Low Molar Absorption Coefficient Research Articles

Sensitivity enhancement of capillary electrophoresis-frontal analysis-based method for characterization of drug-protein interactions using on-line sample preconcentration.

Capillary electrophoresis-frontal analysis is one of the most frequently used approaches for the study of plasma protein-drug interactions as a substantial part of new drug development. However, the capillary electrophoresis-frontal analysis typically combined with ultraviolet-visible detection suffers from insufficient concentration sensitivity, particularly for substances with limited solubility and low molar absorption coefficient. The sensitivity problem has been solved in this work by its combination with an on-line sample preconcentration. According to the knowledge of the authors this combination has never been used to characterize plasma protein-drug binding. It resulted in a fully automated and versatile methodology for the characterization of binding interactions. Further, the validated method minimalizes the experimental errors due to a reduction in the manipulation of samples. Moreover, employing an on-line preconcentration strategy with capillary electrophoresis-frontal analysis using human serum albumin-salicylic acid as a model system improves the drug concentration sensitivity 17-fold compared to the conventional method. The value of binding constant (1.51±0.63) ·104 L/mol obtained by this new capillary electrophoresis-frontal analysis modification is in agreement with the value (1.13±0.28) ·104 L/mol estimated by a conventional variant of capillary electrophoresis-frontal analysis without the preconcentration step, as well as with literature data obtained using different techniques.

Metronidazole Degradation by UV and UV/H2O2 Advanced Oxidation Processes: Kinetics, Mechanisms, and Effects of Natural Water Matrices.

Advanced oxidation technology represented by hydroxyl radicals has great potential to remove residual antibiotics. In this study, we systematically compared the metronidazole (MTZ) degradation behavior and mechanism in the UV and UV/H2O2 systems at pH 3.00 condition. The results show that the initial reaction rates were 0.147 and 1.47 µM min−1 in the UV and UV/H2O2 systems, respectively. The main reason for the slow direct photolysis of MTZ is the relatively low molar absorption coefficient (2645.44 M−1 cm−1) and quantum yield (5.9 × 10−3 mol Einstein−1). Then, we measured as 2.79 (±0.12) × 109 M−1 s−1 by competitive kinetics, and calculated and as 2.43 (±0.11) × 109 M−1 s−1 and 2.36 × 10−13 M by establishing a kinetic model based on the steady-state hypothesis in our UV/H2O2 system. The contribution of direct photolysis and •OH to the MTZ degradation was 9.9% and 90.1%. •OH plays a major role in the MTZ degradation, and •OH was the main active material in the UV/H2O2 system. This result was also confirmed by MTZ degradation and radicals’ identification experiments. MTZ degradation increases with H2O2 dosage, but excessive H2O2 had the opposite effect. A complex matrix has influence on MTZ degradation. Organic matter could inhibit the degradation of MTZ, and the quenching of the radical was the main reason. promoted the MTZ degradation, while and Cl− had no effect. These results are of fundamental and practical importance in understanding the MTZ degradation, and to help select preferred processes for the optimal removal of antibiotics in natural water bodies, such as rivers, lakes, and groundwater

Superparamagnetic Nanoparticles with Efficient Near-Infrared Photothermal Effect at the Second Biological Window.

Superparamagnetic nanoparticles (iron oxide nanoparticles—IONs) are suitable for hyperthermia after irradiating with radiofrequency radiation. Concerning the suitability for laser ablation, IONs present a low molar absorption coefficient in the near-infrared region close to 800 nm. For this reason, they are combined with other photothermal agents into a hybrid composite. Here, we show that IONs absorb and convert into heat the infrared radiation characteristic of the so-called second-biological window (1000–1350 nm) and, in consequence, they can be used for thermal ablation in such wavelengths. To the known excellent water solubility, colloidal stability and biocompatibility exhibited by IONs, an outstanding photothermal performance must be added. For instance, a temperature increase of 36 °C was obtained after irradiating at 8.7 W cm−2 for 10 min a suspension of IONs at iron concentration of 255 mg L−1. The photothermal conversion efficiency was ~72%. Furthermore, IONs showed high thermogenic stability during the whole process of heating/cooling. To sum up, while the use of IONs in the first bio-window (700–950 nm) presents some concerns, they appear to be good photothermal agents in the second biological window.

