The Cubic-Two-State Equation of State: Cross-associating mixtures and Monte Carlo study of self-associating prototypes

A new equation of state for associating fluids has recently been presented by Medeiros and Tellez-Arredondo, the Cubic-Two-State Equation of State (CTS EoS) [Ind. Eng. Chem. Res. 47 (2008) 5723]. This equation arises from the coupling of the Soave–Redlich–Kwong EoS (SRK) with an association term from a two-state association model. The CTS EoS is polynomial in volume and it is able to describe vapor pressures and molar volume of associating fluids such as water, alcohol and phenol, among others. The equation is also able to describe the liquid–vapor equilibria of their mixtures with alkanes. In this paper, the physical and thermodynamic foundations of the CTS EoS are further investigated. In order to verify its applicability for cross-associating systems, the equation was employed in the prediction of phase equilibria behavior of binary alcohol–alcohol and water–alcohol mixtures. Very good agreement between predictions and experimental phase equilibria data was obtained with very simple combining rules and only one adjustable binary parameter. No additional parameters were necessary to describe ternary systems. With the purpose of checking the model's hypothesis and limitations, the two-state association term was coupled with the hard sphere Carnahan–Starling EoS, forming the CS-TS equation and the association characteristic parameters were determined theoretically for prototype association fluids. Monte Carlo NPT simulations of such fluids were performed and the results were compared with the equation's predictions. The CS-TS was able to describe qualitatively the pvT$pvT$ behavior of the prototype; nevertheless, it is not as accurate as those predictions obtained from the combination CS with Wertheim's association term. It seems that, when adjusting parameters of the CTS EoS to real substances, the discrepancies between the predicted and the real association contribution are dissipated among other adjustable parameters, specially on the dispersive term of the SRK equation. Finally, it is shown that CTS EoS isotherms can only have one or three real bigger roots than the co-volume for positive pressures, similar to cubic equations of state, and then it has the desirable form to describe vapor–liquid phase equilibria of associating compounds mixtures.     

Equation of state for aqueous electrolyte systems based on the semirestricted non-primitive mean spherical approximation

The semirestricted non-primitive mean spherical approximation (npmsa) is used in combination with the PC-SAFT equation of state to model completely dissociating aqueous alkali halide systems. The salts are described using ion-specific parameters from tables and correlations. Upon analyzing aqueous electrolyte systems at infinite dilution of the salt it was concluded that for the arithmetic mean ion diameter of anion and cation, the semirestricted npmsa contribution gives no reliable results. Therefore, this parameter is adjusted in this work. The model was applied to aqueous alkali halide systems up to the solubility limit at T = 298.15 K. Mean ionic activity coefficients and osmotic coefficients were correlated with good results. The model was subsequently applied to temperatures up to T = 373.15 K and compared to liquid densities and to system pressures up to the solubility limit of the salts in water. The agreement between experimental data and the proposed equation of state is satisfactory for the liquid densities and excellent in case of the system pressures.     

Atom transfer radical polymerization on the interior of the P22 capsid and incorporation of photocatalytic monomer crosslinks

We have successfully used atom transfer radical polymerization (ATRP) to form linear and crosslinked polyacrylamide and polyacrylate polymers, constrained within the virus like particle (VLP) derived from the bacteriophage P22. Polymerization of Tris(hydroxymethyl)methylacrylamide was initiated, in a spatially controlled manner, using macroinitiators derived from two different mutants of P22, S39C and K118C. Initiation from the S39C mutant results in spatially confined polymer growth on the interior of P22 while initiation from the K118C site results in a polymerized VLP in which some of the polymer is partially exposed on the outside of the capsid. Using the S39C macroinitiator we have demonstrated polymerization of aminoethyl methacrylate (AEMA) monomers, crosslinked by co-polymerization with the multifunctional monomer [Ru(5-methacrylamido-phenanthroline)₃]²⁺ resulting in an active photocatalytic P22 capsid particle.     

