IRREVERSIBLE COATING PARTICLES AND COMPOSITIONS CONTAINING THESE PARTICLES

Abstract: The invention refers to a new composition of a coated pesticidal composition comprising polyhydrosis virus and a process for preparing the pesticidal composition with polyeletolyte molecules selected from both polyacid and polybase group.

Description: TITLE IRREVERSIBLE COATTNG PARTICLES AND COMPOSITIONS CONTAINING THESE PARTICLES The present invention relates to the production of coated material containing, as a core, solid particles such as virus, microorganisms, proteins, protein aggregates, nucleic acids, chemical substances etc. which have inherent charged surface or which may develop their potential electrostatic attraction to opposite charged material with the aim of enhancing the stability and/or biological activity of the said core material. A particular example of coated material of the present invention is coated baculovirus useful as a pesticidal agent. BACKGROUND OF THE INNENTION The stability and/or biological activity of particles, such as chemical substances, virus, protein, protein aggregates, nucleic acids, etc. is frequently influenced by environmental factors such as pH, sunlight, etc. Coating processes have been proposed to solve this problem. Encapsulation is a coating process by which a thin film of polymer, biopolymer, wax, resin, or metal substance is deposited onto a core to produce microcapsules. This kind of coating is used to protect the core material from its surroundings by means of a wall membrane, to control the time place or rate at which the core material (active agent) is released or even to label the said core material to obtain a complex product useful as diagnostic agents, pharmaceuticals, herbicides, pesticides, insecticides, etc. Thus, the coated particles often exhibit properties, which are significantly different to those of the template core, being attractive, both from a scientific and technological viewpoint. One of the most common encapsulation methods is the "complex coacervation". In this process, two colloidal substances, such as gelatin and an anionic polymer, having mutually opposite electric charges, are added to a core-containing suspension to form an aqueous sol which is then pH-adjusted or otherwise treated to form a wall of coacervates on the microdroplets of an oily core material. In a further step, the microdroplets are gelled and the coacervates are hardened with a hardening agent to form microcapsules. US 5,023,024 describes a process based on this technique in which cross-linking occurs among the polymer molecules of gelatin to harden microcapsules. In this document it is mentioned that the mixture of gelatin and a suitable anionic polymer is diluted with warm water followed by the addition of an acidic aqueous solution such as acetic acid to reduce the pH of the system to the isoelectric point of gelatin or below, i.e. to values varying between 4.0 and 5.0 to allow chemical reaction between the polymer and gelatin to occur. This process uses pH adjustment to provide hardness to the wall of coacervates. FR 2 675 398, which is related to sunlight protection microcapsules, also uses the physicochemical phenomenon called coacervation. The process comprises (i) preparation of a polymer colloidal solution and a dispersion of the substance to be encapsulated, (ii) a separation phase (coacervation) with formation of a three-phase system by varying pH value and, therefore, (iii) encapsulation of the dispersed substance. The pH values used in the process range from 3 to 7, preferably from 4 to 5. In this process, pH adjustment is used to permit the separation phase to recover coated particles (coacervates). EP 972563 describes a process for preparing coated capsules and hollow shells by coating particles with alternating layers of oppositely charged nanoparticles and polyelectrolytes. It is mentioned that the driving force for the multilayer film build-up is primarily due to electrostatic attraction and the formation of a complex among the charged species, which are deposited. The process comprises coating the template particles with alternating coatings of nanoparticles and polyelectolyte molecules which have ionically dissociable groups, e.g.: (i) polyacids, such as polyvinyl or polystyrene phosphoric acid, polyvinyl or polystyrene sulfuric acid, polyvinyl or polystyrene sulfonic acid, polyvinyl or polystyrene phosphonic acid, polyacrylic acid and their respective salts, or (ii) polybases, such as polyamines, or poly(ammonium salts). Examples of template particles are organic particles, inorganic particles, biological specimens or a combination thereof. The pH of the aqueous dispersion is adjusted in such a way that the molecules in each alternating layer, e.g. polyelectrolyte molecules and nanoparticles, each have opposite total charges. In EP 972563, it is emphasized that the formation of hollow shells represents an embodiment of particular importance for the use of the shells as a permeable wall. Moreover, it is mentioned that the permeability properties of the shell may be modified by selecting the conditions for decomposing the core, e.g. by selecting the temperature and heating conditions in a calcination procedure. The example is directed to the preparation of alternating SiO 2 -poly (diallyldimethylammonium chloride) (PDADMAC) multilayers and cites the fact that larger amounts of SiO 2 are adsorbed when the adsorbing solution contains NaCl and that the isoelectric point of the SiO 2 particles is 3, therefore SiO 2 is negatively charged under the conditions of adsorption (pH 5-6). US 5,792,903 relates to the radioactive