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ABSTACTThe type II secretion system (T2SS) is a multiprotein machinery spanning the diderm of gram-negative bacteria. T2SS contributes to the virulence of numerous gram-negative pathogens, including the multidrug resistant species Pseudomonas aeruginosa, Acinetobacter baumanii, Klebsiella pneumonia and Vibrio cholerae. Even though the T2SS has been studied extensively over the past three decades, our understanding of the molecular basis of its biogenesis and of its overall structure still remains unclear. Here we show that the core component of the inner membrane platform, the GspLM membrane protein complex, can be isolated as a dimer of dimers. Importantly, the complex is able to bind the T2SS ATPase, GspE, with high affinity. Finally, we have developed single domain VHH camelid antibodies (nanobodies) against the GspLM complex and have identified a nanobody that effectively prevents the cytoplasmic domain of GspL, GspLcyto, from binding to GspE. Our findings suggest that the T2SS ATPase is permanently associated with the inner membrane platform and that the GspELM complex should be considered as a key subassembly for the biogenesis of the T2SS apparatus.

Primary hyperaldosteronism is not as uncommon as we thought, and by recent estimates the prevalance may be as high as 11% among hypertensives. We present a case of a 33 years old male patient came with a complaint of headache in occipital area & weakness in both lower limb since 4 weeks. The patient was a diagnosed case of hypertension and was already on tablet Atenolol (25 mg) once a day. At the time of admission, the patient was found to have a pulse of 96/min and blood pressure of 170/100 mm of Hg. Power was 3/5 for both right and left lower limbs. At the time of admission, serum potassium was 2.8. As a result, the patient was shifted to tablet Metroprolol and Amlodipine (50 + 5 mg) once a day. We also added tablet Cilnidipine (10 mg) and Telmisartan (80 mg) once a day and syrup Potklor thrice a day with water. The patient was sent for renal artery doppler, urine for metanephrines and vanillylmandelic acid, serum aldosterone, plasma aldosterone/plasma renin activity ratio (PAC/PRA ratio), urinary aldosterone, urinary cortisol and adrenocorticotrophic hormone level and computed tomography (CT) abdomen to rule out hyperaldostronism. Plasma aldosterone/plasma renin activity ratio, urinary aldosterone was high and CT abdomen revealed a solitary nodule in the left adrenal gland measuring 1.2 × 1.0 cm in maximum transverse diameter, which was suggestive of adrenal adenoma. Diagnosis of Conn’s syndrome secondary to adrenal adenoma was made. The patient was advised tablet Aldactone (25 mg) once a day and serum electrolytes were repeated which showed normalization with normal blood pressure.

Mass-selected, chlorinated (ClC6Cl+, HC6Cl+) and brominated (BrC6Br+, HC6Br+) derivatives of triacetylene cation produced from polyhalogenated benzenes in a hot-cathode discharge source were trapped in 6 K neon matrices. Absorption is detected with onset at 710.8 nm for BrC6Br+, 655.9 nm for HC6Br+, 649.1 nm for ClC6Cl+ and 624.0 nm for HC6Cl+. Radiative decay from the v' = 0 level of the excited electronic state is observed on laser excitation of the transition. The systems are assigned to the A 2Πg ← 2Πu electronic transition of ClC6Cl+ and BrC6Br+, and A 2Π ← 2Π of HC6Cl+ and HC6Br+. A weaker system commencing at 495.4 nm for BrC6Br+, 574.5 nm for HC6Br+, 519.9 nm for ClC6Cl+ and 499.5 nm for HC6Cl+ is present. This is due to excitation to the 2Πg/- electronic state of the halogenated triacetylene cations. The assignment is based on calculated vertical excitations energies, vibrational frequencies and similarities in the absorption and fluorescence spectra to the 2Πg, A 2Πg ← 2Πu electroni...

Assessment of exposure to polycyclic aromatic hydrocarbons (PAHs) is important due to the widespread presence of PAHs in the environment and their toxicological relevance, especially to susceptible populations such as children and their health. The aim of this study is to compare indoor and outdoor concentrations of particulate matter with a diameter of 2.5 μm or less (PM2.5) and 15 individual PAHs, as well as contribution of the analyzed PAHs to mutagenic and carcinogenic activity. Samples were collected during spring season in two sites in southern Poland (Silesia) representing urban and rural areas. Indoor samples of PM2.5 were sampled in kindergartens. At the same time, in the vicinity of the kindergarten buildings, the collection of the outdoor PM2.5 samples was carried out. Mutagenic (MEQ) and carcinogenic (TEQ) equivalents related to BaP and the percentage share expressed as mutagenic (MP) and carcinogenic (CP) potential of each individual compound to the total mutagenic/carcinogenic potential of the PAH mixture were calculated. The obtained results show that high concentrations of PM2.5 (above 25 μg/m3) and 15 PM2.5-bound PAHs in outdoor and indoor air were similar in the two studied areas. In overall PAHs mutagenic and carcinogenic potential, the percentage share of benzo(a)pyrene (BaP) was dominant and varied from 49.0–54.5% to 62.5–70.0%, respectively. The carried out study indicates the necessity of reducing PAH emission from solid fuel combustion, which is reflected in PM2.5-bound PAHs concentrations and their diagnostic ratios. In the recent years, health effects on children resulting from their activity pattern and air quality in the public places have been a serious problem.

