Multiply Charged Anions,Maximum Charge Acceptance,and Higher Electron Affinities of Molecules,Superatoms,and ClustersSCI北大核心CSCD

The addition of electrons to form gas-phase multiply charged anions (MCAs) normally requires sophisticated experiments or calculations.In this work, the factors stabilizing the MCAs, the maximum electron uptake of gas-phase molecules, X, and the electronic stability of MCAs X^Q-, are discussed. The drawbacks encountered when applying computational and/or conceptual density functional theory (DFT) to MCAs are highlighted. We develop and test a different model based on the valence-state concept. As in DFT, the electronic energy, E(N, v_ex), is a continuous function of the average electron number, N, and the external potential, v_ex, of the nuclei. The valence-state-parabola is a second-order polynomial that allows extending E(N, v_ex) to dianions and higher MCAs. The model expresses the maximum electron acceptance, Q_max, and the higher electron affinities, A_Q, as simple functions of the first electron affinity, A₁, and the ionization energy, I, of the "ancestor" system. Thus, the maximum electron acceptance is Q_{max, calc} = 1 + 12A₁/7(I -A₁). The ground-state parabola model of the conceptual DFT yields approximately half of this value, and it is termed Q_{max, GS} = ${}^{1}\!\!\diagup\!\!{}_{2}\; $ + A₁/(I -A₁). A large variety of molecules are evaluated including fullerenes, metal clusters, super-pnictogens, super-halogens (OF₃), super-alkali species (OLi₃), and neutral or charged transition-metal complexes, AB_mL_n^0/+/-. The calculated second electron affinity A_{2, calc} = A₁-(7/12)(I -A₁) is linearly correlated to the literature references A_{2, lit} with a correlation coefficient R = 0.998. A₂ or A₃ values are predicted for further 24 species. The appearance sizes, n_ap^3-, of triply charged anionic clusters and fullerenes are calculated in agreement with the literature.     

Elastic constants of uniaxial nematic liquid crystals: A comparison between theory and experiment

Using the unified molecular theory developed in our earlier paper (1992, Phys. Rev. A, 45, 974) we study in detail the influence of molecular interactions on the fundamental elastic properties of uniaxial nematic liquid crystals composed of molecules of cylindrical symmetry. The expressions for the elastic moduli associated with 'splay', 'twist' and 'bend' modes of deformations are written in terms of order parameters characterizing the nature and amount of ordering in the phase and the structural parameters which involve the generalized spherical harmonic coefficients of the direct pair correlation function of an effective isotropic liquid. Numerical calculations are done for a model system, the molecules of which have prolate ellipsoid of revolution symmetry and interact via a pair potential having both repulsive and attractive parts. The repulsive interaction is represented by a repulsion between hard ellipsoids of revolution. The attractive potential is represented by the dispersion and electrostatic interactions. Results for the elastic constants are reported for a range of molecular length-width ratio, temperature, density and molecular parameters and are compared with the experimental values of p-azoxyanisole (PAA) and 4'-n-octyloxy-4-cyanobiphenyl (8OCB). It is found that the inclusion of electrostatic interactions reduces the values of the ratios K₂/K₁ and K₃/K₁. The absolute values of the elastic constants and their ratios are in good agreement with the experimental and computer simulation values. The temperature dependence of the elastic constants and their ratios is studied. It is observed that the twist elastic constant has a weak temperature dependence but a pronounced influence is observed on the bend moduli. We also observed a pronounced increase in the values of the twist and bend elastic constants on approaching the nematic-smectic A transition temperature.     

