Effect of end groups on the raman spectra of lycopene and β-carotene under high pressure

On the remarkable nonlinear optical properties of natural tomato lycopene

In line with the renewed interest in developing novel Non Linear Optical (NLO) materials, natural Lycopene’s NLO Properties are reported for the first time within the scientific literature. Correlated to its 1-D conjugated π-electrons linear conformation, it is shown that natural Lycopene exhibits a significantly elevated 3rd order nonlinearity χ⁽³⁾ as high as 2.65 10⁻⁶ esu, the largest value of any investigated natural phyto-compound so far, including β-carotene. In addition to a saturable absorption, the corresponding observed self-defocusing effect in Lycopene seems to be the result of a thermal nonlinearity. The nonlinear response coupled to the observed fluorescence in the Visible spectral range points to a potential photodynamic therapy application as well as the possibility of engineering of novel hybrid Lycopene based NLO nano-materials.

Relations between the Raman spectra and molecular structure of selected carotenoids: DFT study of α-carotene, β-carotene, γ-carotene and lycopene

Using the density functional theory (DFT), we calculated the structures and Raman spectra of trans-isomers of α-carotene, β-carotene, γ-carotene and lycopene as well as trans-isomers of modified β-carotene and lycopene molecules with substituted end or/and side groups. The DFT calculations showed that the position of the CC stretching band depends mainly on the number of conjugated CC bonds and decreases with an increase in the conjugation length. The weak dependence of the position of the CC stretching band on the structure of the carotenoid side and end groups suggests that this band can be used to evaluate the conjugation length for trans-isomers of various molecules containing polyene chains. The CC stretching band shifts towards lower wavenumbers with growth of the conjugation length or masses of the end groups and to higher wavenumbers in the presence of the side CH₃ groups. The intensities of the CC and CC stretching bands are enhanced with growth of the conjugation length or masses of the end groups. The presence of the side CH₃ groups results in bending of the carotenoid backbone, splitting and dumping of intensities of the CC and CC stretching bands.

DFT study of Raman spectra of polyenes and ß-carotene: Dependence on length of polyene chain and isomer type

We carried out calculations of non-resonance Raman spectra of ß-carotene and polyenes CH₂(CHCH)_n-2CHCH₂ using the density functional theory (DFT). We revealed that the peak positions and intensities of the CC and CC stretching bands depend on length of the polyene chain and type of the isomer. Our experimental non-resonance Raman spectra of ß-carotene powder match well the DFT-simulated Raman spectrum of ß-carotene in the all-trans form. The peak positions and relative intensities of the CC and CC stretching bands of ß-carotene turned out to be similar in the resonance and non-resonance Raman spectra. An increase in the number of conjugated double bonds (n = 3-30) in a polyene structure results in a monotonous shift of the positions of the most intense CC and CC bands towards lower wavenumbers with an increase in the band intensities. An increase in the isomer number results in the monotonous decrease of the CC stretching band intensity for polyenes with 9, 10, 11, 15 and 24 double bonds. An increase in the isomer number inhomogeneously influences the form, position and intensity of the CC stretching band.

Study of the Photoluminescence Characteristics of 4,4'-((1E,1'E)-Quinoxaline-2,3-diylbis(ethene-2,1-diyl))bis(N,N-dimethylaniline)

A comparative investigation on the photophysical properties of a quinoxaline derivative 4,4'-((1E,1'E)-quinoxaline-2,3-diylbis(ethene-2,1-diyl))bis(N,N-dimethylaniline) (QDMA2) was performed by employing many spectroscopies. Based on the pump-dump/push-probe measurement, it is found that a solvent-stabilized charge-transfer state can participate in the relaxation of excited QDMA2 with increasing solvent polarity. Meanwhile, the aggregated QDMA2 molecules were engineered into the organic light-emitting diode test, which showed a correlated color temperature value of 1875 K. With the help of a diamond anvil cell, the pressure-dependent photoluminescence of aggregated QDMA2 shows that the intermolecular interaction can affect the color and intensity of photoluminescence through adjusting the band gap and irradiative channel of the aggregated molecules. These results are important for understanding the structure-property relationships and the rational design of functional materials for optoelectronic applications.

Pattern recognition-based Raman spectroscopy for non-destructive detection of pomegranates during maturity

In this study, the feasibility of utilizing Fourier transform Raman spectroscopy, combined with supervised and unsupervised pattern recognition methods was considered, to distinguish the maturity stage of pomegranate "Ashraf variety" during four distinct maturity stages between 88 and 143 days after full bloom. Principal component analysis (PCA) as an unsupervised pattern recognition method was performed to verify the possibility of clustering of the pomegranate samples into four groups. Two supervised pattern recognition techniques namely, partial least squares Discriminant Analysis (PLS-DA) and Soft Independent Modeling of Class Analogy (SIMCA) were also used as powerful supervised pattern recognition methods to classify the samples. The results showed that in all groups of samples, the Raman spectra of the samples were correctly clustered using PCA. The accuracy of the SIMCA classification for differentiation of four pomegranate groups was 82%. Also, the overall discriminant power of PLS-DA classes was about 96%, and 95% for calibration and validation sample sets, respectively. Due to the misclassification among different classes of immature pomegranates, that was lower than the expected, it was not possible to discriminate all the immature samples in individual classes. However, when considering only the two main categories of "immature" and "mature", a reasonable separation between the classes were obtained using supervised pattern recognition methods of SIMCA and PLS-DA. The SIMCA based on PCA modeling could correctly categorize the samples in two classes of immature and mature with classification accuracy of 100%.

