High-performance, lightweight coaxial cable from carbon nanotube conductors.

Coaxial cables have been constructed with carbon nanotube (CNT) materials serving as both the inner and outer conductors. Treatment of the CNT outer and inner conductors with KAuBr(4) was found to significantly reduce the attenuation of these cables, which demonstrates that chemical agents can be used to improve power transmission through CNT networks at high frequencies (150 kHz-3 GHz). For cables constructed with a KAuBr(4)-treated CNT outer conductor, power attenuation per length approaches parity with cables constructed from metallic conductors at significantly lower weight per length (i.e., 7.1 g/m for CNT designs compared to 38.8 g/m for an RG-58 design). A relationship between the thickness of the CNT outer conductor and the cable attenuation was observed and used to estimate the effective skin depth at high frequency. These results establish reliable, reproducible methods for the construction of coaxial cables from CNT materials that can facilitate further investigation of their performance in high-frequency transmission structures, and highlight a specific opportunity for significant reduction in coaxial cable mass.

Carbon nanotube wires and cables: near-term applications and future perspectives.

Wires and cables are essential to modern society, and opportunities exist to develop new materials with reduced resistance, mass, and/or susceptibility to fatigue. This article describes how carbon nanotubes (CNTs) offer opportunities for integration into wires and cables for both power and data transmission due to their unique physical and electronic properties. Macroscopic CNT wires and ribbons are presently shown as viable replacements for metallic conductors in lab-scale demonstrations of coaxial, USB, and Ethernet cables. In certain applications, such as the outer conductor of a coaxial cable, CNT materials may be positioned to displace metals to achieve substantial benefits (e.g. reduction in cable mass per unit length (mass/length) up to 50% in some cases). Bulk CNT materials possess several unique properties which may offer advantages over metallic conductors, such as flexure tolerance and environmental stability. Specifically, CNT wires were observed to withstand greater than 200,000 bending cycles without increasing resistivity. Additionally, CNT wires exhibit no increase in resistivity after 80 days in a corrosive environment (1 M HCl), and little change in resistivity with temperature (<1% from 170-330 K). This performance is superior to conventional metal wires and truly novel for a wiring material. However, for CNTs to serve as a full replacement for metals, the electrical conductivity of CNT materials must be improved. Recently, the conductivity of a CNT wire prepared through simultaneous densification and doping has exceeded 1.3 × 10(6) S/m. This level of conductivity brings CNTs closer to copper (5.8 × 10(7) S/m) and competitive with some metals (e.g. gold) on a mass-normalized basis. Developments in manipulation of CNT materials (e.g. type enrichment, doping, alignment, and densification) have shown progress towards this goal. In parallel with efforts to improve bulk conductivity, integration of CNT materials into cabling architectures will require development in electrical contacting. Several methods for contacting bulk CNT materials to metals are demonstrated, including mechanical crimping and ultrasonic bonding, along with a method for reducing contact resistance by tailoring the CNT-metal interface via electroless plating. Collectively, these results summarize recent progress in CNT wiring technologies and illustrate that nanoscale conductors may become a disruptive technology in cabling designs.

Platinum(II) terpyridyl acetylide complexes on platinized TiO(2): toward the photogeneration of H(2) in aqueous media.

New platinum(II) terpyridyl acetylide complexes having the ability to bind to TiO(2) have been synthesized and assayed in their ability to sensitize platinized titanium dioxide for the photogeneration of H(2) using visible light (lambda > 410 nm). Specifically, the complexes [Pt(tpy-phen-COOH)(C[triple bond]C-C(6)H(5))]Cl (1), where tpy-phen-COOH = 4'-(4-carboxyphenyl)-[2,2';6',2'']terpyridine and C[triple bond]C-C(6)H(5) = phenylacetylide, and [Pt(tpy-COOH)(C[triple bond]C-C(6)H(5))]Cl (2), where tpy-COOH = 4'-carboxy-2,2';6',2''-terpyridine, were prepared to investigate the effectiveness of attachment and proximity to the TiO(2) surface on hydrogen yield. Both complexes 1 and 2 sensitize the photogeneration of hydrogen, but produce fewer turnovers than the unbound chromophore, [Pt(ttpy)(C[triple bond]C-C(6)H(5))]PF(6) (5). On the basis of these observations and electrochemical data, a major limitation to the effectiveness of these chromophores is their instability upon oxidation. To attempt to remedy this problem, two donor-chromophore (D-C) dyads, [Pt(tpy-phen-COOH)(C[triple bond]C-C(6)H(4)CH(2)-PTZ)]PF(6) (3), where C[triple bond]C-C(6)H(4)CH(2)-PTZ = N-(4-ethynylbenzyl)-phenothiazine and [Pt(tpy-COOH)(C[triple bond]C-C(6)H(4)CH(2)-PTZ)]Cl (4) were prepared to function as TiO(2)-attached sensitizers. Transient absorption measurements have shown that the PTZ moiety reductively quenches the Pt center in several picoseconds. While the resultant PTZ(+) radical cation is capable of oxidizing rapidly the triethanolamine sacrificial electron donor, dyads 3 and 4 attached to platinized TiO(2) do not function to generate hydrogen upon irradiation, in contrast with results seen for 1 and 2.

