Low-energy collision-induced fragmentation of negative ions derived from diesters of aliphatic dicarboxylic acids made with hydroxybenzoic acids

Diesters of ortho-hydroxybenzoic acid (salicylic acid) made with glutaric, adipic, and pimelic acids are the monomers of some potential drug candidates for aspirin patches. Collision-induced dissociation (CID) spectra of negative ion derived from these compounds show a 120-Da 'neutral loss' specific to the ortho isomers. In contrast, the anions derived from diesters of meta- and para-hydroxybenzoic acids show a 138-Da loss for an elimination of elements of hydroxybenzoic acid by a charge-remote mechanism. Deuterium labeling studies confirmed that the hydrogen atom transferred for hydroxybenzoic acid loss originates specifically from the alpha position of the dicarboxylic acid moiety. Although all spectra showed a peak at m/z 137, a charge-mediated process specific for the ortho compounds renders it the most prominent peak in the spectra of ortho compounds. Appropriate deuterium labeling experiments demonstrated that the hydrogen atom transferred for the formation of the m/z 137 ion in ortho compounds is specifically derived from the alpha position of the dicarboxylic acid moiety.     

Low-energy collision-induced fragmentation of negative ions derived from ortho-, meta-, and para-hydroxyphenyl carbaldehydes, ketones, and related compounds

Collision-induced dissociation (CID) mass spectra of anions derived from several hydroxyphenyl carbaldehydes and ketones were recorded and mechanistically rationalized. For example, the spectrum of m/z 121 ion of deprotonated ortho-hydroxybenzaldehyde shows an intense peak at m/z 93 for a loss of carbon monoxide attributable to an ortho-effect mediated by a charge-directed heterolytic fragmentation mechanism. In contrast, the m/z 121 ion derived from meta and para isomers undergoes a charge-remote homolytic cleavage to eliminate an *H and form a distonic anion radical, which eventually loses CO to produce a peak at m/z 92. In fact, for the para isomer, this two-step homolytic mechanism is the most dominant fragmentation pathway. The spectrum of the meta isomer on the other hand, shows two predominant peaks at m/z 92 and 93 representing both homolytic and heterolytic fragmentations, respectively. (18)O-isotope-labeling studies confirmed that the oxygen in the CO molecule that is eliminated from the anion of meta-hydroxybenzaldehyde originates from either the aldehydic or the phenolic group. In contrast, anions of ortho-hydroxybenzaldehyde and 2-hydroxy-1-naphthaldehyde, both of which show two consecutive CO eliminations, specifically lose the carbonyl oxygen first, followed by that of the phenolic group. Anions from 2-hydroxyphenyl alkyl ketones lose a ketene by a hydrogen transfer predominantly from the alpha position. Interestingly, a very significant charge-remote 1,4-elimination of a H(2) molecule was observed from the anion derived from 2,4-dihydroxybenzaldehyde. For this mechanism to operate, a labile hydrogen atom should be available on the hydroxyl group adjacent to the carbaldehyde functionality.     

Investigations of the fragmentation pathways of benzylpyridinium ions under ESI/MS conditions

Benzylpyridinium ions are often used as ‘thermometer ions’ in order to evaluate the internal energy distribution of the ions formed in sources of mass spectrometers. However, the detailed fragmentation pathways of these parent ions were not well established. In particular, fragmentation involving a rearrangement (RR) process may be influencing the simulated distribution curves. In a previous study, we suggested that such RR actually occurred under electrospray ionization/mass spectrometry (ESI/MS) and fast atom bombardment/mass spectrometry (FAB/MS) experiments. Here, we present a systematic study of different substituted benzylpyridinium ions. Theoretical calculations showed that RR fragmentation leading to substituted tropylium ions could occur under ‘soft ionization’ conditions, such as ESI or FAB. Experimental results obtained under gas‐phase reactivity conditions showed that some substituted benzylpiridinium compounds actually undergo RR fragmentations under ESI/MS conditions. Mass‐analyzed kinetic experiments were also carried out to gain information on the reaction pathways that actually occur, and these experimental results are in agreement with the reaction pathways theoretically proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

Collision-induced fragmentation of negative ions from N-linked glycans derivatized with 2-aminobenzoic acid

