Triplet State Zero-field Splittings Research Articles

Phosphorescence and optically detected magnetic resonance investigation of the binding of the nucleocapsid protein of the human immunodeficiency virus type 1 and related peptides to RNA.

The RNA and DNA complexes of nucleocapsid protein p7.Zn (NCp7.Zn) of the human immunodeficiency virus type 1 (HIV-1) are studied by phosphorescence and optically detected magnetic resonance (ODMR). The single tryptophan, Trp37, which is located on the C-terminal zinc finger domain is used as an intrinsic probe. Reductions in the triplet state zero-field splitting (zfs) D parameter of Trp37 upon complex formation with poly(I) and poly(U) are observed. These results, in conjunction with the phosphorescence red-shifts and triplet state lifetime reductions that are observed, suggest the presence of aromatic stacking interactions between NCp7.Zn and the bases of the RNA polymers. An alteration of the intersystem crossing pattern upon complex formation, in addition to the above mentioned spectroscopic shifts, also is consistent with previously observed tryptophans that undergo stacking interactions with DNA bases [Zang, L.-H., Maki, A.H., Murphy, J.B., & Chase, J.W. (1987) Biophys. J. 52, 867-872. Tsao, D.H.H., Casas-Finet, J.R., Maki, A.H., & Chase, J.W. (1989) Biophys. J. 55, 927-936]. These conclusions support those from a recent ODMR study [Lam, W.-C., Maki, A.H., Casas-Finet, J.R., Erickson, J.W., Sowder, R.C., II, & Henderson, L.E. (1993) FEBS Lett. 328, 45-48] of NCp7.Zn binding to 5-mercurated polyuridylic acid [poly(5-HgU)] in which stacking interactions between the RNA and NCp7.Zn are inferred from the observation of an external heavy atom effect induced on Trp37.(ABSTRACT TRUNCATED AT 250 WORDS)

Perturbation of tryptophan residues by point mutations in bacteriophage T4 lysozyme studied by optical detection of triplet-state magnetic resonance spectroscopy.

We have investigated perturbations of the triplet-state properties of Trp residues in bacteriophage T4 lysozyme caused by point mutations using low-temperature phosphorescence and optical detection of triplet-state magnetic resonance (ODMR) spectroscopy. Five temperature-sensitive mutants have been studied in detail. These include lysozymes with the point mutations Gln-105----Ala, Gln-105----Gly, Gln-105----Glu, Ala-146----Thr, and Trp-126----Gln. Changes in phosphorescence 0,0 band wavelength, intensity, the triplet-state zero-field splitting (ZFS), and the wavelength dependence of the ZFS were detected only from Trp-138 in each mutant. In the case of the Q105A mutation, the perturbations on Trp-138 have been ascribed to the combination of an increase in the polarizability of the environment and to the loss of hydrogen bonding of the enamine nitrogen of indole. For the Q105G mutation, we believe that Q is replaced by a solvent molecule in H bonding, leading to relatively small changes. In the Q105E mutation, the perturbation results largely from the introduction of a charged residue. In the case of the mutation A146T, the perturbation is associated with a local conformational change in which Trp-138 is shifted to a more solvent-exposed location. On the other hand, no significant spectroscopic changes in Trp-126 and Trp-158 were found in any of the mutants, suggesting that the perturbations are probably localized near Trp-138 for the mutations of positions 105 and 146. However, in the mutation W126Q, which occurs approximately 16 A away from Trp-138, significant changes of Trp-138 are detected, suggesting that the effects of this mutation are propagated over large distances.

Optically detected magnetic resonance at high pressures: Crystalline and molecular compression in organic solids

We report on optically detected magnetic resonance experiments conducted at high pressures on an organic mixed crystal system. Changes in triplet state zero-field splittings (ZFS) of the guest molecule monitored as a function of host crystal compression reveal the existence of three compressional regimes. Up to 7 kbar most contraction is intermolecular with little change in intramolecular distances. From 7 to 25 kbar shrinkage of the lattice is proportional to the decrease in molecular volume. Above 25 kbar this linearity no longer holds, and the ZFS suggests a distortion in molecular geometry.