Three absorption systems starting at 624.1, 601.2, and 590.0 nm were detected in a 6 K neon matrix following deposition of mass selected m/z = 250 ions produced from corannulene vapour in a hot cathode ion source. The two latter systems were also observed after deposition of neutral corannulene in solid neon with concomitant bombardment of the matrix with argon ions. The features in the absorption spectrum are assigned to the 42A′′ ← X 2A′′ transition of cylobutadieno-benzo[ghi]fluoranthene cation and to the 32A′ ← X 2A′′ and 32A′′ ← X 2A′ transitions of two Jahn-Teller structures of bowl-shaped corannulene cations, respectively. The assignment is based on excitation energies calculated with the SAC-CI and CASPT2 methods. The electronic absorption spectrum of protonated corannulene has onsets at 515.1 and 398.8 nm in a neon matrix, following deposition of a mass-selected beam produced by reactions of corannulene with EtOH2 +. The absorptions are assigned, on the basis of theoretical predictions, to the 3,41A ← X 1A transitions. The electronic spectrum was also recorded in the gas phase using a resonant multiphoton fragmentation technique in an ion trap at vibrational and rotational temperatures of 15 K. The 3,41A ← X 1A transitions are observed with origin bands at 521 ± 1 nm and 396.4 ± 0.1 nm. The 31A excited electronic state indicates fast internal conversion of ≈ 5 fs, while the 41A state has a lifetime of ≈ 0.2 ps. A distinct vibrational pattern is discernible in the 41A ← X 1A transition.

The ability of bacteria to infect a host relies in part on the secretion of molecular virulence factors across the cell envelope. Pseudomonas aeruginosa, a ubiquitous environmental bacterium causing opportunistic infections in humans, employs the type II secretion system (T2SS) to transport effector proteins across its cellular envelope as part of a diverse array of virulence strategies. General secretory pathway protein L (GspL) is an essential inner-membrane component of the T2SS apparatus, and is thought to facilitate transduction of the energy from ATP hydrolysis in the cytoplasm to the periplasmic components of the system. However, our incomplete understanding of the assembly principles of the T2SS machinery prevents the mechanistic deconvolution of T2SS-mediated protein secretion. Here we show via two crystal structures that the periplasmic ferredoxin-like domain of GspL (GspLfld) is a dimer stabilized by hydrophobic interactions, and that this interface may allow significant interdomain plasticity. The general dimerization mode of GspLfld is shared with GspL from Vibrio parahaemolyticus suggesting a conserved oligomerization mode across the GspL family. Furthermore, we identified a tetrameric form of the complete periplasmic segment of GspL (GspLperi) which indicates that GspL may be able to adopt multiple oligomeric states as part of its dynamic role in the T2SS apparatus.

Vibrationally resolved electronic absorption spectrum of 1-oxohepta-2,4,6-triyn-ylium cation has been recorded in a 6 K neon matrix after mass-selected deposition of m/z = 101 cations produced from the 1,2,3,4,5-benzenepentacarboxylic acid in an ion source. The band system with origin at 278 nm is assigned to the 21Σ+ ← X1Σ+ transition of the linear-HC7O+ isomer on the basis of theoretical calculations. Vibrational analysis of the electronic spectrum is consistent with the structure.

Four electronic systems with origin bands at 759.5, 559.3, 476.3, and 385.5 nm are detected in a 6 K neon matrix following deposition of mass-selected protonated fluoranthene C16H11(+) produced from a reaction of neutral vapor and ethanol in a hot-cathode ion source. Two cationic isomers are identified as the carriers of these band systems. The 559.3, 476.3, and 385.5 nm absorptions are assigned to 4,3,2 (1)A' ← X (1)A' transitions of isomer E(+) (γ-) and the 2 (1)A' ← X (1)A' system at 759.5 nm is of isomer C(+) (α-) of protonated fluoranthene on the basis of theoretical predictions. The electronic spectrum of E(+) was also recorded in the gas phase using a resonant 1 + 1 two-photon excitation-dissociation technique in an ion trap at vibrational and rotational temperatures of 10 K. The 3,2 (1)A' ← X (1)A' transitions have origin band maxima at 558.28 ± 0.01 and 474.92 ± 0.01 nm. Both the 2 (1)A' and 3 (1)A' excited states have a distinct vibrational pattern with lifetimes on the order of 1 ps.

Three vibrationally resolved absorption systems commencing at 538, 518, and 392 nm were detected in a 6 K neon matrix after mass-selected deposition of C13 H9 (+) ions (m/z=165) produced from fluorene in a hot-cathode discharge ion source. The benz[f]indenylium (BfI(+) : 538 nm), fluorenylium (FL9(+) : 518 nm), and phenalenylium (PHL(+) : 392 nm) cations are the absorbing molecules. Two electronic systems corresponding to neutral species are apparent at 490 and 546 nm after irradiation of the matrix with λ260 nm photons and were assigned to the FL9 and BfI radicals, respectively. The strongest peak at 518 nm is the origin of the 2 (1) B2 ←X̃ (1) A1 absorption of FL9(+) , and the 490 nm band is the 2 (2) A2 ←X̃ (2) B1 origin of FL9. The electronic systems commencing at 538 nm and 546 nm were assigned to the 1 (1) A1 ←X̃ (1) A1 and 1 (2) A2 ←X̃ (2) A2 transitions of BfI(+) and BfI. The 392 nm band is the 1 (1) E'←X̃ (1) A1 ' transition of PHL(+). The electronic spectra of C13 H9 (+) /C13 H9 were assigned on the basis of the vertical excitation energies calculated with SAC-CI and MS-CASPT2 methods.

