Thermodynamic Determination of the Metal/Semiconductor Separation of Carbon Nanotubes Using Hydrogels

The metal/semiconductor separation of single-wall carbon nanotubes (SWCNTs) using hydrogels, such as agarose gel and Sephacryl, together with sodium dodecyl sulfate is one of the most successful techniques necessary for industrial applications. Despite recent improvements in the technique, little is known about the separation mechanism. Here, we show that SWCNTs are reversibly adsorbed onto hydrogels in the presence of sodium dodecyl sulfate. The results enabled us to examine the thermodynamics of the adsorption reaction and thereby elucidate the separation mechanism. The adsorbability of SWCNTs onto the hydrogels was described by the standard Gibbs free energy for the adsorption, as well as the area of the hydrogels allowing the adsorption. We demonstrated, for the first time, that the free energy of adsorption for semiconducting SWCNTs was 0–12 kJ/mol lower than that for metallic SWCNTs in the temperature range of 290–320 K (<i>e.g.</i>, <i>ca</i>. −4 kJ/mol for the agarose gel and <i>ca</i>. −9 kJ/mol for Sephacryl at 300 K), which permits metal/semiconductor separation. Importantly, the difference in the free energy was attributed to the difference in the enthalpy of adsorption: the enthalpy of adsorption of metallic SWCNTs was <i>ca</i>. 70 kJ/mol higher than that of semiconducting SWCNTs. Thus, the enthalpy of adsorption was found to be an important parameter in the metal/semiconductor separation of SWCNTs using hydrogels. In addition, the thermodynamic parameters depended on the hydrogel type and the surfactant concentration, which is most likely why under certain conditions hydrogels and surfactants produce different separations, <i>e.g.,</i> chirality-selective or diameter-selective separation

pH- and Solute-Dependent Adsorption of Single-Wall Carbon Nanotubes onto Hydrogels: Mechanistic Insights into the Metal/Semiconductor Separation

The gel separation of single-wall carbon nanotubes (SWCNTs) suspended in sodium dodecyl sulfate (SDS) is expected to be one of the most successful methods of large-scale and high-purity separation. Understanding the mechanism of the gel separation helps improve the quality and quantity of separation and reveals the colloidal behaviors of SWCNTs, which reflects their band structures. In this study, we characterize the pH- and solute-dependent adsorption of SWCNTs onto agarose and Sephacryl hydrogels and provide a mechanistic model of the metal/semiconductor separation. The adsorbability of SWCNTs is substantially reduced under acidic pH conditions. Importantly, the pH dependence differs between metallic and semiconducting species; therefore, the adsorbability is related to the band-structure-dependent oxidation of the SWCNTs. Oxidation confers positive charges on SWCNTs, and these charges enhance the electrostatic interactions of the SWCNTs with SDS, thereby leading to the condensation of SDS on the SWCNTs. This increase in SDS density reduces the interactions between the SWCNTs and hydrogels. Under highly basic conditions, such as pH ∼12.5, or in the presence of salts, the adsorption is dissociative because of the condensation of SDS on the SWCNTs through electrostatic screening by counterions. Desorption of the SWCNTs from the hydrogels due to the addition of urea implies a hydrophobic interface between SDS-dispersed SWCNTs and the hydrogels. These results suggest that the metal/semiconductor separation can be explained by the alteration of the interaction between SDS-dispersed SWCNTs and the hydrogels through changes in the conformation of SDS on the SWCNTs depending on the SWCNTs’ band structures

Purification of Single-Wall Carbon Nanotubes by Controlling the Adsorbability onto Agarose Gels Using Deoxycholate

