Quantification of crystallinity during indomethacin crystalline transformation from α- to γ-polymorphic forms and of the thermodynamic contribution to dissolution in aqueous buffer and solutions of solubilizer.

The thermodynamic properties and dissolution of indomethacin (INM) were analyzed as models for poorly water-soluble drugs. Physical mixtures of the most stable γ-form and metastable α-form of INM at various proportions were prepared, and their individual signal intensities proportional to their mole fractions were observed using X-ray powder diffraction and Fourier transform infrared spectrometry at standard temperature. The endothermic signals of the α-form, with a melting point of 426 K, and that of the γ-form, with a melting point of 433 K, were obtained by differential scanning calorimetry (DSC). Furthermore, an exothermic DSC peak of the α/γ-phase transition at approximately 428 K was obtained. As we computed the melting entropy of the α-form and that of its transformation, the frequency of the transition was quantitatively determined, which indicated the maximum of the α/γ-phase transition at an α-form proportion of 68%. Subsequently, the thermodynamic contributions of the α- and γ-forms were analyzed using a Van't Hoff plot for solubility in aqueous solutions at pH 6.8. The dissolution enthalpies for α- and γ-forms were 28.2 and 31.2 kJ mol-1, respectively, which are in agreement with the quantitative contribution predicted by the product of the temperature and melting entropy. The contribution of melting entropy was conserved in different dissolution processes with aqueous solvents containing lidocaine, diltiazem, l-carnosine, and aspartame as solubilizers; their γ-form Setschenow coefficients were -39.6, +82.9, -17.3, and +23.2, whereas those of the α-form were -39.7, +80.4, -16.7, and +22.7, respectively. We conclude that the dissolution ability of the solid state and solubilizers indicate their additivity independently.

Enthalpy-Entropy Compensation in the Structure-Dependent Effect of Nonsteroidal Anti-inflammatory Drugs on the Aqueous Solubility of Diltiazem.

Certain combinations of acidic and basic drugs can cause significant changes in physicochemical properties through the formation of ionic liquids, eutectic mixtures, or deep eutectic solvents. In particular, combining indomethacin and lidocaine is known to result in apparent increases in both the partition coefficients (hydrophobicity) and aqueous solubilities (hydrophilicity). The physicochemical interactions between drugs change the water solubility of the drugs and affect the bio-availability of active pharmaceutical ingredients. Therefore, we need to clarify the mechanism of changes of water solubility of drugs through the physicochemical interactions. In the present study, we identified a thermodynamic factor that regulates the dissolution of a basic drug, in the presence of various acidic nonsteroidal anti-inflammatory drugs. The results demonstrated that enthalpy-entropy compensation plays a key role in the dissolution of drug mixtures and that relevant thermodynamic conditions should be considered.

Protein Sensing Device with Multi-Recognition Ability Composed of Self-Organized Glycopeptide Bundle.

We designed and synthesized amphiphilic glycopeptides with glucose or galactose at the C-terminals. We observed the protein-induced structural changes of the amphiphilic glycopeptide assembly in the lipid bilayer membrane using transmission electron microscopy (TEM) and Fourier transform infrared reflection-absorption spectra (FTIR-RAS) measurements. The glycopeptides re-arranged to form a bundle that acted as an ion channel due to the interaction among the target protein and the terminal sugar groups of the glycopeptides. The bundle in the lipid bilayer membrane was fixed on a gold-deposited quartz crystal microbalance (QCM) electrode by the membrane fusion method. The protein-induced re-arrangement of the terminal sugar groups formed a binding site that acted as a receptor, and the re-binding of the target protein to the binding site induced the closing of the channel. We monitored the detection of target proteins by the changes of the electrochemical properties of the membrane. The response current of the membrane induced by the target protein recognition was expressed by an equivalent circuit consisting of resistors and capacitors when a triangular voltage was applied. We used peanut lectin (PNA) and concanavalin A (ConA) as target proteins. The sensing membrane induced by PNA shows the specific response to PNA, and the ConA-induced membrane responded selectively to ConA. Furthermore, PNA-induced sensing membranes showed relatively low recognition ability for lectin from Ricinus Agglutinin (RCA120) and mushroom lectin (ABA), which have galactose binding sites. The protein-induced self-organization formed the spatial arrangement of the sugar chains specific to the binding site of the target protein. These findings demonstrate the possibility of fabricating a sensing device with multi-recognition ability that can recognize proteins even if the structure is unknown, by the protein-induced self-organization process.

