Hydration of mineral surfaces probed at the molecular level

By employing the nonlinear optical, interface selective experiment of sum frequency spectroscopy together with independent ab initio and density functional theory calculations, we determine the functional species of a corundum (001) surface: doubly coordinated OH groups which differ in their bond tilt angles. The interaction of the functional species with the adjacent water molecules is also observed. In a large pH range around the point of zero charge, the interaction is not controlled electrostatically but by hydrogen bonding. The functional species' tilt angles are crucial parameters, determining whether the species act as hydrogen bond donors or acceptors.     

Student Perceptions of a Summer Ventures in Science and Mathematics Camp Experience

“As the world becomes increasingly technological, the value of (the ideas and skills of its population) will be determined in no small measure by the effectiveness of science, technology, engineering, and mathematics (STEM) education in the United States” and “STEM education will determine whether the United States will remain a leader among nations and whether we will be able to solve immense challenges in such areas as energy, health, environmental protection, and national security” (President's Council of Advisors on Science and Technology, 2010, p. vii). Research on the effectiveness of STEM‐focused school and other learning experiences (e.g., short‐term camps) on student attitudes and performance outcomes is sparse. In this study, we documented the influence of an intensive STEM summer program on high school students’ attitudes toward STEM concepts and interests in STEM careers. Attending the summer program was associated with gains on students’ attitudes toward some aspects of STEM as well as specific career interests. Notably, students reported statistically significant views of important aspects of STEM and their attitudes toward science and mathematics were more positive than their attitudes about engineering and technology.     

Tetravalent cerium carbene complexes

The tetravalent organometallic cerium complex [CeL4] is readily accessible from the oxidation of the trivalent [CeL3], L=a bidentate N-heterocyclic carbene alkoxide ligand, [C{(NPri)CHCHN}CH2CMe2O]. The [CeL4] complex should behave like the [UL4] analogue, but the two complexes show significantly different structures, highlighting the differences between 4f and 5f metals.     

Selective oxo functionalization of the uranyl ion with 3d metal cations

The linear uranyl dication [UO2]2+ can be bound in one of two coordination sites in the ditopic Pacman-shaped pyrrolic macrocyle H4L. Incorporation of Mn2+, Fe2+, or Co2+ cations in the second donor compartment affords the first uranyl complexes with a transition-metal-functionalized oxo group.     

Studying pigments on painted plaster in Minoan,Roman and Early Byzantine Crete. A multi-analytical technique approach

Wall paintings spanning two millennia of Cretan painting history and technology were analysed in an effort to determine similarities and evolutions of painting materials and technology. A multi-technique approach was employed that combined the use of (a) laser-induced breakdown spectroscopy (LIBS) and Raman microspectroscopy, based on mobile instrumentation, appropriate for rapid, routine-level object characterization, and (b) non-destructive X-ray diffractometry (XRD), performed directly on the wall painting fragment, which provides detailed information on the minerals constituting the paint. Elemental analysis data obtained through LIBS were compared with molecular and crystal structure information from Raman spectroscopy and XRD. Cross-sections from selected samples were also investigated by means of optical microscopy and scanning electron microscopy coupled to micro-probe analysis and X-ray mapping that enabled identification of several mineral components of the paint confirming the results of the XRD analysis. In parallel, replica wall paintings, created with known pigments and binding media for reference purposes, were examined with optical microscopy and stain tested for organic materials. The overall study shows that the LIBS and Raman techniques offer key advantages, such as instrument mobility and speed of data collection and interpretation that are particularly important when dealing with on-site investigations. Thus, they are capable of providing important compositional information in an effective manner that enables quick surveying of wall paintings and permit targeted sample selection for further analysis by advanced laboratory techniques.     

The crystal and molecular structures of the compounds [(η5-C5H5)Fe(CO)2]2(CH2)n, where 0 n = 3 and 4

The crystal stuctures of [(η⁵-C₅H₅)Fe(CO)₂]₂(CH₂)_n, n = 3 and 4, have been determined.[(η⁵-C₅H₅)Fe(CO)₂]₂(CH₂)₃: a = 21.20, b = 10.39, c = 7.88Å, β = 101.6°, U = 1699ų, C2/c, Z = 4, R = 0.059, 1036 observed data.[(η⁵-C₅H₅)Fe(CO)₂]₂(CH₂)₄: a = 7.63, b = 10.54, c = 21.87Å, β = 96.4°, U= 1748ų, P2₁/c, Z = 4, R = 0.051, 1418 observed data.In each compound the iron atoms are joined by simple chains of sigma bonded CH₂ groups. Bond lengths are similar in both: mean Fe-CO 1.75, C-O 1.15, FeC(cp) 2.11, FeCH₂ 2.08, (cp)CC(cp) 1.41, CH₂CH₂ 1.55Å. The (CH₂)₃ compound retains a 2-fold axis of symmetry in the crystal. The (CH₂)₄ compound has no imposed symmetry, but closely approximates centrosymmetry. The effects of molecular symmetry on the IR spectrum between 2100 and 1900 cm^-1 are discussed. The¹³C and₁H (270 MHz) NMR spectra in solution are shown to be consistent with the structures found crystallographically.     

Regioselective C-H activation of lanthanide-bound N-heterocyclic carbenes

The reaction of Ln(L)N'2 (Ln = Nd, Ce; L = t-BuNCH2CH2[C{NCHCHNt-Bu}], N' = N(SiMe3)2) with trimethylsilyl iodide regiospecifically functionalises the carbene backbone at the C4-carbene ring position to afford the silylated complex Ln(L')N'I; Ln(L')N'2 is isolated after attempted reduction (L' = t-BuNCH2CH2[C{NC(SiMe3)CHNt-Bu}]) which allows a comparison of the structurally characterised complexes Nd(L)N'2, [Nd(L')N'I]2, and Nd(L')N'2.     

The workings of a molecular thermometer: the vibrational excitation of carbon tetrachloride by a solvent

An intriguing energy-transfer experiment was recently carried out in methanol/carbon tetrachloride solutions. It turned out to be possible to watch vibrational energy accumulating in three of carbon tetrachloride's modes following initial excitation of O-H and C-H stretches in methanol, in effect making those CCl(4) modes "molecular thermometers" reporting on methanol's relaxation. In this paper, we use the example of a CCl(4) molecule dissolved in liquid argon to examine, on a microscopic level, just how this kind of thermal activation occurs in liquid solutions. The fact that even the lowest CCl(4) mode has a relatively high frequency compared to the intermolecular vibrational band of the solvent means that the only solute-solvent dynamics relevant to the vibrational energy transfer will be extraordinarily local, so much so that it is only the force between the instantaneously most prominent Cl and solvent atoms that will significantly contribute to the vibrational friction. We use this observation, within the context of a classical instantaneous-pair Landau-Teller calculation, to show that energy flows into CCl(4) primarily via one component of the nominally degenerate, lowest frequency, E mode and does so fast enough to make CCl(4) an excellent choice for monitoring methanol relaxation. Remarkably, within this theory, the different symmetries and appearances of the different CCl(4) modes have little bearing on how well they take up energy from their surroundings--it is only how high their vibrational frequencies are relative to the solvent intermolecular vibrational band edge that substantially favors one mode over another.