UV-visible spectroscopy has been shown to be a useful technique for determining dissolved organic carbon (DOC) concentrations. However, at present we are unaware of any studies in the literature that have investigated the suitability of this approach for tropical DOC water samples from any tropical peatlands, although some work has been performed in other tropical environments. We used water samples from two oil palm estates in Sarawak, Malaysia to: i) investigate the suitability of both single and two-wavelength proxies for tropical DOC determination; ii) develop a calibration dataset and set of parameters to calculate DOC concentrations indirectly; iii) provide tropical researchers with guidance on the best spectrophotometric approaches to use in future analyses of DOC. Both single and two-wavelength model approaches performed well with no one model significantly outperforming the other. The predictive ability of the models suggests that UV-visible spectroscopy is both a viable and low cost method for rapidly analyzing DOC in water samples immediately post-collection, which can be important when working at remote field sites with access to only basic laboratory facilities.
Band gap change in doped ZnO is an observed phenomenon that is very interesting from the fundamental point of view. This work is focused on the preparation of pure and single phase nanostructured ZnO and Cu as well as Mn-doped ZnO for the purpose of understanding the mechanisms of band gap narrowing in the materials. ZnO, Zn0.99Cu0.01O and Zn0.99Mn0.01O materials were prepared using a wet chemistry method, and X-ray diffraction (XRD) results showed that all samples were pure and single phase. UV-visible spectroscopy showed that materials in the nanostructured state exhibit band gap widening with respect to their micron state while for the doped compounds exhibited band gap narrowing both in the nano and micron states with respect to the pure ZnO materials. The degree of band gap change was dependent on the doped elements and crystallite size. X-ray photoelectron spectroscopy (XPS) revealed that there were shifts in the valence bands. From both UV-visible and XPS spectroscopy, it was found that the mechanism for band gap narrowing was due to the shifting of the valance band maximum and conduction band minimum of the materials. The mechanisms were different for different samples depending on the type of dopant and dimensional length scales of the crystallites.
Studying the effect of a magnetic field on oligonucleotide DNA can provide a novel DNA manipulation technique for potential application in bioengineering and medicine. In this work, the optical and electrochemical response of a 100 bases oligonucleotides DNA, cytosine-guanine (CG100), is investigated via exposure to different magnetic fields (250, 500, 750, and 1000 mT). As a result of the optical response of CG100 to the magnetic field, the ultra-violet-visible spectrum indicated a slight variation in the band gap of CG100 of about 0.3 eV. Raman spectroscopy showed a significant deviation in hydrogen and phosphate bonds' vibration after exposure to the magnetic field. Oligonucleotide DNA mobility was investigated in the external electric field using the gel electrophoresis technique, which revealed a small decrease in the migration of CG100 after exposure to the magnetic field.
A simple high-performance liquid chromatographic method using UV detection was developed for the determination of alpha-tocopherol in human plasma. The method entailed direct injection of the plasma sample after deproteinization using acetonitrile-tetrahydrofuran (3:2). The mobile phase comprised methanol-tetrahydrofuran (94:6) and analysis was run at a flow-rate of 1.5 ml/min with the detector operating at 292 nm. A Crestpak C18S (5 microm, 250 mm x 4.6 mm ID) was used for the chromatographic separation. The method had a mean recovery of 93%, while the within-day and between-day coefficients of variation and percentage errors were all less than 7%. The speed, specificity, sensitivity and reproducibility of this method make it particularly suitable for routine determination of alpha-tocopherol in human plasma. Moreover, only a small sample plasma volume (100 microl) is required for the analysis.
Polyporus sp. S133 decolorized the Amaranth in 72 h (30 mg L(-1)) under static and shaking conditions. Liquid medium containing glucose has shown the highest decolorization of Amaranth by Polyporus sp. S133. When the effect of increasing inoculum concentration on decolorization of Amaranth was studied, maximum decolorization was observed with 15 % inoculum concentration. Significant increase in the enzyme production of laccase (102.2 U L(-1)) was observed over the period of Amaranth decolorization compared to lignin peroxidase and manganese peroxidase. Germination rate of Sorghum vulgare and Triticum aestivum was less with Amaranth treatment as compared to metabolites obtained after its decolorization. Based on the metabolites detected by GC-MS, it was proposed that Amaranth was bio-transformed into two intermediates, 1-hydroxy-2-naphthoic acid and 1,4-naphthaquinone. Overall findings suggested the ability of Polyporus sp. S133 for the decolorization of azo dye and ensured the ecofriendly degradation of Amaranth.