Colorimetric sensors for rapid detection of various analytes.

Sensor technology for the rapid detection of the analytes with high sensitivity and selectivity has several challenges. Despite the challenges, colorimetric sensors have been widely accepted for its high sensitive and selective response towards various analytes. In this review, colorimetric sensors for the detection of biomolecules like protein, DNA, pathogen and chemical compounds like heavy metal ions, toxic gases and organic compounds have been elaborately discussed. The visible sensing mechanism based on Surface Plasmon Resonance (SPR) using metal nanoparticles like Au, Ag, thin film interference using SiO2 and colorimetric array-based technique have been highlighted. The optical property of metal nanoparticles enables a visual color change during its interaction with the analytes owing to the dispersion and aggregation of nanoparticles. Recently, colorimetric changes using silica substrate for detection of protein and small molecules by thin film interference as a visible sensing mechanism has been developed without the usage of fluorescent or radioisotopes labels. Multilayer of biomaterials were used as a platform where reflection and interference of scattering light occur due to which color change happens leading to rapid sensing. Colorimetric array-based technique for the detection of organic compounds using chemoresponsive dyes has also been focused wherein the interaction of the analytes with the substrate coated with chemoresponsive dyes gives colorimetric change.

Mineralization of Calcium Carbonate on Multifunctional Peptide Assembly Acting as Mineral Source Supplier and Template.

Crystal phase and morphology of biominerals may be precisely regulated by controlled nucleation and selective crystal growth through biomineralization on organic templates such as a protein. We herein propose new control factors of selective crystal growth by the biomineralization process. In this study, a designed ß-sheet Ac-VHVEVS-CONH2 peptide was used as a multifunctional template that acted as mineral source supplier and having crystal phase control ability of calcium carbonate (CaCO3) during a self-supplied mineralization. The peptides formed three-dimensional nanofiber networks composed of assembled bilayer ß-sheets. The assembly hydrolyzed urea molecules to one carbonate anion and two ammonium cations owing to a charge relay effect between His and Ser residues under mild conditions. CaCO3 was selectively mineralized on the peptide assembly using the generated carbonate anions on the template. Morphology of the obtained CaCO3 was fiber-like structure, similar to that of the peptide template. The mineralized CaCO3 on the peptide template had aragonite phase. This implies that CaCO3 nuclei, generated using the carbonate anions produced by the hydrolysis of urea on the surface of the peptide assembly, preferentially grew into aragonite phase, the growth axis of which aligned parallel to the direction of the ß-sheet fiber axis.

Two-dimensional self-assembly of amphiphilic peptides; adsorption-induced secondary structural transition on hydrophilic substrate.

Adsorption of sequential amphiphilic peptides on solid substrates triggered the spontaneous construction of nanoscaled architecture. An amphiphilic peptide designed with a cationic amino acid as a hydrophilic residue turned an anionic mica substrate into a water-repellent surface, simply by adsorbing it on the substrate surface. In contrast, an amphiphilic peptide designed with an anionic amino-acid residue formed a precisely controlled fiber array comprising a ß-sheet fiber monolayer at the anionic substrate/water interface. This phenomenon was based on the secondary structural transition from random-coil to ß-sheet, which occurred specifically when amphiphilic peptide adsorbed on the substrate surface. Such surface-specific nonorder/order transition was implemented by exploiting the strength of adsorption between the peptide and the substrate. A strategic design exploiting weak bonding such as hydrophobic interactions is essential for constructing precisely controlled nano-architectures in two dimensions.

Spontaneous construction of nanoperiodic architecture by two-dimensional self-assembly of an amphiphilic peptide-polyethylene glycol conjugate at the solid/water interface.

An amphiphilic peptide derivative, conjugated to polyethylene glycol (PEG) via the C-terminus, spontaneously assembled into nanodot and nanofiber arrays aligned with nanometer periodicity at the solid/water interface. The obtained planar structure was precisely controlled by the ß-sheet conformation of the peptide on the surface, while the peptide segment adopted a random-coil in aqueous solution. The peptide and PEG segments were hierarchically segregated after the peptide-PEG conjugate was adsorbed on the substrate, and the peptide segment transitioned from a random-coil to a ß-sheet conformation specifically at the solid/water interface. In this 2D self-assembly, the high dispersity of the peptide-PEG molecule in solution such that it exists as single molecules is essential for improving the uniformity of the 2D patterned nanostructures. The secondary structure based on the peptide segment was controlled by pH of the solution. Configuration of the peptide-PEG conjugate was also controlled by the temperature of the solution, which depended on the lower critical solution temperature (LCST) of the PEG segments. The variation in concentration of the peptide-PEG conjugate drastically influenced the morphologies of the 2D nanostructures because of the difference in the adsorbed amounts at equilibrium.

