Quantitative analysis of complex amino acids and RGD peptides by X‐ray photoelectron spectroscopy (XPS)

The C 1 s, N 1 s, and O 1 s core level binding energies (BEs) of the functional groups in amino acids (glycine, aspartic acid, glutamic acid, arginine, and histidine) with varied side‐chains and cell‐binding RGD‐based peptides have been determined and characterized by X‐ray photoelectron spectroscopy with a monochromatic Al K_α source. The zwitterionic nature of the amino acids in the solid state is unequivocally evident from the N 1 s signals of the protonated amine groups and the C 1 s signature of carboxylate groups. Significant adventitious carbon contamination is evident for all samples but can be quantitatively accounted for. No intrinsic differences in the XP spectra are evident between two polymorphs (α and γ) of glycine, indicating that the crystallographic differences have a minor influence on the core level BEs for this system. The two nitrogen centers in the imidazole group of histidine exhibit an N 1 s BE shift that is in line with previously reported data for theophylline and aqueous imidazole solutions, while the nitrogen and carbon chemical shifts reflect the unusual guanidinium chemical environment in arginine. It is shown that the complex envelopes of C 1 s and O 1 s photoemission spectra for short‐chain peptides can be analyzed quantitatively by reference to the less complex XP spectra of the constituent amino acids, provided the peptides are of high enough purity. The distinctive N 1 s photoemission from the amide linkages provides an indicator of peptide formation even in the presence of common impurities, and variations in the relative intensities of N 1 s were found to be diagnostic for each of the three peptides investigated (RGD, RGDS, and RGDSC). Copyright © 2013 John Wiley & Sons, Ltd.     

Improved Procedure for the Synthesis of DAMGO

A short and straightforward synthesis of DAMGO is described.     

The progress and perspective of strategies to improve tumor penetration of nanomedicines

Tumor penetration is important fo r effectively tumor targeting drug delivery.Recently,many researches are published to overcome the barriers that restrict tumor penetration and improve drug delivery efficiency.In the mini review,we first analyzed the barriers influence the tumor penetration,including tumor microenvironment barriers,nanoparticle properties,and interaction barriers between tumor and nanoparticles.To overcome the barrier,several strategies are developed,including modulating tumor microenvironment,changing particle size,transcytosis enabled tumor penetration,cell penetrating peptide modification and overcoming binding site barrier,which could effectively improve tumor penetration,and finally enhance tumor treatment outcome.     

CdS纳米晶与多肽相互作用研究

研究了半导体CdS纳米晶的表面功能化及荧光光谱特性,并利用静电/配位自组装方法实现了多肽和CdS纳米晶的生物无机偶联,研究了纳米晶多肽偶联体系的荧光光谱以及多肽与CdS纳米晶之间的相互作用.结果表明:含巯基多肽对CdS纳米晶表面形成完善包覆,消除CdS纳米晶表面缺陷,使CdS纳米晶荧光增强;含端氨基多肽使CdS纳米晶荧光出现先升后降趋势;其余不含巯基和氨基的多肽均猝灭CdS纳米晶荧光,猝灭机制属于形成化合物所引起的静态猝灭,它们的结合常数约为2×104,结合位点数约为0.87～1.00.     

Identification of low molecular weight proteins isolated by 2-D liquid separations

Proteins with molecular mass (M(r)) <20 kDa are often poorly separated in 2-D sodium dodecyl sulfate polyacrylamide gel electrophoresis. In addition, low-M(r) proteins may not be readily identified using peptide mass fingerprinting (PMF) owing to the small number of peptides generated in tryptic digestion. In this work, we used a 2-D liquid separation method based on chromatofocusing and non-porous silica reversed-phase high-performance liquid chromatography to purify proteins for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOFMS) analysis and protein identification. Several proteins were identified using the PMF method where the result was supported using an accurate M(r) value obtained from electrospray ionization TOFMS. However, many proteins were not identified owing to an insufficient number of peptides observed in the MALDI-TOF experiments. The small number of peptides detected in MALDI-TOFMS can result from internal fragmentation, the few arginines in its sequence and incomplete tryptic digestion. MALDI-QTOFMS/MS can be used to identify many of these proteins. The accurate experimental M(r) and pI confirm identification and aid in identifying post-translational modifications such as truncations and acetylations. In some cases, high-quality MS/MS data obtained from the MALDI-QTOF spectrometer overcome preferential cleavages and result in protein identification.     

Molecule-Responsive Fluorescent Sensors of α-Helix Peptides Bearing α-Cyclodextrin, Pyrene and Nitrobenzene Units in Their Side Chains

-Helix peptides bearing one unit of -cyclodextrin (-CD), one unit of pyrene and one unit of nitrobenzene (NB) in their side chains have been designed and synthesized as novel molecule-responsive devices.In both the CD-peptides, -PR17 and -PL17, the NB unit is separated from the CD unit by two turns of the helix. Two reference peptides (PL17, and -P17,) have also been synthesized. The circular dichroism studies in the peptide absorption region (200–250 nm)of -PR17 and -PL17 suggestthat the CD-peptides form stable-helixstructures (83–77%), which was destabilized by accommodating guest molecules (e.g., n-pentanol) into the CD cavity. It suggests that formation of intramolecular host–guest(CD–NB) complex stabilized thehelical structure and exogenous guest molecule excluded the appending NB moiety from inside to outside of the CD cavity, thereby causing destabilization of the helical structure and increasing the random coil content. The ICD spectra of the peptides in the pyrene and nitrobenzene absorption region (250–40 nm) suggest that NB forms inclusion complex with CD. The fluorescence studies revealed that the fluorescence of the pyrene unit is quenched by the NB unit in -PR17 and -PL17. The fluorescence intensity increases with increasing guest concentration for the CD-peptides.This guest-responsiveenhancement in the fluorescence intensity can be explained in terms of increased distance between the pyrene and NB moieties, which is caused by exclusion of the NB moiety from the CD cavity by guest accommodation. Using the guest-responsive fluorescence quenching properties of the CD-peptides, we have obtained binding constants for various short chain alkanols. -PL17 has higher binding affinity to the guest molecules than its isomer, -PR17, indicating that the location of functional groups on the peptide scaffold is important in molecule detection.     

The statistical significance of selected sense–antisense peptide interactions

Sense and antisense peptides, encoded by sense and corresponding antisense DNA strands, are capable of specific interactions that could be a driving force to mediate protein–protein or protein–peptide binding associations. The complementary residue hypothesis suggests that these interactions are founded upon the sum of pairwise interactions between amino acids encoded by corresponding sense and antisense codons. Despite many successful experimental results obtained with the hypothesis, however, the physicochemical basis for these interactions is poorly understood. We examined the potential of the hypothesis for general identification of protein–protein interaction sites, and the possible role of the hypothesis in determining folding in a broad set of protein structures. In addition, we performed a structural study to investigate the binding of a complementary peptide to IL‐1F2. Our results suggest that complementary residue pairs are no more frequent or conserved than average in protein–protein interfaces, and are statistically under‐represented amongst contacting residue pairs in folded protein structures. Although our structural results matched experimental observations of binding between the peptide and IL‐1F2, complementary residue interactions do not appear to be dominant in the bound structure. Overall, our data do not allow us to conclude that the complementary residue hypothesis accounts for specific sense–antisense peptide interactions. © 2012 Wiley Periodicals, Inc.