Determination of fenoterol and salbutamol in pharmaceutical formulations by electrogenerated chemiluminescence

Fenoterol and salbutamol were determined by electrogenerated chemiluminescence (ECL) coupled with flow injection analysis (FIA), using Ru(bpy)₃²⁺ as the luminescent substance. Fenoterol and salbutamol oxidize together with the ruthenium 2,2-bipyridyl at a platinum electrode, which leads to an increase in the luminescent intensity, and this increase is proportional to the analyte concentration. For fenoterol a linear calibration curve within the range from 1.0 × 10⁻⁵ to 1.0 × 10⁻⁴ mol l⁻¹ was obtained with a correlation coefficient of 0.998 (n = 5) and for salbutamol the linear analytical curve was also obtained in this range with a correlation coefficient of 0.995 (n = 5). The relative standard deviation was estimated as ≤2.5% for 3 × 10⁻⁵ mol l⁻¹ for fenoterol solution and as ≤1.3% for 5.0 × 10⁻⁵ mol l⁻¹ salbutamol solution for 15 successive injections. The limit of detection for fenoterol was 2.4 × 10⁻⁷ mol l⁻¹ and for salbutamol was 4.0 × 10⁻⁷ mol l⁻¹. Fenoterol and salbutamol were successfully determined in drug tablets and the soluble components of the matrix did not interfere in the luminescent emission. The results obtained using the luminescent methodology were not statistically different from those obtained by UV-spectrophotometry at 95% confidence level.     

Fluorescence of Zn(II) 8-hydroxyquinoline complex in the presence of aqueous micellar media: The special cetyltrimethylammonium bromide effect

Mixtures of Zn(II) and 8-hydroxyquinoline (8QOH) in a 1:2 proportion, in aqueous solutions, result in fast complexation, followed by precipitation. Addition of 0.05 M sodium dodecyl sulfate (SDS), N-dodecyl-N,N-dimethylammonio-1-propanesulfonate (SB3-12), N-hexadecyl-N,N-dimethylammonio-1-propanesulfonate (SB3-16) or Triton X-100 results in considerable retardation of precipitation. In the presence of SDS, SB3-12, SB3-16 and Triton X-100 the 8QOH chelates are only kinetically stable in solution and after 24 h, the precipitation is almost quantitative. Conversely, upon addition of the cationic surfactant hexadecyltrimethylammonium bromide (CTABr), the absorbance of the complex remains constant even after at least six months. The interaction of the ligand 8QOH (and of the (8QO)(2)Zn(II) complex) with the cationic surfactant was studied by ultraviolet and NMR spectroscopy and 8QOH has a pK(a)=9.05 in the presence of the cationic surfactant and the ligand intercalates in the micelle, being preferentially located near the headgroup of the micelle. Although the solubilization site of the (8QO)(2)Zn(II) complex is similar to that of 8QOH, the interaction of the aromatic moiety with the CTA(+) headgroup is much stronger, due to the increased electron density in the aromatic ring of the ligand. As a consequence of this interaction, sphere to rod transition and an increase in microscopic and macroscopic viscosity are observed.     

Global Hypoellipticity for a Class of Pseudo-differential Operators on the Torus

We show that an obstruction of number-theoretical nature appears as a necessary condition for the global hypoellipticity of the pseudo-differential operator \(L=D_t+(a+ib)(t)P(D_x)\) on \(\mathbb {T}^1_t\times \mathbb {T}_x^{N}\). This condition is also sufficient when the symbol \(p(\xi )\) of \(P(D_x)\) has at most logarithmic growth. If \(p(\xi )\) has super-logarithmic growth, we show that the global hypoellipticity of L depends on the change of sign of certain interactions of the coefficients with the symbol \(p(\xi ).\) Moreover, the interplay between the order of vanishing of coefficients with the order of growth of \(p(\xi )\) plays a crucial role in the global hypoellipticity of L. We also describe completely the global hypoellipticity of L in the case where \(P(D_x)\) is homogeneous. Additionally, we explore the influence of irrational approximations of a real number in the global hypoellipticity.

