An improved model of the fringing fields of a quadrupole mass filter

The fringing field region of a quadrupole mass filter is modelled using an iterative finite difference technique to solve Laplace's equation for the electrostatic potential. The results are used to formulate an expression f(z) such that the electrostatic potential of the fringing field, F(x, y, z, t) may be written in the form F(x, y, z, t) = f(z) φ(x, y, t), where φ(x, y, t) is the hyperbolic field of the quadrupole. The function f(z) is expressed in the form f(z) = 1 - exp {- az - bz²}), where a and b are constants and z is in units of r_O, where 2r_O is the spacing of the quadrupole rods. The effect of the distance from the quandrupole rods to the end plate of the quadrupole mass filter, d on f(z) is investigated and the results presented show that for d < 0.125 r_O the function f(z) does not alter significantly.     

Polyfluorinated arylnitrosamines

N-Methyl-, N-n-butyl-, N-t-butylperfluoroarylamines undergo nitrosation with nitrous acid to give the corresponding N-nitroso derivatives. Perfluoroaryl groups were selected from the benzene, indane, biphenyl, naphthalene and pyridine series. According to ¹H and ¹⁹F NMR spectra, N-nitroso-N-methyl derivatives of polyfluoroarenes consist of E and Z isomers with the former prevailing. The more bulky n-butyl group promotes an increase in the formation of Z isomers. Only Z isomers have been obtained from N-t-butyl derivatives of perfluorinated 4-toluidine and 4-aminopyridine. The structure of the Z isomer of N-nitroso-N-methylperfluoro-4-toluidine is confirmed by X-ray data.     

Solid-state structure determination and solution-state NMR characterization of the (2R,4R)/(2S,4S)- and (2R,4S)/(2S,4R)-diastereomers of the agricultural fungicide propiconazole,the (2R,4S)/(2S,4R)-symmetrical triazole constitutional isomer,and a ditriazole analogue

Single-crystal X-ray diffraction analysis was used to determine the structure of a racemic diastereomer of the agricultural fungicide propiconazole [1-(2-(2,4-dichlorophenyl)-4-n-propyl-1,3-dioxolane-2-yl-methyl)-1-H-1,2,4-triazole] and of two by-products (a symmetrical 1,3,4-triazole racemic-constitutional isomer and a propiconazole ditriazole analogue). All three crystalline racemic-diastereomers had (2R,4S)/(2S,4R)-stereochemistry in which then-propyl group was observed in atrans-to-phenyl disposition. Propiconazole (2R,4S)/(2S,4R)-diastereomer gives crystals belonging to the monoclinic space group P2₁,/a, and, at 293 K,a=8.1192(3),b=18.9769(6),c=10.7137(4) å,Β=99.765(3)?,V=1626.8(1) å³, Z=4,R(F)=0.060, andR _w(F)=0.058. The constitutional isomer by-product (2R,4S)/(2S,4R)-1-(2-(2,4-dichlorophenyl)-4-n-pro-pyl-1,3-dioxolane-2-yl-methyl)-1-H-1,3,4-triazole gives crystals belonging to the monoclinic space group P2₁/n, and, at 293 K,a=11.1763(6),b=10.7716(4),c=14.5804(8) å,Β=107.445(4)?,V=1674.6(1) å³, Z=4,R(F)=0.043, andR _w(F)=0.043. The ditriazole byproduct (2R,4S)/(2S,4R)-1-(2-(2-chloro-4-(1,2,4-triazole-1-yl)phenyl)-4-n-propyl-1,3-dioxolane-2-yl-methyl)-1-H-1,2,4-triazole gives crystals belonging to the triclinic space groupP¯ 1, and, at 193 K,a=5.3329(8),b=8.3738(7),c=20.240(2) å, α=84.213(6)?,Β=87.20(1)?,γ=86.23(1)?,V=896.5(2) å³, Z=2,R(F)=0.046, andR _w(F)=0.051. The presence of both propiconazole (2R.4S)- and (2S,4R)-enantiomers enables the formation of a crystalline racemic modification, while the diastereomeric propiconazole (2R,4R)- and (2S,4S)-enantiomers are viscous oils. In the absence of its enantiomorphic partner, the propiconazole (2R,4S)- or (2S,4R)-enantiomers remain as viscous oils rather than form chiral crystals.     

