What is Ascorbyl Glucoside?
It is a new type of stable Vitamin C that is not oxidized, but still shares the same physiological activation mechanism as ordinary Vitamin C (Chemical name: Ascorbic acid). By formulating the product with Ascorbyl Glucoside, the less degradable Vitamin C exerts a sustained action on the skin, bringing about remarkable effects not only in improving discoloration and freckles, but also in stimulating collagen production to prevent the ageing of skin.
Vitamin C is an excellent lightening agent. Preventing the activation of tyrosinase, it blocks the excess melanin formation, the pigment responsible for discoloration and freckles. It also lightens the discoloration and freckles already formed.
Vitamin C - so unstable,highly degradable
Ordinary Vitamin C used to be degraded so easily that it was very difficult to make it work effectively inside the skin.
It is a new type of stable Vitamin C that is not oxidized, but still shares the same physiological activation mechanism as ordinary Vitamin C (Chemical name: Ascorbic acid). By formulating the product with Ascorbyl Glucoside, the less degradable VITAMIN C exerts a sustained action on the skin, bringing about remarkable effects not only in improving discoloration and freckles, but also in stimulating collagen production to prevent the ageing of skin.
The high compounding ratio of ascorbyl glucoside is the secret behind the great lightening effects of 1/f ID white range
All products in the 1/f ID white range contain a remarkably high concentration of Ascorbyl Glucoside. By using the skincare items one over the other, the lightening effect also becomes enhanced. The 1/f ID white range sets out at once to restore skin to its natural, original, newly born condition.
Aggregation of Vitamin C derivatives in water solution:
The basic molecular architecture of amphiphiles is always based on the simultaneous presence in the same molecule of two or more groups of atoms that possess different affinities for a solvent, with which they establish different interactions, and that is generally defined as a "selective solvent". Usually the solvent is water, and then we distinguish a hydrophilic part (the "polar headgroups"), linked to a hydrophobic block made up of one, two, or more hydrocarbon chains (see Fig. 5).
The polar headgroups can be either neutral, cationic, or anionic residues. Typical neutral surfactants contain functionalities such as -OH, -NR2 (R=alkyl or H), esters, ethers, amides, and so forth. Cationic amphiphiles are for example alkyl-ammonium salts (such as dioctadecyldimethylammonium chloride, usually called DODAC), while anionic tensides can be carboxylates, sulfates, or phosphates. On the other hand, phosphatidylcholines are typical zwitterionic amphiphiles.
An interesting class of molecules are the so-called bolaamphiphiles, where two headgroups are bound by one or two chains (see Fig. 5). In this case monolayered structures are formed. These surfactants are typically present in the membranes of Archaebacteria, primordial microorganisms that live in extreme environments, such as volcanoes or under the oceans, and experience very drastic environmental conditions (pH<2, T>70° C, and high pressures).
Amphiphiles promptly form supramolecular aggregates in water, because of the "hydrophobic effect", that is the formation of a hydrophobic central core and of an external hydrophilic shell. This process reduces the hydrocarbon-water repulsion and then minimizes the total energy of the aggregate.
Depending on the chemical structure of the amphiphile, temperature, ionic strenght of the solution, nature and composition of the solvent, different kinds of aggregates can be obtained, with peculiar properties and structures. As Fig. 5 shows, spreading monolayers, adsorption films, micelles, vesicles (or liposomes), microemulsions, and Langmuir-Blodgett multilayers are different supramolecular structures, but they all originate from the same self-assembly of surfactants in the presence of a selective solvent.
Fig. 5 - Schematic structure of amphiphiles and of their self-assembled supramolecular aggregates.
Although the driving force that leads to the formation of these structures is always the "hydrophobic effect", however each one of the supramolecular assemblies possesses peculiar properties that can be studied with different techniques. Just as an example, monomolecular films are basically studied by measuring the "spreading isotherms", that is the plot that one can obtain by measuring the surface pressure as a function of the surface area; micellar solutions can be regarded as dispersions of small particles (usually spheres or ellipsoids) that can be characterized by surface tension measurements, refractive index, light-scattering, neutron-scattering, viscosity, EPR, NMR, and so forth. Emulsions and microemulsions are of great interest when an intimate mixture of lipophilic and hydrophilic components is desidered, such as in drugs, cosmetics, food processing, paper and textile manufacturing, oil recovery, inks and paintings, and so forth, and for this reason the study of their stability and phase behavior as a function of temperature and composition, i.e. the "phase diagram", is strongly needed.
