The aggregation of Span 80 in toluene

The aggregation equilibria of the non-ionic surfactant Span 80 in toluene has been studied by vapour pressure osmometry (VPO) at different temperatures. The experimental data, treated both graphically and numerically using the LETAGROP-SUMPA program, can be explained by assuming the formation of dimers. The thermodynamics of Span 80 in toluene have also been calculated from the van't Hoff equation.     

Solvent effects on dimeric self-association of 2-pyrrolidinone: An ab initio study

Full geometry optimizations were carried out for 2-pyrrolidinone (2-Py) and its dimer structures at the DFT (B3LYP) and HF levels in the gas phase and in solution. Additionally, single-point MP2/6-31G^** calculations were performed on the HF/6-31G^** optimized geometries. The self-association of 2-Py in 1,4-dioxane (=2.21) and in water (=78.54) were studied using the self-consistent reaction field (SCRF) theory. The calculated relative free energies (G) for the dimerization processes predict the cyclic dimer (CD) to be more stable than the open dimer (OD) at all levels of theory in the gas phase and in solution. The results show that, at least for the properties of the hydrogen-bonded systems studied in this work, the B3LYP/6-31G^** calculations give better results than the HF and MP2 calculations with the same basis set. The data obtained from this study were compared with the corresponding experimental results when available.     

Hydrogen bonding and dimeric self-association of 2-pyrrolidinone: An ab initio study

Ab initio calculations on the different associated structures of 2-pyrrolidinone with water and with itself were carried out using 3-21G and 6-31G^* basis sets at the Hartree–Fock level, including electron correlation using second-order Møller–Plesset perturbation theory. The calculated free energy changes for the intermolecular hydrogen bonded dimer and hydrated species indicated that the molecular systems with cyclic dimerization and association with two water molecules are dominant. The results are compared to the available experimental data in the literature.     

On the self-association of the normal alcohols and the glass transition in alcohol-alcohol solutions

The glass-transition temperature (T_g) in mutual binary mixtures of the primary alkanols from methanol throughn-octanol has been measured as a function of composition. For mixtures of the alkanols heavier than ethanol,T _g is found to be a linear function of the number-average molecular length. Methanol and ethanol mixtures show higherT _g values than indicated by this relation. These results are found to be consistent with association of the heavier alkanols into chains of very great length in the supercooled liquid, while ethanol and methanol must form networks with a moderate degree of crosslinking between chains.     

Solvent Effects on the Monomer/Hydrogen‐Bonded Dimer Equilibrium in Carboxylic Acids: (+)‐(S)‐Ketopinic Acid as a Case Study

The hydrogen‐bond‐assisted self‐association process of a chiral semirigid carboxylic acid, namely, (+)‐(S)‐ketopinic acid, has been studied. The multiconformational monomer/dimer equilibrium has been evaluated by means of a concentration‐dependent FTIR study that enabled the experimental equilibrium constants of the dimer formation reaction (K_dim) to be determined in two solvents of different polarity. In CDCl₃, dimeric forms predominate, even in diluted solutions ( =5.074), whereas in CD₃CN the self‐association process is hindered and monomers are always the main species, irrespective of solute concentration ( =0.194). The reliability of the dimerization constants and the derived mono‐ and dimeric experimental fractions have been proven by means of accurate matching between the experimental vibrational circular dichroism spectra of the species and the theoretical spectra generated by considering the simultaneous weighted contributions of the concomitant monomers and dimers.     

Intramolecular Hydrogen-Bonding in a C(10)-Exploded Bilirubinoid

Summary. A new linear tetrapyrrole, with two dipyrrinones connected by a string of 5 carbons, was synthesized from two equivalents of a 9H-dipyrrinone and one of glutaryl dichloride. Unlike typical dipyrrinones, which are intermolecularly hydrogen bonded in the crystal and in CHCl₃ solution, 1,3-bis-[2,3,7,8-tetraethyl-(10H)-dipyrrin-9-carbonyl]propane is a monomer in CHCl₃, as determined by vapor phase osmometry (VPO) measurements. Its crystal structure determination revealed a folded conformation with a novel type of dipyrrinone to dipyrrinone intramolecular hydrogen bonding. Unexpectedly, the same conformation apparently persists in CHCl₃ solution, as shown by ¹H NMR spectroscopy.     

Osmometric Molecular Weight Determinations of Peptides Using o-Chlorophenol

Abstract

Osmometric molecular weight determinations of peptides carried out at 37° using o-chlorophenol as solvent have been found to be precise with the exception of determinations involving peptides containing free carboxyl groups.     

