Experimental evidence for internal structure in aqueous-organic nanodroplets

The spatial distribution of species within an aerosol droplet influences how it interacts with its environment. Despite the ubiquity of multicomponent nanodroplets in natural and technological aerosols, there are no published measurements of their internal structure. Here, we report the first experimental results for structure in aqueous organic nanodroplets based on small angle neutron scattering by high number density aerosols. For H(2)O-n-butanol droplets, fitting of the diffraction patterns confirms the picture of an aqueous core containing approximately 3 mol% alcohol covered by a shell of densely packed alcohol molecules.     

On the structure of palau'amine: evidence for the revised relative configuration from chemical synthesis

Hexacyclic congeners 3 and 4 of palau'amine, which incorporate both guanidine functional groups and have the cis configuration of the azabicyclo[3.3.0]octane core, are prepared in 14 steps from cycloadduct 6. Synthetic access to these analogues allows the first direct comparison of NMR data for hexacyclic diguanidine structures having the originally proposed cis-azabicyclo[3.3.0]octane fragment with data for natural alkaloids of the palau'amine family. This comparison provides convincing evidence in favor of the recently proposed structural revision of these marine alkaloids, fully supporting the trans configuration of the central azabicyclo[3.3.0]octane ring system of palau'amine and congeners.     

Infrared spectrum and structure of the adamantane cation: direct evidence for Jahn-Teller distortion

The fundamentals: the IR spectrum of the adamantane cation, C(10)H(16)(+), has been derived by resonant IR photodissociation of weakly bound C(10)H(16)(+)?L(n) clusters. The analysis of the IR spectrum provides the first spectroscopic characterization of this fundamental cycloalkane carbocation in the gas phase and direct evidence for the Jahn-Teller distortion in the (2)A(1) ground electronic state.     

Reinterpretation of the absorption spectrum of UCl4 single crystal

The absorption spectra of UCl₄ single crystals have been measured from 4000 to 30 000 cm⁻¹ at temperatures ranging from 4.2 K to room temperature. The transitions were assigned by comparing the strong absorption features of UCl₄ to those of ThCl₄:U⁴⁺. The energy levels were fitted to a semiempirical Hamiltonian in D_2d symmetry.A r.m.s. deviation of 60 cm⁻¹ in the fit to 26 assigned levels was achieved using the following set of parameters (cm⁻¹): F² = 42 561 ± 235; F⁴ = 39 440 ± 634; F⁶ = 24 174 ± 185; ξ = 1805 ± 8; α = 31 ± 1; β = −576 ± 168; (γ = 1200); B²₀ = −903 ± 151; B⁴₀ = 766 ± 220; B⁴₄ = −3091 ± 185; B⁶₀ = −1619 ± 482; B⁶₄ = −308 ± 280.     

Origin of the monoclinic-to-monoclinic phase transition and evidence for the centrosymmetric crystal structure of BiMnO3

Structural properties of polycrystalline single-phased BiMnO3 samples prepared at 6 GPa and 1383 K have been studied by selected area electron diffraction (SAED), convergent beam electron diffraction (CBED), and the Rietveld method using neutron diffraction data measured at 300 and 550 K. The SAED and CBED data showed that BiMnO3 crystallizes in the centrosymmetric space group C2/c at 300 K. The crystallographic data are a = 9.5415(2) A, b = 5.61263(8) A, c = 9.8632(2) A, beta = 110.6584(12) degrees at 300 K and a = 9.5866(3) A, b = 5.59903(15) A, c = 9.7427(3) A, beta = 108.601(2) degrees at 550 K, Z = 8, space group C2/c. The analysis of Mn-O bond lengths suggested that the orbital order present in BiMnO3 at 300 K melts above TOO = 474 K. The phase transition at 474 K is of the first order and accompanied by a jump of magnetization and small changes of the effective magnetic moment and Weiss temperature, mueff = 4.69 microB and theta = 138.0 K at 300-450 K and mueff = 4.79 microB and theta = 132.6 K at 480-600 K.     

