A study of mass transfer kinetics of alanyl-alanine on a chiral crown ether stationary phase

The mass transfer kinetics of alanyl-alanine enantiomers in a column packed with a chiral stationary phase (CSP) ChiroSil RCA(+) was studied by means of the moment method. Methanol-water solutions acidified with sulphuric acid were used as the mobile phase. It was shown that the spreading of peaks in the column was strongly affected by abnormal eddy diffusion. This effect was well described within the framework of the Giddings coupling theory. The comprehensive four-term Giddings equation for eddy diffusion was applied, considering simultaneous contribution of the trans-column, trans-channel, short-range inter-channel, and long-range inter-channel dispersion factors. Through these calculations, a predominant importance of the trans-column flow velocity bias was revealed. Besides eddy diffusion, the adsorption kinetic resistance to mass transfer plays a noticeable role in band broadening, all the other contributions (from longitudinal molecular diffusion, external and intraparticle mass transfer) being of minor significance. A relative importance of the mass transfer kinetics increases correlatively with a growth of the retention factor. Both the retention and kinetics of the adsorption of alanyl-alanine on the CSP in study are enantioselective. The influence of the column pressure on retention as well as corrections required because of this influence are also discussed.     

Using the 19F NMR chemical shift anisotropy tensor to differentiate between the zigzag and chiral forms of fluorinated single-walled carbon nanotubes

The structural characterization of different kinds of zigzag and chiral single-walled carbon nanotubes (SWNTs) has been investigated theoretically using (19)F NMR spectroscopy. The chemical shift anisotropy (CSA) tensor is computed at different levels of theory for the (19)F nuclei in different forms of functionalized fluorinated carbon nanotubes (CNT). A set of fluorine CSA parameters comprising the span, skew, and isotropic chemical shift is computed for each form of the fluoronanotubes and multidimensional CSA parameter correlation maps are constructed. We show that these correlations are able to clearly distinguish between the chiral and zigzag forms of fluorinated carbon nanotubes (F-SWNTs). Implications for solid-state and liquid-state NMR experiments are discussed.     

The synthesis of silica-supported chiral BINOL: Application in Ti-catalyzed asymmetric addition of diethylzinc to aldehydes

Chiral BINOL was covalently anchored on two different pore sized mesoporous silica (SBA-15 (7.5 nm) and MCF (14 nm)). These heterogenized ligands were used in Ti-catalyzed asymmetric addition of diethylzinc to aldehydes. High catalytic activity with excellent enantioselectivity (up to 94% ee) for secondary alcohols was achieved using MCF supported chiral BINOL under heterogeneous reaction conditions. Good to excellent enantioselectivity (ee, 68–91%) was also achieved with various small to bulkier aldehydes. The MCF supported catalyst was reused in multiple catalytic runs without loss of enantioselectivity.     

Polyaniline based nucleic acid sensor

Twenty-bases long NH2-modified DNA and PNA probes specific to a pathogen (Mycobacterium tuberculosis) were covalently immobilized onto a polyaniline (PANI)/Au electrode to detect nucleic acid hybridization with complementary, one-base mismatch and noncomplementary targets within 30 s using Methylene Blue. The PNA-PANI/Au electrode exhibits improved specificity (1000 times) and detection limit (0.125 x 10(-18) M) as compared to that of the DNA-PANI/Au electrode (2.5 x 10(-18) M). These PNA-PANI/Au electrodes can be utilized for detection of hybridization with the complementary sequence in 5 min sonicated M. tuberculosis genomic DNA within 1 min of hybridization time. These DNA-PANI/Au and PNA-PANI/Au electrodes can be used 6-7 and 13-15 times, respectively.     

Metal-Free Arylation of Benzothiophenes at C4 by Activation as their Benzothiophene S-Oxides

Benzothiophenes, activated by oxidation to the corresponding S-oxides, undergo C−H/C−H-type coupling with phenols to give C4 arylation products. While an electron-withdrawing group at C3 of the benzothiophene is important, the process operates without a directing group and a metal catalyst, thus rendering it compatible with sensitive functionalities—e.g. halides and formyl groups. Quantum chemical calculations suggest a formal stepwise mechanism involving heterolytic cleavage of an aryloxysulfur species to give a π-complex of the corresponding benzothiophene and a phenoxonium cation. Subsequent addition of the phenoxonium cation to the C4 position of the benzothiophene is favored over the addition to C3; Fukui functions predict that the major regioisomer is formed at the more electron-rich position between C3 and C4. Varied selective manipulation of the benzothiophene products showcase the synthetic utility of the metal-free arylation process.     

