Solvent Attack Research Articles

A [2.2]Isoindolinophanyl-Based Carbene (iPC) Ligand: Synthesis, Electronic and Photophysical Properties, and Application in Photocatalysis.

Cyclic amino(alkyl) and cyclic amino(aryl) carbenes (cAACs/cAArCs) have been established as very useful ligands for catalytic and photonic applications of transition metal complexes. Herein, we describe the synthesis of a structurally related sterically demanding, electrophilic [2.2]isoindolinophanyl-based carbene (iPC) that bears a [2.2]paracyclophane moiety. The latter leads to more delocalized frontier orbitals and intense green fluorescence of (HiPC)OTf (2) from an intra-ligand charge transfer (1ILCT) state in the solid state. Base-promoted synthesis of the free carbene led to an unusual ring expansion and subsequent dimerization reaction, but the beneficial ligand properties can be exploited by trapping in situ at a metal center. The iPC ligand is a very potent π-chromophore, which participates in low energy metal-to-ligand (ML)CT transitions in [RhCl(CO)2(iPC)] (4) and IL-"through-space"-CT transitions in [Au(iPC)2]OTf (5). The steric demand of the iPC leads to high stability of 5 against air, moisture, or solvent attack, and ultralong-lived green phosphorescence with a lifetime of 185 μs is observed in solution. The beneficial photophysical and electronic properties of the iPC ligand, including a large accessible π surface area, were exploited by employing highly efficient energy transfer (EnT) photocatalysis in a [2+2] styrene cycloaddition reaction using 5, which outperformed other established photocatalysts in comparison.

Robust and self-healing under-liquid superlyophobic coating fabricated by a universal strategy for polar-nonpolar liquid separation

Surfaces showing desirable under-liquid superlyophobicity have attracted great interests due to their high potential applications, especially in the liquid separation. Nevertheless, it still remains a challenge to put forward a universal strategy to fabricate robust under-liquid superlyophobic surfaces with self-healing function. Herein, a highly durable and self-healing under-liquid superlyophobic coating is developed that can be applied onto various substrates (e.g., cotton, polyester, filter paper, wool, hemp, sponge, lyocell, etc.) via a two-step coating process, through depositing silica nanoparticles partially grafted by octadecylamine followed by crosslinking of polyurethane macromolecules containing polysorbate20. The obtained substrates show superamphiphilic in air, under-water superoleophobic and under-oil superhydrophobic properties. High-efficiency separations of polar-nonpolar liquids, e.g., water-heavy oil, water-light oil, immiscible organic liquid mixtures, can be achieved when the coated fabric was used as the separation membrane. Moreover, such under-liquid superlyophobic coating demonstrates excellent durability against repeated washing, long time UV irradiation, organic solvent attack, high temperature and plasma treatment. Even the coating surface is damaged chemically or physically, its original superwetting property can be recovered by a short time of heating treatment. This work could provide a guidance for developing durable under-liquid superlyophobic materials with self-healing ability for diversified applications, such as liquid separation, micro-fluid manipulation, anti-adhesive surfaces.

Reversible Growth of Halide Perovskites via Lead Oxide Hydroxide Nitrates Anchored Zeolitic Imidazolate Frameworks for Information Encryption and Decryption.

The low formation energies of metal halide perovskites endow them with potential luminescent materials for applications in information encryption and decryption. However, reversible encryption and decryption are greatly hindered by the difficulty in robustly integrating perovskite ingredients into carrier materials. Here, we report an effective strategy to realize information encryption and decryption by reversible synthesis of halide perovskites, on the lead oxide hydroxide nitrates (Pb13O8(OH)6(NO3)4) anchored zeolitic imidazolate framework composites. Benefiting from the superior stability of ZIF-8 in combination with the strong bond between Pb and N evidenced by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy, the as-prepared Pb13O8(OH)6(NO3)4-ZIF-8 nanocomposites (Pb-ZIF-8) can withstand common polar solvent attack. Taking advantage of blade-coating and laser etching, the Pb-ZIF-8 confidential films can be readily encrypted and subsequently decrypted through reaction with halide ammonium salt. Consequently, multiple cycles of encryption and decryption are realized by quenching and recovery of the luminescent MAPbBr3-ZIF-8 films with polar solvents vapor and MABr reaction, respectively. These results provide a viable approach to integrate the state-of-the-art materials perovskites and ZIF for applications in information encryption and decryption films with large scale (up to 6 × 6 cm2), flexibility, and high resolution (approximate 5 μm line width).

