Carotenoid pigments in male house finch plumage in relation to age, subspecies, and ornamental coloration
ABSTRACT.-Like males of many bird species, male House Finches (Carpodacus mexicanus) have patches of feathers with ornamental coloration that are due to carotenoid pigments. Within populations, male House Finches vary in expression of ornamental coloration from pale yellow to bright red, which previous research suggested was the result of variation in types and amounts of carotenoid pigments deposited in feathers. Here we used improved analytical techniques to describe types and amounts of carotenoid pigments present in that plumage. We then used those data to make comparisons of carotenoid composition of feathers of male House Finches at three levels: among individual males with different plumage hue and saturation, between age groups of males from the same population, and between males from two subspecies that differ in extent of ventral carotenoid pigmentation (patch size): large-patched C. m. frontalis from coastal California and small-patched C. m. griscomi from Guerrero, Mexico. In all age groups and populations, the ornamental plumage coloration of male House Finches resulted from the same 13 carotenoid pigments, with 3-hydroxy echinenone and lutein being the most abundant carotenoid pigments. The composition of carotenoids in feathers suggested that House Finches are capable of metabolic transformation of dietary forms of carotenoids. The hue of male plumage depended on component carotenoids, their relative concentrations, and total concentration of all carotenoids. Most 4-keto (red) carotenoids were positively correlated with plumage redness, and most yellow carotenoid pigments were negatively associated with plumage redness, although the strength of the relationship for specific carotenoid pigments varied among age groups and subspecies. Using age and subspecies as factors and concentration of each component carotenoid as dependent variables in a MANOVA, we found a distinctive pigment profile for each age group within each subspecies. Among frontalis males, hatch-year birds did not differ from adults in mean plumage hue, but they had a significantly lower proportion of red pigments in their plumage, and significantly lower levels of the red piments adonirubin and astaxanthin, but significantly higher levels of the yellow pigment zeaxanthin, than adult males. Among griscomi males, hatch-year birds differed from adults in plumage hue but not significantly in pigment composition, though in general their feathers had lower concentrations of red pigments and higher concentrations of yellow pigments than adult males. Both adult and hatch-year frontalis males differed from griscomi males in having significantly higher levels of most yellow carotenoid pigments and significantly lower levels of most red carotenoid pigments. Variation in pigment profiles of subspecies and age classes may reflect differences among the groups in carotenoid metabolism, in dietary access to carotenoids, or in exposure to environmental factors, such as parasites, that may affect pigmentation. Received 18 January 1999, accepted 11 June 2001.
CAROTENOID PIGMENTS ARE responsible for the bright red, orange, and yellow coloration of plumage. Birds obtain those carotenoids exclusively through their diet. No animal has been shown unequivocally to be capable of in vivo synthesis of carotenoids (Goodwin 1984, 1986; Schiedt 1990). In birds, dietary carotenoids may either be deposited directly into feathers or chemically changed fromingested forms prior to pigment deposition, typically by addition or elimination of oxygen groups to one or both end rings of the molecule (Davies 1985, Goodwin 1986, Tyzckowski and Hamilton 1986a, b; Brush 1990, Schiedt 1990).
The House Finch (Carpodacus mexicanus) is a sexually dichromatic passerine bird species in which males display bright, carotenoid-based patches of color on their crowns, throats, breasts, and rumps, and male House Finches vary in expression of that ornamental coloration from a bright red to a dull yellow (Michener and Michener 1931, Hill 1990, 1993a). The carotenoid pigments responsible for colorful plumage in the House Finch and the pigmentary basis for variation among males in expression of that coloration were first studied by Brush and Power (1976). They attributed plumage color variation to differences in constituent carotenoids in feathers. Red birds had the most complex assemblage of pigments, consisting of beta-carotene, a group of unidentified mixed xanthophylls, orange isocryptoxanthin, and red echinenone; orange birds had the same subset of carotenoids without echinenone; and yellow birds lacked both echinenone and isocryptoxanthin. Recent analyses of several congeneric finch species of the Palearctic Carduelinae done by Stradi et al. (1995a, b; 1996, 1997), using new analytical techniques, revealed a more complex pattern that differed substantially from that described by Brush and Power (1976).
