Thermal analysis of aqueous micellar solutions

A micro differential temperature scanning calorimeter was used to characterize the structural changes between different types of micelles in aqueous solutions of ionic surfactants: anionic — sodium dodecylsulfate (SDS) — and cationic — hexadecyltrimethyl ammonium bromide (CTAB). Moreover, this technique allowed to confirm the existence of peculiar types of complexes between surfactants and selected solutes. In SDS solutions containing polyethylene glycols (PEG), the presence of complexes formed by small micelles adsorbed along the chains of the polymers was evidenced in the case of long enough polymer chains. In CTAB-phenol solutions, due to strong interactions between the polar heads of surfactant and phenol, molecular complexes of a composition of 1:1 molar ratio have been characterized. Depending on the ratio [phenol]/[CTAB], the rheological behaviour was found to change from fluid to viscoelastic and gel-like solutions, owing to the growth of elongated rod-like micelles. With entangled worm-like micelles, the important role of kinetics to reach the thermodynamic equilibria was shown.     

Chlorobromoantimonates(V): New synthesis and 121Sb-NMR study

The new tetraethylammonium tetrachlorodibromoantimonate(V) and dichlorotetrabromoantimonate(V) have been prepared and have been given a cis-structure from their vibrational spectra. The ways of synthesis of all the terms of the series NEt₄⁺SbCl_6?nBr_n^? are discussed; the ¹²¹Sb spectra of their solutions in CH₃CN are given and show halide exchange around Sb(V).     

Cyclometalation of phosphorus ligands by UV irradiation of complexes having transition metal---silicon bonds

UV irradiation of complexes of the type (η⁵-C₅H₅)(CO)_nMSiR₃ (n = 2, M = Fe; n = 3, M = Mo) in the presence of phosphorus ligands such as P(XC₆H₅)₃ (X = O, S, CH₂) and phosphines containing allyl, 1-naphthyl or tolyl groups gives cyclometalated complexes, R₃SiH being eliminated with retention of configuration at Si. In the cyclometalation five-membered rings are formed in preference to six-membered rings, and metalation occurs more easily at sp² than at sp³ carbon atoms. Methylphenyl-1-naphthylphosphine undergoes rapid racemization upon UV irradiation at room temperature.     

Parallux beta-lactam: a capillary-based fluorescent immunoassay for the determination of penicillin-G, ampicillin, amoxicillin, cloxacillin, cephapirin, and ceftiofur in bovine milk

An analytical system was developed for detection of antibiotic residues in bovine milk. The method is based on competitive fluorescent immunoassays in glass capillary tubes (U.S. Patent No. 5,624,850). The system consists of an assay cartridge containing 4 glass capillaries, a reagent tray with 4 wells of dried reagents, and a Parallux processor, which processes the assay, reads fluorescent output, and reports test results. Minimum sensitivity for detection of 6 beta-lactam antibiotics in bovine milk was determined to be penicillin-G, 3.2 ppb; ampicillin, 2.9 ppb; amoxicillin, 3.6 ppb; cloxacillin, 7.4 ppb; cephapirin, 16.3 ppb; and ceftiofur, 33.7 ppb. The assay system was also specific and sensitive for detection of incurred residues at U.S. Food and Drug Administration tolerance levels: penicillin-G, 5 ppb; ampicillin, 10 ppb; amoxicillin, 10 ppb; cloxacillin, 10 ppb; cephapirin, 20 ppb; and ceftiofur, 50 ppb. There was no interference in detection of minimum sensitivity levels of antibiotic by the presence of somatic cells at approximately 1 x 10(6) cells/mL. Milk containing 3 x 10(6) cells/mL bacteria commonly found in mastitic milk also showed no interference when tolerance levels of antibiotic were present. There was no detectable interference on results by a wide variety of non-beta-lactam drugs.     

Characterization of an opioid peptide-containing protein and of bovine α-lactalbumin by electrospray ionization and liquid secondary ion mass spectrometry

Mass spectrometry methods have been used to characterize two proteins: an opioid peptide-containing protein extracted from bovine pituitary, and bovine α-lactalbumin (BAL). A protein that contains β-endorphin was found in bovine pituitary, and that protein was characterized with electrospray ionization mass spectrometry (ESIMS), gel permeation chromatography, reversed-phase high performance liquid chromatography (RP-HPLC), radioimmunoassay, trypsinolysis, and liquid secondary ion mass spectrometry (LSIMS). BAL is a protein that was used as a model to develop analytical methods to study opioid peptide-containing proteins. Commercial BAL was purified by RP-HPLC, and its molecular weight (M.W.) was determined by ESIMS. The shift in mass observed following dithiothreitol (DTT) reduction estimated the number of disulfide bonds. For all of the data obtained for BAL with or without RP-HPLC separation, ESIMS determined the M.W. of the peptides produced by trypsin treatment of BAL, and LSIMS selected a precursor ion, the protonated molecule ion [M + H]⁺, of a tryptic peptide, which was analyzed by tandem mass spectrometry. Following DTT reduction, ESIMS and LSIMS detected each peptide that contained disulfide bonds in that mixture of tryptic peptides.     

