Ascorbic Acid Content and Antioxidant Activities of White and Brown Teff [Eragrostic tef (Zucc.)Trotter] Grains and Injera.

Teff [Eragrostis tef (Zuccagni) Trotter] is a cereal grain originating in Ethiopia as a staple food for millions of people. Its grain is a gluten-free superfood and got acceptance as a medicinal ingredient. Therefore, it is worthwhile to determine the antioxidative activities and L-ascorbic acid contents of teff grain and its baked food (injera). This study aimed to determine the ascorbic acid contents and antioxidant activities in the aqueous extract of the white and brown teff grains and their injera samples using iodimetric titration and UV-Vis spectrophotometric methods, respectively. The ascorbic acid contents in the white and brown teff ranged from 67.9-112.6 mg/100 g and 69.2-117.2 mg/100 g, respectively, and those in injera of the selected teff samples ranged from 30.5-32.9 mg/100 g and 37.3-43.0 mg/100 g, respectively. The antioxidant activities ranged from 1.26-7.04 µmol AAE/g for the white teff grains, 1.44-6.29 µmol AAE/g for the brown teff grains, 1.81-2.47 µmol AAE/g for white teff injera, and 3.89-4.86 µmol AAE/g for the brown teff injera samples. Findings of the present study have revealed that white teff and brown teff grains and their injera were found to have a higher content of ascorbic acid than commonly consumed grains and vegetables. No significant difference (α = 0.05) has been observed between the two varieties of teff grains with respect to the ascorbic acid content and antioxidant activities. However, there was a statistically significant difference (α = 0.05) in the ascorbic acid content and antioxidant activities between the teff grains and their injera samples. Therefore, this study indicated that teff grains and injera are rich in ascorbic acid content and antioxidant activities as compared to other cereal grains and are very crucial for human nutrition and health.

Development of Green UV-Vis Method for Direct Determination of Total Sugars in the Aqueous Extract of Teff (Eragrostis tef (Zuccagni) Trotter) Grains and Other Cereals.

There is no ultraviolet visible (UV-Vis) spectrophotometric method for the direct determination of total sugars in the aqueous extract of teff grain samples. Therefore, the objective of this study was to develop a green UV-Vis spectrophotometric method to determine total sugars in the aqueous extract of white teff, brown teff, white rice, and red wheat grain samples. The calibration curve was established in the range of 20.11-7,907 mg/L using sucrose as a standard with R 2 = 0.9996. The limit of detection and limit of quantification were 4.4 and 14.6 mg/L, respectively. The relative standard deviation (6.9%) of the method for the sucrose standard was within the acceptable range indicating that the method is precise. The amount of total sugars determined in the white teff (5.48-9.44% (w/w), brown teff (6.17-10.32% (w/w)), white rice (3.19% (w/w)), and red wheat (9.22% (w/w)) grain samples was comparable with other reported cereal grains. Furthermore, the accuracy of the developed analytical method was also evaluated by spiking the known amount of the sucrose standard solution to the white teff, brown teff, white rice, and red wheat sample extracts, and percentage recoveries found were in the acceptable range (85 ± 2 - 105 ± 4%) with an average recovery of 93%, confirming that the new green method is quantitatively reproducible. Hence, a fast, simple, inexpensive, widely used, selective, sensitive, precise, and accurate green UV-Vis method was developed and validated for the direct determination of total sugars in the aqueous extract of teff, white rice, and red wheat grain samples.

Development of Analytical Methods for Determination of ß-Carotene in Pumpkin (Cucurbita maxima) Flesh, Peel, and Seed Powder Samples.

