Abstract:
A method for detecting hydrogen peroxide wherein a sample is contacted with a peroxidase or a peroxidatively-active substance and a redox indicator of the following ##STR1## in which A and D independently of one another represent phenyl, pyridyl or imidazolyl, 
     G represents O, CH 2  or S, 
     m represents the number zero or one, and 
     X represents O, ##STR2## or --NR 1  --NR 2  -- R 1  and R 2 , independently of one another, denote hydrogen, alkyl, cycloalkyl, aryl or aralkyl, or --NR 1  R 2  together represent a pyrrolidine, pyrazoline, piperidine, piperazine or morpholine radical and 
     T denotes hydrogen, hydroxyl, alkyl, aryl, alkoxy, phenoxy, SO 3  H, --COOH or ##STR3## whereby a color change is brought out if hydrogen peroxide is present.

Description:
This application is a continuation of application Ser. No. 053,301, filed 5/22/87, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to agents, for detecting redox reactions, containing triaryl- and trihetarylmethane derivatives as redox indicators. These redox indicators can be employed to very good effect for the detection of hydrogen peroxide, particularly with the aid of peroxidases or peroxidatively-active substances 
     These redox indicators are furthermore suitable for the detection of peroxidases or peroxidatively-active compounds, where other peroxides may also be employed as oxidants. 
     Hydrogen peroxide is a reaction product which is produced during the enzymatically catalyzed oxidation of substrates such as, for example, glucose, cholesterol, uric acid, glycerol, glycerol phosphate, galactose, pyruvate or sarcosine by means of an appropriate oxidase such as glucose oxidase, cholesterol oxidase, uricase, glycerol oxidase, glycerol phosphate oxidase, galactose oxidase, pyruvate oxidase or sarcosine oxidase. The substrates mentioned belong to the group of analytical substances which play a role in clinical/chemical analysis. The hydrogen peroxide formed during the oxidase reaction can be detected polarographically, titrimetrically or potentiometrically. The colorimetric determination of hydrogen peroxide has considerably increased in importance due to the discovery of enzymes, such as peroxidase, catalase or haemoglobin, which convert hydrogen peroxide. Peroxidases, and also peroxidatively active substances (for example haemoglobin and methaemoglobin) catalyze the hydrogen peroxide-dependent oxidation of indicators such as guaiacol, dianisidine hydrochloride or ABTS into colored compounds. One of the best known detection reactions for hydrogen peroxide is the so-called &#34;Trinder reaction&#34; (Trinder, P. Ann. Clin Biochem., volume 6 (1969), pp. 24-27). 4-amino-antipyrine is oxidized by hydrogen peroxide in the presence of a peroxidase. The oxidation product is capable of coupling with a phenol or phenol derivative, a usually red quinone imine dyestuff being produced the concentration of which may be determined photometrically. 
     SUMMARY OF THE INVENTION 
     The present invention relates to agents, for the detection of redox reactions, containing compounds of the general formula I ##STR4## in which A, B and D, independently of one another, represent the radical of an aromatic or heteroaromatic compound, 
     G represents O, CH 2  or S, 
     m represents the number 0 or 1, and 
     X represents O, ##STR5## or --NR 1  --NR 2  --, where aromatic radicals are the aryl or naphthyl radicals, and heteroaromatic radicals are the pyridyl, imidazolyl, pyrazinyl and indolyl radicals, which themselves may carry substituents which are conventional in dyestuff chemistry, R 1  and R 2 , independently of one another, denote hydrogen, alkyl, cycloalkyl, aryl or aralkyl which may be substituted by substituents which are conventional in dyestuff chemistry, or --NR 1  R 2  represents a pyrrolidine, pyrazoline, piperidine, piperazine or morpholine radical which may be substituted by substituents which are conventional in dyestuff chemistry, as redox indicators. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing is a graph of extinction vs. λnm. Curve 1 depicts the absorption spectrum at pH 6.57 and curve 2 depicts the absorption spectrum at pH 4.6. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Substituents which are conventional in dyestuff chemistry are, for example, halogen, hydroxyl, alkoxy, aryloxy, aralkoxy, aryl, cycloalkyl, hetaryl, alkylmercapto, arylmercapto, alkylsulphonyl, cyano, alkylcarbonyl, alkylcarbonyloxy, nitro, acylamino, alkylsulphonic acid, arylsulphonic acid, alkylcarboxylic acid, aralkylcarboxylic acid, amino which may be substituted by 1 or 2 alkyl, aryl or aralkyl groups which themselves may again be substituted by halogen, cyano, hydroxyl, sulphonic acid, carboxylic acid or substituted amino, or amino groups the substituents of which are cyclized. 