The bioavailability of minerals, such as zinc and magnesium, has a significant impact on the fermentation process. These metal ions are known to influence the growth and metabolic activity of yeast, but there are few reports on their effects on lactic acid bacteria (LAB) metabolism during sour brewing. This study aimed to evaluate the influence of magnesium and zinc ions on the metabolism of Lactobacillus brevis WLP672 during the fermentation of brewers&rsquo, wort. We carried out lactic acid fermentations using wort with different mineral compositions: without supplementation, supplemented with magnesium at 60 mg/L and 120 mg/L, and supplemented with zinc at 0.4 mg/L and 2 mg/L. The concentration of organic acids, pH of the wort and carbohydrate use was determined during fermentation, while aroma compounds, real extract and ethanol were measured after the mixed fermentation. The addition of magnesium ions resulted in the pH of the fermenting wort decreasing more quickly, an increase in the level of L-lactic acid (after 48 h of fermentation) and increased concentrations of some volatile compounds. While zinc supplementation had a negative impact on the L. brevis strain, resulting in a decrease in the L-lactic acid content and a higher pH in the beer. We conclude that zinc supplementation is not recommended in sour beer production using L. brevis WLP672.

We demonstrate low-operational-current W/Co$_{20}$Fe$_{60}$B$_{20}$/MgO spin Hall nano-oscillators (SHNOs) on highly resistive silicon (HiR-Si) substrates. Thanks to a record high spin Hall angle of the $\beta$-phase W ($\theta_{SH}$ = -0.53), a very low threshold current density of 3.3 $\times$ 10$^{7}$ A/cm$^2$ can be achieved. Together with their very wide frequency tunability (7-28 GHz), promoted by a moderate perpendicular magnetic anisotropy, this makes HiR-Si/W/CoFeB based SHNOs potential candidates for wide-band microwave signal generation. Their CMOS compatibility offers a promising route towards the integration of spintronic microwave devices with other on-chip semiconductor microwave components., Comment: 6 pages, 4 figures

Electronic absorption spectra of linear C6Br+ and C6Br have been recorded in 6 K neon matrices. Two strong absorption systems starting at 555.1 nm and 539.3 nm are assigned to the 1 2Π ← X 2Π electronic transition of C6Br, and 1 3Σ− ← X 3Σ− of C6Br+. Excitation of normal modes along with overtones and combination bands in the excited electronic state are observed. Assignments are based on mass-selection, photobleaching behavior, comparison with the known electronic transitions of linear C6Cl and C6Cl+, and excitation energies obtained with CASPT2 and SAC-CI theory as well as on computed vibrational frequencies.

The C ∼ 2 B 3u ← X ∼ 2 B 2g electronic absorption of butatriene cation (BT + ) has been observed in a 6 K neon matrix. The origin band lies at 511.9 nm. The electronic transition assignment is based on comparison with the photoelectron spectrum of butatriene and the vibrational frequencies of BT + calculated with the CASPT2 (5, 6) method. Three vibrational modes of energy 207, 511 and 813 cm −1 , with their overtones and combinations, are active in the C ∼ 2 B 3u state of BT + . It is shown that the emission observed from a glow discharge of 2-butyne at 491 nm and attributed to the origin band of this electronic transition [1] of BT + is due to another species, because the difference of 850 cm −1 to the absorption spectrum is too large. No fluorescence of BT + was detected in the matrix and it is expected that the C ∼ 2 B 3u electronic state relaxes non-radiatively on a fs time scale.

Two absorption systems of C5H3(+) starting at 350 and 345 nm were detected following mass selective deposition of m/e = 63 ions in a 6 K neon matrix. These are assigned to the 1 (1)A1 ? X (1)A1 electronic transition of 1234 pentatetraenylium H2CCCCCH(+) (isomer B(+)) and 1 (1)B2 ? X (1)A1 of penta 14 diyne 3 ylium HCCCHCCH(+) (C(+)). The absorptions of neutral C5H3 isomers with onsets at 434.5 398.3 369.0 and 267.3 nm are also detected. The first two systems are assigned to the 1 (2)B1 ? X (2)B1 and 1 (2)A2 ? X (2)B1 transitions of isomer B and C respectively and the latter two to ethynylcyclopropenyl (A) and 3 vinylidenecycloprop 1 enyl (D) radicals. The structural assignments are based on the adiabatic excitation energies calculated with the MS CASPT2 method. A vibrational analysis of the electronic spectra based on the calculated harmonic frequencies supports this.

Three absorption systems with origins at 354, 497, and 528 nm were detected after mass-selected deposition of H2C6O+ in a 6 K neon matrix. The ions were formed by the reaction of C2O with HC4H+ in a mixture of C3O2 and diacetylene in a hot cathode source, or by dissociative ionization of tetrabromocyclohexadienone. The 497 and 354 nm systems are assigned to the 12A″ ← X2A″ and 22A″ ← X2A″ electronic transitions of B+, (2-ethynylcycloallyl)methanone cation, and the 528 nm absorption to the 12A2 ← X2B1 transition of F+, 2-ethynylbut-3-yn-1-enone-1-ylide, on the basis of calculated excitation energies with CASPT2.

Electronic absorptions of ferrocenium starting at 632.5 nm were measured in a 6 K neon matrix following mass-selective deposition of the ions. The spectrum shows clear vibrational structure and provides the best-yet resolved view of the electronic states of this cation. The absorption system is identified as the 1 2E1′ ← X 2E2′ transition (D5h symmmetry) on the basis of vertical excitation energies and oscillator strengths calculated at the CASPT2 level. Vibrational bands in the spectrum are assigned with the aid of the ground-state frequencies calculated with the DFT method.

