Structure, stability and spectral signatures of monoprotic carborane acid-water clusters (CBW(n), where n = 1-6)

The gas phase structure, stability, spectra, and proton transfer properties of monoprotic carborane acid-water clusters [CB(11)F(m)H(11-m)(OH(2))(1)]-(H(2)O)(n) (where m = 0, 5, and 10; n = 1-6) have been calculated using density functional theory (DFT) with the Becke's three-parameter hybrid exchange functional and Lee-Yang-Parr correlation functional (B3LYP) using 6-31+G* basis set. Results reveal that Eigen cation defects are found in CBW(n) (where n = 2-6) clusters and these clusters are significantly more stable than the non-Eigen geometry. In addition to the conventional hydrogen bond (H-bond) the role of dihydrogen bond (DHB) and halogen bond (XB) in the stabilization of these clusters can be observed from the molecular graphs derived from the atoms in molecules (AIM) analysis. Spectral information shows the features of Eigen cation and proton oscillation involved in the proton transfer process. The dissociation of proton from the perfluoro derivatives with two water molecules is more favorable when compared to the other derivatives.     

A new route to α-alkyl-α-fluoromethylenebisphosphonates

A new route to α-alkyl-α-fluoromethylenebisphosphonates, 2 has been developed starting from commercially available tetraethyl fluoromethylenebisphosphonate (1), and alkyl halides using either caesium carbonate in DMF or sodium dimsyl. De-esterification of 2 provided biologically important α-alkyl-α-fluoromethylenebisphosphonic acid, 3, while alkoxide-induced carbon-phosphorus bond cleavage of 2 gave α-fluorophosphonates, 4, which are useful synthons in organic synthesis.     

Reductive conjugate addition of haloalkanes to enones to form silyl enol ethers

A new method is presented for tandem reductive conjugate addition and silyl enol ether formation from cyclic and acyclic enones and enals in the presence of a Mn reductant, a Ni(terpyridine) catalyst, and a trialkylchlorosilane. The addition of secondary, tertiary, and hindered primary haloalkanes is demonstrated. Preliminary studies on the mechanism show that the intermediacy of L1(Ni)(η(3)-1-triethylsilyloxyalkenyl)X or in-situ-formed RMnX is unlikely.     

Two minor diterpene glycosides from the leaves of Stevia rebaudiana

Two new new diterpene glycosides, 13-[(2-O-(6-O-beta-D-glucopyranosyl)-beta-D-glucopyranosyl-beta-D-glucopyranosyl)oxy] kaur-16-en-18-oic acid beta-D-glucopyranosyl ester (1) and 13-[(2-O-beta-D-glucopyranosyl-3-O-beta-D-fructofuranosyl-beta-D-glucopyranosyl)oxy] kaur-16-en-18-oic acid beta-D-glucopyranosyl ester (2) were isolated from the leaves of Stevia rebaudiana, along with the known steviol glycosides stevioside, rebaudiosides A-F and dulcoside A. The structures of the two new compounds were established on the basis of extensive 2D NMR (COSY, HSQC, and HMBC), MS and chemical studies.     

Chemical diversity in Mentha spicata: antioxidant and potato sprout inhibition activity of its essential oils

The essential oils from fresh aerial parts of Mentha spicata L. collected from ten different natural habitats of Uttarakhand, India were analyzed by a combination of GC, GC/MS and NMR spectroscopy. The analysis revealed that monoterpenoids (46.1%-91.6%), mainly carvone (15.3%-68.5%), piperetenone oxide (24.0%-79.2%) and alpha-humulene (0.1%-29.9%), were the major constituents of the essential oils, but with significant qualitative and quantitative differences among the other constituents. Cluster analysis of the oil composition was carried out in order to discern the differences and similarities within different accessions collected from different natural habitats. The essential oils were also screened for their antioxidant activities by chelating properties of Fe2+, DPPH radical-scavenging activity, and their reducing power. The essential oils of two chemo variants (viz. carvone and piperetenone oxide types) were also tested for potato (Solanum tuberosum L.) sprout suppressant activity. The results showed that these oils exhibit good sprout inhibition activity in comparison to CIPC and iodine, the standard sprout suppressant.     

Interfacial propulsion by directional adhesion

The rough integument of water-walking arthropods is well-known to be responsible for their water-repellency [1], [2], [3] and [4]; however, water-repellent surfaces generally experience reduced traction at an air-water interface [5], [6], [7] and [8]. A conundrum then arises as to how such creatures generate significant propulsive forces while retaining their water-repellency. We here demonstrate through a series of experiments that they do so by virtue of the detailed form of their integument; specifically, their tilted, flexible hairs interact with the free surface to generate directionally anisotropic adhesive forces that facilitate locomotion. We thus provide new rationale for the fundamental topological difference in the roughness on plants and water-walking arthropods, and suggest new directions for the design and fabrication of unidirectional superhydrophobic surfaces.     

