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ABSTRACT A new series of palladium complexes ( Pd1-Pd5) ligated by symmetrical 2,3-diiminobutane derivatives, 2,3-bis[2,6-bis{bis(4-FC6H4)2CH}2-4-(alkyl)C6H2N]C4H6 (alkyl = Me L1, Et L2, iPr L3, tBu L4) and 2,3-bis[2,6-bis{bis(C6H5)2CH}2-4-{(CH3)3C}C6H2N]C4H6 L5, have been prepared and well characterized, and their catalytic scope toward ethylene polymerization have been investigated. Upon activation with MAO, all palladium complexes ( Pd1-Pd5) exhibited good activities (up to 1.44 × 106 g (PE) mol−1(Pd) h−1) and produced higher molecular weight polyethylene in the range of 105 g mol−1 with precise molecular weight distribution ( Mw/ Mn = 1.37-1.77). One of the long-standing limiting features of the Brookhart type α-diimine Pd(II) catalysts is that they produce highly branched (ca. 100/1000 C atoms) and totally amorphous polymer. Conversely, herein Pd5 produced polymers having dramatically lower branching number (28/1000) as well as improved melting temperature up to 73.1 °C showing well-controlled linear architecture, and very similar to polyethylene materials generated by early-transition-metal based catalysts. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3214-3222 [ABSTRACT FROM AUTHOR]

ABSTRACT In the series of benzene-1,4-diamines ( p-phenylenediamines) investigated, 2-(methoxymethyl)benzene-1,4-diamine (2-methoxymethyl- p-phenylenediamine) is the most slowly oxidized, with removal of the first electron being rate determining. This electron-withdrawing methoxymethyl group also drove a faster coupling step with 3-aminophenol ( m-aminophenol) than for the analogs with electron-donating groups. However, the series parent, benzene-1,4-diamine, exhibited the fastest coupling step. Since both N(1) and N(4) of the primary intermediates react with m-aminophenol, it seems that steric hindrance by the 2-substituents slows the overall rate. When 3-amino-2,6-dimethylphenol is the coupler, the kinetics are biphasic. Nonproductive adducts are formed reversibly with all the primary intermediates by ipso attack at C(6). For 2-(methoxymethyl)benzene-1,4-diamine, formation of this nonproductive adduct is favored more than for the other compounds in the series, in what seems to be a kinetically rather than thermodynamically controlled process. This slows the overall rate of color formation. [ABSTRACT FROM AUTHOR]

By tuning the steric properties of the acyl group to control the efficiency and selectivity of the resolution, 2-phenyl-1-propanol 1a was prepared by lipase-catalysed hydrolysis using a short-chain acyl group, with E -values of up to 66 ( ee up to 95%). 2-Phenylbutan-1-ol 1b was similarly resolved (up to 86% ee ) using the optimised conditions, while the ester of the more sterically demanding 3-methyl-2-phenylbutan-1-ol 1c proved resistant to enzymatic hydrolysis under these conditions. [ABSTRACT FROM AUTHOR]

The main theme of interest is to design functional metal–organic frameworks (MOFs) for exploring structural correlation with photocatalytic activity. So firstly, three different structural MOFs, namely, Cd(APAPT) 2 I 2 ·2H 2 O ( 1 ) ( APAPT = 3-(5-Amino-1H-pyrazol-4-yl)-5-(3-amino-1H-pyrazol-4-yl)-3,5-dihydro-[1,2,4]triazol-4-ylamine), [Mn(APAPT)(SO 4 )(H 2 O)] n ( 2 ) and {[Zn 3 (APAPT) 2 (SO 4 )(OH) 2 ]·(H 2 O)} n ( 3 ) constructed by the same parasol-based ligands and different metal ions are reported here. Complex 1 shows one-dimensional chain linked by mononuclear Cd units through π⋯π interactions. Complex 2 possesses two-dimensional layer with left- and right-handed helical chains. Complex 3 with infinite Zn-cluster chains is a three-dimensional porous framework. The structural diversity indicates that the APAPT with different coordination modes play important roles in tuning the dimensionalities and structures of the title complexes. Photocatalytic studies show that the MB degradation rates were 63.2%, 51.3% and 80.3% for complexes 1 – 3 , respectively. The results manifest that the more extended networks may aid in the transport of excited holes/electrons to the surface to initiate the photocatalytic decomposition reaction with MB. Besides, steric hindrance etc. helical chains or weaving structure may lead to a relative lower photocatalytic activity. [ABSTRACT FROM AUTHOR]

Eight homologous series of 2-(or 3-)substituted phenyl 4ʹ-(4″-alkoxy (2ʹ-, or 3″-substituted phenylazo) benzoates (InXY) were prepared in which the suffix ‘X’ refers to the lateral substituent X attached to the terminal benzene ring that carries the alkoxy group, and the suffix ‘Y’ refers to the substituent attached to the other terminal phenyl group. Within each homologous series, the length of the terminal alkoxy group varies from 8 to 16 carbons, while the lateral polar substituents, X and Y, alternatively varies between CH3and F. The mesophase behaviour was investigated by differential scanning calorimetry and identified by polarised optical microscopy. The results were discussed in terms of the polarity and steric effects of the two lateral substituents. Comparative correlations were made to investigate the effect of the second lateral substituent on the mesophase behaviour of the previously investigated mono-laterally substituted analogues. UV–vis spectroscopic study revealed that the compoundsI8XYexhibited two absorption bands: low intense bands at 254–263 and a broad band at 364–376 nm. These bands are attributed to the π–π∗ transition of the phenyl rings and the whole mesogenic portion. [ABSTRACT FROM PUBLISHER]