Mass selective deposition of C7H3(+) (m/z = 87) into solid neon reveals the 1(1)A1←X(1)A1 electronic absorption system of hepta-1,2,3,4,5,6-heptahexaenylium cation B(+) [H2CCCCCCCH](+) with an origin band at 441.3 nm, 1(1)A'←X(1)A' transition of 2,4-pentadiynylium,1-ethynyl cation C(+) [HCCCHCCCCH](+) starting at 414.6 nm and the 1(1)A1←X(1)A1 one of cyclopropenylium,1,3-butadiynyl cation A(+) [HCCCCC(CH=CH)](+) with an onset at 322.2 nm. Vibrationally resolved fluorescence was observed for isomer B(+) upon laser excitation of the absorption bands in the 1(1)A1←X(1)A1 transition. After neutralization of the cations in the matrix five absorption systems of the C7H3 neutral radicals starting at 530.3, 479.4, 482.3, 325.0 and 302.5 nm were detected. These were identified as the 1(2)A'←X(2)A' and 2(2)A'←X(2)A' electronic transitions of 2-(buta-1,3-diynyl)cycloprop-2yl-1-1ylidene E˙ [HCCCCC(C=CH2)]˙, 1(2)B1←X(2)B1 of 1,2,3,4,5,6-heptahexaenyl B˙ [H2CCCCCCCH]˙, 3(2)B1←X(2)B1 of 3-buta-1,3-diynyl-cyclopropenyl A˙ [HCCCCC(CH=CH)]˙ and 2(2)B1←X(2)A2 transition of 1,2-divinylidene-cyclopropanyl radical F˙ [HCC-cyc-(CCHC)-CCH]˙, respectively. The assignment is based on calculated vertical excitation energies using the CASPT2 method. Comparison of the calculated harmonic vibrational frequencies with those inferred from the spectra supports the assignment.

Electronic absorption spectra of C7O, neutral and cationic, have been obtained after mass selection and deposition into 6 K neon matrices. The band system with origin at 305.1 nm is identified as the (2) 1Σ+ ← X 1Σ+ electronic transition of linear C7O, and the absorption, with onset at 276.0 nm, to (4) 2Σ+ ← X 2Σ+ of C7O+ on the basis of experimental observations and theoretical calculations.

The fragment ions C6HF+ and C6F 2 + produced from fluorobenzenes in a discharge source were trapped in 6 K neon matrices after mass selection. A strong absorption system is detected in the visible range starting at 586.3 nm for C6HF + and 569.3 nm for C6F2 +. Vibrationally resolved fluorescence commencing at the same wavelengths is observed upon laser excitation into each absorption band of these cations. The absorptions are assigned to the A2?g ? X 2?u and A2? ? X2? transitions of linear FC6F+ and HC6F + respectively. The assignment is based on the similarity of the absorption and fluorescence spectra with the A2?g ? X2?u electronic system of linear HC 6H+ as well as the theoretically calculated vibrational and electronic excitation energies of the FC6F+ and HC6F+. © 2013 Elsevier B.V. All rights reserved.

In this Perspective the development and application of a mass selective matrix isolation approach employed with success over the last two decades in the spectroscopic characterization of numerous ions and neutral reactive species is illustrated with original data for hydrocarbon cations and neutrals with a six and a five membered carbon ring fused. The setup allows for the electronic and vibrational assessment of these isolated molecules and ions in the inert neon environment. The transient species of interest are chosen due to their astrophysical relevance and the role they play in flames plasmas combustion organic reactions and atmospheric chemistry. Electronic absorption and fluorescence spectra of indene related polycyclic aromatic hydrocarbon derivatives C9Hy + (y = 7 9) cations are presented. The ions were produced in a discharge source and investigated by means of absorption and emission spectroscopies after selectively trapping them in 6 K neon matrices. Photoconversion between the two C9H 8 + indenylium isomers and upon irradiation H2 loss from C9H9 + were observed. Corresponding neutral species C9Hy are identified by photobleaching the matrices containing the cations. © 2013 the Owner Societies.

Two electronic transitions at 512.3 and 250 nm of linear-C5H(+) are detected following mass-selective deposition of m/z = 61 cations into a 6 K neon matrix and assigned to the 1 (1)Π←X (1)Σ(+) and 1 (1)Σ(+)←X (1)Σ(+) systems. Five absorption systems of l-C5H with origin bands at 528,7, 482.6, 429.0, 368.5, and 326.8 nm are observed after neutralization of the cations in the matrix and identified as transitions from the X (2)Π to 1 (2)Δ, 1 (2)Σ (-), 1 (2)Σ(+), 2 (2)Π, and 3 (2)Π electronic states. The assignment to specific structures is based on calculated excitation energies, vibrational frequencies in the electronic states, along with simulated Franck-Condon profiles.

C7H4O2+ and C7H5O2+ ions and the respective neutrals have been investigated by absorption spectroscopy in neon matrixes following mass selection of ions produced from salicylic acid. Three electronic transitions starting at 649.6, 431.0, and 372.0 nm are detected for C7H4O2+ and assigned on the basis of CASPT2 energies and Franck–Condon simulations as the excitations from the X 2A″ to the 1 2A″, 2 2A″, and 3 2A″ electronic states of 6-(oxomethylene)-2,4-cyclohexadien-1-one ion (A+). Absorptions commencing at 366.4 nm are observed for C7H5O2+ and assigned to the 1 2A′ ← X 2A′ electronic transition of (2-hydroxyphenyl)methanone ion (J+). Neutralization of J+ leads to the appearance of four absorption systems attributed to the 4 2A″, 3 2A″, 2 2A″, and 1 2A″ ← X 2A″ transitions of J with origin bands 291.3, 361.2, 393.8, and 461.2 nm.

