Dynamics of D2 released from the dissociation of D2O on a zirconium surface

Hydrogen is efficiently released during water dissociation on zirconium (Zr), while even very rapid temperature programmed heating of a hydrogen covered Zr surface predominantly leads to dissolution (approximately 99% dissolution). To help resolve these apparently contradictory observations, we have studied the dynamics of water (D2O) dissociation on a crystalline Zr surface by probing the rotational and vibrational energy distributions of the D2 produced using resonant enhanced multiphoton ionization spectroscopy. The internal-state energy distribution of the D2 product was found to be rotationally cold and vibrationally hot with respect to the temperature of the surface. The rotational distribution shows slight deviations from Boltzmann's law, with a mean rotational temperature of 426 K while the surface is at 800 K. The population of the nu"=1 vibration is at least four times higher than a 800 K temperature would allow, this corresponding to a vibrational temperature of 1100 K. Information on the translational energy of the D2 product have also been obtained by time-of-flight spectroscopy and it is found to be nearly thermally equilibrated with the surface temperature. Similar results were obtained from studies of D2 scattered from a clean Zr surface, and of D2 released by a slow thermal desorption process which involves dissolved hydrogen as the source. The reconciliation of the present results with those for thermal desorption of preadsorbed hydrogen implies a role for both surface and subsurface adsorption sites on the Zr surface and clearly demonstrates that at high temperatures, the release of D2 arises from the recombinative desorption of adsorbed hydrogen formed by the complete dissociation of D2O.     

C D : a computer program to generate 1D, 2D and 3D grids of functions dependent on the molecular ab initio electron density

A program to compute many functions dependent on the electron density ρ(r) from the results of ab initio molecular calculations is presented. The program allows the generation of different one-, two-, and three-dimensional grids for further graphical representation or numerical analysis. Other options like extracting separate atom contributions to the function computed or locating maximum and minimum values are also implemented. A number of illustrative applications regarding different ρ(r)-dependent functions are presented and the performance and portability of the program is discussed.     

Structure investigation of Maltacine D1a, D1b and D1c-cyclic peptide lactones of the Maltacine complex from Bacillus subtilis

A new complex of cyclic peptide lactone antibiotics from Bacillus subtilis, which we named Maltacines has recently been described. The structure elucidation of three of them is reported in this paper. The amino acid sequences and structures of the peptides were found by MS(n) of the ring-opened linear peptides that gave uninterrupted sequences of Bn and Y'n ions. The identities of four unknown residues in the sequences were solved by a combination of derivatisation with phenylisothiocyanate (PITC), high-resolution mass spectrometry and H/D exchange. The nature and position of the cyclic structure was disclosed by a chemo-selective ring opening with Na18OH and was found to be a lactone formed between a hydroxyl of residue number 4 and the C-terminal amino acid number 12. For verification of the structure of the B2 + ion, peptides with different combinations of P/Q and P/K at the N-terminus were synthesized. The structures of the four peptides is tentatively suggested to be: D1a: cyclo(4,12)-P-Q-Y-Adip-A-E-T-Y-Orn-HGly-Y-I-OH, D1b: cyclo(4,12)-P-Q-Y-Adip-A-E-T-Y-Orn-S-Y-I-OH and D1c: cyclo(4,12)-P-Q-Y-Adip-A-E-T-Y-K-S-Y-I-OH. Adip = aminodihydroxy pentanoic acid and HGly = hydroxyglycine.     

Tailoring the mobility of a 3D molecule adsorbed on a metal surface

Because of its tetrahedral structure, spirobifluorene is an innovative molecule for molecular mechanics studies by means of scanning tunneling microscopy. On Cu(100), it was observed only anchored at defects because of its mobility at room temperature. To frustrate its diffusion, it was functionalized with phenyl and thiophene groups. Tetraphenylspirobifluorene is also mobile on Cu(100), whereas tetrathienylspirobifluorene is fixed in the middle of the terraces. This very different behavior is an original and unexpected result because both benzene and thiophene are reported to be weakly bound to Cu(100) with almost the same adsorption energy.     