Cyclometalated 6-phenyl-2,2'-bipyridyl (CNN) platinum(II) acetylide complexes: structure, electrochemistry, photophysics, and oxidative- and reductive-quenching studies.

Three cyclometalated 6-phenyl-4-(p-R-phenyl)-2,2'-bipyridyl (CNN-Ph-R) Pt(II) acetylide complexes, Pt(CNN-Ph-R)(CCPh), where R = Me (1), COOMe (2), and P(O)(OEt)(2) (3), have been synthesized and studied. Compounds 1 and 3 have been structurally characterized by single crystal X-ray crystallography and are found to exhibit distorted square planar geometries about the Pt(II) ions. The electrochemical properties of the compounds, as determined by cyclic voltammetry, have also been examined. Complexes 1-3 are brightly emissive in fluid CH(2)Cl(2) solution and in the solid state with lambda(em)(max) of ca. 600 nm and lifetimes on the order of ca. 500 ns in fluid solution. The emissions are assigned to a (3)MLCT transition. The complexes undergo oxidative quenching by MV(2+) with quenching rates near the diffusion-controlled limit (k(q) approximately 1.4 x 10(10) M(-1) s(-1)) in CH(2)Cl(2) solution. Reductive-quenching experiments of complexes 1-3 by the amine donors N,N,N',N'-tetramethylphenylenediamine (TMPD), phenothiazine (PTZ), and N,N,N',N'-tetramethylbenzidine (TMB) follow Stern-Volmer behavior, with very fast quenching rates on the order of 10(9)-10(10) M(-1) s(-1) in CH(2)Cl(2) solution. When the complexes are employed as the sensitizer in multiple component systems containing MV(2+), TEOA, and colloidal Pt in aqueous media, approximately one turnover of H(2) (TN vs mol of chromophore) is produced per hour upon irradiation with lambda > 410 nm but only after at least a 2 h induction period.

Platinum(II) terpyridyl-acetylide dyads and triads with nitrophenyl acceptors via a convenient synthesis of a boronated phenylterpyridine.

Four new Pt(II) terpyridyl acetylide complexes which possess a covalently linked nitrophenyl moiety were prepared and studied. Specifically, the chromophore-acceptor (C-A) dyads reported here include [Pt(ptpy-ph-p-NO(2))(C[triple bond]C-C(6)H(5))](PF(6))(3) (1), where ptpy-ph-p-NO(2) = 4'-{4-(4-nitrophenyl)-phenyl}-[2,2';6',2'']terpyridine, and C[triple bond]C-C(6)H(5) = phenylacetylide and [Pt(ptpy-ph-m-NO(2))(C[triple bond]C-C(6)H(5))](PF(6))(2) (2), where ptpy-ph-m-NO(2) = 4'-(4-m-nitrophenyl-phenyl)-2,2';6',2''-terpyridine, as well as the related donor-chromophore-acceptor (D-C-A) triads [Pt(ptpy-ph-p-NO(2))(C[triple bond]C-C(6)H(4)CH(2)-PTZ)]PF(6) (3), where C[triple bond]C-C(6)H(4)CH(2)-PTZ = 4-ethynylbenzyl-N-phenothiazine, and [Pt(ptpy-ph-m-NO(2))(C[triple bond]C-C(6)H(4)CH(2)-PTZ)]PF(6) (4). Transient absorption spectroscopy and electrochemical analyses were used to characterize these compounds. In contrast to previous observations for closely related multicomponent systems, it appears that, in the current systems, the nitrophenyl group is not an effective quencher of the excited state. The luminescence and transient absorption properties of the C-A dyads are virtually identical to those of the parent chromophore, [Pt(ttpy)(C[triple bond]C-C(6)H(5))]PF(6) (5), where ttpy = 4'-p-tolyl-[2,2';6',2'']terpyridine.

