Long periodic ripple in a 2D hybrid halide perovskite structure using branched organic spacers

Two-dimensional (2D) halide perovskites have great promise in optoelectronic devices because of their stability and optical tunability, but the subtle effects on the inorganic layer when modifying the organic spacer remain unclear. Here, we introduce two homologous series of Ruddlesden–Popper (RP) structures using the branched isobutylammonium (IBA) and isoamylammonium (IAA) cations with the general formula (RA)₂(MA)_n−1Pb_nI_3n+1 (RA = IBA, IAA; MA = methylammonium n = 1–4). Surprisingly, the IAA n = 2 member results in the first modulated 2D perovskite structure with a ripple with a periodicity of 50.6 Å occurring in the inorganic slab diagonally to the [101] direction of the basic unit cell. This leads to an increase of Pb–I–Pb angles along the direction of the wave. Generally, both series show larger in-plane bond angles resulting from the additional bulkiness of the spacers compensating for the MA''s small size. Larger bond angles have been shown to decrease the bandgap which is seen here with the bulkier IBA leading to both larger in-plane angles and lower bandgaps except for n = 2, in which the modulated structure has a lower bandgap because of its larger Pb–I–Pb angles. Photo-response was tested for the n = 4 compounds and confirmed, signaling their potential use in solar cell devices. We made films using an MACl additive which showed good crystallinity and preferred orientation according to grazing-incidence wide-angle scattering (GIWAXS). As exemplar, the two n = 4 samples were employed in devices with champion efficiencies of 8.22% and 7.32% for IBA and IAA, respectively.

Using branched spacer cations results in a modulated rippled 2D perovskite structure and materials for solar cells.     

Hydrogen bonding and cooperativity in isolated and hydrated sugars: mannose, galactose, glucose, and lactose

The conformation of phenyl-substituted monosaccharides (mannose, galactose, and glucose) and their singly hydrated complexes has been investigated in the gas phase by means of a combination of mass selected, conformer specific ultraviolet and infrared double resonance hole burning spectroscopy experiments, and ab initio quantum chemistry calculations. In each case, the water molecule inserts into the carbohydrate at a position where it can replace a weak intramolecular interaction by two stronger intermolecular hydrogen bonds. The insertion can produce significant changes in the conformational preferences of the carbohydrates, and there is a clear preference for structures where cooperative effects enhance the stability of the monosaccharide conformers to which the water molecule chooses to bind. The conclusions drawn from the study of monosaccharide-water complexes are extended to the disaccharide lactose and discussed in the light of the underlying mechanisms that may be involved in the binding of carbohydrate assemblies to proteins and the involvement, or not, of key structural water molecules.     

Synthesis and Crystal Structure Determination by X‐Ray Powder Diffraction of Nickel Tetrametaphosphimate Octahydrate Ni2(PO2NH)4 · 8 H2O

Ni₂(PO₂NH)₄ · 8 H₂O is isotypic with M₂(PO₂NH)₄ · 8 H₂O (M = Mg, Mn, Co, Zn) and crystallizes in the space group P2₁/c, Z = 2, with a = 641.25(1), b = 1041.42(1), c = 1278.18(2) pm and β = 104.243(1)°. The structure is composed of Ni²⁺ and (PO₂NH)₄^4? ions as well as crystal water molecules. The P₄N₄ rings of the (PO₂NH)₄^4? ions exhibit a slightly distorted chair–2 conformation, which has been described by torsion angles, displacement asymmetry parameters and puckering parameters. The tetrametaphosphimate anions are connected forming layers. These layers are linked solely by hydrogen bonds, forming a three‐dimensional network.     

Direct 1H, 13C, and 15N NMR Study of Lanthanum(III), Thulium(III), and Ytterbium(III) Complex Formation with Nitrate and Isothiocyanate

An ¹H, ¹³C, and ¹⁵N NMR study has been completed for the complexes of La(III), Tm(III), and Yb(III) with nitrate and isothiocyanate in aqueous solvent mixtures. Signals for four complexes are observed for both the Tm³⁺–NO₃ ^– and Yb³⁺–NO₃ ^– solutions, with the species identified as the mono-, di-, tetra-, and either the penta - or hexanitrato. These results are consistent with those determined for the nitrate complexes of the Ce(III)–Eu(III) metal ions. The chemical shifts for the Tm(III) and Yb(III) nitrate complexes indicate a pseudocontact binding mechanism prevails. The complexes of diamagnetic La(III) with NO₃ ^– produce three signals in the ¹⁵NO₃ ^– spectra, with assignments paralleling those observed with the paramagnetic lanthanides. Three complexes are formed in the La³⁺–NCS^– solutions, with signals assigned to the mono-, di-, and triisothiocyanato species.     

