Biomineralization, particularly the formation of calcium carbonate structures by organisms under ambient conditions, is of vast fundamental and applied interest. Organisms finely control all aspects of the formation of the biomaterials: composition, polymorph, morphology, and macroscopic properties. While in situ molecular-level characterization of the resulting biominerals is a formidable task, solid-state magic angle spinning NMR is one of the most powerful analytical techniques for this purpose. It is employed in this study to elucidate the structure and composition of biogenic calcite formed by Emiliania huxleyi, a unicellular alga distinguished by its exquisitely sculptured calcite cell coverings known as coccoliths. Strain 371 (CCMP) was grown and harvested from (15)N- and (13)C-enriched growth medium, with biosynthetic labeling to enhance the sensitivity of the NMR measurements. Crystalline and interfacial calcite environments were selectively probed using direct and indirect (cross-polarized) (13)C excitation, respectively. Different crystalline environments, in particular structural defect sites at concentrations of up to 1.4% with P and N moieties incorporated, were identified using (13)C rotational-echo double-resonance (REDOR) NMR. REDOR-derived geometrical constraints show that the P and N atoms at the defect sites are 3.2 and 2.3 (+/-0.2) A apart from a crystalline carbon carbonate. The phosphorus and nitrogen moieties within the biogenic calcite are identified as small, non-protonated moieties, attributed to inorganic ions such as PO4(3-) and NO3(-). The carbonates adjacent to these defects are chemically indistinguishable from bulk crystalline carbonates, yet their immediate environments experience reduced rigidity, as reflected by substantial T1((13)CO3(2-)) shortening. Interfacial carbonates, on the other hand, reside in structurally/chemically perturbed environments, as reflected by heterogeneous line broadening. This study is the first to directly unravel evidence on the incorporation of P/N moieties as structural defects within E. huxleyi biogenic calcite, and on the state of the adjacent crystalline carbonates.

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Interfacial energy band alignment is crucial for applications involving charge transfer and transport. Specifically, efficient photovoltaic (PV) devices require fine tuning of the energy levels at interfaces between the absorber and the electrodes for extraction of photogenerated charges. Infrared (IR) absorbers have a small bandgap, hence such tuning is difficult using common electrode materials. Semiconductor sensitized PV devices typically utilize transparent metal oxide photoanodes, since many semiconductor absorbers can inject photoexcited electrons into their conduction bands. Transparent photocathode electrodes, to which photoexcited holes are transferred from semiconductor absorbers, are less common.Transparent nanostructured photocathodes with beneficial energy level alignment with small bandgap semiconductors can widen the material choices for IR photoelectrodes. Herein we show that CuSCN nanowire (NW) arrays can serve as such photocathodes, with efficient transfer of photogenerated holes from bulk-like PbS absorbing in the IR and near-IR range.Pulsed electrodeposition was used to fabricate high-quality CuSCN NW arrays. Significant NIR and IR photocurrents showed that the CuSCN NW array is an efficient photocathode for PbS sensitized IR photovoltaic devices. Comparison of various electrode materials verified the photogenerated hole injection vs. competing processes such as electron injection and recombination, and suggested that this material system can be used for studying photosensitized hole injection from other small bandgap semiconductors.