CE457/527 Project Report
Matthew
B. Boyle, William W. Gikandi
Zhiyong
Gu, Kassim S. Salih
Department of Chemical
Engineering
University at Buffalo, SUNY
April 8, 2002
1. Introduction and Background
1.1 Some basic information about skin type, skin care, skin cancer, and the necessity of sunscreen
1.2 Brief outline of factors to be considered for the production of sunscreen
Companies producing sunscreen must adhere strictly to the following
criteria outlined below. This is both for the satisfaction of the customer, and
also, more importantly, for safety’s sake:
The properties necessary in a sunscreen are:
1. It
must absorb erythemogenic radiation to a satisfactory level:
·
Suntan preparations
are often sold under the improper premise that they can prevent sunburn and yet
allow tanning. Medically speaking, melanogenesis (tanning) cannot occur without
preceding erythema to trigger the process. Therefore, a good sunscreen must
maintain a balance between allowing sufficient radiation to the skin to cause a
desired tan; and yet keep it at a level that is deemed as safe for the skin.
Ideally, a good sunscreen should not give the user a ‘tan’ on the first day;
but should rather protect the consumer and allow a safe tan to develop over
several days.
2. It must be non-toxic and it must not influence
bodily metabolism.
·
Ingredients in
sunscreen must be ‘inert’ with respect to normal functions of the body. So
that any surface application or ingestion, via subcutaneous penetration or
otherwise, will not cause harmful short-term or long-term effects to the body.
3. It must be dermatologically innocuous, i.e. free
from primary irritant effect and from any danger of sensitization.
·
There are few other
cosmetic preparations which are used repeatedly over such a large area of the
body and which therefore present any greater hazards for toxic, irritating and
sensitizing reactions. Usually, irritation problems occur at or near the folds
of the skin; or near the mucosae. Lips, eyelids, around the nostrils, and the
skin between fingers and toes are all targets for sensitivity. Therefore,
manufacturers should balance effectiveness of the ingredients, active agents
and concentrations they use against the their potential irritability to the
skin.
4. It must not be photo labile.
·
In absorbing the
erythemogenic radiation, it must not undergo any chemical change that would
reduce its efficacy as a sunscreen. More importantly it should not be
converted to any compound will be toxic or innocuous to the skin. Its
structure must also not change in a way that will affect its physical
properties; such as its look or feel, surface coverage, etc.
5. It must be non-volatile, and possess suitable
Solubility Characteristics.
·
Customary vehicles for
sunscreens are hydro alcoholic lotions, water-in-oil or oil-in-water emulsions,
and oily lotions. It is essential that the sun-screening compound be dissolved
or dispersed easily and permanently in the vehicle. Once it is spread on the
skin, it should remain in place as a continuous film, closely adhering to the
surface. It should resist washing off either by perspiration or by immersion
in fresh or salt water. At the same time, its user must be able to wash it
off easily by scrubbing with soap and water at the end of the day.
·
Also, it must not
crystallize during storage or shipping through cold areas, as this will cause
patchy coverage and lower protection. So it’s self solubility or its ability
to remain in an emulsion must be sufficiently high.
6. It should not be absorbed through the skin.
·
Virtually all
chemicals placed on the skin diffuse to some extent through the underlying
tissues. If the percutaneous absorption is marked, the chemicals may be
detected in the blood stream or in the urine. However, complete avoidance of
penetration is not desirable. The fraction of the screen that can perfuse
the upper stratum corneum increases protection against the sun; especially
because it cannot be removed by bathing or abrasion due to clothing. However, a
screen that diffuses into deeper layers and into the blood stream is not
desirable.
7. Its physical properties must be acceptable to the
consumer.
· Having fulfilled all of the above characteristics, the screen must finally please picky consumers. Producers of sunscreens are in heavy competition with each other, and are pressed to come about with a product that will not only be Safe and Effective, but one that will also be pleasant to the touch and smell, and also be aesthetically pleasing.
1.3 How
Sunscreen Works.