A new facile synthetic strategy was developed to prepare bifunctional monophosphinic acid Ln-DOTA derivatives, Gd-DO2AGAP NBn and Gd- DO2AGAP ABn . The relaxivities of the Gd-complexes are enhanced compared to Gd-DOTA. Monophosphinic acid arm of these Gd-complexes affords enhancement of inner sphere water exchange rate due to its steric bulkiness. The different functionalities of DO2AGAP NBn were appended in trans positions and are designed to conjugate identical or different vectors according to the potential applications. The conjugation of Gd-DO2AGAP ABn with E3 peptide known to target apoptosis was successfully performed and in vivo MRI allowed cell death detection in a mouse model. [ABSTRACT FROM AUTHOR]

The adsorption of molecules on metal nanoparticles can be sterically controlled through the use of zeolite crystals, which enhances the product selectivity in hydrogenations of reactants with more than one reducible group. Key to this success was the fixation of Pd nanoparticles inside Beta zeolite crystals to form a defined structure (Pd@Beta). In the hydrogenation of substituted nitroarenes with multiple reducible groups as a model reaction, the Pd@Beta catalyst exhibited superior selectivity for hydrogenation of the nitro group, outperforming both conventional Pd nanoparticles supported on zeolite crystals and a commercial Pd/C catalyst. The extraordinary selectivity of Pd@Beta was attributed to the sterically selective adsorption of the nitroarenes on the Pd nanoparticles controlled by the zeolite micropores, as elucidated by competitive adsorption and adsorbate displacement tests. Importantly, this strategy is general and was extended to the synthesis of selective Pt and Ru catalysts by fixation inside Beta and mordenite zeolites. [ABSTRACT FROM AUTHOR]

In organic chemistry, Comparative Molecular Field Analysis (CoMFA) can be defined as a regression analysis between reaction outcomes and molecular fields, wherein we can extract and visualize important structural information from the coefficients of the constructed regression models. In CoMFA, partial least-squares (PLS) regression, which determines all coefficients in the model, is used for fitting the regression models. However, in organic reactions, steric effects are observed only near the reactive site, indicating that a large number of regression coefficients in the CoMFA of organic reactions should be assigned as 0. The regularized regression method, LASSO/Elastic Net, allows us to fit the regression model while assigning 0 values to unimportant coefficients. Although LASSO/Elastic Net should be suitable for CoMFA, there is no example of its use for organic reaction analysis. Herein, we examine the performance of LASSO/Elastic Net for the quantification of steric effects in CoMFA. We employ digitized molecular structures (the indicator field) as molecular fields that represent steric effects. LASSO/Elastic Net regressions provide highly interpretable models that include less noise than those from PLS regression. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The elucidation of the mechanism of the substituent influence on the properties P (the interaction energies E, interring distances l, and free energies Δ G of interaction) of weak complexes involving aromatic rings is of importance not only theoretically but also from a practical standpoint. This mechanism is little understood. In this work, the literature data on the substituent influence on P properties for 42 series of complexes have been analyzed, using correlation analysis. Generally, the inductive, resonance, polarizability, and steric effects are in operation. The presence or absence of certain effects and the relation between their contributions are determined by the type of series. The polarizability effect (an electrostatic ion-dipole interaction) is caused by an excess charge appearing on the ring substituted fragment of complexes as a result of the complexation. This effect is observed in all series; its contribution ranges up to approximately 50%. [ABSTRACT FROM AUTHOR]

A computational exploration of the predicted molecular weights for Ti- and Zr-catalyzed olefin polymerizations shows that there are considerable opportunities for electronic tuning. Ligand variation mainly affects the propagation rate, whereas chain transfer to the monomer is hardly affected by electronic factors. The results are analyzed in terms of the effects of ligand variation on the relative energies of "connected couples" of reactant local minima and the corresponding transition states on the basis of the Hammond postulate and the Curtin-Hammett principle. For the constrained-geometry catalysts (CGCs) and bis(amido) systems studied, better donating ligands increase the preference for a "planar" metal environment and produce higher molecular weights. [ABSTRACT FROM AUTHOR]

A study of the reactivity of 2-substituted 1,3-butadienes with nitrosocarbonyl compounds in the 4+2 cycloaddition has been carried out showing that the regioselectivity involves a delicate balance of steric and electronic effects. 2-Aryl 1,3-butadienes favor the distal isomer with the magnitude of preference ranging from 4:1 to 15:1 depending on the nature of the nitrosocarbonyl group. However, when bulky 2-substituted dienes are used the proximal isomer is formed preferentially. The results obtained, together with previous theoretical calculations and experimental data, provide further data to aid in synthetic planning. [ABSTRACT FROM AUTHOR]

Thermally induced rearrangements of 4-hydroxycyclobutenones are known to provide clean and reliable access to an array of useful carbocyclic and fused heterocyclic ring systems. Rarely, such reactions have been diverted to an alternative pathway leading to furanone formation. Herein, we show that these switches in the course of the rearrangement occur when a substrate bears a bulky substituent and are due to adverse steric buttressing as the transition state for electrocyclisation is approached. We also show how the reaction provides new opportunities for furanone synthesis and how bulky proton and halogen surrogates can be used to divert classical rearrangement pathways toward furanone formation. Additionally, we show that classical rearrangement pathways can be promoted by the simple expedient of alcohol protection. [ABSTRACT FROM AUTHOR]

We have theoretically studied the competing adsorption of the two- and three-component electrolytes with different sizes and ionic valences near a semi-permeable shell. The present theory provides interesting insights about the steric charge separation occurring at the shell, which cannot be explained by the linearized and nonlinear Poisson-Boltzmann theories. The smaller and divalent ions interact more strongly with the shell than the larger and monovalent ions because the smaller ions can approach more closely to the shell surface and the divalent ions interact more strongly with the charged shell than the monovalent ions. The large steric charge separation occurs at a highly asymmetric electrolyte and a high bulk concentration. The competition between the cations and anions gives rise to the charge reversal and charge inversion even for an uncharged shell. A positively charged surface enhances the charge surface amplification because the shell is impermeable for the anion, whereas a negatively charged surface enhances the charge reversal. The excess osmotic pressure, which is based on a nonlinear Poisson-Boltzmann theory, depends only on the permeated ion density at the shell, and increases with increasing the shell size and surface charge density. [ABSTRACT FROM AUTHOR]