Transport phenomenon as a function of counter and co-ions in solution: chronopotentiometric behavior of anion exchange membrane in different aqueous electrolyte solutions

Anion exchange membrane has been investigated in different electrolyte solutions by chronopotentiometry to explore the influence of co-ion and counterion of the exchange group of the membrane, on the transport phenomena. Chloride, nitrate, sulfate and acetate in sodium salts were used as counterions and sodium, potassium, calcium and ammonium in chloride salts were used as co-ions. The membrane showed a potential drop (E₀) in all these electrolytes when a constant current was applied across it, which remained constant for a period less than τ, called the transition time and rose gradually to a maximum (E_max) value. The parameters such as τ, E₀ and E_max and the potential jump (ΔE) and τ and the inflection zone (Δt) along the time axis have been measured and compared at an applied current density (I) of 10 mA cm⁻² in 10 mM solutions. The values of τ^1/2/z_A[A₀] or τ^1/2/z_C[C₀], with or , E₀ and ΔE with or (where r_A and r_C are the ionic radii of counter and co-ions, respectively) have been correlated. Permselectivity (P) and transference number of the membrane with respect to each one of the above electrolytes have been evaluated and discussed.     

The Ericksen number and Deborah number cascades in sheared polymeric nematics

Samples of liquid crystalline poly(γ-benzyl-glutamate) solutions are sheared between glass surfaces with gaps, d = 10-500 μ, and shearing velocities, V = 0·05-10 000 μs^-1 so that the Ericksen number E ≡ Vdγ₁/K is varied over a large range, E ≈ 1-10⁷. Here γ₁ is the rotational viscosity and K₁ is the Frank splay constant, with γ₁/K₁ estimated to be approximately 1 s μ^-2 for our samples. We observe by polarizing microscopy a sequence of transitions with increasing Ericksen number analogous to that observed in small molecule tumbling nematics: namely rotation of the director out of the shearing plane and into the vorticity direction at Vd ≈ 25 μ² s^-1, and formation of roll cells at Vd ≈ 50 μ² s^-1. The roll cells become finer with increased Vd in accord with predictions of linear stability theory using the Leslie-Ericksen equations, and at Vd ≳ 500 μ² s^-1, the cells become very irregular, producing director turbulence. The turbulence becomes finer in scale as Vd increases, reaching sub-micron, and possibly molecular scales when Vd ≧ 10⁵ μ² s^-1. At the highest velocities, transitions in orientation and texture are controlled by the Deborah number De≡λV/d, where λ is the molecular relaxation time, and uniform texture-free samples are obtained when De ≳ 5.     

Vibrational spectra of σ-allylmanganese pentacarbonyl

The vibrational spectra of σ-(C₃H₅)Mn(CO)₅ are reported. Assignment of bands is made and carbonyl force constants are calculated. The results indicate that the Mn(CO)₅ moiety has C_4ν symmetry. The calculated angle between the axial and equatorial carbonyl groups is approximately 95°. The bonding in this compound is very similar to that in (CH₃)Mn(CO)₅.

In the far-infrared region, seven bands are expected in C_4ν symmetry (3A₁ + 4E), and all are observed.     

Protonation constants of some substituted 2-hydroxy-1-naphthalideneanilines in dioxan-water mixtures

The protonation constants of ten Schiff's bases synthesized by the condensation of 2-hydroxy-1-naphthaldehyde with aniline and o-, m-, and p-substituted methylanilines, ethylanilines and methoxyanilines in various dioxan-water mixtures have been determined potentiometrically using an electrode system calibrated in concentration units of the hydrogen ion. The influence of substituents in the molecular structure on the protonation constants is discussed. The log K₂ values relating to the protonation of imine nitrogen atoms are in accordance with the Hammett relationship for all solvent compositions. A reverse relationship is observed between log K₂ for all Schiff's bases and the mole fraction of dioxan. However, the log K₁ values corresponding to the protonation of naphtholate O-ions have been found to increase with the increase in concentration of dioxan. Both electrostatic and non-electrostatic contributions influencing these constants are briefly discussed.     