Nucleic acid sensor for M. tuberculosis detection based on surface plasmon resonance

Cysteine modified NH(2)-end peptide nucleic acid (PNA) (24-mer) probe and 5'-thiol end labeled deoxyribonucleic acid (DNA) probes specific to Mycobacterium tuberculosis have been immobilized onto BK-7 gold coated glass plates for the detection of complementary, one-base mismatch, non-complementary targets and complementary target sequence in genomic DNA of Mycobacterium tuberculosis using a surface plasmon resonance (SPR) technique. The DNA/Au and PNA/Au bio-electrodes have been characterized using contact angle, atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetric (CV) techniques, respectively. It is revealed that there is a 252 millidegrees SPR angle change in the case of PNA immobilization and 205 millidegrees for DNA immobilization, indicating increased amount of immobilized PNA molecules. Hybridization studies reveal that there is no binding of the non-complementary target to DNA/Au and PNA/Au electrode. Compared to the DNA/Au bioelectrode, PNA/Au electrode has been found to be more efficient for detection of one-base mismatch sequence. The PNA/Au bioelectrode shows better detection limit (1.0 ng ml(-1)) over the DNA-Au bioelectrode (3.0 ng ml(-1)). The values of the association (k(a)) and dissociation rate constant (k(d)) for the complementary sequence in case of the PNA/Au bioelectrode have been estimated as 8.5 x 10(4) m(-1) s(-1) and 3.6 x 10(-3) s(-1), respectively.     

l-Ascorbic acid in organic synthesis: a facile synthesis of 4-(butenolide-5-methylidenyl)-1,4-dihydropyridines

An efficient synthesis of 4-(butenolide-5-methylidenyl)-1,4-dihydropyridines has been achieved via a three-component reaction of β-keto esters or ketones, ammonium acetate and vinylic aldehydes from ascorbic acid in the presence of tetrabutylammonium hydrogen sulfate in ethylene glycol.     

Ansa-bridged eta5-cyclopentadienyl molybdenum and tungsten complexes: synthesis, structure and application in olefin epoxidation

Ansa-bridged eta(5)-cyclopentadienyl molybdenum and tungsten tricarbonyl complexes of formula [M(eta(5)-C(5)H(4)(CH(2))(3)-eta(1)-CH(2))(CO)(3)] (M=Mo or W) were synthesized and the X-ray crystal structure of the tungsten complex is reported. In the epoxidation of cyclooctene the molybdenum compound shows a high catalytic activity, approaching the observed activities for the most reactive unbridged complexes of composition CpMo(CO)(3)X (X=Cl, CH(3)). The activity of the tungsten complex is also amongst the highest catalytic activities for the olefinic epoxidation of complexes with the composition CpW(CO)(3)X and WO(2)X(2)L(2), reported so far. The low ring strain of the ansa-bridged system improves the stability of the complexes under oxidative conditions considerably in comparison to derivatives with a shorter bridge and therefore paves the way to introduction of chirality in these systems.     

Extraction,Isolation and Characterization of Bioactive Compounds from Artemisia and Their Biological Significance: A Review

Diverse medicinal plants such as those from the genus Artemisia have been employed globally for centuries by individuals belonging to different cultures. Universally, Artemisia species have been used to remedy various maladies that range from simple fevers to malaria. A survey conducted by the World Health Organization (WHO) demonstrated that 80% of the global population is highly reliant on herbal medicine for their primary healthcare. WHO recommends artemisinin-based combination therapies (ACT) for the treatment of global diseases such as malaria. Artemisinin is a bioactive compound derived from Artemisia annua leaves. It is a sesquiterpene endoperoxide with potent antimalarial properties. This review strives to instill natural products to chemists and others in diverse fields with a heterogeneous set of knowledge compiled from multifaceted researchers and organizations in literature. In particular, the various Artemisia species and effective extraction, isolation, and characterization methodologies are discussed in detail. An in-depth investigation into the literature reveals that divergent species of Artemisia exhibit a vast array of biological activities such as antimalarial, antitumor, and anti-inflammatory activities. There is substantial potential for bioactive compounds from Artemisia to provide significant relief from differing human ailments, but more meticulous research in this field is needed.     

Quantitative determination of macroelement and microelement content of fresh and processed bamboo shoots by wavelength dispersive X-ray fluorescence spectrometry

Bamboo shoots are considered as healthy and nutritional food as they supply proteins, dietary fiber, phenols, phytosterols, vitamins, and minerals in considerable quantities and capture a novel place in the spectrum of plant foods. Besides nutrients and bioactive compounds, shoots also contain antinutrient (cyanogen) that needs to be removed by adequate processing prior to consumption. This study was undertaken to investigate the effects of fermentation, brine preservation, and boiling on levels of mineral elements in shoots of Dendrocalamus hamiltonii using wavelength dispersive X-ray fluorescence (WD-XRF) spectrometry. WD-XRF spectrometry is a method that causes the least destruction to the raw plant material as no harsh chemicals are used and gives the most accurate results. Fermentation process resulted in significant increase in the levels of Rb (9%), S (11%), Mg (12%), Zn (46%), Ca (56%), and Fe (87%); however, Na (18.79 g/100 g, dry weight), Cl (24.73 g/100 g, dry weight), and Br (20.0 mg/100 g, dry weight) content increased drastically after brine preservation. Boiling increased the levels of Fe by 139% but did not affect the Rb (20.0 mg/100 g, dry weight) and Zn content (10.2 mg/100 g, dry weight) of the shoots. In general, fermentation, which led to the lowest loss of mineral elements, appears the best method in enhancement and retention of the mineral content in bamboo shoots and holds the prospect at industrial and society levels.