Boosting Charge Transport in a 2D/3D Perovskite Heterostructure by Selecting an Ordered 2D Perovskite as the Passivator

We demonstrate that an ordered 2D perovskite can significantly boost the photoelectric performance of 2D/3D perovskite heterostructures. Using selective fluorination of phenyl-ethyl ammonium (PEA) lead iodide to passivate 3D FA_0.8Cs_0.2PbI₃, we find that the 2D/3D perovskite heterostructures passivated by a higher ordered 2D perovskite have lower Urbach energy, yielding a remarkable increase in photoluminescence (PL) intensity, PL lifetime, charge-carrier mobilities (ϕμ), and carrier diffusion length (L_D) for a certain 2D perovskite content. High performance with an ultralong PL lifetime of ≈1.3 μs, high ϕμ of ≈18.56 cm² V⁻¹ s⁻¹, and long L_D of ≈7.85 μm is achieved in the 2D/3D films when passivated by 16.67 % para-fluoro-PEA₂PbI₄. This carrier diffusion length is comparable to that of some perovskite single crystals (>5 μm). These findings provide key missing information on how the organic cations of 2D perovskites influence the performance of 2D/3D perovskite heterostructures.     

Synthesis of a Polymer-bound Sensitizer and its Application in the Photoisomerization of trans-Vitamin D_3 to cis-Vitamin D_3

The photochemistry of the vitamin D family and their precursors has been the subject of extensive studies for many years1-4. Most of the studies focus on the photoisomer- ization of 7-dehydrocholesterol and that of tachysterol to previtamin D3, which is of commercial importance in the synthesis of vitamin D34, 5. Recently the cis/trans isomerization of vitamin D analogs (Scheme 1) draws attention because of its importance in the synthesis of hydroxylated vitamin D metabolites6. However, o…     

Hydroxylation of a vitamin D A-ring fragment

Summary When the benzoate of (S)-(Z)-2-(5-(tert-butyldimethylsiloxy)-2-methylencyclohexyliden)-ethanol (5) is treated with 2.5 equivalents of Hg(OOCCF₃)₂ in dryTHF, a smooth and selective allylic hydroxylation occurs. The C-1 functionalized vitamin D A-ring synthon6 is isolated in 65 to 70% yield in a single step.

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Hydroxylierung eines Vitamin D A-Ring-Fragments (Kurze Mitt.)

Zusammenfassung Umsetzung des Benzoats von (S)-(Z)-2-(5-(tert-Butyldimethylsiloxy)-2-methylencyclohexyliden)-ethanol (5) mit 2.5 Äquivalenten Hg(OOCCF₃)₂ in trockenemTHF führt zu einer selektiven allylischen Hydroxylierung. Damit ist das an C-1 funktionalisierte Vitamin D A-Ring-Fragment6 in einem einzigen Schritt in einer Ausbeute von 65 bis 70% zugänglich.

     

Bridging the Gap between Structurally Distinct 2D Lamellar Zeolitic Precursors through a 3D Germanosilicate Intermediate

There is broad scientific interest in lamellar zeolitic materials for a large variety of technological applications. The traditional synthetic methods towards two‐dimensional (2D) zeolitic precursors have made a great impact in the construction of families of related zeolites; however, the connection between structurally distinct 2D zeolitic precursors is much less investigated in comparison, thereby resulting in a synthetic obstacle that theoretically limits the types of zeolites that can be constructed from each layer. Herein, we report a Ge‐recycling strategy for the topotactic conversion between different 2D zeolitic precursors through a three‐dimensional (3D) germanosilicate. Specifically, the intermediate germanosilicate can be constructed within 150 min by taking advantage of its structural similarity with the parent lamellar precursor. This process enables the conversion of one 2D zeolite structure into another distinct structure, thus overcoming the synthetic obstacle between two families of zeolitic materials.     

