Ultrafast transient absorption spectroscopy was used to investigate the photochemistry of adenosylcobalamin (AdoCbl), methylcobalamin (MeCbl), and n-propylcobalamin (PrCbl) at pH 2 where the axial nitrogenous ligand is replaced by a water molecule. The evolution of the difference spectrum reveals the internal conversion process and spectral characteristics of the S(1) excited state. The photolysis yield in the base-off cobalamins is controlled by competition between internal conversion and bond homolysis. This is in direct contrast to the process in most base-on alkylcobalamins where primary photolysis occurs with near unit quantum yield and the photolysis yield is controlled by competition between diffusive separation of the radical pair and geminate recombination. The absence of the axial nitrogenous ligand in the base-off cobalamins modifies the electronic structure and opens a channel for fast nonradiative decay. This channel competes effectively with the channel for bond dissociation, dropping the quantum yield for primary radical pair formation from unity in base-on PrCbl and AdoCbl to 0.2 ± 0.1 and 0.12 ± 0.06 in base-off PrCbl and AdoCbl, respectively. The photolysis of base-off MeCbl is similar to that of base-off AdoCbl and PrCbl with competition between rapid nonradiative decay leading to ground state recovery and formation of a radical pair following bond homolysis.

Contemporary strategies in STEM education focus on developing pedagogies that more actively engage students in their own learning. A method that has proven effective to this end has been peer instruction and discussion, particularly those in which participating students must organize information in such a way as to be able to verbally articulate it to others. The success of peer learning raises the question of what other communicative activities could lead to similar learning gains. Writing is a reasonable choice for such an activity, as there is strong historical evidence of the value of writing in facilitating student learning. Presented here is "writing-to-teach"; a fusion of writing and peer instruction that is rooted in the theories of meaningful learning and situated cognition as well as research on student-generated explanatory knowledge. Writing-to-teach activities were designed and implemented in an introductory physical chemistry course and evaluated using student surveys. In addition, a novel expert-ranking methodology was employed to evaluate the quality of explanatory writing produced by students engaging in writing-to-teach activities. Lastly, suggestions are given on how writing-to-teach can be implemented more broadly in other STEM classrooms.