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Homochirality is a generic and unique property of all biochemical life, and the fractional circular polarization of light it induces therefore constitutes a potentially unambiguous biosignature. However, while high-quality circular polarimetric spectra can be easily and quickly obtained in the laboratory, accurate measurements in the field are much more challenging due to large changes in illumination and target movement. In this study, we measured various targets in the field, up to distances of a few kilometers, using the dedicated circular spectropolarimeter TreePol. We show how photosynthetic life can readily be distinguished from abiotic matter. We underline the potential of circular polarization signals as a remotely accessible means to characterize and monitor terrestrial vegetation, for example, for agriculture and forestry. In addition, we discuss the potential of circular polarization for the remote detection of extraterrestrial life.

In the present paper a detailed analysis of high-resolution luminescence spectra of Eu(III)-H(2)O species in frozen aqueous solution (T = 5 K) is presented. From the total luminescence spectra (TLS, excitation vs emission) and the luminescence decay matrixes (time vs emission), fundamental species-selective spectroscopic parameters are determined: excitation wavelength λ(exc), decay time τ, crystal field energy splitting ΔE (crystal field strength parameter N(ν)(B(2q))), crystal field parameters B(20) and B(22), asymmetry ratio r, and point symmetry group. The spectroscopic findings clearly show the presence of two distinct Eu(III) aquo species. Samples prepared with different counterions (Cl(-), ClO(4)(-)) and at different pH values (2 and 5) yielded comparable results. Furthermore, in D(2)O solutions the same two species were found, with similar spectral properties but much longer decay times. On the basis of the spectroscopic analysis, the two species were attributed to 8- and 9-fold coordinated Eu(III) aquo ions.

The solvent plays a decisive role in the photochemistry and photophysics of aromatic ketones. Xanthone (XT) is one such aromatic ketone and its triplet-triplet (T-T) absorption spectra show intriguing solvatochromic behavior. Also, the reactivity of XT towards H-atom abstraction shows an unprecedented decrease in protic solvents relative to aprotic solvents. Therefore, a comprehensive solvatochromic analysis of the triplet-triplet absorption spectra of XT was carried out in conjunction with time dependent density functional theory using the ad hoc explicit solvent model approach. A detailed solvatochromic analysis of the T-T absorption bands of XT suggests that the hydrogen bonding interactions are different in the corresponding triplet excited states. Furthermore, the contributions of non-specific and hydrogen bonding interactions towards differential solvation of the triplet states in protic solvents were found to be of equal magnitude. The frontier molecular orbital and electron density difference analysis of the T1 and T2 states of XT indicates that the charge redistribution in these states leads to intermolecular hydrogen bond strengthening and weakening, respectively, relative to the S0 state. This is further supported by the vertical excitation energy calculations of the XT-methanol supra-molecular complex. The intermolecular hydrogen bonding potential energy curves obtained for this complex in the S0, T1, and T2 states support the model. In summary, we propose that the different hydrogen bonding mechanisms exhibited by the two lowest triplet excited states of XT result in a decreasing role of the nπ* triplet state, and are thus responsible for its reduced reactivity towards H-atom abstraction in protic solvents. [ABSTRACT FROM AUTHOR]

Abstract: Fluorescence line-narrowing spectroscopy (FLNS) is a cryogenic technique that can be used to obtain high-resolution fluorescence spectra. The technique has mainly been used for fingerprint identification. However, this review focuses on the trend to use FLNS for probing purposes: obtaining information on interactions with the local environment or determining conformations. We briefly discuss the basics of FLNS, solute-matrix interactions and important instrumental aspects. We describe examples from various bioanalytical fields: DNA adducts of the aromatic carcinogen benzo[a]pyrene (BP); binding of BP metabolites to monoclonal antibodies or the estrogen receptor; FLNS studies of porphyrin-containing proteins; and, photosynthetic systems. As an illustration from the field of environmental chemistry, we discuss the use of luminescence line-narrowing spectroscopy – a special mode of FLNS – to study the complexation of lanthanides to humic substances. [Copyright &y& Elsevier]

Abstract: In an extended introduction, key aspects of resonance Raman spectroscopy (RRS) such as enhanced sensitivity and selectivity are briefly discussed in comparison with normal RS. The analytical potential is outlined. Then achievements in different fields of research are highlighted in four sections, with emphasis on recent breakthroughs: (1) The use of visible RRS for analyzing carotenoids in biological matrices, for pigments and dyes as dealt with in art and forensics, and for characterizing carbon nanotubes. (2) The use of RRS in the deep UV (excitation below 260nm) in the bioanalytical and life sciences fields, including nucleic acids, proteins and protein–drug interactions. Metalloproteins can be studied by visible RRS in resonance with their chromophoric absorption. (3) Progress in theoretical calculations of RRS excitation profiles and enhancement factors, which ultimately might facilitate analytical RRS. (4) Instrumental and methodological achievements including fiber-optic UV–RRS, coupling of RRS to liquid chromatography and capillary electrophoresis. Sensitivities can approach the single-molecule level with surface-enhanced RRS or tip-enhanced RRS. Last but not least, promising fluorescence background rejection techniques based on time-gated detection will be presented. This review ends with a concluding section on future expectations for RRS, in particular its potential as an analytical technique. [Copyright &y& Elsevier]

