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A novel cyclic conjugate of a helical decapeptide and oligo(phenyleneethynylene) (OPE), C-OPE10, was synthesized. The conformation and the optical properties of the cyclic conjugate were studied by circular dichroism (CD), absorption, and emission spectroscopies. In the cyclic conjugate, the rotational motion around the molecular axis of the OPE moiety was hindered to take a chirally twisted conformation, which is a distorted form from the coplanar conjugated structure, as revealed by observation of an induced negative Cotton effect of the OPE moiety. Molecular simulation using time dependant-density functional theory indicated a right-handed twist conformation of the OPE moiety for the negative Cotton effect. This conjugate therefore provides a new way to obtain a π-conjugated compound having main-chain chirality. The optical properties of the OPE moiety taking the twist conformation in the cyclic conjugate are also discussed in depth.

Supramolecular chiral emergence from achiral molecules is studied with amphiphilic polypeptides upon forming molecular assemblies of nanosheets and vesicles in water. A newly designed amphiphilic polypeptide contains a hydrophilic poly(Sar) block, two hydrophobic helical blocks, and a π-conjugate block (SL-π-D). The two helical blocks are (L-Leu-Aib)4and (D-Leu-Aib)4of right- and left-handed helices, respectively, to compensate for the helical chirality resulting in the achiral molecule of SL-π-D. SL-π-D self-assembled in trifluoroethanol (TFE)/water solutions into uniform nanosheets and vesicles depending on the TFE content in the solutions. The induced Cotton effect due to exciton coupling appears in the achiral π-conjugate block upon self-assembling into nanosheets and vesicles. This supramolecular chiral emergence is enhanced in vesicles compared to nanosheets. The origin of the chirality intrinsically arises from the structure of (helix block)-(π-conjugate block)-(helix block) and further from vesicular morphology.

Amphiphilic block polydepsipeptides of AB-type and AB3-type (hydrophilic A block: poly(sarcosine), hydrophobic B block: poly(l-lactic acid)) were prepared, and the N-terminals were arranged by guanidium or guanidino-peptide nucleic acid for loading siRNA in a reverse polymeric micelle. The amphiphilic polymers were successfully dispersed and assembled into reverse micelles in triglyceride or diisopropyl adipate. With loading siRNA into the core of the polymeric micelles, the micelle size was reduced down to a diameter of 25 nm in the case of the guanidino-peptide nucleic acid used as the capturing site. This small-size reverse micelle may be available for a transdermal drug delivery system (DDS) for siRNA.Amphiphilic block polydepsipeptides of AB-type and AB3-type were synthesized and self-assembled into reverse polymeric micelles in organic solvents, N-terminals of which were arranged by guanidium or guanidino-peptide nucleic acid (PNA) for loading siRNA. With loading siRNA into the core of the micelles, the size was reduced to a diameter of 25 nm with the guanidino-PNA as capturing sites.

To develop nanopiezoelectronics, it is necessary to investigate the relationship between the sizes and piezoelectric properties of the material. Peptide nanotubes (PNTs) composed of cyclic β-peptides have been studied as leading candidates for nanopiezoelectric materials. The current drawback of PNTs is aggregation to form a PNT bundle structure due to strong dipole–dipole interactions between PNTs. Here, we report the construction and piezoelectric properties of single PNTs without nonspecific aggregation by side-chain modification of helical peptides. A cyclic tri-β-peptide with a helical peptide was prepared by multiple-step liquid-phase peptide synthesis and assembled into PNTs by the vapor diffusion method. These nanotubes were characterized by polarized light microscopy and Fourier transform infrared (FTIR) spectroscopy. Additionally, atomic force microscopy (AFM) topographic images showed nanotubes with a height of 4 nm, which corresponds to the diameter of a PNT on a gold-coated mica substrate, indicating that a single PNT was prepared successfully. The converted piezoelectric response of a single PNT was determined to be 1.39 ± 0.12 pm/V. This value was consistent with that of a PNT bundle, which reveals that the piezoelectricity of PNTs is induced by deformation of their cyclic skeletons and is independent of the bundled structure. This finding not only demonstrates a new molecular design strategy to construct these smallest piezoelectric biomaterials by controlling the supramolecular hierarchical structures but also provides insights into the correlation between molecular assembly morphology and size-dependent piezoelectric properties.

A series of novel linear conjugates of helical peptides and oligo(phenyleneethynylene) (OPE) were synthesized and studied on the dipole effect of the helical peptide moieties on the electronic structure of the OPE. The helical peptides have a generalized formulation of multiple repeats of l-alanine and α-aminoisobutyric acid, (Ala-Aib)nor m, which are connected to OPE in series of (Ala-Aib)n-OPE-(Ala-Aib)mabbreviated by 2nOPE2m, (n, m) = (4, 0), (4, 4), (8, 0), (8, 4), (8, 8). The conjugates having one or two hexadecapeptides formed well-packed and vertically oriented self-assembled monolayers on gold as revealed by infrared-reflection absorption spectroscopy, cyclic voltammetry, and ellipsometry. Absorption spectra of the OPE moiety in the SAMs showed a bathochromic shift of ca. 25 nm from a reference conjugate of 11-mercaptoundecanoic acid and OPE (C11OPE). The shift is consistent with the density functional theory calculations, showing that an external electric field directed along the molecular axis diminishes the highest occupied molecular orbital−lowest unoccupied molecular orbital gap of OPE. We thus conclude that the electric field generated by the peptide dipoles effectively modulate the electronic structure of the OPE moiety in the SAMs.