UV-VIS spectroscopic analysis of oligonucleotide DNA exposed to different magnetic fields was performed in order to investigate the relationship between DNA extinction coefficients and optical parameters according to magnetic-field strength. The results with the oligonucleotides adenine-thymine 100 mer (AT-100 DNA) and cytosine-guanine 100 mer (CG-100 DNA) indicate that the magnetic field influences DNA molar extinction coefficients and refractive indexes. The imaginary parts of the refractive index and molar extinction coefficients of the AT-100 and CG-100 DNA decreased after exposure to a magnetic field of 750 mT due to cleavage of the DNA oligonucleotides into smaller segments.
Pseudo-first-order rate constants (k(obs)) for alkaline hydrolysis of N-benzylphthalimide (1) show a nonlinear decrease with the increase in [C(m)E(n)]T (total concentration of Brij 58, m = 16, n = 20 and Brij 56, m = 16, n = 10) at constant [CH(3)CN] and [NaOH]. These nonionic micellar effects, within the certain typical reaction conditions, have been explained in terms of the pseudophase micellar (PM) model. The values of micellar binding constants (KS) of 1 are 1.04 x 10(3) M(-1) (at 1.0 x 10(-3) M NaOH) and 1.08 x 10(3) M(-1) (at 2.0 x 10(-3) M NaOH) for C(16)E(20) as well as 600 M(-1) (at 7.6 x 10(-4) M NaOH) and 670 M(-1) (at 1.0 x 10(-3) M NaOH) for C(16)E(10) micelles. The pseudo-first-order rate constants (kM) for hydrolysis of 1 in C(16)E(20) micellar pseudophase are approximately 90-fold smaller than those (kW) in water phase. The values of kM for hydrolysis of 1 in C(16)E(10) micelles are almost zero. Kinetic coupled with UV spectral data reveals significant irreversible nonionic micellar binding of 1 molecules in the micellar environment of nearly zero hydroxide ion concentration at >or=0.14 M C(16)E(20) and 1.0 x 10(-3) M NaOH while such observations could not be detected at or=3 x 10(-3) M C(16)E(10) and 7.6 x 10(-4) M NaOH, while the rate of hydrolysis of 1 is completely ceased at >or=0.05 M C(16)E(10) and 7.6 x 10(-4) M NaOH. The rate of hydrolysis of 1 at 5.0 x 10(-2) and 8.8 x 10(-2) M C(16)E(10) and 1.0 x 10(-3) M NaOH reveals the formation of presumably phthalic anhydride, whereas such observation was not observed in the C(16)E(20) micellar system under similar experimental conditions.
Despite its large band gap, ZnO has wide applicability in many fields ranging from gas sensors to solar cells. ZnO was chosen over other materials because of its large exciton binding energy (60 meV) and its stability to high-energy radiation. In this study, ZnO nanorods were deposited on ITO glass via a simple dip coating followed by a hydrothermal growth. The morphological, structural and compositional characteristics of the prepared films were analyzed using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), and ultraviolet-visible spectroscopy (UV-Vis). Photoelectrochemical conversion efficiencies were evaluated via photocurrent measurements under calibrated halogen lamp illumination. Thin film prepared at 120 °C for 4 h of hydrothermal treatment possessed a hexagonal wurtzite structure with the crystallite size of 19.2 nm. The average diameter of the ZnO nanorods was 37.7 nm and the thickness was found to be 2680.2 nm. According to FESEM images, as the hydrothermal growth temperature increases, the nanorod diameter become smaller. Moreover, the thickness of the nanorods increase with the growth time. Therefore, the sample prepared at 120 °C for 4 h displayed an impressive photoresponse by achieving high current density of 0.1944 mA/cm².
Binding mechanisms of two selected pesticides, propazine (PRO) and quinoxyfen (QUI) with bovine serum albumin (BSA) was examined using fluorescence, absorption and molecular docking methods. Intrinsic fluorescence of BSA was quenched in the presence of both PRO and QUI. The quenching was ascertained to be conversely linked to temperature, which suggested the contribution of static quenching process in the PRO-BSA and QUI-BSA complex formations. This results were validated by the enhancement in absorption spectrum of BSA upon binding with PRO and QUI. Binding constant values (Kf = 9.55-0.60 × 10-3 M-1 for PRO-BSA system; Kf = 7.08-5.01 × 102 M-1 for QUI-BSA system) and number of binding site (n) values for the PRO-BSA and QUI-BSA systems at different temperatures affirmed a weak binding strength with a set of equivalent binding sites on BSA. Thermodynamic data obtained for both the PRO-BSA and QUI-BSA interactions predicted that the association process was spontaneous and non-covalent contacts such as hydrophobic interactions, van der Waals forces and hydrogen bonds participated in the binding reactions. This result was further supported by the molecular docking assessments. Three-dimensional spectral results revealed the microenvironmental alterations near tryptophan (Trp) and tyrosine (Tyr) residues in BSA by the addition of PRO and QUI. The docking analysis demonstrated the binding pattern for the PRO-BSA and QUI-BSA systems and disclosed the preferred binding site of both PRO and QUI as site I (subdomain IIA) of BSA.