The proximate basis of variation in carotenoid-based plumage coloration in House Finches is of interest beyond improved understanding of the physiological control of avian pigmentation. Plumage redness in House Finches has been shown to be a primary criterion used by females in choosing mates (Hill 1990, 1991, 1994a). In addition, plumage brightness in male House Finches is correlated with overwinter survival (Hill 1991), nutritional condition during molt (Hill and Montgomerie 1994), parasite load (Thompson et al. 1997, Brawner et al. 2000), and provisioning of females during incubation (Hill 1991). It has been proposed that male plumage brightness is an honest signal of male condition, because carotenoids may be scarce resources in the environment and carotenoid-based color displays may be costly to produce (Hill 1994b, 1996a, 2002). A thorough understanding of the signal content of carotenoid-based ornamental displays can only be achieved, however, through an understanding of the proximate control of variation among males in expression of these displays (Hill 1992, 1996a, 2002).
Food colorings: pigments make fruits and veggies extra healthful
Crop geneticist Charles R. Brown has spent a decade working to make abetter potato. In the beginning, he focused on beefing up the familiar white-fleshed tuber. His strategy was to recapture healthful traits from old-style spuds from the plant’s native range in South America. He examined many yellow, red, and purple potatoes, none of which grows well in a U.S. climate. While cross breeding these imports with their northern cousins, Brown and his coworkers at the U.S. Department of Agriculture laboratory in Prosser, Wash., began hearing about putative health benefits from the type of pigments, called flavonoids, that give the potatoes their color.
Flavonoids include beta-carotene and related carotenoids, which are responsible for many of the yellows, oranges, reds, and greens in produce. Other reds and most of the blues, purples, and blackish tints–especially in berries and potatoes–trace to flavonoids called anthocyanins.
These chemicals are considered antioxidants because they quash free radicals, naturally forming molecular fragments that have several damaging effects. Free radicals can kill cells, transform some of the blood’s cholesterol-toting lipoproteins into agents of atherosclerosis (SN: 4/21/01, p. 245), and induce DNA damage that might foster cancer (SN: 2/22/97, p. 126).
A few years ago, Brown’s group and a few others around the world began developing new lines of crops explicitly for their intense antioxidant pigments. Some early lines of red and purple potatoes are now on the market, and other colorful crops are heading that way.
Probably the most famous example is known as golden rice. It’s enriched with beta-carotene, a yellow chemical from which the body fashions most of its vitamin A. Swiss and German researchers used biotechnology to design this cereal in the late 1990s to improve vitamin-poor diets in developing countries. The golden grain is still being fine-tuned for eventual commercialization.
Philipp Simon and his colleagues at a USDA lab in Madison, Wis., have been developing carotenoid-enhanced, yellow-orange cucumbers and red and anthocyanin-rich, dark-purple carrots (http:///www.sciencenews.org/articles/20041120/food.asp). This team bred some of the carrots now on the market, which retain the traditional orange color but produce 75 percent more beta-carotene than carrots did 25 years ago. In another example of pigment boosting, researchers at Cornell University are breeding wheat with extra flavonoids.
There’s currently evidence that, in addition to fighting inflammation, heart disease, and cancer, flavonoids can counter obesity and elevated blood sugar. Although scientists have presumed that flavonoids’ benefits derive mainly from their antioxidant activity, some research has recently shown that the chemicals facilitate signaling between cells and silence genes that might otherwise foster disease.
Indeed, James A. Joseph of USDA’s Human Nutrition Research Center on Aging at Tufts University in Boston says that this basic effect may contribute to flavonoids’ broad range of activities.
