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[Display omitted] • Ferrochelatases insert ferrous iron in porphyrins in the heme biosynthesis pathway. • The porphyrin proximal ligand is not conserved in the active site of ferrochelatases. • Proximal mutations alter the H-bonds between the porphyrin and the protein. • Effects on the activity are induced by the polarity of the mutated proximal ligand. • The weak coordination by the proximal ligand is essential for substrate and product. Ferrochelatases catalyze the insertion of ferrous iron into the porphyrin during the heme b biosynthesis pathway, which is fundamental for both prokaryotes and eukaryotes. Interestingly, in the active site of ferrochelatases, the proximal ligand coordinating the porphyrin iron of the product is not conserved, and its catalytic role is still unclear. Here we compare the L. monocytogenes bacterial coproporphyrin ferrochelatase native enzyme together with selected variants, where the proximal Tyr residue was replaced by a His (i.e. the most common ligand in heme proteins), a Met or a Phe (as in human and actinobacterial ferrochelatases, respectively), in their Fe(III), Fe(II) and Fe(II)–CO adduct forms. The study of the active site structure and the activity of the proteins in solution has been performed by UV–vis electronic absorption and resonance Raman spectroscopies, biochemical characterization, and classical MD simulations. All the mutations alter the H-bond interactions between the iron porphyrin propionate groups and the protein, and induce effects on the activity, depending on the polarity of the proximal ligand. The overall results confirm that the weak or non-existing coordination of the porphyrin iron by the proximal residue is essential for the binding of the substrate and the release of the final product. [ABSTRACT FROM AUTHOR]

The distinct thermochromism observed in solutions containing N , N -dimethylaniline (DMA) and N , N -diethylaniline (DEA) and SO 2 was investigated by resonance Raman spectroscopy in a wide range of temperatures. The results indicate in addition to the charge transfer (CT) complexes DMA-SO 2 and DEA-SO 2 , the presence of collision complexes involving the CT complexes and excess DMA and DEA molecules. The latter in fact is the chromophore responsible for the long wavelength absorption originating the color. The Raman signature of the collision complex was attributed to the distinct enhancement of a band at 1140 cm − 1 assigned to ν s (SO 2 ), in contrast to the same mode in the 1:1 complex at 1115 cm − 1 . The intensity of such band, assigned to the collision complex is favored at high temperatures and depends on the steric hindrance associated to amines, as well as the SO 2 molar fraction. Quantum chemical calculations based on time-dependent density functional theory (TDDFT) support the proposed interpretation. [ABSTRACT FROM AUTHOR]

In this study, solids of polydiphenylamine (PDPA) synthesized mechanochemically by reaction with bentonite (PDPAOB) were studied using Raman spectroscopy. It was possible to identify the chemical species in the PDPA–bentonite compound. The spectra obtained were compared to the spectra of PDPA prepared chemically by oxidation of DPA with K 2 S 2 O 8 in the solid state, and PDPA produced electrochemically, with the aim of studying the characteristic frequencies of the aromatic segments (DPB), radical cation (DPB + ) and dication (DPB 2+ ) of N,N-diphenylbenzidine (DPB) in the polymer structure of the PDPA. To analyze the segments present, the band characteristic of C C asymmetric stretching of the aromatic ring in the Raman spectra was deconvoluted because of the widening of the band and shifts observed by irradiation at wavelengths of 532 and 785 nm. This procedure showed that there are three distinct contributions in the spectra which facilitate the monitoring of changes in the contributions of the segments in the materials doped with HCl (PDPAOBD) and de-doped with NH 4 OH, (PDPAOBR). [ABSTRACT FROM AUTHOR]

