HIGHLY FLUORINATED, COINAGE METAL COMPLEXES OF TRIS(PYRAZOLYL)BORATES WITH ADDITIONAL ELECTRON WITHDRAWING GROUPS AND PYRAZOLATE π-STACKINGS WITH ARENES

Tris(pyrazolyl)borates are very popular ligands in inorganic chemistry, bioinorganic chemistry, and organometallic chemistry due to their attractive properties. It is possible to extensively modify the steric and electronic properties of these ligands by changing the pyrazolyl substituent groups. Taking into account the importance and current interest of fluorinated tris(pyrazolyl)borates and weakly coordinating anions in general, three new tris(pyrazolyl)borates, [HB(4-Cl-3,5-(CF₃)₂Pz)₃]-, [HB(3,4,5-(CF₃)3Pz)₃] and [HB(4-(NO₂)-3,5-(CF3)₂Pz)₃]- have been developed (Pz = pyrazolyl). Silver alkene adducts of the ligands have been isolated to evaluate the electronic properties of the ligands and to study their catalytic properties. These adducts found to be the most electron deficient tris(polyazolyl)borates reported. The silver alkene adducts formed by these species are also important due to the scarcity of thermally stable isolable silver ethylene, cis-cyclooctene adducts. Also some of these ligands were used to synthesize copper ethylene and silver carbonyl adducts. The CO stretching frequency of non-classical silver carbonyl adducts appear at a region less sensitive to the ligand electronic effects of tris(azolyl)borate Ag adducts. The alkene ¹³C NMR chemical shift of silver alkene adducts is sensitive to ligand electronic property changes according to the ¹³C NMR. All the silver alkene adducts and a carbonyl adduct were structurally characterized by means of single crystal X-ray diffractions. All the compound reported were characterized by various NMR experiments and elemental analysis. Coinage metal ions supported by highly fluorinated ligands such as fluorinated tris(pyarazolyl)borates are excellent catalysts for carbene insertion into C-H bonds. The activity of silver adducts are particularly noteworthy. The activity and the selectivity of the catalyst can be fine-tuned using the substituents on the supporting ligand. The silver alkene adducts effectively catalyzed the insertion of the carbene moiety of ethyl diazoacetate into C-H bonds of 2,3-dimethylbutane. More electron deficient catalysts have shown higher selectivity towards primary C-H bonds.Moreover our interest was directed towards the chemistry of the primary building block of tris(pyrazolyl)borate, the pyrazolate ligand. This simple ligand has been widely used in inorganic, bioinorganic, and organometallic chemistry. These ligands can strongly bind to the metal ions such as Cu(I), Ag(I) and Au(I). We are interested in the highly fluorinated pyrazolate coinage metal complexes due to the scarcity, their reversed π-stacking ability and the remarkable photophysical properties. The π-acid/ π-base adducts of {[3,5-(CF₃)₂Pz]Cu}₃ [Cu₃] and benzene [Bz], mesitylene [Mes] and naphthalene [Nap] have been isolated. They form columnar structures of the type {[Bz][Cu₃]₂}∞, {[Mes][Cu₃]}∞ and {[Nap][Cu₃]}∞ in the solid state, and are luminescent. The novel coinage metal complexes, C60{[(3,5-(CF₃)₂Pz)Cu]₃}₄ , C60{[(3,5-(CF₃)₂Pz)Ag]₃}₄ and C60{[(3,5-(CF₃)₂Pz)Au]₃}₄, represent the first coinage metal pyrazolate fullerene adducts to the best of our knowledge. Interestingly, these adducts possess same space group to that of “free” C60 and the crystals are formed in their pure form with no co-crystalized solvent molecules

Biology, propagation and utilization of elite coconut varieties (makapuno and aromatics)

Coconut farming is not only a vital agricultural industry for all tropical countries possessing humid coasts and lowlands, but is also a robust income provider for millions of smallholder farmers worldwide. However, due to its longevity, the security of production of this crop suffers significantly from episodes of natural disasters, including cyclone and tsunami, devastating pest and disease outbreaks, while also affected by price competition for the principal products, especially the oil. In order to reduce these pressures, high-value coconut varieties (makapuno and aromatics) have been introduced in some regions, on a limited scale, but with positive outcomes. Even though these two varieties produce fruit with delicious solid or flavoursome liquid endosperm, their distinct biochemical and cellular features unfortunately prevent their in situ germination. In fact, embryo rescue and culture have been developed historically to nurture the embryo under in vitro conditions, enabling effective propagation. In an attempt to provide a comprehensive review featuring these elite coconut varieties, this paper firstly introduces their food values and nutritional qualities, and then discusses the present knowledge of their biology and genetics. Further possibilities for coconut in general are also highlighted, through the use of advanced tissue culture techniques and efficient seedling management for sustainable production of these highly distinct and commercially attractive varieties of coconut

A Multi-year Search for Transits of Proxima Centauri. II. No Evidence for Transit Events with Periods between 1 and 30 days

