UV Resonance Raman Excitation Research Articles

UV resonance Raman finds peptide bond-Arg side chain electronic interactions.

We measured the UV resonance Raman excitation profiles and Raman depolarization ratios of the arginine (Arg) vibrations of the amino acid monomer as well as Arg in the 21-residue predominantly alanine peptide AAAAA(AAARA)(3)A (AP) between 194 and 218 nm. Excitation within the π → π* peptide bond electronic transitions result in UVRR spectra dominated by amide peptide bond vibrations. The Raman cross sections and excitation profiles indicate that the Arg side chain electronic transitions mix with the AP peptide bond electronic transitions. The Arg Raman bands in AP exhibit Raman excitation profiles similar to those of the amide bands in AP which are conformation specific. These Arg excitation profiles distinctly differ from the Arg monomer. The Raman depolarization ratios of Arg in monomeric solution are quite simple with ρ = 0.33 indicating enhancement by a single electronic transition. In contrast, we see very complex depolarization ratios of Arg in AP that indicate that the Arg residues are resonance enhanced by multiple electronic transitions.

UV resonance Raman investigation of the conformations and lowest energy allowed electronic excited states of tri- and tetraalanine: charge transfer transitions.

UV resonance Raman excitation profiles and Raman depolarization ratios were measured for trialanine and tetraalanine between 198 and 210 nm. Excitation within the pi --> pi* electronic transitions of the peptide bond results in UVRR spectra dominated by amide peptide bond vibrations. In addition to the resonance enhancement of the normal amide vibrations, we find enhancement of the symmetric terminal COO(-) vibration. The Ala(3) UVRR AmIII(3) band frequencies indicate that poly-proline II and 2.5(1) helix conformations and type II turns are present in solution. We also find that the conformation of the interior peptide bond of Ala(4) is predominantly poly-proline-II-like. The Raman excitation profiles of both Ala(3) and Ala(4) reveal a charge transfer electronic transition at 202 nm, where electron transfer occurs from the terminal nonbonding carboxylate orbital to the adjacent peptide bond pi* orbital. Raman depolarization ratio measurements support this assignment. An additional electronic transition is found in Ala(4) at 206 nm.

Reversible Dioxygen Binding to Hemerythrin. 1. Electronic Structures of Deoxy- and Oxyhemerythrin

Studies on the electronic structure of the two physiologically relevant forms of hemerythrin (Hr), i.e., deoxyHr (possessing a hydroxo-bridged diferrous site) and oxyHr (having an oxo-bridged diferric site with a terminal hydroperoxide), are presented and discussed. SQUID magnetic susceptibility data for deoxyHr confirm that the two ferrous ions are weakly antiferromagnetically coupled, J = −14(2) cm-1 (ℋ = −2JS1·S2), indicating that at 300 K the entire manifold of ground-state spin sublevels is available for the reaction with O2. From density functional calculations on deoxyHr, evaluated on the basis of experimental data, the redox active orbital on the five-coordinate iron (Fe2) is favorably oriented for a π-bonding interaction with O2 approaching along the open coordination site of that center, and reorientation of the redox active orbital on the six-coordinate iron (Fe1) for electron transfer to O2 through superexchange with Fe2 is energetically accessible. Analysis of existing spectroscopic data for oxyHr using Heller's time-dependent theory leads to the proposal that the peculiar behavior of the UV resonance Raman excitation profile for the symmetric Fe−O−Fe stretching mode ν(Fe−O) to peak with fairly minor absorption features arises from interference effects between oxo-to-Fe charge-transfer excited states. From density functional calculations on oxyHr and related structures the low frequency of the Fe−oxo stretch is ascribed to the hydrogen bond between the hydroperoxide and the bridging oxide, whereas the small |J| value appears to be due primarily to the strong hydroperoxide → Fe2 π-donor interaction that reduces Fe1 → Fe2 electron delocalization.