Green [Cu(1,10-phenanthroline) 2 OH 2 ](ClO 4 ) 2 ( 1 ) reacts with yellow elemental sulfur at room temperature in methanol to yield turquoise blue [Cu(1,10-phenanthro-line) 2 (S 8 )](ClO 4 ) 2 ( 2 ). A comparative study of the EPR spectra of 1 and 2 in solid state and in methanol glass indicates that the S 8 unit in 2 is bound to the metal. High level DFT calculations show that the cation in 2 is five coordinate, distorted square pyramidal with S 8 occupying the apical position. The crucial Cu(II)–S bond is around 2.9 Å. Such long Cu(II)–S bonds occur in oxidized plastocyanin where it is considered to be bonding. Presence of a weak Cu–S 8 bond is revealed in the resonance Raman spectra of 2 . Satisfactory matching of the calculated and experimental IR spectra vindicates the theoretically derived structure of the cation in 2 . [ABSTRACT FROM AUTHOR]

Applying time-dependent density functional theory (TDDFT), we study the resonance Raman spectra for the Q and B bands of the meso-tetrakis(3,5-di-tertiarybutylphenyl)-porphyrin (H2TBPP) molecule including both Raman A term (Franck-Condon term) and Raman B term (Herzberg-Teller term) contributions. It is found that Raman B term can be one order of magnitude larger than Raman A term and dominates resonance Raman for the Q band resonance. In comparison with the recent experimental Raman spectra of H2TBPP with incident light frequency 532nm, we predict the absence of 1580cm-1 band in the resonance Raman spectra which agrees well with the experimental results, whereas the previous theoretical calculation using non-resonance strategy failed to do so. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new proposal for the quantitative evaluation of divalent metal ions (M2+) is developed by the use of the competitive resonance Raman (RR)-based method. Upon excitation with light of the appropriate wavelength (532nm), a strong electric field is generated that couples with the resonance of the complex (zincon-M2+), increasing the character signals of these complexes, resulting in sensitive detection. Herein, the RR probe, zincon-M2+ complex that the RR intensity gets lower with the decreasing of the M2+ concentration, which leads to the transformation of the Raman information. As a result, by using the proposed RR-based method, we could find the liner calibration curves of Cu2+ and Ni2+, which show the potential in quantitative evaluation of an unknown sample. In addition, the abundant fingerprint information shows that RR leads to the successful analysis of a blended solution, which contains two ions: Cu2+ and Ni2+. [Copyright &y& Elsevier]

Abstract: FT-Raman and/or FT-IR spectra of 3-amino-2-cyclohexen-1-one (ACyO) in solid state and/or in solvents of water and acetonitrile were obtained. Density functional theory calculations were done to help elucidate the vibrational band assignments. The A-band resonance Raman spectra of ACyO were acquired in water and acetonitrile solvents to examine the excited state structural dynamics and the state-mixing or curve-crossing tuned by solvents. A preliminary resonance Raman intensity analysis using the time-dependent wave-packet theory and simple model was done for ACyO in acetonitrile solvent. Resonance Raman spectroscopic probing of the excited state curve-crossing or state-mixing was proposed. [Copyright &y& Elsevier]

Abstract: The anionic complexes [Cu(L1−)3]1−, L− =dopasemiquinone or L-dopasemiquinone, were prepared and characterized. The complexes are stable in aqueous solution showing intense absorption bands at ca. 605nm for Cu(II)-L-dopasemiquinone and at ca. 595nm for Cu(II)-dopasemiquinone in the UV–vis spectra, that can be assigned to intraligand transitions. Noradrenaline and adrenaline, under the same reaction conditions, did not yield Cu-complexes, despite the bands in the UV region showing that noradrenaline and adrenaline were oxidized during the process. The complexes display a resonance Raman effect, and the most enhanced bands involve ring modes and particularly the νCC+νCO stretching mode at ca. 1384cm−1. The free radical nature of the ligands and the oxidation state of the Cu(II) were confirmed by the EPR spectra that display absorptions assigned to organic radicals with g =2.0005 and g =2.0923, and for Cu(II) with g =2.008 and g =2.0897 for L-dopasemiquinone and dopasemiquinone, respectively. The possibility that dopamine and L-dopa can form stable and aqueous-soluble copper complexes at neutral pH, whereas noradrenaline and adrenaline cannot, may be important in understanding how Cu(II)-dopamine crosses the cellular membrane as proposed in the literature to explain the role of copper in Wilson disease. [Copyright &y& Elsevier]

