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The mechanism of catalytic chemiluminescence of luminol
L.I. Simdndi (Editor), Dioxygen Actioation and Homogeneous Catalytic Oxidation 0 1991 Elsevier Science Publishers B.V., Amsterdam
417
The mechanism of catalytic chemiluminescence of luminol H. Ojimaa and K. Nonoyamab aDepartment of Chemistry, Aichi Kyoiku University, Kariya, Aichi 448, Japan bK&an Women's College, KGnan, Aichi 483, Japan Abstract Two of catalytic mechanism f o r chemiluminescence of lurninol have been presented using Cu(I1 lamine complexes and Co(II1)ammine complexes as catalysts.The former show the peroxidase like behaviour and the latter behave like the oxygenase. c11
Luminol A(abbreviate, LuH2, LuH- o r Lu2-) emits fluorescence max. at 426nm in neutral and acidic media. In an alkaline solution , the one is not fluorescent, but reacts with @ H H oxidizing agents such as 02, 03, '210' and H202 to emit a weak chemiluminescence with an emission max. at 426nm(same as the max. of fluorescence). The mechanism of this phenomenon was presented as the fluorescence A due to the exited singlet state of 3-aminophthalate anion which was produced by the oxidation of Lu2-c 23 It has been known that the metal complexes of Fe(III),Fe(II), Co(III), Cu(I1) etc. act as efficient catalysts to enhance the emission intensities. Two interpretations for this catalytic mechanism are available: 1 The HO* o r H02. produced by catalytic decomposition of H202 attacks Lu2- to produce the exited state of the 3-aminophthalate anion. 2 The equilibrium to generate the ternary complex involving the Lu2- is established and the one reacts with H202 reducing the activation energy. Although the former seems to be more sensible on the basis of experimental fact that the metal complexes promote effectively the reaction in the presence of H202, this paper reports to support latter using Cu(I1)amine- and Co(II1)ammine complexes.
.
1. MECHANISM OF CATALYTIC CHEKILUMINESCENCE OF
SYSTEM Lu2'@
[Cu(amine)In+* H202
Existence of H202 is required f o r chemiluminescent reaction o f this system. In this reaction, the Cu(I1) c o plexes behave
-.
like the peroxidase to oxidize the substrate,Lu9
On this
418
process, the Lu2' coordinates to Cu2+ to reduce the activation enrgy on reaction with H202. The luminescent solution used for this work: @ Cu(3I)amine complex: 2x1 O-2mmo1 and luminol mono-sodium saltI 10- mmol are in 4.5ml of water, adjusted to be pH=lO.5. @ ~202: 2x10-lmmol is in 0.51~11 of water. The H202 was injected and stirred rapidly under ZOf0.5°C. The emission yield at every second were recorded by lumicounter startirc at the mixing moment of @ with @
.
1
, CU(II )triisopropanolamine(Cu-epa)*~G-e~~02 system
Because of the titled complex is the most efficient promoter among the Cu(I1) complexes used in this work, prepared some data using this ligand f o r elucidation of the mechanism of this system, The ligand triethanolamine(tea1 is also the powerful one
.
1.1.1.
Emission yields depend on pH
The dependence of luminescent intensities on pH is related sensitively to the structural changes of the Cu(1I) complex with changes of pH. The highest emission yield of this system is given at pH=lO.5. The ranges, less than pH=9 and higher than pH=l2, the emission yields are reduced to about 109%o r less of that at the optimum condition. More increase the alkalinity, the emission yield increases again(at 1N-NaOH or more). This phenomenon is irrelative to the catalytic activity of the complex. In this condition, the complex is stabilized as Cu(I1)aminoalkoxo complex which is already incapble of receiving the substrate,Lu2; but is active to make H202 or HO2' decompose. The He, HO* or HOE* thus produced act to the Lu2- directly. 1.1,2.
Structural changes of Cu(I1)-tpa
depend on pH
.
No changeable pattern of the d-d band and charge transfer band of the complex in any ratio of tpa/Cu2+ means that only one species, Cu2+ctpa(and tea also [ 31 )=1i1, exists in any cases The structural change of the 111 complex with pH changes are dominated by dissociation of alcoholic hydroxyl group in the tpa and tea to coordinate. These species thus produced are shown in Fig. 1. The pH at the optimum condition for the chemiluminescence of this system coincides with the pH in which the species B and B' are produced, This is implied that the following equilibrium i. established in the luminescent solutions B(or B' ) 1 .i .3.
+ Lu2'
I.
pre-reactant "Y"(cf.Fig.1)
Isolation of pre-reactant
The direct proof for the mechanism of catalytic chemluminescence of this system could be prepared by isolation of
419
R
2 OH
or R
7
2
- y (pr e-r eac t a n t ) t
-
Y + H02+
z ( r e a c t a Lu nt) Fig. 1 S t r u c t u r a l changes o f Cu(I1.)-tpa with pH changes m d formation o f r e a c t a n t .