Resonance Raman Examination of the Electronic Excited States of Glycylglycine and Other Dipeptides: Observation of a Carboxylate→Amide Charge Transfer Transition

We have examined the UV resonance Raman and the VUV absorption spectra of aqueous glycylglycine and other dipeptides. We observe strong resonance Raman enhancement of the amide I, II, and III bands and the amide CαH bending mode in a manner similar to that we observed previously with excitation within the π→π* transition of N-methylacetamide (Chen, X. G.; Asher, S. A.; Schweitzer-Stenner, R.; Mirkin, N. G.; Krimm, S. J. Am. Chem. Soc. 1995, 117, 2884). However, in addition, we observe strong resonance Raman enhancement of the ca. 1400 cm-1 symmetric COO- stretching vibration, whose 206.5 nm Raman cross section is increased 20-fold compared to that of the carboxylate in sodium acetate, for example. Addition of a methylene spacer between the amide and carboxylate groups causes the resonance Raman enhancement of this symmetric COO- stretch to disappear. The UV resonance Raman excitation profiles, the Raman depolarization ratio dispersion, and the VUV absorption spectra of glycylglycine and other dipeptides d...

Selective UV Resonance Raman Excitation of Vinyl Group Vibrations in an Isomer of Crotyl Chloride

The Raman spectra of cis, trans, and vinyl isomers of crotyl chloride (i.e., cis and trans 1-chloro-2-butene, and 3-chloro-1-butene) have been excited at 218 nm and at 231 nm. With 218-nm excitation the ethylenic mode belonging to the vinyl isomer is only modestly preresonance enhanced. On the other hand, the preresonance enhancement of the peaks belonging to the cis and trans isomers is very noticeable and nearly identical in energy to the peaks of cis and trans polybutadiene, which occur at 1655 and 1665 cm−1, respectively. However, with 231-nm excitation the vinyl-isomer ethylenic mode at 1633 cm−1 is very strongly enhanced, while the cis and trans isomer modes show no corresponding enhancement, but appear to decrease in relative intensity. Responsibility for the strong vinyl group enhancement is assigned to an electronic transition observed as a broad shoulder near 230 nm. By exciting at 231 nm it is possible to detect small amounts of the vinyl isomer in the presence of cis and trans crotyl chloride. Remarkably strong enhancement under 231-nm excitation has been noted as well for the first overtone of the vinyl ethylenic mode observed at 3263 cm−1.

ChemInform Abstract: Tryptophan UV Resonance Raman Excitation Profiles

ChemInformVolume 21, Issue 39 Physical Organic Chemistry ChemInform Abstract: Tryptophan UV Resonance Raman Excitation Profiles J. A. SWEENEY, J. A. SWEENEY Dep. Chem., Univ. Pittsburgh, Pittsburgh, PA 15260, USASearch for more papers by this authorS. A. ASHER, S. A. ASHER Dep. Chem., Univ. Pittsburgh, Pittsburgh, PA 15260, USASearch for more papers by this author J. A. SWEENEY, J. A. SWEENEY Dep. Chem., Univ. Pittsburgh, Pittsburgh, PA 15260, USASearch for more papers by this authorS. A. ASHER, S. A. ASHER Dep. Chem., Univ. Pittsburgh, Pittsburgh, PA 15260, USASearch for more papers by this author First published: September 25, 1990 https://doi.org/10.1002/chin.199039035Read 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, Issue39September 25, 1990 RelatedInformation

Tryptophan UV resonance Raman excitation profiles

We report the first quantitative UV resonance Raman excitation profiles of tryptophan (Trp) in the spectral region between 207 and 250 nm. The Trp excitation profiles ar narrow and show maxima at ca. 224 nm which are 4 nm red-shifted from the ca. 220-nm B b adsorption band maximum. The excitation profile band shapes indicate that Trp can be selectively enhanced in proteins. We see destructive interference between the ca. 195nm B a and the 220-nm B b electronic transitions

Ultraviolet resonance Raman study of the pyrene S4, S3, and S2 excited electronic states

