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Methanolic Solution (methanolic + solution)
Selected AbstractsChemInform Abstract: Molecular Dynamics Study of the Stabilization of the Silica Hexamer Si6O156- in Aqueous and Methanolic Solutions.CHEMINFORM, Issue 17 2008S. Caratzoulas Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Capillary electrophoretic and computational study of the complexation of valinomycin with rubidium cationELECTROPHORESIS, Issue 5 2009Sille Ehala Abstract This study is focused on the characterization of interactions of valinomycin (Val), a macrocyclic dodecadepsipeptide antibiotic ionophore, with rubidium cation, Rb+. Capillary affinity electrophoresis was employed for the experimental evaluation of the strength of the Val,Rb+ complex. The study involved the measurement of the change of effective electrophoretic mobility of Val at increasing concentration of Rb+ cation in the BGE. From the dependence of Val effective electrophoretic mobility on the Rb+ cation concentration in the BGE (methanolic solution of 100,mM Tris, 50,mM acetic acid, 0,1,mM RbCl), the apparent binding (stability) constant (Kb) of the Val,Rb+ complex in methanol was evaluated as log,Kb=4.63±0.27. According to the quantum mechanical density functional theory calculations employed to predict the most probable structure of Val,Rb+ complex, Val is stabilized by strong non-covalent bond interactions of Rb+ with six ester carbonyl oxygen atoms so that the position of the "central" Rb+ cation in the Val cage is symmetric. [source] Systematic investigation of ion suppression and enhancement effects of fourteen stable-isotope-labeled internal standards by their native analogues using atmospheric-pressure chemical ionization and electrospray ionization and the relevance for multi-analyte liquid chromatographic/mass spectrometric proceduresRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2010Daniela Remane In clinical and forensic toxicology, multi-analyte procedures are very useful to quantify drugs and poisons of different classes in one run. For liquid chromatographic/tandem mass spectrometric (LC/MS/MS) multi-analyte procedures, often only a limited number of stable-isotope-labeled internal standards (SIL-ISs) are available. If an SIL-IS is used for quantification of other analytes, it must be excluded that the co-eluting native analyte influences its ionization. Therefore, the effect of ion suppression and enhancement of fourteen SIL-ISs caused by their native analogues has been studied. It could be shown that the native analyte concentration influenced the extent of ion suppression and enhancement effects leading to more suppression with increasing analyte concentration especially when electrospray ionization (ESI) was used. Using atmospheric-pressure chemical ionization (APCI), methanolic solution showed mainly enhancement effects, whereas no ion suppression and enhancement effect, with one exception, occurred when plasma extracts were used under these conditions. Such differences were not observed using ESI. With ESI, eleven SIL-ISs showed relevant suppression effects, but only one analyte showed suppression effects when APCI was used. The presented study showed that ion suppression and enhancement tests using matrix-based samples of different sources are essential for the selection of ISs, particularly if used for several analytes to avoid incorrect quantification. In conclusion, only SIL-ISs should be selected for which no suppression and enhancement effects can be observed. If not enough ISs are free of ionization interferences, a different ionization technique should be considered. Copyright © 2010 John Wiley & Sons, Ltd. [source] Enantiomer discrimination of peptides by tandem mass spectrometry: influence of the peptide sequence on chiral recognitionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2004Christoph Czerwenka The enantiomer discrimination of peptides by electrospray ionization tandem mass spectrometry is described. A cinchona alkaloid derivative, tert -butylcarbamoylquinine, is used as chiral selector. The chiral selector forms diastereomeric complexes with the peptide enantiomers in the liquid phase (methanolic solution), which are then transferred to the gas phase, where their dissociation behaviour is studied in an ion-trap mass spectrometer. Different degrees of dissociation of the diastereomeric complexes allow for the discrimination of the peptide enantiomers. The influence of the peptide sequence on enantiomer discrimination is discussed and molecular recognition information is derived by comparing the results obtained for related peptides. For dipeptides, small amino acid residues at the N-terminus and bulky side chains at the C-terminus were found to enhance chiral recognition, while for tripeptides the effects were rather irregular. Copyright © 2004 John Wiley & Sons, Ltd. [source] Determination of total retronecine esters-type hepatotoxic pyrrolizidine alkaloids