chitosan complex formed by labeling a chitosan, a biocompatible and biodegradable natural polymer, with radionuclide, a radioactive chitosan macroaggregate formed by making chitosan complex into particles, and a kit for preparing radioactive chitosan complex, process for preparation thereof and the use thereof for an internal radiation therapeutic agent. The process for preparing the internal radiation therapeutic composition of claim 1 comprising: (a) irradiating a water-soluble stable radionuclide compound with neutrons in a nuclear reactor to convert the water soluble stable radionuclide compound into an active radionuclide compound; (b) dissolving the active radionuclide compound in water to form a solution; (c) dissolving a chitosan in acidic solution (pH 2-4) to form a chitosan solution; and (d) adding the active radionuclide compound solution to the chitosan solution to form the internal radiation therapeutic composition. Thus, the preparation of the therapeutic composition is based on the solubility characteristics of a polymeric material (chitosan), in the good biocompatibility and biodegradability properties of chitosan and in the binding reaction, which occurs between the radionucleotide compound and chitosan. It must be emphasized that there is not a radionucleotide compound coating but a gel radioactive chitosan complex macroaggregate formation when the pH of the solution is adjusted to a nearly neutral value (physiological condition). US 5,965,123 relates to coated pesticidal agents which retain a significant amount of their original activity after exposure to ultraviolet radiation. The process comprises the steps of: (a) preparing an aqueous mixture of a pH-dependent polymer, (b) dissolving the pH- dependent polymer by adjusting the pH of the mixture of step (a) with a base to a pH above the solubilization pH of the pH-dependent polymer; (c) adding a pesticidal agent, an ultraviolet protector, optionally a stilbene compound, optionally a disintegrating agent and optionally a glidant to the solution of step (b) and blending to produce a homogeneous suspension containing dissolved pH-dependent polymer; (d) drying the homogeneous suspension of step (c); and optionally (e) milling the dried material of step (d). Pesticidal agents are inseticidal pathogens such as viral pathogens, bacterial pathogens and fungal pathogens. Niral pathogens are wild gypsy moth ΝPN, Autographa califomica ΝPN Douglas fir tossock moth ΝPV, European pine saw fly ΝPV and Helliothis zea ΝPN. pH-Dependent polymers are selected from the group consisting of methacrylic acid and methyl methacrylic copolymers, maleic anhydride and styrene copolymers. Claim 2 defines the pH adjustment made in step (b) as between 8.5 and 10. Ignoffo et al (Ignofo, CM. and Batzer, F. 1971. "Microencapsulation and ultraviolet protectants to increase sunlight stability of an insect virus". Journal of Economic Entomology 64: 850-853) also studied the inactivation of microencapsulated Heliothis nucleopolyhedrosis virus caused by exposure to artificial and natural sunlight. The authors compared microcapsules of (1) virus + carbon; (2) virus + Buffalo Black + oil and (3) virus + aluminum powder and concluded that encapsulated virus + carbon was 3.6 times more stable than virus alone and from 1.3 to 2.2 times more stable than other combinations of virus + UN protection agents. In fact, the sunlight-UN (SUN) inactivation of field-applied viral and other microbial insecticides have been a matter of research with the aim of solving many agricultural problems. Examples of studies on the factors influencing the stability of these types of microbial insecticides are: Ignoffo, CM. and Garcia, C. 1994. "Antioxidant and oxidative enzyme effects on the inactivation of inclusion bodies of the Heliothis baculovirus by simulated sunlight-UV" Environmental Entomology. 23(4): 1025-1029; Teakle, R.E. 1995. "Prospects for the use of baculoviruses as bioinseticides". Cooperative Research Centre for Tropical Pest Management - University of Queensland. Australia. 5(6): 345-347; Ignoffo, CM., Hostetter, D.L.and Smith, D.B. 1976. "Gustatory stimulant, sunlight protectant, evaporation retardant: Three characteristics of a microbial insecticidal adjuvant". J. Econ. Entomol. 69(2): 207-210; Ignoffo, CM., Hostetter, D.L., Sikorowski, P.P., Suiter, G. and Brooks, W.M. 1977. 'Inactivation of representative species of entomopathogenic viruses, a bacterium, fungus, and protozoan by an ultraviolet light source". Environmental Entomology. 6(3): 411-415; Shapiro, M. 1985. Effectiveness of B vitamins as UN screens for the gypsy moth (Lepidoptera: Lymantriidae) nucleopolyhedrosis virus". Environmental Entomology. 14(6): 705-708; Ignoffo, CM. and Garcia, C. 1995. "Aromatic/heterocyclic amino acids and the simulated sunlight-ultraviolet inactivation of the Heliothis! Helicoverpa baculovirus". Environmental Entomology. 24(2): 480-482; Ignoffo, CM. and Garcia, C 1992. "Combinations of environmental factors and simulated sunlight affecting activity of inclusion bodies of the Heliothis (Lepidoptera: Νoctuidae) nucleopolyhedrosis virus". Environmental Entomology. 21(1): 210-213. Bull, D.L. 1978. 'Tormulations of microbial insecticides: microencapsulation and adjuvants" . Misc. Publ. Entomol. Soc. Am. 10(5): 11-20. A particularly interesting study was made by Shapiro and Argauer (Shapiro, M. and Argauer, R. 1995. 'Ηffects of pH, temperature, and ultraviolet radiation on the activity of an optical brightener as a viral enhancer for the gypsy moth (Lepidoptera: Lymantriidae) baculovirus". Journal of Economic Entomology. 