Photoreactivity and stability of flavonoid yellows used in cultural heritage

Flavonoid yellows are historical dyes widely found in cultural heritage, in particular those based on the glycosides of luteolin, quercetin and kaempferol. In this research, for the first time, the photodegradation quantum yields (ΦR) were calculated for luteolin, quercetin and kaempferol as well as their glycosides Lut-7-O-Glc, Que-3-O-Glr, Kaem-3-O-Glc and compared to the reactivity of eriodictyol. The results are discussed within the current state of the art on the mechanisms of degradation for these antioxidant compounds, which are reviewed in the introduction. ΦR values were obtained in solution irradiating at 313 nm and 366 nm, providing the quantification of the stability of flavonoid yellows. In particular, by irradiating at 366 nm, a very good stability scale is obtained, with ΦR values for luteolin and the 3-O-glycosides of quercetin and kaempferol on the order of 10−6. The more reactive quercetin and kaempferol are characterized by ΦR values of ca. 3 × 10−5. The relative stability of these yellows can be explained by a photoprotective mechanism based on excited state proton transfer, which is more efficient when there is an OH in the C5 position. In addition, electron transfer, and consequently oxidation, is also enhanced through the OH in position C3 when compared to C5.Solvents effects were also studied and to mimic the environment of the dye in wool, irradiation at 366 nm in a proteinaceous gel was carried out. In this gel, the ΦR values increased for all the molecules studied, reaching 1 × 10−4 and 2 × 10−4 for kaempferol and quercetin, respectively. This drastic enhancement shows that the environment has a major impact on stability. The main degradation products were also studied by irradiation with a xenon source (λirr ≥ 300 nm), and characterized by HPLC-DAD-MS and LC-HRMS/MS. These data, on the reaction mechanism, show that the double bond between C2 and C3, in the C ring, is the most reactive point of the molecules, as in all the flavonoids degradation started by solvent attack, followed in some cases by ring opening and the formation of low molecular weight hydroxyl compounds such as benzoic acids, in agreement with the general reaction scheme proposed in literature.

In-situ construction of a NaF-rich cathode–electrolyte interface on Prussian blue toward a 3000-cycle-life sodium-ion battery

As a kind of high-voltage cathode for sodium-ion batteries (SIBs), the instability of a cathode–electrolyte interface (CEI) of Prussian blue (PB) results in the consumption of electrolyte and poor cycling life. Herein, an artificial NaF-rich CEI is in-situ designed on a PB cathode via a chemically presodiated strategy to remarkably prolong the cycling life of SIBs. Based on a spontaneous redox reaction between a chemical presodiation solvent and a polyvinylidene fluoride (PVDF) binder, a homogeneous, thin, and NaF-rich CEI is conformally coated on the surface of PB, forming CEI@PB. The components of CEI within CEI@PB mainly comprise inorganic Na-salts (NaF, Na2CO3, and NaHCO3) and organic Na-based species (R-O-Na, R–CO–Na, and R–O2CO–Na), which can ensure the rapid transport of Na+ ions while effectively preventing CEI@PB against the attack of organic solvent and improving its cycling stability. Besides, density functional theory calculations also reveal that NaF is a good electronic insulator and ionic conductor, which is suitable as a stable CEI. Benefiting from the aforementioned merits, the CEI@PB cathode with a high areal capacity of 0.61 mAh cm−2 delivers an ultra-long cycling life of 3000 cycles. More importantly, the concept of in-situ CEI can be extended to other cathodes beyond Na batteries discussed herein.