Vegetables are consumed worldwide in fresh as well as processed forms. Pumpkin is considered as an important vegetable due to its nutritional values. The objective of this study was to evaluate all the analytical parameters and improve the performance of the methods for the determination of ß-carotene in pumpkin flesh, peel, and seed samples using UV-VIS, NIR, and FTIR methods. ß-Carotene was measured at 453 nm using the UV-VIS method which showed linear range, 0.1 to 12 µg/mL; R 2, 0.999; LOD, 0.034 µg/mL; LOQ, 0.1 µg/mL; RSD, 1.5% to 11%; and percent recovery, 83% to 93%. ß-Carotene was also measured at 1415 nm using NIR and at 1710 cm-1 using FTIR spectroscopic methods. The NIR method exhibited linear range, 12.5 to 250 µg/mL; R 2, 0.999; LOD, 3.4 µg/mL; LOQ, 10, µg/mL; RSD, 1.8% to 11%; and percent recovery, 92% to 96%, while the FTIR method exhibited linear range, 4 to 100 µg/mL; R 2, 0.999; LOD, 1.3 µg/mL; LOQ, 3.9 µg/mL; RSD, 0.69% to 10%; and percent recovery, 95% to 96%. The characteristic analytical data indicated that any of the three newly developed methods could be used for the determination of ß-carotene in the pumpkin flesh, peel, and seeds. Acetone was used as the extraction solvent for the UV-VIS and NIR spectroscopic methods, and acetonitrile was used as the extraction solvent for the FTIR method. Content of ß-carotene was found higher in pumpkin peel (340-445 µg/g), followed by pumpkin flesh (317-341 µg/g) and pumpkin seed (12-17 µg/g) by the UV-VIS method. ß-Carotene content was obtained ((376-451 µg/g) and (289-313 µg/g); (210-287 µg/g) and (102-148 µg/g)) using NIR and FTIR methods in pumpkin peel and flesh, respectively. ß-Carotene was obtained higher from pumpkin peel by all the three methods than from pumpkin flesh and seed. The ß-carotene content in the pumpkin seed was not detected by NIR and FTIR spectroscopic methods.

In Vitro Antibacterial and Antioxidant Activities of Roasted and Green Coffee Beans Originating from Different Regions of Ethiopia.

Coffee is among the most traded commodities and consumed beverages worldwide primarily for its stimulating effects. Moreover, coffee is known to contain various bioactive compounds with significant health benefits including antibacterial and antioxidant activities. However, Ethiopia as the origin of coffee and producer and exporter of varieties of Coffea arabica has made little study on the health aspects of this beverage. The aim of this study was to examine the antibacterial and antioxidant activities and content of coffee samples from different localities of Yorgacheffe and Jimma; and roasted, ground, and packed samples purchased from a coffee shop in Addis Ababa. Medium-roasted-boiled and lyophilized coffee extracts were tested on eight gram-negative and gram-positive bacterial strains. The agar-well diffusion method was used to test the extracts determining the minimum inhibitory and bactericidal concentrations. For coffee antioxidant activity and content, light-roasted (both field and shop samples) and green coffee bean extracts were tested using the free radical 2.2-diphenyl-l-pict1hydrazyl (DPPH) IC50 percent inhibition protocol. The samples showed strong antibacterial and antioxidant activity and substantial antioxidant content. Significant variation was noted in the antibacterial activities of the different coffee samples. Moreover, the growth-inhibitory strength of each coffee sample was variable for different test bacteria. A coffee sample with the best antibacterial activity had also the highest antioxidant activity/content. The shop coffee had the lowest bioactivity. The observed variations in the antibacterial and antioxidant activities among the samples probably indicate the diversity of the Ethiopian coffee related, among other factors, to the coffee plant genetics and agroecology.

Effect of altitude of coffee plants on the composition of fatty acids of green coffee beans.

BACKGROUND: The fatty acids of green coffee beans are one of the major components that determine the quality of coffee. Fatty acids composition of green coffee beans is affected by soil composition and altitude of coffee plants. This study was aimed to evaluate the effect of altitude of the coffee plants on the composition of fatty acids in green coffee beans. METHODS: Fatty acids contents of 40 green coffee beans samples collected from the coffee plants grown at different altitudes (group 1: 1500-1700, group 2: 1701-1900 and group 3: > 1900 m.a.s.l.) in Ethiopia were determined using gas chromatography-mass spectrometry (GC-MS). Chemometric data analyses were performed to determine the effects of altitude on the fatty acid composition of the green coffee beans. RESULTS: The green coffee beans contained main saturated fatty acid, palmitic acid with an average value of 55.5 mg/g and unsaturated fatty acid, linoleic acid with an average value of 51.6 mg/g. The other major constituents of fatty acids present in green coffee beans were stearic and oleic acids with the value of 12.3 mg/g and 8.92 mg/g, respectively. Palmitic acid content in lowland green coffee beans is significantly different than in the other two regions. On the other hand, stearic and oleic acids contents in the green coffee beans did not show a significant difference between the three topographical regions. While linoleic acid content in the green coffee beans showed significant difference between group 1 and 3 but did not show significant differences between group 1 and 2 and between group 2 and 3. The four major fatty acids, palmitic (R = - 0.574), linoleic (R = - 0.506), stearic (R = - 0.43) and oleic acids (R = - 0.291) in green coffee beans showed a moderate negative correlation with the altitude of coffee plants. CONCLUSION: The fatty acids contents decreases with increasing altitude of the coffee plants and hence affects the quality of coffee. The fatty acid composition of green coffee beans can also be used to determine the topographical origin of coffee plants.

