Changes In Chemical Stability Research Articles

Klasične metode hemijske stabilnosti - komparativna analiza za barute

The main ingredient of gunpowder is nitrocellulose. For slowing down the catalytical decomposition process, predominated stabilizer diphenylamine is in use for single-base gunpowder, as well as for propellants. On the other hand, the stabilizer wears out over time, which causes changes in chemical stability of energetic materials. One of the classical methods for determination the chemical stability is the Bergman-Jung method, which has two subgroups. This paper presents comparative analyses for twelve NC and five NCD gunpowder. Namely, both subgroups are based on the calculation of the volume of nitric oxide gases, but the difference between them depend on the method of collecting and determining released gases.

Changes in chemical stability and bioactivities of curcumin by forming inclusion complexes of beta- and Gama-cyclodextrins

In the present study investigated the effect of curcumin (CUR), beta (β) and gamma (γ) cyclodextrin (CD) complexes on its solubility, stability, antioxidating activity and bioavailability. CUR the active principle of turmeric is a natural antioxidant agent with potent anti-inflammatory activity along with chemotherapeutic and chemopreventive properties. Poor solubility and poor oral bioavailability are the main reasons which preclude CUR use in therapy. Curcumin/CD complex systems were prepared and characterized by FT-IR, UV-Vis and 1HNMR spectroscopies. The content, solubility, dissolution, and stability of the complexes were evaluated and compared with curcumin and their physical mixture. The phase solubility analysis indicated that the solubility of CUR was increased in the presence of CDs and revealed an A(L)-type diagram, suggesting the formation of a 1:1 inclusion complex. The estimated apparent stability constant (K1:1), according to the Higuchi and Connors method, is 1.87 × 105 M−1 and 5.99 × 105 M−1 for CUR/β-CD and CUR/γ-CD respectively. The results of this study confirm the formation of inclusion complexes in solution and suggest that the complexes formation between CUR and CDs could improve the bioavailability of the drug due to the enhancing absorption expected from increased drug solubility. Furthermore, the antioxidant activities of CUR and CDs inclusion complexes were determined by the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) method. The experimental results confirmed the forming of CUR complexes with CDs also these indicated that the CUR/CDs inclusion complexes were the most reactive than its free form into antioxidant activity.

Differential effects of conifer and broadleaf litter inputs on soil organic carbon chemical composition through altered soil microbial community composition

A strategic selection of tree species will shift the type and quality of litter input, and subsequently magnitude and composition of the soil organic carbon (SOC) through soil microbial community. We conducted a manipulative experiment in randomized block design with leaf litter inputs of four native subtropical tree species in a Pinus massoniana plantation in southern China and found that the chemical composition of SOC did not differ significantly among treatments until after 28 months of the experiment. Contrasting leaf litter inputs had significant impacts on the amounts of total microbial, Gram-positive bacterial, and actinomycic PLFAs, but not on the amounts of total bacterial, Gram-negative bacterial, and fungal PLFAs. There were significant differences in alkyl/O-alkyl C in soils among the leaf litter input treatments, but no apparent differences in the proportions of chemical compositions (alkyl, O-alkyl, aromatic, and carbonyl C) in SOC. Soil alkyl/O-alkyl C was significantly related to the amounts of total microbial, and Gram-positive bacterial PLFAs, but not to the chemical compositions of leaf litter. Our findings suggest that changes in forest leaf litter inputs could result in changes in chemical stability of SOC through the altered microbial community composition.

Changes in chemical stability and bioactivities of curcumin by ultraviolet radiation

Curcumin, a yellow pigment from turmeric (Curcuma longa), has shown various health beneficial effects. In the present study, changes in the chemical stability and bioactivities of curcumin by UV radiation were investigated. Curcumin degradation in water or phosphate buffered saline was accelerated under UV radiation (254 nm); the residual levels of curcumin were 36.9 and 16.8%, respectively, after 24 h radiation. Decomposition of curcumin by UV was more prominent at higher pHs. ABTS radical scavenging activity of curcumin after 24 h radiation was reduced significantly (p 0.05) as compared to those of curcumin stored at a dark place. Stabilities and bioactivities of curcumin powder treated under UV radiation were, however, not significantly changed (p>0.05). The present results suggest that certain processing or storing conditions exposed to UV radiation could affect stability and bioactivities of curcumin.