Effect of Dehydrothermal Treatment on the Mechanical Properties and Biocompatibility of Plaster of Paris–CaCO3 Hydrogel Loaded With Cinnamaldehyde for Biomedical Purposes

CaCO3 hydrogel incorporation into Plaster of Paris (POP) formulations decreased the resorption rate of the POP after implantation in the body. Although an inflammatory process is required as part of wound healing, the accumulation and activation of inflammatory cells in the POP–hydrogel CaCO3 implant area needs to be controlled. Therefore, cinnamaldehyde, as an anti-inflammatory agent with a unique α, β-unsaturated aldehyde, was incorporated into the CaCO3 hydrogel. During the incorporation, both the lipophilic and hydrophilic sides of the cinnamaldehyde molecule can influence the physical and mechanical properties of the CaCO3 hydrogel, in which mechanical properties of a tissue engineering scaffold are important to fine tune cellular activity during implantation. On the other hand, as a 3-dimensional polymeric structure, crosslinking is needed for the CaCO3 hydrogel to stabilize and increase its molecular weight for better mechanical strength, and more resistance to heat, wear, and solvent attack. For that purpose, dehydrothermal treatment (DHT) was applied to the crosslink hydrogel system as a favorable crosslinking method to avoid the use of a chemical agent. In this study, 3 groups of hydrogels of CaCO3, namely DHT crosslinked, loaded with cinnamaldehyde, and loaded with cinnamaldehyde followed by DHT crosslinking were developed before being combined with POP in 50 wt%. To evaluate the effect of DHT to the final POP-cinnamaldehyde-loaded CaCO3 hydrogel properties and biocompatibility, scanning electron microscopy, contact angle, surface roughness, hardness, diametral tensile strength, and in vivo biocompatibility studies were conducted. It was observed that cinnamaldehyde with DHT treatment improved the POP–hydrogel CaCO3 properties and had good biocompatibility. Thus, POP-cinnamaldehyde-loaded CaCO3 hydrogel can be a promising bone substitute containing an anti-inflammatory agent.

Improvement of cellulose acetate dimensional stability by chemical crosslinking with cellulose nanocrystals

Low resistance to organic solvent attack is still a limitation in cellulose-derived polymer applications. In this work, cellulose acetate/cellulose nanocrystal composites were prepared using a bifunctional molecule, (3-Isocyanatopropyl)triethoxysilane, as a crosslinking agent. Thehydrolysis-condensation of the silane agent also resulted in the formation of a polysilsesquioxane network. The composite molecular structure, thermal behavior, and morphology were investigated by infrared spectroscopy; 29Si nuclear magnetic resonance; dynamic-mechanical analysis; and scanning and transmission electron microscopies. The morphological analyses of the composites indicated that the polysilsesquioxane domains and cellulose nanocrystals were uniformly distributed throughout the homogeneous crosslinked matrix. The effect of CNC addition and polysilsesquioxane network formation on the composite swelling and dimensional stability was remarkable, particularly for composites containing the highest CNC content.

Wood-Like Material from Thermoplastic Polymer and Landfill Bio-Materials: Dma, Tga and Solvent Resistance Properties

The aim of this work is to explore the potential application of chemically modified olive husk residue (OHR) as naturally occurring fillers to reinforce (Nylon-12) thermoplastic to produce a cost-effective wood like material. The Nylon-12/OHR composite material was fabricated via melt mixing of the Nylon-12 followed by the addition of chemically treated OHR at 180 and 50 rev.min−1 using Brabender internal mixer. The composites were characterized with respect to their dynamic mechanical properties, namely storage and viscous moduli (E′, E”), and mechanical loss factors (tan δ) using dynamic mechanical analyzer (DMA). The thermal stability of the samples with and without chemically treated OHR were examined using thermo-gravimetric analyzer (TGA). The chemical resistance of the composites was evaluated by immersing the samples in acidic and basic media and by exposing the samples to thermo-oxidative ageing (TOA) at 80C for 72h. The influence of TOA and immersion medium on the percentage weight loss, impact strength and hardness of the composites were reported. The effect of TOA and the solvent attack on the microstructure of the fractured samples was viewed by scanning electron microscope (SEM).

3-Trimethylsilylcyclobutylidene. The γ-Effect of Silicon on Carbenes

3-Trimethylsilylcyclobutylidene was generated by pyrolysis of the sodium salt of the tosylhydrazone derivative of 3-trimethylsilylcyclobutanone. This carbene converts to 1-trimethylsilylbicyclobutane as the major product. A labeling study shows that this intramolecular rearrangement product comes from 1,3-hydrogen migration to the carbenic center and not 1,3-silyl migration. Computational studies show two carbene minimum energy conformations, with the lower energy conformation displaying a large stabilizing interaction of the carbene center with the rear lobe of the C3-Si bond. In this conformation, the trimethylsilyl group cannot migrate to the carbene center, and the most favorable process is 1,3-hydrogen migration. When the carbene is generated photochemically in methanol, it reacts by a protonation mechanism giving the highly stabilized 3-trimethylsilylcyclobutyl carbocation as an intermediate. When generated in dimethylamine as solvent, the carbene undergoes preferred attack of this nucleophilic solvent from the back of this C-Si rear lobe stabilized carbene.

