Abstract

1. Solvatochromism and IR Characteristics of Tricyanovinyl Substituted Molecules Sarah Hammond, Rebecca Nagurney and Kyrra Struble Faculty Advisor: Phuong-T. Pham Abstract Materials and Methods Results (cont’d) Spectroscopic grade hexane, ethyl acetate, and methanol were used. Twelve test tubes were prepared with each of the four compounds dissolved in the three selected solvents. UV-Vis spectra were obtained using the Shimadzu UV-Mini 1240 Spectrophotometer. The region scanned was from 200 – 700 nm. Quartz cuvettes were used. A blank was run for each solvent before the actual sample was tested. A consistent trend was observed in the absorption spectra with increasing solvent polarity . IR spectra were obtained using the Lambda FT-IR 7600 and the Universal ZnSe ATR. Cross talk within microenvironment is known to give rise to the complexity of cancer. Studies of protein dynamics and micro-environment heterogeneity are thus important for the understanding of their biological roles. However, due to the difficulties associated with direct experimental characterization of proteins, many recent efforts have focused on the use of sensitive probes that absorb IR light between 1800 and 2600 cm-1, a region that is relatively free from absorptions. One such probe is the cyano (CN) chromophore, which may be appended to different amino acids. In this work, we studied the UV and IR absorptions of a series of compounds containing tricyano-vinylene group (TCV). IR absorptions of CN is observed to shift by about 126.9 cm-1 toward higher frequency when a bromine is introduced. UV-VIS study of these molecules revealed their solvatochromic behavior, another useful characteristic for the study of microenvironments in biological systems. Molecules under study: tricyanovinylbithiophene, 2T-TCV; bromotricyanovinylbithiophene, Br-2T-TCV; tricyanovinyltriphenylamine, Ph3N-TCV; &bromotricyanovinyltriphenyl amine, Br-Ph3N-TCV. CN: 2216.9 cm-1 Ph3N – TCV Hexane < Ethyl acetate < Methanol Dipole moment 0.08 1.88 2.87 Least polar ------------- > Most polar 2363.1, 2332.9 cm-1 Br- Ph3N-TCV Results 2T-TCV and Ph3N-TCV showed a bathochromic shift, which is a shift from shorter to longer wavelength due to increased solvent polarity. Bathochromic shift is also known as red shift because it is a shift toward the red wavelengths (~700nm). Br-2T-TCV and Br-Ph3N-TCV exhibited hypsochromic shift which is a shift from longer to shorter wavelength due to increased solvent polarity. This is known as blue shift because in contrary to the red shift, the shift is toward the blue wavelengths (~450nm). The IR spectra show the distinctive nitrile stretch which clearly shifts toward higher frequency in the presence of a bromine (Br- Ph3N-TCV ; Br-2T-TCV) 2218.9 cm-1 2216.7 cm-1 2T-TCV 2T-TCV 2360.9, 2329.7 cm-1 Br-Ph3N-TCV in Methanol Ph3N-TCV in Hexane Ph3N-TCV in Ethyl Acetate Br-2T-TCV Br- Ph3N-TCV Br-2T-TCV Figure 4: FT-IR spectra of Ph3N-TCV, Br-Ph3N-TCV, T-TCV and Br-T-TCV obtained using ATR sampling technique. Ph3N-TCV in Ethyl Acetate • Ph3N-TCV in Methanol Figure 4: Calc. UV spectra of 2T-TCV and Br-2T-TCV using Density Functional Theory/Spartan Discussion Ph3N - TCV Solvatochromism is generally observed in molecules having large dipole moments. The position and the intensity of electronic bands in the uv-visspectra are mainly due to the difference in dipole moment of the molecule in its ground state and in its excited state. We used UV-VIS spectroscopy to investigate the solvatochromism behavior of a series of compounds containing TCV in hexane (non-polar solvent) and methanol (polar protic solvent). Changes in maximum UV-Vis absorption of brominated and non-brominated compounds varied where the largest shift was observed for Ph3N-TCV (+14 nm) and Br-Ph3N-TCV (-14 nm). IR spectra showed CN that stretches for 2T-TCV and Ph3N-TCV derivatives, both shift to higher frequency when Br is introduced, indicating possible involvement of the CN group in additional intermolecular interactions. Stretching of the CN bond hence require more energy. We also noted that, brominated and non-brominated molecules showed opposite solvatochromic behavior. This indicates either opposite polarization of their corresponding excited states and/or that the bromine atoms are involved in new inter- molecular interaction. 2T-TCV Figure 3: Solvent Effect on Absorbance Figure 2: Structural Effect on Absorbance Introduction • Solvatochromism is defined as a substance’s ability to change color depending on the polarity of the solvent in which it is dissolved. Solvatochromism has many useful applications. Scientists learn a lot about biological environments by studying the effects of solvatochromism. Probes can be placed on different biological molecules, such as enzymes and proteins, to study their surroundings. A nitrile group (CN) placed on a molecule can be used as a probe to study these effects since it is very sensitive to environmental changes as well as structural changes. Color change is an indicator that there is a change in the molecule or its surrounding. IR and UV spectroscopy best show environmental effects of the CN group. IR absorption of CN group is observed in a region free from most absorptions. The small size of the CN group also minimize its effect on structural change. Table 1: Color of Solutions Shown for Compounds in Different Solvent References • Boxer, Steven P., Fafarman, Aaron T., Fenn, Timothy D., et. al • "Quantitative, Directional Measurement of Electric Field Heterogeneity in the Active Site of KetosteroidIsomerase." Quantitative, Directional Measurement of Electric Field Heterogeneity in the Active Site of KetosteroidIsomerase. National Academy of Sciences, 17 Jan. 2012. Web. 09 Apr. 2013. • Biancardi, Alessandro, Marini, Alberto, Mennucci, Benedetta, • Et al. "What Is Solvatochromism?" The Journal of Physical Chemistry. American Chemical Society, 3 Dec. 2010. Web. 7 Apr. 2013 • Table 2: Observed changes in UV/Vis absorbance . • *Bathochromic shift (red shift): Shift to longer wavelength with increased • solvent polarity. • **Hypsochromic shift (blue shift): Shift to shorter wavelength with increased • solvent polarity. Compounds in Ethyl Acetate Compounds in Hexane Compounds in Methanol Figure 1: Compounds Exhibiting Solvatochromism in Solvents of Different Polarities. From left to right: Br-2T-TCV, Br-Ph3N-TCV, 2T-TCV, and Ph3N-TCV