420
the pre-reactant(cf. Fig. 2): To the solution containing 1.2mol of tpa, was added l.Omo1 of f)u(OH)2 prepared newly. The insoluble portion is left out centri fugally. The mono-tpa-copper complex is in the solution. @ 1.0 mol of [Cu(NH3)4JC12 was dissolved into the excess amounts of aq. ammonia, then added 1.0 mol of luminol mono sodium salt. Given the blue transparent solution in which both species are irrelative each other. Mixing @with @ gave the homogeneous dark green solution. ontinuous stirring of the solution c under 4OoC gave the dark green fine crystals(correspond to pre-reactant, Y) with evaporation of excess ammonia. In an alkaline solution, this fine crystal emits strong chemiluminescence contacting with H202.
9
2 [ C U ( N H ~ ) ~ ] C ~+~ tpaH3
H
+
3 NH4C 1
+ LuH2
+
-
5 NH3
, changes into
Y in an 1 (alkaline solution
Fig. 2 Isolation of pre-reactant The structure of this crystal was checked by elementary analysis, IR- and UV-spectra(cf. Fig.3). And the value,)J=1.55 EM, is the resonable one for dimerized structure.
1.1.4.
The relation [Lu2-(variable)l/[Cu2+(constant emission yield
)I
-
In order to obtain another proof for pre-reactant and reactant, the relation between the ratio entitled above and emission yield has been checked(cf. Fig. 4). In all cases, the inflection points appeared at the ratio=O.5. And the range under this point is shown linear relation between the emission yield and the amounts of Luz-. This result means that existence of the pre-reactant and reactant, Y and 2, respectively, and the amounts of them are proportional to the amounts of Lu2-, 1.2.Comparison of catalytic abilities of various Cu(I1)amine complexes The relation between catalytic abilities(emissi0n yield) and ratio of [ligand(variable)]/[Cu2+(constant)] are shown in Fig. 5. All complexes reveal the max. in abilities at each
42 1
100 50 20
1000
10
Y0 5
a a
rl
z 2 w 1
.rl
c
.5
0 .rl
ffl
ffl
*2 .1 at bt c:
d:
.rl
E
0,
10 20 3 0 kK Cu(tpaH-j)2+ in DMF Cu(tpaH)O in mtOH Cu(0H) (tpal2'in NaOH/mtOH pre-reactant Y'(iso1ated)
el Y' in O.1N-NaOH f t
100
LUH-
Fig. 3 UV-spectra o f Y' and its relatives
10
*L t
C Lu2-l/[ CuL*1
a: tpa
b t tea c: N-(3-hydroxypropyl)en d t N- (2-hydroxypropyl) en
Fig.4
Relation between CLu2-]/CCuL] and emission yields
individual point and height. It is definite that the height at any points of the curves correspond to the concentration of the pre-reactant and also reactant(corresp0nd to Y and 2 in Fig. 1, respectively)
.
* L= at tpa
b t N ,N- (diethyl)en c I 2,2 ' -bipyridine d I N-(hydroxyethyl )en
et en f : ethanolamine g I N ,N- (di ethyl ) ethanolamine hi NH it pdidine j r t-butylamine
-
Fig. 5 Comparison of catalyti abilities of various Cu(1I)amine complexes.
422
1.3. ( , a t a l y t i c a l . l y a c t i v e complexes These l i g a r i d s c a u s e t h e mu tu al r e p u l s i o n on f o r m a t i o n o f b i s - c h e l a t e s . To a v o i d su ch s t e r i c h i n d r a n c e t e n d t h e complexes t o form (3-bridged o r o l a t i o n dimers s u c h as:
dimer-1
dimer-2
T h i s t e n d e n c y may m a k e them t o e s t a b l i s h t h e e q u i l i b r i u m i n v o l v i n g t h e Lu2- t o p ro d u ce t h e p r e - r e a c t a n t s u c h as a
from dimer-1 and Lu 2-
from dimer-2 and Lu 2 -
I t seems p l a u s i b l e t h a t t h e max. m o u n t s o f mo n o - c h e la te s Such mono-chelates may e x i s t a t e a c h max. p o i n t i n F i g . 5. behave as mentioned above. Ex ceed ing t h e max. p o i n t s t h e b i s chelates, aminoalkoxo and hydroxo complexes which p r e v e n t t h e Lu2- from f o r m a t i o n o f r e - r e a c t a n t a r e s t a b i l i z e d . Although [ C ~ ( b p y ) n~= l , ~ 2 ~and 3 , p o s s e s s h i g h e r s t a b i l i t i e s , t h e one s c l e f o m e a s i l y i n an al.kal.ine s o l u t i o n t o form o n l y one p r o d u c t , Ibpy-Cu(OK )2-Cu-bpyl2'L1I . T h e r e f o r t h e s e complexes a c t as e f f i c i e n t c a t a l y s t s a t p H=1 2 (h igh e r t h a n t h e o t h e r s ) [ 5 3 . NH , NIi - R , p y r i d i n e e t c . r e v e a l t h e max. o f c a t a l y t i c a c t i v i d e s a$ a b o u t ~ l i g a n d J / ~ C u * ~ 1 = 2 0 0 Ce 6Although 1 these ratios are h i g h e r t h a n t h a t o f t h e o t h e r s , t h e max. amounts o f p r e r e a c t a n t and r e a c t a n t ( c o r r e s p o n d t o Y and Z ) must e x i s t a t each max. p o i n t . I t c a n be s e e n t h a t t h e weaker i s t h e c o o r d i n a t i n g a k i l i t y c f t h e l i g a n d , t h e h i g h e r i s t h e max. p o i n t , 1.4.
i n e r t complexes as c a t a l y s t
C Gu(en 1212+, [ Cu ( p n )2 J2+, [ C u ( d e n ) (H20 12+, [Cu( t r i e n 112+, [ C u ( e d t a ) l o e t c . zre i n e r t . Because o f t h e t h r e e o r f o u r o f c o o r d i n a t i n g s i t e s o f them are a l r e a d y o c c u p i e d , t h e e s t a b l i s h ment o f t h e e q u i l i b r i u m w i t h Lu2- c a n n o t be e x p e c t e d .
