Comparative DFT study to determine if α-oxoaldehydes are precursors for pentosidine formation

We report a comprehensive density functional theory (DFT) study of the mechanism of pentosidine formation. This work is a continuation of our earlier studies in which we proposed pathways for formation of glucosepane (J. Mol. Model. 2011, pp 1-15, DOI 10.1007/s00894-011-1161-x), GODIC (glyoxal-derived imidazolium cross-link), and MODIC (methyl glyoxal-derived imidazolium cross-link; J. Phys. Chem. 2011, 115, pp 13542-13555). Here we show that formation of pentosidine via reaction of α-oxoaldehydes with lysine and arginine in aqueous solution is possible thermodynamically and kinetically, in good agreement with the available experimental evidence. Five pathways, A-E, were characterized, as in our previous GODIC and MODIC work. In pathways A and B, a Schiff base is first formed from lysine and methyl glyoxal (MGO), and this is followed by addition of arginine and glyoxal (GO). By contrast, in pathways C, D, and E, addition of arginine to MGO occurs first, resulting in the formation of imidazolone, which then reacts with lysine and GO to give pentosidine. Our calculations show that the reaction process is highly exergonic and that the three pathways A, C, and E are competitive. These results serve to underline the potentially important role that α-oxoaldehydes play as precursors in pentosidine formation in the complex field of glycation.     

On the Regularity and Koszulness of Modules Over Local Rings

Koszul modules over Noetherian local rings R were introduced by Herzog and Iyengar and they possess good homological properties, for instance their Poincaré series is rational. It is an interesting problem to characterize classes of Koszul modules. Following the idea traced by Avramov, Iyengar, and Sega, we take advantage of the existence of special filtration on R for proving that large classes of R-modules over Koszul rings are Koszul modules. By using this tool we reprove and extend some results obtained by Fitzgerald.     

Decidability and Specker sequences in intuitionistic mathematics

A bounded monotone sequence of reals without a limit is called a Specker sequence. In Russian constructive analysis, Church's Thesis permits the existence of a Specker sequence. In intuitionistic mathematics, Brouwer's Continuity Principle implies it is false that every bounded monotone sequence of real numbers has a limit. We claim that the existence of Specker sequences crucially depends on the properties of intuitionistic decidable sets. We propose a schema (which we call ED ) about intuitionistic decidability that asserts “there exists an intuitionistic enumerable set that is not intuitionistic decidable” and show that the existence of a Specker sequence is equivalent to ED . We show that ED is consistent with some certain well known axioms of intuitionistic analysis as Weak Continuity Principle, bar induction, and Kripke Schema. Thus, the assumption of the existence of a Specker sequence is conceivable in intuitionistic analysis. We will also introduce the notion of double Specker sequence and study the existence of them (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quantitation of atorvastatin in human plasma using directly suspended acceptor droplet in liquid-liquid-liquid microextraction and high-performance liquid chromatography-ultraviolet detection

A simple and sensitive methodology based on liquid-liquid-liquid microextraction (LLLME) followed by high-performance liquid chromatography-ultraviolet detection (HPLC-UV) has been successfully developed for the determination of atorvastatin (AT) in human plasma. AT was first extracted from 4.5 mL acidic aqueous sample (diluted plasma, donor phase, pH 1) at temperature 45 °C through 400 μL 1-octanol for 4.5 min, while being agitated by a stirring bar at 1250 rpm. Then, a 5.5 μL free suspended basic aqueous droplet (acceptor phase, pH 10) was delivered to the top-center position of the organic membrane. The mixture was stirred at 650 rpm for 7.5 min and the analyte was back-extracted into the droplet. Finally, the acceptor phase was taken into a microsyringe and injected directly into the HPLC. An enrichment factor of 187 along with substantial sample clean up was obtained under the optimized conditions. The calibration curve showed linearity in the range of 1-500 ng mL⁻¹ with regression coefficient corresponding to 0.996. Limits of detection (S/N = 3) and quantification (S/N = 10) were 0.4 and 1 ng mL⁻¹, respectively. A reasonable relative recovery (91%) and satisfactory intra-assay (4.4-7.0%, n = 6) and inter-assay (4.9-7.7%, n = 8) precision illustrated good performance of the analytical procedure. This technique was eventually applied for the determination of AT in human plasma after oral administration of 40 mg single dose of drug. The protocol proved to be highly cost-effective and reliable for the screening purpose.     