Guest and host deuterium effects of the large ZFS parameters D of dimethylbenzaldehydes in durene single crystals

The ZFS parameters D of 2,4-, 2,5- and 3,4-dimethylbenzaldehyde-1h₁ and -1d₁ guests in perhydrogenated and perdeuterated durene single crystals are determined by comparing the experimental and calculated resonance curves. It is found that the deuterium substitution of the guest aldehydic group in a given host leads to the decrease of the D values and to the increase of the energy gaps ΔE_T between the zero-point levels of the ³nπ* and ³ππ* states of the guests. On the other hand, the perdeuteration of the host results in the decrease of ΔE_T with a corresponding increase of the D value of a given guest. The D value of 1 cm⁻¹ determined for 2,5-dimethylbenzaldehyde-1h₁ in perdeuterated durene is the lategest ever found for an aromatic carbonyl compound. Correlations between D and ΔE_T indicate that the ZFS parameters D of the guests are determined by contributions from both spin-spin and spin-orbit interactions between the ³nπ* and ³ππ* states. The large guest and host deuterium effects observed on the D values are attributed to the changes of the gaps ΔE_T of the guests.     

Multiparametric curve fitting-XIII Reliability of formation constants determined by analysis of potentiometric titration data

The formation (protonation) constants log K_i, of the acid H_jL are determined by regression analysis of potentiometric titration data when common parameters (log K_i, i = 1,…, j) and group parameters (E⁰′, L₀, H_T) are refined. The influence of three kinds of error on the protonation constants has been investigated: error from the strategy of minimization, random error, and error from uncertain estimates of group parameters. An analysis of variance of the log K_i, matrix was made for 7 identical titrations and 8 computational strategies, or of 7 identical titrations and 8 different options of group parameters to be refined. The influence of the standard potential E⁰ of the glass-electrode cell on the systematic error in log K is greater than that of the acid concentration (L₀) or the concentration of titrant used (H_T). The ill-conditioned group parameters should be refined together with the common parameters (K_i), otherwise the estimates of log K_i, are not accurate enough. Two ways of calibrating the glass electrode cell were compared. Internal calibration (performed during titration) was more accurate than external calibration done separately. Of the programs tested ESAB and ACBA are the most powerful because they permit refinement of group parameters and internal calibration. Citric acid was chosen as model substance.     

Unusual product distribution in ethylene oligomerization promoted by in situ ansa-chloroneodymocene–dialkylmagnesium systems

Ethylene polymerization using in situ combinations between a chloroneodymocene precursor and a dialkylmagnesium reagent has been investigated to prepare tailor-made oligomers. Combinations of [Cp^*₂NdCl₂Li(OEt₂)₂] (1) with 40 equiv. of n-butylethylmagnesium (BEM) or di(n-hexyl)magnesium (DHM) gave oligoethylenes with M_n up to 2500 and narrow molecular weight distributions (M_w/M_n<1.10) in moderate activity (A_{1 h}=79 kg/(mol of Nd h atm) at 80 °C, 1 atm). Under these conditions, ethylene polymerization proceeded in a controlled fashion, with a linear growth of M_n vs monomer conversion, ascribed to an effective chain transfer between the Nd and Mg centers. Combinations of [rac-{Me₂Si(η⁵-2-SiMe₃-4-t-Bu-C₅H₂)₂}Nd(μ-Cl)₂Li(THF)₂] (2) with either BEM or DHM (20–40 equiv.) showed decreased activity, suggesting possibly a different rate-determining-step for ethylene polymerization than for that of higher -olefins. The oligoethylenes obtained from combinations based on 2 have narrow molecular weight distributions (M_w/M_n<1.2) but higher contents of vinyl terminations. Monitoring of the reactions showed also a non-linear growth of M_n vs monomer conversion, especially marked when DHM was used as co-reagent. The 2/DHM combination behaves as a “self-correcting” catalyst system that deviates from the calculated M_n values for a controlled-living polymerization in the early stage of the reaction and re-approach them progressively in the second stage.     

