12 research outputs found
Design and synthesis of fluorescent probes
The fundamental objective of this project is to design, synthesize, and characterize fluorescent dyes, which may be utilized in super resolution imaging techniques. In Chapters 1, 2 and 3, we concentrated on photoswitchable rhodamine dyes. We synthesized several rhodamine dyes and increased their water solubility, installed a bioconjugation unit and, more importantly, we optimized the absorption properties (close to 400 nm) of the rhodamine spirolactams in their closed state and studied their basic photophysical properties as well. In Chapter 4, we synthesized azido-DCDHF fluorogens that can be converted to the bright state after a 1,3-dipolar cycloaddition reaction between an azide-Ph-DCDHF and a strained alkene. We synthesized some strained alkenes, which may speed up the kinetics in 1,3-dipolar cycloaddition. This chemical method of turning the dyes from dark to bright state is a new dimension in the bioconjugation arena. In Chapter 5, we synthesized Nile red derivatives which can switch to a bright state from a dark state by collision on the cell surface utilizing PAINT methodology. We expected that the design of new Nile red derivatives may have better properties than the parent Nile red. Besides the PAINT technique, we worked on some active control of emission by enzymatic cleavage of fluorescent dyes in a dark state to the bright state, which can be utilized in super resolution imaging. Related to the 1,3-dipolar cycloaddition reaction between azido-DCDHF and norbornene, we have examined recently popularized tetrazine chemistry. We linked pyridyl tetrazines to DCDHF with short spacer. In Chapter 6, we describe the preparation of co-crystals between perfluorophenazine and several polynuclear aromatic compounds/polynuclear heteroaromatic compounds. In Chapter 7 we describe the preparation of some partially fluorinated heteropolynuclear aromatic compounds such phenzaine and acridine class of compounds for possible use in organic semiconductors
Genetic variability, heritability and genetic advance for growth, yield and yield related traits in maize genotypes
Evaluation of the genetic variability, heritability and genetic advance of traits is an essential task in any plant improvement program. Twenty maize genotypes were replicated twice in a randomized complete block design on a research plot of Prithu Technical College, Deukhuri Dang of Nepal from June 2017 to September 2017 to determine genetic variability, heritability, and genetic advance for different agronomic traits. Analysis of variance showed significant differences in the traits tassel length, ear height, days to fifty percent tasseling, days to fifty percent silking, kernels’ rows ear-1, kernels row-1 and grain yield. The highest GCV (31.53%) and PCV (39.20%) were recorded on grain yield. Grain yield and ear height recorded high heritability along with high genetic advance as a percent of mean (GAM). Tassel length and kernels row-1 showed high heritability integrated with moderate GAM and moderate heritability integrated with moderate GAM respectively. Further, grain yield showed a significant and positive correlation with plant height, tassel length, ear height, cob length, cob diameter, kernels’ rows ear-1, and kernels row-1. Thus the selection of ear height, tassel length and kernels row-1 is suggested as they performed better in terms of both heritability and GAM than other traits and they also recorded a significant and positive correlation with yield
Small-Molecule Labeling of Live Cell Surfaces for Three-Dimensional Super-Resolution Microscopy
Precise
imaging of the cell surface of fluorescently labeled bacteria
requires super-resolution methods because the size-scale of these
cells is on the order of the diffraction limit. In this work, we present
a photocontrollable small-molecule rhodamine spirolactam
emitter suitable for non-toxic and specific labeling of the outer
surface of cells for three-dimensional (3D) super-resolution (SR)
imaging. Conventional rhodamine spirolactams photoswitch
to the emitting form with UV light; however, these wavelengths can
damage cells. We extended photoswitching to visible wavelengths
>400 nm by iterative synthesis and spectroscopic characterization
to optimize the substitution on the spirolactam. Further, an <i>N</i>-hydroxysuccinimide-functionalized derivative enabled
covalent labeling of amines on the surface of live <i>Caulobacter
