peroxycarboxylic acids for use as medical germicides can be prepared in - situ in aqueous solutions utilizing sodium perborate and acyl / aroyl donating compounds . in its crystalline form , sodium perborate exists as a dimeric cyclic peroxodiborate salt , na 2 [ b 2 ( o 2 ) 2 ( oh ) 4 ]. it may be configured as a powder , compressed powder , or tablet . when added to water , perborate hydrolyses to form the peroxoborate complex ion ( ho ) 3 booh − , and other borate species . at acidic ph , the peroxoborate anion further hydrolyses to form tetrahydroxy borate anions , b ( oh ) 4 − , and hydrogen peroxide , h 2 o 2 . at alkaline ph , however , the peroxoborate species has the ability to donate a peroxo group as a nucleophile to the carbonyl carbon of an acyl / aroyl donor : a compound with an appropriately stable leaving group alpha to the carbonyl carbon ( eg . esters , imides , et al .). this results in the formation of a peracyl anion that then forms an equilibrium amount of the corresponding conjugate peracid . this invention addresses the use of sodium perborate and novel acyl and / or aroyl donors ( those other than acetyl ) to generate peroxycarboxylic acids other than peracetic acid for use as germicide solutions . the present invention takes advantage of the above chemistry to provide a specific formulation useful for both skin topical surface microbial kill and for use as a cold temperature disinfectant / sterilant . in particular , the present composition includes a sodium perborate at percentage levels of from 20 % to 50 %, preferably from 40 % to 45 %. generally speaking , the perborate can be any group i metal perborate but is preferably sodium perborate because of its ease of availability and economics . specifically , perborate is mixed with one or more acyl donors having the following general formula : wherein r equals c 2 - c 10 alkyl , straight chain , branched chain or cyclic . preferably r is c 2 or c 3 making the acyl donors propionyl salicylic acid or butyrylsalicylic acid . the amount of acyl donor should be from approximately 1 . 0 % to 50 % by weight of the powdered composition preferably from 40 % to 45 %. the third essential ingredient is a buffering system of one or more buffers . as used herein , the term buffering system means one or more buffers that performs the following functions : kinetically raises the ph of the solution to approximately 9 for rapid formation of the peracid ; and then the ph then drops to approximately 7 . 5 ± 0 . 5 for improved peracid stability and anti - microbial efficacy . the ph of this buffer system takes approximately 15 - 30 minutes to stabilize at ambient conditions . the composition of the buffering system can be adjusted to bring about desired changes in buffering capacity , ionic strength and osmolarity . the composition of the buffering system can also be adjusted to improve corrosion inhibition . generally speaking , the buffer can be a combination of monobasic , dibasic , and / or tribasic group i phosphates , either as hydrates or anhydrous salts . the rate of dissolution can be controlled in that phosphate hydrates typically dissolve in water faster than anhydrous phosphates . the amount of the buffer in terms of its overall weight to the powdered composition should be from 1 % to 30 %, preferably 5 % to 15 %. a fourth ingredient , not essential but highly preferred for the composition , is a surfactant which facilitates microbial kill . suitable surfactants can come from the list of our earlier common assignee &# 39 ; s u . s . pat . no . 6 , 096 , 348 which is incorporated herein by reference . generally , those can include suitable detergents or surfactants that upon testing may reveal an enhancement of microbial kill . the amount of such surfactant can be within the range of from 0 . 005 % by weight to about 1 . 0 % by weight of the composition preferably from 0 . 01 % to 0 . 5 % by weight of the composition . typical examples include anionics such as alkyl sulfate surfactants . alkyl sulfate surfactants are a type of anionic surfactant of importance for use herein . alkyl sulfates have the general formula roso 3 m wherein r preferably is a c 10 - c 24 hydrocarbyl , preferably an alkyl or hydroxyalkyl having a c 10 - c 20 alkyl component , more preferably a c 12 - c 18 alkyl or hydroxyalkyl , and m is h or a cation , e . g ., an alkali metal cation ( e . g ., sodium , potassium , lithium ), substituted or unsubstituted ammonium cations such as methyl -, dimethyl -, and trimethyl ammonium and quaternary ammonium cations , e . g ., tetramethylammonium and dimethyl piperdinium , and cations derived from alkanolamines such as ethanolamine , diethanolamine , triethanolamine , and mixtures thereof , and the like . typically , alkyl chains of c 12 - 16 are preferred for lower wash temperatures ( e . g ., below about 50 ° c .) and c 16 - 18 alkyl chains are preferred for higher wash temperatures ( e . g ., above about 50 ° c .). alkyl alkoxylated sulfate surfactants are another category of useful anionic surfactant . these surfactants are water soluble salts or acids typically of the formula ro ( a ) m so 3 m wherein r is an unsubstituted c 10 - c 24 alkyl or hydroxyalkyl group having a c 10 - c 24 alkyl component , preferably a c 12 - c 20 alkyl or hydroxyalkyl , more preferably c 12 - c 18 alkyl or hydroxyalkyl , a is an ethoxy or propoxy unit , m is greater than zero , typically between about 0 . 