First evidence for the formation of technetium oxosulfide complexes: synthesis, structure and characterization

The reaction of tetrabutylammonium pertechnetate with bis(trimethylsilyl) sulfide in solution was studied by UV-Visible spectroscopy and mass spectrometry. Experimental results and density functional calculations provide the first evidence for the formation of a TcO(3)S(-) precursor. Larger scale synthesis afforded a solid that was characterized by EDX and XANES spectroscopy. XANES showed the presence of technetium in tetravalent state. EDX indicated the solid contained technetium, sulfur and oxygen.     

Spectroscopic evidence for an oxazolone structure of the b2 fragment ion from protonated tri-alanine

Infrared multiple photon dissociation (IRMPD) spectroscopy is used to identify the structure of the b ₂⁺ ion generated from protonated tri-alanine by collision induced dissociation (CID). The IRMPD spectrum of b ₂⁺ differs markedly from that of protonated cyclo-alanine-alanine, demonstrating that the product is not a diketopiperazine. Instead, comparison of the IRMPD spectrum of b ₂⁺ to spectra predicted by density functional theory provides compelling evidence for an oxazolone structure protonated at the oxazolone N-atom.     

NMR evidence of a supramolecular structure of water

The hypothesis advanced in this paper is based on the formation of dissipative structures, in the form of supramolecular structures of water, by virtue of its hydrogen bonds, structurally similar to a liquid crystal. The supramolecular structure could be a macromolecule typical of a living organism (plant or animal), which as we know is approximately 80% water, with a complex conformation induced initially by an active principle and which remains, organising itself as a result of an input of energy (dynamisation, electromagnetic wave or other). Water is the most abundant substance on earth and has been very well studied with a number of model structures having been proposed and refined. Notwithstanding this, it remains an anomalous liquid where no single model is able to explain all of its properties. Recently our research group in Siena carried out NMR studies on the water molecule measuring nuclear spin relaxation times T1 and T2. The phenomena observed lead to the conclusion that water and aqueous solutions should be regarded as continuous polymorphous self-organizing systems. At the macro-level the water behaviour is related with biodiversity, the core of biological evolution.     

An investigation of the structure of the so-called phenarsazine : Mass spectroscopical evidence for the thermal formation of phenarsazine

The structure of Wieland and Rheinheimer's “phenarsazine” has been reinvestigated. The proposed aromatic structure 3 is not correct, spectral and chemical evidence showing that this compound is 10,10′-bis(5,10-dihydrophenarsazinyl) 16. An attempt to synthesize phenarsazine 3 by base-induced hydrogen chloride elimination was unsuccessful. However, mass spectroscopic evidence indicates that phenarsazine is formed by thermal elimination of either hydrogen chloride or methanol from 10-chloro-5,10-dihydrophenarsazine 7 or 10-methoxy-5,10-dihydrophenarsazine 10, respectively.     

Kinetic evidence for the existence and mechanism of formation of a barrel stave structure from pore-forming dendrimers

A dendritic approach to the construction of a homologous series of pore-forming amphiphiles has been developed, based on the use of spermidine, spermine, lysine, and cholic acid. A kinetic analysis of Na+ transport across bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine by three dendritic amphiphiles has provided the strongest evidence to date for a barrel stave structure.     

Reinterpretation of the fluorescence excitation spectrum of hexafluorobiacetyl in a supersonic jet

The results of the analysis of the fluorescence excitation spectrum of trans-hexafluorobiacetyl published earlier are revised. New values of torsion frequencies and potential barriers of internal rotation of the CF₃ group in the ground and excited states of the molecule are obtained. A procedure for calculating the probabilities of torsional vibronic transitions of molecules is described. Translated fromZhurnal Struktumoi Khirnii, Vol. 38, No. 2, pp. 293–302, March–April, 1997.     

1,2-Diisophthalimidoethane. X-ray diffraction evidence for the structure of the product of acylation of 1,2-diaminoethane with phthaloyl chloride

It was demonstrated by x-ray diffraction investigation of the product of the reaction of 1,2-diaminoethane with phthalic acid dichloride that the resulting compound has the 1,2-diisophthalimidoethane structure. An improved method for its synthesis is proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1320–1323, October, 1987.     

