Bulky Moiety Research Articles

Push-Pull Zinc Phthalocyanine Bearing Hexa-Tertiary Substituted Carbazolyl Donor Groups for Dye-Sensitized Solar Cells.

An asymmetrical, push–pull phthalocyanine bearing bulky tert-butylcarbazolyl moieties as electron donor and carboxylic acid as anchoring group was synthetized and tested as a photosensitizer in dye-sensitized solar cells (DSSC). The new photosensitizer was characterized by 1H and 13C NMR, UV–Vis and mass spectrometry. The bulky tert-butylcarbazolyl moieties avoid the aggregation of the phthalocyanine dye. DFT studies indicate that the HOMO is delocalized throughout the π-electron system of the substituted phthalocyanine and the LUMO is located on the core of the molecule with a sizable electron density distribution on carboxyl groups. The new dye has been used as a photosensitizer in transparent and opaque dye-sensitized solar cells, which exhibit poor efficiencies related to a low Jsc.

Homolytic versus Heterolytic Hydrogen Evolution Reaction Steered by a Steric Effect.

Several H-H bond forming pathways have been proposed for the hydrogen evolution reaction (HER). Revealing these HER mechanisms is of fundamental importance for the rational design of catalysts and is also extremely challenging. Now, an unparalleled example of switching between homolytic and heterolytic HER mechanisms is reported. Three nickel(II) porphyrins were designed and synthesized with distinct steric effects by introducing bulky amido moieties to ortho- or para-positions of the meso-phenyl groups. These porphyrins exhibited different catalytic HER behaviors. For these Ni porphyrins, although their 1e-reduced forms are active to reduce trifluoroacetic acid, the resulting Ni hydrides (depending on the steric effects of porphyrin rings) have different pathways to make H2 . Understanding HER processes, especially controllable switching between homolytic and heterolytic H-H bond formation pathways through molecular engineering, is unprecedented in electrocatalysis.

Homolytic versus Heterolytic Hydrogen Evolution Reaction Steered by a Steric Effect

AbstractSeveral H−H bond forming pathways have been proposed for the hydrogen evolution reaction (HER). Revealing these HER mechanisms is of fundamental importance for the rational design of catalysts and is also extremely challenging. Now, an unparalleled example of switching between homolytic and heterolytic HER mechanisms is reported. Three nickel(II) porphyrins were designed and synthesized with distinct steric effects by introducing bulky amido moieties to ortho‐ or para‐positions of the meso‐phenyl groups. These porphyrins exhibited different catalytic HER behaviors. For these Ni porphyrins, although their 1e‐reduced forms are active to reduce trifluoroacetic acid, the resulting Ni hydrides (depending on the steric effects of porphyrin rings) have different pathways to make H2. Understanding HER processes, especially controllable switching between homolytic and heterolytic H−H bond formation pathways through molecular engineering, is unprecedented in electrocatalysis.

Alpha-Helical Membrane Protein Folding in “Mixed” and “Ideal” Bicelles

Lipid-detergent bicelles are often used in membrane protein studies as an alternative to micelles. The ideal bicelle model contains a segregated lipid core surrounded by a detergent rim, and their morphologies depend on the ratio of lipid to detergent (q-ratio). There are several reports that the most widely used bicelle, containing 1,2-dimyristoyl-sn-glycero-3-phosphocholine and 1,2-dihexanoyl-sn-glycero-3-phosphocholine, forms ideally mixed micelles at q-ratios below 0.5. To date, almost all membrane protein studies using isotropic bicelles, particularly solution NMR spectroscopy, have relied on q-ratios of ∼ 0.3 due to favorable tumbling properties. Designing bicelle mixtures with segregated lipid and detergent across a broad range of q-ratios is, therefore, of high interest for membrane protein applications. We investigated common bicelle mixtures with q-ratios of 0.0-1.0 and measured the short diameter, L, with SAXS. The diameter was previously shown to correspond with the mixing behavior reported by SANS and molecular dynamics simulations, with L equal to two lipid lengths in a lipid-segregated bicelle. All alkyl-chain lipid and detergent combinations with phosphocholine-like head groups form mixed micelles up to ∼ q-ratio = 0.5. Bicelles containing bulky moieties at detergent alkyl tails and head groups were additionally investigated, which we hypothesize will increase segregation between lipid and detergent components at q ratios less than 0.5. The mixtures most promising for ideal bicelle morphologies at low q-ratios were then used to investigate protein fold and backbone dynamics of a polytopic alpha-helical transmembrane protein using continuous-wave EPR and solution NMR spectroscopy. Our results suggest that lipid-protein interactions influence protein fold distinct from detergent-protein interactions.