Fringelite D, a Model of the Protist Photosensory Pigments of the Stentorinand Blepharismin Types: The Hypericinand Fringelite D PhotosensitizedDestruction of Bilirubin

Summary.  Using the hypericin and fringelite D photosensitized destruction of bilirubin together with fluorescence spectroscopy it was found that in contrast to fringelite D hypericin behaves as an effective photodynamic agent producing mainly singlet oxygen. This makes fringelite D and concomitantly the related stentorin and blepharismin pigments better suited for the photosensory transduction chain where, as shown recently, an initial proton expulsion reaction plays the fundamental role. Thus, in organisms using these photosensory pigments the production of deleterious oxygen species becomes diminished as compared to hypericin. In addition it was found that complexation with albumin further inhibits bilirubin destruction. Received June 29, 2000. Accepted July 18, 2000     

超分子体系中轴－轮状D.D.主体分子的立体异构现象

组装了轴一轮状主体分子1,1,6,6-四基乙－2,4－二炔-1,6二醇(1)与天然主物异补骨脂素(2)。茴香醚(3)形成的两种超分子异构体的包结物晶体,它们的主客体分子摩尔比分别为1：2和2：1单晶X射线衍射分析了游离主体分子以及超分子包结物晶体的结构,结果表明在主客体分子摩尔比1：2的晶体中,主体分子与异补骨脂素形成氢键,主体分子采取对位交叉式构象;在主客体分子摩尔比为2：1的晶体中,主体分子这间形成氢键,主体分子采取邻位交叉式构,主体分子所取的构象取决于客体分子的性质,当客体分子为氢键好的受体时,可与主体分子生成1：2的包结物;当客体分子为氢键差的受体时,生成2：1有包结物,本文还对三种晶体是的主体分子的立体构苯环两面角,C(1)和C(6)所连基团的夹角和能量变化规律进行了比较和分析。     

On the heterogeneous behaviour in a 2D fluidized bed

The aim of the present paper is to study the influence of the n -index in the porosity function of Richardson–Zaki on the heterogeneous behaviour in a fluidized bed. This parameter takes into account the group effect of particles on the drag of an isolated particle. We have shown up different behaviours of the bed when changing its value.     

From a 1D Sb Coordination Polymer to a 3D Sb Framework with Pyrazine: Switching off the Stereochemically Active Lone-Pair

The one-dimensional coordination polymer ¹_∞[SbCl₃(pyz)] ( 1 ) and the three-dimensional frameworks ³_∞[Sb₂Cl₆(pyz)₃] ( 2 ) and ³_∞[Sb₂I₆(pyz)₃] ( 3 ) were obtained from SbX₃ (X: Cl, I) and pyrazine (pyz). These coordination polymers are, to the best of our knowledge, among the first Sb-based coordination polymers constructed from antimony halides and N-donor ligands. While the Sb³⁺-cations in 1 are coordinated in a square-pyramidal coordination sphere indicating a stereochemically active lone-pair, no stereochemically active Sb-lone-pair is present in 2 and 3 having octahedral coordination spheres around Sb^III. Since 2 can be obtained by heating of 1 , the character of the Sb-lone-pair in 1 can be changed by thermal treatment. Thereby the interlinkage is increased via an additional pyrazine molecule resulting in the octahedral coordination in 2 .     

Synthesis of the ring system of phomactin D using a Suzuki macrocyclization

[reaction: see text]The ring system of phomactin D was synthesized in racemic form in an efficient manner from 2,3-dimethylcyclohexanone. Notable transformations include (1) an alkylation of the enolate of a vinylogous thiolester to install a quaternary stereocenter, (2) a conjugate addition of cyanide to an alpha,beta-unsaturated aldehyde, (3) the formation of a Weinreb amide directly from a cyanohydrin, and (4) an intramolecular Pd-mediated Suzuki coupling of a B-alkyl-9-BBN derivative and a vinyl iodide to form the macrocyclic ring.     