     

Low‐level Laser (Light) Therapy Increases Mitochondrial Membrane Potential and ATP Synthesis in C2C12 Myotubes with a Peak Response at 3–6 h

Low‐level laser (light) therapy has been used before exercise to increase muscle performance in both experimental animals and in humans. However, uncertainty exists concerning the optimum time to apply the light before exercise. The mechanism of action is thought to be stimulation of mitochondrial respiration in muscles, and to increase adenosine triphosphate (ATP) needed to perform exercise. The goal of this study was to investigate the time course of the increases in mitochondrial membrane potential (MMP) and ATP in myotubes formed from C2C12 mouse muscle cells and exposed to light‐emitting diode therapy (LEDT). LEDT employed a cluster of LEDs with 20 red (630 ± 10 nm, 25 mW) and 20 near‐infrared (850 ± 10 nm, 50 mW) delivering 28 mW cm² for 90 s (2.5 J cm²) with analysis at 5 min, 3 h, 6 h and 24 h post‐LEDT. LEDT‐6 h had the highest MMP, followed by LEDT‐3 h, LEDT‐24 h, LEDT‐5 min and Control with significant differences. The same order (6 h > 3 h > 24 h > 5 min > Control) was found for ATP with significant differences. A good correlation was found (r = 0.89) between MMP and ATP. These data suggest an optimum time window of 3–6 h for LEDT stimulate muscle cells.     

Implementing stepwise solvent elution in sequential injection chromatography for fluorimetric determination of intracellular free amino acids in the microalgae Tetraselmis gracilis

The concept of sequential injection chromatography (SIC) was exploited to automate the fluorimetric determination of amino acids after pre-column derivatization with o-phthaldialdehyde (OPA) in presence of 2-mercaptoethanol (2MCE) using a reverse phase monolithic C₁₈ stationary phase. The method is low-priced and based on five steps of isocratic elutions. The first step employs the mixture methanol: tetrahydrofuran: 10 mmol L⁻¹ phosphate buffer (pH 7.2) at the volumetric ratio of 8:1:91; the other steps use methanol: 10 mmol L⁻¹ phosphate buffer (pH 7.2) at volumetric ratios of 20:80, 35:65, 50:50 and 65:35. At a flow rate of 10 μL s⁻¹ a 25 mm long-column was able to separate aspartic acid (Asp), glutamic acid (Glu), asparagine (Asn), serine (Ser), glutamine (Gln), glycine (Gly), threonine (Thr), citruline (Ctr), arginine (Arg), alanine (Ala), tyrosine (Tyr), phenylalanine (Phe), ornithine (Orn) and lysine (Lys) with resolution >1.2 as well as methionine (Met) and valine (Val) with resolution of 0.6. Under these conditions isoleucine (Ile) and leucine (Leu) co-eluted. The entire cycle of amino acids derivatization, chromatographic separation and column conditioning at the end of separation lasted 25 min. At a flow rate of 40 μL s⁻¹ such time was reduced to 10 min at the cost of resolution worsening for the pairs Ctr/Arg and Orn/Lys. The detection limits varied from 0.092 μmol L⁻¹ for Tyr to 0.51 μmol L⁻¹ for Orn. The method was successfully applied to the determination of intracellular free amino acids in the green alga Tetraselmis gracilis during a period of seven days of cultivation. Samples spiked with known amounts of amino acids resulted in recoveries between 94 and 112%.     

On the interaction of the anthraquinone barbaloin with negatively charged DMPG bilayers

Barbaloin is a bioactive glycosilated 1,8-dihydroxyanthraquinone present in several exudates from plants, such as Aloe vera, which are used for cosmetic or food purposes. It has been shown that barbaloin interacts with DMPG (dimyristoylphosphatidylglycerol) model membranes, altering the bilayer structure (Alves, D. S.; Pérez-Fons, L.; Estepa, A.; Micol, V. Biochem. Pharm. 2004, 68, 549). Considering that ESR (electron spin resonance) of spin labels is one of the best techniques to monitor structural properties at the molecular level, the alterations caused by the anthraquinone barbaloin on phospholipid bilayers will be discussed here via the ESR signal of phospholipid spin probes intercalated into the membranes. In DMPG at high ionic strength (10 mM Hepes pH 7.4 + 100 mM NaCl), a system that presents a gel-fluid transition around 23 degrees C, 20 mol % barbaloin turns the gel phase more rigid, does not alter much the fluid phase packing, but makes the lipid thermal transition less sharp. However, in a low-salt DMPG dispersion (10 mM Hepes pH 7.4 + 2 mM NaCl), which presents a rather complex gel-fluid thermal transition (Lamy-Freund, M. T.; Riske, K. A. Chem. Phys. Lipids 2003, 122, 19), barbaloin strongly affects bilayer structural properties, both in the gel and fluid phases, extending the transition region to much higher temperature values. The position of barbaloin in DMPG bilayers will be discussed on the basis of ESR results, in parallel with data from sample viscosity, DSC (differential scanning calorimetry), and SAXS (small-angle X-ray scattering).     

