Lighter Homologues Research Articles

The effect of targeted silencing of ferritin in the yellow fever mosquito, Aedes aegypti

Mosquitoes are vectors of human pathogens that cause disease, such as malaria, yellow fever and dengue fever. Pathogen transmission occurs when the female mosquito takes a bloodmeal from a human host. The female mosquito must bloodfeed for egg production, or oogenesis. An essential and concentrated nutrient in the blood meal is iron, which is required for optimal egg development and viable offspring. Ferritin is a major iron‐storage and transport protein expressed in mosquitoes. The protein increases following a blood meal in the female ovaries, midgut, fat body and hemolymph. Insect ferritin consists of 24 subunits of the heavy chain homologue (HCH), which contains the site for ferroxidase activity, and the light chain homologue (LCH), which is used for iron storage. This study evaluates the importance of these subunits for iron transport and storage within mosquitoes by suppressing them using RNA interference (RNAi) techniques. We suppressed ferritin expression by injecting the animals with double stranded RNA (dsRNA) and collecting whole animals, their tissues and eggs following blood feeding to examine the effect of message knockdown and protein expression. Interfering with iron delivery and usage in mosquitoes may be a strategy to reduce the number of eggs laid and pathogen transmission rates. Research support from NIH (GM056812), the Undergraduate Biology Research Program and a grant from the Honors College from the University of Arizona.

The effect of bacterial challenge on ferritin regulation in Aedes aegypti

In mammals, ferritin is a cytoplasmic iron storage protein made up of 24 heavy and light chain subunits that can store up to 4500 iron atoms; as wells as an acute phase protein that is secreted upon inflammation. Here we characterize the message and protein expression profiles of Aedes aegypti (yellow fever mosquito) ferritin heavy chain (HCH) and light chain homologue (LCH) subunits in response to iron and bacterial challenge. Mosquito experiments show an increase in midgut HCH and LCH message and protein expression 24 h post‐blood meal (PBM) and decrease 72 h PBM. Fat body and ovary HCH and LCH message and protein expression showed a time‐dependent increase PBM. Heat‐killed bacteria (HKB) had little effect on mosquito tissue ferritin expression. Iron regulatory protein (IRP) binding activity for the iron responsive element (IRE) increased over time in ovary PBM. Midgut and fat body binding activity increased 24 h PBM with a decrease 72 h PBM. Mosquitoes treated with HKB showed no change in IRP/IRE binding activity compared to naïve animals. Cell studies support in vivo results. HCH and LCH message and protein expression reveal a time‐dependent, synergistic up‐regulation of expression in CCL‐125 cells treated with iron and HKB than iron alone. There was also a time‐dependent increase in secreted ferritin as well as decrease IRP/IRE binding activity in cells treated with iron and HKB. Research support from NIH (GM056812), the Agricultural Experiment Station and CALS at the University of Arizona.

Extraction Chromatographic Behavior of Rf, Zr, and Hf in HCl Solution with Styrenedivinylbenzene Copolymer Resin Modified by TOPO (trioctylphosphine oxide)

It is of great interest to study chemical properties of the transactinide elements with atomic numbers (Z) ≥ 104. One of the most important subjects is to establish the position of the elements at the extreme end of the periodic table. To this end we perform studies of chemical properties of these transactinides and compare them with those of their lighter homologues and with the ones expected from extrapolations in the periodic table. So far, chromatographic studies of the transactinides have provided experimental proof of placing rutherfordium (Rf, Z = 104) through hassium (Hs, Z = 108) into groups 4 to 8, respectively. 1-10 Quite recently, copernicium (Cn, Z = 112) has been shown to be a member of group 12. 11 To gain a better understanding, it is even more interesting to study chemical properties of the transactinide elements in greater detail and to compare those with the ones of their lighter homologues. Theoretical calculations predict that the ground state electronic structure of the heaviest elements varies due to strong relativistic effects. Accordingly, chemical properties of these elements may deviate from those expected from linear extrapolations based on lighter homologues. 12-14 Systematically, detailed chemical investigations are, therefore, required to characterize properties of the transactinide elements influenced by relativistic effects.

