Structural and fluorescence quenching characterization of hematite nanoparticles

Nanoparticles of the dominant hematite form (α-Fe(2)O(3)) of iron oxide have been prepared by a simple route of dropping FeCl(3) solution into boiling water. The nanoparticles have been characterized by transmission electron microscopy (TEM), UV-visible electronic absorption spectroscopy, chemical stoichiometry, thermal analysis methods (TGA, DSC and DTA), XRD, FTIR and magnetic susceptibility measurements. Kinetic analysis of the DSC calorigram of thermal dehydration of the nanoparticles reveals one stage of the dehydration process of energy of activation of 29.0 kJ mol(-1). The role of iron oxide nanoparticles in fluorescence quenching of coumarin thiourea derivatives (I-IV) was investigated at room temperature (296 K) by means of steady-state fluorescence spectroscopy. The quenching process was characterized by Stern-Volmer (S-V) plots which display a positive deviation from linearity. This could be explained by static and dynamic quenching models. The positive deviation in the S-V plot is interpreted in terms of ground-state complex formation model and sphere of action static quenching model. Various rate parameters for the ?uorescence quenching process were determined by using the modi?ed Stern-Volmer equation. The sphere of action static quenching model agrees very well with experimental results. Quenching constants for iron oxide nanoparticles are about four orders of magnitudes higher than quenching by Fe(3+) ions.     

Effective widths of boson gas confined in a harmonic rotating trap

In this Letter, we evaluate the radial and axial square radii (effective widths) of a rapidly rotating boson gas. The corresponding effective area and the expansion energy are calculated from these effective widths. A modified semiclassical approximation is suggested. This approach provides significant corrections to these quantities, such as finite size effect and indirectly interaction effect. We show that the effective widths still follow a non-rotating temperature dependence. Rotation leads to expansion or shrinking the effective widths through the change of the harmonic frequencies of the confinement trap.     

Synthesis of Ethyl Methyl Ether Over Solid Acid Catalysts

The alkylation of methanol by triethylamine to form ethyl methyl ether was studied in the temperature range 310-330°C using γ-alumina and silica-aluminas differing in their silica content. The effect of treating γ-alumina with hydrochloric and boric acid on the reaction rate was also investigated. The results obtained for ether formation over γ-alumina show that the reaction is first order for methanol and zero orde for triethylamine. Alumina-H₃BO₃ was found to be the most active catalyst whereas alumina-HCl is the least active towards ether formation. The activity of silica-alumina is proportional to its silica contents.     

PHOTOCHEMICAL BEHAVIOR AND EMISSION CHARACTERISTICS OF 9-VINYLANTHRACENE

9-Vinylanthracene (9-VA) is an efficient fluorescer of fluorescence quantum yield = 0.91 0.03 in methanol (_ex= 365 nm). This is consistent with its low photochemical quantum yields _c (_cx= 365 nm) of 0.005 in the absence of azobisisobutyronitrile (AIBN) radical initiator and _c= 0.02 in the presence of 10^-2 M dm^-3 AIBN. 9-Vinylanthracene was shown to behave as a 9-substituted anthracene undergoing photodimerization rather than the typical vinyl aryl monomer photopolymerization. The photodimer formation is supported by spectroscopic techniques. 9-Vinylanthracene undergoes efficient fluorescence quenching in the presence of AIBN. Stern-Volmer plots indicate a collisional mechanism. 9-Vinylanthracene crystals as well as polycrystalline films give excimeric emission (_max= 510 nm, _cx= 380 nm) which is considerably red shifted ( ca. 100 nm) compared with molecular emission.     

Spectroscopic Behavior and Photophysical Parameters of 2-(Acetoxymethyl)-6-(1,2,4-triazinylaminodihydroquinazolinyl)tetrahydropyran Derivative in Different Solid Hosts

Journal of Fluorescence - Optical and photophysical properties of 6-substituted-1,2,4-Triazine fluorescent derivative dye doped in silicate based sol–gel, homopolymer of methyl methacrylate...     

Simultaneous determination of aliskiren hemifumarate,amlodipine besylate,and hydrochlorothiazide in their triple mixture dosage form by capillary zone electrophoresis

A novel, specific, reliable, and accurate capillary zone electrophoretic method was developed and validated for the simultaneous determination of aliskiren hemifumarate, amlodipine besylate, and hydrochlorothiazide in their triple mixture dosage form. Separation was carried out in a fused‐silica capillary (57.0 cm total length and 50.0 cm effective length, 75.6 μm internal diameter) by applying a potential of 17 kV and a running buffer consisting of 40 mM phosphate buffer at pH 6.0 with UV detection at 245 nm. The method was suitably validated with respect to specificity, linearity, LOD, and LOQ, accuracy, precision, and robustness. The method showed good linearity in the ranges 1–10, 2.5–25, and 30–300 μg/mL with LODs of 0.11, 0.33, and 5.83 μg/mL for amlodipine besylate, hydrochlorothiazide, and aliskiren hemifumarate, respectively. The proposed method was successfully applied for the analysis of the studied drugs in their coformulated tablets. The results of the proposed method were statistically compared with those obtained by the RP‐HPLC reference method revealing no significant differences in the performance of the methods regarding accuracy and precision.     

