Using temperature to modify the reaction conditions and outcomes of polymers formed using transfer-dominated branching radical telomerisation (TBRT).

Transfer-dominated Branching Radical Telomerisation (TBRT) enables the production of branched polymers with step-growth backbones using radical telomerisation chemistry. By conducting identical TBRTs over a broad temperature range, the role of temperature in telomer formation and branching has been evaluated. Elevated temperature limits telomer length, thereby allowing a >10% reduction in the amount of telogen required to produce near identical high molecular weight branched polymers.

A resident preceptor model improves the clerkship experience on general surgery.

BACKGROUND: The frenetic pace of inpatient care on surgical services can create barriers to resident teaching of students. Students are often concerned that busy surgical residents will not be able to adequately evaluate their performance at the end of a clerkship. OBJECTIVE: To determine whether the addition of a resident preceptor would increase the satisfaction of students rotating through the general surgery portion of the required third-year surgery clerkship. STUDY DESIGN: Before implementing a resident preceptor model, third-year students rotating on general surgery were administered a 24-item web-based survey regarding their experience on the general surgery portion of the surgery clerkship. General surgery residents were similarly surveyed. A resident preceptor model was then introduced. Subsequent students and residents were surveyed. Presurveys and postsurveys were compared and mean responses analyzed. RESULTS: The addition of a resident preceptor made students more comfortable with asking residents questions (p = 0.02), increased the time students felt was available for developing relationships with residents (p = 0.03), and improved the feeling that residents would be able to accurately evaluate the student's effectiveness as a team member (p = 0.05). The students felt resident teaching on afternoon rounds was increased with the resident preceptor model (p = 0.05). Residents reported spending more time teaching students on morning rounds (p = 0.03). CONCLUSIONS: Implementation of a resident preceptor model resulted in significant improvement in medical students' perceptions of resident teaching effectiveness and ability to accurately evaluate a student's performance.

Catalytic hydroacetylenation of carbodiimides with homoleptic alkaline earth hexamethyldisilazides.

The homoleptic alkaline earth hexamethyldisilazides, [M{N(SiMe3)2}2(THF)2] (M = Mg 1a; Ca 1b; Sr 1c), have been shown to act as efficient precatalysts for the hydroacetylenation of organic carbodiimides with alkyl- and arylacetylenes. Catalytic activity was observed to increase with the size of the group 2 metal centre employed and to be strongly influenced by the steric properties of the carbodiimide substrate. The intermediate dimeric calcium and strontium bis(amidinate) complexes, [{PhC≡CC(N(i)Pr)2}2M]2 (M = Ca 2b, Sr 2c), have been isolated and crystallographically characterised. Kinetic studies using the strontium precursor, 1c, provided a reaction rate law independent of [acetylene] but proportional to [carbodiimide](2) and inversely proportional to the concentration of the amidine product in solution.

Carbodiimide insertion reactions of homoleptic heavier alkaline earth amides and phosphides.

A series of homoleptic guanidinate-type complexes of the heavier alkaline earth (Ae) metals calcium and strontium have been prepared. The six-coordinate compounds [Ae{(i)PrNC(NPh(2))CN(i)Pr}(2)(THF)(2)] (Ae = Ca and Sr) were synthesised through reactions of the appropriate THF-solvated hexamethyldisilazide [Ae{N(SiMe(3))(2)}(2)(THF)(2)] with two molar equivalents of diphenylamine and 1,3-di-iso-propylcarbodiimide. Both compounds were shown to crystallise with a cisoid arrangement of the two THF molecules at the metal centres. In contrast, the (Me(3)Si)(2)N-substituted calcium guanidinate, [Ca{CyNC{N(SiMe(3))(2)}CNCy}(2)(THF)(2)], contains two coordinated THF molecules with a trans disposition. Further reactions of the free amidine [{(2-FC(6)H(4))N}C(NH(i)Pr)(2)] with either [Ca{N(SiMe(3))(2)}(2)(THF)(2)] or its dimeric unsolvated analogue provided monomeric or dimeric derivatives respectively in which the ligands had tautomerised to an anisobidentate form. A further reaction of the phosphaguanidine [CyN=C(PPh(2))N(H)Cy] with [Sr{N(SiMe(3))(2)}(2)(THF)(2)] provided the first example of a phosphaguanidinate complex of this heavier alkaline earth metal. This compound has also been characterised in the solid state and shown to exist with a transoid configuration of the coordinated THF molecules.

Catalytic 2,3,4-hexatriene formation by terminal alkyne coupling at calcium.

Heteroleptic calcium amides effect the catalytic dimerisation of the terminal alkyne CH(3)OCH(2)C[triple bond, length as m-dash]CH to the hexatriene (CH(3)OCH(2))CH[double bond, length as m-dash]C[double bond, length as m-dash]C[double bond, length as m-dash]CH(CH(2)OCH(3)) under mild conditions; the reaction is proposed to occur via a dimeric calcium acetylide intermediate and to be promoted by polarisation of the electron density within the alkynide C[triple bond, length as m-dash]C bonds.