Unexpected dipivaloyl­ation of 9‐li­thia­ted fluorene: formation of 1‐(fluoren‐9‐yl­idene)‐2,2‐di­methyl­propyl pivalate

Treatment of 9‐li­thia­ted fluorene with pivaloyl chloride provided ap‐9‐pivaloyl­fluorene, (1), the major product, and a minor product ultimately identified as the title compound, C₂₃H₂₆O₂, (2). The latter was also formed directly, but slowly, from 9‐li­thia­ted‐(1) treated with pivaloyl chloride. Although (1) exists exclusively as its less sterically restricted ap rotamer, its sp²‐hybridized anion sterically impedes reaction at the 9‐position from either face. While 9‐li­thia­ted‐(1) is exclusively, but slowly, 9‐methyl­ated with methyl iodide, reaction with pivaloyl chloride, also slow, leads only to the O‐acyl­ated product, (2). The protons of the tert‐butyl‐C=C moiety approach a proton on the fluorene ring to well within the sum of their van der Waals radii, resulting in significant molecular compression, strain and distortion. For example, distortion in the moiety C=C(O)(C) is exhibited by the enlargement of C=C—C angle to 130.6 (2)° at the expense of the corresponding `equivalent' C=C—O angle, which is compressed to 116.46 (19)°.     

sp‐9‐Acetyl­fluorene,the initial acetyl­ation product of 9‐fluorenyl­lithium

The reaction of 9‐fluorenyl­lithium with acetyl chloride (tetra­hydro­furan, 213 K, under argon) provided four products which we have isolated and whose structures we have unequivocally identified for the first time. That of the initially formed component, 9‐acetyl­fluorene (C₁₅H₁₂O), described here, shows it to be exclusively the sp rotamer in its crystalline form. The acetyl C—C=O plane is essentially perpendicular to the planar fluorene ring and there is no indication of rotational restriction. In contrast, related 9‐pivaloyl­fluorene, which we reported previously, is rotationally restricted and exists exclusively as its ap rotamer, in which the pivaloyl C—C=O plane is also almost perpendicular to the fluorene ring.     

Thermal and hydraulic performance of a three-phase fluidized bed cooling tower

An experimental study was made of the thermal and hydraulic characteristics of a three-phase fluidized bed cooling tower. The experiments were carried out in a packed tower of 200 mm diameter and 2.5 m height. The packing used was spongy rubber balls 12.7 mm in diameter and with a density of 375 kg/m³. The tower characteristic was evaluated. The air-side pressure drop and the minimum fluidization velocity were measured as a function of water/air mass flux ratio (0.4–2), static bed height (300–500 mm), and hot water inlet temperature (301–334 K).

The experimental results indicate that the tower characteristics KaV/L increases with increases in the bed static height and hot water inlet temperature and with decreases in the water/air mass flux ratio. It is also shown that the air-side pressure drop increases very slowly with increases in air velocity. The minimum, fluidization velocity was found to be independent of the static bed height.

The data obtained were used to develop a correlation between the tower characteristics, hot water inlet temperature, static bed height, and the water/air mass flux ratio. The mass transfer coefficient of the three-phase fluidized bed cooling tower is much higher than that of packed-bed cooling towers with higher packing height.     

Molecular recognition of nucleobases and amino acids by sulphonato-calixnaphthalene-capped silver nanoparticles

The plasmon resonances of sulphonato-calixnaphthalene-capped silver nanoparticles have been used to study the complexation of the nanoparticles with nucleobases and amino acids. Only in the case of the nanoparticles capped with oxacalix[4]naphthalenesultone, does complexation of both nucleobases and certain amino acids occur. The complexation of the aromatic amino acids, phenylalanine and tryptophan, has previously not been observed for calixarene-capped silver nanoparticles.     

Linked Metal-cluster Systems: Isolation and Characterisation of {anti-[(p-cymene)RuCl]-μ-[κ2-P,P′;κ1-P′′-(PPh2CH2)3CMe]-[AuPt3(CO)3(PCy3)3]}(PF6)2

The new mixed-metal complex {anti-[(p-cymene)RuCl]-μ-[κ ²-P,P′;κ ¹-P′′-(PPh₂CH₂)₃CMe]-[AuCl]}PF₆ and its cluster derivative {anti-[(p-cymene)RuCl]-μ-[κ ²-P,P′;κ ¹-P′′-(PPh₂CH₂)₃CMe]-[AuPt₃(CO)₃(PCy₃)₃]}(PF₆)₂ have been prepared and characterized. Notably, NMR spectroscopy and high resolution FT-ICR mass spectrometry, including a tandem mass spectrometric analysis, demonstrated the formation of these compounds that was also confirmed by single crystal X-ray diffraction analysis.     

High resolution mass spectrometry for studying the interactions of cisplatin with oligonucleotides

Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been used to probe the interaction of the anticancer drug cisplatin with oligonucleotides. The binding kinetics, the nature of the adducts formed, and the location of the binding site within the specifically designed double-stranded DNA oligonucleotides, ds(GTATTGGCACGTA) and ds(GTACCGGTGTGTA), were determined by recording mass spectra over time and/or employing tandem mass spectrometry (MS/MS). The FT-ICR MS studies show that binding to DNA takes place via a [Pt(NH 3) 2Cl] (+) intermediate prior to formation of bifunctional [Pt(NH 3) 2] (2+) adducts. Tandem MS reveals that the major binding sites correspond to GG and GTG, the known preferred binding sites for cisplatin, and demonstrates the preference for binding to guanosine within the oligonucleotide. The obtained results are discussed and compared to published data obtained by other mass spectrometric techniques, NMR spectroscopy and X-ray crystallography.     