There are two main ways in which a sunscreen can protect the skin against the sun:
·
Scattering/ Reflecting Radiation: this
method can be likened to how a mirror works. Shining a concentrated beam of
light to a shiny, uneven mirror will cause the incident beam to be reflected
back in different directions; effectively being scattered instead of harming
the surface. Opaque powders applied to the skin either in the dry state or
incorporated into suitable vehicles ill serve to scatter the erythemal rays
falling upon them. Zinc Oxide is the most effective of such powders, but there
are others of similar efficiencies available. This method seems to be the less
popular among sunscreen producers. The main reason being that the amount of
coating required for sufficient scatter or reflection is quite high. Also, it
would be much easier to wash off powders from the skin, and maintaining
‘enough’ powder for protection in an emulsion may prove to be difficult.
·
Absorbing Radiation: all kinds of organic and inorganic materials
absorb ultraviolet energy. When a photon of energy strikes a molecule of such a
compound, the energy may be absorbed if the molecule may exist in two different
states (isomers). The difference in the energy levels between the two molecular
structures must correspond exactly to the energy of the absorbed photons. The
energy contained in a photon is directly related to its wavelength. Therefore, the active ingredient in
sunscreens of this nature has a chemical isomer whose transition corresponds
very closely to the energy of a photon in the erythemal wavelength range of
light. On absorbing these photons, the active ingredient undergoes a change in
structure to for an ‘excited’ isomer that exists at a higher energy level. This
excited isomer is usually not stable, and so it slowly releases its absorbed
energy into its surroundings, returning to its original state as the active
ingredient. The slow rate of energy release results in a shift of the emitted
photon to a longer wavelength, and the re-emitted energy often lies in the
visible or infrared range; a wavelength that has no harmful erythemal effects.
Note: it is important that the excited isomer be unstable, so that it will return to its original state and absorb more radiation. Otherwise, a stable isomer will stop working and the efficacy of the screen will decrease over time.
It is also important that
the excited isomer does not react with surrounding chemicals or the atmosphere
to form a compound that is different to the original active ingredient.
Ideally, the excited isomer should not be extremely reactive.
2. Main Components and Compositions
of Sunscreen Lotion and their Functions
Compound |
State |
Solvent |
Ethyl
p-dimethyl amino-benzoate |
Solid |
Alcohol |
Ethyl
p-amino-benzoate |
Solid |
Alcohol |
Methyl
anthranilate |
Liquid |
Alcohol |
Homomenthyl
slicylate |
Liquid |
Alcohol |
Phenyl
salicylate |
Solid |
Alcohol |
Menthyl
Salicylate |
Liquid |
Alcohol |
2-Naphthol-6sulphonic
acid |
Solid |
Water |
2-Naphthol-8-Sulphonic
acid |
Solid |
Water |
Compound |
Sunscreen
Index (S.I) at Optical Density 3,080Å (conc. 1%) |
Ethyl
p-dimethylaminobenzoate |
14.8 |
Ethyl
p-aminobenzoate |
9.6 |
Isobutyl
p-aminobenzoate |
9.2 |
n-Butyl
p-aminobenzoate |
8 |
Dehydroacetic
acid |
7 |
Uviteix
RBS |
0.01 |
Uvitex RS |
0.005 |
Rating of Sun Protection Product |
SPF Values |
Protection Level |
Minimal |
2 to 4 |
Least protection; permits tanning.
Recommended for people who rarely burn, but tan profusely. |
Moderate |
4 to 6 |
Moderate protection from sun
burning; permits some sun tanning. Recommended for people who burn minimally
and tan well. |
Extra |
6 to 8 |
Extra protection from sunburn;
permits limited tanning. Recommended for people who burn moderately and tan
gradually. |
Maximal |
8 to 15 |
High
protection from sunburn; permits little or no tanning. Recommended for people
who burn easily and tan minimally. |
Ultra |
15 or more |
Most
protection from sunburn; permits no tanning. Recommended for people who burn
easily and rarely tan. |
3. Surfactants and Polymers in
Sunscreen Lotion
3.1
Surfactants and polymers used in sunscreen lotion. Several
standard/commercial sunscreens used in marketplace.
Surfactants
and polymers are widely used in sunscreen lotions. They are essential
ingredients to modify and/or improve the properties of sunscreen lotions. As we
mentioned in the previous sections, there are many types of vehicles that can
be chosen as the carrier for the sunscreens. The basic vehicles are: emulsions,
gels, oils, sticks, mousses, aerosols, ointments, etc (Lowe & Shaath,
1990). Based on the type of the vehicles used, different surfactants and
polymers can be used.