Triplet state zero-field splitting parameters of a carotenoid determined by optically detected magnetic resonance

Triplet state zero-field splitting parameters for a carotenoid as measured by optically detected magnetic resonance in a carotenoporphyrin have been unambiguously determined.

Investigation of the lowest triplet state of the pyrochlorophyllide a—apomyoglobin complex by zero-field optically detected magnetic resonance spectroscopy

The zero-field fluorescence-detected triplet state magnetic resonance spectra have been obtained for the pyrochlorophyllide a—apomyoglobin complex at 2 K. The triplet state zero-field splittings and spin sublevel dynamics were detected on the resolved features of the structured low-temperature fluorescence. Structured fluorescence is not observed for pyrochlorophylide a in an organic matrix under identical conditions. These data are interpreted in terms of the local binding site of the pyrochlorophyllide a chromophore in the protein and the low-temperature conformation of the protein matrix.

Zero-field optically detected magnetic resonance study of the lowest triplet state of magnesium tetraphenylchlorin

The triplet state zero-field splitting parameters and intersystem crossing (ISC) decay constants for the individual triplet spin sublevels of magnesium tetraphenylchlorin and magnesium porphin dissolved in pyridine are presented. Comparison is made with previously published data for other model photosynthetic compounds and chlorophylls.

Triplet-State Electron Spin Resonance of Chlorophyll a and b Molecules and Complexes in PMMA and MTHF. I: Experimental Determination of Fine-Structure and Rate Constants

The triplet state zero-field splittings and the rate constants for the population and depopulation of the triplet spin sublevels have been investigated for chlorophyll a and chlorophyll b in polymethylmethacrylate (PMMA) and methyltetrahydrofurane (MTHF) as a function of the concentration. In PMMA both chlorophyll a and chlorophyll b yielded only one ESR spectrum in the entire range of concentration which could be covered (1.5 × 10-5 - 1 × 10-3 mole/1). In MTHF the results were more complicated. At low concentrations (up to 103 mole/1) only one spectrum was observed, at higher concentrations additional spectra were detectable (all together two for chlorophyll a and five for chlorophyll b at 10-1 mole/1). The assignment of these spectra was facilitated by observing the "triplet resonance-field identity" which connects the resonancefield strengths for the canonical orientations of one particular species. Furthermore, the rate constants for some of these species could be determined.

Investigation of the effect of metal substitution on the triplet state of chlorophyll by optically detected zero-field magnetic resonance

The triplet state zero-field splittings and individual spin sublevel decay rates have been determined for a series of chlorophyll b molecules at 2 K by optically detected zero-field magnetic resonance. By detecting the microwave-induced changes in fluorescence intensity the triplet states of pheophytin b, calcium chlorophyll b, and cadmium chlorophyll b were investigated. A comparison of the triplet intersystem crossing rates in these systems, as well as chlorophyll b derivatives previously published, suggests that the nonradiative deactivation of chlorophylls may be understood by consideration of the effect of metal center interaction on the spin-orbit coupling centered on the pyrrole nitrogens of the chlorophyll ring.

Structural aspects of the reaction center of photosynthetic bacteria calculated from triplet state zero-field splittings

Since the original observation of photoexcited triplet-state EPR spectra in reaction centers of photosynthetic bacteria by Leigh and Dutton [l-4], there has been a considerable amount of magnetic resonance data accumulated on the triplet states of the pigment molecules, reaction centers and whole cell systems of photosynthetic bacteria [5-91. Zero-field splittings have been measured for the photoexcited triplet state of bacteriochlorophyll a and bacteriochlorophyll b and for a variety of bacterial systems containing these molecules [7,9]. The triplet state data for the bacterial systems have been interpreted as arising from a bacteriochlorophyll dimer within the reaction center observed when the primary electron acceptor has been reduced [4,6]. It has been shown in previous work [6,8,10], that the triplet state properties of a dimer in which the triplet excitation is shared between the two molecules may be calculated from the properties of the monomer and the geometry of the pair. Therefore, since the bacteriochlorophyll triplet state properties are known, the photoexcited triplet state can be used as a probe to investigate the orientation of the pigment molecules in the special pair [6] present in the reaction center of bacterial systems. Since the zero-field splittings are available for a large number of bacteria, we have utilized these data, along with the most recently published bacteriochlorophyll pigment zero-field splittings [8,9] to determine the relative orientation of the pair molecules in the reaction center for the presently

