Synthesis of a novel [60]fullerene pearl-necklace polymer,poly(4,4′-carbonylbisphenylene trans-2-[60]fullerenobisacetamide)

A novel [60]fullerene pearl-necklace polymer, poly(4,4′-carbonylbisphenylene trans-2-[60]fullerenobisacetamide), was synthesized by a direct polycondensation of trans-2-[60]fullerenobisacetic acid with 4,4′-diaminobenzophenone in the presence of large excesses of triphenyl phosphite and pyridine. In the present polymer, [60]fullerene pearls and diamine linkers were attached to each other by methano-carbonyl connectors. The molecular weight M_w of the polymer was determined to be 4.5 × 10⁴ on the basis of the TOF-MS, and a GPC analysis of the polymer using polystyrene standards showed a weight-average molecular weight of 5.3 × 10⁴. The UV-vis spectrum of the resultant polymer in N,N-dimethylacetamide (DMAc) exhibited a broad absorption (λ_max 310 nm, ε 2.1 × 10⁴ L · mol⁻¹ · cm⁻¹), tailing to longer wavelengths, and a fluorenscence peak centered at 550 nm was observed in DMAc. There was observed a large downfield-shift of the cyclopropane methyne proton in the ¹H-NMR spectra from 4.57 ppm of the ethyl ester to 5.78 ppm of the polyamide. These observations indicate that the present polyamide is a high-molecular-weight [60]fullerene pearl-necklace polymer and that the cyclopropane rings are efficient to make the [60]fullerene cages and the diamine components conjugatable. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3632–3637, 1999     

Interactive simulation of aircraft noise in aural and visual virtual environments

This paper describes a novel aircraft noise simulation technique developed at RWTH Aachen University, which makes use of aircraft noise auralization and 3D visualization to make aircraft noise both heard and seen in immersive Virtual Reality (VR) environments. This technique is intended to be used to increase the residents’ acceptance of aircraft noise by presenting noise changes in a more directly relatable form, and also aid in understanding what contributes to the residents’ subjective annoyance via psychoacoustic surveys. This paper describes the technique as well as some of its initial applications. The reasoning behind the development of such a technique is that the issue of aircraft noise experienced by residents in airport vicinities is one of subjective annoyance. Any efforts at noise abatement have been conventionally presented to residents in terms of noise level reductions in conventional metrics such as A-weighted level or equivalent sound level L_eq. This conventional approach however proves insufficient in increasing aircraft noise acceptance due to two main reasons – firstly, the residents have only a rudimentary understanding of changes in decibel and secondly, the conventional metrics do not fully capture what the residents actually find annoying i.e. characteristics of aircraft noise they find least acceptable. In order to allow least resistance to air-traffic expansion, the acceptance of aircraft noise has to be increased, for which such a new approach to noise assessment is required.     

Hyosgerin, a new optically active coumarinolignan, from the seeds of Hyoscyamus niger

Hyosgerin, a new optically active coumarinolignan, has been isolated and characterized along with three other coumarinolignans, venkatasin, cleomiscosin A and cleomiscosin B, from the seeds of Hyoscyamus niger L. The structure was determined on the basis of spectroscopic analysis and chemical conversion. The optical properties and absolute stereochemistry of these coumarinolignans have also been studied and discussed.     

Dielectric studies of molecular complexes ofDDT with some compounds of biological interest

The molecular complexation ofDDT (acceptor) with some compounds of biological interest as donors (e.g. indole, 2-methylindole, 3-methylindole, benzene and naphthalene) have been studied using refractive index,Guggenheim and dielectric titration plot methods. The interaction between these donors with solvents (CCl₄ and C₆H₆) have also been observed by calculating _ind through _ind=_sol–_inert. These data have shown that the molecular interaction between polar solutes and non-polar aromatics is governed by dipole-induced dipole electrostatic attraction. The dipole moment obtained due to charge transfer (_DA) has also been calculated and found that its value increases with the increase in the extent of interaction between donor and acceptor. These data support the charge-transfer complex formation hypothesis for the mode of action ofDDT on molecular level.

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Dielektrizitäts-Untersuchungen an Molekülkomplexen von DDT mit einigen biologisch relevanten Verbindungen

Zusammenfassung Es wurden Molekülkomplexe vonDDT (als Acceptor) mit einigen Verbindungen von biologischem Interesse (als Donoren: Indol, 2-Methyl-indol, 3-Methyl-indol, Benzol und Naphthalin) mittels Brechungsindex,Guggenheim-Methode und dielektrischer Titration untersucht. Dipolmomentberechnungen ergaben, daß die intermolekulare Wechselwirkung von einer Anziehung induzierter Dipol-Dipol bestimmt wird; es wurde auch der charge-transfer-Anteil des Dipolmoments abgeschätzt. Alle diese Daten unterstützen die Annahme der charge-transfer-Komplexierung vonDDT.

