Chiral separation of sympathomimetics and beta-blockers by ligand-exchange CE using Cu(II) complexes of L-tartaric acid and L-threonine as chiral selectors

This paper deals with the use of Cu(II) complexes of L-tartaric acid or L-threonine as selectors for the chiral separation of drugs containing amino alcohol structure by ligand-exchange CE. Using Cu(II) ions as a complexing agent, a series of sympathomimetics and beta-blockers were resolved. It was found that the resolution strongly depends on selector concentration and pH. The optimum pH for complexation was 12.     

Raman scattering and the low-frequency vibrational spectrum of glasses

We present a theory of low-frequency Raman scattering in glasses, based on the concept that light couples to the elastic strains via spatially fluctuating elasto-optic (Pockels) constants. We show that the Raman intensity is not proportional to the vibrational density of states (as was widely believed), but to a convolution of Pockels constant correlation functions with the dynamic strain susceptibilities of the glass. Using the dynamic susceptibilities of a system with fluctuating elastic constants we are able for the first time to describe the Raman intensity and the anomalous vibration spectrum of a glass on the same footing. Good agreement between the theory and experiment for the Raman spectrum, the density of states, and the specific heat is demonstrated at the example of glassy As(2)S(3).     

Wavelength-independent ultrafast dynamics and coherent oscillation of a metal–carbon stretch vibration in photodissociation of Cr(CO)6 in the region of 270–345 nm

In the group-6 metal hexacarbonyls a number of metal-to-ligand charge-transfer (MLCT) and ligand-field (LF or d → d) states can be excited in the near UV. The latter are repulsive. In equilibrium geometry, most of them are higher than the MLCT states. We probed the dynamics of photodissociation of M(CO)₆ → M(CO)₅ + CO (M = Cr; some data also for M = Mo) with improved time resolution (10–40 fs), pumping at different wavelengths (mainly 270–345 nm) and probing by nonresonant photoionization. The initial relaxation (e.g. within 12.5 fs from T_1u excited at 270 nm) is assigned to direct crossing over to the repulsive surface, from where the subsequent dissociation is also remarkably fast (18 fs in this example). That is, there is no detour via the lowest excited singlet state, in contrast to the usual assumption. Also with 318 and 345 nm excitation a direct MLCT → LF relaxation seems to occur before dissociation. The product M(CO)₅ is generated in the S₁ state, also at pump wavelengths (345 nm) with barely sufficient energy. It relaxes to S₀ through a Jahn–Teller induced conical intersection along pseudorotation coordinates, which stimulates a coherent oscillation in S₀ in this vibration. A higher-frequency oscillation, assigned to totally symmetric MC stretch vibrations, is already found in the Franck–Condon region; it persists (with different wavenumbers) also during dissociation and over the subsequent product states. This vibration is transverse to the valley of dissociation, which is barrierless. The wavelength-independent mechanism also implies that there is no triplet contribution (which was previously supposed at long wavelengths) to photochemical dissociation of the hexacarbonyls.     

Photochemical Sandmeyer-type Halogenation of Arenediazonium Salts

Trihalide salts were found to efficiently promote photochemical dediazotizing halogenations of diazonium salts. In contrast to classical Sandmeyer reactions, no metal catalysts are required to achieve high yields and outstanding selectivities for halogenation over competing hydridodediazotization. Convenient protocols are disclosed for synthetically meaningful brominations, iodinations, and chlorinations of diversely functionalized derivatives.     

Photoluminescence in heavily doped Si: B and Si: As

We report the results of low-temperature photoluminescence measurements on a series of heavily-doped Si: As and Si: B samples. New spectra are obtained for very high doping levels (10¹⁹ 2- 10²⁰ cm^-3), and the results for the more lightly doped samples are found to be in good agreement with previously published data. By comparing the luminescence of a Si: As sample before and after partial compensation with B, we verify that minority carriers can be localized even in “metallic” samples.     

Beta–neutrino correlation experiments on laser trapped 38mK, 37K

Laser trapping and cooling techniques are now being applied to the study of nuclear β-decay at several labs. A magneto-optical trap (MOT) provides a localized source of atoms suspended in space, so the low-energy recoiling nuclei can freely escape and be detected in coincidence with the β. This allows reconstruction of the neutrino momentum, and the deduction of the β-v correlation in a more direct fashion than previously possible. In addition, the nuclei can be polarized by atomic techniques, opening a new class of spin correlation measurements to test the degree to which parity is maximally violated in the weak interaction. Our present experiment has detected several hundred thousand recoil-β⁺ coincidences from the 0⁺ → 0⁺ pure Fermi decay of ^38mK, produced at the on-line isotope separators TISOL and ISAC at TRIUMF. Our goal is to set constraints on non-Standard Model scalar bosons competitive with high-energy colliders and more conventional β-v correlation experiments. This revised version was published online in August 2006 with corrections to the Cover Date.