Helicity of N,N′-diaryl-trans-1,2-diaminocyclohexane derivatives. Implications for molecular helicity manipulations

Derivatives of trans-1,2-diaminocyclohexane (DACH), useful as chiral ligands, scaffolds and building blocks, differ in their conformation. The conformation of N,N′-diaryl-DACH derivatives was studied by the semiempirical and DFT computational methods and by exciton-coupled circular dichroism. It was found that, contrary to M-helical N,N′-diimine, N,N′-diimide and N,N′-diamide derivatives, the aromatic residues in N,N′-diphenyl derivatives are oriented to form a P-helix for the (R,R)-DACH absolute configuration. The helicity of the bis-aryl system is modified in the case of 1-naphthyl or 2-naphthyl derivatives. Further switching of helicity has been demonstrated by either protonation or mono-N-acetylation of N,N′-diaryl DACH derivatives.     

Apparent molar volumes and apparent molar heat capacities of aqueous potassium hydrogen phthalate (KHP) and potassium sodium phthalate (KNaP) at temperatures fromT = 278.15 K toT = 393.15 K at the pressure 0.35 MPa

A vibrating-tube densimeter (DMA 512P, Anton Paar, Austria) was used to investigate the densities and volumetric properties of aqueous potassium hydrogen phthalate (KHP) and potassium sodium phthalate (KNaP). Measurements were made at molalities m from (0.006 to 0.66)mol · kg ^− 1, at temperatures from 278.15 K to 368.15 K and at the pressure 0.35 MPa. The densimeter was calibrated through measurements on pure water and on 1.0 mol · kg ^− 1NaCl(aq). We also used a twin fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter (NanoDSC 6100, Calorimetry Sciences Corporation, Spanish Fork, UT, U.S.A.) to measure solution heat capacities. This was accomplished by scanning temperature and comparing the heat capacities of the unknown solutions to the heat capacity of water. Apparent molar volumes V_φand apparent molar heat capacities C_{p, φ}of the solutions were calculated and fit by regression to equations that describe the surfaces (V_φ, T, m) and (C_{p, φ}, T, m). Standard state partial molar volumesV₂^o and heat capacities C_p,2^owere estimated by extrapolation to the m =  0 plane of the fitted surfaces. Previously determinedC_{p, φ} for HCl(aq) and NaCl(aq) were used to obtain (Δ_rC_{p, m}, T, m) for the proton dissociation reaction of aqueous hydrogen phthalate. This (Δ_rC_p,m, T, m) surface was created by subtracting C_p,φfor KHP(aq) and for NaCl(aq) from the sum of C_p,φfor KNaP(aq) and for HCl(aq). Surfaces representing (Δ_rH_m, T, m) and (pQ_a, T, m), where pQ_adenotes the molality equilibrium quotient, were created by integration of our (Δ_rC_p,m, T, m) surface using values for (Δ_rH_m, m) and (pK_a, m) at T =  308.15 K from the literature as integration constants.     

A model for transitional plane Couette flow

A simplified model of plane Couette flow is derived by means of a cross-stream (y) Galerkin expansion in terms of trigonometric functions appropriate for idealized stress-free boundary conditions at the plates. A set of partial differential equations is obtained, governing the in-plane (x–z) space-dependence of a velocity field taken in the form: u=U₀(x,z,t)+[1+U₁(x,z,t)]sin(πy/2), v=V₁(x,z,t)cos(πy/2), w=W₀(x,z,t)+W₁(x,z,t)sin(πy/2). Beyond Lorenz-like Waleffe's modeling (Waleffe 1997), this Swift–Hohenberg type of approach is expected to give an access to the microscopic mechanism of spatiotemporal intermittency typical of the transition to turbulence in plane Couette flow (Pomeau 1986, Bergé et al. 1998).     