Fig. 6 shows the spreading isotherms obtained from 6-O-stearoyl ascorbic acid at pH=6, vitamin K1, and vitamin D3 at 25°C. As expected, 6-O-stearoyl-ascorbic acid produces more condensed films, because of its long aliphatic side chain, whilst the other two components give monolayers that show a more expanded behavior. The spreading behavior of ascorbyl-palmitate has been studied by Balthasar and Cadenhead.
Fig. 6 - Spreading isotherms (surface pressure vs. molecular area) of ascorbyl-stearate, vitamin K1, and vitamin D3.
The formation of self-assembled aggregates in water strongly depends on several factors: surfactant concentration, temperature, ionic strenght, presence of other molecules. When a surfactant is progressively added to water, it will dissolve in the bulk and form an adsorption film at the air/water interface; adding more surfactant will result in the formation of the first aggregates when the concentration equals the "critical micellar concentration", CMC (see Fig. 7).
Fig. 7 - Formation of supramolecular aggregates in a multi-component equilibrium with the surfactant's monomers. The blue spots represent the polar headgroups, and the brown lines indicates the hydrophobic chains.
Fig. 8 - Calculation of the CMC value from the surface tension vs. concentration plot. The red spots are the experimental data, the black lines are the fitting linear curves. CMC is determined as the intersection point of the two lines.
From this plot it is easy to calculate the area per polar headgroup, A; for a nonionic surfactant the following Gibbs' equation holds:
where R=8.31·107 erg/mol·K, T is the absolute temperature, and NA is the Avogadro number. For the previous plot, A was calculated as 47 Å2/molecule. When the surfactant is charged, A must be multiplied by a factor 2.
The CMC value is affected by several factors, first of all by the chamical structure of the tenside (hydrophilic/hydrophobic balance, charges, branching groups, unsaturated bonds), by the temperature and by the presence of other molecules and/or ionic species.
The shape and the size of the supramolecular structures - that is the number of monomers per aggregate ("aggregation number", g) - depend on the chemical nature and geometry of the surfactant, on the monomers' concentration and on the temperature.
More recently the formation of large interface aggregates in non-aqueous solvents and with different types of chains has been reported in several papers, provided that the selective solvent plays different interactions with the two incompatible building blocks of the solute. As an example, a semifluorinated n-alkane, bearing a hydrogenated segment linked to a fluorinated block, can form aggregates in a fluorocarbon such as perfluorooctane, because of the well-known mutual immiscibility of hydrocarbons and fluorocarbons.
The self-assembling of surfactants in water and related properties are well described in several books .
As already mentioned in the previous section, a large number of lipophilic derivatives of vitamin C can be synthesized, where the polar head group is the ascorbic acid moiety, linked to one or two hydrophobic chains. Assembled in such supramolecular structures, vitamin C derivatives protect degradable materials (particularly unsaturated fats or vitamins): in fact the lipophilic molecules are segregated and protected in the micellar hydrophobic core, whilst the ascorbic acid polar head groups face the water phase and perform their radical-scavenger activity. As a matter of fact, when the vitamin C-based surfactants aggregates in micellar structures, the active ascorbic ring is even more exposed to the facing aqueous medium.
Long chain derivatives of ascorbic acid readily produce monomolecular films at the air/water interface, and give stable mixed monolayers with some vitamins that possess an amphiphilic structure as well. This feature is particularly important in order to determine the mutual miscibility of ascorbic acid derivatives and some relevant natural compounds with a perspective of producing stabilized systems where the ascorbyl-derivatives protect the other components against oxidation.
The self-assembly properties of 6-O-octanoyl ascorbic acid in water have been recently studied with viscosity, light-scattering and small-angle neutron-scattering measurements. The data show that small, monodisperse, nearly spherical aggregates are formed, with a hydrodynamic radius of about 25 Å. The oxygen consumption and the reducing activity of this compound have been tested and show that it is at least as powerful as vitamin C.
The structure and properties of another derivative, namely the 5,6-octylidene-ascorbic acid, are currently being studied in aqueous beta-octyl-glucoside micelles.