Analytical quantification of aqueous permanganate: Direct and indirect spectrophotometric determination for water treatment processes

Three spectrophotometric methods have been developed and compared for the quantification of low concentrations (0.03–63 μM) of aqueous permanganate in neutral pH conditions. Although permanganate is a widely used oxidant in drinking water and wastewater treatment, no widely accepted method of quantification has been reported to date. While one method presented does not require the need for any reagent chemicals (direct spectrophotometric analysis), it yielded a relatively low molar absorption coefficient of 3340 M−1 cm−1 at 525 nm and a level of detection (LOD) and quantification (LOQ) of 0.45 and 1.51 μM, respectively. Some instability of permanganate species during direct quantification was found to occur over 60 min, with a total decrease of 0.002 (arbitrary units) of absorbance, equivalent to a decrease in concentration of 0.6 μM. Beyond 60 min, no further degradation was observed. Indirect spectrophotometric analyses using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and sodium iodide (NaI) provided a significantly more sensitive method for permanganate quantification, yielding molar absorption coefficients of 140,030 and 61,130 M−1 cm−1, respectively. The LOD and LOQ were determined to be 0.01 and 0.03 μM for the ABTS method and 0.02 and 0.08 μM for the NaI method, respectively. Although conservative and accurate limits of quantification for both the ABTS and NaI methods are presented, which should be sufficient of most practical applications, lower limits may be possible with further refinement of the methods.

Enhancement of micropollutant degradation in UV/H2O2 process via iron-containing coagulants

The low molar absorption coefficient of H2O2 limits the ultraviolet (UV)/H2O2 process, making it a desirable target to enhance the UV/H2O2 process for organic micropollutant degradation. Therefore, this study investigated the impact of iron-containing coagulants (Fe-coagulants) on micropollutant degradation by UV/H2O2 process. Three typical Fe-coagulants (i.e., polymeric ferric sulfate, polymeric aluminum ferric sulfate, and FeCl3) exhibited the enhancement of sulfamethazine degradation during the UV/H2O2 process. The maximum increasing ratio of the degradation rate constant reached 40%. The pH and Fe-coagulant concentration effects, as well as residual H2O2 were examined. The principal mechanism of micropollutant degradation enhancement via the Fe-coagulants was the photo-Fenton-like reaction between Fe(III) on the Fe-coagulant surface and H2O2 under UV irradiation. Then the influence of Fe-coagulant particle size was discussed. Smaller particles (<0.22 μm), with a lower iron content, a larger specific surface area, and a stronger optical scattering effect, exhibited a greater enhancement on the UV/H2O2 process as compared with larger particles (>0.22 μm). Finally, the enhancement effect of the Fe-coagulants was verified on two water samples from a water treatment plant, which were either pre-coagulation or sand filtered samples. This study explored an existing heterogeneous catalysis process in drinking water treatment, which provides additional information for coagulant selection and improvements to the treatment process for micropollutant removal.

Spectrophotometric determination of ozone in solutions: Molar absorption coefficient in the visible region.

A new approach for the determination of ozone concentration in solutions in organic liquids based on spectrophotometric absorbance measurements in the visible region was proposed and substantiated. The molar absorption coefficient of ozone in the absorption maximum at ~600nm is 8.0mol-1 L cm-1 for hydrocarbons (hexane, heptane, isooctane), CHCl3 and CCl4, and 5.3mol-1 L cm-1 for methanol and 4.5mol-1 L cm-1 for water (±10%). The coefficient monotonically decreases with increasing dielectric constant of the liquid. The low molar absorption coefficient allows the use of spectrophotometric measurements for determination of high ozone concentrations ranging from approximately 1·10-2mol L-1 up to 1.0mol L-1.

