Atomistic Picture of Fluorescent Probes with Hydrocarbon Tails in Lipid Bilayer Membranes: An Investigation of Selective Affinities and Fluorescent Anisotropies in Different Environmental Phases.

By reverting to spectroscopy, changes in the biological environment of a fluorescent probe can be monitored and the presence of various phases of the surrounding lipid bilayer membranes can be detected. However, it is currently not always clear in which phase the probe resides. The well-known orange 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbo-cyanine perchlorate (DiI-C18(5)) fluorophore, for instance, and the new, blue BODIPY (4,4-difluoro-4-bora-3 a,4 a-diaza- s-indacene) derivative were experimentally seen to target and highlight identical parts of giant unilamellar vesicles of various compositions, comprising mixtures of dipalmitoylphosphatidylcholine (DPPC), dioleoylphosphatidylcholine (DOPC), sphingomyelin (SM), and cholesterol (Chol). However, it was not clear which of the coexisting membrane phases were visualized (Bacalum et al., Langmuir. 2016, 32, 3495). The present study addresses this issue by utilizing large-scale molecular dynamics simulations and the z-constraint method, which allows evaluating Gibbs free-energy profiles. The current calculations give an indication why, at room temperature, both BODIPY and DiI-C18(5) probes prefer the gel (So) phase in DOPC/DPPC (2:3 molar ratio) and the liquid-ordered (Lo) phase in DOPC/SM/Chol (1:2:1 molar ratio) mixtures. This study highlights the important differences in orientation and location and therefore in efficiency between the probes when they are used in fluorescence microscopy to screen various lipid bilayer membrane phases. Dependent on the lipid composition, the angle between the transition-state dipole moments of both probes and the normal to the membrane is found to deviate clearly from 90°. It is seen that the DiI-C18(5) probe is located in the headgroup region of the SM/Chol mixture, in close contact with water molecules. A fluorescence anisotropy study also indicates that DiI-C18(5) gives rise to a distinctive behavior in the SM/Chol membrane compared to the other considered membranes. The latter behavior has not been seen for the studied BODIPY probe, which is located deeper in the membrane.

Strong electronic coupling dominates the absorption and fluorescence spectra of covalently bound BisBODIPYs.

The absorption spectrum of a representative BisBODIPY molecule is investigated using high-level quantum chemical methodology; the results are compared with experimental data. The S1 and S2 excited states are examined in detail to illuminate and to understand the electronic coupling between them. With the help of model systems in which the distance between the BODIPY monomers is increased or in which the dihedral angle between the subunits is changed, the electronic coupling is quantified, and its influence on energetics and oscillator strengths is highlighted. For the explanation of the experimental spectrum, orbital interaction effects are found to be important. Because of the large experimental Stokes shift of BisBODIPY, the nature of the emissive state is investigated and found to remain C2 symmetric as the ground state, and no localization of the excitation on one BODIPY subunit occurs. The excitonic coupling is in BisBODIPY still larger than the geometry relaxation energy, which explains the absence of a pseudo-Jahn-Teller effect.

Higher levels of reported sun exposure, and not vitamin D status, are associated with less depressive symptoms and fatigue in multiple sclerosis.

OBJECTIVE: Insufficient sun exposure and vitamin D deficiency have both been associated with increased risk of multiple sclerosis (MS). Depressi on, anxiety, fatigue and cognitive impairment are prevalent and disabling symptoms in MS. Our objective was to examine the associations between personal sun exposure and serum 25-hydroxyvitamin D (25(OH)D), and depression, anxiety, fatigue and cognition. METHODS: A total of 198 participants with multiple sclerosis were followed prospectively for an average of 2.3 years. Assessments of serum 25(OH)D, sun exposure, depression, anxiety and fatigue were carried out biannually; cognition was assessed annually. RESULTS: Personal reported sun exposure was inversely associated with depression scores (ß -0.26 (95%CI -0.40, -0.12);P ≤ 0.001) and fatigue scores (ß -0.65 (95%CI -1.23, -0.07); P = 0.028). Only high levels of 25(OH)D (>80 nm) were inversely associated depression scores (ß -0.64 (95%CI -1.15, -0.13); P = 0.015), but this was not significant after adjustment for reported sun exposure. No associations were seen between reported sun exposure or serum 25(OH)D levels and anxiety or cognition scores. CONCLUSION: We found that higher levels reported sun exposure, rather than 25(OH)D levels, were associated with less depressive symptoms and levels of fatigue. The role of UV or light therapy will need to be evaluated in randomized controlled trials to confirm an effect on these symptoms in MS.

