Mucin at solution/air and solid/solution interfaces

In this paper the surface activity of protein mucin at solution/air interface has been studied. The experiments of the adsorbed protein at solution/air interface have been carried out with a range of protein concentrations at a defined pH. The adsorption of the protein to solid surfaces and the degree of hydrophobicity at solid/solution interface of mucin have been evaluated at different pH and in the presence of Hofmeister electrolyte. The results from these studies have been further substantiated by surface potential measurements of mucin covered surface on stainless steel. Quartz crystal microbalance (QCM) has been used to follow the protein adsorption kinetics from solution to solid surface. The results from these measurements show that the adsorption behavior has a remarkable dependence on the degree of maximum coverage and is almost independent of the ionic strength. Other characteristic features such as maximum adsorption values at the protein isoelectric point (IEP4.7) and low-affinity isotherms that showed surface saturation even under unfavorable electrostatic conditions have been observed. The amount of mucin adsorbed in the presence of electrolytes has been estimated using electron spectroscopy for chemical analysis (ESCA). The study clearly shows that there exists an inverse relationship between the hydrophobicity and surface tension of the protein and also on the hydrated radius of Hofmeister electrolyte used.     

Spreading of oil from protein stabilised emulsions at air/water interfaces

Spreading of a drop of an emulsion made with milk proteins on air/water interfaces was studied. From an unheated emulsion, all oil molecules could spread onto the air/water interface, indicating that the protein layers around the oil globules in the emulsion droplet were not coherent enough to withstand the forces involved in spreading. Heat treatment (90 °C) of emulsions made with whey protein concentrate (WPC) or skim milk powder reduced the spreadability, probably because polymerisation of whey protein at the oil/water interface increased the coherence of the protein layer. Heat treatment of emulsions made with WPC and monoglycerides did not reduce spreadability, presumably because the presence of the monoglycerides at the oil/water interface prevented a substantial increase of coherence of the protein layer. Heat treatment of caseinate-stabilised emulsions had no effect on the spreadability. If proteins were already present at the air/water interface, oil did not spread if the surface tension (γ) was <60 mN/m. We introduced a new method to measure the rate at which oil molecules spread from the oil globules in the emulsion droplet by monitoring changes in γ at various positions in a ‘trough’. The spreading rates observed for the various systems agree very well with the values predicted by the theory. Spreading from oil globules in a drop of emulsion was faster than spreading from a single oil drop, possibly due to the greater surface tension gradient between the oil globule and the air/water interface or to the increased oil surface area. Heat treatment of an emulsion made with WPC did not affect the spreading rate. The method was not suitable for measuring the spreading rate at interfaces where surface active material is already present, because changes in γ then were caused by compression of the interfacial layer rather than by the spreading oil.     

Influence of ammonium nitrate in phase transitions of Langmuir and Langmuir-Blodgett films at air/solution and solid/solution interfaces

The effect of ammonium nitrate on the phase transitions in Langmuir films of amphiphiles-stearic acid, stearyl amine (STAM), stearyl alcohol, dihexadecylphosphate, and the quarternized ammonium salt dioctadecyldimethylammonium bromide have been studied at air/water interface and in local ordering of their Langmuir-Blodgett films (LB films). The study shows that except for the stearyl amine (STAM) all other monolayers exhibit a liquid-expanded to liquid-condensed transition with slight expansion in area in the presence of ammonium nitrate. STAM monolayers show a new phase transition, which possibly arises due to the differently ionized amino groups, and change in solvation sheath due to an ion-dipole type interaction between the amino groups and the ammonium ion in the subphase. Mixed films of the amine with the acid and alcohol did not show such intermediate phases indicating that competing H-bonds between polar groups themselves and dipolar couplings between the polar groups and ammonium nitrate play a major role in the organization of the molecules at the interface. The above effect resulting in a change in the local order is borne out by Brewster angle micrographs (BAM) of the Langmuir films of STAM at air/solution interface. Such behavior is also seen at solid/liquid interfaces where the polar component of surface energy undergoes a drastic change for the amine films transferred onto solid substrates from the air/ammonium nitrate solution interface.     

