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A structure-based design of novel memapsin 2 inhibitors that incorporate methylsulfony alanine as the P(sub 2)-ligand and pyrazole and oxazole-derived heterocycles as the P(sub 3)-ligands is reported. This structure-based design led to the development of very potent and highly selective memapsin 2 inhibitors and X-ray structural analysis of protein-inhibitor complexes has uncovered potentially important molecular interactions useful in the design of selectivity against other aspartyl proteases.

The synthesis, structure and the properties of the various organic single-crystalline p-n junction nanoribbons are analyzed. These nanoribbons are shown to play an extremely significant role in studying the photovoltaic behaviors observed at the organic-organic interfaces.

Two new modes of liquid crystalline (LC) organization are described, where rod-like mesogenic units are parallel to the column axis. The two-dimensional (2D)-to-three-dimensional (3D) transition is important from the theoretical point of view and parallels are drawn with the nematic-smectic-A transition.

A liquid-crystalline (LC) phase is described in polyphilic molecules based on a new polygonal tiling pattern. The studies have provided a new variable for increasing the complexity in LC engineering and have proved the limitless potential of the general concept of polyphilic tectons in the design of new complex soft matter structures.

The recently discovered mode of self-assembly in the liquid-crystalline (LC) soft matter is found to exhibit a triangular cylinder phase.

Density functional theory based ab initio molecular dynamics method, employing a plane wave basis set with pseudopotentials and also by conventional methods with Gaussian basis sets. The mechanism for the intracluster H2 eleimination reaction is explored and finally, the switch off the H2 elimination for n>24 are explored.

Organic-inorganic hybrid perovskite solar cells have demonstrated unprecedented high power conversion efficiencies in the past few years. Now, the universal instability of the perovskites has become the main barrier for this kind of solar cells to realize commercialization. This situation can be even worse for those tin-based perovskites, especially for CsSnI3, because upon exposure to ambient atmosphere the desired black orthorhombic phase CsSnI3 would promptly lose single crystallinity and degrade to the inactive yellow phase, followed by irreversible oxidation into metallic Cs2SnI6. By alloying CsSnI3 with CsPbI3, we herein report the synthesis of alloyed perovskite quantum dot (QD), CsSn1-xPbxI3, which not only can be phase-stable for months in purified colloidal solution but also remains intact even directly exposed to ambient air, far superior to both of its parent CsSnI3 and CsPbI3 QDs. Ultrafast transient absorption spectroscopy studies reveal that the photoexcited electrons in the alloyed QDs can be injected into TiO2 nanocrystals at a fast rate of 1.12 X 1011 s-1, which enables a high photocurrent generation in solar cells. [ABSTRACT FROM AUTHOR]

The extension of the [micro]-oxo-based water oxidation chemistry to metal oxide surfaces is described based on the phosphonate-modified complex. The results have shown that single electron transfer activation of multiple electron transfer and water oxidation can be transferred to the electrode interface on oxide electrodes.

A kinetic isotope effect is measured for excited-state electron injection into TiO2 nanocrystallites, with an empirical deuterium isotope effect of phi inj(N-D) or phi inj(N-H)=1.3-1.5. This finding indicates that energy conversion and interfacial electron transfer can be controlled by nuclear substitution.

A thieno[3,4-b]thiophene-based electron acceptor, ATT-1, is designed and synthesized. ATT-1 exhibits a planar conjugated framework, broad absorption with a large absorption coefficient, and a slightly high LUMO energy level. Bulk-heterojunction (BHJ) solar cells based on PTB7-Th electron donor and ATT-1 electron acceptor delivered power conversion efficiencies of up to 10.07%, which is among the best performances reported for non-fullerene BHJ solar cells using PTB7-Th as the electron donor. [ABSTRACT FROM AUTHOR]