Using a global network of small telescopes, we have obtained light curves of Proxima Centauri at 329 observation epochs from 2006 to 2017. The planet Proxima b discovered by Anglada-Escudé et al. with an orbital period of 11.186 days has an a priori transit probability of ∼1.5%; if it transits, the predicted transit depth is about 5 mmag. In Blank et al., we analyzed 96 of our light curves that overlapped with predicted transit ephemerides from previously published tentative transit detections and found no evidence in our data that would corroborate claims of transits with a period of 11.186 days. Here we broaden our analysis, using 262 high-quality light curves from our data set to search for any periodic transit-like events over a range of periods from 1 to 30 days. We also inject a series of simulated planet transits and find that our data are sufficiently sensitive to have detected transits of 5 mmag depth, with recoverability ranging from ∼100% for an orbital period of 1 day to ∼20% for an orbital period of 20 days for the parameter spaces tested. Specifically, at the 11.186-day period and 5 mmag transit depth, we rule out transits in our data with high confidence. We are able to rule out virtually all transits of other planets at periods shorter than 5 days and depths greater than 3 mmag; however, we cannot confidently rule out transits at the period of Proxima b due to incomplete orbital phase coverage and a lack of sensitivity to transits shallower than 4 mmag

Changes in Soluble Sugars, Sugar Profile, Starch and Proline in Developing Coconut (Cocos nucifera L.) Inflorescences

Changes in soluble sugars, sugars profile, starch and proline levels in inflorescence rachillae from individual coconut palms were investigated during inflorescence development with the aim of determining a possible correlation between these characters and morphogenic potential of inflorescence tissues. Rachillae for analysis were collected from unopened inflorescences of -1 to -13 stages (considering the youngest open inflorescence as 0 stage) in decreasing order of maturity (–1 stage is the most mature stage whereas –13 is the most immature stage). Important differences among the maturity stages were observed for total sugars. In very tender inflorescences (-13 and -12), the total sugar content was very low whereas a gradual increase was observed from -11 to -7 stages, with  -7 stage having the highest level. The total sugar content in more mature inflorescences was relatively low, with the exception of -2 stage, which had a high total sugar content. In regard to sugar profiles, sucrose, fructose and glucose were the main soluble sugars present in coconut inflorescence and sucrose was the most abundant sugar in -5 to -9 maturity stages. Total soluble sugars and sucrose in maturity stages from -5 to -9 showed a very similar variation and significantly higher levels of sucrose were observed in -6 to -8 stages. The proline content in the mature stages, -1 to –3, was significantly lower than in the other stages with no significant variation in the stages –4 to –11. The pattern of variation in starch content was similar to that of proline which decreased with increasing maturity of inflorescence. In view of the results obtained, the higher accumulation of sucrose and total sugars in -6, -7 and -8 stages may have some significance in morphogenesis, especially as an energy source. The 10 cm length inflorescence that responds better for callusing falls within this range. Thus total sugar and sucrose content may be possible biochemical markers for assessing the morphogenic potential of inflorescence explants.</jats:p

A search for transiting extrasolar planets in the open cluster NGC 4755

The search for ESP (extra-solar planets) has become a very popular astronomical research activity since the first discovery of ESP in 1995. Although, there are many ways of finding these exotic bodies, the transit method has become a widely used method; even amateurs have their opportunity to become planet hunters. This requires high precision time-series photometry and light curve analysis of large numbers of stars. When a planet transits, its radii ratio with the primary star can be determined accurately. Thus, combining this ratio with radial velocity data, the mass and radius of the planet can be realized, assuming the primary star's radius is known. The information gained from the transiting planets makes it possible to unravel the structure and composition of ESPs, understand the formation and the evolution process, and find the physical properties of the planet.\ud \ud The detection of a weak, short, periodic transit signal in noisy light curves is a challenging task. As large numbers of light curves are to be analyzed, automation and an optimization of the search and analysis process is a necessity. The fluxes of stars on CCD (Charge Coupled Device) images are measured and the de-trended flux is used to draw the light curve. Normally, the search is done by a ground based detection system; hence the light curve is contaminated with noise components coming from atmospheric variations and systematic errors. To obtain high precision data without atmospheric noise, space based CCD cameras are already active.\ud \ud Based on the above transit theory, this search was first done by using REST (Really Embarrassing Small Telescope) at JCU for field stars in the solar neighbourhood, GL 581, HD 13445 and HD 27894. The CCD images of the stars were subjected to CCD data reduction, pre-processing, differential photometry and analyzing by transit identification algorithms. Differential photometry, the ratio of the target star flux and reference star flux was used to nearly nullify the atmospheric variations.\ud \ud The target open cluster for the main search is NGC 4755, which is widely known as the Jewel Box, in the constellation of the Southern Cross. The Perth Automatic Telescope, which can be remotely controlled, was used to obtain the data for the open cluster. 176 cluster stars brighter than 14th magnitude with published 'B' and 'V' magnitudes and another 994 faint stars in the cluster frame have been analyzed. Several analytical signal-processing methods have been used to process the light curve to get the best light signal, having a SD (Standard Deviation) less than 5 milli-magnitudes. Later, fast wavelet transform was used to remove high frequency noise components and to produce an approximate signal which shows the long-term trend of the light curve and contain a possible transit. While no planetary transits have been identified in this cluster before, the ability to get light curves with standard deviation less than 5 milli-magnitudes is a significant achievement. The approximated light curves (using wavelets) are almost flat indicating that there are no signals with cycle time of 90 minutes or more.\ud \ud The PSD (Power Spectral Density) of the light curve gives the frequency components associated with the curve. As there is a limitation of using this FFT based method, the Lomb-Scargle method was used to generate PSD.\ud \ud This data was compared with 2MASS data to find closer brown dwarfs and a dozen possible candidates were found.\ud \ud Variable stars in the cluster can also be studied with the light curve of stars. As there are at least 19 known variable stars in the NGC 4755; this is an opportunity to study the known variable stars in the cluster as well as to discover additional ones