Several known sesquiterpenoid quinones and quinols (1–9), and kauamide (10), a new polyketide-peptide containing an 11-membered heterocycle, were isolated from the extracts of the Hawaiian marine sponge Dactylospongia elegans. The planar structure of 10 was determined from spectroscopic analyses, and its relative and absolute configurations were established from density functional theory (DFT) calculations of the GIAO NMR shielding tensors, and advanced Marfey’s analysis of the N-MeLeu residue, respectively. Compounds 1 and 3 showed moderate inhibition of β-secretase 1 (BACE1), whereas 1–9 exhibited moderate to potent inhibition of growth of human glioma (U251) cells. Compounds 1–2 and 4–7 were also active against human pancreatic carcinoma (Panc-1) cells.

Four compounds (1-4) were isolated from a Hawaiian sponge of the genus Myrmekioderma. Myrmenaphthol A (1) incorporates two unusual elements into an oxidized steroidal core: a naphthyl AB-ring system and a hydroxy group at C-2. A comparison of the experimental and predicted electronic circular dichroism (ECD) spectra of 1 assigned an S configuration to the lone stereocenter (ΔESI = 0.75; similarity factor 0.8137). Known compounds, cinanthrenol A (2), 3,4-dihydroxypregna-5,17-diene-10,2-carbolactone (3), and 3,4-dihydroxypregna-5,20-diene-10,2-carbolactone (4), were also isolated. Despite literature reports of competitive inhibition at nanomolar levels for 2, neither 2 nor the structurally related 1 showed any activity against estrogen receptors at the concentrations tested.

This work evaluated the ability of 1-ethyl-3-methylimidazolium acetate ionic liquid and potassium hydroxide loaded activated carbon sorbents to remove SO2 and NO2 under simulated atmospheric conditions containing <= 10 ppm of gas contaminants in air at 25 degrees C and relative humidity of 50%. The studies indicate the 1-ethyl-3-methylimidazolium acetate loaded activated carbon, [C(2)mim] [Ac] sorbent, has superior sorption performance for SO2, with breakthrough times greater than pure activated carbon, pelletized KOH activated carbon and granulated KOH loaded activated carbon. The pelletized KOH loaded activated carbon had lowest performance indicating pelletized sorbents are not ideal for use in high flow rate applications such as fuel cells. The SO2 concentration significantly impacted the breakthrough times of the [C(2)mim] [Ac] sorbent, low SO2 concentration resulted in the longest break through times but lowest sorption capacities. The granulated KOH activated carbon and pure activated carbon had highest NO2 break through times compared to [C(2)mim] [Ac] sorbents. The simultaneous SO2 and NO2 sorption studies indicated that the [C(2)mim] [Ac] sorbent had greater selectivity for SO2 than NO2 compared to the KOH sorbents, as evidenced by high breakthrough times for SO2 compared to NO2. Theoretical studies using DFT-B3LYP were performed to elucidate the favored binding interactions of the [C(2)mim] [Ac] with acidic gas contaminants. Theory indicates acidic gas contaminants preferentially interact strongly with the oxygen atoms of the acetate anion compared to the imidazole cation. The computational work also confirmed experiments showing high selectivity of the 1-ethyl-3-methylimidazolium acetate ionic liquid sorbent for SO2 compared to NO2.

Because of the interest attached to compounds based on group 13 elements for their energetic and ecological properties and given the poor reputation of the hydrocarbons on the environment degradation, we examine in this work whether an AxCyH8 combination (A = group 13 element, x + y = 5), could be more optimal in energy and CO2 emission during the hydrogenation and oxidation processes. Starting from pentadiene C5H8 and pure A5H8 (A = B, Al, and Ga) clusters we energetically analyzed C replacement by A (so called metalation) in pentadiene and A replacement C (so called carbonation) in the A5H8 clusters. Moreover, since the release of industrial carbon dioxide is an increasing threat to the environment, compounds which capture and treat CO2 are urgently needed now. However, CO2 treatment and capture requires an energy cost that must be considered in any economic assessment. The CO2 reduction to Methanol CH3OH, widely studied seems to be the perfect way for its recycling but it is not energetically free. That is, the reaction needs to be activated by heating for example. Atomic hydrogen involved in this process also requires an energy input to be produced from natural hydrogen which is in molecular form (H2). Taking all these processes into account, the pure hydrogenated A5H8 cluster composed of group 13 elements seems to be favored for low CO2 release.

