Is there a "chain-foldability" effect without neighboring moiety-assistance?

The coaggregating tendencies of five methyl esters of saturated or uusaturated single-chain carboxylic acids,namely,octanoic (8-Me),dodecanoic (12-Me),stearic (18-Me),oleic (c-18:l-Me) and elaidic (t-18:l-Me) acids,were investigated in five aquiorgano binary solvent systems,V/V DX-H2O (φ=0.50,0.45,0.40,0.30,0.20),using naphthylethyl octyl(Np-8),dodecyl (Np-12),hexadecyl (Np-16) ether as fluorescent probes.The orders of their coaggregating tendencies changed in solvents of different φvalues.Our results could be rationalized by a chain-foldability effect without neighboring moiety participation.     

Fluorescence of 1,3-Di(1-pyrenyl)propane probe incorporated into human serum albumin protein enforced conformations of the probe

 Steady-state and time-resolved fluorescence spectra of 1,3-di(1-pyrenyl)propane (1Py-(3)-1Py) incorporated into macromolecules of human serum albumin (HSA), into micelles of dodecyltrimethylammo-nium chloride (DTAC), and dissolved in 1,4-dioxane were compared. The steady-state fluorescence spectra indicated that in all the mentioned environments, upon excitation of 1Py-(3)-1Py, light was emitted from the single pyrene chromophores (1Py^*) and from the 1Py, 1Py^* excimers. The time-resolved fluo-rescence emission registered at 480 nm (excimer emission) for 1Py-(3)-1Py in the DTAC micelles and dissolved in 1,4-dioxane allowed to monitor formation of excimer with time constant τ₁=40.0 ns and 9.6 ns, for 1Py-(3)-1Py in the DTAC micelles and in 1,4-dioxane, respectively. However, when the 1Py-(3)-1Py probe was located inside of the macromolecules of HSA, only the decay of emission was observed for excimer with our set-up (t>2 ns after excitation). The instantaneous formation of excimer, unrelated to the decay of monomer excitation, indicates that the considerable fraction of 1Py-(3)-1Py in the hydrophobic pockets of HSA is present as the ground state dimer. The red shift (Δλ=8 nm) and broadening of UV absorption for 1Py-(3)-1Py in HSA (when compared with absorption 1Py-(3)-1Py in 1,4-dioxane) and comparison of exci-tation spectra of 1Py-(3)-1Py in HSA and in 1,4-dioxane also indicate that label molecules bound to some sites of HSA are in the ground state in the dimer conformation. Moreover, the close values of the ratios of intensities of monomer emission to excimer emission, registered 2 ns (5 ns gate) after excitation pulse with duration 300 ps and at the steady-state conditions, indicate that the interconversion between conformers of 1Py-(3)-1Py inside of the macro-molecules of HSA is slow in comparison with the decay time of Py chromophore in the excited state in HSA (two-exponential decay with decay times τ₁=2.41 ns, τ₂=69.0 ns). Thus, ratios of the intensities of monomer and excimer emissions of 1Py-(3)-1Py in HSA do not allow to obtain any information on the local microfluidity inside of the protein macromolecules but could be used for discrimination between different conformations of the probe, possibly located in different protein pockets. Received: 29 April 1996 Accepted: 15 August 1996     

Effect of chelating agent on the oxidation rate of PCP in the magnetite/H2O2 system at neutral pH

