On the basis of experiments at 275 GHz, we reconsider the dependence of the continuous-wave EPR spectra of nitroxide spin-labeled protein sites in sensory- and bacteriorhodopsin on the micro-environment. The high magnetic field provides the resolution necessary to disentangle the effects of hydrogen bonding and polarity. In the gxx region of the 275 GHz EPR spectrum, bands are resolved that derive from spin-label populations carrying no, one or two hydrogen bonds. The gxx value of each population varies hardly from site to site, significantly less than deduced previously from studies at lower microwave frequencies. The fractions of the populations vary strongly, which provides a consistent description of the variation of the average gxx and the average nitrogen-hyperfine interaction Azz from site to site. These variations reflect the difference in the proticity of the micro-environment, and differences in polarity contribute marginally. Concomitant W-band ELDOR-detected NMR experiments on the corresponding nitroxide in perdeuterated water resolve population-specific nitrogen-hyperfine bands, which underlies the interpretation for the proteins.

The combination of high-field electron paramagnetic resonance (EPR) with site-directed spin labeling (SDSL) techniques employing nitroxide radicals has turned out to be particularly powerful in revealing subtle changes of the polarity and proticity profiles in proteins enbedded in membranes. This information can be obtained by orientation-selective high-field EPR resolving principal components of the nitroxide Zeeman (g) and hyperfine ( A) tensors of the spin labels attached to specific molecular sites. In contrast to the g- and A-tensors, the (14)N ( I = 1) quadrupole interaction tensor of the nitroxide spin label has not been exploited in EPR for probing effects of the microenvironment of functional protein sites. In this work it is shown that the W-band (95 GHz) high-field electron spin echo envelope modulation (ESEEM) method is well suited for determining with high accuracy the (14)N quadrupole tensor principal components of a nitroxide spin label in disordered frozen solution. By W-band ESEEM the quadrupole components of a five-ring pyrroline-type nitroxide radical in glassy ortho-terphenyl and glycerol solutions have been determined. This radical is the headgroup of the MTS spin label widely used in SDSL protein studies. By DFT calulations and W-band ESEEM experiments it is demonstrated that the Q(yy) value is especially sensitive to the proticity and polarity of the nitroxide environment in H-bonding and nonbonding situations. The quadrupole tensor is shown to be rather insensitive to structural variations of the nitroxide label itself. When using Q(yy) as a testing probe of the environment, its ruggedness toward temperature changes represents an important advantage over the g xx and A(zz) parameters which are usually employed for probing matrix effects on the spin labeled molecular site. Thus, beyond measurenments of g xx and A(zz) of spin labeled protein sites in disordered solids, W-band high-field ESEEM studies of (14)N quadrupole interactions open a new avenue to reliably probe subtle environmental effects on the electronic structure. This is a significant step forward on the way to differentiate between effects from matrix polarity and hydrogen-bond formation.

Distance and relative orientation of functional groups within protein domains and their changes during chemical reactions determine the efficiency of biological processes. In this work on disordered solid-state electron-transfer proteins, it is demonstrated that the combination of pulsed high-field EPR spectroscopy at the W band (95 GHz, 3.4 T) with its extensions to PELDOR ( pulsed electron-electron double resonance) and RIDME (relaxation-induced dipolar modulation enhancement) offers a powerful tool for obtaining not only information on the electronic structure of the redox partners but also on the three-dimensional structure of radical-pair systems with large interspin distances ( up to about 5 nm). Strategies are discussed both in terms of data collection and data analysis to extract unique solutions for the full radical-pair structure with only a minimum of additional independent structural information. By this novel approach, the three- dimensional structure of laser-flash-induced transient radical pairs P(865)(.+)Q(A)(.-) in frozen-solution reaction centers (RCs) from the photosynthetic bacterium Rhodobacter (Rb.) sphaeroides is solved. The measured positions and relative orientations of the weakly coupled ion radicals P-865(.+) and Q(A)(.-) are compared with those of the precursor cofactors P-865 and Q(A) known from X-ray crystallography. A small but significant reorientation of the reduced ubiquinone Q(A) is revealed and interpreted as being due to the photosynthetic electron transfer. In contrast to the large conformational change of Q(B)(.-) upon light illumination of the RCs, the small light-induced reorientation of Q(A)(.-) had escaped previous attempts to detect structural changes of photosynthetic cofactors upon charge separation. Although small, they still may be of functional importance for optimizing the electronic coupling of the redox partners in bacterial photosynthesis both for the charge-separation and charge-recombination processes.

