Polyalkylene Guanidines - Environment Friendly Biocidal Polymers and Auxiliary Products
Polyalkylene guanidines (PAGs) are characterised by low toxicity for human beings. This is due to the presence of ferments causing degradation of the polymers in all the warm-blooded organisms.
PAGs have a wide range of bactericidal activity. They are effective against bacteria and viruses (including dangerous pathogens), and also fungi, algae, and keratophagous insect of several types.
Polyguanidine chemicals developed by the Institute of Ecotechnologies can be applied for safe disinfection of surfaces; for purification and decontamination of water in chlorine-free water preparation technologies; for prevention of biodestruction of construction materials, oil products, rubber, textiles, paper, and polymers.
They can be also used as biocides in agriculture. PAGs are recommended of use in paper industry, rubber production, optics, and galvanic technology as cationic polyelectrolytes.
Environment pollution build-up, mounting number of man-caused catastrophes, recent increase of terrorist attacks of all kinds, including threats of biological weapons application, makes ensuring the ecological safety of people one of the most vital tasks of society and government.
This problem is especially urgent for Russia due to its geographic expanse, recent social and political problems and global tendencies, including the emerging infectious diseases. Only concentrated effort towards prophylactics can prevent the outbreaks or at least minimise the possible human and material losses caused by these threats.
Localisation and decontamination of epidemiologically unsafe regions should be effective, fast, and safe for the human and environment.
This requires, among other measures, application of efficient and environment-friendly antiseptics.
Development of such antiseptics and of technologies of their application is one of the most urgent challenges for chemists, microbiologists, and technologists. The antiseptic application technologies imply prevention of biodestruction of various materials, as well as the traditional disinfection.
According to the modern requirements for biocides, the active chemicals of disinfectants and composites should have a wide range of biocidal activity, while being safe for the humans and environment. Yet another important requirement is compatibility with various materials and absence of corroding properties.
One of the most perspective biocides complying with all these requirements is the series of high-molecular chemicals of the polyalkylene guanidine (PAG) family developed recently by the Institute of Ecotechnologies.
Both Russian and international market is still dominated by the traditional biocides: chlorine-containing, oxygen-containing, quaternary ammonium compounds, and those based on salts of heavy metals (tin, copper, etc.) Chlorine-containing biocides suppress the growth of most microorganisms.
However, they have low or even no efficiency against spore-forming bacteria, viruses, Pseudomonas aeruginosa, and protozoa cysts. Oxygen-containing biocides are still less effective. At the same time most of these chemical compounds are very aggressive and toxic. Their application is dangerous for human health and environment, causes equipment corrosion, damage and discoloration of materials.
Quaternary ammonium compounds are effective against bacteria of various types, but ineffective against viruses. Besides, they are not always safe for human health. Heavy metal containing compounds traditionally used in agriculture and wood protection chemicals, non-fouling paints, etc. are extremely toxic and not environment-friendly.
They tend to get into human and animal organisms via food paths and cause dangerous implications.
The main representatives of the PAG family are the high-molecular salts of polyhexamethylene guanidine (PHMG) with the following generic formula, where n = 20-70, A- is an acid residual of a mineral or an organic acid.
A comparative study of a number of chemical compounds (chlorine-containing derivatives of bisphenyl, triazine, silatrane, stanyl thiosiloxane, chlorothiobenzoic and dithiocarbamic acids, acryl-substituted pyran, compounds of the furan series, etc.) was performed several years ago in the Angara Institute for labour and human ecology.
According to this study, PAGs are the most perspective antiseptics over a number of parameters: combined criteria of efficiency, toxicity and hazard, raw materials availability, technological and environmental safety of production, physical and chemical properties.
The range of biocidal activity of PAGs is very wide. Even low concentrations of PAGs are effective against gram-positive and gram-negative bacteria (including tuberculosis mycobacteria), various fungi (mycelial, yeast-like ones, dermatophytes, etc.).
