Solvent Effects on the Excited-State Processes of Protochlorophyllide: A Femtosecond Time-Resolved Absorption Study

The excited-state dynamics of protochlorophyllide a, a porphyrin-like compound and, as substrate of the NADPH/protochlorophyllide oxidoreductase, a precursor of chlorophyll biosynthesis, is studied by femtosecond absorption spectroscopy in a variety of solvents, which were chosen to mimic different environmental conditions in the oxidoreductase complex. In the polar solvents methanol and acetonitrile, the excited-state dynamics differs significantly from that in the nonpolar solvent cyclohexane. In methanol and acetonitrile, the relaxation dynamics is multiexponential with three distinguishable time scales of 4.0-4.5 ps for vibrational relaxation and vibrational energy redistribution of the initially excited S1 state, 22-27 ps for the formation of an intermediate state, most likely with a charge transfer character, and 200 ps for the decay of this intermediate state back to the ground state. In the nonpolar solvent cyclohexane, only the 4.5 ps relaxational process can be observed, whereas the intermediate intramolecular charge transfer state is not populated any longer. In addition to polarity, solvent viscosity also affects the excited-state processes. Upon increasing the viscosity by adding up to 60% glycerol to a methanolic solution, a deceleration of the 4 and 22 ps decay rates from the values in pure methanol is found. Apparently not only vibrational cooling of the S1 excited state is slowed in the more viscous surrounding, but the formation rate of the intramolecular charge transfer state is also reduced, suggesting that nuclear motions along a reaction coordinate are involved in the charge transfer. The results of the present study further specify the model of the excited-state dynamics in protochlorophyllide a as recently suggested (Chem. Phys. Lett. 2004, 397, 110).

Characterization of bacterial growth and the influence of antibiotics by means of UV resonance Raman spectroscopy

In this work we monitor the bacterial growth of a Bacillus pumilus batch culture by means of UV resonance Raman spectroscopy. Excitation with a wavelength of 244 nm especially enhances the Raman scattering of the aromatic amino acids and the nucleic acid bases and therefore is a good method to track the metabolic changes that occur during bacterial growth. Furthermore, a drug from the fluoroquinolone group is added to the bacterial suspension at the beginning of the exponential growth phase. With the help of chemometrical methods such as hierarchical cluster analysis (HCA) and principal component analysis (PCA) it is possible to visualize the small changes that occur in the UV resonance Raman spectra due to the interaction of the drug with its biological targets DNA and the enzyme gyrase within the bacterial cell.

UV-resonance Raman spectroscopic study of human plasma of healthy donors and patients with thrombotic microangiopathy

Various diseases shift the composition of human plasma; hence, the relative quantification of plasma constituents offers the opportunity to use the dynamic and complex composition of plasma to gain information on novel diagnostic and prognostic factors. Since plasma contains, besides water, mostly proteins, UV-resonance Raman spectroscopy (UVRR) seems to be a suitable method for investigating plasma. With this method the signals of aromatic amino acids and proteins are selectively enhanced. In this study an UV-resonance Raman approach was used for the investigation of human plasma of healthy volunteers and patients with thrombotic microangiopathy. For comparison, selected plasma components were analyzed for a more detailed characterization of cryoprecipitates from human plasma.

Classification of lactic acid bacteria with UV-resonance Raman spectroscopy

UV-resonance Raman spectroscopy is applied as a method for the identification of lactic acid bacteria from yogurt. Eight different strains of bacteria from Lactobacillus acidophilus, L. delbrueckii ssp. bulgaricus, and Streptococcus thermophilus were investigated. At an excitation wavelength of 244 nm signals from nucleic acids and proteins are selectively enhanced. Classification was accomplished using different chemometric methods. In a first attempt, the unsupervised methods hierarchical cluster analysis and principal component analysis were applied to investigate natural grouping in the data. In a second step the spectra were analyzed using several supervised methods: K-nearest neighbor classifier, nearest mean classifier, linear discriminant analysis, and support vector machines.

Identification of single eukaryotic cells with micro-Raman spectroscopy

For a fast identification of eukaryotic cells such as yeast species without a cultivation step it should be possible to perform the investigation on only one single cell. Since yeasts as eukaryotes are heterogeneous and their Raman spectra are therefore dependent on the measuring position, one Raman spectra is not representative of the whole cell. In this contribution we demonstrate the application of average Raman spectra of a line scan over single yeast cells. These average spectra are used for classification with the help of a support vector machine.

