An ab initio study of cooperative effects in ternary complexes X:CNH:Z with X, Z = CNH, FH, ClH, FCl, and HLi: structures, binding energies, and spin-spin coupling constants across intermolecular bonds

A systematic ab initio investigation has been carried out to determine the structures, binding energies, and spin-spin coupling constants of ternary complexes X:CNH:Z and corresponding binary complexes X:CNH and CNH:Z, for X, Z = CNH, FH, ClH, FCl, and HLi. The enhanced binding energies of ternary complexes X:CNH:Z for fixed X as a function of Z decrease in the same order as the binding energies of the binary complexes CNH:Z. In contrast, the enhanced binding energies of the ternary complexes for fixed Z as a function of X do not decrease in the same order as the binding energies of the binary complexes X:CNH, a consequence of the increased stabilities of ternary complexes FCl:CNH:Z due to very strong chlorine-shared halogen bonds. For complexes in which the X···CNH interaction is a D-H···C hydrogen bond for D-H the proton-donor group (N-H, F-H, or Cl-H), spin-spin coupling constants (1)J(D-H) and (2h)J(D-C) in ternary complexes X:CNH:Z decrease in absolute value as the binding energies of binary complexes CNH:Z and the enhanced binding energies of the ternary complexes for fixed X as a function of Z also decrease. However, (2X)J(F-C) increases as the enhanced binding energies of the ternary complexes FCl:CNH:Z decrease, a consequence of the nature of the chlorine-shared halogen bond. The one-bond coupling constants (1)J(N-H) for the CNH···Z interaction in ternary complexes vary significantly, depending on the nature of the X···CNH interaction. The largest values of (1)J(N-H) are found for ternary complexes with FCl as X. Two-bond coupling constants (2h)J(N-A) for A the proton-acceptor atom of Z, and (2d)J(N-H) decrease in absolute value in the order of decreasing enhancement energies of ternary complexes X:CNH:Z for fixed Z as a function of X.     

FCl:PCX complexes: old and new types of halogen bonds

MP2/aug'-cc-pVTZ calculations have been performed to investigate the halogen-bonded complexes FCl:PCX, for X = NC, CN, F, H, CCH, CCF, CH(3), Li, and Na. Although stable complexes with a F-Cl···P halogen bond exist that form through the lone pair at P (configuration I), except for FCl:PCCN, the more stable complexes are those in which FCl interacts with the C≡P triple bond through a perturbed π system (configuration II). In complexes I, the nature of the halogen bond changes from traditional to chlorine-shared and the interaction energies increase, as the electron-donating ability of X increases. The anionic complex FCl:PC(-) has a chlorine-transferred halogen bond. SAPT analyses indicate that configuration I complexes with traditional halogen bonds are stabilized primarily by the dispersion interaction. The electrostatic interaction is the most important for configuration I complexes with chlorine-shared halogen bonds and for configuration II complexes except for FCl:PCNa for which the induction term is most important. The F-Cl stretching frequency is red-shifted upon complexation. EOM-CCSD/(qzp,qz2p) spin-spin coupling constants have been obtained for all FCl:PCX complexes with configuration I. (1)J(F-Cl) decreases upon complexation. (2X)J(F-P) values are quadratically dependent upon the F-P distance and are very sensitive to halogen-bond type. (1X)J(Cl-P) tends to increase as the Cl-P distance decreases but then decreases dramatically in the chlorine-transferred complex FCl:PC(-) as the Cl-P interaction approaches that of a covalent Cl-P bond. Values of (1)J(F-Cl) for configuration II are reduced relative to configuration I, reflecting the longer F-Cl distances in II compared to those of the neutral complexes of I. Although the F-P and Cl-P distances in configuration II complexes are shorter than these distances in the corresponding configuration I complexes, (2X)J(F-P) and (1X)J(Cl-P) values are significantly reduced, indicating that coupling through the perturbed C-P π bond is less efficient. The nature of F-P coupling for configuration II is also significantly different, as evidenced by the relative importance of PSO, FC, and SD components.     