GC-MS profiling of fatty acids in green coffee (Coffea arabica L.) beans and chemometric modeling for tracing geographical origins from Ethiopia.

BACKGROUND: This study was aimed at the development of objective analytical method capable of verifying the production region of the coffee beans. One hundred samples of green coffee (Coffea arabica L.) beans from the major producing regions, comprising various sub-regional types, were studied for variations in their fatty acid compositions by using gas chromatography coupled with mass spectrometry. Principal component analysis (PCA) was used to visualize data trends. Linear discriminant analysis (LDA) was used to construct classification models. RESULTS: Twenty-one different fatty acids were detected in all of the samples. The total fatty acid content varied from 83 to 204 g kg-1 across the regions. Oleic, linoleic, palmitic, stearic and arachidic acids were identified as the most discriminating compounds among the production regions. The recognition and prediction abilities of the LDA model for classification at regional level were 95% and 92%, respectively, and 92% and 85%, respectively, at sub-regional level. CONCLUSION: Fatty acids contain adequate information for use as descriptors of the cultivation region of coffee beans. Chemometric methods based on fatty acid composition can be used to detect fraudulently labeled coffees, with regard to the production region. These can benefit the coffee production market by providing consumers with products of the expected quality. © 2019 Society of Chemical Industry.

Improvement in Analytical Methods for Determination of Sugars in Fermented Alcoholic Beverages.

The main objective of this study was to improve the performance of analytical methods for the determination of sugars in fermented alcoholic beverages based on mid-infrared-partial least squares (MIR-PLS), high-performance liquid chromatography with the ultraviolet detector (HPLC-UV), high-performance liquid chromatography with the refractive index detector (HPLC-RI), and sulfuric acid methods. The MIR-PLS method was found to give good prediction of individual sugars: glucose, fructose, sucrose, and maltose in the alcoholic beverages with less than 4% error. The HPLC-UV method can be used for the determination of glucose in alcoholic beverages after derivatization with p-aminobenzoic acid ethyl ester. The HPLC-RI method was found to be applicable for the determination of individual sugars: glucose, fructose, sucrose, and maltose in the alcoholic beverages. The limit of detection (%, w/w) and recovery (%) of the individual sugars by the HPLC-RI method were fructose 0.001, 89.4-106; glucose 0.002, 92.4-109; and sucrose 0.002, 94.2-95.1. The sulfuric acid method was found to be useful for the determination of total sugar in the alcoholic beverages. The limit of detection (%, w/w) and recovery (%) of the total sugar by the sulfuric acid method were found to be 0.009, 98.2-109. The HPLC-RI method was applied to determine the level of individual sugars, while the sulfuric acid method was used to determine total sugar in Ethiopian traditional fermented alcoholic beverages: Tella, Netch Tella, Filter Tella, Borde, Tej, Korefe, Keribo, and Birz. The sugar contents in the real samples were found in the ranges (%): glucose 0.07-5.60, fructose 0.09-8.50, sucrose and maltose 0.08-3.00, and total sugar 12.0-64.5. The levels of sugars in Ethiopian traditional fermented alcoholic beverages were found to be comparable with literature data.

New fluorescence spectroscopic method for the simultaneous determination of alkaloids in aqueous extract of green coffee beans.

