Schiff Bases Derived from Aminopyridines as Spectrofluorimetric Analytical Reagents

Fluorescence characteristics of Schiff bases derived from aminopyridines and salicylaldehyde were studied and possibilities of their analytical application were discussed. It is shown that these compounds can be used for spectrofluorimetric monitoring of small pH changes as well as for sensitive metal ion determinations. As an illustration of metal ion determination, a spectrofluorimetric procedure for analysis of Cu2+ is presented. Determination of Cu2+ was based on the quenching effect of Cu2+ on the fluorescence of N,N\u27-bis(salicylidene)-2,3-pyridinediamine in dioxan/water 1/1 (volume fraction of dioxan, φ = 50%). Under optimal conditions (pH = 8.9, λex = 340 nm, λem = 385 nm, cligand = 1.0 x 10-5 M), the linearity range of the calibration curve was 30-350 μg L-1 Cu2+. The procedure is fast, simple and reproducible. It is characterized by high sensitivity and satisfactory selectivity. An additional advantage of Schiff bases derived from aminopyridines as analytical reagents lies in the simplicity of preparation procedures, enabling improvement of the determination methods not only by optimization of experimental conditions, but also by designing suitable struetural characteristics of the reagent

SORPTION OF METHYLENE BLUE ONTO ORANGE AND LEMON PEEL

This study examines the sorption of methylene blue on the cheap unconventional bio sorbents, citrus fruits: oranges and lemons. Bio sorbents which was used was: orange and lemon peel, seeds and pulp. The results are compared with results of sorption to mineral sorbents, zeolite clinoptilolite, Pyrolox and Birm. Sorption kinetics and the influence of pH on the sorption of methylene blue on orange and lemon peel was examined. Sorption isotherm of methylene blue onto the orange end lemon peel was determined at 25oC with the initial concentrations of methylene blue 50 – 1000 mg/dm3. The sorption kinetic data were analyzed using pseudo–first–order and pseudo–second-order models. It was found that the pseudo-second-order kinetic model was the best applicable model to describe the sorption kinetics. When the pH of the solution dyes was 2-3, the sorption of methylene blue was slightly weaker than at pH 3-6. In the studied concentration range 50-1000 mg/dm3 sorption of methylene blue on orange and lemon peel was linear, with sorption efficiency of approximately 100%. The capacity of zeolite for methylene blue was 20 mg/g. Sorption capacity of citrus waste was significantly higher than in the mineral sorbents (zeolite, Pyrolox, Birm)

Application of a Novel Lipophilized Derivative of Rhodamine 19 in an Optical Sensor Suitable for Measurements of pH in Alkaline Regions

An optical pH sensor based on the fluorescence of a new lipophilic rhodamine dye immobilized in a thin poly(vinyl chloride) membrane was developed. The response to hydrogen ions was a result of reversible changes in the molecular structure of rhodamine. Excited at 528 nm, the membrane fluoresced at 547 nm. The sensor system showed a usable sensitivity over the 9.5-11.9 pH range and very good reproducibility

Surface-enhanced Raman Scattering Enhancement Factors for RNA Mononucleotides on Silver Nanoparticles

Surface-enhanced Raman scattering (SERS) enhancement factors (EF) were evaluated for RNA mononucleotides: adenosine 5\u27-monophosphate (AMP), guanosine 5\u27-monophosphate (GMP), cytidine 5\u27-monophosphate (CMP) and uridine 5\u27-monophosphate (UMP), on silver nanoparticles, which differed in shape (nanospheres, nanostars) and stabilizing anionic layer (chlorides, citrates) on the metal surface. In freshly prepared silver colloids the enhanced Raman scattering was observed for all the RNA mononucleotides on the chloride coated silver nanospheres, Ag_Cl nsp (EF ≈ 104), for AMP only on the citrate coated silver nanospheres, Ag_cit nsp (EF ≈ 103), while not obtained at all for any of the mononucleotides on the citrate stabilized silver nanostars, Ag_cit nst. Upon aggregation, the SERS activity of all the silver colloids increased, whereby the purine mononucleotides, AMP and GMP, more strongly scattered radiation on Ag_Cl nsp, and the pyrimidine mononucleotides, CMP and UMP, on Ag_cit nsp. Regardless of the silver nanoparticles, the higher EFs were evaluated for AMP and GMP (EF up to 5 × 106), than for CMP and UMP (EF ≈ 5 × 104)