Trapping, pattern formation, and ordering of polyelectrolyte/single-wall carbon nanotube complexes at the air/water and air/solid interfaces

The Langmuir and Langmuir-Blodgett (LB) techniques have been applied in a novel approach to build structurally well-ordered, oriented, and organized assemblies of water-soluble single-wall carbon nanotubes (ws-SWCNTs) at the air/water and air/solid interfaces. The SWCNTs were rendered hydrophilic by complexing them with a quenched polyelectrolyte. We observed that the ws-SWCNT concentration at the air/water interface increases with time condensing into different patterns, among which are isolated soap-froths, rings, and the aggregation of cumuli-like 2D-structures. These patterns were recorded at different compression-expansion stages by Brewster angle microscopy (BAM). From the isotherm measurements, we are able to determine the diffusion process by which ws-SWCNT concentration builds up at the water surface. The corresponding LB films were very stable and could be transferred onto mica substrates easily. Atomic force microscopy (AFM) images revealed that the morphology of these films is surface-pressure dependent, and aligned structures with a nematic-like order formed closely packed mono- or multilayer films. The assembly of 2D-nanostructures by means of this approach offers a great potential for emergent technological applications using modified water-soluble SWCNTs.     

Release of electrolytes from W/O/W double emulsions stabilized by a soluble complex of modified pectin and whey protein isolate

W/O/W double emulsions (DEs) stabilized by charged soluble complexes of whey protein isolate (WPI) and modified pectins were investigated in relation to their stability and the release of two types of electrolytes, NaCl and sodium ascorbate.WPI alone cannot properly stabilize the DEs. The droplet size is relatively large (100 μm) and increases with time. However, addition of modified pectin to form a soluble complex with WPI significantly improved the stability.DEs prepared with two types of oils (medium chain triglycerides (MCT) and R(+)-limonene) were studied by measuring droplet size, creaming, viscosity, and electrolyte release. Irrespective of their very different oil phase nature, both emulsions were stable against coalescence, but R(+)-limonene formed smaller droplets (25 μm) than MCT (35 μm). The electrolyte release rate was significantly higher from the R(+)-limonene that formed DEs with much lower viscosity. R(+)-limonene-DE released 75% of the NaCl after 28 days, while MCT-DE released only 50%. NaCl was released more slowly than sodium ascorbate.Apparently, the release mechanism from R(+)-limonene-DE was found to be “thinning the outer interface and release of the entire inner droplets” while it seems that the release from MCT-DE was slower and “diffusion controlled”.DEs stabilized by WPI/C63 released 12% of the sodium ascorbate after 1 day in milk and remained stable for at least 8 days. However, DEs stabilized with only WPI released about 50% of the sodium ascorbate after 1 day, and phase separated after 8 days.     

Structural, Spectroscopic, and Thermal Behaviour of Bis -(thiosaccharinate)-aqua-cadmium(II)

 The crystal structure of the title complex, [Cd(tsac)₂(H₂O)], has been determined by single crystal X-ray diffraction methods. It crystallizes in the monoclinic space group C2/c (a = 12.236(3), b = 8.919(3), c = 16.655(3) ?, β = 96.18(2)°, Z = 4). The molecular structure was solved from 1705 independent reflections with I > σ(I) and refined to R ₁ = 0.0489. Infrared and Raman spectra of the complex were recorded and are briefly discussed. Its thermal behaviour was investigated by thermogravimetry and differential thermal analysis.     