     Alkyl preferably represents C 1  -C 22  -alkyl, particularly C 1  -C 12  -alkyl, and very particularly C 1  -C 6  -alkyl, and alkenyl preferably represents C 2  -C 5  -alkenyl. 
     Halogen is taken to mean, in particular, fluorine, chlorine and bromine. 
     In particular, cycloalkyl is taken to mean cyclopentyl and cyclohexyl, aryl is taken to mean phenyl and naphthyl, aralkyl is taken to mean benzyl and phenethyl, and hetaryl is taken to mean pyridyl, pyrimidyl, pyrazinyl, triazinyl, imidazolyl, oxazolyl or thiazolyl. 
     Acyl is preferably C 1  - to C 4  -alkylcarbonyl and -sulphonyl and benzoyl. 
     The compounds of the general formula (I) are widely known as color formers, for example for copying paper or thermal printing paper (EP-A 108,382, EP-A 141,962). In the case of copying paper, the color formers are present in encapsulated form. During writing, the capsules are broken and the color formation by the liberated color formers occurs on contact with acid-modified aluminas. 
     Surprisingly, it has now been determined that compounds of the general formula (I) are also very well suited as redox indicators. These compounds are particularly well suited as indicators for the qualitative or quantitative detection of hydrogen peroxide or also for the detection of peroxidases or peroxidatively-active substances. The oxidation of the indicators by the hydrogen peroxide or another peroxide (for example cumenyl hydroperoxide, strontium peroxide, 2,5-dimethylhexane 2,5-dihydroperoxide or diisopropylbenzoyl hydroperoxide) can occur due to the catalytic action of a peroxidase or a peroxidatively-active substance. Suitable peroxidases are those from horseradish or potatoes or those of microbiological origin. Peroxidatively-active substances are taken to mean those substances which catalyze the transfer of the redox equivalents from hydrogen peroxide or another peroxide onto the indicators, such as, for example, haemoglobin, methaemoglobin or myoglobin. Furthermore, the compounds of the general formula (I) are suitable for determining oxidants, such as, for example, persulphate, peracetate, chloramine T or cyanoferrate complexes such as potassium hexacyanoferrate. 
     The compounds of the general formula (I) can be particularly successfully employed in test agents for substrates such as, for example, glucose, cholesterol, uric acid, glycerol, glycerol phosphate, galactose, pyruvate or sarcosine which are oxidized by an appropriate oxidase such as glucose oxidase, cholesterol oxidase, uricase, glycerol oxidase, glycerol-phosphate oxidase, galactose oxidase, pyruvate oxidase or sarcosine oxidase in the presence of oxygen with formation of hydrogen peroxide. The hydrogen peroxide formed is detected using the compounds of the general formula (I). 
     As already discussed, the compounds of the general formula (I) are also suitable for the detection of peroxidases or peroxidatively-active substances. Test systems which may be mentioned here are the detection of occult blood or peroxidase-labelled immune tests. 