88(6): 1602-1606). In the Results it is mentioned that in a separate study using LdNPN (Lyniantria dispar nuclear polyhedrosis virus) and pH buffers (varying from 3.0 to 10.0, viral activity was unaffected at these pHs. Another interesting study about the destructive ultraviolet effect on biological insecticides is shown by WO 98/15183. This document describes a process to coat these insecticides with particles of durable TiO 2 , a modified form of TiO 2 , in enough quantity to get a substantial coating. It is mentioned that, in a preferred embodiment, the addition of aqueous slurry of durable TiO 2 to a stirred aqueous slurry of the baculovirus, or alternately the aqueous dispersion of the virus to the TiO 2 slurry, carried out at neutral pH (typically between 5.5 and 8.0), permits TiO 2 and baculovirus to co-precipitate. However, this process does not provide a durable coating. This kind of behavior was also observed by Lessa and Medugno (Lessa, M.M. and Medugno, C.C 2000. 'Ηeterofloculation of amidine polystyrene latex and Anticarsia gemmatalis nucleopolyhedrovirus as a model system for studying sunlight protection" . Journal of Colloid and Interface Science. 225: 317-322). The authors found that despite the great zeta potential difference between the particles used in the process (amidine polystyrene latex and Baculovirus), low affinity isotherms were obtained and bare regions on the polyhedron surface could be observed under scanning electron microscopy. This unexpected behavior was attributed to the presence of an extra repulsive force able to overcome electrostatic attraction which was identified as a hydration force, present in many colloidal systems as siliceous and proteins. Consequently, it was not possible to keep the polyhedron surface sufficiently covered and obtain a good physical barrier against sunlight. Thus, the aforementioned studies reveal that the satisfactory results of the coating process is not simple to get. On the contrary, this success requires a knowledge about the interaction between the coat material and the core surface with the purpose of reaching a durable and sufficient covering and consequently eliminating protectors agents or at least reducing its concentrations, which are ferquently used in commercial formulations. In fact, it is evident the relevance of enhancing the coating-template particles' binding in seeking efficient and stable coated products, particularly biological pesticides. SUMMARY OF THE --ΝNEΝTIOΝ The object of the present invention is to provide enhanced particle coating by changing pH condition to modify the surface charge of the particle to be coated with the aim of minimizing or eliminating hindering forces that react against an efficient coating-template particles' binding. A first embodiment of the invention refers to stable coated particles comprising (a) a core consisting of a material which is inherently surface charged or which may develop its potential electrostatic attraction to opposite charged material and (b) a surrounding thin layer of a matrix comprising a polymer selected from the group consisting of polyvinyl or polystyrene phosphoric acid, polyvinyl or polystyrene sulfuric acid, polyvinyl or polystyrene sulfonic acid, polyvinyl or polystyrene phosphonic acid, polyacrylic acid and their respective salts and optionally ultrafine particles, wherein the core particles are irreversibly and individually coated. A second embodiment of the invention refers to durable coating baculovirus particles comprising (a) a core consisting of a virus particle selected from the group consisting of Baculovirus anticarsia and a polyhedrosis virus which is inherently surface charged and (b) a surrounding thin layer of a matrix comprising about 5 to 30% of a polymer selected from the group consisting of polyvinyl or polystyrene phosphoric acid, polyvinyl or polystyrene sulfuric acid, polyvinyl or polystyrene sulfonic acid, polyvinyl or polystyrene phosphonic acid, polyacrylic acid and their respective salts and optionally ultrafine particles, wherein the core particles are durable and individually coated. A third embodiment is a process for the preparation of coated particles comprising the steps of: (a) suspending a polymer selected from the group consisting of polyvinyl or polystyrene phosphoric acid, polyvinyl or polystyrene sulfuric acid, polyvinyl or polystyrene sulfonic acid, polyvinyl or polystyrene phosphonic acid, polyacrylic acid and their respective salts and optionally ultrafine particles in water to an appropriate concentration; (b) adjusting pH condition of the aqueous suspension of step (a) to a value lower than 4; (c) suspending the particles to be coated in water to an appropriate concentration and adjusting pH condition of the resulting suspension to a value lower than 4; (d) adding the suspension of step (b) to the suspension of step (c) and gentle stirring of the resulting mixture for a period of time enough to obtain a complete coating of the core particles; (e) adjusting the pH of the suspension of step (d) to 5-7 to obtain a neutral suspension of the coated particles; and optionally (f) recovering the irreversibly coated particles from the aqueous suspension. A fourth embodiment of the invention refers to compositions containing the irreversibly coated Baculovirus, particularly the Baculovirus anticarsia, which is obtained according to the process described above. The physical form of these compositions can be granulates, tablets, dried powder or the like. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates the adsorption isotherm of baculovirus polyhedra coated with sulphate polystyrene latex particles having a particle size of 0.084 μm under pH 3.0; nads/nβv is the number of sulphate polystyrene latex absorved per baculovirus polyhedron; neq/ml is the number of sulphate polystyrene latex particles in equilibrium. Figure 2 exhibits the Scanning Electron Microscopy of baculovirus polyhedra coated with sulfate polystyrene latex particles having a particle size of 0.084 μm after neutralization with NaOH. Figure 3 shows the adsorption isotherm of baculovirus polyhedra coated with sulphate polystyrene latex particles having a particle size of 0.249 μm at (A) pH 3.0 and B) after neutralization; nads/nev is the number of sulphate polystyrene latex absorved per baculovirus polyhedron; neq/ml is the number of sulphate polystyrene latex particles in equilibrium; Figure 4 illustrates the Scanning Electron Microscopy of baculovirus polyhedra coated with sulphate polystyrene latex particles having a particle size of 0.249 μm at pH 3.0. DETAILED DESCRIPTION OF THE INVENTION Many industrial processes for producing coated products are based on electrostatic interactions between opposite charged colloidal particles. But the final physicochemical equilibrium of the states and structures of substances, such as aggregates, complexes, etc., are different and depend on the properties and characteristics of the chemical, biochemical and biological species involved and on the interaction conditions. Opposite charged colloidal particles and macromolecular interactions occur under different mechanisms such as coacervation and heterofloculation. In such processes, the macromolecules frequently form a network which holds or keeps colloidal particles together as a core of the aggregate. The size and concentration relationships of the final aggregates are determinant on the final aggregates stability or particle precipitation as big aggregates. The main difference between coacervation and heterofloculation concerns to the way of coating individual particles. The predominance of one mechanism or another depends especially on the particle size of the species involved and on the existence of hindering forces against the core-coating binding. In the heterofloculation, the coating of individual particles is favored and, uneven of coacervation, the geometry of particles is maintained in the heterofloculation process. According to the most accepted theory of colloidal stability, the Deryaguin, Landau, Nerwey and Overbeek (DLNO) theory, when two oppositely charged particles interact in a given media, flocculation should occur. If the relation between size and number of particles is adequate it is possible to obtain particles totally coated. Interactions between colloidal particles are often explained by DLNO theory, where attractive van der Waals and repulsive double layer forces play a central role (Derjaguin, B.N. and Landau, B.N. 1941. Acta Phvs. Chim. URSS. 14, 633). This theory has been extended to the case of heterofloculation (Derjaguin, B.N. 1954. Discuss. Farady Soc. 18, 85; Devereux, O. F. and De Bruyn, P.L. 1963 "Interaction of plane parallel double layers". MIT Press. Cambridge. MA.) and has been experimentally tested (Islam A.M., Chowdhry, B.Z. and Snowden, M.J. 1995. Adv. Colloid Interface Sci. 62, 109; Overbeek, J.Th.G. 1997. J. Colloid Interface Sci. 58,408). However, many colloidal systems only can be deeply understood by considering other types of interactions. For example, it is well known that some biological surfaces and macromolecules remain separated in aqueous solutions at high ionic strengths, a condition under which coagulation is predicted to occur by DLNO. A possible explanation for this behavior is the presence of repulsive force. Such strong repulsive forces occurring between surfaces separated by a short distance are measured using a Surface Force Apparatus (Pashley, R.M. and Israelachvili, J.Ν. 1984 . J. Colloid Interface Sc 101, 511; Israelachvili, J.Ν. 1985.Chem. Sci. 25,7). As this force occurs also in low energy of wetting solids with water, the repulsive force can be attributed to the energy required to remove water of hydration from the surface. These non-DLNO forces are known as structural or hydration forces. In the present invention, the covering process is accomplished to enhance the coating- template particles' binding and consequently minimizing or eliminating these hindering forces with the purpose of obtaining a durable and sufficient covering while preserving the desirable properties of the template core. The modification of the surface charge of the particle to be coated by changing pH condition is determinant on neutralizing the aforementioned forces. Particularly in the case of polyhedrosis virus, the process is based on the pH lowering to less than 4, in which the surface charge changes from negative to positive and the hindering (mainly hydration) forces are neutralized. The polyhedra have an hydrophobic nature, first described by Small et. all (Small, D.A, Moore, Ν.F. and Entwistle, P.E. 1986. Hydrophobic interactions involved in attachment of a baculovirus to hydrophobic surfaces. Applied and Environmental Microbiology. 