Phase equilibria modeling of biodiesel related mixtures using the GCA-EoS model

In this work, a group-contribution equation of state that takes into account association effects (GCA-EoS) is extended to model the phase behavior of fatty esters (biodiesel) in binary mixtures with glycerol, alcohols and water and ternary mixtures with glycerol and methanol. A new associating group (glycerol hydroxyl group: OH^Gly) was defined to take into consideration the association effects in the glycerol molecule. Self-association of methanol, water and glycerol and cross-association between methanol–glycerol, alcohol–ester, water–ester and glycerol–ester groups were considered. New pure-group, binary interaction and association parameters have been determined. The correlations and predictions of the model are found in acceptable agreement with selected experimental data reported in the literature.     

Thiourea linked peracetylated glucopyranosyl–anthraquinone conjugate as reversible ON–OFF receptor for fluoride in acetonitrile

A new thiourea linked peracetylated glucopyranosyl–anthraquinone conjugate (L) has been synthesized and characterized. The binding properties of L have been studied with nineteen different anions. The L exhibited selective chromogenic as well as fluorescent chemosensor property toward F⁻ by a ∼13-fold increase in the emission intensity upon binding with F⁻. The minimal detection limit for F⁻ is 185 ± 5 ppb in acetonitrile. Interaction of F⁻ led to a bathochromic shift of 80 nm in the absorption band. An INHIBIT logic gate has been proposed using the output obtained from the fluorescence studies. The structure of the species formed upon the interaction of F⁻ with L has been established by DFT computations.     

Thermodynamic and spectroscopic study of the interaction of Cu(II), Ni(II), Zn(II) and Ca(II) ions with 2-amino-N-(2-oxo-2-(2-(pyridin-2-yl)ethyl amino)ethyl)acetamide,a pseudo-mimic of human serum albumin

The protonation equilibria of 2-amino-N-(2-oxo-2-(2-(pyridin-2-yl)ethyl amino)ethyl)acetamide ([H₂(556)–N]) and the complexation of this ligand with Cu(II) Ca(II), Zn(II) and Ni(II) have been studied by glass electrode potentiometry and UV–visible spectrophotometry. From pH ∼2.00–11.00, five models for Cu(II) with the following complexes; MLH, ML, MLH₋₁, MLH₋₂ and MLH₋₃ were generated and observed to describe the experimental data equally well as far as the statistical criteria were concerned. The MLH₋₂ complex predominates at physiological pH in all five models, while the MLH₋₁ complex species exists only at low concentration in two models. The coordination in the MLH₋₂ complex suggested the involvement of one amino, two deprotonated peptides and one pyridyl nitrogen atoms. Molecular mechanics (MM) calculations confirmed the MLH₋₂ complex as the most stable species. Speciation calculations, using a blood plasma model, predicted that the Cu(II)–[H₂(556)–N] complex is able to mobilize Cu(II). Octanol/water partition of CuLH₋₂ showed that 30% of the complex went into the octanol phase, hence promoting percutaneous absorption of copper. The complex is a poor mimic of native copper–zinc superoxide dismutase.     

The Relationship between the IC50 Values and the Apparent Inhibition Constant in the Study of Inhibitors of Tyrosinase Diphenolase Activity Helps Confirm the Mechanism of Inhibition

