Pressure dependent stability and structure of carbon dioxide - A density functional study including long-range corrections

First-principles density functional theory (DFT) is used to study the solid- state modifications of carbon dioxide up to pressures of 60 GPa. All known molecular CO2 structures are investigated in this pressure range, as well as three non-molecular modifications. To account for long-range van der Waals interactions, the dispersion corrected DFT method developed by Grimme and co- workers (DFT-D3) is applied. We find that the DFT-D3 method substantially improves the results compared to the uncorrected DFT methods for the molecular carbon dioxide crystals. Enthalpies at 0 K and cohesive energies support only one possibility of the available experimental solutions for the structure of phase IV: the R3¯c modification, proposed by Datchi and co-workers [Phys. Rev. Lett.103, 185701 (2009)]. Furthermore, comparing bulk moduli with experimental values, we cannot reproduce the quite large—rather typical for covalent crystal structures—experimental values for the molecular phases II and III

Water adsorption on vanadium oxide thin films in ambient relative humidity.

In this work, ambient pressure x-ray photoelectron spectroscopy (APXPS) is used to study the initial stages of water adsorption on vanadium oxide surfaces. V 2p, O 1s, C 1s, and valence band XPS spectra were collected as a function of relative humidity in a series of isotherm and isobar experiments. Experiments were carried out on two VO2 thin films on TiO2 (100) substrates, prepared with different surface cleaning procedures. Hydroxyl and molecular water surface species were identified, with up to 0.5 ML hydroxide present at the minimum relative humidity, and a consistent molecular water adsorption onset occurring around 0.01% relative humidity. The work function was found to increase with increasing relative humidity, suggesting that surface water and hydroxyl species are oriented with the hydrogen atoms directed away from the surface. Changes in the valence band were also observed as a function of relative humidity. The results were similar to those observed in APXPS experiments on other transition metal oxide surfaces, suggesting that H2O-OH and H2O-H2O surface complex formation plays an important role in the oxide wetting process and water dissociation. Compared to polycrystalline vanadium metal, these vanadium oxide films generate less hydroxide and appear to be more favorable for molecular water adsorption

3,12-Diaza-6,9-diazo­nia-2,13-dioxotetra­decane bis­(perchlorate)

The crystal structure of the title diprotonated diacetyl­triethyl­ene­tetra­mine (DAT) perchorate salt, C10H24N4O2 2+·2ClO4 −, can be described as a three-dimensional assembly of alternating layers consisting of diprotonated diacetyl­triethyl­ene­tetra­mine (H2DAT)2+ strands along [100] and the anionic species ClO4 −. The (H2DAT)2+ cations in the strands are connected via N—H⋯O hydrogen bonding between the acetyl groups and the amine groups of neighbouring (H2DAT)2+ cations. Layers of (H2DAT)2+ strands and perchlorate anions are connected by a network of hydrogen bonds between the NH and NH2 groups and the O atoms of the perchlorate anion. The asymmetric unit consits of one perchlorate anion in a general position, as well as of one cation that is located on a center of inversion

Biomimetic synthetic studies on the hicksoane alkaloids

The hicksoane alkaloids contain an unusual propane-2,2-diamine unit embedded within a 1,3,6-triazocane, the only natural product known to possess this eight-membered heterocycle. Herein, we report the results examining a biosynthesis proposal that this heterocycle emerges from a late-stage reaction of a dipeptide with acetone. Ile-Trp-CONH2 and Trp-Ile-CONH2 dipeptides were trialled as substrates; in both cases, the intermediate iminium ion did not engage with the primary amide to form the triazocane, reacting instead to generate an imidazolidinone and a β-carboline, respectively. The results from this study infer the triazocane present in these alkaloids is unlikely to be biosynthesised by the late-stage reaction of a dipeptide with biogenic acetone

Expanding Heteroaromatic and 2-Aminosugar Chemical Space Accessible from the Biopolymer Chitin

Herein, we report the expansion of chemical space available from chitin, accessible via the biogenic N-platforms 3A5AF, M4A2C, and di-HAF. The biologically active heteroaromatics furo[3,2-d]pyrimidin-4-one and furo[3,2-d]pyrimidin-4-amine can be selectively accessed from 3A5AF and M4A2C, respectively. The chiral pool synthon di-HAF is a viable substrate for Achmatowicz rearrangement, providing streamlined access to 2-aminosugars possessing a versatile hydroxymethyl group at C5

CCDC 797519: Experimental Crystal Structure Determination

Related Article: K.A.Wichmann,T.Sohnel,G.J.S.Cooper|2012|J.Mol.Struct.|1012|37|doi:10.1016/j.molstruc.2011.12.02