The local structure of protonated water from x-ray absorption and density functional theory

We present a combined x-ray absorption spectroscopy/computational study of water in hydrochloric acid (HCl) solutions of varying concentration to address the structure and bonding of excess protons and their effect on the hydrogen bonding network in liquid water. Intensity variations and energy shifts indicate changes in the hydrogen bonding structure in water as well as the local structure of the protonated complex as a function of the concentration of protons. In particular, in highly acidic solutions we find a dominance of the Eigen form, H(3)O(+), while the proton is less localized to a specific water under less acidic conditions.     

Particle agglomeration and properties of nanofluids

The present study demonstrates the importance of actual agglomerated particle size in the nanofluid and its effect on the fluid properties. The current work deals with 5 to 100 nm nanoparticles dispersed in fluids that resulted in 200 to 800 nm agglomerates. Particle size distributions for a range of nanofluids are measured by dynamic light scattering (DLS). Wet scanning electron microscopy method is used to visualize agglomerated particles in the dispersed state and to confirm particle size measurements by DLS. Our results show that a combination of base fluid chemistry and nanoparticle type is very important to create stable nanofluids. Several nanofluids resulted in stable state without any stabilizers, but in the long term had agglomerations of 250 % over a 2 month period. The effects of agglomeration on the thermal and rheological properties are presented for several types of nanoparticle and base fluid chemistries. Despite using nanodiamond particles with high thermal conductivity and a very sensitive laser flash thermal conductivity measurement technique, no anomalous increases of thermal conductivity was measured. The thermal conductivity increases of nanofluid with the particle concentration are as those predicted by Maxwell and Bruggeman models. The level of agglomeration of nanoparticles hardly influenced the thermal conductivity of the nanofluid. The viscosity of nanofluids increased strongly as the concentration of particle is increased; it displays shear thinning and is a strong function of the level of agglomeration. The viscosity increase is significantly above of that predicted by the Einstein model even for very small concentration of nanoparticles.     

The effect of hydrogen bonding on the physical and mechanical properties of rigid‐rod polymers

The idea of competing effects between intramolecular and intermolecular hydrogen bonding was investigated. Results indicate that the formation of one type of hydrogen bond does not preclude the formation of the other. The strength of the intermolecular association was measured by ab initio calculations for several polymer systems, including methyl pendant poly(p‐phenylene benzobisimidazole) and poly‐{2,6‐diimidazo[4,5‐b:4′5′‐e]pyridinylene‐1,4(2,5‐dihydroxy)phenylene} (PIPD). Fibers with strong intermolecular association have high compressive strength and torsional modulus. The influence of intermolecular hydrogen bonding on torsional modulus is discussed in light of the transverse texture present in poly(p‐phenylene terephthalamide) and some other high‐performance fibers. Enhanced intermolecular interaction not only influences the aforementioned properties but also results in higher fiber density. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3053–3061, 2000     

Convergent synthesis and preliminary biological evaluations of the stilbenolignan (+/-)-aiphanol and various congeners

Treatment of an equimolar mixture of stilbene 7 and cinnamyl alcohol 8 with silver carbonate in acetone-benzene afforded a ca. 2:1:2:1 mixture of the stilbenolignan (+/-)-aiphanol (1) and congeners 2-4 each of which show significant anti-angiogenic and COX-2 inhibitory properties.     

Synthesis of hybrid framework materials under "dry" hydrothermal conditions: crystal structure and magnetic properties of Mn(2)(H(2)PO(4))(2)(C(2)O(4))

An exploration of the manganese oxalate-phosphoric acid-water system under hydrothermal conditions, and using "reagent" quantities only of water, has led to the isolation of a new mixed anion framework material Mn(2)(H(2)PO(4))(2)(C(2)O(4)). This material features continuous chains of cis edge-sharing MnO(6) octahedra, a motif which is unique among mixed phosphate-oxalate materials identified so far. These octahedral chains are linked into a three-dimensional framework via corner-sharing with H(2)PO(4) tetrahedra, with oxalate ions acting as a bis-bidentate ligand in the third direction. Magnetic susceptibility studies show that this material may be modeled as an antiferromagnetic, S = (5)/(2) Heisenberg chain, with weaker coupling between the chains.     