1.5. E f f e c t o f CN- i n t h e sy stem o f C u (I1 )c o mp le x
Lu2'*
H202
XlthouEh t h i s l u m i n e s c e n t r e a c t i o n ( w i t h o u t CN-) r e v e a l s none o f i n d u c t i o n p e r i o d , a d d i t i o n o f CN- r e v e a l t h e i n d u c t i o n
423
p e r i o d which i s p r o p o r t i o n a l t o t h e amounts o f CN”, and t h e emission y i e l s a r e i n v e r s e l y p r o p o r t i o n a l ( d e c r e a s e 1 “1 1 Fig. 6 shows t h e e f f e c t s of CN’ t o t h e i n d u c t i o n p e r i o d s and luminescent i n d u c t i o n time i n s e e . i n t e n s i t i e s , The i n t e r >. p r e t a t i o n on t h i s phenomenon2 2 25 89 260 880 can be made, i.e.,the r e a c t i o n of CN’ with complex ( a c t i v e c a t a l y s t k .rl 1 0 proceeds n e a r l y s t o i chiometricallyi
5 5
.rl
.4.
ra ra
.d
$ 1 0.5
(active ) A
0.1 0.05
5 10 (3-n/3)B + n CN-+ H+-
50 100 500 1000 t(sec.)
components o f luminescent s o l u t i o n :
n/3 [ C U I ( C N ) ~ ] ~ - + (inert1
Cu N-(2-hyAroxypropyl ) e n 5x1 0-2rnmo1 luminol ----- 5x1 0’2mmol KCN _----o -3~10-2mmo1 K ~ O ~ I 5x1 O-lmmol
----
C
- -- - -
n/3 l i g a n d o f A
.
Fig. 6 I n d u c t i o n p e r i o d s depend on t h e amounts o f CNWhen t h e H202 i s added i n t o t h i s system, t h e c a t a l y t i c a l l y a c t i v e s p e c i e s A r e a p p e a r according t o t h e r e a c t i o n 8 K1 + CNO- + 3 H20 C + L + 3 H202 B ( i n e r t1 (inert 1 L
B + H202
-
K2
+
I A
(active)
CNO-
T h e times o f t h e i n d u c t i o n p e r i o d s depend on t h e r e a c t i o n v e l o c i t i e s o f K 1 and K2. And t h e d e c r e a s e of luminescent int e n s i t i e s w i t h i n c r e a s e o f t h e i n d u c t i o n p e r i o d s mean t h e consumption o f t h e a c t i v e s p e c i e s by excess H202 i n t h e system.
424
2.
MECHllMISM OF' CATALYTIC CHEMILUMINESCENCE OF SYSTEM [CO(NH~)~X~]~"* Lu2-
.
The peculiarity of these system are that the one emit Conspicuously without H20 The optimum condition for the emission obtained by a number of experiments was standardized for this LuH2: 3xl0'3mmol is in 4.5ml of lO%-NazC03, Co(III)complex(cf.Fig.8): 2.5~10-~mrnol is in O.5ml of water. (molar ratio, Lu~-:CO(III)complex=lt8) The emission yields at every second were recorded by lumi20f0.5°C. counter starting at the mixing moment of@and@at Fig. 7 shows the catalytic abilities of various Co(II1)complexes. The ranking,(s), (m) and (w) can be made for the ones, This order corresponds to inverse of stabilities of the complexes, i .e , the more easy is decomposition of complex in an alkaline solution, the more powerful is the one at the catalytic field. In order to elucidate the cata- lytic mechanism of this system carried out the experiments in detail using cis[Co(NH3)4(H2O)IC13 which is in the group(s). The results obtained are as follows: (1) Chemiluminescent reaction of this systems can proceed even if without H202, but is required existence of 02 in the system. Det in min. gassed system does not emit, group ( s 1 (2) The chemiluminescence of " trans-rCoC1 (NH IC1 this system is proceeded on the 2 1 [C0C1(NH3)47Hf031!13 decomposition process of [Co(OH)31 H3)4 H2° 2 G13 (NH )4(H20)]2+ which was from [Co4 t ~c0(0H)(NH3)4(H20)3c1 [Co?NH3)4(H20)]3+ in an alkaline group(m 1 solution. The longer is the left 5: Na3[Co(N02)6] standing time of the complex in 6 : [Co(CO )(NH ) ICl water and alkaline solution, the 7: [ Co (OH3(NH531812 stronger is the catalytic power at 8 I [ CoCl( NH3 51C12 the first stage and the faster is group(w 1 decay rate. 9 : trans-[CoCI (en)elcl It was recognized spectrophoto10: C C( ~C O I~(en;j21~1 metrically that the [Co(NH 14mer-CCo(N02)3(NH3)31 (H20)2]3+ is changed into ?Co(OH)12t cis-CCo(N02)2(NH )41c1 (NH9)4(H20)]2+ in the Na2C03 soh. not into carbonato complex, then 13: [ Co (NH3 5 (H20 1C?3 14: [ Co ( NH-3 61Cl3 decomposes gradually to form Co(OH)3. Fig* 7 Ranking of cO(III)Considering this result, it is complexes in plausible that the catalytic power catalytic abilities depends on the amounts of certain
.