Molecular dynamics study of an insertion/duplication mutant of bacteriophage T4 lysozyme reveals the nature of α → β transition in full protein context

An α→β transition underlies the first step of disease causing amyloidogenesis in many proteins. In view of this, many studies have been carried out using peptide models to characterize these secondary structural transitions. In this paper we show that an insertion/duplication mutant 'L20' of bacteriophage T4 lysozyme (M. Sagermann, W. A. Baase and B. W. Matthews, Proc. Natl. Acad. Sci. U.S.A., 1999, 96, 6078) displays an α→β transition. We performed molecular dynamics (MD) simulation of L20, using the GROMACS package of programs and united atom GROMOS 53a6 force field for a time period of 600 ns at 300 K, in explicit water. Our MD simulation demonstrated that the transition occurs in a duplicated α-helical region inserted tandemly at the N-terminus of the 'parent' helix. We show that a C-terminal β-sheet anchors the parent helix while the loosely held N-terminal loop in the duplicate region is vulnerable to solvent attack and thus undergoes an α→β transition. Main chain-solvent interactions were seen to stabilize the observed β-structure. Thus L20 serves as a good protein model for characterization of α→β transition in a full length protein.

Comparison of Cu(II)-Promoted Leaving Group Stabilization of the Cleavage of a Homologous Set of Phosphate Mono-, Di-, and Triesters in Water, Methanol, and Ethanol

The cleavage of a set of phosphate mono-, di-, and triesters having a Cu(II)-complexed 2-phenanthrolyl group at the ortho-position of a departing phenoxide was studied in water and ethanol. Experimentally observed pH/rate profiles, solvent deuterium kinetic isotope effects, and activation parameters are compared with those obtained in methanol. The pH/rate profile in each solvent exhibits an extended plateau due to solvent attack on forms designated as [Cu(II):1b/c](0) for the monoester, [Cu(II):2b](+), for the diester, and [Cu(II):3a](2+) for the triester. The solvent dkie values (k(H)/k(D)) for the three complexes are 0.91, 0.95, and 0.83 for decomposition of [Cu(II):1b/c](0) in water (W), methanol (M), and ethanol (E), 1.22, 1.09, and 1.29 for [Cu(II):2b](+) in W, M, and E, and 1.94, 2.2, and 1.96 for [Cu(II):3a](2+) in W, M, and E. Near unit, or slightly inverse values for the monoester are taken as evidence for little involvement of solvent in a highly dissociative TS for P-OAr cleavage, with slightly higher solvent dkie values for the diester signifying the onset of some solvent participation in assisting the nucleophilic displacement. The larger primary dkie for the triester gives evidence for a solvent-assisted delivery of ROH in the cleavage through a more associative mechanism. Activation parameters for each substrate in the solvents are compared, indicating that the transition from methanol to ethanol for each substrate involves a near cancellation of the ΔΔH(‡) and -TΔΔS(‡) values (25 °C) so that the respective rates in both solvents are very similar. The transition from alcohol to water produces variable effects, with ΔΔH(‡) and -TΔΔS(‡) values canceling for cleavage of the triester and being additive for the mono and diester, explaining their 100-500 rate reduction in passing from methanol to water. The rate enhancing effects of the Cu(II)-promoted leaving group assistance in all three solvents are substantial and estimated at 10(12)-10(15) for the monoester, 10(12)-10(14) for the diester, and 10(5) for the triester relative to their background reactions.

Multilayer infrared metamaterial fabrication using membrane projection lithography

Membrane projection lithography is extended from a single layer fabrication technique to a multilayer process, adding polymeric backfill and planarization after each layer is completed. Unaligned contact lithography is used as a rapid prototyping tool to aid in process development, patterning resist membranes in seconds without requiring long e-beam write times. The fabricated multilayer structures show good resistance to solvent attack from subsequent process steps and demonstrate in-plane and out of plane multilayer metallic inclusions in a dielectric host, which is a critical step in the path to develop bulklike metamaterials at optical frequencies.

