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).     

Short H· · ·H distances in norbornene derivatives

A short H···H intramolecular interaction was reported previously for an anhydride of syn-sesquinorbornene. The synthesis and structure of a such an anhydride with an additional five-membered dithiole ring has been investigated. While hydrogen atom positions are not accurately located, the 1.62 Å separation indicates this molecule is a candidate for the shortest H···H interaction. Two cycloadducts of norbornadiene, which literature suggests might exhibit additional short interactions, are reported also; however, the isomers with minimal intramolecular interactions are the isolated products. C₂₂H₂₀O₃S₂, 3, crystallizes in P with a = 10.881(4), b = 13.712(8), C = 6.548(8) Å, = 101.32(6), = 107.49(5), = 90.49(4)°, D _calc = 1.445 g cm^–3, and Z = 2, C₂₁H₂₀O₄Cl₈, 5, in P2₁/n with a = 8.168(2), b = 13.488(4), c = 23.500(6) Å, = 94.72(2)°, D _calc = 1.597 g cm^–3, and Z = 4, C₂₁H₂₈O₄, 6, in P> with a = 12.667(2), b = 12.792(2), c = 12.540(2) Å, = 113.51(1), = 98.18(1), = 74.39(1)°, D _calc = 1.276 g cm^–3, and Z = 4.     

Modeling the effect of crosslinking in methyl-pendant poly(p-phenylene benzobisthiazole)

Molecular mechanics and dynamics simulations have been performed on methyl-pendant PBZT to study the effects of intermolecular crosslinking. Several possible crosslinked structures were investigated. The effect of crosslinking was found to be strongly dependent upon crosslink type and, in some instances, crosslink density. A significant axial stress is predicted to occur upon the formation of phenyl-to-phenyl type crosslinks. This provides a reasonable explanation for the experimental observation of transverse cracks in the skin of crosslinked, MePBZT fiber. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3057–3064, 1998     

On the evidence of crosslinking in methyl pendent PBZT fiber

In order to influence the compressive strength of the rigid rod polymeric fibers, methyl pendent poly(p-phenylene benzobisthiazole) fibers have been heat treated in the 400 to 550°C temperature range in air and in nitrogen for varying times to achieve intermolecular crosslinking. These fibers have been examined using Fourier transform infrared (FTIR) spectroscopy, ¹³C solid-state nuclear magnetic resonance (NMR) swelling behavior, and scanning electron microscopy. ¹³C NMR has also been carried out on solutions of as-spun fibers. Fibers heat-treated at 400°C, both in nitrogen and in air, up to heat-treatment times of 60 min are insoluble in 99% chlorosulfonic acid, however no direct evidence of crosslinking has been obtained for these fibers using spectroscopic techniques, suggesting that in these fibers the degree of crosslinking must be very low. Evidence that methyl groups are precursors to certain crosslinks was first seen via a weak methylene resonance in ¹³C solid-state NMR, corresponding to about 2% of the original methyl intensity, in a sample heat-treated at 450°C in air. Fibers heat-treated in nitrogen at 550°C for 10 minutes do not exhibit any swelling in chlorosulfonic acid, are brittle, have lost most methyl groups; however, some CH₂ groups form. In this fiber, the carbon intensity for the CH₂ group in the ¹³C solid-state NMR is 18% of the intensity for the CH₃ group in the as-spun fiber. The fibers heat-treated at 400 and 450°C show a fibrillar morphology, while the fibrillar morphology is not observed in the fibers heat-treated at 550°C in nitrogen for 10 min. Based on this work, it is our judgment that if heat treatment of this material is to improve compressive strength, the heat treatment protocol of time and temperature will probably be critical and the highest temperatures of exposure will probably lie in the 450 to 550°C range. © 1996 John Wiley & Sons, Inc.     

Synthesis,Alkali Metal Picrate Extraction Properties,and X-Ray Crystal Structure of a Novel,Cage-Annulated Monoaza-18-Crown-6 Host

Compound 5, a cage-annulated monoaza-18-crown-6 macrocyclic polyether, has been synthesized, and its alkali metal picrate extraction capabilities have been assessed relative to those of the parent monoaza-18-crown-6 host system. It was observed that both 5 and monoaza-18-crown-6 are selective K⁺ picrate extractants; however, 5 appears generally to be a somewhat more efficient alkali metal picrate extractant than monoaza-18-crown-6. Interestingly, both the avidity and selectivity of 5 toward extraction of alkali metal picrates from aqueous solution into CHCl₃ appears to be pH dependent. In addition, the X-ray crystal structure of an unusual hydronium ion complex of 5 [i.e., 5(HCl)(H ₂ O)-(CHCl ₃ ) ₂] has been determined. The X-ray structure thus determined is compared with the corresponding structure of 5(HCl)(H ₂ O) that has been calculated via application of B3LYP Density Functional Theory.     

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