The solid state structure of [b(10)h(11)](-) and its dynamic NMR spectra in solution

The structure of [PPh(3)(benzyl)][B(10)H(11)] was determined at -123 degrees C and 24 degrees C by single-crystal X-ray analyses. The B(10) core of [B(10)H(11)](-) is similar in shape to that of [B(10)H(10)](2)(-). The 11th H atom asymmetrically caps a polar face of the cluster and shows no tendency for disorder in the solid state. Variable temperature multinuclear NMR studies shed light on the dynamic nature of [B(10)H(11)](-) in solution. In addition to the fluxionality of the cluster H atoms, the boron cage is fluxional at moderate temperatures, in contrast to [B(10)H(10)](2)(-). Multiple exchange processes are believed to take place as a function of temperature. Results of ab initio calculations are presented. Crystal data: [PPh(3)(benzyl)][B(10)H(11)] at -123 degrees C, P2(1)/c, a = 9.988(2) A, b = 18.860(2) A, c = 15.072(2) A, beta = 107.916(8) degrees, V = 2701.5(7) A(3), Z = 4; [PPh(3)(benzyl)][B(10)H(11)] at 24 degrees C, P2(1)/c, a = 10.067(5) A, b = 19.009(9) A, c = 15.247(7) A, beta = 107.952(9) degrees, V = 2775(2) A(3), Z = 4.     

Electron correlation effects at semiconductor surfaces and interfaces: Si(111)-5x5, Si(111)-7x7 and Sn/Ge(111)

Electron correlation effects associated with the dangling bond surface states of Si(111)-5×5, Si(111)-7×7 and Sn/Ge(111)-3×3 are analyzed. In all the cases, extensive LDA-calculations are performed and effective two-dimensional Hamiltonians are deduced. Our analysis of these Hamiltonians shows that: (a) the Si(111)-5×5 surface states exhibits a metal-insulator transition; (b) the Si(111)-7×7 surface shows important similarities with the Si(111)-5×5 case, but it has a dangling bond surface band having a metallic character; (c) finally, the Sn/Ge(111)-3×3 dangling bond surface bands also shows important correlation effects that are found, however, not to affect the metallic character of the surface bands.     

Formation of the solid solution CdS/CdSe from CdS and Se and its thermal stability a thermogravimetric investigation

Selenium and cadmium sulphide react in the temperature range 250–350 to form a solid solution CdSe/CdS. Thermogravimetric (in N₂) and chemical analyses show that this reaction occurs with the elimination of equimolecular amounts of Se and S. The thermal stability of the s.s. (2CdS · CdSe) in an atmosphere of N₂ was studied.

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Zusammenfassung Selen und Kadmiumsulfid reagierten miteinander im Temperaturbereich von 250 bis zu 350 unter Bildung einer festen Lösung CdSe/CdS. Thermogravimetrische (unter N₂) und chemische Untersuchungen bewiesen, da\ die Reaktion unter Elimination Äquimolekularer Mengen von Se und S verlÄuft. Die thermische StabilitÄt der festen Lösung (2CdS · CdSe) in Stickstoff wurde geprüft.

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Résumé Le sélénium et le sulfure de cadmium réagissent entre 250 et 350C en formant une solution solide CdSe/CdS. Les analyses thermogravimétrique (dans l'azote) et chimique montrent que cette réation se produit avec élimination de Se et de S suivant un rapport équimoléculaire. On a contrÔlé la stabilité thermique de la solution solide [2CdS · CdSe] dans l'azote.

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250–350 C, CdSe/CdS; ( ) , Se S; 2 CdS·CdSe N₂.