425
product which is from decomposition process of [ Co (OH)(NH314(H 0)32+, Such product must be generated by following (2) and (39 * 2 ) decomposition process in an alkaline s o h . \ 1111 Ha + HO* -- (1) -CO+ OH2
/ \
2
H*
2 HO.
+
-
02
H202
H202
------ (21 - - - - - - ( 31
The enhancement of catalytic power by left standin in an alkaline solution is due to accumulation of H202 by ( 2 7 and ( 3 ) . Ethylenediamine( en) and CN- inhibit sensitively against ( 3) the catalytic chemiluminescence of this system. When one portion
of the en was added into this system(Co-complexilu2-ien=811 i l ) , the emission yield was reduced to 30% of the standard's. In the case of CN-, also reduced to 50% of standard's at the same condition(cf.Fig.8). The NH3 and pyridine, however, did not show such effect at the same condition. Cinhibiterl/Ccatalystl These results imply 0.1 1.0 that the en and CN- do not behave as the stabiI I lizer for the complex, 11 120 d but behave as the radi0, 100 .rl cal scavengers to conh sume the Ha, HO* or 80 -
5
.ri
rn rn
G
'rl
60
-
40 20
in this
-
curves. The changes of the Co(III)complex, however , display conspicuous changes in shape and height of the decay curves(cf,Fig. 9 ). This behaviours reflect that the Co(II1)complex performs plural roles. The reasonable interpretation for this results can be made as The amounts of He, HO* and H02* produced by o Co(II1)complex are proportional to the amounts of Co(II1)complex in the system. The main role of the Co(II1)complex in this 8 stem is taking t e oxygenase Like behaviour, i.e., substrate, Lu -, coordinates to the complex to reduce the activation energy on reaction with H202, HO* etc.. And this effect is lowerd sensitively with decrease of the amounts o f Co(II1)complex. When enough amounts of 10 100 400 xi 0-bmm0l/4 5ml conc. of inhibiter Fig. 8 Quenching effects of inhibiters in the Co(II1 )complex*Lu2system
9 9
B
426
B
2 H-
+
0,
H2O2 - - - - - - (3)
D D-
h )
+
products
- - - - - - (6)
Scheme 1. Mechanism of catalytic chemiluminescenc of system, Co(I1I)ammine complexes* Lu ;
5
complex exist ( Co-compl ex/ Lu2-=8), such a main role of the complex is completed 2oo showing first order reaction 100 in decay process(~H,=30.2 kcal/mol), but it deviates 3 ..+ from the first order rern20 action when the amounts G of Co(II1)complex was de$10 creased. Under lack of the complex, the emission F: intensities are pro0 2 \ portional to the amounts ..+ of complex. This means that the amounts of He, .d I I I I KO., H02. etc. produced 0 1 0 20 30 40 -50 by decomposition of complex t in min. are proportional to the conc. of catalyst8 complex itself. In this case, 1 1 5x10-2mmo1/4.5mi, it seems to be nothing of 21 1/2, 31 1/4, 41 1/8, 51 1/16, 61 1/32, 71 1/64, oxygenase like behaviour of 81 1/128 the complex. It can be seen that the catalytic mechanism of the Fig. 9. Conc. effects of the Co(1II)complex iffers from catalyst to emission in which that of Fe(CN)b intensities. the change in valency of Fe ion is considered to be responsible for the catalytic action. c The process of catalytic decomposition of H202 b hydroxo complex, [Co(OH) (NH3)4(H20)]2+(behaves like catalasey, is added t o this phenomenon as a side reaction. Gathering of these results led the mechanism of catalytic chemiluminescence of this system as shown in scheme 1.
es
I\
9-
+1 This phenomenon was found by K. Weberr?], and was applied for estimation of CN- by S. MushaC81. +2 Formation of H202 was recognized by M.Iguchi at the oxidation of phenol derivatives by Co(II1) complexes[ 91
.
H.O. Albrecht, 2 . Phys. Chem., 136 (1928) 321. M.M. Rauhut, A.M. Semsel, G.B. Roberts, J. Org. Chem., 31 (1966) 2431. R. Tauler, E. Casassas, M.J.A. Rainer, B .M Rode, Inorg. Chim. Acta, 105 (1985) 165. H. Ojima, Nippon Kagaku Zasshi, 84 (1963 1 787 H. Ojima, ibid., 84 (1963) 909. H. Ojima, ibid.* 79 (1958) 1076. K. Weber, Ber. 76B (1943) 2051 S. Musha, M. Ito, Y. Yamamoto, Y. Inamori, Nippon Kagaku Zasshi, 80 (1959) 1285. 9 M. Iguchi, ibid., 63 (1942) 1752.