Vibrational spectroscopic studies to acquire a quality control method of Eucalyptus essential oils

This article presents a novel and original approach to analyze in situ the main components of Eucalyptus oil by means of Raman spectroscopy. The obtained two-dimensional Raman maps demonstrate a unique possibility to study the essential oil distribution in the intact plant tissue. Additionally, Fourier Transform (FT)-Raman and attenuated total reflection (ATR)-IR spectra of essential oils isolated from several Eucalyptus species by hydrodistillation are presented. Density Functional Theory (DFT) calculations were performed in order to interpret the spectra of the essential oils of the Eucalyptus species. It is shown that the main components of the essential oils can be recognized by both vibrational spectroscopic techniques using the spectral information of the pure terpenoids. Spectroscopic analysis is based on the key bands of the individual volatile substances and therefore allows one to discriminate different essential oil profiles of several Eucalyptus species. It has been found that the presented spectroscopic data correlate very well with those obtained by gas chromatography (GC) analysis. All these investigations are helpful tools to generate a fast and easy method to control the quality of the essential oils with vibrational spectroscopic techniques in combination with DFT calculations.

Adsorption of 6-mercaptopurine and 6-mercaptopurine-ribosideon silver colloid: A pH-dependent surface-enhanced Raman spectroscopy and density functional theory study. II. 6-mercaptopurine-riboside

Surface-enhanced Raman spectroscopy (SERS) has been applied to characterize the interaction of 6-mercaptopurine-ribose (6MPR), an active drug used in chemotherapy of acute lymphoblastic leukemia, with a model biological substrate at therapeutic concentrations and as function of the pH value. Therefore, a detailed vibrational analysis of crystalline and solvated (6MPR) based on Density Functional Theory (DFT) calculations of the thion and thiol tautomers has been performed. 6MPR adopts the thion tautomeric form in the polycrystalline state. The SERS spectra of 6MPR and 6-mercaptopurine (6MP) recorded on silver colloid provided evidence that the ribose derivative shows different adsorption behavior compared with the free base. Under acidic conditions, the adsorption of 6MPR on the metal surface via the N7 and possibly S atoms was proposed to have a perpendicular orientation, while 6MP is probably adsorbed through the N9 and N3 atoms. Under basic conditions both molecules are adsorbed through the N1 and possibly S atoms, but 6MP has a more tilted orientation on the silver colloidal surface while 6MPR adopts a perpendicular orientation. The reorientation of the 6MPR molecule on the surface starts at pH 8 while in the case of 6MP the reorientation starts around pH 6. Under basic conditions, the presence of the anionic molecular species for both molecules is suggested. The deprotonation of 6MP is completed at pH 8 while the deprotonation of the riboside is finished at pH 10. For low drug concentrations under neutral conditions and for pH values 8 and 9, 6MPR interacts with the substrate through both N7 and N1 atoms, possibly forming two differently adsorbed species, while for 6MP only one species adsorbed via N1 was evidenced.

Vibrational spectroscopic characterization of fluoroquinolones

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 1064 nm) and in the resonance region (resonance Raman spectroscopy at 244, 257 and 275 nm). 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.

On the way to a quality control of the essential oil of fennel by means of Raman spectroscopy

Essential oils are one of the most valuable natural products. The price of special essential oils that can be purchased on the market strongly depends on the quality of the product. The quality, which depends on the quantitative and qualitative variation of different monoterpenes, varies with respect of the origin and the harvesting period. This contribution reports on a Raman spectroscopic study on the essential oil occurring in fennel. Cross-sections of fennel seed were investigated by use of Raman spectroscopy and Raman mapping to localize the essential oil and to analyze its chemical composition directly in the plant. Furthermore the practicability of a home-built mobile transportable Raman spectrometer to perform on-site measurements was successfully tested.