     In the context of the present invention, test agents or test systems are taken to mean, for example, those which can be measured in a cell. The test agents contain, besides the redox indicators of the general formula (I), all those reagents, such as enzymes, substrates, coenzymes, effectors, antigens, antibodies etc., which are necessary for the determination of the particular parameter. In addition, these test agents can also contain non-reacting substances, such as, for example, buffers, wetting agents and stabilizers. Reagent combination$, which are present as a solution, as a mixture of powders, as tablets or as a lyophylizate, may be prepared from the reagents and substances mentioned. The reagent combination (if not already present as a solution) is taken up in water or another suitable solvent and made up into a reagent solution. If the reagent combination comprises individual components, these should be mixed with one another. After mixing the sample (for example substrate solution, enzyme solution, blood, serum, plasma or urine) with an aliquot of the reagent mixture, the resultant color is measured on a photometer and the respective concentration or substrate concentration is calculated via the molar extinction coefficients and the volumes of reagent or sample added. Both kinetic and end-point measurements are possible. 
     The compounds of the general formula (I), together with peroxidase or a peroxidatively-active substance, the reagents or other enzymes which are necessary for the determination of the particular parameter, the buffer system, if appropriate wetting agents and activators, and also other adjuvants, may also be impregnated onto absorptive reagent supports such as papers, fleeces, etc. For this purpose, one or more impregnation solutions may be prepared in the form of aqueous or organic or mixed solutions, depending on how the reagents or adjuvants dissolve. Absorptive or swellable supports, preferably filter paper or absorptive glass or plastic fleeces, are impregnated or sprayed with these solutions. The supports are subsequently dried. The reagent supports thus prepared can be employed as rapid diagnostic agents for the direct determination of the contents of liquids (for example in body liquids such as blood, urine or saliva, or in foods, for example fruit juices, milk or others). During this, the liquid is applied directly onto the reagent support or the latter is dipped briefly in the liquid. Semi-quantitative determination is possible by allocating the color produced to a comparison color. Quantitative evaluation can be carried out by remission photometry. In this, the fact that dyestuffs which have their absorption maximum in the long-wave region of the spectrum are usually developed from the compounds of the formula (I) has an advantageous effect. Light diodes can then be used as the light source for the measurement of such dyestuffs. 
     It is also possible to introduce the compounds of the general formula (I) into support matrices which have been prepared from casting solutions. Examples which may be mentioned here are cellulose, cellulose derivatives, gelatins, gelatin derivatives or also plastics such as polyurethanes and acrylamide. It is advantageous here for the compounds of the general formula (I) and, if appropriate, the other necessary reagents to be added directly to the casting solution, it thereby becoming possible for the test device, comprising support and reagents, to be prepared in one step. 
     A reagent solution with which the substrates or enzymes described above can be determined in the cell on a photometer may be prepared by eluting the abovementioned reagents from the absorptive support using water or buffer or serum. 
     Suitable buffers for the test agents mentioned are phosphate, citrate, borate or GOOD buffers having alkali metal or ammonium counterions. However, other systems are likewise practicable. A pH of 6 to 10, particularly 6.5 to 7.5, should be aimed at. 
     Wetting agents are, in particular, anionic and cationic wetting agents which interact ionically with the zwitterionic compounds according to the invention. However, non-ionogenic wetting agents which activate the enzymes are likewise practicable. Sodium lauryl sulphate, dioctyl sodium sulfosuccinate and alkylaryl polyether alcohols are preferred. 
     The known effectors for the particular enzymatic reaction should be employed as effectors. 
     Conventional thickeners, solubilizers, emulsifiers, optical brighteners, contrasting agents, etc., as are known in corresponding tests with other chromogens, may be appropriate as other adjuvants. 
     Of the compounds of the formula (I), the compounds of the formula (II) ##STR6## in which A denotes optionally substituted phenyl, pyridyl or imidazolyl, 