52(l):220-223.). The authors also found that hydrophobic interactions and pH were inversely related, that is, hydrophobic interactions decrease by increasing pH. The relationships of size and concentration among coating and core particles and final aggregates are also important and must be considered. This invention provides small size aggregates containing particles individually coated by a fine and uniform layer constituted by molecules which have an average diameter 5-15 times smaller than the template particles. The particle size of the coating material is about 10 "3 to 1 μm. The core template is an organic, inorganic or biological solid material such as virus, microorganisms, proteins, protein aggregates, nucleic acids, chemical substances as those mentioned in US 4844896, etc.; having a specific structure and shape, e.g. polyhedrosis, spherical, rod-shaped. These template particles may develop their potential electrostatic attraction to opposite charged material or have inherent charged surface which can be changed by modifying the environmental conditions. The process of the present invention for preparing coated particles comprises the steps of: (a) suspending a polymer selected from the group consisting of polyvinyl or polystyrene phosphoric acid, polyvinyl or polystyrene sulfuric acid, polyvinyl or polystyrene sulfonic acid, polyvinyl or polystyrene phosphonic acid, polyacrylic acid and their respective salts and optionally ultrafine particles in water to an appropriate concentration; (b) adjusting pH condition of the aqueous suspension of step (a) to a value lower than 4; (c) suspending the particles to be coated in water to an appropriate concentration and adjusting pH condition of the resulting suspension to a value lower than 4; (d) adding the suspension of step (b) to the suspension of step (c) and gentle stirring of the resulting mixture for a period of time enough to obtain a complete coating of the particles; (e) adjusting the pH of the suspension of step (d) to 5-7 to obtain a neutral suspension of the coated particles; and (f) optionally recovering the irreversibly coated particles from the aqueous suspension. According to the invention, the Baculovirus' coating (BN particle size about 1,0 μm) is carried out under appropriate reagents concentrations to provide a ratio of 10 2 to 3 x 10 3 latex particles/polyhedrosis particle. Suspension of BN containing about 10 8 to 10 12 particles/ml and latex suspensions containing 10 n to 10 12 particles/ml are appropriated to obtain the above mentioned latex/virus ratio. The particle size of the latex material ranges from 10 "2 to 1.0 μm. As mentioned before, the enhanced coating of the Baculovirus is based on the change of its surface charge from negative to positive at pH lower than 4, preferably at pH 3.0, in which the hydration forces are neutralized. In respect to the possibility of adding ultrafine particles as an optional component of the coating layer, they can be selected from organic and inorganic particles, particularly inorganic particles, such as SiO 2 , TiO 2 , carbon black or alike. In the case of Baculovirus coating, optical brightners may also be used to enhance the biological activity of the virus(Shapiro & Argauer, 1995). The coated particles may be recovered by using known purification and separation methods such as centrifugation, membrane processes, drying processes, etc. The coated particles attained in the present invention have their stability and biological activity protected from their surroundings by means of the aforementioned fine and uniform coating which is made stable by neutralizing the hindering forces, e.g. hydration forces. The most preferred embodiment of the present invention is related to the covering of Baculovirus anticarsia (BV). The baculovirus is a double-stranded DNA occluded in a proteinaceos structure called polyhedron. This virus is an environmentally acceptable biological insecticide specific for control of velvetbean caterpillar Anticarsia gemmatatis, one of the main soybean defoliators in several countries. But ultraviolet sunlight is the main destructive factor that affects the persistence of the virus in the field. Consequently, obtaining a good physical barrier against sunlight is desirable. In such a manner, the irreversible coating of this virus according to this invention means an excellent solution for this problem, decreasing or eliminating the amount of sunlight protectors in the commercial formulations which are frequently removed from the virus by the action of the weather conditions (rain, dew, etc). Moreover, it is the guarantee of providing an efficient pesticide against Anticarsia gemmatalis. The coated polyhedrosis virus can be used in the field as an aqueous suspension. Most preferably, aiming to maximize its storage stability and facilitate its handling, the coated polyhedrosis is recovered from the suspension and dried to obtain a solid material which can be used as a dry powder or formulated as tablets or granulated mixtures. In the tablet or granulated form, the coated polyhedrosis virus of the present invention can be formulated with known materials such as silica, attapulgite, kaolinite, bentonite, montmorilonite (see Medugno,CC, Ferraz, J.M.G, Maia, A.de H.N. & Freitas, C.CL. Evaluarion of a Wettable Powder Formulation for the nuclear Polyhedrosis Virus of Anticarsia gemmatalis (Lep.: Noctuidae). Pestic. Sci. 1997.51, 153-156). The following examples are provided for the purpose of further illustrating the present invention and not to be used as limiting it. EXAMPLE 1 Obtaining the polyhedra particles suspension of Baculovirus anticarsia (BV) Fifth-instar larvae of lepdopteran Anticarsia gemmatalis reared on an artificial diet at 28° C were infected with a suspension of 10 7 polyhedra /ml. Six to ten days after infection, the larvae exhibiting symptoms of nucleopolyhedrosis were frozen at -18°C. The polyhedra were then purified using a modification of the method proposed by van der Geest (van der Guest, L.P.S. A method for the purification of polyhedra. J. Invert. Pathol. 