Raman and surface-enhanced Raman spectra of new DNA/RNA-binding compounds consisting of three imidazole (Im) and three pyridine (Py) rings connected by tripodal polyaminomethylene linkages were obtained by the near-infrared excitation at 1064 nm. Study of interactions of Im and Py polyamines with single-stranded RNA polynucleotides (poly A, poly G, poly C, poly U), double-stranded DNA polynucleotides (poly dAdT-poly dAdT, poly dGdC-poly dGdC) and calf thymus DNA (ct-DNA) by surface-enhanced Raman spectroscopy (SERS) reveals unambiguous enhancement of the Raman scattering from the small molecules as well as appearance of new bands in spectra associated mainly with nucleobases. The SERS experiments point toward comparable interactions of Im and Py polyamines with single-stranded purine and pyrimidine polynucleotides. Furthermore, SERS experiments with double stranded polynucleotides reveal the base-pair dependent selectivity of Im and Py, whereby interactions within both, major and minor groove are indicated for poly dAdT-poly dAdT, at variance to preferred binding of Im and Py to only major groove of poly dGdC-poly dGdC. SERS spectra of Im and Py with ct-DNA imply that protonated amino groups of these compounds preferentially interact with N7 atoms (adenine, guanine) while nitrogen in aromatic rings of polyamines might be attracted to C6-NH(2) (adenine), all sites being located at the major groove of the DNA helix. Wavenumber downshift of the imidazole (Im) and pyridine (Py) ring vibrations supports aromatic stacking interactions of imidazole and pyridine aromatic moieties with DNA base-pairs.
Due to their broad-spectrum antimicrobial activity, silver nanoparticles (AgNPs) have been used in a large number of commercial and medical products. Such proliferated AgNP production poses toxicological and environmental issues which need to be addressed. The present study aimed to investigate the effects of AgNPs on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), important enzymes in areas of neurobiology, toxicology and pharmacology. Three different AgNPs, prepared by the chemical reduction using trisodium citrate, hydroxylamine hydrochloride (Cl-AgNPs), and borohydride following stabilization with poly(vinyl alcohol), were purified and characterised with respect to their sizes, shapes and optical properties. Their inhibition potential on AChE and BChE was evaluated in vitro using an enzyme assay with o-nitrophenyl acetate or o-nitrophenyl butyrate as substrates, respectively. All three studied AgNPs were reversible inhibitors of ChEs. Among tested nanoparticles, Cl-AgNP was found to be the most potent inhibitor of both AChE and BChE. Although the detailed mechanism by which the AgNPs inhibit esterase activities remains unknown, structural perturbation of the enzyme may be the common mode of ChE inhibition by AgNPs.
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