Antioxidant properties of two novel lipophilic derivatives of hydroxytyrosol

Two novel lipophilic derivatives of the natural olive oil phenol, hydroxytyrosol (HT), were synthesized using 3,4-dihydroxyphenylacetic acid as starting material. Their antioxidant activities and kinetics compared to HT and TBHQ were assessed by Rancimat, Schaal Oven, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and deep-frying methods. All experiments, including kinetic data analysis based on the Arrhenius equation, utilized in assessing antioxidant activity except the DPPH assay revealed that the new lipophilic HT derivatives exhibited much stronger antioxidant activity than hydroxytyrosol. Tert-butylhydroquinone exhibited stronger antioxidant activity in bulk oil at 65 °C than the new HT derivatives, but showed much lower activity at higher temperatures (>110 °C). This demonstrates that the introduction of bulky alkyl moiety to the ortho-diphenolic structure of HT increased its antioxidant activity. It can be concluded that the new lipophilic HT derivatives satisfy industrial demands for bioactive compounds with strong antioxidant potential at high temperatures.

The morphology, self-assembly, and host-guest properties of cellulose nanocrystals surface grafted with cholesterol

Cellulose nanocrystals (CNC) were prepared using acid hydrolysis of cellulose fiber. The CNC modified topo-chemically by grafting of bulky cholesterol moieties which changed subsequent morphology, thermal behavior, lyotropic crystalline properties, and host-guest release behavior. Bond formation between the cellulose nanocrystals surfaces and cholesterol was confirmed by FT-IR and solid-state NMR. The product indicated strong hydrophobic characteristics with an ordered chiral nematic self-assembly. This novel biomaterials were exploited through uptake of folic acid as part of a preliminary host-guest system. The guest molecule released as a function of physiologically relevant pHs was examined.

Facile Synthesis of π-Conjugated Heteroaromatic Compounds via Weak-Base-Promoted Transition-Metal-Free C–N Coupling

A K2CO3-promoted transition-metal-free C–N coupling reaction was developed. When a solution of 1-(2-aminophenyl)-8-iodo­naphthalenes in DMSO was treated with 2.5 equivalents of K2CO3 and 5.0 equivalents of MeI, intramolecular C–N coupling reaction proceeded smoothly even at low temperature (room temperature) to afford various heteroaromatic compounds in good chemical yields. Additional experiments suggested that this reaction might have proceeded through an unusual SNAr reaction between haloarenes and a bulky tertiary amine moiety.

Cluster core growth upon the decarbonylation of cyclopentadienyl-iron-dicarbonyl ferrocenyltelluride CpFe(CO)2TeFc: Fe1Te1 to Fe3Te3

Formal substitution of aryl group on to the ferrocenyl in [CpFe(CO)(μ-TeR)]2 (R = Ar, Fc) complex dramatically changes its Fe2Te2 core structure and chemical properties. Introduction of electron-rich and bulky ferrocenyl moiety instead of Ph in [CpFe(CO)TePh]2 provide flattening of Fe2Te2 core in [CpFe(CO)(μ-TeFc)]2 (1), further photochemical decarbonylation resulting unusual [(CpFe)3(μ-TeFc)3(μ-CO)(CO)] cluster (2). The electrochemical oxidation of 1 shows two reversible one-electron oxidation waves attributed to oxidation of Fe2Te2 core. Chemical oxidation of 1 is accompanied by isomerization of its core and results in dicationic salt cis-[CpFe(CO)(μ-TeFc)]2 (PF6)2 (3).This study also provides an illustrative example of the increasing nuclearity in Fe1 → Fe2 → Fe3 row, upon the stepwise electron-compensating decarbonylation of iron-carbonyl complexes and (apart from this) insight into the distribution of toluene molecules inclusion inside the channels of crystals of compound 2.

