Localization Of Positive Charge Research Articles

Hydrogen bonding of redox-active tyrosine Z of photosystem II probed by FTIR difference spectroscopy.

The TyrZ./TyrZ FTIR difference spectrum is reported for the first time in Mn-depleted photosystem II (PS II)-enriched membranes of spinach, in PS II core complexes of Synechocystis sp. PCC 6803 WT, and in the mutant lacking TyrD (D2-Tyr160Phe). In Synechocystis, the v7'a(CO) and delta(COH) infrared modes of TyrZ are proposed to account at 1279 and 1255 cm-1. The frequency of these modes indicate that TyrZ is protonated at pH 6 and involved in a strong hydrogen bond to the side chain of a histidine, probably D1-His190. A positive signal at 1512 cm-1 is assigned to the v(CO) mode of TyrZ. on the basis of the 27 cm-1 downshift observed upon 13C-Tyr labeling at the Tyr ring C4 carbon. A second IR signal, at 1532 cm-1, is tentatively assigned to the v8a(CC) mode of TyrZ.. The frequency of the v(CO) mode of TyrZ. at 1512 cm-1 is comparable to that observed at 1513 cm-1 for the Tyr. obtained by UV photochemistry of tyrosinate in solution, while it is higher than that of TyrD. in WT PS II at 1503 cm-1 and that of non-hydrogen-bonded TyrD. in the D2-His189Gln mutant at 1497 cm-1 [Hienerwadel, R., Boussac, A., Breton, J., Diner, B. A., and Berthomieu, C. (1997) Biochemistry 36, 14712-14723]. This latter work and the present FTIR study suggest that hydrogen bonding induces an upshift of the v(CO) IR mode of tyrosyl radicals and that TyrZ. forms (a) stronger hydrogen bond(s) than TyrD. in WT PS II. Alternatively, the frequency difference between TyrZ. and TyrD. v(CO) modes could be explained by a more localized positive charge near the tyrosyl radical oxygen of TyrD. than TyrZ.. The TyrZ./TyrZ spectrum obtained in Mn-depleted PS II membranes of spinach shows large similarities with the S3'/S2' spectrum characteristic of radical formation in Mn-containing but Ca(2+)-depleted PS II, in support of the assignment using ESEEM of TyrZ. as being responsible for the split EPR signal observed upon illumination in these conditions [Tang, X.-S., Randall, D. W., Force, D. A., Diner, B. A., and Britt, R. D. (1996) J. Am. Chem. Soc. 118, 7638-7639]. The peak at 1514 cm-1 is assigned to the v(CO) mode of TyrZ. in these preparations, which indicates that Mn depletion only very slightly perturbs the immediate environment of TyrZ. phenoxyl.

Ligand binding and covalent structure of an oxygen-binding heme protein from Rhodobacter sphaeroides, a representative of a new structural family of c-type cytochromes.

The amino acid sequence of an oxygen-binding heme protein (SHP) from Rhodobacter sphaeroides has been determined. The cysteines, which bind the single heme group in the 112-residue protein, are located at positions 43 and 46. SHP is similar in size to the large membrane-bound form of the class I cytochrome c5 of Azotobacter vinelandii (116 residues) and in the location of the heme binding site at positions 48 and 51. Two extra cysteines in SHP (residues 89 and 97) are located in positions similar to those of cytochrome c5 (residues 98 and 101) and form a disulfide bridge in both proteins. In total, four regions of alpha-helix are predicted, covering 46% of the protein, which is comparable to that in other small cytochromes. SHP is thus distantly related to small class I c-type cytochromes but is representative of a distinct family by virtue of its high-spin nature, the lack of a strong sixth ligand, and its capacity to bind oxygen. Potentially, the most important characteristic of SHP is its ability to transiently bind oxygen during autoxidation, which occurs with a half-life of 3 min with a 4-fold excess of O2. SHP also binds carbon monoxide, azide, and cyanide. The kinetics of reduction by free flavins indicate that SHP is less reactive than other class I cytochromes c and that the heme is less accessible to solvent. There is localized positive charge (+3) at the site of reduction of SHP, although the overall protein charge is -2. This may account in part for the ability of SHP to bind anions.