Seasonal variation in the chemical composition and antimicrobial activity of volatile oils of three species of Leptospermum (Myrtaceae) grown in Brazil

This study investigates the seasonal variation of three species of Leptospermum (Myrtaceae) grown in Brazil. The chemical composition of the volatile oils of L. flavescens and L. petersonii did not show any significant seasonal variation in the major components, while for Leptospermum madidum subsp. sativum the levels of major constituents of the volatile oils varied with the harvest season. Major fluctuations in the composition of L. madidum subsp. sativum oil included α-pinene (0-15.2%), β-pinene (0.3-18.5%), α-humulene (0.8-30%), 1,8-cineole (0.4-7.1%) and E-caryophyllene (0.4-11.9%). Levels of β-pinene (0.3-5.6%), terpinen-4-ol (4.7-7.2%) and nerolidol (55.1-67.6%) fluctuated seasonally in the L. flavescens oil. In L. petersonii, changes were noted for geranial (29.8-32.8%), citronellal (26.5-33.9%) and neral (22.7-23.5%). The activity of the volatile oils against the tested bacteria differed, depending on season the oils were obtained. In general, the volatile oils were more active against Gram-positive bacteria.     

Theoretical study of spectroscopic properties of insulated molecular wires formed by substituted oligothiophenes and cross‐linked α‐cyclodextrin

The inclusion compound formed between cross‐linked α‐cyclodextrin dimer and substituted oligothiophene, was investigated using density functional theory (DFT). Energy gap, spectroscopy (IR, UV–vis, ¹³C NMR, and ¹H NMR) and first hyperpolarizability data were analyzed for the free species and inclusion compound, pp‐PT@(αCD–αCD). The semiconducting property of the included pp‐PT was not substantially affected on inclusion, with the energy gap increasing by only 10% after interaction with αCD–αCD. On the other hand, the nonlinear optical (NLO) response was significantly decreased, with the first hyperpolarizability, β, predicted to be just more than 60% lower for the [2]rotaxane than for free pp‐PT, but still having considerable magnitude. This was explained by the two‐state model based on the charge‐transfer contribution to the electronic transitions. The sensitivity of electronic spectra might also be useful for the inclusion complex characterization. The IR spectrum was slightly sensitive to the host–guest interaction and the calculated ¹³C NMR and ¹H NMR chemical shifts for the pp‐PT guest showed appreciable variations of 5–10 and 1–1.5 ppm, respectively, and so can be used for the characterization of inclusion compounds. We concluded that the formation of inclusion complexes with CDs, seems indeed very promising and the use of encapsulating conducting material should be experimentally pursued. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Characterization of two‐ and three‐photon absorption of polyfluorene derivatives

Fluorene‐based polymer derivatives are promising materials for organic electronic devices because of their photoluminescence and electroluminescence, good film‐forming ability, and favorable chemical and thermal properties. Although optical properties of polyfluorene have already been reported, most of the studies focused on the linear optical properties, whereas nonlinear optical characteristics have only recently received more detailed attention. Here, we report on two polyfluorene derivatives, poly(9,9′‐n‐dihexyl‐2,7‐fluorenediyl) (LaPPS 10) and poly(9,9′‐n‐dihexyl‐2,7‐fluorene‐diyl‐vinylene) (LaPPS 38), which present intense nonlinear absorption and fluorescence. Two‐photon absorption cross‐section properties of both polymers were characterized in the spectral range from 500 nm up to 900 nm, reaching peak values around 2000 Göppert Mayer units. Optical limiting behavior and two‐photon‐induced fluorescence of both polymers have also been investigated. Furthermore, the first molecular hyperpolarizability of the polymers was also studied using hyper‐Rayleigh scattering. In addition, the three‐photon absorption (3PA) spectra of both materials were also investigated, and 3PA cross‐section values in the order of 1 × 10^?78 cm⁶ s² photon^?2 were observed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 747–754     

DNA and RNA aptamers: from tools for basic research towards therapeutic applications

The systematic evolution of ligands by exponential enrichment (SELEX) is a combinatorial oligonucleotide library-based in vitro selection approach in which DNA or RNA molecules are selected by their ability to bind their targets with high affinity and specificity, comparable to those of antibodies. Nucleic acids with high affinity for their targets have been selected against a wide variety of compounds, from small molecules, such as ATP, to membrane proteins and even whole organisms. Recently, the use of the SELEX technique was extended to isolate oligonucleotide ligands, also known as aptamers, for a wide range of proteins of importance for therapy and diagnostics, such as growth factors and cell surface antigens. The number of aptamers generated as inhibitors of various target proteins has increased following automatization of the SELEX process. Their diagnostic and therapeutic efficacy can be enhanced by introducing chemical modifications into the oligonucleotides to provide resistance against enzymatic degradation in body fluids. Several aptamers are currently being tested in preclinical and clinical trials, and aptamers are in the process of becoming a new class of therapeutic agents. Recently, the anti-VEGF aptamer pegaptanib received FDA approval for treatment of human ocular vascular disease.