Detection of somatic and germline pathogenic variants in adult cohort of drug-resistant focal epilepsies.

OBJECTIVE: This study investigates the prevalence of pathogenic variants in the mechanistic target of rapamycin (mTOR) pathway in surgical specimens of malformations of cortical development (MCDs) and cases with negative histology. The study also aims to evaluate the predictive value of genotype-histotype findings on the surgical outcome. METHODS: The study included patients with drug-resistant focal epilepsy who underwent epilepsy surgery. Cases were selected based on histopathological diagnosis, focusing on MCDs and negative findings. We included brain tissues both as formalin-fixed, paraffin-embedded (FFPE) or fresh frozen (FF) samples. Single-molecule molecular inversion probes (smMIPs) analysis was conducted, targeting the MTOR gene in FFPE samples and 10 genes within the mTOR pathway in FF samples. Correlations between genotype-histotype and surgical outcome were examined. RESULTS: We included 78 patients for whom we obtained 28 FFPE samples and 50 FF tissues. Seventeen pathogenic variants (22 %) were identified and validated, with 13 being somatic within the MTOR gene and 4 germlines (2 DEPDC5, 1 TSC1, 1 TSC2). Pathogenic variants in mTOR pathway genes were exclusively found in FCDII and TSC cases, with a significant association between FCD type IIb and MTOR genotype (P = 0.003). Patients carrying mutations had a slightly better surgical outcome than the overall cohort, however it results not significant. The FCDII diagnosed cases more frequently had normal neuropsychological test, a higher incidence of auras, fewer multiple seizure types, lower occurrence of seizures with awareness impairment, less ictal automatisms, fewer Stereo-EEG investigations, and a longer period long-life of seizure freedom before surgery. SIGNIFICANCE: This study confirms that somatic MTOR variants represent the primary genetic alteration detected in brain specimens from FCDII/TSC cases, while germline DEPDC5, TSC1/TSC2 variants are relatively rare. Systematic screening for these mutations in surgically treated patients' brain specimens can aid histopathological diagnoses and serve as a biomarker for positive surgical outcomes. Certain clinical features associated with pathogenic variants in mTOR pathway genes may suggest a genetic etiology in FCDII patients.

Novel crystalline phase and first-order phase transitions of human insulin complexed with two distinct phenol derivatives.

The primary focus of the present work is the study of the effects that two ligands and the crystallization pH have on the crystalline forms of human insulin. For this purpose, human insulin (HI) was co-crystallized with two distinct phenolic derivatives: the organic ligands meta-cresol (m-cresol) and 4-nitrophenol. The formation of polycrystalline precipitates was then followed by means of structural characterization of the individual specimens in terms of unit-cell symmetry and parameters. In both cases, two different polymorphs were identified via X-ray powder diffraction measurements, the first of hexagonal symmetry (R3 space group) at higher pH values and the second of monoclinic symmetry (space group P21) with unit-cell parameters a = 87.4282 (5), b = 70.5020 (3), c = 48.3180 (4) Å, ß = 106.8958 (4)°, the latter of which to our knowledge has never been observed before.

Giant magneto-elastic coupling in multiferroic hexagonal manganites.

The motion of atoms in a solid always responds to cooling or heating in a way that is consistent with the symmetry of the given space group of the solid to which they belong. When the atoms move, the electronic structure of the solid changes, leading to different physical properties. Therefore, the determination of where atoms are and what atoms do is a cornerstone of modern solid-state physics. However, experimental observations of atomic displacements measured as a function of temperature are very rare, because those displacements are, in almost all cases, exceedingly small. Here we show, using a combination of diffraction techniques, that the hexagonal manganites RMnO3 (where R is a rare-earth element) undergo an isostructural transition with exceptionally large atomic displacements: two orders of magnitude larger than those seen in any other magnetic material, resulting in an unusually strong magneto-elastic coupling. We follow the exact atomic displacements of all the atoms in the unit cell as a function of temperature and find consistency with theoretical predictions based on group theories. We argue that this gigantic magneto-elastic coupling in RMnO3 holds the key to the recently observed magneto-electric phenomenon in this intriguing class of materials.