Investigation of Anti-Inflammatory Potential of N-Arylcinnamamide Derivatives.

A series of sixteen ring-substituted N-arylcinnamanilides, previously described as highly antimicrobially effective against a wide spectrum of bacteria and fungi, together with two new derivatives from this group were prepared and characterized. Moreover, the molecular structure of (2E)-N-(2-bromo-5-fluorophenyl)-3-phenylprop-2-enamide as a model compound was determined using single-crystal X-ray analysis. All the compounds were tested for their anti-inflammatory potential, and most tested compounds significantly attenuated the lipopolysaccharide-induced NF-κB activation and were more potent than the parental cinnamic acid. (2E)-N-[2-Chloro-5-(trifluoromethyl)phenyl]-3-phenylprop-2-enamide, (2E)-N-(2,6-dibromophenyl)- 3-phenylprop-2-enamide, and (2E)-N-(2,5-dichlorophenyl)-3-phenylprop-2-enamide demonstrated the highest inhibition effect on transcription factor NF-κB at the concentration of 2 µM and showed a similar effectiveness as the reference drug prednisone. Several compounds also decreased the level of TNF-α. Nevertheless, subsequent tests showed that the investigated compounds affect neither IκBα level nor MAPKs activity, which suggests that the N-arylcinnamanilides may have a different mode of action to prednisone. The modification of the C(2,5)ʹ or C(2,6)ʹ positions of the anilide core by rather lipophilic and bulky moieties seems to be preferable for the anti-inflammatory potential of these compounds.

A Solid-State Fluorescence Sensor for Nitroaromatics and Nitroanilines Based on a Conjugated Calix[4]arene Polymer.

A new conjugated polymer possessing calix[4]arene-oxacyclophane units wired-in-series by phenyleneethynylene linkers was synthesized by a Sonogashira-Hagihara cross-coupling method in high yield. The polymer was structurally characterized by FTIR and 1H/13C/HSQC NMR techniques, and its average Mn (38.5kDa) retrieved from GPC analysis. The polymer is highly emissive (ΦF = 0.55) and exhibits a longer-than-usual excited-state lifetime (1.80ns) for a phenyleneethynylene type polymer. Similar photophysical properties (absorption and fluorescence emission) were observed in solution and in solid-state. This stems from the presence of bulky calixarene moieties along the polymer chains which prevent interchain staking and the formation of ground-state aggregates and/or non-emissive exciplexes, both deleterious to solid-state materials envisioned for fluorescence sensing applications. Moreover, the intrinsic molecular recognition capabilities of its two rigid inner cavities (calixarene and cyclophane sub-units), allied with the high three-dimensionality of the macromolecule that creates additional interstitial voids around the molecular receptors, can boost its sensory responses towards specific analytes. A high sensitive response was observed in the detection of nitroaromatics and nitroanilines in neat vapour phases by casted films of the polymer. The largest sensitivities were obtained for 2,4-dinitrotoluene (a taggant for the explosive TNT; > 85% of fluorescence quenching upon 1min exposure) and ortho-nitroaniline (90% of emission reduction in 30s). The sensory responses attained in solid-state are discussed on the basis of the electron affinities of the analytes and their electrostatic interactions with polymer films. Graphical Abstract Sensing the threats! A high sensitive response was observed in the detection of explosives and noxious nitroanilines in neat vapour phases by thinfilms of a calixarene-based polymer.