Reactivity and Regioselectivity of Noble Gas Endohedral Fullerenes Ng@C60 and Ng2@C60 (Ng=He–Xe)

Recently, it was shown that genuine Ng-Ng chemical bonds are present in the endohedral fullerenes Ng(2)@C(60) in the case of Ng=Xe, while it is more debatable whether a chemical bond exist for Ng=Ar and Kr. The lighter homologues with helium and neon are weakly bonded van der Waals complexes. The presence of a noble gas dimer inside the cage is expected to modify the exohedral reactivity of the C(60) cage with respect to that of free C(60). To investigate the impact of encapsulated diatomic noble gas molecules on the chemical reactivity of C(60), we analyzed the thermodynamics and the kinetics of [4+2] Diels-Alder cycloaddition of 1,3-cis-butadiene at all nonequivalent bonds in free C(60), Ng@C(60), and Ng(2)@C(60) (Ng=He, Ne, Ar, Kr, and Xe). Our BP86/TZP calculations reveal that introduction of single noble gas atoms in Ng@C(60) and noble gas dimers He(2) and Ne(2) in Ng(2)@C(60) has almost no effect on the exohedral reactivity compared to free C(60), in agreement with experimental results. In all these cases cycloaddition is clearly favored at the [6,6] bonds in the fullerene cage. For the endohedral compounds He(2)@C(60) and Ne(2)@C(60) a slight preference (by less than 2 kcal mol(-1)) for bonds closer to the C(5) symmetry axis is found. This picture changes dramatically for the endohedral compounds with heavier noble gas dimers. Encapsulation of these noble gas dimers clearly enhances the reaction, both under thermodynamic and kinetic control. Moreover, in the case of Xe(2)@C(60), addition to [6,6] and [5,6] bonds becomes equally viable. These reactivity changes in endohedral fullerenes are attributed to stabilization of the LUMO, increased fullerene strain energy, and greater compression of the encapsulated Ng(2) unit along the He to Xe series.

Theoretical predictions of adsorption behavior of elements 112 and 114 and their homologs Hg and Pb

Fully relativistic (four-component) density-functional theory calculations were performed for elements 112 and 114 and their lighter homologs, Hg and Pb, interacting with gold systems, from an atom to a Au(n) cluster simulating the Au(111) surface. Convergence of the adatom-metal cluster binding energies E(b) with cluster size was reached for n>90. Hg, Pb, and element 114 were found to preferably adsorb at the bridge position, while element 112 was found to preferably adsorb at a hollow site. Independently of the cluster size, the trend in E(b) is Pb>>114>Hg>112. The obtained E(b) for Pb and element 112 are in good agreement with the measured adsorption enthalpies of these elements on gold, while the Hg value is obviously underestimated, confirming the observation that adsorption takes place not on the surface but in it. A comparison of chemical bonding in various systems shows that element 114 should be more reactive than element 112: A relative inertness of the latter is caused by the strong relativistic stabilization of the 7s atomic orbital. On the contrary, van der Waals bonding in element 114 systems should be weaker than in those of element 112 due to its larger radius.

Cs8−xSi46: A Type‐I Clathrate with Expanded Silicon Framework

The synthesis of the new binary Cs(8-x)Si(46) (shown here) completes the series of binary alkali metal silicides with a clathrate-I structure M(8-x)Si(46) (M = Na, K, Rb, Cs). In contrast with the lighter homologues, Cs(8-x)Si(46) can be prepared only at elevated pressures. The compound was obtained at 1200 degrees C between 2-10 GPa and the Cs content rises with applied pressure.

