TIGER

Other Resources: 32 results
Molecular Models of Natural Products  William F. Coleman
This month's issue of the Journal includes several papers discussing interesting molecules that fall into the broad category of natural products, and four of these papers serve as the source for our featured molecules this time around. Addison Ault weaves an interesting tale of the search for the true structure of eserethole and of the competition between two research groups that of Percy Julian, consisting of two people, and that of the British chemist Robert Robinson, a large group at Oxford (1). David Vosburg describes a case study approach to teaching organic synthesis and includes a number of molecules that have been the basis of student research papers (2). Jean-Michel Lavoie, Esteban Chornet, and André Pelletier have developed an experiment utilizing GCMS to separate terpenes from citrus (3), and Patty Feist, in a paper that may send readers running for their Kafka, has students synthesize a cockroach pheromone that may have wide applicability in cockroach control without the problems created by many insecticides (4).The molecules that have been added to our collection contain a wide variety of functional groups, and would serve as a good source for an exercise in having students recognize these functional groups in a number of different settings. Questions such as How many cyclic ether groups are present?, How many bridgehead carbons?, or How many chiral centers would be useful exercises in organic and introductory non-majors courses. Students could find other pheromone structures and see how they compare with that of blattellaquinone, or explore the various ways in which the steroid backbone shows up in the collection.This collection of molecules also provides a good starting point for students to use the capabilities of Jmol to further explore structural features. The focus here is on measuring bond distance and angles. Double clicking on any atom will change the cursor to a cross-hair (this may take a little practice). One end of a dashed line is now locked to that atom. Dragging the free end of the line to other atoms will show the distance between the two centers in nanometers. Double clicking on a second atom will lock a line segment between those two atoms and display the distance in black. There is now another free end of the segmented line, and dragging that to any other atom will show the angle defined by the three-atom combination. Double clicking on the third atom fixes the second line segment and gives a third segment that can be dragged and double clicked to display dihedral angles. Students could, for example, explore various ring structures in this collection to determine which rings are distorted and which are not.The files that are currently used for the collection are MDL mol files, and do not contain orbital, electrostatic potential, or vibrational data. Beginning next month we will change the file format, and that information will be available to users, either through the Jmol menu (right click on any structure) or through menu choices.Not all of the molecules from the Ault paper (1) have been included, leaving room for students to model and perform calculations on many of the non-eserethole species, and to consider how modern tools of analysis might have simplified the identification of eserethole. They might also wish to determine which pair of eserethole enantiomers are the more stable. (The eserethole structures included here have all been optimized at the 6311++G (d,p) level.)
Natural Products
Molecular Models of Rosmarinic Acid and DPPH  William F. Coleman
The paper by Canelas and da Costa (1) introduces students to the antioxidant rosmarinic acid, and its interaction with the free radical DPPH. Those two molecules are the featured species this month. The original paper shows the 2-dimensional structure of the cis isomer of rosmarinic acid, although the trans isomer exhibits very similar antioxidant properties. Calculations at the DFT/B3LYP 631-G(d) level show that the trans isomer is more stable than the cis isomer in the gas phase, a situation that is expected to carry over into solution. Many antioxidants are phenols, and rosmarinic acid has four such groups available for radical formation. A DFT study by Cao et al. (2) examines the relative stabilities of the radicals formed from loss of each of the phenolic hydrogens. That paper focuses on the trans isomer, and a useful student project would be to repeat the calculations with the cis isomer. An HPLC separation of the isomers of rosmarinic acid has been published (3), and might well lead to an extension of the experiment described in ref 1 in which relative antioxidant efficiencies of the two isomers could be evaluated. DPPH has been used extensively as a standard for determining antioxidant activity. An examination of the molecular orbital occupied by the lone electron shows significant delocalization, providing a partial explanation for the stability of the neutral radical. Our gas phase structure for DPPH, also at the DFT/B3LYP 631-G(d) level, is quite consistent with several crystal structures on DPPH and DPPH in the presence of another species (4).
Natural Products
Umami and Proteins  Robert Hetue
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Proteins / Peptides
ChemPaths 104 M Jan 31  John W. Moore
Today in Chem 104: * Lecture: Biochemistry: Proteins * Reading: Kotz: Chemistry of Life (pp. 496-502); Moore: Ch 3, Sec 11; Ch 12, Sec 7 * Biomolecules Tutorials o Proteins 1 (including debriefing) o Proteins 2 (including debriefing) o Quiz due W Feb. 2, 11:55 PM) * Homework #3 due by 11:55pm F Feb 4.