With growing recognition of the health-promoting biological activity of plant pigments, many researchers are advocating that consumers expand the palette of colors on their dinner plates. For instance, Joseph wrote a book to guide people in choosing healthful foods by their colors (The Color Code, 2003, Hyperion Books).
Joseph acknowledges that color offers, at best, an imperfect measure of potentially beneficial antioxidant flavonoids. However, by choosing foods exhibiting a range of deep colors, he says, a person can be reasonably sure of getting a broad mix of beneficial flavonoids.
HEART-SPARING HINTS Many studies have linked anticancer benefits and protection against heart disease with diets rich in produce, especially carotenoid-rich green, leafy vegetables.
The most recent of these reports, in the Nov. 3, 2004 Journal of the National Cancer Institute, analyzed dietary and health data for almost 72,000 female nurses and 38,000 male health professionals. The study found significantly less risk of chronic illness, especially heart disease, in study participants eating the most fruits and vegetables. Of all foods analyzed, green leafy vegetables appeared most protective. In fact, for each daily serving of spinach or other greens consumed, an individual’s risk of developing cardiovascular disease fell by 11 percent.
In 2003, Tiina H. Rissanen of the University of Kuopio in Finland and her colleagues reported that the more servings of vegetables and fruits that middle-aged men consumed, the lower their risk of dying from heart disease. The data pointed to berries, in particular, as being protective.
These findings were consistent with others published that year by an Australian team. For 6 weeks, nutrition scientists gave 32 men fruit extracts every morning and vegetable extracts every evening. Several potential heart-disease indicators, such as blood concentrations of homocysteine (SN: 1/4/03, p. 5) and susceptibility of cholesterol to oxidation (SN: 4/21/01, p. 245), were far lower in men taking the supplements than in volunteers who had eaten the same diet minus the supplements.
Pigments, color process for ready-mix concrete
With the Standley Color Batch system, ready-mix companies can incorporate Bayferrox C granulated pigments into a dry-to-wet mixing process to obtain all the advantages of liquid colors, but at a lower cost per yard. The process makes liquid colors on a single-batch basis using the producer’s own water. It uses granular pigments and separately weighs each of four primary colors. Pigment and water are mixed within seconds, and the liquefied pigment is transferred to the mixer. Flushing with water after each batch eliminates color contamination. Lanxess Corp. (formerly Bayer Chemicals), 800-526-9377, www.lanxess.com. Circle 33.
Color and UV Stabilization in Pigmented Injection-Molded Polypropylene
A previous study by Kanu, Spotts, and Chesebrough showed that some organic and inorganic pigments noticeably influence the tensile and impact properties of injection-molded polypropylene.1 As an extension of the previous study, this work examines the influence of the same organic and inorganic pigments on the color and UV stabilization of injection-molded polypropylene, specifically the action of these pigments as nucleating agents in the crystallization process of the semi-crystalline polypropylene. However, since organic and inorganic pigments have different chemical compositions and particle sizes, their action as nucleating agents will differ and consequently determine the degree of influence they exert on the properties of injection-molded polypropylene.
Plastics have made significant contributions to our standard of living. In many applications, such as in medical uses for hip bone and heart valve replacement, plastics are often the preferred material because their inherent properties make them more suitable than traditional materials like ceramics, wood, and metals. For example, Kevlar fibers are used in bulletproof vests and some combat protective helmets because of their high strength-to-weight ratio, and the polycarbonate material known as Lexan is used in ophthalmic lenses because it is lightweight, tough, and transparent.