Abstract: In the present work, the resonance Raman, UV–vis–NIR and scanning electron microscopic (SEM) data of nanorods (about ∼300nm in diameter) and nanofibers (about ∼93nm in diameter) of PANI are presented and compared. The PANI samples were synthesized in aqueous media with dodecybenzenesulfonic acid (DBSA) and β-naphtalenesulfonic acid (β-NSA) as dopants, respectively. The presence of bands at 578, 1400 and 1632cm−1 in the Raman spectra of PANI-NSA and PANI-DBSA shows that the formation of cross-linking structures is a general feature of the PANI chains prepared in micellar media. It is proposed that these structures are responsible for the one-dimensional PANI morphology formation. In addition, the Raman band at 609cm−1 of PANI fibers is correlated with the extended PANI chain conformation. [Copyright &y& Elsevier]

Abstract: An UV–vis, Raman, IR and EPR spectroscopic study was performed for the water soluble complexes of Fe(III), Ni(II), Co(II) and Zn(II) coordinated to dioxolene ligands derived from oxidized dopamine. The complexes were obtained and stabilized at neutral pH by the strong reducing agent sodium thiosulfate. Iron(III) stabilizes the ligand in catecholate form as [Fe(III)(Cat)2]1−, Cat=dopacatecholate, and the divalent metals as dopasemiquinone (SQ): [Ni(SQ)3]1−, [Co(SQ)3]1− and [Zn(SQ)3]1−. The resonance Raman spectra of the solid complexes as [CAT][Ni(SQ)3], [CTA][Co(SQ)3] and [CTA][Zn(SQ)3], CTA is the cetyltrimethylammonium, are very similar to the spectra of the complexes in solution, while the Fe(III) complex is a mixture of two iron complexes, with catecholate or dopasemiquinone ligands. [Copyright &y& Elsevier]

Abstract: The IR, resonance Raman (RR) and electronic spectra of two phenylazonaphthol pigments, LRC Scarlet and 4BL Red, have been measured and assignments of the vibrational and electronic spectra were facilitated by ab initio calculation s at the B3-LYP/DZ level. Vibrational spectra indicate that the major species in the solid state are the hydrazo tautomers. Electronic spectra are in accordance with the nature of the electronic transitions predicted by time-dependent B3-LYP/DZ calculations. [Copyright &y& Elsevier]

Abstract: Quinolones are important gyrase inhibitors. Even though they are used as active agents in many antibiotics, the detailed mechanism of action on a molecular level is so far not known. It is of greatest interest to shed light on this drug–target interaction to provide useful information in the fight against growing resistances and obtain new insights for the development of new powerful drugs. To reach this goal, on a first step it is essential to understand the structural characteristics of the drugs and the effects that are caused by the environment in detail. In this work we report on Raman spectroscopical investigations of a variety of gyrase inhibitors (nalidixic acid, oxolinic acid, cinoxacin, flumequine, norfloxacin, ciprofloxacin, lomefloxacin, ofloxacin, enoxacin, sarafloxacin and moxifloxacin) by means of micro-Raman spectroscopy excited with various excitation wavelengths, both in the off-resonance region (532, 633, 830 and 1064nm) and in the resonance region (resonance Raman spectroscopy at 244, 257 and 275nm). Furthermore DFT calculations were performed to assign the vibrational modes, as well as for an identification of intramolecular hydrogen bonding motifs. The effect of small changes in the drug environment was studied by adding successively small amounts of water until physiological low concentrations of the drugs in aqueous solution were obtained. At these low concentrations resonance Raman spectroscopy proved to be a useful and sensitive technique. Supplementary information was obtained from IR and UV/vis spectroscopy. [Copyright &y& Elsevier]

