Benzyl L-aspartate Research Articles

Nanoassemblies of heptamethine cyanine dye-initiated poly(amino acid) enhance ROS generation for effective antitumour phototherapy.

Phototherapy shows great potential for pinpoint tumour treatment. Heptamethine cyanine dyes like IR783 have high potential as agents for antitumour phototherapy due to their inherent tumour targeting ability, though their effectiveness in vivo is unsatisfactory for clinical translation. To overcome this limitation, we present an innovative strategy involving IR783-based polymeric nanoassemblies that improve the dye's performance as an antitumoural photosensitizer. In the formulation, IR783 is modified with cysteamine and used to initiate the ring-opening polymerization (ROP) of the N-carboxyanhydride of benzyl-L-aspartate (BLA), resulting in IR783-installed poly(BLA). Compared to free IR783, the IR783 dye in the polymer adopts a twisted molecular conformation and tuned electron orbital distribution, remarkably enhancing its optical properties. In aqueous environments, the polymers spontaneously assemble into nanostructures with 60 nm diameter, showcasing surface-exposed IR783 dyes that function as ligands for cancer cell and mitochondria targeting. Moreover, the nanoassemblies stabilized the dyes and enhanced the generation of reactive oxygen species (ROS) upon laser irradiation. Thus, in murine tumor models, a single injection of the nanoassemblies with laser irradiation significantly inhibits tumour growth with no detectable off-target toxicity. These findings highlight the potential for improving the performance of heptamethine cyanine dyes in antitumor phototherapy through nano-enabled strategies.

Magnetic nanoparticles with a pH-sheddable layer for antitumor drug delivery

A dually responsive nanocarrier with a multilayer core–shell architecture was prepared based on Fe3O4@SiO2 nanoparticles successively coated with poly(benzyl L-aspartate) (PBLA) and poly(ethylene glycol) (PEG) for the purpose of tumor specific drug delivery applications. In this system, PEG chains are connected to the surface via pH-sensitive benzoic-imine bonds and serve as a pH-sheddable hydrophilic corona. Meanwhile, the PBLA segments serve as a hydrophobic middle layer used to load the drugs via hydrophobic interactions. The Fe3O4@SiO2 nanoparticle functions as a superparamagnetic core used to direct the drug loaded nanocarrier to the target pathological site. The obtained materials were characterized with FT-IR, 1H NMR, dynamic light scattering, zeta-potential, TEM, TGA, and hysteresis loop analysis. An anticancer drug doxorubicin (DOX) was selected as the model drug loaded into the nanocarrier, which was relatively stable under physiological conditions due to its neutral hydrophilic shell, and could quickly release the drug in response to increased acidity via shedding of the PEG shells through cleavage of the intermediate benzoic-imine bonds. Meanwhile, the neutral shell shedding would reveal a positively charged nanoparticle surface that is readily taken up by tumor cells. These pH- and magnetic-responsive nanoparticles showed significant potential for use in the targeted intracellular delivery of hydrophobic chemotherapeutics in cancer therapy.

Imine bond cross-linked poly(ethylene glycol)-block-poly(aspartamide) complex micelle as a carrier to deliver anticancer drugs

The aim of this study is to develop degradable core-cross-linked polymeric micelles based on two water soluble methoxy-poly(ethylene glycol)-block-poly(aspartamide) (mPEG-PA) copolymers using the pH-sensitive imine bond. The ring opening polymerization of N-carboxyanhydride (NCA) was utilized to prepare the diblock copolymer methoxy-poly(ethylene glycol)-block-poly(benzyl L-aspartate). Amino and aldehyde modified mPEG-PAs were obtained by aminolysis and oxidation. The mixture of these two mPEG-PA polymer precursors was shown to form reversible core-cross-linked micelles by the formation of an imine linkage without the addition of cross-linker or catalyst. The structure of the prepared polymers was studied using NMR and FT-IR spectroscopy. The pH-sensitivity of the micelles was characterized by DLS. The mPEG-PA cross-linked micelle exhibited good biocompatibility according to the MTT assay against NIH/3T3 cells. The hydrophobic anticancer drug doxorubicin (DOX) was selected as a model drug and loaded into the micelles where it could be quickly released at low pH and was relatively stable under physiological conditions. Thereby, such an excellent nanocarrier provides a favorable platform to construct smart drug delivery systems for cancer therapy.