6-O-ascorbic acid esters, such as palmitate, are almost insoluble in water at room temperature, however their solubility increases at higher temperature, above which a clear solution is formed. This is due to the formation of micelles from the saturated solution of monomers, and therefore is referred to as the critical micellization temperature, CMT. Upon cooling, the micellar solution solidifies into an opaque curd, that contains more than 80% of water, and is a semicrystalline mesophase, usually called "coagel".
Fig. 9 - Synergic interplay of ascorbic acid, carotenoids and tocopherols in the protection of lipid fats against oxidation.
However, it is important to recall that what has been observed in vitro, may not be automatically transferred to the living systems, as a matter of fact Walther et al. showed that the addition of vitamin E to antioxidant liposomes delivered to fetal lungs significantly reduced the surface activity, and then it may not represent a suitable approach to perform radical scavenging in vivo.
Moreover, the current increasing amount of radical species that are present in the atmosphere (particularly nitrogen oxides), the seasonal partial loss of the ozone layer, and then the increase of the ultraviolet irradiation over the Earth, are all related problems that show the importance of using antioxidant species in protecting the body from the free radicals' attacks, or in minimizing their dangerous activity. On the other hand we must be aware that the fashionable habit of large intakes of ascorbic acid and its derivatives on a regular basis may represent a serious hazard to the human health, for the possible consequences of producing radicals directly into the body, for instance through the reaction with metal ions such as iron and copper.
A huge list of patents already reports several preparations, based on ascorbic acid or on its organic derivatives. Many academic and industrial Laboratories have studied the properties of lotions, creams, drugs, and cosmetic products with the aim of improving the antioxidant protecting activity of tocopherols by adding ascorbic acid or its derivatives, and of widening their applications and uses. Some of these systems require the use of both aqueous and hydrophobic phases, emulsionated with a proper amount of surfactants. Other compounds, like 3-alkyl-ascorbic acids, have been tested as antioxidants and found to be very strong chain-breaking agents with a high affinity for biomembranes, suggesting that some lipophilic derivatives of ascorbic acid could be of benefit for protection against reperfusion injury. Moreover, 3-O-alkyl-ascorbic acids were found to be stable in ointments and to suppress intracellular melanin accumulation in the skin. The effect of 3-alkyl-ascorbic acids has been reported by Nihro et al..
Other studies indicate that 6-O-ascorbyl-alkanoates are much more active in preventing oxidation of linoleic acid than ascorbic acid in SDS, Triton, and CTAB micelles, despite the fact that ascorbic acid-palmitate and ascorbic acid show a similar efficiency in homogeneous solutions. In the case of a lipophilic derivative of ascorbic acid such as ascorbic acid-palmitate, the electrostatic interactions with the polar headgroups of the surfactants (the cationic CTAB or the anionic SDS) are no longer relevant for its antioxidant properties. Another interesting difference between ascorbic acid and its lipophilic derivatives is that in the case of vitamin C the maximum rate is reached for SDS or CTAB concentrations above the CMC, whilst in the case of ascorbic acid-palmitate the rate decreases with increasing surfactant concentration. This may be due to the inter-micellar diffusion dynamics that contributes to the rate-limiting step. The same finding was obtained studying vitamin E in SDS micelles. These results demonstrate that the inter-micellar diffusion is one of the main factors that affect the antioxidant activity and does depend on the lenght of the hydrophobic chain.
The antioxidant synergism of vitamin E and vitamin C has been recognized and extensively studied. The key step is the reaction between the tocopheroxyl radical (TOC·) and vitamin C (ASC):
TOC· + ASC- = TOC + ASC· [ 1 ]
introducing a lipophilic chain in position 5 or 6 in vitamin C does not change its reactivty toward TOC· in homogeneous solutions, but the rate constant for reaction  is lowered by a factor 10 in the presence of phosphatidylcholine liposomes. In this case the lipophilic vitamin C derivative may either reside in the same or in a different micellar structure than that where the TOC· radical is, in the latter case therefore it must diffuse out from its micelle before reacting with TOC·, and then the total rate constant would depend on the lenght of the side chain. The most interesting insight is that a liposome fusion mechanism must be invoked to rationalize the antioxidant activity in vesicles. Liposomes are dynamically stable systems below the transition temperature due to the tremendous hydration repulsion force against the get-together of two liposomes.
