A mechanistic study on the amidation of esters mediated by sodium formamide

Kinetic and computational studies on the amidation of esters with mixtures of formamide and sodium methoxide are described. Rate studies are consistent with a fast deprotonation of formamide followed by two reversible acyl transfers affected by solvent participation. MP2 calculations suggest that the first acyl transfer between the ester and sodium formamide is rate-determining. The transition structures leading to the formation and collapse of the first tetrahedral intermediate are calculated to be isoenergetic.     

Dual surface coil with high-B1 homogeneity for deep organ MR imaging

The theory and construction of a dual surface coil which provides good B₁ homogeneity and sensitivity in a defined volume of interest is described. The probe comprises two coaxial rings, of different diameters and in different planes, which carry opposing currents of different values. Current in the second ring compensates for the roll-off of the B₁ field associated with a single surface coil. Coupling between the rings and a third matching ring is by mutual inductance only. A comparison to a traditional surface coil with practical application to pig brain imaging at a field strength of 7 Tesla is shown.     

Interpolation and inner maps that preserve measure

It is shown, for n ? m ? 1, that there exist inner maps Φ: Bⁿ → B^m with boundary values $\text{Φ}{}_1\text{: B}{}^{\mathrm{n}}\text{→ B}{}^{\mathrm{m}}$ such that $\text{σ}{}_{\mathrm{m}}\text{(A) = σ}{}_{\mathrm{n}}\text{(Φ}{}_1{}^{\mathrm{?1}}\text{(A))}$. where σ_n and σ_m are the Haar measures on ?Bⁿ and ?B^m, respectively, and A ? Bⁿ is an arbitrary Borel set.     

The Gibbs measures and partial differential equations

We investigate the connections of the Gibbs measures, which appear in Euclidean Field Theory, and the corresponding partial differential equations of Classical Euclidean Field Theory.     

Réaction de réformatsky sur les azirnes: synthesés d'aziridines esters et de pyrrolinones

Addition of Reformatsky reagents 1 to two azirines is reported. From 2-phényl-3,3-dimethyl azirine 2, aziridines esters 3 are obtained. 2-Phenyl-3-methyl azirine 4 gives aziridines esters 5 and diazepinones 6. Δ-3-Pyrrolinones or 5-methylene pyrrolidones are obtained from Grignard reagents and aziridines esters 3 and 5. The reaction mechanism is discussed; compounds 7,8,9,11 and 12 result from an aza-1-oxo-2-bicyclo-pentane (2,1,0) intermediate.     

Effect of Temperature in micro-HPLC Separation of PAHs under Isocratic Conditions Using Octadecyl and Alkylamide Phases

The main difficulty in micro-HPLC separation is the manipulation with the composition of the mobile phase (degassing of solvents and a slow establishment of equilibrium) but the problem of elution can be solved by temperature optimalization. The effect of temperature in micro-HPLC separation of the 16 polycyclic aromatic hydrocarbons (PAHs) (mixture SRM 1647 of the US EPA) has been studied using conventional C₁₈ and new developed AP phase (an amide group localized in the hydrophobic ligands). All the investigations have been performed under isocratic conditions (binary hydroorganic mobile phase: acetonitrile/water). The results have shown that, in the case of AP phase, application of temperature gradient (from 298 to 303 K), enabled the attainment of complete 16 PAHs separation (especially of the first 4 solutes).     

In situ dual-beam coincidence second harmonic generation as a probe of spatially resolved dynamics at electrochemical interfaces

In situ dual-beam coincidence second harmonic generation was used to monitor spatially resolved dynamics at the Pt(111)/CO-saturated 0.1 M HClO4 interface. The results obtained showed that, for potential steps from 30 to about 870 mV vs RHE, the full electrooxidation of CO as evidenced from SHG occurred at different times for the two areas of the Pt(111) surface probed by the beams. On this basis, the diffusional rates of adsorbed CO cannot be assumed to be generally large enough as to render the entire surface in a homogeneous state, as invoked by the mean field approximation model.     

A Compact Violet Diode Laser-Based Fluorescence Lifetime Microscope

We have constructed a time-correlated single-photon counting (TCSPC) microscope system using a pulsed violet-laser diode for measuring fluorescence lifetimes below 1 ns. These compact; cool, and fast-pulsed laser diodes are much more suitable for lifetime measurements than the traditional mode-locked lasers used in the past. The laser source (LDH-400, PicoQuant GmbH) is mounted on an optical table above the microscope, and the laser beam is directed into an Olympus BX-60 microscope by means of a dichroic beamsplitter set at 45 degrees. The system operates in backscattering mode with the fluorescence emission passing back through the dichroic beamsplitter and focused into a 100 mm focal length monochromator with a PMT detector. This prototype instrument is compact (80 × 70 × 70 cm) and is nearly fully computer controlled by means of a SPC-730 (Becker & Hickl) PC card. We include preliminary results showing the instrument response function (IRF) of the system, and some of the factors have been adjusted to minimize the temporal width of the IRF. The instrument has been validated using a series of standard fluorophores at different emission wavelengths.     

The logarithmic sobolev inequality for discrete spin systems on a lattice

For finite range lattice gases with a finite spin space, it is shown that the Dobrushin-Shlosman mixing condition is equivalent to the existence of a logarithmic Sobolev inequality for the associated (unique) Gibbs state. In addition, implications of these considerations for the ergodic properties of the corresponding Glauber dynamics are examined.During the period of this research, both authors were partially supported by NSF grant DMS 8913328