Journal o f Molecular Structure, 45 (1978) 423—436 © Elsevier Scientific Publishing Company, Amsterdam — Printed in The Netherlands 423 REGULARITIES UF IFTERilOLZCULAR INTEKAGTION іІіШ ŁłERGY TKAi^SFEK liJ iilLiEu ASSOCxi^IES OF CHLOROPHYLL ili^ D ITS AisALOGS E.I.SsLnkevitch, АчР.Losev» GcA*Kochubeev, G • F . G ‘Orin о VL X Cn , iiJL rj uSori The nature oY xhe in teraction of ch loropLyll n o le - Giiies and energy tran sfe r in aggregates is o f particu ­ la r in te rest in re la t io n to the organization of these molecules in photosynthstic systems. It may be consi­ dered that associates and mixed associates of d iffe ren t pigments are the intermediate linlc betv.'een сг;/зіа1з and so lu t io n s , so f a r as there is d e fin ite ordering in the structure o±' these complexes, and the iatsrm olecu— i a r in teraction energy correspond to the case of loca ­ liz e d exciton. Our in vestiga tion of model syatems is 311 attempt to study general re g u la r it ie s of the mixed association and estimate the effic iec.v of energy trapp­ ing in mixed aggregates of d iffe ren t pigments under vnj7:f±ns, the aggregate compooition, Tne procedures fo r preparation of mixed aggregates of ch lorophyll and i t s analogs in v/ater-dioxane mix­ tures (4 :1 ) and methods of spectral-lum inescent mea­ surements were e ssen tia lly the same as in our previous, papers [ і , 2 І . Protochlorophyll (PChl) and 4 -vin ,y l-pro- tocJilorophyll (4VPChl) of constant concentration G:, were used as a donor component ( in energy tra n s fe r ) w hile the re la t iv e acceptor con- centratxon (cbJLorophyli — Gill, Pd-piieopliytin "a" - PdPh., Cu-pheophytin ”a ‘* - Gupń, bacteriocnloropii.yil - BCb.1) v^af increased Гго:л 0*001 up to еадішсіаг one. The seouencG in the choice o f acceptors C iil, PdPh and CuPh corresponds to the p ro bab ility deterio ration o f deactivation nonradiative processes which fo r CixPh is no less than 10"^ ^ sec"*"^. The basic sp ectra l—luminescent characteristics and energetic parameters are l is te d in Table I . The increasing of re la t iv e acceptor concentra- 424 TABLE 1. SPECTRAL-LUMINESCENT PROPETIES OF AGGRE­ GATED FORMS OF PIGMENTS IN MIXTURE OF DIOXANE-WATER PIGM ENT ABSOR.«« RC».Лмдх nm LUMIK ^MAI nm QU ANTU M УБ1Ц) В MEAN LIFE TIM E SEC. DECREE OP POLARISATKX P. Vo PROTOCHLOROPHVLL 657 641 8.5't0‘ * -гю"'® 34-36 4 -V1N У L- PROTOCH LOROPH VLL 639 642 1,5-10'* -9 -I0 '“ — Chlorophyll ..a" 6K7 693 5.3-Ю'* -4-10"® 11 - 12 Pd-PHEOPHVTIN 6A7 650 3.0-10'^ -7 :o"'* Cu - PHEOPHVTIN .A* 660 — < 10'* < 2-10"'* ----- Bacteriochlorophvll 826 — < 10"® <1-I0"“ Cu-PROTOPHEOPHVTIN 666 ■ < 10"® <. 2-10"‘* -• tion in donor matrix resu lted in the typ ica l changing of so lu tion absorption spectra (P ig , I ) and the trans­ formation o f c irc u la r dichroism (CD) spectra (P ig ,2 ), It should be noted that in the case o f PChl as a donor the op tica l a c t iv ity of the donor component i s almost 425 ?lgare Im JJiattęiag o£ abaozrixxon зресига o£ Fcjtil and Ciii шіхеа asaociates xa wausr-cLLQxaas ralxrure 4:1 under increasing oi‘ Jru. сэп— cenxraxxon. P jgurelA » Changing ot aosorp-cion зоесгга oi PChi and Оцріі mixed aggregai:ea in wa'cezv-oio-' xane mixture 4sX under increasing oi" CuPb c one ea-cr aifi on* 426 Л.пт ?ii:ure одГ GD зрессга ot PGiai ana CŁl aixxed assoc iaxes In waxer-dioxana aiix- ture 4-: I anaer mcreaexng ot Chi concen- xraxxon. reduced up to zero under increasing acceptor concentra­ tion . In contrast to tJais ttie overtuzrn of the sign de­ pendence of donor bands in CD spectra of 4VPChl has been iiscovered under s im ila r conditions. Analysis of our re su lts and comparison of the data obtained with spectra l ch aracte ristics of d iffe ren t pigment aggre— gated forms in water-dioxane m ixtures, investigated e a r l ie r [3 ] , periait us todrcwthe conclusion that under increasing the acceptor (C h i, PdPh,CuPh) concentration in true mixed complexes the pigment-pigment in teraction leads tc the structure changing of both donor and accep tor parts of the mixed pigment aggregate. ■The d irect evidence of mixed association in binar solutions is the e lectron ic exc itation energy tran sfer 427 0, deg. 10 Piguje2A» G h ^ iM S o f CD apeetra of 4VF0iil зле Jio: mixed aggregates In water-dloxane лп.