We will first
give several formulations of the sunscreen that are available in the market,
then we discuss the properties that enhanced/improved by surfactants and
polymers (in section 3.2). Following is some of the formulations currently
available in the marketplace, which illustrate how diversity the sunscreen is
(Lowe & Shaath, 1990).
Formula type: Cream
Comments: Emollient
skinfeel
Expected SPF: 25+
Ingredients:
Phase A %
w/w
Octyl dimethyl PABA 8.0
Benzophenone-3 5.0
Octyl methoxy cinnamate 6.0
Cyclomethicone 10.0
Glyceryl stearate SE 5.0
Phenyldimethicone 2.0
Cetearyl alcohol (and)
ceteareth-20 2.0
Cetyl alcohol 1.0
Octyl palmitate 10.0
Phase B
Water QS
Preservative QS
Glycerine 5.0
Diethynolamine
p-methoxycinnamate 8.0
Titanum dioxide 3.0
Xanthan 0.2
Hydroxyethylcellulose 0.1
Phase C
Fragrance 0.3
Formation
type: Lotion
Comments: Inexpensive
lotion with outstanding high temperature stability
Expected SPF: 15
Ingredients %
w/w
Phase A
Octyl dimethyl PABA 7.0
Benzophenone-3 3.0
Strearic acid XXX 4.0
Mineral oil 10.0
Myreth-3 myristate 4.0
Phase B
Water QS
Preservative QS
Carboner 1342 0.2
Propylene glycol 5.0
Phase C
Triehtanolamine 99% 0.7
Phase D
Fragrance 0.3
Formation
type: Sunscreen oil
Comments: Luxurious
skinfeel
Expected SPF: 15
Ingredients %
w/w
Octayl salicylate 5.0
Menthyl anthranilate 3.5
Benzophenon-3 4.0
Octyl dimethyl PABA 8.0
Tridecyl neopentanoate 15.0
Fragrance 1.0
Cyclomethicone 20.0
Phenyldimethicone 5.0
Mineral oil QS
Formation
type: Sunscreen gel
Comments: Poloxamine
aids in sunscreen solubilization
Expected SPF: 12
Ingredients %
w/w
Phase A
Carboner 940 1.5
Poloxamine 940 7.0
Ethanol QS
Phase B
Dioctyl malate 10.0
Octyl methoxy cinnamate 7.5
Benzophenon-3 4.0
Phase C
Triehtanolamine 99% 0.7
Phase D
PEG-15 cocamine 3.5
Water 12.5
Formation
type: Lip balm stick
Comments: Smooth
application characteristics
Expected SPF: 8
Ingredients %
w/w
Octyl dimethyl PABA 7.0
Benzophenon-3 3.0
Castor oil QS
Octyldodecanol 5.0
Beeswax 15.0
Ozokerite 6.0
Myristyl lactate 4.0
Candililla wax 6.0
Petrolatum 5.0
Fragrance 0.5
Formation
type: Sunscreen mousse
Comments: Excellent
skinfeel
Expected SPF: 2-4
Ingredients %
w/w
Water QS
Propylene glycol 5.0
Quaternium-25 3.0
Octyl methoxy cinnamate 3.0
Cetearyl alcohol (and) ceteareth-20 1.0
Octyldodecanol 5.0
Preservative QS
Package
90% Concentrate
10% A46 propellant
Formation
type: Nose protectant
Comments: Contains
sunscreen and opacifying agents to achieve a very high degree of protection
Expected SPF: 25+
Ingredients %
w/w
Phase A
Octyl dimethyl PABA 7.0
Benzophenon-3 3.5
Mineral oil (and)
lanolin alcohol 5.0
C12-15 Alcohol benzoate 15.0
Phase B
Water QS
Preservative QS
Phase C
Zinc oxide 25.0
Titanium 30.0
3.2 How
does sunscreen emulsion stabilize? – Emulsion stability
Emulsion is
by far the most popular of all sunscreens used for sunscreens, however, emulsion
is the most difficult to stabilize. There are basically two types of emulsions:
oil-in-water and water-in-oil, and two “styles”, cream and
lotion. From a thermodynamic point of view, a stable emulsion is almost
impossible. Actually there are two
phases in an emulsion, one is the small droplet (internal phase), another is
the liquid media (outside phase). Both phases are immiscible. The droplets are
always trying to come together and coalesce, and to form a large drop. So, the
goal of the sunscreen producing is to keep the sunscreen stable for a
relatively long time.
