Estimation of non-constant variance in isothermal titration calorimetry using an ITC measurement model.

Isothermal titration calorimetry (ITC) is the gold standard for accurate measurement of thermodynamic parameters in solution reactions. In the data processing of ITC, the non-constant variance of the heat requires special consideration. The variance function approach has been successfully applied in previous studies, but is found to fail under certain conditions in this work. Here, an explicit ITC measurement model consisting of main thermal effects and error components has been proposed to quantitatively evaluate and predict the non-constant variance of the heat data under various conditions. Monte Carlo simulation shows that the ITC measurement model provides higher accuracy and flexibility than variance function in high c-value reactions or with additional error components, for example, originated from the fluctuation of the concentrations or other properties of the solutions. The experimental design of basic error evaluation is optimized accordingly and verified by both Monte Carlo simulation and experiments. An easy-to-run Python source code is provided to illustrate the establishment of the ITC measurement model and the estimation of heat variances. The accurate and reliable non-constant variance of heat is helpful to the application of weighted least squares regression, the proper evaluation or selection of the reaction model.

The Role of the OH Group in Citric Acid in the Coordination with Fe3O4 Nanoparticles.

The role of the C?OH group in citric acid (CA) in the molecular coordination with Fe3O4 nanoparticles (NPs) has been elusive for a long time. In this study, attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectral deconvolution and thermogravimetric analysis (TGA) have been used to quantitatively clarify its significance in CA adsorption and its corresponding conformation. The experimental results show that the coordination and the corresponding conformation are exclusively determined by COOH not C?OH at pH 3, where its adsorption behavior conforms to the Brunauer?Emmett?Teller (BET) multilayer model with a maximal monolayer coordination number of 2.1/nm2. However, C?OH is involved in the coordination at pH 10, and CA conforms to the Langmuir monolayer model with 1.4/nm2 as its maximal monolayer coordination number, which is more stable than the COOH-only coordination. Especially, the conformational transformation is observed for the first time at pH 3, where the CA molecules adjust their conformation upon elution to maximize the utilization of the available binding sites on Fe3O4 NPs. This finding deepens the understanding on the fundamental mechanism for the interaction between the C?OH and COOH groups containing the organic ligand and metal oxide.

Conformation-Dependent Coordination of Carboxylic Acids with Fe3O4 Nanoparticles Studied by ATR-FTIR Spectral Deconvolution.

The coordination of valeric acid (VA), glutaric acid (GA), and tricarballylic acid (TA) with Fe-OH on the Fe3O4 nanoparticle surface has been systematically studied to elucidate the effects of COOH, molecular configuration, and ligand concentration on the coordination by the combined use of attenuated total reflectance Fourier transform infrared (ATR-FTIR) and thermogravimetric analysis (TGA). The results show that the binding ability of the acids increases with the increase in the COOH number. Multiple conformations coexist for the dicarboxylic and tricarboxylic acid coordinated on the iron oxide NPs. Saturated coordination formed with only a one-, two-, or three-COOH conformation for VA, GA, and TA, respectively, occurs under ligand-scarce conditions, while unsaturated coordination formed with the mixture of uncoordinated, one-, and/or two-COOH conformations for VA, GA, and TA, respectively, exists under ligand-abundant conditions. The maximum coordination numbers for monolayer adsorption for VA, GA, and TA on Fe3O4 NPs are 9, 2.4, and 2.7 nm-2, respectively. This study helps us to understand the fine coordination mechanism caused by the acid molecules with different configurations and elucidates, for the first time, the fine conformational variance incurred by the surrounding ligand with different concentrations and the way in which the ligand is added.

Size-dependent adsorption and its application in determining the number of surfactant molecule adsorbed on multimodal SiO2 particles by 2D-DCS.

Quantitative analysis using surfactant-particles interaction is the basis for many applications. In situ measurements of surfactant adsorption on nanoparticles are important to understanding adsorption kinetics. However, it is quite difficult to determine the individual numbers for each monomodal particles in a multimodal mixture system by current technologies. To cope with this problem, a new method, i.e. 2D differential centrifugal sedimentation (2D-DCS), has been developed and applied in situ to measure the number of CTAB molecules adsorbed on the surface of silica particles, assuming that the adlayer is composed of a compact CTAB monolayer. Results show that 2D-DCS can measure the adsorption amount for particles not only with single size distribution but also with multiple size distributions. The number of adsorbed CTAB per nm2 on silica particles determined by 2D-DCS are 1.4 and 3.9 for the monomodal particles of 210 and 1000 nm, respectively, which is similar to that measured by ζ-potential, DLS and UV-vis spectrometry, and 1.4, 2.3 and 2.5 for 210, 430 and 700 nm particles, respectively, for a trimodal particle system, where the size-dependent adsorption is difficult to be simultaneously measured by other technologies.

Synergetic Determination of Thermodynamic and Kinetic Signatures Using Isothermal Titration Calorimetry: A Full-Curve-Fitting Approach.

Thermodynamic and kinetic signatures are pivotal information for revealing the binding mechanisms of biomolecules, and they play an indispensable role in drug discovery and optimization. While noncalorimetric methods measure only a part of these signatures, isothermal titration calorimetry (ITC) is considered to have the potential to acquire full signatures in an experiment. However, kinetic parameters are generally difficult to extract from ITC curves, as they are inevitably affected by the instrument-response function and the collateral heat of associated process during titrations. Thus, we herein report the development and validation of a full-curve-fitting method to resolve thermal power curves and to maximize the signal extraction using ITC. This method is then employed to quantify the dilution of an aqueous n-propanol solution and examine the inhibition of carbonic anhydrase by 4-carboxybenzenesulfonamide using a commercial instrument with a long apparent response time of ∼13 s.