The spin-polarized EPR spectra at 95 GHz (W-band), 24 GHz (K-band), and 9 GHz (X-band) of the radical pair P{sub 700}{sup {center_dot}+}A{sub 1}{sup {center_dot}-} in highly purified photosystem I particles are presented. The spectra are analyzed to obtain both the magnetic parameters of the radical pair as well as the relative orientation of the two species. From the analysis, the g-tensor of A{sub 1}{sup {center_dot}-} is found to be g{sub xx} = 2.0062, g{sub yy} = 2.0051, and g{sub zz} = 2.0022, and it is shown that A{sub 1} is oriented such that the carbonyl bonds are parallel to the vector joining the centers of P{sub 700}{sup {center_dot}+} and A{sub 1}{sup {center_dot}-}. The anisotropy of the g-tensor is considerably larger than that obtained for chemically reduced phylloquinone in frozen 2-propanol solution. Possible reasons for this difference and their implications for the A{sub 1} binding site are discussed. The relative orientation of P{sub 700}{sup {center_dot}+} and A{sub 1}{sup {center_dot}-} is compared with earlier estimates obtained using less accurate g-values for A{sub 1}{sup {center_dot}-}. A comparison with the spectra of P{sub 865}{sup {center_dot}+}Q{sub A}{sup {center_dot}-} in bacterial reaction centers (bRCs) of Rhodobacter sphaeroides R-26 in which the nonheme iron has been replacedmore » by zinc (Zn-bRCs) allows the structural and magnetic properties of the charge-separated state in the two systems to be compared. 52 refs., 5 figs., 7 tabs.« less

ChemInformVolume 21, Issue 51 Physical Organic Chemistry ChemInform Abstract: Liquid-Phase ESR, ENDOR, and TRIPLE Resonance of Porphycene Anion Radicals J. + SCHLUEPMANN, J. + SCHLUEPMANN Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorM. HUBER, M. HUBER Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorM. TOPOROWICZ, M. TOPOROWICZ Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorM. PLATO, M. PLATO Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorM. + KOECHER, M. + KOECHER Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorE. VOGEL, E. VOGEL Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorH. LEVANON, H. LEVANON Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorK. + MOEBIUS, K. + MOEBIUS Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this author J. + SCHLUEPMANN, J. + SCHLUEPMANN Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorM. HUBER, M. HUBER Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorM. TOPOROWICZ, M. TOPOROWICZ Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorM. PLATO, M. PLATO Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorM. + KOECHER, M. + KOECHER Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorE. VOGEL, E. VOGEL Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorH. LEVANON, H. LEVANON Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this authorK. + MOEBIUS, K. + MOEBIUS Inst. Molekuelphys., FU Berlin, D-1000 Berlin 33Search for more papers by this author First published: December 18, 1990 https://doi.org/10.1002/chin.199051041Read the full textAboutPDF 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. Volume21, Issue51December 18, 1990 RelatedInformation

Chemischer InformationsdienstVolume 14, Issue 7 Physical Organic Chemistry ChemInform Abstract: MULTIPLE MAGNETIC RESONANCE STUDIES ON ORGANIC MOLECULES IN THEIR GROUND AND EXCITED STATES K. + MOEBIUS, K. + MOEBIUSSearch for more papers by this authorW. + FROEHLING, W. + FROEHLINGSearch for more papers by this authorF. LENDZIAN, F. LENDZIANSearch for more papers by this authorW. LUBITZ, W. LUBITZSearch for more papers by this authorM. PLATO, M. PLATOSearch for more papers by this authorC. J. WINSCOM, C. J. WINSCOMSearch for more papers by this author K. + MOEBIUS, K. + MOEBIUSSearch for more papers by this authorW. + FROEHLING, W. + FROEHLINGSearch for more papers by this authorF. LENDZIAN, F. LENDZIANSearch for more papers by this authorW. LUBITZ, W. LUBITZSearch for more papers by this authorM. PLATO, M. PLATOSearch for more papers by this authorC. J. WINSCOM, C. J. WINSCOMSearch for more papers by this author First published: February 15, 1983 https://doi.org/10.1002/chin.198307062Read the full textAboutPDF 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. Volume14, Issue7February 15, 1983 RelatedInformation

AbstractOptimale ENDOR‐Bedingungen (wie Lösungsmitteleigenschaften [Temp., Viskosität], Mikrowellen‐ und rf‐Feldstärken) lassen sich als Funktion von wenigen fundamentalen Kern‐ und/oder Moleküleigenschaften ableiten auf der Grundlage der Freed′schen allgemeinen Relaxationstheorie für Radikale in Lösung.