Humoral immune response after SARS-CoV-2 vaccination in cladribine-treated multiple sclerosis patients.

Multiple sclerosis immunomodulatory treatments such as cladribine, which affects both B- and T-lymphocytes, can potentially alter the humoral response to SARS-CoV-2 vaccination. This monocenter retrospective study reports on anti-SARS-CoV-2 IgG antibody response in cladribine treated MS patients and we compare the response in patients vaccinated before and after an 18-week interval after last cladribine dose. Of the 34 patients (5 patients ≤ 18 weeks and 29 patients > 18 weeks after last cladribine dose) that were included, 32 reached seropositivity (94 %). All patients vaccinated < 18 weeks after last cladribine dose reached seropositivity. This study confirms findings of earlier reports that cladribine-treated MS patients show an adequate humoral response after SARS-CoV-2 vaccination, even when vaccinated early (≤18 weeks) after last cladribine dose.

Regulatory B cells in ANCA-associated vasculitis.

OBJECTIVES: B cells have immunoregulatory function acting as antigen-presenting cells. A separate subset of interleukin (IL)-10 producing B cells (Breg) regulating T cell mediated immunity has been identified. In the present study, we investigated the role of Breg in antineutrophil cytoplasmic antibodies-associated vasculitis (AAV). METHODS: 17 healthy controls (HCs) and 41 patients with AAV were enrolled. 30 patients with AAV were in remission. Furthermore, 11 patients with AAV with active disease were studied. Breg were defined as IL-10(+)CD19(+) B cells upon culture with cytosine-phosphate-guanosine oligodeoxynucleotide (CpG ODN) 2006. Next to Breg, CD4(+)CD127(low)CD25(hi)CD39(neg)/CD39(+) regulatory T-cells (Treg), interferon (IFN)γ(+), IL-4(+) and Il-17A(+)T helper cell subsets were determined via flow cytometry. RESULTS: Patients with active or quiescent disease showed a diminished fraction of Breg as compared with HCs. The frequency of IFNγ(+) T helper cells was negatively associated with Breg in untreated AAV in remission but not in active vasculitis or in HCs. Interestingly, the total Treg population and the CD39(+) Treg subpopulation correlated positively with Breg in inactive patients with AAV. CONCLUSIONS: IL-10 producing B cells are diminished in AAV. Furthermore, Breg might regulate Th1 cells and are associated with Treg in quiescent AAV. Suppression of Th1 cells by Breg may be insufficient in active AAV.

The molecular mechanism of photochromism in photo-enolizable quinoline and napthyridine derivatives.

Photochromism, the change of color upon irradiation, is a general property of quinoline derivatives, yet subtle differences in the geometric structure influence its occurrence. To investigate this relation, the mechanism of photoenolization of the photochromic compounds 3-benzoyl-2-benzyl-1-methyl-1H-quinoline-4-one (1) and 3-benzoyl-1,2-dibenzyl-1H-1,8 naphtyridin-4-one (2) as well as of the structurally closely related but nonphotochromic 3-benzoyl-1-benzyl-2-methyl-1H-1,8-naphtyridin-4-one (3) has been investigated theoretically using state-of-the-art quantum chemical methods. Focusing on the difference between 2 and 3 and stressing the absence of a phenyl group in the latter, the excited state potential energy surfaces along the photoenolization coordinate have been calculated for both. While the initial proton transfer initializing photoenolization is feasible when the phenyl group is present in 1 and 2, it is suppressed in 3.

Calculations of nonlinear response properties using the intermediate state representation and the algebraic-diagrammatic construction polarization propagator approach: two-photon absorption spectra.

