Cation radicals. XXXII. Reaction of N-ethylcarbazole with iodine-silver salts. Nitration of N-ethylcarbazole

Reaction of N-ethylcarbazole ( 1 ) with iodine-silver perchlorate gave a green solution having a singlet esr signal. Reduction of the solution with potassium iodide gave N,N′ -diethyl-3,3′-dicarbazolyl ( 3 , 48%). Small amounts of 3-iodo- ( 4 ) and 3,6-diiodo-N-ethylcarbazole ( 5 ) were also obtained. Compounds 4 and 5 are believed to have been formed by electrophilic iodination of 1 by I₂-AgCIO₄, whereas 3 appears to have been formed via the dimerization of 1 ^.+. In accord with this, reaction of 1 with iodine-silver nitrite gave 3-nitro-N-ethylcarbazole ( 6 , 61%), 9% of another nitro-N-ethylcarbazole ( 7 ), thought to be either 1- or 4-nitro-N-ethylcarbazole, and 28% of 4. Thus, trapping of 1 ^.+ by nucleophilic nitrite ion occurred even though 1 ^.+ is not stable enough toward isolation as the perchlorate.     

Self‐Assembly of DNA–Oligo(p‐phenylene‐ethynylene) Hybrid Amphiphiles into Surface‐Engineered Vesicles with Enhanced Emission

Surface‐addressable nanostructures of linearly π‐conjugated molecules play a crucial role in the emerging field of nanoelectronics. Herein, by using DNA as the hydrophilic segment, we demonstrate a solid‐phase “click” chemistry approach for the synthesis of a series of DNA–chromophore hybrid amphiphiles and report their reversible self‐assembly into surface‐engineered vesicles with enhanced emission. DNA‐directed surface addressability of the vesicles was demonstrated through the integration of gold nanoparticles onto the surface of the vesicles by sequence‐specific DNA hybridization. This system could be converted to a supramolecular light‐harvesting antenna by integrating suitable FRET acceptors onto the surface of the nanostructures. The general nature of the synthesis, surface addressability, and biocompatibility of the resulting nanostructures offer great promises for nanoelectronics, energy, and biomedical applications.     

Residual Dipolar-Coupling-Based Conformational Comparison of Noncovalent Ubiquitin Homodimer with Covalently Linked Diubiquitin

Although the conformation of the polymer chain of Ubiquitin (Ub) mainly depends on the type of isopeptide linkage connecting two Ub molecules, the non-covalent (noncovalent) interaction between two Ub molecules within the chain could also tune their conformational preference. Here, we studied the conformation of noncovalently formed Ub dimers in solution using residual dipolar couplings (RDCs). Comparing the RDC derived alignment tensor of the noncovalently formed dimer with the two most abundant (K11 and K48) covalent linked Ub dimers revealed that the conformation of K11 linked and noncovalent Ub dimers were similar. Between the various NMR and crystal structures of K11 linked Ub dimers, RDC tensor analysis showed that the structure of K11 linked dimer crystalized at neutral pH is similar to noncovalent dimer. Analogous to the experimental study, the comparison of predicted order matrix of various covalent Ub dimers with that of the experimentally determined order matrix of noncovalent Ub dimer also suggests that the conformation of K11 linked dimers crystalized at neutral pH is similar to the noncovalent dimer.     

