1,219 research outputs found
Structure, Photophysics and the Order-Disorder Transition to the Beta Phase in Poly(9,9-(di -n,n-octyl)fluorene)
X-ray diffraction, UV-vis absorption and photoluminescence (PL) spectroscopy
have been used to study the well-known order-disorder transition (ODT) to the
beta phase in poly(9,9-(di n,n-octyl)fluorene)) (PF8) thin film samples through
combination of time-dependent and temperature-dependent measurements. The ODT
is well described by a simple Avrami picture of one-dimensional nucleation and
growth but crystallization, on cooling, proceeds only after molecular-level
conformational relaxation to the so called beta phase. Rapid thermal quenching
is employed for PF8 studies of pure alpha phase samples while extended
low-temperature annealing is used for improved beta phase formation. Low
temperature PL studies reveal sharp Franck-Condon type emission bands and, in
the beta phase, two distinguishable vibronic sub-bands with energies of
approximately 199 and 158 meV at 25 K. This improved molecular level structural
order leads to a more complete analysis of the higher-order vibronic bands. A
net Huang-Rhys coupling parameter of just under 0.7 is typically observed but
the relative contributions by the two distinguishable vibronic sub-bands
exhibit an anomalous temperature dependence. The PL studies also identify
strongly correlated behavior between the relative beta phase 0-0 PL peak
position and peak width. This relationship is modeled under the assumption that
emission represents excitons in thermodynamic equilibrium from states at the
bottom of a quasi-one-dimensional exciton band. The crystalline phase, as
observed in annealed thin-film samples, has scattering peaks which are
incompatible with a simple hexagonal packing of the PF8 chains.Comment: Submitted to PRB, 12 files; 1 tex, 1 bbl, 10 eps figure
An appraisal of the Suzuki cross-coupling reaction for the synthesis of novel fluorescent coumarin derivatives
We report the chemical design and development of 3-aryl-substituted 7-alkoxy-4-methylcoumarins with enhanced fluorogenic properties. The 3-aryl substituents are installed via an optimized Suzuki–Miyaura cross-coupling (SMC) reaction between a 7-alkoxy-3-bromo-4-methylcoumarin and aryl boronic MIDA esters using Pd(OAc)2/XPhos in a catalytic system with K2CO3 in aqueous THF. Under these conditions, an exocyclic ester functionality is found to be unaffected. Subsequent saponification revealed a carboxylic acid functionality that is suitable for conjugation reactions. Evaluation of their fluorescence properties indicated that the installed 3-heteroaryl substituent, particularly benzofuran-2-yl, resulted in a significant red shift of both the excitation and emission wavelengths
Lymphocytes and the Dap12 Adaptor Are Key Regulators of Osteoclast Activation Associated with Gonadal Failure
Bone resorption by osteoclasts is necessary to maintain bone homeostasis. Osteoclast differentiation from hematopoietic progenitors and their activation depend on M-CSF and RANKL, but also requires co-stimulatory signals acting through receptors associated with DAP12 and FcRγ adaptors. Dap12 mutant mice (KΔ75) are osteopetrotic due to inactive osteoclasts but, surprisingly, these mice are more sensitive than WT mice to bone loss following an ovariectomy. Because estrogen withdrawal is known to disturb bone mass, at least in part, through lymphocyte interaction, we looked at the role of mature lymphocytes on osteoclastogenesis and bone mass in the absence of functional DAP12. Lymphocytes were found to stimulate an early osteoclast differentiation response from Dap12-deficient progenitors in vitro. In vivo, Rag1-/- mice lacking mature lymphocytes did not exhibit any bone phenotype, but lost their bone mass after ovariectomy like KΔ75 mice. KΔ75;Rag1-/- double mutant female mice exhibited a more severe osteopetrosis than Dap12-deficient animals but lost their bone mass after ovariectomy, like single mutants. These results suggest that both DAP12 and mature lymphocytes act synergistically to maintain bone mass under physiological conditions, while playing similar but not synergistic co-stimulatory roles in protecting bone loss after gonadal failure. Thus, our data support a role for lymphocytes during osteoclast differentiation and suggest that they may function as accessory cells when regular osteoclast function is compromised
Daidzein Prevents the Increase in CD4+CD28null T Cells and B Lymphopoesis in Ovariectomized Mice: A Key Mechanism for Anti-Osteoclastogenic Effect
