MTDSC Calibration Dependence of the Instrumental Response Upon Experimental Conditions

The heat capacity calibration ‘constants’ of a commercial MTDSC system (TA 3100) were determined in a variety of experimental conditions. For a given modulation frequency, the calibration constants are the same within a few percents for different temperatures, and over a wide range of modulation amplitudes and scan rates. This variation decreases below 1% if hidden instrumental constraints are taken into account, which are related with the capability of the control system to achieve the desired temperature program. On the other hand, the calibration constant changes substantially with the period, and takes anomalously high values for the short modulation periods (20+40 s). Rules to optimize the accuracy of the system are given. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evolution strategy optimization for adiabatic pulses in MRI.

We propose a new type of adiabatic pulses for uniform inversion of the magnetization in magnetic resonance imaging. We produced these pulses with an evolution strategy optimization, by which the search of the "best solution" has been made more efficient than by deterministic algorithms. The pulse parametrization takes into account an "offset-independent adiabaticity condition," which guarantees insensitivity to RF inhomogeneities. The RF pulse power (both peak and mean) contributes to the cost to be minimized, as well as the error function does: in this way we obtain solutions that require lower energy than the well-known hyperbolic-secant pulse, with no loss of quality in the response profile.     

Oxidation of propylene to acrylic acid on a Fe?Mo?Bi oxide system

Data obtained in a flow reactor show that iron(III) molybdate doped by bismuth can oxidize propylene to acrylic acid directly in one step. Part of the catalyst works in a partially reduced form and in the preparation of the catalyst the surface acidity must be controlled.

---

, , (III), , . .

     

Structural basis for the enantioselectivity of an epoxide ring opening reaction catalyzed by halo alcohol dehalogenase HheC

Halo alcohol dehalogenase HheC catalyzes the highly enantioselective dehalogenation of vicinal halo alcohols to epoxides, as well as the reverse reaction, the enantioselective and beta-regioselective nucleophilic ring opening of epoxides by pseudo-halides such as azide and cyanide. To investigate this latter reaction, we determined X-ray structures of complexes of HheC with the favored and unfavored enantiomers of para-nitrostyrene oxide. The aromatic parts of the two enantiomers bind in a very similar way, but the epoxide ring of the unfavored (S)-enantiomer binds in a nonproductive inverted manner, with the epoxide oxygen and Cbeta atom positions interchanged with respect to those of the favored (R)-enantiomer. The calculated difference in relative Gibbs binding energy is in agreement with the observed loss of a single hydrogen bond in the S bound state with respect to the R bound state. Our results indicate that it is the nonproductive binding of the unfavored (S)-enantiomer, rather than the difference in affinity for the two enantiomers, that allows HheC to catalyze the azide-mediated ring opening of para-nitrostyrene oxide with high enantioselectivity. This work represents a rare opportunity to explain the enantioselectivity of an enzymatic reaction by comparison of crystallographic data on the binding of both the favored and unfavored enantiomers.     

Behavior of 5,6-dihydrobenzo[h]cinnolinones towards hydrazine. Synthesis of benzo[h]cinnolinones and of 4-Aminobenzo[h]cinnolinones

Dehydrogenation and amination of 4,4a,5,6-tetrahydro and 5,6-dihydrobenzocinnolinones in refluxing hydrazine hydrate to give new benzo[h]cinnolinones and 4-aminobenzo[h]cinnolinones are reported, and reaction mechanisms proposed. Experiments were also extended to 4,4a-dihydro-5H-indenopyridazinone which underwent hydrazine induced dehydrogenation to 5H-indenopyridazin-3-one but not subsequent amination.     

1H NMR spectra of oxiranes. cis-Arylmethyl oxiranes substituted in the phenyl ring

The ¹H NMR parameters for a number of cis-arylmethyl oxiranes are reported and discussed in comparison with those of trans derivatives and styrene oxides substituted in the phenyl ring. While the macroscopic behaviour of the results is in agreement with a perturbative mechanism through the oxirane ring that is mainly electrostatic in character, a small contribution due to conjugative interaction is not excluded. It seems likely that the effect of substituents in the phenyl ring is mainly transmitted through bonds rather than through space, and that the different polarisation of the C? H bonds in the oxirane ring is mainly responsible for the different behaviour of the protons in cis- and trans- arylmethyl oxiranes towards the effect of substituents.     

Sulle corrispondenze fra tre piani

Sunto In una corrispondenza puntualeC fra tre piani proiettivi, considerata una terna ordinaria O₁, O₂, O₃ di punti corrispondenti, in generale, a due E₂ di centri O₁, O₂ non corrisponde inC un E₂. Orbene, nel presente lavoro, si ricercano le terne di E₂ corrispondenti inC. Fra siffatte terne si considerano poi quelle per cui uno dei tre E₂ è di flesso, pervenendo così, in ciascuno dei tre piani, a nove direzioni particolari (chiamatecaratteristiche odinflessionali) e a sei E₂ intrinsecamente determinati. Le direzioni caratteristiche si distinguono in tre terne e si indica nna proprietà dell'involuzione da esse determinata. Si ottengono anche altri E₂ intrinsecamente determinati daC e una proprietà di essi. Infine si considerano, in ciascuno dei tre piani, certe cubiche che, quando i piani siano euclidei, sono intrinsecamente determinate daC. Alla memoria di Guido Castelnuovo, nel primo centenario della nascita.