11:502.1968). After defrosting, the larvae were ground, filtered through a synthetic fabric and diluted to a concentration of 10 g dm "3 of solids in 1% sodium dodecylsulfate (SDS). The suspension was then centrifuged at 5,000 xg and the solid resuspended in distilled and deionised water. The operation was then repeated until polyhedra of a high degree of purity could be observed by optical microscope; the concentrated dispersions were then kept at 4°C The suspension of Baculovirus (BN) to be coated was obtained by diluting the concentrated suspension to a concentration of 10 s to 10 9 BN particles/ml. EXAMPLE 2 Preparing sulphate polystyrene latex dispersion Sulphate polystyrene latex stock solution, commercially purchased, was diluted to the appropriate particle concentration (10 11 to 10 12 latex particles/ml). The pH of the suspension was adjusted to the final value of 3.0 with HC1 (analytical grade). The properties of sulfate polystyrene latex are given in Table 1. Table 1: Properties of sulfate polystyrene latex used to coat Baculovirus (from Certificate of Supplier) Size (μm) Surface charge density Area per Charge (μC/cm 2 ) Group (A 2 /C (ΝH)ΝH 2 0,084 ±10,5% 0,8 1997 0,249±3,5% 2,08 772 EXAMPLE 3 Baculovirus coating with sulphate polystyrene latex having a particle size of 0.084μm Heteroflocculation was achieved bv mixing the diluted susυension of Baculovirus. at a concentration of l,lxl0 10 particles/ml, as obtained according to Example 1, and the sulphate polystyrene latex suspension (particle size of 0,084μm), as obtained in Example 2. The suspensions were mixed at 25°C and pH 3.0 under mild agitation in a centrifuge tube and to the proportion of 1200 latex particles per BN particle to obtain complete, fine and homogeneous coverage. The mixture was then centrifuged for 30 minutes at 10.000 rpm. At pH 3.0 the polyhedrosis core particle is positively charged and the sulphate polystyrene latex particles have a negative surface charge. The success of the coating process by heteroflocutation was determined by measuring the turbidity of supernatant. The number of particles not bound to Baculovirus was determined by turbidity measurements made on the supernatant at 400 nm and the absorbance value compared with that of the latex calibration curve measured at pH 3.0. Suspensions of 0.084μm latex particles of the same concentration used for heterofloculation were centrifuged in parallel, and a correction factor for latex sedimentation was determinated and introduced to the calculation of the number of free latex particles remaining in the supernatant. Figure 1 shows the high affinity of particles. The ratio of added latex particles/polyhedrosis particles varied from 10 to 1600.1n order to verify the stability of the chemical reaction involved in the coating process, before centrifugation, the pH of a mixture sample was neutralized by adding 0.2 ml ΝaOH 0.1 Ν and absorbance was measured. After two cycles of centrifugation and washing with deionized water, the heterofloculated material was dried and the coating efficacy was documented by microphotographs obtained from a Scanning Electronic Microscope LEO estereoscan 440. Figure 2 illustrates the good results of the coating process of the present invention. EXAMPLE 4 Baculovirus coating with sulphate polystyrene latex having a particle size of 0.249μm Heterofloculation was performed as described in Example 3. The difference is related to the particle size of the coating material. In this example, sulfate polystyrene latex particle having a particle size of 0.249μm. After this, the mixture was centrifuged at 2000 rpm. Control experiments showed that the absorbance of 0.249μm latex suspensions, measured at the same conditions of Example 3 did not change after centrifugation under the above conditions and that zero absorbance can be measured for the supernatant of centrifuged Baculovirus suspensions. The isotherm curve of Figure 3 shows the high affinity ϊl-Mts. Th6 -W&of ti fRrf : sulphate polystyrene latex improves with an increasing number of added particles. The ratio of latex particles/polyhedrosis particles ranged form 5 to 600. As in Example 3, before centrifugation the pH of a mixture sample was neutralized by adding 0.2 ml NaOH 0.1 N and absorbance was measured. The results obtained from the supernatant turbidity measurements on the heterofloculated samples before and after neutralization are identical, thus prove the stability of the coating of the present invention. Figure 4 shows a microphotograph obtained from a Scanning Electronic Microscope LEO estereoscan 440 illustrating these results. EXAMPLE 5 Comparison between the coating particles and process of the present invention with coating particles and process using particles of amidine polystyrene latex Heterofloculation was achieved by mixing, under gentle agitation, a fresh preparation of Baculovirus and a suspension of latex particles of 0.120μm and 0.172μm, positively charged with amidine (purchased from the Dynamic Corp.), in a concentration of 1200 particles/polyhedron at 25°C The mixture was then centrifuged for 30 minutes at 2000 rpm. Under this condition, latex do not precipitate and the number of particles not bound to BN can be determined by turbidity. The results evidenced the low affinity of the particles, showing coating factors of 64 and 56% to 0.120 and 0.172μm particles respectively. This experiment proves that the number of latex particles necessary to neutralize the superficial charge of BN, determined by adsorption, depends on the size of particles and is bigger than those which remain bound to a biological surface. Indeed, these results can only be explained by the presence of extra repulsive forces (e.g. hydration forces) acting over the system as mentioned hereinbefore.