Studies on separation of no-carrier-added 177W from bulk lutetium

Irradiation of natural lutetium oxide target with 7Li beam results in the formation of no-carrier-added 177W radionuclide in the matrix. An efficient radiochemical procedure for the separation of no-carrier-added (nca) 177W (T 1/2 = 2.21 h) radionuclide is presented using liquid-liquid extraction (LLX). A high separation factor between nca 177W from the target Lu has been achieved with 0.1 M TOA and 8 M HCl. About 85% of 177W has been extracted in the organic phase keeping Lu in the aqueous phase in a single run. Using this production and separation method radiochemically pure 177W can be obtained. The separation has also been tried with a greener approach viz. aqueous biphasic extraction. In this case, aqueous biphasic extraction is not a good method for separation of 177W. The radionuclide 177W thus obtained can be used to study the extraction pattern of lighter homologue of the element 106 (Sg) together with Mo, which in turn is important to investigate the chemistry of Sg.

Supramolecular architecture elucidation of the room temperature columnar mesophases exhibited by mixed-valent diruthenium alkoxybenzoates

Three series of mesogenic coordination polymers based on mixed-valent diruthenium tetracarboxylates, namely Ru2(3,4-B2OCn)4Cl, Ru2(3,5-B2OCn)4Cl and Ru2(3,4,5-B3OCn)4Cl [3,4-B2OCn = 3,4-(CnH2n+1O)2C6H3CO2−, 3,5-B2OCn = 3,5-(CnH2n+1O)2C6H3CO2− and 3,4,5-B3OCn = 3,4,5-(CnH2n+1O)3C6H2CO2−] have been synthesized and characterized, with the aim of obtaining columnar liquid crystalline phases. These equatorial BmOCn ligands have been selected under the assumption that they will efficiently fill the intermolecular space around the axial Cl atoms, thus warranting a parallel arrangement of the polymeric ⋯Ru2–Cl–Ru2–Cl⋯ strands in the crystalline phase, which should facilitate the occurrence of Col mesophases. The liquid crystalline character of the synthesized compounds has been studied by means of polarized optical microscopy, differential scanning calorimetry, and variable temperature X-ray diffraction. They all exhibit thermotropic ColH mesophases, the 3,4-B2OCn derivatives also exhibit a lamellar mesophase. Many of the studied compounds exhibit room temperature mesomorphism. The thermal stability domain of the ColH mesophases of the 3,5-B2OCn and 3,4,5-B3OCn derivatives is remarkably wide, from below 0 °C to ca. 300 °C in some cases. Based on pieces of structural information coming from XRD experiments, dilatometry, and local probes (magnetic susceptibility measurements, resonance Raman and IR spectroscopies, and Exafs) we suggest a model for the structural arrangement of the polymeric strands in the mesophase, in which the central polar backbone of the polymeric strands is in a zig-zag conformation, surrounded by a continuum of molten aliphatic chains. A crystallographic study of the non-mesogenic light homologue Ru2(3,4,5-B3OC2)4Cl confirms these aspects of the model, and shows the predicted preorganization of the polymeric strands in the crystalline phase.

Passive Air Sampling of Polychlorinated Biphenyls and Organochlorine Pesticides at the Korean Arctic and Antarctic Research Stations: Implications for Long-Range Transport and Local Pollution