Experimental studies of suspended ferromagnetic fibers in a magnetic field

The analysis of the rotation of a ferromagnetic ellipsoid suspended in a Newtonian fluid and subjected to a uniform magnetic field is extended to include a long, slender cylindrical fiber which is magnetically saturated. Experimental observations of rotating nickel cylinders with aspect ratiosL/D ranging from 5 to 40 agree with the theoretical predictions that: (1) the proper magnetoviscous time constant for the motion is _MV = _s/µ ₀ M _s ² , (2) larger fiber aspect ratios result in considerably longer orientation times; and (3) the strength of the applied external field has only a slight effect on the overall fiber rotation, and has no effect on the maximum angular velocity achieved. Quantitative agreement of theory and experiments is obtained for fibers withL/D 20; for the shorter fibers, the theory tends to overpredict the fiber rotation rate by as much as 30%. D diameter of the cylinder - D ^P (r) position-dependent demagnetization tensor, implicitly defined in eq. (2.5) - D _xx,D _yy,D _zz volume-averaged demagnetizing factors for an ellipsoid equivalent to a uniformly magnetized cylinder, defined in eq. (2.6) - H _i ;H _i magnetic field inside a ferromagnetic body; magnitude ofH _i - H ₀;H ₀ magnetic field applied by external sources; magnitude ofH ₀ - k geometric parameter in the hydrodynamic resistance of a body rotating in a Newtonian fluid, eq. (2.2) - L length of the cylinder - L ^(h);L _z ^(h) hydrodynamic torque exerted on a rotating body; thez-component ofL ^(h) on the cylinder - L ^(m);L _z ^(m) magnetic torque exerted on a magnetic body in a magnetic field, eq. (2.4); thez-component ofL ^(m) on the cylinder - M the magnetization of a magnetic material - M _s the saturation magnitude ofM, approached by all ferromagnetic materials asH _i becomes large - r position vector of a point within a ferromagnetic body - V volume of a magnetic particle - x, y, z rectangular coordinate axes fixed in the cylinder according to figure 1 - angle of inclination of the axis of the cylinder with respect toH ₀ - shear rate - small parameter of slender body theory,=1/ln (2L/D) - _s constant viscosity of the suspending fluid - µ ₀ the magnetic permeability of free space,µ ₀=4 · 10^–7 H/m - _MV the magnetoviscous time constant, a characteristic time for a process involving a competition of viscous and magnetic stresses - ₁ the first normal-stress coefficient - ; _z angular velocity of a rotating body; angular velocity of a cylinder about thez-axis, _z =– d/dt     

X-ray emission from clusters of galaxies and cosmological parameters

Clusters of galaxies are excellent probes of cosmic structure and evolution. X-ray studies of clusters provide some of their key parameters, viz., temperature of the hot intra-cluster gas, its metallicity, X-ray luminosity and surface brightness giving mass distribution and mass-flow rate in the case of cooling flows. X-ray measurements for a large sample of clusters have lead to estimates of the total gravitating mass in them, which can be compared to the virial masses derived from dynamical considerations and gravitational lensing in some of them. X-ray derived total masses are consistent with masses obtained from the other methods after the effects due to the presence of cooling flows are taken into account in the analyses. Estimated virial masses, lack of evolution in X-ray properties, and detection of several very hot clusters at high redshifts indicate a Universe with a low value (≤ 0.3) for the Ω parameter.     

Synthetic Studies of Nitro-Chlorotropones and Trihalotropones

Nitration of 2-chlorotropone with fuming nitric acid gave 2-chloro- 4,7-dinitrotropone in good yield. 2,4,7-Trichlorotropone, a new compound, and 2,4,7-tribromotropone have been derived successfully from 2-chloro-4,7-dinitrotropone by heating with hydrogen chloride or hydrogen bromide in acetic acid. The structures of 2-chloro-4,7-dinitrotropone, 2,4,7-trichlorotropone and 2,4,7-tribromotropone have been confirmed on the basis of chemical facts together with the spectroscopical evidences. The chemical and physical properties of the above compounds have also been investigated.     

The role of aromatic groups in the Tobey-Simon additivity rule for vinylic protons

The Tobey-Simon (additivity) rule for aromatic groups which was devised about 40 years ago has been found to need revision. The rule shows an aromatic group attached to a C==C double bond as causing a downfield chemical shift of a cis-related vinylic proton and a small upfield shift of a trans-related proton. A search of data in the recent literature has shown that this rule should apply mainly to monosubstituted phenyl groups and some polynuclear aromatics. In contrast with them, 2,6-disubstituted phenyl, 2,4,6-trisubstituted phenyl and 9-anthracenyl groups cause cis-related vinylic protons to resonate upfield of comparable trans-related protons. Further, the current rule for o-substituted phenyl groups has been found to be inaccurate. In writing a rule for aromatic groups, therefore, greater attention needs to be given to the diversity of effects that these groups have on chemical shifts of vinylic protons.