Several kinds of molecular assemblies are prepared from polypeptides and cyclic peptides at various levels of structural regularities, which lead to the current proposal to categorize molecular assemblies into primary to quaternary structures. The categorization places a focal point on phase separation in molecular assemblies because highly sophisticated molecular assemblies have hierarchical organizations of molecules that accompany phase separation and the regular arrangement of chromophores, as frequently observed in nature. Examples of the peptide-based molecular assemblies are thus explained in accordance with the primary to quaternary structures with the aim of implementing nanomaterials in the coming era. Categorization of molecular assemblies of primary to quaternary structures is herein proposed with citing typical examples of peptide molecular assemblies for each category. Primary structure; tubes and vesicles, Secondary structure; chimeric morphology, Tertiary structure; phase-separated tubes, Quaternary structure; hierarchical organization of molecular assemblies.

An amphiphilic polypeptide, poly(sarcosine)-b-(l-Leu-Aib)8(SL16), was reported to self-assemble into vesicles. A GxxxG motif, which is known to induce helix dimerization, is incorporated into the hydrophobic helical block of SL16 to synthesize poly(sarcosine)-b-(l-Leu-Aib)2-(Gly-Aib-l-Leu-Aib-Gly-Aib)-(l-Leu-Aib)3(SG16). SG16 shows helix association in ethanol at a high concentration and low temperatures, which is not observed with SL16. SG16 self-assembles into vesicles, but are found to be more susceptible to rupture by the addition of Triton X-100 than SL16 vesicles. A mixture of SL16 and SG16 self-assembles into small sheets and micelles likely because of mismatch of the modes of helix association arising from sterical accommodation of iso-butyl groups at the helix–helix interface.

A cyclic tri-β-peptide containing β-naphthylalanine (β-Ala(nap)), cyclo(β-Ala(nap)-β-Ala-β-Ala) (C3NAA), and its analog with an ethylenediamine-succinic acid sequence (ED-SA), cyclo(β-Ala(nap)-ED-SA) (C3NES) self-assemble into peptide nanotube bundles on gold, where the surfaces of the substrates are modified by the self-assembled monolayers (SAMs). The C3NAA nanotube generates a threefold larger macrodipole along the long axis of the nanotube than is present on the C3NES nanotube. The orientation of the peptide nanotube bundles change from horizontal to perpendicular on the substrates due to the methanol-vapor annealing process. The surface potential of the C3NAA nanotube bundle on the guanidium-terminated SAM is larger than that of the C3NES nanotube bundle due to the larger macrodipole of the C3NAA nanotube than the C3NES nanotube, but the converse piezoelectric responses are insignificant. On the other hand, the C3NAA nanotube bundles positioned horizontally along the gold substrate generate a relatively large surface potential, and the converse piezoelectric response is as high as approximately 9 pm/V. The piezoelectric response likely becomes larger when the macrodipole is perpendicular to the applied electric field and is sensitive to the extent to which the dipoles are arranged in a noncentrosymmetric structure.

Two kinds of amphiphilic polypeptoids having different types of hydrophilic polypeptoids, poly(sarcosine)-b-(l-Leu-Aib)6(ML12) and poly(N-ethyl glycine)-b-(l-Leu-Aib)6(EL12), were self-assembled via two paths to phase-separated nanotubes. One path was via sticking ML12 nanotubes with EL12 nanotubes and the other was a preparation from a mixture of ML12 and EL12 in solution. In either case, nanotubes showed temperature-induced phase separation along the long axis, which was observed by two methods of labeling one phase with gold nanoparticles and fluorescence resonance energy transfer between the components. The phase separation was ascribed to aggregation of poly(N-ethyl glycine) blocks over the cloud point temperature. The addition of 5% trifluoroethanol was needed for the phase separation because the tight association of the helices in the hydrophobic region should be loosened to allow lateral diffusion of the components to be separated. The phase separation in molecular assemblies in water based on the hydrophilic-region-driven-type mechanism therefore requires sophisticated balances of association forces exerting among the hydrophilic and hydrophobic regions of the amphiphilic polypeptoids.

A series of Boc-(l-Ala-Aib)n-OCH3(n= 2, 4, 6, 8) and Boc-(l-Leu-Aib)n-OCH3(n= 2, 4, 6, 8) peptides were synthesized and subjected to terahertz time-domain (THz-TD) spectroscopy. Signals specific to helical peptides were observed around 2 and 3 THz, which were assignable to accordion-like oscillation modes, based on DFT calculations. Boc-(l-Ala-Aib)8-OCH3showed intensified signal when compared with Boc-(l-Leu-Aib)8-OCH3, which is due to the large amplitude of the accordion-like oscillation. The accordion-like oscillation modes are discussed in relation with the higher ability of (l-Ala-Aib)8than (l-Leu-Aib)8as an electron-transfer mediator.Boc-(l-Ala-Aib)n-OCH3(n= 2, 4, 6, 8) and Boc-(l-Leu-Aib)n-OCH3(n= 2, 4, 6, 8) were synthesized and subjected to terahertz time-domain spectroscopy. Signals specific to helical peptides were observed, which were assignable to accordion-like oscillation modes on the basis of DFT calculations. Boc-(l-Ala-Aib)8-OCH3showed intensified signal when compared with Boc-(l-Leu-Aib)8-OCH3, which is considered to be due to the large amplitude of the accordion-like oscillation.