To assess levels and patterns of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in polar regions, XAD-resin based passive air samplers were deployed for one year at the Korean polar research stations at Ny-Alesund, Norway (2005-2006) and King George Island, Antarctica (2004-2005). Backward trajectories suggest that these stations are affected by long-range transport from source regions in Northern Europe and Russia and the southern tip of South America, respectively. Relatively high levels of PCB-11, averaging 60 pg x m(-3), were observed in Antarctica, suggesting an unusual source of PCB-11 to the Southern Hemisphere. Reflecting the hemispheric distribution of global PCB emissions, the average level of sigma205PCB (excluding three mono-CBs and PCB-11) was five times higher in the Arctic (95 pg x m(-3)) than in the Antarctic (19 pg x m(-3)). Levels of sigma9PCB at Ny-Alesund were similarto those reported for other Arctic sites, while levels at King George Island were lower than at other sites on the Antarctic Peninsula but 1 order of magnitude higher than background levels measured at a more remote Antarctic site. Light homologues were predominant in all samples (except for one Arctic sample), consistent with the hypothesis of global fractionation and predictions of long-range transport potential. Dominance of heavy PCBs on the roof of the main building at Ny-Alesund and a concentration gradient with distance from the main building at King George Island strongly indicated the influence of local sources. OCP levels were also influenced by long-range transport but not by local sources. This study highlights the feasibility of using passive air sampling to assess both long-range transport and local pollution in remote regions.

Stable CI3+salts and attempts to prepare CHI2+and CH2I+

The room-temperature stable CI3+ salts [CI3+[pftb](-)1 and [CI3]+[al-f-al](-) 2([pftb](-) = [Al(OC(CF3)3)4](-); [al-f-al](-) = [((CF3)3CO)3Al-F-Al(OC(CF3)3)3](-)) were prepared in quantitative yields from purified CI4 and the corresponding silver aluminates with total exclusion of light (NMR, IR, UV-VIS, X-ray diffraction). The isolated CI(3)(+) cation is trigonal planar with a sum of <(I-C-I) = 360.0 degrees (1) and 359.9 degrees (2). Attempts to prepare CHI2+ and CH2I+ salts from CHI3 or CH2I2/Ag[pftb] mixtures remained unsuccessful; the reaction with CH2I2 leads to the formation of the adduct [Ag(CH2I2)3]+[pftb](-)3, while for HCI3, dismutation with formation of 1 as well as 3 was observed. All particles were also calculated at the MP2/TZVPP level to predict the vibrational and electronic spectra as well as to calculate the Gibbs free energies of all reactions (DeltaG degrees , gas phase and CH2Cl2 solution). Quantum chemical calculations were also used to investigate the stability of the [pftb](-) anion against the electrophilic attack of the CX3+ and CHnX3-n+ cations (X = F-I, n = 1-3). The strength of the Lewis acidity of these cations and of the isoelectronic boron halides BX()and BHnX3-n have been established on the basis of their fluoride ion affinities (FIAs). The FIAs of the carbon and the boron containing compounds show opposite trends, with fluorinated halomethyl cations being stronger acids than their heavier congeners but iodinated holoboranes being stronger acids than their lighter homologues.

Superheavy element chemistry at GSI – status and perspectives

Superheavy elements have been synthesized and chemically characterized one-atom-at-a-time up to element 108. Presently, the quest for identification and investigation of element 112 is one of the hottest topics in this field. The transactinide elements 104 to 108 are members of group 4 to 8 of the periodic table and element 112 belongs into group 12. For some of these elements detailed chemical properties have been revealed which show stunning deviations from simple extrapolations within their respective group while others exhibit great similarities with their lighter homologues. All presently known chemical properties of seaborgium (Sg, element 106) — the heaviest element whose behavior was investigated in aqueous solution — and hassium (Hs, element 108) were obtained in experiments performed at the GSI in large international collaborations. Recently, the highly efficient and very clean separation of Hs was applied for nuclear studies of various Hs nuclides investigating their cross section and their nuclear decay properties in the region of the N=162 neutron shell. To overcome certain limitations of the presently used on-line chemical separations the new TransActinide Separator and Chemistry Apparatus (TASCA) — with a gas-filled recoil separator as a front-end tool — was designed and built at the GSI in a collaborative effort. Presently in its commissioning phase, TASCA shall be a key instrument for a big leap into quantitatively and qualitatively new experiments in the region of superheavy elements.

