Electronic Absorption Spectra of Some 2-Thiouracil Derivatives

Abstract

The electronic absorption spectra of 2-thiouracil and some of its derivatives were investigated using polar and nonpolar solvents. The present analysis is facilitated via computer deconvolution of the observed spectra and molecular orbital (MO) computations. Comparison between the experimentally observed and theoretically computed spectra in addition to a quantitative assignment of all transitions observed were undertaken. The computed dipole moments are used to indicate the polarity of the excited state and hence predict its solvent dependence. The spectra are, in general, very well predicted and assigned using INDO/S computational results. The spectrum of the trifluoro derivative is much more complicated and the corresponding states show much more solvent dependence than those observed for other thiouracil studied.     

Empirical expression for hot wire with corrections for temperature drift

In using the empirical expression of King's law,E ² =E ₀ ² + BU, to correlate the data obtained from constant temperature hot wire in real low turbulence flow, the value of exponentn can assume widely differing values and is never a universal constant. Also corrections must be employed for varying ambient fluid temperature from the temperature at which calibration was carried out.This paper discuss the possibility of replacing King's law by another empirical expression,E ²=E ₀ ² + BU ^0.5 + CU, in which the exponentn will be fixed at a value 0.5 and the termCU is regarded as a correction factor for changing the exponentn in King's law as well as for the effect of ambient temperature drift.The advantages of using the new expression, beside incorporating the required corrections, are reflected on reducing the errors in local sensitivity resulted from using approximated exponent in King's law, and its validity for very low mean velocities.

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Empirische Formel für den Hitzdraht mit Korrekturen für Temperaturänderungen

Zusammenfassung Benützt man den empirischen Ausdruck des Kingschen Gesetzes,E ²=E ₀ ² + BU ⁿ , um die Meßwerte eines Konstanttemperatur-Hitzdrahtes bei sehr niedriger Turbulenz zu korrelieren, so kann der Wert des Exponentenn sehr unterschiedliche Werte annehmen und ist nie eine universelle Konstante. Es müssen auch Korrekturen angebracht werden, wenn die Fluid temperatur von der Temperatur abweicht, bei der der Hitzdraht geeicht wurde.Dieser Aufsatz diskutiert die Möglichkeit, das Kingsche Gesetz durch eine andere empirische Formel,E ²=E ₀ ² +BU ^0.5 +CU, zu ersetzen, in der der Exponentn zu 0,5 festgelegt wird und in der der AusdruckCU als Korrekturfaktor für den sich ändernden Exponentenn in dem Kingschen Gesetz und auch für den Einfluß abweichender Umgebungstemperatur betrachtet wird.Die Vorteile dieser neuen Formulierung mit den vorgeschlagenen Änderungen liegen in der Reduzierung von Fehlanalysen bei örtlich besserer Empfindlichkeit und in der Gültigkeit des Ansatzes auch für sehr niedrige Geschwindigkeiten.

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Nomenclature B slope of the best fit line which relatedE ² andU ^0.5 - C correction factor in equation (3) - C _l correction factor for temperature drift - C _E correction factor for same output voltage - C _s correction factor for same sensitivity - C error in correction factor - E output voltage of hot wire, volt - E _a output voltage atT _a , volt - E _c output voltage atT _c , volt - E ₀ extrapolated value whereU=zero, volt - r.m.s. for voltage fluctuations, volt - n exponent in King's law - n error in exponentn - Re Reynold's number - S local sensitivity=dE/dU - T _a fluid temperature,^°C - T _c fluid temperature during calibration,^°C - T _w hot wire temperature,^°C - T T _a -T _c ,^° CU mean velocity, m/s - r.m.s. for velocity fluctuation, m/s -      

1H/2H NMR studies of geometric H/D isotope effects on the coupled hydrogen bonds in porphycene derivatives

The 1H and 2H NMR spectra of porphycene (1), 2,3,6,7,12,13,16,17-octaethylporphycene (2), 2,7,12,17-tetra-n-propylporphycene (3), and 2,7,12,17-tetra-(tert-butyl)-3,6-13,16-dibenzo[cde;mno]porphycene (4) partially deuterated in the mobile proton sites are reported. These compounds exhibit two intramolecular NHN hydrogen bonds of increasing strength representing models of the concerted HH transfer in the parent compound, porphycene. The 1H chemical shifts of the mobile protons are correlated with the difference of the energies of the amino- and imino-N1s orbitals reported by Ghosh A.; Moulder J.; Br?ring M.; Vogel E. Angew. Chem., Int. Ed. 2001, 113, 445-448. The chemical shifts of 4 indicate a reduced contribution of the aromatic ring current as compared to the other compounds which is associated to the nonplanarity of this molecule. The primary H/D isotope effects on the chemical shifts give information about the primary, secondary, and vicinal geometric isotope effects of the two inner hydrogen bonds of porphycenes. The vicinal effects indicate a cooperative coupling of the two hydrogen bonds which may favor a concerted double proton-transfer mechanism.     

A mechanism for the addition of ethylene to nickel bis‐dithiolene

Density functional theory calculations predict a new lower energy route for the formation of the desired interligand addition product from the reaction between ethylene and nickel bis(dithiolene). The new route involves the initial binding of ethylene along the nickel–sulfur bond. The barrier heights for adding ethylene along this bond for the neutral and anionic nickel complexes are compared to each other as well as to a previously published previous mechanism. Selected structural parameters of the studied species have been analyzed to highlight the structural change on specific reactions. It was found that the ethylene/nickel bis‐dithiolene reaction occurs preferably via the nickel–sulfur bond of the neutral species, forming a complex which then rearranges to a desired interligand adduct via a low barrier. © 2012 Wiley Periodicals, Inc.     