While intrinsic properties make plastics attractive for many applications, the advantages of this material are only realized when the plastic resins are transformed into useful objects by primary processing techniques such as injection molding, extrusion, blow molding, rotational molding, compression and transfer molding, and thermoforming. However, if not done properly, the fabrication process that not only results in significant benefits can also diminish plastics’ attractive properties. For example, an abnormally high processing temperature employed in a fabrication process such as injection molding can degrade the plastic material, resulting in a finished product with lower mechanical properties and perhaps unacceptable visual effects such as blemishes and burn marks. Another potential disadvantage in the transformation process is the use of additives to achieve specific features in the finished products. For example, flame retardants are used to prevent plastic television casings from bursting into flames in the presence of electrical sparks, and processing aids or lubricants such as waxes are used to improve production of PVC pipes and vinyl sidings. In some cases, additives do achieve the expected results but also cause unpredictable property changes in the finished product; hence, additives may improve a product’s mechanical properties while simultaneously reducing its processiblity. Given this background, the authors examined the effects of some organic and inorganic pigments on the color and ultraviolet (UV) stabilization of injection-molded polypropylene (PP) tensile specimens.
Motivation
There are several studies that have sought to clarify the effects of additives on the physical, mechanical, optical, and rheological properties of polymeric materials. Jaffe et al. investigated Theologically effective organic pigments, and Yu et al. studied the effects of carbon black dispersion on polymer performance.2,3 Other authors like Spano and Steen examined the optical properties of pigmented polypropylene, while Krisher and Marshall studied the effects of pigments on the mechanical properties of polypropylene.4,5 In another study, Charvat et al. examined the shift in color in pigmented plastics after the injection molding of plastic parts.6 Concurrent with these studies is a discussion within the plastics industry concerning the use of both organic and inorganic pigments in the manufacture of plastics products, primarily because of health and environmental concerns; inorganic pigments are known to contain traces of potentially harmful impurities such as dioxins as well as heavy metals such as cadmium, lead, chromium, and mercury.7,8 To address these concerns, this study sought to examine and compare the influence of organic and inorganic pigments on the color and UV stabilization of injection-molded polypropylene. A secondary goal was to use the study as a pedagogical tool to reinforce important theoretical concepts involving pigmentation of plastics, injection molding, extrusion, reflectance spectrophotometry, and amorphous, semicrystalline, and nucleated crystallization properties.
Definitions
The following section defines some key concepts and technical terms used in this paper.
AMORPHOUS PLASTICS
In the amorphous state, plastics molecules exhibit no definite form of order. On a molecular scale, this state has been aptly described as resembling a bowl of cooked spaghetti.9 The nature of amorphous plastics is predominately amorphous while in the solid state, and mainly because of their irregular molecular structure, these materials show no tendency to crystallize. Examples of amorphous plastics are poly (methyl methacrylate), commercially known as acrylics (Atohaas’ Plexiglas, Id’s Lucite and Cyro Industries’ Acrylite); polycarbonate (GE Plastics’ Lexan); and atatic polystyrene, commercially known as generalpurpose polystyrene or crystal polystyrene.
Metal oxide pigments
Add vibrant colors to a wide range of concrete products with Ferrotint metal oxide pigments. Reportedly produced with the most advance manufacturing processes, these pigments can be used in ready-mixed concrete, precast products (block, pavers), roof tiles, and even brick. At the plant these pigments undergo strict quality control (QC) to ensure their uniform color, strength, and lightfastness in all applications as well as that they meet the customer’s exact requirements.
The company’s QC program also includes batch identification codes for accurate traceability. Other pigment features include water insolubility, alkali and weather resistance, and ultra-violet stability. Adaptable packaging options include water-degradable paper and plastic bags for hatched and pre-mixed concrete applications, and bulk bags for handling large volumes.
Colors of the cosmos: red, green, and blue may mean one thing to a scientist and something different to everybody else - Universe
Only a few objects in Earth’s nighttime sky emit or reflect enough light to trigger our retinas’ color-sensitive cones. The red planet Mars can do it. So can the blue supergiant star Rigel (Orion’s left kneecap) and the red supergiant Betelgeuse (Orion’s right armpit). But aside from these standouts, the pickings are slim. To the unaided eye, space is a dark and colorless place.