Proteomic Analysis of the Protein Expression Profile in the Mature <Emphasis Type="Italic">Nigella sativa</Emphasis> (Black Seed)

Nigella sativa (N. sativa) seed has been used as an important nutritional flavoring agent and in traditional medicine for treating many illnesses since ancient times. Understanding the proteomic component of the seed may lead to enhance the understanding of its structural and biological functional complexity. In this study, we have analyzed its proteome profile based on gel-based proteome mapping technique that includes one-dimensional gel electrophoresis followed by liquid chromatography and tandem mass spectrometry strategy. We have not come across any such studies that have been performed in N. sativa seeds up to date. A total of 277 proteins were identified, and their functional, metabolic, and location-wise annotations were carried out using the UniProt database. The majority of proteins identified in the proteome dataset based on their function were those involved in enzyme catalytic activity, nucleotide binding, and protein binding while the major cellular processes included regulation of biological process followed by regulation of secondary biological process, cell organization and biogenesis, protein metabolism, and transport. The identified proteome was localized mainly to the nucleus then to the cytoplasm, plasma membrane, mitochondria, plastid, and others. A majority of the proteins were involved in biochemical pathways involving carbohydrate metabolism, amino acid and shikimate pathway, lipid metabolism, nucleotide, cell organization and biogenesis, transport, and defense processes. The identified proteins in the dataset help to improve our understanding of the pathways involved in N. sativa seed metabolism and its biochemical features and detail out useful information that may help to utilize these proteins. This study could thus pave a way for future further high-throughput studies using a more targeted proteomic approach.     

Determination of glucose using a coupled-enzymatic reaction with new fluoride selective optical sensing polymeric film coated in microtiter plate wells

The determination of glucose in beverages is demonstrated using newly developed fluoride selective optical sensing polymeric film that contains aluminum (III) octaethylporphyrin (Al[OEP]) ionophore and the chromoionophore ETH7075 cast at the bottom of wells of a 96-well polypropylene microtiter plate. The method uses a dual enzymatic reaction involving glucose oxidase enzyme (GOD) and horseradish peroxidase (HRP), along with an organofluoro-substrate (4-fluorophenol) as the source of fluoride ions. The concentration of fluoride ions after enzymatic reaction is directly proportional to the glucose level in the sample. The method has a detection limit of 0.8 mmol L⁻¹, a linear range of 0.9-40 mmol L⁻¹ and a sensitivity of 0.125 absorbance/decade of glucose concentration. Glucose levels in several beverage samples determined using the proposed method correlate well with a reference spectrophotometric enzyme method based on detection of hydrogen peroxide using bromopyrogallol red dye (BPR). The new method can also be used to determine H₂O₂ concentrations in the 0.1-50 mmol L⁻¹ range using a single enzymatic reaction involving H₂O₂ oxidation of 4-fluorophenol catalyzed by HRP. The methodology could potentially be used to detect a wide range of substrates for which selective oxidase enzymes exist (to generate H₂O₂), with the high throughput of simple microtiter plate detection scheme.     

A novel potentiometric biosensor for selective L-cysteine determination using L-cysteine-desulfhydrase producing Trichosporon jirovecii yeast cells coupled with sulfide electrode

Trichosporon jirovecii yeast cells are used for the first time as a source of l-cysteine desulfhydrase enzyme (EC 4.4.1.1) and incorporated in a biosensor for determining l-cysteine. The cells are grown under cadmium stress conditions to increase the expression level of the enzyme. The intact cells are immobilized on the membrane of a solid-state Ag₂S electrode to provide a simple l-cysteine responsive biosensor. Upon immersion of the sensor in l-cysteine containing solutions, l-cysteine undergoes enzymatic hydrolysis into pyruvate, ammonia and sulfide ion. The rate of sulfide ion formation is potentiometrically measured as a function of l-cysteine concentration. Under optimized conditions (phosphate buffer pH 7, temperature 37 ± 1 °C and actual weight of immobilized yeast cells 100 mg), a linear relationship between l-cysteine concentration and the initial rate of sulfide liberation (dE/dt) is obtained. The sensor response covers the concentration range of 0.2-150 mg L⁻¹ (1.7-1250 μmol L⁻¹) l-cysteine. Validation of the assay method according to the quality control/quality assurance standards (precision, accuracy, between-day variability, within-day reproducibility, range of measurements and lower limit of detection) reveals remarkable performance characteristics of the proposed biosensor. The sensor is satisfactorily utilized for determination of l-cysteine in some pharmaceutical formulations. The lower limit of detection is ∼1 μmol L⁻¹ and the accuracy and precision of the method are 97.5% and ±1.1%, respectively. Structurally similar sulfur containing compounds such as glutathione, cystine, methionine, and d-cysteine do no interfere.     

Spectrophotometric and spectrofluorimetric methods for the determination of tranexamic acid in pharmaceutical formulation

Two simple and sensitive spectrophotometric and fluorimetric methods for the determination of tranexamic acid in tablets are developed. The methods are based on condensation the primary amino group of tranexamic acid with acetyl acetone and formaldehyde producing a yellow coloured product, which is measured spectrophotometrically at 335 nm or fluorimetrically at 480 nm the colour was stable for at least 1 h. Beer's law was valid within a concentration rang of 0.05-2.0 microg ml-1 spectrophotometrically and 0.05-0.25 microg ml-1 fluorimetrically. All the variables were studied to optimize the reaction conditions. No interference was observed in the presence of common pharmaceutical excipints. The validity of both methods was tested by analyzing tranexamic acid in its pharmaceutical preparations. Good recoveries were obtained and the results were comparable with those obtained by standard method.