Surfactants having general formula (II) ##STR1## wherein X=8-14; n=2-8. The process for obtaining such surfactants comprises the following steps; PA1 a) producing nitroarginin; b) producing N.sub..alpha. -acyl-nitroarginin c) producing N.sub..alpha. N.sub..omega. bis (N.sub..alpha. acyl-arginin).sub..alpha.,.sub..omega. diaminoalkylamide dichlorohydrate. Said surfactants are antimicrobial agents which can be applied in cosmetics, pharmacy and food industry.

INTRODUCTION 
As is well known, the surfactants are organic molecules which contain two 
functional groups with opposed characteristics. A conventional surfactant 
contains an absorbent group (water soluble) and a hydrophobic group 
(insoluble in water) both in the same molecule. This structure is known as 
amphiphilic structure. 
Though at present it may be considered that the industry has available the 
suitable surfactants, the ecological demands, currently force research and 
development of new alternatives which protect and improve the environment 
and quality of life. 
Numerous structural modifications have been made to improve the 
biocompatibility of these compounds, either parting from natural raw 
materials such as aminoacids and/or sugars, or by increasing the 
hydrophobic interaction of these compounds in an intent to potentiate 
their surface activity and in consequence their efficiency. 
Among the numerous structural modifications described in literature, the 
following deserve our attention; those which give arise to dimeric or 
geminal surfactants characterized by containing in the same molecule, two 
or more hydrophobic chains together with various ionic groups. It is 
described that such structures reinforce the intra or intermolecular 
hydrophobe interactions, with the consequent result of different highly 
efficient surfactants and in some cases with excellent aqueous solubility 
properties. 
These materials have demonstrate that they have unforeseeable 
physico-chemical properties (i.e. extremely low CMCs and great absorbant 
effectivity on the surfactants) which consequently contributes to optimize 
the environmental aspects of the surfactants. 
Among the ionic geminal surfactants, the bicationic quaternary ammonium 
salts must be highlighted, which are also known as bis-QUATS, for their 
excellent antimicrobial properties, especially versus Gram negative 
bacteria, when compared with the classical mono-QUATS. However, since they 
are quaternary ammonium salts, it is known that they are resistant to 
biodegradation and in consequence their ecological acceptability is 
questioned. 
The present invention pretends to overcome this aspect by dimerizing 
ecologically acceptable cationic surfactants, such as the monocatenaries y 
derivatives of the N.sup..alpha. -acyl-arginin. The new structure shall 
present the double advantage of being efficient as regards surface (due to 
its geminal structure) and biodegradable (since it is an aminoacid 
derivate). 
PRIOR ART TO THE INVENTION 
Though the literature includes a great variety of descriptions on 
antimicrobial surfactants with geminal bicationic structures, the 
compounds which are the object of the present patent are a novelty and no 
similar reference is described in the same. The novelty of the present 
invention is the result of the combination of one same molecule with two 
residues of N.sup..alpha. -acyl-arginin in one geminal mimetic structure 
to the bis-QUATS. 
The synthesis and development of the monocatenary derivatives of the 
N.sub..alpha. -acylarginin have been carried out by our team after many 
years of study, which has originated a great number of results and 
publications (Spanish Patent 512.643; M. R. Infante, J. Molinero and P. 
Erra, JAOCS, Vol.69, N97, 1992; J. Molinero, M. R. Julia, P. Erra, M. 
Robert and M. R. Infante, JAOCS, Vol. 65, No. 6 1988; C. Solans, M. A. 
Pes; N. Azemar and M. R. Infante, Progr. Colloid Polym Sci81.pp 144-150, 
1990). 
On the other hand, since the 50's, numerous bifunctional structures are 
known, of the type bis-QUATS ((A) C. A. Bunton, L. Robinson, J. Schaak and 
M. F. Stam, J. Org. Chem., 1971, 36, 2346; (b) R. Zana, M. Benrraou and R. 
Rueff, Langmuir, 1991,. 7.1072; (c) F. Dvinski, L. Lacko and T. Imam, J. 
Colioid Interface Sci., 1991, 143,336; (d) R. Zana and Y. Talmon, Nature, 
1993,. 362.228; (f) H. C. Parreira, E. R. Lukenbach and M. K. Lindemann, 
J. Am. Oil chem. SOC., 1979, 56,1015) the formula of which could be the 
diagram according to I. 