     T denotes hydrogen, hydroxyl, alkyl, aryl, alkoxy, phenoxy, SO 3  H, --COOH or ##STR7## where R 1  and R 2  have the abovementioned meaning, and X, G, D and m have the abovementioned meaning, are preferred. 
     Compounds of the formula (III) ##STR8## in which W denotes hydrogen, ##STR9## alkyl, alkoxy or halogen, T denotes hydrogen, alkyl, alkoxy or ##STR10## X denotes ##STR11## or --NH--NR 1  --, D denotes the radical phenyl, naphthyl or indolyl, and 
     G, R 1 , R 2  and m have the abovementioned meaning, are of particular interest. 
     Very particularly preferred compounds are those of the formula (IV) ##STR12## in which X denotes ##STR13## or --NH--NR 1 , W denotes hydrogen or ##STR14## T denotes hydrogen, C 1  -C 4  -alkyl, C 1  -C 4  -alkoxy or ##STR15## G denotes 0, m denotes 0 or 1, and 
     Y and Z denote hydrogen or a fused benzo ring, and 
     R 1  and R 2 , independently of one another, denote hydrogen, C 1  -C 4  -alkyl which may be substituted by halogen, hydroxyl, cyano, C 1  -C 5  -alkoxycarbonyl, --SO 3  H or --COOH, or denote aryl or aralkyl, or 
     NR 1  R 2  denotes a pyrrolidine, piperidine or morpholine radical. 
     Very particularly preferred compounds are those of the formula (V) ##STR16## in which W, R 1 , R 2 , Y, Z and m have the abovementioned meaning. 
     Processes for the preparation of the compounds mentioned are described in EP-A 141,962 and EP-A 108,382. 
     The present invention is described in greater detail and illustrated by means of the following examples. 
     EXAMPLE 1 
     4.15 g of 3,3-bis-(4-dimethylaminophenyl)-6-dimethylamino-phthalide are refluxed in 20 ml of ethanol with 10 ml of hydrazine hydrate. After 3 hours, the reaction batch is discharged into 100 ml of ice-water and filtered under suction. The crude product of the following constitution ##STR17## melts at 263° C. 
     EXAMPLE 2 
     4.15 g of 3,3-bis-(4-dimethylaminophenyl)-6-dimethylamino-phthalide are heated for 2 hours at 150° C. with 20 ml of diethanolamine. The solution is allowed to cool and discharged into ice-water, and the yellowish precipitate is filtered off under suction. After recrystallization from ethanol, the substance of the follow-constitution ##STR18## melts at 252° C. 
     Color of the oxidation product: yellow-orange 
     EXAMPLE 3 
     31.8 g of 3,3-bis-(4-hydroxyphenyl)-1(3H)-isobenzofuranone are refluxed in 150 ml of ethanol with 30 ml of hydrazine hydrate. After 5 hours, the mixture is poured onto ice and acidified using acetic acid. The precipitate, after filtering off under suction, is recrystallized from ethanol. The substance, melting at 279° C., has the following formula ##STR19## 
     Color of the oxidation product: orange 
     EXAMPLE 4 
     15.7 g of 2-(2-hydroxy-4-diethylamino)benzoylbenzoic acid are introduced into 62 ml of sulphuric acid monohydrate at a temperature of 8° to 12° C. 9.95 g of 4-methoxy-diphenylamine are subsequently added and the mixture is stirred for 2 days at room temperature. The reaction solution is then discharged onto ice and adjusted to pH 11 using a sodium hydroxide solution, a layer of 300 ml of toluene is added, and the mixture is refluxed for 3 hours. The toluene phase is subsequently separated off and concentrated by evaporation. After treatment with activated charcoal, the following substance, having the melting point 194° C., crytallizes from toluene. ##STR20## 
     Color of the oxidation product: grey-violet. 
     EXAMPLE 5 
     4.62 g of 3-diethylamino-7-anilinofluoroan are refluxed for 1 hour in 25 ml of ethyl glycol with 6 ml of hydrazine hydrate. After cooling, ice-water is added dropwise and the precipitation is filtered off under suction. The compound of the following constitution melts at 146° C. ##STR21## 
     The compounds mentioned below are prepared analogously. *=color of the oxidation product 
     EXAMPLE 6 ##STR22## 
     EXAMPLE 7 ##STR23## 
     EXAMPLE 8 ##STR24## 
     EXAMPLE 9 ##STR25## 
     EXAMPLE 10 ##STR26## 
     EXAMPLE 11 ##STR27## 
     EXAMPLE 12 ##STR28## 
     EXAMPLE 13 ##STR29## 
     EXAMPLE 14 ##STR30## 
     EXAMPLE 15 ##STR31## 
     EXAMPLE 16 ##STR32## 
     EXAMPLE 17 ##STR33## 
     EXAMPLE 18 ##STR34## 
     EXAMPLE 19 ##STR35## 
     EXAMPLE 20 ##STR36## 
     EXAMPLE 21 ##STR37## 
     EXAMPLE 22 ##STR38## 
     EXAMPLE 23 
     
