Carbon molecular sieve based micro‐matrix‐solid‐phase dispersion for the extraction of polyphenols in pomegranate peel by UHPLC‐Q‐TOF/MS

A rapid, simple, and efficient sample extraction method based on micro‐matrix‐solid‐phase dispersion (micro‐MSPD) was applied to the extraction of polyphenols from pomegranate peel. Five target analytes were determined by ultra‐HPLC coupled with Q‐TOF/MS. Carbon molecular sieve (CMS) was firstly used as dispersant to improve extraction efficiency in micro‐MSPD. The major micro‐MSPD parameters, such as type of dispersant, amount of dispersant, grinding time, and the type and the volume of elution solvents, were studied and optimized. Under optimized conditions, 26 mg of pomegranate peel was dispersed with 32.5 mg of CMS, the grinding time was selected as 90 s, the dispersed sample was eluted with 100 μL of methanol. Results showed that the proposed method was of good linearity for concentrations of analytes against their peak areas (coefficient of determination r² > 0.990), the LOD was as low as 3.2 ng/mL, and the spiking recoveries were between 88.1 and 106%. Satisfactory results were obtained for the extraction of gallic acid, punicalagin A, punicalagin B, catechin, and ellagic acid from pomegranate peel sample, which demonstrated nice reliability and high sensitivity of this approach.     

2‐(2‐Aminoethylamino)‐5‐nitropyridine as a basic matrix for negative‐mode matrix‐assisted laser desorption/ionization analysis of phospholipids

Fast and easy analysis of phospholipids (PLs) by matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) has been well demonstrated. However, when using common organic matrices, such as 2,5‐dihydroxybenzoic acid (DHB), the detection of most PL classes in positive‐ion mode is difficult when PLs containing zwitterionic groups, such as phosphatidylcholines (PCs) and sphingomyelins (SMs) are present. To reduce this limitation, 2‐(2‐aminoethyloamino)‐5‐nitropyridine (AAN), a basic compound, was evaluated as an alternative matrix. Negative‐ion spectra showed enhanced detection of phosphatidyl ethanolamines (PEs), phosphatidyl serines (PSs), phosphatidyl glycerols (PGs), and phosphatidyl inositols (PIs) in simple mixtures and in a crude methanolic soybean extract. The relative ionization efficiency (RIE) was highest for PIs and lowest for PGs, PSs, and PEs. Compared to DHB and para‐nitroaniline, AAN resulted in greater sensitivity for the detection of PL classes in the negative mode. Indeed, the S/N ratio was nearly an order of magnitude higher than that reported for similar PI concentrations but with DHB. MALDI spots produced with AAN were homogeneous thus allowing automation and improved reproducibility. Positive‐mode traces could also be acquired with AAN as the matrix, but with lower sensitivity than in the negative mode. Copyright © 2008 John Wiley & Sons, Ltd.     

Computerized implementation of higher‐order electron‐correlation methods and their linear‐scaling divide‐and‐conquer extensions

We have implemented a linear‐scaling divide‐and‐conquer (DC)‐based higher‐order coupled‐cluster (CC) and Møller–Plesset perturbation theories (MPPT) as well as their combinations automatically by means of the tensor contraction engine, which is a computerized symbolic algebra system. The DC‐based energy expressions of the standard CC and MPPT methods and the CC methods augmented with a perturbation correction were proposed for up to high excitation orders [e.g., CCSDTQ, MP4, and CCSD(2)_TQ]. The numerical assessment for hydrogen halide chains, polyene chains, and first coordination sphere (C1) model of photoactive yellow protein has revealed that the DC‐based correlation methods provide reliable correlation energies with significantly less computational cost than that of the conventional implementations. © 2017 Wiley Periodicals, Inc.     