Interaction of Over-the-Counter Drugs with Curcumin: Influence on Stability and Bioactivities in Intestinal Cells

Curcumin, a major constituent in rhizomes of Curcuma longa L., has shown various biological activities. It has widely been used as a food additive to provide potential health benefits. In the present study, we investigated changes in chemical stability and cytotoxic properties of curcumin and commonly consumed over-the-counter (OTC) drugs including ibuprofen, acetylsalicylic acid (Asp), and acetaminophen (AAP), through their interactions. Stability of curcumin was significantly improved in phosphate-buffered saline or 0.01 N HCl containing each OTC drug; Asp showed the most prominent effect. Stability of Asp or AAP during 24 h incubation with curcumin was not changed significantly. Cytotoxic effects of curcumin were enhanced in the presence of the OTC drugs on INT 407 normal intestinal and HCT 116 colon cancer cells. Relative cytotoxicity of curcumin (>10 μM) under the drug-treated conditions was significantly higher. Cellular uptake of curcumin in HCT 116 cells increased significantly when incubated with Asp or AAP. Intracellular thiol levels of the cells treated with curcumin were further reduced in the presence of the OTC drugs. The present study provides information that commonly consumed OTC drugs affect chemical stability of curcumin in physiological conditions, and certain bioactivities of curcumin can be altered through their interactions.

Synthesis and thermal behavior of new liquid crystals arylaldoxime esters

We report the synthesis of a series of liquid-crystalline materials based on arylaldoxime esters and the characterization of these materials by ¹H, 13C NMR, ATR/FT-IR spectroscopy and elemental analysis. The chemical stability and liquid-crystalline as well as photophysical properties of the compounds are described being dependent on the heating/cooling cycles. The changes in chemical stability and the liquid crystals properties of arylaldoxime esters were observed during these thermal cycles by IR analysis. All samples underwent a thermal degradation yielding the corresponding nitriles and carboxylic acid as evidenced by IR and ¹H NMR spectra. Due to the decomposition process, information about the mesomorphic behaviour is lost. The UV-Vis absorption spectra in solution display three absorption bands between 230 and 340 nm. The fluorescence spectra exhibit a broad and structureless emission band located at 430 nm. Ab initio calculations were performed to obtain information on the molecular structure and properties of the title compounds.

Epigallocatechin-3-gallate의 화학안정성 및 세포독성에 미치는 각종 항산화제의 영향

본 연구에서는 다양한 생리활성이 보고된 폴리페놀 화합물인 EGCG의 화학안정성, H2O2 생성능 및 세포독성에 대하여 다양한 항산화제와의 조합에 의한 변화를 분석하였다. EGCG는 생리적 조건에서 갈색화합물로 산화되면서 불안정화되는데, catalase를 제외한 각종 항산화제제 SOD, ascorbic acid, NAC 및 GSH는 EGCG 갈색산화물의 생성을 유의적으로 저해하였다. EGCG에 의해 생성되는 <TEX>$H_2O_2$</TEX>는 catalase에 의해 거의 완벽하게 제거되었으며, SOD와 NAC에 의해서도 유의적으로 감소하였다. 하지만 GSH 및 고농도의 ascorbic acid의 존재 시 오히려 <TEX>$H_2O_2$</TEX> 수준이 증가하는 현상을 나타내었다. EGCG의 HeLa 및 HT-29 세포에 대한 독성은 catalase, SOD 및 NAC 등과 같은 항산화제 존재 하에 유의적으로 감소하였고 NAC에 의한 EGCG 세포독성의 감소는 첨가된 NAC의 농도 증가에 따라 더욱 두드러졌다. 그러나 GSH 존재하에 EGCG의 독성은 GSH와 EGCG농도에 따라 다른 조절 양상을 나타내었으며, ascorbic acid에 의해서 EGCG의 세포독성이 약간 증가하는 현상을 나타내었다. 본 결과는 EGCG와 함께 처리된 다양한 항산화제들이 ROS의 소거 뿐만 아니라 EGCG 화학안정성 등 다른 요인에 영향을 미칠 수 있으며, 항산화제의 존재 하에 변형된 EGCG활성에 대해 ROS관련 기작 외에 다양한 요인들에 대한 고려가 함께 이루어져야 함을 시사한다. Epigallocatechin-3-gallate (EGCG) is a polyphenolic compound frequently found in green tea, and its physiological actions have been extensively investigated. In the present study, changes in chemical stability and cytotoxic properties of EGCG in the presence of different types of antioxidants were investigated. The antioxidants used modulated the chemical stability of EGCG. Superoxide dismutase (SOD) significantly increased EGCG stability; EGCG was less stable in the presence of catalase. Ascorbic acid, N-acetylcysteine (NAC), and glutathione (GSH) stabilized EGCG concentration dependently. The <TEX>$H_2O_2$</TEX> level generated from EGCG was decreased by catalase, SOD, and NAC but not by GSH. The cytotoxic effects of EGCG also decreased in the presence of NAC, catalase, and SOD. GSH, however, showed a complicated modulatory pattern according to the EGCG and GSH concentrations, and ascorbic acid rather enhanced EGCG toxicity. The results suggest that certain antioxidants could modulate the cytotoxic properties of EGCG in a cell culture system not only by removing reactive oxygen species but by modulating chemical stability and other factors, which should be considered carefully when studying reactive oxygen species-dependent mechanisms of EGCG.