BACKGROUND: There is no fluorescence spectroscopic method for the determination of trigonelline and theobromine in green coffee beans. Therefore, the objective of this study was to develop a new fluorescence spectroscopic method to determine the alkaloids simultaneously in the aqueous extract of green coffee beans. RESULTS: The calibration curves were linear in the range 2-6, 1-6, 1-5 mg/L for caffeine, theobromine and trigonelline, respectively, with R2 ≥ 0.9987. The limit of detection and limit of quantification were 2, 6 and 7 µg/L and 40, 20 and 20 µg/L for caffeine, theobromine and trigonelline, respectively. Caffeine and trigonelline exhibited well separated fluorescence excitation spectra and therefore the two alkaloids were selectively quantified in the aqueous extract of green coffee. While theobromine showed overlapping fluorescence excitation spectra with caffeine and hence theobromine could not be determined in the aqueous extract of green coffee beans. The amount of caffeine and trigonelline in the three samples of green coffee beans were found to be 0.95-1.10 and 1.00-1.10% (w/w), respectively. The relative standard deviations (RSD ≤ 4%) of the method for the three compounds of interest were of very good. The accuracy of the developed analytical method was evaluated by spiking standard caffeine and trigonelline to green coffee beans and the average recoveries were 99 ± 2% for both the alkaloids. CONCLUSIONS: A fast, sensitive and reliable fluorescence method for the simultaneous determination of caffeine and trigonelline in the aqueous extract of green coffee beans was developed and validated. The developed method reflected an effective performance to the direct determination of the two alkaloids in the aqueous extract of green coffee beans.

Dual fluorescence of (E)-N-(4-(dimethylamino)benzylidene)-2H-1,2,4-triazol-3-amine (DMABA-Amtr): A ground state perspective.

We present the absorption and fluorescence spectra of (E)-N-(4-(dimethylamino)benzylidene)-2H-1,2,4-triazol-3-amine (DMABA-Amtr), an electron donor-π-acceptor system. The molecule shows a single fluorescence emission band in non-polar solvents while dual emissions were observed in polar aprotic solvents. Although several researchers over the years provide different explanations for the mechanism of the phenomena, based on solvent assisted excited state geometry changes of such systems, it is still a matter of controversy since such systems are unique as they contradict Kasha's rule. The emission spectrum of the molecule shows strong dependence on solvent polarity and excitation wavelength. This observation together with a single iso-emissive point found in the area normalize emission spectra indicates the presence of two ground state equilibrium structures of the compound which are both fluorescent. Density functional theory (DFT) and time-dependent (TD-DFT) calculations also support the experimental findings.

Development of new analytical methods for the determination of caffeine content in aqueous solution of green coffee beans.

BACKGROUND: This study was conducted to develop fast and cost effective methods for the determination of caffeine in green coffee beans. In the present work direct determination of caffeine in aqueous solution of green coffee bean was performed using FT-IR-ATR and fluorescence spectrophotometry. Caffeine was also directly determined in dimethylformamide solution using NIR spectroscopy with univariate calibration technique. RESULTS: The percentage of caffeine for the same sample of green coffee beans was determined using the three newly developed methods. The caffeine content of the green coffee beans was found to be 1.52 ± 0.09 (% w/w) using FT-IR-ATR, 1.50 ± 0.14 (% w/w) using NIR and 1.50 ± 0.05 (% w/w) using fluorescence spectroscopy. The means of the three methods were compared by applying one way analysis of variance and at p = 0.05 significance level the means were not significantly different. The percentage of caffeine in the same sample of green coffee bean was also determined by using the literature reported UV/Vis spectrophotometric method for comparison and found to be 1.40 ± 0.02 (% w/w). CONCLUSION: New simple, rapid and inexpensive methods were developed for direct determination of caffeine content in aqueous solution of green coffee beans using FT-IR-ATR and fluorescence spectrophotometries. NIR spectrophotometry can also be used as alternative choice of caffeine determination using reduced amount of organic solvent (dimethylformamide) and univariate calibration technique. These analytical methods may therefore, be recommended for the rapid, simple, safe and cost effective determination of caffeine in green coffee beans.

Non-destructive determination of ethanol levels in fermented alcoholic beverages using Fourier transform mid-infrared spectroscopy.