N-Linked glycans from bovine ribonuclease B, chicken ovalbumin, bovine fetuin, porcine thyroglobulin and human alpha(1)-acid glycoprotein were derivatized with 2-aminobenzoic acid by reductive amination and their tandem mass spectra were recorded by negative ion electrospray ionization with a quadrupole time-of-flight mass spectrometer. Derivatives were also prepared from 2-amino-5-methyl- and 2-amino-4,5-dimethoxybenzoic acid in order to confirm the identity of fragment ions containing the reducing terminus. Major fragments from the [M - H](-) ions from the neutral glycans retained the derivative (Y-type cleavages) and provided information on sequence and branching. Other major fragments were products of A-type cross-ring cleavages giving information on antenna structure. Singly doubly and triply charged ions were formed from sialylated glycans. They produced major fragments by loss of sialic acid and a series of singly charged ions that were similar to those from the neutral analogues. Doubly charge ions were also produced by the neutral glycans and were fragmented to form product ions with one and two charges. Again, the fragment ions with a single charge were similar to those from the singly charged parents, but branching information was less obvious because of the occurrence of more abundant ions produced by multiple cleavages. Detection limits were around 200 fmol (3 : 1 signal-to-noise ratio).     

Negative charge induced dissociation: fragmentation of deprotonated N‐benzylidene‐2‐hydroxylanilines in electrospray ionization mass spectrometry

Unimolecular reactivities of different N‐benzylidene‐2‐hydroxylaniline anions were investigated in gas phase by electrospray ionization tandem mass spectrometry. All the collision‐induced dissociation spectra of N‐benzylidene‐2‐hydroxylaniline anions show similar ions at phenyl anions, neutral loss of benzonitrile and benzoxazole anions, respectively. The possible fragmentation pathway was probed through deuterium labeling and various group substituents experiments. Computational results were applied to shed light on the mechanism of fragmentation patterns. The proton in the CH=N is reactive in the formation of the concerned ions. Its direct transfer to the oxygen results in 2‐hydroxyphenyl anion. Proton abstraction between benzoxazole and phenyl anion leads to the formation of benzene and benzoxazole anion. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparison of CID spectra of singly charged polypeptide antibiotic precursor ions obtained by positive-ion vacuum MALDI IT/RTOF and TOF/RTOF, AP-MALDI-IT and ESI-IT mass spectrometry

Various classes of polypeptide antibiotics, including blocked linear peptides (gramicidin D), side-chain-cyclized peptides (bacitracin, viomycin, capreomycin), side-chain-cyclized depsipeptides (virginiamycin S), real cyclic peptides (tyrocidin, gramcidin S) and side-chain-cyclized lipopeptides (polymyxin B and E, amfomycin), were investigated by low-energy collision induced dissociation (LE-CID) as well as high-energy CID (HE-CID). Ion trap (IT) based instruments with different desorption/ionization techniques such as electrospray ionization (ESI), atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDI) and vacuum MALDI (vMALDI) as well as a vMALDI-time-of-flight (TOF)/curved field-reflectron instrument fitted with a gas collision cell were used. For optimum comparability of data from different IT instruments, the CID conditions were standardized and only singly charged precursor ions were considered. Additionally, HE-CID data obtained from the TOF-based instrument were acquired and compared with LE-CID data from ITs. Major differences between trap-based and TOF-based CID data are that the latter data set lacks abundant additional loss of small neutrals (e.g. ammonia, water) but contains product ions down to the immonium-ion-type region, thereby allowing the detection of even single amino-acid (even unusual amino acids) substitutions. For several polypeptide antibiotics, mass spectrometric as well as tandem mass spectrometric data are shown and discussed for the first time, and some yet undescribed minor components are also reported. De novo sequencing of unusually linked minor components of (e.g. cyclic) polypeptides is practically impossible without knowledge of the exact structure and fragmentation behavior of the major components. Finally, the described standardized CID condition constitutes a basic prerequisite for creating a searchable, annotated MS(n)-database of bioactive compounds. The applied desorption/ionization techniques showed no significant influence on the type of product ions (neglecting relative abundances of product ions formed) observed, and therefore the type of analyzer connected with the CID process mainly determines the type of fragment ions.     