                       TABLE 1______________________________________                            Extinction                Absorption  difference/pH     Color         maximum (nm)                            5 minutes______________________________________4.55   yellow        415         1.7076.57   yellow-orange 490         1.3517.80   yellow-orange 490         1.803______________________________________ 
    
     EXAMPLE 24 
     
                       TABLE 2______________________________________Extinction difference/5 minutes      H.sub.2 O.sub.2             Concentration (ext. at 240 nm)      0.021  0.045    0.083    0.168______________________________________Compound from Ex. 1        0.116    0.229    0.419  0.888490 nm       0.114    0.225    0.441  0.910DCHBS/aminopy        0.139    0.274    0.546  1.076510 nm       0.144    0.273    0.534  1.103______________________________________ 
    
     EXAMPLE 25 ##STR39## 
     EXAMPLE 26 ##STR40## 
     EXAMPLE 27 ##STR41## 
     EXAMPLE 28 ##STR42## 
     EXAMPLE 29 ##STR43## 
     EXAMPLE 30 ##STR44## 
     EXAMPLE 31 ##STR45## 
     EXAMPLE 32 ##STR46## 
     EXAMPLE 33 ##STR47## 
     EXAMPLE 34 ##STR48## 
     EXAMPLE 35 ##STR49## 
     EXAMPLE 36 ##STR50## 
     EXAMPLE 37 ##STR51## 
     EXAMPLE 38 ##STR52## 
     EXAMPLE 39 ##STR53## 
     EXAMPLE 40 
     In order to test the compound of Example 1 as an indicator in an H 2  O 2  /peroxidase test system, this compound was dissolved in DMF to a concentration of 5 mM. This solution was then mixed 1+1 with buffer (citrate 0.1 M/l, pH 4.55, THAM 0.1 M/l, pH 6.57 and pH 7.8, and 5 μl of peroxidase (500 kU/l) were added to 0.5 ml of this solution. After addition of 10 μl of H 2  O 2  (3.4 mM/l=E 240  =0.168) and an incubation time of 5 minutes, the extinctions were measured. As FIG. 1 shows, the absorption maximum shifts depending on the pH. 
     Curve 1 shows the absorption spectrum at pH 6.57 and curve 2 at pH 4.6. 
     Table 1 shows the extinctions measured at the different wavelengths and pHs. 
     
                       TABLE 1______________________________________                            Extinction                Absorption  difference/pH      Color        maximum (nm)                            5 minutes______________________________________4.55    yellow       415         1.7076.57    yellow-orange                490         1.3517.80    yellow-orange                490         1.803______________________________________ 
    
     In order to test the function and linearity, 5 μl of peroxidase (500 kU/l) and 5 μl of H 2  O 2  of different concentration were added to 0.5 ml of the above solution with THAM buffer pH 7.8. Table 2 shows the results compared to the &#34;Trinder color system&#34; 4-aminoantipyrine/dichloro-2-hydroxybenzenesulphonic acid. 
     
