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Paul Müller

Publications and source records attributed to Paul Müller.

26 records · Page 2Linked to original sources
PubMed2004

The MEPUC concept adapts the C-arm fluoroscope to image-guided surgery.

Image-guided surgery requires surgeons to be able to manipulate the imaging modality themselves and without delay. Intraoperative fluoroscopic imaging does not meet this requirement as the C-arm fluoroscope cannot be operated or positioned by the surgeons themselves. The Motorized Exact Positioning Unit for C-arm (MEPUC) concept aims to optimize the workflow of positioning the C-arm fluoroscope. The hardware component of the MEPUC equips the fluoroscope with electric stepping motors. The software component allows the surgeon to control the fluoroscope's movements. The study presented here showed that translational movements within the x-y plane are most frequently performed when positioning the C-arm fluoroscope. Furthermore, reproducing a former projection was found to be a frequent task during image-guided procedures. In our opinion, the MEPUC concept adapts the fluoroscope to image-guided surgery. The most important improvement being definition of a bidirectional data exchange between the surgeon and the C-arm fluoroscope: positioning data from the surgeon to the C-arm fluoroscope and-subsequently-image information from C-arm fluoroscope to the surgeon.

Femoral Fractures↗
PubMed2004

Asymmetric transfer of carbenes with phenyliodonium ylides.

Phenyliodonium ylides, readily available upon treatment of CH-acidic compounds such 1,3-dicarbonyl derivatives with iodobenzene diacetate, react in the presence of rhodium(II) or copper catalysts to afford products derived from carbenoid pathways. Chemo- and enantioselectivity of the reactions are identical to those of the corresponding diazocompounds, indicating metallocarbene intermediates with both precursors. An exception to this occurs in the intramolecular cyclopropanation of phenyliodonium ylides, where a competing uncatalyzed pathway intervenes at room temperature. When phenyliodonium ylides are generated in the presence of Rh(II) catalysts and olefins, they react in situ to afford cyclopropanes.

Journal Article↗
PubMed2003

Experimental and quantum-chemical studies on the thermochemical stabilities of mercury carbodiimide and mercury cyanamide.

Calorimetric dissolution measurements of the solid compounds mercury carbodiimide HgNCN(I) and mercury cyanamide HgNCN(II) in aqueous HCl that targeted at their thermochemical stabilities show the cyanamide species HgNCN(II) to be the more stable phase in terms of both enthalpy and Gibbs energy with an enthalpy difference of 2-3 kJ mol-1. While the stability ranking of HgNCN(I) and HgNCN(II) thus perfectly matches Pearson's HSAB concept, quantum-chemical stability predictions using common parametrizations of density functional theory appear to be fundamentally flawed. An analysis of the error is attempted on the basis of correlated wave functions for related molecules.

Journal Article↗
PubMed2003

Influence of carbocation stability in the gas phase on solvolytic reactivity: beyond bridgehead derivatives.

The intrinsic gas-phase stability of bicyclic secondary carbocations has been determined by Dissociative Proton Attachment of chlorides and alcohols, respectively. From these data, Gibbs free energies for hydride transfer relative to 1-adamantyl (Delta(r)G degrees (8,exp)) are derived after application of appropriate leaving group corrections, and good agreement with theoretical values, (Delta(r)G degrees (8,comp)), calculated at the G2(MP2) or MP2/6-311G(d,p) level, is reached (Table 1). The relative rate constants for solvolysis (log(k/k(0))) of the bicyclic secondary derivatives correlate with the stabilities of the respective carbocations in the same manner as tertiary bridgehead derivatives, but simple monoderivatives and acyclic derivatives solvolyze faster than predicted on the grounds of the ion stabilities. The corresponding stabilities of cyclopropyl- and benzyl-substituted carbocations have been obtained by a combination of experimental and computational data available in the literature with computational methods. Correlation of the rate constants for solvolysis vs ion stabilities for these compounds reveals a trend similar to that observed for bridgehead derivatives, but with much more scatter, which is attributed to nucleophilic solvent participation and/or nucleophilic solvation.

Journal Article↗
PubMed2002

Synthesis, structure determination, and quantum-chemical characterization of an alternate HgNCN polymorph.

A novel, possibly metastable form of HgNCN, designated HgNCN(II), is accessible under soft-chemical reaction conditions, and its existence has been established from combined X-ray/neutron Rietveld refinements (P2(1)/a, a = 6.8521(4) A, b = 6.9797(4) A, c = 5.5516(4) A, beta = 113.212(4) degrees ), vibrational spectroscopy investigations, and plane-wave DFT calculations utilizing pseudopotentials. In contrast to the known mercury carbodiimide HgNCN(I) with two practically identical N-C double bonds of 1.22 A, the true cyanamide HgNCN(II) is characterized by a short ("triple") N-C bond (1.12 A) and a long ("single") C-N bond (1.35 A); two Hg atoms coordinate the asymmetrically shaped NCN(2)(-) unit only on the side of the C-N "single" bond. Mercury carbodiimide HgNCN(I) and mercury cyanamide HgNCN(II) are thermochemically separated from each other by such a high energy barrier that thermal decomposition prevents structural interconversion. The structure-chemical relationship of the two HgNCN phases is discussed in terms of bond-stretch and linkage isomerism.

Journal Article↗
PubMed2002

Intrinsic (gas phase) thermodynamic stability of 2-adamantyl cation. Its bearing on the solvolysis rates of 2-adamantyl derivatives.

The standard enthalpy of formation of gaseous 2-adamantyl chloride(2-Ad-Cl) was determined by calorimetric techniques. The standard Gibbs energy change for the chloride anion exchange between 1-adamantyl (1-Ad+) and 2-adamantyl (2-Ad+) cations in the gas phase was obtained by Fourier transform ion cyclotron resonance spectroscopy (FT ICR). Theoretical calculations at the G2(MP2) level were performed on these and other relevant species. This and data from the literature provided three highly consistent independent estimates of the relative stabilities of 2-Ad+ and 1-Ad+. This difference in gas-phase stability was compared to the differential structural effects on the rates of solvolysis of the corresponding chlorides and tosylates, and it was shown that the thermodynamic stability of the secondary cation is the leading factor determining the solvolytic reactivity of the precursors in the absence of solvent effects. Thus, under these conditions, the previously established linear free energy correlation between carbenium ion stability and solvolytic reactivity of bridgehead derivatives applies also to secondary derivatives.

Journal Article↗