Phenomenological characterization and thermal analysis of flame spread over jet fuel: influence of radiant exposure time

Journal of Thermal Analysis and Calorimetry - The high-temperature objects widely exist in industrial and civil building such as the nearby burning pool fires, the heated walls and the hot smoke...     

Phase separation of polymer mixtures induced by polarization‐selective chemical reactions: spatial symmetry breaking and mode selection

Phase separation of polystyrene/poly (vinyl methyl ether) (PS/PVME) blends was induced and controlled by irradiation with linearly polarized light. The PS component was made photosensitive by chemically labeled with either anthracene or trans‐stilbene. The former was used to crosslink the PS component whereas the latter induces phase separation by changing polymer segmental volumes. The phase separation and reaction kinetics were observed and discussed in terms of mode‐selection process.     

Mapping protein interfaces by chemical cross-linking and Fourier transform ion cyclotron resonance mass spectrometry: application to a calmodulin / adenylyl cyclase 8 peptide complex

Chemical cross-linking--an established technique in protein chemistry--has re-emerged, in combination with mass spectrometric analysis of the reaction products, as a valuable tool to identify interacting amino acid sequences in protein complexes. In the present study, we are mapping the interface of the calcium-dependent complex between calmodulin (CaM) and a peptide derived from the C-terminal region of adenylyl cyclase 8 (AC 8). Cross-linking reactions are performed using the two amine-reactive, isotope-labeled (d0 and d4) cross-linkers BS(3) (bis[sulfosuccinimidyl]suberate) and BS(2)G (bi[sulfosuccinimidyl] glutarate) as well as the 'zero-length' cross-linker (EDC, ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride). After separation of the cross-linking reaction mixtures by one-dimensional gel electrophoresis (sodium dodecyl sulphate polyacrylamide gel) and in-gel digestion of the cross-linked complexes, the resulting peptide mixtures are analyzed by nano-high-performance liquid chromatography/ nano-electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The identified intermolecular cross-linking products will give further insight into calmodulin/adenylyl cyclase 8 interaction.     

Chemical alterations to murine brain tissue induced by formalin fixation: implications for biospectroscopic imaging and mapping studies of disease pathogenesis

Understanding biochemical mechanisms and changes associated with disease conditions and, therefore, development of improved clinical treatments, is relying increasingly on various biochemical mapping and imaging techniques on tissue sections. However, it is essential to be able to ascertain whether the sampling used provides the full biochemical information relevant to the disease and is free from artefacts. A multi-modal micro-spectroscopic approach, including FTIR imaging and PIXE elemental mapping, has been used to study the molecular and elemental profile within cryofixed and formalin-fixed murine brain tissue sections. The results provide strong evidence that amino acids, carbohydrates, lipids, phosphates, proteins and ions, such as Cl(-) and K(+), leach from tissue sections into the aqueous fixative medium during formalin fixation of the sections. Large changes in the concentrations and distributions of most of these components are also observed by washing in PBS even for short periods. The most likely source of the chemical species lost during fixation is the extra-cellular and intra-cellular fluid of tissues. The results highlight that, at best, analysis of formalin-fixed tissues gives only part of the complete biochemical "picture" of a tissue sample. Further, this investigation has highlighted that significant lipid peroxidation/oxidation may occur during formalin fixation and that the use of standard histological fixation reagents can result in significant and differential metal contamination of different regions of tissue sections. While a consistent and reproducible fixation method may be suitable for diagnostic purposes, the findings of this study strongly question the use of formalin fixation prior to spectroscopic studies of the molecular and elemental composition of biological samples, if the primary purpose is mechanistic studies of disease pathogenesis.     

Application of simplified complementary tristimulus colorimetry to chemical kinetics in solution-I: analysis of reaction mixtures and determination of first- or pseudo first-order rate constants

A graphical method is described which allows estimation of the number of reacting light-absorbing species from the plots of complementary colour points which are obtained with the use of simplified complementary tristimulus colorimetry (SCTS method) from absorption spectra of a series of kinetics solutions. It is shown that the mole function of the reactant or the product at any time can be calculated from the complementary colour points, so that the rate constant can also be determined. The present method has some advantages over the common approach to the determination or reaction rates in presence of a colour impurity.     