Proteins / Peptides
Polypeptide Chains  Ed Vitz, John W. Moore
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Proteins / Peptides
Primary Protein Structure  Ed Vitz, John W. Moore
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Proteins / Peptides
Secondary Protein Structure  Ed Vitz, John W. Moore
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Proteins / Peptides
Higher-Order Structure  Ed Vitz, John W. Moore
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Proteins / Peptides
Molecular Models of Resveratrol  William F. Coleman
The featured molecules this month are from the paper "Resveratrol Photoisomerization: An Integrative Guided-Inquiry Experiment" by Bernard, Gernigon, and Britz-McKibbin exploring trans to cis photoisomerization in resveratrol. Examination of Figure 1 in that paper, where the hydrogen atoms have been omitted, might lead one to conclude that the structures are relatively straightforward. These isomers provide students an excellent opportunity to test their ability to take a two-dimensional representation and envision the three-dimensional structure of the molecule and to consider the competing factors that might lead to the three-dimensional structures being non-planar. The two-dimensional models focus attention on the possibility of extended pi-electron delocalization. Addition of the hydrogen atoms clearly suggests that delocalization will compete with non-bonded H-H repulsions in the cis isomer. Further examination of the trans isomer shows that such non-bonded interactions are, in what one might call a first-order approximation, like those in biphenyl interactions that lead biphenyl to be non-planar in both the gas phase and in a variety of solvents. The backbone of the trans isomer of resveratrol, trans-stilbene, has been the subject of a number of theoretical and experimental investigations (1, 2). In general, Hartree-Fock calculations predict a non-planar geometry for this molecule while Density Functional Calculations, using the same basis sets, predict an essentially planar structure. Spectroscopic evidence supports a temperature-dependent structure for trans-stilbene with the molecule being planar at low temperature and non-planar at high temperatures. Our calculations on trans-resveratrol produce similar results. Hartree-Fock calculations using the 6-31G** (6- 31G(d,p)) basis set predict a dihedral angle of approximately 24 degrees between each ring and the central carbon-carbon double bond. This result is consistent with the reported value of 23 degrees using the 6-31G* basis set. We also find that DFT calculations using the B3LYP functional and the 6- 31G** basis set, lead to a planar configuration. We include several versions of trans-stilbene and trans-resveratrol in the molecule collection so that students can explore these structural questions in more detail. For each molecule, structures obtained from PM3, HF(6-31G**), and DFT(B3LYP/6-31G**) calculations are included, as well as planar and non-planar structures of biphenyl. Measurement of the various bond and torsion angles using Jmol will help students develop a sense of the distance dependence of the non-bonded interactions and their importance in determining the actual structure. They might also wish to consider what additional degree(s) of freedom resveratrol and stilbene have that biphenyl does not, allowing the trans-form of the former molecules to remain planar under certain conditions, while minimizing the effect of the non-bonded repulsions.
Plant Chemistry |
Natural Products
Molecular Models of Antioxidants and Radicals  William F. Coleman
This month's featured molecules come from the paper by John M. Berger, Roshniben J. Rana, Hira Javeed, Iqra Javeed, and Sandi L. Schulien (1) describing the use of DPPH to measure antioxidant activity. DPPH was one of the featured molecules in September 2007 (2) and the basics of antioxidant activity were introduced in last month's column (3). In addition, some of the other molecules in the paper are already in the featured molecules collection (4). The remaining structures in the Figure 1 and Table 1 of the paper have been added to the collection. All structures have been optimized at the 6-311G(D,P) level. These molecules suggest a number of possible student activities, some reminiscent of previous columns and some new. (R,R,R)-α-tocopherol is one of the molecules in the mixture that goes by the name vitamin E. These molecules differ in the substituents on the benzene ring and on whether or not there are alternating double bonds in the phytyl tail. In (R,R,R)-α-tocopherol the R's refer to the three chiral carbon atoms in tail while α refers to the substituents on the ring. (R,R,R)-α-Tocopherol is the form found in nature. An interesting literature problem would be to have students learn more about the vitamin E mixture and the differing antioxidant activity of the various constituents. Additionally they could be asked to explore the difference between the word natural as used by a chemist, and "natural" as used on vitamin E supplements. Can students find regulations governing the use of the term "natural"? Can they suggest alternative legislation, and defend their ideas? If students read about vitamin C they will discover that only L-ascorbic acid is useful in the body. It would be interesting to extend the experiment described in the Berger et al. paper (1) to include D-ascorbic acid. How do the antioxidant abilities of the enantiomers, as determined by reaction with DPPH compare? Is this consistent with the behavior in the body? Why or why not? Berger et al. mention two other stable neutral radicals, TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and Fremy's salt. In a reversal from the use of stable radicals to measure antioxidant properties, these two molecules have proven to be very versatile oxidation catalysts in organic synthesis, and would make a rich source of research papers for students in undergraduate organic courses.