A route to produce a stable colloidal suspension is essential if mono-dispersed particles are to be successfully synthesized, isolated, and used in subsequent nanocomposite manufacture. Dispersing nanoparticles in fluids was found to be an important approach for avoiding poor dispersion characteristics. However, there is still a great tendency for colloidal nanoparticles to flocculate over time. Steric stabilization can prevent coagulation by introducing a thick adsorbed organic layer which constitutes a significant steric barrier that can prevent the particle surfaces from coming into direct contact. One of the main features of hydrothermal synthesis technique is that it offers novel approaches for sustainable nanoparticle surface modification. This manuscript reports on the sustainable steric stabilization of titanium dioxide nanoparticles. Nanoparticle surface modification was performed via two main approaches including post-synthesis and in situ surface modification. The tuneable hydrothermal conditions (i.e. temperature, pressure, flow rates, and surfactant addition) were optimized to enable controlled steric stabilization in a continuous fashion. Effective post synthesis surface modification with organic ligand (dodecenyl succinic anhydride (DDSA)) was achieved; the optimum surface coating temperature was reported to be 180–240 °C to ensure DDSA ring opening and binding to titania nanoparticles. Organic-modified titania demonstrated complete change in surface properties from hydrophilic to hydrophobic and exhibited phase transfer from the aqueous phase to the organic phase. Exclusive surface modification in the reactor was found to be an effective approach; it demonstrated surfactant loading level 2.2 times that of post synthesis surface modification. Titania was also stabilized in aqueous media using poly acrylic acid (PAA) as polar polymeric dispersant. PAA-titania nanoparticles demonstrated a durable amorphous polymeric layer of 2 nm thickness. This manuscript revealed the state of the art for the real development of stable colloidal mono-dispersed particles with controlled surface properties. [ABSTRACT FROM AUTHOR]

(4 S)- and (4 R)-configured aminoproline (Amp) residues were used as pH-responsive probes to tune the thermal stability of collagen triple helices in acidic and basic environments. The different steric and stereoelectronic properties of amino versus ammonium groups lead to a switch of the ring pucker of Amp upon changing the pH. The choice of the position of Amp within collagen model peptides (CMPs) as well as the absolute configuration at C(4) of the pH-responsive probe allows for tuning of the stability of Amp-containing collagen triple helices over a broad range. Comparative quantum chemical calculations on the steric and stereoelectronic effects of amino and ammonium groups versus fluorine, hydroxy, chlorine, and methyl substituents support the experimental findings. The research also shows that substitution of the naturally occurring hydroxy group in collagen by electron-withdrawing groups with a larger hydration shell than that of the hydroxy group is not tolerated. [ABSTRACT FROM AUTHOR]

We report a formal [4+2] cycloaddition reaction of styrenes under visible-light catalysis. Two styrene molecules with different electronic or steric properties were found to react with each other in good yield and excellent chemo- and regioselectivity. This reaction provides direct access to polysubstituted tetralin scaffolds from readily available styrenes. Sophisticated tricyclic and tetracyclic tetralin analogues were prepared in high yield and up to 20/1 diasteroselectivity from cyclic substrates. [ABSTRACT FROM AUTHOR]

Kinetic regularities of arenesulfonylation of N-alkylanilines in binary water-organic solvents of variable composition have been studied. The rate constants for these reactions increase with increasing the water content in a system. The steric factor has the decisive influence on reactivity of N-alkylamines. The character of the influence of the composition and nature of a solvent on the rate constants for arenesulfonylation was discussed with the assistance of results of quantum chemical simulation of molecular complexes of the nucleophiles studied with the components of the binary systems. Calculation of potential energy surface for the reaction of N-methylaniline with benzenesulfonyl chloride showed that in the gas phase the process occurs by the S2 mechanism. [ABSTRACT FROM AUTHOR]

Deposition of graphene on environmental surfaces will dictate its transport and risks. In this work, the deposition, mobilization, and transport of 14 C-labeled few-layer graphene (FLG) in saturated quartz sand were systematically examined. Increasing solution ionic strength (IS) (1–100 mmol/L NaCl) resulted in greater retention of FLG (33–89%) in the sand and more hyper-exponential distribution of FLG along the sand column. Only a small fraction (≤7.4%) of the retained FLG was remobilized due to perturbation of IS by deionized water. These results indicate that trapping in pore spaces (i.e., physical straining) plays a dominant role in FLG deposition rather than attachment onto the surfaces of the sand. When IS, FLG input concentration, and flow velocity favor particle-particle interaction over particle-collector interaction, concurrent agglomeration within the pores promotes straining. In addition, electrostatic and steric repulsion that derived from the adsorbed organic macromolecules on FLG effectively reduced agglomeration and thereby enhanced transport and release of FLG. Moreover, the recovery of FLG (that deposited at 100 mmol/L NaCl) in the effluent reached 33% after speeding up the deionized water flushing rate. These findings highlight the need for FLG management in view of variations in transport behavior when assessing water quality and associated risks. [ABSTRACT FROM AUTHOR]

