Metal oxides are widely used in industry and academia. [1,2] As their electron-acceptor or acidic strengths play vital roles in their applications, there needs to be a general scale that can quantitatively compare their relative acidic strengths. Conventionally, calorimetric heat measurements during adsorption of probe molecules, [3] infrared spectroscopic analyses of adsorbed bases or acids, [5,6] application of indicator dyes, [4] and temperature-programmed desorption of the pre-adsorbed bases are standard methods for the analyses of their acidic strengths. [6][7][8] However, these methods are not suitable for a quantitative comparison. Thus, unlike metal ions in solution, [9] no such scales have been available for metal oxides.One of the important types of interaction between adsorbates and metal oxides is the formation of coordinate covalent bonding between adsorbates and the surface metal ions. For instance, in the case of TiO 2 , those compounds that have enediol, [10][11][12][13][14] carboxylate, [15][16][17][18] and nitrile [19,20] groups have been shown to form coordinate covalent bonding with the surface Ti 4+ ions. In this type of interaction, the adsorbateto-metal charge-transfer interaction is often the lowestenergy electronic transition. However, in the case of alizarin (Figure 1 a, inset) on TiO 2 , a theoretical study has suggested that the intramolecular charge-transfer (IMCT) band from the catechol moiety to the entire ring system is the lowestenergy transition. [11] Electronegativity (EN) is one of the most important fundamental properties of an atom, which represents "the power of an atom in a compound to attract electrons to itself". [21,22] Among various EN scales that have been developed, [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] Sandersons scale and the associated EN equalization principle [31][32][33][34][35] are successful in calculating the bond energies of various compounds [32][33][34][35][36] , elucidating the acidic and basic properties of zeolites, [37,38] and establishing the relationship between the reactivity and the composition of the zeolite that served as the guideline for the preparation of optimum zeolite catalysts.[39] These methods have also been used for various other purposes. [40][41][42][43][44] However, owing to a lack of experimental data, Sandersons EN scale has not been extended to lanthanides (Ln) during the last five decades, despite the fact that lanthanide-containing compounds are widely used.Herein, we report that the IMCT transition of alizarin is still the lowest-energy transition when it is adsorbed on various metal oxides and sulfides, regardless of the nature of the metal ion. The charge-transfer transition serves as a highly sensitive and accurate probe for the quantitative comparison of the acidic strengths of the metal oxides and sulfides. We also report the factors that govern the surface acidity, which allows us to assign for the first time the important Sandersons EN values of Ln 3+ ions (S Ln 3+) and Ce 4+. To experimentally ver...
Zeolites are crystalline nanoporous aluminosilicates widely used in industry. In order for zeolites to find applications as innovative materials, they need to be organized into large two- and three-dimensional (2D and 3D) arrays. We report that uniformly aligned polyurethane films can serve as templates for the synthesis of uniformly aligned 2D and possibly 3D arrays of silicalite-1 crystals, in which the orientations of the crystals are controlled by the nature of the polymers. We propose that the supramolecularly organized organic-inorganic composites that consist of the hydrolyzed organic products and the seed crystals are responsible for this phenomenon.
Dye-sensitized nanoporous TiO 2 solar cells (DSSCs) can be classified into two types, namely, Type-I and Type-II. Type-I DSSCs are the DSSCs in which electrons are injected from the adsorbed dyes by photoexcitation of the dyes followed by electron injection from the excited dyes to TiO 2 (pathway A). Type-II DSSCs are the DSSCs in which electrons are injected not only by pathway A but also by direct one-step electron injection from the dyes to TiO 2 by photoexcitation of the dye-to-TiO 2 charge-transfer (DTCT) bands (pathway B). The DSSCs employing catechol (Cat) or its derivatives as the sensitizers have been the typical examples of Type-II DSSCs. However, their solar energy-to-electricity conversion efficiencies (η) have never exceeded 0.7%, and the external quantum efficiencies (EQE) at the absorption maximums of the DTCT bands have never exceeded 10%. We found that the attachment of electron-donating compounds such as (pyridin-4-yl)vinyl and (quinolin-4-yl)vinyl, respectively, to Cat (designated as Cat-v-P and Cat-v-Q, respectively) leads to 2-and 2.7-fold increases, respectively, in η, driven by large increases in short circuit current (J sc ). The EQE increased from 8.5 to 30% at 400 nm upon changing from Cat to Cat-v-P, at which only the DTCT band absorbs. In the case of the Cat-v-Q-sensitized DSSC, even the η obtained by exciting only the DTCT band was higher than 1%. Interestingly, the illumination of only the DTCT band resulted in the increase of fill factor from 62.6% to 72.3%. This paper provides for the first time an insight into the strategy to increase the η values of Type-II DSSCs.
