Cyclic Sesquiterpene-Flavanone [4+2] Hybrids, Syzygioblanes A-C, Found in an Indonesian Traditional Medicine, "Jampu Salo" (Syzygium oblanceolatum).

A plant used in an Indonesian traditional herbal medicine as a diabetes treatment and known locally as "Jampu Salo" was collected on Sulawesi Island, Indonesia. It was identified as Syzygium oblanceolatum (C. B. Rob.) Merr. (Myrtaceae) and found for the first time in Sulawesi; it was previously reported only in the eastern Philippines and Borneo. A phytochemical study of S. oblanceolatum led to the isolation of three unprecedented meroterpenoids, syzygioblanes A-C (1-3, respectively). These compounds might be biosynthesized through [4+2] cycloaddition of various germacrane-based cyclic sesquiterpenoids with the flavone desmethoxymatteucinol to form a spiro skeleton. The unique and complex structures were elucidated by microcrystal electron diffraction analysis in addition to general analytical techniques such as high-resolution mass spectrometry, various nuclear magnetic resonance methods, and infrared spectroscopy. Synchrotron X-ray diffraction and calculations of electronic circular dichroism spectra helped to determine the absolute configurations. The newly isolated compounds exhibited collateral sensitivity to more strongly inhibit the growth of a multidrug resistant tumor cell line compared to a chemosensitive tumor cell line.

X-ray and Electron Diffraction Observations of Steric Zipper Interactions in Metal-Induced Peptide Cross-ß Nanostructures.

The steric zipper is a common hydrophobic packing structure of peptide side chains that forms between two adjacent ß-sheet layers in amyloid and related fibrils. Although previous studies have revealed that peptide fragments derived from native protein sequences exhibit steric zipper structures, their de novo designs have rarely been studied. Herein, steric zipper structures were artificially constructed in the crystalline state by metal-induced folding and assembly of tetrapeptide fragments Boc-3pa-X1-3pa-X2-OMe (3pa: ß-(3-pyridyl)-l-alanine; X1 and X2: hydrophobic amino acids). Crystallographic studies revealed two types of packing structures, interdigitation and hydrophobic contact, that result in a class 1 steric zipper geometry when the X1 and X2 residues contain alkyl side chains. Furthermore, a class 3 steric zipper geometry was also observed for the first time among any reported steric zippers when using tetrapeptide fragments with (X1, X2) = (Thr, Thr) and (Phe, Leu). The system could also be extended to a knob-hole-type zipper using a pentapeptide sequence.

Strategic advantages of reactive polyiodide melts for scalable perovskite photovoltaics.

Despite tremendous progress in efficiency and stability, perovskite solar cells are still facing the challenge of upscaling. Here we present unique advantages of reactive polyiodide melts for solvent- and adduct-free reactionary fabrication of perovskite films exhibiting excellent quality over large areas. Our method employs a nanoscale layer of metallic Pb coated with stoichiometric amounts of CH3NH3I (MAI) or mixed CsI/MAI/NH2CHNH2I (FAI), subsequently exposed to iodine vapour. The instantly formed MAI3(L) or Cs(MA,FA)I3(L) polyiodide liquid converts the Pb layer into a pure perovskite film without byproducts or unreacted components at nearly room temperature. We demonstrate highly uniform and relatively large area MAPbI3 perovskite films, such as 100 cm2 on glass/fluorine-doped tin oxide (FTO) and 600 cm2 on flexible polyethylene terephthalate (PET)/indium tin oxide (ITO) substrates. As a proof-of-concept, we demonstrate solar cells with reverse scan power conversion efficiencies of 16.12% (planar MAPbI3), 17.18% (mesoscopic MAPbI3) and 16.89% (planar Cs0.05MA0.2FA0.75PbI3) in the standard FTO/c(m)-TiO2/perovskite/spiro-OMeTAD/Au architecture.

Photovoltaic Rudorffites: Lead-Free Silver Bismuth Halides Alternative to Hybrid Lead Halide Perovskites.