Modification of dipeptides by alkyl chloroformate—alkanol mixtures for analysis by gas chromatography/mass spectrometry with electron and chemical ionization and collisional activation: Differentiation of isomers

A possibility of dipeptide derivatization by alkyl chloroformate—alkanol (Alk = Me, Et, Pr, Bu) mixed reactants for their determination and differentiation of isomers in mixtures by gas chromatography/mass spectrometry with electron and chemical ionization and collisional activation was studied. Prospects for using derivatization by mixtures of methyl chloroformate with 2,2,2-trifluoroethanol, 2,2,3,3,3-pentafluoropropanol, and 2,2,3,3,4,4,4-heptafluorobutanol were shown. Diagnostic ions that make it possible to determine the amino acid sequence in dipeptides and distinguish residues of isomeric leucine and isoleucine were revealed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2200–2204, December, 2006.     

Quantitative analysis of biomarkers of liver and kidney injury in serum and urine using ultra‐fast liquid chromatography with tandem mass spectrometry coupled with a hydrophilic interaction chromatography column: Application to monitor injury induced by Euphorbiae pekinensis Radix

Fast and sensitive monitoring of drug‐induced liver and kidney injury in early stage is beneficial. An ultrafast liquid chromatography with tandem mass spectrometry assay was developed and validated to simultaneously determine ten endogenous biomarkers in serum and urine, including hippuric acid, phenylacetylglycine, 5‐oxoproline, cholic acid, taurine, indoleacetic acid, 3‐indoxyl sulfate, guanidinosuccinic acid, guanidinoacetic acid and uric acid. A CAPCELL CORE PC column (2.1 × 150 mm, 2.7 μm) was adopted for analytes separation. Gradient elution was performed with acetonitrile and water containing 5 mM ammonium acetate. Simple protein precipitation was applied in sample preparation. Good linearities were achieved with all the regression coefficients above 0.9911. Accuracy was 2.9–14.2% in serum and 4.1–14.6% in urine. The mean recovery was above 70% with acceptable matrix effects. The method was applied to monitor injury induced by Euphorbiae pekinensis Radix with a subacute rats model. All the biomarkers showed obvious concentration changes during the injury period. Furthermore, several biomarkers showed significant changes in earlier stage when compared with the current clinical serum bio‐parameters. The method might be helpful for early diagnosis of drug induced liver and kidney injury in clinical after tested on more drugs.     

Sequential analysis of polyesters by stepwise chemical degradation: Application to oligo and poly(alkylene terephthalate)s

A specifically tailored reagent was used to label the hydroxyl end groups of poly(ethylene/butylene terephthalate), which is synthesized by transesterification of the corresponding homopolymers. The terminal monomeric unit was then eliminated, together with the attached label, as a low molecular-weight cyclic compound. Specially synthesized reference compounds containing ethylene terephthalate and butylene terephthalate units enabled the terminal monomeric unit to be identified as butylene terephthalate, although the copolymer showed an otherwise random distribution. Despite the practical and theoretical reasons that restrict this sequential degradation to the last monomeric unit for polymers, the principle can be used in a wider range of applications if combined with selective degradation and separation by means of HPLC, which results in chemically uniform oligomers. The ultimate and penultimate monomeric units of ethylene/butylene terephthalate type oligomers can be identified using the cyclodegradation procedure described here. © 1993 John Wiley & Sons, Inc.     

Confirmatory analysis of sulfonamide antibacterials in bovine liver and kidney: extraction with hot water and liquid chromatography coupled to a single- or triple-quadrupole mass spectrometer

A simple, specific, and rapid confirmatory method for determining 12 sulfonamide (SAs) antibacterials in bovine liver and kidney is presented. This method is based on the matrix solid-phase dispersion technique with hot water as extractant followed by liquid chromatography/mass spectrometry (LC/MS) with an electrospray ion source. The method was tailored for use with both single-quadrupole MS (I) and triple-quadrupole MS (II) instruments. After acidification and filtration of the aqueous extract, a 250-microL aliquot was injected into instrument I while only 25 microL was analyzed by instrument II. With instrument I MS data acquisition was performed in the selected ion monitoring (SIM) mode, selecting at least three ions for each target compound. With instrument II the selected reaction monitoring (SRM) mode with three fragmentation reactions for each compound was chosen. With the exception of sulfaquinoxaline (SQX), recovery of the analytes at the 50 ppb level in both liver and kidney was 72-96% with relative standard deviations (RSDs) ranging between 3 and 11%. The very poor recovery of SQX was due to its rapid enzymatic oxidation when in contact with the two tissues. With instrument I, limits of quantification (LOQs, S/N = 10) were 5-14 ppb of SAs. Even lower LOQs (1-8 ppb) were estimated by using instrument II, even though the extract volume analyzed was ten times lower than that with instrument I. With both matrices and using instrument I, severe ion signal suppression was experienced for the early-eluted SAs when trying to fractionate analytes by using a short chromatographic run time. This effect was traced to polar endogenous co-extractives eluted in the first part of the chromatographic run that interfered with gas-phase ion formation for SAs. Adopting more selective chromatographic conditions minimized this effect.     

