Direct electrochemistry and electrocatalysis of hemoglobin in gelatine film modified glassy carbon electrode

Direct electrochemical and electrocatalytic behavior of hemoglobin (Hb) immobilized on glass carbon electrode (GCE) containing gelatine (Gel) films was investigated. The characteristics of Hb/Gel film modified GC electrode were performed by using SEM microscopy, UV-vis spectroscopy and electrochemical methods. The immobilized Hb showed a couple of quasi-reversible redox peak with a formal potential of −0.38 V (versus SCE) in 0.1 M pH 7.0 PBS. The formal potential changed linearly from pH 4.03 to 8.41 with a slope value of −52.0 mV pH⁻¹, which suggested that a proton transfer was accompanied with each electron transfer (ET) in the electrochemical reaction. The Hb/gelatine/GCE displayed a rapid amperometric response to the reduction of H₂O₂ and nitrite.     

Zum Scherverhalten unzerstörter Grenzflächenstrukturen gespreitetern-Octadecansäuremonoschichten und adsorbierter Gelatineschichten an fluiden Phasengrenzen

Zusammenfassung Eine Apparatur zur Bestimmung grenzflächenrheologischer Kriechkurven wird beschrieben.In Übereinstimmung mit theoretischen Analysen über die Beanspruchung der Phasengrenze durch einen die Grenzfläche berührenden Ring können minimal Oberflächenscherviskositäten von 10^–3 mNs/m hinreichend genau bestimmt werden.Die Funktionsfähigkeit der Apparatur wurde an ausgewählten Meßbeispielen demonstriert. Gespreiteten-Octadecansäuremonoschichten zeigen im Bereich der untersuchten Oberflächenkonzentrationen typisch Newtonsches Grenzflächenfließverhalten. Die für diese Systeme ermittelten Oberflächenscherviskositäten stimmen gut mit Literaturdaten überein. Die Reproduzierbarkeit beträgt 5–8%.Adsorbierte Gelatineschichten zeigen bereits bei sehr geringen Konzentrationen typisch viskoelastisches Verhalten. Bei Einhaltung eines strengen Meßregimes können grenzflächenrheologische Parameter mit einer Reproduzierbarkeit von 15–20% ermittelt werden.

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Summary An equipment for the measurement of interfacional rheologic creep curves is described. Minimal surface shear viscosities of 10^–3 mNs/m can be detected with sufficient accuracy in agreement with the theoretical analysis on the treatment of the interface with an interface-touching ring.Results are reported for different systems. Insoluble monolayers ofn-octadecanoic acid show a typical Newton surface flow in the interval of surface concentrations measured. The results are in good agreement with those of other equipments. The reproducibility is about 5–8%.Adsorbed gelatin-layers show typical viscoelastic behaviour at low concentrations. Surface theological parameters are determined with a reproducibility of about 15–20% by following a definite procedure of preparing the gelatinsolutions.

     

Zum Scherverhalten unzerstörter adsorbierter tensidmodifizierter Gelantineschichten

Zusammenfassung Untersucht wurde das grenzflächenrheologische Verhalten unzerstörter 0.2% Gelatine/Natrium-dodecylsulfat (10^–4, 10^–5 M/l)-Adsorptionsschichten bei Scherung an der Phasengrenze Luft/Lösung. Bei der Ermittlung der rheologischen Parameter muß eine Fließgrenze berücksichtigt werden, unterhalb derer lediglich spontan- und verzögert-elastisches Verhalten zu beobachten ist. Das Kriechdeformationsverhalten wurde mit einem Schofield-Scott-Blair-Modell beschrieben. Eine Analyse zur Modellierung des Fließvorganges ergab, daß Messungen bei diskontinuierlichen Scherbedingungen, bei denen die Fließgrenze nicht im gesamten Bereich der Scherung überschritten wird, wegen des dabei realisierten großen Meßeffekts für die Parameterbestimmung am geeignetsten sind. Die das Fließverhalten der Phasengrenzschicht beschreibenden Parameter weisen eine geringe Streuung (< 10%) auf, Die Ignorierung der Fließgrenze führt zu einer scheinbaren Erhöhung der plastischen Grenzflächenscherviskosität.Der Zusatz von Natrium-dodecylsulfat zu Gelatine bewirkt im untersuchten Konzentrationsbereich mit steigender Tensidkonzentration neben dem Auftreten der Fließgrenze eine erhebliche Erhöhung aller rheologischen Parameter, welche sich nicht additiv aus den Parametern der Einzelkomponenten ergibt. Das Ansteigen der rheologischen Parameter wird als Strukturverfestigung interpretiert.

