Collective effects by agglomerated debris particles in the backscatter

We present an analysis of backscattered light by agglomerated debris particles whose size is comparable with the wavelength. We consider agglomerates that consist of one or two large central particles and a few relatively small fragments surrounding the particles. We find that for the particles we studied, the attachment of small fragments onto the particles leads to a decrease of the negative polarization branch (NPB) at small phase angles in comparison with the branch produced by the isolated particles. For relatively large agglomerates (with size parameters x about 25) the internal scatter in the agglomerates may produce a secondary minimum of the NPB. In this case the second order of scatter between constituents of aggregates plays the dominant role.     

Observation of a shell gap at N = 152 in the 246 Cm(t,p) 248 Cm reaction

Previous reports of two-neutron stripping reactions in the actinide nuclei have not indicated any excited 0⁺ strength below an excitation energy of 1.5 MeV. In contrast, the ²⁴⁶ Cm(t,p) ²⁴⁸Cm reaction shows a relatively strong 0⁺ state at 1.084 MeV. We believe that this result, coupled with a marked change in ground-state transition strenghts between ²⁴⁶ Cm and ²⁴⁸ Cm targets, indicates a gap in the single-particle orbitals that is larger than the pairing gap.     

A homogeneous gallium(III) compound selectively catalyzes the epoxidation of alkenes

We demonstrate that a simple gallium(III) complex, [Ga(phen)(2)Cl(2)]Cl (phen = 1,10-phenanthroline), can serve as a homogeneous catalyst for the epoxidation of alkenes. The olefin epoxidations proceed relatively quickly at mild temperatures and, under optimum conditions, are highly selective for the epoxide product.     

Asymmetric band profile of the Soret band of deoxymyoglobin is caused by electronic and vibronic perturbations of the heme group rather than by a doming deformation

We measured the Soret band of deoxymyoglobin (deoxyMb), myoglobin cyanide (MbCN), and aquo-metmyoglobin (all from horse heart) with absorption and circular dichroism (CD) spectroscopies. A clear non-coincidence was observed between the absorption and CD profiles of deoxyMb and MbCN, with the CD profiles red- and blueshifted with respect to the absorption band position, respectively. On the contrary, the CD and absorption profiles of aquametMb were nearly identical. The observed noncoincidence indicates a splitting of the excited B state due to heme-protein interactions. CD and absorption profiles of deoxyMb and MbCN were self-consistently analyzed by employing a perturbation approach for weak vibronic coupling as well as the relative intensities and depolarization ratios of seven bands in the respective resonance Raman spectra measured with B-band excitation. The respective B(y) component was found to dominate the observed Cotton effect of both myoglobin derivatives. The different signs of the noncoincidences between CD and absorption bands observed for deoxyMb and MbCN are due to different signs of the respective matrix elements of A(1g) electronic interstate coupling, which reflects an imbalance of Gouterman's 50:50 states. The splitting of the B band reflects contributions from electronic and vibronic perturbations of B(1g) symmetry. The results of our analysis suggest that the broad and asymmetric absorption band of deoxyMb results from this band splitting rather than from its dependence on heme doming. Thus, we are able to explain recent findings that the temperature dependences of CO rebinding to myoglobin and the Soret band profile are uncorrelated[Ormos et al., Proc. Natl. Acad. Sci U.S.A. 95, 6762 (1998)].     

DDA simulations of light scattering by small irregular particles with various structure

We present DDA investigations of light scattering by irregular particles whose size is comparable with wavelength. We consider four types of randomly irregular particles: strongly damaged spheres, rough-surface spheres, pocked spheres, and agglomerated debris particles. Each type of particle is generated with a well defined algorithm producing an ensemble of stochastically different particles that have a common origin. The different types of irregular particles produce different angular dependencies of intensity and linear polarization degree. Transformation of phase curves of intensity and polarization with changing size parameter for irregular particles tends to be more monotonic, unlike spheres. We find that the magnitude of the negative polarization branch (NPB) tends to shrink as particle absorption increases; whereas, the maximal value and position of the positive polarization branch tends to increase. The most frequently observed shape of the negative polarization at small phase angles is asymmetric with a shift of the minimum position towards the angle of polarization sign inversion. All types of considered irregular particles reveal such asymmetry at x<10. Symmetric negative polarization branches occur seldom. The necessary conditions for their appearance are a relatively large size parameter x?10 to 12 and low absorption.     

Optimized matrix inversion technique for the T-matrix method

We suggest a new approach to calculate the inverse matrix in scattering calculations using the T-matrix method. Instead of inversion of the full matrix, we suggest the inversion of two matrices, each of which contains half the number of rows. This approach allows significant time savings and a noticeable increase of the precision of scattering calculations due to fewer arithmetical operations. An iterative method can be applied to matrices whose dimension is also divisible by factors of 2, which can further increase the time savings and accuracy.     

Synthesis and Anti‐proliferative Activity of N,N′‐bis‐substituted 1,2,4‐Triazolium Salts against Breast Cancer and Prostate Cancer Cell Lines

A series of 1,4‐N,N′‐bis‐substituted 1,2,4‐triazolium bromide salts were synthesized and tested for anti‐proliferative activity. 1,4‐Bis(naphthalen‐2‐ylmethyl)‐1,2,4‐triazolium bromide ( 2 ) showed activity against MDA‐MB‐468 breast cancer and PC‐3 prostate cancer cell lines.     

The structure of the cyclooctadecane ring system. 1,10-Cyclooctadecanedione

The crystal structure of the title compound was determined by X-ray crystallography and solved by direct methods; the molecule has C_2h symmetry. The carbon atoms are arranged in a diamondoid lattice, but not of the rectangular type that might have been expected. The dipole moment for the conformation found in the crystal is zero, while the observed dipole moment of the compound in solution is 2.78 D. Molecular mechanics calculations were carried out on several of the large number of possible conformation. Of those studied, the conformation found in the crystal had the lowest energy.     

Propargylic CH activation using a Cu(II) 2-quinoxalinol salen catalyst and tert-butyl hydroperoxide

The oxidation of alkynes to α,β-acetylenic carbonyls was achieved using only 1?mol% of a Cu(II) 2-quinoxalinol salen catalyst with tert-butyl hydroperoxide. These reactions proceed under mild conditions (70?°C) with excellent selectivity, producing yields up to 78%, and were used on a variety of alkyne substrates to produce the desired corresponding α,β-acetylenic ketones. In addition, these reactions can be run under aqueous conditions using a sulfonated version of the 2-quinoxalinol salen with good yields, reducing the need for volatile organic solvents.