A theoretical study on the selectivity of hexaprotonated form of preorganized azacyclophane C3-trenphen (H L ) for halide anions in the gas phase and solution is reported. The calculated formation and interaction energies show the following trend: [F⊂H L] > [Cl⊂H L] > [Br⊂H L] > [I⊂H L]. Our calculations in both the gas phase and solution, in agreement with the experimental observations, show that the H L host has the largest selectivity for fluoride anion. Indeed, the stronger host-guest interaction in [F⊂H L] complex effectively compensates the unfavourable strain energy of the host and desolvation energy of fluoride anion. Furthermore, herein, the solvent effect does not change the observed trend for gas-phase formation energies. In continuation, in order to find the origin of longer X···aromatic ring (X···cntr) distance than X···bridgehead nitrogen (X···N) in the present complexes, the X···CH and X···NH systems were simulated, respectively. The calculated interaction energies for two latter systems in different X···CH and X···NH distances clearly showed that the repulsion force between X and nitrogen atom is larger than that between X and aromatic ring. Thus, only when there are the strong N-H···X interactions in top of the cage, the N···X distance is considerably smaller than cntr···X one. Graphical Abstract: [ABSTRACT FROM AUTHOR]

The potential interplay of steric and substitution pattern effects of the monothiooxalamide side arms on the structure, conformational features, and self-assembly of a series of phenylene bis-monothiooxalamides was investigated. Herein we have demonstrated that phenylene bis-monothiooxalamides self-associate in the solid state, through intermolecular hydrogen bonding as meso-helices when the thioamide NR group is s Bu and through dispersive CO···CX (X = O, S, π), S···S, and C-H···S interactions when R is t Bu, independently from the substitution pattern in the phenyl ring. The helical structures are exclusively developed through NCSH···O hydrogen bonding. The steric strain imposed by the ortho-substitution pattern has the effect of moving both monothiooxalyl units out of the phenyl plane enabling dimerization through strong NCOH···O intermolecular hydrogen bonds and promotes the formation of meso-helices. The steric demand of the thioamide NR group rules the conformation adopted by meta-substituted derivatives and the self-association arrangement of para-substituted derivatives. Infrared data support the blue-shifted nature of the NCSH···O hydrogen bond. NMR data in solution agree with the extensive intramolecular hydrogen bonding scheme. Results are supported by density functional theory theoretical calculations. Monothiooxalamide unit offers considerable potential as a key moiety for crystal engineering. [ABSTRACT FROM AUTHOR]

Cis-enediyne-type compounds have received much attention as potent antitumor antibiotics. The conventional synthesis of cis-enediynes in solution typically involves multiple steps and various side reactions. For the first time, selective one-step synthesis of cis-enediyne from a single reactant is reported on a Ag(111) surface with a yield up to 90 %. High selectivity for the formation of cis-enediyne originates from the steric effect posed by weak intermolecular interactions, which protect the cis-enediyne from further reaction. A series of comparative experiments and DFT-based transition-state calculations support the findings. The described synthetic approach for directing reaction pathways on-surface may illuminate potential syntheses of other unstable organic compounds. [ABSTRACT FROM AUTHOR]

Cyclic (alkyl)(amino)carbenes cAACcy (1b) and cAACmenthyl (1c) react with [Ni(CO)4] to give the 18 VE complexes [Ni(CO)3(cAACcy)] (2b) and [Ni(CO)3(cAACmenthyl)] (2c). With these in hand, the donor-strength and the steric profile of the respective cAAC ligands were evaluated. CAACcy and cAACmenthyl possess similar overall-donating properties (Tolman electronic parameter (TEP) = 2046 (1b) and 2042 (1c)) as common NHCs, though they are also known to be better π-acceptors. 3,3-Diamino-2-aryloxyacrylimidamide 3b, arising from the reaction of cAACcy (1b) with released CO molecules, was obtained as side-product of CO substitution reactions at nickel carbonyls. In contrast to cAACmenthyl (%V bur = 42), the sterically less encumbered cAACcy (%V bur = 38) undergoes a subsequent CO substitution at [Ni(CO)3(cAACCy)] (2b) to afford the 16 VE complex [Ni(CO)(cAACcy)2] (4b). Treatment of both [Ni(CO)3(cAACmethyl)] (2a) and [Ni(CO)(cAACmethyl)2] (4a) with allyl bromides led to the formation of cAAC-stabilized allyl nickel complexes [NiBr(η³-H2 C-CH-CH2)(cAACmethyl)] (5a) and [NiBr(η³-H2 C-CH-CMe2)(cAACmethyl)] (5b). The chloro complex [NiCl(η³-H2 C-CMe-CH2)(cAACmethyl)] (6) was synthesized from [Ni(COD)2] (COD = 1,5-cyclooctadiene) by consecutive treatment with allyl chloride and cAAC. The allyl halide complexes 5 and 6 are thermally labile and decompose in solution already within a few hours at room temperature. One of the decomposition products, the dinuclear nickel complex [Ni2(μ-Br)2(η³-(cAAC methyl)-CH-CH(CH3))2] (7), was crystallographically characterized. [ABSTRACT FROM AUTHOR]

X-ray crystal structures of three Λ-[Ru(L)2dppz]2+ complexes (dppz=dipyridophenazine; L=1,10-phenanthroline (phen), 2,2′-bipyridine (bpy)) bound to d((5BrC)GGC/GCCG) showed the compounds intercalated at a 5′-CG-3′ step. The compounds bind through canted intercalation, with the binding angle determined by the guanine NH2 group, in contrast to symmetrical intercalation previously observed at 5′-TA-3′ sites. This result suggests that canted intercalation is preferred at 5′-CG-3′ sites even though the site itself is symmetrical, and we hypothesise that symmetrical intercalation in a 5′-CG-3′ step could give rise to a longer luminescence lifetime than canted intercalation. [ABSTRACT FROM AUTHOR]