Various amphiphilic block polypeptides having aromatic groups at the C terminal of a Leu-based hydrophobic helical block, poly(sarcosine)-b-(l-Leu-Aib)6-ethylcarbazole, poly(sarcosine)-b-(d-Leu-Aib)6-naphthalimide, and poly(sarcosine)-b-(d-Leu-Aib)6-porphyrin, were synthesized and self-assembled in water. Molecular assemblies of distorted sheet, saddle-like sheet, and micelle were identified, which were different from the curved sheet of poly(sarcosine)-b-(l-Leu-Aib)6without any aromatic groups, indicating that the attachment of the aromatic groups to the C terminal significantly influenced the morphology. Upon heating at 90 °C, vesicles were generated with the three amphiphilic polypeptides with aromatic groups as opposed to the nanotubes of poly(sarcosine)-b-(l-Leu-Aib)6. The precise observations of these vesicles by AFM revealed formation of monolayer for poly(sarcosine)-b-(l-Leu-Aib)6-ethylcarbazole and bilayers for poly(sarcosine)-b-(d-Leu-Aib)6-naphthalimide and poly(sarcosine)-b-(d-Leu-Aib)6-porphyrin. Attachment of aromatic groups at the C terminal therefore influences morphology and monolayer/bilayer alteration in accordance with the type of aromatic groups.Various amphiphilic block polypeptides having aromatic groups at the C terminal of Leu-based hydrophobic helical block were prepared and self-assemblies of various vesicles were identified. The precise observations of vesicles by AFM revealed formation of monolayers and bilayers. Attachment of aromatic groups at the C terminus therefore influences morphology and monolayer/bilayer alteration in accordance with the type of the aromatic groups.

Three kinds of cyclic tri-β-peptides having different numbers of benzyl ester groups are synthesized. The cyclic peptides formed peptide nanotube bundles showing different surface potentials, piezoelectricity, and electrical conductivity, which are explained by the number of the benzyl ester groups and the rotational symmetry of the cyclic peptides.Three kinds of cyclic tri-β-peptides having different numbers of benzyl ester groups are synthesized. The cyclic peptides formed peptide nanotube bundles showing different surface potentials, piezoelectricity, and electrical conductivity, which are explained by the number of benzyl ester groups and the rotational symmetry of the cyclic peptides.

Directional switching of photocurrent generation in response to oxygen is attained with the self-assembled monolayer (SAM) composed of porphyrin- and fullerene-terminated helical peptides. The anodic photocurrent of the porphyrin SAM under argon gas is successfully switched over to the cathodic photocurrent in the presence of oxygen gas only in the copresence of the fullerene-terminated helical peptide. The first-principle calculations explain that the cathodic photocurrent is promoted as a result of suppression of the anodic photocurrent due to the small electron coupling between the lowest unoccupied molecular orbitals of fullerene and the amide moieties of electron mediating helix peptides.

Vesicles were prepared from poly(sarcosine)-b-(l-Leu-Aib)8(SL16), and the membrane leakage of the encapsulated K+was evaluated to be ca. 4% for 15 min at 30 °C. The osmotically induced leakage of the encapsulated 5(6)-carboxy fluorescein was negligible below 50 °C. The robustness of SL16 vesicle was considered to be due to the interdigitated structure of Leu side chains in the monolayer.Vesicles were prepared from poly(sarcosine)-b-(l-Leu-Aib)8(SL16), and the membrane leakage of the encapsulated K+was evaluated to be ca. 4% for 15 min at 30 °C. The osmotically induced leakage of the encapsulated 5(6)-carboxy fluorescein was negligible below 50 °C. The robustness of SL16 vesicle was considered to be due to the arrangement of iso-butyl side chains of neighbor helices packing in a straight line in the interdigitated monolayer.

Photocurrent generation of porphyrin-terminated helical peptide self-assembled monolayers (SAMs) was studied in an aqueous solution. The anodic photocurrent was prevailing, but the cathodic photocurrent was observed with applying negative bias voltage on the working electrode. The bias dependence of the photocurrent was explained successfully by theoretical calculation with taking into account the redox potential shift by J-aggregate of porpyrins, the helix dipole, and photoenergy migration in the SAM. The dark current was insignificant even at the forward bias voltage.

Amphiphilic helical peptides with opposite helicities and different hydrophobic helical block lengths were combined to prepare self-assemblies in water for constructing novel morphologies. (Sar)25-b-(L-Leu-Aib)6and (Sar)25-b-(D-Leu-Aib)6(sarcosine (Sar) chain, a hydrophobic helix of leucine (Leu) and a-aminoisobutyric acid (Aib)) have been reported to self-assemble into well-defined nanotubes, but a 1:1 mixture of these components self-assembles into vesicles. Their mixtures at molar ratios 8:2 and 2:8 have yielded round-bottom flask-shaped molecular assemblies, which are an AB-type conjugate morphology of a vesicle (A) and a nanotube (B). Here, we expand the conjugate morphologies to new AB-type, ABA-type, ABA'-type and A3B-type. The new AB-type conjugate morphology had a nano-test-tube shape. Two types of the nano-test-tube-shaped self-assemblies were prepared using different combinations of nanotubes and vesicles. One thin nanotube was sealed with vesicles at both open ends to generate the ABA-type conjugate morphology with a dumbbell shape. When the round-bottom flask-shaped self-assembly was combined with a small vesicle, the ABA'-type conjugate morphology was obtained. The combination of a three-neck nanotube with a vesicle produced the A3B-type morphology. These self-assemblies were thermodynamically stable owing to the phase separation in their fused membranes. Therefore, these self-assemblies are termed ‘peptide rafts’ as an analogy to ‘lipid rafts’.