The faithful pairing of nucleobases, through complementary hydrogen-bond (H-bond) donors and acceptors, forms the foundation of the genetic code. However, there is no reason to assume that the requirements for duplex stability and replication must limit the genetic alphabet to only two base pairs, or for that matter, hydrogen-bonded base pairs. 1 Expansion of this alphabet to contain a third base pair would allow for the encoding of additional information and would make possible a variety of in vitro experiments using nucleic acids with unnatural building blocks. In recent progress toward expanding the genetic alphabet, 2 a variety of unnatural nucleobases have been characterized that form pairs based not on hydrogen bonds but rather on interbase hydrophobic interactions. One of the most promising of these third base-pair candidates is the self-pair formed between two 7-azaindole nucleosides (7AI, Figure 1a). However, following incorporation, 7AI inhibits continued primer extension. Here we show that mammalian polymerase can efficiently extend primers containing 7AI and, when combined with the Klenow fragment of Escherichia coli polymerase I (KF), can efficiently replicate DNA containing the unnatural self-pair with reasonable fidelity.Pol is a mammalian polymerase that functions primarily to gap-fill during base excision repair. Pol can also substitute for DNA pol I in the synthesis of the short stretches of DNA required to join Okazaki fragments in E. coli, which suggests that the polymerase is able to play a role in replicative synthesis. 3 Pol can perform trans-lesion synthesis on templates containing abasic sites, 4 cis-syn thymine dimers, 5 and cisplatin adducts, all of which are strong replication blocks to most DNA polymerases. Interestingly, during in vitro DNA replication, pol can replace other stalled polymerases at a modified base and extend the 3′-terminus of the intermediate. 6 Pol incorporation kinetics were first examined with fully natural DNA using a 23-nt primer annealed to a 45-nt template (Scheme 1) that contained a native base (dG, dA, dT, or dC) at position X. Steady-state kinetics were performed using literature procedures. 2 For the natural bases, pol incorporated the correct dNTP at 37°C with efficiencies of 3.4 × 10 5 M -1 min -1 for dATP opposite dT; 1.9 × 10 6 M -1 min -1 for dTTP opposite dA; 6.6 × 10 5 M -1 min -1 for dCTP opposite dG; and 7.0 × 10 5 M -1 min -1 for dGTP opposite dC.The unnatural d7AITP was then evaluated as a substrate for pol , using the same 23-nt primer and 45-nt template containing 7AI at position X. Pol inserted d7AITP, as well as each natural dNTP, opposite 7AI with a k cat /K M that was less than 10 3 M -1 min -1 . These rates are significantly slower than those for native synthesis and more than 10 2 slower than the rate at which KF inserts d7AITP opposite 7AI. Therefore, in contrast to KF, pol does not efficiently insert the unnatural triphosphate opposite any base in the template, including 7AI.To examine the pol -mediated extension of the 7AI:7AI selfp...
Synthesis of semiconductor nanoparticles with uniform shapes, sizes, and compositions in series with a gradual size reduction has not been achieved for two-dimensional molecular sheets. We report a large-scale (>2.6 g) synthesis of 0.75-nm-thick diamond-shape lepidocrocite-type titanate molecular sheets with the sizes decreasing from (27.3, 19.1) to (7.7, 5.5), where the numbers in parentheses represent the long and short diagonal lengths, respectively, in nm. This is the first example of synthesizing semiconductor nanoparticles in series with the dimensionality reduction from two to zero, without coating the surfaces with surface-passivating ligands. The titanate molecular sheets showed three exciton-absorption bands in the 4.0-6.5 eV region, the absorption energies of which increased with decreasing the area. Contrary to the common belief, the per-unit cell oscillator strengths gradually increased with increasing area and the per-particle oscillator strengths increased in proportion to the area. The average reduced exciton masses along the two diagonal axes were 0.10 and 0.11 m e, respectively, which were much smaller than those of bulk titanates (by 60-130 times). The estimated average Bohr radii along the two-diagonal axes were 4.8 and 4.3 nm, respectively.
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