.
.
417
The mechanism of catalytic chemiluminescence of luminol H. Ojimaa and K. Nonoyamab aDepartment of Chemistry, Aichi Kyoiku University, Kariya, Aichi 448, Japan bK&an Women's College, KGnan, Aichi 483, Japan Abstract Two of catalytic mechanism f o r chemiluminescence of lurninol have been presented using Cu(I1 lamine complexes and Co(II1)ammine complexes as catalysts.The former show the peroxidase like behaviour and the latter behave like the oxygenase. c11
Luminol A(abbreviate, LuH2, LuH- o r Lu2-) emits fluorescence max. at 426nm in neutral and acidic media. In an alkaline solution , the one is not fluorescent, but reacts with @ H H oxidizing agents such as 02, 03, '210' and H202 to emit a weak chemiluminescence with an emission max. at 426nm(same as the max. of fluorescence). The mechanism of this phenomenon was presented as the fluorescence A due to the exited singlet state of 3-aminophthalate anion which was produced by the oxidation of Lu2-c 23 It has been known that the metal complexes of Fe(III),Fe(II), Co(III), Cu(I1) etc. act as efficient catalysts to enhance the emission intensities. Two interpretations for this catalytic mechanism are available: 1 The HO* o r H02. produced by catalytic decomposition of H202 attacks Lu2- to produce the exited state of the 3-aminophthalate anion. 2 The equilibrium to generate the ternary complex involving the Lu2- is established and the one reacts with H202 reducing the activation energy. Although the former seems to be more sensible on the basis of experimental fact that the metal complexes promote effectively the reaction in the presence of H202, this paper reports to support latter using Cu(I1)amine- and Co(II1)ammine complexes.
.
1. MECHANISM OF CATALYTIC CHEKILUMINESCENCE OF
SYSTEM Lu2'@
[Cu(amine)In+* H202
Existence of H202 is required f o r chemiluminescent reaction o f this system. In this reaction, the Cu(I1) c o plexes behave
-.
like the peroxidase to oxidize the substrate,Lu9
On this
418
process, the Lu2' coordinates to Cu2+ to reduce the activation enrgy on reaction with H202. The luminescent solution used for this work: @ Cu(3I)amine complex: 2x1 O-2mmo1 and luminol mono-sodium saltI 10- mmol are in 4.5ml of water, adjusted to be pH=lO.5. @ ~202: 2x10-lmmol is in 0.51~11 of water. The H202 was injected and stirred rapidly under ZOf0.5°C. The emission yield at every second were recorded by lumicounter startirc at the mixing moment of @ with @
.
1
, CU(II )triisopropanolamine(Cu-epa)*~G-e~~02 system
Because of the titled complex is the most efficient promoter among the Cu(I1) complexes used in this work, prepared some data using this ligand f o r elucidation of the mechanism of this system, The ligand triethanolamine(tea1 is also the powerful one
.
1.1.1.
Emission yields depend on pH
The dependence of luminescent intensities on pH is related sensitively to the structural changes of the Cu(1I) complex with changes of pH. The highest emission yield of this system is given at pH=lO.5. The ranges, less than pH=9 and higher than pH=l2, the emission yields are reduced to about 109%o r less of that at the optimum condition. More increase the alkalinity, the emission yield increases again(at 1N-NaOH or more). This phenomenon is irrelative to the catalytic activity of the complex. In this condition, the complex is stabilized as Cu(I1)aminoalkoxo complex which is already incapble of receiving the substrate,Lu2; but is active to make H202 or HO2' decompose. The He, HO* or HOE* thus produced act to the Lu2- directly. 1.1,2.
Structural changes of Cu(I1)-tpa
depend on pH
.
No changeable pattern of the d-d band and charge transfer band of the complex in any ratio of tpa/Cu2+ means that only one species, Cu2+ctpa(and tea also [ 31 )=1i1, exists in any cases The structural change of the 111 complex with pH changes are dominated by dissociation of alcoholic hydroxyl group in the tpa and tea to coordinate. These species thus produced are shown in Fig. 1. The pH at the optimum condition for the chemiluminescence of this system coincides with the pH in which the species B and B' are produced, This is implied that the following equilibrium i. established in the luminescent solutions B(or B' ) 1 .i .3.
+ Lu2'
I.
pre-reactant "Y"(cf.Fig.1)
Isolation of pre-reactant
The direct proof for the mechanism of catalytic chemluminescence of this system could be prepared by isolation of
419
R
2 OH
or R
7
2
- y (pr e-r eac t a n t ) t
-
Y + H02+
z ( r e a c t a Lu nt) Fig. 1 S t r u c t u r a l changes o f Cu(I1.)-tpa with pH changes m d formation o f r e a c t a n t .
420
the pre-reactant(cf. Fig. 2): To the solution containing 1.2mol of tpa, was added l.Omo1 of f)u(OH)2 prepared newly. The insoluble portion is left out centri fugally. The mono-tpa-copper complex is in the solution. @ 1.0 mol of [Cu(NH3)4JC12 was dissolved into the excess amounts of aq. ammonia, then added 1.0 mol of luminol mono sodium salt. Given the blue transparent solution in which both species are irrelative each other. Mixing @with @ gave the homogeneous dark green solution. ontinuous stirring of the solution c under 4OoC gave the dark green fine crystals(correspond to pre-reactant, Y) with evaporation of excess ammonia. In an alkaline solution, this fine crystal emits strong chemiluminescence contacting with H202.