The complex [Rh(CO)₂Cl]₂ reacts with two molar equivalent of pyridine carboxylic acids ligands Py-2-COOH(a), Py-3-COOH(b) and Py-4-COOH(c) to yield rhodium(I) dicarbonyl chelate complex [Rh(CO)₂(L^/)](1a) {L^/ = η²-(N,O) coordinated Py-2-COO⁻(a^/)} and non-chelate complexes [Rh(CO)₂ClL^//](1b,c) {L^// = η¹-(N) coordinated Py-3-COOH(b), Py-4-COOH(c)}. The complexes 1 undergo oxidative addition (OA) reactions with different electrophiles such as CH₃I, C₂H₅I, C₆H₅CH₂Cl and I₂ to give penta coordinated Rh(III) complexes of the types [Rh(CO)(CORⁿ)XL^/], {n = 1,2,3; R¹ = CH₃(2a); R² = C₂H₅(3a); X = I and R³ = CH₂C₆H₅ (4a); X = Cl}, [Rh(CO)I₂L^/](5a), [Rh(CO)(CORⁿ)ClXL^//] {R¹ = CH₃(6b,c); R² = C₂H₅(7b,c); X = I and R³ = CH₂C₆H₅ (8b,c); X = Cl} and [Rh(CO)ClI₂L^//](9b,c). The complexes have been characterized by elemental analysis, IR and ¹H NMR spectroscopy. Kinetic data for the reaction of 1a–b with CH₃I indicate a first order reaction. The catalytic activity of 1a–c for the carbonylation of methanol to acetic acid and its ester is evaluated and a higher turn over number (TON = 810–1094) is obtained compared with that of the well-known commercial species [Rh(CO)₂I₂]⁻ (TON = 653) at mild reaction conditions (temperature 130 ± 5 °C, pressure 35 ± 5 bar).     

Improved photovoltaic performance of 2,7-pyrene based small molecules via the use of 3-carbazole as terminal unit

Small molecule of Py-2DTBTCz with an Ar(A–D)₂ framework was designed and synthesized as photovoltaic donor materials, in which 2,7-pyrene (Py) and benzothiadiazole (BT) were respectively used as central aryl (Ar) and arm acceptor (A), while 3-carbazole (Cz) as terminal donor (D). For comparison, an A–Ar–A type SM of Py-2DTBT without Cz terminal unit was also prepared. The effects of Cz on optical, electrochemical, hole mobility and photovoltaic properties were investigated. In solution-processed solar cells, it was observed that the Py-2DTBTCz based devices show significant improvement in photovoltaic performance compared to those of Py-2DTBT. Power conversion efficiency (PCE) of Py-2DTBTCz could be as high as 2.89% with a short-circuit current density (J_sc) of 7.68?mAcm^?2. The results indicate that appending an enlarged Cz π-system to the terminal of A–Ar–A-type small molecules for the construction of an Ar(A–D)₂ framework can significantly improve the photovoltaic performance of SMs.     

Electrochemical behavior of <Emphasis Type="Italic">meso</Emphasis>-substituted iron porphyrins in alkaline aqueous media

The effect meso-substitution in iron porphyrin complexes has on their redox behavior in alkaline aqueous solutions is studied via cyclic voltammetry. The voltammetric features of the reduction of iron pyridylporphyrins suggest that the sites of electron transfer lie at the ligand, the metal ion, and the pyridyl moieties. The electron transfer reactions between the different forms of these compounds, including the oxygen reduction reaction they mediate, are outlined to show the sequence and potential ranges in which they occur in alkaline aqueous media. Under our experimental conditions, the iron porphyrins exist as μ-oxo dimmers whose activity for the electrocatalytic reduction of oxygen displays a considerable dependence on the nature of the substitutents and nitrogen isomerization (for pyridylporphyrins) and grows in the order (Fe(ms-Ph)₄P)₂О, (Fe[ms-(Py-3)Ph₃]P)₂O, (Fe[ms-(Py-4)₄]P)₂O, and (Fe[ms-(Py-3)₄]P)₂O.     

Molecular dynamics in the nematic,SA and SC phases of 8S5 and 9S5 as studied by dielectric methods

Abstract

Two experimental techniques—time domain spectroscopy (TDS) and a steady state frequency method—have been used to study dielectric spectra for the isotropic, nematic, S_A, S_C and S_Y phases of two thioesters (4-n-pentylphenyl-4′-n-octyloxy-and 4′-n-nonyloxythiobenzoates (C _n H_2n+1 O?C₆ H₄?COS?C₆H₄?C₅H₁₁, where n = 8 and n = 9) known as 8S5 and 9S5, in the frequency range from 10 Hz to 10 GHz. In the case of 8S5 a deuteriated sample (8S5-d ₂₈) has been used to study relaxation processes in the nematic and smectic phases.     