Calcium carbonate biomineralization utilizing a multifunctional ß-sheet peptide template.

We designed a novel multifunctional ß-sheet peptide template for calcium carbonate mineralization. The template self-supplies the mineral source, a carbonate ion, by hydrolysis of urea, and regulates the crystal phase and morphology of the obtained calcium carbonate.

Design of a nanocarrier with regulated drug release ability utilizing a reversible conformational transition of a peptide, responsive to slight changes in pH.

We investigated the drug releasing behavior of a novel nanocarrier system, utilizing a peptide to act as a nanogate to the mesopore, on a mesoporous silica nanoparticle. The surface peptide on mesoporous silica displayed pH-dependant mesopore cap-uncap switching behavior, enabled by the reversible ß-sheet-to-random coil conformational transition resulting from slight pH changes between 8.0 and 6.0. The peptide adopted a ß-sheet structure under weakly basic conditions (pH 8.0) and a random coil conformation under weakly acidic conditions (pH 6.0). We demonstrated the pH-dependant regulation of the material's drug release property by the reversible conformational transition of the surface peptide. Under basic pH conditions, the drug release from the nanocarrier was significantly inhibited. However, under acidic pH conditions, the drug in the mesopore was gradually released.

TiO2 synthesis inspired by biomineralization: control of morphology, crystal phase, and light-use efficiency in a single process.

Hydroxyapatite is mineralized along the long axis of collagen fiber during osteogenesis. Mimicking such biomineralization has great potential to control inorganic structures and is fast becoming an important next-generation inorganic synthesis method. Inorganic matter synthesized by biomineralization can have beautiful and functional structures that cannot be created artificially. In this study, we applied biomineralization to the synthesis of the only photocatalyst in practical use today, titanium dioxide (TiO(2)). The photocatalytic activity of TiO(2) mainly relates to three properties: morphology, crystal phase, and light-use efficiency. To optimize TiO(2) morphology, we used a simple sequential peptide as an organic template. TiO(2) mineralized by a ß-sheet peptide nanofiber template forms fiber-like shapes that are not observed for mineralization by peptides in the shape of random coils. To optimize TiO(2) crystal phase, we mineralized TiO(2) with the template at 400 °C to transform it into the rutile phase and at 700 °C to transform it into a mixed phase of anatase and rutile. To optimize light-use efficiency, we introduced nitrogen atoms of the peptide into the TiO(2) structure as doped elemental material during sintering. Thus, this biomineralization method enables control of inorganic morphology, crystal phase, and light-use efficiency in a single process.

Artificial extracellular matrix proteins containing phenylalanine analogues biosynthesized in bacteria using T7 expression system and the PEGylation.

In vivo incorporation of phenylalanine (Phe) analogues into an artificial extracellular matrix protein (aECM-CS5-ELF) was accomplished using a bacterial expression host that harbors the mutant phenylalanyl-tRNA synthetase (PheRS) with an enlarged binding pocket. Although the Ala294Gly/Thr251Gly mutant PheRS (PheRS**) under the control of T5 promoter allows incorporation of some Phe analogues into a protein, the T5 system is not suitable for material science studies because the amount of materials produced is not sufficient due to the moderate strength of the T5 promoter. This limitation can be overcome by using a pair of T7 promoter and T7 RNA polymerase instead. In the T7 expression system, it is difficult, however, to achieve a high incorporation level of Phe analogues, due to competition of Phe analogues for incorporation with the residual Phe that is required for synthesis of active T7 RNA polymerase. In this study, we prepared the PheRS** under T7 promoter and optimized culture condition to improve both the incorporation level of recombinant aECM protein and the incorporation level of Phe analogues. Incorporation and expression levels tend to increase in the case of p-azidophenylalanine, p-iodophenylalanine, and p-acetylphenylalanine. We evaluated the lower critical transition temperature, which is dependent on the incorporation ratio and the turbidity decreased when the incorporation level increased. Circular dichromism measurement indicated that this tendency is based on conformational change from random coil to ß-turn structure. We demonstrated that polyethylene glycol (PEG) can be conjugated at reaction site of Phe analogues incorporated. We also demonstrated that the increased hydrophilicity of elastin-like sequences in the aECM-CS5-ELF made by PEG conjugation could suppress nonspecific adhesion of human umbilical vein endothelial cells (HUVEC).

