Water-Soluble imide-amide copolymers. II. Preparation and characterization of poly (acrylamide-co-p-maleimidobenzoic acid)

The comonomer required, p-maleimidobenzoic acid (MBA) was first prepared in good yield by refinements of published methods. p-Carboxysuccinanilic acid (CSA), and p-succinimidobenzoic acid (SBA), were also prepared to provide models useful for IR and NMR for spectroscopic assignments of the new copolymers. Polymerization of MBA with acrylamide in glacial acetic acid at 60°C gave copolymers with estimated viscosity average molecular weights of 60,000 to 90,000. Yields and viscosity average molecular weights decreased as the MBA to acrylamide monomer feed ratio was increased. The rate of incorporation of MBA into the copolymer rose from 7 to 23% when the mole ratio in the feed was raised from 5 to 20%. Decreasing the initiator concentration increased molecular weights by less than predicted and reduced the yield of copolymer for any given feed ratio of MBA to acrylamide. In all cases about 30–40% of the MBA units in the purified copolymers were hydrolyzed. A change to dimethyl sulfoxide solvent gave good, and poor yields of copolymer at 5 and 10 mol % MBA, respectively, and no copolymer at 20 mol % MBA. Viscosity average molecular weights of the copolymer products prepared in DMSO were somewhat lower than obtained for the copolymers prepared in acetic acid. Polymerization in a DMSO-water mixture gave a negligible yield of polymeric product. Instead, only hydrolysates of MBA precipitated when the coloured polymerization solutions were added to methanol.     

Revised Assignment of the Raman Active Fundamental Vibrations of Tetracyanoethylene

We present a revised assignment of the Raman active fundamental vibrations of TCNE which utilizes new information obtained from Raman studies of electron donor/acceptor complexes of TCNE. This new assignment is consistent with and supported by all available evidence from previous studies.     

Thermal Intercalation of Alkali Halides into Kaolinite

Solid state intercalation of alkali halides into kaolinite takes place by heating pressed disks of dimethylsulfoxide (DMSO)-kaolinite complex ground in different alkali halides. This reaction involves diffusion of the DMSO outside the interlayer space and the alkali halide into the interlayer space. IR and Raman spectroscopy reveal two types of intercalation complexes: (i) almost non-hydrous, obtained during thermal treatment of the DMSO complex; and (ii) hydrated, obtained by regrinding the disk in air. The strength of the hydrogen bonds between intercalated water or halide anions and the inner surface hydroxyls decreases in the order Cl⁻>Br⁻>I⁻. Chlorides penetrate the ditrigonal holes and form hydrogen bonds with the inner OH groups. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermodynamic properties of AuyAgx bimetallic clusters through the evolutive ensemble

The caloric and specific heat curves for the bimetallic nanoclusters Au_7-xAg_x (x=0,3,4,7) are obtained through a statistical determination of the configurational density of states in the evolutive ensemble obtained with a genetic algorithm. The effect of the value of x (the relative concentrations) on the thermodynamics is studied. Three peaks are observed in the specific heat curves for all values of x. This is interpreted as being due to melting, and fragmentation of the cluster into first two, and then into 3 or more parts. A fourth pre-melting peak is observed for Au₄Ag₃ and is attributed to a new phenomena related to the breaking of the degeneracy of the permutational isomers. The melting transition for the bimetallic clusters is significantly wider than that for the pure clusters. The boiling transition displays a larger specific heat for the bimetallic clusters.     

Initial State Interaction in the (π+,3p) Reaction on N, Ar and Xe

The pion absorption reaction (π^{+,3 p} ) on Ar was studied at pion energies of 70, 118, 162 and 239 MeV, and on N and Xe at 239 MeV. The 3p cross section with a 50 MeV cut on the missing energy is presented. The existence of an initial state interaction (ISI) component to the reaction was investigated. The portion of the 3p cross section assigned to the ISI process is less than one half and at lower energies significantly so. Received: 11 December 1997     

Study of the interaction between caesium bromide and kaolinite by differential thermal analysis

The reaction occurring during the wet grinding of kaolinite with CsBr was studied by simultaneous Differential Thermal Analysis -Thermogravimetry (DTA-TG), supplemented by infrared spectroscopy of isothermally treated CsBr disks. The DTA and TG curves were compared with those of untreated kaolinite and of kaolinite mixed or air ground with different alkali halides. A new endothermic DTA peak at 75–115°, accompanied by weight loss, is due to the desorption of surface and interparticle water located mainly at the interface between the mineral and the salt. A second endothermic peak at about 500° represents the simultaneous dehydroxylation of the clay and thermal hydrolysis of CsBr. The presence of a separate CsBr phase was identified from two endothermic peaks which characterize melting and boiling of the salt; only mixtures with more than 140 mmol CsBr per 100 g kaolinite show the presence of this phase. All of the CsBr below this concentration occurs in the CsBrHOH-kaolinite intercalation complex. This degree of saturation is smaller than that obtained previously for CsCl.