Role of alcohol in microemulsions as determined from volume and heat capacity data for the water-sodium dodecylsulfate -n-butanol system at 25°C

Densities and heat capacities of the ternary system water-sodium dodecylsulfate — n-butanol were measured at 25°C over the complete alcohol mole-fraction or solubility range. Apparent and partial molar volumes and heat capacities of n-butanol were derived and have been analyzed as a function of the concentration of both the surfactant and the alcohol. Characteristic changes suggest that, at low concentrations, n-butanol is partially solubilized in mixed micelles but, in concentrated alcohol solutions, n-butanol largely exists in the form of microaggregates stabilized by the surfactant. Results would also suggest that at low concentrations of n-butanol another transition zone occurs in the micellar structure around 0.2–0.3 mol-kg^–1 in sodium dodecylsulfate.     

Excess molar heat capacities and excess molar volumes of some mixtures of propylene carbonate with aromatic hydrocarbons

Excess molar volumes V ^E and excess molar heat capacities C _P ^E at constant pressure have been measured, at 25°C, as a function of composition for the four binary liquid mixtures propylene carbonate (4-methyl-1,3-dioxolan-2-one, C₄H₆O₃; PC) + benzene (C₆H₆;B), + toluene (C₆H₅CH₃;T), + ethylbenzene (C₆H₅C₂H₅;EB), and + p-xylene (p-C₆H₄(CH₃)₂;p-X) using a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. All the excess volumes are negative and noticeably skewed towards the hydrocarbon side: V ^E (cm³-mol^–1) at the minimum ranges from about –0.31 at x₁=0.43 for {x₁C₄H₆O₃+x₂p-C₆H₄(CH₃)₂}, to –0.45 at x₁=0.40 for {x₁C₄H₆O₃+x₂C₆H₅CH₃}. For the systems (PC+T), (PC+EB) and (PC+p-X) the C _P ^E s are all positive and even more skewed. For instance, for (PC+T) the maximum is at x _1,max =0.31 with C _P,max ^E =1.91 J-K^–1-mol^–1. Most interestingly, C _P ^E of {x₁C₄H₆O₃+x₂C₆H₆} exhibits two maxima near the ends of the composition range and a minimum at x _1,min =0.71 with C _P,min ^E =–0.23 J-K^–1-mol^–1. For this type of mixture, it is the first reported case of an M-shaped composition dependence of the excess molar heat capacity at constant pressure.Communicated at the Festsymposium celebrating Dr. Henry V. Kehiaian's 60^th birthday, Clermont-Ferrand, France, 17–18 May 1990.     

Thermal and volumetric properties of chloroform+benzene mixtures and the ideal associated solution model of complex formation

In the ideal associated solution model, activity coefficients of all species (labelled A, B, and AB here) at equilibrium are taken to be unity at all compositions and temperatures. We have applied this model to an analysis of thermodynamic properties (vapor pressures, excess enthalpies, partial molar enthalpies of solution, excess heat capacities, and excess volumes) of the chloroform+benzene system in terms of K, H, C _p , and V for the equilibrium represented by A+B=AB. It is demonstrated that there is reasonably good consistency between this simple model and all of the thermodynamic data, which shows that the model is realistic enough to be useful in assessing the properties of the not-very-stable AB complex in the chloroform+benzene system. New thermal (partial molar enthalpies of solution and excess heat capacities) and volumetric properties of the chloroform+benzene system have been measured, with results presented here.     

(E)‐(4‐Hydroxyphenyl)(4‐nitrophenyl)diazene, (E)‐(4‐methoxyphenyl)(4‐nitrophenyl)diazene and (E)‐[4‐(6‐bromohexyloxy)phenyl](4‐cyanophenyl)diazene

Syntheses and X‐ray structural investigations have been carried out for (E)‐(4‐hydroxy­phenyl)(4‐nitro­phenyl)­diazene, C₁₂H₉N₃O₃, (Ia), (E)‐(4‐methoxy­phenyl)(4‐nitro­phenyl)­diazene, C₁₃H₁₁N₃O₃, (IIIa), and (E)‐[4‐(6‐bromo­hexyl­oxy)­phenyl](4‐cyano­phenyl)­diazene, C₁₉H₂₀BrN₃O, (IIIc). In all of these compounds, the mol­ecules are almost planar and the azo­benzene core has a trans geometry. Compound (Ia) contains four and compound (IIIc) contains two independent mol­ecules in the asymmetric unit, both in space group P (No. 2). In compound (Ia), the independent mol­ecules are almost identical, whereas in crystal (IIIc), the two independent mol­ecules differ significantly due to different conformations of the alkyl tails. In the crystals of (Ia) and (IIIa), the mol­ecules are arranged in almost planar sheets. In the crystal of (IIIc), the mol­ecules are packed with a marked separation of the azo­benzene cores and alkyl tails, which is common for the solid crystalline precursors of mesogens.