There is an
equation describing the particle interaction: Stokes law (Lowe & Shaath,
1990):
where V is
the velocity of sedimentation (interaction); d is the diameter of the particles
of the dispersed phase; p1 is the specific gravity of the dispersed
phase; p2 the specific gravity of the external phase, g =
gravitational constant; n = viscosity of the external phase.
So there are
two ways to reduce the sedimentation speed:
·
decrease the value of the numerator
·
increase the value of the denominator
It’s obvious
that reducing the diameter of the dispersed droplets can increase the emulsion
stability. Several ways can be used to reduce the particle size, in which the
most important one is using emulsifier (as we discussed in the next section). Another
way to reduce the size of the droplet is by mechanical stirring. When high
shear is introduced to the sunscreen lotion, the size of the drop will be
reduced.
Another way
to decrease the V value is to decrease the (p1-p2) value.
In other words, to make the specific densities of the external and internal
phases as close as possible. Since it is not very easy to change the specific
gravity of the internal (normally oil) phase, it is a feasible way to change
the specific gravity of external phase (normally water), e.g., adding some
alcohol to the water phase.
Instead of
changing the numerator, we can also change the denominator, i.e., by changing n,
the viscosity of the external phase. There are many ways to change the
viscosity of the external phase: (a) add more external phase; (b) reduce the
particle size; (c) add a fatty moiety to form liquid crystal; or (d) add a
thickener (“gum”) to the external phase.
3.3 Attributes of Sunscreen Lotion Enhanced by Colloidal and Surfactant Aspects.
·
Emulsion Stability – Emulsifier
As we
mentioned in the early section, emulsifier is a good way to reduce the
dispersion droplet size, thus stabilize the emulsions. HLB (hydrophilic
lipophilic balance) is the oldest and most widely used method to select
emulsifiers (Lowe & Shaath, 1990). The HLB can be determined for each
emulsifier. There are both nonionic and anionic emulsifiers. Anionic emulsifier is more widely used than nonionic
emulsifier, for example, triethanol-amine strearate.
·
Film Formers
Film
formation is very important to increase the efficacy of sunscreens. One of the
primary factors that affect the sunscreen to achieve a high SPF is the uniformity
of the sunscreen film on the skin. SO it is crucially important that the film
is thick and uniform. There are several materials that can be used to develops
this type of films. Cellulosic gums are very good candidates, which actually
can be incorporated in almost any kind of
sunscreens. Polyvinylpyrillidone (PVP) is another good candidate.
·
Emmollients
There are
both oil-soluble and water-soluble emollients, but the oil-soluble ones are the
most widely used. They can provide a silky skinfeel upon application, acting as
the vehicles in which the oil-sunscreen is delivered. There are several types
of emollients: esters (liquid and solid), waxes, fatty alcohols, and mineral
oils, in which esters are widely used in the compounds of sunscreens.
·
Stabilizers/Protectants
Since emulsion is very delicate, it is
subject to many directions. Thickeners (gum) are one of the sunscreen
stabilizers. Antioxidants are another type of stabilizers. BHA, BHT, propyl
gallate, and dilauryl thiodipropionate are four of the most popular
antioxidatants (Lowe & Shaath, 1990). Preservatives are another type of
stabilizers. They should be kept in the water phase so that it can protect the
sunscreen emulsion.
There are many other properties that can be
improved or enhanced by surfactant or polymers, like spreadibility, washability, sunscreen
substantivity, sunscreen rheology, etc. Here we will not introduce each one of them.
This section will address the chemical processes that underlie the mechanism of sun-blocking by sunscreens. To start, the reader is given the following equation which is critical in understanding the sun-blocking process. It is the equation relating the energy of the suns rays to the wavelength of these rays and is given below as follows;
(1) E = hc/l
Where E = The energy of the wave; h = Planck’s Constant; c = The speed of light; l = The wavelength of the ray
It is observed from this equation that the higher the wavelength a ray possess, the lower in energy it will be. The higher a wavelength is, the more damage it inflicts upon the skin. In the electromagnetic spectrum, the most damaging rays from sunlight are the ultraviolet rays.