We propose a strategy to modulate the electronic structure of gallium arsenide (GaAs) semiconductors by the covalent deposition of uniform monolayers of helical peptides. After the optimization of coupling groups and reaction conditions, structures of peptide monolayers on GaAs were characterized by the combination of grazing incidence-X-ray scattering and Fourier transform infrared spectroscopy yielding the thickness, the area occupied by one peptide helix, and the tilt angle of helical axis with respect to the surface normal. The deposition of the same peptides on high electron mobility transistor (HEMT) devices resulted in a clear change in the carrier mobility depending on the length of peptide helices. The obtained results demonstrated that the macrodipole potential of oriented peptide helices can be utilized for flexible tuning of the electronic structure (band bending) of semiconductors, which can offer a unique alternative to the commonly used doping of charge carriers.

Amid‐Trittsteine: Zwischen den Enden α‐helicaler Peptide, die sich in selbstorganisierten Monoschichten (SAMs) auf einer Goldoberfläche befinden, findet ein Elektronenaustausch statt, wobei die Amidgruppen als Zentren für den Hüpfvorgang fungieren (siehe Bild). Die Geschwindigkeitskonstante von 0.45 s−1für das 64‐mere Peptid ist ungewöhnlich hoch für einen Elektronentransfer durch ein organisches Dielektrikum.

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Novel 310-helical peptides having a disulfide group at the N-terminal and carrying naphthyl groups at the side chains in a linear arrangement were synthesized, those are 9mer, 18mer, and 27mer peptides with three, six, and nine naphthyl groups, respectively. Spectroscopic measurements of the peptide solutions showed that there was no interaction between the neighboring naphthyl groups. 310-Helical conformation was confirmed by circular dichroism spectroscopy and computational molecular modeling. The peptides were self-assembled on gold by an Au-S linkage, and the defect sites in the self-assembled monolayers (SAMs) were filled up with dodecanethiol. Cyclic voltammetry, ellipsometry, and infrared reflection-absorption spectroscopy studies on the SAMs showed that the peptides formed the densely-packed monolayers with vertical orientation. Upon photoexcitation of the naphthyl groups in an aqueous solution containing electron donors, the monolayer generated an anodic photocurrent by photoinduced electron transfer from the electron donor via the naphthyl groups to gold. The longest 27mer peptide generated the largest photocurrent among the peptides. Theoretical simulations successfully demonstrated that the helix scaffold with many naphthyl groups in a linear arrangement was effective to suppress quenching of the excited naphthyl group by gold due to the elongation of the helix length, and to promote electron hopping among the naphthyl groups enabling long-range electron transfer from the distant naphthyl group to gold, eventually realizing an efficient photocurrent generation molecular system.

Novel helix-peptide wheels, in which three helices were connected by using a template, were prepared, and the dipole–dipole interactions among the helices were studied in relation to the formation of a planar triangle structure containing three helices. The helical segments had a 310-helix structure. 13C spin-lattice relaxation time (T1) measurements showed that the helical segments had restricted mobility. Deuterium exchange rates of amide protons were accelerated in the helix-peptide wheels compared to the respective linear helix peptides, suggesting that there is torsion on the cylindrical shape. Therefore, the predominant structure of the helix-peptide wheels is a planar triangle in solution. Further, the triangle structure was successfully transferred onto a gold substrate.

A novel cyclic hexamer of acetylated β‐glycosamino acid was synthesized and its conformation and molecular assembly formation was investigated. Variable temperature NMR study indicated that the cyclic hexapeptide took a C3 symmetric conformation at room temperature, but at elevated temperatures a C6 symmetric one, which was not due to averaging of the C3 symmetric conformation, appeared. Computational geometry optimization showed that the C6 symmetric conformation was a highly planar structure with amide groups orienting perpendicular to the ring plane. The cyclic hexa‐β‐peptide formed rod‐shaped crystals from an N,N‐dimethyl formamide solution at elevated temperature. The optical microscopy observation with a sensitive tint plate under cross‐nicol configuration and electron diffraction analysis of the crystals revealed that the cyclic hexa‐β‐peptides were stacked one after the other to form a regular nanotube structure. © 2007 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 88: 150–156, 2007.This article was originally published online as an accepted preprint. The ‘Published Online’ date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com

A novel cyclic trimer and tetramer of protected -glycamino acids were synthesized and investigated on conformation and assembly formation. A characteristic point of these cyclic -glycamino acids is their better solubility than other cyclic -amino acids due to the pyranose rings. Thus, the assembling process of the cyclic molecules could be examined by CD or NMR spectroscopy. FT-IR and NMR measurements and geometry optimization revealed a highly symmetric and planar conformation for each cyclic -peptide with all-transamide groups. The amide groups in the cyclic peptides took a vertical orientation against the cyclic skeleton to be suitably arranged for intermolecular hydrogen bonds, which should promote formation of molecular assembly in a columnar structure through molecular stacking. These cyclic -peptides were successfully crystallized to yield rod-shaped molecular assemblies in nanometer sizes. Evidence for the columnar structure in the crystals was obtained by electron diffraction analysis, which showed a layer spacing of ca. 4.8 Å. Interestingly, the molecular assembly of the cyclic trimer showed a high aspect ratio, width less than 40 nm, and length more than 2 m, suggesting stable molecular stacking in the column.