Synthesis and properties of polyaniline doped with iron-substituted silicotungstate isomers with Keggin structure

Four polyaniline hybrid materials doped with iron-substituted silicotungstate isomers α,?β _i - K_5?n H _n [SiW₁₁Fe(H₂O)O₃₉]?·?xH₂O (β_i?=?β₁, β₂, β₃) were prepared. The materials were characterized by elemental analysis, IR spectra, UV-Vis spectra, scanning electron microscopy (SEM), TG-DTA and X-ray diffraction (XRD). The conductivity and fluorescence were determined and thermal stability was studied. The UV-Vis, IR and XRD results confirm the existence of Keggin anions. Thermal analysis indicates that SiW₁₁Fe/PANI has better thermal stability. The images of scanning electron microscopy (SEM) show that the materials are microporous. The materials exhibit excellent proton conductivity of 8.5?×?10^?2?S?cm^?1 at room temperature (20°C). The spectral data indicate that polyaniline doped with α, β_i-SiW₁₁Fe have similar fluorescence, λ_em?=?418–470?nm, and emit blue light.     

Temperature response of aqueous solutions of pyrene end‐labeled poly(N‐isopropylacrylamide)s probed by steady‐state and time‐resolved fluorescence

Aqueous solutions of a series of monodisperse poly(N‐isopropylacrylamide)s end‐labeled with n‐butyl‐1‐pyrene at one or both chain ends (Py_n‐PNIPAMs with n = 1 or 2) were studied by turbidimetry, light scattering, and fluorescence. For a given polymer concentration and heating rate, the cloud point (T_c) of an aqueous Py_n‐PNIPAM solution, determined by turbidimetry, was found to increase with the number‐average molecular weight (M_n) of the polymer. The steady‐state fluorescence spectra and time‐resolved fluorescence decays of Py_n‐PNIPAM aqueous solutions were analyzed and all parameters retrieved from these analyses were found to be affected as the solution temperature passed through T_c, the solution cloud point, and T_m, the temperature where dehydration of PNIPAM occurred. The trends obtained by fluorescence to characterize the aqueous Py_n‐PNIPAM solutions as a function of temperature were found to be consistent with the model proposed for telechelic PNIPAM by Koga et al. in 2006. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 308–318     

Structural and Magnetic Properties of CoGen− (n=2–11) Clusters: Photoelectron Spectroscopy and Density Functional Calculations

A series of cobalt‐doped germanium clusters, CoGe_n^?/0 (n=2–11), are investigated by using anion photoelectron spectroscopy combined with density functional theory calculations. For both anionic and neutral CoGe_n (n=2–11) clusters, the critical size of the transition from exo‐ to endohedral structures is n=9. Natural population analysis shows that there is electron transfer from the Ge_n framework to the Co atom at n=7–11 for both anionic and neutral CoGe_n clusters. The magnetic moments of the anionic and neutral CoGe_n clusters decrease to the lowest values at n=10 and 11. The transfer of electrons from the Ge_n framework to the Co atom and the minimization of the magnetic moments are related to the evolution of CoGe_n structures from exo‐ to endohedral.     

