Thermodynamics of hydrogen solution and hydride formation in Pd-Mn alloys. 1. Disordered alloys and a correlation effect

The thermodynamics of H(2) solution and hydride formation/decomposition have been determined by reaction calorimetry (303 K) for disordered face centered cubic (fcc) Pd-Mn alloys. This alloy system belongs to the expanded lattice category which predicts that and DeltaH(plat) for H(2) absorption should be more exothermic than those for Pd; the experimental results are that the former is more exothermic, at least at the higher Mn contents, but the latter is not. There is a regular decrease in the H capacity (at p(H)2 = 0.2 MPa) with atom fraction Mn. A linear dependence of log p(H)2 upon H content is found in the single hydride phase for all of these alloys suggesting that DeltaH(H) and DeltaS(H) are also linear functions of r in this region. This is confirmed using the Pd(0.875)Mn(0.125) alloy which has no two-phase region (303 K). It is shown for the Pd(0.875)Mn(0.125) alloy and for Pd that the changes of partial enthalpies and entropies with H content are correlated so as to minimize changes of mu(H).     

Using computer software in the teaching of mechanics

The paper looks at ways of using computer software in the teaching of mechanics. The various reasons for using software are discussed to justify the use of software. A number of examples are then considered to show how different types of software can be used. Examples shown are taken from very specific types of software, more general simulation software and mathematical software. The paper discusses using software to explore mechanics, to challenge ‘misconceptions’, to make links between mathematical representations and motion and to solve non-standard problems. The paper also stresses the need for structured approaches to the use of software.     

High-yield syntheses and reactivity studies of Fe10 "ferric wheels": structural, magnetic, and computational characterization of a star-shaped Fe8 complex

Convenient, high-yield routes have been developed to [Fe 10(OMe) 20(O 2CR) 10] ( 1) "ferric wheels" involving the alcoholysis of [Fe 3O(O 2CR) 6(H 2O) 3] (+) salts in MeOH in the presence of NEt 3. Reactivity studies have established [Fe 10(OMe) 20(O 2CMe) 10] ( 1a) to undergo clean carboxylate substitution with a variety of other RCO 2H groups to the corresponding [Fe 10(OMe) 20(O 2CR) 10] product. In contrast, the reaction with phenol causes a nuclearity change to give a smaller [Fe 8(OH) 4(OPh) 8(O 2CR) 12] ( 2) wheel. Similarly, reactions of [Fe 10(OMe) 20(O 2CR) 10] with the bidentate chelate ethylenediamine (en) cause a structural change to give either [Fe 8O 5(O 2CMe) 8(en) 8](ClO 4) 6 ( 3) or [Fe 2O(O 2CBu (t))(en) 4](NO 3) 3 ( 4), depending on conditions. Complex 3 possesses a "Christmas-star" Fe 8 topology comprising a central planar [Fe 4(mu 4-O)] (10+) square subunit edge-fused to four oxide-centered [Fe 3(mu 3-O)] (7+) triangular units. Variable-temperature, solid-state dc and ac magnetization studies on complexes 1a- 4 in the 5.0-300 K range established that all the complexes possess an S = 0 ground state. The magnetic susceptibility data for 4 were fit to the theoretical chi M versus T expression derived by the use of an isotropic Heisenberg spin Hamiltonian and the Van Vleck equation, and this revealed an antiferromagnetic exchange parameter with a value of J = -107.7(5) cm (-1). This value is consistent with that predicted by a previously published magnetostructural relationship. Theoretically computed values of the exchange constants in 3 were obtained with the ZILSH method, and the pattern of spin frustration within its core and the origin of its S = 0 ground state have been analyzed in detail.     

Mixed transition metal-lanthanide complexes at high oxidation states: heteronuclear CeIVMnIV clusters

The syntheses of the first mixed-metal CeIVMnIV complexes are reported. [CeMn2O3(O2CMe)(NO3)4(H2O)2(bpy)2](NO3) (1; bpy=2,2'-bipyridine) was obtained from the reaction of Mn(NO3)2.xH2O and bpy with (NH4)2Ce(NO3)6 in a 1:1:2 molar ratio in 25% aqueous acetic acid. The complexes [CeMn6O9(O2CR)9(X)(H2O)2]y+ (R=Me, X=NO3-, y=0 (2); R=Me, X=MeOH, y=+1 (3); R=Et, X=NO3-, y=0 (7)) were obtained from reactions involving a [Mn(O2CR)2].4H2O/CeIV ratio of approximately 1:1.5 in concentrated aqueous carboxylic acid. A related reaction in less-concentrated aqueous acetic acid and in the presence of L (where L=2-hydroxy-6-methylpyridine (mhpH), 2-pyrrolidinone (pyroH), or pyridine (py)) gave [Ce3Mn2O6(O2CMe)6(NO3)2(L)a(H2O)b] (L=mhpH, a=4, b=0 (4); L=pyroH, a=2, b=3 (5)) and {{(pyH)3[Ce3Mn2O6(O2CMe)7.5(NO3)3].(HO2CMe)0.5.(H2O)2}2(NO3)}n (6), respectively. Solid-state magnetic susceptibility (chiM) data for compounds 1, 4, and 5 were fit to the theoretical chiMT versus T expression for a MnIV2 complex derived using the isotropic Heisenberg spin Hamiltonian (H=-2J?1? 2) and the Van Vleck equation. The obtained fit parameters were (in the format J, g) 1, -45.7(3) cm(-1), 1.95(5); 4, -0.40(10) cm(-1), 2.0(1); and 5, -0.34(10) cm(-1), 2.0(1), where J is the exchange interaction constant between the two MnIV ions. The data for compound 3 were fit by a matrix diagonalization method that gave J1=-5.8 cm(-1), J2=-0.63 cm(-1), J3 approximately 0, and g=2.0(1), where J1 and J2 are the exchange interactions for the [MnIV2O2(Omicron2CMe)] and [MnIV2O(Omicron2CMe)2] units, respectively, and J3 for a uniform next-nearest-neighbor interaction. Theoretical estimates of the exchange constants in compounds 1 and 3 obtained with the ZILSH method were in excellent and good agreement, respectively, with the values obtained from fits of the magnetization data. The difference for 3 is assigned to the presence of the Ce4+ ion, and atomic bond indices obtained from the ZILSH calculations were used to rationalize the values of the various exchange constants based on metal-ligand bond strengths.     

Investigation of cell culture media infected with viruses by pyrolysis mass spectrometry: Implications for bioaerosol detection

Mass spectrometry coupled with a pyrolysis inlet system was used to investigate media from cell cultures infected with viruses. Cell culture media is an intricate mixture of numerous chemical constituents and cells that collectively produce complicated mass spectra. Cholesterol and free fatty acids were identified and attributed to lipid sources in the media (blood serum supplement and plasma membranes of host cells). These lipid moieties could be utilized as signature markers for rapidly detecting the cell culture media. Viruses are intracellular parasites and are dependent upon host cells in order to exist. Therefore, it is highly probable that significant quantities of media needed to grow and maintain viable host cells would be present if a viral agent were disseminated as an aerosol into the environment. Cholesterol was also detected from a purified virus sample, further substantiating its use as a target compound for detection. Implications of this research for detection of viral bioaerosols, using a field-portable pyrolysis mass spectrometer, is described.