Claims: CLAIMS 1. A coated particle characterized by comprising (a) a core consisting of a material which is inherently surface charged or may develop its potential electrostatic attraction to an opposite charged material and (b) a surrounding thin layer of a matrix comprising a polymer selected from the group consisting of polyvinyl or polystyrene phosphoric acid, polyvinyl or polystyrene sulphuric acid, polyvinyl or polystyrene sulfonic acid, polyvinyl or polystyrene phosphonic acid, polyacrylic acid and their respective salts and optionally (c) ultrafine particles wherein the core particles are irreversibly and individually coated. 2. The coated particle according to claim 1 characterized by being the core material a o polyhedrosis virus. 3. The coated particle according to claim 2 characterized by being the polyhedrosis virus a Baculovirus. 4. The coated particle according to claim 3 characterized by being the Baculovirus a Baculovirus anticarsia. 5 5. The coated particle according to claim 1 and 3 characterized by the surrounding thin layer of a matrix comprising a polystyrene sulphuric acid latex, in a ratio latex particles/polyhedrosis particles ranging from 10 2 to 3 x 10 3 . 6. The coated particle according to claim 1 and 3 characterized by the surrounding thin layer of a matrix comprising a polystyrene sulphate latex, in a ratio latex particles/polyhedrosis o particles ranging from 10 2 to 3 x 10 3 . 7. A process for preparing coated particles characterized by comprising the steps of: a) suspending a polymer selected from the group consisting of polyvinyl or polystyrene phosphoric acid, polyvinyl or polystyrene sulphuric acid, polyvinyl or polystyrene sulphonic acid, polyvinyl or polystyrene phosphonic acid, polyacrylic acid and their 5 respective salts and optionally ultrafine particles in water at appropriate concentration; b) adjusting pH condition of the aqueous suspension of step a) to a value lower than 4; c) suspending particles to be coated, which consist of a material that is inherently surface charged or may develop its potential electrostatic attraction to an opposite charged material, in water at an appropriate concentration and adjusting pH condition of the o resulting suspension to a value lower than 4; d) adding the suspension of step b) to the suspension of step c) and gentle stirring of the resulting mixture for enough time to obtain a complete coating of the particles; e) adjusting the pH of the suspension of step d) to 5-7 to obtain a nearly neutral suspension of the coated particles; and f) optionally recovering the irreversibly coated particles from the aqueous suspension. 8. The process according to claim 7 characterized by comprising the polymer used in step a) a polystyrene sulphuric acid latex. 9. The process according to claim 7 characterized by the particles to be coated of step c) being polyhedrosis virus particles. 10. The process according to claim 11 characterized by being the polyhedrosis virus a Baculovirus. 11. The process according to claim 10 characterized by being the Baculovirus a Baculovirus anticarsia. 12. The process according to claim 7 and 10 characterized by the pH of the suspensions of steps b) and c) being adjusted to 3.0. 13. The process according to claim 7 characterized by the ratio latex particles/ polyhedrosis particles ranging from 10 2 to 3 x 10 3 14. The process according to claim 13 characterized by the polymer concentration ranging from 10 π to 10 12 latex particles/ml. 15. The process according to 13 characterized by ranging the concentration of the core material from 10 8 to 10 9 latex particles/ml. 16. A pesticidal composition characterized by comprising the polyhedrosis virus of claim 2 and compatible ingredients in a solid form. 17. The pesticidal composition according to claim 16 characterized by being the polyhedrosis virus a Baculovirus. 18. The pesticidal composition according to claim 17 characterized by being the Baculovirus a Baculovirus anticarsia. 19. The pesticidal composition according to claim 16 characterized by being the solid form a tablet, granulate or dry powder. 