Sensitive inkjet printing paper-based colormetric strips for acetylcholinesterase inhibitors with indoxyl acetate substrate

A new paper-based biosensing approach has been developed for sensitive and rapid detection of acetylcholinesterase (AChE) inhibitors. The biosensing zone of the paper strip is constructed with an inkjet printing method, and the biomolecule AChE is immobilized into two layers of biocompatible sol-gel-derived silica ink with a “sandwich” form. Indoxyl acetate (IDA) is used as a chromogenic substrate, which is colorless and can be catalytically hydrolyzed into blue-colored indigo dipolymer. When the enzymatic activity of AChE is inhibited after incubation with organophosphate pesticides (OPs), there is a decreased hydrolysis of IDA accompanying with a drop in color intensity. Paraoxon and trichlorfon are used as the representative OPs in the assay. Due to the low solubility and high molar absorption coefficient of the IDA dipolymer product, the paper-based strip can form a neat blue sensing zone and shows obviously improved sensitivity with a limit of detection (LOD) of 0.01ngmL−1 paraoxon and 0.04ngmL−1 trichlorfon (S/N=3) and the LODs for visual detection are 0.03ngmL−1 for paraoxon and 0.1ngmL−1 for trichlorfon comparing with the previously reported colorimetric methods. The concentrations of paraoxon in apple juice samples are also detected, and the results are in accord well with these results from high-performance liquid chromatography, showing great potential for on-site detection of OPs in practical application. The developed assay can be used to qualitatively and semiquantitatively estimate with naked eyes and quantitatively assess OPs through image analysis.

Silicon Nanocrystals Coated By Porphyrins As Light-Harvesting Antennae

Silicon (Si) is a widely used semiconductor, in part because it is abundant, widely available and essentially non-toxic. From the photophysical point of view, it exhibits weak light absorption and emission because it has an indirect bandgap. Conversely, Si nanocrystals (SiNCs) in the quantum size range (2-12 nm) can be made as viable light emitters with emission wavelength that can be tuned from the near-infrared (NIR) into the visible by decreasing their size [1-3]. Covalent Si-to-carbon bonding also offers the possibility of integrating inorganic and organic components into robust structures. Most optical studies of SiNCs have focused on alkyl-passivated nanocrystals, while little is known about the interaction between such nanocrystals and chromophoric units attached to the core. Therefore we have studied the interaction of an inorganic silicon nanoparticle core with appended organic chromophores for the development of novel luminescent materials. The synthesis of luminescent colloidal nanocrystals of silicon is still a difficult task in terms of reliability and reproducibility. We report the thermal decomposition of hydrogen silsequioxane, followed by etching and hydrosilylation [4]. This method isolated SiNCs with good yields, high surface coverage and exceptional control over the dimensions and optical properties of the materials. In the present work, the H-terminated nanocrystals were used as a platform for co-passivation with dodecene and different organic chromophores [5] by thermal hydrosilylation. For example, we functionalised two families of SiNC of average diameter of 2.5 and 5 nm with porphyrin chromophores: porphyrin excitation results in an efficient energy transfer to the nanocrystal core. To the best of our knowledge this is the first time in which highly efficient light harvesting from photoactive units to the silicon core have been demonstrated. This approach enabled us to circumvent the drawback of the low molar absorption coefficient of SiNCs. The investigated hybrid material exhibits high quantum yield also in the NIR spectral region with lifetime in the µs range. [1] Brus, L. E.; Szajowski, P. F.; Wilson, W. L. Harris, T. D.; Schuppler, S.; Citrin, P. H. J. Am. Chem. Soc. 1995, 117, 2915-2922. [2] Mastronardi, M. L.; Henderson, E. J.; Puzzo,D. P.; Ozin, G. A. Adv. Mater. 2012, 24, 5890-5898. [3] Kelly, J. A.; Hendersonw, E. J.; Veinot, J. G. C. Chem. Commun. 2010, 46, 8704–8718 [4] Hessel, C. M.; Reid,D.; Panthani, M. G.; Rasch, M. R.;Goodfellow, B. W.; Wei, J.; Fujii, H.; Akhavan,V.; Korgel, B. A. Chem. Mater. 2012, 24, 393−401. [5] Locritani, M.; Yu, Y.; Bergamini, G.; Molloy, J. K.; Baroncini, M.; Korgel, B. A.; Ceroni, P. J. Phys. Chem. Lett. 2014, 5, 3325-3329. Figure 1