                       TABLE 2______________________________________Extinction difference/5 minutes         H.sub.2 O.sub.2               Concentration (ext. at 240 nm)         0.021 0.045    0.083  0.168______________________________________Compound from Ex. 1           0.116   0.229    0.419                                 0.888490 nm          0.114   0.225    0.441                                 0.910DCHBS/aminopy,  0.139   0.274    0.546                                 1.076510 nm          0.144   0.273    0.534                                 1.103______________________________________ 
    
     Table 3 shows the results of the test for interferences by ascorbic acid. For this test, 5 μl of an H 2  O 2  solution (H 2  O 2  concentration in the sample=E 240  =0.242) and a further 5 μl of an ascorbic acid solution of 1mM/l are added to the above batch and the resulting extinction is measured. 
     
                       TABLE 3______________________________________         E.sub.1              E.sub.2  ΔE.sub.490 nm______________________________________without ascorbic acid           0.694  1.963    1.269           0.720  1.992    1.272           0.709  2.002    1.293 - x = 1.278with ascorbic acid           0.585  1.899    1.314           0.573  1.859    1.286           0.577  1.854    1.277 - x = 1.292______________________________________ 
    
     The values measured in the presence of ascorbic acid are, on average, about 1.1% above the values which were measured in the absence of ascorbic acid. The present test is thus not influenced by ascorbic acid. 
     EXAMPLE 41 
     Test of the compound from Example 5 Batch: 
     1,000 μl of buffer (citrate 0.1 M/l pH 5, THAM 0.1 M/l pH 7 and pH 9) 
     900 μl of DMF 
     100 μl of the compounds from Example 5, 2.02 mM in DMF 
     20 μl of peroxidase (1,000 kU/l) 
     20 μl of H 2  O 2  solution 
     The measured absorption maximum is at 720 nm. The extinction differences at different pH values are listed in Table 4. The sample concentration was 5 mM/l with respect to H 2  O 2 . 
     
                       TABLE 4______________________________________         ΔE.sub.720 after 5 minutes______________________________________pH 5            0.110pH 7            0.185pH 9            0.040______________________________________ 
    
     The decrease in the extinction within 20 minutes (color stability) is 0.8%. The interference by ascorbic acid was tested analogously to Example 40. Table 5 shows the results. 
     
                       TABLE 5______________________________________         E.sub.1              E.sub.2  ΔE.sub.720 nm______________________________________without ascorbic acid           0.138  0.374    0.236           0.148  0.380    0.232           0.140  0.375    0.235 - x = 0.234with ascorbic acid           0.107  0.349    0.242           0.107  0.353    0.246           0.103  0.358    0.255 - x = 0.248______________________________________ 
    
     In the presence of ascorbic acid, the measured values are, on average, about 5.7% higher. 
     Table 5 shows the linearity and function test. H 2  O 2  solutions of different concentrations were added to the above test batch and the extinction was measured after 5 minutes. 
     
                       TABLE 6______________________________________   Compound        Comparison   Example 5       4-AAP/DCHBS (Trinder)[H.sub.2 O.sub.2 ] sample     pH 7      720 nm  pH 7.5    510 nmE.sub.240 E.sub.1            E.sub.2                   ΔE.sub.720                         E.sub.1                               E.sub.2                                     ΔE.sub.510______________________________________0.072     0.146  0.204  0.058 0.010 0.321 0.3110.099     0.139  0.248  0.109 11    0.714 0.7030.151     0.139  0.275  0.136 10    1.040 1.0300.200     0.140  0.333  0.193 15    1.402 1.3870.258     0.148  0.371  0.223 10    1.703 1.6930.303     0.139  0.400  0.261 11    1.976 1.9650.371     0.138  0.418  0.280 12    2.270 2.2580.413     0.139  0.432  0.293 12    2.405 2.3930.460     0.148  0.440  0.292 11    2.678 2.6670.512     0.139  0.443  0.304 10    2.771 2.781______________________________________ 
    
     It is understood that the specification and examples are illustrative but not limitative of the present invention and that other embodiments within the spirit and scope of the invention will suggest themselves to those skilled in the art.