An earlier proposed approach to molecular response functions based on the intermediate state representation (ISR) of polarization propagator and algebraic-diagrammatic construction (ADC) approximations is for the first time employed for calculations of nonlinear response properties. The two-photon absorption (TPA) spectra are considered. The hierarchy of the first- and second-order ADC∕ISR computational schemes, ADC(1), ADC(2), ADC(2)-x, and ADC(3/2), is tested in applications to H(2)O, HF, and C(2)H(4) (ethylene). The calculated TPA spectra are compared with the results of coupled cluster (CC) models and time-dependent density-functional theory (TDDFT) calculations, using the results of the CC3 model as benchmarks. As a more realistic example, the TPA spectrum of C(8)H(10) (octatetraene) is calculated using the ADC(2)-x and ADC(2) methods. The results are compared with the results of TDDFT method and earlier calculations, as well as to the available experimental data. A prominent feature of octatetraene and other polyene molecules is the existence of low-lying excited states with increased double excitation character. We demonstrate that the two-photon absorption involving such states can be adequately studied using the ADC(2)-x scheme, explicitly accounting for interaction of doubly excited configurations. Observed peaks in the experimental TPA spectrum of octatetraene are assigned based on our calculations.

Vitamin D status in patients with MS is negatively correlated with depression, but not with fatigue.

BACKGROUND: Depressive symptoms and fatigue are frequent and disabling symptoms of multiple sclerosis (MS). Depression and fatigue have been associated with a poor vitamin D status, and a poor vitamin D status is often found in MS. AIM: Assess whether vitamin D status contributes to depressive symptoms and fatigue in MS. METHODS: Patients with MS that participated in previous studies in which depression and fatigue were assessed and of whom serum 25-hydroxyvitamin D (25(OH)D) levels were available within a timeframe of less than one half-life of 25(OH)D were included. Depression and fatigue were assessed with the Hospital Anxiety and Depression Scale and the Multidimensional Fatigue Inventory. RESULTS: Fifty-nine patients were included. Mean scores of fatigue and depression were 14.6 (SD 4.2) and 6.2 (SD 4.4), respectively. The mean vitamin D status was 62.3 nm (SD 27.8). Vitamin D status correlated negatively with depression (r=-0.326, P=0.006). No significant correlation was found between vitamin D status and fatigue. In a multiple regression model, vitamin D status was not a significant contributor to depression, after controlling for age Expanded Disability Status Scale score and fatigue (P=0.078). Alternatively, depression and fatigue did not contribute to vitamin D status. DISCUSSION: This study shows a negative correlation between vitamin D status and depressive symptoms in patients with MS. Although multiple confounders exist, we observed an indication that vitamin D status might contribute to the presence of depressive symptoms in MS. Therefore, further studies on vitamin D in MS should include depressive symptoms as outcome measures to confirm these findings.

Quantum chemical study of conformational fingerprints in the photoelectron spectra and (e, 2e) electron momentum distributions of n-hexane.

The main purpose of the present work is to simulate from many-body quantum mechanical calculations the results of experimental studies of the valence electronic structure of n-hexane employing photoelectron spectroscopy (PES) and electron momentum spectroscopy (EMS). This study is based on calculations of the valence ionization spectra and spherically averaged (e, 2e) electron momentum distributions for each known conformer by means of one-particle Green's function [1p-GF] theory along with the third-order algebraic diagrammatic construction [ADC(3)] scheme and using Kohn-Sham orbitals derived from DFT calculations employing the Becke 3-parameters Lee-Yang-Parr (B3LYP) functional as approximations to Dyson orbitals. A first thermostatistical analysis of these spectra and momentum distributions employs recent estimations at the W1h level of conformational energy differences, by Gruzman et al. [J. Phys. Chem. A 2009, 113, 11974], and of correspondingly obtained conformer weights using MP2 geometrical, vibrational, and rotational data in thermostatistical calculations of partition functions beyond the level of the rigid rotor-harmonic oscillator approximation. Comparison is made with the results of a focal point analysis of these energy differences using this time B3LYP geometries and the corresponding vibrational and rotational partition functions in the thermostatistical analysis. Large differences are observed between these two thermochemical models, especially because of strong variations in the contributions of hindered rotations to relative entropies. In contrast, the individual ionization spectra or momentum profiles are almost insensitive to the employed geometry. This study confirms the great sensitivity of valence ionization bands and (e, 2e) momentum distributions on the molecular conformation and sheds further light on spectral fingerprints of through-space methylenic hyperconjugation, in both PES and EMS experiments.