Perfluorinated porphyrazines

Nucleophilic substitution of fluorine atoms in the phenyl rings by alkoxy groups was performed in perfluorosubstituted zinc(II) octaphenylporphyrazine [ZnPAF₄₀]. Up to 12 fluorine atoms are substituted in the reaction with sodium butoxide in boiling butanol leading to the formation of [ZnPAF_40-n(OBu)_n] (n = 6–12). Up to eight monosaccharide groups are introduced in the reaction with 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose (Gal´) in toluene in the presence of sodium hydride leading to the formation of [ZnPaF_(40-n)(Gal´)_n] (n = 6–8). It was possible to obtain a water-soluble glycoconjugated zinc(II) porphyrazine [ZnPaF_(40-n)(Gal)_n] after removal of the isopropylidene protecting groups by treatment with trifluoroacetic acid. Substitution products are characterized by electron absorption spectroscopy, NMR spectroscopy, and mass spectrometry. Substituting the fluorine atoms with monosaccharide residues leads to an increase in the fluorescence quantum yield from Ф_F = 0.19 for [ZnPAF₄₀] to 0.29 for [ZnPA(Gal´)_nF_40-n] (n = 6–8).

     

Synthesis and Polymerization of Surface-Active Sodium Acrylamidoundecanoate

The polymerizable surfactant sodium 11-acrylamidoundecanoate (Na 11-AAU) was synthesized from acryloyl chloride and 11-aminounde-canoic acid. It had a low critical micelle concentration (CMC) of 4.3 × 10^?4 mol/L. Polymerization of Na 11-AAU initiated by K₂S₂O₈ was very fast in aqueous solution, with an activation energy of only 63.2 kJ/mol. The polymerization followed first-order kinetics with respect to Na 11-AAU and one-half order with respect to K₂S₂O₈. The MW of poly(Na 11-AAU) was very high (1–2 million) but the MWD was rather narrow ( M _w / M _n = 1.45). Polymerization of Na 11-AAU in the micellar state may be responsible for the phenomena observed.     

Ab initio calculation of the band structure of some boron polymers

Ab initio calculations using a STO-3G basis set have been performed on the polymer systems (HBX) _n where X = Be, BH, CH₂, NH, and O. Energy band diagrams and accompanying density-of-states plots have been obtained. The highest filled orbital of (HBNH) _n and (HBO) _n occurs at the X-point and possesses character while the - framework orbital at the X- point is the highest filled level for (HBBe) _n , (HBBH) _n , and (HBCH₂) _n . The conduction band for all five species has symmetry and the band gap of the (HBX) _n species increases in the order X = Be < BH < NH < O < CH₂. An estimate of the energy of polymerisation of the (HBX) _n systems suggests that HBNH is particularly stabilised by polymerisation. The electron distribution in (HBBe) _n shows a - electron drift towards boron, while in the other four systems the net electron transfer is directed away from boron. There is significant electron back-donation to boron in (HBO) _n and (HBNH) _n .     

A new member of the Nbn(μ3-X)n−2(μ-X)nLn+6 (n > 2) cluster family: Nb4Cl10(PEt3)4(H2NPh)2. Synthesis,structure, and relationship to other members

NbCI₅ was reduced by Na/Hg in THF in the presence of Ph₂N₂ and PEt₃ and afforded a rhomboidal tetranuclear niobium cluster compound, Nb₄Cl₁₀(PEt₃)₄ (H₂NPh)₂. Crystallographic data for the compound are: space group P ,a = 12.147(3),b = 12.338(3),c = 11.657(2) Å, = 92.31(2),(2), = 115.99(1) = 63.27(2)°,V = 1375.5(6) ų,Z = 1. Two sets of Nb-Nb edges and one diagonal have lengths of 2.8952(5), 2.9414(8), and 3.O001(6) Å, respectively corresponding well to five Nb-Nb single bonds. The structure, chemistry, and relationship of this compound to other members of the Nb _n (₃-X) _n–2-(-X)_n L _n+6 (n >2) family are discussed.     