An accurate simplified data treatment for the initial adsorption kinetics in conditions of laminar convection in a slit: application to protein adsorption

We present the derivation of a simple approximation for the original expression of the adsorption rate [Langmuir 10 (1994) 3898] in conditions of laminar flow in a slit, to relate the measured initial kinetic constant k with the interfacial kinetic constant k_a and the transport-limited Lévêque constant k_Lev. The same method of derivation is applied here to get a simple approximation of the average kinetic constant 〈k〉 [Biomaterials 20 (1999) 1621]. For the local value, at distance x from the entrance of the slit, we propose k(x)/k_a=(u−1)(au−1)/(bu+1), where u=k(x)/k_Lev, a=0.452, b=−0.625, with a maximal error of 1% in comparison with the exact solution. For the average value over the length of the slit, we propose 〈k〉/k_a=(U−1)(AU−1)/(BU+1), where U=〈k〉/〈k_Lev〉, A=0.203, B=−0.273, with a maximal error of 0.03%. These approximations lead to an easy determination of the adsorption constant and diffusion coefficient D of the solute, as appropriate plots of experimental data provide k_a and D^2/3 as the intercepts of the curve with the ordinate and abscissa axes, respectively. It is pointed out that the linear approximation k⁻¹=k_a⁻¹+k_Lev⁻¹ would lead to the overestimation of both the diffusion coefficient and adsorption kinetic constant. As an example, the application to the analysis of experimental data for adsorption of α-chymotrypsin onto mica plates is provided.     

Fine structure of the 1s5f and 1s5g levels of He I

The fine structure of the 1s5f and 1s5g levels of He I was measured using microwave spectroscopy. The helium atoms were excited by ion impact, and the eleven allowed 1s5f ^2S+1 F _J –1s5g ^2S′+1 G _J , transitions near ν≈15 GHz were induced and detected by measuring the 1s4d–1s2p or 1s3d–1s2p spectral-line intensities of the impact radiation as a function of the microwave frequency. The measured transition frequencies are in accord with theoretical values and, except for one transition frequency, with earlier experimental data. The existing discrepancy between these earlier data and theory could be solved.     

A different approach to X-ray stress analysis

A different approach to X-ray stress analysis has been developed. At the outset, it must be noted that the material to be analyzed is assumed homogeneous and isotropic. If a sphere with radius r within a specimen is subjected to a state of stress, the sphere is deformed into an ellipsoid. The semi-axes of the ellipsoid have the values of (r + ε_x), (r + ε_y), and (r + ε_z), which are replaced by d_x, d_y, and d_z, or for the cubic case, a_x, a_y, and a_z. In this technique, at a particular ϕ angle (see Fig. 1), the two-theta position of a high angle (hkl) peak is determined at ψ angles of 0, 15, 30, and 45°. These measurements are repeated for 3 to 6 ϕ angles in steps of 30°. The d_ϕψ or a_ϕψ values are then determined from the peak positions. The data is then fitted to the general quadratic equation for an ellipsoid by the method of least squares. From the coefficients of the quadratic equation, the angle between the laboratory and the specimen coordinates (direction of the principle stress) can be determined. Applying the general rotation of axes equations to the quadratic, the equation of the ellipse in the x–y plane is determined. The a_x, a_y, and a_z values for the principal axes of the lattice parameter ellipsoid are then evaluated. It is then possible to determine the unstressed a₀ value from Hooke's Law using a_x, a_y, and a_z. The magnitude of the principal strains/stresses is then determined.     