Not until you aim large telescopes at it does the universe show its true colors. Glowing objects such as stars come in shades of red, white, and blue–a cosmic fact that would have pleased the Founding Fathers. Interstellar gas clouds can take on practically any color at all, depending on which chemical elements are present, whereas a star’s color follows directly from its surface temperature: Cool stars are red. Tepid stars are white. Hot stars are blue. Very hot stars are … still blue. How about very, very hot places, like the 15,000,000 [degrees] center of the Sun? Blue. To an astrophysicist, red-hot foods and red-hot lovers both leave room for improvement. It’s just that simple.
Or is it?
A conspiracy of astrophysical law and human physiology just about rules out the existence of green stars. How about yellow stars? Some astronomy textbooks, many science fiction stories, and nearly every person on the street belong to the Sun-Is-Yellow Movement. Professional photographers, however, would swear the Sun is blue; daylight film is color balanced on the expectation that the light source (presumably the Sun) is strong in the blue part of the spectrum. The old blue-dot flash cubes were just one example of the attempt to simulate the Sun’s blue light for indoor shots when using daylight film. On the other hand, painters with loft studios consider sunlight to be pure white, offering them the most accurate possible view of their pigments.
No doubt the Sun acquires a yellow-orange patina near the dusty horizon during sunrise and sunset. But at 12:00 noon, when atmospheric scattering is at a minimum, the color yellow does not spring to mind. Indeed, light sources that are truly yellow make white things look yellow. So if the Sun were pure yellow, then snow would look yellow–whether or not it had fallen near fire hydrants.
To an astrophysicist, “cool” objects have surface temperatures between 1,000 [degrees] and 4,000 [degrees] Kelvin and are generally described as red. Yet the filament of a white incandescent lightbulb cannot exceed 3,000 [degrees] Kelvin by much–tungsten melts at 3,680 [degrees]. Below about 1,000 [degrees], objects become dramatically less luminous in the visible part of the spectrum. Gaseous orbs with these temperatures happen to be failed stars. We call them brown dwarfs even though they are not brown and they emit hardly any visible light at all.
While we’re on the subject, black holes aren’t really black. Depending on its mass, a black hole can lose energy across the entire spectrum. In a process that resembles evaporation, black holes emit small quantities of light from their event horizons. Physicist Stephen Hawking was the first to describe this phenomenon, in which the evaporation rate increases as the black hole gets smaller, ending its life in a runaway flash of gamma rays.
Modern scientific images occasionally use a false-color palette. The meteorologists who make TV weather maps might denote heavy rainfall with one color and light rainfall with another. Or better yet, snow with one color, sleet with a second color, and rain with a third. When astrophysicists create false-color images of cosmic objects, they often assign an arbitrary sequence of colors to an image’s range of brightness. The brightest parts might be red and the dimmest parts blue. So the colors you see bear no relation to the actual colors of the object. As in meteorology, some of these images have color sequences that relate to other attributes, such as the object’s chemical composition or temperature. And it’s not uncommon to see an image of a spiral galaxy that has been color coded for its rotation: the parts coming toward you are shades of blue, while the parts moving away are shades of red. In this case, the assigned colors evoke the widely recognized blue and red Doppler shifts that reveal an object’s motion.
In the cosmic microwave background (the energetic remnants of the big bang), some areas are hotter than average. And, of course, some are cooler than average. The range spans a mere 0.00001 [degrees]. How do you display this fact on a map? Make the hot spots blue and the cold spots red or cold spots blue and hot spots red. In either case, a teeny fluctuation in temperature shows up as an obvious difference on the picture.
In other cases, we create a full-color image of a cosmic object by using invisible light, such as infrared or radio waves. What we do is assign the three colors to which the human retina is sensitive (red, green, and blue, or RGB for short) to three different parts of the spectrum. This way, we construct the full-color image we would see if we were born with the capacity to see colors in otherwise invisible bands.