Hybrid CPbX3 (C: Cs, CH3 NH3 ; X: Br, I) perovskites possess excellent photovoltaic properties but are highly toxic, which hinders their practical application. Unfortunately, all Pb-free alternatives based on Sn and Ge are extremely unstable. Although stable and non-toxic C2 ABX6 double perovskites based on alternating corner-shared AX6 and BX6 octahedra (A=Ag, Cu; B=Bi, Sb) are possible, they have indirect and wide band gaps of over 2 eV. However, is it necessary to keep the corner-shared perovskite structure to retain good photovoltaic properties? Here, we demonstrate another family of photovoltaic halides based on edge-shared AX6 and BX6 octahedra with the general formula Aa Bb Xx (x=a+3 b) such as Ag3 BiI6 , Ag2 BiI5 , AgBiI4 , AgBi2 I7 . As perovskites were named after their prototype oxide CaTiO3 discovered by Lev Perovski, we propose to name these new ABX halides as rudorffites after Walter Rüdorff, who discovered their prototype oxide NaVO2 . We studied structural and optoelectronic properties of several highly stable and promising Ag-Bi-I photovoltaic rudorffites that feature direct band gaps in the range of 1.79-1.83 eV and demonstrated a proof-of-concept FTO/c-m-TiO2 /Ag3 BiI6 /PTAA/Au (FTO: fluorine-doped tin oxide, PTAA: poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], c: compact, m: mesoporous) solar cell with photoconversion efficiency of 4.3 %.

Importance of Reducing Vapor Atmosphere in the Fabrication of Tin-Based Perovskite Solar Cells.

Tin-based halide perovskite materials have been successfully employed in lead-free perovskite solar cells, but the tendency of these materials to form leakage pathways from p-type defect states, mainly Sn4+ and Sn vacancies, causes poor device reproducibility and limits the overall power conversion efficiencies (PCEs). Here, we present an effective process that involves a reducing vapor atmosphere during the preparation of Sn-based halide perovskite solar cells to solve this problem, using MASnI3, CsSnI3, and CsSnBr3 as the representative absorbers. This process enables the fabrication of remarkably improved solar cells with PCEs of 3.89%, 1.83%, and 3.04% for MASnI3, CsSnI3, and CsSnBr3, respectively. The reducing vapor atmosphere process results in more than 20% reduction of Sn4+/Sn2+ ratios, which leads to greatly suppressed carrier recombination, to a level comparable to their lead-based counterparts. These results mark an important step toward a deeper understanding of the intrinsic Sn-based halide perovskite materials, paving the way to the realization of low-cost and lead-free Sn-based halide perovskite solar cells.

Filopodia formation by crosslinking of F-actin with fascin in two different binding manners.

Filopodia are finger-like protrusions at the leading edge of migrating cells that play a crucial antennal function during cell motility. It is known that actin filaments are bundled hexagonally and provide rigidity to filopodia by virtue of fascin, which plays a central role in actin filament bundling. However, the molecular mechanisms underlying their formation remain unclear. Here, we observed the filopodia of intact whole cells fixed by rapid freezing and revealed their three-dimensional structure by cryo-electron tomography and image processing; the actin filament bundling structure by fascin was clarified at high resolution under physiological conditions. It was found that actin filaments in vivo were more numerous than in bundles reconstructed in vitro, and each filopodial actin filament had limited variability in helical twisting. In addition, statistical analysis of actin filament bundles unveiled their detailed architecture. In filopodia, actin filaments had highly ordered structures, and the shift between cross-links of each adjacent actin filament was approximately 2.7 nm, similar to the monomer repeat of actin filaments. We then proposed a plausible actin-fascin cross-link model at the amino acid level and identified three fascin binding sites on two adjacent actin filaments: one filament bound fascin at two discrete, widely separated regions and the other bound fascin in a single small region. We propose that these two different binding modalities should confer rigid bundles that retain flexibility and dynamic performance. © 2016 Wiley Periodicals, Inc.

Overcoming Short-Circuit in Lead-Free CH3NH3SnI3 Perovskite Solar Cells via Kinetically Controlled Gas-Solid Reaction Film Fabrication Process.