Parameters of the reproductive tract, spermatogenesis, daily sperm production and major seminal plasma proteins of tropically adapted morada nova rams.

This study describes the reproductive parameters of Morada Nova rams, a breed of hair sheep from Brazil and with unique adaption to tropical environments. At 42 weeks of age, 15 rams were subjected to semen collection and, 1 week later, animals were slaughtered for collection of testes, epididymis and accessory sex glands. We conducted 2-D electrophoresis of seminal plasma proteins and major spots of stained gels were identified by LC-MS/MS. Total RNA was isolated from testis, epididymis and vesicular glands and subjected to qPCR. At slaughter, scrotal circumference and testicular weight were 27.5 ± 0.5 cm and 109.5 ± 6.0 g, respectively. Seminiferous tubule (ST) diameter was 188.3 ± 4.0 µm and each testis contained 1.9 ± 0.1 Sertoli cells (×10(9) ). Each Sertoli cell supported 0.1 ± 0.01 A spermatogonia, 3.0 ± 0.2 pachytene spermatocytes and 7.7 ± 0.5 round spermatids/tubule cross section. Daily sperm production reached 5.6 × 10(6)  cells/g of testis parenchyma. Testis size appeared as indicative of ST diameter and associated with epididymal measurements, as well as with the population of round spermatids and Sertoli cells/testis. Rams with heavier testes had greater daily sperm production and more Sertoli cells/testis. We detected 90.9 ± 9.6 spots per 2-D gel of seminal plasma. Major seminal proteins were identified as ram seminal vesicle proteins at 14 and 22 kDa, representing 16.2% and 12.8% of the total intensity of valid spots in the gels, respectively. Expression of both genes was greater in the vesicular glands as compared to testis and epididymis. Pixel intensity for those proteins in the 2-D gels was significantly correlated with seminal vesicle weight. This is the first description of the basic reproductive aspects of Morada Nova rams, including protein profiles of their seminal plasma. These findings will allow a better understanding of their reproductive physiology.

The Materials Science beamline upgrade at the Swiss Light Source.

The Materials Science beamline at the Swiss Light Source has been operational since 2001. In late 2010, the original wiggler source was replaced with a novel insertion device, which allows unprecedented access to high photon energies from an undulator installed in a medium-energy storage ring. In order to best exploit the increased brilliance of this new source, the entire front-end and optics had to be redesigned. In this work, the upgrade of the beamline is described in detail. The tone is didactic, from which it is hoped the reader can adapt the concepts and ideas to his or her needs.

Exploring high-throughput synchrotron X-Ray powder diffraction for the structural analysis of pharmaceuticals.

Synchrotron radiation offers a host of advanced properties, surpassing conventional laboratory sources with its high brightness, tunable phonon energy, photon beam coherence for advanced X-ray imaging, and a structured time profile, ideal for capturing dynamic atomic and molecular processes. However, these benefits come at the cost of operational complexity and expenses. Three decades ago, synchrotron radiation facilities, while technically open to all scientists, primarily served a limited community. Despite substantial accessibility improvements over the past two decades, synchrotron measurements still do not qualify as routine analyses. The intrinsic complexity of synchrotron science means experiments are pursued only when no alternatives suffice. In recent years, strides have been made in technology transfer offices, intermediate synchrotron-based analytical service companies, and the development of high-throughput synchrotron systems at various facilities, reshaping the perception of synchrotron science. This article investigates the practical application of synchrotron X-Ray Powder Diffraction (s-XRPD) techniques in pharmaceutical analysis. By utilizing concrete examples, we demonstrate how high-throughput systems have the potential to revolutionize s-XRPD applications in the pharmaceutical industry, rapidly generating XRPD patterns of comparable or superior quality to those obtained in state-of-the-art laboratory XRPD, all in less than 5 s. Additional cases featuring well-established pharmaceutical active ingredients (API) and excipients substantiate the concept of high throughput in pharmaceuticals, affirming data quality through structural refinements aligned with literature-derived unit cell parameters. Synchrotron data need not always be state-of-the-art to compete with lab-XRPD data. The key lies in ensuring user-friendliness, reproducibility, accessibility, cost-effectiveness, and the streamlined efforts associated with synchrotron instrumentation to remain highly competitive with their laboratory counterparts.