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The surface-rheological behaviour of undestroyed 0.2% gelatine/sodium-dodeylsulfate (10^–4, 10^–5 M/l)-adsorption-layers at the interface air/liquid was investigated. For the determination of the rheological parameters a yield value must be taken into account. By stressing the structure below this yield value only instantaneous and retarded-elastic deformations were detected. The creep behaviour of the investigated structures was described by a Schofield-Scott-Blair-model. At discontinuous shear-conditions the yield value is not reached in the whole range of shearing. Analysing the flow-process it was shown, that using those conditions a high measuring effect is realized for the determination eached of the rheological parameters.The rheological parameters describing the creep-process deviate from its average by < 10%. Ignoring the yield value causes an apparent increasing of the plastic surface viscosity.The addition of SDS to the gelatine causes the yield value and an increasing of all rheological parameters in the investigated concentration-range. This increasing is not additiv and leads to an interpretation of a strong rise of solidity of the surface structure.

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Abkürzungen A ₁ eine die Fließgrenzef ₁ berücksichtigende Scherspannung, def. durch (30) - A ₂ eine die Fließgrenzef ₂ berücksichtigende ScherspannungF — Kraft - G ₁ ^s Schermodul der spontanen Elastizität - G ₂ ^s Schermodul der verzögerten Elastizität - M Drehmoment - S effektive Scherspannung - f ₁ Fließgrenze der plastischen Viskosität - f ₂ Fließgrenze der elastischen Viskosität - r Radialkoordinate - r ₁ Ringradius - r ₂ Gefäßradius - r _O1 kritischer Radius fürf ₁ - r _O2 kritischer Radius fürf ₂ - t Zeit - t _O Expositionszeit, Zeitpunkt der Entlastung des Systems - x Deformation - Deformation in rad - _O spontan-elastische Deformation - ^* irreversible Deformation - ₁ ^s plastische Grenzflächenscherviskosität - ₂ ^s elastische Grenzflächenscherviskosität - Retardationszeit ₂ ^s /G ₂ ^s     

A dynamic U-tube rheometer of novel design for the study of weak gels and foams

A novel rheometer based on the U-tube technique of Saunders and Ward has been developed to determine the shear moduli of very weak gels and foams. The instrument is fully automatic and operates in both static and oscillatory modes. The change of the shear modulus, with the time, was monitored in three series of samples to illustrate the performance of the instrument. The first series comprised gelatinized maize starch aqueous suspensions ranging in starch concentration from 6% to 12%. The second was a series of gelatine aqueous solutions ranging in gelatine content from 2% to 12%. The third was two commercial samples of shaving foam. The results indicated that the instrument is particularly suitable for the study of the gelation mechanism in very weak gels as well as for the study of the stability of foams in relation to time.     

Analytical characterisation of glutardialdehyde cross-linking products in gelatine-gum arabic complex coacervates

Encapsulates having shells of cross-linked mixtures of proteins and polysaccharides are widely used in the food and pharmaceutical industry for controlled release of actives and flavour compounds. In order to be able to predict the behaviour and the release characteristics of the microcapsules, a better understanding of the nature and extent of the cross-linking reaction is needed. Several analytical techniques were applied for the characterisation of glutardialdehyde (GDA) cross-linked encapsulates made of gelatine and gum arabic. To allow the use of sensitive, high-resolution methods such as chromatography and mass spectrometry, the sample first had to be hydrolysed. In this way, a mixture of amino acids, small peptides and the cross-link moieties was obtained. High-resolution liquid chromatography coupled to high-resolution mass spectrometry (HPLC-MS) was applied to detect possible cross-link markers through a comparison of HPLC-MS mass-chromatograms obtained for cross-linked and non-cross-linked coacervates. HPLC-MS/MS was used to identify the species responsible for the differences. Cross-linking occurred between GDA molecules and lysine and hydroxylysine epsilon-amino groups, and up to eight cross-link products of different nature could be identified. They included pyridinium ions and Schiff bases, and also unreacted GDA condensation products. Next, based on the insight gained in the possible chemical structures present in the cross-link markers, methods for selective labelling of these functionalities were employed to allow easier detection of related reaction products. Both liquid chromatography (LC) and gas chromatography (GC) were used in these experiments. Unfortunately, these approaches failed to detect new cross-link markers, most likely as a result of the low levels at which these are present.     