Aggregation−induced emissions in columnar wedge−shaped pyridinium−based ionic liquid crystals

Two series of ILCs derived from wedge−shaped N-phenylpyridiniums 1–2 were prepared and their mesomorphic properties were investigated. The X−ray crystal structure analyses of two single crystals 2-PF6 (n = 12) and 2-NTf2 (n = 12) revealed that bilayer structures induced by H−bonds in the solid state were observed. A complementary dimeric structure induced by H−bonds in such type of wedge−shaped cation (or anion) moiety was attributed to the formation of columnar phases. The type of counter anions has a significant influence on the formation of the mesophase; five counter anions (i.e. X = PF6‾, BF4‾, OTf‾, SCN‾, RSO3‾) induced columnar mesophase. In contrast, anion X = Tf2N‾ as a bulky moiety and less H−bond active sites formed crystal phase. The powder XRD data appeared that the diameter of the hard columnar part increased with the effective ionic radius for different counter ion. A linear correlation plot (R2 = 0.9203) was obtained. All ethanol solutions of compounds 1–2 were detected without any observable signals on photoluminescence. But compounds 2-X will aggregate in the aqueous mixture with high water fractions (ƒw) needed to turn on their light emission process. Weak PL signals are recorded at ƒw < 50% because the luminogens 2-OTf are fully dissolved and quenched in these solvent compositions. The PL intensity started to enhance at ƒw > 50% till it reached to the maximum intensity at ƒw ~70%.

π–π interaction effect in insertion polymerization with α-Diimine palladium systems

Control of branching densities of polyolefins by polymerization conditions is a great challenge in the field of α-diimine palladium catalyzed olefin (co)polymerization. In this contribution, a series of acenaphthene-based highly sterically hindered α-diimine ligands bearing bulky diarylmethyl moiety and corresponding palladium catalysts have been designed, synthesized, characterized and investigated for ethylene polymerization and copolymerization with several polar monomers. The π-π interaction between the acenaphthene moiety and the phenyl of diarylmethyl moiety was observed. It was suggested that this π-π interaction could freeze the N-aryl-bond rotation at room temperature, resulting in the enhanced axial steric bulk as well as the low branching densities of the polyethylene products. In contrast, at high temperature, the π-π interaction was weaken and resulted in significantly increased branching densities of polyethylene products, indicating branching densities of polyolefins are adjustable within a wide range by polymerization conditions using this catalytic system.

Solvent-Free Synthesis of Amidated Carboxymethyl Cellulose Derivatives: Effect on the Thermal Properties.

The present work explores the possibility of chemically modifying carboxymethyl cellulose (CMC), a widely diffused commercial cellulose ether, by grafting of hydrophobic moieties. Amidation of CMC, at high temperature and in heterogeneous conditions, was selected as synthetic tool for grafting on CMC a panel of commercially available amines (bearing long aliphatic chains, alkyl aromatic and heteroaromatic groups, more or less spaced from the cellulose backbone). The reaction was successfully carried out in absence of solvents, catalysts and coupling agents, providing a promising and more sustainable alternative to conventional amidation procedures. Relationships between the chemical structure of the obtained CMC derivatives and their thermal properties were carefully studied, with a particular attention to the thermal behavior. Grafting of aromatic and heteroaromatic alkyl amines, presenting a linear alkyl chain between CMC backbone and a terminal bulky moiety, allowed for efficiently separating the polysaccharide chains, improving their mobility and resulting in a consequent lowering of the glass transition temperature (Tg). The Tg values obtained (90–147 °C) were found to be closely dependent on both the size of the aliphatic spacer, the structure of the aromatic ring and the extent of amidation.