Chemical composition of lipids present in cat and dog oocyte by matrix-assisted desorption ionization mass spectrometry (MALDI- MS).

The aim of the present study was to investigate the level of information on the chemical structures and relative abundances of lipids present in cat and dog oocytes by matrix-assisted laser desorption mass spectrometry (MALDI-MS). The MALDI-MS approach requires a simple analysis workflow (no lipid extraction) and few samples (two or three oocytes per analysis in this work) providing concomitant profiles of both intact phospholipids such as sphingomyelins (SM) and phosphatidylcholines (PC) as well as triacylglycerols (TAG). The lipids were detected in oocytes by MALDI using dihydroxybenzoic acid (DHB) as the matrix. The most abundant lipid present in the MS profiles of bitch and queen oocytes was a PC containing 34 carbons and one unsaturation [PC (34:1)]. Oocytes of these two species are characterized by differences in PC and TAG profiles detected qualitatively as well as by means of principal component analysis (PCA). Cat oocytes were mainly discriminated by more intense C52 and C54 TAG species and a higher number of unsaturations, indicating predominantly linoleic and oleic fatty acyl residues. Comparison of the lipid profile of bitch and queen oocytes with that of bovine oocytes revealed some similarities and also some species specificity: TAG species present in bovine oocytes were also present in bitches and queens; however, a more pronounced contribution of palmitic, stearic and oleic fatty acid residues was noticed in the lipid profile of bovine oocytes. MALDI-MS provides novel information on chemical lipid composition in canine and feline oocytes, offering a suitable tool to concomitantly monitor, in a nearly direct and simple fashion the composition of phospholipids and TAG. This detailed information is highly needed to the development of improved protocols for in vitro culture and cryopreservation of cat and dog oocytes.

A High Energy X-ray Diffraction Study of Amorphous Indomethacin.

Amorphous pharmaceuticals often possess a wide range of molecular conformations and bonding arrangements. The x-ray pair distribution function (PDF) method is a powerful technique for the characterization of variations in both intra-molecular and inter-molecular packing arrangements. Here, the x-ray PDF of amorphous Indomethacin is shown to be particularly sensitive to the preferred orientations of the chlorobenzyl ring found in isomers in the crystalline state. In some cases, the chlorobenzyl ring has no preferred torsional angle in the amorphous form, while in others evidence of distinct isomer orientations are observed. Amorphous samples with no preferred torsion angles of the chlorobenzyl ring are found to favor enhanced inter-molecular hydrogen bonding, and this is reflected in the intensity of the first sharp diffraction peak. These significant variations in structure rule out amorphous Indomethacin as a possible standard for x-ray PDF measurements. At high humidity, time resolved PDF's for >40 h reveal water molecules forming hydrogen bonds with Indomethacin molecules. A simple linear hydrogen bond model indicates that water molecules in the wet amorphous form have similar hydrogen bond strengths to those found between Indomethacin dimers or chains in the dry amorphous form.

Clonostachys rosea BAFC3874 as a Sclerotinia sclerotiorum antagonist: mechanisms involved and potential as a biocontrol agent.