Fluorescence spectra of protonated pyrene and coronene in solid neon have been observed. Laser excitation of the Sn ← S0 transitions of the cations results in an extended, vibrationally-resolved S1 → S0 fluorescence with onset at 487.8 and 695.4 nm for protonated pyrene and coronene, respectively. Vibrational assignment of the spectra has been made on the basis of the calculated frequencies of normal modes in the ground electronic state. The astrophysical relevance of the frequencies inferred for these protonated cations is discussed.

Polybrominated diphenyl ethers (PBDEs) are a group of persistent organic pollutants. They are used as flame retardants in plastics, paints, varnishes and textile materials. PBDEs pose great risk to the environment because of their high persistence and ability to get into the environment easily due to the lack of chemical bonds with the matrix of materials, to which they are added. Global research studies confirmed the occurrence of those compounds in the majority of elements of water and land environment. Analysis of PBDEs in environmental samples is one of the specific analytical methods of criteria that comprise low detection limits and high selectivity. The analysis of PBDEs in environmental samples is one of the specific analytical methods, in which the main criteria are low detection limits and high selectivity. In this article, a literature review of methods for environmental sample preparation and analysis of the PBDE content was presented. The article discusses the potential of modern extraction techniques such as: solid-phase microextraction, single-drop microextraction, dispersive liquid-liquid microextraction, microwave-assisted extraction, cloud point extraction, hollow fibre-liquid phase microextraction and others for the separation of PBDEs from environmental samples with a complex matrix. Among the methods for qualitative and quantitative determination of PBDEs, a particular focus was put on gas chromatography/mass spectrometry with various injection techniques and different types of sample ionisation.

Two experimental methods were applied to identify the structure and electronic transitions of C4H3Cl+ isomers. The first is a direct absorption technique where mass-selected ions are embedded in 6 K neon matrices using a mass-selected ion beam and absorption spectra of different C4H3Cl+ isomers were thus observed. The second is a gas phase method on ions which have been collisional cooled with cryogenic helium inside of a 22-pole ion trap. The c-type (1)2 A′ ← X 2 A″ electronic transition of a C4H3Cl+ isomer could then be measured by a one-colour, two-photon technique at 20 and 50 K in the gas phase. The two sets of data, complemented by calculated excitation energies, allowed the assignment of particular isomers. Rotational structure in the gas phase spectra was resolved for C4H3 35Cl+ and C4H3 37Cl+ isomers of cis-1-chlorobutenynylium. The analysis leads to the spectroscopic constants: T 00 = 19 184.680(5), , , , , and (all in cm−1).

Amyloid fibrils, which are often associated with certain degenerative disorders, reveal a number of intriguing spectral properties. However, the relationship between the structure of fibrils and their optical traits remains poorly understood. Poly(L-glutamic) acid is a model polypeptide shown recently to form amyloid-like fibrils with an atypical infrared amide I' band at 1595 cm(-1), which has been attributed to the presence of bifurcated hydrogen bonds coupling C═O and N-D groups of the main chains to glutamate side chains. Here we show that this unusual amide I' band is observed only for fibrils grown from pure enantiomers of the polypeptide, whereas fibrils precipitating from equimolar mixtures of poly(L-glutamic) and poly(D-glutamic) acids have amide I' bands at 1684 and 1612 cm(-1), which are indicative of a typical intermolecular antiparallel β-sheet. Pure enantiomers of polyglutamic acid form spirally twisted superstructures whose handedness is correlated to the amino acid chirality, while fibrils prepared from the racemate do not form scanning electron microscopy (SEM)-detectable mesoscopically ordered structures. Vibrational circular dichroism (VCD) spectra of β-aggregates prepared from mixtures of all L- or D-polyglutamic acid in varying ratios indicate that the enhancement of VCD intensity correlates with the presence of the twisted superstructures. Our results demonstrate that both IR absorption and enhanced VCD are sensitive to subtle packing defects taking place within the compact structure of amyloid fibrils.

Benzyl and tropyl in charge: Electronic spectra of mass-selected benzylium (Bz+) and tropylium (Tr+) cations embedded in solid neon are reported for the first time. They reveal a weak (1)1B1←equation image1A1 visible (see picture) and a much stronger (1)1A1←equation image1A1 ultraviolet transition for Bz+ (C2v symmetry). The lowest dipole-allowed 1A′′2←equation image1A′1 absorption in the ultraviolet region for Tr+ (D7h) is also observed.

Electronic transitions of protonated benzene (Ã (1)B(2)←X̃ (1)A(1), origin at 325 nm) and α-protonated fulvene (Ã (1)A'←X̃ (1)A', at 335 nm) trapped in 6 K neon matrices have been detected. The cations were produced from several different precursors, mass-selected, and co-deposited with neon. After neutralization of the cations, the electronic transitions of cyclohexadienyl (onsets at 549 and 310 nm) and α-hydrogenated fulvene (532 and 326 nm) radicals were identified. Upon excitation of cyclohexadienyl to the B̃ (2)B(1) state, photoisomerization to an open-chain structure and α-hydrogenated fulvene was observed.