Ab initio study of ternary complexes X:(HCNH)(+):Z with X, Z = NCH, CNH, FH, ClH, and FCl: diminutive cooperative effects on structures, binding energies, and spin-spin coupling constants across hydrogen bonds

Ab initio calculations have been performed on a series of complexes in which (HCNH)(+) is the proton donor and CNH, NCH, FH, ClH, and FCl (molecules X and Z) are the proton acceptors in binary complexes X:HCNH(+) and HCNH(+):Z, and ternary complexes X:HCNH(+):Z. These complexes are stabilized by C-H(+)···A and N-H(+)···A hydrogen bonds, where A is the electron-pair donor atom of molecules X and Z. Binding energies of the ternary complexes are less than the sum of the binding energies of the corresponding binary complexes. In general, as the binding energy of the binary complex increases, the diminutive cooperative effect increases. The structures of these complexes, data from the AIM analyses, and coupling constants (1)J(N-H), (1h)J(H-A), and (2h)J(N-A) for the N-H(+)···A hydrogen bonds, and (1)J(C-H), (1h)J(H-A), and (2h)J(C-A) for the C-H(+)···A hydrogen bonds provide convincing evidence of diminutive cooperative effects in these ternary complexes. In particular, the symmetric N···H(+)···N hydrogen bond in HCNH(+):NCH looses proton-shared character in the ternary complexes X:HCNH(+):NCH, while the proton-shared character of the C···H(+)···C hydrogen bond in HNC:HCNH(+) decreases in the ternary complexes HNC:HCNH(+):Z and eventually becomes a traditional hydrogen bond as the strength of the HCNH(+)···Z interaction increases.     

2JC,H index: a nondestructive NMR method for differentiation of aldohexopyranosyl residues

A new 2J(C,H) index method is described for identification of aldohexopyranose. This method is based on a fact that 2J(C,H) values reflect the stereochemistry for glycol connectivity. Based on the observed 2J(C,H) values for galactose, glucose, and mannose, 2J(C,H) profiles for other aldohexopyranoses are proposed. A combination of 2J(C,H) values was found to be useful for identification of aldohexopyranosyl residues in glycans. [structure: see text]     

QSID Tool: a new three-dimensional QSAR environmental tool

QSID Tool (Quantitative structure–activity relationship tool for Innovative Discovery) was developed to provide an easy-to-use, robust and high quality environmental tool for 3D QSAR. Predictive models developed with QSID Tool can accelerate the discovery of lead compounds by enabling researchers to formulate and test hypotheses for optimizing efficacy and increasing drug safety and bioavailability early in the process of drug discovery. QSID Tool was evaluated by comparison with SYBYL^® using two different datasets derived from the inhibitors of Trypsin (Böhm et al., J Med Chem 42:458, 1999) and p38-MAPK (Liverton et al., J Med Chem 42:2180, 1999; Romeiro et al., J Comput Aided Mol Des 19:385, 2005; Romeiro et al., J Mol Model 12:855, 2006). The results suggest that QSID Tool is a useful model for the prediction of new analogue activities.     

Characterizing hydrogen bonding and proton transfer in 2:1 FH:NH3 and FH:collidine complexes through one- and two-bond spin-spin coupling constants across hydrogen bonds

Ab initio equation-of-motion coupled cluster singles and doubles calculations have been carried out on a variety of 2:1 FH:NH(3) complexes (F(b)H(b):F(a)H(a):NH(3)) to investigate the effects of structural changes on one- and two-bond spin-spin coupling constants across F(a)-H(a)-N and F(b)-H(b)-F(a) hydrogen bonds and to provide insight into experimentally measured coupling constants for 2:1 FH:collidine (2:1 FH:2,4,6-trimethylpyridine) complexes. Coupling constants have been computed for 2:1 FH:NH(3) equilibrium structures and proton-transferred perpendicular and open structures at 2:1 FH:NH(3), FH:pyridine, and FH:collidine geometries. (2h)J(Fa)(-)(N), (1)J(Fa)(-)(Ha), and (1h)J(Ha)(-)(N) exhibit expected dependencies on distances, angles, and the nature of the nitrogen base. In contrast, one- and two-bond coupling constants associated with the F(b)-H(b)-F(a) hydrogen bond, particularly (2h)J(F)()b(-)(F)()a, vary significantly depending on the F-F distance, the orientation of the hydrogen-bonded pair, and the nature of the complex (HF dimer versus the anion FHF(-)). The structure of the 2:1 FH:collidine complex proposed on the basis of experimentally measured coupling constants is supported by the computed coupling constants. This study of the structures of open proton-transferred 2:1 FH:NH(3), FH:pyridine, and FH:collidine complexes and the coupling constants computed for 2:1 FH:NH(3) complexes at these geometries provides insight into the role of the solvent in enhancing proton transfer across both N-H(a)-F(a) and F(b)-H(b)-F(a) hydrogen bonds.     