AIMS: To establish the modes of action of the antagonistic fungal strain Clonostachys rosea BAFC3874 isolated from suppressive soils against Sclerotinia sclerotiorum and to determine its potential as a biocontrol agent. METHODS AND RESULTS: The antagonistic activity of C. rosea BAFC3874 was determined in vitro by dual cultures. The strain effectively antagonized S. sclerotiorum in pot-grown lettuce and soybean plants. Antifungal activity assays of C. rosea BAFC3874 grown in culture established that the strain produced antifungal compounds against S. sclerotiorum associated with secondary metabolism. High mycelial growth inhibition coincided with sclerotia production inhibition. The C. rosea strain produced a microheterogeneous mixture of peptides belonging to the peptaibiotic family. Moreover, mycoparasitism activity was observed in the dual culture. CONCLUSIONS: Clonostachys rosea strain BAFC3874 was proved to be an effective antagonist against the aggressive soil-borne pathogen S. sclerotiorum in greenhouse experiments. The main mechanisms involve peptaibiotic metabolite production and mycoparasitism activity. SIGNIFICANCE AND IMPACT OF THE STUDY: Clonostachys rosea BAFC3874 may be a good fungal biological control agent against S. sclerotiorum. In addition, we were also able to isolate and identify peptaibols, an unusual family of compounds in this genus of fungi.

Beam-induced damage on diffractive hard X-ray optics.

The issue of beam-induced damage on diffractive hard X-ray optics is addressed. For this purpose a systematic study on the radiation damage induced by a high-power X-ray beam is carried out in both ambient and inert atmospheres. Diffraction gratings fabricated by three different techniques are considered: electroplated Au gratings both with and without the polymer mold, and Ir-coated Si gratings. The beam-induced damage is monitored by X-ray diffraction and evaluated using scanning electron microscopy.

The role of the quaternary structure in the activation of human L-asparaginase.

Human L-asparaginase-like protein 1 (ASRGL1) has hydrolytic activity against L-asparagine and isoaspartyl dipeptides. As an N-terminal nucleophile hydrolase family member, its activation depends on an intramolecular autoprocessing step between G167 and T168. In vitro, autoprocessing reaches only 50% completion, which restrains the activity and hampers the full understanding of the activation process. The ASRGL1 dimer interface plays a critical role in intramolecular processing, and the interactions within oligomers can offer relevant information about autoprocessing. In this work, a fully processed trimeric conformation of ASRGL1 was observed for the first time, and we combined biophysical and structural proteomics assays to characterize trimeric ASRGL1. Our analyses show that oligomerization is critical for autoprocessing, hydrolytic activity and thermal stability. The newest trimeric ASRGL1 conformation enhances protein activity and presents a melting temperature deviation of 4.33 °C in comparison to the monomeric conformation. The interaction of the third monomer in the trimeric conformation is driven by an α-helix comprising residues KVNLARLTLF (227-236).

Analysis of the healthy rabbit lens surface using MAC Mode atomic force microscopy.

In this investigation healthy rabbit crystalline lenses were characterized by atomic force microscopy (AFM). The lenses were cut in slices with thickness with 1mm and thus, put after cortex distinct regions of nucleus and cortex for AFM examination. AFM analysis were carried out using a PicoSPM I operating in Mac Mode. We obtained topographic images of rabbit lenses and a quantitative analysis of the width and height of fibers for nucleus and cortex regions. The longitudinal section analysis of fibers in the nucleus region indicated structures with an average width of 200nm and average height of 200nm. The intershells distance was determined as 4microm. Fiber cell cross-section dimensions, longitudinal and transverse widths, could be estimated in these regions from the AFM images. Structures with average widths as small as 1.0microm are observed in the nucleus; the intershell distance is 4.0microm. In cortical regions, hexagonal structures with average longitudinal and transverse widths of 5.0mum and 3.0mum, respectively, were identified. Three-dimensional images of tissue sections with resolution on a nanometer scale were obtained. The potential of AFM analysis for characterizing healthy and pathologic lens tissues is discussed.

Smile and laughter elicited by electrical stimulation of the frontal operculum.