Criteria for selecting fluorescent dye tracers for soil hydrological applications using Uranine as an example

Abstract Calibrating and verifying 2-D and 3-D vadose zone flow and transport models requires detailed information on water and solute redistribution. Among the different water flow and mass transfer determination methods, staining tracers have the best spatial resolution allowing visualization and quantification of fluid flow including preferential flow paths. Staining techniques have been used successfully for several decades; however, the hydrological community is still searching for an “ideal” vadose zone tracer regarding flow path visualization. To date, most research using staining dyes is carried out with Brilliant Blue FCF. Fluorescent dyes such as Uranine, however, have significant advantages over nonfluorescents which makes them a promising alternative. This paper presents the first analysis of key properties any fluorescent substance must possess to qualify as a staining fluorescent tracer in vadose zone hydrological applications. First, we summarize the main physico-chemical properties of Uranine and evaluate its staining tracer potential with conventional suitability indicators and visibility testing in a soil profile. Based on numerical analysis using the theory of fluorescence, we show that a low molar absorption coefficient is a crucial parameter to quantify concentration accurately. In addition, excitation of a tracer on wavelengths different from the maximum excitation wavelength can extend the linear range of the concentration-fluorescence relationship significantly. Finally, we develop criteria for evaluating the suitability of any potential fluorescent soil staining compound for soil hydrological applications: 1) high quantum yield, 2) low molar absorption coefficient, 3) fluorescence independent of temperature, 4) low photodecomposition rates, and 5) fluorescence stable across a wide range of pH values.

Photophysics of a Xanthenic Derivative Dye Useful as an “On/Off” Fluorescence Probe

The photophysical behavior of a new fluorescein derivative has been explored by using absorption and steady-state and time-resolved fluorescence measurements. The influence of ionic strength, as well as total buffer concentration, on both the absorbance and fluorescence has been investigated. The apparent acidity constant of the dye determined by absorbance is almost independent of the added buffer and salt concentrations. A semiempirical model is proposed to rationalize the variations in the apparent pKa values. The excited-state proton-exchange reaction around the physiological pH becomes reversible upon addition of phosphate buffer, inducing a pH-dependent change of the steady-state fluorescence and decay times. Fluorescence decay traces, collected as a function of total buffer concentration and pH, were analyzed by global compartmental analysis, yielding the following values of the rate constants describing excited-state dynamics: k01 = 1.29 x 10(10) s(-1), k02 = 4.21 x 10(8) s(-1), k21 approximately 3 x 10(6) M(-1) s(-1), k12B= 6.40 x 10(8) M(-1) s(-1), and k21B = 2.61 x 10(7) M(-1) s(-1). The decay rate constant values of k01, k21, k21B, along with the low molar absorption coefficient of the neutral form, mean that coupled decays are practically monoexponential at buffer concentrations higher than 0.02 M and any pH. Thus, the pH and buffer concentration can modulate the main lifetime of the dye.