Conformational study of 9-dehydro-9-trifluoromethyl cinchona alkaloids via 19F NMR spectroscopy: emergence of trifluoromethyl moiety as a conformational stabilizer and a probe

The trifluoromethyl substituent has been incorporated into quinidine as a conformational stabilizer and a probe to provide straightforward insight into the conformational behavior of cinchona alkaloids. By significantly decreasing the rotation rate of the quinoline-carbinol bond, the relatively bulky CF(3) group enables the NMR signals of the syn and anti conformers to be differentiated at room temperature. In addition to the stabilizing effect, the introduction of the fluorinated moiety also facilitates the application of (19)F NMR spectroscopy, thereby allowing conformational studies under various conditions without the use of deuterated solvents.     

A fully automated iterative moving averaging (AIMA) technique for baseline correction

Baseline correction is one of the pre-processing steps in the analysis of metabolite signals from chemometric analytical instruments. Fully automated baseline correction techniques, although more convenient to use, tend to be less accurate than semi-automated baseline correction. A fully automated baseline correction algorithm, the automated iterative moving averaging algorithm (AIMA), is presented and compared with three recently introduced semi-automated algorithms, namely the adaptive iteratively reweighted penalized least squares (airPLS), Asymmetric Least Squares baseline correction (ALS) and a parametric method, using NMR, Raman and HPLC chromatograms. AIMA's potential in increasing the accuracy of multivariate analysis via SELTI-TOF and LCMS chromatograms was also assessed. The results show that the AIMA's accuracy is comparable to these semi-automated algorithms and has the advantage of ease of use. An AIMA plug-in for an open source metabolomics analysis tool, MZmine, was also developed. The AIMA plug-in is available at http://padel.nus.edu.sg/software/padelaima.     

Anthropogenic chemical carbon cycle for a sustainable future

Nature's photosynthesis uses the sun's energy with chlorophyll in plants as a catalyst to recycle carbon dioxide and water into new plant life. Only given sufficient geological time, millions of years, can new fossil fuels be formed naturally. The burning of our diminishing fossil fuel reserves is accompanied by large anthropogenic CO(2) release, which is outpacing nature's CO(2) recycling capability, causing significant environmental harm. To supplement the natural carbon cycle, we have proposed and developed a feasible anthropogenic chemical recycling of carbon dioxide. Carbon dioxide is captured by absorption technologies from any natural or industrial source, from human activities, or even from the air itself. It can then be converted by feasible chemical transformations into fuels such as methanol, dimethyl ether, and varied products including synthetic hydrocarbons and even proteins for animal feed, thus supplementing our food chain. This concept of broad scope and framework is the basis of what we call the Methanol Economy. The needed renewable starting materials, water and CO(2), are available anywhere on Earth. The required energy for the synthetic carbon cycle can come from any alternative energy source such as solar, wind, geothermal, and even hopefully safe nuclear energy. The anthropogenic carbon dioxide cycle offers a way of assuring a sustainable future for humankind when fossil fuels become scarce. While biosources can play a limited role in supplementing future energy needs, they increasingly interfere with the essentials of the food chain. We have previously reviewed aspects of the chemical recycling of carbon dioxide to methanol and dimethyl ether. In the present Perspective, we extend the discussion of the innovative and feasible anthropogenic carbon cycle, which can be the basis of progressively liberating humankind from its dependence on diminishing fossil fuel reserves while also controlling harmful CO(2) emissions to the atmosphere. We also discuss in more detail the essential stages and the significant aspects of carbon capture and subsequent recycling. Our ability to develop a feasible anthropogenic chemical carbon cycle supplementing nature's photosynthesis also offers a new solution to one of the major challenges facing humankind.     

Non-Darcian and Anisotropic Effects on Free Convection in a Porous Enclosure

The free convective flow and heat transfer, within the framework of Boussinesq approximation, in an anisotropic fluid filled porous rectangular enclosure subjected to end-to-end temperature difference have been investigated using Brinkman extended non-Darcy flow model. The studies involve simultaneous consideration of hydrodynamic and thermal anisotropy. The flow and temperature fields in general are governed by, Ra, the Rayleigh number, AR, the aspect ratio of the slab, K*, the permeability ratio and k*, the thermal conductivity ratio, and Da, Darcy number. Numerical solutions employing the successive accelerated replacement (SAR) scheme have been obtained for 100 ≤ Ra ≤ 1000, 0.5 ≤ AR ≤ 5, 0.5 ≤ K* ≤ 5, 0.5 ≤ k* ≤ 5, and 0 ≤ Da ≤ 0.1. It has been found that [`(Nu)]{\overline {Nu}}, average Nusselt number increases with increase in K* and decreases as k* increases. However, the magnitude of the change in [`(Nu)]{\overline {Nu}} depends on the parameter Da, characterizing the Brinkman extended non-Darcy flow.