Color and chirality: carotenoid self-assemblies in flower petals

The presence of free palmitic acid modulates the effects of lutein on structural and dynamic properties of lipid membranes

Free fatty acids, like palmitic acid (PA), and xanthophyll pigments, like lutein (LUT) are the natural membrane compounds in plants. To study the effect of PA on LUT and their organization, a model membrane of 1,2-dimyristoyl-sn-glycerol-3-phosphocholine (DMPC) enriched with 2 mol% PA and 1 mol% LUT was formed. Molecular mechanisms underlying the interaction between these two compounds were examined with application of molecular spectroscopy techniques, e.g., visible spectroscopy, electron paramagnetic resonance and Fourier transform infrared. We determined the monomeric/dimeric organization of LUT in the membrane. We proved that the presence of PA in the lipid phase facilitated and stabilized the formation of LUT structures in the membrane. Lutein with PA did not form strong molecular aggregates like H- and J-structures. We presented the simplified model membrane that could be a suitable representation of the physiological process of de-esterification of PA from LUT appearing in natural biomembranes in humans.

Effect of environmental factors on the aggregation behavior of astaxanthin in water

Molecular aggregation is a common phenomenon widely found in natural organisms, which is crucial for some specific functions of biological systems. To study the aggregating behavior of hydrophobic carotenoids in water, astaxanthin was employed and dispersed under different surroundings to induce aggregation. The results showed that astaxanthin tended to form J- or H-type aggregates when the water content was higher than 60%. Both hydrochloric acid (HCl) and sodium hydroxide (NaOH) were beneficial for the formation of astaxanthin J-aggregates, but they were not good for inducing H-aggregates. Small-molecule electrolytes, like sodium salts, mostly played an enormous hindrance role to the formation of astaxanthin H- and J-aggregates, except for sodium chloride (NaCl) which helped astaxanthin to form J-aggregates. Both sodium periodate (NaIO₄) and sodium acetate (CH₃COONa) could prevent the formation of astaxanthin H- and J-aggregates, but sodium chloride (NaCl) could only hinder the formation of H-aggregates. As for polyelectrolytes chitosan and DNA, the difference of chain structure led to different aggregation effects. The soft single chain of chitosan tended to induce J-aggregates formation, while double-stranded DNA preferred to guide the formation of H-aggregates. By choosing and integrating the advantageous environmental factors that facilitate each type of astaxanthin aggregates, J- and H-type astaxanthin aggregates were stably loaded in DNA/CS nanoparticles with distinct particle sizes. Controlled preparation of either H- or J-type aggregates is of great significance for further studies concerning the structure-activity relationship of carotenoid aggregates.

Selectivity and bio-compatibility of self-assembled chiral flower-like and helical nanostructures

The molecular building block NDI–LCA was synthesized via substitution of NDA at the di-imide position with two lithiocholic acid moieties, resulted into chiral flower line and helical nanostructures.

Structure of supramolecular astaxanthin aggregates revealed by molecular dynamics and electronic circular dichroism spectroscopy

Biomolecular aggregation is omnipresent in nature and important for metabolic processes or in medical treatment; however, the phenomenon is rather difficult to predict or understand on the basis of computational models. Recently, we found that electronic circular dichroism (ECD) spectroscopy and closely related resonance Raman optical activity (RROA) are extremely sensitive to the aggregation mechanism and structure of the astaxanthin dye. In the present study, molecular dynamics (MD) and quantum chemical (QC) computations (ZIndo/S, TDDFT) are used to link the aggregate structure with ECD spectral shapes. Realistic absorption and ECD intensities were obtained and the simulations reproduced many trends observed experimentally, such as the prevalent sign pattern and dependence of the aggregate structure on the solvent type. The computationally cheaper ZIndo/S method provided results very similar to those obtained by TDDFT. In the future, the accuracy of the combined MD/QC methodology of spectra interpretation should be improved to provide more detailed information on astaxanthin aggregates and similar macromolecular systems.

Hydrodynamic instabilities in active cholesteric liquid crystals

We describe the basic properties and consequences of introducing active stresses, with principal direction along the local director, in cholesteric liquid crystals. The helical ground state is found to be linearly unstable to extensile stresses, without threshold in the limit of infinite system size, whereas contractile stresses are hydrodynamically screened by the cholesteric elasticity to give a finite threshold. This is confirmed numerically and the non-linear consequences of instability, in both extensile and contractile cases, are studied. We also consider the stresses associated to defects in the cholesteric pitch ([Formula: see text] lines) and show how the geometry near to the defect generates threshold-less flows reminiscent of those for defects in active nematics. At large extensile activity [Formula: see text] lines are spontaneously created and can form steady-state patterns sustained by constant active flows.