crescentus</i> cells. Resulting 3D SR reconstructions of the
labeled cell surface reveal uniform and specific sampling with thousands
of localizations per cell and excellent localization precision in <i>x</i>, <i>y</i>, and <i>z</i>. The distribution
of cell stalk lengths (a sub-diffraction-sized cellular structure)
was quantified for a mixed population of cells. Pulse-chase experiments
identified sites of cell surface growth. Covalent labeling with the
optimized rhodamine spirolactam label provides a general
strategy to study the surfaces of living cells with high specificity
and resolution down to 10–20 nm
Small-Molecule Labeling of Live Cell Surfaces for Three-Dimensional Super-Resolution Microscopy
Precise
imaging of the cell surface of fluorescently labeled bacteria
requires super-resolution methods because the size-scale of these
cells is on the order of the diffraction limit. In this work, we present
a photocontrollable small-molecule rhodamine spirolactam
emitter suitable for non-toxic and specific labeling of the outer
surface of cells for three-dimensional (3D) super-resolution (SR)
imaging. Conventional rhodamine spirolactams photoswitch
to the emitting form with UV light; however, these wavelengths can
damage cells. We extended photoswitching to visible wavelengths
>400 nm by iterative synthesis and spectroscopic characterization
to optimize the substitution on the spirolactam. Further, an <i>N</i>-hydroxysuccinimide-functionalized derivative enabled
covalent labeling of amines on the surface of live <i>Caulobacter
crescentus</i> cells. Resulting 3D SR reconstructions of the
labeled cell surface reveal uniform and specific sampling with thousands
of localizations per cell and excellent localization precision in <i>x</i>, <i>y</i>, and <i>z</i>. The distribution
of cell stalk lengths (a sub-diffraction-sized cellular structure)
was quantified for a mixed population of cells. Pulse-chase experiments
identified sites of cell surface growth. Covalent labeling with the
optimized rhodamine spirolactam label provides a general
strategy to study the surfaces of living cells with high specificity
and resolution down to 10–20 nm
Synthesis and properties of fluorine tail-terminated cyanobiphenyls and terphenyls for chemoresponsive liquid crystals
Synthesis and properties of hydroxy tail-terminated cyanobiphenyl liquid crystals
<p>Two series of new hydroxy tail-terminated cyanobiphenyl compounds are described. The 4′-ω-hydroxyalkynyl-4-cyanobiphenyl compounds (<b>1a</b>–<b>1g</b>) were synthesised as the key intermediates to the 4′-?ω-hydroxyalkyl-4-cyanobiphenyl compounds (<b>2a</b>–<b>2g</b>) obtained upon reduction of the acetylenes. Many of these ω-hydroxyalkynyl and ω-hydroxyalkyl cyanobiphenyl compounds exhibit nematic mesophases and they also serve as precursors for the synthesis of other interesting materials. Using density functional theory, we calculate the dipole moment of all relevant ω-hydroxyalkynyl and ω-hydroxyalkyl cyanobiphenyl compounds and find a correlation between the calculated dipole moments and measured crystalline to nematic or isotropic liquid transition temperatures.</p
Design of Chemoresponsive Liquid Crystals through Integration of Computational Chemistry and Experimental Studies
We
report the use of computational chemistry methods to design
a chemically responsive liquid crystal (LC). Specifically, we used
electronic structure calculations to model the binding of nitrile-containing
mesogens (4′-<i>n</i>-pentyl-4-biphenylcarbonitrile)
to metal perchlorate salts (with explicit description of the perchlorate
anion), which we call the coordinately saturated anion model (CSAM).
The model results were validated against experimental data. We then
used the CSAM to predict that selective fluorination can reduce the
strength of binding of nitrile-containing nematic LCs to metal-salt-decorated
surfaces and thus generate a faster reordering of the LC in response
to competitive binding of dimethylmethylphosphonate (DMMP). We tested
this prediction via synthesis of fluorinated compounds 3-fluoro-4′-pentyl[1,1′-biphenyl]-4-carbonitrile
and 4-fluoro-4′-pentyl-1,1′-biphenyl, and subsequent
experimental measurements of the orientational response of LCs containing
these compounds to DMMP. These experimental measurements confirmed
the theoretical predictions, thus providing the first demonstration
of a chemoresponsive LC system designed from computational chemistry