Effects of Surface Charges on the Bactericide Activity of CdTe/ZnS Quantum Dots: A Cell Membrane Disruption Perspective.

The inhibitory effects of CdTe/ZnS quantum dots (QDs) modified with 3-mercaptopropionic acid (negatively charged) or cysteamine (positively charged) on the metabolic activity of Escherichia coli were investigated using biological microcalorimetry. Results show that the inhibitory ratio of positive QDs is higher than that of negative QDs. Transmission electron microscopy images indicate that QDs are prone to be adsorbed on the surface of E. coli. This condition disturbs the membrane structure and function of E. coli. Fluorescence anisotropy results demonstrate that positive QDs show a significant increase in the membrane fluidity of E. coli and dipalmitoylphosphatidylcholine (DPPC) model membrane. Furthermore, fluorescence anisotropy values of DPPC membrane in the gel phase decreased upon the addition of positive QDs. By contrast, anisotropy values in the liquid-crystalline phase are almost constant. The change in membrane fluidity is associated with the increased permeability of the membrane. Finally, the kinetics of dye leakage from liposomes demonstrate that the surface charge of QDs is crucial to the interaction between QDs and membrane.

Impact of multiple quaternary ammonium salts on dynamic properties of BSA adsorption layer at different pH values.

The interaction mechanism of multiple quaternary ammonium salts (MQAS) with bovine serum albumin (BSA) was examined by the fluorescence quenching method and circular dichroism (CD) spectra. Moreover, the effects of MQAS on the dynamic properties of BSA adsorption layers at different pH values were investigated using dilational interfacial rheology. Results show that the quenching constants increase with an increase in pH values and decrease with an increase in the experiment temperature at pH 5.3. The quenching mechanism is static quenching, and the electrostatic force dominates the interaction between MQAS and BSA at pH 5.3. Due to three positive head groups, MQAS can significantly affect the dynamic interfacial activity of BSA molecules at a relatively low concentration. At pH 4.3, the electrostatic repulsion is unfavorable for the formation of MQAS/BSA complexes. Consequently, MQAS molecules will replace BSA molecules from the interface by competitive adsorption. At the pH value above the isoelectric point of BSA, the electrostatic attraction is better for the formation of MQAS/BSA complexes, which exhibit a rapid adsorption rate and an enhanced interfacial activity. Moreover, the kinetic dependencies of interfacial dilational elasticity for the MQAS/BSA mixtures become nonmonotonous. The appearance of the maximum interfacial elasticity values can be attributed to the formation of tails and loops, which suggests that the addition of MQAS destroys the secondary and tertiary structure of protein in the bulk phase. In addition, the effects of MQAS on the secondary structure of protein were demonstrated by CD spectra.

[Study on quantitative mechanism and the interference of the UV spectrum of HABS reduced by ß-Cyclodextrin].

A novel ultraviolet absorption spectrometry method was developed for the quantitative determination of HABS by adding ß-cyclodextrin with the molar ratio of 1:1 in strong interference aqueous solution. The results indicated that the effect of several common interfering flooding agents (SAS, OP-10, HPAM) on the determination of HABS could be greatly reduced in ß- cyclodextrin aqueous solution. Thus, the determination errors of the determined HABS were less than 2.0% under strong inter- ference, and the detection limit (S/N==3) of the method could be also as high was 8.3-9.1 x 10(-4) mg · L(-1). Various characterization results including 1H-NMR, TG-DSC and FTIR showed the interaction between ß-cyclodextrin and HABS. The results of H-NMR analysis showed that HABS molecule could enter into the interior of the cavity of ß-cyclodextrin molecule. TG-DSC analysis exhibited that the stable inclusion of ß-cyclodextrin and HABS could be automatically formed. The interactions between the functional groups of ß-cyclodextrin and HABS were showed by FTIR analysis, which also exhibited that the stable inclusion could be formed by HABS entering from the narrow or the broad mouth of the ß-cyclodextrin. The interference of the UV spectrum of HABS could be reduced by ß-cyclodextrin since the interaction between ß-cyclodextrin due to the interaction between ß-cyclodextrin and HABS in the inclusion complex.

[Study on the enhanced spectrum quantitative analysis of SDBS induced by beta-cyclodextrin].

A novel enhanced ultraviolet absorption spectrometry method was developed for the quantitative analysis of SDBS induced by beta-cyclodextrin(beta-CD) with strong interferences. The ultraviolet absorption spectra of SDBS indicated that the presence of beta-CD could result in the enhancement of absorption intensities of SDBS. A good linearity was obtained between the UV-absorption intensity of the system and the concentration of SDBS. The results indicated that the determination precision and the determination ranges of SDBS could be greatly improved by beta-CD. The effect of several common interfering substances (SDS, OP-10, HPAM) on the determination of SDBS could be significantly reduced in beta-CD aqueous solution. Therefore, the maximum errors of the determined SDBS were less than 2.0% under multifactor interferences, and the precision of the method was also as high as 10(-2) - 10(-3) mg x L(-1). The stable inclusion of beta-CD and SDBS could be automatically formed in water with molar ratio of 1 : 1. The stability constant of the inclusion, K(a), was 87 and the standard Gibbs function of molar reaction, delta(gamma)G(m)(see symbol) (298 K), was -11.064 kJ x mol(-1). FTIR analysis exhibited that SDBS could be induced by beta-CD since the phenyl group in SDBS molecule could exist stably in the cavity of beta-CD and form the inclusion.

Impact of carbon quantum dots on dynamic properties of BSA and BSA/DPPC adsorption layers.

The effects of carbon quantum dots (CQDs) on the dynamic properties of bovine serum albumin (BSA) were investigated using pendant drop profile analysis method. Moreover, the effects of CQDs on the competitive adsorption of BSA and dipalmitoyl phosphatidylcholine (DPPC) were examined. CQDs reduce the fluorescence intensity of BSA and cause a red shift in fluorescence emission. The quenching constant at pH 4.3 is almost twice as large as that of the value obtained at pH 6.0. A small amount of CQDs does not influence the dynamic surface adsorption properties of BSA molecules. As the CQD concentration increases, a gradual increase in adsorption rate of BSA molecules is observed. Moreover, the addition of CQDs results in a significant transition of kinetic dependencies of surface elasticity of BSA solution when the CQD concentration exceeds a critical value. The appearance of the maximum surface elasticity value is probably attributed to the formation of tails and loops. When the dynamic surface properties are dominated by BSA molecules, the effects of CQDs on the surface properties of BSA/DPPC mixture are similar to those of BSA alone. However, when the surface film mainly consists of DPPC, CQDs can obviously change the interfacial properties of DPPC monolayer.