Design and characterization of programmable DNA nanotubes

DNA self-assembly provides a programmable bottom-up approach for the synthesis of complex structures from nanoscale components. Although nanotubes are a fundamental form encountered in tile-based DNA self-assembly, the factors governing tube structure remain poorly understood. Here we report and characterize a new type of nanotube made from DNA double-crossover molecules (DAE-E tiles). Unmodified tubes range from 7 to 20 nm in diameter (4 to 10 tiles in circumference), grow as long as 50 microm with a persistence length of approximately 4 microm, and can be programmed to display a variety of patterns. A survey of modifications (1) confirms the importance of sticky-end stacking, (2) confirms the identity of the inside and outside faces of the tubes, and (3) identifies features of the tiles that profoundly affect the size and morphology of the tubes. Supported by these results, nanotube structure is explained by a simple model based on the geometry and energetics of B-form DNA.     

An analogue system displaying all the important processes of the catalytic cycles involving monooxomolybdenum(VI) and desoxomolybdenum(IV) centers

The mononuclear monooxomolybdenum(VI) complex hydrotris(3,5-dimethyl-1-pyrazolyl)borato(bis-4-ethoxyphenolato)oxomoylybdenum(VI) cation, [LMoVIO(p-OC6H4-OC2H5)2]+, where L- = hydrotris(3,5-dimethyl-1-pyrazolyl)borate, has been synthesized by chemical and electrochemical oxidation from the corresponding neutral oxomolybdenum(V) species, LMoVO(p-OC6H4-OC2H5)2. The molybdenum(VI) species has been characterized by NMR, IR, and resonance Raman spectroscopies, mass spectrometry, and electronic spectroscopy. Acetonitrile solutions of cationic [LMoVIO(p-OC6H4-OC2H5)2]+ react with tertiary phosphines (PR3) to generate phosphineoxide-bound adducts, [LMoIV(OPR3)(p-OC6H4-OC2H5)2]+, which subsequently generate the cationic desoxo species, [LMoIV(p-OC6H4-OC2H5)2]+ and OPR3. In the presence of water and an oxidizing agent the desoxo species generates the monooxomolybdenum(V), LMoVO(p-OC6H4-OC2H5)2, and completes the catalytic cycle. The oxygen atom transfer reaction has been probed by isotope-labeling experiments, vibrational spectroscopies, and mass spectrometry. This study describes an analogue complex that can exhibit all important processes of the catalytic cycle involving monooxomolybdenum(VI) and desoxomolybdenum(IV) centers.     

Water penetration in nylon 6,6: Absorption,desorption, and exchange studied by NMR microscopy

The uptake of water by nylon 6,6 [42DB Adipure (trade name of Dupont Canada Inc.)] at 100°C has been monitored by a combination of one-dimensional proton NMR spectroscopy, relaxation time (T₁ and T₂) measurements and proton microscopic NMR imaging techniques. The relaxation times of the water absorbed into the nylon matrix are very short at room temperature, (T₂ < 1 ms and T₁ ≈ 1 s) indicating that the water is located in a highly restricted environment and suggesting that strong interactions exist between the absorbed water and the polymer. The diffusion profiles measured at room temperature indicate that the diffusion of water into nylon 6,6 at 100°C is Case I Fickian diffusion. The spatial dependence of the T₂ relaxation time constant and its variation with the water content was also examined. The results reveal that both T₂ and T₂^* decrease toward the center of the sample in samples that have a concentration gradient of sorbed water. In fully saturated samples, no spatial dependence was observed. The overall values of T₂ and T₂^* are also observed to increase as a function of exposure time. An evaluation of the desorption process at room temperature and at 100°C was performed. A continuous, exponentially decreasing solvent profile was observed for the desorption process which again indicates Case I Fickian kinetics. The exchange process of external bulk and atmospheric water with deuterium oxide (D₂O) saturated nylon rods has also been studied using the microscopic imaging technique. © 1993 John Wiley & Sons, Inc.     

A dual-polarization InSb receiver for 461/492 GHz

A dual-polarization InSb hot-electron bolometer-mixer receiver has been built for the James Clerk Maxwell Telescope, for operation at 461 and 492 GHz (the frequencies of theJ=43 rotational transition of CO and of the³ P ₁³ P ₀ transition of neutral carbon). Receiver noise temperatures of 500K have been obtained at 461 GHz, in observing bandwidths of 3 MHz. The receiver was designed as a common-user or facility instrument. Here we describe those aspects of the design and construction which enabled this goal to be realized.     

Structural and spectroscopic characterization of a cationic aquanitrato copper(II) complex with the tetradentate Schiff-base ligand N,N′-bis[1–(2–pyridyl)ethylidene]ethane-1,2–diamine

Cu(NO3)2·3H2O reacts with 1 equiv. of the tetradentate Schiff base N,N-bis[1–(2–pyridyl)ethylidene]ethane-1,2–diamine (LA) in refluxing acetone to yield the [CuLA(ONO2)(H2O)](NO3) complex in ca. 80% yield. The structure of this salt has been determined by single-crystal X-ray crystallography. The copper is six-coordinated with the LA ligand in the equatorial plane and weakly bonded aqua and nitrato ligands above and below this plane. The complex cation is hydrogen-bonded to the nitrate counter-ion. The complex was also characterized by elemental analyses, molar conductivity, room-temperature magnetic susceptibility and spectroscopic (i.r., far-i.r., u.v.–vis, e.s.r.) studies. The data are discussed in terms of the nature of bonding and the known structure.     

A quantum metric of organizational performance: Terrorism and counterterrorism

Political terrorism and insurgency have become the primary means of global war among states. Lacking comparable military and political means to compete directly with Western civilization, many failed states and tribes have honed the art of asymmetric warfare. But traditional models of organizations do not work under normal or these extreme circumstances, precluding realistic models of terrorism and a fruitful search among alternatives for potential solutions. In contrast to traditional models, we have made substantial progress with a quantum model of organizations, which we further develop in this study with the introduction of a case study of a normal organization in the process of being restructured. We apply preliminary results from our model to terrorist organizations and counter terrorism.     

Microwave-Driven In-liquid Plasma in Chemical and Environmental Applications. III. Examination of Optimum Microwave Pulse Conditions for Prolongation of Electrode Lifetime,and Application to Dye-Contaminated Wastewater

Generating in-liquid plasma using continuous microwave radiation has proven problematic as the surface of the electrode undergoes significant deterioration because of the generated plasma. This article describes a method by which this problem can be resolved by the utilization of pulsed microwave radiation from a magnetron microwave generator and presents results in the search for optimal pulsed microwave irradiation conditions; these would avoid damage to the electrode and would afford reduced power consumption. Results show that continuous generation of in-liquid plasma that avoids electrode (antenna) damage requires strict and very limited pulsed oscillation conditions. Evaluation of this device was investigated by the discoloration of a rhodamine-B (RhB) dye-contaminated wastewater, for which it was shown that higher treatment efficiency can be obtained compared to more traditional methods such as the UV photolysis (UV), the UV-assisted photocatalytic TiO₂ method (UV/TiO₂), and the NaClO methodology (NaClO). The energy consumed during the 3 min needed to discolor 50 mL of a 0.10 mM aqueous RhB dye solution was 6.3?×?10^?3 kWh per mg of RhB; complete mineralization of the dye solution by the in-liquid plasma occurred within 15 min (loss of TOC).