Direct Self‐Assembly of a 2D and 3D Star of David

Two‐ and three‐dimensional metallosupramolecules shaped like a Star of David were synthesized by the self‐assembly of a tetratopic pyridyl ligand with a 180° diplatinum(II) motif and Pd^II ions, respectively. In contrast to other strategies, such as template‐directed synthesis and stepwise self‐assembly, this design enables the formation of 2D and 3D structures in one step and high yield. The structures were characterized by both one‐dimensional (¹H, ¹³C, ³¹P) and two‐dimensional (COSY, NOESY, DOSY) NMR spectroscopy, ESI‐MS, ion‐mobility mass spectrometry (IM–MS), AFM, and TEM. The stabilities of the 2D and 3D structures were measured and compared by gradient tandem mass spectrometry (gMS²). The high stability of the 3D Star of David was correlated to its high density of coordination sites (DOCS).     

Fringelite D, a Model of the Protist Photosensory Pigments of the Stentorinand Blepharismin Types: The Hypericinand Fringelite D PhotosensitizedDestruction of Bilirubin

 Using the hypericin and fringelite D photosensitized destruction of bilirubin together with fluorescence spectroscopy it was found that in contrast to fringelite D hypericin behaves as an effective photodynamic agent producing mainly singlet oxygen. This makes fringelite D and concomitantly the related stentorin and blepharismin pigments better suited for the photosensory transduction chain where, as shown recently, an initial proton expulsion reaction plays the fundamental role. Thus, in organisms using these photosensory pigments the production of deleterious oxygen species becomes diminished as compared to hypericin. In addition it was found that complexation with albumin further inhibits bilirubin destruction.     

Dynamic control of 3D chemical profiles with a single 2D microfluidic platform

Dynamic control of three-dimensional (3D) chemical patterns with both high precision and high speed is important in a range of applications from chemical synthesis, flow cytometry, and multi-scale biological manipulation approaches. A central challenge in controlling 3D chemical patterns is the inability to create rapidly tunable 3D profiles with simple and direct approaches that avoid complicated microfabrication. Here, we present the ability to rapidly and precisely create 3D chemical patterns using a single two-dimensional (2D) microfluidic platform. We are not only able to create these 3D patterns, but can rapidly switch from one mode to another (e.g. from a focused to a defocused pattern in less than 1 second) via simple changes in inlet pressures. A feedback control scheme with a pressure modulation mechanism controls the pressure changes. In addition to experiments, we conducted computational simulations for guiding the optimum design of the channels as well as revealing the sensitivity of the patterns to the channel dimensions; these simulations have high experimental correlations. We also show that microvortices play an important role in creating these tunable 3D patterns in this microfluidic platform. We quantitatively determine the degrees of the focused patterns in 2D cross-sections using a focus index with a 2D Gaussian function. Our integrated approach combining feedback control with simple microfluidics will be useful for researchers in diverse disciplines including chemistry, engineering, physics, and biology.     

Construction of 3D layer-pillared homoligand coordination polymers from a 2D layered precursor

Herein, we present a new method for preparing homoligand 3D coordination polymers. First, a layered metal-organic framework Zn3(BDC)3(H2O)2 x 4DMF 1 (BDC is terephthalate, DMF is N,N-dimethylformamide) was fabricated from a H2BDC by liquid-liquid diffusion. Second, the layered product, 1, was used as a precursor to solvothermally react with further H2BDC at 140-180 degrees C, resulting in two products of BDC insertion into the layered structure. These are [Zn3(p-BDC)4] x 2HPIP, 2 (HPIP is partly protonated piperazine), and [Zn3(p-BDC)3(H2BDC)] x (C6H15NO) x H2O x 3DMF, 3 (C6H15NO is triethylamine N-oxide). Single-crystal X-ray diffraction shows that 2 possesses a layer-pillared structure of mu4-BDC, with 1D channels, while 3 has a layer-pillared structure of mu2-BDC, with 2D channels. N2-sorption experiments show 3 has a relatively high BET surface area of 750 m(2)/g. It is proposed that 2 follows the crystal growth mechanism of Ostwald ripening, whereas the crystal structure of 3 might be formed by an insertion mechanism.