Despite the dominant position of aromatic fluorophores, we report herein the design and synthesis of quinoidal fluorophores based on rarely emissive quinoidal bithiophene. Quinoidal bitheno[3,4-fc]thiophene, QBTT-C6, consisting of cruciform-fused (E)-1,2-bis(5-hexylthiophen-2- yl)ethene and quinoidal bithiophene, shows a fluorescence quantum yield of 8.5%, 25-fold higher than that of the parent quinoidal QBT chromophore, but its maximum emission is at similar wavelengths. QBTT-Ar's featuring intramolecular charge transfer can further shift the maximum emission into the near-infrared region. The intramolecular charge transfer is programmably enhanced by tuning the substituents on the aryl groups from the electron-withdrawing trifluoromethyl to the electron-donating methoxy groups. Unexpectedly, a positive relationship between intramolecular charge transfer and fluorescence quantum yield is observed; as a result, QBTT-FL gives an unprecedentedly high fluorescence quantum yield of up to 53.1% for quinoidal oligothiophenes. With detailed photophysical and theoretical investigations, we demonstrate that the nonradiative intersystem crossing (S1 → T2) is significantly restrained in QBTT-Ar's, which can be attributed to the faster reverse intersystem crossing (T2 → S1) characteristic of a small activation energy. This work reveals the possibility for developing red/near-infrared fluorophores from the less explored quinoidal molecules because of their intrinsically narrow bandgaps. [ABSTRACT FROM AUTHOR]

Thiophene-based materials have occupied a crucial position in the development of organic electronics. However, the energy band gaps of oligo- and polythiophenes are difficult to modulate without resorting to push -pull electronic effects. We describe herein a new series of monodisperse oligo (thieno [3,4- bjthiophene) derivatives with well-defined regioregular structures synthesized efficiently by direct C-H arylation. These compounds show a unique palette of colors and amphoteric redox properties with widely tunable energy band gaps. The capacity to stabilize both cations and anions results in both anodic and cathodic electrochromism. Under excitation, these compounds can produce photoionized states able to interconvert into neutral triplet or form these through singlet exciton fission or intersystem crossing. These features arise from a progressive increase in quinoidization on a fully planar platform making the largest effective conjugation length among hetero-oligomers. Oligo(thieno[3,4-b]thiophene)s might represent the more distinctive family of oligothiophenes of this decade. [ABSTRACT FROM AUTHOR]

Due to the unique crystallinity of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), it is an excellent model polymer to study the structure--property relationship in organic devices, especially those relying on junctions of electron- and hole-transporting materials. Here, we report the synthesis and characterization of a series of monodisperse PBTTT oligothiophenes (n = 1-5) and systematically examine the evolution of crystalline behavior, morphology, and interaction with [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as the molecular conjugation length increases. We discovered that fullerene intercalation occurs when there is enough free volume between the side chains to accommodate the fullerene molecule. The intercalation of PCBM is observed beyond BTTT-2 and longer oligomers, likely similar to that of PBTTT. Interestingly, both experiments and molecular simulations show that PCBM intercalation also appears to "catalyze" a more efficient packing of the BTTT-2 dimers. Crystal structure analysis revealed that the straight BTTT-2 side chains form one-dimensional (ID) channels that could perfectly host PCBM but, in the pure material, accommodate the interdigitated side chains from adjacent layers. In the blend with PCBM, these channels are maintained and enable the cocrystallization and intercalation of PCBM. This is the first time the actual sublattice cell of PCBM has been determined from the X-ray data, and demonstration the utility of the oligomers as model systems for their polymer counterparts. Among the organic photovoltaic devices (OPVs) made from the BTTT oligomers and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) blends, the ones containing the BTTT-2 dimer exhibit the highest performance. [ABSTRACT FROM AUTHOR]

