Nonpolar Solutions Research Articles

A Generic Method for Rational Scalable Synthesis of Monodisperse Metal Sulfide Nanocrystals

A rational synthetic method is developed to produce monodisperse metal sulfide nanocrystals (NCs) in organic nonpolar solutions by using (NH(4))(2)S as a sulfide precursor. (NH(4))(2)S is stabilized in an organic primary amine solution and exhibits high reactivity toward metal complexes. This novel technique exhibits wide applicability for organic phase metal sulfide NC synthesis: a large variety of monodisperse NCs have been synthesized, including Cu(2)S, CdS, SnS, ZnS, MnS, Ag(2)S, and Bi(2)S(3). The stoichiometric reactions between (NH(4))(2)S and metal salts afford high conversion yields, and large-scale production of monodisperse NCs (more than 30 g) can be synthesized in a single reaction. The high reactivity of (NH(4))(2)S enables low temperature (<100 °C) syntheses, and the air-stable materials (such as CdS NCs) can be produced in air. Moreover, this low-temperature technique can be used to produce small size NCs which are difficult to be synthesized by the conventional high temperature methods, such as sub-5 nm Ag(2)S and Bi(2)S(3) quantum dots.

Photodynamics of intramolecular proton transfer in polar and nonpolar biflavonoid solutions

Using methods of steady state luminescence and femtosecond spectroscopy, we have studied the mechanism of intramolecular proton transfer in synthesized 3,7-dihydroxy-2,8-di(4-methoxyphenyl)-4H,6H-pyrano[3,2-g]chromen-4,6-dion in polar and nonpolar solutions, films, and polycrystals at 293 and 77 K. In an excited singlet state, intramolecular proton transfer occurs in two stages. At the first stage, a tautomer with one transferred proton (OTP tautomer) is formed from the Franck-Condon state within τ1 = 0.6 ps. At the second stage, the second proton is transferred within τ2 = 3.1 ps and a tautomer with two transferred protons (TTP tautomer) is formed, which fluoresces in toluene at 293 K with a high quantum yield, Φ f = 0.66, and the fluorescence spectrum of which is characterized by a large Stokes shift, 9900 cm−1. At 293 K, polar solvents (dimethylformamide, dimethyl sulfoxide, ethanol, etc.) solvate the BFV molecule in the ground state, while, in the excited state, an OTP tautomer is mainly formed. In polar ethanol at 77 K, a dual fluorescence spectrum is observed, which is caused by the fluorescence emission of polysolvates with λ max f = 460 nm and TTP phototautomers at λ max f = 610 nm.

Synthesis and Self-Association of Double-Helical AADD Arrays

The design and syntheses of four self-complementary oligomers that contain an underlying AADD hydrogen bond sequence are presented, and their self-association was examined in the solution and solid state. The molecular recognition between the two strands is highly sensitive to substitutions of their component heterocycles. Substitution with electron-donating and -withdrawing groups and the influence of preorganization has a large effect on the overall stabilities of the complexes studied. In particular, a wide range (>10(5) M(-1)) of stabilities with respect to substitutions at various positions in the AADD oligomers was demonstrated. In the most extreme case, the dimerization constant measured (K(dimer) ≥4.5×10(7) M(-1)) is comparable to the most stable homodimers of neutral AADD arrays reported to date.

Effects of Trace Water on Charging of Silica Particles Dispersed in a Nonpolar Medium