A facile water-induced complexation of lycopene and pectin from pink guava byproduct: Extraction, characterization and kinetic studies

The redfleshed pulp discarded from pink guava puree industry is a rich source of lycopene and pectin. In this study, we developed a facile extraction process employing water as the primary extraction medium to isolate the lycopene and pectin from pink guava decanter. When the decanter was suspended in water, the complexation of lycopene and pectin formed the cloudy solution, where the colloidal complexes were recovered through centrifugation. The presence of lycopene and pectin in the complex was confirmed by the spectroscopic, microscopic and chromatographic analyses. The lycopene fractionated from the complexes had a purity level of 99% and was in all-trans configuration. The colloidal complexes yielding the highest concentration of lycopene was obtained at pH 7, 1% (w/v) solid loading and 25 °C. The experimental data of time-course extraction of lycopene-pectin complex were best fitted with two-site kinetic model, hinting the fast- and slow-release phases in the extraction process.

Development of a quantitative approach using Raman spectroscopy for carotenoids determination in processed sweet potato

The orange-fleshed sweet potato is a vegetable-rich in carotenoids. The thermic treatment for sweet potato processing can decrease the content of these constituents in the foods, lowering their bioactive properties. Raman spectroscopy has been growing as a fast tool to food analysis, especially for detection of low concentrations of carotenoids and to the monitoring of its degradation profile over time. Therefore, in this work were evaluated two methods of drying, hot air and microwaving with rotary drum, combined with quantitative Raman spectroscopy. The results showed carotenoids degradation around 50% for both types of drying processes studied. PCA plot proved the potential of reproducibility of analyses for microwave drying samples. For samples heated with hot air, the best linear correlation achieved was R² = 0.90 and by microwave was R² = 0.88. Also, partial least squares (PLS) regression models were constructed obtaining a satisfactory coefficient of determination.

Effects of Molecular Symmetry on the Electronic Transitions in Carotenoids

The aim of this work is the verification of symmetry effects on the electronic absorption spectra of carotenoids. The symmetry breaking in cis-β-carotenes and in carotenoids with nonlinear π-electron system is of virtually no effect on the dark transitions in these pigments, in spite of the loss of the inversion center and evident changes in their electronic structure. In the cis isomers, the S2 state couples with the higher excited states and the extent of this coupling depends on the position of the cis bend. A confrontation of symmetry properties of carotenoids with their electronic absorption and IR and Raman spectra shows that they belong to the C1 or C2 but not the C2h symmetry group, as commonly assumed. In these realistic symmetries all the electronic transitions are symmetry-allowed and the absence of some transitions, such as the dark S0 → S1 transition, must have another physical origin. Most likely it is a severe deformation of the carotenoid molecule in the S1 state, unachievable directly from the ground state, which means that the Franck-Condon factors for a vertical S0 → S1 transition are negligible because the final state is massively displaced along the vibrational coordinates. The implications of our findings have an impact on the understanding of the photophysics and functioning of carotenoids.

Use of time-resolved spectroscopy as a method to monitor carotenoids present in tomato extract obtained using ultrasound treatment

INTRODUCTION

Compounds exhibiting antioxidant activity have received much interest in the food industry because of their potential health benefits. Carotenoids such as lycopene, which in the human diet mainly derives from tomatoes (Solanum lycopersicum), have attracted much attention in this aspect and the study of their extraction, processing and storage procedures is of importance. Optical techniques potentially offer advantageous non-invasive and specific methods to monitor them.

OBJECTIVES

To obtain both fluorescence and Raman information to ascertain if ultrasound assisted extraction from tomato pulp has a detrimental effect on lycopene.

METHOD

Use of time-resolved fluorescence spectroscopy to monitor carotenoids in a hexane extract obtained from tomato pulp with application of ultrasound treatment (583 kHz). The resultant spectra were a combination of scattering and fluorescence. Because of their different timescales, decay associated spectra could be used to separate fluorescence and Raman information. This simultaneous acquisition of two complementary techniques was coupled with a very high time-resolution fluorescence lifetime measurement of the lycopene.

RESULTS

Spectroscopic data showed the presence of phytofluene and chlorophyll in addition to lycopene in the tomato extract. The time-resolved spectral measurement containing both fluorescence and Raman data, coupled with high resolution time-resolved measurements, where a lifetime of ~5 ps was attributed to lycopene, indicated lycopene appeared unaltered by ultrasound treatment. Detrimental changes were, however, observed in both chlorophyll and phytofluene contributions.

CONCLUSION

Extracted lycopene appeared unaffected by ultrasound treatment, while other constituents (chlorophyll and phytofluene) were degraded.

Following the mechanisms of bacteriostatic versus bactericidal action using Raman spectroscopy

Antibiotics cure infections by influencing bacterial growth or viability. Antibiotics can be divided to two groups on the basis of their effect on microbial cells through two main mechanisms, which are either bactericidal or bacteriostatic. Bactericidal antibiotics kill the bacteria and bacteriostatic antibiotics suppress the growth of bacteria (keep them in the stationary phase of growth). One of many factors to predict a favorable clinical outcome of the potential action of antimicrobial chemicals may be provided using in vitro bactericidal/bacteriostatic data (e.g., minimum inhibitory concentrations—MICs). Consequently, MICs are used in clinical situations mainly to confirm resistance, and to determine the in vitro activities of new antimicrobials. We report on the combination of data obtained from MICs with information on microorganisms’ “fingerprint” (e.g., DNA/RNA, and proteins) provided by Raman spectroscopy. Thus, we could follow mechanisms of the bacteriostatic versus bactericidal action simply by detecting the Raman bands corresponding to DNA. The Raman spectra of Staphylococcus epidermidis treated with clindamycin (a bacteriostatic agent) indeed show little effect on DNA which is in contrast with the action of ciprofloxacin (a bactericidal agent), where the Raman spectra show a decrease in strength of the signal assigned to DNA, suggesting DNA fragmentation.