http://idea.library.drexel.edu/handle/1860/785 Search the Channel search http://idea.library.drexel.edu/simple-search http://idea.library.drexel.edu/handle/1860/2626 Title: Identification of a novel lysophospholipid acyltransferase in Saccharomyces cerevisiae <br/> <br/>Authors: Shilpa, Jain; Stanford, NaTaza; Bhagwat, Neha; Seiler, Brian; Costanzo, Michael; Boone, Charles; Oelkers, Peter <br/> <br/>Abstract: The incorporation of unsaturated acyl chains into phospholipids during de novo synthesis is primarily mediated by the 1-acylsn- glycerol-3-phosphate acyltransferase reaction. In S. cerevisiae, Slc1 has been shown to mediate this reaction but distinct activity remains after its removal from the genome. To identify the enzyme that mediates the remaining activity, we performed synthetic genetic array analysis using a slc1Δ strain. One of the genes identified by the screen, LPT1, was found to encode for an acyltransferase that uses a variety of lysophospholipid species, including 1-acyl-sn-glycerol-3-phosphate. Deletion of LPT1 had a minimal effect on 1-acyl-snglycerol- 3-phosphate acyltransferase activity but over-expression increased activity 7-fold. Deletion of LPT1 abrogated the esterification of other lysophospholipids and over-expression increased lysophosphatidylcholine acyltransferase activity 7-fold. The majority of this activity co-purified with microsomes. To test the putative role for this enzyme in selectively incorporating unsaturated acyl chains into phospholipids, in vitro, substrate concentration series experiments were performed with the four acyl-CoA species commonly found in yeast. While the saturated palmitoyl-CoA and stearoyl-CoA showed a lower apparent Km, the monounsaturated palmitoleoyl-CoA and oleoyl-CoA showed a higher apparent Vmax. Arachidonyl-CoA, although not abundant in yeast, also had a high apparent Vmax. Pulse-labeling of lpt1Δ strains showed a 30% reduction in [3H]oleate incorporation into phosphatidylcholine only. Therefore, Lpt1p, a member of the membrane bound o-acyltransferase gene family, seems to work in conjunction with Slc1 to mediate the incorporation of unsaturated acyl-chains into the sn-2 position of phospholipids. http://idea.library.drexel.edu/handle/1860/2616 Title: Asymmetric band profile of the Soret band of deoxymyoglobin is caused by electronic and vibronic perturbations of the heme group rather than by a doming deformation <br/> <br/>Authors: Schweitzer-Stenner, Reinhard; Gorden, John Paul; Hagarman, Andrew <br/> <br/>Abstract: We measured the Soret band of deoxymyoglobin deoxyMb , myoglobin cyanide MbCN , and aquo-metmyoglobin all from horse heart with absorption and circular dichroism CD spectroscopies. A clear non-coincidence was observed between the absorption and CD profiles of deoxyMb and MbCN, with the CD profiles red- and blueshifted with respect to the absorption band position, respectively. On the contrary, the CD and absorption profiles of aquametMb were nearly identical. The observed noncoincidence indicates a splitting of the excited B state due to heme-protein interactions. CD and absorption profiles of deoxyMb and MbCN were self-consistently analyzed by employing a perturbation approach for weak vibronic coupling as well as the relative intensities and depolarization ratios of seven bands in the respective resonance Raman spectra measured with B-band excitation. The respective By component was found to dominate the observed Cotton effect of both myoglobin derivatives. The different signs of the noncoincidences between CD and absorption bands observed for deoxyMb and MbCN are due to different signs of the respective matrix elements of A1g electronic interstate coupling, which reflects an imbalance of Gouterman’s 50:50 states. The splitting of the B band reflects contributions from electronic and vibronic perturbations of B1g symmetry. The results of our analysis suggest that the broad and asymmetric absorption band of deoxyMb results from this band splitting rather than from its dependence on heme doming. Thus, we are able to explain recent findings that the temperature dependences of CO rebinding to myoglobin and the Soret band profile are uncorrelated Ormos et al., Proc. Natl. Acad. Sci U.S.A. 95, 6762 1998 . http://idea.library.drexel.edu/handle/1860/2612 Title: Interactions of methane, ethane and pentane with the (110C) surface of γ−alumina <br/> <br/>Authors: Cai, Shu-Hui; Chihaia, Viorel; Sohlberg, Karl <br/> <br/>Abstract: Adsorptions of methane, ethane and pentane on the γ-alumina (110C) surface are investigated with semi-empirical (PM3) cluster calculations. It is found that the abstraction of an H atom accompanied by the formation of a C-O bond is the most favorable reaction for methane on the alumina surface. For ethane- and pentane-alumina interactions, the abstraction of two H atoms accompanied by the formation of an alkene is the most favorable reaction. The surface Al atoms help to promote the reactions, but are not directly involved in the bond formation. http://idea.library.drexel.edu/handle/1860/1824 Title: Migration of aluminum atoms in the transformation of γ− to θ−alumina <br/> <br/>Authors: Cai, Shu-Hui; Sohlberg, Karl <br/> <br/>Abstract: γ− and θ−alumina are two metastable phases of aluminum oxide observed along the thermal dehydration sequence of boehmite before conversion to the final product α−alumina. The transformation from γ− to θ−alumina was studied by using Al16O24 cells. Motion of some Al atoms from their γ−alumina positions to new positions and no O motions result in an approximate structure that, upon relaxation by first-principles calculations, becomes the known θ−alumina structure. Total-energy calculations along the paths of the atomic motions have