A series of T-shaped polyphilic molecules composed of a rigid linear biphenyl core with a polar glycerol group at each end and one swallow-tail semiperfluorinated lateral chain were synthesized and their thermotropic liquid crystalline (LC) phases were investigated by X-ray diffraction, calorimetry, and microscopy. The compounds have a long alkyl spacer between the aromatic core and the fluorinated CnF2n+1 ends, where n = 4, 6, 8, and 10. Upon melting, all compounds start with lamellar LC phases, followed on heating by a rectangular columnar ribbon phase vnth clmm symmetry. Unusually, a ribbon is a flat bundle of molecular cores highly aligned parallel to the ribbon axis. On further heating, for n = 8 and 10, this phase is succeeded by a bicontinuous cubic phase with Ia3d symmetry. This is a new variant of the "gyroid" phase, with axiaDy oriented rod-like molecular cores forming the skeleton of the two infinite networks and junctions separated by exactly two molecular lengths. In this tricontinuous core-shell structure (aromaticaliphatic-perfluoroalkyl), the polar glycerol domains of appreciable size, contained vwthin the skeleton, can be considered as micellar. [ABSTRACT FROM AUTHOR]

The lipid carrier specificity of the protein N-glycosylation enzyme C. jejuni PglB was tested using a logical, synthetic array of natural and unnatural C10, C20, C30, and C40 polyisoprenol sugar pyrophosphates, including those bearing repeating cis-prenyl units. Unusual, short, synthetically accessible C20 prenols (nerylnerol 1d and geranylnerol 1e) were shown to be effective lipid carriers for PglB sugar substrates. Kinetic analyses for PglB revealed clear KM-only modulation with lipid chain length, thereby implicating successful in vitro application at appropriate concentrations. This was confirmed by optimized, efficient in vitro synthesis allowing >90% of Asn-linked β-N-GlcNAc-ylated peptide and proteins. This reveals a simple, flexible biocatalytic method for glycoconjugate synthesis using PglB N-glycosylation machinery and varied chemically synthesized glycosylation donor precursors. [ABSTRACT FROM AUTHOR]

We investigated the structure–morphology–performance relationship of diketopyrrolopyrrole (DPP)-based low band gap polymers with different donor cores in organic field effect transistors (OFETs) and organic photovoltaics (OPVs). The change in the chemical structure led to strong physical property differences, such as crystalline behavior, blend morphology, and device performance. In addition, the choice of solvents and additives enabled one to fine tune the properties of these materials in the condensed state. For instance, when thin films were processed from solvent mixtures, both in the pure polymer and in a blend, we observed an enhanced edge-on orientation and the formation of thinner and longer polymer fibrils. In the BHJ blends, processing from a solvent mixture reduced the size scale of the phase separation and promoted the formation of a fibrillar network morphology, having a polymer–PCBM mixture filling the interfibrillar regions. The characteristic length scale of the fibrillar network dictated the specific inner surface area, which directly correlated to the performance in the OPV devices. When the BHJ mixture was processed from a single solvent, a large-scale phase separated morphology was observed that was stratified, normal to the film surface. A strong scattering anisotropy was observed in the resonant soft X-ray scattering of the blends that provided insight into the packing of the polymer chains within the fibrils. The morphology and performance trend in OPVs paralleled the performance in an OFET, suggesting that similar processing conditions should be considered in OFET fabrication. [ABSTRACT FROM AUTHOR]

Through-space metal/hydrogen shift is an important strategy for transition-metal-catalyzed C–H bond activation. Here we describe the synthesis and characterization of a Rh(I) 2,6-dimethoxybenzoate complex that underwent stoichiometric rearrangement via a highly unusual 1,3-rhodium migration. This aryl-to-aryl 1,3-Rh/H shift was also demonstrated in a Rh(I)-catalyzed decarboxylative conjugate addition to form a C–C bond at a meta position instead of the ipso-carboxyl position. A deuterium-labeling study under the conditions of Rh(I)-catalyzed protodecarboxylation revealed the involvement of an ortho-methoxy group in a multistep pathway of consecutive sp³ and sp² C–H bond activations. [ABSTRACT FROM AUTHOR]