Photoinduced electron transfer in platinum(II) terpyridyl acetylide chromophores: reductive and oxidative quenching and hydrogen production.

A series of luminescent platinum(II) terpyridyl acetylide complexes, ([Pt(tpy)(CCPh)]ClO4 (1) and [Pt(ttpy)(CC-p-C6H4R)]ClO4, where tpy=terpyridine, ttpy=4'-p-tolylterpyridine, R=H, Cl, Me) (2-4) were studied with regard to excited-state quenching by dialkylated bipyridinium cations as electron acceptors and triethanolamine (TEOA) as an electron donor and the photogeneration of hydrogen from systems containing the chromophore, the dialkylated bipyridinium cations, TEOA, and colloidal Pt as a catalyst. The dialkylated bipyridinium cations include methyl viologen (MV2+) and a series of diquats prepared from 2,2'-bipyridine or 4,4'-dimethyl-2,2'-bipyridine. The quenching rates for the diquats for one of the chromophores (2) are close to the diffusion-controlled limit. The most effective electron acceptor and relay for hydrogen evolution has been found to be 4,4'-dimethyl-1,1'-trimethylene-2,2'-bipyridinium (DQ4) which on photoreduction by the chromohore provides the strongest reducing agent of the diquats studied. The rate of hydrogen evolution depends in a complex way on the concentration of the bipyridinium electron relay, increasing with concentration at low concentrations and then decreasing at high concentrations. The rate of H2 photogeneration also increases with TEOA concentration at low values and eventually reaches a plateau. The most effective system examined to date consists of the chromophore 2 (2.2x10(-5) M), DQ4 (3.1x10(-4) M), TEOA (2.7x10(-2) M), and Pt colloid (6.0x10(-5) M), and has produced 800 turnovers of H2 (67% yield based on TEOA as sacrificial electron donor) after 20 h of photolysis with lambda>410 nm.

Solution behavior of a novel biopharmaceutical drug candidate: a gonadotropin-toxin conjugate.

There is little known about the solution structure and stability of peptide-protein conjugates, which comprise a new class of potential biopharmaceutical agents. This study describes the solution behavior of gonadotropins-releasing hormone (GnRH) chemically conjugated to pokeweed antiviral protein (PAP). The conjugate adopts a well-defined conformation across a pH range of 4 to 8. Even after heating to 80 degrees C, the conjugate retains a significant amount of secondary and tertiary structure. Heating for 1 h at 60 degrees C does lead to chemical damage, as determined by cation exchange chromatography. Using an experimental design approach, the optimal pH and salt concentration for limiting chemical damage was determined.

Photocatalytic generation of hydrogen from water using a platinum(II) terpyridyl acetylide chromophore.

The cationic complex [Pt(tolylterpyridine)(phenylacetylide)]+ has been used as a photosensitizer for the reduction of aqueous protons in the presence of a sacrificial electron donor to make H2. In this system, triethanolamine (TEOA) acts as the sacrificial reducing agent, methyl viologen (MV2+) serves as an electron transfer agent, and colloidal Pt stabilized by polyacrylate functions as the catalyst for H2 generation. The Pt(II) chromophore undergoes both oxidative and reductive quenching, but H2 is only seen when both TEOA and MV2+ are present. Irradiation of the reaction solution for 10 h with lambda > 410 nm leads to 85 turnovers and an overall yield of 34% based on TEOA. While H2 evolution is maximized for the system at pH 7, it is also seen at pH 5 and 9, in contrast with earlier reports using Ru(bpy)32+ as the photosensitizer. This is the first time that a Pt diimine or terpyridyl complex has been used as the photosensitizer for H2 generation from aqueous protons.