The interactive effect of agitation condition and titania particle size in hydrothermal synthesis of titanate nanostructures

The nucleation and growth mechanisms of hydrothermal synthesized nanotitanates are proposed based on the interaction effect between agitation condition and pristine titania particle size. TEM examination and N₂ adsorption measurements revealed distinct morphology and textural properties depending on TiO₂ particle size in constant agitation condition. Regarding to the supersaturation degree, heterogeneous nucleation dominates for nanotubes formation from large particle size of raw material. On the other hand, homogeneous nucleation determines nanospheres formation from small particle size of raw material. The nanotubes have an outer diameter ranging from 8 to 10 nm and inner diameter of 2 to 3 nm. The nanospheres have diameters ranging from 50 to 100 nm.     

Optically active diamide as a model for studying interactions between mineral salts and nylon type polyamides in methanol solutions

N,N′-Dicaproyl (–)1,2-diaminopropane (I) was used as a convenient model for the study of the optical activity of a nylon type polyamide: polysebacamide (–)1,2-diaminopropane (II). ORD of I was measured in different solvents. A peculiar behavior is observed in methanol in the presence of mineral salts. The influence of 0.1M potassium salts (Cl^?, Br^?, SCN^?, NO₃^?, SO₄^?2) and 0.1M alkaline chlorides and alkaline earth chloride hexahydrates on the optical activity of I in methanol are described. Alkaline salts and MgCl₂ give approximately the same effect: there is a decrease of the rotations without change of sign. SrCl₂ and CaCl₂ shift ORD curves towards the negative rotations, the last one giving complete inversion. This inversion is directly related to the CaCl₂ concentration and is attributed to adduct formation between amide groups and salt. Assuming that the different species are at equilibrium, an apparent equilibrium constant is obtained from the optical rotations for a complex of one mole of CaCl₂ with one mole of I. Results are used to discuss the complex ORD of poly(?) 1,2-diaminopropane sebacamide in methanol saturated with CaCl₂.     

Facile Biosynthesis of Silver Nanoparticles Using <Emphasis Type="Italic">Descurainia sophia</Emphasis> and Evaluation of Their Antibacterial and Antifungal Properties

The objective of the present study was to evaluate efficiency of silver nanoparticles (Ag-NPs) biosynthesis using Descurainia sophia as a novel biological resource. The resulting synthesized Ag-NPs were characterized using UV visible spectroscopy, X-ray diffraction, transmission electron microscopy and dynamic light scattering (DLS). The UV–Vis spectra gave surface plasmon resonance at ~420 nm. TEM images revealed formation spherical shaped Ag-NPs with size ranged from to 1–35 nm. DLS confirmed uniformity of the synthesized Ag-NPs with an average size of ~30 nm. Following, the antibacterial and antifungal activities of the synthesized Ag-NPs were investigated. The concentration 25 µg/ml of the Ag-NPs showed maximum inhibitory effect on mycelium growth of Rhizoctonia solani (More than 86 % inhibition), followed by 15 µg/ml (55 % inhibition) and 10 µg/ml (63 % inhibition). The minimum inhibitory concentration and minimum bactericidal concentration of Ag-NPs against Agrobacterium tumefaciens (strain GV3850) and A, rhizogenes (strain 15843) were 4 and 8 µg/ml, respectively. The Ag-NPs were stable in vitro for 3 months without any precipitation or decrease of antifungal effects. Finally, it could be concluded that D. sophia can be used as an effective method for biosynthesis of nanoparticles, especially Ag-NPs.     

Removal, preconcentration and determination of Mo(VI) from water and wastewater samples using maghemite nanoparticles

Removal and recovery of Mo(VI) from aqueous solutions were investigated using maghemite (γ-Fe₂O₃) nanoparticles. Combination of nanoparticle adsorption and magnetic separation was used to the removal and recovery of Mo(VI) from water and wastewater solutions. The nanoscale maghemite with mean diameter of 50 nm was synthesized by reduction coprecipitation method followed by aeration oxidation. Various factors influencing the adsorption of Mo(VI), e.g. pH, temperature, initial concentration, and coexisting common ions were studied. Adsorption reached equilibrium within <10 min and was independent of initial concentration of Mo(VI). Studies were performed at different pH values to find out the pH at which maximum adsorption occurred. The maximum adsorption occurred at pHs between 4.0 and 6.0. The Langmuir adsorption capacity (q_max) was found to be 33.4 mg Mo(VI)/g of the adsorbent. The results showed that nanoparticle (γ-Fe₂O₃) is suitable for the removal of Mo(VI), as molybdate, from water and wastewater samples. The adsorbed Mo(VI) was then desorbed and determined spectrophotometrically using bromopyrogallol red as a complexation reagent. This allows the determination of Mo(VI) in the range 1.0–86.0 ng mL⁻¹.