Carotenoid deposition in plant and animal foods and its impact on bioavailability

Over the past decades, an enormous body of literature dealing with the natural deposition of carotenoids in plant- and animal-based foods has accumulated. Prominent examples are the large solid-crystalline aggregates in carrots and tomatoes or the lipid-dissolved forms in dairy products and egg yolk. Latest research has identified lipid-dissolved forms in a rare number of plant foods, such as tangerine tomatoes and peach palm fruit (Bactris gasipaes Kunth). In addition, liquid-crystalline forms were assumed in so-called tubular chromoplasts of numerous fruits, e.g., in papaya, mango, and bell pepper. The bioavailability of carotenoids from fresh and processed foods strongly depends on their genuine deposition form, since their effective absorption to the human organism requires their liberation from the food matrix and subsequent solubilization into mixed micelles in the small intestine. Consequently, a broad overview about the natural array of carotenoid deposition forms should be helpful to better understand and modulate their bioavailability from foods. Furthermore, naturally highly bioavailable forms may provide biomimetic models for the improved formulation of carotenoids in food supplements. Therefore, this review paper presents scientific evidence from human intervention studies associating carotenoid deposition forms with their bioavailability, thus suggesting novel technological and dietary strategies for their enhanced absorption.

Pre-resonance enhancement of exceptional intensity in Aggregation-Induced Raman Optical Activity (AIROA) spectra of lutein derivatives

Recently reported new phenomenon of Aggregation-Induced Raman Optical Activity is demonstrated here for the first time in the pre-resonance conditions for lutein diacetate and 3'-epi-lutein supramolecular self-assembles. We demonstrate that minor alterations in the lutein structure (e.g. acetylation of hydroxyl groups or different configuration at one of the chiral center) can lead to definitely different spectral profiles and optical properties due to formation of aggregates of different structure and type. Lutein forms only H-aggregates, lutein diacetate only J-aggregates, while 3'-epi-lutein can occur in both forms simultaneously. Variety of aggregates' structures is so large that not only the type of aggregation is different, but also their chirality. It is remarkable that even in the pre-resonance conditions, aggregation of lutein derivatives can lead to the intense ROA signal, and moreover, 3'-epi-lutein demonstrated the highest resonance ROA CID ratio that has ever been reported.

Composition of Carotenoids and Flavonoids in Narcissus Cultivars and their Relationship with Flower Color

Narcissus is widely used for cut flowers and potted plants, and is one of the most important commercial bulbous flowers in the floricultural industry. In this study, ten carotenoid and eighteen flavonoid compounds from the perianths and coronas of fifteen narcissus cultivars were measured by HPLC–APCI-MS/MS and UPLC-Q-TOF-MS/MS. Among these, six carotenoids, a total of seventeen flavonols and chlorogenic acid were identified in narcissus for the first time. A multivariate analysis was used to explore the relationship between flower color and pigment composition. We found that all-trans-violaxanthin and total carotenoid content were the main factors that affected flower color. These investigations could provide a global view of flower color formation and a theoretical basis for hybridization breeding in narcissus.

Nondestructive monitoring of carotenogenesis in Haematococcus pluvialis via whole-cell optical density spectra

We investigated the feasibility of rapid, nondestructive assay of carotenoid-to-chlorophyll (Car/Chl) ratio and total carotenoids (Car) in cell suspensions of the carotenogenic chlorophyte Haematococcus pluvialis Flotow under stressful conditions. Whole-cell spectra are characterized by variable nonlinear contributions of Car and chlorophylls (Chl), with a strong influence of Car packaging and sieve effect inherent to stressed H. pluvialis cells. Nevertheless, nondestructive assay of Car/Chl in the range of 0.55-31.2 (Car content up to 188 mg L(-1); 5.4 % of the cell dry weight) turned to be achievable with a simple spectrophotometer lacking an integrating sphere upon deposition of the cells on glass fiber filters. The scattering-corrected optical density (OD) in the blue-green region of the whole-cell spectrum, normalized to that in the red maximum of Chl absorption (OD500/OD678), was tightly related (r (2) = 0.96) with the Car/Chl ratio found in extracts. Some features such as the amplitude and position of the minimum of the normalized first-derivative OD whole-cell spectra also exhibited a strong (r (2) > 0.90) nonlinear correlation with Car/Chl. These spectral indices were also tightly related with Car, but the slope of the relationship varied with the stressor intensity. The importance of calibration over the widest possible range of pigment contents and a correct choice of biomass load per filter are emphasized. The advantages and limitations of nondestructive monitoring of carotenogenesis in H. pluvialis are discussed in view of its possible application in optical sensors for laboratory cultivation and mass production systems of the algae.