Free Radicals |
Natural Products
Molecular Models of Lycopene and Other Carotenoids  William F. Coleman
Over the past decade or so the phrase emerging research suggests has entered the argot of advertising, and that phrase has been applied to this month's Featured Molecule, lycopene, particularly with regard to potential health benefits of tomatoes. The paper by Jie Zhu, Mingjie Zhang, and Qingwei Liu (1) describes an extraction and purification of lycopene from tomato paste using an emulsion rather than the traditional solvent-based extraction. Lycopene is a member of the family of molecules called carotenoids, the most familiar of which is beta-carotene. This family of natural products includes more than 500 members that have been isolated and whose structures have been determined. Professor Hanspeter Pfander's research group at the University of Bern maintains a Web site with a significant amount of information on carotenoid structure, synthesis, and activity (2). Structurally one can think of carotenoids as consisting of three segments, a relatively rigid conjugated central portion with end groups. The end groups are, in general, flexible with respect to rotation about the bond connecting them to the central portion. For example, in beta-carotene, the dependence of total energy on the dihedral angle shown in Figure 1, displays a very broad range of essentially isoenergetic conformations (Figure 2). The energies shown in Figure 2 were calculated at the PM3 level using Hyperchem 7.5 (3). Calculations at the HF/631-G(d,p) level, with many fewer data points, show a similar trend. Many of the health benefits derived from various carotenoids are attributed to their antioxidant activities. Carotenoids react with singlet-oxygen in a physical, diffusion-controlled, quenching process that results in ground state triplet-oxygen and, following a non-radiative relaxation, ground state carotenoid. Of the various carotenoids that have been studied, lycopene and beta-carotene show the greatest quenching rate constants (4). The carotenoids provide us with countless explorations by students and teachers looking for connections between fundamental chemical concepts and real-world applications. Structure, reactivity, chemical synthesis, biosynthesis, and stereochemistry are just a few of the concepts involved in understanding the manifest important roles that these molecules play.
Plant Chemistry |
Natural Products
Molecular Models of Annatto Seed Components  William F. Coleman
In January 2008 the focus of this column was on the plant pigments lycopene and beta-carotene (1). Our attention this month returns to two papers discussing the pigments in annatto seeds (Figure 1), including direct precursors to lycopene. The paper by Teixeira, Dur�n, and Guterres describes the extraction and encapsulation of annatto seed components (2). The McCullagh and Ramos paper describes the separation of the pigment bixin from these seeds by TLC and column chromatography (3). These molecules could form the basis of interesting exercises across the chemistry curriculum. In courses designed for non-majors, students could choose a molecule from the table and search the literature for both scientific and non-scientific sources. Are the claims made in the latter sources regarding the health benefits of these molecules consistent with the scientific data? That discussion could be expanded to the more general question of how one tests the validity of statements made in what are essentially advertisements. Are any of these precursor molecules to lycopene considered to have anticancer properties (4)? In introductory or general chemistry courses, students could explore the various bond lengths and bond angles in the molecules to see whether they are consistent with their expectations based on simple bonding models. In introductory, organic, or biochemistry classes, the thermodynamics of hydrogenation and dehydrogenation could be examined. This might make an interesting alternative to the oft-discussed Haber Process. What conditions would one propose for a dehydrogenation process? Why are dehydrogenation reactions important? What enzymes catalyze the various dehydrogenation steps from phytoene to lycopene? These molecules could also be used in a variety of computational exercises in introductory and physical chemistry courses. Hartree�Fock calculations on a molecule such as phytoene may prove time-consuming depending on the nature of the computing system available. A good place to begin would be to perform semi-empirical calculations on the various molecules. Do the optimized structures match experimental results or the results of larger calculations? Does the HOMO�LUMO gap correlate with the observed electronic absorption spectra? Which is more important in determining the difference in absorption between phytoene and phytofluene, the total number of double bonds or the number of bonds in the region of conjugation? Of course the aspect of these molecules that is most likely to capture student attention is their color, and they provide nice examples of the origin of color, the relationship between color observed and color absorbed, and, in upper level courses, the more detailed relationships of the energies of the ground and excited states.
Plant Chemistry |
Natural Products
Wave Mechanics and Carotenoids  Ed Vitz
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Quantum Chemistry |
Natural Products
Carboxylic Acids in Entomology  Robert Hetue
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Carboxylic Acids |
Natural Products
PH and pOH in Food Color  Sofia Erazo
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
pH |
Natural Products
Indicators in foods  Sofia Erazo
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Acids / Bases |
Natural Products
Secondary Protein Structure with Cultural Connections  Garrett Schwarzman
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Proteins / Peptides |
Consumer Chemistry
ChemPaths 104 W Feb 2  John W. Moore
Today in Chem 104: * Lecture: Biochemistry: Proteins * Reading: Biomolecules Tutorials o Proteins 1 (including debriefing) o Proteins 2 (including debriefing) o Quiz due TODAY, 11:55 PM) * Homework #3 due by 11:55pm F Feb 4.