Recipe for success: smart partnering can transform a lone inventor into a market force
PRODUCT DESCRIPTION: Karyo’s company produces a line of silicone bakeware cooking tools with superior heat transfer and nonstick properties. The odor-resistant products, priced from $15 to $25 apiece, let users bake more efficiently, thanks to such features as even cooling and heat distribution. Silicone products had been used in commercial kitchens previously, but Karyo was the first to create a consumer line.
. FIND A VOID IN THE MARKET. “I was working as a consultant to develop a kitchenware [line] for a company that primarily sold silicone products to the medical industry,” says Karyo of how he uncovered this market opportunity. “I found that, while several European companies were selling silicone products to the commercial market, no one had a true consumer product. I felt that consumers and home bakers could benefit from silicone technology. I verified [this] with buyers for kitchen stores.” But by that time, the company he consulted for had changed its mind about entering the market, so Karyo went out on his own to develop a silicone line. The typical drawback to filling a market void is that you have to create a market for your product. Fortunately, Karyo didn’t have to deal with this obstacle–the existing popularity of silicone in commercial kitchen markets convinced buyers to give Karyo’s products a try.
2. DETERMINE HOW TO STAY IN A LEADING MARKKET POSITION. Karyo knew that being first to market wouldn’t be enough for him to remain a market leader. “I felt from the beginning that the key to staying on top in the market was to have ‘better than them’ product quality, unique designs and moderate prices that would give us a competitive advantage over much bigger housewares companies,” he says. So Karyo expanded his vision to include features that would differentiate his product from competitors: “The surface of SiliconeZone products is high gloss, not matte, and the product comes in vibrant colors that competitors can’t duplicate.”
3. IF NECESSARY, FIND A PARTNER. Karyo is a sales and marketing person–not a manufacturer. The high quality he was after called for manufacturing expertise and a willingness to help develop the product. Karyo knew he couldn’t afford to pay someone for development, nor could he afford to buy from a factory as a customer and keep prices down. “I knew I needed a partner company experienced in silicone,” says Karyo. “I talked to my father, Maurice, who had done business in the Far East for 40 years. He [found] a company in Hong Kong that made silicone products for the electronics industry. We formed a 50/50 joint venture with the owners, Ken and Ricky Yeung, where [they paid] development and tooling costs, while I paid for sales and marketing. Then we split the profits.” If you don’t have a connection to find a source you need, go online or to your local library to check out the Thomas Register of American Manufacturers, which lists manufacturers you can talk to about potentially setting up a partnership.
4. SELL THE MARKET ON WHY YOUR PRODUCTS IS THE CLEAR CHOICE. With some products, customers can tell right away which product is best based on visual clues, such as fit and finish, expensive materials or packaging. But in Karyo’s case, buyers didn’t understand that his product was of higher quality. So Karyo gave them a straightforward pitch: “I showed buyers the factors that determined a quality product.” He pushed three main differentiating factors: the high quality of his proprietary silicone formula, a denser and heavier product that provides better heat conductivity; the high-gloss finish, which calls for a slower production process and hand-polished tooling; and the vibrancy of the color, which results from using high-quality silicone material and pigments.
5. STRENGTHEN YOUR BRAND. Karyo ran an ad campaign to get the word out about his business. “We didn’t have any sales, but I wanted buyers of independent stores and major retailers to know and remember that we were the first ones in the market,” he says. “I took out ads in key trade magazines like HFN (Home Furnishing News), Home World Business and Kitchenware News.” He says people still remark to him at shows, “I remember you being the first in the market
In my Garment there is nothing but God: recent work by Ibrahim el Salahi
Ibrahim el Salahi was born in the Sudan in 1930, and is widely recognized as one of the progenitors of modern painting in that country. (1) He studied in Khartoum at the School of Design Gordon Memorial College, in London at the Slade School, and then returned to the Sudan to teach. (2) Briefly imprisoned under Nimeiri in 1975, el Salahi left the Sudan upon his release and he has since been in self-imposed exile in Qatar and Oxford, England.
