, New Delhi and Nano Science and Technology
Initiative programme of the Department of Science and Technology, New Delhi for
providing instrumental facilities