Proteins / Peptides |
Amino Acids
Proteins  Ed Vitz, John W. Moore
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Proteins / Peptides |
Enzymes
Plants-ACS Science for Kids  American Chemical Society
ACS Science for Kids activities exploring the properties and chemistry of plants.
Plant Chemistry |
Natural Products |
Photosynthesis |
Transport Properties
The World's Food Supply  
Volume 04, issue 05 of a series of leaflets covering subjects of interest to students of elementary chemistry distributed in 1929 - 1932.
Proteins / Peptides |
Carbohydrates |
Lipids |
Nutrition
The World's Food Supply  
Volume 05, issue 10 of a series of leaflets covering subjects of interest to students of elementary chemistry distributed in 1929 - 1932.
Proteins / Peptides |
Carbohydrates |
Lipids |
Nutrition
Limiting Reagent Protein Nutrition  Ed Vitz
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Stoichiometry |
Proteins / Peptides |
Amino Acids
Anthropology and Protein Stoichiometry  Ed Vitz
A section of ChemPrime, the Chemical Educations Digital Library's free General Chemistry textbook.
Stoichiometry |
Proteins / Peptides |
Amino Acids
Nutrition  American Chemical Society
ACS Science for Kids activities that explore the chemical properties of food and nutrition.
Lipids |
Physical Properties |
Proteins / Peptides |
Nutrition |
Carbohydrates
Biomolecules (Netorials)  Rachel Bain, Mithra Biekmohamadi, Liana Lamont, Mike Miller, Rebecca Ottosen, John Todd, and David Shaw
Biomolecules: this is a resource in the collection "Netorials". This set of modules will provide you with a descriptive overview of the four major classes of biomolecules found in all living organisms: carbohydrates, lipids, proteins, and nucleic acids. The Netorials cover selected topics in first-year chemistry including: Chemical Reactions, Stoichiometry, Thermodynamics, Intermolecular Forces, Acids & Bases, Biomolecules, and Electrochemistry.
Bioorganic Chemistry |
Carbohydrates |
Nucleic Acids / DNA / RNA |
Lipids |
Proteins / Peptides
The World's Food Supply  
Volume 03, issue 09 of a series of leaflets covering subjects of interest to students of elementary chemistry distributed in 1929 - 1932.
Plant Chemistry |
Photosynthesis |
Proteins / Peptides |
Carbohydrates |
Lipids |
Nutrition
Your Body  American Chemical Society
ACS Science for Kids activities explore the chemistry of the human body.
Bioenergetics |
Applications of Chemistry |
Nutrition |
Lipids |
Proteins / Peptides |
Carbohydrates |
Food Science
Mage; A Tool for Developing Interactive Instructional Graphics  Stephen F. Pavkovic
Mage is a graphics program especially well suited for visualizing three-dimensional structures of proteins and other macromolecules. It is an important tool for biochemists and finds many applications in biochemistry courses. We utilize Mage to create interactive instructional graphics of potential use in a wider range of undergraduate chemistry courses, and present some of those applications here.
Crystals / Crystallography |
Group Theory / Symmetry |
VSEPR Theory |
Molecular Properties / Structure |
Stereochemistry |
Proteins / Peptides
Netorials  
The Netorials cover selected topics in first-year chemistry including: Chemical Reactions, Stoichiometry, Intermolecular Forces, Acids & Bases, Biomolecules, and Electrochemistry.
Acids / Bases |
Stoichiometry |
Proteins / Peptides |
Enzymes |
Carbohydrates |
Nucleic Acids / DNA / RNA |
Lipids |
Oxidation / Reduction |
Noncovalent Interactions
Food  American Chemical Society
ACS Science for Kids activities that explore the chemical properties of foods.
Plant Chemistry |
Dyes / Pigments |
Lipids |
Proteins / Peptides |
Carbohydrates |
Molecular Properties / Structure |
Applications of Chemistry |
Nutrition |
Acids / Bases |
Chromatography
Characteristics of Materials  American Chemical Society
What makes diapers absorbent? Is peanut butter stickier than syrup or jelly? Strong, stretchy, sticky, or sweet—everything around us has special properties which make them unique. See if you can identify and compare the characteristics of materials.
Industrial Chemistry |
Physical Properties |
Reactions |
Consumer Chemistry |
Gases |
Carbohydrates |
Proteins / Peptides |
Crystals / Crystallography |
Water / Water Chemistry |
Plant Chemistry |
Dyes / Pigments |
Lipids |
Molecular Properties / Structure |
Applications of Chemistry |
Nutrition |
Acids / Bases |
Chromatography |
Magnetic Properties |
Metals |
Polymerization |
Solutions / Solvents |
Descriptive Chemistry |
Food Science