Photoionization mechanism of aniline derivatives in aqueous solution studied by laser flash photolysis

The photoionization mechanism of a series of aniline derivatives in aqueous solution was investigated by 266 or 308 nm laser flash photolysis to determine the molecular properties which play an important role in the photoionization of solute molecules in aqueous medium. The ionization potentials of the investigated compounds in the gas phase (IP gas) are in the range 6.87–8.64 eV. In compounds with IP gas values of less than approximately 7.8 eV, photoelectron ejection takes place mainly from the non-relaxed S 1 state by one-photon absorption at 266 nm (4.66 eV) or 308 nm (4.03 eV), showing that significant polarization stabilization of the cation as well as of the photoejected electron should occur in aqueous solution. Contrary to expectation, the hydrated electron yield ( Φ e − aq ) determined from transient absorption measurements tends to increase with increasing IP gas. The Φ e − aq value increases with increasing positive charge (i.e. formal charge) on the nitrogen atom of the resulting cations, indicating that the interaction between the local positive charge on the cation and the solvent water molecules is one of the key factors in the photoionization of aqueous aniline derivatives. © 1997 Elsevier Science S.A.

Direct visualization of extensibility in isolated titin molecules

“Molecular combing” induced by a receding meniscus has been shown to extend individual titin molecules. Electron microscopy reveals that both ends of the molecule tend to attach to a mica substrate, probably due to their local positive charges. This leaves the remainder of the molecule free to be straightened and extended by forces of up to ∼800 pN. A small region in the I-band part of the molecule, which probably corresponds to sequence high in P, E, V and K residues, is the most compliant and appears to extend by an unfolding of the polypeptide chain. Other parts of the molecule are also capable of extension. These mechanical extensions in titin are probably reversible.

The Importance of Being Modified: Roles of Modified Nucleosides and Mg2+ in RNA Structure and Function

Publisher Summary This chapter summarizes the relationships between modified nucleosides and transfer RNA (tRNA) function. In vivo and in vitro syntheses of modified nucleoside-containing RNAs have been developed for physicochemical and biochemical studies. The different approaches to RNA synthesis are compared in the chapter. An understanding of the chemistry, structure, and function of modified nucleosides of tRNAs is applicable to the study of modified nucleosides of other RNAs and DNA. The structure–function relationships of the simplest of nucleoside modifications may provide insights into the “RNA World” and could be applied to the design of nucleic acids with new or altered functions. Nucleosides are modified after the polymerization of the nucleic acid. To accomplish site-specific modifications of the bases in DNA and the bases and ribose of RNA, a very large investment in genetic information, energy, and material resources has been made d. Nucleic-acid modifications have been linked to the control of gene expression at both the level of transcription and translation. Although a few modifications have been found in DNA, 93 modified nucleosides exist in various RNAs. Nucleic-acid stability is enhanced through the modifications that introduce local positive charges, neutralizing the anionic phosphate backbone.

35] Use of cationic detergents to enhance reactivityof protein sulfhydryls

Publisher Summary This chapter discusses the use of cationic detergents to enhance reactivity of protein sulfhydryls. One such reagent is hexadecyltrimethylammonium bromide, also known as “cetyltrimethylammonium bromide” (CTABr). This cationic detergent binds to proteins, enhancing the local positive charge density and decreasing the sulfhydryl p K a values by one or two pH units. In addition, when used in conjunction with labeling reagents having a net negative charge, the positive charge caused by the bound detergent can enhance the observed rates by increasing the local concentration of the labeling reagent. The binding of the detergent also results in changes in the protein conformation that result in the exposure of buried sulfhydryls. The chapter describes the conditions used to enhance protein–SH reactivities by means of the addition of the cationic detergent CTABr. The labeling reagent used is N -iodoacetyl-3-( 125 I)iodotyrosine([ 125 I]IAIT). The reactivity of protein thiols is markedly increased by allowing a cationic detergent (CTABr) to bind to the proteins, thereby increasing the thiol ionization and the accessibility to the dianionic IAIT labeling reagent. Another useful property of added CTABr is its enhancement of the rate of dithiothreitol (DTT) reduction of protein disulfides. However, the cationic detergent also induces enhanced reactivity of the DTT. Therefore, for proper quantification, the excess DTT must be removed before the IAIT labeling is performed.

Faster superoxide dismutase mutants designed by enhancing electrostatic guidance.