Molecular weight determination from light scattering and refraction in solutions. A new and coherent theoretical equation

The classical theoretical equation allowing for the determination of the solute's molecular weight (M₂) from light scattering (LS) and refractive measurements in diluted solutions is reexamined. Serious theoretical and practical defects in its derivation and application are pointed out, especially about the refraction increment dn/dc. A new theoretical equation is deduced from a more consistent application of the basic molecular orientation formulae to binary liquid mixtures. More adequate additive molecular properties, the specific mean polarizability ( /M and the specific square of the mean polarizability instead of and , are considered with respect to refraction and LS, respectively. Inadequate approximations are avoided and a corrected LS intensity expression is used. The new equation is tested upon several typical mixtures of small molecules from measurements either performed in this work or collected in the literature (for LS perpendicular to the incident beam) to ensure objectivity. Examples of measurements in macromolecule solutions from other authors are also analysed. The new equation is suitable for practical applications, because it is based upon easy relative measurements only, and allows for a reliable determination of the M₂ values in macromolecules. The reasons for which the classic equation leads to realistic values, in spite of its theoretical inconsistency, are also explained.     

Dielectric and elastic properties of a nematic phase induced by charge transfer interaction in a binary system containing disc-shaped molecules

The dielectric constants and the elastic coefficients for splay (K₁) and bend (K₃) of the charge transfer induced nematic (N_c) phase of tridecyl pentakis(phenylethynyl)phenyl ether (1) doped with different amounts of 2,4,7-trinitrofluorenone (2) were determined by studying the electric field induced bend deformation using the capacitance method. A negative dielectric anisotropy was observed. For the bend elastic constant K₃ values up to 22 × 10^-12 N are found which are one order of magnitude higher than the respective values of discotic nematic (N_D) phases. Values of 0·6-0·8 are obtained for the ratio K₁/K₃; these show a minimum for the equimolar complex.     

High-resolution ODMR- and ODNQR spectroscopy of acridine-d9 in its lowest excited triplet state

High-resolution ODMR- and ODNQR spectroscopy have been performed on acridine-d₉ in its photoexcited triplet state. The nuclear quadrupole constants e²qQ/h = −4.36(3) MHz and η = 0.22(1) have been measured for the ¹⁴N nucleus, where the sign of e²qQ/h is determined relative to the signs of the fine structure parameters, D and E. The ¹⁴N ODNQR spectrum, with linewidths as low as 60 kHz, exhibits a satellite structure attributable to the ²D nucleus located at the meso-position in the molecule. For this nucleus |e²qQ/h| = 180(30) kHz may be estimated. The intensity behaviour of the ODNQR transitions as a function of the NMR rf power level leads to a coarse determination of the in-plane components of the ¹⁴N hyperfine tensor with |A_yy^N| 0.2 MHz and |A _yy^N| 4.7 MHz. Owing to accidental overlap of two transitions in the 2E-ODMR spectrum of acridine, the ODNQR technique had to be extended to a five-pulse sequence.     

Investigation on the viscoelasticity of synchronous hepatocellular carcinoma cells

Having made use of the micropipette aspiration technique, we here investigated the viscoelastic properties of hepatocellular carcinoma (HTC) cells from the view of cell cycle. The synchronous G₁ and S phase cells were achieved through thymine-2-desoryriboside and colchicine sequential blockage method and double thymine-2-desoryriboside blockage method, respectively. The synchronization results detected with flow cytometer showed that it could meet the requirements of the experiments nicely. Experimental results were analyzed with a standard linear solid viscoelastic model, in which an elastic element, K₁, is in parallel with a Maxwell element composed of another elastic element, K₂, in series with a viscous element, μ. The results indicated that high K₁, K₂ values and low μ value was the general characteristics of the cells; G₁ phase cells had higher K₁ values and low μ value than S phase cells, which endowed G₁ phase cells with higher elasticity and faster passive deformability than S phase cells. The results maybe also reflected the difference of cytoskeleton between G₁ and S phase cells, and suggested that G₁ phase cells were more suitable for surviving and metastasis in blood circulation than S phase cells.     

