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Two electronic transitions at 512.3 and 250 nm of linear-C5H+ are detected following massselective deposition of m/z = 61 cations into a 6 K neon matrix and assigned to the 1 ¹Π ← X¹Σ+ and 1 ¹Σ+ ← X¹Σ+ 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 ²Π to 1 ²Δ, 1 ²Σ -, 1 ²Σ+, 2 2Π, and 3 ²Π 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. [ABSTRACT FROM AUTHOR]

The electronic transitions of 9-fluorenone FL + and 2,3,6,7-dibenzotropone DBT + cations were detected in 6 K neon matrices following a mass-selective deposition. The absorptions at 649.2 and 472.2 nm are assigned to the 2 ²B1←X˜²A2 FL+ and 22A′←X˜2A′ DBT+ transitions. Absorption spectra of protonated 9-fluorenone H +-FL and 2,3,6,7-dibenzotropone H +-DBT have also been measured. Protonation of the oxygenated polycyclic aromatic hydrocarbons is carried out in a hot cathode source via in situ produced protonated ethanol. Vibrationally resolved absorptions commencing at 423.3 nm of H-FL + and two band systems of H-DBT + with origins at 502.4 and 371.5 nm are assigned to the 21A′←X˜1A′ electronic transition of 9-hydroxy-fluorenyl cation and 1 ¹A←X˜¹A, 2 ¹A←X˜¹A of 2,3,6,7-dibenzocycloheptenol cation. The assignments are based on vertical excitation energy calculations with time dependent density functional theory, symmetry adapted cluster configuration interaction, and MS-CASPT2 methods. [ABSTRACT FROM AUTHOR]

The 1³Σu- ← X³Σg- transition of linear HC5H (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 H C 2 B + 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 1¹A1 ← X¹A1 transition of the cumulene carbene pentatetraenylidene H2C5 (B). [ABSTRACT FROM AUTHOR]

We present a remarkable enhancement by 300% of the exchange-bias field at room temperature, without affecting the coercivity value, via optimum magnetic annealing (250 ° C/3 kOe) in ion-beam sputtered FeMn(30 nm)/NiFe(10 nm) bilayers. This specific behavior has been attributed to a higher degree of γ-FeMn(111) orientation that offers more interfacial FeMn moments to get pinned with the moments of the adjacent NiFe layer. Unlike the absence of training effect at room temperature, a pronounced training effect and an accompanying magnetization reversal asymmetry are evidenced upon field cooling below 50K due to the presence of biaxial exchange induced anisotropy across the interdiffused FeMn/NiFe interface. The present findings not only have technological significance but also are of relevance to the understanding of interfacial spin disorder and frustration in these exchange-biased systems. [ABSTRACT FROM AUTHOR]

The positive exchange bias (PEB) at room temperature in bottom pinned as-deposited IrMn(15 nm)/ CoFeB(10 nm) ion-beam sputtered bilayers is reported without any field cooling protocol. The necessary antiferromagnetic coupling of the interfacial spins and uniaxial exchange anisotropy in amorphous ferromagnetic CoFeB are caused by the energetic sputtered atoms that modify the local magnetic microstructure in situ. On magnetic annealing, enhancement in the coercivity and disappearance of PEB is observed due to the irreversible changes in the interfacial spin structure and CoFeB layer changing to ordered bcc (110). [ABSTRACT FROM AUTHOR]

Electronic absorption spectra of linear HC2n+1H+ (n=2–7) were recorded in 6 K neon matrices following their mass-selective deposition. Four new electronic band systems are identified; the strongest E 2Πg/u←X 2Πu/g lies in the UV and the second most intense C 2Πg/u←X 2Πu/g is located in the visible range. The known A 2Πg/u←X 2Πu/g absorption is an order of magnitude weaker than C 2Πg/u←X 2Πu/g. Transitions to the B and D states are also discussed. The wavelengths of the HC2n+1H+ (n=2–7) electronic systems obey a linear relation as a function of the size of the cations, similar to other carbon chains. The B 3Σu-←X 3Σg- transition in the UV of neutral HC2n+1H (n=4–7) has also been identified upon photobleaching of the cations trapped in the matrices. [ABSTRACT FROM AUTHOR]

