Detection of Hydrogen Sulfide with Squaraine
Rotaxanes
Michael Kokot
15347 Roscommon Lane
Granger, IN 46530
219-775-2922
mkokot25@gmail.com
Ken Andrzejewski
1311 South Logan
Mishawaka, IN 46544
574-259-5257
kandrzejewski@marianhs.org
Experimentation dates: 10/01/11 – 02/01/12
Total Cost: $540.50
Requested Funding: $300
The hypothesis is that squaraine rotaxane dyes can be used as a selective sensor for hydrogen
sulfide.
Abstract
Hydrogen sulfide detection is important because over exposure can lead to undesirable
health conditions. Currently, there are some detection methods available for hydrogen sulfide,
but they are not selective and are susceptible to detecting thiols, sulfenic acids, and sulfites in
cells as well, making detection unreliable. The goal of this experiment is to develop a selective
method of hydrogen sulfide detection using squaraine rotaxane dyes, which are bright, near
infrared, modifiable, fluorescent dyes. Squaraine dyes contain an electrophilic core that is
susceptible to nucleophilic attack by sulfur containing molecules, of any size. When
encapsulated by a macrocycle though, squaraine dye becomes a squaraine rotaxane. The
macrocycle of the squaraine rotaxane will protect the dye from other sulfur containing molecules
but still will allow the small molecule hydrogen sulfide to attack the electrophilic core, causing a
loss of the fluorescence. The change in fluorescence will be monitored by UV visible absorbance
and fluorescence spectroscopy. The hypothesis is that some squaraine rotaxane will be
susceptible to all sulfur containing compounds and others will not be susceptible. The
experiment will identify squaraine rotaxanes that will be selective in detecting hydrogen sulfide.
Introduction
Being able to detect hydrogen sulfide is a large interest within the scientific community.
Hydrogen sulfide over exposure can lead to serious health problems including unconsciousness,
irritation of the mucus membrane, and respiratory paralysis (Cao). With that information, this
project is based off finding the best way of detecting hydrogen sulfide, making a safer and
healthier world.
Previous studies have been done prior to this one with the goal of detecting hydrogen
sulfide. These however were often vulnerable to detecting cells containing thiols, sulfenic acids,
and sulfites as well as the hydrogen sulfide, making them
unreliable. The goal for this project is to go beyond detection
methods of the past that could detect many things, and take it a step
further by making it more selective, detecting only hydrogen
Figure 1 squarine rotaxane
sulfide. This will be made possible with squarine rotaxanes (SR).
Figure 2 Nuclophilic attack of squarine rotaxane by hydrogen sulfide2, 4
SRs were first synthesized by the Smith laboratory in 2005 (Gassensmith). SRs are
bright, near infrared (Arunkumar), modifiable, fluorescent dyes. Squaraine dyes, or a central
component of SR, contain an electrophilic core that is susceptible to nucleophilic attack by
sulfur-containing molecules. Although this is helpful, it cannot be used for hydrogen sulfide
detection because it can pick up other sulfur containing molecules as well. When encapsulated
by a molecule containing nine or more atoms (called a macrocycle) though, squaraine dye
becomes a squaraine rotaxane. The macrocycle of squaraine rotaxane will protect the dye from
other sulfur containing molecules but will still allow the small molecule hydrogen sulfide to
attack the electrophilic core, causing a loss of the fluorescence that can be detected.
My personal interest with this project stems from my love of science. Science has always
been there throughout my life as I try to figure out the world around me. As a curious,
questioning person, science always offers me ways of shedding light on some of the mysteries
that surround the world we live in. Also, my interest with this project comes from a yearning to
help people around me. Besides volunteer work and other services for the community, there is no
better way to serve others than to develop a detection method of a hazardous substance that does
threaten many people around the world.
With the help of the SR, detecting the hazardous substances will be made possible. The
hypothesis of this experiment is that some SRs will be susceptible to all sulfur-containing
compounds and others will not be susceptible. The experiment will identify SRs that will be
selective in detecting hydrogen sulfide.
Method
Within this project, a variety of water soluble SRs with different functional groups will
be evaluated as possible detectors for hydrogen sulfide. To conduct this experiment UV and
fluorescence spectroscopy and the Beer-Lambert law (B-L) (Reusch) will be used. The B-L law
states that the absorbance of a compound is equal to the molar absorptivity constant times the
path length times the concentration of the compound in the solution (abs = εlc). Each of the SRs
will be evaluated by two methods.
The first method is that a known
concentration of SR in buffer will
be
evaluated
and
the
molar
absorptivity recorded. To this
sample a known concentration of
hydrogen sulfide or a hydrogencontaining
Figure 3 Absorbance 'blue' and emission 'red' spectra of squarine
rotaxane2
molecule
such
as
mercaptoethanol, in buffer, will be
added. The change in absorbance
will then be recorded over time to determine how long it takes hydrogen sulfide to eliminate the
absorbance signal from SRs. Different concentrations of SR and the ratios of SR to hydrogen
sulfide will be evaluated. To analyze the data, graphs of the absorbance maxima versus time for
each experiment will be made and compared.