This paper presents an investigation of the effects of trace water on the charging of silica (SiO(2)) particles dispersed in a nonpolar medium. There are a growing number of applications that seek to use electrostatic effects in apolar media to control particle movement and aggregation stability in such systems. One factor that is often overlooked in the preparation of nonpolar colloidal dispersions is the amount of water that is introduced to the system by hygroscopic particles and surfactants. The amount and location of this water can have significant effects on the electrical properties of these systems. For nonpolar surfactant solutions it has been shown that water can affect the conductivity, and it has been speculated that this is due to swelling of the polar cores of inverse micelles, increasing the fraction of them that are charged. Some studies have suggested that particle surface charging may also be sensitive to water content, but a clear mechanism for the process has not been fully developed. The situation with particles is further complicated by the fact that it is often unclear whether the water resides on the particle surfaces or in the polar cores of inverse micelles. The current work explores not only the effect of water content on reverse micelle and particle charging but seeks to differentiate between water bound to the particles and water located in the micelles. This is accomplished by measuring the solution conductivity and the electrophoretic mobility of silicon dioxide particles dispersed in solutions of Isopar-L and OLOA 11000. The water content is determined for both the dispersion and the supernatant after centrifuging the particles out. It is found that at equilibrium the majority of the water in the system adsorbs to the surface of the hygroscopic silica particles. In addition, the effect of water on particle electrophoretic mobility is found to be dependent on surfactant concentration. At small OLOA concentrations, additional water results in an increase in particle mobility due to increased particle charging. However, at large OLOA concentrations, additional water leads to a decrease in particle mobility, presumably as a result of increased electrostatic screening or neutralization. Thus, particle charging and electrophoretic mobility in an apolar surfactant solution are found to be highly sensitive to both the total water content in the system and to its concentration relative to the amount of surfactant present.

Analysis of amino acid contributions to protein solubility using short peptide tags fused to a simplified BPTI variant

Protein solubility is usually characterized in terms of a hydrophobicity scale, which refers to the free energy of transfer of a molecule from an aqueous to a nonpolar solution and is not a “solubility propensity scale” per se. Using a “host–guest” approach, we measured the effects of short poly-amino-acid tags (guests) on the solubility of a host protein, a simplified bovine pancreatic trypsin inhibitor (BPTI), to which they were fused at the C-terminus. We analyzed 10 amino acid types, representing the full range of biophysical properties (acidic, basic, polar, and hydrophobic). As anticipated, positively charged residues significantly increased the solubility of the model protein, at both pH 4.7 and 7.7, whereas very hydrophobic poly-Ile markedly reduced the solubility of BPTI. Poly-Asp and poly-Glu barely affected BPTI solubility at pH 4.7, but induced an eight to ten-fold increase at pH 7.7, attributable to the ionization of their side chains. Although Pro is the most soluble amino acid, poly-Pro did not affect the protein's solubility. The effects of the other tags on BPTI solubility ranged from none to an eight-fold increase. To ensure that the measured solubility values were context independent and could provide a “solubility propensity scale”, we confirmed that the tags remained independent of the structure, thermal stability, and biochemical activity of the host protein. These observations suggest that this approach is valuable for measuring the solubility propensities of amino acids, which could eventually allow the calculation of a polypeptide's relative solubility from its amino acid sequence.

Influence of the Environment on the Protective Effects of Guaiacol Derivatives against Oxidative Stress: Mechanisms, Kinetics, and Relative Antioxidant Activity

The peroxyl radical scavenging activity of five guaiacol derivatives (GD) has been studied in nonpolar and aqueous solutions, using the density functional theory. The studied GD are guaiacol, vanillin, vanillic alcohol, vanillic acid, and eugenol. It was found that the environment plays an important role in the peroxyl scavenging activity of these compounds. They were all found to react faster in aqueous solution than in nonpolar media. The order of reactivity in nonpolar environments was found to be vanillic alcohol > eugenol > guaiacol > vanillin > vanillic acid, while, in aqueous solution, at physiological pH, it becomes vanillic acid > vanillic alcohol > guaiacol ≈ eugenol > vanillin. It was also found that in aqueous solution as the pH increases so does the reactivity of GD toward peroxyl radicals. The environment also has important effects on the relative importance of the hydrogen transfer (HT) and the sequential proton electron transfer (SPET) mechanisms, which are the ones relevant to the peroxyl radical scavenging activity of GD. The HT from the phenolic OH was identified as the main scavenging process in nonpolar media, and in aqueous solution at pH ≤ 4. On the other hand, SPET is proposed to be the one contributing the most to the overall peroxyl scavenging activity of GD in aqueous solution at pH ≥ 6.