Design,synthesis, and optical/electronic properties of a series of sphere-rod shape amphiphiles based on the C<Subscript>60</Subscript>-oligofluorene conjugates

A series of sphere-rod shape amphiphiles were designed and synthesized by connecting the rod-like oligofluorenes with different lengths (OF _n ) to the different positions of the spherical [60]fullerene (C₆₀) through a rigid linkage. The conjugates were characterized by ¹H-NMR, ¹³C-NMR, FTIR, EA and MALDI-TOF mass spectrometry. The optical and electronic properties of the conjugates were studied by UV-Vis absorption spectroscopy, fluorescence spectrometry, and cyclic voltammetry. The results from UV-Vis absorption spectroscopy and cyclic voltammetry indicated that the energy profiles of C₆₀ and OF _n remained unchanged when different lengths of OF _n were attached to C₆₀. The electron affinities of the OF _n -C₆₀ conjugates were close to that of C₆₀, while slight electronic interaction was found between the two individual chromophores (C₆₀ and OF _n ) in their ground states. The fluorescence spectra exhibited a complete fluorescence quenching in the toluene solution, suggesting an effective energy transfer from OF _n to C₆₀. It presents a systematic study on the self-assembly, structure-property relationship, and potential technical applications of the conjugates.     

Impact of the Aliphatic Dicarboxylate Chain of Novel Dinuclear Palladium(Ⅱ) Complexes: Synthesis and Biological Evaluation

Five dinuclear palladium(II) complexes with HOOC(CH₂)_nCOOH (n=2–6) and 2,2′‐bipyridine ligands were synthesigned by a reaction with K₂PdCl₄. To prepare such complexes with different aliphatic dicarboxylate chain lengths was in an attempt to correlate this length factor, which influences the biological activity of the complexes, with fluorescence spectra, DNA cleavage and cytotoxic activity. The results indicate that the complexes bind to fish sperm DNA (FS‐DNA) in an intercalative mode via fluorescence spectra, and the five complexes show different cleavage of supercoiled DNA, and then a cytotoxicity assay of these dinuclear palladium(II) complexes on human tumor cell lines was performed. In most of the cell lines, complex 5 (n=6) and 4 (n=5) showed much higher cytotoxicity than cis‐platin. On the other hand, complex 3 (n=4) was found to be moderately active, and complex 1 (n=2), complex 2 (n=3) were found only marginally cytotoxic. Implications of these findings were discussed from a structure‐activity relationship.     

Electron transfer in the photochemical reactions of phenothiazine with halomethanes

Photochemical transformations of phenothiazine (PTA) in solutions of halomethanes CH_nX_4–n (X = Cl, Br; n = 0, 1, 2) and in n-hexane—CH_nX_4–n mixtures under the irradiation with = 337 and 365 nm were studied. The rate constants of quenching of PTA fluorescence with halomethanes (k _q) are 4·10⁵—1.3·10¹⁰ L mol^–1 s^–1. The process occurs due to electron transfer with the C—X bond cleavage in the radical anion fragment of the primary radical ion pair. This results in the formation of the stable radical cation salt (PTA^·+X^–). The plot of k _q vs. free energy of electron transfer corresponds to the Rehm—Weller empirical equation for a one-electron process and is satisfactorily described in terms of the theory of nonradiative electron transitions in the approximation of one quantum vibration.     

The Diversity of Difluoroacetylene Coordination Modes Obtained by Coupling Fluorocarbyne Ligands on Binuclear Manganese Carbonyl Sites

One Mn or two? The fluorocarbyne manganese carbonyl complexes [Mn(CF)(CO)_n] (n=3, 4) and [Mn₂(CF)₂(CO)_n] (n=4–7; see picture) have been investigated by density functional theory. In mononuclear complexes the CF ligand behaves very much like the NO ligand in terms of π‐acceptor strength. In binuclear complexes the two CF ligands couple in many of the low‐energy structures to form a bridging C₂F₂ ligand derived from difluoroacetylene.