The sulfur S n - n = 2, 3 anions produced in a hot cathode discharge ion source were mass-selected and embedded in a neon matrix at 6 K. A long progression with the excitation of up to 12 vibrational quanta is observed in the A 2Πu ← X 2Πg electronic spectrum of S 2 - , with the onset at 467.1 nm. The inferred spectroscopic constants in the A 2Πu state are: ν0−0 = 21,407 ± 4 cm−1, ω 0 ′ = 328.4 ± 1 cm−1, ω 0 ′ x 0 ′ = 2.4 ± 0.1 cm−1. The electronic spectrum of S 3 - in a neon matrix exhibits a rich vibrational structure with a bimodal intensity distribution. This results from the overlap of two electronic transitions, C ∼ 2 A 2 ← X ∼ 2 B 1 and ( D ∼ or E ∼ ) ← X ∼ 2 B 1 , with origins at 701.3 and 619.1 nm. The frequencies (cm−1) of the totally symmetric modes ν1 and ν2 are 466, 184 in the C ∼ 2 A 2 and 446, 177 in the ( D ∼ or E ∼ ) states.

The polyacetylene HC2nH+ n = 2-7 cations were produced from a mixture of diacetylene with helium in a hot cathode-discharge source. After a mass-selective deposition, their absorption spectra were studied in 6 K neon matrixes. Besides the known A2Pi-- X2Pi system, several new transitions to higher excited 2Pi electronic states of these cations have been observed. In the case of HC4H+ and HC6H+, only one new weak absorption system has been detected with the onset at 336.1 and 417.2 nm, respectively. These C2Pi-- X2Pi transitions form a series that extends to HC10H+. Two further electronic transitions are observed for HC8H+ through to HC14H+; a weaker B2Piu-- X2Pig and a strong E2Piu-- X2Pig in the UV. The integrated intensity of the UV system of the polyacetylene cations exceeds that of the A2Pi-- X2Pi transition by an order of magnitude.

The fulvenallenyl radical was produced in 6 K neon matrices after mass-selective deposition of C7H5(-) and C7H5(+) generated from organic precursors in a hot cathode ion source. Absorption bands commencing at λ=401.3 nm were detected as a result of photodetachment of electrons from the deposited C7H5(-) and also by neutralization of C7H5(+) in the matrix. The absorption system is assigned to the 1 (2)B1 ←X (2)B1 transition of the fulvenallenyl radical on the basis of electronic excitation energies calculated with the MS-CASPT2 method. The vibrational excitation bands detected in the spectrum concur with the structure of the fulvenallenyl radical. Employing DFT calculations, it is found that the fulvenallenyl anion and its radical are the global minima on the potential energy surface among plausible structures of C7H5.

The $1 ^3\Sigma_u^- \leftarrow X^3\Sigma_g^-$ transition of linear HC$_5$H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC$_{2n+1}$H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the $1 ^1 A_1 \leftarrow X ^1 A_1$ transition of the cumulene carbene pentatetraenylidene H$_2$C$_5$ (B)., Comment: 7 pages, 4 figures, 5 tables

The electronic spectrum of a nonlinear carbon chain radical C4H4+ was observed after mass-selective deposition in a 6 K neon matrix. The corresponding gas-phase spectra of C4H4+ and C4D4+ have been observed in the 512 to 513 nm region and at 710 nm for C8H4+. These were detected in direct absorption by cavity ringdown spectroscopy through a supersonic planar discharge. The electronic transition energies of these nonlinear carbon chain radicals correlate well with those of the polyacetylene cations HCnH+ (n = 4, 6, 8). The observed profiles are reproduced with rotational constants obtained by ab initio geometry optimizations and extrapolation between the ground and excited electronic states. Key words: nonlinear carbon chain, carbon cation, electronic transition, diffuse interstellar bands, molecular structure.

Electronic and infrared absorption spectra of mass-selected C6+, generated by dissociative electron impact ionization of C6Cl6 and C6Br6, have been recorded in 6 K neon matrices. Linear and cyclic forms of C6+ have been observed. The 2Pig--Chi2Piu electronic transition of linear C6+ has its origin band at 646 nm whereas for the (2) 2B2--Chi2A1 system of the cyclic isomer it lies at 570 nm. An infrared active fundamental mode in the ground electronic state of C6+ is observed at 2092 and 1972 cm(-1) for the linear and cyclic isomer, respectively.

Electronic absorption spectra of C6Cl, C6Cl+, C5Cl, and C5Cl+ have been recorded in 6 K neon matrices. The bands observed are assigned to the B 2Π ← X 2Π electronic transition of C6Cl, 3Σ- ← X 3Σ- of C6Cl+, and 1Σ+ ← X 1Σ+ of C5Cl+ with band origins at 545.8, 527.4, and 226.1 nm, respectively. Two electronic band systems are apparent for C5Cl and these are tentatively assigned to a 2Π ← X 2Π transition with a band origin at 247.1 nm and to Σ+ ← X 2Π at 532.3 nm. For each of the four molecules, several transitions due to the excitation of vibrational modes in the excited electronic states are observed. The spectral assignments in each case are based upon the observation of clear, vibronic progressions with appropriate spacing for C−C and C−Cl stretching modes and by comparison with the absorption spectra of the isoelectronic sulfur-terminated carbon chains.

A high-resolution gas-phase spectrum of a molecular absorption band around 604 nm is assigned as due to an electronic transition of a nonlinear C6H4+ planar species starting from its 2A″ electronic ground state. The spectrum is observed in direct absorption by cavity ringdown spectroscopy through a supersonic planar discharge through a mixture of acetylene in helium. The spectrum has a clear rotational and K-type structure. This allows an accurate determination of the B and C rotational constants and an estimate for the A rotational constant in ground and electronically excited states. The resolved spectrum of the fully deuterated species C6D4+ has been obtained as well. The results are compared both to the outcome of ab initio geometry optimizations and low-resolution absorption spectra in 6 K neon matrices obtained after mass-selective deposition.