     

C-H stretching vibrations of methyl, methylene and methine groups at the vapor/alcohol (N = 1-8) interfaces

In IR and Raman spectral studies, the congestion of the vibrational modes in the C-H stretching region between 2800 and 3000 cm(-1) has complicated spectral assignment, conformational analysis, and structural and dynamics studies, even with quite a few of the simplest molecules. To resolve these issues, polarized spectra measurement on a well aligned sample is generally required. Because the liquid interface is generally ordered and molecularly thin, and sum frequency generation vibrational spectroscopy (SFG-VS) is an intrinsically coherent polarization spectroscopy, SFG-VS can be used for discerning details in vibrational spectra of the interfacial molecules. Here we show that, from systematic molecular symmetry and SFG-VS polarization analysis, a set of polarization selection rules could be developed for explicit assignment of the SFG vibrational spectra of the C-H stretching modes. These polarization selection rules helped assignment of the SFG-VS spectra of vapor/alcohol (n = 1-8) interfaces with unprecedented details. Previous approach on assignment of these spectra relied on IR and Raman spectral assignment, and they were not able to give such detailed assignment of the SFG vibrational spectra. Sometimes inappropriate assignment was made, and consequently misleading conclusions on interfacial structure, conformation and even dynamics were reached. With these polarization rules in addition to knowledge from IR and Raman studies, new structural information and understanding of the molecular interactions at these interfaces were obtained, and some new spectral features for the C-H stretching modes were also identified. Generally speaking, these new features can be applied to IR and Raman spectroscopic studies in the condensed phase. Therefore, the advancement on vibrational spectra assignment may find broad applications in the related fields using IR and Raman as vibrational spectroscopic tools.     

Molecular level structures of poly(n-alkyl methacrylate)s with different side chain lengths at the polymer/air and polymer/water interfaces

Sum frequency generation (SFG) vibrational spectroscopy has been successfully applied to study molecular structures of several poly(n-alkyl methacrylate)s (PAMAs) with different side chain lengths at the PAMA/air and PAMA/water interfaces. We have observed that the ester side chains from all PAMAs always dominate the interface, but the orientation information of the methyl end group on the side chains varies, depending on the length of the side chain. The contributions from methylene groups on the side chains have been evaluated, and the surface structures have been related to the surface tension of these polymers. Different water restructuring behaviors have been observed for different PAMAs. This phenomenon and its reversibility are strongly dependent on the glass transition temperature of each polymer, which is influenced by the side chain length. Detailed data fitting and analysis has been discussed.     

Topographical and microanalytical investigation of corrosion processes on the solid material in the system metal-metalloid glassy alloy (Fe,Cr)80(P,C,Si)20, aqueous FeCl3 solution, and air in the region of the “amorphous solid/liquid/air” phase interface

Ribbons of the metal-metalloid glassy alloy (Fe,Cr)₈₀(P,C,Si)₂₀ and Fe₇₅Cr₅P₈C₁₀Si₂, respectively, were treated with an aqueous solution of FeCl₃ (29 mass%) in an ultrasonic bath. The surface of the amorphous solid is maximally influenced at the flux line as the contact zone of glass/solution/ air. This region of the amorphous solid was studied by light microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA) as well as the electron beam micro analysis (EBMA) after the treatment. Changes in the surface stage and the surface behaviour take place independently of the state of the initial glass surface (shiny or dull side of a ribbon). Reaction products of different morphology were formed. In the flux line of the glass an enrichment of Si and Fe could be detected. These results agree with those of electrochemical measurement. According to this, a chloride ion containing acid aqueous solution is rather corrosive to this glassy alloy.     

Energy level alignment at interfaces between 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butyl phenyl)-1, 2, 4-triazole (TAZ) and metals (Ca,Mg, Ag,and Au): experiment and theory

We have performed ultraviolet photoelectron spectroscopy measurements and density functional theory calculations to study the electronic structure at the interface between organic semiconductor (3-(4-biphenylyl)-4-phenyl-5-(4-tert-butyl phenyl)-1,2,4-triazole (TAZ)) and metals (Ca, Mg, Ag, and Au). The basic mechanism of interface states at organic–metal interfaces can be understood by controlling the injection of charge carriers at these interfaces. The position of highest occupied molecular orbital relative to the Fermi level and the magnitude of the interface dipole are measured for each organic–metal interface. For TAZ on Ca, Mg, and Ag, interface states are observed near the Fermi level. However, no interface state is observed for TAZ on Au. It is analyzed qualitatively that the interface state is formed due to interaction of TAZ lowest unoccupied molecular orbital composed of C2p and metal s levels. It is suggested that the interface state plays an important role in charge transport at the interface. The mechanism of formation of interface states and electrical properties are discussed.     