Biostimulation of Na,K-ATPase by low-energy laser irradiation (685 nm, 35 mW): comparative effects in membrane, solubilized and DPPC:DPPE-liposome reconstituted enzyme

OBJECTIVE: The aim of the present work was to investigate the effect of low-energy laser irradiation (685 nm, 35 mW) on the ATPase activity of the different forms of the Na,K-ATPase. METHODS: Membrane-bound and solubilized (alphabeta)(2) form of Na,K-ATPase was obtained from the dark red outer medulla of the kidney and proteoliposomes of DPPC:DPPE and Na,K-ATPase was prepared by the co-solubilization method. Irradiations were carried out at 685 nm using an InGaAIP diode laser. RESULTS: The ATPase activity of the membrane fraction was not altered with exposition to irradiation doses between 4 and 24 J/cm(2). However, with irradiation doses ranging from 32 to 40 J/cm(2), a 28% increase on the ATPase activity was observed while when using up to 50 J/cm(2) no additional enhancement was observed. When biostimulation was done using the solubilized and purified enzyme or the DPPC:DPPE-liposome reconstituted enzyme, an increase of about 36-40% on the ATPase activity was observed using only 4-8 J/cm(2). With irradiation above these values (24 J/cm(2)) no additional increase in the activity was observed. These studies revealed that the biostimulation of ATPase activity from different forms of the Na,K-ATPase is dose dependent in different ranges of irradiation exposure. The stimulation promoted by visible laser doses was modulated and the process was reverted after 2 h for the enzyme present in the membrane and after about 5 h for the solubilized or the reconstituted in DPPC:DPPE-liposomes.     

Mechanisms of exchange modulation in trimethylenemethane-type biradicals: the roles of conformation and spin density

The molecular structures and magnetic properties of six dinitroxide biradicals are described. Five of the dinitroxides are trimethylenemethane-type (TMM-type) biradicals; that is, the intramolecular exchange parameter, J, is modulated by a carbon-carbon double bond. However, the efficacy of the carbon-carbon double bond as an exchange coupler is determined by the molecular conformation. Our results show that the exchange parameters correlate with phenyl-ring torsion angles (phi) via a simple Karplus-Conroy-type relation: J = 44 cos(2) phi - 17. Comparison of these results to those obtained for our isostructural series of bis(semiquinone) biradicals shows that both the magnitude of J and the resistance of ferromagnetic J to bond torsions is proportional to the spin density adjacent to the exchange coupler.     

Fractionated illumination in oesophageal ALA-PDT: effect on ferrochelatase activity

BACKGROUND AND OBJECTIVE: Administration of 5-aminolevulinic acid (ALA) induces accumulation of the photosensitive compound protoporphyrin IX (PpIX) in certain tissues. PplX can be used as photosensitizer in photodynamic therapy (PDT). More selective or higher PpIX accumulation in the area to be treated could optimize the results of ALA-PDT. Porphobilinogen deaminase (PBGD) is rate-limiting in PpIX formation whereas ferrochelatase converts PpIX into haem by chelation of ferrous iron into PpIX. This results in a moment of close interaction (ferrochelatase binding to PpIX) during which ferrochelatase could selectively be destroyed resulting in an increased PpIX concentration. The aim of the present study was to investigate whether illumination before PDT can selectively destroy ferrochelatase. and whether this results in higher PpIX accumulation and thereby increases the PDT effect. Furthermore, the effect of a second ALA dose was tested. STUDY DESIGN/MATERIALS AND METHODS: Oesophageal tissue of 60 rats were allocated to 2 groups of 30 animals each. In one group, enzyme and PpIX measurements were performed after ALA administration (200 mg/kg orally, n=20), or a second dose of 200 mg/kg ALA at 4 h (n=10), half of each group with and without illumination at 1 h with 12.5 J/cm diffuser length. In the second group, PDT was performed. Ten animals were illuminated at 3 h after ALA administration with 20 (n=5) or 32.5 J/cm (n=5), 10 animals were illuminated at 1 h (12.5 J/cm) and received intra-oesophageal PDT treatment (20 J/cm) at 3 h (n=5) or 4 h (n=5) after ALA. Additionally, 10 animals received a second dose of 200 mg/kg ALA at 4 h and were illuminated (20 J/cm) at 7 h after the first dose of ALA with (n=5) or without (n=5) illumination at 4 h (12.5 J/cm). RESULTS: Illumination with 12.5 J/cm at 1 h after ALA administration caused inhibition of the activity of ferrochelatase at 3 and 4 h after ALA (P=0.02 and P<0.001, respectively), but not at 7 h (P=0.3). In animals sacrificed at 4 h the ratio PBGD:ferrochelatase was higher in animals illuminated at 1 h compared to non-illuminated animals (P<0.001). PpIX concentration was highest (42.7 +/- 3.2 pmol/mg protein) at 3 h after ALA administration and did not increase by illumination at 1 h. Administration of a second dose of ALA did not result in higher PpIX accumulation. After PDT, no difference in epithelial or muscular damage was found between the various groups. CONCLUSION: Illumination at 1 h after ALA administration can cause selective destruction of ferrochelatase, resulting in a higher ratio of PBGD:ferrochelatase. This does not result in accumulation of more porphyrins, even when a second dose of ALA is given. Therefore, under the conditions used in this study fractionated illumination does not enhance ALA-PDT-induced epithelial ablation of the rat oesophagus.     

