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Chart of chain length of glycols….
Was reading an old thread on glycols and antimicrobial activity, and Dr Phil mentioned that the chain length was instrumental to the functionality of their antimicrobial prowess.
Does anyone have a link to a nice chart/illustration of glycol chain lengths for those commonly used in cosmetics?
So basically, I am asking…what are the commonly used cosmetic glycols that have a longer chain length than pentylene glycol?
Aloha.
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17 Replies
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6 carbon glycols: hexylene glycol, and 1,2-hexanediol (when OH groups are specifically at 1st and 2nd position); 7C 1,2-heptanediol, 8C caprylyl glycol, 10C decylene glycol. It’s good to keep in mind that increasing chain length decreases water solubility.
Some materials which are used similarly to previously mentioned diols are ethylhexylglycerin and caprylyl glyceryl ether. -
Formulator said:6 carbon glycols: hexylene glycol, and 1,2-hexanediol (when OH groups are specifically at 1st and 2nd position); 7C 1,2-heptanediol, 8C caprylyl glycol, 10C decylene glycol. It’s good to keep in mind that increasing chain length decreases water solubility.
Some materials which are used similarly to previously mentioned diols are ethylhexylglycerin and caprylyl glyceryl ether.Thank you…I think I must have most of the bases covered…as I use pentylene glycol, a blend of 1,2-hexanediol and 1,2-octanediol, and EHG in every formula.
The only ones I am lacking are the 7 and the 10. -
Antimicrobial activity of fatty acids and their derivatives (e.g. glycols and more precisely 1,2-diols, fatty alcohols, sphingosines, monoglyceryl and methyl esters, glyceryl ethers) increases with chain length but, as @Formulator mentioned, water solubility drops. Hence, there is an optimum around C10 (C8-C12) depending on the derivative. The main antimicrobial effect at least of medium chain fatty acid derivatives is by destabilising membranes and seems to be common with all derivatives though secondary effects can not be excluded and are likely the reason why different derivatives have different antimicrobial spectra with regard to chain length. That’s also why there is not a single graph but actually a bunch of publications… a small and by far not comprehensive bunch, to be honest.
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Pharma said:Antimicrobial activity of fatty acids and their derivatives (e.g. glycols and more precisely 1,2-diols, fatty alcohols, sphingosines, monoglyceryl and methyl esters, glyceryl ethers) increases with chain length but, as @Formulator mentioned, water solubility drops. Hence, there is an optimum around C10 (C8-C12) depending on the derivative. The main antimicrobial effect at least of medium chain fatty acid derivatives is by destabilising membranes and seems to be common with all derivatives though secondary effects can not be excluded and are likely the reason why different derivatives have different antimicrobial spectra with regard to chain length. That’s also why there is not a single graph but actually a bunch of publications… a small and by far not comprehensive bunch, to be honest.
does mixing glycols with different chain lengths boost antimicrobial activity?
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Yes, I have about the same question…. Is a blend of glycols better than say…just more of one good one?
I always assumed that glycols were cell membrane disruptors….so if all the longer chain ones simply disrupt cell membranes….can a synergy be created…or a single good glycol in functional amounts will suffice?
Aloha.
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Let me take this one step further…into preservation…. We see a trend of brands trying to ‘naturally preserve’ with primarily glycols. If they primarily disrupt the cell membrane of bacteria….I always assumed this was softening up….laying the ground work for ….. something else to come in…and finish off the bacteria… like phenoxyethanol (or others). So, is it realistic to expect industry acceptable bacteria protection from JUST cell membrane disruptors? Does not seem super logical to me…. But hey…I was a business major.
For the moment…I am not including yeast/mold/fungi…. just a bacteria discussion.
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One more extension of this concept… If C 10 is the optimal cell membrane disruptor….and I did notice a number of vendors promoting C 10 for deodorant actives….something near and dear to me…as I am putting the wraps on an emulsified deo… Would that mean C 10 type would be the most effective in deodorant?
Or did @Pharma mean that C 10 was the optimal balance between cell membrane disruption….and water solubility?
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The mechanisms of preservative efficacy is generally just speculation based on superficial if not crap research. Membrane damage ? Hit a cell with a hammer, stuff leaks out and conclude membrane damage.
Preservatives likely have multiple impacts on cell viability. Development is more Edisonian than thoughtful. Use what works in useful combinations and don’t worry about “mechanism.”