One of the key challenges to the industrialization of single-wall carbon nanotubes (SWCNTs) is the commercial-scale production of highly purified SWCNTs separated into metallic and semiconducting species. In the present study, the purification of SWCNTs, i.e., the removal of amorphous carbon or bundled SWCNTs, was performed by quantifying and controlling their adsorbability onto agarose gel. The quantification of the adsorbability was achieved by assuming the Langmuir isotherm, and control over the adsorbability was exerted using 0.05–1% sodium deoxycholate (DOC). The results show that the adsorbability depends on the concentration of DOC. At a low DOC concentration (approximately 0.05%), impurities such as amorphous carbon or bundled SWCNTs were preferentially adsorbed onto the gels, whereas, at an intermediate DOC concentration (ca. 0.25%), high-purity SWCNTs were mainly adsorbed onto the gels. Thus, the impurities, which are difficult to remove by conventional methods, could be separated from unpurified SWCNTs by controlling the adsorbability, leading to the extraction of high-purity SWCNTs. In the purification, diameter-selective separation of SWCNTs was also observed. The purification method using a gel column can be conducted simply and continuously, so that it can be applied for the high-throughput production of high-purity SWCNTs

Molecular Dynamics Simulation of the Arginine-Assisted Solubilization of Caffeic Acid: Intervention in the Interaction

We have previously demonstrated that arginine increases the solubility of aromatic compounds that have poor water solubility, an effect referred to as the “arginine-assisted solubilization system (AASS)”. In the current study, we utilized a molecular dynamics simulation to examine the solubilization effects of arginine on caffeic acid, which has a tendency to aggregate in aqueous solution. Caffeic acid has a hydrophobic moiety containing a π-conjugated system that includes an aromatic ring and a hydrophilic moiety with hydroxyl groups and a carboxyl group. While its solubility increases at higher pH values due to the acquisition of a negative charge, the solubility was greatly enhanced by the addition of 1 M arginine hydrochloride at any pH. The results of the simulation indicated that the caffeic acid aggregates were dissociated by the arginine hydrochloride, which is consistent with the experimental data. The binding free energy calculation for two caffeic acid molecules in an aqueous 1 M arginine hydrochloride solution indicated that arginine stabilized the dissociated state due to the interaction between its guanidinium group and the π-conjugated system of the caffeic acid. The binding free energy of two caffeic acid molecules in the arginine hydrochloride solution exhibited a local minimum at approximately 8 Å, at which the arginine intervened between the caffeic acid molecules, causing a stabilization of the dissociated state of caffeic acid. Such stabilization by arginine likely led to the caffeic acid solubilization, as observed in both the experiment and the MD simulation. The results reported in this paper suggest that AASS can be attributed to the stabilization resulting from the intervention of arginine in the interaction between the aromatic compounds

Molecular Dynamics Simulation of the Arginine-Assisted Solubilization of Caffeic Acid: Intervention in the Interaction

We have previously demonstrated that arginine increases the solubility of aromatic compounds that have poor water solubility, an effect referred to as the “arginine-assisted solubilization system (AASS)”. In the current study, we utilized a molecular dynamics simulation to examine the solubilization effects of arginine on caffeic acid, which has a tendency to aggregate in aqueous solution. Caffeic acid has a hydrophobic moiety containing a π-conjugated system that includes an aromatic ring and a hydrophilic moiety with hydroxyl groups and a carboxyl group. While its solubility increases at higher pH values due to the acquisition of a negative charge, the solubility was greatly enhanced by the addition of 1 M arginine hydrochloride at any pH. The results of the simulation indicated that the caffeic acid aggregates were dissociated by the arginine hydrochloride, which is consistent with the experimental data. The binding free energy calculation for two caffeic acid molecules in an aqueous 1 M arginine hydrochloride solution indicated that arginine stabilized the dissociated state due to the interaction between its guanidinium group and the π-conjugated system of the caffeic acid. The binding free energy of two caffeic acid molecules in the arginine hydrochloride solution exhibited a local minimum at approximately 8 Å, at which the arginine intervened between the caffeic acid molecules, causing a stabilization of the dissociated state of caffeic acid. Such stabilization by arginine likely led to the caffeic acid solubilization, as observed in both the experiment and the MD simulation. The results reported in this paper suggest that AASS can be attributed to the stabilization resulting from the intervention of arginine in the interaction between the aromatic compounds