The second method is the titration of hydrogen
sulfide or sulfur-containing molecules into a solution of a
known concentration of SR. In this one the fluorescent
spectra of SR will be recorded (Lakowicz). To this solution;
hydrogen sulfide will be titrated into the sample. The
fluorescent spectra will be recorded until no more change is
Figure 4 Change in fluorescence intensity
with addition of hydrogen sulfide7
observed, or the fluorescent signal from SR has been quenched. To analyze the data from the
second fluorescence method, graphs of fluorescence maxima versus equivalence of hydrogen
sulfide will be made and compared (Galardon). The results of both methods will be used to
determine the overall selectivity each water soluble SR has for the detection of hydrogen sulfide.
Significance
This project certainly has influence on my future. While working at Notre Dame with
Brad Smith, my mentor, I will be observing how the world of science works, and how real
scientists go about doing real work in a laboratory to solve real problems that face our world
today. Not only will I be observing this, but I will be getting to do the experiments myself,
allowing me to actually work as a professional scientist would. With this information, I will see
if being a scientist is something I want to do with my life.
As well as helping me decide if science is a good career choice for me to go into, the
project has other far reaching benefits. By submitting my work in the Northern Indiana Regional
Science Fair, the Indiana Junior Science and Humanities Symposium, the Indiana Science Talent
Search, and the Indiana Junior Academy of Science Competition, I will be able to compete with,
and share, my project. With these great competitions and science gatherings, I could receive
numerous scholarship opportunities, and gain access to more prestigious and rewarding colleges
as I begin looking for potential colleges next year.
Besides benefitting me, this project has a larger, far-reaching significance. This project
will allow for the detection of Hydrogen Sulfide, which, as stated, currently poses substantial
health risks to people around the world. After this project finds a detection method, people will
be able to avoid the health risks posed by hydrogen sulfide, by avoiding it completely.
Budget
Materials asked for from the IAS:
Materials
Source
Cost
Sodium sulfide nonahydrate
Sigma Aldrich 208043-100G
$38
Fluorimeter cuvette
Sigma Aldrich C9292-1EA
$252.50
Squarine rotaxane
Smith Lab
$250
Total
$540.50
Materials supplied by Smith Lab:
1.
2.
3.
4.
5.
6.
7.
8.
9.
UV visible spectrometer
Fluorimeter
TLC plates
Gas-tight analytical syringe
Volumetric flasks
Other analytical glassware
Ultra-pure water
Gloves, goggles, and other safety equipment
Magnetic stir bar
All expenses not covered by the IAS will be covered by Smith Lab.
Works Cited
Cao, X., W. Lin, and L. He. "A Near-Infrared Fluorescence Turn-On Sensor for Sulfide
Anions." Organic Letters 13 (2011): 4176-719. Print.
Gassensmith, J., J. M. Baumes, and B. D. Smith. "Discovery and Early Development of
Squaraine Rotaxanes." Chemical Communications (2009): 6329-338. Print.
Arunkumar, Easwaran, Christopher C. Forbes, Bruce C. Noll, and Bradley D. Smith. "SquaraineDerived Rotaxanes: Sterically Protected Fluorescent Near-IR Dyes."Journal of the American
Chemical Society 127.10 (2005): 3288-289. Print.
Reusch, William. "UV-Visible Spectroscopy." Michigan State University :: Department of
Chemistry. 20 June 2010. Web. 04 Oct. 2011.
Lakowicz, Joseph R. "Introduction to Fluorescence." Principles of Fluorescence Spectroscopy.
New York: Springer, 2006. 1-8. Print.
Galardon, Erwan, Alain Tomas, Pascal Roussel, and Isabelle Artaud. "New Fluorescent Zinc
Complexes: towards Specific Sensors for Hydrogen Sulfide in Solution." Dalton Transactions 42
(2009): 9126. Print.
To Whom It May Concern:
Michael Kokot is participating in research in the laboratory of Dr. Bradley Smith, Ph.D. at the
University of Notre Dame. I am a fourth year graduate student in his lab and will be assisting
and supervising Mike in his research. His project is to investigate the use of squaraine rotaxane
dyes as hydrogen sulfide sensors. The Smith laboratory will be providing the necessary
chemicals, safety equipment, and instrumentation for this project.
Sincerely,
Erin L. Cole, B.S.
Department of Chemistry and Biochemistry
University of Notre Dame
Smith Laboratory
378 Stepan Chemistry Hall
Notre Dame, IN 46556
phone: (574) 631-7629