The Cn+ n=7–9 cations were produced by electron-impact ionization of perchloronaphthalene, mass selected, and their electronic absorption spectra in 6 K neon matrices recorded. The linear and cyclic isomers of C7+ and C8+ are detected. Three systems of linear C7+ are observed with origin bands near 770, 332, and 309 nm. The cyclic C7+ shows two transitions near 676 and 448 nm. One system of linear C9+ is observed commencing at 371 nm. Linear C8+ shows five dipole-allowed electronic transitions from the X 2Πg ground state, and the strongest ones have the origin bands at 890.8 and 308.1 nm. Five electronic transitions of cyclic C8+ are also discernible. [ABSTRACT FROM AUTHOR]

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 2Πg←Χ 2Πu electronic transition of linear C6+ has its origin band at 646 nm whereas for the (2) 2B2←Χ 2A1 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. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electronic absorption spectra of HC2n+1H and HC2n+1H+ (n=2-7) in neon matrices have been obtained. The species were prepared by codeposition of mass selected HC2n+1H+ ions with neon at 5 K. For each species the 000 band of the electronic transition as well as frequencies of fundamental vibrations in the excited state have been determined. The wavelength of the origin band in this homologous series is linearly dependent on the number of carbon atoms. Isotopic labeling supports the vibrational assignment and confirms the presence of two equivalent hydrogen atoms for HC2n+1H and HC2n+1H+. Based on spectroscopic considerations, a linear geometry is assumed with one hydrogen atom located at each end, and that the observed spectra of HC2n+1H are their 3Σu-←X 3Σg- transition. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electronic absorption spectra of linear C-6, C6, and C6H have been identified in neon matrices at 5 K. The species were produced by codepositing mass selected cations and anions with neon. The ions were generated in a hot cathode discharge source using diacetylene. The spectra of C-6 and C6 could also be observed using a pure carbon anion source or laser vaporization of graphite. The assignment is based on the mass selection, experimental and spectroscopic evidence, leading to the location of the 000 transitions of C-6: 2Πg←X 2Πu, C6: 3Σ-u←X 3Σ-g, and C6H: 2Π←X 2Π at 16 458, 19 558, and 18 854 cm-1, respectively. The frequencies of the symmetric carbon stretching vibrations have been obtained for these species in their excited electronic states. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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 Ã2Πg ← 2Πuelectronic transition of ClC6Cl+and BrC6Br+, and Ã2Π ← 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 the2Πg/-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 the2Πg, Ã2Πg ← 2Πuelectronic systems of triacetylene cation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 ofm/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 the21Σ+←X1Σ+transition of the linear-HC7O+isomer on the basis of theoretical calculations. Vibrational analysis of the electronic spectrum is consistent with the structure. [ABSTRACT FROM AUTHOR]

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 C13H9+ 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 λ<260 nm photons and were assigned to the FL9 and BfI radicals, respectively. The strongest peak at 518 nm is the origin of the 2 1B2←X̃ 1A1 absorption of FL9+, and the 490 nm band is the 2 2A2←X̃ 2B1 origin of FL9. The electronic systems commencing at 538 nm and 546 nm were assigned to the 1 1A1←X̃ 1A1 and 1 2A2←X̃ 2A2 transitions of BfI+ and BfI. The 392 nm band is the 1 1E′←X̃ 1A1′ transition of PHL+. The electronic spectra of C13H9+/C13H9 were assigned on the basis of the vertical excitation energies calculated with SAC-CI and MS-CASPT2 methods. [ABSTRACT FROM AUTHOR]