The ultraviolet spectrum can be broken up into three categories; the UVC region, the UVB region, and the UVA region. Of these three, the UVC region is the most damaging to human beings. Fortunately, most UVC radiation is filtered out by the stratospheric ozone layer (however the use of chlorofluorohydrocarbons(CVC’s), a pollutant, is depleting this layer). The UVB and UVA regions are not filtered out by the ozone. These ultraviolet rays cause the most damage to skin and hair.
Suncreens have two main components which protect the skin. These components are; physical blockers, and chemical absorbers. Physical blockers are the first line of defense in skin protection. They are chemicals the reflect and scatter ultraviolet rays. Some examples of physical blockers are; zinc oxide, titanium oxide, and red petrolatum. However physical blockers alone are not a sufficient source of protection from UVB and UVA rays. The other component optimized in sunscreens is the chemical absorber. The function of the chemical absorber is to take the UV radiation react with it and release it back into the atmosphere in the form of heat. This way the radiation will not react with the skin and cause harm. There are many chemical absorbers, some that only absorb in the UVB region, and some which will only absorb in the UVA region. The UVA and UVB ranges are given below as follows;
UVA : 320 – 360 (nanometers)
UVB : 290 – 320 (nanometers)
Some examples of UVA chemical absorbers are; benzophones, anthranilates, and dibenzoyl methanes. Some examples of UVB chemical absorbers are; PABA derivatives, salicylates, cinnamates, and camphor derivatives.
It is important to understand the mechanism behind sunscreen action. Most sunscreen chemicals are aromatic compounds conjugated with a carbonyl group. While the ring itself is usually unreactive, the side chain will undergo what is known as a “photochemical reaction”. Very often, the side chain has an electron – releasing group(usually an amine or a methoxyl group). This is important because in the UVA and UVB regions , the energy of the radiation quanta is in the same order of magnitude as the resonance energy of electron delocalization in aromatic compounds. This means that the energy absorbed from UV radiation corresponds to the energy required to cause a “photochemical excitation” in the sunscreen molecule (Lowe & Shaath, 1990). The sunscreen chemical gets excited to a higher state (p*) from its ground state (n) by absorbing the UV radiation. The sunscreen molecule then releases the high energy rays as low energy rays ( rays with a longer wavelength). After releasing these rays back into the atmosphere, the sunscreen molecule will then return to its ground state.
Another important factor in sunscreen is the solvent that the chemical absorbers are in solution with. Depending on the polarity of the chemical, the range in which that chemical absorbs the radiation in will change. This is very important because if the absorber is too polar or too apolar, the range of the chemical could get shifted out of the UVA and/or UVB regions, rendering it useless. There two types of shifts a sunscreen chemical absorber could undergo. One type is a hypochromic shift, the other is a bathochromic shift.
A hypochromic shift occurs when the chemical absorber is a polar compound in a polar solvent. For a polar compound in a polar solvent, the ground state of the compound stabilizes. This means that it will require a greater amount of energy for this compound to reach its excited state (Lowe & Shaath, 1990). As a result, the wavelength reflected back by the sunscreen will be lower(this is the hypochromic shift).
For less polar compounds in polar solvents, the excited state will be more polar than the ground state. The polar solvent will stabilize the excited state of the compound (Lowe & Shaath, 1990). This will lower the requirement for an energy transition, so a higher maximum occurs for the wavelength(this is the bathochromic shift).
Finally, the last important consideration for sunscreen protection is the molar extinction coefficient. The extinction coefficient is the primary indicator for effectiveness of a sunscreen chemical. The chemicals that have a higher extinction coefficient are better at absorbing more of the energy from harmful UV radiation. Typically, a compound that is symmetric(and therefore has symmetry - allowed electron transitions) has a higher extinction coefficient than a compound that does not have symmetry(these compounds have symmetry - forbidden electron transitions). Another contributor to an increased extinction coefficient value are conjugated bonds within the molecule. This is due to the increased resonance delocalization in a conjugated double bond. A desirable value for the molar extinction coefficient is 20,000 or greater.
5. Processing & Suppliers.
This section give some sunscreens produced from vegetable oil and plant phenols, which contains the consumer and manufacture information, also the unit operations and other processing informations.
