Main works of Masaharu Okazaki are presented briefly. 1) Reaction of radical-pair intermediates produced in a nano-cage (mainly as the photo-reaction intermediates) can be controlled by manipulating the spin state. 2) Alcohol molecules flow collectively in the nanochannel of MCM-41. Evidences are given by the spin probe and radical-pair probe techniques.

1. Spin Chemistry and Nano flow in MCM-41:Brief Survey:
1) Reaction-control by spin manipulation (RCSM) and product-yield-detected ESR (PYESR):1-5)
Figure 1 Reaction Control by Spin Manipulation
Upper: The process of photoreduction of xanthone(XO) in
the presence of xanthene (XH2, a hydrogen donor) can be
switched at the stage of intermediate radical pair 3(XOH•
•XH) by the spin manipulation technique: “spin inversion”
accelerates the coupling reaction of the two radicals and
“spin locking” decelerates it.2)
Lower: The effect of spin inversion on the HPLC of product
solution. The (XH)2 peak decreased to about 1/2 by the
"spin inversion".3)
"Reaction Control by Spin Manipulation" is briefly explained here on the photoreduction of xanthone (XO) in SDS micellar solution. UV-irradiation
of the system yields xanthone excited in the lowest excited triplet state, 3XO*, from 1XO* via the intersystem crossing process. Then, 3XO* abstracts
a hydrogen atom from a hydrogen donor, xanthene (XH2) in the present case, and the "geminate radical pair" in the triplet state 3(XH・・XOH) is
formed in the cage (SDS micelle). If one of the electron spins of this radical pair is inverted by the ESR (electron spin resonance) method, the coupling
reaction of the component radicals is accelerated to yield the "cage product" XH-XOH. Instead, when a high power resonance rf-field is irradiated, the
spin state of radical pair is locked to the triplet state, and the recombination reaction is inhibited.6) When the yield of one of these compounds is
plotted as a function of the magnetic field strength, the ESR spectra of both the radicals are traced in the overlapped form. The spectrum thus obtained
has been named product-yield-detected ESR or PYESR in short.4,5) The first paper was published in Nature in1986.5) Until this publication no
reaction yield had been monitored to obtain the ESR spectrum of the intermediate radical pair, so we named the method PYESR as usual. Spin locking
of the radical pair is rather difficult, since it needs a microwave field much larger than the internal magnetic interactions, such as hyperfine coupling.
Therefore, it has been most clearly demonstrated with the perdeuteriated systems.6)
From the quantum mechanical point of view, it is true that similar experiments had been made by the Nobosibirsk group (ODESR, optical detection
of ESR)7) and also by the Argonne group (FDMR, fluorescence detected magnetic resonance).8) They produced transient ions by ionizing radiation,
and detected their ESR spectrum by detecting the fluorescence, which is emitted upon charge neutralization of the two ions upon returning to the
original states. Most of the scientists in the field of "Spin Chemistry" presume these experiments as the early trials of the "reaction-yield-detected
magnetic resonance".9,10) However, they observed a process that is not directly related with chemical reaction or its products. A few years before these
experiments, Frankevich et al. detected the ESR spectrum of a triplet exciton by its annihilation fluorescence in a crystal.11). They named their
experiment RYDMR, reaction yield detected magnetic resonance, where "reaction" was used as an analogy for exciton annihilation. This experiment
is a modification of the ODMR (optical detected magnetic resonace) method as IUPAC Gold Book classifies. ODMR experiments had been made
from the 1960's to observe the ESR of exciton.9,10,12) Therefore, their naming of RYDMR is misleading. The important point of PYESR experiment
is that the chemical bond formation is controlled by the spin operations, and this kind of experiment had not been made before ours.12,13) In the full
article in the following section, the application of "pulse-PYESR" is described. This method is very powerful to study the dynamics of the radical pair
in micelle as well as the dynamics of micelle.
2) Collective molecular flow in the MCM-41 nanochannel
Figure 2: SEM images of the MCM-41 particles (A) and the
model structure of the nanochannels (B) MCM-41 was

2. synthesized from tetraethoxysilane (Si(C2H5O)4) by the
template method.
MCM-41 is an interesting material composed of cylindrical nanochannels,14-16) which may serve as a "nano-chemical factory" in the future. To
realize this idea the chemicals must be transported continueously in the nanochannels and out of there after the synthetic reaction. As a first trial we
made an experiment by using a flow apparatus with an UV-transmitting column packed with MCM-41 (i.d. 3.0 mm; Length=100 mm) where UV
irradiation is made. Two bottles are equipped to store the reactant solution and the pure solvent (used for washing the flow system), which are
deoxygenated by Ar gas bubbling. A pump for liquid chromatography makes the flow of reactant solution in the column and UV-laser irradiates the
reactant solution.