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 C13H9+ 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 λ<260 nm photons and were assigned to the FL9 and BfI radicals, respectively. The strongest peak at 518 nm is the origin of the 2 1B2←X̃ 1A1 absorption of FL9+, and the 490 nm band is the 2 2A2←X̃ 2B1 origin of FL9. The electronic systems commencing at 538 nm and 546 nm were assigned to the 1 1A1←X̃ 1A1 and 1 2A2←X̃ 2A2 transitions of BfI+ and BfI. The 392 nm band is the 1 1E′←X̃ 1A1′ transition of PHL+. The electronic spectra of C13H9+/C13H9 were assigned on the basis of the vertical excitation energies calculated with SAC-CI and MS-CASPT2 methods. [ABSTRACT FROM AUTHOR]

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 l=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 ²B1←X²B1 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. [ABSTRACT FROM AUTHOR]

The fulvenallenyl radical was produced in 6 K neon matrices after mass-selective deposition of C7Hf and C7H5+ generated from organic precursors in a hot cathode ion source. Absorption bands commencing at I = 401.3 nm were detected as a result of photodetachment of electrons from the deposited C-flf and also by neutralization of C7H5+ in the matrix. The absorption system is assigned to the 1 ²B1 ↑ X²B1 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. [ABSTRACT FROM AUTHOR]

Electronic absorption spectra of linear C 6 Br + and C 6 Br 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 2 Π ← X 2 Π electronic transition of C 6 Br, and 1 3 Σ − ← X 3 Σ − of C 6 Br + . 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 C 6 Cl and C 6 Cl + , and excitation energies obtained with CASPT2 and SAC-CI theory as well as on computed vibrational frequencies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Two absorption systems of C5H3+starting at 350 and 345 nm were detected following mass-selectivedeposition of m/e= 63 ions in a6 K neon matrix. These are assigned to the 11A1← X 1A1electronic transitionof 1,2,3,4-pentatetraenylium H2CCCCCH+(isomer B+) and 11B2← X 1A1of penta-1,4-diyne-3-yliumHCCCHCCH+(C+). Theabsorptions of neutral C5H3isomers with onsetsat 434.5, 398.3, 369.0, and 267.3 nm are also detected. The firsttwo systems are assigned to the 12B1← X 2B1and 12A2← X 2B1transitions ofisomer Band C, respectively, and the lattertwo to ethynylcyclopropenyl (A) and 3-vinylidenecycloprop-1-enyl(D) radicals. The structural assignments are based onthe adiabatic excitation energies calculated with the MS-CASPT2 method.A vibrational analysis of the electronic spectra, based on the calculatedharmonic frequencies, supports this. [ABSTRACT FROM AUTHOR]

Three absorption systems with originsat 354, 497, and 528 nm weredetected 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 C3O2anddiacetylene in a hot cathode source, or by dissociative ionizationof tetrabromocyclohexadienone. The 497 and 354 nm systems are assignedto the 12A″ ← X2A″ and22A″ ← X2A″ electronictransitions of B+, (2-ethynylcycloallyl)methanonecation, and the 528 nm absorption to the 12A2← X2B1transition of F+, 2-ethynylbut-3-yn-1-enone-1-ylide, on the basis ofcalculated excitation energies with CASPT2. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Absorptions of FC6F+ and HC6F+ in neon matrixes were observed for the first time. [•] The A2Πg ←X2Πu electronic transition of FC6F+ is identified at 569.3nm. [•] The A2Π←X2Π electronic transition of HC6F+ is identified at 586.3nm. [•] Structures are determined as linear carbon chains terminated with heteroatoms. [Copyright &y& Elsevier]

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+← X1Σ+electronic transition of linear C7O, and the absorption, with onset at 276.0 nm, to (4)2Σ+← X2Σ+of C7O+on the basis of experimental observations and theoretical calculations. [ABSTRACT FROM AUTHOR]