Estrogen deficiency leads to an upregulation of TNF-α producing T cells and B-lymphopoesis which augments osteoclastogenesis. Estrogen deficiency also increases the population of premature senescent CD4+CD28null T cells which secrete a higher amount of TNF-α thus leading to enhanced osteoclastogenesis. Isoflavonoids like daidzein and genistein are found mostly in soybeans, legumes, and peas. These share structural similarity with 17β-stradiol (E2) and have osteoprotective role. This study explores the effect of daidzein (Daid) on the proliferation of TNF-α producing T cells, premature senescent T cells and B cell lymphopoesis under estrogen deficient conditions. For this study adult Balb/c mice were treated with Daid at 10 mg/kg body weight dose by oral gavage daily post ovariectomy (Ovx). After six weeks animals were autopsied and bone marrow and spleen cells were collected for FACS analysis. Blood serum was collected for ELISA. It was observed that Ovx mice treated with Daid for six weeks show reduction in Ovx induced expansion of CD4+ T cells in bone marrow and spleen when analysed by flow cytometry. Estrogen deficiency led to increased prevalence of TNF-α secreting CD4+CD28null T cells, however, treatment with Daid increased the percentage of CD4+CD28+ T cells. Co-culture of CD4+CD28null T cells and bone marrow resulted in enhanced osteoclastogenesis as evident by increased tartarate resistant acid phosphatase (TRAP) expression, an osteoclast marker. However, treatment with Daid resulted in reduced osteoclastogenesis in CD4+CD28null T cells and bone marrow cell co-culture. Daid also regulated B lymphopoesis and decreased mRNA levels of RANKL in B220+ cells. Taken together, we propose that one of the mechanisms by which Daid prevents bone loss is by reversing the detrimental immune changes as a result of estrogen deficiency
Assessing cumulative dose distributions in combined radiotherapy for cervical cancer using deformable image registration with pre-imaging preparations
Functionalized Poly(3-hexylthiophene)s via Lithium–Bromine Exchange
Poly(3-hexylthiophene) (P3HT) is one of the most extensively investigated conjugated polymers and has been employed as the active material in many devices including field-effect transistors, organic photovoltaics and sensors. As a result, methods to further tune the properties of P3HT are desirable for specific applications. Herein, we report a facile postpolymerization modification strategy to functionalize the 4-position of commercially available P3HT in two simple steps–bromination of the 4-position of P3HT (Br–P3HT) followed by lithium−bromine exchange and quenching with an electrophile. We achieved near quantitative lithium–bromine exchange with Br–P3HT, which requires over 100 thienyl lithiates to be present on a single polymer chain. The lithiated-P3HT is readily combined with functional electrophiles, resulting in P3HT derivatives with ketones, secondary alcohols, trimethylsilyl (TMS) group, fluorine, or an azide at the 4-position. We demonstrated that the azide-modified P3HT could undergo Cu-catalyzed or Cu-free click chemistry, significantly expanding the complexity of the structures that can be appended to P3HT using this method.National Science Foundation (U.S.) (ECCS-0939514
Design and Synthesis of Heterocyclic Cations for Specific DNA Recognition: From AT-Rich to Mixed-Base-Pair DNA Sequences
The compounds synthesized in this research were designed with the goal of establishing a new paradigm for mixed-base-pair DNA sequence-specific recognition. The design scheme starts with a cell-permeable heterocyclic cation that binds to AT base pair sites in the DNA minor groove. Modifications were introduced in the original compound to include an Hbond accepting group to specifically recognize the G-NH that projects into the minor groove. Therefore, a series of heterocyclic cations substituted with an azabenzimidazole ring has been designed and synthesized for mixed-base-pair DNA recognition. The most successful compound, 12a, had an azabenzimidazole to recognize G and additional modifications for general minor groove interactions. It binds to the DNA site −AAAGTTT− more strongly than the −AAATTT− site without GC and indicates the design success. Structural modifications of 12a generally weakened binding. The interactions of the new compound with a variety of DNA sequences with and without GC base pairs were evaluated by thermal melting analysis, circular dichroism, fluorescence emission spectroscopy, surface plasmon resonance, and molecular modeling
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