Increased inflammasome related gene expression profile in PBMC may facilitate T helper 17 cell induction in multiple sclerosis.

The NLRP3 inflammasome is a macromolecular complex importantly involved in IL-1ß processing. A role for this has been described in multiple sclerosis (MS). One mechanism by which IL-1ß might be involved in MS is by inducing pathogenic Th17 cells, i.e. GM-CSF+ Th17 cells. In the present study, we show that expression of the inflammasome related genes, NLRP3, caspase-1, IL-1ß and the IL-1ß/IL-1Ra ratio, was increased in PBMC from MS patients compared to healthy controls (HC). However, in an in vitro inflammasome activity assay with PBMC, IL-1ß protein secretion and the IL-1ß/IL-1Ra protein ratio were similar in MS patients and HC. Th cells cultured in the presence of supernatant derived from LPS/ATP inflammasome activated PBMC showed increased Th17 and GM-CSF+ Th17 cell frequencies in HC and MS patients and decreased anti-inflammatory IL-10+Th cell frequency in HC compared to Th cells cultured in the presence of control supernatant. Moreover, addition of the immune modulator calcitriol to the former condition resulted in reduced frequencies of Th17 and GM-CSF+Th17 cells, and also of IL-10+ Th cells. Evidently, our data indicate that inflammasome activity can skew the Th cell population toward a more pro-inflammatory composition, an effect that might be inhibited by vitamin D, and that might be importantly involved in inflammation within the central nervous system.

GM-CSF production by CD4+ T cells in MS patients: regulation by regulatory T cells and vitamin D.

BACKGROUND/OBJECTIVE: Data from animal models of MS suggest that GM-CSF(+)CD4(+)T cells are pathogenic cells. Therefore, GM-CSF production by CD4(+)T cells of MS patients and their susceptibility to regulatory mechanisms were investigated. METHODS: Intracellular flowcytometry was performed to determine the GM-CSF(+)CD4(+)T cell fraction in PBMC and CSF of MS patients and controls. The effect of regulatory T cells (Tregs) on GM-CSF production by CD4(+)T cells was studied in MS patients using a proliferation-suppression assay. Finally, GM-CSF(+)CD4(+)T cell fraction and GM-CSF protein levels in supernatant were assessed in anti-CD3-stimulated CD4(+)T cell cultures derived from healthy controls and MS patients, in the presence or absence of the active vitamin D metabolite calcitriol. RESULTS: The GM-CSF(+)CD4(+)T cell fraction in the peripheral blood did not differ between controls and MS patients. This T cell population could also be detected in the CSF of both subjects with MS as well as subjects with another diagnosis. In the CSF, it comprised a significant fraction of the T cell population. Upon in vitro stimulation of PBMC with anti-CD3 antibody, no differences were observed in GM-CSF(+)CD4(+)T cell frequencies. GM-CSF secretion was susceptible to regulation by Treg and vitamin D. Suppression of GM-CSF secretion by vitamin D was reduced in MS patients. CONCLUSIONS: Our study showed no elevation in GM-CSF(+)CD4(+)T cell fractions in MS patients compared to controls. Furthermore, GM-CSF secretion was prone to regulation by Treg and vitamin D, the latter being less effective in MS patients.

Safety of three toothbrushes.