Laughter and smile are typical expressions of mirth and fundamental means of social communication. Despite their general interest, the current knowledge about the brain regions involved in the production of these expressions is still very limited, and the principal insights come from electrical stimulation (ES) studies in patients, in which, nevertheless, laughter or smile have been elicited very rarely. Previous studies showed that laughter is evoked by the stimulation of nodes of an emotional network encompassing the anterior cingulate, the superior frontal and basal temporal cortex. A common feature of these stimulation studies is that the facial expression was always accompanied by motor awareness and often by mirth, in line with the affective functions attributed to these regions. Little is known, in contrast, on the neural basis of the voluntary motor control of this expression. The objective of this study was to investigate the effect of ES of the frontal operculum (FO), which is considered a crucial node for the linkage of the voluntary motor system for emotional expression and limbic emotional network. We report the case of ES applied to the frontal operculum (FO) in four patients with drug-resistant focal epilepsy undergoing stereo-electroencephalographic (SEEG) implantation of intracerebral electrodes. In all patients, ES applied to the FO produced laughter or smile. Interestingly, in one patient, the production of a smiling expression was also clearly accompanied by the lack of motor awareness. Since the lack of motor awareness has been previously observed only after the stimulation of the voluntary motor network, we speculate that FO is involved in the voluntary control of facial expressions, and is placed at the interface with the emotional network, gating limbic information to the motor system.

ACE gene titration in mice uncovers a new mechanism for ACE on the control of body weight.

Mice harboring 1, 2, or 3 copies of the angiotensin-converting enzyme (ACE) gene were used to evaluate the quantitative role of the ACE locus on obesity. Three-copy mice fed with a high-fat diet had lower body weight and peri-epididymal adipose tissue than did 1- and 2-copy mice (P < 0.05). On regular diet, 3-copy mice had to eat more to maintain the same body weight; on a high-fat diet, they ate the same but weighed less than 1- and 2-copy mice (P < 0.05), indicating a higher metabolic rate in 3-copy mice that was not affected by ANG II AT(1) blocker treatment. A catalytically inactive form of thimet oligopeptidase (EC 3.4.24.15; EP24.15) was used to isolate ACE substrates from adipose tissue. Liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) identified 162 peptide peaks; 16 peptides were present in both groups (1- and 3-copy mice fed with a high-fat diet), whereas 58 of the 72 unique peptides were found only in the 3-copy mice. Peptide size distribution was shifted to lower molecular weight in 3-copy mice. Two of the identified peptides, LVVYPWTQRY and VVYPWTQRY, which are ACE substrates, inhibited in vitro protein kinase C phosphorylation in a concentration-dependent manner. In addition, neurolysin (EC 3.4.24.16; EP24.16) activity was lower in fat tissue from 3- vs. 1-copy mice (P < 0.05). Taken together, these results provide evidence that ACE is associated with body weight and peri-epididymal fat accumulation. This response may involve the generation of oligopeptides that inhibit the activity of EP24.16 and other oligopeptidases within the adipose tissue.

Surgical treatment of cavernoma-related epilepsy.

Cerebral cavernous malformations (CCMs) are frequently associated with a seizure disorder, and the risk of developing drug-resistant epilepsy (DRE) is substantial, especially for temporal lobe lesions. This article includes a review of the literature on the surgical treatment of epilepsy associated to CCMs in the magnetic resonance imaging (MRI) era, as well as an analysis of the Authors' experience in this field. It is concluded that microsurgery is a valuable treatment option, which may provide excellent results on seizures, with 76% of patients on average being seizure-free after surgery. Nevertheless, the optimal surgical strategy to achieve seizure control has not been clearly identified, and several attitudes have been reported in the literature. The choice of lesionectomy, associated or not to removal of surrounding hemosiderin, versus resections extended to epileptogenic cortex depends on the accurate scrutiny of several factors, which should be investigated through an adequate epileptological presurgical workup. This should include an epilepsy-oriented brain MRI study, integrated by an appropriate neurophysiological and clinical assessment, and if needed by other functional evaluations. Besides representing the optimal option in CCM-related DRE cases, microsurgery should be considered also at seizure presentation or in cases with recent-onset sporadic seizures, to protect the patient from both the possible development of drug resistance and the risk of haemorrhage.

