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An exciting new development in main group chemistry has been the use of a constrained, "flat", phosphorus-based complex to mediate in reactions such as the dehydrogenation of ammonia borane (AB), and the activation of the N-H bond in primary amines. Its importance is based on the fact that it shows that main group compounds, when properly designed, can be as effective as transition metal complexes for doing significant chemical transformations. What the current computational study, employing density functional theory (DFT), reveals is that a common, general mechanism exists that accounts for the behavior of the flat phosphorus compound in the different reactions that have been experimentally reported to date. This mechanism, which involves the mediation by a base as a proton transfer agent, is simpler and energetically more favorable than the previous mechanisms that have been proposed for the same reactions in the literature. It is likely that the knowledge gained from the current work about the chemical behavior of this phosphorus compound can be utilized to design new constrained phosphorus-based compounds. [ABSTRACT FROM AUTHOR]

In this work, we have designed andsynthesized a series of fattyacid amphiphiles that have the same structural skeleton but differenthydrogen-bonding (H-bonding) functional groups in the hydrocarbonchain. To examine the importance of the H-bonding interaction on theformation of a one-dimensional (1D) aggregate in organic solvents,we have compared the gelation behavior of these amphiphiles in somecommon organic solvents at room temperature. Despite the structuralsimilarity, the amphiphiles were observed to exhibit different gelationbehavior. The organogels were characterized using conventional techniquessuch as field emission scanning electron microscopy, X-ray diffraction,and rheology. A systematic analysis of the FT-IR and 1HNMR spectral data, gel melting temperatures, and mechanical strengthsof the organogels in a given solvent suggested the importance of H-bondingas well as van der Waals interaction in the gelation process. In thisstudy, we have made an attempt to estimate qualitatively the relativecontribution of H-bonding and van der Waals interactions between gelatormolecules forming organogels. The results suggest that strong andweaker H-bonding affects the gelation ability of gelators. However,when the H-bonding interaction is weak, an increase in van der Waalsinteractions can result in gelation, but when both H-bonding and vander Waals interactions are weak, that is, when the amphiphiles areliquid and semisolid, no gelation is observed. It is concluded thata balance between H-bonding and van der Waals interactions is necessaryfor physical gelation. [ABSTRACT FROM AUTHOR]

The major driving force for organogelationis known to be hydrogenbonding for gelators containing functional groups capable of forminghydrogen bond(s). In order to examine this, we have investigated thegelation behavior of two 4-(N-tetradecanoyl)aminohydroxybutanoicacid amphiphiles in a series of organic solvents and compared withthose of the corresponding unsubstituted amphiphile 4-(N-tetradecanoyl)aminobutanoic acid (C14-ABA). The gelationability of the nonhydroxyl amphiphile C14-ABA was foundto be better than the hydroxyl group substituted amphiphiles. An attemptwas also made to correlate gelation abilities of the amphiphiles withthe solvent polarity parameters. The driving force for the gelationwas studied by Fourier transform infrared and 1H NMR spectroscopy.The organogels were characterized by electron microscopy and XRD.The thermal stability of the gels was investigated by measuring thesol-to-gel transition temperature. Rheological measurements were performedin order to determine the mechanical stability of the organogels.The gelation ability and thermal and mechanical stability of the organogelswere correlated with the intermolecular hydrogen-bonding interactionsbetween amphiphile head groups. [ABSTRACT FROM AUTHOR]

A series of l-cysteine-derived double hydrocarbonchainamphiphilic gelators l-(3-alkyl-carbamoylsulfanyl)-2-(3-alkylurido)propionicacid with different hydrocarbon chain lengths (C6–C16) wasdesigned and synthesized. These gelators efficiently gelate only aromaticsolvents. The gelation ability increased with the increase of chainlength up to C14, but then it dropped with further increase of chainlength. The C12 and C14 derivatives also gelled ethanol/water mixtures.The gels were characterized by a number of methods, including FT-IR,NMR, and XRD spectroscopy, electron microscopy, and rheology. Theamphiphiles were observed to form either flat lamellar or ribbonlikeaggregates in aromatic solvents as well as in ethanol/water mixtures.The gelation in all the solvents employed was observed to be thermoreversible.The gel-to-sol transition temperature as well as mechanical strengthof the organogels were observed to increase with the hydrocarbon chainlength. Both types of gels of C8–C16 amphiphiles have gel-to-soltransition temperatures above the physiological temperature (310 K).FT-IR and variable temperature 1H NMR measurements suggestedthat van der Waals interactions have major contribution in the gelationprocess. The gel-to-sol transition temperature and mechanical strengthof the organogels in ethanol/water mixtures was observed to be higherthan those of benzene organogel. [ABSTRACT FROM AUTHOR]