Silane‐functionalized graphene oxide/epoxy resin nanocomposites: Dielectric and thermal studies

ABSTRACTImproved dispersion of graphene oxide (GO) in the epoxy resin, as nanofiller, requires surface modification. Hence, functionalization of GO with small silane (GONSi) and bulky silane moieties (GOSi) has been carried out. Structural confirmation analysis of the prepared GO and modified forms have been performed using different analytical techniques. Cationic photocuring polymerization of pure aliphatic epoxy resin (CE) and loaded samples with GO, GOSi, or GONSi in amounts 0.5 and 1 wt % has been followed by FTIR. Loading of CE showed a passive effect for the modified filler on the conversion of the CE during photocuring, whereas the thermal stability of loaded epoxy resin is enhanced. Dielectric properties investigations revealed that the insulation feature of CE is not seriously reduced by the addition of GO or its modified forms. The secondary relaxation β process originating from the fluctuations of the side functional hydroxyl group can be described by the semi‐empirical Cole–Cole function. The dielectric loss values are decreasing in the order GONSi &gt; GOSi &gt; GO &gt; CE. Furthermore, it was found that the activation energy of the dynamic process is related to the conversion and to the ratio of the modified filler. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48253.

Conducting copolymers nanocomposite coatings with aggregation-controlled luminescence and efficient corrosion inhibition properties

Luminescent coatings may provide low-cost techniques for studying the corrosion mechanism of coatings and for getting an early indication of corrosion processes. Here, a series of conducting copolymers and their nanocomposites has been synthesized and the effect of adding bulky moieties and/or nanocomposite formation on the solubility, thermal stability, corrosion inhibition, and photoluminescence of these copolymer coatings has been investigated. A significant enhancement in both solubility and thermal stability of the copolymers has been demonstrated upon the nanocomposite formation or presence of bulky groups. The nanocomposites displayed an inhibition efficiency of 97% for mild steel corrosion in an acidic environment which is much higher than that of the corresponding copolymers. Interestingly, the as-prepared copolymers and nanocomposites with tert-butyl group displayed an aggregation-induced emission with quantum yields higher than analogs without the tert-butyl group. Quantum chemical calculations attributed this enhancement in the quantum yields to the change in the degree of π-π interactions between the polymer chains. Moreover, aggregation-controlled luminescence has been demonstrated for the prepared copolymers.

Phosphonic and Phosphinic Acid Derivatives as Novel Tyrosinase Inhibitors: Kinetic Studies and Molecular Docking.

A dozen of phosphonic and phosphinic acid derivatives containing pyridine moiety were synthesized and its inhibitory activity toward mushroom tyrosinase was investigated. Moreover, molecular docking of these compounds to the active site of the enzyme was performed. All the compounds (1-10) demonstrated the inhibitory effect with the IC50 and inhibition constants ranging millimolar concentrations. The obtained results indicate that the compounds show different types of inhibition (competitive, noncompetitive, mixed), but all of them are reversible inhibitors. The obtained outcomes allowed to make the structure-activity relationship (SAR) analysis. Compound 4 ([(benzylamino)(pyridin-2-yl)methyl]phenylphosphinic acid) revealed the lowest IC50 value of 0.3 mm and inhibitory constant of Ki 0.076 mm, with noncompetitive type and reversible mechanism of inhibition. According to SAR analysis, introducing bulky phenyl moieties to phosphonic and amino groups plays an important role in the inhibitory potency on activity of mushroom tyrosinase and could be useful in design and development of a new class of potent organophosphorus inhibitors of tyrosinase. Combined results of molecular docking and SAR analysis can be helpful in designing novel tyrosinase inhibitors of desired properties. They may have broad application in food industry and cosmetology.

Glass-forming non-symmetric bis-styryl-DWK-type dyes for infra-red radiation amplification systems

A series of D-π-A type organic dyes with bulky triphenylmethyl moiety containing 2,6-bis-(4-substituted)styryl-4H-pyran-4-ylidene donor (D) fragments and different electron acceptors (A) were synthesized and investigated, mostly for potential applications in organic solid-state lasers as infra-red (IR) radiation amplification medium. Dye glass transition temperature is above 99 °C with thermal stability in the region from 173 °C to 326 °C which was slightly influenced by the electron acceptor fragment attached to the 4H-pyrane ring in 4-position. Introducing substituents in 4-position within one of the styryl-fragments with stronger electron withdrawing properties decreased ASE excitation threshold values (Eth) up to 180 μJ/cm2 in dye spin-cast neat films and shifted photoluminescence and amplified spontaneous emission (ASE) processes into the infra-red (IR) region. Although more studies are required, some of the investigated non-symmetric bis-styryl-DWK-dyes show potential as a solution-processable gain medium for IR radiation amplification.