Poly-L-glutamic acid (PLGA) often serves as a model in studies on amyloid fibrils and conformational transitions in proteins, and as a precursor for synthetic biomaterials. Aggregation of PLGA chains and formation of amyloid-like fibrils was shown to continue on higher levels of superstructural self-assembly coinciding with the appearance of so-called β2-sheet conformation manifesting in dramatic redshift of infrared amide I' band below 1600 cm(-1). This spectral hallmark has been attributed to network of bifurcated hydrogen bonds coupling C = O and N-D (N-H) groups of the main chains to glutamate side chains. However, other authors reported that, under essentially identical conditions, PLGA forms the conventional in terms of infrared characteristics β1-sheet structure (exciton-split amide I' band with peaks at ca. 1616 and 1683 cm(-1)). Here we attempt to shed light on this discrepancy by studying the effect of increasing concentration of intentionally induced defects in PLGA on the tendency to form β1/β2-type aggregates using infrared spectroscopy. We have employed carbodiimide-mediated covalent modification of Glu side chains with n-butylamine (NBA), as well as electrostatics-driven inclusion of polylysine chains, as two different ways to trigger structural defects in PLGA. Our study depicts a clear correlation between concentration of defects in PLGA and increasing tendency to depart from the β2-structure toward the one less demanding in terms of chemical uniformity of side chains: β1-structure. The varying predisposition to form β1- or β2-type aggregates assessed by infrared absorption was compared with the degree of morphological order observed in electron microscopy images. Our results are discussed in the context of latent covalent defects in homopolypeptides (especially with side chains capable of hydrogen-bonding) that could obscure their actual propensities to adopt different conformations, and limit applications in the field of synthetic biomaterials.

The A 2Δu←X 2Πg, B 2Σu−←X 2Πg, and C 2Σu+←X 2Πg electronic transitions of C3− were observed in a neon matrix and in the gas phase, although the energy of the excited electronic states involved in these transitions is 1–1.5 eV above the photodetachment threshold. The excited Feshbach states are sufficiently long-lived that some of the bands in the gas-phase photodetachment spectrum exhibit rotational structure. Assignment of the transitions is made on the basis of rotational analysis or profile simulations and theoretical calculations. The b 4Πu←X 2Πg transition is also weakly observed. The presence of such discrete bands, though in the continuum, provides a means of detection for anions in the interstellar medium.

Three electronic transitions of the isoelectronic species HC2nH- and HC2n-1N- and one of the neutral polyacetylenes HC2nH (n = 6−12) have been observed by absorption spectroscopy in neon matrixes. Anions produced in an electron impact source were mass-selected and codeposited with excess of neon at 6 K. The HC2nH species were formed from the anions by photodetachment. A well-structured band system at 780 nm for HC12H-, and shifting by regular increments to 1325 nm for HC24H-, is assigned to two overlapping electronic transitions of 2Π ← X2Π symmetry. Another 2Π ← X2Π transition with broader features is observed in the 300−480 nm region. Corresponding transitions are observed for the isoelectronic cyanosubstituted anions HC2n-1N-. The neutral polyacetylenes show a vibrationally well-resolved UV band system attributed to the 1 ← X1 electronic transition. The energy of the electronic transition shows a characteristic inverse dependence on the carbon chain length.

The 1 2 A 2 ″ ← X 2 A 1 ′ electronic transition of the B 3 molecule with origin band at 5990 cm −1 has been observed in a 6 K neon matrix. A vibrational progression in the spectrum corresponds to the excitation of the ν 1 ( a 1 ′ ) vibrational mode in the 1 2 A 2 ″ state with a frequency of ∼1092 cm −1 . The band system was detected after laser ablation of a boron rod and the origin band also after mass-selected deposition of B 3 - anions with subsequent neutralization.

Three open-chain isomers of C6H4(+) and two cyclic ones were detected following mass-selective trapping in 6 K neon matrixes. The open-chain cations 5-hexene-1,3-diyne (CH2═CH-CC-CC-H)(+) and cis- (cis-HCC-CH═CH-CCH)(+) and trans-3-hexene-1,5-diyne (trans-HCC-CH═CH-CCH)(+), possess two absorption systems commencing at 609 and 373, 622 and 385, and 585 and 373 nm, respectively. They are assigned to the 1 (2)A" and 2 (2)A" ← X (2)A", 1(2)A2 and 2 (2)A2 ← X (2)B1, and 1 (2)Bg and 2 (2)B(g) ← X (2)A(u) electronic transitions of these cations. Two overlapping systems are detected at around 420 nm and tentatively assigned to the 1 (2)A" ← X (2)A" electronic transitions of propargyl cyclopropene and 2 (2)B1 ← X (2)A2 of o-benzyne cation structures. The assignment of the electronic transitions is based on theoretical vertical excitation energies calculated with CASPT2 and EOMEE-CCSDT methods for 12 isomers of C6H4(+). These have been carried out at the geometries optimized using several ab initio methods. Adiabatic excitation energies were calculated for the five identified isomers of C6H4(+).