The enzyme Cu, Zn superoxide dismutase (SOD) protects against oxidative damage by dismuting the superoxide radical O2-. to molecular oxygen and hydrogen peroxide at the active-site Cu ion in a reaction that is rate-limited by diffusion and enhanced by electrostatic guidance. SOD has evolved to be one of the fastest enzymes known (V(max) approximately 2 x 10(9) M-1 s-1). The new crystal structures of human SOD show that amino-acid site chains that are implicated in electrostatic guidance (Glu 132, Glu 133 and Lys 136) form a hydrogen-bonding network. Here we show that site-specific mutants that increase local positive charge while maintaining this orienting network (Glu----Gln) have faster reaction rates and increased ionic-strength dependence, matching brownian dynamics simulations incorporating electrostatic terms. Increased positive charge alone is insufficient: one charge reversal (Glu----Lys) mutant is slower than the equivalent charge neutralization (Glu----Gln) mutant, showing that the newly introduced positive charge disrupts the orienting network. Thus, electrostatically facilitated diffusion rates can be increased by design, provided the detailed structural integrity of the active-site electrostatic network is maintained.

Electron-transfer reactions of cytochrome f with flavin semiquinones and with plastocyanin. Importance of protein-protein electrostatic interactions and of donor-acceptor coupling.

Reduction of turnip ferricytochrome f by flavin semiquinones and oxidation of this ferrocytochrome f by French bean cupriplastocyanin are studied by laser flash photolysis over a wide range of ionic strengths. Second-order rate constants (+/- 15%) at extreme values of ionic strength, all at pH 7.0 and 22 degrees C, are as follows: with FMN semiquinone at 1.00 and 0.0040 M, 5.0 x 10(7) and 3.9 x 10(8) M-1 s-1; with riboflavin semiquinone at 1.00 and 0.0040 m, 1.7 x 10(8) and 1.9 x 10(8) M-1 s-1; with lumiflavin semiquinone at 1.00 and 0.0045 M, 1.8 x 10(8) and 4.5 x 10(8) M-1 s-1; with cupriplastocyanin at 1.00 and 0.100 M, 1.4 x 10(6) and 2.0 x 10(8) M-1 s-1. These reactions of cytochrome f are governed by the local positive charge of the interaction domain (the exposed heme edge), not by the overall negative charge of the protein. Lumiflavin semiquinone behaves as if it carried a small negative charge, probably because partial localization of the odd electron gives this electroneutral molecule some polarity; local charge seems to be more important than overall charge even for relatively small redox agents. The dependence of the rate constants on ionic strength was fitted to the equation of Watkins; this model recognizes the importance of local charges of the domains through which redox partners interact. There is kinetic evidence that a noncovalent complex between cytochrome f and plastocyanin exists at low ionic strength.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of fixed electron‐beam‐induced positive oxide charge

AbstractContrary to previous beliefs, electron‐beam‐induced positive charges in insulators persist where created for at least several weeks without discernible movement. Formerly, coating with a thin metal overlay was thought to allow the charge to leak away. Coating with a conductor is shown to shield electric fields from affecting the imaging probe, but to remove no charge from the specimen. A new technique is introduced for the evaluation of the properties of electron‐beam‐induced positive charges in metal‐oxide‐semiconductor (MOS) capacitors. MOS structures were subjected to partial area exposure in a scanning electron microscope. These exposures resulted in the creation of areas of localized positive charge within the oxide, which was observed as steps in the capacitance‐voltage data. A systematic study was performed. It related the exposed area to the step height and the amount of induced charge to the voltage shift of the step. A model describing the observed phenomenon is presented, followed by a comparison of theoretical and experimental results. The progress of the charge over time was studied by performing capacitance‐voltage analysis 30 min after electron beam exposure and up to 4 weeks later.