Synthesis and Drug Release of Star‐Shaped Poly(benzyl L‐aspartate)‐block‐poly(ethylene glycol) Copolymers with POSS Cores

Star-shaped amphiphilic block copolymers with polyhedral oligomeric silsesquioxanes (POSS) as cores are synthesized using the "arm-first" strategy. First, the block copolymer poly(benzyl L-aspartate)-block-poly(ethylene glycol) (PBLA-b-PEG) is synthesized via ring-opening polymerization of β-benzyl L-aspartate-N-carboxyanhydride (BLA-NCA) with α-methoxy-ω-aminopoly(ethylene glycol) (mPEG-NH2 ) as a macroinitiator. The copolymers are then immobilized on the eight groups of the polyhedral oligomeric silsesquioxanes (POSS-COOH). The star-shaped copolymers (POSS-g-(PBLA-b-PEG)) are characterized by (1) H NMR and FT-IR spectroscopy and gel permeation chromatography. The star-shaped block copolymers self-assemble into micelles in aqueous medium. Quercetin is used as a model drug and the drug loading content and encapsulation efficiency increases with increasing chain length of the PBLA blocks. The drug release behaviors of drug loaded micelles are investigated and the cytotoxicity assay demonstrates that the POSS-g-(PBLA-b-PEG) copolymers are non-toxic. The star-shaped block copolymers are potential carriers for anticancer drug delivery.

Mechanism of the screw-sense reversal of tightly hydrogen-bonded α-helical network triggered by the side-chain conformation

The paper presents theoretical treatment of a screw-sense reversal of tightly hydrogen-bonded α-helical polypeptide chains. The transition is triggered by the conformational free-energy difference ( s) of the side chain flanking the chiral (right(r)- or left(ℓ)-handed) backbone. The two-parameter scheme ( s, σ) corresponding to a zipper-type transition model starting from one terminal has been constructed and applied to the thermally-induced helix–helix transition characteristic of polyaspartic acid esters observed in the helicoidal solution. The weighting parameter σ takes care of the instability associated with the ℓ/r junction, i.e., the unfolded site where at least three successive hydrogen-bonds should become free to change their partner. The enthalpy of transition (ca. 2 kJ/mol) of poly(β-phenethyl l-aspartate) (PPLA) ( Mv = 6 × 10 4) observed in the lyotropic liquid crystalline state in 1,1,2,2-tetrachloroethane has been reproduced with the instability parameter σ = 0.001–0.0001. Attempts were further extended to interpret the thermally-induced helix–helix transition behaviors of the PPLA homopolymers and random copolymers involving benzyl l-aspartate residues observed under various conditions.

Synthesis and characterization of poly(L-lactic acid-co-ethylene oxide-co-aspartic acid) and its interaction with cells

Multiblock terpolymer of poly(L-lactic acid)/poly(ethylene oxide)/poly(L-aspartic acid), (PLLA/PEO/PAsp) was synthesized by ring opening polymerization of beta -benzyl L-aspartate N-carboxyanhydride, Asp(OBzl)-NCA with alpha-omega -hydroxy terminated triblock PLLA/PEO/PLLA copolymer. The resulting multiblock terpolymer was characterized by several techniques including Fourier transform infrared spectroscopy and differential scanning calorimetry.(1)H nuclear magnetic resonance spectra indicated the molar ratio of PLLA/PEO/PAsp (OBzl) to be 86/10/4. Thermal gravimetric analysis and environmental scanning electron microscopy data showed that PLLA/PEO/PAsp had crystalline and brittle structure. In order to improve its mechanical and physical properties, the terpolymer was blended with high molecular weight poly(L-lactic-co-glycolic acid) copolymer, PLGA(85/15) (M(w): 95000 gmol(-1)) in 25/75 and 50/50 mole ratios. The hydrolytical degradation properties of these polymers were studied. Degradation experiments were performed during a 48-day period in pH:7.4 phosphate-buffered saline (PBS) at 37 degrees C. The observed molecular weight losses were 91% and 67% for the 25/75 and 50/50 mixtures, respectively. In vitro attachment and growth of L929 mouse fibroblasts on these biopolymers were also investigated. Cell growth experiments indicated that the copolymer blend allowed the attachment and growth of cells.

Nitrogen-15 chemical shift tensors and conformation of solid polypeptides containing 15N-labeled L-alanine residue by 15N NMR. 2. Secondary structure is reflected in .sigma.22