Nonpolar Solvothermal Fabrication and Electromagnetic Properties of Magnetic Fe3O4 Encapsulated Semimetal Bi Nanocomposites

Magnetic Fe3O4 nanoparticles (NPs) encapsulated semimetal Bi nanocomposites were fabricated by a solvothermal method based on the nonpolar 1-octadecene. Bi and Fe ions were introduced into the oil phase by the complex with sodium oleate in the as-prepared solution. The nanocomposites were oil soluble and dispersed well in any nonpolar solution with the surface modification of oleic acid. It is argued that hydroxyl groups as the reductant induce the formation of Bi microspheres and prevent Fe3O4 NPs from oxidation. The frequency dependence of complex permittivity and permeability indicates that Bi and interface polarization of Bi/Fe3O4 nanocomposites are responsible for the dielectric resonances, and superparamagnetic Fe3O4 NPs weaken the natural resonance.

Acetylated microfibrillated cellulose as a toughening agent in poly(lactic acid)

AbstractComposites from poly(lactic acid) (PLA) and acetylated microfibrillated cellulose (MFC) were prepared by a solvent casting technique. MFC, mechanically isolated from never‐dried bleached birch Kraft pulp, was used as a reinforcement. The acetylation reaction was carried out at 105°C in toluene and proved to be an effective way of increasing the dispersion of MFC in a nonpolar solution of PLA in chloroform. The maximum acetyl content (10.3%) was achieved after 30 min of reaction time. This could be translated to a degree of substitution (DS) of 0.43. The acetylation was confirmed by Fourier transform infrared spectroscopy. MFC with a higher DS exhibited a more pronounced effect on the properties of PLA. Mechanical testing showed that Young's modulus increased by approximately 70% and the tensile strength increased by approximately 60% at a fiber weight fraction of 20%. At an MFC loading of 10 wt %, the strain at break and toughness, expressed as the work of fracture, increased by around 500%. The Young's modulus increased by approximately 15%, whereas the tensile strength remained the same. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2012

2-(4-Pyridyl)imino nitroxide-tetraphenylporphyrin zinc(II): A chemosensing ensemble for nicotine

2-(4-Pyridyl)imino nitroxide and tetraphenylporphyrin zinc(II) formed a stable complex by noncovalent bonding in a nonpolar solution. Nicotine displaced 2-(4-pyridyl)imino nitroxide when it was added to a solution of 2-(4-pyridyl)imino nitroxide-tetraphenylporphyrin zinc(II). The fluorescence intensity of tetraphenylporphyrin zinc(II) was altered by sequentially addition of 2-(4-pyridyl)imino nitroxide and nicotine. This was used to develop a new method for detection of nicotine.

On the peroxyl scavenging activity of hydroxycinnamic acid derivatives: mechanisms, kinetics, and importance of the acid–base equilibrium

The peroxyl radical scavenging activity of four hydroxycinnamic acid derivatives (HCAD) has been studied in non-polar and aqueous solutions, using the density functional theory. The studied HCAD are: ferulic acid (4-hydroxy-3-methoxycinnamic acid), p-coumaric acid (trans-4-hydroxycinnamic acid), caffeic acid (3,4-dihydroxycinnamic acid), and dihydrocaffeic acid (3-(3,4-dihydroxyphenyl)-2-propionic acid). It was found that the polarity of the environment plays an important role in the relative efficiency of these compounds as peroxyl scavengers. It was also found that in aqueous solution the pH is a key factor for the overall reactivity of HCAD towards peroxyl radicals, for their relative antioxidant capacity, and for the relative importance of the different mechanisms of reaction. The H transfer from the phenolic OH has been identified as the main mechanism of reaction in non-polar media and in aqueous solution at acid pHs. On the other hand, the single electron transfer mechanism from the phenoxide anion is proposed to be the one contributing the most to the overall peroxyl scavenging activity of HCAD in aqueous solution at physiological pH (7.4). This process is also predicted to be a key factor in the reactivity of these compounds towards a large variety of free radicals.