BACKGROUND: Traditional fermented alcoholic beverages are indigenous to a particular area and are prepared by the local people using an age-old techniques and locally available raw materials. The main objective of this work was the direct determination of ethanol in traditional fermented alcoholic beverages using mid infrared spectroscopy with partial least squares regression, verifying the robustness of the calibration models and to assess the quality of beverages. RESULTS: The level of ethanol determination in Ethiopian traditional fermented alcoholic beverages was done using mid infrared spectroscopy with partial least squares regression (MIR-PLS). The calibration and validation sets, and real samples spectra were collected with 32 scans from 850-1200 cm-1. A total of 25 synthetic standards (calibration and validation sets) with ethanol (2-10% w/w) and sugars (glucose, fructose, sucrose and maltose) (0-5% w/w) compositions were used to construct and validate the models. Twenty-five different calibration models were validated by cross-validation approach with 25 left out standards. A large number of pre-treatments were verified, but the best pre-treatment was subtracting minimum + 2nd derivative. The model was found to have the highest coefficients of determination for calibration and cross-validation (0.999, 0.999) and root mean square error of prediction [0.1% (w/w)]. For practical relevance, the MIR-PLS predicted values were compared against the values determined by gas chromatography. The predicted values of the model were found to be in excellent agreement with gas chromatographic measurements. In addition, recovery test was conducted with spiking 2.4-6.4% (w/w) ethanol. Based on the obtained recovery percentage, 85.4-107% (w/w), the matrix effects of the samples were not considerable. CONCLUSION: The proposed technique, MIR-PLS at 1200-850 cm-1 spectral region was found appropriate to quantify ethanol in fermented alcoholic beverages. Among the studied beverages (Tella, Netch Tella, Filter Tella, Korefe, Keribo, Borde and Birz), the average ethanol contents ranged from 0.77-9.1% (v/v). Tej was found to have the highest ethanol content whereas Keribo had the least ethanol content. The developed method was simple, fast, precise and accurate. Moreover, no sample preparation was required at all. However, it should be noted that the present procedure is probably not usable for regulatory purposes (e.g. controlling labelling).

Preparative HPLC for large scale isolation, and salting-out assisted liquid-liquid extraction based method for HPLC-DAD determination of khat (Catha edulis Forsk) alkaloids.

BACKGROUND: Khat (Catha edulis Forsk) is an evergreen shrub of the Celastraceae family. It is widely cultivated in Yemen and East Africa, where its fresh leaves are habitually chewed for their momentary pleasures and stimulation as amphetamine-like effects. The main psychostimulant constituents of khat are the phenylpropylamino alkaloids: cathinone, cathine and norephedrine. RESULTS: In this study, simple procedures based on preparative HPLC and salting-out assisted liquid-liquid extraction (SALLE) based methods were developed respectively for large scale isolation and the extraction of psychoactive phenylpropylamino alkaloids; cathinone, cathine and norephedrine, from khat (Catha edulis Forsk) chewing leaves, a stimulant and drug of abuse plant. The three khat alkaloids were directly isolated from the crude oxalate salt by preparative HPLC-DAD method with purity > 98%. In addition, a modified (SALLE) method has been developed and evaluated for the extraction efficiency of psychoactive phenylpropylamino alkaloids from khat (Catha edulis Forsk) chewing leaves. An in situ two steps extraction protocol was followed without dispersive SPE clean up. The method involves extraction of the samples with 1% HAc and QuEChERS salt (1.0 g of CH3COONa and 6.0 g of MgSO4) followed by subsequent in situ liquid-liquid partitioning by adding ethyl acetate and NaOH solution. The optimized method allowed recoveries of 80-86% for the three alkaloids from khat sample with relative standard deviation (RSD) values less than 15% and limits of detection (0.85-1.9 µg/mL). CONCLUSION: The method was found to be simple, cost-effective and provides cleaner chromatogram with good selectivity and reproducibility. The SALLE based protocol provided as good results as the conventional extraction method (ultrasonic assisted extraction followed by solid phase extraction, UAE-SPE) and hence the method can be applicable in forensic and biomedical sectors.

A (-)-norephedrine-based molecularly imprinted polymer for the solid-phase extraction of psychoactive phenylpropylamino alkaloids from Khat (Catha edulis Vahl. Endl.) chewing leaves.