PURPOSE: To assess the oral soft tissue safety and tolerability of two electric toothbrushes, the Crest Spin Brush and Colgate ActiBrush, and one manual toothbrush, the Oral B 40. MATERIALS AND METHODS: A total of 104 subjects were enrolled in this single center, randomized, examiner-blind parallel study over a 4-wk test period. Subjects were randomized to treatment and were instructed to brush in their normal manner, twice per day for 60 s. A detailed oral soft tissue examination and interview were conducted by a trained clinician at baseline, 3 days and 4 wks to assess clinical signs and symptoms associated with use of the toothbrushes. RESULTS: Over the 4-wk period, a total of 19 subjects (18% of the study population) were observed for signs/symptoms. The adverse events were distributed across test groups with 12 subjects in the Oral B 40 group, 4 subjects in the Crest Spin Brush group, and 3 subjects in the Colgate ActiBrush group experiencing at least one adverse event. All adverse events were mild in severity indicating the general safety of all three toothbrushes. The most frequently encountered event was localized gingivitis. The Oral B 40 test group was observed with more adverse events when compared to the Crest Spin Brush and Colgate ActiBrush at 4 wks but not at 3 days. The proportion of subjects experiencing an adverse event in the Crest Spin Brush test group was similar to that of Colgate ActiBrush group. All three toothbrushes were generally well tolerated by subjects enrolled in the study with the Crest Spin Brush and Colgate ActiBrush being the best tolerated. CLINICAL SIGNIFICANCE: The results of this study indicated that abnormal oral soft tissue findings were distributed among the treatment groups, indicating that daily use of an electric toothbrush is at least as safe as a manual toothbrush.

Effect of denture adhesive on retention of the mandibular and maxillary dentures during function.

The purpose of this study was to determine the effect of denture adhesive on retention of mandibular and maxillary dentures over a four-hour period. Denture movements were measured using an alternating magnetic field tracking device that determines the position of magnetic receiver coils relative to a transmitter coil positioned over the head. Ten adults with complete maxillary dentures and complete mandibular implant overdentures were enrolled in the study. Specially fabricated mandibular dentures contained a relief area that exposed the implant post which no longer anchored the denture, but now served as an attachment point for a receiver coil that measured mandibular movement. The denture coil was attached lateral to the post coil on a shelf cut into the denture. Mandibular denture movements were recorded as the difference between the mandible movement signal and the mandible + mandibular denture signals. Measurements of denture movements were made at baseline (no adhesive) and at 0, 2, 4 hours post-adhesive application with Fixodent cream for standardized chewing and biting. The MoveTrack signals were recorded on a digital data cassette recorder for subsequent computer analysis. The results of the measurements were analyzed using paired sample t-tests. Specifically, the following comparisons of movement means were made: mandibular vs. maxillary, baseline vs. post-baseline and successive changes (e.g., baseline vs. hour 0, hour 0 vs. hour 2, etc.). Results of these analyses showed that: 1) mandibular denture movements under both adhesive and non-adhesive conditions were significantly greater than maxillary denture movements; 2) the adhesive significantly reduced movement of the maxillary and mandibular dentures during both chewing and biting; and 3) the improvement occurred immediately post-application of the adhesive and was maintained for the four hours of follow-up.

A comparison of intraoral antimicrobial effects of stabilized stannous fluoride dentifrice, baking soda/peroxide dentifrice, conventional NaF dentifrice and essential oil mouthrinse.

The intraoral antimicrobial activity of four commercial oral products-conventional NaF dentifrice (Crest), baking soda/peroxide/NaF dentifrice (Mentadent), essential oil mouthrinse (Listerine) and SnF2 dentifrice (Crest Plus Gum Care)-have been compared in three test regimens. Formulations were compared for their ability to suppress the regrowth and apical extension of dental plaque following toothbrushing during thirty hours of non-brushing where products were used as oral rinses (30-hour plaque regrowth model). Formulations were also compared for their ability to suppress the colony-forming units (cfu) of facultative anaerobic bacteria sampled from buccal gingival surfaces following use (Gingival Surface Microbial Index-GSMI model). Lastly, formulations were compared for effects in suppressing the glycolytic metabolic activity and regrowth activity of in vivo-treated dental plaques sampled at various periods following topical use and incubated under controlled ex vivo conditions (Plaque Glycolysis and Regrowth-PGRM model). In thirty-hour plaque regrowth testing, the rank ordered antimicrobial efficacy of formulations followed SnF2 > essential oils > NaF = water = baking soda/peroxide. In GSMI testing, all formulations were shown to suppress the cfu of facultative anaerobic bacteria relative to baseline, although SnF2 treatment was observed to reduce bacterial levels to a significantly greater degree than NaF dentifrice or baking soda/peroxide dentifrice up to two hours following brushing. In PGRM testing, the SnF2 dentifrice provided significant inhibition of bacterial metabolism and regrowth following topical application when compared with the NaF dentifrice as control. The baking soda/peroxide dentifrice provided no reduction in either bacterial metabolism or regrowth in PGRM. Previous studies had demonstrated modest effects for essential oil rinse in reducing PGRM plaque regrowth, with no effects for this treatment on plaque metabolism. Overall, these results demonstrate that SnF2 dentifrice provides substantial intraoral antimicrobial effects. The essential oil mouthrinse also exhibits significant intraoral antimicrobial effects, albeit apparently less than SnF2 dentifrice. The baking soda/peroxide dentifrice did not produce any antimicrobial effects following in vivo use compared with conventional dentifrice. These results provide mechanistic rationale for the chemotherapeutic efficacy of SnF2 and essential oil formulations in reducing gingivitis, while providing no support for the expectation of clinical efficacy for formulations containing baking soda and peroxide.

