250
14 Creating Genetic Materials of Metal Clusters
According to the procedure by Miller et al. [191], F-SAM surfaces were prepared
by soaking the substrate (a glass layer, 1.6 mm thick, covered with 50 Å of Ti and
1000 Å of polycrystalline gold) in a 1-mM solution of CF 3 (CF 2 ) 7 (CH 2 ) 2 SH in
ethanol for a few days [193]; and then the surfaces were then rinsed and sonicated
in ethanol several times before modification by the low-energy ion beams. F-SAM
surface was examined before and after the deposition of the ions with the use of
132 Xe
·+ sputtering for surface analysis. The spectral results (Fig. 14.5b vs. c) showed
that, after the deposition experiment, only a single prominent new ion species was
observed with m/z = 147 assigned to (CH 3 ) 3 SiOSi (CH 3 )
+
2 . Some other similar softlanding experiments confirmed the availability of soft-landing of polyatomic ions
at the F-SAM surfaces [191]. These results indicated successful soft-landing and
retrieval of polyatomic ions favored by relatively bulky steric groups [188].
Laskin and coworkers [195] demonstrated the soft-landing of mass-selected
peptide ions on SAM surfaces. Surfaces modified with peptides are commonly
used in biological and medical applications, including characterization of molecular recognition events at the amino acid level, identification of biologically active
motifs in proteins, as well as the development of novel biosensors and substrates
for improved cell adhesion [196, 197]. For example, in one of their studies they
showed the potential use to prepare conformation-specific peptide arrays by using
the singly protonated Ac-A 15 K peptide (Ac = acetyl, A = alanine, K = lysine) which
was selected as a model system in their study as this peptide forms a very stable αhelical conformation due to the interaction between the protonated C-terminal lysine
residue and the dipole of the helix [194]. Experiments were performed using an electrospray ionization (ESI) cluster source and an ion deposition apparatus as shown in
Fig. 14.6. Based on such instrumentation, the physical and chemical properties of
peptide film on substrates were determined by noticing very different FTIR spectra
obtained following deposition of the AcA 15 K peptide from solution and from the gas
phase (Fig. 14.7).
The spectrum obtained by electrospray deposition (ESD) showed a dominant
absorption band corresponding to a mixture of the β-sheet, α-helix and other
secondary structure motifs; however, the spectrum obtained by soft-landing yields a
narrow amide-I band that corresponds to the α-helical conformation [195]. In comparison, a narrow α-helical amide-I band was also obtained following reactive-landing
of Ac–A 15 K on a NHS-SAM. These findings indicated that, while ESD resulted
in the formation of a peptide layer dominated by the β-sheet structure, a stable αhelical peptide layer was formed by both soft-landing and reactive-landing, which
enables a technique for controllable preparing of conformation-selected peptide
layers [178, 195].
14.4.2 Soft-Landing onto Unreactive Solid Supports
Previous studies have revealed that, clusters with kinetic energies of less than 1 eV
per atom could be nondestructively landed on bare substrates, but severe impact
14 Creating Genetic Materials of Metal Clusters
According to the procedure by Miller et al. [191], F-SAM surfaces were prepared
by soaking the substrate (a glass layer, 1.6 mm thick, covered with 50 Å of Ti and
1000 Å of polycrystalline gold) in a 1-mM solution of CF 3 (CF 2 ) 7 (CH 2 ) 2 SH in
ethanol for a few days [193]; and then the surfaces were then rinsed and sonicated
in ethanol several times before modification by the low-energy ion beams. F-SAM
surface was examined before and after the deposition of the ions with the use of
132 Xe
·+ sputtering for surface analysis. The spectral results (Fig. 14.5b vs. c) showed
that, after the deposition experiment, only a single prominent new ion species was
observed with m/z = 147 assigned to (CH 3 ) 3 SiOSi (CH 3 )
+
2 . Some other similar softlanding experiments confirmed the availability of soft-landing of polyatomic ions
at the F-SAM surfaces [191]. These results indicated successful soft-landing and
retrieval of polyatomic ions favored by relatively bulky steric groups [188].
Laskin and coworkers [195] demonstrated the soft-landing of mass-selected
peptide ions on SAM surfaces. Surfaces modified with peptides are commonly
used in biological and medical applications, including characterization of molecular recognition events at the amino acid level, identification of biologically active
motifs in proteins, as well as the development of novel biosensors and substrates
for improved cell adhesion [196, 197]. For example, in one of their studies they
showed the potential use to prepare conformation-specific peptide arrays by using
the singly protonated Ac-A 15 K peptide (Ac = acetyl, A = alanine, K = lysine) which
was selected as a model system in their study as this peptide forms a very stable αhelical conformation due to the interaction between the protonated C-terminal lysine
residue and the dipole of the helix [194]. Experiments were performed using an electrospray ionization (ESI) cluster source and an ion deposition apparatus as shown in
Fig. 14.6. Based on such instrumentation, the physical and chemical properties of
peptide film on substrates were determined by noticing very different FTIR spectra
obtained following deposition of the AcA 15 K peptide from solution and from the gas
phase (Fig. 14.7).
The spectrum obtained by electrospray deposition (ESD) showed a dominant
absorption band corresponding to a mixture of the β-sheet, α-helix and other
secondary structure motifs; however, the spectrum obtained by soft-landing yields a
narrow amide-I band that corresponds to the α-helical conformation [195]. In comparison, a narrow α-helical amide-I band was also obtained following reactive-landing
of Ac–A 15 K on a NHS-SAM. These findings indicated that, while ESD resulted
in the formation of a peptide layer dominated by the β-sheet structure, a stable αhelical peptide layer was formed by both soft-landing and reactive-landing, which
enables a technique for controllable preparing of conformation-selected peptide
layers [178, 195].
14.4.2 Soft-Landing onto Unreactive Solid Supports
Previous studies have revealed that, clusters with kinetic energies of less than 1 eV
per atom could be nondestructively landed on bare substrates, but severe impact