Experimental and quantum chemical study of pyrrole self-association through N-H?π hydrogen bonding

An FT-IR study of pyrrole self-association in CCl₄ solutions was carried out. According to the IR measurements, pyrrole forms self-associated dimeric species via N-H?π hydrogen bonding. This was also confirmed by quantum chemical calculations for pyrrole monomer and dimer at B3LYP/6-31++G(d,p) level of theory. A T-shaped minimum was located on B3LYP/6-31++G(d,p) PES of pyrrole dimer characterized with a hydrogen bond of an N-H?π type, with centers-of-mass separation of monomeric units of 4.520 Å, H?π distance of 2.475 Å, the interplanar angle between the two monomeric units being 72.9°. The anharmonic vibrational frequency shift upon dimer formation calculated on the basis of 1D DFT vibrational potentials is in excellent agreement with the experimental data (84 vs. 87 cm⁻¹). Harmonic vibrational analysis predicts somewhat smaller shift (68 cm⁻¹). On the basis of NIR spectroscopic data, anharmonicity constants for the 2ν(N-H) and 2ν(N-H?π) vibrational transitions were calculated. The orientational dynamics of monomeric and self-associated pyrrole species was studied within the framework of the transition dipole moment time correlation function formalism. The period of essentially free rotation in the condensed phase reduces from 0.05 ps for the monomeric pyrrole to 0.02 ps for the proton-donor molecule within the dimer.     

Gas chromatographic indicator of the ability of five- and six-membered heterocyclic nitrogen-containing compounds for self-association in pure liquids

The retention indices of five- and six-membered nitrogen-containing heterocyclic compounds (pyrrole, pyrazole, imidazole, 1,2,4-triazole, pyridine, pyridazine, pyrimidine, pyrazine, 1,3,5-triazine, isoxazole, and oxazole) were determined on a capillary column with the OV-101 nonpolar stationary phase. The difference between the experimentally determined boiling point of the sorbate and that calculated from GC data (δT _b.p.) was proposed as a gas chromatographic indicator sensitive to the ability of substances to form self-associates in pure liquids. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 730–733, April, 1999.     

Electrical conductivity study of the self-association of ionic surfactants in solution in ethyleneglycol,formic acid and formamide

The self-association of several cationic surfactants has been investigated by means of solubility and electrical conductivity measurements in ethyleneglycol, formic acid and formamide. Operational critical micelle concentrations (CMC_op) have been obtained from the vs. surfactant concentrationC plots by the usual interpolation procedure. It has been found that for the surfactant-solvent systems investigated the value of CMC_op increases with the extent of theC-range investigated. This result together with others concerning the effect of temperature and surfactant chain length reveal that the CMC_op-values have an ambiguous meaning concerning the surfactant self-association. Comparison of the vs.C plots for cetyltrimethylammonium chloride and tetramethylammonium chloride, for instance, reveals that some surfactant self-association takes place, probably leading to small, highly ionized surfactant aggregates, but the systems do not show true critical micelle concentration. Solubility measurements as a function of temperature lead to the same conclusion. The results are discussed according to our present understanding of the process of micellization and the necessity of using solvents of very high cohesive energy density in order to observe, with ionic surfactants, true CMCs corresponding to a highly cooperative association process. This appears to be the case only with water and hydrazine, not with formamide and other less cohesive solvents.     

Formation of regular clusters through self-association of intramolecularly hypercrosslinked polystyrene-type nanosponges

Atactic polystyrene of M = 330,000 Da and M_w/M_n = 1.04 was subjected to chloromethylation. By the heating of chloromethylpolystyrene with SnCl₄ in a very dilute solution in ethylene dichloride, the polymeric coils were converted into intramolecularly hypercrosslinked macromolecules, nanosponges, of molecular weight of about 370,000 Da and a diameter of about 17 nm. When in solution, the nanosponges tend to reversibly self-assemble into regular clusters. Size exclusion chromatography and sedimentation analysis corroborate the suggestion that the clusters consist of 13 spherical subunits and thus acquire a molecular weight of about 5.0 × 10⁶ Da and a diameter of about 45 nm. © John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3847–3852, 1997     

Hydrogen-Bonded Dimers in Dipyrrinones and Acyldipyrrinones

Summary.  A crystal structure determination of the 9-acyl-dipyrrinone 9-butanoyl-2,3,7,8-tetramethyl-(10H)-dipyrrin-1-one indicates the presence of intermolecularly hydrogen-bonded dimers; however, in CHCl₃ solution the pigment is monomeric as determined by vapor pressure osmometry measurements. Lacking an alkyl group at C(8), the 9-acyl-dipyrrinone exhibits only a weak tendency to form dimers in CHCl₃ (K _A ∼ 60 M ⁻¹) as determined by analysis of variable temperature ¹H NMR data. In contrast, when the 9-acyl group is replaced by formyl or when the acyl group is fixed in a syn orientation to the pyrrole NH, the dipyrrinone is strongly prone to dimerization in CHCl₃. Received August 22, 2000. Accepted September 5, 2000     

气相渗透法测定数均分子量的仪器常数问题研究

讨论了蒸气压渗透计仪器常数的分子量依赖性问题．通过对某些已知分子量化合物的温差信号随时间变化的研究，提出了测量四个低分子一种改进的ＶＰＯ信号的测量手续和数据处理方式，可以得到更为准确的数均分子量．     