Synthesis of highly transparent and heat‐resistant polyimides containing bulky pendant moieties

AbstractA new diamine with bulky pendant biphenyl and ortho‐position dimethyl structures, 4,4′‐((1,1′‐biphenyl)‐4‐ylmethylene)bis(2,6‐dimethylaniline), was synthesized via a one‐pot reaction of 4‐biphenyl carboxaldehyde and 2,6‐dimethylaniline. The diamine was employed to polymerize with several dianhydrides via one‐step condensation under high‐temperature conditions. The light yellow or colorless polyimide (PI) films obtained were found to have cut‐off wavelengths in the range 286–358 nm and transmittance over 80% in the visible region (400–780 nm). Meanwhile, these PIs possessed excellent solubility in common organic solvents, even in low‐boiling‐point solvents such as chloroform (CHCl3), dichloromethane (CH2Cl2) and tetrahydrofuran. The glass transition temperatures (Tg) of the PIs were determined to exceed 343 °C, even to 456 °C. All PI films were flexible with a tensile strength of 78–119 MPa, a Young's modulus of 2.0–2.5 GPa and elongation at break of 4.0%–8.2%. Therefore, these colorless PIs can be used as candidate materials for flexible display substrates. © 2019 Society of Chemical Industry

Improved synthesis, X-ray structure, and antifungal activity of a sugar-psoralen conjugate: 4,4′-Dimethylxanthotoxol 2,3,4,6-tetra-O-Acetyl-β-D-glucoside

An improved synthesis for 4,4′-dimethylxanthotoxol 2,3,4,6-tetra-O-acetyl-β-D-glucoside (1) starting from resorcinol was developed. Crystallographic analysis of glucoside 1 indicated that the dihedral angles between the mean planes of the tricyclic ring system of adjacent molecules was 54.820(22)° probably due to the steric hindrance caused by the bulky O-glucoside moiety, which prevents the molecules from packing via π···π stacking between the tricyclic cores. The antifungal screening data revealed that glucoside 1 had higher inhibition than its parent compound 4,4′-dimethylxanthotoxol and azoxystrobin against Rhizoctonia solani, Pyricularia grisea, and Alternaria alternate Japanese pear pathotype, with the inhibitory rates of 75.4, 65.7 and 70.1%, respectively, at the 50 µg/mL concentration.

Novel polyhydrazides and polyoxadiazoles based on 1,3,4‐thiadiazole moiety in the main chain with high thermal stability, good solubility, and notable antimicrobial activity

ABSTRACTPolyoxadiazoles (PODs) and polyhydrazides (PHs) have wide potential applications; however, PODs are normally insoluble in organic solvents, do not melt, and do not express glass‐transition temperature (Tg), and also PHs do not have high‐temperature resistance. In this work, novel PHs based on 1,3,4‐thiadiazole in the polymer main chain were synthesized by low‐temperature polycondensation. New PODs were then obtained by cyclodehydration of the PHs. The thermal behavior, surface morphology, and crystalline structure were studied using differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and X‐ray diffraction. In addition, the viscosity, solubility, UV–visible absorption, and antimicrobial activity were examined. The new polymers showed melting, Tg, high thermal stability, good solubility in polar aprotic solvents, and significant antimicrobial activities. The enhanced solubility may be attributed to the ability of thiadiazole moiety to form hydrogen bonding with the solvent molecules. Also, it can be concluded that introducing 1,3,4‐thiadiazole and other bulky moieties like the oxadiazole ring into the polymer main chain encouraged more free volumes and weakened the chains packing; hence, the solubility was enhanced and Tg decreased without affecting the thermal stability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47770.