54 SUN CARE
transfer that excited state energy to oxygen, initiating a series of chemical reactions that may generate ROS; the photosensitiser may be chemically changed in this process as well. Although both UVA and UVB rays can generate ROS, it is now widely recognised that photosensitisation causes many of the detrimental biological effects associated with UVA. In contrast, it is generally accepted that most of the damaging effects of UVB result from its direct interaction with chromophores in the skin such as DNA. Many ROS are normal byproducts of cellular metabolism; however, an imbalance in or elevation of ROS levels can cause significant damage to cells through oxidative stress. For example, singlet oxygen has a relatively long lifetime (10-6
s -close to 100 s) and reacts indiscriminately with a wide range of biological targets, including DNA, RNA, proteins and lipids. In addition, the hydroxyl radical is a highly reactive and indiscriminate oxidant that can cross cell membranes, further increasing the range of and potential for UVA-induced oxidative damage. Unfortunately, visible light can damage human skin just as UVA does. There are plenty of chromophores in human skin that can absorb energy from sunlight in the visible range. Chromophores excited by visual light can serve as photosensitisers and generate ROS. However, protecting
OO O hv 266 nm isc 3 OO O * APPs
O
12 10 8 6 4
0.0 0.5 1.0 1.5 2.0 λ (nm)
N C O NMC O N C O Kq APP-1 =(4.2±0.3)x109 M-1 s-1 Kq=(7.5±0.4)x109 M-1 s-1
Laser flash photolysis of Keto-Avobenzone (266nm, 5ns pulse width) in deoxygenated acetonitrile solutions. To determine the quenching rate constant of triplet Keto-Avobenzone, decay traces of the triplet absorption of keto-Avobenzone in the absence and presence of varying concentrations of APP-1 or NMC were recorded. Keto-Avobenzone was generated by photolysis of enol-Avoenzone at 350nm.
Figure 2: Triplet state quenching rate constant measured using laser flash photolysis.
against ROS generated by visible light demands a paradigm shift, since traditional sunscreens protect skin from UV irradiation by blocking the energy with UV filters, and any filters that block visible light will have a distinct colour that consumers do not find aesthetically pleasing. To solve this seemingly impossible dilemma, Hallstar
Formulation 1 and 2: Sunscreen Formula using AvoBrite: Phase Tradename
A HallBrite EZ-FLO TDX AvoBriteTM HallBrite BHB
HallStar GMS SE/AS HallStar GMS PURE HallStar TA-1618 Olivem© Tween 60
800
SP-10 Kobo GTCC
B INCI Name (INN/SAN) (Other Information)
Butyloctyl Salicylate, Titannium Dioxide(nano), Triceteareth-4 Phosphate,Dimethicone Crosspolymer, Silica
Acrylates copolymer Butyloctyl Salicylate
Glyceryl Stearate, PEG-100 Stearate Glyceryl Stearate Cetearyl Alcohol
Ceteareth-6 Olivate Polysorbate 60
Nylon 12 Caprylic/Capric Trigly Ceride
GalSORB Avobenzone Butyl Methoxydibenzoylmethane [Avobenzone] EDTA-2Na D.I-Water
Disodium EDTA Water
C
Olivem 1000 Xanthan gum
D
E F
1,3-Butylene glycol 1,2-Hexanediol Trienthanolamine Water D.I. Parsol HS DC 345
PERSONAL CARE EUROPE
Cetearyl Olivate, Sorbitan Olivate Xanthan gum
1,3-Butylene glycol 1,2-Hexanediol Trienthanolamine Water D.I.
Phenylbenzimidazole Sulfonic Acid Cyclopentasiloxane, Cyclohexasiloxane
% Wt 6.00
6.00 6.00 2.00 1.00 1.00 1.00 0.50 1.00 1.50 3.00 0.05
22.65 3.00 0.3
3.00 1.00 3.00
30.00 6.00 2.00
invented Micah™ technology. Results
Principles of photostabilisation When irradiated, active species capable of absorbing light energy normally convert to their singlet excited states before converting via intersystem crossing to their triplet excited states. Both the singlet excited states and the triplet excited states are capable of returning to the ground state via radiative or non-radiative relaxation pathways.
Depending on the structure of the light- absorbing species, these relaxation pathways are often not efficient enough in returning the excited state molecules to their ground states. When this happens, the excited state energy can be diverted to molecular oxygen, which will in turn become excited singlet oxygen, the leading source of reactive oxygen species (ROS). Alternatively, these excited state molecules easily undergo chemical structure alterations, leading to photodegradation of the original molecules. Both ROS-generation and photodegradation can be significantly reduced or avoided when Hallstar photostabilisers (quenchers) are introduced in the system. Photostabilisers rapidly quench the excited states of the active species, bringing them to ground state unchanged. This also eliminates the possible transfer of excited energy to oxygen, stopping ROS generation. Rapid regeneration of ground state active species increases their efficacy in handling light irradiation.
Photostabilisers use two mechanisms to stabilise excited molecules. One mechanism involves the photostabiliser
November 2018
1/τ (106 T
S-1
)
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