UV resonance Raman excitation within the S2, S3, and S4 π→π* electronic transitions of pyrene results in strong enhancement of totally symmetric ring vibrations. The Raman modes most strongly enhanced within these electronic transitions derive from vibrations exhibiting Franck–Condon vibronic structure in the absorption spectrum. The 1597 cm−1 (b3g) mode shows selective enhancement between the S3 and S4 transitions, and between the S2 and S3 transitions due to Herzberg–Teller coupling between these symmetry-allowed states. The experimentally observed S4 resonance Raman excitation profiles of the totally symmetric pyrene fundamentals agree closely with those calculated using resonance Raman transform theory if non-Condon contributions are included. We see an increased non-Condon contribution with an increasing vibrational frequency, indicating nonadiabatic vibronic interactions. The high incident energy fluxes of the Nd-YAG laser-based excitation source cause saturation of the pyrene Raman intensities since molecular absorption depletes the ground state population. The long-lived S1 singlet excited state bottlenecks relaxation back to the ground electronic state. Formation of pyrene phototransients is also observed with high incident energy fluxes at particular excitation wavelengths.

ChemInform Abstract: UV Resonance Raman Excitation Profiles of Tyrosine: Dependence of Raman Cross Sections on Excited‐State Intermediates

ChemInform Abstract: UV Resonance Raman Excitation Profiles of Tyrosine: Dependence of Raman Cross Sections on Excited‐State Intermediates

High-Repetition-Rate Excimer-Based UV Laser Excitation Source Avoids Saturation in Resonance Raman Measurements of Tyrosinate and Pyrene

UV resonance Raman excitation using low-duty-cycle pulsed lasers such as the Nd:YAG can result in photophysical processes that interfere with Raman spectral studies of ground-state species due to the high incident laser energy fluxes. Depletion of the ground state occurs due to optical absorption and due to the population of intermediate levels which have lifetimes comparable to or longer than the excitation pulse width. In addition, formation of photochemical intermediates can occur. For example, excitation in resonance with the tyrosinate La electronic transition (∼240 nm) results in formation of tyrosyl radicals which deplete the concentration of ground-state tyrosinate molecules; as a result, decreased resonance Raman intensities are observed for vibrational modes of ground-state tyrosinate. For pyrene, excitation in resonance with the S4 electronic transition results in population of the long-lived S1 state via rapid internal conversion. This long-lived state bottlenecks relaxation back to the ground state, thus causing saturation of the ground-state pyrene Raman intensities. Given similar incident average laser powers and focusing conditions, higher-duty-cycle lasers result in decreased saturation. A comparison between a 20-Hz Nd:YAG and a 200-Hz excimer laser-based UV Raman excitation source demonstrates superiority of the excimer in avoiding both Raman saturation and interferences from photochemical transients. For the identical energy flux per pulse, the accompanying tenfold increase in average energy flux for the excimer, over the YAG, results in a dramatic improvement in the spectral signal-to-noise ratios. We report the first measurement of the absolute resonance Raman cross section of pyrene within the S4 transition. The Raman cross section of 48 barns/str measured for the 1632-cm−1 vibration with 240-nm excitation is the largest observed to date.

UV resonance Raman excitation profiles of l‐cystine

AbstractThe UV Raman excitation profiles of l‐cystine have been measured between 220 and 514.5 nm. No enhancement is observed from the lowest energy electronic transition (λmax = 245 nm). The excitation profiles for the SS, CS and CO stretching vibrations are each satisfactorily modeled by standard Albrecht A‐term pre‐resonance expressions which indicate that the Raman intensities derive from a state(s) at ca 170 nm which is probably σ → σ* in character. Selective enhancement of disulfide stretching vibrations in proteins will require excitation in the vacuum UV spectral region.

ChemInform Abstract: UV Resonance Raman Excitation Profiles of the Aromatic Amino Acids.

ChemInform Abstract: UV Resonance Raman Excitation Profiles of the Aromatic Amino Acids.

UV Resonance Raman excitation profiles of the aromatic amino acids

UV Resonance Raman excitation profiles of the aromatic amino acids

UV resonance Raman excitation profile through the 1B2u state of benzene

Mesure de la dispersion de la section efficace differentielle totale de diffusion Raman pour la vibration du cycle entre 600 et 217 nm. Contribution predominante des etats 1 E 1u et peut-etre 1 B 1u