Polymer membrane and cell models for drug discovery

This paper reviews the functional polymer membrane and membrane based cell drug evaluation models for drug discovery. Based on the characteristics of biological membranes in vivo, chemical modification methods of synthetic membrane, including blending and surface modification are explored to mitigate the membrane fouling and improve biocompatibility. Different membrane-based cell models used in drug investigation and related trouble shooting are analyzed in detail. Specific attention is given to the current studies on ADME/Tox of drugs using membrane-based in vitro models of cells including Caco-2, hepatocytes or renal cells, which can be used to evaluate the feasibility of polymer membrane in drug investigation. The progress toward solving present bottlenecks of the facilitated cell models are supposed to provide great benefits to drug discovery in pharmaceutical industry.     

An investigation of the energetics of peptide ion dissociation by laser desorption chemical ionization fourier transform mass spectrometry

The energy dependence of competing fragmentation pathways of protonated peptide molecules is studied via laser desorption—chemical ionization in a Fourier transform ion cyclotron resonance spectrometer. Neutral peptide molecules are desorbed by the technique of substrate-assisted laser desorption, followed by post-ionization with a proton transfer reagent ion species. The chemical ionization reaction activates the protonated peptide molecules, which then fragment in accordance with the amount of excess energy that is deposited. Chemical ionization forms a protonated molecule with a narrower distribution of activation energy than can be formed by activation methods such as collision activated dissociation. Furthermore, the upper limit of the activation energy is well defined and is approximately given by the enthalpy of the chemical ionization reaction. Control over the fragmentation of peptide ions is demonstrated through reactions between desorbed peptide molecules with different reagent ion species. The fragmentation behavior of peptide ions with different internal energies is established by generation of a breakdown curve for the peptide under investigation. Breakdown curves are reported for the peptides Val-Pro, Val-Pro-Leu, Phe-Phe-Gly-Leu-Met NH₂, and Arg-Lys-Asp-Val-Tyr. The derived breakdown curve of Val-Pro has been fitted by using quasi-equilibrium Rice-Ramsperger-Kassel-Marcus theory to model the unimolecular dissociation of the protonated peptide to provide a better understanding of the mechanisms for the formation of fragment ions that originate from protonated peptides.     

A novel type of matrix for surface-assisted laser desorption–ionization mass spectrometric detection of biomolecules using metal-organic frameworks

A 3D metal-organic framework (MOF) nanomaterial as matrix for surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) and tandem mass spectrometry (MS/MS) was developed for the analysis of complex biomolecules. Unlike other nanoparticle matrices, this MOF nanomaterial does not need chemical modification prior to use. An exceptional signal reproducibility as well as very low background interferences in analyzing mono-/di-saccharides, peptides and complex starch digests demonstrate its high potential for biomolecule assays, especially for small molecules.     

本征导电聚合物涂层及界面

本文结合我们实验研究结果及国外最近的研究进展，对在绝缘基质的表面本征导电聚合物涂层的形成、结构和性能作了扼要的分析，指出了化学反应法中通过单体向整体聚合物表层扩散聚合形成的导电膜、界面的偶联作用和电荷转移作用等几种新近证实的原理，在加速导电聚合物涂层的应用中，具有重要意义。     

Review of molecular modification techniques for improved detection of biomolecules by mass spectrometry

After a soft ionizing method was established, MS (mass spectrometry) has become a more common tool in biochemistry because soft ionization made it possible to detect large molecules such as proteins. Many kinds of applications were established to further utilize MS for the identification or quantitation of biomolecules. In this review, we introduce recent applications with special focus on chemical modification techniques and chemical probes developed for the MS determination of biomolecules.     