Salah Hassan has divided el Salahi’s oeuvre into three periods–an early period (late 1950s-1970s) characterized by muted, earthy tones and a linear compositional style; a second period (late 1970s) with more vibrant colors and “abstract human and animal-like figures rendered in geometric design”; and a third phase (late 1970s to present) in which works are mainly in black and white (Hassan 1998:31-2). This discussion of the artist’s work, however, addresses currents that run through these divisions. Specifically, el Salahi’s own narration of his career trajectory reveals a consistent interest in negotiating and bridging the distance between his body and his work. He considers the process of coming to the canvas or paper as the meeting of two bodies and subjectivities–his own and the canvas’s–and the work then grows from a conversation (and sometimes an argument) between the two. This negotiation takes place throughout his career at several levels–through prayer and meditation, media, compositional construction, and imagery. Further, el Salahi’s attempts to link his own body (as a creator) to the work (as a creation) shift slowly over time from engagement with the exterior, physical body to representations of an interior, spiritual body. This transformation in turn mirrors his ongoing use of prayer and meditation as a means to bring himself closer to God.
Rather than limit art historical engagement to the formal development of el Salahi’s works, this analysis of his oeuvre draws upon embodied models that are more often applied to the study of performance arts in Africa, such as masquerades (see, for example, Bourdieu 1977 and Connerton 1989). The use of such models widens the scope of analysis and allows us to more thoroughly consider the artist’s physical experience of creation in both the phenomenological and spiritual sense. Additional meaning is drawn from the artist’s implicit bodily performances over time. Within such a framework, the borders of what constitutes the “work” expand, and the drawings and paintings themselves are recast as fragments of a broader, equally significant, and ongoing embodied experience.
Prayer
El Salahi is a Muslim of a Sufi sect and notes that he prays five times a day and will often pray again before he starts to draw or paint. (3) This has been true throughout his life, except for a brief period when he was enrolled in a British school in the Sudan. El Salahi’s definition of prayer and his discussion of its role in his work is significant. In one interview, he described the process of washing, preparing his body before prayer, the motions he goes through as he prays which distract him from his surroundings, the words he speaks, and what they mean.
Leaf Science: Pigments on Parade! - Brief Article - Statistical Data Included
With the beginning of autumn, the leaves of deciduous trees seem to magically turn an incredible natural palette of yellow, brown, orange, and red. Your students can discover for themselves how these “hidden colors” materialize in leaves by doing a simple experiment in paper chromatography.
Color Activity
Every grade-schooler knows about mixing paints together to get new colors. In this experiment, your students will do the opposite, taking pigments apart to see what colors emerge. Encourage your class to predict what colors may be present in different water-based markers and then test their hypotheses.Give students four 1″-wide strips of paper towel each and ask them to select 4 different colors of marker, one for each strip. Next they draw a single line lengthwise from the top and stop 1″ from the bottom.
* Ask students to dip the bottom edge of their paper strips into small cups of water. As the water is absorbed by the paper strip, the pigments will begin to flow up the strip, slowly separating into their component colors.
* Tie this activity back into the idea of changing leaves by asking students why different trees turn different colors.
* Your students can create an autumn art project with leaf shapes cut from paper towels. Ink a large brown dot in the center of each leaf, and use a dropper to apply water to the paper. The result will be an array of unique and colorful leaves.