5.1 Major suppliers of sunscreen with a link to their website, and a brief description of their product and it’s efficacy
Lipase-catalyzed transesterification reactions yield novel ferulyl-substituted or coumaryl-substituted acylglycerols with properties suitable for use as sunscreen agents having broad spectrum UV protection. These agents have the advantage of being synthesized from natural materials, while providing a value-added use for vegetable oils. They are readily incorporated into standard sunscreen formulations.
The ferulyl-substituted triacylglycerols of this invention are
characterized by the properties of having the UV absorptivity of a cinnamate
ester and the water-insoluble properties of a lipid, thereby rendering them
useful as sunscreen agents for the skin that do not readily wash off with
water. The UV absorbance of these products extends from about 280 nm to about
350 nm, and is particularly effective in the range of about 310-350 nm. This is
predominantly in the UVA range, but also covers part of the UVB range. For
additional UVB protection, the subject compounds may be formulated with other
sunscreen agents as discussed, below.
The sunscreen agents of the invention as defined by the general formula
(I) may be formulated into any cosmetic preparations that are especially
designed to be water-resistant. The total level of sunscreen agent in these
preparations will typically be on the order of about 0.1 to 20%, by weight, and
preferably within the range of about 1-10%, by weight. The amount of sunscreen
agent currently approved in the United States for inclusion in a topical skin
treatment formulation is 15%. It is contemplated that the agents of this
invention will be incorporated into formulations that are both effective and
safe. An effective amount (or photo protective amount) is that amount which is
sufficient to significantly induce a positive effect of protection against UV
sunlight as compared to a control. One measure of the effectiveness of the
sunscreen agent is the Sun Protection Factor (SPF) of the composition. SPF is a
commonly used measure of photo protection of a sunscreen against sunburn. The
SPF is defined as the ratio of the UV energy required to produce minimal
erythema on protected skin to that required to produce the same minimal
erythema on unprotected skin in the same individual. See Federal Register, 43,
No. 166, pp. 38206-38269, Aug. 25, 1978). A safe amount is that which does not
produce serious side effects.
I- Transesterification of Ethyl Ferulate with
Triolein in Solvent.
Triolein (Nu-Chek-Prep.RTM. Elysian, Minn., 447 mg, 0.5 mmol) was dissolved in
5 mL of toluene in a 25 mL Schlenk tube at 60 0C. Ethyl ferulate
(ethyl 4-hydroxy-3-methoxy cinnamate, γ-Aldrich, 111 mg, 0.5 mmol) was added to the reaction mixture
followed by Novozym.RTM. 435 lipase [Candida antarctica, with a 1-2% (w/w)
water content, 110 mg, combined mass of the enzyme and its support]. Thus the
ethyl ferulate and triolein reactants were present in a 1:1 mol ratio and were
catalyzed by 1 wt equivalent (with respect to ethyl ferulate) of lipase. The
reaction was performed under a nitrogen atmosphere using standard Schlenk line
techniques. The suspension was stirred at 60 0C., and 100 .mu.L. The
reaction reached equilibrium after 72 h.
This reaction resulted in a 44% conversion of ethyl ferulate to the desired
ferulyl monoolein and ferulyl diolein.
Sunscreen cream (W/O)
Phase |
Name |
% |
A |
Compound from the above |
3.00 |
|
Arlacel 581 |
7.00 |
|
Paraffin highly liquid (Item No. 7174) |
6.00 |
|
Arlamol S 7 |
2.00 |
|
Lunacera M |
5.00 |
|
Dow Corning 344 |
4.00 |
|
Miglyol 812 |
2.00 |
|
Oxynex 2004 (Item No. 6940 |
|
B |
Glycerol (Item No. 4093) |
2.00 |
|
Magnesium sulfate heptahydrate (Item No. 5882) |
0.17 |
Preservative q.s.
Water, demineralized to 100.00 |
Preparation:
Heat phase A to 75 0C. and phase B to 80 0C. Slowly stir
phase B into phase A. Homogenize. Cool with stirring. If desired perfume at 40 0C.