A methodology to define the Cubic Equation of State of a simple fluid

A method to define the Cubic Equation of State (CES) of a simple substance is presented in this work. CES is constructed with only three parameters of the fluid, namely, the critical compressibility Z_c≡P_cv_c/RT_c, the acentric factor ω ≡ − log  (P^(sat)/P_c) − 1 (where P^(sat) is the saturated vapor pressure), and the saturated vapor volume v^(sat) at the temperature T^(sat)/T_c = 0.7 (where T_c is the critical temperature, v_c is the critical volume, and P_c is the critical pressure). The resulting CES is unique for each substance and, in general, it is different from other known CES in the literature.     

Structural, spectral and thermal studies of substituted N-(2-pyridyl)-N′-phenylthioureas

N-2-(3-picolyl)-N′-phenylthiourea, 3PicTuPh, monoclinic, P2₁/n, a=7.617(2) b=7.197(5), c=22.889(5) Å, β=94.63(4)°, V=1250.7(1) Å³ and Z=4; N-2-(4-picolyl)-N′-phenylthiourea, 4PicTuPh, triclinic, P-1, a=7.3960(5), b=7.9660(12), c=21.600(3) Å, α=86.401(4), β=84.899(8), γ=77.769(8)°, V=1237.5(3) Å³ and Z=4; N-2-(5-picolyl)-N′-phenylthiourea, 5PicTuPh, monoclinic, P2₁/c, a=14.201(1), b=4.905(3), c=17.689(3) Å, β=91.38(1)°, V=1231.8(7) Å³ and Z=4; N-2-(6-picolyl)-N′-phenylthiourea, 6PicTuPh, monoclinic, C2/c2, a=14.713(1), b=9.367(1), c=18.227(1) Å, β=92.88(1)°, V=2515.5(1) Å³ and Z=8 and N-2-(4,6-lutidyl)-N′-phenylthiourea, 4,6LutTuPh, monoclinic, C2/c, a=11.107(2), b=11.793(2), c=20.084(4) Å, β=96.10(3)°, V=2616(1) Å³ and Z=8. Intramolecular hydrogen bonding between N′H and the pyridyl nitrogen and intermolecular hydrogen bonding involving the thione sulfur are affected by substitution of the pyridine ring, as is the planarity of the molecule. ¹H NMR studies in CDCl₃ show the NH′ hydrogen resonance considerably downfield from other resonances in the spectrum for each thiourea.     

Effect of blending way on β-crystallization tendency of compatibilized β-nucleated isotactic polypropylene/poly(ethylene terephthalate) blends

The main purpose of this study is to investigate the β-crystallization tendency in the β-nucleated iPP blends. The β-nucleated iPP/compatibilizers blends, β-nucleated iPP/PET blends and its compatibilized versions with four kinds of compatibilizers (PP-g-MA, PP-g-GMA, POE-g-MA, and EVA-g-MA) were prepared by different blending ways. The effect of compatibilizers and blending ways on the non-isothermal crystallization and melting characteristics and the β-crystallization tendency of β-nucleated iPP blends were studied by differential scanning calorimetry. The relative content of the β-phase were characterised by the k _β values determined on the basis of the wide angle X-ray diffractogram. The results indicated that the β-crystallization tendency of β-nucleated iPP blends depends on the kinds of compatibilizer. Addition of PP-g-MA significantly reduced the β-crystallization tendency of β-nucleated iPP, while PP-g-GMA, POE-g-MA, and EVA-g-MA have little effect on it. In the compatibilized β-nucleated iPP/PET blends, the blending ways, which controlled the dispersion of β-nucleating agent, influences the β-crystallization tendency intensively. The high β-crystallization tendency and β-crystal content were obtained for compatibilized β-nucleated iPP/PET blends prepared firstly at high temperature and β-nucleating agent added into blends at low temperature; however, the type of compatibilizers has little effect on β-crystallization tendency and melting behavior of blends.     