in plant materials by pre-column derivatization high-performance liquid chromatographyBIOMEDICAL CHROMATOGRAPHY, Issue 6 2009Ai-zhen Xiong Abstract A pre-column derivatization high-performance liquid chromatography method with diode array detection was developed and validated to determine the total retronecine esters-type hepatotoxic pyrrolizidine alkaloids (RET-HPAs) in herbs. The RET-HPAs reacted with o -chloranil in methanolic solution heated for 3 h, and an oxidative derivative was produced that could be detected at a maximal absorption of 223 nm. The analysis was performed using a C18 column with an isocratic elution of methanol and aqueous 0.01% triethylamine (adjusted to pH 4 with formic acid), and the detection was carried out with DAD at 223 nm. The validation of the method included linearity, sensitivity, recovery and stability. It showed a good linear regression (r2 > 0.9900) in the range of 2.5,250 µm with a limit of detection (S/N = 3) of 0.5 µm. The method provided desirable repeatability with overall intra- and inter-day variations of less than 4.6%. The obtained recoveries for both of the extraction and derivatization process were between 94.6 and 100.7% (n = 3). Copyright © 2009 John Wiley & Sons, Ltd. [source] Study of Intramolecular Competition between Carboxylate and Phosphonate for PtII with the Aid of a Novel Tridentate Carboxylato-Thioether-Phosphonato LigandCHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2007Matthieu Hamel Dr. Abstract The tridentate dianionic ligand 2-[2,-(hydroxyisopropoxyphosphoryl)phenylsulfanyl]benzoate (L2,) reacts with cis -[Pt(NH3)2(H2O)2]2+ to form an S,O-chelate in which the O-coordinated group is either carboxylate or phosphonate, depending on the degree of protonation of the complex. Carboxylate appears to be the stronger ligand, and the stoichiometric reaction between cis -[Pt(NH3)2(H2O)2]2+ and L2, yields the neutral species [Pt(L)(NH3)2], with L bound by sulfanyl and carboxylate groups, both in solution and in the solid state. Upon protonation of [Pt(L)(NH3)2], the stronger basicity of the carboxylate causes the Pt coordination to switch from carboxylate to phosphonate, and the uncoordinated carboxylate group becomes protonated. In methanolic solution, the first-order kinetics of this rearrangement could be observed by 31P,NMR spectroscopy. Both complexes,the carboxylate-bound neutral complex [Pt(L)(NH3)2],H2O (triclinic, P (no.,2), a=9.529(6), b=9.766(6), c=12.299(7),Å, ,=106.91(2), ,=101.71(2), ,=102.05(2)°, Z=2) and the perchlorate salt of the phosphonate-bound complex [Pt(LH)(NH3)2]ClO4,H2O (monoclinic, P21/c (no.,14), a=12.095(2), b=14.046(2), c=14.448(2),Å, ,=95.55(2)°, Z=4),were characterized by X-ray crystallography. [source] The World of , - and , -Peptides Comprised of Homologated Proteinogenic Amino Acids and Other ComponentsCHEMISTRY & BIODIVERSITY, Issue 8 2004Dieter Seebach The origins of our nearly ten-year research program of chemical and biological investigations into peptides based on homologated proteinogenic amino acids are described. The road from the biopolymer poly[ethyl (R)-3-hydroxybutanoate] to the , -peptides was primarily a step from organic synthesis methodology (the preparation of enantiomerically pure compounds (EPCs)) to supramolecular chemistry (higher-order structures maintained through non-covalent interactions). The performing of biochemical and biological tests on the , - and , -peptides, which differ from natural peptides/proteins by a single or two additional CH2 groups per amino acid, then led into bioorganic chemistry and medicinal chemistry. The individual chapters of this review article begin with descriptions of work on , -amino acids, , -peptides, and polymers (Nylon-3) that dates back to the 1960s, even to the times of Emil Fischer, but did not yield insights into structures or biological properties. The numerous, often highly physiologically active, or even toxic, natural products containing ,- and ,-amino acid moieties are then presented. Chapters on the preparation of homologated amino acids with proteinogenic side chains, their coupling to provide the corresponding peptides, both in solution (including thioligation) and on the solid phase, their isolation by preparative HPLC, and their characterization by mass spectrometry (HR-MS and MS sequencing) follow. After that, their structures, predominantly determined by NMR spectroscopy in methanolic solution, are described: helices, pleated sheets, and turns, together with stack-, crankshaft-, paddlewheel-, and staircase-like patterns. The presence of the additional CC bonds in the backbones of the new peptides did not give rise to a chaotic increase in their secondary structures as many protein specialists might have expected: while there are indeed more structure types than are observed in the , -peptide realm , three different helices (10/12 -, 12 -, and 14 -helix) if we include oligomers of trans -2-aminocyclopentanecarboxylic acid, for