Flower color alteration in Lotus japonicus by modification of the carotenoid biosynthetic pathway

To establish a model system for alteration of flower color by carotenoid pigments, we modified the carotenoid biosynthesis pathway of Lotus japonicus using overexpression of the crtW gene isolated from marine bacteria Agrobacterium aurantiacum and encoding beta-carotene ketolase (4,4'-beta-oxygenase) for the production of pink to red color ketocarotenoids. The crtW gene with the transit peptide sequence of the pea Rubisco small subunit under the regulation of the CaMV35S promoter was introduced to L. japonicus. In most of the resulting transgenic plants, the color of flower petals changed from original light yellow to deep yellow or orange while otherwise exhibiting normal phenotype. HPLC and TLC analyses revealed that leaves and flower petals of these plants accumulated novel carotenoids, believed to be ketocarotenoids consisting of including astaxanthin, adonixanthin, canthaxanthin and echinenone. Results indicated that modification of the carotenoid biosynthesis pathway is a means of altering flower color in ornamental crops.

Novel procedure for the extraction and concentration of carotenoid-containing chromoplasts from selected plant systems

Natural sources of carotenoids for nutraceutical use are desired by the food industry as a result of the increased production of convenience and other highly processed foods. As new physiological roles are discovered for some of the minor carotenoids that are found in only small amounts in present sources, the need for discovery of new sources will amplify. Thus, a method is needed that will effectively and gently concentrate carotenoids from potential new sources for subsequent identification and analysis. A procedure is presented by which carotenoid-containing tissue chromoplasts can be extracted and subsequently concentrated by precipitation, all in an aqueous milieu. The chromoplasts are extracted and solubilized with 0.3% sodium dodecyl sulfate (SDS) in water. The addition of a nominally equal volume of acetonitrile to the chromoplasts in SDS immediately precipitates the chromoplasts out of solution with generally >90% recovery. Carotenoids contained in the concentrated, still-intact chromoplasts can then be solubilized by organic solvent extraction for subsequent analysis. This methodology offers a means to effectively and gently concentrate carotenoids from fruit tissues where yields are often low (e.g., yellow watermelon).

Potential of NIR-FT-Raman spectroscopy in natural carotenoid analysis

This paper demonstrates the special advantages of FT-Raman spectroscopy for in situ studies of several carotenoids that occur ubiquitously in the plant kingdom. Spectra obtained from various tissues of a range of plant species indicate that the wavenumber location of C=C stretching vibrations is mainly influenced both by the length as well as by the terminal substituents of the polyene chain of carotenoids and by their interaction with other plant constituents. The obtained results show also the usefulness of Raman spectroscopy in the investigation of cis-trans isomerization of carotenoids during processing. Additionally, 2-D Raman mappings present a unique possibility to evaluate the individual distribution of carotenoids in the intact plant tissue; in this context different 7-, 8-, and 9-double bond conjugated carotenoids can be analyzed independently in the same sample. Furthermore, the use of Raman spectroscopy for in situ detection of unstable substances such as epoxycarotenoids is discussed.

1H HR-MAS NMR of carotenoids in aqueous samples and raw vegetables

Carotenoids are linear C40 tetraterpenoid hydrocarbons and represent a wide category of natural pigments. They are components of the pigment system of chloroplasts and are involved in the primary light absorption and the photon canalization of photosynthesis. Moreover, they also behave as quenchers of singlet oxygen, protecting cells and organisms against lipid peroxidation. Carotenoids have a strong lipophilic character and are usually analyzed in organic solvents. However, because of their biological activity, the characterization of these compounds in an aqueous environment or in the natural matrix is very important. One of the most important dietary carotenoids is beta-carotene, which has been extensively studied both in vivo and in model systems, but because of the low concentration and strong interaction with the biological matrix, beta-carotene has never been observed by NMR in solid aqueous samples.In the present work, a model system has been developed for the detection and identification of beta-carotene in solid aqueous samples by 1H HR-MAS NMR. The efficiency of the model has led to the identification of beta-carotene in a raw vegetable matrix.

Structure and chiroptical properties of supramolecular flower pigments

Research over the last 30 years has shown that at physiological concentrations of ca. 5 x 10(-3) M, flower pigments composed of anthocyanins, either alone or complexed with flavone copigments, and frequently with metals, are self-assembled into non-covalent, chiral supramolecular complexes. This serves several biological functions including color stability, protection against UV radiation and provision for specific colors to attract insects for pollination. Self-association of the monomers takes place under conditions of molecular crowding by precise matching of the pi-pi stacking interactions of the aromatic chromophores and intermolecular hydrogen bonding between the attached sugars. The resulting handedness is controlled by the chiral information provided by the sugars joined glycosidically at certain positions around the periphery of the aromatic nuclei. This review gives an overview of (i) the physicochemical evidence including circular dichroism, (1)H NMR, and X-ray analysis for the structure and supramolecular chirality of these amphiphilic complexes, (ii) the role of the sugars on directing the chirality of the resulting supramolecules, (iii) the energetics of monomer association, and (iv) the possible influence of stacking chirality on insect pollination.

