4/16/2018
Spectral Characteristics of Colorants (Dyes & Pigments)
Spectral Characteristics of Colorants (Dyes & Pigments)
Nuri Andarwulan SEAFAST Center, IPB Southeast Asian Food & Agr. Sci & Tech Center
Department of Food Sci & Technology, IPB
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Scope
–The chemical and structural properties of dyes and pigments, as well as the relationship between light and color.
Outline • Dyes & Pigments • Color & Constitution • Light & Color • Case Study: Discoloration • Others
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Dyes & Pigments
• Dyes and pigments are the most important colorants used to add a color or to change the color of something. • They are widely used in the textile, pharmaceutical, food, cosmetics, plastics, paint, ink, photographic and paper industries.
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Definition Colorant is any chemical, either natural or synthetic, that impart color
Pigments are natural substances in cell and tissues of plants and animals that impart color
Dyes are any substances that lend color in common to material referring for colorant used in the textile industry, but in USA dyes are referred to as “ certified colors ‘ which have been approved by FDA as food-grade water soluble colorant
Lakes are dyes extended on substratum and they are oil dispersible
Dyes & Pigments
• The color, which is highly dependent on the chemical and physical properties of a matter, is a result of the interaction between light and substance.
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Color & Constitution
• The absorption of electromagnetic radiations in the UV and visible regions by a molecule causes to the electronic excitation and an electron moves to higher electronic energy level from a lower. • A covalently unsaturated group responsible for absorption in the UV or visible region is known as a chromophore.
• For example: C=C, C≡C, C=O, C≡N, N=N, NO2 etc
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Color & Constitution
• Chromophores like C=C or C≡C having π electrons undergo π → π* transitions • Those having both π and non-bonding electrons, e.g., C=O, C≡N or N=N, undergo π → π*, n → π* and n → ς* transitions. • Since the wavelength and intensity of absorption depend on a number of factors, there are no set rules for the identification of a chromophore.
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UV light Absorption by Proteins – due to 2 Amino Acids
Color & Constitution
• The organic dye molecules contained three main components such as: – Chromogen, – Chromophore, and – Auxochrome.
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Color & Constitution
– The chromophore is a chemical group that is responsible for the appearance of color in compounds (the chromogen) where it is located. – The colorants are sometimes also classified according to their main chromophore (e.g., azo dyes contain the chromophore –N=N–) (Iqbal 2008).
Color & Constitution
– The auxochrome is a substituent group found in a chromogen that influences its color. Whereas, the chromophore or chromophoric group is responsible for chromogen which will be colored.
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Color & Constitution
– The chromogen is a chemical compound that is either colored or could be made colored by the attachment of suitable substituent. – The chromophore and the auxochrome(s) are also part of the chromogen (Carmen and Daniela 2012).
4-Hydroxyazobenzene (Solvent Yellow 7)
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Β-Carotene Carotenal
The relation of chromophore group, conjugation and color.
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Effects of substituent groups within an azo-dye system
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Changes in Absorption Spectra
• Bathochromic shift (from Greek βαθύσ bathys, "deep"; and χρῶμα chrōma, "color"; hence less common alternate spelling "bathychromic") is a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a longer wavelength (lower frequency).[1] Because the red color in the visible spectrum has a longer wavelength than most other colors, the effect is also commonly called a red shift.
• Hypsochromic shift (from ancient Greek ὕψοσ (upsos) "height"; and χρῶμα chrōma, "color") is a change of spectral band position in the absorption, reflectance, transmittance, or emission spectrum of a molecule to a shorter wavelength (higher frequency). Because the blue color in the visible spectrum has a shorter wavelength than most other colors, this effect is also commonly called a blue shift.
https://en.wikipedia.org/wiki/Bathochromic_shift https://en.wikipedia.org/wiki/[email protected]
Color & Constitution
• Unlike most organic compounds, colorants possess color because they: – absorb light in the visible spectrum (400–700 nm), – have at least one chromophore (color-bearing group), – have a conjugated system, i.e. a structure with alternating double and single bonds, and – exhibit resonance of electrons, which is a stabilizing force in organic compounds (Hossain 2014).
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Light & Color
Light & Color
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Spectrophotometry
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Case Study: Discoloration
Discoloration
• Ingredients: Daging, lemak, es, ISP, garam (nitrate- nitrit), STPP, tepung, bumbu, pewarna sintetik (Ponceau 4R/Allura Red/Erythosine, Tartrazine).
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Ponceau 4R Allura Red AC
Tartrazine
Discoloration • Faktor eksternal – Cahaya – Suhu – Oksigen – Sausage’s casing
• Faktor internal – Colorants Sensitizer – Lemak teroksidasi – Kandungan mineral (Fe)
– Pewarna TiO2 (?) photocatalysis untuk Ponceau 4R
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Others: Nanocolorants
Others: Nanocolorants
• Nanocolorants were regarded as a new class of colorants that could get out of dilemma between dyestuffs and organic pigments. • Nanocolorants are new kind of colorants that can combine the advantages of both pigments and dyes, and will be promisingly applied to photoelectric high-tech fields (Zhang 2010).
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Figure: Gold and silver nanoparticles of varying sizes and shapes. From left to right: 80 nm silver nanospheres, 20 nm silver nanospheres, 40 nm gold nanospheres, 12 nm gold nanospheres, 200 nm silver nanoplates, 120 nm silver nanoplates, 60 nm silver nanoplates https://nanocomposix.com/pages/plasmonics-and-nanophotonics
Others: Nanocolorants
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SUMMARY
Terima kasih
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