Quantitative analysis of temperature programmed reaction (TPR) spectra of formic acid, acetic acid, propionic acid, and butyric acid decomposition on Ru(0001) and phosphorus (P)-modified Ru(0001) surfaces show that both the length of carboxylic acids alkyl substituents (i.e., R=H, CH3, CH2CH3, and CH2CH2CH3) and the presence of P atoms alter the intrinsic activation energy for bond rupture. Inversion analysis of TPR spectra reveal that the intrinsic activation energy barriers on Ru(0001) for C–H bond cleavage in formate is 94 kJ mol−1, while C–C bond cleavage (decarboxylation) barriers for acetate, propionate, and butyrate are 67, 49, and 55 kJ mol−1, respectively. The activation energies to decarboxylate all four of these species correlate linearly with differences between the homolytic dissociation energies of the relevant bonds (e.g., H-COOH, CH3-COOH, CH3CH2-COOH, and CH3CH2CH2-COOH), which suggests that longer alkyl substituents (e.g., propyl and butyl) stabilize bond rupture transition states by donating electron density to the R–COOH bond via inductive effects. Simultaneously, longer alkyl chains also promote self-stabilizing lateral interactions between carboxylates via van der Waals forces that increase the barriers for R–COOH bond rupture slightly (by ∼1–5 kJ mol−1) at high surface coverages. The addition of P atoms to Ru(0001) increases the intrinsic activation energies for the rupture of all bonds (i.e., C–O, C–H, and C–C bonds), specifically, by 5–50 kJ mol−1 for C–H and C–C bonds. P atoms change the Ru(0001) surface likely via an electronic effect by decreasing the extent of electron back donation from Ru atoms to the antibonding orbitals of the carboxylate intermediate. These results provide useful information for transition metal phosphide catalyst design and carboxylic acid alkyl substituent selection to tailor selectivity toward C–O, C–H, and C–C bond rupture.
Sonographically guided biopsy is performed by one of two techniques: the freehand and needle-guided techniques. To our knowledge, the relationship between the location of the local anesthetic tract and the biopsy needle tract as well as direct comparison of the two biopsy techniques has not been previously validated. The aim of this study was to validate the different parameters related to the two biopsy techniques using computed tomography as the reference standard for assessing final tract positions. There were statistically significant differences between the freehand and guided techniques in the following parameters: number of passes required for contrast agent injection (P = .003), number of passes required to insert the needle (P = .005), time required to inject the anesthetic/contrast agent (P = .005), time required to insert the biopsy needle (P = .02), and distance between contrast tract and final needle position (P = .03). No statistical difference was identified for the angle between the contrast tract and needle position. This difference likely reflects the confidence of the radiologist in identifying the needle location during the procedure. Using a commercially available guide that has a fixed angle can result in a faster, more efficient, and reproducible biopsy technique compared to the freehand technique, especially for those who have less experience in performing sonographically guided biopsies.
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