Determination of interconversion barriers by dynamic gas chromatography: epimerization of chalcogran

The four stereoisomers of chalcogran 1 ((2RS,SRS)-2-ethyl-1,6-di-oxaspiro[4.4]nonane), the principal component of the aggregation pheromone of the bark beetle pityogenes chalcographus, are prone to interconversion at the spiro center (C5). During diastereo- and enantioselective dynamic gas chromatography (DGC), epimerization of 1 gives rise to two independent interconversion peak profiles, each featuring a plateau between the peaks of the interconverting epimers. To determine the rate constants of epimerization by dynamic gas chromatography (DGC), equations to simulate the complex elution profiles were derived, using the theoretical plate model and the stochastic model of the chromatographic process. The Eyring activation parameters of the experimental interconversion profiles, between 70 and 120 C in the presence of the chiral stationary phase (CSP) Chirasil-beta-Dex, were then determined by computer-aided simulation with the aid of the new program Chrom-Win: (2R,5R)-1: deltaG(++) (298.15 K) = 108.0 +/-0.5 kJ mol(-1), deltaH(++) = 47.1+/-0.2 kJ mol(-1), deltaS(++) = -204+/-6 JK(-1) mol(-1): (2R,5S)-1: deltaG(++) (298.15 K) = 108.5+/-0.5 kJ mol(-1), deltaH(++) = 45.8+/-0.2 kJ mol(-1), deltaS(++) = -210 +/-6 J K mol(-1); (2S,5S)-1: deltaG(++) (298.15 K)= 108.1+/-0.5 kJ mol(-1), deltaH(++) = 49.3+/-0.3 kJ mol(-1), deltaS(++) = -197+/-8 J K(-1) mol(-1); (2S,5R)-1: deltaG(++) (298.15 K)=108.6+/-0.5 kJ mol(-1), deltaH(++) = 48.0+/-0.3 kJ mol(-1), deltaS(++) = -203+/-8 J K(-1) mol(-1). The thermodynamic Gibbs free energy of the E/Z equilibrium of the epimers was determined by the stopped-flow multidimensional gas chromatographic technique: deltaG(E/Z) (298.15 K)= -0.5 kJ mol(-1), deltaH(E/Z) = 1.4 kJ mol(-1) and deltaS(E/Z) = 6.3 J K(-1) mol(-1). An interconversion pathway proceeding through ring-opening and formation of a zwitterion and an enol ether/alcohol intermediate of 1 is proposed.     

Metal fluorides form strong hydrogen bonds and halogen bonds: measuring interaction enthalpies and entropies in solution

The organometallic compound trans-(tetrafluoropyrid-2-yl)bis(triethylphosphine)-fluoronickel(II) (NiF) is shown to serve as a strong hydrogen bond and halogen bond acceptor in solution via intermolecular interactions with the fluoride ligand. The nature of the interactions has been confirmed by multinuclear NMR spectroscopy. Experimental binding constants, enthalpies, and entropies of interaction with hydrogen-bond-donor indole and halogen-bond-donor iodopentafluorobenzene have been determined by 19F NMR titration. In toluene-d8 solution indole forms a 1:1 and 2:1 complex with NiF (K1 = 57.9(3), K2 = 0.58(4)). Interaction enthalpies and entropies are -23.4(2) kJ mol-1 and -44.5(8) J mol-1 K-1, respectively, for the 1:1 complex; -14.8(8) kJ mol-1 and -53(3) J mol-1 K-1, respectively, for the 2:1 complex. In toluene-d8 solution iodopentafluorobenzene forms only a 1:1 complex (K1 = 3.41(9)) with enthalpy and entropy of interaction of -16(1) kJ mol-1 and -42(4) J mol-1 K-1, respectively. A marked solvent effect was observed for the halogen bond interaction. NMR titrations in heptane solution indicated formation of both 1:1 and 2:1 complexes of iodopentafluorobenzene with NiF (K1 = 21.8(2), K2 = 0.22(4)). Interaction enthalpies and entropies are -26(1) kJ mol-1 and -63(4) J mol-1 K-1, respectively, for the 1:1 complex; -21(1) kJ mol-1 and -83(5) J mol-1 K-1, respectively, for the 2:1 complex. There is a paucity of such experimental energetic data particularly for halogen bonds despite substantial structural data. These measurements demonstrate that halogen bonds are competitive with hydrogen bonds as intermolecular interactions and provide a suitable benchmark for theoretical calculations and quantitative input into design efforts in supramolecular chemistry and crystal engineering.     

