Design, synthesis, conformational analysis and nucleic acid hybridisation properties of thymidyl pyrrolidine-amide oligonucleotide mimics (POM)

Pyrrolidine-amide oligonucleotide mimics (POM) 1 were designed to be stereochemically and conformationally similar to natural nucleic acids, but with an oppositely charged, cationic backbone. Molecular modelling reveals that the lowest energy conformation of a thymidyl-POM monomer is similar to the conformation adopted by ribonucleosides. An e cient solution phase synthesis of the thymidyl POM oligomers has been developed, using both N-alkylation and acylation coupling strategies. 1H NMR spectroscopy con rmed that the highly water soluble thymidyl-dimer, T2-POM, preferentially adopts both a con guration about the pyrrolidine N-atom and an overall conformation in D2O that are very similar to a typical C3 -endo nucleotide in RNA. In addition the nucleic acid hybridisation properties of a thymidyl-pentamer, T5-POM, with an N-terminal phthalimide group were evaluated using both UV spectroscopy and surface plasmon resonance (SPR). It was found that T5-POM exhibits very high a nity for complementary ssDNA and RNA, similar to that of a T5-PNA oligomer. SPR experiments also showed that T5-POM binds with high sequence delity to ssDNA under near physiological conditions. In addition, it was found possible to attenuate the binding a nity of T5-POM to ssDNA and RNA by varying both the ionic strength and pH. However, the most striking feature exhibited by T5-POM is an unprecedented kinetic binding selectivity for ssRNA over DNA

Study of the polyoxymethylene and its sputtered fragments: Implications for comets

Laboratory mass spectra of sputtered polyoxymethylene (POM) reveals a fragmentation pattern consistent with observed peaks in the PICCA experiment on board the Giotto spacecraft. Both commercially available POM and radiation synthesized POM have been used in the studies. Synthesized POM was identified using infrared absorption spectra after proton irradiation of H2CO ice on silicate grains at 20 K. Laboratory results suggest that similar type sputtering is a possible mechanism for removing species from comet grains

QCD motivated approach to soft interactions at high energies: nucleus-nucleus and hadron-nucleus collisions

In this paper we consider nucleus-nucleus and hadron-nucleus reactions in the kinematic region: g A^{1/3} G_{3\pom} \exp\Lb \Delta Y\Rb \approx 1 G^2_{3\pom} \exp\Lb \Delta Y\Rb \approx 1 , where G_{3\pom} is the triple Pomeron coupling, $g$ is the vertex of Pomeron nucleon interaction, and 1 + \Delta_{\pom} denotes the Pomeron intercept. We find that in this kinematic region the traditional Glauber-Gribov eikonal approach is inadequate. We show that it is necesssary to take into account inelastic Glauber corrections, which can not be expressed in terms of the nucleon-nucleon scattering amplitudes. In the wide range of energies where \alpha'_\pom Y \ll R^2_A,the scattering amplitude for the nucleus-nucleus interaction, does not depend on the details of the nucleon-nucleon interaction at high energy. In the formalism we present, the only (correlated) parameters that are required to describe the data are \Delta_{\pom}, G_{3\pom} and $g$. These parameters were taken from our description of the nucleon-nucleon data at high energies \cite{GLMM}.The predicted nucleus modification factor is compared with RHIC Au-Au data at $W = 200 GeV.$ Estimates for LHC energies are presented and discusssed.Comment: 18pp. 14 fugure

Applying Item Response Theory (IRT) Modeling to an Observational Measure of Childhood Pragmatics: The Pragmatics Observational Measure-2

Assessment of pragmatic language abilities of children is important across a number of childhood developmental disorders including ADHD, language impairment and Autism Spectrum Disorder. The Pragmatics Observational Measure (POM) was developed to investigate children's pragmatic skills during play in a peer-peer interaction. To date, classic test theory methodology has reported good psychometric properties for this measure, but the POM has yet to be evaluated using item response theory. The aim of this study was to evaluate the POM using Rasch analysis. Person and item fit statistics, response scale, dimensionality of the scale and differential item functioning were investigated. Participants included 342 children aged 5-11 years from New Zealand; 108 children with ADHD were playing with 108 typically developing peers and 126 typically developing age, sex and ethnic matched peers played in dyads in the control group. Video footage of this interaction was recorded and later analyzed by an independent rater unknown to the children using the POM. Rasch analysis revealed that the rating scale was ordered and used appropriately. The overall person (0.97) and item (0.99) reliability was excellent. Fit statistics for four individual items were outside acceptable parameters and were removed. The dimensionality of the measure showed two distinct elements (verbal and non-verbal pragmatic language) of a unidimensional construct. These findings have led to a revision of the first edition of POM, now called the POM-2. Further empirical work investigating the responsiveness of the POM-2 and its utility in identifying pragmatic language impairments in other childhood developmental disorders is recommended