Three-arm helices (TA16, TA8), in which three hydrophobic helical peptides were tethered together at their C-terminals, were synthesized, and self-assembling property in water was investigated. TA16 (m.w. = 5228) was dispersed easily in water even though this compound has no explicit hydrophilic moiety in the molecule. Dynamic light scattering measurement and transmission electron microscopy images of water dispersions of TA16 and TA8 revealed that spherical assemblies with diameter of 70 nm (TA16) and 100 nm (TA8) were formed. The central tertiary amine moiety in TA16 and TA8 should act as a hydrophilic part due to the convergent point of the three negatively polarized C-terminals of helices.

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Photoresponsive helical peptides, which are composed of two helical peptide segments with an intervening azobenzene unit, were synthesized, and the self-assembled monolayers (SAMs) were formed on gold. The helical peptides were shown to take vertical orientation on gold by Fourier transform infrared reflection-absorption spectroscopy, and to change the molecular orientation reversibly upon UV and visible light irradiation due to photoisomerization of the azobenzene unit. The structural changes upon photoirradiation resulted in alterations of the surface potential of the peptide SAMs. The helical peptides in the SAM are suggested to change the molecular orientation in a cooperative manner upon photoirradiation.

Hyaluronic acid and chondroitin were successfully synthesized as representative molecules of glucosaminoglycans and galactosaminoglycans found in a glycosaminoglycan family via enzymatic polymerization catalyzed by testicular hyaluronidases. A newly designed N-acetylhyalobiuronate oxazoline derivative with a β-D-glucuronyl-(1→3)-N-acetyl-D-glucosamine disaccharide structure served as a transition-state analogue substrate monomer for the enzyme, giving rise to artificial hyaluronic acid in 52% yields with a number-average molecular weight of 1.35 × 10⁴ through ring-opening polyaddition in a perfect regioselective and stereoselective manner. A novel N-acetylchondrosine oxazoline derivative with a β-D-glucuronyl-(1→3)-N-acetyl-D-galactosamine disaccharide structure also acted as a transition-state analogue substrate monomer for the enzyme, yielding artificial chondroitin in 35% yields with a number-average molecular weight of 2.5 × 10³. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3541–3548, 2003

Helical peptides having a disulfide group at one terminal, Lipo-(Leu-Aib)12-OBzl (Lipo and OBzl represent lipoic acid and benzyl ester, respectively, SSL24B), and Boc-NHCH2CH2NHCO-Fc-CO-Ala-(Leu-Aib)8-lipoamide (Boc, Fc, and lipoamide represent t-butyloxycarbonyl, ferrocene, and lipoamine, respectively, FcL16SS), were synthesized, and self-assembled monolayers (SAMs) of the helical peptides were prepared on gold. When the SSL24B SAM was observed at high-bias voltage by scanning tunneling microscopy (STM) under ultrahigh vacuum, bright spots with higher conductivity appeared in the STM image. The image was restored again to a homogeneous surface with lower bias voltage, suggesting that Au–S linkage should be reversibly changed to a conductive state. The current/voltage (I-V) curve by scanning tunneling spectroscopy (STS) at the bright domains demonstrated a rectification behavior where current increases drastically at a positive bias voltage above 3.0 V. However, the I-V curve of the FcL16SS SAM showed a current increase at negative bias voltage below −1.5 V. The redox group is, thus, a determining factor for the direction of this flow. However, STS at low-bias voltage and with the tip being inserted in the peptide SAM revealed a zero-conductance region in the I-V curve. The peptide layer may act as a molecular capacitor because of a large dielectric constant of the helical peptide. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3493–3500, 2003

The present article focuses on in vitro synthesis of cellulose and related polysaccharides, in which polymer synthesis using an isolated enzyme as catalyst (‘enzymatic polymerization’) as the major part and conventional chemical synthesis are described. Typical natural polysaccharides such as cellulose, xylan and chitin having a β(1→4) structure have been successfully synthesized for the first time by using enzymatic polymerization. Hydrolases were most often employed as catalyst, which catalyze the bond-cleavage (hydrolysis) of polysaccharides in vivo, but the glycosidic bond-formation in vitro to give polysaccharides. All enzymatic polymerizations gave a polysaccharide having structure with perfect control of regio- and stereo-selectivity. A key issue for the polymerization to occur is the appropriate design of monomers which is considered to be close in structure to that of the hydrolysis transition state. This principle was extended to the synthesis of unnatural polysaccharides. In relation to the polymerization mechanism, fundamental mechanistic aspects of in vivo reaction of these enzymes are also discussed. Oligo and polysaccharide synthesis is achieved by using other classes of enzymes as catalysts, such as glycosyltransferases, phosphorylases and artificial glycosynthases prepared by mutation of glycosylases. Conventional chemical syntheses are based on polycondensation, ring-opening polymerization, and stepwise elongation. Some characteristics of these syntheses are described.

