scholarly journals Transformation Pathways of Reductones in the Advanced Maillard Reaction

2009 ◽  
Vol 27 (Special Issue 1) ◽  
pp. S149-S152 ◽  
Author(s):  
M. Konečný ◽  
K. Cejpek ◽  
L. Čechovská ◽  
J. Velíšek
Keyword(s):  
Maillard Reaction ◽  
Binary Systems ◽  
Amperometric Detection ◽  
Electrochemical Activity ◽  
Active Compounds ◽  
Condensation Products ◽  
Hplc System ◽  
Electrochemically Active ◽  
Transformation Pathways ◽  
Unknown Structure

The transformation of methylene-active reducing Maillard intermediates 4-hydroxy-5-methyl-2<I>H</I>-furan-3-one (norfuraneol, 1) and 2,3-dihydro-3,5-dihydroxy-6-methyl-4<I>H</I>-pyran-4-one (DDMP) was studied in heated (at 70–95°C up to 2 h) model aqueous binary systems containing various reactive carbonyl Maillard intermediates. Among them, furan-2-carbaldehyde and its derivatives 5-hydroxymethylfuran-2-carbaldehyde and pyrrol-2-carbaldehyde react intensely with the above reductones resulting in significant formation of consecutive reducing products. The active products formation and changes in total electrochemical activity were evaluated by using HPLC system with amperometric detection. The active products are consisted of primary reductone-carbaldehyde adducts (2a, b) that dehydrate to major active stereoisomeric condensation products (3a, b). The latter are hydrolysed to still electrochemically active compounds (4a, b) with yet unknown structure. Norfuraneol is transformed by 67–94% after 2 h heating at 95°C and pH 7 depending on a carbaldehyde, while DDMP react much slowly. Up to 42% of the initial norfuraneol electrochemical activity remains retained in the consecutive products depending on time and carbaldehyde involved.

scholarly journals THE STRUCTURE OF THE COLLODION MEMBRANE AND ITS ELECTRICAL BEHAVIOR

1944 ◽  
Vol 27 (5) ◽  
pp. 433-449 ◽  
Author(s):  
Karl Sollner ◽  
Joan Anderman
Keyword(s):  
Solvent Mixture ◽  
Exchange Capacity ◽  
Acid Number ◽  
Electrochemical Activity ◽  
Time Base ◽  
Equivalent Weight ◽  
Base Exchange ◽  
Electrochemically Active ◽  
Organic Solvent Mixture ◽  
High Base

1. The electrochemical behavior ("activity") of collodion membranes depends upon acidic, dissociable groups located in the interstices of the membranes. The active groups can be determined by base exchange measurements. High base exchange capacity is always found with preparations of great "electrochemical activity;" medium and low base exchange capacities occur with electrochemically active as well as with inactive preparations. The observed base exchange capacity is determined by two factors: the inherent acidity of the collodion (its mean equivalent weight) and the submicroscopic micellar structure of the collodion. A comparison of the base exchange capacity of various collodion preparations and their inherent acidities therefore allows certain conclusions to be drawn concerning the relative availability of the micellar surfaces in the different preparations. 2. The inherent acidity of various collodion preparations, their "acid number," was determined by electrometric titration. Collodion in the acidic state, i.e. after exchange of all other cations for H+ ions, was titrated in an organic solvent mixture with alcoholic KOH using a quinhydrone electrode. Details of the experimental procedure are given in the paper. The acid numbers, expressed in milliliters of 0.01 N KOH per gram dry collodion, vary from 1.0 for a highly purified collodion preparation of very low electrochemical activity to 3.3 for a highly oxidized sample of very high activity. Acid numbers of about 1.5 (corresponding to an equivalent weight of about 67,000) are found both with inactive commercial and with fairly active oxidized preparations. The base exchange capacity of the same preparations in the fibrous state as measured after 48 hours of exchange time varies from 0.0013 ml. 0.01 N NaOH per gm. dry collodion for the most inactive preparation up to 0.26 ml. 0.01 N NaOH per gm. for the most active preparation. Thus the acid numbers over the whole range investigated differ only in the ratio of 1:3.3, whereas the base exchange values differ in the range of 1:200. 3. In the inactive preparation only one in 770 acid groups is available for base exchange, in the most active collodion one group in 13; values between these extremes are found with commercial and alcohol purified oxidized preparations. 4. The high base exchange capacity of the electrochemically active preparations is not so much due to their higher acid number as to their more open structure. This difference in structure is ascribed to the presence of a small fraction of low molecular weight material which inhibits normal formation and arrangement of the micelles. 5. Short time base exchange experiments with fibrous collodion indicate that the number of acid groups available for the typical electrochemical membrane functions may be estimated to be about 50 to 1000 times less numerous than those found in the 48 hour base exchange experiments. It is estimated that in membranes prepared even from the most active collodion not more than one in 500 acid groups may be available for the typical membrane functions; with the less active preparations this ratio is estimated to be as high as one in 1,000,000 or more.

