Storage Stability Of Solutions Research Articles

Hollow Bioelectrodes Based on Buckypaper Assembly. Application to the Electroenzymatic Reduction of O2.

A new concept of hollow electrode based on the assembly of two buckypapers creating a microcavity which contains a biocatalyst is described. To illustrate this innovative concept, hollow bioelectrodes containing 0.16–4 mg bilirubin oxidase in a microcavity were fabricated and applied to electroenzymatic reduction of O2 in aqueous solution. For hemin-modified buckypaper, the bioelectrode shows a direct electron transfer between multi-walled carbon nanotubes and bilirubin oxidase with an onset potential of 0.77 V vs. RHE. The hollow bioelectrodes showed good storage stability in solution with an electroenzymatic activity of 30 and 11% of its initial activity after 3 and 6 months, respectively. The co-entrapment of bilirubin oxidase and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) in the microcavity leads to a bioelectrode exhibiting mediated electron transfer. After 23 h of intermittent operation, 5.66 × 10−4 mol of O2 were electroreduced (turnover number of 19,245), the loss of catalytic current being only 54% after 7 days.

Effect of pH and concentration on the chemical stability and reaction kinetics of thiamine mononitrate and thiamine chloride hydrochloride in solution

Thiamine (vitamin B1) is an essential micronutrient in the human diet, found both naturally and as a fortification ingredient in many foods and supplements. However, it is susceptible to degradation due to heat, light, alkaline pH, and sulfites, among effects from other food matrix components, and its degradation has both nutritional and sensory implications as in foods. Thiamine storage stability in solution was monitored over time to determine the effect of solution pH and thiamine concentration on reaction kinetics of degradation without the use of buffers, which are known to affect thiamine stability independent of pH. The study directly compared thiamine stability in solutions prepared with different pHs (3 or 6), concentrations (1 or 20 mg/mL), and counterion in solution (NO3−, Cl−, or both), including both commercially available salt forms of thiamine (thiamine mononitrate and thiamine chloride hydrochloride). Solutions were stored at 25, 40, 60, and 80 °C for up to one year, and degradation was quantified by high-performance liquid chromatography (HPLC) over time, which was then used to calculate degradation kinetics. Thiamine was significantly more stable in pH 3 than in pH 6 solutions. In pH 6 solutions, stability was dependent on initial thiamine concentration, with the 20 mg/mL thiamine salt solutions having an increased reaction rate constant (kobs) compared to the 1 mg/mL solutions. In pH 3 solutions, kobs was not dependent on initial concentration, attributed to differences in degradation pathway dependent on pH. Activation energies of degradation (Ea) were higher in pH 3 solutions (21–27 kcal/mol) than in pH 6 solutions (18–21 kcal/mol), indicating a difference in stability and degradation pathway due to pH. The fundamental reaction kinetics of thiamine reported in this study provide a basis for understanding thiamine stability and therefore improving thiamine delivery in many foods containing both natural and fortified thiamine.

High-performance CdSe/CdS@ZnO quantum dots enabled by ZnO sol as surface ligands: A novel strategy for improved optical properties and stability

Colloidal semiconductor quantum dots (QDs) have attracted great attention in field of optoelectronic devices. However, the surface organic ligands of QDs involving in optical instability and limited passivation remain challenging, thus bringing additional difficulties in practical application. Here, the high-performance CdSe/CdS@ZnO QDs were successfully prepared by ZnO sol as surface ligands. Importantly, this kind of CdSe/CdS@ZnO QDs maintained the typical advantages of conventional QDs, such as superior monodispersity and long-term storage stability in solution. Because of the effective surface passivation provided by inorganic sol ligands and the deionization effect that electron transferring from surface state of QDs to ZnO acceptor, CdSe/CdS@ZnO QDs showed the remarkably enhanced photostability and biexciton lifetime, as well as further suppressed Auger process and PL blinking. Meanwhile, the CdSe/CdS@ZnO QDs demonstrated PL thermal stability much higher than that of pristine CdSe/CdS QDs under heating to 100 °C, which was efficiently improved 3 times that from ~20% to ~63% of their initial emission intensity. Moreover, a stable amplified spontaneous emission process was observed in CdSe/CdS@ZnO QDs film and still retained a lower ASE threshold (~28 μJ cm−2). Finally, we successfully fabricated a high-performance vertical cavity surface-emitting laser based on CdSe/CdS@ZnO QDs, which presented spatially directional single-mode lasing output with an ultralow threshold of ~3.3 μJ cm−2. We believe that this work could not only enrich the family of surface ligands passivated semiconductor QDs but also provide a novel strategy towards constructing stable and functionalized colloidal nanomaterials for all-inorganic optoelectronic devices.

Determination of folic acid via its quenching effect on the fluorescence of MoS2 quantum dots.