Tyrosinase is the enzyme involved in melanization and is also responsible for the browning of fruits and vegetables. Control of its activity can be carried out using inhibitors, which is interesting in terms of quantitatively understanding the action of these regulators. In the study of the inhibition of the diphenolase activity of tyrosinase, it is intriguing to know the strength and type of inhibition. The strength is indicated by the value of the inhibition constant(s), and the type can be, in a first approximation: competitive, non-competitive, uncompetitive and mixed. In this work, it is proposed to calculate the degree of inhibition (iD), varying the concentration of inhibitor to a fixed concentration of substrate, L-dopa (D). The non-linear regression adjustment of iD with respect to the initial inhibitor concentration [I]0 allows for the calculation of the inhibitor concentration necessary to inhibit the activity by 50%, at a given substrate concentration (IC₅₀), thus avoiding making interpolations between different values of iD. The analytical expression of the IC₅₀, for the different types of inhibition, are related to the apparent inhibition constant (KIapp). Therefore, this parameter can be used: (a) To classify a series of inhibitors of an enzyme by their power. Determining these values at a fixed substrate concentration, the lower IC₅₀, the more potent the inhibitor. (b) Checking an inhibitor for which the type and the inhibition constant have been determined (using the usual methods), must confirm the IC₅₀ value according to the corresponding analytical expression. (c) The type and strength of an inhibitor can be analysed from the study of the variation in iD and IC₅₀ with substrate concentration. The dependence of IC₅₀ on the substrate concentration allows us to distinguish between non-competitive inhibition (iD does not depend on [D]0) and the rest. In the case of competitive inhibition, this dependence of iD on [D]0 leads to an ambiguity between competitive inhibition and type 1 mixed inhibition. This is solved by adjusting the data to the possible equations; in the case of a competitive inhibitor, the calculation of KI1app is carried out from the IC₅₀ expression. The same occurs with uncompetitive inhibition and type 2 mixed inhibition. The representation of iD vs. n, with n=[D]0/KmD, allows us to distinguish between them. A hyperbolic iD vs. n representation that passes through the origin of coordinates is a characteristic of uncompetitive inhibition; the calculation of KI2app is immediate from the IC₅₀ value. In the case of mixed inhibitors, the values of the apparent inhibition constant of meta-tyrosinase (Em) and oxy-tyrosinase (Eox), KI1app and the apparent inhibition constant of metatyrosinase/Dopa complexes (EmD) and oxytyrosinase/Dopa (EoxD), KI2app are obtained from the dependence of iD vs. n, and the results obtained must comply with the IC₅₀ value.     

The regioselectivity of the formation of 2-pyrazolylthiazoles and their precursors from the reaction of 2-hydrazinothiazoles with 4,4,4-trifluoro-1-hetaryl-1,3-butanediones

Reaction of 2-hydrazinothiazoles 1 with 1-thienyl- and 1-furyl-1,3-butanediones 2a,b in methanol in the presence of hydrochloric acid mainly leads to a mixture of pyrazoles 3 and pyrazolines 4 or pyrazoles 3 and 5 in strong acidic conditions. Isomeric hydrazones 6 and pyrazolines 4 were formed and isolated in these reactions in the absence of hydrochloric acid. It has been shown that the regioselectivity in the reaction of diketones 2 with hydrazine 1 is governed by both the concentration of acid and the nature of substituents in the 1,3-diketones 2. Cyclization of hydrazones 6 is shown to occur under milder conditions than dehydration for pyrazolines 4. The new heterocyclic compounds were prepared and fully characterized by NMR spectra and by X-ray analysis for 3c.     

A short, simple and general approach for the synthesis of (3S,4S)-3-methoxy-4-methylamino pyrrolidine and (3S,4R)-3-methoxy-4-methylamino pyrrolidine

A general and efficient stereoselective approach for the synthesis of (3S,4S) and (3S,4R)-3-methoxy-4-methylamino pyrrolidines, a part of the structure of AG-7352, a naphthyridine antitumor agent and quinoline antibacterial compounds has been described.     

Molecular structure and spectral properties of thionaphthalimides

The molecular structure and absorption spectra of monothio- and dithio-naphthalimides were compared to their naphthalimide analogues using AM1, PM3 and ZINDO/S semiempirical quantum chemical methods. The substitution of the 4R-naphthalimide oxygen atoms by sulphur atoms resulted in a red-shift of the absorption spectra by Δλ_max60-65 and 100-140 nm, respectively. The thionated naphthalimide derivatives do not show observable fluorescence due to intersystem crossing to the triplet -states localised at the CS groups. The -absorption bands of monothioimides are located at 525-580 nm (ε=60-80) and those for dithioimides at 535-560 nm (ε=140-390) and 628-686 nm (ε=34-68). None of these transitions are solvent sensitive. The -transitions of N-phenylthioimides have also a small contribution from -states due to a partial conjugation between CS group and π-electronic system of the N-phenyl ring. As a result, the bands of aromatic substituted N-phenylthioimides are red-shifted as compared to those of the aliphatic N-methyl-thioimides.     

