J. Biol. Macromol., 9 (1) 3−12 (2009)

Review

DNA as functional material
with one-dimensionally oriented molecular chains
Nahoko Morii† and Hisayuki Morii*
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8566, Japan
Received January 19, 2009; Accepted February 18, 2009Materials with the structures in nanometer scale have emerging importance in the technology. In
the present article, the development in molecular chain alignment of DNA was reviewed, including ourrecent new technologies to fabricate molecular chain-oriented DNA films. It was found that two different
mechanisms play essential roles in the orientation of DNA molecular chains. One is the alignment along
the boundary of a solution of DNA, which occurs as liquid crystal formation accompanying theconcentrating process caused by the evaporation and the transportation in a droplet. The other is amagnetic effect, which regulates aromatic groups such as nucleic acid bases to be in parallel to amagnetic field. The best result was obtained by the combination of these for a thin-layer solution ofdiluted DNA. The method for DNA materials with one-dimensionally oriented molecular chains could beapplied to the fabrication of the various composite materials bearing anisotropic properties.
Furthermore, this is, in turn, found to be useful and convenient for determining the DNA-binding
manners of pharmaceutical compounds such as anticancer reagents.
Keywords: DNA molecular chain, orientation, interfacial effect, magnetic field, anisotropic material

Introduction
Engineered membrane with one-dimensionallyoriented organic molecules is one of the frontiers ofdeveloping functional materials [1-4]. The
technology to regulate molecular orientation is
expected to enhance the potential of materials. As forthe orientation of DNA, for example, ameniscus-driven method along with the translation of
an interface, the Langmuir-Blodgett method, amethod using dielectric polarization, and amechanical stretching method have been developed[5-8]. As extrinsic factors, both electric field andmagnetic one are generally known for the handlingof molecules including the orientation. The former iswidespread and applied to apparatuses such as
electrophoresis. In contrast, the latter is less popular
for the purpose of molecular handling. Though these
two extrinsic fields resemble each other, the actions
are quite different. For example, electric field can*Corresponding author: tel., +81-29-861-9466;e-mail, morii.hi@aist.go.jp† present address; National Institute for Materials
Science (NIMS), Tsukuba, Ibaraki 305-0044, Japancause transport of molecules, however magnetic field
is almost limited to bringing about the change inmolecular orientation [9,10].
The representative action of magnetic field isexpressed as “Aromatic ring is suited for being inparallel as for a magnetic field”. This originates inrelatively large diamagnetic effect of an aromatic
molecule in the orientation perpendicular to outermagnetic field (Fig. 1). In a DNA molecule, aromaticgroups with anisotropic response for a magnetic field
are nucleic acid bases, which form stacking structure
regularly along the axis of double-stranded DNA
molecule. Therefore, molecular chain of DNA shouldorientate in perpendicular to magnetic field. However,this does not mean one-dimensional orientation,
because the perpendicular direction is not unique but
distributed by 360 degrees circumferentially likevanes of a windmill in the wind. In other words,
one-dimensional orientation cannot be realized if
only by a magnetic field. Additionally, magneticallyinduced mechanical energy is extremely smaller thanthe energy of thermal motion causing randomorientation. The former is evaluated to be 10-25−10-23

4

Molecular Orientation of DNA

Fig. 1. Anisotropy of magnetic susceptibility ofbenzene as a representative aromatic compound. The
benzene molecule was located in 3 orientations so as
to make its 3 orthogonal directions, x, y, and z, lie
along a magnetic field, respectively. The lines of
induced magnetic force are shown around themolecules. Overall diamagnetic vectors are indicatedwith black arrows.