20. A pesticidal composition characterized by comprising the polyhedrosis virus of claim 2 and compatible ingredients in a aqueous suspension form. AMENDED CLAIMS [received by the International Bureau on 29 May 2001 (29.05.01); original claims 5-6 and 10-12 amended; remaining claims unchanged (2 pages] 1. A coated particle characterized by comprising (a) a core consisting of a material which is inherently surface charged or may develop its potential electrostatic attraction to an opposite charged material and (b) a surrounding thin layer of a matrix comprising a polymer selected from the group consisting of polyvinyl or polystyrene phosphoric acid, polyvinyl or polystyrene sulphuric acid, polyvinyl or polystyrene sulfonic acid, polyvinyl or polystyrene phosphonic acid, polyacrylic acid and their respective salts and optionally (c) ultrafine particles wherein the core particles are irreversibly and individually coated. 2. The coated particle according to claim 1 characterized by being the core material a polyhedrosis virus. 3. The coated particle according to claim 2 characterized by being the polyhedrosis virus a Baculovirus. 4. The coated particle according to claim 3 characterized by being the Baculovirus a Baculovirus anticarsia. 5. The coated particle according to claim 3 characterized by the surrounding thin layer of a matrix comprising a polystyrene sulphuric acid latex, in a ratio latex particles/polyhedrosis particles ranging from 10 2 to 3 x 10 3 . 6. The coated particle according to claim 3 characterized by the surrounding thin layer of a matrix comprising a polystyrene sulphate latex, in a ratio latex particles/polyhedrosis particles ranging from 10 2 to 3 x 10 3 . 7. A process for preparing coated particles characterized by comprising the steps of: a) suspending a polymer selected from the group consisting of polyvinyl or polystyrene phosphoric acid, polyvinyl or polystyrene sulphuric acid, polyvinyl or polystyrene sulphonic acid, polyvinyl or polystyrene phosphonic acid, polyacrylic acid and their respective salts and optionally ultrafine particles in water at appropriate concentration; b) adjusting pH condition of the aqueous suspension of step a) to a value lower than 4; c) suspending particles to be coated, which consist of a material that is inherently surface charged or may develop its potential electrostatic attraction to an opposite charged material, in water at an appropriate concentration and adjusting pH condition of the resulting suspension to a value lower than 4; d) adding the suspension of step b) to the suspension of step c) and gentle stirring of the resulting mixture for enough time to obtain a complete coating of the particles; e) adjusting the pH of the suspension of step d) to 5-7 to obtain a nearly neutral suspension of the coated particles; and f) optionally recovering the irreversibly coated particles from the aqueous suspension. 8. The process according to claim 7 characterized by comprising the polymer used in step a) a polystyrene sulphuric acid latex. 9. The process according to claim 7 characterized by the particles to be coated of step c) being polyhedrosis virus particles. 10. The process according to claim 7 characterized by being the polyhedrosis virus a Baculovirus. 11. The process according to claim 10 characterized by being the Baculovirus a Baculovirus anticarsia. 12. The process according to claim 7 characterized by the pH of the suspensions of steps b) and c) being adjusted to 3.0. 13. The process according to claim 7 characterized by the ratio latex particles/ polyhedrosis particles ranging from 10 2 to 3 x 10 3 14. The process according to claim 13 characterized by the polymer concentration ranging from 10 11 to 10 12 latex particles/ml. 15. The process according to 13 characterized by ranging the concentration of the core material from 10 s to 10 9 latex particles/ml. 16. A pesticidal composition characterized by comprising the polyhedrosis virus of claim 2 and compatible ingredients in a solid form. 17. The pesticidal composition according to claim 16 characterized by being the polyhedrosis virus a Baculovirus. 18. The pesticidal composition according to claim 17 characterized by being the Baculovirus a Baculovirus anticarsia. 19. The pesticidal composition according to claim 16 characterized by being the solid form a tablet, granulate or dry powder. 20. A pesticidal composition characterized by comprising the polyhedrosis virus of claim 2 and compatible ingredients in a aqueous suspension form.

Inventors: LESSA MARINA MORAES, MEDUGNO CLAUDIA CONTI, LESSA, MARINA, MORAES, MEDUGNO, CLAUDIA, CONTI
Applicants: EMBRAPA EMPRESA BRASILEIRA DE, LESSA MARINA MORAES, MEDUGNO CLAUDIA CONTI, EMBRAPA-EMPRESA BRASILEIRA DE PESQUISA AGROPECUARIA, LESSA, MARINA, MORAES, MEDUGNO, CLAUDIA, CONTI
Application year: 2000
Main classification: A01N63
IPC codes: A01N25, A01N63, A61K9, C12N7