We report a well controlled method to make carbon nanotube tips for a scanning probe microscope (SPM). A multiwalled carbon nanotube, which is purified by the electrophoresis, is transferred onto a conventional Si tip for a SPM using a scanning electron microscope (SEM) equipped with two independent specimen stages. The nanotube is fixed on the Si tip by electron beam deposition of carbon. A force curve measurement of nanotubes using the nanotube tips in the SEM reveals that Young's modulus of a nanotube of 20 nm diameter is 1.1 TPa and the fixing of nanotubes by the carbon deposit is effective. The nanotube tips are used to image plasmid deoxyribonucleic acids on mica by tapping mode. The average resolution by using the nanotube tips is about two times higher than that by the best Si tips.
Abstract Background Natural products play a key role as potential sources of biologically active substances for the discovery of new drugs. This study aimed to identify secondary metabolites from actinomycete library extracts that are potent against the asexual stages of Plasmodium falciparum ( P. falciparum ). Methods Secondary metabolites from actinomycete library extracts were isolated from culture supernatants by ethyl acetate extraction. Comprehensive screening was performed to identify novel antimalarial compounds from the actinomycete library extracts ( n = 28). The antimalarial activity was initially evaluated in vitro against chloroquine/mefloquine-sensitive (3D7) and-resistant (Dd2) lines of P. falciparum . The cytotoxicity was then evaluated in primary adult mouse brain (AMB) cells. Results Out of the 28 actinomycete extracts, 17 showed parasite growth inhibition > 50% at a concentration of 50 µg/mL, nine were identified with an IC 50 value < 10 µg/mL, and seven suppressed the parasite significantly with an IC 50 value < 5 µg/mL. The extracts from Streptomyces aureus strains HUT6003 (Extract ID number: 2), S. antibioticus HUT6035 (8), and Streptomyces sp. strains GK3 (26) and GK7 (27), were found to have the most potent antimalarial activity with IC 50 values of 0.39, 0.09, 0.97, and 0.36 µg/mL (against 3D7), and 0.26, 0.22, 0.72, and 0.21 µg/mL (against Dd2), respectively. Among them, Streptomyces antibioticus strain HUT6035 (8) showed the highest antimalarial activity with an IC 50 value of 0.09 µg/mL against 3D7 and 0.22 µg/mL against Dd2, and a selective index (SI) of 188 and 73.7, respectively. Conclusion Secondary metabolites obtained from the actinomycete extracts showed promising antimalarial activity in vitro against 3D7 and Dd2 cell lines of P. falciparum with minimal toxicity. Therefore, secondary metabolites obtained from actinomycete extracts represent an excellent starting point for the development of antimalarial drug leads.
We present results on the dynamic fluorescence properties of bioconjugated nanocrystals or quantum dots (QDs) in different chemical and physical environments. A variety of QD samples was prepared and compared: isolated individual QDs, QD aggregates, and QDs conjugated to other nanoscale materials, such as single-wall carbon nanotubes (SWCNTs) and human erythrocyte plasma membrane proteins. We discuss plausible scenarios to explain the results obtained for the fluorescence characteristics of QDs in these samples, especially for the excitation time-dependent fluorescence emission from clustered QDs. We also qualitatively demonstrate enhanced fluorescence emission signals from clustered QDs and deduce that the band 3 membrane proteins in erythrocytes are clustered. This approach is promising for the development of QD-based quantitative molecular imaging techniques for biomedical studies involving biomolecule clustering.
Plasmodium falciparum's resistance to available antimalarial drugs highlights the need for the development of novel drugs. Pyrimidine de novo biosynthesis is a validated drug target for the prevention and treatment of malaria infection. P. falciparum dihydroorotate dehydrogenase (PfDHODH) catalyzes the oxidation of dihydroorotate to orotate and utilize ubiquinone as an electron acceptor in the fourth step of pyrimidine de novo biosynthesis. PfDHODH is targeted by the inhibitor DSM265, which binds to a hydrophobic pocket located at the N-terminus where ubiquinone binds, which is known to be structurally divergent from the mammalian orthologue. In this study, we screened 40,400 compounds from the Kyoto University chemical library against recombinant PfDHODH. These studies led to the identification of 3,4-dihydro-2H,6H-pyrimido[1,2-c][1,3]benzothiazin-6-imine and its derivatives as a new class of PfDHODH inhibitor. Moreover, the hit compounds identified in this study are selective for PfDHODH without inhibition of the human enzymes. Finally, this new scaffold of PfDHODH inhibitors showed growth inhibition activity against P. falciparum 3D7 with low toxicity to three human cell lines, providing a new starting point for antimalarial drug development.