Molar excess volumes of ternary mixtures of nonelectrolytes

Molar excess volumes V^E_ijk of methylenebromide i + pyridine j + β-picoline (k, cyclohexane (i) + pyridine (j) + β-picoline(K), benzene(i)+toluene(j)+1,2-dichloroethane(k), benzene(i) + 0-xylene(j) + 1,2-dichloroethane(k) and benzene(i) + p-xylene(j) + 1,2-dichloroethane(k) mixtures have been determined dilatometrically at 298.15 K. The data have been examined in terms of Sanchez and Lacombe theory and the graph-theoretical approach, and it is found that they are described well by the latter. Self- and cross-volume interaction coefficients V_jk, V_jjk and V_jkk, etc., have also been evaluated and the values utilised to study molecular interactions between the jth and kth molecular species in the presence of the ith in these i + j + k mixtures.     

Copper(I) catalysis: Synthesis of N,N′-diarylated and N-aryl,N′-formylated chiral C2-symmetric diamines

Chiral N,N′-diaryl C₂-symmetric diamines and N-aryl,N′-formyl-trans-(1R,2R)-diaminocyclohexane are readily accessed by copper catalyzed N,N′-diarylation and N-aryl,N′-formylation of trans-(1R,2R)-diaminocyclohexane with aryl bromides. N,N′-diarylation using (R)-1,1′-binaphthyl-2,2′-diamine and iodobenzene gave the corresponding (R)-N,N′-diphenyl-1,1′-binaphthyl-2,2′-diamine derivative in 83% yield.     

Semiclassical variational study of size effects in neutral and charged jellium droplets

An analytic expression for the total energy of metallic clusters composed ofN identical atoms of valencev and with net chargeQ is obtained by means of a variational solution of the Thomas-Fermi-Weizsäcker energy density functional within the spherical jellium model. The minimum energy is given as an expansion in decreasing powers of the cluster radiusR=r _s Z ^1/3, withZ=vN andr _s the radius per electron of the bulk metal. The coefficients are obtained as functions ofr _s . Terms of volume (R ³), surface (R ²), curvature (R), constant (R ⁰), (1/R) and (1/R ²) are clearly separated in the formula, as well as the different contributions (kinetic, coulombic and exchange-correlation) to each of them. The asymptotic values (R→∞) for the work functions,W(r _s ), and surface energies σ(r _s ), are compared to analogous semiclassical and Kohn-Sham calculations of jellium-like surfaces and to the experimental values. The size dependent behaviour of chemical potentials, μ(R), electron affinities,AF(R), and ionization potentials,IP(R), are easily obtained for any kind of metallic clusters. In particular we discuss the Coulomb and quantum corrections to the coefficients β, δ in the asymptotic formulae:IP?W+β/R andAF?W+δ/R.     

Synthesis of enantiopure cyclitols from (±)-3-bromocyclohexene mediated by intramolecular oxyselenenylation employing (S,S)-hydrobenzoin and (S)-mandelic acid as chiral sources

Reaction of 3-bromocyclohexene with (S,S)-hydrobenzoin and (S)-mandelic acid and subsequent intramolecular oxyselenenylation of the resulting allylic ethers followed by oxidation-elimination afforded the valuable cis-fused bicyclic olefins, (1S,3S,4S,6R)-3,4-diphenylbicyclo[4,4,0]-2,5-dioxa-7-decene and (1S,3S,4R)-3-phenyl-4a,7,8,8a-tetrahydro-benzo[1,4]dioxan-2-one, respectively. Further stereoselective transformation of these cis-fused bicyclic olefins afforded the enantiopure cyclohexitols, muco-quercitol, d-chiro-inocitol and allo-inocitol.     