     

First-principle computational study on the full conformational space of L-threonine diamide, the energetic stability of cis and trans isomers

First-principle computations were carried out on the conformational space of trans and cis peptide bond isomers of HCO-Thr-NH2. Using the concept of multidimensional conformational analysis (MDCA), geometry optimizations were performed at the B3LYP/6-31G(d) level of theory, and single-point energies as well as thermodynamic functions were calculated at the G3MP2B3 level of theory for the corresponding optimized structures. Two backbone Ramachandran-type potential energy surfaces (PESs) were computed, one each for the cis and trans isomers, keeping the side chain at the fully extended orientation (chi1=chi2=anti). Similarly, two side chain PESs for the cis and trans isomers were generated for the (phi=psi=anti) orientation corresponding to approximately the betaL backbone conformation. Besides correlating the relative Gibbs free energy of the various stable conformations with the number of stabilizing hydrogen bonds, the process of trans-->cis isomerization is discussed in terms of intrinsic stabilities as measured by the computed thermodynamic functions.     

Small molecule‐mediated control of hydroxyapatite growth: Free energy calculations benchmarked to density functional theory

The unique, plate‐like morphology of hydroxyapatite (HAP) nanocrystals in bone lends to the hierarchical structure and functions of bone. Proteins enriched in phosphoserine (Ser‐OPO₃) and glutamic acid (Glu) residues have been proposed to regulate crystal morphology; however, the atomic‐level mechanisms remain unclear. Previous molecular dynamics studies addressing biomineralization have used force fields with limited benchmarking, especially at the water/mineral interface, and often limited sampling for the binding free energy profile. Here, we use the umbrella sampling/weighted histogram analysis method to obtain the adsorption free energy of Ser‐OPO₃ and Glu on HAP (100) and (001) surfaces to understand organic‐mediated crystal growth. The calculated organic‐water–mineral interfacial energies are carefully benchmarked to density functional theory calculations, with explicit inclusion of solvating water molecules around the adsorbate plus the Poisson–Boltzmann continuum model for long‐range solvation effects. Both amino acids adsorb more strongly on the HAP (100) face than the (001) face. Growth rate along the [100] direction should then be slower than in the [001] direction, resulting in plate‐like crystal morphology with greater surface area for the (100) than the (001) face, consistent with bone HAP crystal morphology. Thus, even small molecules are capable of regulating bone crystal growth by preferential adsorption in specific directions. Furthermore, Ser‐OPO₃ is a more effective growth modifier by adsorbing more strongly than Glu on the (100) face, providing one possible explanation for the energetically expensive process of phosphorylation of some proteins involved in bone biomineralization. The current results have broader implications for designing routes for biomimetic crystal synthesis. © 2013 Wiley Periodicals, Inc.     

Oxide-dependent adsorption of a model membrane phospholipid, dipalmitoylphosphatidylcholine: bulk adsorption isotherms

The importance of substrate chemistry and structure on supported phospholipid bilayer design and functionality is only recently being recognized. Our goal is to investigate systematically the substrate-dependence of phospholipid adsorption with an emphasis on oxide surface chemistry and to determine the dominant controlling forces. We obtained bulk adsorption isotherms at 55 degrees C for dipalmitoylphosphatidylcholine (DPPC) at pH values of 5.0, 7.2, and 9.0 and at two ionic strengths with and without Ca(2+), on quartz (alpha-SiO(2)), rutile (alpha-TiO(2)), and corundum (alpha-Al(2)O(3)), which represent a wide a range of points of zero charge (PZC). Adsorption was strongly oxide- and pH-dependent. At pH 5.0, adsorption increased as quartz < rutile approximately corundum, while at pH 7.2 and 9.0, the trend was quartz approximately rutile < corundum. Adsorption decreased with increasing pH (increasing negative surface charge), although adsorption occurred even at pH > or = PZC of the oxides. These trends indicate that adsorption is controlled by attractive van der Waals forces and further modified by electrostatic interactions of oxide surface sites with the negatively charged phosphate ester (-R(PO(4)-)R'-) portion of the DPPC headgroup. Also, the maximum observed adsorption on negatively charged oxide surfaces corresponded to roughly two bilayers, whereas significantly higher adsorption of up to four bilayers occurred on positively charged surfaces. Calcium ions promote adsorption beyond a second bilayer, regardless of the sign of oxide surface charge. We develop a conceptual model for the structure of the electric double layer to explain these observations.     

Reactivity and Synthetic Utility of 1,3,2λ5-Dioxaphospholanes

Abstract

The kinetics of Lewis acid-mediated decomposition and definitions of the synthetic applicability of 1,3,2λ⁵-dioxaphospholanes for (i) the syntheses of highly-hindered epoxides, and (ii) the stereospecific functionalizations of stereocenters in 1,2-diol arrays are described.     

Crystallographic characterization of Kr@C60 in (0.09Kr@C60/0.91C60). (NiII(OEP)).2C6H6

A sample of C60 containing ca. 9% Kr@C60 has been used to form crystalline (0.09Kr@C60/0.91C60).(NiII(OEP)).2C6H6 whose X-ray crystal structure reveals that the Kr atom is centered within the carbon cage and does not produce a detectable change in the size of the fullerene.     

Separation of N2@C60 and N@C60

We describe the HPLC separation and identification of N@C60 and N2@C60. These species were observed after eleven sequential HPLC separations. Their retention times are in the same range as those of the other noninteractive endohedral species of C60, such as noble gas endohedral C60. The separation factors of these endohedrals were evaluated by using a mixture of hexane/toluene as eluent. We note that this is the first evidence for the N2@C60 molecule existing in the form of endohedral C60 complex.