Scheme 1. Formation of radical pair in the
photoreduction of xanthone in the presence of
xanthene in the nano "cage".
The reaction system with XO and XH2 in 2-propanol was selected for the first study in this series, since we had been studied extensively the same
system in the SDS micellar solution (see ref. 2 and papers cited there). The radical pair formation in SDS micelle proceeds as in the scheme shown as
scheme 1.3)
Figure 3: The assumed reaction process for the
photoreduction of XO in the presence of XH2 in the
column packed with MCM-41 (upper), and the
HPLC diagrams for the reaction products obtained
under the various conditions (lower). G-bead and
PrOH represent glass beads and 2-propanol,
respectively, and M(d) is for MCM-41 with
nanochannels of which diameter is d nm.
The solution after the photolysis with this apparatus was collected and analyzed. 17) The HPLC traces are given as Figure 3 with the reaction
mechanism modified from scheme 1. Since a reversed phase column was employed, a polar product appears in the early part (left) of the HPLC
diagram. When MCM-41 composed of the nanochannels with the inner diameter of 2.5 nm are employed (abbreviated as M(2.5) in Figure 3), the
height of the (XH)2 peak relative to the XH-XOH peak was 1/5 of that in the bulk phase reaction and the coupling product between the alcohol radical
and the xantyl radical becomes one of the main product. The considerable magnetic field effect observed on the yields (third and forth HPLC)
indicates that the cage effect, which has been described precisely by Turro et al. for the reaction in the SDS micellar solution,18) is also working
effectively in the nanochannel of 2.5 nm.
According to the third HPLC, XH-ROH, whose extinction coefficient may be about 2/3 of the other products with two C13O groups (peak a),
becomes the main product in the 2.5 nm nanochannel. This result indicates that the probability for the photoexcited XO to collide with the XH2
decreases almost zero in the nanochannel of MCM-41(2.5)(d=2.5 nm).19) Since half the open space in the reaction column is the bulk space between
the MCM-41 granules, where the photoreaction also occurs as shown in the first and second HPLC diagrams, all these analyses on the third HPLC
indicates that the solution should flow smoothly in the nanochannel. This hypothesis had been made in the first paper, since the shape of nanochannel
has very large length/diameter ratio. Simple "adsorption and diffuse in/out of the pore model" cannot explain the large cage effect on the product yield
detected in the solution flew out of the column. The Poiseuille’s law does not hold in this case. The model of this flow is given below and named as
“collective molecular flow”, where the plug flow near the inlet continues deep inside with the help of intensified intermolecular hydrogen-bond
network among the alcohol molecules and their slipping on the smooth surface of nanochannel.

3. Figure 4: Mechanism of the "collective molecular
flow" in the nanochannel of MCM-41 1. In the
usual tube flow the liquid near the wall is
decelerated and the radial distribution of the flow
speeds becomes parabolic; 2. In the nanochannel the
plug flow continues; 3. the intensified hydrogen
bond network between solvent molecules weakens
interaction of those with the channel wall. The lodlike alcohol flows or diffuse rapidly by slipping the
wall of nanochannel.
The above flow model are based on the assumptions: a) alcohol molecules intensity the hydrogen network and the interaction between the alcohol
molecule and the wall silica of the nanochannel is weakened; b) the diffusion of the solute molecules is seriously hindered by the H-bond networking
of the solvent. Since the surface surface must be smooth and the diameter of the nanochannel is constant in the atomic level, the solution may slip on
the surface. This slip of the solution on the tube wall must elongate the induction period from the plug flow near the inlet of the tube to the Poiseuille's
flow. These models have been strongly suggested by two spin probe studies. In the first study, we clarified that condensation of alcohol in the
nanochannel proceeds by two steps: 1) first layer of the wall is covered by the alcohol molecules; 2) a part of the nanochannel is filled by the liquid
alcohol without completing the second molecular layer. 20) In the second paper, it has been shown that collision between the solute-spin probe
molecules is almost prohibitted. This conclusion was based on the absence of spin exchange broadening for the spin probe solution even at 30 mM.19)
Although we proposed the "collective molecular flow " model for the MCM-41 nanochannel, we do not insist that the slip flow model should holds
for the same type of nanochannel with infinite length. In addition, we don't know about the length of the plug flow nor the length of the nanochannel.
To confirm the solution flow in the nanochannel, alcoholic solution of a spin probe, di-t-butylnitroxide (DTBN), was let flow in the column, with or
without MCM-41, and real time ESR spectra were observed. The time-dependence of the concentration in the column was determined by ESR
observation.21)
Figure 5: Left: "Apparent"
concentration of DTBN at the ESR
sensitive region as functions of flow
volume. 0.4 mL of its ethanol
solution at 30 mM was let flow at
0.05 mL/min in the open column
(0.81 mm i.d.)(a) or in the column
packed with MCM-41 (b); Right:
ESR spectra of the ethanol solution
of DTBN flowing in the column
packed with MCM-41(spectrum c),
or in the open column (spectrum d).