We have theoretically investigated how the low-energy conformers of the neutral and the zwitterionic forms of glycine as well as methylcarbamic acid are stabilized by the presence water. The MP2/6-311++G(d,p) method was utilized to conduct calculations on glycine and methylcarbamic acid in both isolated clusters and in clusters embedded in the conductor-like polarizable continuum model (C-PCM), where the clusters explicitly contain between one and ten water molecules. The neutral forms of glycine and methylcarbamic acid were found to have similar hydration energies, whereas the neutral methylcarbamic acid was determined to be approximately 32 kJ mol(-1) more stable than the neutral glycine in the isolated clusters and 30 kJ mol(-1) more stable in the C-PCM embedded clusters. Both the number and strength of the hydrogen bonding interactions between water and the zwitterions drive the stability. This lowers the relative energy of the glycine zwitterion from 50 kJ mol(-1) above neutral glycine, when there are two water molecules in the clusters to 11 kJ mol(-1) below for the clusters containing ten water molecules. For the methylcarbamic acid clusters with two water molecules, the zwitterion is 51 kJ mol(-1) higher in energy than the neutral form, but it remains 13 kJ mol(-1) above the neutral methylcarbamic acid in the clusters containing ten water molecules. When the bulk water environment is simulated by the C-PCM calculations, we find both the methylcarbamic acid and glycine zwitterionic forms have similar energies at 20 kJ mol(-1) above the neutral methylcarbamic acid energy and 10 kJ mol(-1) lower than the neutral glycine energy. Although neither methylcarbamic acid nor glycine have been detected in the interstellar medium yet, our findings indicate that methylcarbamic acid is the more stable product from methylamine and carbon dioxide reactions in a water ice. This suggests that methylcarbamic acid likely plays a role in the intermediate steps if glycine is formed in the interstellar medium.

The Al(3)H(9) and Al(3)H(7) potential energy surfaces were explored using quantum chemistry calculations to investigate the H(2) loss mechanism from Al(3)H(9), which provide new insights into hydrogen production from bulk alane, [AlH(3)](x), a possible energy storage material. We present results of B3LYP/6-311++G(d,p) calculations for the various Al(3)H(9) and Al(3)H(7) optimized local minima and transition state structures along with some reaction pathways for their interconversion. We find the energy for Al(3)H(9) decomposition into Al(2)H(6) and AlH(3) is slightly lower than that for H(2) loss and Al(3)H(7) formation, but the calculations show that H(2) loss from Al(3)H(9) is a lower energy process than for losing hydrogen from either Al(2)H(6) or AlH(3). We found four transition state structures and reaction pathways for Al(3)H(9) → Al(3)H(7) + H(2), where the lowest energy activation barrier is around 25-73 kJ/mol greater than the experimental value for H(2) loss from bulk alane. Intrinsic reaction coordinate calculations show that the H(2) loss pathway involves considerable rearrangement of the H atom positions around a single Al center. Three of the pathways start with the formation of an AlH(3) moiety, which then enables a terminal H on the AlH(3) to get within 1.1 to 1.2 Å of a nearby bridging H atom. The bridging and terminal H atoms eventually combine to form H(2) and leave Al(3)H(9). One implication of these H(2) loss reaction pathways is that, since the H atoms in bulk alanes are all at bridging positions, if a similar H(2) loss mechanism were to apply to bulk alane, then H(2) loss would most likely occur on the bulk alane surface or at a defect site where there should be more terminal H atoms available for reaction with nearby bridging H atoms.