In Situ Measurement of Surface Functional Groups on Silica Nanoparticles Using Solvent Relaxation Nuclear Magnetic Resonance.

In situ analysis and study on the surface of nanoparticles (NPs) is a key to obtain their important physicochemical properties for the subsequent applications. Of them, most works focus on the qualitative characterization whereas quantitative analysis and measurement on the NPs under their storage and usage conditions is still a challenge. In order to cope with this challenge, solvation relaxation-based nuclear magnetic resonance (NMR) technology has been applied to measure the wet specific surface area and, therefore, determine the number of the bound water molecules on the surface of silica NPs in solution and the hydrophilic groups of various types grafted on the surface of the NPs. By changing the surface functional group on silica particles, the fine distinction for the solvent-particle interaction with different surface group can be quantitatively differentiated by measuring the number of water molecules absorbed on the surface. The results show that the number of the surface hydroxyl, amine, and carboxyl group per nm2 is 4.0, 3.7, and 2.3, respectively, for the silica particles with a diameter of 203 nm. The method reported here is the first attempt to determine in situ the number of bound solvent molecules and any solvophilic groups grafted on nanoparticles.

Alloyed Crystalline Au-Ag Hollow Nanostructures with High Chemical Stability and Catalytic Performance.

For bimetallic nanoparticles (NPs), the degree of alloying is beginning to be recognized as a significant factor affecting the NP properties. Here, we report an alloyed crystalline Au-Ag hollow nanostructure that exhibits a high catalytic performance, as well as structural and chemical stability. The Au-Ag alloyed hollow and porous nanoshell structures (HPNSs) with different morphologies and subnanoscale crystalline structures were synthesized by adjusting the size of the sacrificial Ag NPs via a galvanic replacement reaction. The catalytic activities of the nanomaterials were evaluated by the model reaction of the catalytic reduction of p-nitrophenol by NaBH4 to p-aminophenol. The experimental results show that the subnanoscale crystalline structure of the Au-Ag bimetallic HPNSs has much greater significance than the apparent morphology does in determining the catalytic ability of the nanostructures. The Au-Ag alloyed HPNSs with better surface crystalline alloying microstructures and open morphologies were found to exhibit much higher catalytic reaction rates and better cyclic usage efficiencies, probably because of the better dispersion of active Au atoms within these materials. These galvanic replacement-synthesized alloyed Au-Ag HPNSs, fabricated by a facile method that avoids Ag degradation, have potential applications in catalysis, nanomedicine (especially in drug/gene delivery and cancer theranostics), and biosensing.

Optimization of influencing factors of nucleic acid adsorption onto silica-coated magnetic particles: application to viral nucleic acid extraction from serum.

We present a detailed study of nucleic acid adsorption onto silica-coated magnetic particles in the presence of guanidinium thiocyanate, and extraction of nucleic acid from two important transfusion-transmitted viruses using these particles. Silica-coated magnetic particles were prepared by encapsulating Fe3O4 nanoparticles with tetraethylorthosilicate (TEOS) hydrolysis. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS) and vibrating sample magnetometer (VSM) were used for particle characterization. The results indicate that silica-coated magnetic particles are spheroid with a narrow hydrodynamic size distribution of about 500nm. VSM data indicates that these particles display paramagnetic behavior with saturation magnetization of about 30emu/g. The adsorption capacities were evaluated with DNA from salmon sperm and RNA of Escherichia coli strain JM109 in the presence of guanidinium thiocyanate. The maximum of adsorption is up to 10.6mg DNA or 7.7mg RNA per 1g of silica-coated magnetic particles with 4M guanidinium thiocyanate (GTC) at pH 5.5 without adding ethanol. The influencing factors were analyzed in term of the adsorption of nucleic acids onto silica-coated magnetic particles. The adsorption capacity in acidic condition is found to be larger than that in alkaline condition and increases with adding equivalent volume of ethanol. A simple method was therefore established to extract nucleic acids of two important transfusion-transmitted viruses from serum and compared with the commercial kits. The results indicate that the extraction method based on silica-coated magnetic particles can be adapted to rapidly and facilely isolate viral nucleic acid for diagnosis of viral infection from serum within 30min, irrespective of genome compositions of virus.

A graphene oxide-carbon nanotube grid for high-resolution transmission electron microscopy of nanomaterials.

A novel grid for use in transmission electron microscopy is developed. The supporting film of the grid is composed of thin graphene oxide films overlying a super-aligned carbon nanotube network. The composite film combines the advantages of graphene oxide and carbon nanotube networks and has the following properties: it is ultra-thin, it has a large flat and smooth effective supporting area with a homogeneous amorphous appearance, high stability, and good conductivity. The graphene oxide-carbon nanotube grid has a distinct advantage when characterizing the fine structure of a mass of nanomaterials over conventional amorphous carbon grids. Clear high-resolution transmission electron microscopy images of various nanomaterials are obtained easily using the new grids.

Preparation and self-assembly of uniform TiO2/SiO2 composite submicrospheres.

Monodisperse spheres of silica were uniformly coated with titania through the hydrolysis of titanium alkoxide in order to increase the refractive index of complex submicrospheres and keep their monodispersity as well as their surface morphology. On the basis of the hydrolysis of tetrabutyl orthotitanate (TBOT), a continuous-feeding procedure was used to fabricate 10-nm titania coatings on monodisperse colloidal silica submicrospheres of diameter 200 nm. The TiO2/SiO2 composite spheres were assembled to achieve structures with three-dimensional order by gravity sedimentation and vertical deposition. The complex sphere composition, quality, and morphology were characterized by different techniques.