The significant biaxial anisotropy contribution below 50 K is evidenced and identified as a cause of asymmetric 'kinked' magnetization reversal behaviour and strong single cycle training effect in ion-beam sputtered IrMn/NiFe bilayers. The minor loop measurement clearly suggests that the magnetization reversal along the descending branch of the hysteresis loop takes place in two distinct steps comprising initial magnetization rotation followed by irreversible domain processes. Our experimental observations of characteristic magnetoresistance and minor loop measurements unambiguously endorse the recent theoretical prediction of Hoffmann suggesting the critical role of the symmetry of antiferromagnetic anisotropy on the reversal asymmetry and training effect. [ABSTRACT FROM AUTHOR]

Abstract: Fluorescence spectra of protonated pyrene and coronene in solid neon have been observed. Laser excitation of the S n ←S0 transitions of the cations results in an extended, vibrationally-resolved S1 →S0 fluorescence with onset at 487.8 and 695.4nm 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. [Copyright &y& Elsevier]

Using magnetoresistance as a probe we demonstrate the correlation between reversal asymmetry and training effect in ion-beam sputtered IrMn/NiFe bilayers. During the training procedure, both exchange bias field and the degree of asymmetry decrease monotonically following a very similar trend. The analysis of the magnetoresistance behaviour establishes that the two distinct training mechanisms are operative. The first one is exhibited by an abrupt single cycle training effect and an accompanying pronounced reversal asymmetry, attributed to the presence of biaxial anisotropy in the IrMn layer. The second one displays a gradual cycling dependence due to thermal depinning of uncompensated antiferromagnetic spins. [ABSTRACT FROM AUTHOR]

Abstract: The structural and magnetic properties of as-grown 5–50nm thin ion-beam sputter deposited transition metal–metalloid Co20Fe60B20 (CFB) films are reported in this communication. A broad peak observed at 2θ∼45° in the glancing angle X-ray diffraction pattern revealed the formation of very fine nano-sized grains embedded in majority amorphous CFB matrix. Although no magnetic field is applied during deposition, the longitudinal magneto-optic Kerr effect measurements performed at 300K in these as-grown films clearly established the presence of in-plane uniaxial magnetic anisotropy (K u ). It is argued that this observed anisotropy is strain-induced. This is supported by the observed dependence of direction of K u on the angle between applied magnetic field and crystallographic orientation of the underlying Si(100) substrate, and increase in the coercivity with the increase of the film thickness. [Copyright &y& Elsevier]

A set of arenes (phenylacetylene, indene, and naphthalene cations and C11H9+ isomers) was produced from 2,4-hexadiyne diluted in helium in a hot-cathode discharge source. The mass-selected ions were codeposited with neon at 6 K and investigated by electronic absorption spectroscopy. This reveals that fused-ring species are readily formed from an acyclic precursor in such a source. After photobleaching of matrices containing C11H9+, neutral C11H9· radicals were also characterized. Assignment of the observed transitions to different m/z = 141 cationic and corresponding neutral isomers is given and supported by experiments using other precursors, fluorescence measurements, and time-dependent density functional and second-order approximate coupled cluster calculations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Electronic transitions of protonated benzene (A 1B2←X1A1, origin at 325 nm) and α-protonated fulvene (A 1A″←X1A″, 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 a-hydrogenated fulvene (532 and 326 nm) radicals were identified. Upon excitation of cyclohexadienyl to the B 2B1 state, photoisomerization to an open-chain structure and α-hydrogenated fulvene was observed. [ABSTRACT FROM AUTHOR]

Model fibrillating homopolypeptides have been providing many insightful analogies to the clinically important phenomena of protein misfolding and amyloidogenesis. Here we show that the β2structural variant of poly(l-glutamic) acid forms fibrils with an amyloid-like morphology, ability to enhance fluorescence of thioflavin T, and seeding properties. The β2fibrils are formed upon heating of aqueous solutions of α-helical poly(l-glutamic) acid, which leads to a significant increase of pD (pH) of unbuffered samples and a concomitant precipitation of fibrils with unusual infrared traits: amide I′ band being dramatically red-shifted to 1596 cm−1, and the −COOD stretching band split into two peaks around 1730 and 1719 cm−1. We are proposing that formation of three-center hydrogen bonds involving bifurcated peptide carbonyl acceptors (>CO) and main chains’ NH, as well as side chains’ −COOH proton donors is likely to underlie the observed infrared characteristics of β2fibrils. Such bonds provide additional conformational constraints in a tightly packed environment around glutamate side chains resulting in the decreased overall acidity of the polypeptide. The presence of bifurcated hydrogen bonds in amyloid fibrils may be an overlooked factor in fibrils’ robustness, thermodynamic stability and the ability to propagate their own growth. [ABSTRACT FROM AUTHOR]