Quantum chemistry calculations are used to explore H-2 loss from AlH3 and Al2H6 and provide insight into the hydrogen production mechanism from polyalanes, a candidate material for energy storage. We present optimized structures for AlH3, Al2H4, Al2H5, and Al2H6 and some reaction pathways for their interconversion. We have found two pathways for the reaction Al2H6 -> Al2H4 + H-2, which have activation barriers lower in energy than for the removal of H-2 from AlH3. However, the low-energy H-2 loss pathway from Al2H6 suggests that the noninteracting Al-H bonds in the transition state structure favor having bonding similar to that occurring in AlH3. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 1639-1645, 2011

We investigated theoretically the interaction between methylamine (CH3NH2) and carbon dioxide (CO2) in the presence of water (H2O) molecules thus simulating the geometries of various methylamine-carbon dioxide complexes (CH3NH2/CO2) relevant to the chemical processing of icy grains in the interstellar medium (ISM). Two approaches were followed. In the amorphous water phase approach, structures of methylamine-carbon dioxide-water [CH3NH2/CO2/(H2O)(n)] clusters (n = 0-20) were studied using density functional theory (DFT). In the crystalline water approach, we simulated methylamine and carbon dioxide interactions on a fragment of the crystalline water ice surface in the presence of additional water molecules in the CH3NH2/CO2 environment using DFT and effective fragment potentials (EFP). Both the geometry optimization and vibrational frequency analysis results obtained from these two approaches suggested that the surrounding water molecules which form hydrogen bonds with the CH3NH2/CO2 complex draw the carbon dioxide closer to the methylamine. This enables, when two or more water molecules are present, an electron transfer from methylamine to carbon dioxide to form the methylcarbamic acid zwitterion, CH3NH2+CO2-, in which the carbon dioxide is bent. Our calculations show that the zwitterion is formed without involving any electronic excitation on the ground state surface; this structure is only stable in the presence of water, i.e. in a methyl amine-carbon dioxide-water ice. Notably, in the vibrational frequency calculations on the methylcarbamic acid zwitterion and two water molecules we find the carbon dioxide asymmetric stretch is drastically red shifted by 435 cm(-1) to 1989 cm(-1) and the carbon dioxide symmetric stretch becomes strongly infrared active. We discuss how the methylcarbamic acid zwitterion CH3NH2+CO2- might be experimentally and astronomically identified by its asymmetric CO2 stretching mode using infrared spectroscopy.

We have theoretically investigated the low energy conformers of neutral glycine (NH(2)CH(2)COOH) and its isomer methylcarbamic acid (CH(3)NHCOOH) in the gas phase. A total of 16 different levels of the theory, including CCSD(T), MP2 and B3LYP methods with various Pople and Dunning type basis sets with and without polarization and diffuse functions were used. We found eight low energy glycine conformers, where the heavy atoms in three have a planar backbone, and four low energy methylcarbamic acid conformers all with non-planar backbones. Interestingly at all levels of theory, we found that the most stable methylcarbamic acid conformer is significantly lower in energy than the lowest energy glycine conformer. The MP2 level and single point CCSD(T) calculations show the lowest energy methylcarbamic acid conformer to be between 31 to 37 kJ mol(-1) lower in energy than the lowest energy glycine conformer. These calculations suggest that methylcarbamic acid might serve as a precursor to glycine formation in the Interstellar Medium (ISM). We also report the theoretical harmonic vibrational frequencies, infrared intensities, moment of inertia, rotational constants and dipole moments for all of the conformers. In order to understand how glycine or methylcarbamic acid might be formed in the ISM, larger calculations which model glycine or its isomer interacting with several surrounding molecules, such as water, are needed. We demonstrate that B3LYP method should provide a reliable and computationally practical approach to modeling these larger systems.

We compare the first few natural molecular shells of several small molecules to the corresponding "restricted Hartree-Fock," "second-order Moller-Plesset," and "local density approximation" molecular shells. Occupation probabilities of each molecular shell are computed ab initio, especially the single-occupation and double-occupation probabilities, that is, the probabilities that the molecular shell is occupied by exactly one electron or by exactly two electrons. We observe that among corresponding molecular shells, the natural molecular shell has the least single-occupation probability and the greatest double-occupation probability. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem 111: 4158-4173, 2011