Paralytic shellfish toxins (PSTs) are produced by marine and freshwater microalgae and accumulate in shellfish including mussels, oysters, and scallops, causing possible fatalities when inadvertently consumed. Monitoring of PST content of shellfish is therefore important for food safety, with currently approved methods based on HPLC, using pre- or postcolumn oxidation for fluorescence detection (HPLC-FLD). CE is an attractive alternative for screening and detection of PSTs as it is compatible with miniaturization and could be implemented in portable instrumentation for on-site monitoring. In this study, CE methods were developed for C(4) D, FLD, UV absorption detection, and MS-making this first report of C(4) D and FLD for PSTs detection. Because most oxidized toxins are neutral, MEKC was used in combination with FLD. The developed CZE-UV and CZE-C(4) D methods provide better resolution, selectivity, and separation efficiency compared to CZE-MS and MEKC-FLD. The sensitivity of the CZE-C(4) D and MEKC-FLD methods was superior to UV and MS, with LOD values ranging from 140 to 715 ng/mL for CZE-C(4) D and 60.9 to 104 ng/mL for MEKC-FLD. With the regulatory limit for shellfish samples of 800 ng/mL, the CZE-C(4) D and MEKC-FLD methods were evaluated for the screening and detection of PSTs in shellfish samples. While the CZE-C(4) D method suffered from significant interferences from the shellfish matrix, MEKC-FLD was successfully used for PST screening of a periodate-oxidized mussel sample, with results confirmed by HPLC-FLD. This confirms the potential of MEKC-FLD for screening of PSTs in shellfish samples.
Capillary zone electrophoresis methods for the simultaneous determination of the beta-blocker drugs, atenolol, chlorthalidone and amiloride, in pharmaceutical formulations have been developed. The influences of several factors (buffer pH, concentration, applied voltage, capillary temperature and injection time) were studied. Using phenobarbital as internal standard, the analytes were all separated in less than 4 min. The separation was carried out in normal polarity mode at 25 degrees C, 25 kV and using hydrodynamic injection (10 s). The separation was effected in an uncoated fused-silica capillary (75 mum i.d. x 52 cm) and a background electrolyte of 25 mm H(3)PO(4) adjusted with 1 m NaOH solution (pH 9.0) and detection at 198 nm. The method was validated with respect to linearity, limit of detection and quantification, accuracy, precision and selectivity. Calibration curves were linear over the range 1-250 microg/mL for atenolol and chlorthalidone and from 2.5-250 microg/mL for amiloride. The relative standard deviations of intra- and inter-day migration times and corrected peak areas were less than 6.0%. The method showed good precision and accuracy and was successfully applied to the simultaneous determination of atenolol, chlorthalidone and amiloride in various pharmaceutical tablets formulations.
A sensitive and accurate high performance liquid chromatography with ultraviolet/visible light detection (HPLC-UV/VIS) method for the quantification of 2,6-bis-(4-hydroxy-3-methoxybenzylidene)-cyclohexanone (BHMC) in rat plasma was developed and validated. BHMC and the internal standard, harmaline, were extracted from plasma samples by a simple liquid-liquid extraction using 95% ethyl acetate and 5% methanol. Plasma concentration of BHMC and internal standard were analyzed by reversed phase chromatography using a C₁₈ column (150 × 4.6 mm I.D., particle size 5 µm) and elution with a gradient mobile phase of water and methanol at a flow rate of 1.0 mL/min. Detection of BHMC and internal standard was done at a wavelength of 380 nm. The limit of quantification was 0.02 µg/mL. The calibration curves was linear (R² > 0.999) over the concentration range of 0.02-2.5 µg/mL. Intra- and inter-day precision were less than 2% coefficient of variation. The validated method was then applied to a pharmacokinetic study in rats by intravenous administration of BHMC at a single dose of 10 mg/kg. Pharmacokinetic parameters such as half-life, maximum plasma concentration, volume of distribution, clearance and elimination rate constant for BHMC were calculated.