Rapid access to unexplored chemical space by ligand scanning around a ruthenium center: discovery of potent and selective protein kinase inhibitors

An important objective for the discovery of compounds with unique biological activities is the development of methods for the synthesis of molecular scaffolds with defined three-dimensional shapes. We are currently investigating the scope of using metal complexes to accomplish this goal. In these compounds, the metal center has the role of organizing the orientation of the organic ligands, thus defining the overall shape of the molecule. A strategy is presented that allows a rapid scanning of ligands around a ruthenium center in the search for ligand spheres that are complementary in shape and functional group presentation to ATP binding sites of protein kinases. Following this approach, we have identified octahedral ruthenium complexes as potent inhibitors for the protein kinases Pim1, MSK1, and GSK3alpha.     

Characterization of micros-ms dynamics of proteins using a combined analysis of 15N NMR relaxation and chemical shift: conformational exchange in plastocyanin induced by histidine protonations

An approach is presented that allows a detailed, quantitative characterization of conformational exchange processes in proteins on the micros-ms time scale. The approach relies on a combined analysis of NMR relaxation rates and chemical shift changes and requires that the chemical shift of the exchanging species can be determined independently of the relaxation rates. The applicability of the approach is demonstrated by a detailed analysis of the conformational exchange processes previously observed in the reduced form of the blue copper protein, plastocyanin from the cyanobacteria Anabaena variabilis (A.v. PCu) (Ma, L.; Hass, M. A. S.; Vierick, N.; Kristensen, S. M.; Ulstrup, J.; Led, J. J. Biochemistry 2003, 42, 320-330). The R1 and R2 relaxation rates of the backbone 15N nuclei were measured at a series of pH and temperatures on an 15N labeled sample of A.v. PCu, and the 15N chemical shifts were obtained from a series of HSQC spectra recorded in the pH range from 4 to 8. From the R1 and R2 relaxation rates, the contribution, Rex, to the transverse relaxation caused by the exchanges between the different allo-states of the protein were determined. Specifically, it is demonstrated that accurate Rex terms can be obtained from the R1 and R2 rates alone in the case of relatively rigid proteins with a small rotational anisotropy. The Rex terms belonging to the same exchange process were identified on the basis of their pH dependences. Subsequently the identifications were confirmed quantitatively by the correlation between the Rex terms and the corresponding chemical shift differences of the exchanging species. By this approach, the Rex terms of 15N nuclei belonging to contiguous regions in the protein could be assigned to the same exchange process. Furthermore, the analysis of the exchange terms shows that the observed micros-ms dynamics in A.v. PCu are caused primarily by the protonation/deprotonation of two histidine residues, His92 and His61, His92 being ligated to the Cu(I) ion. Also the exchange rate of the protonation/deprotonation process of His92 and its pH and temperature dependences were determined, revealing a reaction pathway that is more complex than a simple specific-acid/base catalysis. Finally, the approach allows a differentiation between two-site and multiple-site exchange processes, thus revealing that the protonation/deprotonation of His61 is at least a three-site exchange process. Overall, the approach makes it feasible to obtain exchange rates that are sufficiently accurate and versatile for studies of the kinetics and the mechanisms of local protein dynamics on the sub-millisecond time scale.     

Two-stage Off-Gel isoelectric focusing: protein followed by peptide fractionation and application to proteome analysis of human plasma

This paper presents the recently introduced Off-Gel electrophoresis (OGE) technology as a versatile tool to reproducibly fractionate intact proteins and peptides into discrete liquid fractions. The coupling of two stages of OGE, i.e., the separation of intact proteins in a first-stage followed by fractionation of peptides derived from each protein fraction after proteolysis in a second stage, results in an array of 15 x 15 fractions that are directly amenable to additional peptide fractionation like reverse-phase liquid chromatography (RPC). The analysis of all second-stage peptide fractions from only the first-stage protein fraction representing pH 5.0 -5.15 by on-line reverse-phase LC-tandem mass spectrometry resulted in the identification of 53 proteins (337 peptides), of which 10 were on different immunoglobulin (Ig) chains, with an input of only 1.5 mg human blood plasma proteins. Increasing the protein load to approximately 12 mg increased the number of identified proteins in the same protein fraction to 73 proteins (449 peptides), of which 15 were Ig-related. Immunodepletion of six of the most abundant proteins (albumin, transferrin, haptoglobin, IgG, IgA, and alpha-1-antitrypsin) prior to first-stage OGE with an input of 1.5 mg of protein (equivalent to approximately 10 mg nondepleted plasma) resulted in the identification of 81 proteins (660 peptides), of which three were still Ig fragments. The pI-based separation of peptides appears to be nonuniform based on the theoretically determined pI values of identified peptides. This observation specifically accounts for the neutral zone (pI 5-8) and can be accounted for by the physicochemical properties of the peptides given by their amino acid composition. The power of OGE separation of proteins and peptides is discussed with a focus on the use of the knowledge about the pI of proteins and peptides that assist the validation of correct identifications together with the retention time of peptides on RPC.     