A new naphthoxazole-derived probe, 2-(2-Hydroxyphenyl)-naphtho[1,2 -d ]oxazole-5-sulfonate (HL), was conveniently synthesized and characterized. The presence of Zn 2+ caused an obvious fluorescence enhancement at 458 nm upon excitation at 391 nm, which could be distinguished with the naked eye under a UV lamp. Remarkably, the compound exhibited excellent selective and sensitive response to Zn 2+ over other common cations with a micromolar limit of detection (0.69 μM) in DMSO/HEPES (v/v, 1:1) buffer. The results from absorption spectra, 1 H NMR, ESI–MS, density functional theory (DFT) calculations, and pH effect, implied that during the process of complexation, the fluorescence intensity was enhanced by the inhibition of the excited state intramolecular proton transfer (ESIPT) in free HL and the formation of a large π-electron conjugation system. The steric hindrance effect from a hydrogen atom on naphthoxazole determined the selectivity of Zn 2+ over other metal ions. The most appropriate environments for the detection of Zn 2+ were neutral and weak alkali. In addition, the probe of detecting the Zn 2+ has been evaluated with relatively lower toxicity in living MCF7 cell, suggesting the practical application in physiological system. [ABSTRACT FROM AUTHOR]

Steric and relaxation as components of deformation density are characterised by topological analysis; and critical points are found as important descriptors for interatomic and intermolecular interactions. In this respect, repulsive and attractive types of electron density redistribution can be examined distinctly, with their own critical points. The steric component as repulsive interaction is appeared as a local minimum critical point, while relaxation component as attractive component appears as a local maximum in the Cartesian space. The formalism is applied to extensively different complexes including closed- and open-shell interactions, and the results fairly agree with chemical interpretation of these two types of interactions. [ABSTRACT FROM PUBLISHER]

Shape complementarity between close-packed residues plays a critical role in the amyloid aggregation process. Here, we probe such "steric zipper" interactions in amyloid-β (Aβ40), whose aggregation is linked to Alzheimer's disease, by replacing natural residues by their stereoisomers. Such mutations are expected to specifically destabilize the shape sensitive "packing" interactions, which may potentially increase their solubility and change other properties. We study the stereomutants DF19 and DL34 and also the DA2/DF4/DH6/DS8 mutant of Aβ40. F19-L34 is a critical contact in a tightly packed region of Aβ, while residues 1-9 are known to be disordered. While both DF19 and DL34 slow down the kinetics of aggregation and form amyloid fibrils efficiently, only DL34 increases the final solubility. DF19 gives rise to additional off-pathway aggregation which results in large, kinetically stable aggregates, and has lower net solubility. DA2/DF4/DH6/DS8 does not have an effect on the kinetics or the solubility. Notably, both DF19 and DL34 oligomers have a significantly lower level of interactions with lipid vesicles and live cells. We conclude that stereoisomers can cause complex site dependent changes in amyloid properties, and provide an effective tool to determine the role of individual residues in shaping the packed interiors of amyloid aggregates. [ABSTRACT FROM AUTHOR]

Novel 5,5′-disubstituted BMP32C10 derivatives bearing different sized substituents were designed and prepared. The stoichiometries and complexation behavior between these hosts and paraquats were studied. It was found that bulky 5,5′-substituents disfavor complexation with paraquats by hindering the formation of [2]pseudorotaxane and 'taco' complexes. [ABSTRACT FROM AUTHOR]

DNA adenine methyltransferase identification (DamID) is an enzymatic technology for detecting DNA regions targeted by chromatin-associated proteins. Proteins are fused to bacterial DNA adenine methyltransferase (Dam) and expressed in cultured cells or whole organisms. Here, we used DamID to detect DNA regions bound by the cardiac-restricted transcription factors (TFs) NKX2-5 and SRF, and ubiquitously-expressed co-factors ELK1 and ELK4. We compared targets bound by these TFs as N- and C-terminal fusions with Dam, for both wild type (WT) NKX2-5 and mutant proteins mimicking those found in congenital heart disease. Overall, DamID is highly robust: while the orientation of WT Dam fusions can affect the size of the target sets, their signatures remained largely reproducible. Furthermore, a severe NKX2-5 mutant lacking the homeodomain showed strong steric effects negatively impacting target discovery. The extent of steric effect is likely to be dependent on the protein in question and the orientation of Dam fusion. [ABSTRACT FROM AUTHOR]

This study investigated the effect of various cations (Ca2+, Mg2+, Al2+, Mn2+, Zn2+) on the autoaggregation (AAg) and surface hydrophobicity (SHb) of three different bacteria (Brevibacillus panacihumi strain (ZB1), Lysinibacillus fusiformis strain (ZB2) and Enterococcus faecalis strain (ZL)) using a 2-level factorial design. The AAg ratio was measured from the changes in the absorbance of the media. Results show that ZB2 had maximum AAg for the three bacteria investigated. A microscopic clustering of cells was observed when Ca2+ was added to ZB2. The AAg was in the range of 62%, 58% and 34% for ZB2, ZB1 and ZL, respectively and correlated to the SHb. The aggregation and SHb of the microbial cells increased with increasing ionic strength due to the repulsive steric or overlap forces between the polymer covered surfaces. Ca2+ demonstrated a more significant effect on aggregation and SHb of microbial cells due to an attractive binding force. [ABSTRACT FROM AUTHOR]

Hypothesis Accessing the phase inversion temperature by microwave heating may enable the rapid synthesis of small lipid nanoparticles. Experiments Nanoparticle formulations consisted of surfactants Brij 78 and Vitamin E TPGS, and trilaurin, trimyristin, or miglyol 812 as nanoparticle lipid cores. Each formulation was placed in water and heated by microwave irradiation at temperatures ranging from 65 °C to 245 °C. We observed a phase inversion temperature (PIT) for these formulations based on a dramatic decrease in particle Z-average diameters. Subsequently, nanoparticles were manufactured above and below the PIT and studied for (a) stability toward dilution, (b) stability over time, (c) fabrication as a function of reaction time, and (d) transmittance of lipid nanoparticle dispersions. Findings Lipid-based nanoparticles with distinct sizes down to 20–30 nm and low polydispersity could be attained by a simple, one-pot microwave synthesis. This was carried out by accessing the phase inversion temperature using microwave heating. Nanoparticles could be synthesized in just one minute and select compositions demonstrated high stability. The notable stability of these particles may be explained by the combination of van der Waals interactions and steric repulsion. 20–30 nm nanoparticles were found to be optically transparent. [ABSTRACT FROM AUTHOR]