Towards relativistic ECP / DFT description of chemical bonding in E112 compounds: spin-orbit and correlation effects in E112X versus HgX (X=H, Au)

Abstract The relativistic effective core potential (RECP) approach combined with the spin-orbit DFT electron correlation treatment was applied to the study of the bonding of eka-mercury (E112) and mercury with hydrogen and gold atoms. Highly accurate small-core shape-consistent RECPs derived from Hartree-Fock-Dirac-Breit atomic calculations with Fermi nuclear model were employed. The accuracy of the DFT correlation treatment was checked by comparing the results in the scalar-relativistic (spin-orbit-free) limit with those of high level scalar-relativistic correlation calculations within the same RECP model. E112H was predicted to be slightly more stable than its lighter homologue (HgH). The E112-Au bond energy is expected to be ca. 25–30 % weaker than that of Hg-Au. The role of correlations and magnetic (spin-dependent) interactions in E112-X and Hg-X (X=H, Au) bonding is discussed. The present computational procedure can be readily applied to much larger systems and seems to be a promising tool for simulating E112 adsorption on metal surfaces.

La(OH)2I(H2O): Closing a Gap in Rare Earth Hydroxide Halide Structural Chemistry.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Extraction of short-lived zirconium and hafnium isotopes using crown ethers: A model system for the study of rutherfordium

Summary The extraction of zirconium and hafnium from hydrochloric acid media was studied using the crown ethers dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6 (DC18C6) and dicyclohexano-24-crown-8 (DC24C8) as extractants. The goal was to find an extraction system that exhibits a high selectivity between the members of group 4 of the periodic table and is suitable for the study of rutherfordium. It was found that Zr and Hf are both extracted using DB18C6, DC18C6 and DC24C8. The extraction yield increases with increasing acid concentration and increasing concentration of crown ether. The extracted species most likely consists of an ion-association complex formed between a Zr or Hf chloro complex and a hydronium crown ether complex. Conditions can be found for each extractant that provide for the separation of Zr from Hf. This selective separation between Zr and Hf makes the extraction with crown ethers from HCl well suited to study the extraction behaviour of Rf and compare it to the behaviour of Zr and Hf. These extraction systems can be used to determine whether the extraction behaviour of Rf is similar to Zr, similar to Hf or follows the trend established by the lighter homologs. The extraction kinetics are fast enough for the study of the 78-s isotope 261mRf.

Binding of Benzyltrimethylammonium Bromide and its Alkyldimethylbenzylammonium Homologues by β-Cyclodextrin in Water

The binding constants, K′, for the reaction between some alkyldimethylbenzylammonium bromide homologues (alkyl = methyl, ethyl, propyl, butyl, hexyl, decyl, and dodecyl, respectively) and β-cyclodextrin in water at 25.0 ± 0.1 ∘C have been determined, by applying the spectral displacement technique with phenolphthalein as the displacing anion. It has been shown that the ln K′ values increase linearly with the number of carbon atoms in the alkyl chain for the salts whose alkyl chain has at least four carbon atoms. The ln K′ values estimated for the parent compound benzyltrimetylammonium bromide and its two nearest homologues are distinctly lower than might be expected by extrapolation of the linear relation found for the higher homologues. Assuming that it is the organic cation that undergoes association with β-cyclodextrin, then one may suppose that a change occurs in the mode of inclusion of the cation upon passing to higher homologues. In the case of the lighter homologues, it is the phenylene group that undergoes inclusion. This model of inclusion is confirmed by analysis of rotating-frame overhauser effect spectroscopy (ROESY) spectra.