Estimation of dermal and oral exposure of children to scented toys: analysis of the migration of fragrance allergens by dynamic headspace GC-MS

Fragrances capable of inducing contact allergy in skin potentially can migrate from the toy to the child via oral or dermal contacts. The goal of this work was the developing of an analytical method based on dynamic headspace GC-MS to determine the concentration of 24 fragrances in saliva or sweat simulant. Under optimized conditions, 5 mL of the migration simulant with 2 g sodium chloride were incubated for 10 min at 30°C. The headspace was purged at a flow rate of 50 mL/min. The compounds were quantified by internal calibration resulting in good linearity (>0.991). The recovery was greater than 66.3% for most of the compounds. The limits of detection ranged between 0.5 ng/mL for hydrophobic and 196.0 ng/mL for hydrophilic fragrances. The method was subsequently applied to seven real toys purchased from the market. The highest migration rate could be observed for benzyl benzoate with 268.0 ng/cm(2)/min. Based on the migration data measured, the ranges of dermal and oral exposure of children to fragrances in scented toys were calculated. The maximum oral and dermal exposure levels were estimated at 22.2 μg per kg body weight (BW) and day (d) for benzyl benzoate and 605.0 μg/kg BW/d for benzyl alcohol, respectively.     

Determination of the number and relative molecular mass of subunits in an oligomeric protein by two-dimensional electrophoresis Application to the subunit structure analysis of rat liver amidophosphoribosyltransferase

To determine simultaneously the relative molecular mass (M_r) of a native oligomeric protein, and the number and M_r of its subunits, a method using two-dimensional electrophoresis was developed. To determine the M_r of a native oligomeric protein, pore gradient gel electrophoresis was performed for the first dimension. Native proteins were dissociated into their subunits by sodium dodecyl sulphate (SDS) in a gel slice, then applied to SDS polyacrylamide gel electrophoresis for the second dimension to determine the M_r of subunits. The advantage, accuracy, limitations and application of the method are discussed.     

Matrix effects during analysis of plasma samples by electrospray and atmospheric pressure chemical ionization mass spectrometry: practical approaches to their elimination

Some cases of occurrence of matrix effects (mostly ion suppression) in protein-precipitated plasma samples, and their influence on the validity of plasma concentrations and pharmacokinetic parameters, are discussed. The comparison of matrix effects using either electrospray (TurboIonspray, TISP) or atmospheric pressure chemical ionization (APCI) indicated that APCI is less prone to matrix effects. Nevertheless, TISP is usually the first choice of ionization technique since unknown thermally labile metabolites might be present in the plasma samples causing erroneous results. A high impact of ion suppression on the plasma concentrations after intravenous (i.v.) administration was found, depending on the drug formulation (vehicle). Since ion suppression caused significantly lower plasma concentrations (by a factor of up to 5.5) after i.v. dosing, the area under the curve (AUC) was underestimated and the plasma clearance was consequently erroneously high, with an impact on drug candidate selection. By simple stepwise dilution (e.g. 10-fold and 50-fold) of the supernatant of protein-precipitated plasma samples, including all calibration and quality control samples, the matrix effects were recognized and eliminated.     

Toward direct determination of conformations of protein building units from multidimensional NMR experiments VI: chemical shift analysis of his to gain 3D structure and protonation state information