Iron gall ink-induced corrosion of cellulose: aging,degradation and stabilization. Part 1: model paper studies

Cellulose in historic paper documents is often damaged by the writing media used, especially iron gall ink or copper pigments. Degradation induced by iron gall ink is suggested to be a synergistic process comprising both hydrolytic and oxidative reactions. These processes were studied on very low sample amounts according to the CCOA and FDAM method, i.e. by fluorescence labeling of carbonyl and carboxyl groups in combination with GPC-MALLS, respectively. This study focused on preventive means to stop the deterioration induced by iron gall ink of cellulose and to prevent further damage, keeping in mind that a suitable conservation treatment has to hinder both, hydrolytic and oxidative processes, at the same time. A combination of the complexing agent calcium phytate and calcium hydrogencarbonate in aqueous solution was proved to give optimum results. To gain insight into long term stability, an aging step was performed after treatment and different ink modifications were tested. Recording the molecular weight distributions and the carbonyl group content over time GPC analysis verified for the first time the preventive effect of this treatment. This effect was not only seen for the ink-covered areas, but extended also to areas remote from the ink lines. Ink containing copper ions responded equally positively to the calcium phytate/hydrogencarbonate treatment as the iron gall ink papers did. Gelatine, sometimes used in a similar way due to an alleged cellulose-stabilizing effect did not have a beneficial influence on cellulose integrity when metal ions were present.     

Gelatine sizing and discoloration: A comparative study of optical spectra obtained from ancient and artificially aged modern papers

The role of gelatine sizing in ancient paper discoloration is still subject to debate. In this report we have addressed this issue by comparing the optical reflectance of sized and non-sized artificially aged modern papers with reflectance data obtained from a set of ancient specimens. We have used different ageing procedures and prepared the gelatine following methods set down in ancient recipes. Gelatine-sized aged papers showed an optical response comparable with that of ancient paper specimens, while very small reflectance modifications were observed in pure cellulose unsized samples under the same ageing conditions. In addition, measurements carried out on pure gelatine films confirmed that gelatine plays a major role in paper discoloration. Some differences in discoloration effects induced by artificial and natural ageing on sized paper are discussed and a possible explanation is proposed.     

Growth and spectroscopic characterization of CdSe nanoparticles synthesized from CdCl2 and Na2SeSO3 in aqueous gelatine solutions

CdSe nanoparticles were synthesized in comparatively mild conditions from Na₂SeSO₃ and CdCl₂ in aqueous gelatine solutions. Kinetics of the formation and growth of CdSe nanocrystals as well as the effect of various parameters of reacting mixture on the size of CdSe nanocrystals are investigated. Optical properties of thin gelatine films, containing CdSe nanoparticles of different size, are characterized using absorption and Raman spectroscopy.     

Apparatus for rapid adjustment of the degree of alignment of NMR samples in aqueous media: verification with residual quadrupolar splittings in (23)Na and (133)Cs spectra

NMR spectra of (23)Na(+) and (133)Cs(+) in gelatine in a silicone rubber tube that was stretched to various extents showed remarkably reproducible resonance multiplicity. The relative intensities of the components of the split peaks had ratios, 3:4:3, and 7:12:15:16:15:12:7, respectively, that conformed with those predicted using a Mathematica program. The silicone-rubber tube was sealed at its lower end by a small rubber stopper and placed inside a thick-walled glass tube. Gelatine was injected in solution into the silicone tube and 'set' by cooling below 30 degrees C. A plastic thumb-screw held the silicone tube at various degrees of extension, up to approximately 2-fold. After constituting the gel in buffers containing NaCl and CsCl, both (23)Na and (133)Cs NMR spectroscopy revealed that after stretching the initial single Lorentzian line was split into a well-resolved triplet and a heptet, respectively. This was interpreted as being due to coupling between the electric quadrupoles of the nuclei and the average electric field gradient tensor of the collagen molecules of gelatine; these molecules became progressively more aligned in the direction of the main magnetic field, B(0), of the vertical bore magnet, as the gel was stretched. This apparatus provides a simple way of demonstrating fundamental physical characteristics of quadrupolar cations, some characteristics of gelatine under stretching, and a way to invoke static distortion of red blood cells. It should be useful with these and other cell types, for studies of metabolic and membrane transport characteristics that may change when the cells are distorted, and possibly for structural studies of macromolecules.