Thioamination of Alkenes with Hypervalent Iodine Reagents

An efficient thioamination of alkenes mediated by iodine(III) reagents is described. The use of different sulfur nucleophiles allows the flexible synthesis of 1,2‐aminothiols from alkenes. By employing chiral iodine(III) reagents, a stereoselective version of the thioamination protocol has also been developed.     

Designed amino acid ATRP initiators for the synthesis of biohybrid materials

A synthetic strategy to prepare peptide-polymer conjugates with precise sites of attachment is described. Amino acids modified with atom transfer radical polymerization (ATRP) initiators for the polymerization of styrenes and methacrylates were prepared. Fmoc-4-(1-chloroethyl)-phenylalanine (5) was synthesized in four steps from Fmoc-tyrosine. HATU-mediated amidation with glycine-OMe resulted in dipeptide (6). The initiator was effective for Cu(I)/bipyridine mediated bulk polymerization of styrene. Kinetic studies indicated a controlled polymerization, with high conversion (97%), and a polydispersity index (PDI) of 1.25. Fmoc-O-(2-bromoisobutyryl)-serine tert-butyl ester (10) was synthesized from Fmoc-Ser(OTrt)-OH in three steps. This initiator was employed in the ATRP of 2-hydroxyethyl methacrylate (HEMA), and kinetic studies indicated a controlled polymerization. Different monomer to initiator ratios resulted in poly(HEMA) of different molecular weights and narrow PDIs (1.14-1.25). Conversions were between 70 and 99%. HEMA modified with N-acetyl-D-glucosamine (GlcNAc) was also polymerized to 84% conversion and the resulting PDI was 1.19. The t-butyl ester protecting group of 10 was removed, and the resulting amino acid (11) was incorporated into VM(11)VVQTK by standard solid-phase peptide synthesis. Polymerization resulted in the glycopolymer-peptide conjugate in 93% conversion and a PDI of 1.14.     

Sensitization of ruthenium nitrosyls to visible light via direct coordination of the dye resorufin: trackable NO donors for light-triggered NO delivery to cellular targets

Three nitrosyl-dye conjugates, namely, [(Me 2bpb)Ru(NO)(Resf)] ( 1-Resf), [(Me 2bQb)Ru(NO)(Resf)] ( 2-Resf), and [((OMe) 2bQb)Ru(NO)(Resf)] ( 3-Resf) have been synthesized via direct replacement of the chloride ligand of the parent {Ru-NO} (6) nitrosyls of the type [(R 2byb)Ru(NO)(L)] with the anionic tricyclic dye resorufin (Resf). The structures of 1-Resf- 3-Resf have been determined by X-ray crystallography. The dye is coordinated to the ruthenium centers of these conjugates via the phenolato-O atom and is trans to NO. Systematic red shift of the d pi(Ru) --> pi*(NO) transition of the parent nitrosyls [(R 2byb)Ru(NO)(L)] due to changes in R and y in the equatorial tetradentate ligand R 2byb (2-) results in its eventual merge with the intense absorption band of the dye around 500 nm in 3-Resf. Unlike the UV-sensitive parent [(R 2byb)Ru(NO)(L)] nitrosyls, these dye-sensitized nitrosyls rapidly release NO when exposed to visible light (lambda >/= 465 nm). Comparison of the photochemical parameters reveals that direct coordination of the light-harvesting chromophore to the ruthenium center in the present nitrosyls results in a significantly greater extent of sensitization to visible light compared to nitrosyls with appended chromophore (linked via alkyl chains). 1-Resf has been employed as a "trackable" NO donor to promote NO-induced apoptosis in MDA-MB-231 human breast cancer cells under the control of light. The results of this work demonstrate that (a) the d pi(Ru) --> pi*(NO) transition (photoband) of {Ru-NO} (6) nitrosyls can be tuned into visible range via careful alteration of the ligand frame(s) and (b) such nitrosyls can be significantly sensitized to visible light by directly ligating a light-harvesting chromophore to the ruthenium center. The potential of these photosensitive nitrosyl-dye conjugates as (i) biological tools to study the effects of NO in cellular environments and (ii) "trackable" NO donors in photodynamic therapy of malignancies (such as skin cancer) has been discussed.     

Structure and absolute stereochemistry of the anticancer agent EBC-23 from the Australian rainforest

EBC-23 (2), a prostate anticancer agent, was isolated from the fruit of Cinnamomum laubatii (family Lauraceae) in the Australian tropical rainforest. Extensive NOE experiments enabled the relative stereochemistry of the proposed EBC-23 (2) structure to be determined. Total synthesis of both enantiopodes over nine linear steps, involving challenging RCM and spiroacetal cyclizations, confirmed the gross structure and relative and absolute stereochemistry.