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Self-assembled monolayers (SAMs) of helix peptides oriented vertically to a gold surface were prepared. Negative surface potentials of a few hundred millivolts were observed for the helix peptide SAMs when they were immobilized on gold through the N terminal of the peptides. However, positive surface potentials were generated in the helix peptide SAMs when the N terminal of the peptides was directed the opposite way. The large dipole moment of the helical peptide was thought to be the major factor for generation of the surface potential. The effect of the dipole moment on the electron transfer through the helix peptide SAMs was investigated. Photocurrent generation by photoexcitation of the N-ethylcarbazolyl group of the peptide SAMs was accelerated by the dipole moment directed toward the gold substrate. Helical peptides were thus shown to be a suitable medium for electron transfer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4826–4831, 2000

Monolayers at the air/water interface and self-assembled monolayers (SAMs) on a gold substrate were prepared from helical peptide derivatives carrying a 9-ethyl-3-carbazolyl group and a disulfide group. π-AIsotherms and circular dichroism spectra of Langmuir-Blodgett monolayers on a quartz substrate showed that the helical peptides were lying at the air/water interface. The molecular arrangement in the monolayer was analyzed by fluorescence quenching using in situ fluorescence spectroscopy. Computer simulations for the quenching experiment under the assumption of the mixed arrangement of parallel and antiparallel orientations explain the experimental data. On the other hand, the helical peptides in the SAMs were found to take standing orientation and a parallel arrangement by Fourier transform infrared reflection-absorption spectroscopy and fluorescence spectroscopy.

Cation recognition of self‐assembled monolayers (SAMs) of helical peptides having a crown ether unit was investigated by the impedance spectroscopy and cyclic voltammetry. Lipo–(Ala–Aib)8–Ala–Cr and Boc–Glu(Cr)–(Ala–Aib)8–Lipoa (Lipo, Lipoa, and Cr represent lipoic acid, lipoamide, and amidobenzo‐18‐crown‐6, respectively) were synthesized and the helix SAMs were prepared. The peptides having a crown ether unit formed SAMs oriented nearly vertically to the substrate. The capacitance of the Lipo–(Ala–Aib)8–Ala–Cr SAM changed specifically with the addition of cations, and the binding constants of the SAM were larger than those of the crown ether in aqueous solution because of a large dipole moment of the helical peptide. In the case of the Boc–Glu(Cr)–(Ala–Aib)8–Lipoa SAM, the cation binding to the SAM showed a drastic decrease in the peak current of the cyclic voltammetry around 10−5M of K+ion. In either capacitance measurement or cyclic voltammetry, the helical peptide SAM played an important role in the sensitive response to cations. © 2001 John Wiley & Sons, Inc. Biopolymers (Pept Sci) 55: 391–398, 2000

Cation recognition of self-assembled monolayers (SAMs) of helical peptides having a crown ether unit was investigated by the impedance spectroscopy and cyclic voltammetry. Lipo–(Ala–Aib)8–Ala–Cr and Boc–Glu(Cr)–(Ala–Aib)8–Lipoa (Lipo, Lipoa, and Cr represent lipoic acid, lipoamide, and amidobenzo-18-crown-6, respectively) were synthesized and the helix SAMs were prepared. The peptides having a crown ether unit formed SAMs oriented nearly vertically to the substrate. The capacitance of the Lipo–(Ala–Aib)8–Ala–Cr SAM changed specifically with the addition of cations, and the binding constants of the SAM were larger than those of the crown ether in aqueous solution because of a large dipole moment of the helical peptide. In the case of the Boc–Glu(Cr)–(Ala–Aib)8–Lipoa SAM, the cation binding to the SAM showed a drastic decrease in the peak current of the cyclic voltammetry around 10⁻⁵M of K⁺ ion. In either capacitance measurement or cyclic voltammetry, the helical peptide SAM played an important role in the sensitive response to cations. © 2001 John Wiley & Sons, Inc. Biopolymers (Pept Sci) 55: 391–398, 2000

Based on our initial work with green tea, in which repeated topical applications of (-)-epigallocatechin gallate (EGCG), the main green tea polyphenol, inhibited tumor promotion in a two-stage carcinogenesis experiment on mouse skin (Phytother Res 1, 44-47, 1987), numerous scientists have since provided so much additional evidence of the benefits of drinking green tea that it is now an acknowledged cancer preventive in Japan, and will possibly soon be recognized as such in other countries. Our work has so far produced several important results with EGCG and green tea: a wide range of target organs in animal experiments for cancer prevention, wide bioavailability of 3H-EGCG in various organs of mice, delayed cancer onset of patients with a history of consuming over 10 cups of green tea per day, and absence of any severe adverse effects among volunteers who took 15 green tea tablets per day (2.25 g green tea extracts, 337.5 mg EGCG, and 135 mg caffeine) for 6 months. This paper introduces three new findings: 1) EGCG interacted with the phospholipid bilayer membrane resulting in confirmation of the sealing effect of EGCG; 2) EGCG inhibited TNF-α gene expression in the cells and TNF-α release from the cells; 3) high consumption of green tea was closely associated with decreased numbers of axillary lymph node metastases among premenopausal Stage I and II breast cancer patients, and with increased expression of progesterone and estrogen receptors among postmenopausal ones. These results provide new insights into our understanding of the mechanisms of action of tea polyphenols and green tea extract as a cancer preventive.