While thermodynamic penalties associated with protein−water interactions are the key driving force of folding, perturbed hydration of destabilized protein molecules may trigger aggregation, which in vivooften causes cellular and histological damage. Here we show, that the denatured state of an α-helical protein, insulin, converts to a non-native β-sheet-rich structure upon de novo“refolding” in an anhydrous environment. The β-pleated conformer precipitates from solutions of DMSO-denatured insulin upon dilution with chloroform. DMSO destroys hydrogen bond network of the native protein acting as a strong acceptor of main chain hydrogen bonds. Upon the addition of chloroform, which is a weak hydrogen bond donor per se, competitive hydrogen bonds between DMSO and chloroform are formed. This leads to the release of unfolded insulin molecules. In the absence of water, the imminent saturation of polypeptide’s dandling hydrogen bonds does not produce the native and predominantly α-helical state but a β-sheet-rich structure, which is morphologically and spectrally distinct from insulin amyloid fibrils. Unlike insulin fibrils, the β-sheet conformer is metastable and refolds spontaneously to the native form in an aqueous environment. This implies that “folding” in the absence of water results in inefficient burial of hydrophobic side-chains, and thermodynamic frustration at the water−protein interface. [ABSTRACT FROM AUTHOR]

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

The polyacetylene HC2nHn2−7 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 Ã2← 2system, several new transitions to higher excited 2electronic states of these cations have been observed. In the case of HC4Hand HC6H, only one new weak absorption system has been detected with the onset at 336.1 and 417.2 nm, respectively. These 2← 2transitions form a series that extends to HC10H. Two further electronic transitions are observed for HC8Hthrough to HC14H; a weaker 2u← 2gand a strong 2u← 2gin the UV. The integrated intensity of the UV system of the polyacetylene cations exceeds that of the Ã2← 2transition by an order of magnitude. [ABSTRACT FROM AUTHOR]

The anions of CsC2and CsC4produced by sputtering a graphite surface with Cswere mass-selected and trapped in neon matrixes at 6 K. The electronic absorption spectra of CsC2and CsC4, obtained by photodetachment of electrons from the anions, were measured subsequently and reveal strong absorptions in the visible range, which resemble the known band systems of C2-and C4-, respectively. The origin band of CsC2(500.4 nm) and CsC4(442.6 nm) is shifted by ∼1100 or by ∼700 cm-1to the blue from the position of the %@mt;sys@%0%@sx@%0%@be@%0%@sxx@%%@mx@%band of C2-or C4-. The observed system of CsC2is assigned to the 2B2−X 2A1electronic transition of the T-shaped form. The CsC4spectrum is consistent with a C4-chain slightly perturbed by the Cs atom. The oscillator strength of the observed electronic transition of CsC2and CsC4is an order of magnitude larger than for the respective carbon anions. CsC2-has a weak electronic transition, assigned to 1B2−X 1A1in the C2vform, with origin band at 516.5 nm. [ABSTRACT FROM AUTHOR]

Electronic absorption spectra of the protonated polyacetylenic chains H2CnH(n 4, 6, 8) and the neutral H2C8H have been observed in 6 K neon matrixes after mass selection. The wavelength of the H2CnHelectronic transitions depends quasi-linearly on n, typical of carbon chains. The origin band is at 286.0, 378.6, and 467.6 nm for n 4, 6, and 8, respectively. Two ground-state vibrations of H2C4Hin the IR absorption spectrum were also detected. On the basis of the spectroscopic trends and the assignment of the vibrational frequencies in the ground and excited electronic states, it is concluded that the H2CnHspecies are C2vlinear carbon chains with one H atom on one end and two on the other. [ABSTRACT FROM AUTHOR]