Schiff Bases Derived from Aminopyridines as Spectrofluorimetric Analytical Reagents

Fluorescence characteristics of Schiff bases derived from aminopyridines and salicylaldehyde were studied and possibilities of their analytical application were discussed. It is shown that these compounds can be used for spectrofluorimetric monitoring of small pH changes as well as for sensitive metal ion determinations. As an illustration of metal ion determination, a spectrofluorimetric procedure for analysis of Cu2+ is presented. Determination of Cu2+ was based on the quenching effect of Cu2+ on the fluorescence of N,N\u27-bis(salicylidene)-2,3-pyridinediamine in dioxan/water 1/1 (volume fraction of dioxan, φ = 50%). Under optimal conditions (pH = 8.9, λex = 340 nm, λem = 385 nm, cligand = 1.0 x 10-5 M), the linearity range of the calibration curve was 30-350 μg L-1 Cu2+. The procedure is fast, simple and reproducible. It is characterized by high sensitivity and satisfactory selectivity. An additional advantage of Schiff bases derived from aminopyridines as analytical reagents lies in the simplicity of preparation procedures, enabling improvement of the determination methods not only by optimization of experimental conditions, but also by designing suitable struetural characteristics of the reagent

METHYLENE BLUE SORPTION CHARACTERISATION ONTO ORANGE AND LEMON PEELS

Chemical properties of cationic biosorbents, the orange peel and the lemon peel, have been studied. ATR and Raman spectra indicated that the functional groups in the peels structure responsible for dye sorption are carboxyl groups (COOH and COOM, M=Na+,K+,Ca2+,Mg2+) and hydroxyl groups (OH). Increasing the mass of the peels in water suspensions a decrease in dissociation of both, the –COOH and –COOM groups was obtained. Sorption isotherms of methylene blue onto the biosorbents had two sorption plateaus. Hence the carboxyl groups interacted with methylene blue up to the first plateau, while sorption by also the hydroxyl groups occurred from the first to the second plateau. A very good agreement between the amounts of the carboxyl groups estimated in the peels and the amounts of the dye molecules sorbed onto the peels was obtained

Surface-enhanced Raman scattering study of the binding modes of a dibenzotetraaza[14]annulene derivative with DNA/RNA polynucleotides

Binding modes of a dibenzotetraaza[14]annulene (DBTAA) derivative with synthetic nucleic acids were studied using surface-enhanced Raman spectroscopy (SERS). Changes in SERS intensity and appearance of new bands in spectra were attributed to different complexes formed between the DBTAA molecules and DNA/RNA polynucleotides. A decrease in intensity pointed to intercalation as the dominant binding mode of the annulene derivative with poly dGdC-poly dGdC and poly rA-poly rU, whereas new bands in the spectra at 735 cm−1 and 1345 cm−1 revealed binding within the minor groove of poly dAdT-poly dAdT. When all the dominant binding sites were occupied, SERS spectra implied that small molecules bind on the outside of the DNA analogues, while exist mainly as free molecules in equimolar ratio with the synthetic RNA polynucleotide, thereby indicating higher affinity for DNA than for RNA

The Detection of Carious Lesion Porphyrins Using Violet Laser Induced Fluorescence