Fullerenes have attracted considerable interest as an electron-transporting layer in perovskite solar cells. Fullerene-based perovskite solar cells produce no hysteresis and do not require high-temperature annealing. However, high power conversion efficiency has been only achieved when the fullerene layer is thermally evaporated, which is an expensive process. In this work, the limitations of a solution-processed fullerene layer have been identified as high crystallinity and the presence of remnant solvents, in contrast to a thermally deposited C 60 film, which has low crystallinity and no remaining solvents. As a solution to these problems, a mixed C 60 and C 70 solution-processed film, which exhibits low crystallinity, is proposed as an electron-transporting layer. The mixed-fullerene-based devices produce power conversion efficiencies as high as that of the thermally evaporated C 60 -based device (16.7%) owing to improved fill factor and open-circuit voltage. In addition, by vacuum-drying the mixed fullerene film, the power conversion efficiency of the solution-processed perovskite solar cells is further improved to 18.0%. This improvement originates from the enhanced transmittance and charge transport by removing the solvent effect. This simple and low-cost method can be easily used in any type of solar cells with fullerene as the electron-transporting layer.

A systematic study of the importance of functional group position and type on the gelator efficiencies of structurally simple, low molecular-mass gelators is reported. Thus, the gelation abilities of a series of positional isomers of ketooctadecanoic acid (n-KSA) are compared in a wide range of liquids. The gelation abilities of the n-KSA as a function of n, the keto group position along the chain, are characterized by several structural, thermal, and rheological techniques and are compared with those of the corresponding hydroxyoctadecanoic acid isomers (n-HSA) and the parent molecule, octadecanoic acid (SA). Analyses of the gels according to the strengths of functional group interactions along the alkyl chain in terms of group position and type are made. The conclusions derived from the study indicate that gel stability is enhanced when the functional group is located relatively far from the carboxylic headgroup and when group-group interactions are stronger (i.e., hydrogen-bonding interactions are stronger in the n-HSA than dipole interactions in the n-KSA, which are stronger than the London dispersion interactions in SA). Co-crystals of the keto- and hydroxy-substituted octadecanoic acids are found to be less efficient gelators than even the ketooctadecanoic acids, due to molecular packing and limited group interactions within the gelator networks.

A series of amino acid-based gelators N-(n-alkylcarbamoyl)-L-alanine were synthesized, and their gelation abilities in a series of organic solvents were tested. No gelation was observed in pure solvents employed. All the amphiphilic molecules were found to form stable organogels in the solvents in the presence of a small amount of water, methanol, or urea. The volume of solvent gelled by a given amount of the gelator was observed to depend upon the volume of added water. The gelation behavior of the amphiphiles in a given solvent containing a known volume of water was compared. The effects of chirality and substitution on the acid group on the gelation ability were examined. Although the corresponding N-(n-tetradecylcarbamoyl)-DL-alanine was found to form only weak organogel in pure solvents, the achiral amphiphilic compound N-(n-tetradecylcarbamoyl)-β-alanine, however, did not form gel in the absence of water. The methyl ester of N-(n-tetradecylcarbamoyl)-L-alanine was also observed to form gels in the same solvents, but only in the presence of water. The organogels were characterized by several techniques, including (1)H NMR, Fourier transform IR, X-ray diffraction, and field emission scanning electron microscopy. The thermal and rheological properties of the organogels were studied. The mechanical strength of the organogel formed by N-(n-tetradecylcarbamoyl)-DL-alanine was observed to increase upon the addition of water. It was concluded that water-mediated intermolecular hydrogen-bonding interaction between amphiphiles caused formation of supramolecular self-assemblies.

Six L-histidine-based amphiphiles, N(alpha)-(4-n-alkyloxybenzoyl)-L-histidine of different hydrocarbon chain lengths, were designed, synthesized, and examined for their ability to gelate water. Four of members of this family of amphiphiles were observed to form thermoreversible hydrogels in a wide range of pH at room temperature. The structural variations were characterized by critical gelation concentration, gelation time, gel melting temperature (T(gs)), rheology, and electron microscopy. Among the amphiphiles, the n-octyl derivative showed better gelation ability in the studied pH range. The amphiphiles were found to have T(gs) higher than body temperature (37 degrees C) showing their stability. Also, relatively higher yield stress (>1000 Pa) values of the hydrogels show their higher strength. The effective gelator molecules self-assemble into fibrous structures. Scanning electron microscopic picture of the hydrogels revealed large ribbons with right-handed twist. Small-angle XRD and circular dichroism spectroscopy were also employed to characterize the hydrogels. It was observed that pi-pi stacking, hydrophobic interaction, amide hydrogen bonding, and solubility factor contribute to the stability and strength of the hydrogels.