Supramolecular structures formed by H4TPPS42-have been widely used for different applications.In this paper,the stability of H4TPPS42? nanorods on mica substrate is investigated by atom force microscopy (AFM) observation.An irreversible transformation of H4TPPS42-from nanorods (3.8±0.4 nm in height) to a lower film structure (1.9±0.4 nm in height) was found with the samples incubated at various relative humidities (RH).The transformation rate depends strongly on the RH and environment temperature.
Peptide frictions in water nanofilms of various thicknesses on a mica surface are studied via molecular dynamics simulations. We find that the forced lateral motion of the peptide exhibits stick-slip behaviour at low water coverage; in contrast, the smooth gliding motion is observed at higher water coverage. The adsorbed peptide can form direct peptide-surface hydrogen bonds as well as indirect peptide-water-surface hydrogen bonds with the substrate. We propose that the stick-slip phenomenon is attributed to the overall effects of direct and indirect hydrogen bonds formed between the surface and the peptide.
Many environmental factors can cause DNA damage, such as radiation, heat, oxygen free radical, etc., which can induce mutation during DNA replication. Meanwhile, DNA molecules are subjected to various mechanical forces in numerous biological processes. However, it is unknown whether the mechanical force would induce DNA damage and introduce mutation during DNA replication. With the combination of single-molecule manipulation based on atomic force microscopy (AFM), single molecular polymerase chain reaction (SM-PCR) and Sanger's sequencing, we investigated the effect of mechanical force on DNA. The results show that mechanical force can cause DNA damage and induce DNA mutation during amplification.
ZHANG ChenDUAN NaDAI BinZHANG YiZHANG DonghuaHU Jun
A mathematical model of polymerase chain reaction (PCR) containing uncertain and time-varying parameters has become important for model-based guidance experiment design. In this study, the local and global sensitivity analyses were conducted to identify that the responses of PCR process vary with their parameters of initial reactant concentrations and rate constants. Our results showed that the template concentration in initial reactant concentrations had the largest effect on DNA amplification yield. The rate constant characteristics showed that the local sensitivity basically determined the specific reactions; and the global sensitivity, the non-specific reactions. Our work should be helpful for optimizing PCR experimental conditions, and determining the PCR parameter sensitivities.
Graphene and its derivative,graphene oxide (GO) have been substantively used as the main framework for dispersing or building nanoarchitectures because of their excellent properties in electronics and catalysis.The requirement to obtain superior graphene-metal hybrid nanomaterials has led us to explore a facile way to design 4-aminobenzenethiol/1-hexanethiolate-protected gold nanoparticles (aAuNPs)-functionalized graphene oxide composite (aAuNPs-GO) in solution.We demonstrate that when aAuNPs with amino groups are exposed to GO,well-dispersed coverage of Au nanoparticles are mainly observed on the edge of GO sheet.In contrast,when 1-hexanethiolate-protected gold nanoparticles (hAuNPs) without amino groups are exposed to GO,hAuNPs simply aggregate on the surface of GO.This indicates that amino groups located on the surface of Au nanoparticles are an essential prerequisite for attachment of nearly monodispersed aAuNPs.The strategy described here for the fabrication of aAuNPs-GO provides a straightforward approach to develop graphene-based nanocomposites with undamaged sheets structure and good solubility and also improve the conductivity of GO sheets evidently.