NMR--chemical shift structure correlations were investigated by using GIAO-RB3LYP/6-311++G(2d,2p) formalism. Geometries and chemical shifts (CSI values) of 103 different conformers of N'-formyl-L-histidinamide were determined including both neutral and charged protonation forms. Correlations between amino acid torsional angle values and chemical shifts were investigated for the first time for an aromatic and polar amino acid residue whose side chain may carry different charges. Linear correlation coefficients of a significant level were determined between chemical shifts and dihedral angles for CSI[(1)H(alpha)]/phi, CSI[(13)C(alpha)]/phi, and CSI[(13)C(alpha)]/psi. Protonation of the imidazole ring induces the upfield shift of CSI[(13)C(alpha)] for positively charged histidines and an opposite effect for the negative residue. We investigated the correspondence of theoretical and experimental (13)C(alpha), (13)C(beta), and (1)H(alpha) chemical shifts and the nine basic conformational building units characteristic for proteins. These three chemical shift values allow the identification of conformational building units at 80% accuracy. These results enable the prediction of additional regular secondary structural elements (e.g., polyProlineII, inverse gamma-turns) and loops beyond the assignment of chemical shifts to alpha-helices and beta-pleated sheets. Moreover, the location of the His residue can be further specified in a beta-sheet. It is possible to determine whether the appropriate residue is located at the middle or in a first/last beta-strand within a beta-sheet based on calculated CSI values. Thus, the attractive idea of establishing local residue specific backbone folding parameters in peptides and proteins by employing chemical shift information (e.g., (1)H(alpha) and (13)C(alpha)) obtained from selected heteronuclear correlation NMR experiments (e.g., 2D-HSQC) is reinforced.     

Synthesis and characterization of carbene derivatives of Th@C3v(8)-C82 and U@C2v(9)-C82: exceptional chemical properties induced by strong actinide–carbon cage interaction

Chemical functionalization of endohedral metallofullerenes (EMFs) is essential for the application of these novel carbon materials. Actinide EMFs, a new EMF family member, have presented unique molecular and electronic structures but their chemical properties remain unexplored. Here, for the first time, we report the chemical functionalization of actinide EMFs, in which the photochemical reaction of Th@C_3v(8)-C₈₂ and U@C_2v(9)-C₈₂ with 2-adamantane-2,3′-[3H]-diazirine (AdN₂, 1) was systematically investigated. The combined HPLC and MALDI-TOF analyses show that carbene addition by photochemical reaction afforded three isomers of Th@C_3v(8)-C₈₂Ad and four isomers of U@C_2v(9)-C₈₂Ad (Ad = adamantylidene), presenting notably higher reactivity than their lanthanide analogs. Among these novel EMF derivatives, Th@C_3v(8)-C₈₂Ad(I, II, III) and U@C_2v(9)-C₈₂Ad(I, II, III) were successfully isolated and were characterized by UV-vis-NIR spectroscopy. In particular, the molecular structures of first actinide fullerene derivatives, Th@C_3v(8)-C₈₂Ad(I) and U@C_2v(9)-C₈₂Ad(I), were unambiguously determined by single crystal X-ray crystallography, both of which show a [6,6]-open cage structure. In addition, isomerization of Th@C_3v(8)-C₈₂Ad(II), Th@C_3v(8)-C₈₂Ad(III), U@C_2v(9)-C₈₂Ad(II) and U@C_2v(9)-C₈₂Ad(III) was observed at room temperature. Computational studies suggest that the attached carbon atoms on the cages of both Th@C_3v(8)-C₈₂Ad(I) and U@C_2v(9)-C₈₂Ad(I) have the largest negative charges, thus facilitating the electrophilic attack. Furthermore, it reveals that, compared to their lanthanide analogs, Th@C_3v(8)-C₈₂ and U@C_2v(9)-C₈₂ have much closer metal–cage distance, increased metal-to-cage charge transfer, and strong metal–cage interactions stemming from the significant contribution of extended Th-5f and U-5f orbitals to the occupied molecular orbitals, all of which give rise to their unusual high reactivity. This study provides first insights into the exceptional chemical properties of actinide endohedral fullerenes, which pave ways for the future functionalization and application of these novel EMF compounds.

Photochemical reaction of Th@C_3v(8)-C₈₂ and U@C_2v(9)-C₈₂ with 2-adamantane-2,3′-[3H]-diazirine (AdN₂, 1) afforded three isomers of Th@C_3v(8)-C₈₂Ad and four isomers of U@C_2v(9)-C₈₂Ad (Ad = adamantylidene), respectively.     

Preparation of seven- and eight-membered rings by carbon-carbon bond formation induced by samarium diiodide: 7-endo- and 8-endo-trig type cyclization to bicyclo[5.3.0]decanolone, bicyclo[5.4.0]undecanolone, and bicyclo[6.4.0]dodecanolone

Compounds with an enone-aldehyde/ketone were treated with SmI₂ to form the bicyclic ketols, bicyclo[5.3.0]decanolones, and bicyclo[5.4.0]undecanolones, in different ratios depending on the reaction conditions (with or without different amounts of additives, low temperature or rt). The tendency to form seven-membered rings was different from that of six-membered rings and the mechanisms for these reactions are proposed. Cyclization to an eight-membered ring was attempted realizing in the yield of 26%.