The electronic absorption spectra of linear C6H+ and C8H+ were recorded in 6 K neon matrixes following mass selective deposition. The (1) 3Σ-−X 3Σ- electronic transition is identified with the origin band at 515.8 and 628.4 nm for l-C6H+ and l-C8H+, respectively. One strong (near 267 nm) and several weaker electronic transitions of l-C8H+ have also been observed in the UV. The results of ab initio calculations carried out for linear and cyclic C6H+ are consistent with the assignment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Using micromagnetic simulations, we study the interplay between strongly voltage-controlled magnetic anisotropy (VCMA), Δ K = ± 200 kJ/m3, and gate width, w = 10–400 nm, in voltage-gated W/CoFeB/MgO based nano-constriction spin Hall nano-oscillators. The VCMA modifies the local magnetic properties such that the magnetodynamics transitions between regimes of (i) confinement, (ii) tuning, and (iii) separation with qualitatively different behaviors. We find that the strongest tuning is achieved for gate widths of the same size as the constriction width, for which the effective damping can be increased an order of magnitude compared to its intrinsic value. As a consequence, voltage control remains efficient over a very large frequency range, and subsequent manufacturing advances could allow spin Hall nano-oscillators to be easily integrated into next-generation electronics for further fundamental studies and industrial applications. [ABSTRACT FROM AUTHOR]

Absorptions commencing at 602.6 nm are detected following deposition of mass-selected C[sub 7]H[sub 4] [sup +] in a 6 K neon matrix produced from a 1 : 1 mixture of diacetylene and propyne in an ion source. The 602.6 nm system, and a weaker one near 421.1 nm, are assigned to the A [sup 2]E ← X [sup 2]E and B [sup 2]E ← X [sup 2]E electronic transitions of methyltriacetylene cation (C [sub 3V] symmetry), based on mass-selection, spectroscopic analysis of the vibrational structure, and the excitation energies calculated with CASPT2. Structured fluorescence is detected in the 600-760 nm range upon laser excitation at wavelengths of the CH[sub 3]C[sub 6]H[sup +] absorptions. The vibrational bands observed in the absorption and fluorescence spectra are assigned with the aid of calculated frequencies of the totally symmetric (a[sub 1]) vibrations of methyltriacetylene cation. [ABSTRACT FROM AUTHOR]

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' 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. [ABSTRACT FROM AUTHOR]

In this work, we report a study of the influence of large anisotropy of CoFe layer on the reversal asymmetry and training effect in exchange biased IrMn/CoFe bilayers. The existence of a strong single cycle training effect and an accompanying distinct reversal asymmetry at 15 K have been demonstrated using magnetoresistance as a probe. The temperature dependent change in the symmetry (uniaxial to biaxial) of IrMn anisotropy has been proposed as the primary cause of the occurrence of pronounced reversal asymmetry and large training effect below 50 K. In particular, the present findings indicate that the observed differences between IrMn/CoFe and IrMn/NiFe [Fulara et al., Appl. Phys. Lett. 101, 142408 (2012)] systems in their asymmetric behaviour of magnetization reversal and training effect are linked with the interplay between the interfacial spin frustration and the intrinsic ferromagnetic anisotropy. [ABSTRACT FROM AUTHOR]