Polyoxometalate multi-electron-transfer catalytic systems for water splitting

The viable production of solar fuels requires a visible-light-absorbing unit, a H2O (or CO2) reduction catalyst (WRC), and a water oxidation catalyst (WOC) that work in tandem to split water or reduce CO2 with H2O rapidly, selectively, and for long periods of time. Most catalysts and photosensitizers developed to date for these triadic systems are oxidatively, thermally, and/or hydrolytically unstable. Polyoxometalates (POMs) constitute a huge class of complexes with extensively tunable properties that are oxidatively, thermally, and (over wide and adjustable pH ranges) hydrolytically stable. POMs are some of the fastest and most stable WOCs to date under optimal conditions. This Microreview updates the very active POM WOC field; it reports the application of POMs as WRCs and initial self-assembling metal oxide semiconductor–photosensitizer–POM catalyst triad photoanodes. The complexities of investigating these POM systems, including but not limited to the study of POM-hydrated metal-ion–metal-oxide speciation processes, are outlined. The achievements and challenges in POM WOC, WRC, and triad research are outlined

Comparison between bulk and FDSOI POM flash cell: a multiscale simulation study

In this brief, we present a multiscale simulation study of a fully depleted silicon-on-insulator (FDSOI) nonvolatile memory cell based on polyoxometalates (POMs) inorganic molecular clusters used as a storage media embedded in the gate dielectric of flash cells. In particular, we focus our discussion on the threshold voltage variability introduced by random discrete dopants (random dopant fluctuation) and by fluctuations in the distribution of the POM molecules in the storage media (POM fluctuation). To highlight the advantages of the FDSOI POM flash cell, we provide a comparison with an equivalent cell based on conventional (BULK) transistors. The presented simulation framework and methodology is transferrable to flash cells based on alternative molecules used as a storage media

Hydrologic controls on seasonal and inter-annual variability of Congo River particulate organic matter source and reservoir age

We present dissolved organic carbon (DOC) concentrations, particulate organic matter (POM) composition (δ13C, δ15N, ∆14C, N/C), and particulate glycerol dialkyl glycerol tetraether (GDGT) distributions from a 34-month time-series near the mouth of the Congo River. An end-member mixing model using δ13C and N/C indicates that exported POM is consistently dominated by C3 rainforest soil sources, with increasing contribution from C3 vegetation and decreasing contribution from phytoplankton at high discharge. Large C4 inputs are never observed despite covering ≈ 13% of the catchment. Low and variable ∆14C values during 2011 [annual mean = (− 148 ± 82) ‰], when discharge from left-bank tributaries located in the southern hemisphere reached record lows, likely reflect a bias toward pre-aged POM derived from the Cuvette Congolaise swamp forest. In contrast, ∆14C values were stable near − 50‰ between January and June 2013, when left-bank discharge was highest. We suggest that headwater POM is replaced and/or diluted by C3 vegetation and pre-aged soils during transit through the Cuvette Congolaise, whereas left-bank tributaries export significantly less pre-aged material. GDGT distributions provide further evidence for seasonal and inter-annual variability in soil provenance. The cyclization of branched tetraethers and the GDGT-0 to crenarchaeol ratio are positively correlated with discharge (r ≥ 0.70; p-value ≤ 4.3 × 10− 5) due to the incorporation of swamp-forest soils when discharge from right-bank tributaries located in the northern hemisphere is high. Both metrics reach record lows during 2013, supporting our interpretation of increased left-bank contribution at this time. We conclude that hydrologic variability is a major control of POM provenance in the Congo River Basin and that tropical wetlands can be a significant POM source despite their small geographic coverage

Photoelectrical and photoelectrochemical characterization of the materials used in dye-sensitized and perovskite solar cells.