Review: derivatization in mass spectrometry-6. Formation of mixed derivatives of polyfunctional compounds

The review describes chemical transformations of multifunctional compounds (amino acids and peptides, amino alcohols, amino thiols, hydroxy acids, oxo acids, oxo alcohols, compounds containing simultaneously three or more different groups etc.) by using step-wise or one-step modification or protection of functional groups. Some chemical aspects of mixed derivatization performed for improving the physical-chemical properties and mass spectral characteristics are discussed. Application of mixed derivatization to qualitative and quantitative analysis of various multifunctional compounds mainly in biological fluids and other matrices by gas chromatography/mass spectrometry in electron ionization, chemical ionization, negative-ion chemical ionization and selected ion monitoring modes is considered.     

Polymer characterization by combining liquid chromatography with MALDI and ESI mass spectrometry

High-performance polymers are complex mixtures of materials of different size and chemical composition and with different end groups and architecture. To determine the molecular heterogeneity of such systems, hyphenation of several techniques is required. The value of coupling mass spectrometry (MS) with separation techniques has already been recognized - such methods have proved to be among the most powerful for molecular characterization of complex polymer systems.The review focuses on matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) MS coupled with liquid chromatography (LC). Such hyphenation has been used for most polymer analysis by mass spectrometry coupled with separation techniques. The advantages and/or limitations of these techniques for polymer characterization are discussed. Future prospects are briefly outlined.     

Characterization of plasma polymerized C, H, and O containing compounds by MALDI mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is used for the first time to characterize radio frequency plasma-deposited polymers and for investigation of the plasma polymerization process. The MALDI mass spectra of the plasma polymers of allyl alcohol, di(ethylene glycol) vinyl ether and ethylene glycol butyl vinyl ether are all reported using solvent-based MALDI sample preparation approaches. The MALDI mass spectra of each of the three plasma polymers contain distinctive polymer series ion signals having molecular weight distributions below 2000 Da. Unexpectedly, however, the ion signals from each of the three plasma polymers show a common polymer repeat unit of 44 Da, for which the chemical formula is most likely -(C(2)H(4)O)-, and no evidence of the expected radical chain polymerization polymer is detected. These results are discussed in terms of the likely involvement of gas-phase radical species having different stabilities in the radio frequency plasma environment.     

Modification of Polymer Membranes for Use in Organic Solvents

The chemical stability of polymer membranes, i.e., their ability to preserve the size, shape, and pore structure in contact with aggressive organic solvents, largely determines their separation characteristics in filtration of organic media. Methods for enhancing the stability of porous membranes based on commercial polymers (polysulfone, polyphenylsulfone, polyacrylonitrile) by chemical and/or physical modification are considered. Chemical modification consists in covalent cross-linking of matrix polymer chains; in some cases, cross-linking of macromolecules requires their preliminary functionalization. Physical modification involves blending of a matrix polymer with another polymer. A promising way to stabilize various membranes is combining a matrix polymer with a chemically cross-linked additional polymer, i.e., forming a semi-interpenetrating network.

     

De novo sequencing of novel neuropeptides directly from Ascaris suum tissue using matrix-assisted laser desorption/ionization time-of-flight/time-of-flight

Direct analysis of tissue by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) allows for the rapid profiling of biological molecules with minimal loss of sample or degradation and reduced likelihood of chemical modification. However, there are still considerable challenges to overcome due to the complexity of tissue and the low quantity of endogenous peptide in a single cell. These problems are exacerbated in the nematode Ascaris suum because of the small size of individual neurons and the paucity of peptide per cell. In an effort to address these difficulties, the recently developed matrix-assisted laser desorption/ionization time-of-flight/time-of-flight (MALDI-TOF/TOF) technology was used in combination with an on-target derivatization in order to sequence novel neuropeptides directly from Ascaris nervous tissue. Direct MALDI-TOF/TOF analysis of Ascaris tissue provided the complete amino acid sequences for a previously characterized neuropeptide as well as for three novel peptides with homologues found in other nematodes. These results demonstrate a method for the rapid characterization of sub-femtomolar amounts of peptide directly from tissue using MALDI-TOF/TOF.     