Interactions of metal extractant reagents: VII. Aggregation of tri-n-dodecylammonium chloride and perchlorate in toluene at 40°C

The self-association and mixed species formation equilibria of tri-n-dodecylammonium chloride (TLAHCl) and tri-n-dodecylammonium perchlorate (TLAHClO₄) dissolved in toluene have been studied by vapor pressure osmometry at 40°C. The experimental data can be fitted best by the formation of the aggregates (TLAHCl)₂ (log _2,0=1.35±0.06), (TLAHClO₄)₂ (log _0,2=2.4±0.1) and the mixed species (TLAHCL) (TLAClO₄)₂ (log _1,2=6.4±0.5), (TLAHCl)₂(TLAHClO₄)(log _2,1=7.1±0.6) and (TLAHCl)₂(TLAHClO₄)₂ (log _2,2=9.9±0.7).     

Effect of preferential solvation of polymer chains on vapor-pressure osmometry results: Computer simulation study

Preferential solvation of polymer chains by molecules of the thermodynamically better component of the solvent mixture is a general phenomenon which affects properties of dissolved chains and has to be taken into account in the interpretation of results of methods for analysis and characterization of polymers. We have investigated (i) the effect of preferential solvation on vapor-pressure osmometry results in mixed solvents close to θ-conditions and (ii) the danger of formation of associates by coarse-grained computer simulations. The study shows that both effects are negligible and the measurements in mixed solvents can be safely performed.     

The effect of self-association on the reactivity of calix[4]resorcinolarene anions with respect to esters of phosphorus acids

The kinetics of reactions of amphiphilic anions derived from calix[4]resorcinolarenes and their aggregates withp-nitrophenyl esters of phosphorus acids were studied by spectrophotometry. The effect of hydrophobicity of the substituent R and of the composition of aqueous dimethylformamide solvent (30, 50, 80% (v/v) DMF) on these processes was investigated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 275–279, February, 1998.     

关于气相渗透法仪器常数问题——一个新模式

气相渗透法广泛用于测定齐聚物和低分子量聚合物的数均分子量(M_n)。分析文献数据和本文的实验证明,仪器常数K值随溶质的分子量而变化。本文提出了一种新的说明 VPO法 K值依赖于溶质分子量的模式,根据此模式,可清楚地说明这种依赖关系。     

ANTIMICROBIAL ACTIVITY OF COPOLYMERS OF 2,4-DICHLOROPHENYL ACRYLATE WITH STYRENE: SYNTHESIS, CHARACTERIZATION AND REACTIVITY RATIOS

 Some copolymers of 2,4-dichlorophenyl acrylate (2,4-DCPA) with styrene (St) of different feed compositions were prepared by free radical polymerization technique using 2,2 -azobisisobutyronitrile (AIBN) as an initiator, and the copolymers were characterized by IR spectroscopy. The copolymer composition obtained by UV-spectra led to determination of reactivity ratio by employing Fineman-Ross (F-R) and Kelen-Tudos (K-T) methods. Average molecular weight, as well as intrinsic viscosity, was obtained by vapor pressure osmometry (VPO) and Ubbleholde viscometer. Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) of copolymers were carried out under nitrogen atmosphere. Antimicrobial effects of the homo and copolymers were also investigated against various microorganisms such as bacteria, fungi and yeasts.     

Crystallographic report: Dipyridium mercaptoacetotrichlorophenylstannate

The tin atom in the anion of [C₅H₅NH]₂[PhSn(SCH₂COO)Cl₃] is six‐coordinated within an octahedral geometry defined by a CCl₃OS donor set; the cations and anion interact via hydrogen bonds. Copyright © 2005 John Wiley & Sons, Ltd.     

Two Modifications of NH4HPO3F: Synthesis and Crystal Structure

The α and β modifications of NH₄HPO₃F were synthesized and characterized with single crystal X‐ray diffraction. The crystal structure of α‐NH₄HPO₃F determined at 180 K is monoclinic, space group P2₁/n, with a = 7.4650(1), b = 15.586(2), c = 7.5785(9) Å, β = 108.769(9)°, V = 834.9(2) ų, Z = 8, and R₁ = 0.0376 and wR₂ = 0.0818. β‐NH₄HPO₃F measured at 310 K crystallizes in the triclinic space group, P 1, with a = 7.481(1), b = 7.511(1), c = 7.782(1) Å, α = 84.31(1), β = 84.20(1), γ = 68.67(2)°, V = 404.31(9) ų, Z = 4, and R₁ = 0.0254 and wR₂ = 0.0735. A phase transition was not observed between 180 and 310 K for β‐NH₄HPO₃F. Both modifications of NH₄HPO₄F consist of HPO₃F^– and NH₄⁺ units. Two pairs of two unique anions are linked to each other by O–H…O hydrogen bonds to form cyclic tetramers held together by N–H…O bonds. No O–H…F or N–H…F bonds were observed.