Ordered nanopattern arrangement of gold nanoparticles on ß-sheet peptide templates through nucleobase pairing.

We have demonstrated a unique method for rational arrangement of gold (Au) nanoparticles on a ß-sheet peptide template through nucleobase pairing. For the template, the 16-mer peptide 1 was synthesized, which is based on an alternating amphiphilic sequence of Asp-Leu. Here Leu at the sixth position is replaced by thymine-modified Lys, and a polyethylene glycol chain is introduced to the C-terminus. The surface of Au nanoparticles was modified with the complementary adenyl group. Peptide 1 formed a stable ß-sheet monolayer at the air/water interface under an appropriate surface pressure. The monolayer film transferred onto a mica surface by the Langmuir-Blodgett method showed a linearly striped pattern with 6.1 nm average stripe width and 6 nm average interval between stripes, derived from ß-sheet assembly. The adenine-bound Au nanoparticles were successfully immobilized on the thymine-bound template through a complementary adenine-thymine hydrogen bonding pair. Interestingly, linear assembly structures of the Au nanoparticles were observed, thus being successfully reproduced by the original striped pattern of the template of 1. Our method might readily fabricate Au materials with our desirable 2D pattern through fine-tuning of ß-sheet sequence and nucleobase position.

Multistep growth mechanism of calcium phosphate in the earliest stage of morphology-controlled biomineralization.

We studied the effect of surface-functional-group position on precipitate morphology in the earliest stage of calcium phosphate biomineralization and determined the detailed mechanism of precipitation starting from nucleation to precipitate growth. The biomineralization template was a ß-sheet peptide scaffold prepared by adsorption with carboxyl groups arranged at strict 7 Å intervals. Phosphate was then introduced. Within 10 s, highly ordered embryos of calcium phosphate were formed and confined by a peptide nanofiber pattern. They repeatedly nucleated and dissolved, with the larger embryos absorbing the smaller ones in a clear demonstration of an Ostwald-ripening-like phenomenon, then aggregated in a line pattern, and finally formed highly ordered nanofibers of amorphous calcium phosphate. This multistep growth process constitutes the earliest stage of biomineralization.

Synthesis and properties of terthiophene and bithiophene derivatives functionalized by BF2 chelation: a new type of electron acceptor based on quadrupolar structures.

Terthiophene and bithiophene derivatives functionalized by BF(2) chelation were synthesized as a new type of electron acceptor, and their properties were compared to those of bifuran and biphenyl derivatives. These new compounds are characterized by quadrupolar structures due to resonance contributors generated by BF(2) chelation. The bithiophene derivative has a strong quadrupolar character compared with the bifuran and biphenyl derivatives because their hydrolytic analyses indicated that the bithiophene moiety has a larger on-site Coulomb repulsion than the others. The terthiophene derivative has a smaller on-site Coulomb repulsion than the bithiophene derivative due to the addition of a thiophene spacer. These BF(2) complexes exhibit long-wavelength absorptions and according to measurements of ionization potentials and absorption edges they have energetically low-lying HOMOs and LUMOs. The crystal structure of the bithiophene derivative is of the herringbone type, with short F···S and F···C contacts affording dense crystal packing. n-Type semiconducting behaviour was observed in organic field-effect transistors based on these BF(2) complexes.

Morphology control of calcium phosphate by mineralization on the beta-sheet peptide template.

To investigate the influence of the spatial placement of the organic functional groups in mineralization, an amphiphilic peptide assembled monolayer with strictly arrayed carboxyl groups was applied to a mineralization system of calcium phosphate.

Self-assembling peptide nanofiber scaffolds for controlled release governed by gelator design and guest size.

The aim of this study was to develop controlled drug delivery by network scaffolds based on self-assembling peptide RADAFI and RADAFII. These two peptides self-assembled into interconnected nanofibrilar network structures with distinct physical morphologies. The hydrogels were also utilized for entrapment and release of some model guests, promising their future application as a drug delivery vehicle. Fickian diffusion controlled the release kinetics. Furthermore, the obtained release function was dependent on both rational design of the peptides used for hydrogel formation and choice of the entrapped molecules. On the basis of the striking different releases of these two peptide scaffolds, we suggested that guest size and lipophilicity influenced the release competitively. The release of RADAFI system was dominated by guest size, and the guest lipophilicity controlled the release behavior in RADAFII system. In a word, this work would potentially provide a spatially and temporally controlled delivery system for some functional drugs in the future.

