Skin chromophores

Burns result from exposure to extremes of heat. The lowest temperature at which a burn can occur has been estimated to be 44 °C (111 °F) (Moritz and Henriques 1947). Burns may be of industrial, domestic or environmental origin. Industrial burns are common (Moritz and Henriques 1947 Cason 1981) and may have characteristic occupational patterns (Renz and Sherman 1994 Woods et al. 1996). Apart from direct contact with hot objects or radiation heat [infrared radiation (IR)], accidental exposure to laser energy may cause thermal destruction through absorption by skin chromophores such as melanin and haemoglobin, well known from the therapeutic application of different lasers in dermatology. Classification of burns is based on the depth of the burn as first, second, or third degree (Table 1) (Burke and Bondoc 1993). 

Keywords— skin chromophores, melanin, pheomelanin, eumelanin, modified Beer-Lambert law. 

In skin care industry and dermatology, analysis of human skin tone is an important parameter for evaluating the current condition of the skin. Research has shown that the human skin tones are due to the combination of skin chromophores (pigments) such as melanin, haemoglobin, bilirubin and beta-carotene [Buxton, 2003]. Tsumura however proposed that skin tone is mainly determined by melanin in the epidermal layer and haemoglobin in the derma layer [Tsumura, 2008]. 

DNA strongly absorbs UV radiation, especially mid-range UVB (290 to 320 nm) radiation. Two major DNA lesions are induced following UV exposure, pyrimidine dimers and 6-4 pyrimidine-pyrimidone photoproducts. Because the action spectrum (induction of a biological activity as a function of wavelength) for erythema closely matches the action spectrum for pyrimidine dimer formation, DNA is believed to be the chromophore for sunburn.6 Pyrimidine dimer formation, or more properly, the failure to adequately repair dimers after solar irradiation is also the primary cause of sunlight-induced skin cancer formation.7-8... 

Melanin is a complicated mixture of optically absorbing materials. chromophores), of which melanin is the most important. Melanin is a complicated mixture of optically absorbing materials, formed as an end product during the photo-assisted metabolism of the amino acid tyrosine. Both are bound covalently to the surrounding proteins within the skin, and other pigmented regions of the body. 

An albino does not have the ability to generate melanin, so their hair is snow white, and their skin looks pale pink in colour because the blood corpuscles beneath its surface are the only chromophore they have. 

Certain disease states also produce alterations in the skin s optical properties. Alterations of the skin s surface, such as by psoriatic plaques, decrease transmitted fight. The effect may be lessened by application of oils whose refractive index is similar to that of skin (Anderson and Parrish, 1981). Disorders such as hyperbilirubinemia, porphyrias, and blue skin nevi result in increased absorption of visible light due to accumulation or altered distribution of endogenous chromophoric compounds. 

Phototherapy is the generic term covering therapies which use light either with or without a sensitiser. Those that do not require a sensitiser use the natural chromophores within the tissue to perform this function e.g. treatment of vitamin D deficiency in rickets, and neonatal jaundice). Those that do use an added sensitiser include photochemotherapy (largely psoriasis and skin disorders) and photodynamic therapy (currently mainly cancer). Photodynamic therapy is differentiated from photochemotherapy by its additional requirement for the presence of oxygen at molecular or ambient levels.In this text we will deal only with photodynamic therapy since, at the present time, this is the main driving force in phototherapy. ° ... 

In TPM, fluorescence emission of a fluorophore (either intrinsic to the sample or an exogenously applied chromophore) is detected. A fluorophore is used to obtain specific chemical information in the skin, as discussed in more detail below. To excite the fluorophore, two-photon excitation is used, which is achieved by the simultaneous... 

III. IMAGING FOR CHEMICAL INFORMATION IN THE SKIN WITH EXOGENOUS CHROMOPHORES... 

ROS in skin can be detected by exogenous chromophores like dihydrorhodamine (DHR) (Figure 2.5). DHR is nonfluorescent until reaction with ROS when it becomes fluorescent rhodamine-123 (R123, = 535 nm). The reaction scheme is given in... 

The tetraazatriphenylene chromophore attached to the cyclene ring acted as an efficient sensitiser for Eu3+ and Tb2+ emission but also intercalated between the base pairs of DNA. The complexes were tested as cellular imaging and reactive probes using the mouse fibroblast cell line. The complexes were quickly taken up by the fibroblast cells and localised in nucleus and around the cell membrane. The process was visualised by fluorescence microscopy. Photolysis at 340 nm and 350 nm damaged plasmid supercoiled DNA producing nicked (form II) and linear (form III) DNA. DNA damage is known to induce apoptotic cell death and these complexes may be therefore considered for the development as therapeutic probes, for example in the treatment of accessible tumours, such as skin melanoma. 

Another obvious genetic aspect of toxicology has to do with the level in skin of melanin, a pigment that makes skin dark. Melanin levels vary widely with genotype. Melanin confers resistance to the effects of solar ultraviolet radiation, which is absorbed by DNA in skin cells, causing damage that in the worst-case results in deadly melanoma skin cancer. Skin melanin is a chromophore (a... 

Figure 15.5 Absorption spectra of water and main chromophores of the skin...

The presence of unsymmetrical dialkyl ditcllurium and unsymmetrical diaryl ditellurium" compounds in solution was confirmed by Te-NMR spectroscopy H-NMR spectroscopy , and mass spectroscopy . Cyclohexyl methyl ditellurium was claimed to have been isolated from a reaction mixture obtained by sequential addition of cyclohexyl bromide and methyl iodide to a solution of tetratelluride anions in dimethylformamide . The chromophoric Te —Te group in the aliphatic and aromatic ditellurium compounds imparts a characteristic orange to red color caused by an absorption maximum at approximately 400 nm. Most of the aromatic ditellurium derivatives are stable as solids toward atmospheric agents, but oxidize slowly when dissolved. The short-chain aliphatic ditellurium compounds are distillable red liquids having an obnoxious odor that clings to skin and clothes. Ditellurium compounds with more than ten carbon atoms in each aliphatic group are low melting solids that can be handled in air. 

The first step in XJVR-induced skin cancer is UVR-initiated DNA mutation, which causes the transformation of the normal cells to malignant cells. For UVR to initiate a biological reaction, it has to be absorbed by endogenous molecules (chromophores). UVB is absorbed directly by the DNA, and therefore can directly induce DNA mutation (224), in the form of thymine dimer formation (289). Some protein components may also ad as chromophores for UVB (224). UVA is absorbed by the reduced forms of the co-enzymes nicotinamide adenine dinucleotide (NADH) and nicotinamide adenine dinucleotide phosphate (NADPH), tryptophan, riboflavin, and melanin (224,290). UVA-induced DNA damage is believed to be mediated by oxygen reactive species that are released after the absorption of UVA by those endogenous chromophores and results in photooxidation of selected bases... 

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