been used to map out transformation pathways. The model accurately predicts experimentally observed domain boundaries in θ−alumina and the γ− to θ−alumina conversion rate. http://idea.library.drexel.edu/handle/1860/1823 Title: Correlation of substituent parameter values to electronic properties of molecules <br/> <br/>Authors: Carroll, Natalie R.; Matsunaga, Nikita; Sohlberg, Karl <br/> <br/>Abstract: There are a vast number of organic compounds that could be considered for use in molecular electronics. Because of this, the need for efficient and economical screening tools has emerged. We have demonstrated that the substituent parameter values (σ), commonly found in advanced organic chemistry textbooks, correlate very strongly with features of the charge migration process. This result supports the use of the σ values as a low cost time saving tool in the selection of compounds for use in molecular electronic devices. http://idea.library.drexel.edu/handle/1860/1822 Title: The thermodynamic stability of three near-degenerate phases of platinum dioxide <br/> <br/>Authors: Zhuo, Shuping; Sohlberg, Karl <br/> <br/>Abstract: The thermodynamic stability of the three nearly energy degenerate crystal structures of PtO2 is studied here with first-principles-based calculations of their free energies. For P = 0 the α-(CdI2) structure is the thermodynamically stable phase at low temperature, while the β-(CaCl2) structure is stable at high pressure. The β'- (rutile) structure represents an unstable fixed point on the potential energy surface, or is possibly just barely bound. These results reconcile seemingly contradictory findings and answer longstanding questions about PtO2. http://idea.library.drexel.edu/handle/1860/1820 Title: Gao et al. Reply <br/> <br/>Authors: Gao, H. J.; Sohlberg, Karl; Xue, Z. Q.; Chen, H.Y.; Hou, S. M.; Ma, L. P.; Fang, X.W.; Pennycook, Stephen J. http://idea.library.drexel.edu/handle/1860/1817 Title: The Influence of Surface Reconstruction and C-impurities on Photocatalytic Water Dissociation by TiO2 <br/> <br/>Authors: Nie, Xiliang; Sohlberg, Karl <br/> <br/>Abstract: TiO2 is well known as a prototype photocatalyst for water dissociation. To understand the mechanism of its photocatalytic water dissociation we performed first-principles calculations. We find that the surface of the catalytically favorable (TiO) termination is very different from the physically favorable (oxygen) termination. The calculated surface energy of the catalytically favorable (TiO) termination is about 10 times larger than that of the physically favorable (oxygen) termination. Analysis of the surface band structure suggests that while O-vacancies are intrinsic active sites for water dissociation into H2 and O2 gas, they are not essential for photocatalytic water dissociation. We also find that carbon impurities decrease the band-gap of TiO2, in agreement with previously reported experimental results. Moreover, we identify the origin of the arcane “double band gap” in carbon doped TiO2. The two onsets seen in the photoabsorption spectrum result from excitations from two of three C p-states within the band gap, not from domains of different composition. http://idea.library.drexel.edu/handle/1860/1816 Title: Phase transformation mechanism between γ- and θ-alumina <br/> <br/>Authors: Cai, Shu-Hui; Rashkeev, Sergey N.; Pantelides, Sokrates T.; Sohlberg, Karl <br/> <br/>Abstract: y-alumina transforms to θ-alumina and finally to a-alumina in the sequence of thermal dehydration of boehmite. We report a detailed theoretical investigation of the y- to θ-alumina transformation based on first principles density-functional calculations. Although the unit cells of cubic y-alumina and monoclinic θ-alumina look quite different, we have identified cells for both the polytypes (with the composition Al16O24) that look very similar and can be continuously transformed one to another. The transformation may be described by a set of aluminum atom migrations between different interstitials while the oxygen atoms remain fixed. Total-energy calculations along the paths of the atomic migrations have been used to map out possible transformation pathways. The calculated conversion rate accurately predicts the experimentally measured transformation temperature. The deduced orientation relationships between the y- and θ-alumina forms also agree with experimental observations. The formation of several different interfaces observed in domain boundaries of u-alumina may correspond to different migration paths of the aluminum atoms in neighboring domains during the y- to θ-alumina phase transition. http://idea.library.drexel.edu/handle/1860/1812 Title: Chromium and lanthanum on transition alumina surfaces: The role of bulk point-defect distributions on catalytic activity <br/> <br/>Authors: Rashkeev, Sergey N.; Sohlberg, Karl; Glazoff, M. V.; Novak, J.; Pennycook, Stephen J.; Pantelides, Sokrates T. <br/> <br/>Abstract: We employ a combination of Z-contrast scanning transmission electron microscopy (ZSTEM) and first-principles density-functional calculations to investigate the interaction between metal atoms and cubic alumina catalytic supports. We show that there are two observed La sites at the porous γ- alumina surface, and that single La atoms do not exhibit a tendency to cluster. Cr behaves very differently from La - it has a tendency to cover the alumina surface in ordered, periodic raft-like patches. The degradation of the chromia/alumina catalyst is related to the possibility for the chromium to move away from the surface into the bulk, and the activation barrier for such a process is higher in η- alumina than in γ- alumina, i.e., η- alumina is a more durable support for chromium catalyst.