х- tiire isX under increasing ox’ Jii.. conc^; TiratiOE- 428 wiiich is iiisnifested in the donor iLuninescence quenching under increasing acceptor concentration and fo r Chi as an acceptor - in the aenaitiaation of i t s fluorescence using exc iting l ig h t ot ^sb4 6 0 noi (absorption шазятит of donor). The energy m igration in th is case does take place betneen molecules belonging to one mixed aggregat so f a r as under i n i t i a l l y used pigment concentrations in aolu lions (‘=^ 1 0 ' ^ “ / l ) the energy tran s fe r between d iffe re n t m olecules of d iffe re n t complexes would be im= possib le due to th e ir sp a t ia l disconnectiono The calcu­ la t io n of the experimental values of the tran s fe r e f f i ­ ciency i s associate determined by the donor lumines«=» cence quenching was made using i - Da i - T( U )“ S° Из, Ti - T ł On the other hand in the case o f luminescing acceptor (C h i ) assuming that the acceptor i s excited only due tc the energy tran s fe r process 9 i t i s possib le to calcu­ la te experimental values o f the tran s fe r e ffic ien cy from a e rs it lz a t io n data ę ^ ^ MEAS ^ S i ( i ” T s ) i _______ S s 2^) A Бэ U - Tu) Sd Е.Д (C) Here* D and T are the corresponding op tica l densities and transmittances o f so lu tions; subscript S re fe rs to the to ta l aubsorption (o r transm ittance); subscripts D qnd A, r e fe r to the donor and acceptor ch aracteristics of complexes; index 0 i s connected with op tica l propeiw t ie a o f the staindazd which i s the long«w.avelength aggre« gate o f pure donor (C .^ -^, »10'"^ ™/l) in the w a te r -d i- oxane mixture-XXs 4) • Values S are corresponding areas under luminescence spectral ■=- quantum y ie ld o f donor 1и-ш.1>:?;Озсс:рое ■'n t-ii!? /.'b ?v : r.f* t r a ? } - - 3 f ‘The fa c to r Вд(0^ t&ji'i'... aeooimt tiie -'oncentrafetoa change of acceptor Хитлпезселоо qURiatuoi y ie ld wblcb. f o r Chi had been experim entally meaaared in the ваша conditions.» compares experimental inT estigation re su lts of PChl luminescence quenching by d iffe re n t acceptors in mixed associates» Q?iae data obtai.ned fo r every p a ir of pigments in the complex are pract.ioalXy independent o f exc itation v/avelengtho .Furthermore the ca lcu la tion 429 Figure 3» Ohanging o f PGhl luminescence reiatJxve quantum згівіа in mixea aesocxates =mder increasing o f relati^re concentration of d iffe ren t acceptors ( I - Chi, 2- PdPh. 3- CuPh, 4- B C h lb Gpchl*'^^"^ ’“/ la c o n s t . using formulas ( I ) and (2 ) fo r PGhJ. »»» Chi system showed that the transfer e ffic ie n c ie s deteimdlaed by PChl lumi­ nescence quenching were p ra c t ic a lly the sariie aa the mi­ gration e ffic ie n c ie s determined by Chi fluorescence зед sitizatioa-c. Therefore, the excitation energy tran sfe r in mixed pigment associates takes place without losses* Fig*3 shows that under s im ila r conditions a l l accep­ tors as excitation traps may be ordered as fo llo w s : 3C h l ates of pigments are the complicated polimers contain­ ing dozens or perhaps hundreds of monomeiric molecules. I t can be seen from Table I that under so lution emi­ ssion excitation into PChl absorption band ( ^ s460run) the fluorescence po larization data o f ind iv idua l PChl ana Chi aggregates are considerably d iffe re n t . But in mixed associates the high degree o f fluorescence po- la.r2.zaMXon excited under the вате conditions mea— ;=urea in 00tn