JP4423388B2 - Oriented molecular mass spectrometry - Google Patents

Description

  The present invention relates to an oriented molecular mass spectrometer capable of estimating not only mass but also a molecular spatial structure.

  A conventional mass spectrometer ionizes a target substance, moves the ion by applying an electric field or a magnetic field, and measures the mass of the target substance based on the difference in the movement. As the above ionization method, it is common to irradiate a substance with a laser beam and an electron beam to peel off the electron from the substance and ionize it. However, in general substances, especially in substances with a large molecular weight, the molecules are decomposed and fragmented (fragmented) at the time of ionization. It was difficult to estimate molecular weight and molecular structure. As one solution for the fragmentation, a matrix-assisted laser desorption / ionization method (MALDI method) has been developed that allows soft ionization without breaking the target substance. However, even in the MALDI method, the molecular weight is obtained, and it was impossible to know the structure of the molecule.

  The reason for this is that, as shown in Fig. 1 (1), in the conventional mass spectrometer, the orientation of the target molecules is random, so the way the decomposition products scatter is scattered, and the molecular structure information Is lost.

As a method of performing ionization and decomposition by distinguishing and orienting the head and tail of a molecule, a method combining an electrostatic field and a laser light photoelectric field (see Non-Patent Document 1 below) and a method using only a laser light photoelectric field (See Non-Patent Documents 2 and 3).
In addition, in the above-mentioned orientation and ionization, when the orientation of the molecules is random, the head and tail are distinguished for almost all molecules and oriented in a certain direction, and the molecules that are slow to the orientation operation are randomly selected. This includes a case where the head and tail are distinguished from a group of different states and selected to be ionized by orientation in a certain direction.

The outline of the method using only the photoelectric field of laser light is described below. The target substance is irradiated with laser light (hereinafter referred to as “phase control light”) that is composed of two wavelengths λ ₁ and λ _{2 and} has a ratio of λ ₁ : λ ₂ = 2: 1. Ionize. The photoelectric field E (t) of the phase control light is expressed by the following equation.
E (t) = E ₁ cos (2πct / λ) + E ₂ cos (2πct / (λ / 2) + φ)
Here, c is the speed of light. Further, the wavelengths λ ₁ = λ and λ ₂ = λ / 2 are set, the amplitudes of the light components of the wavelengths λ and λ / 2 are E ₁ and E ₂ , respectively, and the relative phase difference between the wavelengths λ and λ / 2 is φ and did. The phase control light has a waveform as shown in FIG. 2 depending on when the relative phase is φ = 0 and φ = π, and has an asymmetric shape in which the amplitude of the photoelectric field is positive and negative with respect to the traveling direction of the light. Since the permanent dipole of a molecule is oriented in the direction of a large electric field, the head and tail of the molecule are distinguished and oriented to cause ionization and photolysis, or only the oriented molecule is selected to cause ionization and photolysis.
H. Ohmura, T. Nakanaga, M. Tachiya, Phys. Rev. Lett. 92, 113002 (2004). H. Ohmura and T. Nakanaga, J. Chem. Phys. 120, 5176 (2004). H. Sakai et.al., Phys. Rev. Lett. 90, 083001 (2003).

  In normal mass spectrometry, the only physical quantity to be measured is mass (molecular weight), and it is difficult to further estimate the molecular structure from the molecular weight.

  As shown in FIG. 1 (2), the present invention aims to estimate the structure of the molecule from the orientation (decomposition) of the decomposition products, and the molecular structure, as shown in FIG. 1 (2). Information on the three-dimensional structure of the molecule can also be obtained.

  As a method for aligning molecules, there are a method in which an electrostatic field and a photoelectric field of laser light are combined, and a method in which only a photoelectric field of laser light is used. Conventional methods may be used for ionization and decomposition of the molecules.

  In the present invention, it is possible to perform mass spectrometry capable of estimating not only the molecular weight of a molecule but also the structure of the molecule.

  Hereinafter, as an embodiment of the present invention, an example in which a method of using only a photoelectric field for photolysis by distinguishing and aligning the head and tail of a molecule will be described with reference to FIGS.

One embodiment of the present invention comprises three parts: 1) a laser unit, 2) a phase control unit (optical interferometer), and 3) a mass spectrometer.
FIG. 3 is a schematic diagram of the first laser unit. As the laser, a pulse laser is used. The wavelength of the laser beam is suitably 200 nm to 20000 nm, the pulse width is 10 femtoseconds to 100 nanoseconds, and the light intensity is suitably 10 ⁶ W / cm to 10 ²⁰ W / cm. As an example, a wavelength of 800 nm, a pulse of 130 fs, and a light intensity of 10 ¹² W / cm ² were employed. When the wavelength of the laser is λ, a part of the laser light is wavelength-converted so as to be λ / 2 or 2λ. In the wavelength conversion, a part of the laser beam (wavelength 800 nm) was converted into a wavelength λ / 2 (400 nm) by second harmonic generation by a nonlinear optical crystal.