Human insulin polymorphism upon ligand binding and pH variation: the case of 4-ethylresorcinol.

This study focuses on the effects of the organic ligand 4-ethylresorcinol on the crystal structure of human insulin using powder X-ray crystallography. For this purpose, systematic crystallization experiments have been conducted in the presence of the organic ligand and zinc ions within the pH range 4.50-8.20, while observing crystallization behaviour around the isoelectric point of insulin. High-throughput crystal screening was performed using a laboratory X-ray diffraction system. The most representative samples were selected for synchrotron X-ray diffraction measurements, which took place at the European Synchrotron Radiation Facility (ESRF) and the Swiss Light Source (SLS). Four different crystalline polymorphs have been identified. Among these, two new phases with monoclinic symmetry have been found, which are targets for the future development of microcrystalline insulin drugs.

The ionized methylene transfer from the distonic radical cation (+)CH 2-O-CH 2 to heterocyclic compounds. A pentaquadrupole mass spectrometric study.

Ion-molecule reactions of the mass-selected distonic radical cation (+)CH2-O-CH 2 (·) (1) with several heterocyclic compounds have been investigated by multiple stage mass spectro- metric experiments performed in a pentaquadrupole mass spectrometer. Reactions with pyridine, 2-, 3-, and 4-ethyl, 2-methoxy, and 2-n-propyl pyridine occur mainly by transfer of CH 2 (+·) to the nitrogen, which yields distonic N-methylene-pyridinium radical cations. The MS(3) spectra of these products display very characteristic collision-induced dissociation chemistry, which is greatly affected by the position of the substituent in the pyridine ring. Ortho isomers undergo a δ-cleavage cyclization process induced by the free-radical character of the N-methylene group that yields bicyclic pyridinium cations. On the other hand, extensive CH 2 (+·) transfer followed by rapid hydrogen atom loss, that is, a net CH(+) transfer, occurs not to the heteroatoms, but to the aromatic ring of furan, thiophene, pyrrole, and N-methyl pyrrole. The reaction proceeds through five- to six-membered ring expansion, which yields the pyrilium, thiapyrilium, N-protonated, and N-methylated pyridine cations, respectively, as indicated by MS(3) scans. Ion 1 fails to transfer CH 2 (+·) to tetrahydrofuran, whereas a new α-distonic sulfur ion is formed in reactions with tetrahydrothiophene. Unstable N-methylene distonic ions, likely formed by transfer of CH 2 (+·) to the nitrogen of piperidine and pyrrolidine, undergo rapid fragmentation by loss of the α-NH hydrogen to yield closed-shell immonium cations. The most thermodynamically favorable products are formed in these reactions, as estimated by ab initio calculations at the MP2/6-31G(d,p)//6-31G(d,p) + ZPE level of theory.

Multiple stage pentaquadrupole mass spectrometry for generation and characterization of gas-phase ionic species. The case of the PyC2H 5 (+·) isomers.