Carbon Nanotubes Facilitate Oxidation of Cysteine Residues of Proteins

The adsorption of proteins onto nanoparticles such as carbon nanotubes (CNTs) governs the early stages of nanoparticle uptake into biological systems. Previous studies regarding these adsorption processes have primarily focused on the physical interactions between proteins and nanoparticles. In this study, using reduced lysozyme and intact human serum albumin in aqueous solutions, we demonstrated that CNTs interact chemically with proteins. The CNTs induce the oxidation of cysteine residues of the proteins, which is accounted for by charge transfer from the sulfhydryl groups of the cysteine residues to the CNTs. The redox reaction simultaneously suppresses the intermolecular association of proteins via disulfide bonds. These results suggest that CNTs can affect the folding and oxidation degree of proteins in biological systems such as blood and cytosol

Clinical characteristics according to ALDH2 activity (<i>ALDH2 *1/*1</i> active vs. <i>*1/*2</i> or <i>*2/*2</i> inactive) and drinking status in Japanese patients with type 2 diabetes.

<p>Values are mean±SD.</p><p>^bp<0.001 vs. lifetime abstainers with <i>*1/*1</i>,</p><p>^dp<0.01,</p><p>^cp<0.001 vs. lifetime abstainers with <i>*2</i>,</p><p>^ap<0.001 vs. drinkers with <i>*1/*1</i> in an unadjusted model.</p><p>Clinical characteristics according to ALDH2 activity (<i>ALDH2 *1/*1</i> active vs. <i>*1/*2</i> or <i>*2/*2</i> inactive) and drinking status in Japanese patients with type 2 diabetes.</p

Metabolic parameters according to ALDH2 activity (<i>ALDH2 *1/*1</i> active vs. <i>*1/*2</i> or <i>*2/*2</i> inactive) and drinking status in Japanese patients with type 2 diabetes.

<p>HOMA2%-B, homeostasis model assessment β-cell function; HOMA2-IR, homeostasis model assessment insulin resistance; HS-CRP, high-sensitivity C-reactive protein. Values are expressed as mean ± SD or percentage. HS-CRP and triglyceride are presented as geometric means [95% confidence interval].</p><p>^ap<0.05,</p><p>^ep<0.01,</p><p>^bp<0.001 vs. lifetime abstainers with <i>*1/*1</i>,</p><p>^fp<0.05,</p><p>^cp<0.01,</p><p>^dp<0.001 vs. lifetime abstainers with <i>*2</i>,</p><p>^gp<0.001 vs. drinkers with <i>*1/*1</i> in an unadjusted model.</p><p>Metabolic parameters according to ALDH2 activity (<i>ALDH2 *1/*1</i> active vs. <i>*1/*2</i> or <i>*2/*2</i> inactive) and drinking status in Japanese patients with type 2 diabetes.</p

L'Auto-vélo : automobilisme, cyclisme, athlétisme, yachting, aérostation, escrime, hippisme / dir. Henri Desgranges

27 mai 19281928/05/27 (A29,N0)

Blood pressure and diabetic complications according to ALDH2 activity (<i>ALDH2 *1/*1</i> active vs. <i>*1/*2</i> or <i>*2/*2</i> inactive) and drinking status in Japanese patients with type 2 diabetes.

<p>eGFR, estimated glomerular filtration rate; CKD, chronic kidney disease. Values are expressed as mean ± SD or percentage. Urinary albumin excretion is presented as geometric means [95% confidence interval].</p><p>^cp<0.05,</p><p>^dp<0.01,</p><p>^ap<0.001 vs. lifetime abstainers with <i>*1/*1</i>,</p><p>^bp<0.01 vs. lifetime abstainers with <i>*2</i>,</p><p>^ep<0.01 vs. drinkers with <i>*1/*1</i> in an unadjusted model.</p><p>Blood pressure and diabetic complications according to ALDH2 activity (<i>ALDH2 *1/*1</i> active vs. <i>*1/*2</i> or <i>*2/*2</i> inactive) and drinking status in Japanese patients with type 2 diabetes.</p