Molecular weight determination from light scattering and refraction in solutions. A new and coherent theoretical equation

The classical theoretical equation allowing for the determination of the solute's molecular weight (M₂) from light scattering (LS) and refractive measurements in diluted solutions is reexamined. Serious theoretical and practical defects in its derivation and application are pointed out, especially about the refraction increment dn/dc. A new theoretical equation is deduced from a more consistent application of the basic molecular orientation formulae to binary liquid mixtures. More adequate additive molecular properties, the specific mean polarizability and the specific square of the mean polarizability instead of ga and , are considered with respect to refraction and LS, respectively. Inadequate approximations are avoided and a corrected LS intensity expression is used. The new equation is tested upon several typical mixtures of small molecules from measurements either performed in this work or collected in the literature (for LS perpendicular to the incident beam) to ensure objectivity. Examples of measurements in macromolecule solutions from other authors are also analysed. The new equation is suitable for practical applications, because it is based upon easy relative measurements only, and allows for a reliable determination of the M₂ values in macromolecules. The reasons for which the classic equation leads to realistic values, in spite of its theoretical inconsistency, are also explained.     

Evaluation of carrier gases for use in high-field asymmetric waveform ion mobility spectrometry

Effects of carrier gas type (N₂, O₂, CO₂, N₂O, and SF₆) on changes in the ratio of high- to low-field ion mobility, K_h/K, of cesium, gramicidin S, tetrahexylammonium, heptadecanoic acid, and aspartic acid in fields of up to 67 Td are presented. The theory of the mobility of ions at high E/N in different gases is discussed. Plots of K_h/K as a function of the ionic energy parameter, E/N, for the five ions in each of the gases were derived from experimental data collected using a high-field asymmetric waveform ion mobility spectrometer. The change in the ratio of high- to low-field ion mobility of cesium in carrier gases of O₂ and N₂ showed excellent agreement with literature values. The behavior of cesium in O₂ and N₂ is used to illustrate that the ratio K_h/K as a function of effective temperature is invariant with gas type as long as the well depth of the interaction potential significantly exceeds thermal energy. From these results, it appears that the well depth of the interaction potential of the heavier ions studied here, including gramicidin S, tetrahexylammonium, and heptadecanoic acid, with bath gases such as N₂ and O₂, is shallow relative to thermal energy.     

Adriblastina-single stranded DNA interaction with statistical analysis

The electrochemical behavior of adriblastina has been studied at in situ mercury film electrode (in situ MFE) and platinum electrode (PtE) in the presence of phosphoric acid as supporting electrolyte using Osteryoung square-wave stripping voltammetry (OSWSV) and cyclic voltammetry (CV). Optimal experimental and operational parameters have been selected for the drug accumulation and determination in aqueous medium. The interaction of the drug with single stranded DNA (ssDNA) has been studied and validated by using classical least square and partial least square with propagation of error. The formal potentials E° and E°′ and the equilibrium constants K₁ and K₂ have been calculated. It was found that K₂ for the oxidized form of adriblastina is 63 times than K₁ for the reduced form. Among several possible interfering metal ions, a complex formation reaction was observed between adriblastina and Cu(II) ions at in situ MFE. Cu(II) ions formed 1:2 metal:drug complex which is more stable than ssDNA–drug interaction and consequently it inhibits drug biochemical damage effects. The copper complex offers sub-nanograms determination of adriblastina in that 5.80 and 180 pg/ml could be easily detected in aqueous and urine media, respectively, with R.S.D. less than 4%. F-test and t-test have been applied in urine media giving good results that indicated the high accuracy of the proposed method.     