Eleven isomers with the PyC2H 5 (+·) composition, which include three conventional (1-3) and eight distonic radical cations (4-11), have been generated and in most cases successfully characterized in the gas phase via tandem-in-space multiple-stage pentaquadrupole MS(2) and MS(3) experiments. The three conventional radical cations, that is, the ionized ethylpyridines C2H5-C5H4N(+·) (1-3), were generated via direct 70-eV electron ionization of the neutrals, whereas sequences of chemical ionization and collision-induced dissociation (CID) or mass-selected ion-molecule reactions were used to generate the distonic ions H2C(·)-C5H4N(+)-CH3 (4-6), CH3-C5H4N(+)-CH 2 (·) (7-9), C5H5N(+)-CH2CH 2 (·) (10), and C5H5N(+)-CH(·)-CH3 (11). Unique features of the low-energy (15-eV) CID and ion-molecule reaction chemistry with the diradical oxygen molecule of the isomers were used for their structural characterization. All the ion-molecule reaction products of a mass-selected ion, each associated with its corresponding CID fragments, were collected in a single three-dimensional mass spectrum. Ab initio calculations at the ROMP2/6-31G(d, p)//6-31G(d, p)+ZPE level of theory were performed to estimate the energetics involved in interconversions within the PyC2H5 (+·) system, which provided theoretical support for facile 4⇌7 interconversion evidenced in both CID and ion-molecule reaction experiments. The ab initio spin densities for the a-distonic ions 4-9 and 11 were found to be largely on the methylene or methyne formal radical sites, which thus ruled out substantial odd-spin derealization throughout the neighboring pyridine ring. However, only 8 and 9 (and 10) react extensively with oxygen by radical coupling, hence high spin densities on the radical site of the distonic ions do not necessarily lead to radical coupling reaction with oxygen. The very typical "spatially separated" ab initio charge and spin densities of 4-11 were used to classify them as distonic ions, whereas 1-3 show, as expected, "localized" electronic structures characteristic of conventional radical ions.

Differential inhibition of Candida albicans CYP51 with azole antifungal stereoisomers.

Azole antifungal compounds are important in agriculture and in the treatment of mycotic infection. The target enzyme, sterol 14 alpha-demethylase (CYP51), is inhibited through binding of triazole N-4 to the haem of this P450, as a sixth ligand together with the N-1 substituent groups interacting in some way with the apoprotein. Here we use Saccharomyces cerevisiae expression systems for the target enzyme of Candida albicans to investigate binding of enantiomers of the azole antifungal compounds SCH39304 and tetraconazole. A molecular model produced previously provided qualitative explanations for these differences. Interaction of the azole antifungal aromatic group with Phe-233 or -235 may cause the higher activity for (R)-tetraconazole while inactivity of the (SS)-enantiomer of SCH39304 was predicted to result from incompatibility of the hydrophilic sulfonyl moiety when located into the hydrophobic pocket of the active site.

Primary and secondary kinetic isotope effects in proton (H(+)/D(+)) and chloronium ion ((35)Cl(+)/(37)Cl(+)) affinities.

The Cooks' kinetic method and tandem-in-space pentaquadrupole QqQqQ mass spectrometry were used to measure primary and secondary kinetic isotope effects (KIEs) in H(+) and Cl(+) (X(+)) affinity for a series of A/A(') isotopomeric pairs. Gaseous, isotopomeric, and loosely bound dimers [A...X(+)...A(')] were formed in combinations in which X = H(+), D(+), (35)Cl(+) or (37)Cl(+) and A/A(') = acetonitrile/acetonitrile - d(3), acetonitrile/acetonitrile-(15)N, acetonitrile-d(3)/acetonitrile-(15)N, acetone/acetone-d(6), acetone/acetone-(18)O, acetone-d(6)/acetone-(18)O, pyridine/pyridine-d(5), pyridine/pyridine-(15)N, pyridine-d(5)/pyridine-(15)N, or 3-((35)Cl)chloropyridine/3-((37)Cl)chloropyridine. Under nearly the same experimental conditions, the dimers were mass-selected and then dissociated by low-energy collisions with argon, yielding AX(+) and A(')X(+) as the fragment ions. KIEs were measured from the changes in ion affinities of the neutrals (DeltaX(+)) as estimated by the AX(+)/A(')X(+) abundance ratios. Using [A...H(+)(D(+))...A(')] and [A...(35)Cl(+)((37)Cl(+))...A(')] dimers and by comparing their extent of dissociation under nearly identical collision-induced dissociation conditions, the kinetic method was also applied, for the first time, to measure primary KIEs of the central ion as well as their influence on secondary KIEs. Becke3LYP/6-311++G(2df,2p) calculations were found to provide Delta(DeltaZPE)s for the competitive dissociation reactions that accurately predict the nature (normal or inverse) of the measured KIEs.