Lipid‐induced secondary structures and orientations of the two enantiomeric [Leu5]‐enkephalins, L‐Tyr‐Gly‐Gly‐ L‐Phe‐L‐Leu, and D‐Tyr‐Gly‐Gly‐D‐Phe‐ D‐Leu, on flat multi‐bilayers of 1‐palmitoyl‐2‐oleoyl‐sn‐ glycero‐3‐phosphocholine (POPC) were examined with polarized attenuated total reflection IR (IRATR) spectroscopy and molecular mechanics procedures. The membrane‐bound peptides showed identical IR spectra in the amide I and II band regions that indicated membrane‐induced secondary structures and specific orientations of the non‐zwitterionic molecules. A Lorentzian band shape analysis based on second derivatives of the original curves and the observed band polarizations suggested the presence of helical structures (βIII‐and α‐turns), oriented more or less perpendicular to the membrane surface. Other folded structures, e.g.βI‐ and γ turns, were not excluded. Molecular modelling of non‐zwitterionic [Leu5]‐enkephalin with two βIII‐turns or an α‐turn resulted in essentially four low‐energy conformers containing (i) two βIII‐turns, (ii) one α‐turn, (iii) a βIII‐turn fused to an α‐turn, and (iv) a βIII‐turn fused to a βI‐turn as in the crystallographic molecular conformation described by Aubry et al. [Biopolymers28, 27–40 (1989)]. Zwitterionic [Leu5]‐enkephalin with two β III‐turns collapsed to a C13turn (a distorted α‐ turn) bridged by a γI‐turn (v). The alignment of the amide I oscillators within the helical structures, (i), (ii) and (iii), and the double‐bend structures, (iv) and (v), explained the observed amide I and II polarizations. Differences between these and other lipid‐induced [Leu5]‐enkephalin conformers reported in the literature may be caused by the lipid polymorphism of the model membranes used. Possible implications of the new conformers for the molecular mechanism of opioid receptor selection are discussed in terms of the membrane compartments theory. © 1997 European Peptide Society and John Wiley & Sons, Ltd.

Regular assemblies of peptide molecules to exhibit novel functionalities have been prepared in two different ways. One of them is a helix-bundle structure in which two or three hydrophobic α-helical peptides are connected together by a tie molecule. The helix-bundle structure formed an ion channel across lipid bilayer membrane at lower concentrations than a single-chain pepide. The other example is a two-dimensional assembly of amphiphilic peptide molecules carrying a chromophoric group. The assembly was an efficient photo-energy collector to generate photo-electron and to reduce cytochrome c.

The interaction of amphiphilic helical peptides with phospholipid membranes of various diameters was studied. H-(Leu-Aib-Lys-Aib-Aib-Lys-Aib)3-OCH3(P21OMe) was bound to large unilamellar vesicles (LUV) of 100 nm and larger diameter or to small unilamellar vesicles (SUV) of dimyristoylphosphatidylcholine (DMPC). The helix content of P21OMe increased remarkably upon partition to phospholipid bilayer membrane. A short peptide, H-Leu-Aib-Lys-Aib-Aib-Lys-Aib-OBzl (P7Bz), did not take helical conformation, and was not bound to any type of vesicle. Therefore, the amphiphilic helical structure is a key factor for peptide binding to phospholipid bilayer membranes. Two octadecyl chains at the C terminus of a short peptide, H-Leu-Aib-Lys-Aib-Aib-Lys-Aib-Ala-N(C18H37)2, increase the affinity to the phospholipid membrane. On the other hand, the connection of two octadecyl chains to P21OMe, H-(Leu-Aib-Lys-Aib-Aib-Lys-Aib)3-Ala-N(C18H37)2(P21D), prevents the peptide from binding to LUV of diameters larger than 100 nm, while it is partitioned to SUV. It was thus shown that the effect of two octadecyl chains on the peptide binding to phospholipid bilayer membranes changes, depending on the peptide and the size of phospholipid vesicles.

Ca2+-induced aggregation of peptides having an Asp residue in phospholipid bilayer membrane was studied on the basis of excimer formation of pyrenyl group in the peptide. A part of the peptides incorporated into the membrane formed aggregates. The degree of peptide aggregation in the membrane was maximum at the lipid/peptide molar ratio of 40—80, and decreased with increasing the amount of the lipid and dissociation of the carboxyl group. Cross-linking of the peptide by Ca2+was observed only when the peptide concentration in the membrane was high and the carboxyl group was dissociated. The membrane fluidity at the surface and in the hydrophobic core was not influenced so much by the peptide aggregation, indicating that the peptide/Ca2+complex is not very rigid.

a-Helical polypeptides having a glyco moiety at one end and a fluorescent probe at the other were prepared and investigated on the interaction with a lipid bilayer membrane. A glycopeptide composed of poly(alanine) and maltose was incorporated into the lipid membrane with the glyco moiety exposed to the aqueous phase and the peptide chain buried in membrane above the phase-transition temperature of the lipid membrane. However, below the phase-transition temperature, the glycopeptide induced the aggregation of dimyristoylphosphatidylcholine (DMPC) small unilamellar vesicles (SUV). Another glycopeptide composed of poly(?-benzyl glutamate) and glucose also induced the aggregation of DMPC SUV, indicating that such the hydrophobic peptide tends to disturb the membrane structure significantly upon binding. The arrangement of the glycopeptide in a membrane was investigated by using a fluorescent probe connected to the end of the peptide chain. The terminal region of the peptide chain was located at the hydrophobic core of lipid membrane. However, the glycopeptide composed of 25 Ala residues had a smaller fraction taking perpendicular orientation to the membrane than that composed of 15 Ala residues. It was therefore considered that a part of the former glycopeptide molecules exits on the membrane surface, forming aggregates.