Abstract: A key process in the development of new drugs is elucidation of the interaction between the drug molecule and the target protein. Such knowledge then makes it possible to make systematic structural modifications of the drug molecule to optimize the interaction. Many analytical techniques can be applied to proteins in solution such as circular dichroism, ultraviolet, and fluorescence spectroscopy but these all have limitations. In this paper, we investigate the feasibility of using relatively simple, visible light Raman spectroscopic methods to investigate amino acids and related biopolymers. [Copyright &y& Elsevier]

Abstract: We report here electronic absorption, fluorescence and resonance Raman studies of rhodamine 6G laser dye dispersed in the polymethylcyanoacrylate matrix. In the electronic absorption and fluorescence spectra of dispersed rhodamine 6G, band maxima are red shifted compared to solution. Raman spectra show some new bands. These spectral changes arise due to matrix effect and interaction between rhodamine 6G and the host material involving amine group of rhodamine. [Copyright &y& Elsevier]

A weak visible absorption spectrum of p-benzoquinone (p-BQ) in CS2 due to n-π* singlet–triplet transition was measured. Using the resonance Raman (RR) effect in liquid-core optical fiber (LCOF), we have obtained the 514.5 nm excited RR spectra of p-benzoquinone near 1445 cm-1 and have demonstrated that the new characteristic RR band is attributed to the symmetric C&z.dbnd6;O stretch (νC&z.dbnd6;O) of n-π* singlet–triplet transition of p-BQ. The effect of solution concentration on the RR band was investigated at very low concentrations. The RR peak spreads toward short wavelength side with decreasing solution concentration ranging from 10-7 to 10-11 mol L-1, whereas the blue-shift isn’t obvious when the concentration is, at single molecule level, lower than 10-11 mol L-1. Our result is useful for single molecule detection to some extent. [Copyright &y& Elsevier]

We investigated the complexation of valinomycin (VM) in different solvent environments with the aid of the UVRR spectroscopy. By probing the 206.5 and 229 nm excited Raman spectra, we showed that new bands are observed around 1700 and 1290 cm-1. We assigned the 1700 cm-1 band to the hydrogen bonded ester carbonyl stretching vibration. In a polar solvent, VM–K+ complexation shows significant intensity changes in amide and ester carbonyl stretching region. Because of the small amount of conformational interconversion, complexation has a negligible effect on other band intensities including, the amide III, CαH, and amide II. We also showed the effects of the solvent polarity on the solution conformation of VM. [Copyright &y& Elsevier]

[Display omitted] • Ultraviolet resonance Raman (UVRR) spectroscopy for molecular recognition of peptides/proteins. • Current limitations of UVRR application in real-life binding events in proteins and possible solutions. • UVRR spectroscopy of artificial ligands as selective carboxylate or lysine binders. • Prospects of Kerr gate-based UVRR for suppression of UV-excited fluorescence. Ultraviolet resonance Raman scattering (UVRR) has been frequently used for studying peptide and protein structure and dynamics, while applications in supramolecular chemistry are quite rare. Since UVRR offers the additional advantages of chromophore selectivity and high sensitivity compared with conventional non-resonant Raman scattering, it is ideally suited for label-free probing of relatively small artificial/supramolecular ligands exhibiting electronic resonances in the UV. In this perspective article, we first summarize results of UVRR spectroscopy in supramolecular chemistry in the context of peptide/protein recognition. We focus on selected artificial ligands which were rationally designed as selective carboxylate binders (guanidiniocarbonyl pyrrole, GCP, and guanidiniocarbonyl indole, GCI) and selective lysine binder (molecular tweezer, CLR01), respectively, via a combination of non-covalent interactions involving electrostatics, hydrogen bonding, and hydrophobic effects/van der Waals forces. Current limitations of applying UVRR as a universally applicable method for label-free and site-specific probing of molecular recognition between supramolecular ligands and proteins are highlighted. We then propose solutions to overcome these limitations for transforming UVRR spectroscopy into a generic tool in supramolecular chemistry on proteins, with an emphasis on mono- and multivalent GCP- and GCI-based ligands. Finally, we outline specific cases of supramolecular ligands such as molecular tweezers where alternative approaches such as laser-based mid-IR spectroscopy are required since UVRR can intrinsically not provide the required molecular information. [ABSTRACT FROM AUTHOR]