Optical resolution of oriented enantiomers via photodissociation: quantum model simulations for H2POSD

We demonstrate quantum mechanically how to resolve enantiomers from an oriented racemic mixture taking advantage of photodissociation. Our approach employs a femtosecond ultraviolet (UV) laser pulse with specific linear polarization achieving selective photodissociation of one enantiomer from a mixture of L and R enantiomers. As a result, the selected enantiomer is destroyed in the electronically excited state while the opposite enantiomer is left intact in the ground state. As an example we use H2POSD which presents axial chirality. A UV pulse excites the lowest singlet excited state which has nsigma* character and is, therefore, strongly repulsive along the P-S bond. The model simulations are performed using wavepackets which propagate on two dimensional potential energy surfaces, calculated along the chirality and dissociation reaction coordinates using the CASSCF level of theory.     

125I-labelling and pharmacokinetics of protease

Protease, an enzyme obtained fromPseudomanas aeruginosa, was radioiodinated using chloramine T method of (¹²⁵I) iodide oxidation. The labelled product was purified using Sephadex G-50. The radiochemical yield reached 26.36% with a product specific activity 6.25 μCi/mg. Blood level curves, following intravenous injection of the labelled protease into mice, showed a biphasic blood level with a rapid initial declining phase; the characteristic of two-compartment open model. The rate constants K₂₁, K₁₂, and K₁₀ were 0.05044, 0.006236, and 0.008264 min⁻¹ respectively indicating a sharp decline in the serum concentration of the toxin, with a t1/2 of 83.85 min. The organ uptake of radioactivity follows the sequence liver>kidneys>lungs>heart>spleen>thyroid. A correlation between uptake and the incidence of tissue-hemorrhage is discussed.     

A DFT study of the complexation behavior of hemispherands toward alkali metal cations

A density functional theory study of the behavior of hemispherands toward alkali metal ions (Li⁺, Na⁺, and K⁺) is performed. The effect of the replacement of the rigid anisyl group(s) by the mobile ether group(s) on the binding energy of hemispherands with alkali metal ions is investigated. The results indicated that the binding energies are inversely proportional to the ionic radius of the cations. Moreover, increasing the flexibility of the ligand results in decreasing the binding toward small ions. The structures of the hosts and the guests are correlated to the binding energies, and the correlations are interpreted in terms of the principle of preorganization. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Experimental evaluation of pneumatic atomizers by hot film

The spray characteristics of pneumatic atomizers are examined using hot film anemometry. Measurements of drop size distribution, concentration profile and drop frequency are carried out over wide ranges of relative position between air peripheral jet exit and the concentric water nozzle exit. The objective is to clarify the role of turbulence in producing a wide spectrum of particle sizes and numbers in the spray. The output signal from hot film contained multispikes with different amplitudes and thickness which has been correlated to the drop number density and the droplet size through the use of probability density function. Generally it is found that an increase of the guide relative position enhances the mixing process and produces finer spray. This is attributed to the utilization of high wave number eddies in shortening the liquid jet break up length.

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Versuchsauswertung eines pneumatischen Pulverisators durch einen Heißfilm

Zusammenfassung Die Spraykennzeichen eines pneumatischen Pulverisators sind mit der Heißfilmanemometrie untersucht worden. Es wurden Messungen über die Tropfengrößenverteilung, Konzentrationsprofile und Tropffrequenz über weite Bereiche der relativen Position von äußerem Luftstromausgang und dem konzentrischen Wasserdüsenausgang durchgeführt. Das Ziel ist die Funktionsklärung der Turbulenzen in der Produktion von einem weiten Spektrum der Teilchengrößen und Teilchenzahlen im Spray. Das Ausgangssignal vom Heißfilm beinhaltet mehrere Impulsspitzen mit verschiedenen Amplituden und Breiten. Diese wurden für die Tropfenzahldichte und Tröpfchengröße mit der Wahrscheinlichkeitsdichte-Funktion berechnet. Im allgemeinen wurde herausgefunden, daß ein Erhöhen der relativen Position des Führungsrohres den Mischprozeß verbessert und einen feineren Spray ergibt. Dies ist darauf zurückzuführen, daß hochfrequente Wirbel die Abbruchlänge des Flüssigkeitsstroms verkürzen.

     

Antimycobacterial activity of ferutinin alone and in combination with antitubercular drugs against a rapidly growing surrogate of Mycobacterium tuberculosis

The aim of this study was to investigate the antimycobacterial activity of the major daucane constituent, ferutinin (jaeschkeandiol p-hydroxybenzoate, 1), four of its natural analogues, its hydrolysis products, as well as methyl p-hydroxybenzoate (methylparaben) against Mycobacterium smegmatis, a rapidly growing surrogate of Mycobacterium tuberculosis. The agar dilution assay was utilised for an antimycobacterial evaluation of single compounds. A modified agar dilution assay, the checkerboard method, was utilised for evaluating the potentiating effect of 1 on different antitubercular drugs, namely isoniazid, ethionamide, rifampin and streptomycin. In the agar dilution assay, 1 exhibited higher potency (minimum inhibitory concentration [MIC] 10?μg?mL?1) than streptomycin and rifampin (MIC 20?μg?mL?1 for each). Of the natural analogues, 8,9-epoxyjaeschkeandiol p-hydroxybenzoate and 8,9-epoxyjaeschkeandiol benzoate exhibited marginal activity (MIC?≥?40 and 80?μg?mL?1, respectively). The checkerboard method showed that the combination of 1 with each antitubercular drug led to mutual enhancement of the antimycobacterial activity with isoniazid and ethionamide, while no such effect was observed with rifampin or streptomycin. Based on this study and earlier studies with Staphylococcus aureus, the major constituent 1 may be responsible for the major part of the antimicrobial activity of the root of Ferula hermonis.