Sometimes business majors have good insight. -
As @PhilGeis pointed out, cell membrane disruption is just an educated guess. If something exhibits a pharmacological effect, there has to be a reason… if you can’t prove how then you go with what you have even if it means speculating. If there were a single way to disrupt membranes, then there would be no point in blending and then there would be less differences between all those preservatives which allegedly disrupt membranes. Also, soap does the same and emulsifiers are supposed to do the same as well… how comes they don’t exhibit an equally good preservation?As said, the 10 (plus minus 2) carbon chain length is just something which happens to be close to the sweet spot for many similar chemicals and many different microbes (with as many exceptions).I do think that due all those smaller and larger differences, using blends is ehh.. maybe not more efficient but safer (less chances for exceptions slipping through). Also, longer chains mean higher chance that those preservatives mess with the emulsifiers and viscosity whilst shorter chains come with humectant properties and the like. If you want to blend ingredients, maybe blend different chemical structures, say, a glycol with a glyceryl ester?@Graillotion You’re correct. The basic understanding is that ‘softening up’ membranes makes the job of ‘real’ preservatives easier and more efficient. Hence the recommendation to not rely solely on membrane destabilising preservatives aka boosters. However, dosage makes the poison and enough of more or less anything can kill. With traditional preservatives, you want to keep tham as low as needed whilst ‘newer’ multifunctional ones may be used at higher levels not for preservation but solely for feel and all that fancy schmancy fluff. Which also means that the choice which boosters to combine might as well be based on ‘secondary’ effects than a chain length which hasn’t much to say unless you prove that it works best in specific case A (and possibly fails in case
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What makes undecylene chain special? Though I suppose undecylene derivatives don’t work the same. (because of targeting primarily towards fungus unlike glycols and others which are thought to be insufficient)But one would think they look alike.
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It’s an untypical fatty acid for two reasons: It has an odd-numbered chain and a terminal double bond which happens to be approximately in the middle of an ordinary fatty acid chain. The unsaturation at that position is the most effective to affect membrane integrity/crystallinity (and the reason why nature loves oleic acid). Apart from that, C11 (C12 being more theoretically active but limited by its poor solubility and resulting micelle formation) and the lower melting point due to unsaturation is just hitting the sweet spot a tad better than more frequently found medium chain fatty acids (even-numbered and saturated) and their derivatives.
Monolaurin (glyceol monolaurate) is equally, if not even more, effective (hard to tell due a lack of comparative studies) but somehow never really made it into the world of preservatives. It doesn’t have that off-putting odour of undecylenic acid but alas, has considerable emulsifying properties which makes it a bit unpredictable in emulsions and that isn’t great if it’s not added as emulsifier. On the other hand, it became a hyped food supplement. Sometimes, a molecule needs luck and coincidence more than evidence and scientific publications to become appreciated for a certain use.
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BTW two more things:1: I was a bit astonished that propanediol esters weren’t used as preservatives… turns out that Symrise offers one: Crinipan PMC. I’m always a tad too late as it seems (my idea predates their patent from 2019 but how do I prove that? LoL!). Notably, propylene glycol esters are also offered as preservatives by Abitec: Capmul 907P and 908P.2: Glycinates and lactylates of medium chain fatty acids also exhibit antimicrobial properties. Forgot to mention these derivatives earlier.
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Pharma said:BTW two more things:1: I was a bit astonished that propanediol esters weren’t used as preservatives…
@Pharma I should have asked earlier… what about just plain propanediol…(not the esters) where does it fall into this discussion. I use it as a humectant, with the hope that it is also contributing to the overall preservation.
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Propanediol (Zemea) is a good addition to a preservative system. you’ll see this in some Estee Lauder products - but not by itself.
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Graillotion said:… what about just plain propanediol…(not the esters) where does it fall into this discussion.
In the OT section?
It’s a diol, not a glycol. Mode of action is unknown. As an educated guess, propanediol as well as propylene glycol and methylpropanediol might interfere with glycerin metabolism (and, at high enough %, reduce water activity and exhibit solvent-like properties which messes with all kinds of biological processes). -
does mixing glycols with different chain lengths boost antimicrobial activity?
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https://drive.google.com/file/d/11qb1KU47IkdATt4TN5PNfhBSgGlTuAOJ/view?usp=drivesdk
This has some charts
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