However, fusion could be induced by some ionophores or fusogens, such as Ca2+ which may form a bridge between two liposomes facilitating the fusion. The incorporation of ascorbic acid-derivatives into lecithin liposomes would make the liposomal surface negatively charged. Of course attractive electrostatic interactions between oppositely charged liposomes would serve as a driving force to induce the fusion. The intraliposomal diffusion may also contribute, because subsequent to the liposome fusion the two substrates must subject to fast lateral intraliposomal diffusion to find each other for the reaction to occur.
Preliminary biological assays have been performed to check if the same findings occur in the case of biomembranes. The antioxidant activities of octanoyl- and palmitoyl-ascorbic acid are much better than that of ascorbic acid and tocopherol, both in vivo and in vitro. An interesting observation is the delicate balance played by the lenght of the side hydrophobic chain, in fact longer alkyl segments facilitate the insertion of the ascorbic acid derivative into the bilayer, but they also make the interfacial diffusion more difficult. Lauroyl-ascorbic acid seems to be the best agent in that sense.
Similar conclusions were drawn by Liu et al. in their study on the antioxidant activities of ascorbic acid and ascorbyl-palmitate, carrying out ESR measurements on bilayered vesicles made up of an anionic surfactant (SPHS = 1-pentadecyl hexadecyl sulphate) and a stable lipophilic nitroxide probe (TEMPO-16). The results indicate the occurrence, in the case of ascorbic acid, of a two-step reaction that first involves the external vesicle surface that interacts with vitamin C dissolved in the aqueous bulk phase, and only in a second time the TEMPO molecules that are confined in the inner layer will enter into the aqueous medium after a flip-flop diffusion motion across the membrane. On the other hand, when palmitoyl-ascorbic acid is directly incorporated into the SPHS vesicles a much fast reaction occurs, that can be explained, again, with a vesicle fusion mechanism.
The radical attack operated by an initiator usually follows the following general path:
As radical initiator the following molecules are mostly used, depending on the medium where the reaction is going to be taken: DPPH (alpha,alpha-diphenyl-beta-picrylhydrazyl), water soluble; AMVN (2,2'-azobis(2,4-dimethyl-valeronitrile)), oil soluble; AAPH (2,2'-azobis(2-amidinopropane)dihydrochloride), water soluble; AIBN(2,2'-azobisisobutyronitrile), oil soluble; DBHP (di-tert-butyl hyponitrite), water soluble.
Fig. 10 shows that ascorbic acid esters incorporated into phospholipid vesicles (liposomes) significantly suppress the oxidation of the unsaturated components, and produce an induction period, after which the peroxidation proceeds with the same slope as in the absence of the radical scavenger.
The next plot (Fig. 11) shows the time dependence of absorbance when a solution of linoleic acid is first treated with some radical initiator (AIBN or DPPH, depending on the solvent medium), and then with some radical scavenger. The curve indicates that as soon as the radical promoter is added, the unsaturated fatty acid is attacked and forms the conjugated diene that absorbs at 234 nm. The radical scavenger momentarily stops the peroxidation of linoleic acid until it is completely consumed as the second plateau indicates, and then the oxidation starts again with the same kinetic as before.
Fig. 11 - The oxidation process of linoleic acid can be monitored by measuring the absorbance at 234 nm as a function of time. The arrows indicate the addition of the radical initiator and of the radical scavenger to the solution.
The antioxidant activity of different natural and synthetic chemicals is a very important property, especially for industrial applications. A simple method to evaluate such parameter consists in measuring the absorbance before and after the addition of each antioxidant to an ethanolic solution of a proper radical initiator, such as DPPH (see structure below). This radical promoter is deeply colored (purple) and absorbs at 517 nm. The addition of an antioxidant agent determines the fading of its color, and the rate is related to the efficiency of the radical scavenging. The reducing activity (RA, %) can be easily derived from the following equation:
where A(0) and A(20) are the absorbance values (at 517 nm) before adding the reducing agent and 20 minutes after its addition, respectively. Some products have been tested according to this procedure, and the results are shown in Fig. 12.
Asorbyl Glucoside:this form is largely used by Japanese cosmetics companies for whitening and brightening purposes. It works best in a synergy with other skin-lighteners like kojic acid, bearberry extract, mulberry extract, etc. It helps prevent abnormal melanin formation and retention.