J for a general molecule in 10-tesla magnetic field
and the latter is 2x10-21 J per a degree of freedom
estimated with Boltzmann constant [11]. As
explained below, such disadvantageous situation was
overcome by intrinsic feature of DNA molecules asforming liquid-crystal structure [12]. DNA
membrane with one-dimensional orientation cametrue due to liquid-crystal formation based on two
cooperative regulations, that is, magnetic effect andinterface-dependent orientation [12]. In the present
paper, we describe the methods and the mechanism
for one-dimensionally oriented DNA molecules,
which is the world's first, referring to interesting
phenomena discovered in the course of research.
The DNA membrane with one-dimensional
orientation is expected to be applied to various fields.
The DNA membranes including DNA-binding dyes
such as intercalators will be useful as opticallyanisotropic films. One promising application on thebasis of the same principle is our originallydeveloped method to determine the DNA-binding
manner, which can conveniently clarify whether a
newly synthesized pharmaceutical molecule, e.g.,
anticancer agent, is intercalator type or minor-groove
binding one for DNA [13]. For fundamental science,the chain-oriented DNA membrane may contribute torevealing the electric conductivity of DNA, which
would be a candidate of electronic device in future[14-16]. DNA itself as a molecule has been
investigated since more than half a century ago [17].
When Wilkins and Franklin analyzed X-ray
diffraction of DNA in 1930's, it was necessary toalign the direction of DNA molecular chains [18,19].
The atomic-resolution structure was differently
revealed by X-ray crystallography for oligo DNA in
1980 at last [20]. Meanwhile, various efforts havebeen made to realize the orientation of DNA
molecules, resulting in the developments of adrawing-brush method, a stretch process, andinduced polarization in a solution under the electricfield [5,6,7,21]. These methods have respective
merits, however our method applying the magnetic
field gave the best orientation of DNA in a solid film
[12].

Methods for preparation of DNA solid film withmolecular chain orientation
Recently, mass production of DNA as amaterial becomes possible by using a large amountof salmon sperm as by-product of food industry. In
our study, such commercially available DNA wasused only after sonication to provide several classesof averaged molecular weight. In order to realize
molecular orientation we examined two different
methods, namely ‘method A’ and ‘method B’, for the
fabrication of DNA films as described below (Fig. 2).
The ‘method A’ involves the process to dry a droplet

Fig. 2. Two types of method for preparation of DNA
solid films. In the method A and B, the drying process
starts from a thick-layer solution and a thin-layer one
on glass plates, respectively. As for the method B, theDNA solution is relatively diluted and a horizontal
magnetic field is given all through the drying process.
In the bottom of the Figure, the patterns of molecularorientation are exhibited with thin lines and curves.

N. Morii and H. Morii

5

of DNA solution in the ordinary atmosphere,
providing DNA solid films bearing a strange patternof molecular orientation made up of both annular andradial ones as shown in Fig. 2 [22]. On the other
hand, ‘method B’ involves the drying process forthin-layered DNA solution under a magnetic field[12]. For this method, it is crucial that the initialconcentration of DNA solution is rather low enoughnot to form liquid crystal structure. The DNA filmwith good molecular orientation was obtained at theinitial concentration of 50 mM DNA, and 10 teslamagnetic field brought about a favorable result.

Evaluation and analysis on molecular orientationof DNAThe X-ray diffraction of hydrated DNA fibers iswell known to show X-shaped pattern characteristicof helical structures. Also, there appears the intensive
axial diffraction of 0.34 nm corresponding to theinterval of stacking base-pairs [19]. Our DNA film
obtained by method B using a magnetic field wasfound to have a similar X-ray diffraction pattern as
above. By using X-ray radiation from three different
directions, the orientation of DNA in the film wasanalyzed. The dependence of diffraction intensity at
0.34 nm on the azimuthal angles is shown in Fig. 3.
Characteristically, the radiation along the normal of
the film (Fig. 3a) and that tilted to the direction of amagnetic field used for the preparation (Fig. 3c) gave
homologous diffraction patterns (Figs. 3b and 3d,respectively). On the other hand, the diffraction
pattern for the film tilted in a perpendicular manner
as for the case of Fig. 3e showed rather broad peaks(Fig. 3f), which had biased intensities. These results
suggest that the DNA molecular chains are oriented
in parallel each other and in perpendicular to themagnetic field (Figs. 3g and 3h). In conclusion, theunique orientation of DNA molecular chains inparallel for the film can be realized by the method B[22].
The orientation of DNA molecular chains could
be also confirmed by polarization microscopy. The
polarization property was analyzed by using theequipment of a sensitive tint plate at 530 nm (Fig.
4a). Based on the color changes caused by therotation of the sample by 45 degrees, the DNA film
prepared by a drawing-brush method was found tohave almost one-dimensional orientation of DNA