Triplet state properties of the benzo[α]pyrene-DNA complex as determined by optically detected zero-field magnetic resonance

The zero-field transitions in the photoexcited triplet state of benzo[α]pyrene bound to DNA have been observed by optical detection of magnetic resonance of 2 K. The transition frequencies individual spin sublevel intersystem crossing rates were measured by monitoring the microwave-induced intensity changes of the triplettriplet absorption at 465.8 nm. The triplet state zero-field splitting and dynamics for the benzo[α]pyrene DNA complex are compared with these properties measured for benzo(α)pyrene in other solvent systems.

Investigation of the structure of the reaction center in photosynthetic systems by optical detection of triplet state magnetic resonance

Properties expected of the triplet state of a pair of interacting pigment molecules in photosynthetic systems are described in terms of the triplet state properties of the monomer pigment. The triplet state zero-field splittings and intersystem crossing rate constants measured in isolated chlorophylls and the same properties measured in vivo are utilized to elucidate the geometry of the eraction center in photosynthetic systems.

ChemInform Abstract: THE TRIPLET STATE OF CHLOROPHYLLS

Chemischer InformationsdienstVolume 7, Issue 36 Physical Organic Chemistry ChemInform Abstract: THE TRIPLET STATE OF CHLOROPHYLLS RICHARD H. CLARKE, RICHARD H. CLARKESearch for more papers by this authorROBERT E. CONNORS, ROBERT E. CONNORSSearch for more papers by this authorTJEERD J. SCHAAFSMA, TJEERD J. SCHAAFSMASearch for more papers by this authorJOOP F. KLEIBEUKER, JOOP F. KLEIBEUKERSearch for more papers by this authorROELOF J. PLATENKAMP, ROELOF J. PLATENKAMPSearch for more papers by this author RICHARD H. CLARKE, RICHARD H. CLARKESearch for more papers by this authorROBERT E. CONNORS, ROBERT E. CONNORSSearch for more papers by this authorTJEERD J. SCHAAFSMA, TJEERD J. SCHAAFSMASearch for more papers by this authorJOOP F. KLEIBEUKER, JOOP F. KLEIBEUKERSearch for more papers by this authorROELOF J. PLATENKAMP, ROELOF J. PLATENKAMPSearch for more papers by this author First published: September 7, 1976 https://doi.org/10.1002/chin.197636037AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume7, Issue36September 7, 1976 RelatedInformation

Investigation of the structure of the reaction center in photosynthetic bacteria by optical detection of triplet state magnetic resonance

Measurements of the triplet state zero-field splitting and intersystem crossing rate constants for isolated bacteriochlorophyll a and for chemically reduced photosynthetic bacteria are utilized to investigate the geometry of the bacteriochlorophyll dimer in the reaction center.

Triplet State Zero-Field Splittings of Some Structurally Related Aromatic Hydrocarbon and Heterocyclic Molecules1

Abstract : The triplet state zero field splitting parameters D and E have been determined from the delta m = plus or minus 1 EPR spectra of the photo-excited triplet states of several structurally related aromatic hydrocarbons and aromatic heterocyclic molecules, using diethyl ether glasses at 77 K. The values of the splitting parameters per cm for the various molecules are as follows: biphenyl D = 0.1092, E = 0.0036; fluorene D = 0.1075, E = 0.0033; carbazole D = 0.1022, E = 0.0066; dibenzofuran D = 0.1071, E = 0.0092; dibenzothiophen D = 0.1130, E = 0.0021. The uncertainties in these numbers are plus or minus 0.2 Mk for D and plus or minus 0.1 Mk for E. Lifetimes of the triplet states were also determined. A discussion of the results in terms of conjugation of the hetero atom with the aromatic rings is given. The results are compared to the published values of D and E for phenanthrene. It is found that biphenyl is a better hydrocarbon model than phenanthrene for the heterocyclics investigated in this report. (Author)