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Zusammenfassung Mittels simultaner DTA-TG wurde die sich während des Naßmahlens von Kaolinit mit CsBr stattfindende Reaktion untersucht, ergänzt durch IR-spektroskopische Untersuchungen von isotherm wärmebehandelten CsBr-Plättchen. Die DTA und TG Kurven wurden mit denen von unbehandeltem Kaolinit und von Kaolinit, vermischt oder an Luft gemahlen mit verschiedenen Alkalihalogeniden. Ein neuer endothermer DTA-Peak bei 75–115°C., begleitet von einem Gewichtsverlust, wird der Desorption von Oberflächen- oder interpartikelgebundenem Wasser zugeschrieben, das hauptsächlich an den Übergangsflächen Mineral/Salz lokalisiert ist. Ein zweiter endothermer Peak bei 500°C steht für die gleichzeitige Dehydroxylierung der Tonerde und die thermische Hydrolyse von CsBr. Aus zwei für Schmelzen und Sieden des Salzes charakteristischen endothermen Peaks konnte auf eine separate CsBr-Phase geschlossen werden; nur Gemische mit mehr als 141 mmol CsBr pro 100 g Kaolinit zeigen die Gegenwart einer solchen Phase. Unterhalb dieser Konzentrationsgrenze ist alles CsBr in CsBr-HOH-Kaolinit Durchdringungskomplexen vorhanden. Dieser Sättigungsgrad ist niedriger als der für CsCl.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday

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S. Y. and A. N. are grateful to the Internal Fund of the Hebrew University of Jerusalem for financial support.     

Photoacoustic infrared spectroscopy of Syncrude post-extraction oil sand

Rapid- and step-scan photoacoustic (PA) infrared spectra of three fractions of a Syncrude post-extraction oil sand were analyzed in detail in this work. The rapid-scan spectra showed that the samples were comprised primarily of kaolinite, quartz, silica, siderite, and residual hydrocarbons, and that the proportions of these constituents were different for each fraction. Depth profiling of the three post-extraction oil sands was accomplished using both rapid- and step-scan PA infrared spectroscopy. The results confirmed that kaolinite is more abundant in the near-surface region, whereas quartz and hydrocarbons are concentrated at greater depths. The modulation frequency dependence of the PA intensities for all three fractions was consistent with a model in which the samples are thermally thick; in other words, the thermal diffusion length (roughly equal to the sampling depth) was less than the particle sizes of all three samples. The results of this study are consistent with published reports on the PA infrared spectra of fine tailings generated during bitumen extraction and the spectroscopic and thermophysical characterization of clay soils and an appropriate model clay.     

Chirality, defects, and disorder in gold clusters

Theoretical and experimental information on the shape and morphology of bare and passivated gold clusters is fundamental to predict and understand their electronic, optical, and other physical and chemical properties. An effective theoretical approach to determine the lowest-energy configuration (global minimum) and the structures of low energy isomers (local minima) of clusters is to combine genetic algorithms and many-body potentials (to perform global structural optimizations), and first-principles density functional theory (to confirm the stability and energy ordering of the local minima). The main trend emerging from structural optimizations of bare Au clusters in the size range of 12-212 atoms indicates that many topologically interesting low-symmetry, disordered structures exist with energy near or below the lowest-energy ordered isomer. For example, chiral structures have been obtained as the lowest-energy isomers of bare Au₂₈ and Au₅₅ clusters, whereas in the size-range of 75-212 atoms, defective Marks decahedral structures are nearly degenerate in energy with the ordered symmetrical isomers. For methylthiol-passivated gold nanoclusters [Au₂₈(SCH₃)₁₆ and Au₃₈(SCH₃)₂₄], density functional structural relaxations have shown that the ligands are not only playing the role of passivating molecules, but their effect is strong enough to distort the metal cluster structure. In this work, a theoretical approach to characterize and quantify chirality in clusters, based on the Hausdorff chirality measure, is described. After calculating the index of chirality in bare and passivated gold clusters, it is found that the thiol monolayer induces or increases the degree of chirality of the metallic core. We also report simulated high-resolution transmission electron microscopy (HRTEM) images which show that defects in decahedral gold nanoclusters, with size between 1-2 nm, can be detected using currently available experimental HRTEM techniques.     

Infrared observation of OC-C2H2, OC-(C2H2)2 and their isotopologues

ABSTRACT

The fundamental band for the OC-C₂H₂ dimer and two combination bands involving the intermolecular bending modes ν₉ and ν₈ in the carbon monoxide CO stretch region are re-examined. Spectra are obtained using a pulsed supersonic slit jet expansion probed with a mode-hop free tuneable infrared quantum cascade laser. Analogous bands for OC-C₂D₂ and the fundamental for OC–DCCH as an impurity are also observed and analysed. A much weaker band in the same spectral region is assigned to a new mixed trimer, CO-(C₂H₂)₂. The trimer band is composed uniquely of a-type transitions, establishing that the CO monomer is nearly aligned with the a-inertial axis. The observed rotational constants agree well with ab initio calculations and a small inertial defect value indicates that the trimer is planar. The structure is a compromise between the T-shaped structure of free acetylene dimer and the linear geometry of free OC-C₂H_2. A similar band for the fully deuterated isotopologue CO-(C₂D₂)₂ confirms our assignment.     

Mid-infrared photoacoustic spectroscopy of solids using an external-cavity quantum-cascade laser

We describe the use of a pulsed external-cavity quantum-cascade laser (EC-QCL) for the acquisition of mid-IR photoacoustic (PA) spectra of solids. The EC-QCL employed in this work operates from 990 to 1075 cm(-1) (9.30-10.10 microm). A gas-microphone PA cell was used as the detector, and the signal was demodulated using a lock-in amplifier. PA EC-QCL spectra of solids display bands significantly narrower than those in corresponding PA Fourier transform infrared spectra.