Fig. 3. Evaluation on the extent of molecular chainorientation. The X-ray was radiated to DNA films
mounted at vertical or tilted positions (a, c, and e).
The diffraction intensities, ID, corresponding to thespacing periodicity of base-pair stacking were plottedagainst azimuthal angles, χm (b for a, d for c, and f fore). The estimated molecular chain orientation in thefilm is exhibited with a cylinder model (g) and aball-and-stick model (h) in the same location. The
magnetic field for the fabrication is indicated with anarrow B. The structural model in Fig. 3h was adopted
from the data 1IO4 in Protein Data Bank.

molecules (Fig. 4b). Similarly, the DNA film bymethod B had well-aligned one-dimensional
orientation (Fig. 4c). The homogeneous appearanceof colors for the latter film means a uniform
thickness of the film.
Additionally, by UV spectroscopy with linearlypolarized light it was revealed that these DNA films
have linear dichroism reflecting the anisotropy ofelectronic transition dipole moments. The absorbanceof the films was the largest at the arrangement where
the polarization vector accords with the plane of
nucleic acid bases. This is consistent with the resultby X-ray diffraction, so that the polarization UV

6

Molecular Orientation of DNA

Fig. 4. Analysis on molecular chain-oriented DNA
films by polarization microscopy with sensitive tint
plate. The observation was carried out using thesensitive tint plate inclined by 45 degrees (a). The
DNA films prepared by drawing-brush method and by
the method B changed in apparent colors dependingon the rotational angles (b and c, respectively). The
film prepared by the method A showed two different
manners of orientation (d). Estimated molecular chainorientations are exhibited with thin lines and curves at
the right of the corresponding photographs (b, c, andd). (See original Figures in the references for theactual colors under observation [12,22].)

measurement seems convenient to identify the
direction of DNA molecular orientation.
In the course of experiment for molecularorientation, we observed a peculiar pattern oforientation in a DNA film prepared by method A
without a magnetic field (Fig. 4d). Since thedifference in colors, i.e., blue or yellowish,corresponds to the orientation of molecules, we caneasily identify the directions of DNA molecular
chains at respective positions by the method using asensitive tint plate. The orientation of DNA in thisfilm was rotationally symmetric as for the center ofthe droplet of initial DNA solution. At the central
part of the droplet-derived film, the DNA chainsoriented in radial directions. In contrast, at its outerregion the orientation was found completely annular.
In the region around the boundary of these two, DNA
molecular chains were less-ordered. These

Fig. 5. Time course of the drying process. Thechanges in the side views of droplets are shown fromthe top to the bottom (a for pure water, b for DNA
solution). The correlation between the diameter andthe height of a droplet was plotted (c; open circle,
water; closed circle, DNA solution).

orientation patterns seems to be brought about in amanner of ‘interface-induced orientation’ as
explained below.

Mechanism for the orientation of DNA byinterfacial effect
The DNA film involving annular orientation ofmolecular chains can be obtained by drying a dropletof DNA solution [22]. To reveal the mechanism
underlying this phenomenon, we tracked the timecourse of drying for a droplet solution on a glass
plate in the atmosphere (Fig. 5). After an initial quick
decrease in the thickness, a droplet of pure water
underwent a further drying course, keeping thecontact angle constant at the edge (Figs. 5a and 5c).
In other words, the droplet became small in a similar
form during this process. In contrast with pure water,a droplet of DNA solution underwent a transition oflowering the thickness of the droplet withoutchanging its diameter largely (see Fig. 5b and theregion from 6 to 4.5 nm in diameter shown in Fig.
5c). Following this process, only the diameterdecreased from 4.5 to 2 nm, and at the final stage thedroplet became dried up rapidly.