Absbrct: A series of polypeptides [Ala*,X], containing I5N-labeled L-alanine (Ala*) and other amino acids (X; natural abundance of 15N) such as glycine, L-alanine, palanine, L-leucine, &benzyl L-aspartate, y-benzyl L-glutamate, y-methyl L-glutamate, L-valine, L-isoleucine, and sarcosine were synthesized by the a-amino acid N-carboxy anhydride (NCA) method. Conformations of these polypeptides in the solid state were characterized on the basis of conformation-dependent I3C chemical shifts in the I3C cross-polarization-magic-angle spinning (CP-MAS) NMR spectra and of the characteristic bands in the infrared (IR) and far-IR spectra. Further, isotropic 15N chemical shift (ab) and chemical shift tensors (ull, u2, and uaa) of the polypeptides were measured by the 15N CP-MAS and the 15N CP-static (powder pattern) methods, respectively. It was found that ai, is useful for the conformational study of homopolypeptides and copolypeptides with identical primary structures (amino acid sequences). In addition, it was demonstrated that the u22 value of the Ala* residue in copolypeptide is closely related to the main-chain conformations (such as the right-handed and left-handed a-helices, and the &sheet forms) rather than the amino acid sequence. Consequently, the uz2 value is very useful for conformational analysis of solid copolypeptides. Recently, high-resolution and solid-state 15N NMR has been increasingly applied to the investigation of polypeptides, proteins, and biopolymers.'-I2 This is primarily due to rapid progress in the development of both methodology and instrumentation. For example, sensitivity of the I5N resonance has been greatly improved by introduction of the cross-polarization magic-angle spinning (CP-MAS) methods. However, little attempt has yet been made to relate the 15N chemical shifts and chemical shift tensors to the structural parameters or primary, secondary, and higher ordered structures of synthetic polypeptides or natural proteins in the solid state. Furthermore, since a nitrogen atom possesses lone-pair electrons, it is of interest to examine the effects of the lone-pair electrons on the isotropic 15N chemical shift (P~) and the principal values of the I5N chemical shift tensors (ull, uZ2, and uj3 from the downfield side), which are a measure of the electronic structure. Thus, it is now expected that I5N NMR spectroscopy will contribute to and become increasingly important in the study on the structures and dynamics of synthetic polypeptides and natural proteins in the solid state. In our previous papers,I3J4 we have demonstrated that (1) the uho value determined by the ISN CP-MAS NMR method is very sensitive to the primary structure such as the variety of amino acid residue and the amino acid sequence, as well as the secondary structure (particular conformations) such as the a-helix and @-sheet forms of polypeptides in the solid state and (2) the ullr 92, and uj3 values determined by the CP-static (powder pattern) spectra for I5N-labeled copolypeptides are strongly influenced not only by the local conformations but also by the chemical nature of individual amino acid residues. In particular, it is noteworthy that one of the principal values, u22, may be useful for determination of the backbone conformation of polypeptides in the solid state. In this paper, therefore, we attempt to elucidate the origin of the individual components of the I5N chemical shift tensors of polypeptides in connection mainly with the primary structure such as the variety of amino acid residue and amino acid sequence and the secondary structure such as right-handed a-helix (a-helix), left-handed a-helix (aL-helixI5), and &sheet conformations. For this purpose, we have prepared a series of 15N-labeled polypeptides,

CONFORMATIONAL CHANGES IN SOLID FILMS AMONG α-HELICES WITH DIFFERENT HELIX SENSES AND π-HELIX FOR COPOLYMERS OF POLY (ASPARTATE ESTERS) WITH BENZYL AND (m-PHENYLAZO)BENZYL SIDE CHAINS

Abstract Copolymers of β-(m-phenylazo)benzyl L-aspartate and β-benzyl L-aspartate exist as left-handed α-helix (αL), right-handed α-helix (αR) or π-helix (πL) in solid films at 25 °C. Conformational transitions from αL to πL and from αR to πL were found to occur by heating.

Light-induced Conformational Changes of Polypeptides. Photoisomerization of Azoaromatic Polypeptides

Abstract Copolymers of β-benzyl l-aspartate with β-m- or p-(phenylazo)benzyl l-aspartate were prepared in order to investigate the effect of side-chain photoisomerization on their conformations. These polymers in 1,2-dichloroethane show a CD band at 222 nm characteristic of left-handed α-helices. After irradiation, remarkable changes of the 222 nm band were observed for both meta and para copolymers with more than 50 % azo residues. The decrease in ellipticity observed for the meta copolymers indicates that photoisomerization induces a significant instability in the left-handed α-helical conformation. On the other hand, the para copolymers change their sign from positive to negative by irradiation, confirming the reversal in the helix sense. In the course of subsequent relaxation of the irradiated para copolymer with 59% azo residues, an abrupt change in the CD spectra was found above 50% cis followed by a gradual change on decreasing the content of cis isomers. Concerning the polymers with azoaromatic side chains including copolymers with γ-benzyl l-glutamate, the helical sense seems to affect appreciably the sign of the side-chain CD bands.

Nuclear Magnetic Resonance and Optical Rotatory Dispersion of L-Alanine Blocks Flanked by Benzyl L-Glutamate, Benzyl L-Aspartate, and N ε-Carbobenzoxy-L-lysine

Nuclear Magnetic Resonance and Optical Rotatory Dispersion of L-Alanine Blocks Flanked by Benzyl L-Glutamate, Benzyl L-Aspartate, and N ^ε-Carbobenzoxy-L-lysine