Structures of a tetradentate ferrocenyl ligand and its oxorhenium(V) complex in solution and in the solid state

The novel ferrocenyl ligand rac-1,6-diferrocenyl-N,N'-bis(2-hydroxypropyl)-2,5-diazahexane (1, H(2)L) was synthesized from ferrocenylcarboxaldehyde and ethylenediamine followed by the reduction of the Schiff base with LiAlH(4) and subsequent N-alkylation with 1,2-propyleneoxide. The dianion of H(2)L reacted with [ReO(PPh(3))(2)Cl(3)], and the product was treated with NH(4)PF(6) to afford the complex [ReO(L-N(2)O(2))PPh(3)]PF(6) (2). Both the ferrocenyl ligand and the complex were characterized in solution by NMR spectroscopy and in the solid state by single-crystal X-ray diffraction studies. NMR investigations reveal two solvent-dependent isomers for the ferrocenyl ligand in solution of which the major form is the more ordered one. The cation of 2 displays a nonsymmetrically coordinated N(2)O(2) ligand.     

The electrochemical behavior of N-n-undecy1-N＇-（sodium-p- amino-benzenesulfonate） thiourea and its interaction with bovine serum albumin

In pH 5.5 phosphate buffer solution, N-n-undecyl-N＇-（sodium-p-amino-benzenesulfonate） thiourea （UPT） produced a pair of redox peaks on the bare glassy carbon electrode. At the multi-walled carbon nanotube （MWNT） modified electrode, the electrochemical behavior of UPT enhanced greatly. In the presence of bovine serum albumin （BSA）, the peak currents of UPT decreased linearly due to the formation of a super-molecular complex. This method was successfully applied to the determination of BSA in a bovine serum sample.     

Properties of pH-responsive mixed aggregates of polystyrene-block-poly(L-lysine) and nonionic surfactant in solution and adsorbed at a solid surface

Poly(styrene) 388- block-poly( l-lysine) 138 could be dispersed in water with the aid of the nonionic surfactant C 12E 6. Light scattering and direct imaging techniques show that the copolymer/surfactant aggregates are polydisperse spherical micelles. The rather broad size distribution can be attributed to the glassy state of the polystyrene core of the micelles hampering equilibration. Nevertheless, the poly( l-lysine) block remains pH sensitive in these mixed aggregates and circular dichroism measurements show that poly( l-lysine) block adopts a random coil conformation at low pH and an beta-sheet conformation at pH > or = 11 without any change in the micellar shape. Samples prepared by evaporation of drops of the solutions on graphite wafers exhibit different wetting patterns depending on the polypeptide conformation as indicated by atomic force microscopy.     

Mass fragmentographic determination of diphenylhydantoin and its main metabolite, 5-(4-hydroxyphenyl)-5-phenylhydantoin, in human plasma.

A method is described for the mass fragmentographic determination of diphenylhydantoin and its main metabolite, 5-(-4-hydroxyphenyl)-5-phenylhydantoin (4-OH-DPH), in human plasma as their dimethyl and trimethyl derivatives, respectively. The derivatives are formed by using the recently described extractive alkylation technique. Pentadeuterated 4-OH-DPH is used as the internal standard. Following acidic hydrolysis of the plasma sample, conjugated 4-OH-DPH and, indirectly, the dihydrodiol metabolite, 5-(3,4-dihydroxy-1,5-cyclohexadien-1-yl)-5-phenylhydantoin, are measured. Using 100-mul plasma samples, the lower limit of detection is about 10 ng/ml 00.03 nmole/ml).     

