Monolayer study of plastoquinones, α-tocopherol quinone, their hydroquinone forms and their interaction with monogalactosyldiacylglycerol. Charge-transfer complexes in a mixed monolayer

TY - JOUR

T1 - Monolayer study of plastoquinones, α-tocopherol quinone, their hydroquinone forms and their interaction with monogalactosyldiacylglycerol. Charge-transfer complexes in a mixed monolayer

AU - Kruk, Jerzy

AU - Strzałka, Kazimierz

AU - Leblanc, Roger

PY - 1992/11/23

Y1 - 1992/11/23

N2 - The surface pressure-area isotherms of pure plastoquinone-9 (PQ-9), plastoquinone-3 (PQ-3), α-tocopherol quinone (α-TQ), their reduced (hydroquinone) forms and mixtures of these molecules with monogalactosyldiacylglycerol (MGDG) have been studied by a monolayer technique. The collapse pressures of all hydroquinones (QH2) were higher than those of the corresponding quinones (Q), the difference being highest between PQ-9 and PQH2-9. The limiting molecular areas of hydroquinones were higher than those of the corresponding quinones except for α-TQH2. All Q-QH2 mixtures showed miscibility throughout the whole range of the components' ratios. There was no deviation from the addivitiy rule observed for any of the Q-QH2 mixture, as well as for the mixtures of MGDG with PQ-3, PQH2-9, α-TQ and α-TQH2. On the other hand, PQ-9/MGDG and PQH2-3/MGDG mixtures showed positive and negative deviations, respectively. All the isotherms of Q-MGDG and QH2-MGDG mixtures showed a kink point above the collapse pressure of the Q or QH2 examined, indicating that with the increase in surface pressure, Q or QH2 were gradually squeezed out from the monolayer. The percent content of Q and QH2 in the monolayer as a function of surface pressure was also calculated. The hydroquinones were more difficult to remove from monolayers than the corresponding quinones, and among the investigated quinones, PQ-9 was most easily and α-TQ most difficultly squeezed out. The surface pressure-are isotherms of the three-component mixtures of PQ-9/PQH2-9/MGDG showed a shift to lower molecular areas in comparison with the corresponding two-component mixtures, especially at higher surface pressures. This indicates that the presence of PQ-9 lowered the PQH2-9 content in the monolayer, especially at higher pressures, which was explained by charge-transfer complex formation upon interaction of PQ-9 with PQH2-9. The comparison of surface potential-area isotherms of PQ-9/PQH2-9/MGDG mixtures with those of the corresponding binary mixtures also suggest charge-transfer complex formation upon interaction of PQ-9 content in the monolayer, especially at quinones and quinols in the thylakoid membrane and significance of charge-transfer interactions in functioning of PQ-9 has been discussed.

AB - The surface pressure-area isotherms of pure plastoquinone-9 (PQ-9), plastoquinone-3 (PQ-3), α-tocopherol quinone (α-TQ), their reduced (hydroquinone) forms and mixtures of these molecules with monogalactosyldiacylglycerol (MGDG) have been studied by a monolayer technique. The collapse pressures of all hydroquinones (QH2) were higher than those of the corresponding quinones (Q), the difference being highest between PQ-9 and PQH2-9. The limiting molecular areas of hydroquinones were higher than those of the corresponding quinones except for α-TQH2. All Q-QH2 mixtures showed miscibility throughout the whole range of the components' ratios. There was no deviation from the addivitiy rule observed for any of the Q-QH2 mixture, as well as for the mixtures of MGDG with PQ-3, PQH2-9, α-TQ and α-TQH2. On the other hand, PQ-9/MGDG and PQH2-3/MGDG mixtures showed positive and negative deviations, respectively. All the isotherms of Q-MGDG and QH2-MGDG mixtures showed a kink point above the collapse pressure of the Q or QH2 examined, indicating that with the increase in surface pressure, Q or QH2 were gradually squeezed out from the monolayer. The percent content of Q and QH2 in the monolayer as a function of surface pressure was also calculated. The hydroquinones were more difficult to remove from monolayers than the corresponding quinones, and among the investigated quinones, PQ-9 was most easily and α-TQ most difficultly squeezed out. The surface pressure-are isotherms of the three-component mixtures of PQ-9/PQH2-9/MGDG showed a shift to lower molecular areas in comparison with the corresponding two-component mixtures, especially at higher surface pressures. This indicates that the presence of PQ-9 lowered the PQH2-9 content in the monolayer, especially at higher pressures, which was explained by charge-transfer complex formation upon interaction of PQ-9 with PQH2-9. The comparison of surface potential-area isotherms of PQ-9/PQH2-9/MGDG mixtures with those of the corresponding binary mixtures also suggest charge-transfer complex formation upon interaction of PQ-9 content in the monolayer, especially at quinones and quinols in the thylakoid membrane and significance of charge-transfer interactions in functioning of PQ-9 has been discussed.

KW - Charge-transfer complex

KW - Monogalactosyldiacylglycerol

KW - Monolayer

KW - Plastoquinone

KW - α-Tocopherol quinone

UR - http://www.scopus.com/inward/record.url?scp=0026453479&partnerID=8YFLogxK

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U2 - 10.1016/0005-2736(92)90248-K

DO - 10.1016/0005-2736(92)90248-K

M3 - Article

C2 - 1420266

AN - SCOPUS:0026453479

VL - 1112

SP - 19

EP - 26

JO - Biochimica et Biophysica Acta - Biomembranes

JF - Biochimica et Biophysica Acta - Biomembranes

SN - 0005-2736

IS - 1

ER -