Synchronized separation of seven medications representing most commonly prescribed antihypertensive classes by using reversed‐phase liquid chromatography: Application for analysis in their combined formulations

A reversed‐phase high‐performance liquid chromatography method was developed for the simultaneous determination of the diuretic, hydrochlorothiazide, along with six drugs representing the most commonly prescribed antihypertensive pharmacological classes such as atenolol, a selective β₁ blocker, amlodipine besylate, a calcium channel blocker, moexipril hydrochloride, an angiotensin‐converting‐enzyme inhibitor, valsartan and candesartan cilexetil, which are angiotensin II receptor blockers, and aliskiren hemifumarate, a renin inhibitor, using irbesartan as an internal standard. The chromatographic separation was achieved using acetonitrile/sodium phosphate dibasic buffer (0.02 M, pH 5.5) at a flow rate of 1 mL/min in gradient elution mode at ambient temperature on a stationary phase composed of an Eclipse XDB‐C₁₈ (4.6 × 150 mm, 5 μm) column. UV detection was carried out at 220 nm. The method was validated according to ICH guidelines. Linearity, accuracy, and precision were satisfactory over the concentration ranges of 2–40 μg/mL for hydrochlorothiazide and candesartan cilexetil, 20–120, 10–160, 5–40, 20–250, and 5–50 μg/mL for atenolol, valsartan, moexipril hydrochloride, aliskiren hemifumarate, and amlodipine besylate, respectively. The method was successfully applied for the determination of each of the studied drugs in their combined formulations with hydrochlorothiazide. The developed method is suitable for the quality control and routine analysis of the cited drugs in their pharmaceutical dosage forms.     

Atomic additivity of the correlation energy in molecules—an ab initio MP4 and G3 study

It is shown that the closed shell valence electron molecular correlation energy of organic molecules in their ground states is a homogeneous multilinear function of the numbers of neutral atoms in their canonical hybridization state. The additivity is a robust feature, which holds for MP2(fc), MP3(fc) and MP4(fc) model calculations. The latter results obtained on a test set of 91 widely different organic molecules, exhibiting a whole gamut of electronic structure patterns, are excellent as evidenced by the absolute average deviation from the additivity values (AAD) of only 1.4 kcal mol^?1 and R ² = 0.999 93. The maximum absolute deviation (MAD) is 5.3 kcal mol^?1. The additivity formula for the total molecular electron correlation retrieved from G3 calculations also has an excellent performance (AAD = 1.2 kcal mol^?1, R ² = 0.999 98 and MAD = 7.2 kcal mol^?1). If it is taken into account that the additivity formulae require only back of the envelope calculations, these results are remarkable indeed, in particular since the G3 correlation energies span a very large range from 180.7 (methane) to 1642.8 (hexafluorocyclopropane) kcal mol^?1. Comparison of the exact electron correlation energies in free atoms with the corresponding average correlation energies in molecules reveals that a substantial increase in the latter provides an important contribution in overcoming a very strong Coulomb repulsion between the nuclei. It is shown that the additivity formulae are useful in detecting some special molecular features such as strong resonance and anti-aromaticity.     

Thermochemistry of the reactions between CN+ and H2O in the gas phase

The [H₂, C, N, 0]⁺ potential energy surface (PES) has been explored by means of high-level ab initio calculations, carried out in the framework of the G2 theory. From this survey we concluded that the predominant products of the CN⁺ + H₂O reaction are the result of the dissociation of HNCOH⁺ species and to a much lesser extent of the CNHOH⁺ cation to yield CNH⁺ + OH. According to our results HCN⁺ should not be a product of this reaction because all pathways leading to its formation are unfavourable with regards to other competitive processes. Other reactive channels lead to the formation of the H₂ONC⁺ structure which dissociates into CN + H₂O⁺. The loss of NH(3σ) and O(³P) seems to take place following spin-forbidden reaction paths through an intersystem crossing between the singlet and the triplet PESs. The global minimum of the PES, H₂NCO⁺ is easily accessible and should lead to the loss of carbon monoxide which has not been experimentally observed in CN⁺ + H₂O reactions. We cannot offer a clear explanation for this disagreement between theory and experiment.