Micro-Raman spectroscopic identification of bacterial cells of the genus Staphylococcus and dependence on their cultivation conditions

Microbial contamination is not only a medical problem, but also plays a large role in pharmaceutical clean room production and food processing technology. Therefore many techniques were developed to achieve differentiation and identification of microorganisms. Among these methods vibrational spectroscopic techniques (IR, Raman and SERS) are useful tools because of their rapidity and sensitivity. Recently we have shown that micro-Raman spectroscopy in combination with a support vector machine is an extremely capable approach for a fast and reliable, non-destructive online identification of single bacteria belonging to different genera. In order to simulate different environmental conditions we analyzed in this contribution different Staphylococcus strains with varying cultivation conditions in order to evaluate our method with a reliable dataset. First, micro-Raman spectra of the bulk material and single bacterial cells that were grown under the same conditions were recorded and used separately for a distinct chemotaxonomic classification of the strains. Furthermore Raman spectra were recorded from single bacterial cells that were cultured under various conditions to study the influence of cultivation on the discrimination ability. This dataset was analyzed both with a hierarchical cluster analysis (HCA) and a support vector machine (SVM).

Quality control ofHarpagophytum procumbensand its related phytopharmaceutical products by means of NIR-FT-Raman spectroscopy

NIR-FT-Raman spectroscopy was used for identification and quantification of harpagoside in secondary roots of Harpagophytum procumbens as well as in related phytopharmaceutical products, e.g., ethanolic extracts and tablets. Applied Raman mappings reveal the spatial distribution of this valuable iridoid glycoside within the different samples. The same technique can be used for quality control purposes beginning from the plant to its final products. Based on the obtained spectral data and reference HPLC values of harpagoside, a reliable multivariate calibration model was developed.

Identification of Biotic and Abiotic Particles by Using a Combination of Optical Tweezers and In Situ Raman Spectroscopy

A highly versatile setup, which introduces an optical gradient trap into a Raman spectrometer, is presented. The particular configuration, which consists of two lasers, makes trapping independent from the Raman excitation laser and allows a separate adjustment of the trapping and excitation wavelengths. Thus, the excitation wavelength can be chosen according to the needs of the application. We describe the successful application of an optical gradient trap on transparent as well as on reflective, metal-coated microparticles. Raman spectra were recorded from optically trapped polystyrene beads and from single biological cells (e.g., erythrocytes, yeast cells). Also, metal-coated microparticles were trapped and used as surface enhanced Raman spectroscopy (SERS) substrates for tests on yeast cells. Furthermore, the optical gradient trap was combined with a SERS fiber probe. Raman spectra were recorded from trapped red blood cells using the SERS fiber probe for excitation.

In situ Raman investigation of single lipid droplets in the water-conducting xylem of four woody plant species

A micro-Raman spectroscopy approach was used for the direct in situ characterization of lipid bodies in the water-conducting branch xylem of an African resurrection plant and three deciduous European tree species. Because of average diameters of at least 1 microm, the lipid bodies of all investigated species proved to be easily accessible by this technique. All vesicle-forming xylem lipids were identified as fatty acid esters, which may correspond to phospholipids. Whereas in the resurrection plant saturated lipids were dominant, the lipid bodies of the European trees consisted of highly unsaturated fatty acids. A comparison of the spectra of lipid droplets of lime obtained in situ and from isolated xylem sap revealed slightly different signatures. This finding suggests that micro-Raman spectroscopy may be used to detect modifications of the chemical composition of biological substances as a result of the extraction mode.

The application of a SERS fiber probe for the investigation of sensitive biological samples

The applicability of an etched and silver or gold coated SERS fiber probe in combination with a commercially available laboratory micro-Raman setup or a home built mobile micro-Raman setup to perform on-site field measurements was evaluated and successfully tested on different biological samples. The SERS fiber probe allows one to perform measurements with high spatial resolution. Simultaneously, the laser power used for Raman spectroscopy on biological samples as compared with conventional Raman experiments can be reduced by more than two orders of magnitude. This experimental arrangement was tested to investigate sensitive biological samples like mint plants (Bergamot mint, spear mint) and citrus fruits (kumquat). Furthermore, traces of fungicides on wine leaves were detected by means of such a SERS fiber probe setup.

Raman spectroscopic study of spatial distribution of propolis in comb of Apis mellifera carnica (Pollm.)