     

青霉素G钾盐对SDS水溶液物理化学性质的影响及其在SDS/n-C5H11OH/H2O体系中的释放

The effects of penicillin potassium salt （PenK） on the solubility, Krafft temperature TK, critical micelle concentration CMC of SDS micelle and the phase behavior of SDS/n-C5H11OH/H2O system were studied. The partial phase diagrams of SDS/PenK/H2O system at different temperatures were determined. The release amounts of PenK in SDS/n-C5H11OH/H2O system and the distribution coefficient of PenK between micelle and water were measured by UV-Vis spectroscopy. The results show that in the presence of PenK, the CMC of SDS was decreased while the TK of SDS was increased and the solubility of SDS in both water and SDS/n-C5H11OH/H2O oil in water （O/W） microemulsion was decreased, but increased in water in oil （W/O） microemulsion. SDS micelles and SDS/n- C5H11OH/H20 O/W microemulsion could accelerate the release rate of PenK. The addition of SDS and water could both increase the release rate of PenK, whereas the presence of n-C5H11OH reduced the release rate of PenK. The above results were related to the electrostatic repulsion between PenK and SDS.     

AIE Fluorescent Gelators with Thermo‐, Mechano‐, and Vapochromic Properties

A series of aggregation‐induced emission (AIE) fluorescent gelators (TPE‐C_n‐Chol) were synthesized by attaching tetraphenylethylene (TPE) to cholesterol through an alkyl chain. The properties of the gel, nano‐/microaggregate, and condensed phases were studied carefully. TPE‐C_n‐Chol molecules form AIE fluorescent gels in acetone and in DMF. Their fluorescence can be reversibly switched between the “on” and “off” states by a gel–sol phase transition upon thermal treatment. The AIE properties of aggregated nano‐/microstructures in acetone/water mixtures with different water fractions were studied by using fluorescence spectrometry and scanning electron microscopy (SEM). In different acetone/water mixtures, the TPE‐C_n‐Chol molecules formed different nano‐/microaggregates, such as rodlike crystallites and spherical nanoparticles that showed different fluorescence colors. Finally, the condensed phase behavior of TPE‐C_n‐Chol was studied by using polarizing microscopy (POM), differential scanning calorimetry (DSC), fluorescence spectrometry, fluorescence optical microscopy, and wide‐angle X ray scattering (WAXS). The clover‐shaped TPE unit introduced into the rodlike cholesterol mesogen inhibits not only the formation of a liquid‐crystal phase but also recrystallization upon cooling from the isotropic liquid phase. Very interestingly, TPE‐C_n‐Chol molecules in the condensed state change their fluorescence color under external stimuli, such as melting, grinding, and solvent fuming. The phase transition is the origin of these thermo‐, mechano‐, and vapochromic properties. These findings offer a simple and interesting platform for the creation of multistimuli‐responsive fluorescent sensors.     

The deexcitation of the S1 state of aminoanthraquinones: A steadystate and timeresolved study

The non-radiative processes of deactivation from the lowest singlet excited state of aminoanthraquinones have been studied using steady-state and time-resolved methods. The fluorescence decay rate constant, k_f correlates well with the solvent polarity parameter, E_T(30), in nonhydrogen bonding solvents. Large deuterium isotope effects in fluorescence lifetimes (τ_f) and quantum yields (ϕ_f) are observed in the case of 1-amino (AAQ) and 1-methylaminoanthraquinones (MAQ), where the S₁ state is mainly deactivated through internal conversion to the ground state. The temperature-dependence of the fluorescence quantum yields of various aminoanthraquinones was also investigated. The ϕ_f and τ_f exhibited strong temperature-dependence in the case of 1-acetylaminoanthraquinone (ACAQ). In the case of ACAQ, the intersystem crossing to the triplet state is a major deactivation channel from the S₁ and in this derivative a close-lying T₂ state seems to be responsible for the high k_isc rate. The fluorescence properties of 1,5-diaminoanthraquinone (DAQ) are affected by intermolecular hydrogen bonding with alcohols. Increasingn-alkyl chain length in the case of l-(n-alkyl)aminoanthraquinones from methyl to butyl does not produce any change in the fluorescence properties, whereas a hydroxypropyl substitution results in a small decrease of ϕ_f and τ_f in these compounds, indicating an interaction of the hydroxyl group with the carbonyl group of the aminoanthraquinones.