example , the structures are already observable with chains made up of only four components, and, having now undergone a learning process, we are able to construct them by design. The structures of the shorter , -peptides can also be reliably determined by molecular-dynamics calculations (in solution; GROMOS program package). Unlike in the case of the natural helices, these compounds' folding into secondary structures is not cooperative. In , - and , -peptides, it is possible to introduce heteroatom substituents (such as halogen or OH) onto the backbones or to incorporate heteroatoms (NH, O) directly into the chain, and, thanks to this, it has been possible to study effects unobservable in the world of the , -peptides. Tests with proteolytic enzymes of all types (from mammals, microorganisms, yeasts) and in vivo examination (mice, rats, insects, plants) showed , - and , -peptides to be completely stable towards proteolysis and, as demonstrated for two , -peptides, extraordinarily stable towards metabolism, even when bearing functionalized side chains (such as those of Thr, Tyr, Trp, Lys, or Arg). The , -peptides so far examined also normally display no or only very weak cytotoxic, antiproliferative, antimicrobial, hemolytic, immunogenic, or inflammatory properties either in cell cultures or in vivo. Even biological degradation by microbial colonies of the types found in sewage-treatment plants or in soil is very slow. That there are indeed interactions of ,- and ,-peptides with biological systems, however, can be seen in the following findings: i) organ-specific distribution takes place after intravenous (i.v.) administration in rats, ii) transport through the intestines of rodents has been observed, iii) , -peptides with positively charged side chains (Arg and Lys) settle on cell surfaces, are able to enter into mammalian cells (fibroplasts, keratinocytes, HeLa cells), and migrate into their cell nuclei (and nucleoli), and iv) in one case, it has already been established that a , -peptide derivative can up- and down-regulate gene expression rates. Besides these less sharply definable interactions, it has also been possible to construct , - and , -peptide agonists of naturally occurring peptide hormones, MHC-binding , -peptides, or amphipathic , -peptide inhibitors of membrane-bound proteins in a controlled fashion. Examples include somatostatin mimics and the suppression of cholesterol transport through the intestinal brush-border membrane (by the SR-BI-protein). The results so far obtained from investigations into peptides made up of homologues of the proteinogenic amino acids also represent a contribution to deepening of our knowledge of the natural peptides/proteins, while potential for biomedicinal application of this new class of substances has also been suggested. [source] Decomposition of monochlorobiphenyl isomers in supercritical water in the presence of methanolAICHE JOURNAL, Issue 7 2004Gheorghe Anitescu Abstract Comprehensive studies of monochlorobiphenyl (MCB) decomposition in supercritical water in the presence of methanol and other cosolvents, both with and without oxygen, are being conducted to understand the reaction kinetics and pathways of individual PCB isomers and to determine the structure,reactivity relationships. In the present study the disappearance rate of MCBs, delivered in an isothermal plug-flow tubular reactor as methanolic solutions, is investigated at 25 MPa and temperatures of 673, 723, and 773 K. Experiments are conducted at nominal MCB feed concentrations of 1,100 ,mol/L (reaction conditions) using MCB/MeOH and H2O2/H2O solutions (1,3 g/L and 0,10 wt. %, respectively). Molar conversions of these isomers vary from 3% (2-CB, 773 K, 2 s) to 30% (4-CB, 773 K, 46 s) without oxygen (SCWT) and from 1% (2-CB, 673 K, 3.8 s) to 97% (4-CB, 773 K, 24.5 s) with oxygen (SCWO). For SCWT the overall conversion follows apparent first order, whereas for SCWO the conversion is second order. The regressed data lead to Arrhenius parameters of frequency factor and activation energy with values of 1020.5,1021.3 s,1 and 320,331 kJ/mol for SCWT and 1024.1,1024.8 s,1 (mol/L),1 and 281,292 kJ/mol for SCWO, respectively. The reactivity of the MCB isomers increases in the order 2-MCB < 3-MCB < 4-MCB. The positively identified reaction products by GC-MSD and GC-FID/ECD/TCD analyses are mainly biphenyl, open-ring biphenyl compounds such as acetophenone and benzaldehydes, and mineral products (CO, CO2, and HCl). More studies are in progress regarding the role of the second solvent on reaction rates and reaction mechanisms and pathways. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1536,1544, 2004 [source] Redox reactions of copper(II) upon electrospray ionization in the presence of acridine ligands with an amide side chainJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2009Aura Tintaru Abstract The complexation of copper(II) to acridine derivatives has been studied by means of electrospray ionization (ESI) mass spectrometry. Under soft conditions of ionization, the ESI mass spectra of methanolic solutions of copper(II) chloride and the acridine ligands show abundant signals of the mononuclear complexes formed from the metal and ligand. Depending on the position of the N -benzoylamino substituent in the acridinic heterocycle, however, the copper atom involved in the complexation process adopts different oxidation states in the resulting cations. Hence, the metal is reduced to copper(I) in the monocationic complex with the compound substituted in position 2, whereas it keeps its divalent state in the monocation formed with the compound substituted in position 4. As a consequence, the regioisomers lead to monocations with different masses in the ESI spectra. In order to understand this unusual behavior of two isomeric compounds, additional experiments have been performed with quinoline as a model. Copyright © 2008 John Wiley & Sons, Ltd. [source] Controlled polymerizations of 2-(dialkylamino)ethyl methacrylates and their block copolymers in protic solvents at ambient temperature via ATRPJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2004Baowei Mao Abstract Very well-controlled polymerizations of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 2-(diethylamino)ethyl methacrylate (DEAEMA) in aqueous and methanolic solutions via atom transfer radical polymerization (ATRP) at ambient temperature were demonstrated. Poly(DMAEMA) and poly(DEAEMA) of low polydispersity index (PDI) of ,1.07 were obtained using the p -toluenesulfonyl chloride/CuCl/1,1,4,7,10,10-hexamethyl-triethylenetetramine (p -TsCl/CuCl/HMTETA) system. Excellent control of polymerization was achieved even in pure methanol. This is in contrast with the very poor control of DMAEMA ATRP in methanol reported previously using a different intiator/catalyst/ligand system. The initiator p -TsCl underwent hydrolysis reaction in aqueous methanolic solutions with a second-order rate constant of 6.1 × 10,4 dm3 mol,1 s,1 at 25 °C. Both poly(DMAEMA) and poly(DEAEMA) retained almost full chlorine-functionization at the chain ends. Well-defined block copolymers of DEAEMA and DMAEMA were successfully obtained by starting with either macroinitiators of DEAEMA or DMAEMA. Other well-defined diblock copolymers could be prepared using these macroinitiators. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5161,5169, 2004 [source] Can radical cations of the constituents of nucleic acids be formed in the gas phase using ternary transition metal complexes?,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2005Sheena Wee Electrospray ionization (ESI) tandem mass spectrometry (MS/MS) of ternary transition metal complexes of [M(L3)(N)]2+ (where M,=,copper(II) or platinum(II); L3,=,diethylenetriamine (dien) or 2,2,:6,,2,-terpyridine (tpy); N,=,the nucleobases: adenine, guanine, thymine and cytosine; the nucleosides: 2,deoxyadenosine, 2,deoxyguanosine, 2,deoxythymine, 2,deoxycytidine; the nucleotides: 2,deoxyadenosine 5,-monophosphate, 2,deoxyguanosine 5,-monophosphate, 2,deoxythymine 5,-monophosphate, 2,deoxycytidine 5,-monophosphate) was examined as a means of forming radical cations of the constituents of nucleic acids in the gas phase. In general, sufficient quantities of the ternary complexes [M(L3)(N)]2+ could be formed for MS/MS studies by subjecting methanolic solutions of mixtures of a metal salt [M(L3)X2] (where M,=,Cu(II) or Pt(II); L3,=,dien or tpy; X,=,Cl or NO3) and N to ESI. The only exceptions were thymine and its derivatives, which failed to form sufficient abundances of [M(L3)(N)]2+ ions when: (a) M,=,Pt(II) and L3,=,dien or tpy; (b) M,=,Cu(II) and L3,=,dien. In some instances higher oligomeric complexes were formed; e.g., [Pt(tpy)(dG)n]2+ (n,=,1,13). Each of the ternary complexes [M(L3)(N)]2+ was mass-selected and then subjected to collision-induced dissociation (CID) in a quadrupole ion trap. The types of fragmentation reactions observed for these complexes depend on the nature of all three components (metal, auxiliary ligand and nucleic acid constituent) and can be classified into: (i) a redox reaction which results in the formation of the radical cation of the nucleic acid constituent, N+.; (ii) loss of the nucleic acid constituent in its protonated form; and (iii) fragmentation of the nucleic acid constituent. Only the copper complexes yielded radical cations of the nucleic acid constituent, with [Cu(tpy)(N)]2+ being the preferred complex due to suppression, in this case, of the loss of the nucleobase in its protonated form. The yields of the radical cations of the nucleobases from the copper complexes follow the order of their ionization potentials (IPs): G (lowest IP),>,A,>,C,>,T (highest IP). Sufficient yields of the radical cations of each of the nucleobases allowed their CID reactions (in MS3 experiments) to be compared to their even-electron counterparts. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||