Summer 2006
This summer Bobby Repousis, Gilbert Monyancha, and Robert Detig, are working in the lab with me. I will be working on modifying the FTIR to collect Step-Scan spectra, their projects are outlined below. You could also look at the posters Robert and Bobby prepared. Bobby and Gilbert worked on synthesizing molecules that can absorb light causing them change their shape to fit a template like the guanidyl end of arginine. Structure I (shown bound to the guanidinium ion) has been shown to change its shape by isomerizing into the cis,cis isomer when irradiated in the presence of the guanidinium ion. Gilbert and Bobby are working on molecules similar to II that can absorb visible light and are structurally similar to I.
Robert worked on the synthesis of some stereisomers that we will use in the future to study the weakening of chemical bonds that occurs as the result of absorbing light.
Professor Charles Hicks, Gilbert Monyancha, Robert Detig, and Bobby Repousis.
Project 1
Gilbert
Effect of Binding Templates on Photochemical Yields of cis-trans Isomerization.
Abstract
The action of a drug depends on its ability to bind to a target molecule and alter the molecule’s function. The strength with which a drug binds depends upon its structure being complementary in both shape and the distribution of electrical charge, with that of the target. The traditional approach to searching for complementary structures is to synthesize families of molecules and determine each of their individual binding characteristics. Structures containing double bonds can adapt different rigid conformations that can be changed by exposure to light. In this work, a structure containing double bonds and a metal chromophore [Ru(bpy)2 L2](PF6) (L=3-Pyridin-4-yl-acrylic acid) to increase the efficiency of light absorption, will be synthesized and photochemical studies performed to evaluate its ability to adapt its shape to become more complementary to a binding target. The studies will include 1H NMR, UV-Vis Absorption, and Emission spectroscopy.
Goals
1) Synthesize and purify 2-Methyl-3-pyridin-4-yl-but-2-enoic acid from the Wittig reaction of 4-Acetylpyridine 1-(4-pyridinyl)ethanone and Triethyl phosphonoacetate using a published procedure (J. Boutagy, R. Thomas, Chem. Rev. 74, 87 1974). This will involve mixing stoichiometric amounts of each compound, reacting with gentle heating overnight, and purifying by column chromatography.
2) Synthesize (Ru(bpy)2 L2]Cl2 (bpy=2,2’-bipyridine; L=3-Pyridin-4-yl-acrylic acid) by reaction of 2-Methyl-3-pyridin-4-yl-but-2-enoic acid with Ru(bpy)2Cl2. This will involve mixing stoichiometric amounts of each compound, reacting with gentle heating overnight, and purifying by column chromatography. This is a new synthesis for which no procedure exists.
3) Characterize this molecule by 1H and 13C NMR, UV-Vis Absorption, and Emission spectroscopy. This will require preparation of solutions of appropriate concentration for each technique, training in the operation of the instruments, and analysis of the data to confirm the structures of the products obtained.
4) Measure the pKa of the carboxylate groups to determine the best pH for it to bind to a cationic target. (if time allows).
5) Measure rates of isomerization in the presence of binding targets by irradiating the samples with visible light and detecting changes in the 1H NMR spectrum (if time allows).
Results
The complex outlined above turned out to be unstable so the project was continued with a slightly different complex, some spectra are shown below.
1H NMR Spectrum of the dialkene ligand
1H NMR Spectrum of the dialkene metal complex
Molar Absorptivity of Dialkene Metal Complex in water.
Project 2
Bobby
Synthesis and Photochemical Properties of a Metal Complex that can Change its Shape to Fit a Binding Template
Abstract
Alkenes are molecules that have rigid structures because the double bonds they contain are unable to rotate. This rigidity leads to stereoisomers- molecules that have the same set of atoms connected in the same order but with different three-dimensional shapes. When exposed to light, alkenes can undergo isomerization, a process where rotation of the double bond can occur and a different stereoisomer is formed. The result of this is that the molecule can change its shape in response to light. This project will investigate the effect of a template that preferentially binds one of the stereoisomers on the efficiency of formation of that stereoisomer when exposed to light. This work will be performed on a molecule for which I previously developed a synthesis. The first part of the project will involve synthesizing the molecule in large enough quantities to perform NMR studies. The studies that will be performed will include determining the quantum yield for isomerization with and without a binding template using 1H NMR, and/or UV-Vis Absorption. The results will be analyzed by constructing mathematical models that will be integrated numerically to obtain solutions. The collected data will then be compared to these solutions in order to determine the simplest model that adequately explains the data to determine if the molecule is significantly altering its structure to become more complementary to the binding template.
