The dissolution of monosodium urate monohydrate crystals: formulation of a biocompatible buffer solution with potential use in the treatment of gouty arthropathies

The dissolving abilities (DAs) of several aqueous media for microcrystalline monosodium urate monohydrate (MSU, NaC5N4O3H3·H2O) have been investigated using UV spectrophotometry for quantitative analytical determinations and X-ray diffraction, scanning electron microscopy and polarized light optical microscopy to assess structural aspects. High DAs were found for a buffer labeled TMT which contains tris(hydroxymethyl)aminomethane (TRIS), tris(hydroxymethyl)aminomethane hydrochloride (TRIS·HCl), D-mannitol (MAN) and taurine (TAU) and gave DA30=1298(5) mg/L for synthetic MSU after 30 min incubation at 37°C and pH 7.4, most of the dissolution taking place within the first 5-10 min. Semiempirical molecular modelling techniques (ZINDO/1) show a favorable energy balance for the formation of a TRIS-urate-TRIS adduct which might explain the high DA values. Buffers containing linear or dendrimeric polyamines gave DA values which suggest that complex formation toward sodium cations is less important. An ex vivo MSU sample was found to have a significantly lower DA value (DA30=1124(5) mg/L in TMT) as well as a lower crystallinity than its synthetic counterpart, possibly related to the presence of a non-crystalline impurity such as endogenous proteins. Cytotoxicity tests based on the MTT assay were used to check the biocompatibility of the TMT buffer and showed only moderate cell mortality after 24 h contact with the buffer solution

Hollandite Nanoparticles for Chemical Sensing: Strain or Pseudosymmetry?

Parm

(Na,□)5[MnO2]13nanorods: A new tunnel structure for electrode materials determined ab initio and refined through a combination of electron and synchrotron diffraction data

(Nax□1 - x)5[MnO2]13has been synthesized with x = 0.80 (4), corresponding to Na0.31[MnO2]. This well known material is usually cited as Na0.4[MnO2] and is believed to have a romanèchite-like framework. Here, its true structure is determined, ab initio, by single-crystal electron diffraction tomography (EDT) and refined both by EDT data applying dynamical scattering theory and by the Rietveld method based on synchrotron powder diffraction data (X2= 0.690, Rwp= 0.051, Rp= 0.037, RF2= 0.035). The unit cell is monoclinic C2/m, a = 22.5199 (6), b = 2.83987 (6), c = 14.8815 (4) Å , β = 105.0925 (16)°, V = 918.90 (4) Å3, Z = 2. A hitherto unknown [MnO2] framework is found, which is mainly based on edge- and corner-sharing octahedra and comprises three types of tunnels: per unit cell, two are defined by S-shaped 10-rings, four by eggshaped 8-rings, and two by slightly oval 6-rings of Mn polyhedra. Na occupies all tunnels. The so-determined structure excellently explains previous reports on the electrochemistry of (Na,□)5[MnO2]13. The trivalent Mn3+ions concentrate at two of the seven Mn sites where larger Mn-O distances and Jahn-Teller distortion are observed. One of the Mn3+sites is five-coordinated in a square pyramid which, on oxidation to Mn4+, may easily undergo topotactic transformation to an octahedron suggesting a possible pathway for the transition among different tunnel structures

The dissolution of monosodium urate monohydrate crystals: formulation of a biocompatible buffer solution with potential use in the treatment of gouty arthropathies