FIG. 4 is a schematic diagram of the second phase controller (optical interferometer). Light of wavelengths λ and λ / 2 emitted from the laser unit is guided to the phase control unit. The optical interferometer shown in FIG. 4 is a modification of the Mach-Zehnder interferometer. The laser beam having the wavelength λ is guided to the optical path 1, and the laser beam having the wavelength λ / 2 is guided to the optical path 2. By controlling the optical path length of one of the optical paths, the optical path length 1 and the optical path length 2 are made to coincide with each other with an accuracy of 1/100 or less of the light wavelength λ. In this embodiment, the optical path length of the optical path 2 is controlled by the following method.
(Coarse adjustment) A translation stage that can be coarsely adjusted by ~ λ is inserted in the optical path of wavelength λ / 2.
(Fine adjustment) Laser light is passed through a parallel plate type optical medium (in one embodiment, a quartz plate, thickness: 3 mm). By rotating the parallel plate optical medium, the length of the laser beam passing through the parallel plate optical medium is finely adjusted with an accuracy of λ / 100.
A half-wave plate (optical path 1 in one embodiment) is inserted into one of the optical paths, and the laser beams with wavelengths λ and λ / 2 are aligned and overlapped on the same axis. At this time, the wavelength λ and the λ / 2 laser light are spatially and temporally overlapped and output from the optical interferometer as phase control light whose relative phase is controlled.

  The phase control light is guided to the mass spectrometer. In the mass spectrometer, the target substance is oriented and ionized by the phase control light. Photolysis is caused by ionization, and the mass spectrum of the resulting photolysis product ions is measured. As the mass spectrometer, a mass spectrometer that can measure the initial velocity of the photolysis product or the emission angle distribution of the photolysis product during photolysis is used. In this example, a time-of-flight mass spectrometer was used.

  FIG. 5 is an example of a mass spectrum of carbonyl sulfide (COS) molecules by an oriented molecular mass spectrometer. C ions, O ions, CO ions, S ions, CS ions, and COS ions are observed. Therefore, the measured molecule is a triatomic molecule COS containing C, O, and S, and it is understood that other ions (fragment ions) were observed by decomposition. Each fragment ion is observed as a pair of two peaks. This reflects the initial velocity during photolysis. That is, the component having a fast flight time is due to ions jumping in the direction of the ion detector during photolysis, and the component having a slow flight time is due to ions jumping in the direction opposite to the position of the ion detector. . In the measurement result of randomly oriented molecules, a symmetrical spectral shape is observed in which the components of the fast component and the slow component are equal.

However, when the molecule is oriented with the permanent dipole moment of the molecule directed in the direction opposite to the position of the ion detector as shown in Fig. 5, the C ion, O ion, and CO ion are The fast component is observed to be large, and the S ion and CS ion have a large component with a slow time, resulting in an asymmetric spectral shape. This indicates that there are O and C at the beginning of the permanent dipole vector of the COS molecule, and C and S at the end of the permanent dipole vector. It can be seen that the atoms are aligned with O-C-S from the start point to the end point. Thus, it is possible to estimate not only the mass but also how the molecules are arranged (molecular structure). Photolysis is a general phenomenon that occurs with ordinary substances and is therefore a highly versatile technique.

The present invention can be used to determine the structure of all inorganic compounds, all organic compounds, cluster molecules, metal cluster complexes, proteins, or biopolymers. Possible fields of use include the chemical synthesis field, the pharmaceutical field or the biotechnology field.
In addition, it is expected to be an important analytical technique for identifying isomers having the same mass but different structures. For example, thalidomide has optical isomers (those with exactly the same atomic structure that cannot be overlapped like the left and right hands), are effective in the L form, and have side effects in the D form. Can be distinguished and recognized.

Illustration of the principle of an oriented molecular mass spectrometer Conceptual diagram of molecular orientation distinguishing head and tail by phase control light Schematic diagram of laser unit Schematic diagram of phase controller Example of measurement of carbonyl sulfide (COS) molecules by an oriented molecular mass spectrometer

Claims (11)

Molecules are ionized and decomposed in the state of being oriented to analyze motion status at the time of the decomposition of the decomposed debris oriented molecular mass analysis and estimates the structure of the molecule based on the movement status Way . The oriented molecular mass spectrometry method according to claim 1, wherein the orientation distinguishes between a molecular head and a tail. The oriented molecular mass spectrometry method according to claim 1, wherein the orientation is performed by an electric field and light. The oriented molecular mass spectrometry method according to claim 1, wherein the orientation is performed by light. The method according to claim 4, wherein the light is phase control light. The oriented molecular mass spectrometry method according to claim 1, wherein the ionization and decomposition are performed by light. The method according to claim 6, wherein the light is phase control light. The oriented molecular mass spectrometry method according to claim 1, wherein the analysis of the motion state is performed by a mass spectrum or an emission angle distribution of the fragments. The oriented molecular mass spectrometry method according to claim 8, wherein the mass spectrum is measured by a time-of-flight method . The oriented molecular mass spectrometry method according to claim 9, wherein a molecular structure is estimated based on the pattern of the mass spectrum. The oriented molecular mass spectrometry method according to claim 10, wherein the pattern focuses on a peak indicated by each fragment.