Goals
1) Synthesize and purify L=3-[4'-(2-Carboxy-1-methyl-vinyl)-[2,2']bipyridinyl-4-yl]-but-2-enoic acid
from the Wittig reaction of 2,2’-bipyridine-4,4’-dicarboxaldehyde and Triethyl 2-phosphonopropionate . This will involve mixing stoichiometric amounts of each compound, reacting with gentle heating overnight, and purifying by column chromatography.
2) Synthesize [Ru(bpy)2 L2]Cl2 (bpy=2,2’-bipyridine) by reaction of L with Ru(bpy)2Cl2. This will involve mixing stoichiometric amounts of each compound, reacting with gentle heating overnight, and purifying by column chromatography.
3) Characterize this molecule by 1H and 13C NMR, UV-Vis Absorption, and Emission spectroscopy. This will require preparation of solutions of appropriate concentration for each technique, training in the operation of the instruments, and analysis of the data to confirm the structures of the products obtained.
4) Measure the pKa of the carboxylate groups to determine the best pH for it to bind to a cationic target (if time allows).
5) Measure rates of isomerization in the presence of binding targets by irradiating the samples with visible light and detecting changes in the 1H NMR spectrum (if time allows).
Project 3
Robert Detig
Synthesis and Photochemical Reactivity of the cis and trans Stereoisomers of [Ru(bpy)2(CN)2Co(NH3)4Cl]Cl2
Abstract
Absorption of light can lead to strengthening or weakening of chemical bonds within a molecule. In some cases it has been shown that these changes can also be correlated with increases in the acid-base characteristics of the molecules. Recent studies of the complex trans-Ru(bpy)2(CN)2Rh(NH3)4Br suggest that the weakening of the CN-Rh bond correlates with the well established decrease in basicity of the CN groups in Ru(bpy)2CN2. (Fan, J.; Helmy, R.; Kassis, A.; Grunseich, A.; Mangubat, P.; Hicks, C.; Stevens, N.; Gafney, H. D.; Inorg. Chem.; (Communication) (2003), 42(8); 2486-2488) The weakening of this bond has been shown to be so extreme that the excited state may be better described as two separate species trapped in a solvent cage. In this work, two related stereoisomeric bimetallic complexes (cis- and trans-[Ru(bpy)2(CN)2Co(NH3)4Cl ]Cl2 will be synthesized. These compounds will be characterized using 1H NMR, UV-Vis Absorption, and Emission spectroscopy. The stereochemistry of these species will allow future studies to be performed to determine whether the excited state is a fully separated pair from analysis of the quantum yields of isomerization and decomposition.
Goals
1) Synthesize and purify cis- and trans-Co(NH3)4Cl2 from published procedures (J. Chem. Ed. 80, 7 2000 p 803-805).
2) Synthesize cis and trans-[Ru(bpy)2(CN)2Co(NH3)4Cl]Cl from Ru(bpy)2(CN)2 and cis- and trans-Co(NH3)4Cl2. Our approach will involve mixing stoichiometric amounts of each compound, reacting with gentle heating overnight, and purifying by column chromatography. This is a new synthesis for which no procedure exists.
3) Characterize the cis and trans isomers by 1H and 13C NMR, UV-Vis Absorption, and Emission spectroscopy. This will require preparation of solutions of appropriate concentration for each technique, training in the operation of the instruments, and analysis of the data to confirm the structures of the products obtained.
4) Measure the quantum yields for decomposition and isomerization for each isomer (if time allows).
Results
FTIR Spectra taken of a reaction mixture showing the formation of a bond between a cyanide ligand of Ru(bpy)2(CN)2 and the cobalt of cis-Co(NH3)4Cl2+1. IR absorption spectra obtained in a KBr pellet are shown for a sample of the reaction mixture before (red) and after reflux (black).
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