Suppliers:
(1) E. Merck, Darmstadt
(2) ICI, Essen
(3) LW Fuller, Luneburg
(4) Dow Corning, Dusseldorf
(5) Huls Troisdorf AG, Witten
II-Transesterification of Ethyl Ferulate with Triolein without SolventUsing
Recycled Lipase
The catalytic stability of Novozym.RTM. 435 lipase was demonstrated by repeating the transesterification of ethyl ferulate and with neat TO with previously used lipase. After equilibrium was reached in the reaction as described from the above(I), the triolein was decanted, and fresh triolein was added to the reaction vessel. Residual quantities of ethyl ferulate and reaction products from the reaction above (I) were determined by HPLC and subtracted from the yields obtained from the second reaction. Ethyl ferulate was added to initiate the reaction, which stirred for an additional 120 h. HPLC analysis revealed that the second glycerolysis produced 31% ferulyl monolein and 43% ferulyl diolein, a combined yield of 74%. The residual amounts of ethyl ferulate and ferulyl glycerol after 120 h were 17% and 9%, respectively. The slightly higher quantity of unreacted ethyl ferulate present at equilibrium (17%) compared to the quantity of unreacted ethyl ferulate present at equilibrium in the original glycerolysis (13%) is attributed to the shorter reaction time. These results indicate that Novozym.RTM. 435 lipase remains active at 600C for weeks and is able to catalyze multiple glycerolysis reactions.
Sunscreen milk (W/O)
Phase |
Name |
% |
A |
Compound from the above |
3.00 |
|
Pionier L-15 |
19.00 |
Paraffin highly viscous (Item No. 7160 |
15.00 |
|
B |
Glycerol (Item No. 4093) |
5.00 |
Magnesium sulfate heptahydrate (Item No. 5882) |
0.50 |
|
Preservative q.s. Water, demineralized to 100.00 |
Preparation:
Heat phase A to 75 0C. and phase B to 80 0C. Slowly stir
phase B into phase A. Homogenize. Cool with stirring. If desired perfume at 40 0C.
Suppliers:
(1) E. Merck, Darmstadt
(2) Hansen & Rosenthal, Hamburg
Sunscreen oil
Phase |
Name |
% |
A |
Compound from (I) |
3.00 |
Arlatone T |
2.00 |
|
Miglyol 812 |
14.00 |
|
Cetiol B |
22.50 |
|
Isopropyl myristate |
7.50 |
|
Paraffin highly liquid (Item No. 4174) |
48.85 |
|
Oxynex 2004 (Item No. 6940) |
0.05 |
|
B |
Perfume oil |
0.10 |
Preparation:
Heat phase A to 70.degree. C. with stirring until all components are dissolved,
stir until cold and add phase B at 40.degree. C.
Suppliers:
(1) E. Merck, Darmstadt
(2) ICI, Essen
(3) Huls Troisdorf AG, Witten
(4) Henkel, Dusseldorf
(5) Haarmann & Reimer, Holzminden
3.2 Processing (unit operations) involved in production of a basic sunscreen
product. (Including purpose of each operation.)
Tanning involves the formation of melanin polymers in our
skin. Melanin monomers are already present in the outer layer of the
skin, but in a reduced state. When oxidized upon exposure to UV, the
melanin polymer forms and absorbs light in the visible and ultraviolet
region. We notice the effect because of the absorption of visible light,
thus the darkening of our skin. Since the level of melanin monomers is
regulated in the skin, prolonged exposure to UV leads to the production of
additional melanin monomers, again a photochemical process using UV light
energy. The complete reaction is shown below:
Tyrosine is the enzyme that
initiates the production of melanin using the amino acid tyrosine. (A
genetic deficiency of tyrosine leads to albino skin.) While this process
seems sufficient for ordinary circumstances, prolonged exposure to sunlight
(and its UV component) can overwhelm the skin’s natural mechanisms and lead to
damage, including skin cancer. Sun blocks and sunscreens were invented to
supplement the body’s natural defenses.
Sun blocks work
on a fairly simple premise. They work by absorbing all of the UV light
before it reaches the skin and tend to reflect visible light, which is why they
are often white. Most sun blocks contain either ZnO or TiO2.
Sunscreens, however, are generally a colorless cream or oil made of one or more
organic compounds that specifically absorb UV radiation. They rely on
UV-specific energy absorbance to use the energy from the UV light and thus keep
it from causing photochemical reactions in human cells.