Dextran sulfate blocks antibody binding to the principal neutralizing domain of human immunodeficiency virus type 1 without interfering with gp120-CD4 interactions

The mechanism of the antiviral activity of sulfated polysaccharides on human immunodeficiency virus type 1 (HIV-1) was investigated by determining the effect of dextran sulfate on the binding of CD4 and several anti-gp120 monoclonal antibodies to both recombinant and cell surface gp120. Dextran sulfate did not interfere with the binding of sCD4 to rgp120 on enzyme-linked immunosorbent assay (ELISA) plates or in solution and did not block sCD4 binding to HIV-1-infected cells expressing gp120 on the cell surface. Dextran sulfate had minimal effects on rgp120 binding to CD4+ cells at concentrations which effectively prevent HIV replication. In contrast, it potently inhibited the binding of both rgp120 and cell surface gp120 to several monoclonal antibodies directed against the principal neutralizing domain of gp120 (V3). In an ELISA format, dextran sulfate enhanced the binding of monoclonal antibodies against amino-terminal regions of gp120 and had no effect on antibodies directed to other regions of gp120, including the carboxy terminus. The inhibitory effects of polyanionic polysaccharides on viral binding, viral replication, and formation of syncytia therefore appear mediated by interactions with positively charged amino acids concentrated in the V3 region. This high local positive charge density, unique to the V3 loop, leads us to propose that this property is critical to the function of the V3 region in mediating envelope binding and subsequent fusion between viral and cell membranes. The specific interaction of dextran sulfate with this domain suggests that structurally related molecules on the cell surface, such as heparan sulfate, may be additional targets for HIV binding and infection.

X-ray photoelectron spectroscopy studies of deprotonated polypyrrole and its complexes

Oxidized polypyrrole (PPY) was subjected to deprotonation by 0.5 M NaOH. The interactions of the deprotonated pyrrolylium nitrogens with various protonic acids and organic electron acceptors were studied by X-ray photoelectron spectroscopy (XPS) and were found to be similar to those observed for the imine nitrogens in the emeraldine oxidation state of polyaniline. However, the cyclic acid/base treatments of the deprotonated PPY were not completely reversible. The interactions with the halobenzoquinones, such as o-chloranil, p-chloranil and o-bromanil, resulted in the formation of positively charged nitrogens and the halogen and benzoquinone anions. In the case of interaction with TCNE, cyano anions were involved while interaction with DDQ involved all three types of anions. The charge transfer (CT) behaviour of the deprotonated pyrrolylium nitrogens towards acid protonation, and ‘doping’ by the organic acceptors, together with the charge neutrality considerations, suggested the presence of localized units positive charge on the pyrrolylium nitrogens.

Mechanism of ionization and initial fragmentation in electron impact mass spectra of 3‐halogenobenzanthrones

AbstractElectron‐impact mass spectra of 3‐halogenobenzanthrones (halogen X = Cl, Br, I) were measured and ionization efficiency curves and three kinds of linked‐scan spectra were obtained for several fragment ions. The fundamental mechanisms of ionization and initial fragmentation were interpreted by the penetration length of an impacting electron or the density distribution on the molecular surface of a rejected electron and its orbital energy. The apparent ionization energy (IE) of a singly charged molecular ion seems to be the lower one of non‐bonding electrons on O or X, and that of a doubly charged molecular ion the sum of three terms, the IE of non‐bonding electron on O, that on X and the electrostatic repulsion between two positive charges. Two competing pathways of decomposition from the molecular ion M+· to an ion [M ‐ CO,‐ X]+ were observed: one is the initial detachment of CO in chloro and bromo compounds and the other is the initial elimination of the iodine atom in the iodo compound. The sequence of these reactions was confirmed by metastable ion analysis with linked‐scan spectra and the relative magnitudes of the appearance energies. They can be explained by the driving force of a localized positive charge or unpaired electron on a heteroatom.

Schiff bases of nickel(II), copper(II) porphyrins and dibenzo-18-crown-6 interspersedbis-metal porphyrins. Protonation studies

Schiff-base (SB) derivatives of Ni(II) and Cu(II) porphyrins endowed with various amine functions (R−NH2),n-butylamine,p-anisidine andm-nitroaniline have been prepared from corresponding formyl porphyrins. Protonation studies of these SB derivatives reveal a marked red shift of the optical absorption bands in the visible region relative to the unprotonated imines. The magnitude of the observed red shifts in the protonated derivatives, (SBH+) are found to depend on the electron-withdrawing or electron-donating nature of the R group of the amines. The results of the optical absorption,1H NMR, EPR, and cyclicovoltammetric studies are illustrative of the fact that protonation of the SB derivatives results in a localized positive charge,\(P - C(H) = \bar N(H) - R\) in the periphery of the porphyrin (p) system. The dibenzo-18-crown-6 interspersedbisporphyrin schiff bases have been prepared fromtrans 4,4′-diamino dibenzo-18-crown-6 and formyl porphyrins. The protonation of these SB derivatives is found to proceed in a concerted fashion. The cation complexation studies by the crown ether entity in thebisporphyrin systems have been investigated using optical absorption, magnetic resonance and electrochemical methods. The redox characteristics of the protonated dimeric SB porphyrins reveal that the first oxidation step involves a two-electron transfer reaction. This is important in view of their possible usage in multielectron transfer reactions of biological and catalytic interest.