A molecularly imprinted polymer (MIP) was prepared using (-)-norephedrine as the template, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker and chloroform as the porogen. The MIP was used as a selective sorbent in the molecularly imprinted solid-phase extraction (MIP-SPE) of the psychoactive phenylpropylamino alkaloids, norephedrine and its analogs, cathinone and cathine, from Khat (Catha edulis Vahl. Endl.) leaf extracts prior to HPLC-DAD analysis. The MIP was able to selectively extract the alkaloids from the aqueous extracts of Khat. Loading, washing and elution of the alkaloids bound to the MIP were evaluated under different conditions. The clean baseline of the Khat extract obtained after MIP-SPE confirmed that a selective and efficient sample clean-up was achieved. Good recoveries (90.0-107%) and precision (RSDs 2.3-3.2%) were obtained in the validation of the MIP-SPE-HPLC procedure. The content of the three alkaloids in Khat samples determined after treatment with MIP-SPE and a commercial Isolute C18 (EC) SPE cartridge were in good agreement. These findings indicate that MIP-SPE is a reliable method that can be used for sample pre-treatment for the determination of Khat alkaloids in plant extracts or similar matrices and could be applicable in pharmaceutical, forensic and biomedical laboratories. Copyright © 2015 John Wiley & Sons, Ltd.

Distribution of polycyclic aromatic hydrocarbons in sediments of Akaki River, Lake Awassa, and Lake Ziway, Ethiopia.

The quantification of 14 polycyclic aromatic hydrocarbons (PAHs) was carried out in sediment samples collected from Akaki River, Lake Awassa, and Lake Ziway, Ethiopia. The concentration of PAHs in the samples was determined using gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring (SIM) mode, after microwave-assisted extraction (MAE), using acetone/n-hexane (1:1, v/v) mixture. The accuracy of the method was determined by extracting and analyzing New York/New Jersey waterway sediment standard reference material (SRM 1944). The measured concentrations of PAHs in SRM 1944 agreed well with the certified values. In samples from Akaki River, Lake Awassa, and Lake Ziway, the total content of PAHs determined ranged from 0 to 3070 ng/g (average 534 ng/g), 24.9 to 413 ng/g (average 169 ng/g), and 15.0 to 305 ng/g (average 175 ng/g), respectively. Source ratios indicated that the PAHs were mainly from petrogenic origin. Sediments from all sampling sites indicated negligible levels of toxicity with no risk of adverse biological effects.

Occurrence, distribution, and ecological risk assessment of potentially toxic elements in surface sediments of Lake Awassa and Lake Ziway, Ethiopia.

Microwave-assisted acid digestion and modified aqua regia (HNO3:HCl:HF:H3BO3) leaching techniques were used for the determination of 15 potentially toxic elements (V, Cr, Fe, Mn, Co, Ni, Cu, Zn, As, Se, Ag, Cd, Sn, Hg and Pb) in sediment samples from Lake Awassa and Lake Ziway, Ethiopia. The digests were subsequently analyzed by inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectrometry (ICP-OES). Mercury was directly determined in the solid samples using an elemental mercury analyzer. The precision and accuracy of the digestion procedures were verified using certified reference materials. The experimental results were in good agreement with the certified values (P < 0.05) and the recoveries were quantitative (>90%). The average relative standard deviations were below 10%. There is significant correlation between the two lakes at the 0.01 level (2-tailed). Using the sediment quality guidelines, both lakes are heavily polluted with Zn and some of the sites are heavily polluted with Cu, Ni and Pb. Based on effect range low (ERL) - effect range medium (ERM), in both lakes for Ag were greater than the ERM, indicating that the areas could be toxic to aquatic organisms, while for Cr, Cu, As and Hg the values were less than ERL.

Solvent polarity and excitation wavelength dependence of the dual fluorescence in N,N-diethyl-4-nitrosoaniline.

Dual fluorescence in N,N-Diethyl-4-nitrosoaniline (DENA) has been studied employing absorption, excitation and emission spectroscopic techniques and computational methods. The absorption and fluorescence spectra of DENA were measured in solvents of various polarities at room temperature. The emission spectra of DENA were found to exhibit a single emission band in non polar solvent (cyclohexane) and in a highly polar solvent (acetonitrile). In the contrary, two emission bands were observed in medium polar solvents (tetrahydrofuran, 1,2-dichloroethane and dichloromethane) whereby the short (local excited; LE) and long (charge transfer; CT) emission maxima correspond to the emission maxima of the compound observed in cyclohexane and acetonitrile solutions, respectively. Moreover, the two emission bands have shown strong excitation wavelength dependence, and area normalization resulted in an iso-emissive point. The two emission maxima were in addition found to correspond to two excitation maxima in 3D fluorescence spectra. Further, two minima were obtained in potential energy surface calculation of DENA. From the experimental and computational results it was concluded that the dual fluorescence may be attributed to the presence of two different ground state structural conformers of DENA in equilibrium that are stabilized through solute-solvent interaction.