The Food and Drug Administration codified Sun Protection Factor (SPF) in 1993 for labeling and marketing purposes. It is defined as the ratio of delayed sunburn on protected skin to unprotected skin, where the protected skin is covered by 2mg/cm2 of sunscreen. (Abney, 1998; Federal Register, 1999) It is defined as the ratios of the minimal erythema doses (MED) of UV radiation leading to delayed sunburn on protected versus unprotected skin. Thus, it is based on the physiological response in the wearer; SPF 34 should protect you from burning for thirty-four times the time of unprotected skin.
In starting to
prepare for this laboratory, was choose a range of materials that included
sunscreens in the SPF 30 region, face lotions that claimed SPF 15.
The
procedure used by Abney et al (1998), the experimental procedure by Abney et al
was based on extracting the organic compound active in the sunscreen. The
Abney procedure would be more comparable to the sunscreens. Abney et al
also claimed less than two percent error on repeated trials.
Sunscreens
contain the following active ingredients:
These compounds, and other
sunscreens, are structurally characterized as highly conjugated compounds
containing aromatic rings and oxygen containing functional groups. (Kimbrough,
1997) Note that these compounds tend to have polar functional groups and
short hydrocarbon chains. This could provide evidence for why sunscreens
tend to lose their effectiveness when exposed to water – they are soluble in
(polar) water. Insoluble compounds tend not to have polar functional groups or
to have long hydrocarbon chains.
While there
is a limit to the number as of 1999 permitted active ingredients, since the
federal Food and Drug Administration limits the maximum concentration of any
one ingredient by mass. The maximum concentrations for sunscreens and sun
blocks are listed below:
Amino benzoic acid |
15% |
|
Octyl salicylate |
5% |
Avobenzone |
3% |
|
Oxybenzone |
6% |
Cinoxate |
3% |
|
Padimate O |
8% |
Dioxybenzone |
3% |
|
Phenylbenzimidazole sulfonic
acid |
4% |
Homosalate |
15% |
|
Sulisobenzone |
10% |
Methyl anthranilate |
5% |
|
Titanium dioxide |
25% |
Octocrylene |
10% |
|
Trolamine salicylate |
12% |
Octyl methoxycinnamate |
5% |
|
Zinc oxide |
25% |
(FDA, 1999, p27687)
Generally, a consumer product
will contain a variety of these FDA approved compounds, each of which much (per
FDA regulations) be of sufficient concentration to increase the finished
product’s SPF by 2 or more.
To test the products, dissolve 0.1g of sunscreen in 10mL of isopropyl alcohol,
for a solution containing 10g/L of sunscreen. Heat the solutions in a
water bath at 45-50ºC for one minute with mild agitation, than allow the
solution to return room temperature. When at room temperature, shake
vigorously for one minute, and allow to settle. The supernatant can be
stored until ready for use – in this case, the prepared solution was prepared
one week prior to testing.
Before testing for absorbance, dilute the supernatant 1:100 with isopropyl alcohol. More concentrated solutions of the supernatant were tested, but resulted in absorbance values above the range measured accurately by the laboratory instrument available. In the 325 to 400 nm range that we were interested in, the Spec 20 did not provide absorbance values similar to those of the automated UV/V is spectrometer, and had no additional lower range even without a UV bulb in the spectrometer. Most importantly, because the Spec20 is not designed to measure absorbance in the high 300nm range, the absorbance values were not always reproducible in the same machine in the same sample.
Brand Name |
SPF |
Mass(g) |
|
Brand Name |
SPF |
Mass (g) |
Lubriderm (Face) |
15 |
0.1025 |
Nexus (Hair) |
N/A |
0.1934 |
|
Neutrogena (Face) |
15 |
0.1186 |
V05 (Hair) |
N/A |
0.1583 |
|
L’Oreal (Face) |
15 |
0.1844 |
L’Oreal (Hair) |
N/A |
0.2061 |
|
PreSun (General) |
28 |
0.1029 |
Face refers to products marketed as
face creams; General to those marketed as sunscreens; Hair to hair products. |
|||
Banana Boat (General) |
30 |
0.1000 |
||||
BioSun (General) |
30 |
0.1000 |
Final Tip: 10 Rules for Sensitive Sun Protection (from http://www.sunprotection.org/)
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