In contrast to chlorhexidine bigluconate (low-molecular analogue of PAGs widely applied in other countries), that are effective only against aerobic and anaerobic microflora, PAGs are also effective against viruses.
Moreover, PAGs kill the keratophagous insects (clothes-moth larvae etc.) and timber-worm. Antimicrobial activity of PAGs against pathogens of dangerous infectious diseases (glanders, plague, and legionellosis) was established.
PAGs effectively suppress dangerous microflora and algae in water media. Research institute for applied microbiology performed a comparative study of biocide efficiency for prevention of biocorrosion in cooling systems.
Twenty biocides of various types have been compared (“Progress”, Twin-40, Triton X-100, Syntanol ДС-10, sodium dodecylsulphate, glutaric aldehyde, dichlor glyoxime, N cetyl pyridine chloride, catamine AB, etc.).
PHMG chloride proved to be one of the most perspective biocides. It is efficient against the combination of 45 biodestructive microorganisms found in cooling systems.
The studies performed by the Senega laboratory for wood protection have shown that PAGs effectively suppress up to 30 types of fungi causing mould, staining, and destruction of timber. This allows using PAGs for protection both of raw timber and woodwork.
Research centre for technical documentation studied the properties of fungicide for protection of cinema and photo films made of various plastics. Quaternary ammonium compounds, wellknown fungidines (salicylanilide, trilan, mertiolate, Ampholan, phyton, chlorhexidine bigluconate, etc.), polyethyleneimine and its derivatives, antibiotics, propylene oxide, parapharm, trichloro and pentachlorophenolates, and many others have been studied.
PAGs were proven to be among the few chemicals that ensure stable enough fungicide protection, while preserving the optical characteristics and technical state of the film surface.
Wide range of bactericide activity of PAGs is due to the repeated guanidine groups in the macromolecule. Such groups are the active components of several natural and synthesised medicines and antibiotics (Sulfaguine, Ismeline, Faringosept, streptomycin, etc.). Mechanism of biocidal action of PAGs is the following.
Phospholipid cell membranes of the microorganisms absorb the biocide polycation that destroys the cell membrane, inhibits the exchange function of ferments, disrupts the reproduction capability of nucleic acids and proteins, and suppresses the respiratory system. All this causes the death of the microorganism.
In contrast to the high biocide activity towards a number of microorganisms, PAGs have low toxicity for humans and warm-blooded animals. The leading Russian research centres for toxicology have made a comprehensive study of PAGs toxicity and hazards. The study resulted in development of hygienic recommendations for handling PAGs. Average lethal dose for various PAGs is 10 000 - 15 000 mg/kg for skin exposure, and 815 - 3200 mg/kg for oral exposure. No mutagenic or cancerogenic hazard have been established.
According to this study, the PAG compounds were classified as low-hazard chemicals (4th class) for skin exposure, and medium-hazard chemicals (3rd class) for oral exposure (according to the Russian state standard ГОСТ 12.1.007). Dynamic observation over 25 tests has shown that the threshold dose in human organism is 1 mg/kg, and non-effective (safe) dose is 0.15 mg/kg. Estimated safe dose for water solutions of PHMG chloride is 3 mg/kg (according to the sanitary toxicological hazard criterion).
Low toxicity of PAGs is due to the presence of ferment systems in the warm-blooded organisms that cause degradation of guanidine-containing polymers. The first metabolism stage of PHMG chloride and PHMG phosphate in the organism is substitution of chloride or phosphate anion with gluconate anion. Later guanidine groups transform into ureal groups via hydrolysis, and polymeric chains decompose into fragments.
Solid forms of PAGs are very stable with respect to oxidative and thermal destruction, and ageing (storage term is 15 years). Water solutions of PAGs are also stable, and preserve their physical and chemical properties and biocide activity for a long time.
PAGs have neither colour, nor smell, they cause no irritation of skin and mucous coats, no discoloration of fabrics, no corrosion of equipment. After the solution drying a thin polymer film imperceptible to touch is formed. This ensures a lasting surface protection from a microorganism attack.