The detection of nitrated tyrosine in neuropeptides: a MALDI matrix-dependent response

Neuropeptides are a diverse class of signaling molecules that typically have one or more posttranslational modifications. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is an effective tool for identification and characterization of neuropeptides from samples as small as individual neurons. However, the detection of one particular posttranslational modification—nitrotyrosine—has been problematic because of the lability of the nitro group of nitrotyrosine under MALDI-MS conditions. The detection of nitrated tyrosine in peptide standards was dependent on the MALDI matrix used for the analysis. Specifically, sinapinic acid was the optimum matrix tested to observe this modification while it was not consistently detected with matrices such as 2,5-dihydroxybenzoic acid. Using the optimized procedures, several identified nitric-oxide-synthase positive neurons from Lymnaea stagnalis were tested to determine if the neuropeptides present were nitrated. In all cases, the nitrated form of the neuropeptide was not observed. The dependence on the sample-preparation procedures of observing this particular chemical modification demonstrates the need for careful selection of sample-preparation methods with MALDI or the use of other ionization methods.     

Synthèse de polyalcadiènes à extrémités fonctionnelles chlorure d'acide—étude de la réactivité de ces fonctions terminales

Two types of chemical modification of polymers are considered: attachment of functional groups as end-groups for diene polymers and also reaction of these end-groups with diamines. The deactivation, by means of the di-acid chloride of ortho-phthalic acid, of living polybutadiene or living polyisoprene leads to polydienes with molecules having one or two acid chloride end-groups. Chemical modification of these end-groups by an aliphatic diamine leads either to a new polymer having amine end-groups or to a polycondensation causing a substantial increase in molecular weight, depending upon the conditions.     

Characterization of low and intermediate molecular weight hydrogen silsesquioxanes by mass spectrometry

Hydrogen silsesquioxanes (HSQ or H-resin), represented by (HSiO3/2)2n or TH(2n), are an important class of polymers that have gained popularity as spin-on dielectrics by the electronic industry. Previously in the literature, small oligomeric species such as (HSiO3/2)2n, where n = 4-16, have been identified by GC-MS. However, nondestructive mass spectral results for larger H-resin molecules have not been reported, likely due to the nonpolar nature of these molecules. We have utilized a number of "soft" ionization techniques such as field desorption (FD), desorption chemical ionization (DCI), and matrix-assisted laser desorption/ionization (MALDI), and demonstrated that they are amenable to hydrogen silsesquioxanes. The [TH(2n) - H]+* ions were observed by FD-MS while [TH(2n) + NH4]+ and [TH(2n) + Na]+ ions were found utilizing DCI and MALDI, respectively. Based upon the MS results, the polymer compositions as well as molecular weight information can be easily obtained. The detailed structures of H-resin components, however, remain a difficult issue, which cannot be answered by MS data alone. With these preliminary MS results, we have clearly demonstrated that mass spectrometry with the above-mentioned ionization techniques is an invaluable tool that can be utilized when attempting to solve the challenge set forth by the complexity of hydrogen silsesquioxane materials.     

Molecular properties of conjugates formed by synthetic hydrophilic polymers and sterically hindered phenols

Water-soluble conjugates are prepared via the chemical modification of poly(vinyl alcohol) and poly(ethylene glycol) by antioxidants taken from the family of sterically hindered phenols. The effects of the degree of substitution of conjugates on the dimensions of molecules and their aggregates are studied by viscometry and light scattering in dilute solutions. It is shown that an increase in the amount of antioxidant groups incorporated into the poly(vinyl alcohol) chain leads to a decrease in the dimensions of single conjugate molecules owing to attraction of hydrophobic groups. Poly(ethylene glycol) molecules carrying end groups of sterically hindered phenols form micellar aggregates that are absent in the solution of the initial polymer. The mean number of molecules involved in such an aggregate is 83. It is found that the presence of hydrophobic end groups in poly(ethylene glycol) molecules causes a sharp reduction in the lower critical solution temperature of a solution relative to that of the initial polymer.     