DDLm: A New Dictionary Definition Language

A previous paper [Spadaccini and Hall J. Chem. Inf. Model. doi:10.1021/ci300074v] details extensions to the STAR File [Hall J. Chem. Inf. Comput. Sci.1991, 31, 326-333] syntax that will improve the exchange and archiving of electronic data. This paper describes a dictionary definition language (DDLm) for defining STAR File data items in a domain dictionary. A dictionary that defines the ontology and vocabulary of a discipline is built with DDLm, which is itself implemented in STAR, and is extensible and machine parsable. The DDLm is semantically rich and highly specific; provides strong data typing, data enumerations, and ranges; enables relationship keys between data items; and uses imbedded methods written in dREL [Spadaccini et al. J. Chem. Inf. Model. doi:10.1021/ci300076w] for data validation and evaluation and for refining data definitions. It promotes the modular definition of the discipline ontology and reuse through the ability to import definitions from other local and remote dictionaries, thus encouraging the sharing of data dictionaries within and across domains.     

Magnetic exchange coupling in bis-nitroxides: a theoretical analysis of the solvent effects

Magnetic properties of nitroxide radicals can be greatly affected by solvent effects. In this study, the change of the magnetic exchange interaction J, coupling the two unpaired electrons of a model solvated antiferromagnetic bis-iminyl-nitroxide molecule (2IN), is rationalized thanks to different geometric and electronic criteria provided by density functional theory calculations. It is shown that for a given geometry, simple tools can be used to analyze with good accuracy the dependence of J with the solvent polarity. Estimates of two important magnetic parameters are given: the magnetic orbitals exchange and the in-site energy gap between ionic and neutral configurations. 2IN can be engaged in different hydrogen-bonds with first shell water molecules, modifying both the 2IN geometry and the electrostatic potential felt by the molecule. In all, the additivity of electrostatic and hydrogen-bond solvent effects is found to be responsible for J variations as large as 50%.     

Effect of organic solvents on J aggregation of pseudoisocyanine dye at mica/water interfaces: morphological transition from three-dimension to two-dimension

Morphological and spectroscopic properties of pseudoisocyanine (PIC) J aggregates produced at mica/solution interfaces have been characterized by absorption/fluorescence spectroscopy, fluorescence microscopy, and atomic force microscopy. Addition of organic solvents (1-propanol (PrOH) or 1,4-dioxane (Dox)) into aqueous solutions of the PIC dye induced a transition of the morphology of the interfacial J aggregates. The characteristic feature of this transition is the thickness (or height) change of the aggregate domain layers from three-dimensions to two-dimensions: The domain area of the J aggregates was dependent on the amount of the organic cosolvent, while the domain thickness was dependent on the type of the cosolvent. In pure aqueous solution, the J aggregates at the mica/water interface had a three-dimensional structure with the height of approximately 3 nm (multilayer structure). In mixed solvents of PrOH/water or Dox/water (5 or 10 vol%), the interfacial aggregates became a bilayer or monolayer structure, respectively, assuming that PIC molecules are adsorbed on their molecular plane perpendicular to the mica surface. Meanwhile, optical properties (band width and peak position) of the J band were invariant upon addition of the organic cosolvents, suggesting that molecular packing in the J aggregates is essentially unchanged. These results revealed that spectroscopic properties of the interfacial PIC J aggregates were determined only by the lateral (two-dimensional) interaction within the adsorbed monolayer of PIC molecules on mica, and interlayer interaction in the multilayered J aggregate was consequently small.     