N. Morii and H. Morii

The rate of decrease in the thickness wasevaluated as 0.08 mm/min in this experiment. On theother hand, the diffusion rate of DNA molecules is
estimated on the basis of Einstein-Stokes equation to
be only one tenth of the above (Fig. 6a) [23].
Therefore, it is suggested that longer DNA molecules
are prone to remain near air-liquid interface due toFig. 6. Proposed model for the phenomena occurringin the drying process. a, Diffusion of DNA andtransition of air-liquid interface, indicating the former
is slower than the latter. b, Uneven evaporation fromthe surface of a droplet and capillary flow in a solution
induced by the evaporation. c, Estimation for the
distribution of DNA concentration. d, The early stageof the local formation of a solid DNA film at theboundary edge of a droplet. The top plan view exhibits
the formation of molecular chain alignment along theshape of the edge. e, The closing stage of film
formation. The rapid transition of the boundary
towards the center causes the trailing of molecular
chains.

7

such slow movement (Fig. 6c). In fact, theconcentration of DNA near the surface of a solution
was found to be higher than that at its bottom byanalyzing local solutions sampled directly. As well as
the vertical concentrating as described above, thehorizontal accumulation of the mass is likely to occur
in a drying course, because the DNA film thus
prepared was found to have unequal thickness alongradial direction (Fig. 6e). Especially, the region close
to the initial edge was remarkably thick. Thus, thefirst stage of a drying course can be elucidated byboth the accumulation at the air-liquid interface andthe transportation to the edge of the droplet, which
seem to be induced by the evaporation of water (Figs.
6a and 6b). The thick edge region of the film should
be brought about by the radial flow called ‘capillary
flow’ toward the boundary of the droplet, which
occurs due to relatively high rate of evaporation in
the edge region [24].
Though the initial concentration is quite low incomparison with that for the formation of DNA
liquid crystal, the local concentration near the surface
and also at the edge of a droplet should come up to
be high enough to form the liquid crystal owing to
the evaporation. The process of accumulation also
seems to cause molecular packing of DNA along thesurface of the solution, which would lead to theliquid crystal. Since the molecular orientation of
DNA is aligned in parallel to the outer edge of thedroplet as revealed by polarization microscopy (Figs.
4d and 6d), the formation of liquid crystal should be
conducted by the boundary of the droplet.
This hypothetical model for the annularorientation of DNA molecules could be supported byother related experiments (Table 1). In the case using
DNA samples with short molecular chains and/or
single-stranded ones, the obtained films were foundto have no molecular orientation. This is probably
due to their small hydrodynamic radii. In addition,
the preparation of DNA film under low temperature
resulted in poor orientation. In these unfavorable
conditions, it is suggested that the movement of
DNA molecules seems to be faster than the transition
speed of air-liquid interface due to rapid diffusion or
slow decrease in the thickness of a solution. Theseexperiments clearly showed that relatively low
motility of the molecules in comparison with theaccumulation and the transportation is an important

8

Molecular Orientation of DNA

Table 1. Comparison of various conditions for the preparation of DNA solid films. The case 1 is a standard
and the others, the case 2, 3, and 4, are different from the case 1 in the points denoted by underlined boldcharacters. (* theoretically calculated values, ** experimentally obtained values)
DNA sample and condition
Strand type
Molecular weight [kbp]**
Chain length [nm]Statistical chain element [nm]*Radius of coil structure [nm]*Temperature [℃]**
Averaged rate of diffusion [mm/min]*Descending rate of luquid surface [mm/min]**
Extent of molecular chain alignment