A selective and sensitive reversed-phase (RP) high-performance liquid chromatographic method is developed for the quantitative analysis of five naturally occurring flavonoids of Blumea balsamifera DC, namely dihydroquercetin-7,4'-dimethyl ether (DQDE), blumeatin (BL), quercetin (QN), 5,7,3',5'-tetrahydroxyflavanone (THFE), and dihydroquercetin-4'-methyl ether (DQME). These compounds have been isolated using various chromatographic methods. The five compounds are completely separated within 35 min using an RP C18, Nucleosil column and with an isocratic methanol-0.5% phosphoric acid (50:50, v/v) mobile phase at the flow rate of 0.9 mL/min. The separation of the compounds is monitored at 285 nm using UV detection. Identifications of specific flavonoids are made by comparing their retention times with those of the standards. Reproducibility of the method is good, with coefficients of variation of 1.48% for DQME, 2.25% for THFE, 2.31% for QN, 2.23% for DQDE, and 1.51% for BL. The average recoveries of pure flavonoids upon addition to lyophilized powder and subsequent extraction are 99.8% for DQME, 99.9% for THFE, 100.0% for BL, 100.6% for DQDE, and 97.4% for QN.
Varied pharmacological responses have been reported for mitragynine in the literature, but no supportive scientific explanations have been given for this. These studies have been undertaken without a sufficient understanding of the physicochemical properties of mitragynine. In this work a UV spectrophotometer approach and HPLC-UV method were employed to ascertain the physicochemical properties of mitragynine. The pKa of mitragynine measured by conventional UV (8.11 ± 0.11) was in agreement with the microplate reader determination (8.08 ± 0.04). Mitragynine is a lipophilic alkaloid, as indicated by a logP value of 1.73. Mitragynine had poor solubility in water and basic media, and conversely in acidic environments, but it is acid labile. In an in vitro dissolution the total drug release was higher for the simulated gastric fluid but was prolonged and incomplete for the simulated intestinal fluid. The hydrophobicity, poor water solubility, high variability of drug release in simulated biological fluids and acid degradable characteristics of mitragynine probably explain the large variability of its pharmacological responses reported in the literature. The determined physicochemical properties of mitragynine will provide a basis for developing a suitable formulation to further improve its solubility, stability and oral absorption for better assessment of this compound in preclinical studies.
To investigate and compare the effect of three analytical methods, hydrogen bromide titrimetry (HBr titrimetry), infrared spectroscopy (IR spectroscopy), and first derivative UV-spectrophotometry (FDUV-spectrophotometry) in the determination of degree of deacetylation (DD) of chitosan.
Biogenic amines have attracted interest among researchers because of their importance as biomarkers in determining the quality of food freshness in the food industry. A rapid and simple technique that is able to detect biogenic amines is needed. In this work, a new optical sensing material for one of the biogenic amines, histamine, based on a new zinc(II) salphen complex was developed. The binding of zinc(II) complexes without an electron-withdrawing group (complex 1) and with electron-withdrawing groups (F, complex 2; Cl, complex 3) to histamine resulted in enhancement of fluorescence. All complexes exhibited high affinity for histamine [binding constant of (7.14 ± 0.80) × 104, (3.33 ± 0.03) × 105, and (2.35 ± 0.14) × 105 M-1, respectively]. Complex 2 was chosen as the sensing material for further development of an optical sensor for biogenic amines in the following step since it displayed enhanced optical properties in comparison with complexes 1 and 3. The optical sensor for biogenic amines used silica microparticles as the immobilisation support and histamine as the analyte. The optical sensor had a limit of detection for histamine of 4.4 × 10-12 M, with a linear working range between 1.0 × 10-11 and 1.0 × 10-6 M (R2 = 0.9844). The sensor showed good reproducibility, with a low relative standard deviation (5.5 %). In addition, the sensor exhibited good selectivity towards histamine and cadaverine over other amines, such as 1,2-phenylenediamine, triethylamine, and trimethylamine. Recovery and real sample studies suggested that complex 2 could be a promising biogenic amine optical sensing material that can be applied in the food industry, especially in controlling the safety of food for it to remain fresh and healthy for consumption.