Supported single-layer MoS2 is a well-established catalyst used by the petroleum industry to remove sulfur from fossil fuels. It is believed that the catalytic activity occurs at the edge of the MoS2 nanoparticles. Recently, atomic-scale images of MoS2 nanoclusters under catalytic working conditions have been obtained with scanning tunneling microscopy (STM). These images show that certain triangular-shaped “magic clusters” are formed, where the triangular shape is attributed to stabilization from excess sulfur at the cluster edges. Much of the recent theoretical rationalization of the MoS2 cluster structures has been formulated by using plane-wave DFT calculations. However, the clusters observed in the recent STM images are small enough that their structures and properties can be evaluated using direct space DFT calculations. We present the theoretically optimized structures obtained with DFT calculations for the series of Mo10Sx clusters with x = 12, 18, 24, 30, and 36. From consideration of their relative energies and simulated STM images, we find the cluster with the Mo10 core most likely being imaged in the STM experiments is the Mo-edge cluster Mo10S24. This contrasts with the assignment to the S-edge cluster Mo10S24 by the experimentalists and their suggestion that Mo-edge clusters are less favored than S-edge clusters when there are 21 or less Mo atoms. Furthermore, despite being able to build initial Mo10Sx structures with a high degree of symmetry, we find the fully optimized Mo10Sx clusters to have essentially no symmetry, and we discuss how this could be playing a role in the MoS2 catalytic activity. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

A single crystal of Ag-12-A (zeolite LTA) was prepared by the dynamic ion-exchange of Na-12-A with aqueous 0.05 M AgNO3. It was washed with CH3OH and allowed to react with a stream of 0.05 M KCl in CH3OH at 294 K. The crystal structure of the product vertical bar K2.35Ag1.1(Ag4Cl4)(0.45)(C3H3O3)(1.1)(K3Cl)(3.45)(K-3(OH)(2))(0.55)(H2O)(>= 3.0)vertical bar-[Si12Al12O48]-LTA (a = 12.292(1) angstrom) was determined by single-crystal X-ray diffraction in the cubic space group Pm (3) over barm at 294 K. It was refined to the final error index, R-1 = 0.052, based on the 371 reflections for which F-o > 4 sigma(F-o). Ag4Cl4 nanoclusters were found in about 45% of the sodalite cavities. Each Ag4Cl4 cluster (interpenetrating tetrahedra; symmetry T-d, Ag-Cl = 3.105(17) angstrom) is held in place by the coordination of each of its four Ag+ ions to three oxygens of the zeolite framework (Ag-O = 2.493(5) angstrom) and by the coordination of each of its four Cl- ions to a K+ ion through a 6-ring (Cl-K = 2.70(3) angstrom). In each of the remaining 55% of the sodalite cavities, two reduced planar 1,3,5-tripyrylium cations, [(CH)(3)O-3](2)(2+) (C-O = 1.52(3) angstrom), are found. These parallel eclipsed rings (symmetry D-3d) have an interplanar distance of only 2.43 angstrom due to sigma double bonding between the rings, the result of four electrons in 12-center bonding pi* orbitals, and to polar attraction. Each ring makes three strong hydrogen bonds (CH center dot center dot center dot O = 2.84(3) angstrom) to oxygens of the zeolite framework, and a Ag+ ion coordinates to the three oxygens of one ring (Ag-O = 2.68(9) angstrom). The large cavities are filled with K+, Cl-, Ag+, OH-, and H2O; the K3Cl2+ unit predominates. The 1,3,5-tripyrylium ring, isoelectronic with benzene, had not been reported before.

The potential energy surfaces (PES) for the singlet and triplet H2O2 molecular system were studied by using the CASSCF, CASPT2, QCISD, QCISD(T), and CCSD(T) methods with the aug-cc-pVDZ, aug-cc-pVTZ, and 6-311+G(3df,2p) basis sets. The CASSCF and CASPT2 results show some significant differences from the QCISD, QCISD(T), and CCSD(T) calculations. The QCISD(T)//QCISD and CCSD(T)//QCISD calculations were found to be suitable for examining most of the species and reaction paths on the H2O2 PES except for a few open shell species which have a multi-reference character. The CASSCF and CASPT2 methods were found to be better suited for treating these open shell species. Consistent with previous theoretical and experimental work we find the hydrogen abstraction reaction O-1 + H2O -> (OH)-O-2 + (OH)-O-2 to have a small or no energy barrier suggesting this pathway may have relevance to the astrochemical formation of hydrogen peroxide in an extraterrestrial environment.