The sharp component (spectrum e) is
due to DTBN in the nanochannel,
which is obtained by subtracting the
bulk spectrum d from spectrum c.
The open and closed circles of the left diagram of Fig. 5 trace the time dependent ESR intensities for the columns without and with MCM-41,
respectively. The latter curve shift a little to the larger volume and the area under this curve is about 86% of that obtained for the open column. The
relative volumes (∝σ(i) ) of the nanochannel, space between granules, and silica wall are 0.35, 0.44, and 0.21, respectively. Which were determined by
the XRD data, BET surface area, denisty of silica layer, and the packed weight and volume in the column. If the solution flows equally in the two
spaces, the integrated area of curve b should be 0.79 times of that of curve a. This is simply because the solution flows in the column whose sectional
area becomes 21 % less than that for the column without MCM-41. The experimental result is similar to this case (86%), and only by 7% larger than
the ideal value. This difference indicates a little part of the solution stays somewhere for a while. This result cannot be explained with the model,
where the solution does not flow in the nanochannel but the solute is distributed into the two spaces with an equilibrium constant K:
(1)
If the solution does not flow in the nanochannel, the relative flow rate of spin probe solution (in mL/min) becomes smaller than that through the
column without packed granules, since the spin probe flows downstream only when it exists out of the nanochannel. Therefore, the solute delays from
the solvent by the factor of :
(2)
Since K=0.419 is obtained from the signal ratio of the two components in spectrum c of Fig. 5, curve b in Fig.5 (left) must have been extended about 1.33 times
in the horizontal direction and compressed by about 0.59 times in the vertical direction compared with curve a. The observed results of Fig. 5 (left) are far from
this prediction. Therefore the solution should flow in the nanochannel. This conclusion is valid even if there exists some imperfections in the packing of MCM41 particles, if the column condition was invariant during the experiments for Figs.5. It is quite difficult to pack particles with irregular shapes in a thin column,
there may be some imperfections.22)

4. Referece
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
M. Okazaki, Y. Konishi, K. Toriyama, Chem. Lett., 737 (1994).
M. Okazaki, K. Toriyama, J. Phys. Chem., 99, 489 (1995).
M. Okazaki, K. Toriyama, J. Phys. Chem., 100, 9403 (1996).
M. OKazaki, R. Konaka, S. Sakata, T. Shiga, J. Chem. Phys., 86, 6792 (1987).
M. Okazaki, T. Shiga, Nature, 323, 240(1986).
M. Okazaki, K. Toriyama, J. Phys. Chem., 99, 17244 (1995).
O.A.Anisimov, V.M. Grigoryants, V.K. Molchanov, Yu.N. Molin, Chem. Phys. Lett., 66, 265(1977).
A.D. Trifunac, J.P.Smith, Chem. Phys. Lett., 73, 94(1980).
A.L. Buchachenko, E.L. Frankevich, "Chemical Generation and Reception of Radio- and Microwaves", Wiley-VCH, New York, 1994
U.E. Steiner, H-J. Wolff, in "Photochemistry and Photophysics" vol.4, eds. J.F. Rabek, CRC Press, Boca Raton, 1991, Chap.1
E.L. Frankevich, A.I. Pristupa, V.I. Lesin, Chem. Phys. Lett., 47, 304(1977).
Yu. N. Molin, in "Foundation of Modern EPR", eds. G.R. Eaton, S.S, Eaton, K.M. Salikhov, World Scientific, 1998, Chap. H12.
H. Hayashi, in "Introduction to Dynamic Spin Chemistry", World Scientific, 2004, chap.14, section 3 (page 222).
C.T. Cresge, M.E. Leonowitz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature, 359, 710 (1992).
T. Yanagisawa, T. Shimizu, K. Kuroda, C. Kato, Bull. Chem. Soc., JPN, 63, 988, (1990)
For example, A. Coma, Chem. Rev., 97, 2373 (1997).
M. Okazaki, Y. Konishi, K. Tpriyama, Chem. Phys. Lett., 328, 251 (2000).
N.J. Turro, Proc. Natl. Acad. Sci., USA, 80, 609 (1983).
M. Okazaki, K. Toriyama, J. Phys. Chem., part C, 111, 9122 (2007).
M. Okazaki, S. Iwamoto, Y. Sueishi, K. Toriyama, J. Phys. Chem., part C, 112, 786 (2008).
M. Okazaki, et al., J. Phys. Chem., part C, 113, 11086 (2009).
F.A.L. Dullien, "Porous Media, Fluid Transport and Pore Structure", 2'nd ed. Academic Press, New YTork, 1992.
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