β-Amyrin synthase incubation experiments have been conducted to determine the influence of steric effects at the 6-, 10- and 15-positions of 2,3-oxidosqualene on the polycyclisation pathway. Nor- and ethyl-substituted oxidosqualene analogues were synthesised. Cyclisation of the ethyl-substituted analogues did not occur, but the nor analogues underwent a polycyclisation cascade to yield fully cyclised products with 6/6/6/6/6-fused pentacyclic scaffolds generated via a final oleanyl cation. Previously, we reported that 19- and 23-ethyl-substituted analogues underwent polycyclisation reactions. Therefore, the catalytic domain involved in earlier cyclisation steps is notably compact. In contrast, the catalytic domain in the later cyclisation steps is more loosely packed (less compact) to accommodate the bulky ethyl group. The reaction cavities for recognising branched methyl groups are discussed by comparing β-amyrin synthase with other triterpene cyclases such as lanosterol and hopene synthases. [ABSTRACT FROM AUTHOR]

We have synthesized and characterized the monomeric diiminophosphinate-stabilized Group 13 metal(I) complexes [DipLE:], DipL=Ph2P(NDip)2, Dip=2,6- iPr2C6H3; E=Ga ( 1), In ( 2) and Tl ( 3). In addition, we structurally characterized the dimeric complex [(DipLGa)2], 12. Similar synthetic attempts using MesL=Ph2P(NMes)2, Mes=2,4,6-Me3C6H2 afforded product mixtures from which the mixed oxidation state species [(MesL)3Ga4I3] 4 was isolated. [DipLGa:] 1 is converted with dry air to the gallium(III) oxide species [(DipLGaO)2] 5. Density Functional Theory studies on [DipLE:] and [(DipLE)2], E=Al−Tl, shed light on the bonding in these compounds and show that the newly formed E−E bonding interactions can be described as weak single σ-bond with no significant π-bonding contribution for E=Al, Ga. A large contribution to the dimer binding enthalpies results from London dispersion forces. [ABSTRACT FROM AUTHOR]

Analogues of the [2Fe-2S] subcluster of hydrogenase enzymes in which the central group of the three-atom chain linker between the sulfur atoms is replaced by GeR2 and SnR2 groups are studied. The six-membered FeSCECS rings in these complexes (E=Ge or Sn) adopt an unusual conformation with nearly co-planar SCECS atoms perpendicular to the Fe-Fe core. Computational modelling traces this result to the steric interaction of the Me groups with the axial carbonyls of the Fe2(CO)6 cluster and low torsional strain for GeMe2 and SnMe2 moieties owing to the long C−Ge and C−Sn bonds. Gas-phase photoelectron spectroscopy of these complexes shows a shift of ionization potentials to lower energies with substantial sulfur orbital character and, as supported by the computations, an increase in sulfur character in the predominantly metal-metal bonding HOMO. Cyclic voltammetry reveals that the complexes follow an ECE-type reduction mechanism (E=electron transfer and C=chemical process) in the absence of acid and catalysis of proton reduction in the presence of acid. Two cyclic tetranuclear complexes featuring the sulfur atoms of two Fe2S2(CO)6 cores bridged by CH2SnR2CH2, R=Me, Ph, linkers were also obtained and characterized. [ABSTRACT FROM AUTHOR]

5 regioisomers of N,N-dimethyl(((phenylethynyl)phenyl)ethynyl)aniline (nDPEA) were synthesized by Sonogashira cross-coupling reaction and well characterized. The spectroscopic properties of these regioisomers were studied and discussed. nDPEAs 1b and 1d show shorter λabs and lower ΦF due to meta- branching disrupts the π-electron conjugation. nDPEAs 1c and 1e show shorter λabs because of their steric effects. Based on the high ΦF values of 1a, 1c and 1e, the π-electrons of these nDPEAs are delocalized over the whole molecules. These results are consistent with the theoretical calculations. Time dependent density functional theory computations were performed with the B3LYP or CAM-B3LYP for the identification of vertical transitions in 1a-1e. The predicted and observed absorption spectra of 1a-1e are well consistent. [ABSTRACT FROM AUTHOR]

Sulfonamides represent an important class of biologically active compounds. A sulfonamide possessing carbonic anhydrase (CA) inhibitory properties obtained from a pyrazole based sulfonamide, ethyl 1-(3-nitrophenyl)-5-phenyl-3-((5-sulfamoyl-1,3,4-thiadiazol-2-yl)carbamoyl)-1H-pyrazole-4-carboxylate (1), and its metal complexes with the Ni(II) for (2), Cu(II) for (3) and Zn(II) for (4) have been synthesized. The structures of metal complexes (2–4) were established on the basis of their elemental analysis,1H NMR, IR, UV–Vis and MS spectral data. The inhibition of two human carbonic anhydrase (hCA, EC 4.2.1.1) isoenzymes I and II, with1and synthesized complexes (2–4) and acetazolamide (AAZ) as a control compound was investigatedin vitroby using the hydratase and esterase assays. The complexes2,3and4showed inhibition constant in the range 0.1460–0.3930 µM for hCA-I and 0.0740–0.0980 µM for hCA-II, and they had effective more inhibitory activity on hCA-I and hCA-II than corresponding free ligand1and than AAZ. [ABSTRACT FROM PUBLISHER]