An excellent combination of biocide, toxicological, physical, and chemical properties makes PAGs perspective for application both as independent disinfecting agents, and as biocide additives and auxiliary chemicals.
The chemical properties of PAGs are in many points similar to those of polyamines and quaternary ammonium compounds. Polyalkylene guanidine chemicals are high-molecular cationic polyelectrolytes. Their alkaline properties are stronger than those of another alkaline polymer, polyethyleneimine, are. Variation of PAG properties is possible via the change of anion A- chemical type, and also via changing the length and composition of the hydrocarbon chain (see the Formula shown above).
Possibility of PAGs modification is due to a relatively high reactivity of guanidine groups. Low-molecular guanidine compounds lose their biocide properties with any chemical transformation, whereas PAG polymers retain their biocide activity after various chemical reactions due to the following.
Guanidine groups in PAGs are integrated into a polymer chain, so only a part of these groups take part in the reaction. The remaining guanidine groups are responsible for the biocide properties of the new compound.
PAGs react easily with low-molecular and high-molecular compounds and form both soluble and cross-linked interpolymer complexes and covalent-bonded interpolymers. This way of chemical modification leads to creating organomineral sorbents and products soluble in organic solvents. The latter form waterproof polymeric films with durable biocide effect on the treated surfaces.
PHMG was first synthesised by American chemists Bolton and Koffman in 1940 via several polycondensation processes. Later the research in this direction was suspended for several reasons. Doctor P.A. Gembitsky resumed these studies at the Institute for petroleum synthesis, Russian Academy of science. Dr. Gembitsky developed several simple and safe techniques for synthesis of the PAG series chemicals.
PHMG chloride and PHMG phosphate (Methacide and Phogucide) have found most practical applications. Later the Moscow university for applied biotechnology developed several new types of polyguanidine chemicals for waterproof biocide coatings.
These chemicals based on PHMG chloride are insoluble in water. Fortunately, PAG find increasing recognition nowadays. A number of Russian and Ukrainian research institutions are trying to reproduce the PHMG synthesis techniques described in 1970-th and 1980-th. The progress of the studies is different in these institutes.
The Institute of Ecotechnologies performs intensive studies of PHMG and other PAGs. This research includes development of new forms of PAGs and the study of their properties, quality enhancement, synthesis technology perfection, and application of PAGs as additives to various materials.
Doctor Petr Gembitsky who in fact originated the research of PAGs is leading these studies at the Institute of ecotechnologies. His group has developed a series of new biocide substances and chemicals (Biopag, Phosphopag, Ecopag, Ceopag, Septopag, Biokrapag, Gembicide, etc.).
This series includes water-soluble chemicals and those soluble in organic solvents that have a specific action: against fungi, against viruses. A chemical of the PAG family was specially developed to have hydrophobic properties.
Polyguanidine chemicals developed by the Institute of Ecotechnologies can be applied for disinfection of medical, food-production, veterinary, and any other facilities. Bacteriostatic and bactericide activity of these chemicals equals or even exceeds that of the best foreign disinfectants. This issue is described in more detail in the paper of Irina Vointseva, Dr. Sci. (chemistry), and Petr Gembitsky, Dr. Sci. (chemistry), leading researcher of the Institute of Ecotechnologies.
Application of PAGs for water treatment and decontamination without chlorine has a special place in the studies of the Institute. A positive experience has been accumulated using PAG as biocides in agriculture, construction, for protection from biodestruction of oil products, rubber goods, textiles, timber, paper, plastics, paints, varnishes, etc.
However, PAGs have other remarkable properties besides the biocidal ones. They are recommended for application as cationic polyelectrolytes in paper and rubber producing industry, and in optics. PAGs are a valuable substitute for high-toxicity compounds in galvanic technology. Application of PAGs in any technological process can reduce toxicity and hazard, suppresses putrefaction and fermentation, and decontaminates sewage.
Director of the Institute of Ecotechnologies