scholarly journals Advances in Chemistry of Isothiocyanate-derived Colourants

2009 ◽  
Vol 27 (Special Issue 1) ◽  
pp. S207-S210
Author(s):  
K. Cejpek ◽  
J. Velíšek
Keyword(s):  
Amino Acids ◽  
Essential Oils ◽  
Maillard Reaction ◽  
Heterogeneous Group ◽  
Model Systems ◽  
Alkaline Media ◽  
Reaction Conditions ◽  
Condensation Products ◽  
Amino Compounds ◽  
Methylene Group

This study is focused on the reactions of isothiocyanates (ITCs) in the presence of amino compounds leading to coloured structures <I>via</I> substituted 2-thiohydantoins. A series of complementary experiments has been done and appropriate reaction conditions and structural prerequisites have been defined. Low-molecular colourants isolated and characterised from the model systems can be sorted into three groups. Yellow to red diastereomeric dehydrodimers of 2-thiohydantoin derivatives that contain an acidic methylene group are formed in mixtures consisted of ITCs and amino acids with &alpha;-methylene group in mild acidic to mild alkaline systems. The condensation products of the 2-thiohydantoins with reactive aromatic or heterocyclic carbaldehydes from the Maillard reaction, essential oils etc. comprise a heterogeneous group of mostly yellow colourants. Blue compounds of two types are structurally more complicated structures that arise from <I>N</I>-substituted amino acids and ITCs in alkaline media.

scholarly journals Metallization of Organically Modified Ceramics for Microfluidic Electrochemical Assays

Micromachines ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 605 ◽  
Author(s):  
Bonabi ◽  
Tähkä ◽  
Ollikainen ◽  
Jokinen ◽  
Sikanen
Keyword(s):  
Three Dimensional ◽  
Amperometric Detection ◽  
Optical Transparency ◽  
Near Ultraviolet ◽  
Electrochemically Active ◽  
Organically Modified ◽  
On Chip ◽  
Electrophoresis Separation ◽  
Substantial Interest ◽  
Uv Range

Organically modified ceramic polymers (ORMOCERs) have attracted substantial interest in biomicrofluidic applications owing to their inherent biocompatibility and high optical transparency even in the near-ultraviolet (UV) range. However, the processes for metallization of ORMOCERs as well as for sealing of metallized surfaces have not been fully developed. In this study, we developed metallization processes for a commercial ORMOCER formulation, Ormocomp, covering several commonly used metals, including aluminum, silver, gold, and platinum. The obtained metallizations were systematically characterized with respect to adhesion (with and without adhesion layers), resistivity, and stability during use (in electrochemical assays). In addition to metal adhesion, the possibility for Ormocomp bonding over each metal as well as sufficient step coverage to guarantee conductivity over topographical features (e.g., over microchannel edges) was addressed with a view to the implementation of not only planar, but also three-dimensional on-chip sensing elements. The feasibility of the developed metallization for implementation of microfluidic electrochemical assays was demonstrated by fabricating an electrophoresis separation chip, compatible with a commercial bipotentiostat, and incorporating integrated working, reference, and auxiliary electrodes for amperometric detection of an electrochemically active pharmaceutical, acetaminophen.

scholarly journals THE STRUCTURE OF THE COLLODION MEMBRANE AND ITS ELECTRICAL BEHAVIOR

1943 ◽  
Vol 26 (3) ◽  
pp. 309-323 ◽  
Author(s):  
Karl Sollner ◽  
Charles W. Carr
Keyword(s):  
Structural Theory ◽  
Electrochemical Activity ◽  
Electrical Behavior ◽  
Phase Theory ◽  
Varying Thickness ◽  
Maximum Value ◽  
Electrochemically Active ◽  
Concentration Potential ◽  
Characteristic Concentration ◽  
Constant Maximum

1. Experiments were carried out to decide whether or not the electromotive properties of dried collodion membranes depend upon their thickness. 2. A number of dried collodion membranes of varying thickness, 3–160 µ, were prepared from collodion preparations of different electrochemical activity. The characteristic concentration potentials across them were measured and the means of these values determined for each thickness. 3. The characteristic concentration potentials across dried collodion membranes are a function of their thickness. The thinnest membranes yield in all cases the lowest concentration potentials; increasingly thicker membranes give increasingly higher potential values, until a constant value is reached which is characteristic of the particular collodion preparation used. With electrochemically active collodion, characteristic concentration potentials approaching the thermodynamically possible maximum are obtained with membranes of only 10 µ thickness, thinner membranes giving appreciably lower values. With two rather inactive commercial collodion preparations the characteristic concentration potential increases from about 30 mv. for membranes 3 µ thick to about 42 mv. for 20 µ membranes; still thicker membranes do not show a significant increase in the potential values. With a highly purified collodion preparation the constant maximum value was found to be about 32 mv., 4 µ thick membranes giving only about 22 mv. 4. These results do not support the homogeneous phase theory as applied to the dried collodion membrane. They are readily compatible with the micellar-structural theory. Several special possible cases of the latter as applied to the dried collodion membrane are discussed.

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