A miniature gas turbine (MGT) is proposed as a promising future energy source. Increasingly stringent requirements related to harmful combustible gas emissions and a trend towards improved energy generation efficiency drive the quest for new MGT technologies. Variable geometry systems are promising due to enhanced heat management and flow control. Variable combustor cooling and dilution holes together with the variable area nozzle (VAN) system allow for the improvement of gas turbine performance and reduction in pollutant emissions. The proposed systems are based on hot-section geometry changes, in which the size of the combustion chamber holes and turbine nozzle angle can be adjusted. Component and module experimental research were performed at the Warsaw University of Technology, on an MGT test stand. A significant decrease in fuel consumption (up to 47% reduction) and harmful nitrogen oxide emission reduction (NO–by 78% and NO2–by 82%) were achieved. These results are related to combustor turbine inlet temperature (TIT) increase up to 1230 K. The tests of the variable geometry systems have also shown an impact on gas turbine power and specific fuel consumption. [ABSTRACT FROM AUTHOR]

Abstract: The electronic transition of the B3 molecule with origin band at 5990cm−1 has been observed in a 6 K neon matrix. A vibrational progression in the spectrum corresponds to the excitation of the ν 1 vibrational mode in the state with a frequency of ∼1092cm−1. The band system was detected after laser ablation of a boron rod and the origin band also after mass-selected deposition of anions with subsequent neutralization. [Copyright &y& Elsevier]

This study reports the growth and investigation of (001)-oriented MnN/Fe thin films on the W buffer layer, focusing on detailed exchange bias (EB) studies, including thermal evolution (300–10 K) and the training effect. At room temperature, the magnetically annealed α -W/MnN/Fe/Ta stack exhibits an EB field ( H E B ) of 118 Oe. With decreasing temperature, particularly below 100 K, both H E B and coercive field ( H C ) show substantial increases, with H E B displaying a more pronounced enhancement. Analysis of the temperature-dependent H E B and H C data reveals an exponential trend, indicative of a spin-glass-like interface in the MnN/Fe system. At 10 K, the pronounced EB is accompanied by an asymmetric "kinked" magnetization reversal, suggesting a transition from uniaxial to biaxial anisotropy below 50 K due to spin-glass-like magnetic frustration at the interdiffused MnN/Fe interface. Training effect measurements further support the spin-glass-like MnN/Fe interface, with two distinct training mechanisms observed at 10 K: "athermal" and "thermal." Finally, the spin-glass model demonstrates an excellent fit for the training effect data, validating the presence of spin-glass-like disorder at the MnN/Fe interface. [ABSTRACT FROM AUTHOR]

The A [sup 2]Δ[sub u]←X [sup 2]Π[sub g], B [sup 2]Σ[sub u][sup -]←X [sup 2]Π[sub g], and C [sup 2]Σ[sub u][sup +]←X [sup 2]Π[sub g] electronic transitions of C[sub 3][sup -] 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 [sup 4]Π[sub u]←X [sup 2]Π[sub g] 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. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a laboratory evidence that highly saturated hydrocarbons with carbon numbers 6-12 may be the carriers of some of the diffuse interstellar bands (DIB) in the range 480-1,000 nanometers. Deposition of mass-selected molecules in a neon matrix at 5 Kelvin and measurement of near-infrared, visible and ultraviolet spectra; Correspondence of 15 lines to 15 DIBs.

In this study, we present the observations of extreme-ultraviolet (EUV) waves associated with an M6.5 flare on 2013 April 11. The event was observed by Solar Dynamics Observatory (SDO) in different EUV channels. The flare was also associated with a halo CME and type II radio bursts. We observed both fast and slow components of the EUV wave. The speed of the fast component, which is identified as a fast-mode MHD wave, varies in the range from 600 to 640 km s − 1 , whereas the speed of the slow-component is ≈ 140 km s − 1 . We observed the unusual phenomenon that, as the fast-component EUV wave passes through two successive magnetic quasi-separatrix layers (QSLs), two stationary wave fronts are formed locally. We propose that part of the outward-propagating fast-mode EUV wave is converted into slow-mode magnetohydrodynamic waves, which are trapped in local magnetic field structures, forming successive stationary fronts. Along the other direction, the fast-component EUV wave also creates oscillations in a coronal loop lying ≈ 225 Mm away from the flare site. We have computed the energy of the EUV wave to be of the order of 10 20 J . [ABSTRACT FROM AUTHOR]