Ultraviolet resonance Raman spectroscopy is carried out using a continuous wave frequency-doubled argon ion laser operated at 229, 244, and 257 nm in order to characterize the overtones and combination bands for several classes of organic compounds in liquid solutions. Contrary to what is generally anticipated, for molecules such as pyrene and anthracene, strong overtones and combination bands can show up; it is demonstrated that their intensity depends critically on the applied laser wavelength, lithe excitation wavelength corresponds with a purely electronic transition—this applies to a good approximation for 244-nm excitation in the case of pyrene and for 257-nm excitation in the case of anthracene—mostly fundamental vibrations (up to 1700 cm-1) are observed. Overtones and combination bands are detected but are rather weak. However, if the laser overlaps with the vibronic region—as holds for 229- and 257-nm excitation for pyrene and 244-nm excitation for anthracene—very strong bands are found in the region 1700-3400 cm-1. As illustrated for pyrene at 257 nm, all these bands can be assigned to first overtones or binary combinations of fundamental vibrations. Their intensity distribution can roughly be simulated by multiplying the relative intensities of the fundamental bands. Significant bands can also be found in the region 3400-5000 cm-1, corresponding with second overtones and ternary combinations. It is shown that these findings are not restricted to planar and rigid molecules with high symmetry. Substituted pyrenes exhibit similar effects, and relatively strong overtones are also observed for adenosine monophosphate and for abietic acid. The reasons for these observations are discussed, as well as the potential applicability for analytical purposes. [ABSTRACT FROM AUTHOR]

A new approach for studying antibody--antigen interactions of DNA adducts and metabolites of polycyclic aromatic hydrocarbons (PAHs) is demonstrated in which fluorescence line-narrowing spectroscopy (FLNS) is used. It is based on the fact that in an FLN spectrum the relative intensifies of the line-narrowed bands (that correspond to the excited-state vibrations) are, in general, strongly dependent on the local environment of the fluorophore. Information on the nature of the interactions can be obtained by comparing the FLN spectra of the antigen-antibody complexes to the spectra of the antigen in different types of solvents (H-bonding, aprotic, and π-electron-containing solvent molecules) recorded wider the same conditions. The antigens used were the DNA adduct 7-(benzo[α]pyren-6-yl)guanine (BP-6-N7Gua) and the metabolite (+)-trans-anti-7,8,9,10-benzo[α]pyrenetetrol (BP-tetrol) of benzo[α]pyrene; two monoclonal antibodies (MAbs) have been developed to selectively bind these compounds. It is shown that, for BP-tetrol, H-bonding solvents have a pronounced effect on the FLN spectra. The presence of π electrons in the solvent molecules results in relatively small but still significant changes in the spectra. When BP-tetrol is bound to its MAb, however, neither of these effects is observed; its spectrum is very similar to the one obtained with an aprotic solvent, methylcyclohexane. Therefore, we can conclude that this MAb has an internal binding site in which the interaction with BP-tetrol is of a hydrophobic character. For BP-6-N7Gua, however, there is a strong effect of the presence of π electrons in the solvent molecules. The FLN spectrum of this antigen bound to its MAb is very similar to its spectrum in acetone, indicating that π--π interactions play an important role in the binding. [ABSTRACT FROM AUTHOR]

In column liquid chromatography (LC) coupled to conventional Raman spectroscopy (RS) removal of the spectral background of the eluent is often demanding, because of the strong signals of the organic modifier. A new chemometrical method is proposed, called the eluent background subtraction (EBS) method, which can correct for small shape and intensity differences of the eluent spectra. The variations in the eluent spectra are modelled using principal component analysis (PCA). The PCA loading vectors are subsequently used for eluent background correction of the elution spectra of the analyte. The loading vectors are fitted under these spectra by an asymmetric least-squares method. This method was successfully applied under various experimental conditions and performed much better than conventional background correction methods. Analyte detectability was improved by (weighted) averaging of all elution spectra and smoothing via a p-spline function. [Copyright &y& Elsevier]

High-resolution Shpol''skii spectra (recorded at 10 K in n-octane) of 3-hydroxychromone (3HC) substituted at the 2-position with a furan (3HC-F), a benzofuran (3HC-BF) or a naphthofuran group (3HC-NF) are presented. Being close analogues of 3-hydroxyflavone (3HF), these compounds can undergo excited-state intramolecular proton transfer (ESIPT). Luminescence can occur from the normal N* state (blue) or from the tautomeric T* state (green). Whether blue or green emission is observed is strongly dependent on hydrogen-bonding interactions with the environment. For all three chromones studied, high-resolution emission spectra in the green region (T*→T) were obtained in pure n-octane, showing four sites with distinct emission bands and detailed vibrational structures, whereas no blue emission was detected. Contrary to the spectra published for 3HF, the emission lines were very narrow (line-broadening effects beyond detection) which implies that the ESIPT rate constants are >1012 s−1, at least 25 times lower than for 3HF. In order to study the effects of hydrogen-bonding solvents, four isomers of octanol (1-, 2-, 3- and 4-octanol) were added, forming 1:1 complexes with the 3HC derivatives. For all the combinations considered both blue and additional green emission was observed and in some cases narrow-banded spectra were obtained, mostly in the green. Only for the 3HC-NF/2-octanol complex, narrow-banded emission was found both in the blue and in the green region. It is demonstrated that these emissions come from different configurations of the complex. Possible structures for the two complex species are proposed, supported by semi-empirical calculations on complex formation enthalpies. [Copyright &y& Elsevier]