9
2 [ C U ( N H ~ ) ~ ] C ~+~ tpaH3
H
+
3 NH4C 1
+ LuH2
+
-
5 NH3
, changes into
Y in an 1 (alkaline solution
Fig. 2 Isolation of pre-reactant The structure of this crystal was checked by elementary analysis, IR- and UV-spectra(cf. Fig.3). And the value,)J=1.55 EM, is the resonable one for dimerized structure.
1.1.4.
The relation [Lu2-(variable)l/[Cu2+(constant emission yield
)I
-
In order to obtain another proof for pre-reactant and reactant, the relation between the ratio entitled above and emission yield has been checked(cf. Fig. 4). In all cases, the inflection points appeared at the ratio=O.5. And the range under this point is shown linear relation between the emission yield and the amounts of Luz-. This result means that existence of the pre-reactant and reactant, Y and 2, respectively, and the amounts of them are proportional to the amounts of Lu2-, 1.2.Comparison of catalytic abilities of various Cu(I1)amine complexes The relation between catalytic abilities(emissi0n yield) and ratio of [ligand(variable)]/[Cu2+(constant)] are shown in Fig. 5. All complexes reveal the max. in abilities at each
42 1
100 50 20
1000
10
Y0 5
a a
rl
z 2 w 1
.rl
c
.5
0 .rl
ffl
ffl
*2 .1 at bt c:
d:
.rl
E
0,
10 20 3 0 kK Cu(tpaH-j)2+ in DMF Cu(tpaH)O in mtOH Cu(0H) (tpal2'in NaOH/mtOH pre-reactant Y'(iso1ated)
el Y' in O.1N-NaOH f t
100
LUH-
Fig. 3 UV-spectra o f Y' and its relatives
10
*L t
C Lu2-l/[ CuL*1
a: tpa
b t tea c: N-(3-hydroxypropyl)en d t N- (2-hydroxypropyl) en
Fig.4
Relation between CLu2-]/CCuL] and emission yields
individual point and height. It is definite that the height at any points of the curves correspond to the concentration of the pre-reactant and also reactant(corresp0nd to Y and 2 in Fig. 1, respectively)
.
* L= at tpa
b t N ,N- (diethyl)en c I 2,2 ' -bipyridine d I N-(hydroxyethyl )en
et en f : ethanolamine g I N ,N- (di ethyl ) ethanolamine hi NH it pdidine j r t-butylamine
-
Fig. 5 Comparison of catalyti abilities of various Cu(1I)amine complexes.
422
1.3. ( , a t a l y t i c a l . l y a c t i v e complexes These l i g a r i d s c a u s e t h e mu tu al r e p u l s i o n on f o r m a t i o n o f b i s - c h e l a t e s . To a v o i d su ch s t e r i c h i n d r a n c e t e n d t h e complexes t o form (3-bridged o r o l a t i o n dimers s u c h as:
dimer-1
dimer-2
T h i s t e n d e n c y may m a k e them t o e s t a b l i s h t h e e q u i l i b r i u m i n v o l v i n g t h e Lu2- t o p ro d u ce t h e p r e - r e a c t a n t s u c h as a
from dimer-1 and Lu 2-
from dimer-2 and Lu 2 -
I t seems p l a u s i b l e t h a t t h e max. m o u n t s o f mo n o - c h e la te s Such mono-chelates may e x i s t a t e a c h max. p o i n t i n F i g . 5. behave as mentioned above. Ex ceed ing t h e max. p o i n t s t h e b i s chelates, aminoalkoxo and hydroxo complexes which p r e v e n t t h e Lu2- from f o r m a t i o n o f r e - r e a c t a n t a r e s t a b i l i z e d . Although [ C ~ ( b p y ) n~= l , ~ 2 ~and 3 , p o s s e s s h i g h e r s t a b i l i t i e s , t h e one s c l e f o m e a s i l y i n an al.kal.ine s o l u t i o n t o form o n l y one p r o d u c t , Ibpy-Cu(OK )2-Cu-bpyl2'L1I . T h e r e f o r t h e s e complexes a c t as e f f i c i e n t c a t a l y s t s a t p H=1 2 (h igh e r t h a n t h e o t h e r s ) [ 5 3 . NH , NIi - R , p y r i d i n e e t c . r e v e a l t h e max. o f c a t a l y t i c a c t i v i d e s a$ a b o u t ~ l i g a n d J / ~ C u * ~ 1 = 2 0 0 Ce 6Although 1 these ratios are h i g h e r t h a n t h a t o f t h e o t h e r s , t h e max. amounts o f p r e r e a c t a n t and r e a c t a n t ( c o r r e s p o n d t o Y and Z ) must e x i s t a t each max. p o i n t . I t c a n be s e e n t h a t t h e weaker i s t h e c o o r d i n a t i n g a k i l i t y c f t h e l i g a n d , t h e h i g h e r i s t h e max. p o i n t , 1.4.
i n e r t complexes as c a t a l y s t
C Gu(en 1212+, [ Cu ( p n )2 J2+, [ C u ( d e n ) (H20 12+, [Cu( t r i e n 112+, [ C u ( e d t a ) l o e t c . zre i n e r t . Because o f t h e t h r e e o r f o u r o f c o o r d i n a t i n g s i t e s o f them are a l r e a d y o c c u p i e d , t h e e s t a b l i s h ment o f t h e e q u i l i b r i u m w i t h Lu2- c a n n o t be e x p e c t e d .