Fraction of IL-10+ and IL-17+ CD8 T cells is increased in MS patients in remission and during a relapse, but is not influenced by immune modulators.

In the present study, circulating proportions of CD8(+) T (Tc) cell subsets, including IL-17 (Tc17) and IL-10 (Tc10) producing cells, were assessed in relapsing-remitting MS (RRMS) patients and a possible effect of beta interferon (IFN-ß), glatiramer acetate (GA), and vitamin D (VitD) on these cell subsets was investigated. We show that both Tc17 and Tc10 cell fractions are elevated in the circulation of RRMS patients in remission compared to healthy subjects and that these Tc subsets remain unaffected by current immune modulating regimens.

The band 12 issue of norbornane: a study of higher shake-up states.

In line with a recent study of the electronic structure of the cage compound norbornane (J. Chem. Phys. 121 (2004), 10525; J. Phys. Chem. A 109 (2005), 4267), symmetry adapted cluster expansion configuration interaction (SAC-CI) general R calculations have been performed and compared with results obtained by the third order algebraic diagrammatic construction scheme [ADC(3)]. Comparison has been made with previously performed electron momentum spectroscopy (EMS) and ultraviolet photo-electron measurements. The region around ~25 eV (band 12), characterized by an elaborated band in the EMS spectrum which is missing in previous Green's function and ADC calculations, is investigated. This study is completed with outer-valence Green's function (OVGF) and SAC-CI/SD-R calculations, and results are obtained by employing (single and double) ionization extended second order ADC [ADC(2)-x]. Since ADC(3) only includes 2h-1p shake-up states, while SAC-CI general-R also includes higher order states, the agreement between both methods assures that the higher order shake-up states do not play an important role in the ionization spectrum of norbornane. While the band-12 issue of norbornane is therefore still open for further discussion, a tentative description in terms of ultrafast nuclear dynamical effects and autoionization processes has become more plausible.

In vivo MRI of intraspinally injected SPIO-labelled human CD34+ cells in a transgenic mouse model of ALS.

BACKGROUND/AIM: Administration of stem cells is a promising novel approach for treatment of neurodegenerative diseases. For in vivo monitoring of transplanted cells, non-invasive imaging modalities are needed. In this study we determined the tracking efficiency of a superparamagnetic iron oxide (SPIO)-labelled canine cell line (MTH53A) in vitro as well as the human CD34(+) umbilical cord blood stem cells (hUCBCs) in vitro and in vivo efficiency by magnetic resonance imaging (MRI). MATERIALS AND METHODS: SPIO-labelled MTH53A cells and hUCBCs were scanned in agar gel phantoms at 1.0 T or 7.0 T. For in vivo detection, 100,000 labelled hUCBCs were injected into the spinal cord of a transgenic amyotrophic lateral sclerosis (ALS) mouse and scanned at 7.0 T. RESULTS: In vitro, 100,000 MTH53A cells and 250,000 hUCBCs were visible at 1.0 T. Scanning with 7.0 T revealed 25,000 detectable MTH53A cells. In vivo, 7.0 T MRI showed clear signals of 100,000 implanted cells. CONCLUSION: MRI combined with SPIO nanoparticles provides valuable potential for non-invasive, non-toxic in vivo tracking of cells implanted into the spinal cord.