Chemischer InformationsdienstVolume 11, Issue 14 Physical Organic Chemistry ChemInform Abstract: EVALUATION AND ASSIGNMENT OF PROTON AND NITROGEN HYPERFINE COUPLING CONSTANTS IN THE FREE-RADICAL 1-PICRYL-2,2-DIPHENYLHYDRAZYL. AN NMR, ELECTRON-NUCLEAR DOUBLE RESONANCE, AND ELECTRON-NUCLEAR-NUCLEAR TRIPLE RESONANCE STUDY R. BIEHL, R. BIEHLSearch for more papers by this authorK. + MOEBIUS, K. + MOEBIUSSearch for more papers by this authorS. E. O'CONNOR, S. E. O'CONNORSearch for more papers by this authorR. I. WALTER, R. I. WALTERSearch for more papers by this authorH. ZIMMERMANN, H. ZIMMERMANNSearch for more papers by this author R. BIEHL, R. BIEHLSearch for more papers by this authorK. + MOEBIUS, K. + MOEBIUSSearch for more papers by this authorS. E. O'CONNOR, S. E. O'CONNORSearch for more papers by this authorR. I. WALTER, R. I. WALTERSearch for more papers by this authorH. ZIMMERMANN, H. ZIMMERMANNSearch for more papers by this author First published: April 8, 1980 https://doi.org/10.1002/chin.198014057AboutPDF 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. Volume11, Issue14April 8, 1980 RelatedInformation

Chemischer InformationsdienstVolume 11, Issue 14 Physical Organic Chemistry ChemInform Abstract: ALKALI AND H ENDOR ON AROMATIC ION PAIRS IN SOLUTION. AN INDO APPROACH W. LUBITZ, W. LUBITZSearch for more papers by this authorM. PLATO, M. PLATOSearch for more papers by this authorK. + MOEBIUS, K. + MOEBIUSSearch for more papers by this authorR. BIEHL, R. BIEHLSearch for more papers by this author W. LUBITZ, W. LUBITZSearch for more papers by this authorM. PLATO, M. PLATOSearch for more papers by this authorK. + MOEBIUS, K. + MOEBIUSSearch for more papers by this authorR. BIEHL, R. BIEHLSearch for more papers by this author First published: April 8, 1980 https://doi.org/10.1002/chin.198014054Read the full textAboutPDF 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 onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue14April 8, 1980 RelatedInformation

Chemischer InformationsdienstVolume 10, Issue 9 Physical Organic Chemistry ChemInform Abstract: ENDOR OF ORGANIC TRIPLET- AND QUARTET-STATE MOLECULES IN LIQUID SOLUTIONS AND IN RIGID MEDIA B. KIRSTE, B. KIRSTESearch for more papers by this authorH. VAN WILLIGEN, H. VAN WILLIGENSearch for more papers by this authorH. KURRECK, H. KURRECKSearch for more papers by this authorK. MOEBIUS, K. MOEBIUSSearch for more papers by this authorM. PLATO, M. PLATOSearch for more papers by this authorR. BIEHL, R. BIEHLSearch for more papers by this author B. KIRSTE, B. KIRSTESearch for more papers by this authorH. VAN WILLIGEN, H. VAN WILLIGENSearch for more papers by this authorH. KURRECK, H. KURRECKSearch for more papers by this authorK. MOEBIUS, K. MOEBIUSSearch for more papers by this authorM. PLATO, M. PLATOSearch for more papers by this authorR. BIEHL, R. BIEHLSearch for more papers by this author First published: February 27, 1979 https://doi.org/10.1002/chin.197909048Read the full textAboutPDF 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 onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume10, Issue9February 27, 1979 RelatedInformation

The radical anions of 2-phenylcycl[3.2.2]azine and 6-methyl-2-phenyl-5-azacycl-[3.2.2]azine were prepared by reaction with Na and with Li. Proton hyperfine couplings have been determined using electron-nuclear double resonance (ENDOR) spectroscopy. Assignments of couplings have been made by a combination of four methods: radio frequency coherence effects, calculations of relative ENDOR intensities, computer simulation of the ESR spectra, and MO calculations of π-spin distribution. Successful use of the two first methods has experimentally corroborated the theory of ENDOR line-shapes in the presence of both saturating and non-saturating nuclear radio frequency fields.

Chemischer InformationsdienstVolume 4, Issue 16 Physical Organic Chemistry ChemInform Abstract: UNTERSUCHUNGEN DER PI-SIGMA-DELOKALISATION AN DEN RADIKALIONEN DES RUBRENS MIT ENDOR IN LOESUNG R. BIEHL, R. BIEHLSearch for more papers by this authorK.-P. DINSE, K.-P. DINSESearch for more papers by this authorK. MOEBIUS, K. MOEBIUSSearch for more papers by this authorM. PLATO, M. PLATOSearch for more papers by this authorH. KURRECK, H. KURRECKSearch for more papers by this authorU. MENNENGA, U. MENNENGASearch for more papers by this author R. BIEHL, R. BIEHLSearch for more papers by this authorK.-P. DINSE, K.-P. DINSESearch for more papers by this authorK. MOEBIUS, K. MOEBIUSSearch for more papers by this authorM. PLATO, M. PLATOSearch for more papers by this authorH. KURRECK, H. KURRECKSearch for more papers by this authorU. MENNENGA, U. MENNENGASearch for more papers by this author First published: April 17, 1973 https://doi.org/10.1002/chin.197316067Read the full textAboutPDF 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. Volume4, Issue16April 17, 1973 RelatedInformation

AbstractDie Endor‐Spektren der Verbindungen (I) werden untersucht.