Poly(amido-amines)s with novel molecular architecture: Synthesis and thermodynamic studies of protonation and metal [Cu(II), Zn(II)] ion complexes

New short chain poly(amido-amine)s (SPAAs) carrying amido- and tertiary amino groups along the polymer chain separated by a single methylene group have been synthesized by polycondensation of N,N′-bis(2-chloro- or bromo-acetyl)-piperazine with N,N ′-dimethyl-ethylenediamine, N,N′-dimethyl-hexamethylenediamine or 2-methyl-piperazine. The basicity of the SPAAs was lower compared to the PAAs obtained previously by polyaddition of bis-amines to bis-acrylamides. The shortening of the methylene chain from two (PAAs) to one (SPAAs) reduced the log K values of both tertiary amino groups present in the repeating unit due to inductive effects. Furthermore, the shortening resulted in basicity constants, that depend on pH, with respect to the first step of protonation. The real changes in enthalpy (–ΔH0) of protonation of the SPAAs are greater than those found for PAAs, due to the fact that protonated nitrogens and amido C=O groups are closer, favouring the formation of five-member rings. Five-membered rings are formed also with metal(II) ions, such as Cu(II) and Zn(II), giving complex species more stable than those of PAAs, with higher log β and larger –ΔH0 values. Low entropy changes (ΔS0) and molar absorption coefficient (ε) values support strongly a well ordered chelate structure involving three condensed five-membered rings in an octahedral distorted geometry.

Poly(amido-amines)s with novel molecular architecture: Synthesis and thermodynamic studies of protonation and metal [Cu(II), Zn(II)] ion complexes

New short chain poly(amido-amine)s (SPAAs) carrying amido- and tertiary amino groups along the polymer chain separated by a single methylene group have been synthesized by polycondensation of N,N′-bis(2-chloro- or bromo-acetyl)-piperazine with N,N ′-dimethyl-ethylenediamine, N,N′-dimethyl-hexamethylenediamine or 2-methyl-piperazine. The basicity of the SPAAs was lower compared to the PAAs obtained previously by polyaddition of bis-amines to bis-acrylamides. The shortening of the methylene chain from two (PAAs) to one (SPAAs) reduced the log K values of both tertiary amino groups present in the repeating unit due to inductive effects. Furthermore, the shortening resulted in basicity constants, that depend on pH, with respect to the first step of protonation. The real changes in enthalpy (–ΔH0) of protonation of the SPAAs are greater than those found for PAAs, due to the fact that protonated nitrogens and amido C=O groups are closer, favouring the formation of five-member rings. Five-membered rings are formed also with metal(II) ions, such as Cu(II) and Zn(II), giving complex species more stable than those of PAAs, with higher log β and larger –ΔH0 values. Low entropy changes (ΔS0) and molar absorption coefficient (ε) values support strongly a well ordered chelate structure involving three condensed five-membered rings in an octahedral distorted geometry.

A spectrophotometric and phosphorimetric study of a new class of heteroaromatic ketones: the six thienyl-pyridyl ketone isomers

The six thienyl-pyridyl ketone isomers were synthesized and investigated by absorption and emission spectroscopy. Based on spectral region, vibronic structure, low molar absorption coefficient and solvent effect on the absorption spectra, the lowest S 0→S 1 transitions of all molecules were assigned to n, π* excitation. Acid–base properties were measured in acetonitrile–water solutions; the p K a values were determined by the position of nitrogen, while they were scarcely affected by the position of sulfur. Low intensity phosphorescence emissions (quantum yield <10 −3) were observed in fluid solutions. The emission lifetimes were on the microsecond scale. Emission spectral features point to mixed ( n, π*– π, π*) triplet states.

Inhibition of bovine carbonic anhydrase by 5-methyl-1,10-phenanthroline. Direct spectrophotometric evidence for ternary complex between the enzyme and chelating agent

For the removal of the cobalt ion from cobalt-bovine carbonic anhydrase with 5-methyl-1,10-phenanthroline, it was proved spectrophotometrically that the substitution mechanism proceeded through the ternary complex in which the central metal ion bound with the protein and the chelating agent. The spectrum of the ternary complex had low molar absorption coefficient in visible region, so that it was assumed that the ternary complex had a five- or six-coordination geometry.