Bent-shaped rigid-core molecules with flexible chiral dendrons grafted to the outer side of the bend were synthesized and characterized by circular dichroism, differential scanning calorimetry, X-ray scatterings, and transmission electron microscopy in solution and the solid state. The bent aromatic rods based on hepta- and nonaphenylene with nitrile groups at both ends self-assemble into well-ordered hollow tubular structures in aqueous solution, while the bent rod based on heptaphenylene without nitrile groups showed no apparent aggregations in aqueous solution. In the solid state, the rigid-flexible molecules based on heptaphenylene rod without the nitrile group self-assemble into a 2D oblique columnar structure with the columnar cross-section containing two interlocked molecules. Remarkably, the rigid flexible molecules based on hepta-, nona-, and undecaphenylene with nitrile groups self-assemble into a hexagonal columnar structure with weak 3D order. A model of vesicular channel structure is proposed based on small- and wide-angle X-ray diffraction on oriented fibers, density measurement, reconstruction and simulation of electron density maps, and molecular dynamics simulation. In contrast to the hollow tubular structure found in solution, in the solid both the outside and the interior of the columns are filled by the pendant aliphatic coils. Filling of the interior of these vesicular channels is made possible by some bent rod molecules turning their obtuse apex inward. One in 7, 2 in 8, and 4 in 10 molecules are thus inverted in a column slice in compounds with hepta-, nona-, and undecaphenylene cores, respectively. These are new examples of vesicular double-segregated columnar structures recently discovered in some dendrons. [ABSTRACT FROM AUTHOR]

T-shaped bolaamphiphiles composed of abiphenyl rigid core, a semiperfluorinated lateral chain, two polar 1,2-diol groups in the terminal positions and flexible alkyl spacers connecting the poiar groups with the biphenyl core have been synthesized and investigated by polarizing microscopy, DSC and X-ray scattering. The influence of spacer length and position of the spacer on the self-assembly in liquid-crystalline phases was studied. A series of four different columnar phases (Colhex/p6mm, Colrec/p2gg, Colsqu/p4gm and Colsqu/p4mtn), representing liquid-crystalline honeycomb structures composed of cylinders having hexagonal, pentagonal, and square cross section, were found on increasing the spacer length. It is also shown that introduction of aliphatic spacers in the backbone of the T-shaped bolaamphiphiles replaces the Colrec/c2mm phase made up of rhombic cylinders with the Colsqu/p4mm phase composed of square cylinders. It also causes the 2d lattice of pentagonal cylinders to increase the symmetry from Colrec/p2ggto Colsqu/p4gm. A temperature-dependent second-order phase transition between these two pentagonal cylinder structures was observed for the first time. Beside these effects on cylinder shape and phase symmetry the flexible spacer units also lead to reduced phase transition temperatures and allow adjustment of cylinder side length to envelop a wider range of side-chain sizes. Electron density maps suggest that this may involve sacrificing some of the hydrogen bonds. [ABSTRACT FROM AUTHOR]

Two series of polyphilic molecules composed of a rigid and linear p-terphenyl core, terminated at both ends with polar glycerol groups capable of hydrogen bonding, and two branched swallow tail-type lateral chains, composed of a fluorinated and a nonfluorinated branch or two fluorinated branches, were synthesized and investigated by differential scanning calorimetry, polarizing microscopy, and X-ray diffraction (XRD) with respect to their self-assembly in thermotropic liquid crystalline (LC) phases. Hexagonal columnar phases were formed by all molecules, at least at the highest temperature. In these phases the columns are composed of a core of aromatic rods and an aliphatic shell. The aromatic rods form bundles which are rotationally averaged and lie parallel to the column long axis. This unique organization is proven by different optical and XRD methods. The aromatic and glycerol groups inside the rod bundles are segregated into alternating segments. Depending on temperature and molecular structure, long-range intercolumnar correlation of this periodicity could take place, leading to a 3D-ordered LC phase with rhombohedral R¯3m symmetry. The bundles are embedded in the matrix of the lateral chains, which is divided into fluoroalkyl- and aliphatic-rich regions. In the 2D columnar phase the fluorinated regions take the form of either straight columns running along the edges of the hexagonal Voronoi cells or, for compounds with a higher degree of fluorination, fuse to a hexagonal honeycomb enclosing the aromatic cores. In the R¯3m phase the fluorine-rich chains are preferentially found along right- and left-handed helices wound around the 31 screw axes between the main aromatic columns. [ABSTRACT FROM AUTHOR]