An approach towards optimal usage of immobilized sensor chips in Surface Plasmon Resonance based biosensor

In recent decades, there was a surge of interest in Surface Plasmon Resonance (SPR) biosensor based bimolecular interaction analysis. The unique characteristics of this technique made it possible to measure real time unlabelled bimolecular interactions with great sensitivity. However, the major challenge in SPR is providing the ability to re-use the surface of the chip. The main goal of this study was to address the problem faced in establishing an ideal regeneration condition and removing non-covalently bound analyt without disturbing ligand. Considering four different types of proteins including virus, hormone, cells and antibody, a comprehensive regeneration protocol for protein-protein interaction was developed and compared with common regeneration methods. The presented protocol screened five multi-ingredient stock solutions that represented the five most common chemical properties such as acidic, basic, ionic, chelating and non-polar water soluble solvent solutions employed as regeneration agents. Upon three cycles of screening, it was found out that enveloped virus–antibody complexes could be effectively regenerated via a combination of acidic and chelating solution whilst non-enveloped viruses needed a basic solution for successful regeneration. Both insulin-antibody and cell-enveloped virus complexes could be detached efficiently using acidic solutions. Regenerations using non-polar water soluble solvents presented a harsh reaction, whilst ionic solutions were too mild. Thus, incomplete regeneration occurred. In summary, this study will serve as a platform of reference for multiple regenerations for a cluster of protein-protein complexes. Key words: Surface Plasmon Resonance (SPR), regeneration, virus, insulin, monoclonal antibody, cell.

Efficient Photochromic Transformation of a New Fluorenyl Diarylethene: One- and Two-Photon Absorption Spectroscopy

Efficient reversible phototransformation of a new diarylethene-fluorene derivative, 1,2-bis(5-(9,9-didecyl-7-nitro-9H-fluoren-2-yl)-2-methylthiophen-3-yl)cyclopent-1-ene (1), was demonstrated in organic media under low-intensity laser excitation. Linear photophysical characterization of 1 was performed at room temperature in solvents of different polarity and viscosity. Significantly, close to unity quantum yield for the cyclization reaction of 1 was shown in nonpolar solutions. The lifetimes of the excited states of the open (OF) and closed (CF) forms of 1 were measured by a femtosecond transient absorption technique, and corresponding values of ∼0.7 and ∼0.9 ps were shown in dichloromethane (DCM), respectively. Degenerate two-photon absorption (2PA) spectra of the OF and CF of 1 were obtained over a broad spectral range by the open aperture Z-scan method under 1 kHz femtosecond excitation. The values of 2PA cross sections of the OF in DCM (∼50-70 GM) were found to increase up to 1 order of magnitude (∼600 GM) after cyclization to the CF. The nature of cyclization and cylcoreversion processes were investigated by quantum chemistry with employment of DFT-based methods implemented in the Gaussian'09 program. The potential of 1 for application in optical data storage was shown using poly(methyl methacrylate)-doped films and two-photon fluorescence microscopy readout.

Local Structure around Dopant Site in Ga-Doped ZnO from Extended X-ray Absorption Fine Structure Measurements

The local structure around dopant sites in Ga-doped ZnO (GZO) films has been compared with that of Zn sites by means of X-ray absorption fine structure (XAFS) measurements. The near-edge part of XAFS (XANES) showed that the Ga 3+ ions occupied the Zn sites substitutionally in GZO. It was found, from the analysis of the extended part of XAFS (EXAFS), that the first nearest Ga–O distances were shorter than Zn–O distances, which is consistent with Ga 3+ having a smaller ionic radius than Zn 2+ . The next nearest Ga–Zn distances were found, on the contrary, to be longer than Zn–Zn distances. This agrees with the behavior of the lattice constants of GZO, which increase with Ga concentration. We argue that these behaviors are the result of a Coulomb interaction originating from the excess charge at the dopant Ga site, which does not arise in nonpolar solid solutions.