A spectroscopic study on medium polarity in fluorous alcohol

The paper describes the polarities of three fluorous (F) aliphatic alcohols: perfluorinated tert-butanol (F-t-BuOH), n-butanol (F-n-BuOH), and n-heptanol (F-n-HepOH). For the purpose, we conducted absorption and fluorescence spectroscopies of coumarin 153 (C153) and 102 (C102) in three F and 13 non-fluorous (non-F) alcohols and determined their maximum energies: ν^a (absorption) and ν^f (fluorescence). We obtained linear relationships between the Stokes shifts of the dyes (i.e., (ν^a − ν^f)) and a medium polarity parameter for 13 non-F alcohols, f(x): f(x) = [(D_s − 1)/(2D_s + 1) − (n² − 1)/(2n² + 1)], where D_s and n were the dielectric constant and refractive index of a solvent, respectively. By comparing the Stokes shifts of the dyes in three F alcohols with those in 13 non-F alcohols (i.e., (ν^a − ν^f) vs. f(x) plot), the D_s values in F-t-BuOH, F-n-BuOH, and F-n-HepOH were evaluated to be 2.7-3.9, 4.3-5.1, and 4.0-5.2, respectively, while those in the relevant non-F alcohols were 12.5, 17.5, and 12.9, respectively. Thus, the present experiments demonstrated that the polarities of these F alcohols were much lower than those of the relevant non-F alcohols.     

Molecular self-induced configuration for improving dissymmetry factors in tetradentate platinum(II) enantiomers cycloaddition

Two pairs of Pt(II) enantiomers ((RR)/(SS)-PyPt, ((RR)/(SS)-Py: N,N'-(1,2-diphenylethane-1,2-diyl)dipicolinamide; (RR)-P/M-QPt, ((RR)/(SS)-Q: N,N'-((1R,2R)-1,2-diphenylethane-1,2-diyl)bis(quinoline-2-carboxamide)) were synthesized, respectively, with good circularly polarized luminescence (CPL) and tunable dissymmetry factors (g) by molecular self-induction with (RR)/(SS)-1,2-diphenylethane-1,2-diamine as carbon chiral sources. In the (RR)-P-QPt and (SS)-M-QPt, specific P- and M-configurations were effectively induced from intrinsic chiral carbon centres (R or S), ingeniously avoiding the racemic mixture formation and chiral separation. Furthermore, the chirality originating from both chiral carbon centres and helicene-like structure improves the g factor significantly, which provides a new molecular design strategy for chiral Pt(II) enantiomers with good CPL properties.     

Über den Einfluß der elektrostatischen Wechselwirkungen auf die α-Helixbildung von basischen Poly-[α-aminosäuren]

A theoretical treatment of the electrostatic interactions influencing the conformation of poly-[α-aminoacids] containing ionogenic side-chains is reported. Using the Gouy-Chapman-equation for the relation between the density of surface chargeσ _e and surfacepotentialψ the latter one will be determined on the surface of anα-helix of a basic poly-[α-aminoacid] in an aqueous electrolyte solution. As it could be shown,ψ decreases with the electrolyte concentrationc. The equilibrium constants for the propagation step of theα-helix-formation is expressed as a function ofψ and a parameterK ₀ containingΔS₀ andΔH₀ dependent onc, considering the electrostatic energy of neighboured basic groups. The temperature at the mid-point of the transitionT _m is a function of the reciproce ionic strengthI. In a solution of an 1-1-electrolyte,T _m depends linearly on 1/√c. The experimental data for Poly-[L-lysine] are in a very good agreement with the straight line given by this relation. However, in the case of a 1∶1 copolymer ofL-lysine andL-leucine the calculated values are much lower than the measured ones, obviously due to neglecting the hydrophobic interactions of the leucine side chains. Furthermore, a relation for the change of theα-helix-contentf _H with 1/T is given. In this case, in the well-known relation (?f _H/? (1/T))=?ΔH⁰/4Rσ ^1/2, the cooperative parameterσ is substituted by a modified parameterΣ depending on the ionic strength. According to this equation and agreeing with the experimental results,T _m increases with the ionic strength, because the electrostatic potentialψ at theα-helix-surface decreases. However, in contrast to reality, the inclination of thef _H-T-curves increases withI orc, respectively. This may be due to an increase ofσ with the electrolyte concentration.