Solar energy is one of the most important alternative renewable energy sources to fulfill the increasing demand of energy in the world. Third-generation solar cells like dye-sensitized solar cells, perovskite solar cells, quantum dot solar cells, and organic solar cells are extensively studied to increase their photoconversion efficiency, and ultimately for their large-scale implementation. A dye-sensitized solar cell consists of a photoanode of a mesoporous film of titania sensitized with dye sandwiched with a counter electrode, which is usually a platinum-coated transparent conducting oxide, and a redox couple injected between the photoanode and counter electrode. Doping titania with rare-earth metal oxides (REOs) has been an interesting approach to improve the conversion efficiency of dye-sensitized solar cells. REOs have been doped into titania paste to show an improvement in the photovoltaic performance of dye-sensitized solar cells, however, most of the reported cells are not efficient enough to conclude whether the enhancement is due to doping or it is because of the cell quality. We incorporated nanoparticles (NPs) of REOs in titania paste and built highly reproducible dye-sensitized solar cells using amphiphilic C101 dye and iodide/triiodide redox couple in nitrile-based solvent (Z960 electrolyte). The doping level for optimized cells was 2.0 % for neodymium oxide and 1.0 % for erbium oxide. We did the measurements of photocurrent, impedance, incident photon-to-electron conversion efficiency (IPCE), and dye loading to investigate the mechanism of enhancement of the photovoltaic performance by REO NPs. Electrochemical impedance spectroscopy measurements showed that doping with REO decreased the total impedance of the cell and IPCE measurements revealed enhanced photon absorption by the dye in REO-doped cells. In the same fashion, the REO-doped anodes showed larger dye loading compared to undoped anodes, which was maximum for 1.0 % doping of erbium oxide and 2.0 % doping of neodymium oxide. REOs not only enhance dye adsorption but also facilitate electron transport through the mesoporous layer, thereby increasing the collection efficiency of the photoexcited electrons. To further explore the mechanism for the interaction between REO NPs and titania, an electrical and electrochemical study of REO-doped nanostructured titania films was performed. Doped films were found to be 40-50 times more conductive than undoped films, with linear current-voltage characteristics. Cyclic voltammograms of doped samples showed an enhanced scan rate dependence in the deep trap regime due to a slower charge trapping rate. Finally, electrochemical impedance measurements revealed a decrease in space charge density and a shift in the flat-band potential. Taken together, these results suggest that charge transfer from the REO neutralizes the deep trap states in the nanostructured titanium dioxide (NTD) film, decreasing charge scattering, and improving the NTD performance as an electron acceptor and electron transport material. Perovskite solar cells (PSCs) were first made when the dye-loaded semiconductor of dye-sensitized solar cell was replaced by perovskite layer and liquid electrolyte by a hole transport layer. The light harvesting perovskite layer is sandwiched between electron-transport and hole transport layers. Organic-inorganic perovskites, also known as hybrid perovskites have fascinating optoelectronic properties for their applications in highly efficient solar cells. The stability in ambient conditions and hysteresis in current-potential curves are two main challenges. The ease with which the separation of photogenerated charge carriers, electron-hole pairs (excitons), takes place is very critical for the performance of PSCs. In addition to the work function difference of electron-transport and hole transport layers, the intrinsic built-in potential in the perovskite films can play a significant role in the separation of these excitons. The internal electric originates from the local polarization of the film due to non-centrosymmetric lattice and ionic polarization and can be measured through an AC photocurrent technique. The polarization of a pristine sample is strongly dependent on the size of grains and can be used to determine the quality of the film. After poling the film by applying a potential through interdigitated Au electrodes, the devices with different grain sizes behaved differently upon relaxation. We observed that the polarization of a mixed halide hybrid perovskite film strongly depends on the background environment. The Quartz Crystal Microbalance measurements reveal that the perovskite film adsorbs Ar gas in the presence of solar light. The combination of Ar gas and solar illumination results in the enhancement of the electric polarization of the mixed halide hybrid perovskite film. Consequently, the photocurrent is increased due to the stronger driving force for the separation of excitons. This observation is illustrated in an actual PSC where the photovoltaic enhancement is observed with Ar gas. Our results suggest that the contribution from the background environment should be taken into consideration when describing the photovoltaic performance of a PSC

Modelling of a reverse flow catalytic membrane reactor for the partial oxidation of methane

Gas-To-Liquid (GTL) processes have great potential as alternative to conventional oil and coal processing for the production of liquid fuels. In GTL-processes the partial oxidation of methane (POM) is combined with the Fischer-Tropsch reaction. An important part of the investment costs of a conventional GTL-plant is related to cryogenic air separation. These costs could be substantially reduced by separating air with recently developed oxygen perm-selective perovskite membranes, which operate at similar temperatures as a POM reactor. Integration of these membranes in the POM reactor seems very attractive because oxygen reacts at the membrane surface resulting in a high driving force over the membrane increasing the oxygen permeation