Various 4-aryl substituted 5-carboethoxy-2-oxo-1,2,3,4-tetrahydropyridines were oxidized to their corresponding 4-aryl-5-carboethoxy-2-oxo-1,2-dihydropyridines by potassium peroxydisulfate in aqueous acetonitrile under thermal conditions. The products were obtained in good to excellent yields. Based on the proposed mechanism, the removal of the hydrogen from the C-atom of the heterocyclic ring by the hydroxyl radical formed in situ is occurred in the rate determining step, which is influenced by the steric and electronic effects of the substituted aryl group attached to this atom and also the stability of the radical intermediate involved in the oxidation reaction. The experimental results were supported by the computational studies. [ABSTRACT FROM AUTHOR]

Alkenyl gold complexes are common intermediates in gold-catalyzed transformations of allenes and alkynes, and numerous methods for their functionalization have been explored. Particularly valuable are cross-coupling reactions, which result in the formation of a new C-C bond. Several strategies are known that enable α-selective cross-coupling of alkenyl gold complexes with aryl, allyl, or acyl coupling partners. We describe the direct β-selective cross-coupling of alkenyl gold complexes with simple alkyl electrophiles. We also describe the effects of the steric and electronic properties of alkenyl gold complexes on the selectivity of the cross-coupling reaction. [ABSTRACT FROM AUTHOR]

ABSTRACT Thermally expandable core-shell microcapsules (TEM) were fabricated with an organic steric stabilizer and an inorganic Pickering emulsifier. In order to fabricate a TEM, acrylonitrile (AN) and metacrylonitrile (MAN) were used as monomers. Halloysite nanotubes (HNTs) and poly(vinylpyrrolidone) (PVP) were used as the inorganic Pickering emulsifier and the organic stabilizer, respectively. The liquid hydrocarbon content in the core, and the thermal and expansion properties, of TEMs with two different emulsifiers were compared. The mechanical properties of polypropylene (PP) foams containing TEMs prepared with two types of stabilizers were analyzed. The TEMs polymerized with PVP showed a finer expanded cell, while those fabricated with HNTs resulted in a larger expanded cell in the PP matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44247. [ABSTRACT FROM AUTHOR]

Anion-templated rotaxanes are a rare class of functional organic molecules capable of novel switching and mechanical behaviors. Yet, investigations of these properties are limited by existing synthetic strategies. We show a high-yielding synthesis (80%) of [3]rotaxanes using shape-persistent macrocycles, cyanostars, and anionic organo-phosphate templates catalyzed by low steric-demand click chemistry. The reaction yields correlate with the template's binding affinities. Use of longer linkers relieves steric congestion to enable a reversible acid–base response, opening the way to molecular switching. [ABSTRACT FROM AUTHOR]

Nitrogen-containing pyridine and quinoline are outstanding platforms on which excellent ionophores and sensors for metal ions can be built. Steric and stereochemical effects can be used to modulate the affinity and selectivity of such ligands toward different metal ions on the coordination chemistry front. On the signal transduction front, such effects can also be used to modulate optical responses of these ligands in metal sensing systems. In this review, steric modulation of achiral ligands and stereochemical modulation in chiral ligands, especially ionophores and sensors for zinc, copper, silver, and mercury, are examined using published structural and spectral data. Although it might be more challenging to construct chiral ligands than achiral ones, isotropic and anisotropic absorption signals from a single chiroptical fluorescent sensor provide not only detection but also differentiation of multiple analytes with high selectivity. [ABSTRACT FROM AUTHOR]

The possibility of sterically hindered allyl thiocyanates undergoing sigmatropic rearrangement was demonstrated. On the basis of kinetic studies and quantum chemical calculations, the intramolecular isomerization mechanism of 1-[( E )-3-thiocyanoprop-1-en-1-yl]adamantane to 1-(1-isothiocyanoprop-2-en-1-yl)adamantane was confirmed. [ABSTRACT FROM AUTHOR]

A series of bicholesteryl-based gelators with different central linker atoms C, N, and O (abbreviated to GC, GN, and GO, respectively) have been designed and synthesized. The self-assembly processes of these gelators were investigated by using gelation tests, field-emission scanning electron microscopy, field-emission transmission electron microscopy, UV/Vis absorption, IR spectroscopy, X-ray diffraction, rheology, and contact-angle experiments. The gelation ability, self-assembly morphology, rheological, and surface-wettability properties of these gelators strongly depend on the central linker atom of the gelator molecule. Specifically, GC and GN can form gels in three different solvents, whereas GO can only form a gel in N, N-dimethylformamide (DMF). Morphologies from nanofibers and nanosheets to nanospheres and nanotubes can be obtained with different central atoms. Gels of GC, GN, and GO formed in the same solvent (DMF) have different tolerances to external forces. All xerogels gave a hydrophobic surface with contact angles that ranged from 121 to 152°. Quantum-chemical calculations indicate that the GC, GN, and GO molecules have very different steric structures. The results demonstrate that the central linker atom can efficiently modulate the molecular steric structure and thus regulate the supramolecular self-assembly process and properties of gelators. [ABSTRACT FROM AUTHOR]

We use fluorescence microscopy to examine the dynamics of the crowding-induced mixing transition of liquid ordered (Lo)-liquid disordered (Ld) phase separated lipid bilayers when the following particles of increasing size bind to either the Lo or Ld phase: Ubiquitin, green fluorescent protein (GFP), and nanolipoprotein particles (NLPs) of two diameters. These proteinaceous particles contained histidine-tags, which were phase targeted by binding to iminodiacetic acid (IDA) head groups, via a Cu2+ chelating mechanism, of lipids that specifically partition into either the Lo phase or Ld phase. The degree of steric pressure was controlled by varying the size of the bound particle (10-240 kDa) and the amount of binding sites present (i.e., DPIDA concentrations of 9 and 12 mol%) in the supported lipid multibilayer platform used here. We develop a mass transfer-based diffusional model to analyze the observed Lo phase domain dissolution that, along with visual observations and activation energy calculations, provides insight into the sequence of events in crowding-induced mixing. Our results suggest that the degree of steric pressure and target phase influence not only the efficacy of steric-pressure induced mixing, but the rate and controlling mechanism for which it occurs. [ABSTRACT FROM AUTHOR]