5 and about 6 , more preferably between about 0 . 5 and about 3 , and m is h or a cation which can be , for example , a metal cation ( e . g ., sodium , potassium , lithium , calcium , magnesium , etc . ), ammonium or substituted - ammonium cation . alkyl ethoxylated sulfates as well as alkyl propoxylated sulfates are contemplated herein . specific examples of substituted ammonium cations include methyl -, dimethyl -, trimethyl - ammonium and quaternary ammonium cations , such as tetramethyl - ammonium , dimethyl piperydinium and cations derived from alkanolamines , e . g ., monoethanolamine , diethanolamine , and triethanolamine , and mixtures thereof . exemplary surfactants are c 12 - c 18 alkyl polyethoxylate ( 1 . 0 ) sulfate , c 12 - c 18 alkyl polyethoxylate ( 2 . 25 ) sulfate , c 12 - c 18 alkyl polyethoxylate ( 3 . 0 ) sulfate , and c 12 - c 18 alkyl polyethoxylate ( 4 . 0 ) sulfate wherein m is conveniently selected from sodium and potassium . other anionic surfactants useful for detersive purposes can also be included in the compositions hereof . these can include salts ( including , for example , sodium , potassium , ammonium , and substituted ammonium salts such as mono -, di - and triethanolamine salts ) of soap , c 9 - c 20 linear alkylbenzenesulphonates , c 8 - c 22 primary or secondary alkanesulphonates , c8 - c24 olefinsulphonates , sulphonated polycarboxylic acids , alkyl glycerol sulfonates , and fatty acyl glycerol sulfonates . the most preferred , because it has been found to be the most universally effective , are alkylarylsulphonates and most preferably dodecylbenzenesulphonic acid salts , and most preferably the sodium salts of such acids . the composition can also of course include other minors . by minors , applicant means compounds which do not affect the microbial action but which have other desirable properties and may be added to tailor for a specific use including , but not limited to corrosion inhibitors such as fatty amine salts , for example , n - n ′, dibutylurea . minors may also include those to make the composition more pharmaceutically elegant such as for example , odorants or dyes , etc . generally these minors are at levels of from 0 . 001 % by weight to about 5 % by weight . as those skilled in the art know , d - value determination provides a graphic representation of the kill kinetics of a disinfection / sterilization method . there are several methodologies to obtain the average d - value , the negative reciprocal of the slope of a ( straight ) line of a graph of time versus population , and is defined as the time interval required to reduce a microbial population 1 log , or 90 %. each species for a particular disinfectant / sterilant will have its own d - value . generally , the lipid viruses and vegetative bacteria are easiest to kill ( shortest d - value ), with bacterial spores being the most resistant ( longest d - value ). the following examples are shown to illustrate but not limit the invention . both of the above formulations were blended , then dissolved in 500 ml of water . the ph of the solution at 1 hour was approximately 7 . 6 . the d - value here achieved is typically 2 - 3 minutes and a six log reduction of the challenge spore ( bacillus stearothermophilus ) is consistently achieved with example 2 . thus a d - value of approximately 3 minutes or less can be obtained . moreover , as illustrated by the above example , indications are such that it can be used effectively for instrument disinfection or sterilization and topical microbial kill . it also demonstrates potential automated endoscope reprocessor ( aer ) compatibility , low toxicity and a linear kill rate .
a powder composition which reacts in water to form in situ peroxycarboxylic acids at an anti - microbially effective concentration . importantly , its utility is both for topical anti - microbial application and for effective low temperature disinfection / sterilization of instruments . it comprises the combination of a perborate , one or more novel acyl and / or aroyl donors , a buffering system which allows the ph to arise to about 9 for rapid formation of the peroxycarboxylic acids and then drop to about 7 . 5 for sustained stability and microbial kill . it preferably includes a surfactant facilitating antimicrobial efficacy , as well as other minors .