Nitration of Chitin Monomer: From Glucosamine to Energetic Compound

The nitration of chitin monomer in a mixture of nitric acid and acetic anhydride was conducted and a highly nitrated (3R,4R,6R)-3-acetamido-6-((nitrooxy)methyl)tetrahydro-2H-pyran-2,4,5-triyl trinitrate (1) was obtained. Its structure was fully characterized using infrared spectroscopy, NMR spectroscopy, elemental analysis, and X-ray diffraction. Compound 1 possesses good density (ρ: 1.721 g·cm⁻³) and has comparable detonation performance (V_d: 7717 m·s⁻¹; P: 25.6 GPa) to that of nitrocellulose (NC: V_d: 7456 m·s⁻¹; P: 23 GPa; I_sp = 239 s) and microcrystalline nitrocellulose (MCNC; V_d: 7683 m·s⁻¹; P: 25 GPa; I_sp = 250 s). However, Compound 1 has much lower impact sensitivity (IS: 15 J) than the regular nitrocellulose (NC; IS: 3.2 J) and MCNC (IS: 2.8 J). Compound 1 was calculated to exhibit a good specific impulse (I_sp: 240 s), which is comparable with NC (I_sp: 239 s) and MCNC (I_sp: 250 s). By replacing the nitrocellulose with Compound 1 in typical propellants JA2, M30, and M9, the specific impulse was improved by up to 4 s. These promising properties indicate that Compound 1 has a significant potential as an energetic component in solid propellants.     

Book Review: Encyplopedia of Pharmaceutical Technology

James Swarbrick:Pharmaceutech, Inc., Pinehurst, North Carolina and aaiPharma Inc., Wilmington, North Carolina, U.S.A.; James J. Boylan: Pharmaceutical Consultant, Gurnee, Illinois, U.S.A.; This revised version was published online in August 2006 with corrections to the Cover Date.     

State-to-state inelastic scattering of OH by HI: a comparison with OH-HCl and OH-HBr

Relative state-to-state cross sections and steric asymmetries have been measured for the scattering process: OH (X (2)Pi(32),v=0,J=32,M(J)=32,f)+HI ((1)Sigma,v=0,J<4)-->OH (X (2)Pi,v=0,Omega=12,J=12-52 and Omega=32,J=32-92,ef)+HI, at 690 cm(-1) collision energy. Comparison with the previously studied systems OH-HCl and OH-HBr reveals relevant features of the potential energy surfaces of these molecular systems. Some measured differences concerning the internal energy distribution after collision and the propensities for the impact with one or the other side of the OH molecule in scattering by HCl, HBr, and HI molecules are discussed.     

Effect of molecular rotation on the atomic alignment dependence in the oriented Ar (3P2) + CF3H reaction

Atomic alignment effect for the CF3* formation in the oriented Ar (3P2, MJ = 2) + CF3H reaction has been investigated at different two CF3H beam conditions: effusive and supersonic beams. The chemiluminescence intensity of CF3* was measured as a function of the magnetic orientation field direction in the collision frame. A significant contribution of rank 4 moment was recognized. The cross-section for each magnetic M'(J) substate in the collision frame, sigma|M'(J)|, was determined to be sigma(|M'(J)|=0):sigma(|M'(J)|=1):sigma(|M'(J)|=2) = 1.00:0.84 +/- 0.02:0.88 +/- 0.02 for the effusive CF3H beam condition. The atomic alignment effect was found to significantly depend on the CF3H beam condition. For the supersonic beam condition, sigma(|M'(J)|=0&1) was changed to be smaller than sigma(|M'(J)|=2).     

Intrinsic viscosities of polyelectrolytes: determination and modeling of the effects of extra salt

Based on early measurements of J. J. Hermans and co-workers (D. T. F. Pals, J. J. Hermans, Recl. Trav. Chim. Pays-Bas 1952, 71, 513-520; D. T. F. Pals, J. J. Hermans, J. Polym. Sci. 1950, 5, 733-734; D. T. F. Pals, J. J. Hermans, J. Polym. Sci. 1948, 3, 897-898), the present contribution demonstrates how primary data should be evaluated in order to obtain reliable intrinsic viscosities. This procedure yields detailed information on the changes of the intrinsic viscosities and of the corresponding viscometric interaction parameters caused by an increasing salinity of water. Both quantities decline from a maximum value in the pure solvent to a minimum value, which is approached in the limit of sufficiently high salt concentrations, and can be modeled quantitatively by means of a Boltzmann sigmoid. Particular attention is paid to the significance of results obtained by means of the method of isoionic dilution, proposed by J. J. Hermans and co-workers.