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Bulk samples and thin films of polyamides (PA6 and PA12) were exposed to fluorine (1 - 10 vol.-% F2 in N2) and analysed with photoelectron (XPS) and infrared spectroscopy. Fluorination affects both, the amide and the hydrocarbon parts of the polymers. However, only the carbon atom next to the carbonyl is readily fluorinated. Chemical modification of the amide group is apparent in a large binding energy shift (+5 eV) of the N1s level and the appearance of a CO band at 1734 cm-1. It is concluded that the amide C-N bond is cleaved in the fluorination process and that COOH and NF2 end groups are formed. This conclusion is corroborated by the appearance of ester oxygen in the XPS and by the 19F NMR spectra of the volatile products that show fluorine signals chemically shifted about 200 ppm towards lower field as compared with the CHF environment.
Thin polyamide-6 films were exposed to fluorine gas and analysed with photoelectron and infrared spectroscopies. Fluorine cleaves the amide CN bond resulting in the formation of the COOH and NF2 terminal groups. This is evident from large shifts in the N1s binding energy (+5 eV) and C=O stretching frequency (~80 cm-1), appearance of ester oxygen in the XPS spectra, as well as by the 19F nmr spectra of volatile products consistent with a terminal NF2 group.
Efficient formation of difluoramino (NF2) groups within the polymer matrix upon exposure of polyamides (PA6 and PA12) to elemental fluorine is reported. The reaction was assessed on bulk and thin-film samples by means of RA-FTIR (reflection–absorption FTIR), XPS (X-ray photoelectron spectroscopy), and NMR (nuclear magnetic resonance) techniques. Direct fluorination causes cleavage of the amide C–N bond and concomitant formation of the NF2 chain-end functionalities as evident from an exceptionally large shift (+5 eV) of the N 1s binding energy and an increase of the v(CO) frequency by about 80 cm-1. The structural model is supported by the 19F NMR spectra of volatile reaction products that clearly reveal the presence of the NF2 group.
Low-energy secondary electrons are the most abundant radiolysis species which are thought to be able to attach to and damage DNA via formation and decay of localized molecular resonances involving DNA components. In this study, we analyze the consequences of low-energy electron impact on the ability of DNA to hybridize (i.e., to form the duplex). Specifically, single-stranded thymine DNA oligomers tethered to a gold surface are irradiated with very low-energy electrons (E = 3 eV, which is below the 7.5 eV ionization threshold of DNA) and subsequently exposed to a dye-marked complementary strand to quantify by a fluorescence method the electron induced damage. The damage to (dT)25 oligomers is detected at quite low electron doses with only about 300 electrons per oligomer being sufficient to completely preclude its hybridization. In the microarray format, the method can be used for a rapid screening of the sequence dependence of the DNA-electron interaction. We also show for the first time that the DNA reactions at surfaces can be imaged by secondary electron (SE) emission with both high analytical and spatial sensitivity. The SE micrographs indicate that strand breaks induced by the electrons play a significant role in the reaction mechanism.
Immobilization of silanized DNA on glass: influence of the silane tether on the DNA hybridization
(2010)
Two trifunctional (trimethoxy and triethoxy) and one difunctional (methyldimethoxy) 3-mercaptopropyl-alkoxysilanes were covalently tethered to thiolated DNA oligonucleotides in solution. After deposition as microarrays onto glass, the immobilized DNA probes were tested for hybridization ability by a florescence-based method. The results demonstrate a large enhancement in the fluorescence signal when the functionality of the silane tether is reduced from three to two. An XPS analyses revealed that this is not due to a higher DNA surface density. FTIR spectra of the spin-coated silanes showed that the trifunctional silanes form branched and cyclic siloxane moieties, whereas the difunctional silane generates predominantly short straight siloxane chains. Therefore, the propensity of trifunctional silanes to form more complex networks leads to conformations of the bound DNA which are less favorable for the specific interaction with the complementary strand. The data implicate that further significant improvements in the DNA hybridization ability are possible by adroit choice of the silane system.
We report surface plasmon resonance (spr) and confocal fluorescence results concerning the interaction of a gene-5-protein (g5p) with single-stranded DNA oligonucleotides (dT25) tethered to a gold surface. The spr data show that a highly stable g5pssDNA complex is readily formed on a gold surface with koff = 1.7 × 10-3 s-1. The extent of the complexion indicated involvement of the cooperative proteinprotein interactions within the binding to DNA. In the experiments where dT25 coexist with g5p in the solution, the fluorescence data show that g5p also mediates the binding between the non-complementary oligonucleotides in the solution and those immobilised on the surface.