The distribution of hydroxyl ions at the surface of anodic alumina

Barrier‐type anodic films 3–15 nm thick have been formed on electropolished 99.999% aluminium. Variable‐angle XPS has been used to identify a significant proportion of hydroxyl ions at the surface of the relatively compact alumina films. The location of an oxygen‐rich region at the outer surface of the oxide has been confirmed by medium‐energy ion scattering (MEIS). Combining the information from these two techniques leads to the conclusion that a hydroxyl‐containing surface region is responsible for this oxygen‐rich surface layer, MEIS revealing an approximately linear relationship between the total oxide thickness and the thickness of the hydroxyl‐rich surface region. From consideration of the mechanisms of amorphous alumina formation by ionic transport, with incorporation of electrolyte‐derived species into the thickening film, the generation of the hydroxyl‐rich outermost region is considered to result from the formation of gel‐like material at the film/electrolyte interface. Copyright © 2003 John Wiley & Sons, Ltd.     

Reactivity of gaseous sodiated ions derived from benzene dicarboxylate salts toward residual water in the collision gas

The sodium adduct of disodium salts of benzene dicarboxylic acids (m/z 233), when subjected to collision‐induced dissociation (CID), undergoes a facile loss of CO₂ to produce an ion of m/z 189, which retains all the three sodium atoms of the precursor. The CID spectrum of this unusual m/z 189 ion shows significant peaks at m/z 167, 63 and 85. The enigmatic m/z 167 ion, which appeared to represent a loss of a 22‐Da neutral fragment from the precursor ion is in fact a fragment produced by the interaction of the m/z 189 ion with traces of water present in the collision gas. The change of the m/z 167 peak to 168, when D₂O vapor was introduced to the collision gas of a Q‐ToF instrument, proved that such an intervention of water could occur even in collision cells of tandem‐in‐space mass spectrometers. The m/z 189 ion has such high affinity for water; it forms an ion/molecule complex even during the brief residence time of ions in collision cells of triple quadrupole instruments. The complex formed in this way then eliminates elements of NaOH to produce the ion observed at m/z 167. In an ion trap, the relative intensity of the m/z 167 peak increases with longer activation time even at the lowest possible collision energy setting. Similarly, the m/z 145 ion (which represents the sodium adduct of phenelenedisodium, formed by two consecutive losses of CO₂ from the m/z 233 ion of meta‐ and para‐isomers) interacts with water to produce a fragment ion at m/z 123 for the sodium adduct of phenylsodium. Other uncommon ions that originate also from water/ion interactions are observed at m/z 85 and 63 for [Na₃O]⁺ and [Na₂OH]⁺, respectively. Tandem mass spectrometric experiments conducted with appropriately deuterium‐labeled compounds confirmed that the proton required for the formation of the [Na₂OH]⁺ ion originates from traces of water present in the collision gas and not from the ring protons of the aromatic moiety. Copyright © 2010 John Wiley & Sons, Ltd.     

The atmospheric pressure Meerwein reaction

We have already shown that the in-vacuum gas-phase Meerwein reaction of (thio)acylium ions is general in nature and useful for class-selective screening of cyclic (thio)epoxides. Herein we report that this gas-phase reaction can also be performed efficiently at atmospheric pressure under both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) conditions. This alternative expands the range of molecules that can be reacted by gas-phase Meerwein reaction. Phenyl epoxide, thiirane, 3-methoxy-2,2-dimethyloxirane, propylene oxide, 2,2'-bioxirane, trans-1,3-diphenyl-2,3-epoxypropan-1-one, epichloridrine and propylene oxide are shown to react efficiently in both ESI and APCI conditions. Tetramethylurea (TMU) and (thio)TMU were both used as dopants, being co-injected with either toluene, acetonitrile or methanol solutions of the (thio)epoxides, with similar results. In both ESI and APCI, (thio)TMU is protonated preferentially, and these labile species dissociate promptly to yield (CH3)2N-C+=O and (CH3)2NCS+, which are the least acidic and most reactive (thio)acylium ions so far tested in the gas-phase Meerwein reaction. Under the low-energy ESI conditions set to favor both the formation of the (thio)acylium ion and ion/molecule reactions, (CH3)2NCO(S)+ react competitively with (thio)TMU to form acylated (thio)TMU and with the (thio)epoxide to form the characteristic Meerwein products. Enhanced selectivity in structural characterization or for the screening of (thio)epoxides is achieved by performing on-line collision-induced dissociation of Meerwein products, particularly for the more structurally complex (thio)epoxides.     