Imaging momentum orbital densities of conformationally versatile molecules: a benchmark theoretical study of the molecular and electronic structures of dimethoxymethane.

The main purpose of the present work is to predict from benchmark many-body quantum mechanical calculations the results of experimental studies of the valence electronic structure of dimethoxymethane employing electron momentum spectroscopy, and to establish once and for all the guidelines that should systematically be followed in order to reliably interpret the results of such experiments on conformationally versatile molecules. In a first step, accurate calculations of the energy differences between stationary points on the potential energy surface of this molecule are performed using Hartree-Fock (HF) theory and post-HF treatments of improving quality (MP2, MP3, CCSD, CCSD(T), along with basis sets of increasing size. This study focuses on the four conformers of this molecule, namely the trans-trans (TT), trans-gauche (TG), gauche-gauche (G+G+), and gauche-gauche (G+G-) structures, belonging to the C2v, C1, C2, and Cs symmetry point groups, respectively. A focal point analysis supplemented by suited extrapolations to the limit of asymptotically complete basis sets is carried out to determine how the conformational energy differences at 0 K approach the full CI limit. In a second step, statistical thermodynamics accounting for hindered rotations is used to calculate Gibbs free energy corrections to the above energy differences, and to evaluate the abundance of each conformer in the gas phase. It is found that, at room temperature, the G+G+ species accounts for 96% of the conformational mixture characterizing dimethoxymethane. In a third step, the valence one-electron and shake-up ionization spectrum of dimethoxymethane is analyzed according to calculations on the G+G+ conformer alone by means of one-particle Green's function [1p-GF] theory along with the benchmark third-order algebraic diagrammatic construction [ADC(3)] scheme. A complete breakdown of the orbital picture of ionization is noted at electron binding energies above 22 eV. A comparison with available (e,2e) ionization spectra enables us to identify specific fingerprints of through-space orbital interactions associated with the anomeric effect. At last, based on our 1p-GF/ADC(3) assignment of spectral bands, accurate and spherically averaged (e,2e) electron momentum distributions at an electron impact energy of 1200 eV are computed from the related Dyson orbitals. Very significant discrepancies are observed with momentum distributions obtained for several outer-valence levels using standard Kohn-Sham orbitals.

Probing molecular conformations in momentum space: the case of n-pentane.

A comprehensive study, throughout the valence region, of the electronic structure and electron momentum density distributions of the four conformational isomers of n-pentane is presented. Theoretical (e,2e) valence ionization spectra at high electron impact energies (1200 eV+electron binding energy) and at azimuthal angles ranging from 0 degrees to 10 degrees in a noncoplanar symmetric kinematical setup are generated according to the results of large scale one-particle Green's function calculations of Dyson orbitals and related electron binding energies, using the third-order algebraic-diagrammatic construction [ADC(3)] scheme. The results of a focal point analysis (FPA) of relative conformer energies [A. Salam and M. S. Deleuze, J. Chem. Phys. 116, 1296 (2002)] and improved thermodynamical calculations accounting for hindered rotations are also employed in order to quantitatively evaluate the abundance of each conformer in the gas phase at room temperature and reliably predict the outcome of experiments on n-pentane employing high resolution electron momentum spectroscopy. Comparison with available photoelectron measurements confirms the suggestion that, due to entropy effects, the trans-gauche (tg) conformer strongly dominates the conformational mixture characterizing n-pentane at room temperature. Our simulations demonstrate therefore that experimental measurements of (e,2e) valence ionization spectra and electron momentum distributions would very consistently and straightforwardly image the topological changes and energy variations that molecular orbitals undergo due to torsion of the carbon backbone. The strongest fingerprints for the most stable conformer (tt) are found for the electron momentum distributions associated with ionization channels at the top of the inner-valence region, which sensitively image the development of methylenic hyperconjugation in all-staggered n-alkane chains.