Supramolecular exciton chirality of carotenoid aggregates

The conventional organic chemistry concept of chirality relates to single molecules. This article deals with cases in which exciton chirality is generated by the interaction of associated carotenoids. The handed property responsible for exciton signals in these systems is due to the alignment of neighboring molecules held together by secondary chemical forces. Their mutual positions are characterized by the overlay angle. Experimental manifestation is obtained by spectroscopic studies on carotenoid aggregates. Compared to molecular spectra, both UV/visible and circular dichroism spectroscopic observations reveal modified absorption bands and induced Cotton effects of opposite sign (exciton couplets), respectively. A new term, "supramolecular exciton chirality," is suggested for these phenomena, allowing the detection of weak chemical interactions not readily accessible for experimental studies, although highly important in the mechanism of biological processes.

Direct superoxide anion scavenging by a disodium disuccinate astaxanthin derivative: Relative efficacy of individual stereoisomers versus the statistical mixture of stereoisomers by electron paramagnetic resonance imaging

Carotenoids are a related group of greater than 600 natural compounds, irrespective of geometric- and stereoisomers, with demonstrated antioxidant efficacy. The carotenoids are broadly divided into "carotenes," or non-oxygen substituted hydrocarbon carotenoids, and "xanthophylls," oxygen-substituted carotenoids. The natural compounds are excellent singlet oxygen quenchers as well as lipid peroxidation chain-breakers; this dual antioxidant capacity is generally attributed to the activity of the polyene chain, and increases with the number of conjugated double bonds along the polyene chain length. However, the poor aqueous solubility of most carotenes and the vast majority of xanthophylls limits their use as aqueous-phase singlet oxygen quenchers and direct radical scavengers. A variety of introduction vehicles (e.g., organic solvents, cyclodextrins) have been used to introduce the insoluble carotenoids into aqueous test systems. Hawaii Biotech, Inc. (HBI) successfully synthesized a novel carotenoid derivative, the disodium disuccinate derivative of astaxanthin (3,3(')-dihydroxy-beta,beta-carotene-4,4(')-dione) in all-trans (all-E) form. The novel derivative is a water-dispersible symmetric chiral molecule with two chiral centers, yielding four stereoisomeric forms: 3R,3(')R and 3S,3(')S (enantiomers), and the diastereomeric meso forms (3R,3(')S and 3(')R,3S). The individual stereoisomers were synthesized at high purity (>90% by HPLC) and compared directly for efficacy with the statistical mixture of stereoisomers obtained from the synthesis from the commercial source of astaxanthin (1:2:1 ratio of 3S,3(')S, meso, and 3R,3(')R, respectively). Direct scavenging of superoxide anion was evaluated in a standard in vitro isolated human neutrophil assay by electron paramagnetic resonance (EPR) imaging, employing the spin-trap DEPMPO. Each novel derivative was tested in pure aqueous formulation and in ethanolic formulation shown to completely disaggregate the compounds in solution. In each case, the ethanolic formulation was a more potent scavenging vehicle. No significant differences in scavenging efficiency were noted among the individual stereoisomers and the statistical mixture of stereoisomers, suggesting that the polyene chain alone was responsible for superoxide scavenging. Dose-ranging revealed that the statistical mixture of stereoisomers of the novel derivative, at millimolar (mM) concentrations, could nearly completely eliminate the superoxide anion signal generated in the activated human neutrophil assay. All ethanolic formulations of the novel derivatives exhibited increased scavenging efficiency over equimolar concentrations of non-esterified astaxanthin delivered in a dimethyl sulfoxide (DMSO) vehicle. These novel compounds will likely find utility in applications requiring aqueous delivery of a highly potent direct radical scavenger.

Chiral detection of carotenoid assemblies

Carotenoid assemblies were produced by aqueous dilution of ethanolic solutions. UV/VIS and CD spectroscopy revealed the formation of J- and H-types of aggregates of both right- and left-handed kinds. Simulation of UV/VIS spectra of the aggregates showed characteristic differences between the two types. 6'-Epimers of capsanthol ((all-E,3R,3'S,5'R)-beta,kappa-carotene-3,3',6'-triols) formed assemblies with increased chirality in dilute solution. While the absorption of 6'R-capsanthol giving H-type aggregate does not depend on the concentration, 6'S-capsanthol yielding J-type assembly showed concentration-dependent absorption intensity. Dilute aggregate of 6'R-capsanthol is characterized by an extremely large A value of -6,600. The transformation of J- to H-type assembly was observed in the mixtures of the epimers producing an intermediate kind of aggregate. A hypothetical structure for H-type assemblies is proposed.