Stabilization of lithium metal anodes using silane-based coatings

For energy storage systems that use a charged cathode, the source of lithium is typically lithium metal. For several high energy systems under study, notably those that utilize elemental sulfur or oxygen (air) as the cathode, their very high capacity makes lithium metal anodes essential. In this study we evaluated the cycling performance of a series of silane-based coatings formed on a cleaned lithium metal surface before exposure to electrolyte. These substituted silane (R 3Si-) based coatings are formed from the self-terminating reaction of the R 3Si-Cl with lithium surface hydroxyl groups. The cycling performance of a trimethyl silyl coated surface and a triisopropyl silyl coated surface were compared to an uncoated sample and the results explained by a combination of surface coverage density and the ability of the coating to inhibit free solvent attack of the metal electrode surface.

ChemInform Abstract: Formation and Reactivity of 1-Pyrrolyl-2,2,2-trifluoroethyl Cations.

1-(1-Methyl-2-pyrrolyl)-2,2,2-trifluoroethyl p-nitrobenzoate (3) reacts by carbocation formation with an m value for the dependence of rate on the solvent polarity parameter YOTs of 0.56, and a rate 41 times slower than (1-methyl-2-pyrrolyl)methyl p-nitrobenzoate. The products from 3 include significant amounts of material derived from solvent attack at the 5-position of the pyrrole ring. The results indicate a high degree of charge delocalization by the strongly donating pyrrolyl group, resulting in a low k(H)/k(CF3) rate ratio and nucleophilic attack on the ring. 1,1, l-Trifluoro-2-(1-methyl-2-pyrrolyl)propan-2-ol (10) reacted with CF3CO2H via a tertiary carbocation, which led to dimeric products resulting from electrophilic substitution on the pyrrole ring. Keywords: pyrrole, trifluoromethyl substituents, carbocations.

The Role of Solvent on the Mechanism of Proton Transfer to Hydride Complexes: The Case of the [W3PdS4H3(dmpe)3(CO)]+ Cubane Cluster

The kinetics of reaction of the [W(3)PdS(4)H(3)(dmpe)(3)(CO)](+) hydride cluster (1(+)) with HCl has been measured in dichloromethane, and a second-order dependence with respect to the acid is found for the initial step. In the presence of added BF(4) (-) the second-order dependence is maintained, but there is a deceleration that becomes more evident as the acid concentration increases. DFT calculations indicate that these results can be rationalized on the basis of the mechanism previously proposed for the same reaction of the closely related [W(3)S(4)H(3)(dmpe)(3)](+) cluster, which involves parallel first- and second-order pathways in which the coordinated hydride interacts with one and two acid molecules, and ion pairing to BF(4) (-) hinders formation of dihydrogen bonded adducts able to evolve to the products of proton transfer. Additional DFT calculations are reported to understand the behavior of the cluster in neat acetonitrile and acetonitrile-water mixtures. The interaction of the HCl molecule with CH(3)CN is stronger than the W-H...HCl dihydrogen bond and so the reaction pathways operating in dichloromethane become inefficient, in agreement with the lack of reaction between 1(+) and HCl in neat acetonitrile. However, the attacking species in acetonitrile-water mixtures is the solvated proton, and DFT calculations indicate that the reaction can then go through pathways involving solvent attack to the W centers, while still maintaining the coordinated hydride, which is made possible by the capability of the cluster to undergo structural changes in its core.

Kinetic study of Orange II oxidation using peroxynitrous acid

AbstractThe reaction of Orange II with peroxynitrous acid has been studied by a spectrophotometrical method. The reaction rate is complex because the order changes from zero to one in function of substrate and oxidant concentration. The influence of pH and ionic strength has been investigated, but their effect on the reaction rate appears to be negligible under the experimental conditions used. A reaction mechanism based on the experimental results is proposed, involving a radical cage solvent attack from peroxynitrous acid to Orange II. Copyright © 2009 John Wiley & Sons, Ltd.