Theoretical and infrared studies on the conformations of monofluorophenols

Abstract Theoretical calculations for the isolated state indicate the presence of two conformers ( A and B ) for 2- and 3-fluorophenols, while a single form exists for 4-fluorophenol, as it is well known. The conformer with the hydroxyl hydrogen directed toward the fluorine atom ( A ) in 2-fluorophenol is calculated to be significantly more stable than the second form, while similar behavior is not obtained for the meta isomer. The infrared C–F stretching intensities confirm these findings in cyclohexane solution, where internal hydrogen bonding in 2-fluorophenol is supposed to be a stabilizing effect of A , but the figure changes in acetonitrile solution and neat liquid, where the most polar conformer B is preferred and intermolecular hydrogen bonding seems to take place, as confirmed by the broadening and shifting of the O–H stretching band. In fact, the strong solvent effect in 2-fluorophenol suggests that conformer A is the most stable form in the isolated state and nonpolar solution predominantly due to dipolar repulsion in B .

Cis,cis-1,3,5-Trihydroxynonamethylcyclohexasilane: A Cyclopolysilane with Unusual Properties

cis,cis-Trihydroxynonamethylcyclohexasilane (2) is easily accessible by the controlled hydrolysis of Cl3Si6Me9 in the presence of Et3N as an auxiliary base. The crystal structure of 2, as determined by single-crystal X-ray crystallography, exhibits “barrel-type” face-to-face dimeric aggregates held together by six intermolecular hydrogen bonds. NMR and IR spectra suggest that these OH-bonded aggregates are also present in nonpolar solutions. Full geometry optimization (B3LYP/TZVP) of the gas-phase structure of 2 further reveals unusually high energy differences between different conformers and a considerable stabilization of the molecule upon dimerization due to O−H hydrogen bonding. Time-dependent DFT B3LYP/TZVP calculations allow for a detailed interpretation of the UV absorption spectra of 2. The electronic transitions occur between occupied molecular orbitals with predominant σ(Si−Si) character and a small contribution of the oxygen lone pairs, and virtual MOs with contributions from σ*(Si−C), σ*(Si−O), and σ*(Si−Si) type orbitals. If 2 is reacted with MeSiCl3/Et3N, the adamantane-like cage MeSi(O3Si6Me9) (4) is obtained without the formation of considerable amounts of polymeric material, which is most likely a consequence of the preferred conformation of 2 with three adjacent OH groups in axial positions.

Cyclization Reaction Dynamics of a Photochromic Diarylethene Derivative as Revealed by Femtosecond to Microsecond Time-Resolved Spectroscopy

Cyclization reaction of a photochromic diarylethene derivative, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene (BT), in nonpolar alkane solutions with different viscosity was investigated by means of femtosecond−microsecond transient absorption spectroscopy and a time-correlated single-photon counting method. Transient absorption measurements revealed that a ring closure rapidly occurred with a time constant of 450 fs. In addition to this rapid cyclization, transient species with longer lifetimes (ca. 150 ps and ca. 1 μs) were observed. The faster time constant of 150 ps was independent of the solvent viscosity and was assigned to the fluorescence lifetime of a conformer with molecular geometry unfavorable for the ring closure. The longer component was strongly quenched in the solution purged with O2 and was attributed to the triplet state of the open-ring form. Steady-state measurement and nanosecond transient absorption spectroscopy revealed that the cyclization process did not occur via the trip...