An unprecedented ortho effect in mass spectrometric fragmentation of even-electron negative ions from hydroxyphenyl carbaldehydes and ketones

A mass spectrometric peak for a carboxylate anion is observed in collision-induced dissociation (CID) mass spectra recorded from negative ions derived from ortho isomers of hydroxyphenyl carbaldehydes and ketones. For example, CID spectra of 2-hydroxy derivatives of benzaldehyde, acetophenone, propiophenone, isobutyrophenone, and pivalophenone show peaks at m/z 45, 59, 73, 87, and 101 for the formate, acetate, propionate, isobutyrate, and pivalate anions, respectively.     

An unprecedented rearrangement in collision-induced mass spectrometric fragmentation of protonated benzylamines

The collision-induced dissociation (CID) mass spectra of several protonated benzylamines are described and mechanistically rationalized. Under collision-induced decomposition conditions, protonated dibenzylamine, for example, loses ammonia, thereby forming an ion of m/z 181. Deuterium labeling experiments confirmed that the additional proton transferred to the nitrogen atom during this loss of ammonia comes from the ortho positions of the phenyl rings and not from the benzylic methylene groups. A mechanism based on an initial elongation of a C--N bond at the charge center that eventually cleaves the C--N bond to form an ion/neutral complex of benzyl cation and benzylamine is proposed to rationalize the results. The complex then proceeds to dissociate in several different ways: (1) a direct dissociation to yield a benzyl cation observed at m/z 91; (2) an electrophilic attack by the benzyl cation within the complex on the phenyl ring of the benzylamine to remove a pair of electrons from the aromatic sextet to form an arenium ion, which either donates a ring proton (or deuteron when present) to the amino group forming a protonated amine, which undergoes a charge-driven heterolytic cleavage to eliminate ammonia (or benzylamine) forming a benzylbenzyl cation observed at m/z 181, or undergoes a charge-driven heterolytic cleavage to eliminate diphenylmethane and an immonium ion; and (3) a hydride abstraction from a methylene group of the neutral benzylamine to the benzylic cation to eliminate toluene and form a substituted immonium ion. Corresponding benzylamine and dibenzylamine losses observed in the spectra of protonated tribenzylamine and tetrabenzyl ammonium ion, respectively, indicate that the postulated mechanism can be widely applied. The postulated mechanisms enabled proper prediction of mass spectral fragments expected from protonated butenafine, an antifungal drug.     

Evidence for the intermediacy of arylbenzylnitrenium ions in the thermal rearrangement of isoxazolidines derived from C,N-diarylnitrones and 2-morpholin-4-yl-acrylonitrile

In contrast to the diaryl, dialkyl, alkylaryl, and parent series, nothing is known about the generation and chemical behavior of arylbenzylnitrenium ions. Herein, we report that these species can be generated by a process involving an unprecedented thermal rearrangement of isoxazolidines derived from C,N-diarylnitrones and 2-morpholin-4-yl-acrylonitrile. The products from these reactions are dramatically dependent upon the nature of the nitrone. Most of the observed chemistry originates from the singlet state.     

Loss of benzene to generate an enolate anion by a site-specific double-hydrogen transfer during CID fragmentation of o-alkyl ethers of ortho-hydroxybenzoic acids

Collision-induced dissociation of anions derived from ortho-alkyloxybenzoic acids provides a facile way of producing gaseous enolate anions. The alkyloxyphenyl anion produced after an initial loss of CO(2) undergoes elimination of a benzene molecule by a double-hydrogen transfer mechanism, unique to the ortho isomer, to form an enolate anion. Deuterium labeling studies confirmed that the two hydrogen atoms transferred in the benzene loss originate from positions 1 and 2 of the alkyl chain. An initial transfer of a hydrogen atom from the C-1 position forms a phenyl anion and a carbonyl compound, both of which remain closely associated as an ion/neutral complex. The complex breaks either directly to give the phenyl anion by eliminating the neutral carbonyl compound, or to form an enolate anion by transferring a hydrogen atom from the C-2 position and eliminating a benzene molecule in the process. The pronounced primary kinetic isotope effect observed when a deuterium atom is transferred from the C-1 position, compared to the weak effect seen for the transfer from the C-2 position, indicates that the first transfer is the rate determining step. Quantum mechanical calculations showed that the neutral loss of benzene is a thermodynamically favorable process. Under the conditions used, only the spectra from ortho isomers showed peaks at m/z 77 for the phenyl anion and m/z 93 for the phenoxyl anion, in addition to that for the ortho-specific enolate anion. Under high collision energy, the ortho isomers also produce a peak at m/z 137 for an alkene loss. The spectra of meta and para compounds show a peak at m/z 92 for the distonic anion produced by the homolysis of the O--C bond. Moreover, a small peak at m/z 136 for a distonic anion originating from an alkyl radical loss allows the differentiation of para compounds from meta isomers. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Structure and further fragmentation of significant [a3 + Na − H]+ ions from sodium‐cationized peptides