Micro-Raman spectroscopy and Raman mapping are applied to investigate the spatial distribution and chemical composition of wax and propolis in the comb of Apis mellifera carnica (Pollm). A thick layer of propolis at the rim of some cells is identified by Raman spectroscopy. Raman mapping is applied to resolve the distribution of propolis and wax on a micron scale. Both components are connected at the rim of the cell with a mixture of wax and propolis. A layer of almost pure propolis is found on top of the mixture. It appears that even in the mixture, where both components come into close contact, the propolis and the wax remain separated and keep their chemical identity.

Chemotaxonomy of mints of genus Mentha by applying Raman spectroscopy

The characterization of mints is often problematic because Mentha is a taxonomically complex genus. In order to provide a fast and easy characterization method, we use a combination of micro-Raman spectroscopy and hierarchical cluster analysis. A classification trial of different mint taxa is possible for one collection time. For spectra measured at different points during the growing season, a more sophisticated pretreatment of the data is necessary to receive good discrimination between the species, as well as between the subspecies and varieties of the mints.

Laser scanning microscopy study on adsorption of biologically relevant proteins on implant materials

The adsorption of proteins at implant surfaces plays a key role in osseointegration and is therefore of great importance in biomaterial science. Laser scanning microscopy (LSM) is described, a method that is used here for the first study of the adsorption of proteins on implant surfaces. These LSM measurements provide information on the surface morphology, and the spatial distribution of adsorbed proteins can be deduced.

Raman spectroscopy investigation of biological materials by use of etched and silver coated glass fiber tips

The results for surface enhanced Raman scattering (SERS) studies on biological samples are reported. Etched and silver coated glass fiber tips were used as a SERS substrate. This method enabled the recording of spectra of biological samples, such as plant tissue or microbiological cells, with a high spatial resolution. Because of the low laser power used with the fiber tips, it was even possible to investigate tissues that are very sensitive toward laser power as it is used in a common micro-Raman setup.

Neonatal mouse model: review of methods and results

The neonatal mouse model, in various forms, has been used experimentally since 1959 and a large number of chemicals have been tested. The neonatal model is known to be very sensitive for the detection of carcinogens that operate via a genotoxic mode of action. In contrast, it is known not to respond to chemicals that act via epigenetic mechanisms, commonly observed in the two-year carcinogenicity studies. As such, the model has a high sensitivity and specificity in its response. Dose selection for the neonatal model is based on the maximum tolerated or feasible dose. Traditionally, compounds have been tested via the IP route of administration in this model. In some cases, this has limited the amount of material that can be administered because of the low dosing volumes (10 to 20 microL) that can be administered IP. For the ILSI project, the neonatal model was adapted for oral administration, which has the advantages of being the same route for which most pharmaceuticals are administered. In addition, a 10-fold increase in the volume of administration (100 to 200 microL) and the ability to dose drugs in suspension, permits much higher doses to be used as compared to the IP route of administration. The spontaneous tumors in the neonatal model occurred mainly in the liver of male mice and lung of male and female mice with a few tumors observed in the Harderian gland. The positive control, DEN produced a robust, uniform, and reproducible tumor response with the target organs essentially limited to liver and lung. A total of 13 compounds out of the 21 ILSI ACT compounds were evaluated in the neonatal model involving 18 studies with duplicate studies for some compounds. The genotoxic carcinogens including those used as positive controls were clearly positive (cyclophosphamide, diethylnitrosamine, 6-nitrochrysene). The non-genotoxic rodent carcinogens were clearly negative (chlorpromazine, sulfisoxazole, sulfamethoxazole, clofibrate, DEHP, haloperidol, metaproteranol, and phenobarbital). The non-genotoxic human carcinogen (cyclosporin) was clearly negative. The two other human carcinogens phenacetin and DES were negative and interestingly estradiol was negative in one of the two oral studies, but was clearly positive in the other. Considering the mode of action for three of the human carcinogens (DES, cyclosporin and phenacetin), which were negative in this model, the mode of action in humans is likely to be epigenetic. Overall, for the 3 clearly genotoxic chemicals, all were positive. For the 9 clearly non-genotoxic chemicals, all 9 were negative. The two human carcinogens for which genotoxicity may or may not play a role (DES and phenacetin) were negative and estradiol was positive in I of the two oral studies. Overall, the extensive database for compounds tested in the neonatal mouse model would support its use as an alternative model for the assessment of the carcinogenic potential of a chemical. The model responds to chemicals that act via a genotoxic mode of action that represent a greater concern for human cancer risk.