acceptor and donor emlseion bands remain^ constant up to ЖІ •10"^ ®/l (P ig .4 ) , *№.ls regu larity Is a lso typ ica l fo r otner donoz^ accept or p a irs . Conse­ quent ly, tne formation of mixed associates does not cnange the ordered structure of donor m atrix. In addi­ tion tne high degree of the acceptor (Ghl and BCSil) fluorescence po larization being excited imdt*-n these conditions due to the energy tran sfe r from the donor component of aggregate points to the high degree of mo­ lecu la r organisation of donor and acceptor parte in 430 431 Р,% 40 30 20 10 о 30 20 10 о 30 20 10 О 30 20 10 о РСЫ 1— 'Ле L 2 - Ле» = 1 !=■=»=* i=8=S PCW І.-Х 2~ "Х' :: PCh 1- А« 2 - Л« - - В "О* СМ '465п1и 465nm + Pd Ph« I »=460nn I *=460niII + Cu Ph« 0 »=460nrr x=440nn 4VHChl+Chl 1 - аІх =470nnł 2-АЬ=470 і / Am -64 A m“ 68(' Л Ат = 6Л Atn“7<’(10 Am*G41 Am *6^ Am=64!; Am=693 nm mn 2' Lnm nm nm rim \ nm nm -8 :?lj;ure 4» P lo t o£ lumxnesседое p o ia r ie a t io n degree D3f pigment mixed aesocxatee in .vater—l i e — xane m ixture Ф ;І on acceptor conceatratio : mixed complexes. Eventually, th.eee data shew that ener-^ g v - oiigration in such systems occurs £гсш tha lowest excited electron ic state of donor component. Discussion Let os consider the physical reasons fo r a d i f f e r ­ ent quenching a b i l i t y of investigated acceptors. 2be 432 procesa of tranafer and excitation trapping In mixed аззосд.агез шау be presented as J^oUoirs: I ) the m igrati­ on along tile donor m atrix (the p ro b a b ility .F ^ )» 2) the rransfer from matrix moleeulei to acceptor molecules (the p robab ility I t should be noted that fo r Ghl, CuPh and BGhl the energy d ifference between f i r s t excited e lectron ic le v e ls o f donor (PGhl) and acceptoz is substan tia lly greater than. kT, Therefore, the usual bacJc transfer from the Boltzmann v ib ra tion a l le v e l o f the acceptor excited e lectron ic state to the donor is hardly probable fo r these systema. !?he low 11ml r of tne tran sfe r p robab ility from PGnl matrix molecules to the acceptor may be estimated by Forarer*-GaIani,n theory Г4*5] taking into account tne distance between molecules in aggregate !.■:> IC and using donor cnar&cxeristics l is t e d in Table 1* Band overlap fa c to rs fo r the donor-acceptor paxirs in­ vestigated were taken from [o ] • Taking into account the high degree of molecular ordering in tne complex ve took the value of the orientation fa c to r ecus. :Г'^ =с4. Thus, the corresponding value o f was calcu- *T* ^ -t- »1 la ted as F^ ^ -^«5 * lO"*^ sec” "^ * The energy m igration pro­ b a b ility Ft may be estimated from CD spectra of POhl long-wavelength aggregates. Bear to symmetrical tne sp lit t in g in CD spectra of these aggregates permits us to estimate the exciton in teraction energy xn sucn which corresponds to an "excxta- sec. j?-rom systems 'm' tion tran sfe r time" in matrix = 8*IG these d£?fca the p robab ility of energy tran sfe r along the donor component of complex was found to be p - cr 433 дз«= 1,2 The estimates c ited are jlxl a good agreement witii analogous values we oOtalned d i r e c t l y from escperimental data on investigation tiae energy transfer from donors witn low luminescence e ffic iency© Sued Joigii Taiues cf excitation tran sfe r p robab ili­ t ie s peimit us to explain the discovering o f energy migration fo r systems in wJaioii tiie overlap of donor Ішпіпезсехюе spectra and acceptor absoirption i s ex— tremelv small CPCm <^БСЫ)» But in contrast to tiie other acceotors (СЫ , . OuPr.; ore e ffic ien cy c-r excitation trapping os tne sm allest fo r system Plr.1 BChi due to osd concmt"ons fo r tns resonance d ipo le - iip o le in tc i’action between tran sition dipole moments of ionor and acceptor molecules. Probably tne la t te r fa c to r is tn& pnysicai reason of tne weak influence cf BGhl molecules on aosorption and CP speetz-a o f PGh.1 in mi xed aggregates in comparison Witn the other acceptor£ it is jcnown that moxecules of GuPn do nc: possess measurable fluorescence because of the presence of ur.