The development of Sn-based perovskite solar cells has been challenging because devices often show short-circuit behavior due to poor morphologies and undesired electrical properties of the thin films. A low-temperature vapor-assisted solution process (LT-VASP) has been employed as a novel kinetically controlled gas-solid reaction film fabrication method to prepare lead-free CH3NH3SnI3 thin films. We show that the solid SnI2 substrate temperature is the key parameter in achieving perovskite films with high surface coverage and excellent uniformity. The resulting high-quality CH3NH3SnI3 films allow the successful fabrication of solar cells with drastically improved reproducibility, reaching an efficiency of 1.86%. Furthermore, our Kelvin probe studies show the VASP films have a doping level lower than that of films prepared from the conventional one-step method, effectively lowering the film conductivity. Above all, with (LT)-VASP, the short-circuit behavior often obtained from the conventional one-step-fabricated Sn-based perovskite devices has been overcome. This study facilitates the path to more successful Sn-perovskite photovoltaic research.

High open circuit voltage in regioregular narrow band gap polymer solar cells.

The regioregular narrow band gap (E(g) ~1.5 eV) conjugated polymer PIPCP was designed and synthesized. PIPCP contains a backbone comprised of CPDT-PT-IDT-PT repeat units (CPDT = cyclopentadithiophene, PT = pyridyl[2,1,3]thiadiazole, IDT = indacenodithiophene) and strictly organized PT orientations, such that the pyridyl N-atoms point toward the CPDT fragment. Comparison of PIPCP with the regiorandom counterpart PIPC-RA illustrates that the higher level of molecular order translates to higher power conversion efficiencies (PCEs) when incorporated into bulk heterojunction (BHJ) organic solar cells. Examination of thin films via absorption spectroscopy and grazing incidence wide-angle X-ray diffraction (GIWAXS) experiments provides evidence of higher order within thin films obtained by spin coating. Most significantly, we find that PIPCP:PC61BM blends yield devices with an open circuit voltage (V(oc)) of 0.86 V, while maintaining a PCE of ~6%. Comparison against a wide range of analogous narrow band gap conjugated polymers reveals that this V(oc) value is particularly high for a BHJ system with band gaps in the 1.4-1.5 eV range thereby indicating a very low E(g) - eV(oc) loss.

α,α'-Diarylacenaphtho[1,2-c]phosphole P-oxides: divergent synthesis and application to cathode buffer layers in organic photovoltaics.

A divergent method for the synthesis of α,α'-diarylacenaphtho[1,2-c]phosphole P-oxides has been established; α,α'-dibromoacenaphtho[c]phosphole P-oxide, which was prepared through a Ti(II)-mediated cyclization of 1,8-bis(trimethylsilylethynyl)naphthalene, underwent a Stille coupling with three different kinds of aryltributylstannanes to afford the α,α'-diarylacenaphtho[c]phosphole P-oxides in moderate to good yields. X-ray crystallographic analyses and UV/Vis absorption/fluorescence measurements have revealed that the degree of π-conjugation, the packing motif, the electron-accepting ability, and the thermal stability of the acenaphtho[c]phosphole π-systems are finely tunable with the α-aryl substituents. All the P=O and P=S derivatives exhibited high stability in their electrochemically reduced state. To use this class of arene-fused phosphole π-systems as n-type semiconducting materials, we evaluated device performances of the bulk heterojunction organic photovoltaics (OPV) that consist of poly(3-hexylthiophene), an indene-C(70) bisadduct, and a cathode buffer layer. The insertion of the diarylacenaphtho[c]phosphole P-oxides as the buffer layer was found to improve the power conversion efficiency of the polymer-based OPV devices.

Soluble precursors of 2,3-naphthalocyanine and phthalocyanine for use in thin film transistors.

Soluble precursors of 2,3-naphthalocyanine (Nc) and phthalocyanine (Pc) were prepared and were converted into insoluble semiconducting thin films of Pc and Nc by heating after fabrication via spin-coating.