Electronic absorption spectra of silicon molecules Sin and Sin- (n = 2−4) in 5 K neon matrices have been observed. The approach is based on mass-selection and codeposition with neon. The neutral species become apparent after photodetachment. The band systems detected are assigned using available calculations and photoelectron spectra. In the case of Si3 (C2v), electronic transitions from the X 1A1 ground state to the excited electronic states 1B1, 1A1, 1B1, and 1B2 have been identified. Their bands are at 778.9, 579.7, 522.3, and 388.3 nm, respectively. Two band systems, with origin bands at 925.3 and 466.6 nm, are assigned to the 1B3u ← X 1Ag and 1B1u ← X 1Ag transitions of Si4 (D2h). Two known electronic transitions are obtained for Si2, but a reported band system with origin at 288.3 nm cannot be due to this molecule. The following electronic transitions were detected for the anions: Si2-, 2Πu ← X Si3- (C2v), 2A1 ← X 2A1; Si4- (D2h), 2B1u ← X 2B2g, with origin bands at 432.7, 1036.7, and 872.6 nm. Vib...

Alpha- and beta-protonated naphthalenes (α- and β-HN(+)) were investigated by electronic absorption and fluorescence spectroscopies in 6 K neon matrixes using a mass-selected C(10)H(9)(+) ion beam. The absorption spectra reveal S(1)/S(2) ← S(0) transitions with onsets at 502.1 and 396.1 nm for α-HN(+), and 534.5 and 322.3 nm in the case of β-HN(+). Wavelength-dispersed fluorescence was detected for α-HN(+), starting at 504.4 nm. Light-induced α-HN(+) → β-HN(+) isomerization was observed upon S(2) ← S(0) excitation of α-HN(+), whereas β-HN(+) relaxed back into the more stable alpha form either upon excitation to S(1) or via thermal population of the ground state vibrational levels near the top of the energy barrier between the two isomers. The intramolecular proton transfer leading to the α-HN(+) ↔ β-HN(+) photoisomerization is fully reversible. The observations are explained with the support of theoretical calculations on the ground- and excited states of the isomers, vertical excitation and adiabatic energies, minimum-energy pathways along the relevant reaction coordinates, and conical intersections between the electronic states.

Absorption spectra observed between 400 and 2500 nm in 5 K neon matrices have been assigned to electronic transitions of linear C−2n (n=2–10): 2Π←X 2Π, C2n (n=3–7): 3Σ−u←X 3Σ−g, and C2nH (n=3–8): 2Π←X 2Π chains. The species have been produced by mass selected deposition of cations or anions produced in a hot cathode discharge source (C2n, C−2n, C2nH) and by laser vaporization of graphite (C2n, C−2n). In addition to experimental and chemical evidence, the dependence of the absorption wavelength on the number of carbon atoms was used to assign the electronic transitions. Infrared absorptions which were recorded around 2000 cm−1 are attributed to asymmetric stretching frequencies of C8, C10, and C12. This is based on correlation of their intensities with the identified electronic bands. The possible relevance of the electronic spectra of these carbon chains to astrophysical observations of diffuse interstellar bands is discussed.

The A 2Π←X 2Π transitions and vibrational frequencies in the excited electronic states have been determined for the cyanopolyacetylene cations H–(C≡C)n–CN+ (n=2–6) and NC–(C≡C)n–CN+ (n=1–5). The spectroscopic information was derived by absorption measurements after cations from a mass selected beam were condensed together with excess of neon to form a 5 K matrix. Spectra have been also obtained for ions with odd number of π‐centers and are tentatively assigned to H–C2n−1–CN+ (n=3–6) and NC–C2n−1–CN+ (n=3–5). The assignments are based on trends observed for the homologous series of these cations, known gas phase data on three of the smaller species, and the free electron molecular orbital model.

Under favorable conditions of pH and temperature, poly(L-glutamic acid) (PLGA) adopts different types of secondary and quaternary structures, which include spiral assemblies of amyloid-like fibrils. Heating of acidified solutions of PLGA (or PDGA) triggers formation of β(2)-type aggregates with morphological and tinctorial properties typical for amyloid fibrils. In contrast to regular antiparallel β-sheet (β(1)), the amide I' vibrational band of β(2)-fibrils is unusually red-shifted below 1600 cm(-1), which has been attributed to bifurcated hydrogen bonds coupling C═O and N-D groups of the main chains to glutamic acid side chains. However, unlike for pure PLGA, the amide I' band of aggregates precipitating from racemic mixtures of PLGA and PDGA (β(1)) is dominated by components at 1613 and 1685 cm(-1)-typically associated with intermolecular antiparallel β-sheets. The coaggregation of PLGA and PDGA chains is slower and biphasic and leads to less-structured assemblies of fibrils, which is reflected in scanning electron microscopy images, sedimentation properties, and fluorescence intensity after staining with thioflavin T. The β(1)-type aggregates are metastable, and they slowly convert to fibrils with the infrared characteristics of β(2)-type fibrils. The process is dramatically accelerated under high pressure. This implies the presence of void volumes within structural defects in racemic aggregates, preventing the precise alignment of main and side chains necessary to zip up ladders of bifurcated hydrogen bonds. As thermodynamic costs associated with maintaining void volumes within the racemic aggregate increase under high pressure, a hyperbaric treatment of misaligned chains leads to rectifying the packing defects and formation of the more compact form of fibrils.

Absorption spectra for a series of mass selected&H: systems (k = 4-16) isolated in neon matrices at 5 K have been measured in the visible and near infrared region. Application of the free-electron molecular-orbital model reveals two homologous series corresponding to the deposition of systems containing even or odd numbers of carbon atoms. With the aid of previous gas-phase data, even-numbered carbon systems are identified as cations of polyacetylenic chains. Positions of the A ‘fI +X *fI origin bands as well as fundamental vibrational frequencies in the excited state for the systems H-( C=C),-H f (n = 4-8) have been obtained. For the deposition of ions containing an odd number of carbons, absorption transitions are tentatively assigned to H&n+, H+, wheren=2-7.