factor for molecular orientation of DNA. In summary,it is proposed that annular orientation of DNA
molecular chains is based on the mechanism
illustrated in Figs. 6a−6d.
The molecular chain orientation in a central
region of the droplet was different from that in aedge region as mentioned above, showing radial
orientation (Fig. 6e). This orientation occurred at the
final stage of a drying course. Since the boundary ofa droplet displaces rapidly to the center, theaccumulation of DNA molecules seems to bedifficult. Instead, each molecular chain should exist
in both solid and liquid phases at once in a form
spanning the liquid-solid interface. Accompanying
the displacement of the interface, a part of DNA
molecule in liquid phase seems to be transported but
the other part remains fixed in solid phase.
Consequently, it is suggested that the rapid
displacement of the interface make DNA molecular
chain trailed along the direction to the center (Fig.
6e). Thus, two different manners of molecular chainorientation occur depending on the speed ofliquid-solid interface.

Mechanism for magnetically-induced orientationof DNA
Organic compounds are generally diamagnetic[11]. Especially, aromatic compounds such as
benzene also have remarkable anisotropy inmagnetization property, which derives from spatiallyanisotropic π-electron system [25]. Aromatic groups
have larger diamagnetic susceptibility in the
direction along its normal than in the other directions,so that the parallel orientation of the normal withrespect to a magnetic field is relatively unstable (Fig.
7). Similarly, DNA molecules are expected to havecase 1
double
29
1000
100
500
23
8
80
high

case 2
double
1
30
100
50
23
20
80
low

case 3
double
29
1000
100
500
0
8
4
very lowcase 4
single
29
1000
1
50
23
20<
80
very low

the anisotropy because of the structure with nucleic
acid bases stacked in parallel. The magnetic
susceptibilities were experimentally evaluated for 4
kinds of nucleic acid bases in 1960's [26]. Then, it
was reported that DNA molecules actually respond toa magnetic field in a solution [27,28]. Since thenormal of each nucleic acid base is in line with theaxis of molecular chain of double-stranded DNA, themolecular chains of DNA should favor theorientations perpendicular to a magnetic field (Fig.
8a). This is at least consistent with the experimental
results shown in Fig. 2. However, DNA molecular
chains under a magnetic field cannot have a uniqueorientation in a solution but exist in the forms along
various directions with two-dimensional freedom asshown in Fig. 8b. Therefore, another effect inaddition to a magnetic one should be taken into

Fig. 7. Diamagnetic susceptibility of the aromaticcompounds and the base pairs of DNA. Threeorthogonal line segments above the molecules indicate
the components of the susceptibility along x, y, and z
coordinates of the molecules. The vectors exhibit thedirection and the intensity of overall anisotropy.

N. Morii and H. Morii

Fig. 8. Model illustration for the orientation of DNA
molecular chains. a, Comparison of the stabilities for
3 orthogonal orientations under a magnetic field B.
DNA molecular chains are represented with cylinders.
b, Probable orientations of DNA chains in a solution
under a horizontal magnetic field. The directions of
the molecular chains distribute 2-dimensionally. c,
Molecular chain alignment by the interfacial effect inaddition to the orientation shown in Fig. 8b.

consideration to elucidate the formation of DNA
films with completely aligned molecular chains as
Fig. 8c.
By the simple method as drying in a magnetic
field, we have succeeded in preparing highly-ordered
DNA films [12]. The extent of molecular chainorientation seems superior to that by the method
without a magnetic field, such as method A in Fig. 2
or a drawing-brush method. As for the preparation ofmolecular chain-oriented DNA films under amagnetic field, we have proposed the mechanism asfollows. In a early stage of drying from thin-layer
solution according to the method B shown in Fig. 2,
DNA molecules are oriented to various directions but
lie in a plane directed by a horizontal magnetic field(Fig. 8b). Subsequently, following the evaporationfrom the surface of the solution, DNA molecules areconcentrated in parallel to fit the air-liquid interface.
When the concentration near the surface rises above
a critical concentration for liquid-crystal formation,
the parallel orientation of DNA chains are fixed from
top to bottom to be a solid DNA film finally. Thus,
for the molecular chain orientation by the method B,
it is concluded that both the magnetic field and the9Fig. 9. Dependence of the extent of DNA molecularorientation on the molecular weights (a) and magnetic
intensities (b). The extent of orientations wasevaluated with the values of birefringence. The
orientation at 0 tesla occurred only by the interfacial
effect.