A good understanding of gas‐phase fragmentation chemistry of peptides is important for accurate protein identification. Additional product ions obtained by sodiated peptides can provide useful sequence information supplementary to protonated peptides and improve protein identification. In this work, we first demonstrate that the sodiated a₃ ions are abundant in the tandem mass spectra of sodium‐cationized peptides although observations of a₃ ions have rarely been reported in protonated peptides. Quantum chemical calculations combined with tandem mass spectrometry are used to investigate this phenomenon by using a model tetrapeptide GGAG. Our results reveal that the most stable [a₃ + Na ? H]⁺ ion is present as a bidentate linear structure in which the sodium cation coordinates to the two backbone carbonyl oxygen atoms. Due to structural inflexibility, further fragmentation of the [a₃ + Na ? H]⁺ ion needs to overcome several relatively high energetic barriers to form [b₂ + Na ? H]⁺ ion with a diketopiperazine structure. As a result, low abundance of [b₂ + Na ? H]⁺ ion is detected at relatively high collision energy. In addition, our computational data also indicate that the common oxazolone pathway to generate [b₂ + Na ? H]⁺ from the [a₃ + Na ? H]⁺ ion is unlikely. The present work provides a mechanistic insight into how a sodium ion affects the fragmentation behaviors of peptides. Copyright © 2015 John Wiley & Sons, Ltd.     

Ionization energies of multiply protonated polypeptides obtained by tandem ionization in Fourier transform mass spectrometers

Ionization energies (IE) of [M + zH](z+) (z+) electrospray-produced polypeptides were determined by electron ionization in a Penning cell of 4.7 and 9.4 T Fourier transform mass spectrometers. For z = 1+ and substance P, the found IE value of 11.0 +/- 0.4 eV is in agreement with that obtained earlier for ions generated with matrix-assisted laser desorption/ionization. For higher z, the following values were found: 11.7 +/- 0.3 eV for 2+ of [Arg-8]-vasopressin, 11.1 +/- 0.6 eV for 2+ of substance P, 12.2 +/- 0.7 eV for 2+ of renin substrate, 13.3 +/- 0.4 eV for 3+ of B-chain of insulin and 14.6 +/- 0.6 eV for 4+ and 15.1 +/- 0.4 eV for 5+ of melittin. It was found that 90% of existing IE data on polypeptides in the 1.0-3.5 kDa mass range are described with 相似文献   

Synthetic Reactions Using Low‐valent Titanium Reagents Derived from Ti(OR)4 or CpTiX3 (X = O‐i‐Pr or Cl) in the Presence of Me3SiCl and Mg

In the presence of Me₃SiCl, Ti(OR)₄ or CpTiX₃ (X = O‐i‐Pr or Cl) is reduced by Mg powder in THF to gradually generate a specific low‐valent titanium (LVT) species that mediates several synthetic reactions. The LVT‐catalyzed C–O bond‐cleaving reactions of allyl and propargyl ethers and esters generate parent alcohols and carboxylic acids, respectively. O‐allyl and propargyl carbamates are also readily deprotected by the LVT to afford parent amines. In addition, the respective reductive N–S or O–S bond cleavage of sulfonamides or sulfonyl esters mediated by the LVT was developed as a novel facile deprotection method. The reagent catalyzes intra‐ and intermolecular alkyne or alkyne/nitrile cycloaddition to produce substituted benzenes and pyridines, while epoxides and oxetanes are reduced to alcohols via an LVT‐mediated homolytic ring opening. The McMurry coupling of aryl aldehydes and ketones proceeds with the LVT under homogeneous and mild reaction conditions and is effective for the polymerization of aromatic dialdehydes, generating conjugated polymers. Finally, imino‐pinacol coupling of imines is mediated by the LVT to provide 1,2‐diamines.     