On the electronic structure of molecular UO2 in the presence of Ar atoms: evidence for direct U-Ar bonding

Calculations via scalar-relativistic density functional theory (DFT) and ab initio CCSD(T) methodologies are used to explore the possibility of direct interactions between molecular UO2 and Ar atoms. The 3Hg electronic state of UO2, which is an excited state of the isolated molecule, exhibits significant bonding to Ar in the model complexes UO2(Ar) and UO2(Ar)5. The calculated vibrational frequencies of ground-state 3Phiu UO2 and UO2(Ar)5 with an (fphi)1(fdelta)1 electron configuration agree well with the observed frequencies of UO2 in solid neon and solid argon, respectively. The results strongly suggest that the ground electron configuration of UO2 changes from 5f17s1 to 5f2 when the matrix host is changed from neon to argon.     

Direct evidence of binuclear structure in a silica-supported copper catalyst

Structures of two copper catalysts, one with high catalytic activity, prepared from copper(II) acetate monohydrate and the reference prepared from tetraamminecopper(II), were determined by EXAFS and XANES. In the former catalyst, about 65% of the copper takes a binuclear structure highly dispersed on silica, whereas highly dispersed mononuclear species are dominant in the latter.     

Infrared spectroscopy of cationized arginine in the gas phase: direct evidence for the transition from nonzwitterionic to zwitterionic structure

The gas-phase structures of protonated and alkali metal cationized arginine (Arg) and arginine methyl ester (ArgOMe) are investigated with infrared spectroscopy and ab initio calculations. Infrared spectra, measured in the hydrogen-stretch region, provide compelling evidence that arginine changes from its nonzwitterionic to zwitterionic form with increasing metal ion size, with the transition in structure occurring between lithium and sodium. For sodiated arginine, evidence for both forms is obtained from spectral deconvolution, although the zwitterionic form is predominant. Comparisons of the photodissociation spectra with spectra calculated for low-energy candidate structures provide additional insights into the detailed structures of these ions. Arg*Li+, ArgOMe*Li+, and ArgOMe*Na+ exist in nonzwitterionic forms in which the metal ion is tricoordinated with the amino acid, whereas Arg*Na+ and Arg*K+ predominately exist in a zwitterionic form where the protonated side chain donates one hydrogen bond to the N terminus of the amino acid and the metal ion is bicoordinated with the carboxylate group. Arg*H+ and ArgOMe*H+ have protonated side chains that form the same interaction with the N terminus as zwitterionic, alkali metal cationized arginine, yet both are unambiguously determined to be nonzwitterionic. Calculations indicate that for clusters with protonated side chains, structures with two strong hydrogen bonds are lowest in energy, in disagreement with these experimental results. This study provides new detailed structural assignments and interpretations of previously observed fragmentation patterns for these ions.     

Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene

Molecular distortion of dynamic molecules gives a clear signature in the vibrational spectra, which can be modeled to give estimates of the energy barrier and the sensitivity of the frequencies of the vibrational modes to the reaction coordinate. The reaction coordinate method (RCM) utilizes ab initio‐calculated spectra of the molecule in its ground and transition states together with their relative energies to predict the temperature dependence of the vibrational spectra. DFT‐calculated spectra of the eclipsed (D_5h) and staggered (D_5d) forms of ferrocene (Fc), and its deuterated analogue, within RCM explain the IR spectra of Fc in gas (350 K), solution (300 K), solid solution (7–300 K), and solid (7–300 K) states. In each case the D_5h rotamer is lowest in energy but with the barrier to interconversion between rotamers higher for solution‐phase samples (ca. 6 kJ mol^?1) than for the gas‐phase species (1–3 kJ mol^?1). The generality of the approach is demonstrated with application to tricarbonyl(η⁴‐norbornadiene)iron(0), Fe(NBD)(CO)₃. The temperature‐dependent coalescence of the ν(CO) bands of Fe(NBD)(CO)₃ is well explained by the RCM without recourse to NMR‐like rapid exchange. The RCM establishes a clear link between the calculated ground and transition states of dynamic molecules and the temperature‐dependence of their vibrational spectra.