1.5. E f f e c t o f CN- i n t h e sy stem o f C u (I1 )c o mp le x
Lu2'*
H202
XlthouEh t h i s l u m i n e s c e n t r e a c t i o n ( w i t h o u t CN-) r e v e a l s none o f i n d u c t i o n p e r i o d , a d d i t i o n o f CN- r e v e a l t h e i n d u c t i o n
423
p e r i o d which i s p r o p o r t i o n a l t o t h e amounts o f CN”, and t h e emission y i e l s a r e i n v e r s e l y p r o p o r t i o n a l ( d e c r e a s e 1 “1 1 Fig. 6 shows t h e e f f e c t s of CN’ t o t h e i n d u c t i o n p e r i o d s and luminescent i n d u c t i o n time i n s e e . i n t e n s i t i e s , The i n t e r >. p r e t a t i o n on t h i s phenomenon2 2 25 89 260 880 can be made, i.e.,the r e a c t i o n of CN’ with complex ( a c t i v e c a t a l y s t k .rl 1 0 proceeds n e a r l y s t o i chiometricallyi
5 5
.rl
.4.
ra ra
.d
$ 1 0.5
(active ) A
0.1 0.05
5 10 (3-n/3)B + n CN-+ H+-
50 100 500 1000 t(sec.)
components o f luminescent s o l u t i o n :
n/3 [ C U I ( C N ) ~ ] ~ - + (inert1
Cu N-(2-hyAroxypropyl ) e n 5x1 0-2rnmo1 luminol ----- 5x1 0’2mmol KCN _----o -3~10-2mmo1 K ~ O ~ I 5x1 O-lmmol
----
C
- -- - -
n/3 l i g a n d o f A
.
Fig. 6 I n d u c t i o n p e r i o d s depend on t h e amounts o f CNWhen t h e H202 i s added i n t o t h i s system, t h e c a t a l y t i c a l l y a c t i v e s p e c i e s A r e a p p e a r according t o t h e r e a c t i o n 8 K1 + CNO- + 3 H20 C + L + 3 H202 B ( i n e r t1 (inert 1 L
B + H202
-
K2
+
I A
(active)
CNO-
T h e times o f t h e i n d u c t i o n p e r i o d s depend on t h e r e a c t i o n v e l o c i t i e s o f K 1 and K2. And t h e d e c r e a s e of luminescent int e n s i t i e s w i t h i n c r e a s e o f t h e i n d u c t i o n p e r i o d s mean t h e consumption o f t h e a c t i v e s p e c i e s by excess H202 i n t h e system.
424
2.
MECHllMISM OF' CATALYTIC CHEMILUMINESCENCE OF SYSTEM [CO(NH~)~X~]~"* Lu2-
.
The peculiarity of these system are that the one emit Conspicuously without H20 The optimum condition for the emission obtained by a number of experiments was standardized for this LuH2: 3xl0'3mmol is in 4.5ml of lO%-NazC03, Co(III)complex(cf.Fig.8): 2.5~10-~mrnol is in O.5ml of water. (molar ratio, Lu~-:CO(III)complex=lt8) The emission yields at every second were recorded by lumi20f0.5°C. counter starting at the mixing moment of@and@at Fig. 7 shows the catalytic abilities of various Co(II1)complexes. The ranking,(s), (m) and (w) can be made for the ones, This order corresponds to inverse of stabilities of the complexes, i .e , the more easy is decomposition of complex in an alkaline solution, the more powerful is the one at the catalytic field. In order to elucidate the cata- lytic mechanism of this system carried out the experiments in detail using cis[Co(NH3)4(H2O)IC13 which is in the group(s). The results obtained are as follows: (1) Chemiluminescent reaction of this systems can proceed even if without H202, but is required existence of 02 in the system. Det in min. gassed system does not emit, group ( s 1 (2) The chemiluminescence of " trans-rCoC1 (NH IC1 this system is proceeded on the 2 1 [C0C1(NH3)47Hf031!13 decomposition process of [Co(OH)31 H3)4 H2° 2 G13 (NH )4(H20)]2+ which was from [Co4 t ~c0(0H)(NH3)4(H20)3c1 [Co?NH3)4(H20)]3+ in an alkaline group(m 1 solution. The longer is the left 5: Na3[Co(N02)6] standing time of the complex in 6 : [Co(CO )(NH ) ICl water and alkaline solution, the 7: [ Co (OH3(NH531812 stronger is the catalytic power at 8 I [ CoCl( NH3 51C12 the first stage and the faster is group(w 1 decay rate. 9 : trans-[CoCI (en)elcl It was recognized spectrophoto10: C C( ~C O I~(en;j21~1 metrically that the [Co(NH 14mer-CCo(N02)3(NH3)31 (H20)2]3+ is changed into ?Co(OH)12t cis-CCo(N02)2(NH )41c1 (NH9)4(H20)]2+ in the Na2C03 soh. not into carbonato complex, then 13: [ Co (NH3 5 (H20 1C?3 14: [ Co ( NH-3 61Cl3 decomposes gradually to form Co(OH)3. Fig* 7 Ranking of cO(III)Considering this result, it is complexes in plausible that the catalytic power catalytic abilities depends on the amounts of certain
.