Collision‐induced dissociation of oligonucleotide anions fully modified at the 2'‐position of the ribose: 2'‐F/‐H and 2'‐F/‐H/‐OMe mix‐mers

Gas‐phase dissociation of various 2'‐position modified oligonucleotide anions has been studied as a function of precursor ion charge state using ion trap and low energy beam‐type collision‐induced dissociation (CID). For a completely 2'‐O‐methyl modified 6‐mer, all possible dissociation channels along the phosphodiester linkage, generating complementary (a‐B)/w‐, b/x‐, c/y‐, d/z‐ion series, were observed with no single dominant type of dissociation pathway. Full sequence information was generated from each charge state via ion trap CID. More sequential fragmentation was noted under beam‐type CID conditions. Comparison with model DNA, in which all 2'‐OH groups are converted to 2'‐H, and RNA anions suggests that the 2'‐OMe substitution stabilizes the phosphodiester linkage with respect to fragmentation relative to both DNA and RNA oligomers. For modified mix‐mer anions, comprised of DNA nucleotides and 2'‐F substituted nucleotides or a mixture of DNA nucleotides and 2'‐O‐methyl (2'‐OMe) and 2'‐F substituted nucleotides, 3'‐side backbone cleavage was found to be inhibited by the 2'‐OMe or 2'‐F modification on the nucleotides under ion trap CID conditions. Thus, the sequence information was limited to the a‐Base/w‐fragments from the cleavage of the 3' C‐O bond of the 2'‐H (DNA) nucleotides. Under beam‐type CID conditions, limited additional cleavage adjacent to 2'‐OMe substituted nucleotides was noted but 2'‐F modified residues remained resistant to cleavage. Copyright © 2012 John Wiley & Sons, Ltd.     

Low‐energy collision‐induced dissociation (low‐energy CID), collision‐induced dissociation (CID), and higher energy collision dissociation (HCD) mass spectrometry for structural elucidation of saccharides and clarification of their dissolution mechanism in DMAc/LiCl

The dissolution mechanism of oligosaccharides in N,N‐dimethylacetamide/lithium chloride (DMAc/LiCl), a solvent used for cellulose dissolution, and the capabilities of low‐energy collision‐induced dissociation (low‐energy CID), collision‐induced dissociation (CID), and higher energy collision dissociation (HCD) for structural analysis of carbohydrates were investigated. Comparing the spectra obtained using 3 techniques shows that, generally, when working with monolithiated sugars, CID spectra provide more structurally informative fragments, and glycosidic bond cleavage is the main pathway. However, when working with dilithiated sugars, HCD spectra can be more informative providing predominately cross‐ring cleavage fragments. This is because HCD is a nonresonant activation technique, and it allows a higher amount of energy to be deposited in a short time, giving access to more endothermic decomposition pathways as well as consecutive fragmentations. The difference in preferred dissociation pathways of monolithiated and dilithiated sugars indicates that the presence of the second lithium strongly influences the relative rate constants for cross‐ring cleavages vs glycosidic bond cleavages, and disfavors the latter. Regarding the dissolution mechanism of sugars in DMAc/LiCl, CID and HCD experiments on dilithiated and trilithiated sugars reveal that intensities of product ions containing 2 Li⁺ or 3 Li⁺, respectively, are higher than those bearing only 1 Li⁺. In addition, comparing the fragmentation spectra (both HCD and CID) of LiCl‐adducted lithiated sugar and NaCl‐adducted sodiated sugar shows that while, in the latter case, loss of NaCl is dominant, in the former case, loss of HCl occurs preferentially. The compiled evidence implies that there is a strong and direct interaction between lithium and the saccharide during the dissolution process in the DMAc/LiCl solvent system.     

The effect of hydrogen ions on the steady state multiplicity of substrate-inhibited enzymatic reactions

The present investigation concentrates on the study of the complex phenomenon of multiplicity in membranes carrying substrate-inhibited, hydrogen ion-sensitive enzyme. The investigation takes into consideration both symmetrical and asymmetrical steady states. The number of steady states (symmetrical and asymmetrical) found in this case is quite large, giving rise to multiple hysteresis loops and multiple “isolas.”