Transfer RNA contains sites of localized positive charge: carbon NMR studies of [13C]methyl-enriched Escherichia coli and yeast tRNAPhe.

The possibility of positively charged nucleosides in tRNA has been suspected because certain posttranscriptional methylations produce quaternary nitrogens. To investigate this possibility and the importance of such methylations to tRNA structure, we have continued our studies of [13C]methyl-enriched phenylalanine tRNA of Escherichia coli [Kopper, R.A., Schmidt, P.G., & Agris, P.F. (1983) Biochemistry 22, 1307-1401] and yeast [Smith, C., Petsch, J., Schmidt, P.G., & Agris, P.F. (1985) Biochemistry 24, 1434-1440]. E. coli and yeast tRNA were 13C-enriched in their methyl groups in vivo, and phenylalanine-specific tRNA was isolated. Methyl proton and carbon signal assignments were confirmed and correlated for the purified tRNAs under native conditions via the first application of two-dimensional carbon-proton correlation NMR spectroscopy to a native nucleic acid. The methyl proton chemical shift of the 7-methylguanosine (m7G) signal from tRNA was easily determined, although by conventional 1H NMR spectroscopy it would have been hidden by ribose resonances and H2O. The chemical shift for 1-methyladenosine (m1A) protons was shown to be 3.01 ppm. Resolution of close or overlapping peaks was greatly enhanced by the two-dimensional experiment especially for the proton methyl resonances. In addition, proton-carbon chemical shift correspondence has been determined for the two 5-methylcytidines (m5C's), the methyl esters of wybutosine (Y), and the two ribose methyl groups, Gm and Cm, of yeast tRNAPhe. Thermal denaturation and Mg2+ depletion affect the methyl carbon NMR chemical shifts of tRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Charges on proteins and distances of electron transfer in metalloprotein redox reactions.

A modified form of the Debye-Marcus equation relating electron transfer rate constants to charges on proteins and distances of electron transfer has been applied to the reaction of chemically modified cytochrome f, in which positively charged amino groups are replaced with negatively charged carboxyl groups. The rate of electron transfer from reduced cytochrome f to ferricyanide decreased with increasing ionic strength when the native and singly substituted cytochrome f were used, although a sharp decrease was observed in the former case. When doubly or more than triply substituted cytochrome f was used, the rate of electron transfer was almost constant or increased with increasing ionic strength, respectively. The kinetic-ionic strength effects on this reaction can be well explained by the Debye-Marcus equation in which the charge and radius of the protein are treated as variable parameters. The results show the importance of local positive charges of about 2.0 on native cytochrome f and effective radius of about 11 A of cytochrome f for the electron transfer to ferricyanide. Since the net charge on the native cytochrome f is negative and the calculated radius of the protein is 22.8 A, the above results indicate that positive charges on the electron transfer site control the electrostatic interactions in this reaction. Previously reported data which had been analyzed by using the total net charge and full radius of the protein, were also well explained by the local charge and effective radius of the protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Importance of local positive charges on cytochrome f for electron transfer to plastocyanin and potassium ferricyanide.