(POCOP)IrI(CO) [POCOP = κ³-C6H3-2,6-(OPR2)2 for R = tBu, iPr] and (PCP)IrI(CO) [PCP = κ³-C6H3-2,6-(CH2PR2)2 for R = tBu and iPr] complexes can add hydrogen via two distinct pathways. When R = tBu, (POCOP)Ir(CO) and (PCP)Ir(CO) complexes only add hydrogen via a proton-catalyzed pathway due to steric effects, yielding trans-dihydride complexes. For R = iPr, both systems oxidatively add hydrogen to give cis-dihydride complexes which thermally isomerize to more thermodynamically favorable trans-dihydride species, consistent with previous reports. Proton-catalyzed hydrogen addition pathways are also observed for both iPr-substituted (pincer)Ir(CO) complexes. (PCP)Ir(CO) complexes add hydrogen under milder conditions than the analogous POCOP species. Intermediate hydrido-pyridine Ir(III) carbonyl complexes from the proton-catalyzed pathway have been synthesized and characterized. This is the first report of a series of complexes shown to add hydrogen via concerted oxidative addition or a proton-catalyzed pathway to the same iridium center. [ABSTRACT FROM AUTHOR]

Crystals in the isostructural series Au 2 (μ-dppe)X 2 (dppe is 1,2-bis(diphenylphosphino)ethane, X = Cl, Br, I) form centrosymmetric, dimeric structures with two short Au⋯Au contacts between the component molecules. We found no evidence for a second polymorph for any member of the Au 2 (μ-dppe)X 2 series, although two polymorphs were observed previously for the related Au 2 (Ph 2 As(CH 2 ) 2 AsPh 2 )X 2 series. Crystals of Au 2 (μ-dcpe)X 2 (where dcpe is 1,2-bis(dicyclohexylphosphino)ethane) show structures that differ appreciably from those of Au 2 (μ-dppe)X 2 . The bulky cyclohexyl substituents appear to be playing a major role in eliminating the formation of polymeric or dimeric structures. Au 2 (μ-dcpe)Cl 2 has a monomeric structure without aurophilic interactions. In contrast, Au 2 (μ-dcpe)Br 2 and Au 2 (μ-dcpe)I 2 have similar structures with intramolecular aurophilic interactions. Au 2 (μ-dcpe)I 2 displays a form of aggregation-induced emission. It displays a red-pink luminescence in crystalline form but is non-emissive in solution. [ABSTRACT FROM AUTHOR]

The structure of the gas-phase bimolecular complex formed between (E)-1-chloro-2-fluoroethylene and hydrogen fluoride is determined via Fourier transform microwave spectroscopy from 6.9-21.6 GHz. Although the complex adopts a geometry very similar to that of previously studied dihalosubstituted ethylene-HF species, trends observed in the values of structural parameters such as bond lengths, bond angles, and deviations of the primary hydrogen-bonding interaction from linearity provide information regarding the balance among electrostatic, steric, and resonance effects in the structures of these complexes. Consideration of the ab initio interaction potential between (E)-1-chloro-2-fluoroethylene and hydrogen fluoride suggests that it is the strength of the intermolecular bond formed between the hydrogen atom of HF and the fluorine atom of the substituted ethylene that plays the significant role in determining the geometry. In addition to determining the complete nuclear quadrupole coupling constant tensor for the (E)-1-chloro-2-fluoroethylene-HF complex, the corresponding tensor for (E)-1-chloro-2-fluoroethylene itself was measured with greater precision than previously availabe, including the first reported determination of the single, nonzero off-diagonal element, χab. [ABSTRACT FROM AUTHOR]

Various Grubbs-Hoveyda second-generation catalysts activated by intramolecular steric strain were prepared. The variant bearing a 9-anthracenyl group in the ligand moiety exhibited the highest catalytic activity. The new anthracenyl-type-activated catalyst was used in a ring-closing metathesis reaction to effectively provide a 4-substituted product effectively. [ABSTRACT FROM AUTHOR]

An algorithm is described for the interaction of a hierarchy of objects that seeks to circumvent a fundamental problem in coarse-grained modelling which is the loss of fine detail when components become bundled together. A “currants-in-jelly” model is developed that provides a flexible approach in which the contribution of the soft high-level objects (jelly-like) are employed to protect the underlying atomic structure (currants), while still allowing them to interact. Idealised chains were used to establish the parameters to achieve this degree of interaction over a hierarchy spanning four levels and in a more realistic example, the distortion experienced by a protein domain structure during collision was measured and the parameters refined. This model of steric repulsion was then combined with sets of predicted distance constraints, derived from correlated mutation analysis. Firstly, an integral trans-membrane protein was modelled in which the packing of the seven helices was refined but without topological rearrangement. Secondly, an RNA structure was ‘folded’ under the predicted constraints, starting only from its 2-dimensional secondary structure prediction. [ABSTRACT FROM AUTHOR]

The aim of this study was experimental and modelling analysis of the nanofiltration process used for the removal of chromium(III) ions from salt solution characterized by low pH. The experimental results were interpreted with Donnan and Steric Partitioning Pore (DSP) model based on the extended Nernst-Planck equation. In this model, one of the main parameters, describing retention of ions by the membrane, is pore dielectric constant. In this work, it was identified for various process pressures and feed compositions. The obtained results showed the satisfactory agreement between the experimental and modelling data. It means that the DSP model may be helpful for the monitoring of nanofiltration process applied for treatment of chromium tannery wastewater. [ABSTRACT FROM AUTHOR]

Density functional calculations indicate that, the steric and packing factors seem to play a much more significant role than the electronic effects in influencing the bending of the rhodium(I) complexes of bisphosphonitocarbaborane(12)s. [ABSTRACT FROM AUTHOR]