Ground and Excited States of Retinal Schiff Base Chromophores by Multiconfigurational Perturbation Theory
We have studied the wavelength dependence of retinal Schiff base absorbencies on the protonation state of the chromophore at the multiconfigurational level of theory using second order perturbation theory (CASPT2) within an atomic natural orbital basis set on MP2 optimized geometries. Quantitative agreement between calculated and experimental absorption maxima was obtained for protonated and deprotonated Schiff bases of all-trans- and 11-cis-retinal and intermediate states covering a wavelength range from 610 to 353 nm. These data will be useful as reference points for the calibration of more approximate schemes.Retinal is the chromophore in several photosensitive proteins where it converts light energy into structural changes (1): in the visual pigments or rhodopsins, the light-induced isomerization of 11-cis-retinal to all-trans initiates the visual cycle. In hacteriorhodopsin. all-trans-retinal is transformed by light into the 13-cis isomer, which starts the proton pumping cycle across the bacterial cell wall of Halobacterium salinarium
One particular aspect in retinal protein chemistry concerns the ultraviolet-visible spectral changes in these pigments, which serve specific needs: from ancient bacteria that use sensory rhodopsins to test the composition of light (2) to the human eye where three different rhodopsins enable the perception of colors (3). Understanding the physical origin of these changes has been a major challenge to theory ever since the original concept of the external point charge model has been introduced in the literature (4). Advances in x-ray crystallography have provided a multitude of bacteriorhodopsin structures, including intermediates of the proton pumping cycle (5) and have culminated recently in the threedimensional structure of bovine rhodopsin (6) and its first photointermediate, bathorhodopsin (7). These structures, which reveal the geometry of the retinal chromophore and its environment in atomic detail, have been instrumental for theoretical studies of retinal protein spectral shuts using diverse quantum-mechanical schemes (8-13). The dilemma that these studies face is exemplified by the fact that two of them arrive at very reasonable values for the theoretically calculated ahsorhance of rhodopsin, yet their results for the simple 11-cis-retinal protonated Schilf base (pSb). which forms the basis for the ensuing quantum mechanical and molecular mechanical (QM/MM) calculations, differ by 0.56 eV or 176 nm.
Recently the gas phase absorption spectra of several retinal Schiff bases in different protonation states have been determined (14.15) and found to peak at 610/620 nm (transpSb in Scheme 1 ). 487 nm (trans-SbN^sup +^), and 610 nm (cis-pSb). These data define much needed reference points for the calculation of retinal protein spectra, both for the protonated chromophores in vacuo and for the effect of a positive charge in a defined relative orientation to the chromophore. To cover the short-wavelength region of retinal Schiff base spectra, we also include the neutral species trans-Sb whose absorbance in the nonpolar solvent 3-methylpentane peaks at 353 nm (16). In the following, we show that CASPT2 theory at a very high level of sophistication is able to quantitatively reproduce these data.
In view of the huge computational requirements, the /(-butyl group in Scheme 1 was reduced to methyl (the solvent spectra of the two pSbs are essentially identical) (17) and N(CH^sub 3^)^sub 3^^sup +^ to NH^sub 3^^sup +^. Geometry optimization at the CASPT2 level for systems of this size is still prohibitive in computer resources. We therefore resorted to MP2 and its analytical gradients, which allow for an efficient geometry search with a correlated wave function. Starting with the DFT-optimized structures (18). the chromophores were reoptimized with MP2 using a 6-31G** basis set (19).
All four chromophores exhibit strong bond alternation (Fig. 1), which is. however, significantly reduced between C9 and N16 in the three positively charged systems. A further reduction is observed in trans- and cis-pSb, where the positive charge is part of the ?-system. From C6 to N16, all chromophores are essentially planar with the exception of r/.s-pSb. which is twisted by 7° and 3° about the C11=C12 and the C12-C13 bonds, respectively, and moves the C13-N16 fragment away from the bulky ?-ionone ring.
Ground and excited state energies were calculated with the CASSCF method as provided by the MOLCAS set of routines (20). Six-root state-averaged wave functions were expanded in an atomic natural orbital basis set (21) with the contraction C,N[4s3p1d)/H[2s]. The active space was (12,12), i.e.. all pseudo ?-clectrons and valence pscudo ?-orbitals were considered. Second-order corrections to the CASSCF energies were calculated with CASPT2. All core orbitals were kept frozen during the calculations. To avoid the effect of intruder states, the level shift was set uniformly to 0.3 au. These parameters are identical to the ones we used in recent studies on retinal model