Synthesis and structural characterization of dendritic‐linear PMA‐APM‐r‐PS copolymers for a self‐assembled microporous matrix

A set of dendritic‐linear copolymers, poly(maleic anhydride‐grafted‐3,3′‐dimethyl‐(4‐aminophenylazanediyl)bis(2‐methylpropanoate))‐random‐polystyrene (PMA‐APM‐r‐PS), was successfully prepared by copolymerization of the novel dendritic macromonomer, 4‐(4‐(bis(3‐(4‐(bis(3‐methoxy‐2‐methyl‐3‐oxopropyl)amino)phenylamino)‐2‐methyl‐3‐oxopropyl)amino)phenylamino)‐4‐oxobut‐2‐enoic acid (MA‐APM), with styrene monomer. The dendritic MA‐APM macromonomer dendron 3,3′‐dimethyl‐(4‐aminophenylazanediyl)bis(2‐methylpropanoate) (APM) was then grafted by using the divergent growth method. FTIR, ¹H NMR, and ¹³C NMR spectra were used to identify the structures of the dendron, the dendritic macromonomer, and the dendritic‐linear PMA‐APM‐r‐PS copolymer. Furthermore, microporous dendritic‐linear PMA‐APM‐r‐PS copolymer films were prepared by using solvent‐induced phase separation at room temperature. We investigated the phase separation behavior and morphological structures of the dendritic‐linear copolymer film as functions of dendritic GMA‐HPAM segments in the content using SEM. Self‐assembly of the dendritic‐linear PMA‐APM‐r‐PS copolymer in the MG2‐X system, which represented the second generation dendron containing X wt % of the dendritic MA‐APM segment, resulted in submicron phase segregation. Interestingly, the submicron phase segregation morphology of the MG2–43 sample presented a uniform size distribution of ordered‐array structures. The results of this study demonstrate that controlling the appropriate macromonomer content via the grafting of a three‐dimensional structure results in a self‐assembly process that is capable of providing an ordered‐array microporous morphology in a polymer film. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3290–3301, 2010     

Shapeable matrix‐free Spectra® fiber‐reinforced polymeric composites via high‐temperature high‐pressure sintering: Process‐structure‐property relationship

In an exploratory effort to find a new way to make high‐performance composites used in ballistic protective applications, matrix‐free Spectra® fiber‐reinforced polymeric composites are produced via a novel processing method called high‐temperature high‐pressure sintering. Mechanical testing at ambient and elevated temperatures proves that the fibers can maintain their properties after processing. The characteristics and properties of the final products vary with different processing conditions. Their microstructure and morphology were investigated using SEM and WAXD. Their mechanical properties, including interlayer adhesion, rigidity, and ballistic performance, were measured and compared with those of the conventional composites. The sintering mechanism is proposed and verified. Spectra cloth is capable of being shaped to produce complex double curvatures by a thermoforming process, using a simple hemispherical mold. Success in different molding sequences and procedures shows the versatility in manufacturing. The theoretical background for the thermoformability is explained in terms of molecular interaction, microstructure, and morphology. Selective thermomechanical properties of the molded structures were measured. By combining the knowledge and information from the aforementioned studies, the process‐structure‐property relationship is established, which gives in‐depth and better understanding of this unique high‐temperature high‐pressure sintering process for consolidating Spectra cloth. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2767–2789, 2005     

Formation of interfacial microstructures of Mo‐coating modified SiCf/Mo/Ti‐6Al‐4V composites

This paper addresses the role of Mo coating to modify the interface of SiC fiber reinforced Ti‐6Al‐4V composite (SiC_f/Mo/Ti‐6Al‐4V). The formation of microstructure as well as the diffusion of elements in the interface of as‐prepared and heat‐treated SiC_f/Mo/Ti‐6Al‐4V composites was investigated. The results show that the phases formed at the interfacial zone are: Mo coating∣TiC∣Mo + β‐Ti∣β‐Ti∣β‐Ti + α‐Ti_strip, ordering from fiber to matrix. Mo coating can effectively hinder the diffusion of elements between the matrix and fiber to some extent, thus it can inhibit fiber/matrix interfacial reaction and protect the fiber from damage. It is believed that the β‐Ti layer formed around the interface can improve the formability of composites. Furthermore, it indicates that Mo coating exhibits excellent thermal stability bellow 700 °C according to the heat treatment of the composites at 700 °C for up to 200 h. Copyright © 2012 John Wiley & Sons, Ltd.     