The dissolving abilities (DAs) of several aqueous media for microcrystalline monosodium urate monohydrate (MSU, NaC5N4O3H3·H2O) have been investigated using UV spectrophotometry for quantitative analytical determinations and X-ray diffraction, scanning electron microscopy and polarized light optical microscopy to assess structural aspects. High DAs were found for a buffer labeled TMT which contains tris(hydroxymethyl)aminomethane (TRIS), tris(hydroxymethyl)aminomethane hydrochloride (TRIS·HCl), D-mannitol (MAN) and taurine (TAU) and gave DA30=1298(5) mg/L for synthetic MSU after 30 min incubation at 37°C and pH 7.4, most of the dissolution taking place within the first 5-10 min. Semiempirical molecular modelling techniques (ZINDO/1) show a favorable energy balance for the formation of a TRIS-urate-TRIS adduct which might explain the high DA values. Buffers containing linear or dendrimeric polyamines gave DA values which suggest that complex formation toward sodium cations is less important. An <em>ex vivo</em> MSU sample was found to have a significantly lower DA value (DA30=1124(5) mg/L in TMT) as well as a lower crystallinity than its synthetic counterpart, possibly related to the presence of a non-crystalline impurity such as endogenous proteins. Cytotoxicity tests based on the MTT assay were used to check the biocompatibility of the TMT buffer and showed only moderate cell mortality after 24 h contact with the buffer solution

Gas sensing properties and modeling of YCoO3 based perovskite materials.

YCoO 3 perovskite powder was prepared by the classical sol–gel method, which was extended to the preparation also of non stoichiometric materials or samples containing platinum or palladium, incor- porated either during synthesis or a posteriori through impregnation. The prepared powders were characterized in terms of composition and structure, using X-ray diffraction (XRD) and Rietveld refine- ment. The compounds show a tunnel structure with octahedral framework. The surface properties of these powders were investigated studying their catalytic activity in CO oxi- dation, as well as their adsorptive features towards oxygen and their redox behavior by means of TPD and TPR respectively. Sensing films of the prepared powders were realized by a screen-printing tech- nique. The electrical properties and response to various gases were studied and found to be correlated to composition and structure of the different materials. Moreover the influence of the mictrostructure was analyzed and a model was developed. The responses to both oxidizing and reducing gases such as CO, NO 2 , NO, and CH 4 were evaluated and discussed both in an inert environment (nitrogen) and in the presence of oxygen (air). All the YCoO 3 based sensors show p-type semiconducting properties in the tested environments within the temperature range of 100–380 ◦ C. All the studied materials respond to CO in the high temperature range with a limited response but a large response speed. The response to NO x is optimum in the low temperature range between 160 ◦ C and 200 ◦ C; moreover even at these temperatures both the response and the recovery time are satisfactory. The response towards CH 4 results much lower. Finally, the gas sensor properties of the proposed materials proved to be insensitive to ambient humidity

Gas-sensing properties and modeling of silver doped potassium hollandite

In this paper the gas sensing properties of Ag–K-hollandite prepared by K–Ag ion exchange are investi- gated. The proposed material was used as the active layer of micromachined conductometric gas sensors and tested in different environmental conditions with a number of target gases such as CO and NOx . The response to test gases was evaluated in a temperature interval from 200 to 350 ◦ C where surface phe- nomena can completely explain the sensor behavior. The proposed material was studied also by means of XPS and thermal analyses. The investigated material is a p-type semiconductor and shows a repro- ducible response and a complete recovery. Data obtained are discussed and a model based on surface states describing the material behavior is proposed

Gas sensing properties of YMnO3 based materials for the detection of NOx and CO

This paper deals with chemoresistive behavior of hexagonal YMnO3 produced by gel combustion. Stoichiometric, defective and doped compositions were studied and both reducing (CO) and oxidizing test gases (NOx) were used. The materials were characterized by means of X-ray diffraction, CO conversion tests, and oxygen temperature programmable desorption (TPD) and temperature programmable reduction (TPR) with H2. Experiments indicate that, besides the oxygen chemisorption, the direct adsorption of the target gases at the material surface plays an important role in resistive gas sensing. A model based on these assumptions was developed and excellently fits the transient response of the sensors under test to NO2 in the absence of oxygen. All the tested materials behave as p-type semiconductors and have a fast reversible response to NO2 which is optimum at temperatures close to 180&nbsp;°C (30% @10&nbsp;ppm NO2, after about 1&nbsp;min). In particular, it was found that the best sensor performance in NO2 detection is obtained with defective materials in terms of response, while an interesting trade-off between temperature response and gas response is obtained with Pd doped materials. Regarding CO detection, materials impregnated with Pd showed the best performance both in terms of speed and of response, with an optimum temperature of 300&nbsp;°C