Chemical studies on rutherfordium (Rf) at JAERI

SummaryChemical studies on element 104, rutherfordium (Rf), at JAERI (Japan Atomic Energy Research Institute) are reviewed. The transactinide nuclide261Rf has been produced in the reaction248Cm(18O, 5n) at the JAERI tandem accelerator with the production cross section of about 13 nb. On-line anion-exchange experiments on Rf together with the lighter homologues, group-4 elements Zr and Hf, in acidic solutions have been conducted with a rapid ion-exchange separation apparatus. From the systematic study of the anion-exchange behavior of Rf, it has been found that the properties of Rf in HCl and HNO3solutions are quite similar to those of Zr and Hf, definitely confirming that Rf is a member of the group-4 elements. However, we have observed an unexpected chemical behavior of Rf in HF solutions; the fluoride complex formation of Rf is significantly different from those of the homologues. Prospects of extending chemical studies on transactinide elements in the near future at JAERI are briefly considered.

Predictions of adsorption behaviour of the heaviest elements in a comparative study from the electronic structure calculations

Summary Thermodynamics of adsorption of gaseous species on the surface of a gas chromatography column is considered using the knowledge of the electronic structure of the adsorbate. Relevant equations based on a model of mobile adsorption are offered to predict the adsorption temperature, T ads, of a heavy-element (or its compound) with respect to T ads of its lighter homolog (or the same type of compound). A case of adsorption of OsO4 and HsO4 on an inert (quartz or silicon nitride) surface of a chromatography column is taken, as an example. The influence of various properties of the adsorbate, such as molecular weight and size, on T ads is analyzed to show that those factors should not be ignored in intentionally accurate predictions of T ads. A comparison of the desorption constants of OsO4 and HsO4 obtained with the use of the calculated spectroscopic properties shows that HsO4 should be significantly more volatile than OsO4, mainly due to the entropy factor.

Simultaneous Prediction of the Critical and Subcritical Phase Behavior in Mixtures of Ethane−n-Alkanes

The present study compares the ability of three semipredictive approaches, namely, the global phase diagram based semipredictive approach (GPDA), predictive Soave−Redlich−Kwong (PSRK), and linear combination of the Vidal and Michelsen mixing rules (LCVM), to describe the experimental data in the binary homologue series of ethane−n-alkanes. The applicability of GPDA has been extended by attachment of an additional empirical functionality. Now it can predict not only the data of a homologues series to which the reference system belongs but also other series that include solvents from the same chemical group. Yet, both GPDA and PSRK appear as entirely predictive models. However, LCVM has a correlative character rather than predictive. Although the models under consideration yield rather similar results for the light homologues of the series, starting from ethane−n-decane, GPDA shows a clear superiority over PSRK and LCVM. Moreover, it is demonstrated that the GE mixing rules of both PSRK and LCVM generate th...

The hydrolysis of actinium

The first hydrolysis constant (pK1h = 9.4) of Ac3+ cations has been determined using 228Ac radiotracer. The pK1h value of Ac3+is compared to the pK1h values of other Group 3 cations. It is shown that, in contrast to the Group 2, 11, 12 and 13, the heaviest member of the Group 3 Ac3+ hydrolyses at less extent than its lighter homologs. The linearity of the log K1h-1/ri (where ri is the ionic radius) function indicates that the electrostatic model of hydrolysis describes well the hydrolysis of Group 3 cations.

Perspective for the determination of chemical properties of element 112

We present here results of thermochromatographic model studies with Rn and Hg, conducted in order to prepare future gas-adsorption chromatographic investigations of element 112. The adsorption properties of Rn on various transition metals were investigated by vacuum thermochromatography. From the results of these experiments, predictions have been deduced for the adsorption behavior of hypothetically noble-gas-like elements 112 and 114. Empirical predictions of the adsorption interaction of a noble metallic element 112 and its lighter homologues with transition metal surfaces are given in the literature. The results of these calculations are compared with experimental data obtained in thermochromatographic model experiments with Hg. The most efficient way to chemically identify element 112 is the use of a cryo-on-line detector (COLD)-like setup, which was already successfully applied in the chemical investigation of hassium. Modifications of this device needed for the on-line thermochromatographic investigation of element 112 are presented together with results of test experiments with short-lived isotopes of Rn and Hg.