425
product which is from decomposition process of [ Co (OH)(NH314(H 0)32+, Such product must be generated by following (2) and (39 * 2 ) decomposition process in an alkaline s o h . \ 1111 Ha + HO* -- (1) -CO+ OH2
/ \
2
H*
2 HO.
+
-
02
H202
H202
------ (21 - - - - - - ( 31
The enhancement of catalytic power by left standin in an alkaline solution is due to accumulation of H202 by ( 2 7 and ( 3 ) . Ethylenediamine( en) and CN- inhibit sensitively against ( 3) the catalytic chemiluminescence of this system. When one portion
of the en was added into this system(Co-complexilu2-ien=811 i l ) , the emission yield was reduced to 30% of the standard's. In the case of CN-, also reduced to 50% of standard's at the same condition(cf.Fig.8). The NH3 and pyridine, however, did not show such effect at the same condition. Cinhibiterl/Ccatalystl These results imply 0.1 1.0 that the en and CN- do not behave as the stabiI I lizer for the complex, 11 120 d but behave as the radi0, 100 .rl cal scavengers to conh sume the Ha, HO* or 80 -
5
.ri
rn rn
G
'rl
60
-
40 20
in this
-
curves. The changes of the Co(III)complex, however , display conspicuous changes in shape and height of the decay curves(cf,Fig. 9 ). This behaviours reflect that the Co(II1)complex performs plural roles. The reasonable interpretation for this results can be made as The amounts of He, HO* and H02* produced by o Co(II1)complex are proportional to the amounts of Co(II1)complex in the system. The main role of the Co(II1)complex in this 8 stem is taking t e oxygenase Like behaviour, i.e., substrate, Lu -, coordinates to the complex to reduce the activation energy on reaction with H202, HO* etc.. And this effect is lowerd sensitively with decrease of the amounts o f Co(II1)complex. When enough amounts of 10 100 400 xi 0-bmm0l/4 5ml conc. of inhibiter Fig. 8 Quenching effects of inhibiters in the Co(II1 )complex*Lu2system
9 9
B
426
B
2 H-
+
0,
H2O2 - - - - - - (3)
D D-
h )
+
products
- - - - - - (6)
Scheme 1. Mechanism of catalytic chemiluminescenc of system, Co(I1I)ammine complexes* Lu ;
5
complex exist ( Co-compl ex/ Lu2-=8), such a main role of the complex is completed 2oo showing first order reaction 100 in decay process(~H,=30.2 kcal/mol), but it deviates 3 ..+ from the first order rern20 action when the amounts G of Co(II1)complex was de$10 creased. Under lack of the complex, the emission F: intensities are pro0 2 \ portional to the amounts ..+ of complex. This means that the amounts of He, .d I I I I KO., H02. etc. produced 0 1 0 20 30 40 -50 by decomposition of complex t in min. are proportional to the conc. of catalyst8 complex itself. In this case, 1 1 5x10-2mmo1/4.5mi, it seems to be nothing of 21 1/2, 31 1/4, 41 1/8, 51 1/16, 61 1/32, 71 1/64, oxygenase like behaviour of 81 1/128 the complex. It can be seen that the catalytic mechanism of the Fig. 9. Conc. effects of the Co(1II)complex iffers from catalyst to emission in which that of Fe(CN)b intensities. the change in valency of Fe ion is considered to be responsible for the catalytic action. c The process of catalytic decomposition of H202 b hydroxo complex, [Co(OH) (NH3)4(H20)]2+(behaves like catalasey, is added t o this phenomenon as a side reaction. Gathering of these results led the mechanism of catalytic chemiluminescence of this system as shown in scheme 1.
es
I\
9-
+1 This phenomenon was found by K. Weberr?], and was applied for estimation of CN- by S. MushaC81. +2 Formation of H202 was recognized by M.Iguchi at the oxidation of phenol derivatives by Co(II1) complexes[ 91
.
H.O. Albrecht, 2 . Phys. Chem., 136 (1928) 321. M.M. Rauhut, A.M. Semsel, G.B. Roberts, J. Org. Chem., 31 (1966) 2431. R. Tauler, E. Casassas, M.J.A. Rainer, B .M Rode, Inorg. Chim. Acta, 105 (1985) 165. H. Ojima, Nippon Kagaku Zasshi, 84 (1963 1 787 H. Ojima, ibid., 84 (1963) 909. H. Ojima, ibid.* 79 (1958) 1076. K. Weber, Ber. 76B (1943) 2051 S. Musha, M. Ito, Y. Yamamoto, Y. Inamori, Nippon Kagaku Zasshi, 80 (1959) 1285. 9 M. Iguchi, ibid., 63 (1942) 1752.
.
.