Anti-glaucoma latanoprost-loaded ocular implants provide prolonged delivery and enhanced bioavailability relative to the conventional eye drops. This study aims at the development and validation of a reversed-phase high-performance liquid chromatography method for quantitative analysis of nanogram levels of latanoprost in the eye, and for the first time, compares the use of fluorescence vs ultraviolet (UV) detectors in latanoprost quantification. The mobile phase was composed of acetonitrile:0.1% v/v formic acid (60:40, v/v) with a flow rate of 1 mL/min and separation was done using a C18 column at temperature 40°C. The fluorescence excitation and emission wavelengths were set at 265 and 285 nm, respectively, while the UV absorption was measured at 200 nm. The latanoprost concentration-peak area relationship maintained its linearity (R2 = 0.9999) over concentration ranges of 0.063-10 μg/mL and 0.212-10 μg/mL for the fluorescence and UV detectors, respectively. The UV detector showed better precision, while the fluorescence detector exhibited higher robustness and greater sensitivity, with a detection limit of 0.021 μg/mL. The fluorescence detector was selected for quantification of latanoprost released from ocular implants in vitro and in porcine ocular tissues. The developed method is a robust, rapid and cost-effective alternative to liquid chromatography-mass spectrometry for routine analysis of latanoprost released from ocular implants.
The aim of this study is to investigate the dissolution properties of poorly soluble drugs from their pure form and their amorphous formulation under physiological relevant conditions for oral administration based on surface dissolution ultraviolet (UV) imaging. Dissolution of two poorly soluble drugs (cefuroxime axetil and itraconazole) and their amorphous formulations (Zinnat® and Sporanox®) was studied with the Sirius Surface Dissolution Imager (SDI). Media simulating the fasted state conditions (compendial and biorelevant) with sequential media/flow rate change were used. The dissolution mechanism of cefuroxime axetil in simulated gastric fluid (SGF), fasted state simulated gastric fluid (FaSSGF) and simulated intestinal fluid (SIF) is predominantly swelling as opposed to the convective flow in fasted state simulated intestinal fluid (FaSSIF-V1), attributed to the effect of mixed micelles. For the itraconazole compact in biorelevant media, a clear upward diffusion of the dissolved itraconazole into the bulk buffer solution is observed. Dissolution of itraconazole from the Sporanox® compact is affected by the polyethylene glycol (PEG) gelling layer and hydroxypropyl methylcellulose (HPMC) matrix, and a steady diffusional dissolution pattern is revealed. A visual representation and a quantitative assessment of dissolution properties of poorly soluble compounds and their amorphous formulation can be obtained with the use of surface dissolution imaging under in vivo relevant conditions.
Silver nanoparticles were successfully prepared in two different solvents using a microwave heating technique, with various irradiation times. The silver nanoparticles were dispersed in polar liquids (distilled water and ethylene glycol) without any other reducing agent, in the presence of the stabilizer polyvinylpyrrolidone (PVP). The optical properties, thermal properties, and morphology of the synthesized silver particles were characterized using ultraviolet-visible spectroscopy, photopyroelectric technique, and transmission electron microscopy. It was found that for the both solvents, the effect of microwave irradiation was mainly on the particles distribution, rather than the size, which enabled to make stable and homogeneous silver nanofluids. The individual spherical nanostructure of self-assembled nanoparticles has been formed during microwave irradiation. Ethylene glycol solution, due to its special properties, such as high dielectric loss, high molecular weight, and high boiling point, can serve as a good solvent for microwave heating and is found to be a more suitable medium than the distilled water. A photopyroelectric technique was carried out to measure thermal diffusivity of the samples. The precision and accuracy of this technique was established by comparing the measured thermal diffusivity of the distilled water and ethylene glycol with values reported in the literature. The thermal diffusivity ratio of the silver nanofluids increased up to 1.15 and 1.25 for distilled water and ethylene glycol, respectively.
The white-rot fungus Pleurotus eryngii F032 showed the capability to degrade a three fused-ring aromatic hydrocarbons fluorene. The elimination of fluorene through sorption was also investigated. Enzyme production is accompanied by an increase in biomass of P. eryngii F032 during degradation process. The fungus totally degraded fluorine within 23 d at 10-mg l(-1) solution. Fluorene degradation was affected with initial fluorene concentrations. The highest enzyme activity was shown by laccase in the 10-mg l(-1) culture after 30 d of incubation (1620 U l(-1)). Few activities of enzymes were observed in the fungal cell at the varying concentration of fluorene. Three metabolic were detected and separated in ethylacetate extract, after isolated by column chromatography. The metabolites, 9-fluorenone, phthalic acid, and benzoic acid were identified using UV-vis spectrophotometer and gas chromatography-mass spectrometry (GC-MS). The results show the presence of a complex mechanism for the regulation of fluorene-degrading enzymes.