Thermal decomposition of poly(1,4-dioxan-2-one)

To evaluate the feasibility of poly(1,4-dioxan-2-one) (PPDO) as a feed stock recycling material, the pyrolysis kinetics of PPDO were investigated. The pyrolysis of PPDO exclusively resulted in the distillation of 1,4-dioxan-2-one (PDO). From thermogravimetric measurements conducted at different heating rates, the kinetic parameters of the pyrolysis: activation energy, E_a=127 kJ mol⁻¹; order of reaction, n=0; and pre-exponential factor, A=2.3×10⁹ s⁻¹, were estimated by plural analytical methods. The estimates show that the decomposition of PPDO proceeds by unzipping depolymerization as main reaction and random degradation process with lower E_a and A values. Equivalent isothermal degradation curves calculated from the thermogravimetric curves were supported by experimental isothermal degradation data. The calculation that PPDO is converted smoothly into PDO at 270°C agrees with the reported ceiling temperature of PPDO.     

Rapid measurement of fish freshness indices by an amperometric flow-injection system with a 16-way switching valve and immobilized enzyme reactors

A novel flow-injection system is proposed for the rapid measurement of the fish freshness indices K₁ and K₂: K₁=[([HxR+[Hx])×100/([IMP]+[HxR]+[Hx])] and K₂=[[Hx]×100/([HxR]+[Hx])], where [IMP], [HxR] and [Hx] are inosine-5′-monophosphate, inosine and hypoxanthine concentrations, respectively. For the estimation of index K₁, 5′-nucleotidase immobilized reactor and nucleoside phosphorylase (NP)/xanthine oxidase (XO) coimmobilized reactor were incorporated in series in the flow-injection line made up by a 16-way switching valve with two sample loops. For the estimation of index K₂, NP and XO immobilized reactors were also incorporated in the similar flow-line. Two sample portions passed through the flow-line with different residence times so that two peaks were obtained. The first and second peaks obtained in the K₁-determining system corresponded to the total of HxR and Hx and the total of Hx, HxR and IMP, respectively. Similarly, the first and second peaks obtained in the K₂-determining system corresponded to Hx and the total of Hx and HxR, respectively. Therefore, the indices K₁ and K₂ can be estimated by

where i₁ and i₂ present the peak current of the first and second peaks, respectively, and f the ratio of the peak currents of the first and second peaks for a Hx standard solution. A sea bream was selected as a model fish and it was stored at 4 °C after death. A good correlation was found between the index K₁ and the storage time over a period of 400 h, with a correlation coefficient of 0.992, but no correlation between the index K₂ and the storage time. The measurements could be performed at a rate of 22 samples per hour with satisfactory precision (0.6–1.2% R.S.D.), without calibration for each species, accurate weighing of fish meat and any interferences in fish meat.     

Absorption spectrum of deuterated hydrazoic acid, DN3 in the microwave and millimeterwave regiont

Thirty b-type P, Q and R branch rotational transitions and nineteen a-type Q and R branch transitions have been detected and measured for the slightly asymmetric rotor molecule D¹⁴N₃ in the frequency range from 8 to 340 GHz. The information obtained from the analysis of the observed frequencies are greatly improved values of the K-dependent parameters A_O = 344746.589(64) MHz, and D_K = 92.242(33) MHz, refined values for the rotational constants B_O and C_O, a complete set of quartic centrifugal distortion constants and several sextic distortion constants. Both a and b components of the electric dipole moment were determined giving a total dipole moment of μ = 1.76(5) debye.     

The constitution of the grignard reagent VII. The degree of association of ethylmagnesium compounds in diisopropyl ether

The degrees of association of ethylmagnesium bromide, diethylmagnesium and of a mixture of diethylmagnesium and magnesium bromide in the weakly basic solvent diisopropyl ether have been measured at concentrations up to 0.040 M at 27.7°. It is concluded that: (1), ethylmagnesium bromide is present as a dimer, (2), diethylmagnesium is present in a dimer-tetramer equilibrium with K₁ = 24.9 1/mol, and (3), when magnesium bromide is added to an excess of diethylmagnesium it reacts to form ethylmagnesium bromide. Diethylmagnesium and ethylmagnesium bromide are also in equilibrium with (EtMgBr·Et₂Mg), with K₃ approximately 2.5.