Solubility of Structurally Complicated Materials: 3. Hair

Hair is composed of proteins, lipids, water, and small amounts of trace elements. All proteins in animal and human bodies are built from permutations of amino acid molecules in a polypeptide string. The polypeptide chains of protein keratin are organized into filaments in hair cells. Hair is one of the most difficult proteins to digest or solubilize. Among the most common dissolving procedures for hair are acidic, alkaline, and enzymatic hydrolysis. For the analysis of hair, the solid samples are transferred by solubilization via digestion into a liquid phase. Small molecular solvents and molecules with hydrophobic groups appear to have higher affinity for hair. A good solvent attacks the disulfide bonds between cystine molecules and hydrates the hair shaft. Consequently, the hair becomes a jelly-like mass.

Highly Stable Organic Monolayers for Reacting Silicon with Further Functionalities: The Effect of the C−C Bond nearest the Silicon Surface

Crystalline Si(111) surfaces have been alkylated in a two-step chlorination/alkylation process using various organic molecules having similar backbones but differing in their C-C bond closest to the silicon surface (i.e., C-C vs C=C vs C[triple bond]C bonds). X-ray photoelectron spectroscopic (XPS) data show that functionalization of silicon surfaces with propenyl magnesium bromide (CH3-CH=CH-MgBr) organic molecules gives nearly full coverage of the silicon atop sites, as on methyl- and propynyl-terminated silicon surfaces. Propenyl-terminated silicon surface shows less surface oxidation and is more robust against solvent attacks when compared to methyl- and propynyl-terminated silicon surfaces. We also show a secondary functionalization process of propenyl-terminated silicon surface with 4'-[3-Trifluoromethyl-3H-diazirin-3-yl]-benzoic acid N-hydroxysuccinimide ester [TDBA-OSu] cross-linker. The Si-CH=CH-CH3 surfaces thus offer a means of attaching a variety of chemical moieties to a silicon surface through a short linking group, enabling applications in molecular electronics, energy conversion, catalysis, and sensing.

Covalent Molecular Assembly in a Supercritical Medium: Formation of Nanoparticles Encapsulated in Immobilized Dendrimers

This work demonstrates the feasibility of forming metallic nanoparticles within the confines of dendrimer-laden ultrathin films that are immobilized on a solid surface. The functional property of the poly amido amine dendrimer (PAMAM) as a sequestering agent for Cu nanoparticles was exploited by the introduction of copper acetylacetonate (Cu(acac)2) as a precursor. The nanoparticle precursors were introduced into the matrix using supercritical carbon dioxide and liquid tetrahydrofuran (THF) as processing media. The precursors were subsequently reduced to form the nanoparticles. The resulting film assemblies were characterized via X-ray photoelectron and UV−visible absorption spectroscopies, atomic force, scanning electron, transmission electron microscopies, and ellipsometry. Higher yield, a denser distribution of nanoparticles, and greater stability toward polar solvent attack were observed when the structures were assembled in supercritical CO2 than when THF was employed. TEM images revealed that the embedded nanoparticles are fairly tightly distributed in terms of size with an average diameter of 7 nm.

Effects of Conformation on the Stereochemistry of Solvent Attack on Benzylic β-Hydroxycarbocations: Mechanisms of Epoxide Hydrolysis Reactions

The rates and products from the acid-catalyzed and the pH-independent reactions of two diastereomeric 6-methoxy-trans-1,2,3,4,4a,10a-hexahydrophenanthrene 9,10-oxides (5b and 7b), along with their cis and trans chlorohydrins, have been determined in dioxane/water solutions. The mechanisms of the acid-catalyzed hydrolysis of 5b and 7b involve rate-limiting formation of benzylic carbocations (6b and 8b), which have sufficient lifetimes to be trapped by azide ion. Each carbocation is stabilized by the 6-methoxy group and held in single conformation by the adjacent trans-fused cyclohexane ring. The stereochemistry of the attack of water on each carbocation is independent of whether the precursor is an epoxide, a cis chlorohydrin, or a trans chlorohydrin, and the major diol hydrolysis product from each compound results from the axial attack of a solvent molecule on the carbocation intermediate. The hydrolysis of the trans chlorohydrin formed from the reaction of 5b with HCl exhibits a common ion rate depression. The major product from the pH-independent reaction of 5b is a trans diol, and the major product from the pH-independent reaction of 7b is an isomeric ketone. The rate of the pH-independent reaction of 7b is >10(4) times faster than that of 5b.