A graph-theoretical method for stepwise factorisation of symmetric graphs for simultaneous determination of eigenvectors and eigenvalues

A simple pictorial algorithm for factorisation of symmetric chemical graphs (weighted and unweighted) leading to simultaneous determination of their eigenvalues and eigenvectors has been devised. The method does not require group-theoretical techniques (viz. identification of the point group of the species under study, formation of symmetryadopted linear combinations using character tables etc.). It requires consideration of only one symmetry element, e.g., a reflection plane and is based on elementary row and column operations which keep the secular determinant of the adjacency matrix unchanged (except possibly for a multiplicative constant).     

The effect of temperature on the stability of compounds used as UV‐MALDI‐MS matrix: 2,5‐dihydroxybenzoic acid, 2,4,6‐trihydroxyacetophenone, α‐cyano‐4‐hydroxycinnamic acid, 3,5‐dimethoxy‐4‐hydroxycinnamic acid,nor‐harmane and harmane

The thermal stability of several commonly used crystalline matrix‐assisted ultraviolet laser desorption/ionization mass spectrometry (UV‐MALDI‐MS) matrices, 2,5‐dihydroxybenzoic acid (gentisic acid; GA), 2,4,6‐trihydroxyacetophenone (THA), α‐cyano‐4‐hydroxycinnamic acid (CHC), 3,5‐dimethoxy‐4‐hydroxycinnamic acid (sinapinic acid; SA), 9H‐pirido[3,4‐b]indole (nor‐harmane; nor‐Ho), 1‐methyl‐9H‐pirido[3,4‐b]indole (harmane; Ho), perchlorate of nor‐harmanonium ([nor‐Ho + H]⁺) and perchlorate of harmanonium ([Ho + H]⁺) was studied by heating them at their melting point and characterizing the remaining material by using different MS techniques [electron ionization mass spectrometry (EI‐MS), ultraviolet laserdesorption/ionization‐time‐of‐flight‐mass spectrometry (UV‐LDI‐TOF‐MS) and electrospray ionization‐time‐of‐flight‐mass spectrometry (ESI‐TOF‐MS)] as well as by thin layer chromatography analysis (TLC), electronic spectroscopy (UV‐absorption, fluorescence emission and excitation spectroscopy) and ¹H nuclear magnetic resonance spectroscopy (¹H‐NMR). In general, all compounds, except for CHC and SA, remained unchanged after fusion. CHC showed loss of CO₂, yielding the trans‐/cis‐4‐hydroxyphenylacrilonitrile mixture. This mixture was unambiguously characterized by MS and ¹H‐NMR spectroscopy, and its sublimation capability was demonstrated. These results explain the well‐known cluster formation, fading (vanishing) and further recovering of CHC when used as a matrix in UV‐MALDI‐MS. Commercial SA (SA 98%; trans‐SA/cis‐SA 5 : 1) showed mainly cis‐ to‐trans thermal isomerization and, with very poor yield, loss of CO₂, yielding (3′,5′‐dimethoxy‐4′‐hydroxyphenyl)‐1‐ethene as the decarboxilated product. These thermal conversions would not drastically affect its behavior as a UV‐MALDI matrix as happens in the case of CHC. Complementary studies of the photochemical stability of these matrices in solid state were also conducted. Copyright © 2008 John Wiley & Sons, Ltd.     