We report computational studies on Al[sup +](H[sub 2]O)[sub n], n = 6-9, and HAIOH+(H[sub 2]O)[sub n-1], n = 6-14, by the density functional theory based ab initio molecular dynamics method, employing a planewave basis set with pseudopotentials, and also by conventional methods with Gaussian basis sets. The mechanism for the intracluster H[sub 2] elimination reaction is explored. First, a new size-dependent insertion reaction for the transformation of AI[sup +](H[sub 2]O)[sub n] into HAIOH[sup +](H[sub 2]O)[sub n-1] is discovered for n ≥ 8. This is because of the presence of a fairly stable six-water-ring structure in Al[sup +](H[sub 2]O)[sub n] with 12 members, including the AI[sup +]. This structure promotes acidic dissociation and, for n ≥ 8, leads to the insertion reaction. Gaussian based BPW91 and MP2 calculations with 6-31 G[sup *] and 6-31G[sup **] basis sets confirmed the existence of such structures and located the transition structures for the insertion reaction. The calculated transition barrier is 10.0 kcal/mol for n = 9 and 7.1 kcal/mol for n = 8 at the MP2/6-31G[sup **] level, with zero-point energy corrections. Second, the experimentally observed size-dependent H[sub 2] elimination reaction is related to the conformation of HAIOH[sup +](H[sub 2]O)[sub n-1], instead of AI[sup +](H[sub 2]O)[sub n]. As n increases from 6 to 14, the structure of the HAIOH[sup +](H[sub 2]O)[sub n-1] cluster changes into a caged structure, with the AI-H bond buried inside, and protons produced in acidic dissociation could then travel through the H[sub 2]O network to the vicinity of the AI-H bond and react with the hydride H to produce H[sub 2]. The structural transformation is completed at n = 13, coincident approximately with the onset of the H[sub 2] elimination reaction. From constrained ab initio MD simulations, we estimated the free energy barrier for the H[sub 2] elimination reaction to be 0.7 eV (16 kcal/mol) at n = 13, 1.5 eV (35 kcal/mol) at n = 12, and... [ABSTRACT FROM AUTHOR]

Investigates the use of ab initio molecular dynamics (MD) for unimolecular decomposition. Combination of MD and molecular orbital methods; Analysis of the density functional theory-based MD method with planewave basis set and pseudopotentials; Localization of energy barrier and transition structure.

Examines the syntheses, structures and electroluminiscence of blue/green luminescent chelate compounds: Zn(2-py-in)2(THF), BPh2(2-py-in), Be(2-py-in)2, and BPh2(2-py-aza). Use of modified indole and 7-azaindole ligands in blue/green luminescent compounds synthesis; Photoluminescent and electroluminescent properties of the compounds.

The article examines light-driven catalytic water oxidation which occurs as the terminal step in photosystem II at the oxygen evolving complex. It is also a potential half-reaction for artificial photosynthesis and photochemical energy conversion based on water splitting. The origins of catalyst deactivation point to the evolution of a family of surface-bound catalysts for water oxidation.

The article reports the first experimental evidence that nuclear isotopic substitution of molecular sensitizers can indeed be used to control excited-state interfacial electron injection yields. The synthesis of the ruthenium ammine compounds is very similar to reported procedures for closely related compounds. The extent of the reaction was monitored by infrared spectroscopy, wherein the N-H stretching modes decreased with a concomitant increase of the N-D stretching intensity. It was found that the N-H stretching bands were essentially gone after four consecutive exchanges in MeOD.

Describes the proton-inverse detected deuteron nuclear magnetic resonance (NMR) spectroscopy. Sensitivity enhancement of [sup 2] NMR by an order of magnitude or more; Heteronuclear multiple-quantum coherence approach.

The article details the design a number of potent inhibitors incorporating a nonhydrolyzable Leu-Ala hydroxyethylene dipeptide isostere. It provides molecular insight into the ligand-binding site interactions of the memapsin active site. The structure-based design led to the development of very potent and highly selective memapsin 2 inhibitors.