##STR2## 
These compounds contain per molecule two hydrophobic chains, two groups of 
quaternary ammonium and one spacer chain, Y, of alkylic or etheroatomic 
nature. 
The growing interest for these bifunctional surfactant agents is a 
consequence of their unusual physio-chemical properties (high absorption 
affectivity, a rich basic polymorphism and a great capacity of 
selfaddition) which gives place to their interesting applications in 
biological researches.((A) J. H. Fuhrhop and U. Uman, J. Am. Chem. Soc., 
1984,106,4643; (b) C. Tanford, the Hydrophobic Effect, Wiley, N.Y.;1980; 
(C) M. Lissel, D. Feldman, M. Nir and M. Rabinovitz, Tetrahedron Lett., 
1989, 30, 1683). In this sense, our group has recently patented new 
surfactants bis-QUATS, characterized by having in the spacer chain, a 
disulphur bridge, (Spanish Patent 9200443), to be applied mainly on 
keratinic substrates. 
DESCRIPTION OF THE INVENTION 
The present invention refers in particular to a new family of dimeric 
surfactants derived from arginin of cationic nature, the structural 
formula of which is indicated in II 
##STR3## 
These compounds simultaneously group together in the same molecule two 
residues of N.sup..alpha. -acyl-arginin linked through an alkylic spacer 
chain. They have been designed in such a manner that the length of the 
spacer contributes to reinforce the inter or intramolecular hydrophobic 
interactions, giving place in consequence to a different behaviour in the 
absorption properties and the molecular aggregation, and additionally, 
since it is cationic, to a different antimicrobial behaviour. 
Structurally speaking, they are symmetric compounds and contain in the same 
molecule, two saturated or unsaturated hydrocarboned chains of 6 to 20 
atoms of carbon as hydrophobe part, linked to various rests of the arginin 
aminoacid, which are interlinked through a spacer chain of the 
alkyldiamino type. The residue of N.sub..alpha. acyl arginin acts as 
source both of the hydrophobe part and of the cationic group. Each one of 
the functional groups which constitutes the molecule (fatty acid, 
aminoacid, alkyldiamine) are interlinked through amide links which assures 
the stability of the molecule to values of pH: 3-9 at the same time as the 
molecule is more biodegradable in comparison with the already known 
bisQUATS. The hydrolysis products which are to be expected to be fatty 
acid, arginin and a diamine, none of which is hazardous, both from the 
biological and from the ecological point of view. 
The synthesis of these compounds has taken place in four phases: 
a) Formation of nitroarginin, using start from aminoacid Larg, D-arg or 
DL-arg and as protector of the guanidine group of the arginin, the nitro 
group. 
b) Formation of N.sub..alpha. -acyl-nitroarginin parting from the 
nitroarginin and fatty acid, using lineal oil acid chlorides, of 8 to 18 
atoms as acylants of the nitroarginin in a hydroalcoholic medium. 
c) Formation of N.sub..alpha.,N.sub..omega., bis (N.sub..alpha. 
-acyl-nitroarginin) .alpha.,.omega. diaminoalkylamide starting from 
N.sub..alpha. -acyl-nitroarginin and diaminoakyl, using condensation 
agents such as BOP (hexafluorphosphate of benzotriazo 
N-oxytris-dimethylamino-phosphoni) or DCCD (Dicycloxylcarbodimide). 
d) Formation of N.sub..alpha. N.sub..omega. (N.sub..alpha. -acylarginin) 
.alpha.,.omega. diaminoalkylamide dichlorhydrate by means of a catalytic 
hydrogenation, in PD/C (palladium/carbon) and methanol-formic acid in a 
proportion comprised between 30-50% of formic acid, of N.sub..alpha. 
N.sub..omega. bis (N.sub..alpha. -acylnitroarginin) .alpha.,.omega. 
diaminoalkyl. 
The present invention refers to new geminal bicationic surfactant compounds 
derived from the arginin aminoacid specifically designed to act as 
efficient surface agents and in consequence as powerful antimicrobial 
agents. The variations of the activity shall be a function of the length 
of the fatty chain, as well as of the length of the spacer chain. 
