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71.
Neeraj Soni Shivendra Singh Shubham Sharma Gayatri Batra Kush Kaushik Chethana Rao Navneet C. Verma Bhaskar Mondal Aditya Yadav Chayan K. Nandi 《Chemical science》2021,12(10):3615
The structure–function relationship, especially the origin of absorption and emission of light in carbon nanodots (CNDs), has baffled scientists. The multilevel complexity arises due to the large number of by-products synthesized during the bottom-up approach. By performing systematic purification and characterization, we reveal the presence of a molecular fluorophore, quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA), in a large amount (∼80% of the total mass) in red emissive CNDs synthesized from o-phenylenediamine (OPDA), which is one of the well-known precursor molecules used for CND synthesis. The recorded NMR and mass spectra tentatively confirm the structure of QXPDA. The close resemblance of the experimental vibronic progression and the mirror symmetry of the absorption and emission spectra with the theoretically simulated spectra confirm an extended conjugated structure of QXPDA. Interestingly, QXPDA dictates the complete emission characteristics of the CNDs; in particular, it showed a striking similarity of its excitation independent emission spectra with that of the original synthesized red emissive CND solution. On the other hand, the CND like structure with a typical size of ∼4 nm was observed under a transmission electron microscope for a blue emissive species, which showed both excitation dependent and independent emission spectra. Interestingly, Raman spectroscopic data showed the similarity between QXPDA and the dot structure thus suggesting the formation of the QXPDA aggregated core structure in CNDs. We further demonstrated the parallelism in trends of absorption and emission of light from a few other red emissive CNDs, which were synthesized using different experimental conditions.Herein we unveil the presence of a molecular fluorophore quinoxalino[2,3-b]phenazine-2,3-diamine (QXPDA) in a colossal amount in red emissive CNDs synthesized from o-phenylenediamine, a well-known precursor molecule used for CND synthesis. 相似文献
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73.
Platt M Muthukrishnan G Hancock WO Williams ME 《Journal of the American Chemical Society》2005,127(45):15686-15687
The conjugation of 14 nm diameter CoFe2O4 nanoparticles to the surface of biotinylated microtubules enables their manipulation with externally applied magnetic fields of small, permanent NdFeB magnets. Microtubules are selectively patterned on kinesin motor-modified glass surfaces in coparallel arrays that mimic the orientation of the magnetic field lines over millimeter distances. The magnetic field is simultaneously used to increase surface loading of microtubules. We demonstrate that motility across the kinesin motor surface is retained following magnetic functionalization of the microtubules, while gliding speed is dependent on loading level of the neutravidin linker as well as magnetic nanoparticles. 相似文献
74.
Kitron-Belinkov M Marmur A Trabold T Dadheech GV 《Langmuir : the ACS journal of surfaces and colloids》2007,23(16):8406-8410
Spontaneous capillary flow (SCF) of a drop in a groove with an ideally sharp corner is possible when the Concus-Fin (CF) condition is fulfilled. However, since ideally sharp corners do not exist in reality, it is important to understand the effect of finite corner curvature on SCF. This effect is analytically studied for long drops in a V-shaped groove with a curved corner, leading to a generalization of the CF condition for such drops. The generalized condition implies that SCF depends on the geometry of the corner as well as on the dimensionless length of the drop, in addition to its dependence on the opening angle and contact angle that is covered by the CF condition. Specific calculations are presented for rounded corners. In addition, this effect is numerically calculated for short drops in V-shaped grooves with rounded corners, using the Surface Evolver software. The results of both types of calculations show that even a relatively small corner radius strongly affects the possibility of SCF: when the corner is not ideally sharp, SCF requires conditions that are more difficult to achieve than predicted by the CF condition; also, the spreading of the drop stops at a finite length and does not proceed indefinitely. 相似文献
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76.
High Yielding Synthesis of Carboranes Under Mild Reaction Conditions Using a Homogeneous Silver(I) Catalyst: Direct Evidence of a Bimetallic Intermediate
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Dr. Mohamed E. El‐Zaria Kunal Keskar Dr. Afaf R. Genady Dr. Joseph A. Ioppolo Dr. James McNulty Dr. John F. Valliant 《Angewandte Chemie (International ed. in English)》2014,53(20):5156-5160
Methods used to prepare functionalized carboranes generally require heating to high temperatures, and thus limits the range of derivatives which can be prepared directly from alkynes. We show here that by using a homogeneous silver(I) catalyst it is now possible to prepare carboranes in good to excellent yield at temperatures below 40 °C, including at room temperature. The process is general and provides an important new synthetic strategy for the preparation of functionalized boron clusters. 相似文献