The effect of the hydrophobic interaction on the association in aqueous media of tyrosine-containing cyclic dipeptides and 1-acyl-4-bromobenzenes having various lengths of acyl chain was investigated by quenching of the fluorescence of the former compounds by the latters. In ethanol, the change of fluorescence intensity (I0⁄I) was linearly related to the quencher concentration according to the Stern-Volmer’s plot, which was attributed to a dynamic quenching. In this case, structures of fluorophores and quenchers did not affect the quenching constant. However, in a buffer solution, I0⁄Iwas linearly related to the quencher concentration according to the Perrin’s plot, which was attributed to a static quenching. Perrin’s quenching constants depended on the structure of fluorophores and quenchers. In some cases, a quencher molecule was bound to a fluorophore by hydrophobic interaction in a favorable arrangement for fluorescent quenching. In aqueous solution, fluorophores and quenchers formed comparatively large aggregates with nonspecific arrangement for fluorescent quenching. In this case, Perrin’s quenching constants were independent of the nature of quenchers and related with the size of formed aggregates.

Polyamide microcapsules with diameters in the range of 1–5 μm were prepared by interfacial polycondensation between terephthaloyl dichloride and a mixture of l-lysine and piperazine. The carboxyl groups of l-lysine residues involved in the polyamide microcapsules were reacted with alkylamine by using water-soluble carbodiimide as a coupling reagent. The alkylated polyamide microcapsules were incubated with liposome to have the surface of the polyamide microcapsules coated with lipid bilayer membrane. The amount of lipid assemblies adsorbed on the polyamide microcapsules with octyl chains increased up to 1.5 times as much as that on the polyamide microcapsules without octyl chains. The synthetic glycopeptides were introduced to the lipid membrane adsorbed on the surface of the polyamide microcapsules. Interactions of the glycopeptides with the lipid membrane on the polyamide microcapsules and of the glycopeptides in the lipid membrane on the polyamide microcapsules with lectin were investigated.

In an organic liquid membrane system, 4′-(ferrocenylcarbonylamino)benzo-18-crown-6 (FCC) dissolved in a dichloromethane membrane was found to reduce hexacyanoferrate(III) ions in the aqueous phase to hexacyanoferrate(II) ions at a rate dependent on the type of metal ion coexisting in the aqueous phase, and bound to the benzo-18-crown-6 unit of FCC.

Two chains of amphiphilic α-helical dodecapeptides were connected to a cyclic octapeptide in a parallel or antiparallel arrangement. Conformation, orientation, and association of the dodeca-peptide chains in the presence of dimyristoylphosphatidylcholine (DMPC) liposome were studied. The peptides were easily incorporated into the bilayer membrane. CD measurements revealed that the dodecapeptides took a distorted a-helix conformation due to intramolecular association. Fluorescence quenching measurement of a probe connected to each terminal region of the dodecapeptides revealed that the dodecapeptide chain was located on the membrane surface with a parallel orientation to the surface. Thermal denaturation of the helical structure was suppressed by connecting the two dodecapeptide chains to the cyclic peptide. These experimental results indicate that a supersecondary structure composed of associated α-helices was constructed on the surface of DMPC liposome by using a cyclic peptide as a template.

Poly[N-(3-aminopropyl)glycine] (PolyNAPGly, 5) and its derivatives were synthesized as model peptides of the membrane-bound enzymes, and investigated on their interactions with lipid membrane. PolyNAPGly (5) was shown to be distributed to dipalmitoylphosphatidyl choline bilayer membrane without destruction of the vesicle structure. Dodecyl groups were introduced to the side chains of PolyNAPGly (5), and found to facilitate binding of the polymer to lipid membrane. However, the introduction of the excess amount of hydrophobic groups to PolyNAPGly (5) caused the formation of polymer micelles, and the addition of such polymers to lipid vesicles destroyed the membrane structure. The derivative of PolyNAPGly (5) (n=35) bearing one or two dodecyl groups and some Ne-benzyloxycarbonylhistidyl groups was found to be bound tightly to lipid membrane without destruction of the membrane structure. The addition of these polypeptides to vesicles decreased the membrane fluidity.

Tetrathiafulvalene (TTF) and chloranil were introduced at the side chains of different cyclic tripeptides, which were self‐assembled into peptide nanotubes (PNTs). PNTs were used as scaffolds for alignment of the charge‐transfer complexes between TTF and chloranil, and they were prepared via two methods, one is that mixing a PNT comprising only TTF with a PNT comprising only chloranil (method 1), and the other is that one pot mixing of cyclic tripeptides with TTF and cyclic tripeptides with chloranil to be self‐assembled into PNTs (method 2). These PNTs naturally associated to form PNT bundles. The surface potentials of the PNT bundles became larger for the PNTs carrying charge‐transfer complexes along the PNT (method 2) than those between PNTs (method 1). This bundle of PNT carrying charge‐transfer complexes along the PNT (method 2) showed a hysteresis response in the piezoelectric force curve with varying bias voltages according to piezoelectric force microscope measurements.

Hydrophobic helical peptide molecules with a lactose unit at the C terminal, Nap-(Ala-Aib)n-NHCH2CH2NH-Lac (Nap, Aib, and Lac represent 2-naphthylacetic acid group, 2-aminoisobutyric acid, and lactobionic acid group, respectively, n=4, 6, 8), were synthesized and their formation of self-assemblies in water was investigated. Nap-(Ala-Aib)4-NHCH2CH2NH-Lac was spontaneously dispersed in water and formed aggregates of 70 nm diameter, shown by dynamic light scattering measurement. Cryo-TEM observation revealed that the aggregates took on a vesicular structure with a single membrane. The membrane is suggested to be composed of helical peptide molecules with an interdigitated antiparallel packing on the basis of circular dichroism and fluorescence measurements. On the other hand, the dodecapeptide formed a fibrous assembly, and the hexadecapeptide could not be dispersed in water.