Nanofibrous scaffold from self-assembly of beta-sheet peptides containing phenylalanine for controlled release.

Scaffold nanostructures from self-assembly of beta-sheet peptides, RADAFI and RADAFII, containing same amino acid compositions but different positions of one phenylalanine residue, were investigated. Atomic force microscopy (AFM) images clearly showed that peptide RADAFI self-assembled into twisted nanofibers with multiple molecular sized width and height, but no twisted nanofiber, characterized by a stacked bilayer model with single molecular sized width, was obtained in RADAFII scaffold. Two models of the hierarchical self-assembling behaviors could be illustrated for RADAFI and RADAFII scaffolds. The peptide scaffolds might also be promising for a variety of possible biomedical applications, including drug delivery, and the results revealed some relationships among the peptide sequence, the network nanoarchitecture, and the controlled release. From the remarkably large difference between the architecture and properties of the self-assembling materials based on the two similar peptides, it could be concluded that the self-assembly behaviors were delicate and could be dramatically altered by small modifying peptide structural features due to subtle changing the phenyl group position. The presence of a center pi-pi stacking between two beta-sheet-forming strands in the peptide sequence was demonstrated to be an important factor in promoting the twisted nanofiber morphology and a stronger network. Also, the concept of dominating the network nanostructures could be harnessed in the de novo design of delivery materials for some special biomolecules.

Controlled release and entrapment of enantiomers in self-assembling scaffolds composed of beta-sheet peptides.

As a first step toward utilizing self-assembling peptide scaffolds to create tunable matrices for drug delivery, peptide RADAFI and RADAFII, containing the same amino acid composition but different positions of one phenylalanine residue, scaffolds were prepared for controlled release of chiral enantiomers. The release behaviors depended on the network nanostructures and the guest chirality and were well tailored via loading different amounts of guests. This contribution addressed the relationships among the peptide sequence, the network nanoarchitecture, and the controlled release. RADAFII systems provided a means of controlling the release kinetics for L- and D-phenylalanine, which was achieved through the facile pi-pi stacking between the aromatic rings of L-isomer and those in RADAFII sequence and through the appropriate scaffold nanoarchitecture. The concept of controlled release for enantiomers via dominating the network nanostructures can also be harnessed in the de novo design of delivery systems with specific structural features for some special biomolecules.

Stimuli induced structural changes of gold nanoparticle assemblies having sequential alternating amphiphilic peptides at the surface.

Gold nanoparticles having sequential alternating amphiphilic peptide chains, Phe-(Leu-Glu)8, on the surface have been prepared. We describe structural control of the amphiphilic peptide coated gold nanoparticle assembly by a conformational transition of the surface peptides. Under the acidic condition, the conformation of the surface amphiphilic peptide was converted to a beta-sheet structure from an aggregated alpha-helix by incubation. Under this condition, the amphiphilic peptide coated gold nanoparticles formed a nanosheet assembly. The plasmon absorption maximum of the gold nanoparticles shifted to a shorter wavelength with the formation of the beta-sheet assembly of the surface peptide. This suggests that the structure of the peptide coated gold nanoparticle assembly could be controlled by the conformational transition of the surface peptide. Furthermore, the core gold nanoparticle could be fixed in the beta-sheet assembly in the state that stood alone. This system may be useful for novel molecular devices that exhibit quantized properties.

Self-assembled pH-responsive hydrogels composed of the RATEA16 peptide.

Peptide RATEA16 spontaneously self-assembled into higher-order nanofiber hydrogels with extremely high water content (>99.5% (wt/vol)) under physiological condition. The hydrogels could undergo pH-reversible transitions from viscous solution to elastic hydrogel and to precipitate. The supramolecular self-assembly and the three phase transitions are driven by hydrophobic interactions, intermolecular hydrogen bonds, and a combination of attractive or repulsive electrostatic interactions. These hydrogels are rich in beta-sheet nanofibers, as demonstrated by CD and FTIR data. Rheological measurements reveal that the viscoelasticity of the material can be tuned by environmental pH and peptide concentration. The storage modulus of the hydrogels increases with increasing peptide concentration, and the self-assembled hydrogels are able to recover from mechanical breakdowns. AFM images show that the elasticity is attributed to a network nanostructure consisting of fibrous self-assemblies. The hydrogels are promising for a variety of possible biomedical applications, including drug delivery.