Throwing light on dark states of α-oligothiophenes of chain lengths 2 to 6: radical anion photoelectron spectroscopy and excited-state theory

In this work, we apply photodetachment photoelectron spectroscopy (PD-PES) on radical anions to access the lowest excited electronic states of neutral α-oligothiophenes nT (n = 2-6, where n denotes the number of thiophene rings) in the gas phase. Besides electron affinities, the spectra provide the energies of the T(1) and T(2) states which are otherwise difficult to investigate in neutral molecules due to spin selection rules. The assignment of the spectra is assisted by quantum chemical calculations using a combined density functional theory and multi-reference configuration interaction approach. For all α-oligothiophenes investigated in this work, the T(2) state is situated below S(1). In the gas phase, the S(1) state energies lie higher than in non-polar solution (0.2 to 0.4 eV). The geometry optimizations show that the S(0) state and especially the excited states gain planarity with increasing chain length. A non-planar structure or out-of-plane vibrational activity is needed to allow an efficient intersystem crossing (ISC) dynamics from S(1) to T(2), followed by internal conversion to T(1). Our theoretical calculations predict that in 6T a doubly excited state becomes nearly isoenergetic to S(1). This state is not observed by PD-PES, which is explained by the analysis of the calculated contributing electron configurations.

Color tuning of Novel 2,1,3-Naphthothiadiazole and 2,1,3-Benzoselenadiazole based D-A-D′ Type dopants to realize highly efficient saturated red emission in non-polar solvents

By introduction of 2,1,3-naphthothiadiazole (NT) and 2,1,3-benzoselenadiazole (BS) electron withdrawing units, a series of D-A-D′ type red dopants were synthesized. All of them realized saturated red emission with high fluorescent quantum yields (Φf) in non-polar toluene solutions, especially for MC6, which shows a deep red emission at 643 nm with a Φf of 0.51.

ChemInform Abstract: Intramolecular Excited-State Proton Transfer in Jet-Cooled 2- Substituted 3-Hydroxychromones and Their Water Clusters.

Intramolecular excited‐state proton transfer (ESPT) of 3‐hydroxychromone (3‐HC), 3‐hydroxyflavone (3‐HF) and 2‐(2‐naphthyl)‐3‐hydroxychromone (2‐NHC), and of their water clusters, was investigated in a supersonic expansion. The visible tautomer fluorescence excitation spectra of these compounds exhibit considerably well‐resolved vibrational structures, while no significant uv fluorescence excitation spectrum due to the normal form was observed. The upper limit of the rate constant of the tautomer formation was estimated to be 1.77×101 2 s− 1 for 3‐HC, 6.5×101 1 s− 1 for 3‐HF, and 1.54×101 1 s− 1 for 2‐NHC in supersonic expansion by simulation of the linewidth of the respective origin bands in the visible fluorescence excitation spectra. The order of rate constants of the tautomer formations in the supersonic free jet are consistent with that of the ESPT of these compounds in nonpolar solution. The fluorescence excitation and dispersed fluorescence spectra demonstrate 1:1 and 1:2 water complex formations of 3‐HF and 2‐NHC and no ESPT in these water clusters. However, no evidence of water complex formation was obtained in jet‐cooled 3‐HC.

Comparison of the Mobilities of Negative and Positive Ions in Nonpolar Solutions

The mobilities of organic radical ions of different molecular volumes have been determined in squalane and hexane solutions to study the influence of the ion charge sign on the ionic mobility in a weakly polar liquid. The relative mobility of geminate radical ions was measured using the method of time-resolved electric field effect in the recombination fluorescence. To determine the mobility of cations and anions separately, a trend in the value of the relative mobility was analyzed by varying the mobility of one of the geminate partners. The ratios between the mobilities of the anion and the cation of the same molecules were found to be about 1.1. It was shown that in liquid alkanes, the solvent electrostriction was the main factor determining a decrease in the mobility of an ion as compared to the parent neutral molecule. The strong dependence of the electrostrictive effect on the radius of the ionic solvation shell allows the observed difference between negative and positive charge carriers by a small but systematic difference in the effective radii of the ions to be explained.