{[K.18-Crown-6]Br3}n: a unique tribromide-type and columnar nanotube-like structure for the oxidative coupling of thiols and bromination of some aromatic compounds

Reaction of 18-crown-6 with KBr and then with bromine (Br₂) afforded a unique tribromide salt with a nanotube-like structure ({[K.18-crown-6]Br₃}_n). Oxidative coupling of thiols and bromination of some aromatic compounds is the first report on the chemistry of this reagent.     

Dilute solution behaviour of progressively hydrolyzed polyacrylamide in water-N, N dimethylformamide mixtures

The intrinsic viscosities [η’s] of anionic (hydrolyzed; low and high carboxyl content) and nonionic polyacrylamide (unhydrolyzed) were measured in water-N, N dimethylformamide mixtures at various temperatures. Non-polyelectrolyte behavior of low carboxyl content polyacrylamide was observed in mixed solvent system. The plots of [η] vs. solvent composition in a mixed solvent system pass through minima for both high as well as low carboxyl content polymers but through a maximum for nonionic polyacrylamide. Observed minimum for charged polymers may be attributed to the loss of polymer sites available to interact with solvent for H-bonding interaction between neighboring amide and the acid groups. The maximum for nonionic polymer at the particular solvent composition arises for the most powerful cosolvent effect. Existence of two antagonistic effects is apparent in [η] values of nonionic polymer at various temperatures. Huggins constant (K_H) also indicates a significant variation of cosolvency as a function of solvent composition. Activation parameters of viscous flow were calculated using Frenkel-Eyring equation. The volume related parameter and the shape factor were also computed. Shape factor data indicate that polymer molecules are more or less rigid spheres and are not affected by temperature and composition of solvent.     

Isolation of C60(CF3)n (n = 2, 4, 6, 8, 10) with high compositional purity

The high temperature reaction of C₆₀ with silver(I) trifluoroacetate followed by 500 °C sublimation and subsequent HPLC purification has led to the isolation of the five trifluoromethyl[60]fullerenes C₆₀(CF₃)_n (n=2, 4, 6, 8, 10). Four of them have >90% compositional purity. Two of the compounds, C₆₀(CF₃)₄ and C₆₀(CF₃)₆, were obtained as C₁-symmetry isomers with >90% isomeric purity, and a sample of C₆₀(CF₃)₂ also contained ca. 15-20% of a C_s-symmetry isomer of C₆₀(CF₃)₄. The new compounds were characterized by IR and EI mass spectrometry (all five compounds), NMR spectroscopy (C₆₀(CF₃)₂, C₆₀(CF₃)₄, and C₆₀(CF₃)₆), and 2D COSY NMR spectroscopy (C₆₀(CF₃)₄ and C₆₀(CF₃)₆). Calculations at the AM1 and DFT levels of theory have led to the prediction of the most likely structures for C₆₀(CF₃)₂, C₁-C₆₀(CF₃)₄, C_s-C₆₀(CF₃)₄, and the two most likely structures of C₁-C₆₀(CF₃)₆.     

Fluorinated stannanes : Part 1. The stereospecific synthesis of fluorinated stannanes via a novel transmetalation of fluorinated zinc and cadmium reagents

Fluorinated stannanes are versatile synthetic intermediates. Reaction of fluorinated vinyl, alkyl and aryl zinc or cadmium reagents with tri-n-butyltin chloride at room temperature yielded the corresponding tri-n-butyl stannanes in moderate to excellent yields. The zinc or cadmium reagents also reacted efficiently with other trialkyl and triaryl chlorostannanes. These zinc and cadmium reagents were prepared in excellent yields by stirring the fluorinated halides with activated zinc or cadmium metal.