The invention refers to molecules with structural characteristics as 
follows: 
To possess in the same molecule two fatty hydrocarbonated chains, two 
cationic groups of the guanidine type provided by the two lateral residues 
of the arginin aminoacid and a spacer chain of the alkyl type of different 
length. These molecules, since they are geminal, will show a strong 
synergy in their hydrophobic interaction, being cationic they shall have a 
specific substantivity by the microorganisms acting as effective 
antimicrobial agents and by being derivatives of the N.sub..alpha. 
-acyl-arginin shall be biodegradable compounds and compatible with the 
environment. 
The compounds have been prepared with a 99% purity using for this a 
synthetic route systematically confronted parting from raw material and 
non competitive cost intermediates. 
The preparation of the final products has taken place during four phases 
such as has been indicated in the general diagram 1: 
##STR4## 
The preparation of the N.sub..alpha. -acyl-nitroarginin takes place during 
the two first stages by means of already known procedures. The compound 
formed by means of the simultaneous condensation of the alkylic diamine 
with two molecules of the N.sub..alpha. -acyl-nitroarginin is a novelty, 
though it takes place using the classic condensation agent BOP. 
The obtention of the final products is achieved during the last stage by 
catalytic hydrogenation in Pd/C and formic. 
All these reactions take place at low temperatures and employing solvents 
such as : H.sub.2 O, EtOH, CL.sub.2 CH, and formic/MeOH. 
Under these conditions, the products are isolated without difficulty, 
keeping them stable through-out all the process. 
The purification of the intermediate and final products is conducted by 
liquid/liquid, liquid/solid, extractions, crystallization and preparative 
HPLC. 
The synthesized compounds are antimicrobial cationic surfactants of high 
purity, soluble in water and stable in an aqueous medium at pH values 
comprised between 3 and 9 and at temperatures of up to 70.degree. C. Their 
appearance is of very hygroscopic white solids. 
As regards their corresponding monomers (Pat. No. 2512.643), the compounds 
of the present invention present great efficiency for being absorbed in 
the aqueous surfaces, great facility for forming micelles and show a 
substantial improvement in the antimicrobial activity specially versus 
Gram positive bacteria. 
The compounds are prepared as has been previously indicated, in four steps: 
a) Conducted by means of the following reaction: disolve hydrochloride of 
L-arginin in concentrated sulphuric acid, in the proportion of 50% volume, 
eliminating the hydrochloric acid formed, into air; to this solution is 
added a quantity of pulverized ammonium nitrate and left to react at least 
15 minutes at room temperature and after eliminating the gas which has 
formed, pour the mixture on ground ice and cool at 0.degree. C. the 
solution is brought to 6.8 pH by the addition of concentrated ammonium and 
kept at a temperature of 0.degree. C. until the total precipitation of the 
product, approximately 48 hours; the thus formed precipitate is filtered 
and crystallized with hot water. 
b) A solution is prepared in the range of 0.10-0.30 mol of nitroarginin and 
Na(OH) in an aqueous solution of 20 to 30% acetone; next add slowly an 
equimolecular quantity of fatty acid chloride keeping the pH comprised 
between 11 and 13 by means of the addition of Na (OH). The mixture is 
maintained, agitating during various hours, and HCl is added up to acid 
pH, a white precipitate appearing, which is filtered, washed with water 
and ether and finally, crystallized in ethanol-ether. 
c) A solution is prepared of 0.30-0.50 mol of N.sub..alpha. 
-acyl-nitroarginin and an excess of tertiary organic base (triethylamine 
or N-methylmorpholin) in chloroform or else dimethylformamide. To this 
mixture is added the condensing agent BOP in a concentration comprised 
between 0.30-0.50 mol and the alkyldiamine in a concentration comprised 
between 0.15 and 0.25 mole. The mixture of the reaction is maintained 
under agitation between 15-30 hours at a temperature comprised between 10 
and 25.degree. C., subsequently adding ether, a precipitate appearing 
which is washed various times with ether. 
d) It is conducted by means of the deprotection of the nitro group for 
obtaining the dimers N.sup..alpha. -acyl-nitroarginin by a catalytic 
hydrogenation in a medium which contains PD/C and methanol-formic acid in 
a proportion comprised between 30-50% in formic acid to a pressure of at 
least 50 atm, room temperature and in a maximum time of 24 hours.