Excitation wavelength dependence of dual fluorescence of DMABN in polar solvents.

Steady-state absorption, fluorescence excitation and emission spectra of 4-(N,N-dimethylamino)benzonitrile (DMABN) have been measured at room temperature in cyclohexane, 1,4-dioxane, dichloromethane, and acetonitrile solutions. The fluorescence spectra of DMABN are found to exhibit dual emission in 1,4-dioxane, dichloromethane, and acetonitrile solutions and single emission in cyclohexane solution. The effect of solvent polarity and excitation wavelength on the emission spectra has also been studied. The fluorescence excitation spectra of DMABN monitored at the emission bands are different. The presence of two different conformations of the same molecule in the ground state has lead to two close lying excited states; local excited (LE) and charge transfer (CT), and thereby results in the dual fluorescence of the compound. The experimental studies were supported by ab initio density functional theory (DFT) calculations performed at the B3LYP/6-31Gd level of theory. On the basis of the experimental results and our theoretical calculations, we suggest that there are two conformers of DMABN, which are stable in the ground state, equilibrated in solution at room temperature that give rise dual fluorescence upon excitation.

Indirect voltammetric determination of caffeine content in coffee using 1,4-benzoquinone modified carbon paste electrode.

In this paper a simple and highly sensitive electroanalytical method for the determination of caffeine content using 1,4-benzoquinone modified carbon paste electrode is presented. The method is based on suppression of 1,4-benzoquinone peak current on addition of caffeine. Square-wave and cyclic voltammetric techniques were utilised for the investigation. The 1,4-benzoquinone modified electrode exhibited a well-defined peak with reproducible peak current values for repetitive measurements; and showed a decrease in peak current value with an increase in caffeine content. The result revealed two linear range regions between 0 mmol L(-1) and 0.5 mmol L(-1) and 0.5 mmol L(-1) and 8.0 mmol L(-1), with detection limits of 0.3 micromol L(-1) and 5.1 micromol L(-1), respectively. The method was then successfully applied to the determination of caffeine content in coffee samples. The effects of pH, electrode composition, step potential, pulse amplitude and square-wave frequency on the voltammetric responses were also investigated.

A distinctive example of the cooperative interplay of structure and environment in tuning of intramolecular charge transfer in second-order nonlinear optical chromophores.

The strongly enhanced cooperative influence of medium polarity and organic structural design on the first hyperpolarizability beta of a novel family of highly polarizable azinium-(CH=CH-thienyl)-dicyanomethanido chromophores 1-3 is described. The dyes can be efficiently synthesized by regioselective protonation/alkylation of the corresponding bidentate anion precursors. Consecutive annelation of the pyridyl ring of 1 (pyridine-->quinoline-->acridine) and medium polarity effects are responsible for an extraordinarily variable range of intramolecular charge transfer (ICT), leading to a large set of pi-electron distribution patterns. Accordingly, systems with remarkably different zwitterionic/quinoid character in the ground and excited states present beta values in a broad range, eventually switching from negative to positive. Our investigation is based on a combination of experimental (UV/Vis spectroscopy, multinuclear NMR spectroscopy, and electrooptical absorption measurements) and computational (ab initio) approaches. It is shown that: 1) beta and mubeta are dramatically influenced, even by orders of magnitude, by a complex, non-monotonic interplay of structure and medium action, which in turn affects molecular ICT and bond length alternation (BLA), 2) the computations, validated by different experimental data, are to be recommended as an extremely useful tool in the search for a greatly improved set of molecular nonlinear optical (NLO) responses (in the case of 1-3 they show that such conditions may be attained only in a narrow and limited range of dielectric constants in which the annelation effect operates most efficiently), and 3) the search for the most favorable molecular NLO response of a highly polarizable chromophore both in solution and in solid matrices should simultaneously take into account not only the molecular design supplemented by annelation effects but also the polarity of the medium.