Characterization of the chemical components on the surface of different solids with electrospray-assisted laser desorption ionization mass spectrometry

In this study we demonstrate that electrospray-assisted laser desorption ionization (ELDI) mass spectrometry (MS) can be used to rapidly characterize major chemical components on the surfaces of different solids under ambient conditions. The major chemical components in (a) dried milks with different fat contents, (b) different color-regions of a painting, (c) the thin coating on a compact disc, (d) drug tablets, and (e) porcine brain tissue were rapidly characterized as protonated molecules [M+H](+) or sodiated molecules [M+Na](+) by ELDI-MS with minimum sample pretreatment. The ionized ions of synthetic polymer and dye standards were detected directly from dried sample solutions using either positive or negative ion mode. Further structural information for the FD&C Red dye was obtained through tandem mass spectrometric (MS/MS) analysis using an ion trap mass analyzer attached to the ELDI source.     

Effect of the Maillard reaction on properties of casein and casein films

The use of biodegradable natural polymers has increased due to the over-solid packaging waste. In this study, a chemical modification of the casein molecule was performed by Maillard reaction, and the modified polymer was evaluated by polyacrylamide gel electrophoresis (PAGE), thermogravimetry/derivative thermogravimetry (TG/DTG), FT-IR, and ¹H-NMR spectroscopy. Subsequently, films based on the modified casein were obtained and characterized by mechanical analysis, water vapor transmission, and erosion behavior. The PAGE results suggested an increase of molecular mass of the modified polymer, and FT-IR spectroscopy data indicated inclusion of C–OH groups into this molecule. The TG/DTG curves of modified casein presented a different thermal decomposition profile compared to the individual compounds. Mechanical tests showed that the chemical modification of the casein molecules provided higher elongation rates (45.5%) to the films, suggesting higher plasticity, than the original molecules (13.4%). The modified casein films presented higher permeability (0.505 ± 0.006 μg/h mm³) than the original polymer (0.387 ± 0.006 μg/h mm³) films at 90% relative humidity (RH). In pH 1.2, modified casein films presented higher erosion rates (32.690 ± 0.692%) than casein films (19.910 ± 2.083%) after 8 h, suggesting an increased sensibility for erosion of the modified casein films in acid environment. In water (pH 7.0), the films erosion profiles were similar. Those findings indicate that the modification of molecule by Maillard reaction provided films more plastic, hydrophilic, and sensitive to erosion in acid environment, suggesting that a new polymer with changed properties was founded.     

Derivatization in mass spectrometry--8. Soft ionization mass spectrometry of small molecules

This is the first of two reviews devoted to derivatization approaches for "soft" ionization mass spectrometry (FAB, MALDI, ESI, APCI) and deals, in particular, with small molecules. The principles of the main "soft" ionization mass spectrometric methods as well as the reasons for derivatizing small molecules are briefly described. Derivatization methods for modification of amines, carboxylic acids, amino acids, alcohols, carbonyl compounds, monosaccharides, thiols, unsaturated and aromatic compounds etc. to improve their ionizability and to enhance structure information content are discussed. The use of "fixed"-charge bearing derivatization reagents is especially emphasized. Chemical aspects of derivatization and "soft" ionization mass spectrometric properties of derivatives are considered.     

Review: derivatization in mass spectrometry--5. Specific derivatization of monofunctional compounds

The present paper is complementary to the foregoing reviews and describes some additional methods of the derivatization of particular functional groups mainly to enhance the structural information content of electron ionization and chemical ionization mass spectra. Derivatization approaches for the modification of unsaturated compounds, alcoholic, carboxylic, carbonyl, amine and other functional groups, are discussed. Derivatization for separation and quantitative determination of chiral enantiomeric compounds is also considered. Preliminary chemical and physicalchemical degradation for structure elucidation of high molecular weight compounds (biopolymers, synthetic polymers) is mentioned. Chemical aspects of derivatizations and characteristic mass spectral features of derivatives are described briefly. Some particular applications of chemical modification, in conjunction with mass spectral measurements for the analysis of various important bioorganic compounds and compounds in biological fluids, air, environmental etc., are considered.