U istraživanju se željelo odrediti spektralna područja za lasersku ekscitaciju otopina protoporfirina IX (PP-a), koproporfirina (CP-a) i uroporfirina (UP-a) s različitim pH-vrijednostima. Drugi je cilj bio usporediti spektre laserski inducirane fluorescencije (LIF-a) otopina PP-a, CP-a i UP-a različitih pH-vrijednosti s fluorescencijom prirodne karijesne lezije i rezultatima ostalih istraživanja. Materijali i postupci: Apsorpcijski spektri otopina PP-a, CP-a i UP-a s pH-vrijednostima u rasponu od 0,6 do 13 izmjereni su spektrofotometrom (model Varian). Laser od 405 nm (10mW) odabran je prema najvišoj apsorpciji porfirina za mjerenja spektra laserski inducirane fluorescencije (LIF-a) PP-a, CP-a i UP-a te prirodne karijesne lezije. Rezultati: Ovisno o pH-vrijednosti, LIF-ove otopine PP-a, CP-a i UP-a pokazuju pomak prema višim valnim duljinama. U kiseloj otopini PP-a uočeni su fluorescencijski vršci na 601 nm i 655 nm nakon ekscitacije lasera na valnoj duljini od 405 nm. Zaključak: In vitro mjerenja LIF-a porfirinskih otopina ljubičastim laserom pokazuju sličnosti s valnim duljinama prave karijesne lezije i vrhovima fluorescencijskih vrpci prirodnih zuba poznatih iz literature. Ipak, fluorescencija testiranih porfirina ne objašnjava potpuno fluorescencijske spektre zubnog karijesa te su potrebna daljnja istraživanja. Čini se da pH ima važan utjecaj na svjetlosnu apsorpciju i emisiju porfirina.Objectives: The aim of the study was to establish spectral regions for laser excitation of protoporphyrin IX (PP), coproporphyrin (CP) and uroporphyrin (UP) solutions under different pH conditions. The second aim was to compare laser induced fluorescence (LIF) spectra of PP, CP and UP solutions with various pH to the fluorescence of natural carious lesion and the results of other studies. Materials and methods: Absorption spectra of PP, CP and UP solutions with pH values in range from 0.6-13.0 were taken on a Varian model spectrophotometer. According to the peak absorption of the porphyrins used, laser at 405 nm (10 mW) was selected for LIF measurements of PP, CP and UP solutions, as well as the natural carious lesion. Results: Depending on the pH value, the LIF of the PP, CP and UP solutions exhibited the red shift toward higher wavelengths. Using excitation at 405 nm laser wavelength, fluorescence bands peaking at 601 nm and 655 nm of the acidic PP solution were observed. Conclusions: Violet LIF peaks of porphyrin solutions measured in vitro are similar to the wavelengths of a real carious lesion and fluorescence band peaks of natural teeth known from literature. However, the fluorescence of tested porphyrins does not completely explain the fluorescence spectra of dental caries and further studies are needed. pH seems to have an important influence on the light absorption and emission of porphyrins

Laser Induced Fluorescence of Carious Lesion Porphyrins

Svrha: U radu su predstavljeni preliminarni rezultati mjerenja laserski inducirane fluorescencije u nekoliko porfirinskih otopina. Koproporfirin i uroporfirin sastavni su dijelovi karijesnih lezija. Njihovo svojstvo fluorescencije pri obasjavanju svjetlom određene valne duljine može se uporabljati kao način detekcije karijesnih lezija. Materijali i postupci: U otopinama koproporfirina i dihidroklorida te uroporfirina i dihidroklorida s različitim pH-uvjetima izmjereni su apsorpcijski koeficijenti kako bi se identificirale spektralne regije za učinkovitu ekscitaciju laserima. Za indukciju fluorescencije odabrani su laseri s diskretnim valnim duljinama na 420 nm, 473 nm i 532 nm. Rezultati: Kod svih laserskih valnih duljina uočena je zanimljiva fluorescencijska emisija na 591 nm, 619 nm i 652 nm za koproporfirin i na 617 nm i 680 nm za uroporfirin. Zaključak: Kada se emisije svih porfirina međusobno kombiniraju, trebali bi odgovarati spektralnim strukturama koje se mogu naći u stvarnim karijesnim lezijama.Objectives: This paper reports the preliminary results of the measurements of laser induced fluorescence in several porphyrin solutions. Coproporphyrin and uroporphyrin are common constituents of carious lesions. Their property to exhibit fluorescence when irradiated with a light of certain wavelength could be used as a means to detect carious lesions. Materials and methods: Absorption coefficient measurements of coproporphyrin I dihydrochloride and uroporphyrin I dihydrochloride solutions were performed under different pH conditions in order to identify spectral regions for effective laser excitation. Lasers with discrete wavelengths at 420 nm, 473 nm and 532 nm were used for the induction of the fluorescence. Results: At all laser wavelengths interesting fluorescence bands peaking at 591 nm, 619 nm and 652 nm for coproporphyrin and at 617 nm and 680 nm for uroporphyrin were observed. Conclusions: When combined together all bands should correspond to the spectral band structures found in real carious lesions