A pitfall of using 2‐[(2E)‐3‐(4‐tert‐butylphenyl)‐2‐methylprop‐2‐enylidene]malononitrile as a matrix in MALDI TOF MS: chemical adduction of matrix to analyte amino groups

2‐[(2E)‐3‐(4‐tert‐Butylphenyl)‐2‐methylprop‐2‐enylidene]malononitrile (DCTB) has been considered as an excellent matrix for matrix‐assisted laser desorption/ionization (MALDI) of many types of synthetic compounds. However, it might provide troublesome results for compounds containing aliphatic primary or secondary amino groups. For these compounds, strong extra ion peaks with a mass difference of 184.1 Da were usually observed, which might falsely indicate the presence of some unknown impurities that were not detected by other matrices. On the basis of the possible mechanisms proposed, these extra ions are the products of nucleophilic reactions between analyte amino groups and DCTB molecules or radical cations. In these reactions, an amino group replaces the dicyanomethylene group of DCTB forming a matrix adduct via a ? C?N‐bond. An aliphatic primary amine could react easily with DCTB and the reaction could start once they are mixed in a MALDI solution. For an aliphatic secondary amine, on the other hand, the reaction most likely occurs in the gas phase. Protonation of amino groups by adding acid seems to be a useful way to stop DCTB adduction for compounds with one single amino group, but not for compounds with multiple amino groups. Unlike aliphatic primary or secondary amines, aliphatic tertiary amines and aromatic amines do not yield DCTB adducts. This is because tertiary amines do not have the required transferrable H‐(N) atom to form an extra ? C?N‐bond, while aromatic amines are not sufficiently nucleophilic to attack DCTB. In view of the possible matrix adduction, care should be taken in MALDI time‐of‐flight mass spectrometry (TOF MS) when DCTB is used as the matrix for compounds containing amino group(s). Copyright © 2010 John Wiley & Sons, Ltd.     

UV‐Irradiation Cured Organic‐inorganic Hybrid Nanocomposite Initiated by Ethoxysilane‐modified Multifunctional Polymeric Photoinitiator through Sol‐gel Process

The UV‐cured organic‐inorganic hybrid nanocomposite (nano‐Si‐m‐PI) was prepared through the photopolymerization of acrylic resin initiated by ethoxysilane‐modified multifunctional oligomeric photoinitiator (Si‐m‐PI). The esterification reaction of 2‐hydroxy‐4′‐(2‐hydroxyethoxy)‐2‐methylpropiophenone (Irgacure 2959) with thioglycolic acid, and the following addition reactions with dipentaerythritol hexaacrylate and then 3‐aminopropyltriethoxysilane were carried out for preparing the Si‐m‐PI. The Si‐m‐PI exhibits the similar UV absorption and molar extinction coefficient with Irgacure 2959. The photoinitiating activity study by photo‐DSC analysis showed that the Si‐m‐PI possesses high photopolymerization rate at the peak maximum (R_p^max) and final unsaturation conversion (P^f) in the cured hybrid films. From the scanning electron microscope (SEM) observation, the SiO₂ nanoparticles dispersed uniformly in the formed nano‐Si‐m‐PI, whereas the aggregation of nanoparticals occurred in nano‐Irg, which was prepared through the photopolymerization of acrylic resin initiated by Irgacure 2959. Moreover, compared with the UV‐cured pure polymer and nano‐Irg, the nano‐Si‐m‐PI showed remarkably enhanced thermal stability and mechanical properties.     

Automated error control in divide‐and‐conquer self‐consistent field calculations

In linear‐scaling divide‐and‐conquer (DC) electronic structure calculations, a buffer region is used to control the error introduced by the DC approximation. In this study, an energy‐based error estimation scheme is proposed for the DC self‐consistent field method with a two‐layer buffer region scheme. Based on this scheme, a procedure to automatically determine the appropriate buffer region in the DC method is proposed. It was confirmed that the present method works satisfactorily in calculations of water clusters and proteins, although its performance was insufficient for the calculation of a delocalized graphene system. © 2018 Wiley Periodicals, Inc.     

