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M. Dantus and C.L. Kalcic
molecular structure in the gas phase. The high-throughput capabilities are routinely
used in the field of proteomics to efficiently analyze thousands of peptides. A typical MS/MS experiment first isolates the precursor ion population using a magnetic
or electric field, and then activates this ion population to cause dissociation. The resulting product ions are recorded as the MS/MS spectrum [10]. A variety of ion activation methods can be employed, causing dissociation of the precursor ions along
different pathways and leading to complementary MS/MS spectra [11]. These tandem mass spectra can be analyzed by hand or electronically using algorithms to
map out the most likely structure of the original precursor ion. An ion activation
method capable of breaking many different bonds within a molecule is desirable
because the corresponding MS/MS spectrum will be more “information rich.” In
other words, it will contain a greater number of overlapping product ions that can
be used to assign a more complete precursor structure with higher confidence. An
ion activation method is suitable for peptide samples if it can generate sufficient
product ions for unambiguous sequencing and mapping of structural modifications
[12]. This structure determination can become problematic if certain regions in a
peptide resist fragmentation, or if weakly bound peptide modifications dissociate
preferentially to other bonds along the peptide backbone. In order to find a solution
to these challenges, there is great interest in the development and characterization
of new ion activation methods. Each method serves as an additional tool for tandem
mass spectrometry experiments.
Given the expertise of our research group in ultrafast laser science and pulse
shaping, the development of an ion activation method that utilized Femtosecond
laser irradiation seemed fitting. The coupling of tandem mass spectrometry with a
femtosecond laser was especially promising given developments in the field of femtosecond photoionization. In 1980, Zewail commented that the use of sufficiently
short pulses would allow one to beat the timescale of energy redistribution, which
typically takes place in tens of picoseconds [13]. As a result, a handful of research
groups turned their focus to new experiments in laser control. The application of
femtosecond lasers to study photodissociation processes in real time [14] led to the
observation that bond dissociation can take place on a timescale of ∼200 fs, which is
two or three orders of magnitude faster than energy redistribution within a molecule.
The optimization of laser fields to control chemical reactions and therefore the observed fragmentation patterns was proposed by Tannor and Rice [15]. Brumer and
Shapiro realized that coherent light from the laser would cause interference between
particular photochemical pathways, opening an attractive means for laser control of
chemistry with nanosecond lasers [16]. The concept of creating a molecular wave
packet that could be followed in time to cause selective chemistry by two or more
carefully timed pulses was outlined by Rice, Kosloff and Tannor [17]. By the 1990’s,
scientists began to modify femtosecond laser pulses by adding linear chirp, first to
control wave packet motion [18], and then to control the yield of chemical reactions
[19].
The experimental work on adaptive quantum control was reviewed by Brixner
and Gerber in 2003 [20]. Our group published a comprehensive review of modern
(1997–2005) experimental results on coherent laser control of physicochemical processes [21]. The combination of shaped femtosecond pulses with mass spectrometry
M. Dantus and C.L. Kalcic
molecular structure in the gas phase. The high-throughput capabilities are routinely
used in the field of proteomics to efficiently analyze thousands of peptides. A typical MS/MS experiment first isolates the precursor ion population using a magnetic
or electric field, and then activates this ion population to cause dissociation. The resulting product ions are recorded as the MS/MS spectrum [10]. A variety of ion activation methods can be employed, causing dissociation of the precursor ions along
different pathways and leading to complementary MS/MS spectra [11]. These tandem mass spectra can be analyzed by hand or electronically using algorithms to
map out the most likely structure of the original precursor ion. An ion activation
method capable of breaking many different bonds within a molecule is desirable
because the corresponding MS/MS spectrum will be more “information rich.” In
other words, it will contain a greater number of overlapping product ions that can
be used to assign a more complete precursor structure with higher confidence. An
ion activation method is suitable for peptide samples if it can generate sufficient
product ions for unambiguous sequencing and mapping of structural modifications
[12]. This structure determination can become problematic if certain regions in a
peptide resist fragmentation, or if weakly bound peptide modifications dissociate
preferentially to other bonds along the peptide backbone. In order to find a solution
to these challenges, there is great interest in the development and characterization
of new ion activation methods. Each method serves as an additional tool for tandem
mass spectrometry experiments.
Given the expertise of our research group in ultrafast laser science and pulse
shaping, the development of an ion activation method that utilized Femtosecond
laser irradiation seemed fitting. The coupling of tandem mass spectrometry with a
femtosecond laser was especially promising given developments in the field of femtosecond photoionization. In 1980, Zewail commented that the use of sufficiently
short pulses would allow one to beat the timescale of energy redistribution, which
typically takes place in tens of picoseconds [13]. As a result, a handful of research
groups turned their focus to new experiments in laser control. The application of
femtosecond lasers to study photodissociation processes in real time [14] led to the
observation that bond dissociation can take place on a timescale of ∼200 fs, which is
two or three orders of magnitude faster than energy redistribution within a molecule.
The optimization of laser fields to control chemical reactions and therefore the observed fragmentation patterns was proposed by Tannor and Rice [15]. Brumer and
Shapiro realized that coherent light from the laser would cause interference between
particular photochemical pathways, opening an attractive means for laser control of
chemistry with nanosecond lasers [16]. The concept of creating a molecular wave
packet that could be followed in time to cause selective chemistry by two or more
carefully timed pulses was outlined by Rice, Kosloff and Tannor [17]. By the 1990’s,
scientists began to modify femtosecond laser pulses by adding linear chirp, first to
control wave packet motion [18], and then to control the yield of chemical reactions
[19].
The experimental work on adaptive quantum control was reviewed by Brixner
and Gerber in 2003 [20]. Our group published a comprehensive review of modern
(1997–2005) experimental results on coherent laser control of physicochemical processes [21]. The combination of shaped femtosecond pulses with mass spectrometry