interfacial effect are crucially important [12].
In addition, unlike with thin-layer solution
system, drying thick-layer solution of DNA in amagnetic field resulted in very characteristic zonal
patterns of molecular orientation depending on themagnetic intensity (Figure not shown). In this case,major interfacial effect appeared at the parts of theboundary edge of a droplet locating in perpendicular
to a magnetic field. For not only the method ofdrying from thin-layer solution but also that fromthick-layer one, the significant molecular orientationis perpendicular to a magnetic field and the extent ofregularity was found remarkably high. It is importantfor good results that the initial concentration of DNA
is low enough to assure molecular motion fororientation without causing a tangle in the course ofconcentrating.

Effect of molecular weight and magnetic intensity
on molecular orientation
In order to explore the possibility for the
improvement of molecular orientation, its
dependence on the molecular weight was examined.
DNA molecular chains are known to be cut

10

Molecular Orientation of DNA

mechanically by the action of sonication without
losing intact double-stranded structure. By selecting
the time period of treatment with ultrasonic wave,
various DNA samples with different averaged
molecular weights can be prepared. DNA solid films
were fabricated from the solutions of these DNA
samples by the method B in the same conditions
under a magnetic field. The extent of molecular chainorientation was evaluated as birefringence by using
polarization microscopy (Fig. 9a). As increasing the
averaged molecular weight, the birefringence of the
DNA films increased. This suggests that themolecular orientation depends on the balance
between the motility and the liquid crystal formation.
Probably, DNA molecules with larger molecularweight would have an advantage in respects of slow
diffusion, slow rotation, and large stabilizationenergy by a magnetic field, which are favorable forthe molecular alignment through the process from its
concentrating to the formation of liquid crystal.
By means of similar experiments under amagnetic field with various intensities, the extent ofmolecularalignment
wasevaluated.
Thebirefringence of the obtained DNA films wereplotted against magnetic intensities (Fig. 9b). The
orientation of molecular chain was significantly
enhanced above 4 tesla of a magnetic field. And, itreached a saturation level at 8 tesla, so that theregulation of the orientation by a magnetic fieldshould sufficiently overcome the randomization due
to thermal motion at this magnetic intensity.

General aspects on magnetic effect for polymer
chains
The availability of a magnetic field formolecular orientation is not limited to the processfrom isotropic solution to anisotropic solid films as
the case of DNA described above. For example,
synthetic polymers such as polyamide are fabricatedby the method of melt spinning in some cases to haveanisotropic
properties
involvingmechanicaltoughness and excellent thermal resistance. The
application of a magnetic field may be effective in
regulating the molecular chain alignment of suchpolymers at the stage after the achievement of basic
orientation by a mechanical method. Polyamides
contain at least amide groups and, in a case, aromaticgroups in a main chain. The normals of these

π-electron systems are generally perpendicular to theaxis of the polymers in contrast with the case of
DNA. Therefore, these two representative types ofpolymers are illustrated in Fig. 10, where DNA andpolyamide are indicated with cylinders and slenderplates, respectively, at the stage that somepreliminary orientations of polymer chains are
performed.
Consideringtheanisotropic
magnetic
susceptibility, the application of a magnetic field in
the direction perpendicular to polymer axes seems
effective for the orientation of DNA as shown with ashort black arrow (Fig. 10a). On the other hand,some of polyamide chains are likely to bedisconcerted at first as shown with a white arrow(Fig. 10b). However, this change is expected to besettled in the form parallel to a magnetic field, so that
this process may be effective for the secondary
regulation of polyamide chains. In contrast, theapplication of a magnetic field parallel to polymer
axes seems to cause the dislocation of aligned
polymer chains of DNA (Fig. 10c). Though, theparallel magnetic field will be advantageous to theregulation of polyamide chains as shown with shortFig. 10. Regulation of molecular orientation by amagnetic field for the different types of polymers insemi-oriented states. A magnetic field was given fromthe direction perpendicular (a and b) and parallel (cand d) to the axes of the polymers. DNA wasrepresented with cylinders (a and c) and polyamide
chains were with slim thin plate (b and d). Black
arrows indicate possible extents of wobbling motions
under a magnetic field. White arrows express theforces towards stable orientations originated from theanisotropic susceptibility.