Multi‐Stimuli‐Responsive Polymeric Prodrug for Enhanced Cancer Treatment

Accomplishing efficient delivery of a nanomedicine to the tumor site will encounter two contradictions as follows: 1) a contradiction between prolonged circulation time and endocytosis by cancer cells; 2) a dilemma between the stability of nanomedicine during blood circulation and intracellular drug release. While developing a nanomedicine which can solve the above two contradictions simultaneously is still a challenge, here, a multi‐stimuli‐responsive polymeric prodrug (PLys‐co‐(PLys‐DA)‐co‐(PLys‐SS‐PTX))‐b‐PLGLAG‐mPEG (P‐PEP‐SS‐PTX‐DA) is synthesized which is multi‐sensitive to overexpressed matrix metalloproteinase‐2 (MMP‐2), low pH, and high concentration of glutathione in tumors. The P‐PEP‐SS‐PTX‐DA can be dePEGylated and reversed from negative at normal physiological pH to positive charge at tumor extracellular microenvironment; in this way, it can solve the contradiction between prolonged circulation time and endocytosis by cancer cells. Owing to the high reductive conditions in cancer cells, P‐PEP‐SS‐PTX‐DA is ruptured to release paclitaxel (PTX) intracellular efficiently; therefore, it can resolve the dilemma between the stability of nanomedicine during blood circulation and intracellular drug release. These indicate that the multi‐stimuli‐responsive polymeric prodrug has potential application prospects in drug delivery and cancer therapy.     

Morphology and mechanical properties of blown films of a low‐density polyethylene/linear low‐density polyethylene blend

The morphologies of films blown from a low‐density polyethylene (LDPE), a linear low‐density polyethylene (LLDPE), and their blend have been characterized and compared using transmission electron microscopy, small‐angle X‐ray scattering, infrared dichroism, and thermal shrinkage techniques. The blending has a significant effect on film morphology. Under similar processing conditions, the LLDPE film has a relatively random crystal orientation. The film made from the LDPE/LLDPE blend possesses the highest degree of crystal orientation. However, the LDPE film has the greatest amorphous phase orientation. A mechanism is proposed to account for this unusual phenomenon. Cocrystallization between LDPE and LLDPE occurs in the blowing process of the LDPE and LLDPE blend. The structure–property relationship is also discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 507–518, 2002; DOI 10.1002/polb.10115     

Characterization of N‐Boc/Fmoc/Z‐N′‐formyl‐gem‐diaminoalkyl derivatives using electrospray ionization multi‐stage mass spectrometry

N‐Boc/Fmoc/Z‐N′‐formyl‐gem‐diaminoalkyl derivatives, intermediates particularly useful in the synthesis of partially modified retro‐inverso peptides, have been characterized by both positive and negative ion electrospray ionization (ESI) ion‐trap multi‐stage mass spectrometry (MSⁿ). The MS² collision induced dissociation (CID) spectra of the sodium adduct of the formamides derived from the corresponding N‐Fmoc/Z‐amino acids, dipeptide and tripeptide acids show the [M + Na‐NH₂CHO]⁺ ion, arising from the loss of formamide, as the base peak. Differently, the MS² CID spectra of [M + Na]⁺ ion of all the N‐Boc derivatives yield the abundant [M + Na‐C₄H₈]⁺ and [M + Na‐Boc + H]⁺ ions because of the loss of isobutylene and CO₂ from the Boc protecting function. Useful information on the type of amino acids and their sequence in the N‐protected dipeptidyl and tripeptidyl‐N′‐formamides is provided by MS² and subsequent MSⁿ experiments on the respective precursor ions. The negative ion ESI mass spectra of these oligomers show, in addition to [M‐H]^?, [M + HCOO]^? and [M + Cl]^? ions, the presence of in‐source CID fragment ions deriving from the involvement of the N‐protecting group. Furthermore, MSⁿ spectra of [M + Cl]^? ion of N‐protected dipeptide and tripeptide derivatives show characteristic fragmentations that are useful for determining the nature of the C‐terminal gem‐diamino residue. The present paper represents an initial attempt to study the ESI‐MS behavior of these important intermediates and lays the groundwork for structural‐based studies on more complex partially modified retro‐inverso peptides. Copyright © 2013 John Wiley & Sons, Ltd.