Molybdenum disulfide quantum dots (MoS2 QDs) are used in a fluorometric method for the determination of folic acid (FA) based on fluorescence quenching. The MoS2 QDs synthesized by a hydrothermal method possess bright blue fluorescence (with excitation/emission maxima of 325/415nm), quantum yield of 3.7%, and excellent storage stability in solution (30days in the refrigerator). Their fluorescence is quenched by FA, and intensity decreases linearly in the 0.1 to 125μM FA concentration range. The detection limit is 0.1μM (atS/N= 3), and the relative standard deviation (forn= 5) is 2.8% for 25μM concentrations ofFA. Studies on the quenching mechanism suggest that the effect is due to static quenching. The FA in commercial FA tablets was successfully determined. Graphical abstract Schematic representation of the hydrothermal method for the preparation ofmolybdenum disulfide quantum dots (MoS2 QDs) with about 2.7 ± 0.5nm diameterusing Na2MoO4 and L-cysteine as Mo and S sources, and the fluorescence method for the determination of folic acid (FA) based on fluorescence quenching of MoS2 QDs.

Primary Screening of Photosensitizers of the Bacteriochlorin Series for Photodynamic Therapy of Malignant Neoplasms

Primary screening of photosensitizers of the bacteriochlorin series containing aminoamide, propyl, and carbohydrate substituents was carried out; it included an assessment of spectral characteristics of these compounds, their storage stability in solution under darkened conditions and light exposure, and the study of photoinduced activity and cytotoxicity on tumor of HEp2 cells. According to the results of absorption and fluorescence analyzes, dyes with aminoamide substituents had a maximum at 754 ± 2 nm, are not stable during storage (fluorescence intensity decreased by 33–56% during a day); compounds with propyl and carbohydrate substituents absorbed in the region of 780–831 nm were characterized by stability during storage and irradiation. All PS except the dye with the carbohydrate residue in the exocycle E, exhibited photoinduced activity and lack of dark toxicity. The highest photoactivity was detected in compounds with aminoamide fragments in the macrocyclic ring (during 2 h-incubation the IC50 ranged from 17 nM to 49 nM). Taking into consideration physicochemical and biological properties, as well as technology of production and stability during storage and irradiation, O-propyloxime-N-propoxybacteriopurinimide methyl ester was chosen for further research aimed at creating a new PS generation for photodynamic therapy of malignant tumors.

New Japanese certified reference materials for electrolytic conductivity measurements

The National Metrology Institute of Japan (NMIJ) has established three certified reference materials (CRMs) in electrolytic conductivity with a primary Jones-type cell: aqueous solutions of potassium chloride with different molalities (1 mol kg−1, 0.1 mol kg−1 and 0.01 mol kg−1) all supplied in glass bottles. The uncertainties were estimated from standard uncertainties of measurements (impedance, temperature and integrity of cell geometry), measurement’s repeatability, homogeneity of a batch and the storage stability of solutions. The storage stability of candidate NMIJ CRMs of upper and lower concentrations was examined with a secondary cell.

Oriented growth of magnetite along the carbon nanotubes via covalently bonded method in a simple solvothermal system

Abstract A new type of CNTs/magnetite hybrid material was prepared via covalently bonded method in a simple solvothermal system using FeCl 3 as iron source, ethylene glycol as the reducing agent, and 4-aminophenoxyphthalonitrile-grafted CNTs as templates. The magnetite nanoparticles, with the diameters of 70–80 nm, were self-assembled along the CNTs. The FTIR, UV–vis and DSC revealed that a stable covalent bond between nitriles group and iron ion promoted the oriented growth of magnetite nanoparticles along the CNTs, resulting in good dispersibility and solution storage stability. The magnetic properties measurements indicated that a higher saturated magnetization (70.7 emu g −1 ) existed in the CNTs/magnetite hybrid material, which further enhanced the electromagnetic properties. The magnetic loss was caused mainly by natural resonance, which is in good agreement with the Kittel equation results. The novel electromagnetic hybrid material is believed to have potential applications in the microwave absorbing performances.

Highly efficient processing of silk fibroin nanoparticle-l-asparaginase bioconjugates and their characterization as a drug delivery system

Silk fibroin (SF) when dissolved in highly concentrated CaCl2 solution formed a series of degraded polypeptides with a molecular mass range of 10–70 kDa. After the liquid silk, mixed mildly with L-asparaginase (ASNase), was introduced rapidly into excess acetone, the enzyme not only was not inactivated but was also well immobilized in simultaneously formed silk fibroin nanoparticles (SFNs). The resulting SFN–ASNase bioconjugates were easily isolated from acetone solution by centrifugation. The bioconjugates were crystalline globular particles of 50–120 nm in diameter, with high enzyme activity and showed similar enzymatic kinetics such as pH, reactive temperature, thermostability in solution and Michaelis constant to the native form. The bioconjugates could resist a high temperature of 90 °C in dry conditions for 30 min, and had a high recovery (90%), a greatly increased resistance to trypsin digestion, and better stability in serum, and storage stability in solution. No leakage of the enzyme from the nanoparticles occurred. These results indicated that ASNase was uniquely and efficiently bioconjugated in the protein nanoparticles that possessed a fine crystallinity. Thus, the highly efficient processing technology and use of silk nanoparticles as a novel drug delivery system has potential in research and development.