N. Morii and H. Morii

black arrows (Fig. 10d). Thus, depending on theinitial states of polymer chain orientation, the methodwith a magnetic field would be available for further
regulation of the orientation. It should be noted thatthe magnetic effect has permeability even for the
deep inside of materials. This is a great merit for the
regulation of molecular orientation and further
development in the applications is expected.

Composite materials of molecular chain-oriented
DNA with other compounds
In the previous sections, DNA solid films withwell-aligned molecular chains were described. For
the DNA films by the method B, it was revealed thatthe orientation of DNA molecular chains are
regulated by both the magnetic field and theinterfacial effect including the formation of liquid
crystal. The simplicity of the procedure is one of theadvantages in its applications. As for the extent ofmolecular orientation, the X-ray diffraction analysis
gave relatively broad patterns (Fig. 3), which can be
attributed to that the normals of nucleic acid bases
intrinsically incline by a little degrees from the axisof a molecular chain. The actual regularity in theorientation is estimated to be rather fairly highenough to be used in various applications.
Based on the methods for the fabrication ofmolecular chain-oriented DNA films, the composite
DNA films with organic dyes were developed [13].
The dye-DNA films were prepared by drying themixed solutions of DNA and the dyes such as
acridine orange, ethidium bromide, and Hoechst
33258 under a magnetic field. The obtained
composite films were found to have excellent opticalanisotropy, exhibiting not only dichroism in opticalabsorption but also secondary dichroism influorescence emission. The optical anisotropy ofthese dye-DNA films seem to be comparable toorganic liquid crystals. The advantage may be
expressed in the easy selection of specificwavelengths bearing dichroism only by the choice oforganic dyes. It is obvious that the anisotropy ofdye-DNA films is closely relevant to the well-aligned
orientation of DNA chains and specific binding
manners of the dyes, i.e., the minor-groove bindingor the intercalation.
In addition, this method was applied for thecomposite films of DNA and porphyrins [29].

11

Though it is predicted that the porphyrin derivatives
are too large to undergo specific binding manners for
DNA unlike the dyes such as acridine orange, several
types of porphyrins were found to have characteristicorientation in porphyrin-DNA films. Tetra(4sulfonatophenyl)-porphyrin formed H-aggregation
bearing the orientation, in which the normal ofporphyrin plane was parallel to the axis of DNA. In
contrast, tetra(N-methylpyridinium-4-yl)-porphyrin
exhibited the patch-like binding for the surface ofDNA. These finding may pioneer a new technology
for molecular orientation in addition to that the
chain-aligned DNA can provide linear void space forguest molecules.
In summary, composite films based onmolecular chain-oriented DNA are expected to bepromising anisotropic materials. The convenient
procedure for their preparation would enhance theavailability of this technique. Furthermore, thismethod is useful not only for the development of
anisotropic composite materials but also for analysisof the binding manners of organic compounds toDNA. It should be noted that the latter application
may enable the high throughput analysis for
DNA-binding manners of pharmaceutical products.

Acknowledgments
The authors are grateful to Prof. Dr. Giyuu
Kido (National Institute for Material Science) andProf. Dr. Takeo Konakahara (Tokyo University of
Science), and also to the members of the related
laboratories in AIST and NIMS for various supports
in the works described here.
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Communicated by Masayuki Oda