Pigments reactions

Co-pigmentation of anthocyanins generally produces more intensely colored and more stable pigments than anthocyanin only. Two types of co-pigmentation reactions are mentioned in the literature. The first one involves intramolecular... 

Figure 12.2a. Photosynthetic Z-scheme for green plants. Abbreviations not included in the text are PQ, plastiquinone Cyt bse, a form of cytochrome b absorbing at 564 nm FD, ferredoxin FP a flavoprotein. Long vertical arrows indicate steps arising from photoactivation of pigment reaction centers dashed arrows indicate uncertain pathways.0185...

Altundag MK, Barista I. False-positive urine melanin pigment reaction caused by rifampin. Ann Pharmacother 1998 32(5) 610. 

Light-harvesting complex (multiple proteins and pigments), reaction center (multisubunit protein with associated pigments and electron carriers)... 

Photosystem II (PSIl) membranes which are reasonably pure and stable can be isolated from chloroplasts and cyanobacteria (2,3). These PSIl membranes contain the antenna pigments, reaction centre chlorophylls, O2 evolution complex and the two polypeptides D2 and Di, which bind the primary quinone acceptors Qa and Qb respectively. They are, therefore, capable of light-induced O2 evolution in the presence of artificial PSIl acceptors such as dimethyl benzoquinone (DMBQ) or dichlorobenzoquinone (DCBQ). The PSIl membranes can be deposited on TI02 without appreciable loss of photosynthetic activity. 

The dependence of quantum efficiency on qjv estimated by extrapolation was approximately linear and nearly proportional to 1-qjv (Eqn. 3). If the value of Pe were 0, these data would conform to the original three-state hypothesis put forward by Duysens and Sweers [11] — that PS 2 centers are reversibly transformed to a form that performs non-photochemical quenching of absorbed quanta rather than photochemistry. The significant non-zero intercept may be real, as accommodated by the four-state model of Weis and Berry [1], or it may be related to curvature originating, for example, from excitation transfer between PS 2 pigment-reaction center complexes [1]. 

Next, a further advanced LB assembly as a biomimetic model system to seek to mimic the three successive aspects of photosynthesis, antenna pigment, reaction center, and quinone pool, is examined [124, 125). In natural photosynthesis... 

Finally ring closure occurs to give the pigment. Reaction conditions and those of after-treatment are of first importance in obtaining a physical form which will maximize the hue and other properties of the CuPc these steps are described as conditioning . 

So far we have exclusively discussed time-resolved absorption spectroscopy with visible femtosecond pulses. It has become recently feasible to perfomi time-resolved spectroscopy with femtosecond IR pulses. Flochstrasser and co-workers [M, 150. 151. 152. 153. 154. 155. 156 and 157] have worked out methods to employ IR pulses to monitor chemical reactions following electronic excitation by visible pump pulses these methods were applied in work on the light-initiated charge-transfer reactions that occur in the photosynthetic reaction centre [156. 157] and on the excited-state isomerization of tlie retinal pigment in bacteriorhodopsin [155]. Walker and co-workers [158] have recently used femtosecond IR spectroscopy to study vibrational dynamics associated with intramolecular charge transfer these studies are complementary to those perfomied by Barbara and co-workers [159. 160], in which ground-state RISRS wavepackets were monitored using a dynamic-absorption technique with visible pulses. 

Lead(II) sulphide is oxidised to lead(II) sulphate this reaction has been used in the restoration of old pictures where the white lead pigment has become blackened by conversion to lead sulphide due to hydrogen sulphide in urban air ... 

The reaction between phthalonitrUe and copper also takes place readily in feoihng quinoline or a-methyhiaphthalene the pigment is precipitated as fast as it is formed as a crystalline product. It is separated from the excess of copper by shaking with alcohol, when the metal sinks and the pigment, which remains in suspension, can be poured off the process may be repeated to give the pure compound. 

Azobisnittiles are efficient sources of free radicals for vinyl polymerizations and chain reactions, eg, chlorinations (see Initiators). These compounds decompose in a variety of solvents at nearly first-order rates to give free radicals with no evidence of induced chain decomposition. They can be used in bulk, solution, and suspension polymerizations, and because no oxygenated residues are produced, they are suitable for use in pigmented or dyed systems that may be susceptible to oxidative degradation. 

Stabilizers and pigments are normally slurried with macroglycol and added to the polymeric glycol charge, prior to diisocyanate addition. Therefore, care must be taken to avoid additives that react significantly with diisocyanates or diamines under processing conditions. Also, stabilizers should be chosen that have no adverse catalytic effect on the prepolymer or chain-extension reactions. 

Tripotassium hexakiscyanoferrate [13746-66-2] K2[Fe(CN)g], forms anhydrous red crystals. The crystalline material is dimorphic both orthorhombic and monoclinic forms are known. The compound is obtained by chemical or electrolytic oxidation of hexacyanoferrate(4—). K2[Fe(CN)g] is soluble in water and acetone, but insoluble in alcohol. It is used in the manufacture of pigments, photographic papers, leather (qv), and textiles and is used as a catalyst in oxidation and polymerisation reactions. 

Prussian Blue. Reaction of [Fe(CN)3] with an excess of aqueous h on(Ill) produces the finely divided, intensely blue precipitate Pmssian Blue [1403843-8] (tetrairon(Ill) tris(hexakiscyanoferrate)), Fe4[Fe(CN)3]. Pmssian Blue is identical to Turnbull s Blue, the name which originally was given to the material produced by reaction of [Fe(CN)3] with excess aqueous h on(Il). The soHd contains or has absorbed on its surface a large and variable number of water molecules, potassium ions (if present in the reaction), and h on(Ill) oxide. The h on(Il) centers are low spin and diamagnetic h on(Ill) centers are high spin. Variations of composition and properties result from variations in reaction conditions. Rapid precipitation in the presence of potassium ion affords a colloidal suspension of Pmssian Blue [25869-98-1] which has the approximate composition KFe[Fe(CN)3]. Pmssian Blue compounds are used as pigments in inks and paints and its formation on sensitized paper is utilized in the production of blueprints. 

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