• A versatile ultraviolet resonance Raman spectroscopy setup. • Continuously tunable picosecond pulsed laser excitation source in 210–2600 nm range. • Triple stage-OPA based excitation source providing <15 cm−1 linewidth pulses. • UVRR excitation profile of artificial supramolecular ligand guanidiniocarbonyl pyrrole, GCP. We present a UVRR spectroscopy setup which is equipped with a picosecond pulsed laser excitation source continuously tunable in the 210–2600 nm wavelength range. This laser source is based on a three-stage optical parametric amplifier (OPA) pumped by a bandwidth-compressed second harmonic output of an amplified Yb:KGW laser. It provides <15 cm−1 linewidth pulses below 270 nm, which is sufficient for resolving Raman lines of samples in condensed phase studies. For demonstrating the capability of this tunable setup for UVRR spectroscopy we present its application to the artificial ligand guanidiniocarbonyl pyrrole (GCP), a carboxylate binder used in peptide and protein recognition. A UVRR excitation study in the range 244–310 nm was performed for identifying the optimum laser excitation wavelength for UVRR spectroscopy of this ligand (λ max = 298 nm) at submillimolar concentrations (400 µM) in aqueous solution. The optimum UVRR spectrum is observed for laser excitation with λ exc = 266 nm. Only in the relatively narrow range of λ exc = 266–275 nm UVRR spectra with a sufficiently high signal-to-noise ratio and without severe interference from autofluorescence (AF) were detectable. At longer excitation wavelengths the UVRR signal is masked by AF. At shorter excitation wavelengths the UVRR spectrum is sufficiently separated from the AF, but the resonance enhancement is not sufficient. The presented tunable UVRR setup provides the flexibility to also identify optimum conditions for other supramolecular ligands for peptide/protein recognition. [ABSTRACT FROM AUTHOR]

Using quantum chemistry computations TDDFT//B3LYP/6-31G(d), we study resonance Raman spectra of the Q band for meso-tetrakis(3,5-di-tertiarybutylphenyl)-porphyrin (H 2 TBPP) molecule due to the Franck-Condon and non-Condon mechanisms including the Herzberg-Teller and second-order Herzberg-Teller terms. Generally, the Herzberg-Teller terms are large. However, for some vibrational modes, the second-order Herzberg-Teller terms are the strongest and dominate resonance Raman spectra, which may also impact on fluorescence and absorption spectra. Hence, the Taylor expansion of the electric dipole transition moment with respect to the normal coordinates at the equilibrium structure of the ground electronic state may not converge for H 2 TBPP. A method to solve this problem is suggested. Unlabelled Image • Raman A, B, C and D terms are investigated for resonance Raman of H 2 TBPP. • Raman D term predominates for some vibrational modes. • A method of solving the large D term problem is suggested. [ABSTRACT FROM AUTHOR]

β-carotene, an important biomolecule from the carotenoid family, plays a vital role in biosystem, the characteristic features of electronic and vibrational spectra will shed light on its photophysical properties. Here, in-situ high pressure Raman spectra of β-carotene are measured up to 26 GPa. Two possible phase transitions are identified at about 7 GPa and 14 GPa, respectively, through analysis of the frequency-pressure relationships. In order to clarify the intensity changes of Raman bands, high pressure UV–Vis absorption measurements of β-carotene are conducted. Besides resonance Raman enhancement effect, a new mechanism, fluorescence enhancement of normal Raman scattering, is proposed, which provides new methods and approaches for Raman spectroscopy. Unlabelled Image • In-situ high pressure Raman spectra of β-carotene have been measured up to 26 Gpa. • Two possible phase transitions are detected at about 7 Gpa and 14 Gpa from the frequency-pressure relationships. • High pressure UV–Vis absorption spectra of β-carotene crystal are obtained for the first time. • A new mechanism, fluorescence enhancement of normal Raman scattering, is proposed. [ABSTRACT FROM AUTHOR]