Determination of lead in solution by solid phase extraction, elution, and spectrophotometric detection using 4-(2-pyridylazo)-resorcinol

Lead (+2) was selectively adsorbed on a solid phase extraction (SPE) gel (molecular recognition technology, MRT), quantitatively extracted, and spectrophotometrically determined as the Pb(II)-PAR (4-(2-pyridylazo)-resorcinol) complex. The linear range was 0.01 to 0.75 mg L^?1 and the detection limit was 6.4 µg L^?1. The MRT-SPE allows selective Pb(II) extraction from complex ion-rich matrices, which is difficult with other techniques. Interference from common matrix ions such as Fe²⁺, Ni²⁺, Cu²⁺ or Co²⁺ is minimized.      

Energy transfer from poly(vinyl carbazole) to a fluorene-vinylene copolymer in solution and in the solid state

This article reports a comparative study of the energy transfer processes in solution and the solid state from poly(vinyl carbazole; the donor) to dimethylphenyl-terminated poly[(9,9-dioctylfluorenyl-2,7-divinylene-fluorene)-co-alt-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene}] (the acceptor). The results in solutions suggest that a decrease of the donor emission intensity with an increasing acceptor concentration is more closely related to the trivial energy transfer process, indicating that the donor and acceptor chains are not in close contact during the lifetime of the donor excited state. This conclusion was reached using the amplitude-averaged lifetime of the donor, which is practically independent of the acceptor concentration. In the solid state, the polymer blends showed a decrease in the donor emission with an increasing acceptor concentration, and a decrease in the donor lifetime was also observed. Thus, in the solid state, changes in morphology interfere with the nonradiative resonant energy transfer process, but influence on the trivial process cannot be completely neglected. The lifetime does not follow a continuous decrease with the PFO-MEHPV concentration like the emission intensity does. The changes in the lifetime values occur over the same concentration range as do the changes of morphology, as shown by the scanning electron micrographs.     

Organoselenium(II) and selenium(IV) compounds containing 2-(Me2NCH2)C6H4 moieties: solution behavior and solid state structure

The cleavage of the Se-Se bond in [2-(Me₂NCH₂)C₆H₄]₂Se₂ (1) was achieved by treatment with SO₂Cl₂ (1:1 molar ratio) or elemental halogens to yield [2-(Me₂NCH₂)C₆H₄]SeX [X = Cl (2), Br (3), I (4)]. Oxidation of 1 with SO₂Cl₂ (1:3 molar ratio) gave [2-(Me₂NCH₂)C₆H₄]SeCl₃ (5). [2-(Me₂NCH₂)C₆H₄]SeS(S)CNR₂ [R = Me (6), Et (7)] were prepared by reacting [2-(Me₂NCH₂)C₆H₄]SeBr with Na[S₂CNR₂] · nH₂O (R = Me, n = 2; R = Et, n = 3). The reaction of 3 with K[(SPMe₂)(SPPh₂)N] resulted in isolation of [2-(Me₂NCH₂)C₆H₄]Se-S-PMe₂N-PPh₂S (8). The compounds were characterized by solution NMR spectroscopy (¹H, ¹³C, ³¹P, ⁷⁷Se, 2D experiments). The solid-state molecular structures of 2, 4-8 were established by single crystal X-ray diffraction. All compounds are monomeric, with the N atom of the pendant CH₂NMe₂ arm involved in a three-center-four-electron N?Se-X (X = halogen, S) bond. This results in a T-shaped coordination geometry for the Se(II) atom in 2, 4, 6-8. In 5, the Se(IV) atom achieves a square pyramidal coordination in the mononuclear unit. Loosely connected dimers are formed through intermolecular Se?Cl interactions (3.40 Å); the overall coordination geometry being distorted octahedral. In all compounds hydrogen bonds involving halide or sulfur atoms generate supramolecular associations in crystals.