Soft nanotechnology with soft nanoparticles

The last decade of research in the physical sciences has seen a dramatic increase in the study of nanoscale materials. Today, "nanoscience" has emerged as a multidisciplinary effort, wherein obtaining a fundamental understanding of the optical, electrical, magnetic, and mechanical properties of nanostructures promises to deliver the next generation of functional materials for a wide range of applications. While this range of efforts is extremely broad, much of the work has focused on "hard" materials, such as Buckyballs, carbon nanotubes, metals, semiconductors, and organic or inorganic dielectrics. Meanwhile, the soft materials of current interest typically include conducting or emissive polymers for "plastic electronics" applications. Despite the continued interest in these established areas of nanoscience, new classes of soft nanomaterials are being developed from more traditional polymeric constructs. Specifically, nanostructured hydrogels are emerging as a promising group of materials for multiple biotechnology applications as the need for advanced materials in the post-genomic era grows. This review will present some of the recent advances in the marriage between water-swellable networks and nanoscience.     

Symmetric binuclear complexes with an ‘end-off’ compartmental Schiff base ligand

Four binuclear transition metal(II) complexes: [Co₂L(-Cl)Cl₂] · 2H₂O, [Ni₂L(-Cl)Cl₂(H₂O)₂] · 2H₂O, [Cu₂L(-Cl)Cl₂] · 2H₂O and [Zn₂L(-Cl)Cl₂] · 2H₂O, where LH is the binucleating ligand 2,6-diformyl-4-methylphenol bis(2-hydrazino benzothiazole), were prepared. Based on the i.r. spectra, elemental analysis, conductivity measurements and thermal analysis, we propose that these complexes contain an endogenous phenoxide bridge and an exogenous chloride bridge. Magnetic and spectral data supports the existence of a weak antiferromagnetic interaction between the metal ions, and octahedral for Ni^II and a square pyramidal environment for remaining complexes. The compounds show significant growth inhibitory activity against the fungi, Aspergillus niger and Candida albicans, as compared to antibacterial activity against Bacillus cirroflagellosus and Pseudomonas auregenosa.     

Dispersion of nitric acid-treated SWNTs in organic solvents and solvent mixtures

The dispersion of pristine and nitric acid-treated single-wall carbon nanotubes (SWNTs) has been studied in organic solvents and solvent mixtures using optical absorption, as a function of settling time. The extinction coefficients of both the pristine and acid-treated tubes at 500-nm wavelength was measured to be 25.5 (mg/L)(-1) cm(-1) in various solvents. The dispersibility of nitric acid-treated tubes increased with the solvent's hydrogen-bonding ability and reached 27 mg/L in ethanol and 35 mg/L in water. Nitric acid-treated tubes could also be dispersed in butanol/toluene and xylene/ethanol mixtures, which are known to be poor solvents for the pristine SWNTs.     

Pentacoordinate phosphoranes with reversed apicophilicity as stable intermediates in a mitsunobu-type reaction

Diisopropyl azodicarboxylate (DIAD) undergoes a cycloaddition reaction with the cyclic phosphites CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)PX (1) [X = NCS (a), N(3) (b), Cl (c), NHMe (d) and Ph (e)] to afford the novel pentacoordinate phosphoranes 2a-e as crystalline solids. This result is different from the reaction of PPh(3) with DIAD used in the well-known Mitsunobu reaction. X-ray crystallography of 2a, 2b, and 2d reveals that the nitrogen, rather than the oxygen, occupies an apical position of the trigonal bipyramidal phosphorus. This is in violation of the commonly accepted preferences for substituents in trigonal bipyramidal phosphorus. In 2e, although the oxygen of the five-membered ring occupies the expected apical position, the phenyl group also occupies (the other) apical position, forcing the more electronegative oxygen atoms of the eight-membered ring to span equatorial-equatorial positions. In contrast to the above, the isocyanato compound CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)PNCO (1f), upon treatment with DIAD, affords compound 3 to which a tetracoordinate structure is assigned.     

Structure and properties of potential nonlinear optical materials

The synthesis, structure and properties of four ferrocene derivatives of 2-amino-1,2,3-triazole are reported. Solvatochromism is used as a screening process to assess the potential nonlinear optical behavior of these compounds. In general, this technique involves a number of assumptions, which may not be valid for organometallic complexes. Compound 3 crystallizes in space group P-1 with cell dimensions a = 5.771(2), b = 19.048(5), c = 19.343(5) Å and = 61.104(4), = 88.410(5), = 89.858(5)°; compound 5 crystallizes in space group P2₁/c with cell dimensions a = 12.545(2), b = 13.308(2), c = 20.513(4) Å and = 104.035(3)°; compound 9 crystallizes in space group P2₁/n with cell dimensions a = 12.599(4), b = 14.734(4), c = 13.619(5) Å, and = 107.63(2); compound 11 crystallizes in space group P-1 with cell dimensions a = 7.638(3), b = 9.619(4), c = 12.692(5) Å and = 77.588(7), = 78.416(7), = 71.357(7).