To study the relationship between the electron transfer rate and the net or local charge of protein, chemically modified cytochrome f, in which positively charged amino groups are replaced with negatively charged carboxyl groups, has been prepared by using an arylating reagent 4-chloro-3,5-dinitrobenzoic acid. Four distinct species of chemically modified cytochrome f, having 1 to 4 mol of modified amino residues per mol of cytochrome f, were separated by preparative polyacrylamide gel electrophoresis. The rate of electron transfer from the reduced singly substituted cytochrome f to the oxidized spinach plastocyanin was only about 50% of that of the native unmodified cytochrome f. The reaction rate further decreased about 50% upon the modification of each amino residue. The biphasic oxidation of cytochrome f by plastocyanin was observed when more than 2 mol of amino residues were modified. The rate of the second phase also decreased with an increasing number of modified amino residues. On the other hand, the oxidation of chemically modified cytochrome f by potassium ferricyanide was clearly monotonic. The rate decreased about 30% upon the modification of each amino residue. The midpoint potentials of chemically modified cytochrome f were almost the same as that of the native protein. These results clearly indicate the importance of local positive charges on cytochrome f, since the overall net charge of cytochrome f is negative at neutral pH. The theory of electrostatic corrected outer-sphere electron transfer of Marcus explained the effect of charge on cytochrome f for the reaction with the small molecule of ferricyanide well, but not the reaction with the protein of plastocyanin.

Ph-dependence of the α-lactalbumin structure : A fluorescence study

The fluorescence parameters of demetallized alpha-lactalbumin in the range from pH 8 to 2 show an extreme around pH 5-4 (a minimum in quantum yield and wavelength and a maximum in polarization). This extreme is not due to a competition between Ca2+ and protons but rather to a stabilization of the conformation of the protein near the isoelectric pH by the ionic interactions between local positive and negative charges on the protein. The calcium-free protein has similar fluorescence characteristics at pH 2 and 8 but the thermal transition curve is different. The influence of 0.1 M NaCl is also considered.

雪雲の電気的構造

The electrical and precipitation-physical structures of snow clouds were observed by means of "Altielectrographs", "Snow Crystal Sondes", electric charge sondes and the usual radiosondes on the Ishikari Coast, Hokkaido in the winter seasons of 1969 and 1970, simultaneously with ground-based observation.The following results were obtained.1. A thick layer of positive space charge was found generally distributed in the middle layer of the snow clouds. The charge was carried by small snow' crystals. A thin layer of negative space charge was found below the layer of positive space charge. This charge was carried by large snow crystals.2. Local positive space charges carried by positively charged graupel pellets frequently existed in the active regions in the lower portion or below the cloud base. This probably caused the electrical structure of snow clouds to be complicated.3. Good correspondences between the patterns of electrical structures observed in clouds and on the ground showed that the structure aloft was transported by the descent of graupel pellets and snow crystals to the ground without any remarkable modifications.4. The positive electrification of graupel pellets were presumably caused by the collision with neighboring unrimed snow crystals in the warm temperature region between -5°C and -10°C levels.

Prediction of proton affinities and protonation sites using a multivariate linear correlation

We have shown, for a large set of compounds, including oxygen, nitrogen, and carbon bases, that it is possible to express the gas-phase proton affinities (PA) as a linear function of 1s binding energies and first ionization potentials. This multivariate correlation holds for molecules of different homologous series and we conclude that it contains the two most important factors which contribute to the basicity of a given molecule. We have also shown that some species which deviate from single correlations between PAs and 1s binding energies, e.g. NN-dialkylanilines, naphthalene, etc. fit our multivariate correlation very well. These systems are stronger bases than expected from the 1s ionization energy of their basic centres, due to their special ability to accommodate a highly localized positive charge. We have shown that similar correlations can be obtained using orbital energies, calculated using an STO3G minimal basis set, instead of experimental ionization energies. Several cases are fully discussed.

Ion–molecule reactions in the binary mixture of acetaldehyde and trioxane. II. Mechanism for the reaction of acetaldehyde molecular ion with trioxane

The ionic reaction of CH3CHO+with trioxane in acetaldehyde–trioxane mixtures has been studied using a time-of-flight mass spectrometer. The product ions, C3H5O2+, C3H6O2+, and C3H7O2+, were formed by condensation–elimination reactions, which involve the elimination of aformaldehyde molecule. The dissociation of the intermediate-complex, CH3CHO(CH2O)3+*, leads to the formation of the product ions. The structure of the complex is linear with localized positive charge. Rearrangement of hydrogen atoms occurs in the complex but not extensive scrambling. From the distribution of the isotopic product ions in acetaldehyde-d4–trioxane mixtures it was proposed that the origins of the product ions are the acetaldehyde molecule (reactant ion) and fragments from trioxane. The rate constants for the product ions formed in acetaldehyde (or acetaldehyde-d4)–trioxane mixtures were obtained.