- 7aired d -e lectron in central Cu ion resu ltin g in tne- proDability aeterio ration of iatersystem crossing into the t r ip le t state i_7i* Th.erefore.it may be supposes that the greatest quenciiing action of GuPh in compari­ son with Chi and PdPh is connected not only witn eno-r- gy transfer out with tne perturbing action of Cu ion of CtiPh molecule on nonradiative transxtion orobabiid - t ies in PChl molecules surrounding acceptor mo_i.eeule xn mixed accocLate. In order to checK thxs aasumpt±c:i the luminescence auenening of с»~іЧ aggregate by Gu-*prc>— topneopnytin CCuPPn) in mixed aggregatea was in v e s t i- 434 ІЧяйдгэ 5ш ■ Lmnlneacence геіатітв quantuin jricLd ci {JźlL ав іГшісххэп ot CuPPh. cozicen-crardod іл діхасі aggregates. С^-|» І 0 ^ ^/l=.const gated. Acćor-lx33g to the energetxc poaxtxoc, of excite;: state le v e ls CuPPn is the poten tia l energy donor ic r dial. ? ig .5 snovsB tnat appreciable ChJL fluorescence xuencnxng by CuPPn molecules i s obeervea only under equxmoiar concentrations of these pxgments xn mixed complex, iffhen the ra t io between Ghl and CuPPh molecules X3 ecual to ІОООгІ no quencnine ef fect x& lound while xn tne case of PChl -► GuPh p a ir under tne same ra t ic of oomponent concentrations the PChl luminescence quenching majces up 20% (P ig «3 )* Table I ehoire that the excitation deactivation p ro b a b ility In Guph molecule i s equal to 10^^ аес”""^ while for Qhl and PdPh these values are considerably 435 JTQ «и» Т ТУsm aller CIO sec and 10 sec'"*^, correspondingly,- In tbat oaee so f a r as tiie e n e i^ m igration probabi­ l i t i e s along donor m atrix (F j ) and d ire c t ly to tne acceptor component (P 2 ) mixed associate are com­ parable ШІШ tne v ib ra t io n a l re laxation p robab ility in complex organic molecules (W-^IO - 10 sec the low trapping e ffic ien cy o f РСШ. excitation by Chi and PdFh molecules in comparison with CuPn may be explained by the existence o f the bacX befor-re«^ laxation energy tran s fe r from Ghl and PdPh to PCShl* Such back enezgy m igration must take place before or during the process o f Boltzmann d is tr ibu tio n of v ibrationa l energy in acceptor excitaa exec tronie sta te . 2he energy tran s fe r from PGhl to GuPh is essen :;iall.Y ir re y e rs ib le due to the high excitation deac- vivation p robab ility in the acceptor. Otar use o f a r t i f i c i a l mixed aggregates of ch ioro- pnyil and i t s deriYatiyee with varied concentration of acceptoza i s the necessary lin k to account fo r tne behavior of photosynthetic systems, in wnich trapping esxiitatlon energy out of a la rge a iray ox pigment mo­ lecu les I s an e ssen tia l step in th e ir function. AcknoifleqjBBenta. іШе authors wish to tnank Miss :a. y.Sarahevskaya and Miss N.B.Lyalkova fo r th e ir sK iLCull help In the prepisratioa a»?d p u rifica tio n s o f pigments. 436 References !• AePoboaeVs E*I<>Zenkevitelię GoPeGiirinovitcn, Jourael Prikladnoy Spectroscop ii* 262, 1973. 2* E.I^.Zenke'Titcii, АоР.Ьоает, GoPeGurinovltoii, Moleeulyaraaya B io log iya , 516, 1975. 3* S^I^ZenkeTltcb., GoA«KochubeeT», А«РоЬоавт, G«P» GuxlnoTitcli, MoleeuXvsEsi^a B io log iya , 1977, (to b@ published )* 4* fbePoreter, Рійогешгепг oxganiacher yerbindungen, ?andexihoeck und Ruprecht in Gottingen, 1951# 5* MoD.Gslsnin, Eeudy pyaicheakogo In s t itu ta Akade=- ШІІ Hank SSSR, 12, 3 , I960* 6* S*X*Zenkevltoh, AoPebosey, G.PeGurlnoyitcii, Hie Energy M igration Between Pigments o f Plant Hiotosynthetic Apparatus «Preprint of the In stitu te of Physics, Academy of Sciences o f the BSSR, Minsk I97X, 7ф ЕвЬеАке, MoGouterman, S ieoret* Шііш* Acta (B e r i . ) , І ^ , 20, 1969# t