The intermetallic compound Mg21Zn25

The crystal structure of the intermetallic compound henicosa­magnesium pentacosazinc, Mg₂₁Zn₂₅, has been determined by single‐crystal X‐ray diffraction. It is isomorphous with Zr₂₁Re₂₅ and deviates slightly from the rules that define the Frank–Kasper phases.     

Changes of Chlorophyll(ide) Fluorescence Yield Induced by a Short Light Pulse as a Probe to Monitor the Early Steps of Etioplast Phototransformation in Dark-Grown Leaves

The fluorescence yield of chlorophyll(ide) (Chl[ide]) excited by weak modulated light was recorded at room temperature during a 2 h period after a short actinic light pulse that transformed all photoactive protochlorophyllide in dark-grown barley leaves. A typical pattern of fluorescence yield variations was found whatever the age of the leaf but with age-dependent changes in rates. Its successive phases were related to the Chl(ide) spectral shifts observed in low-temperature emission spectra. The fluorescence yield started at a high level and strongly declined during the formation of Chlide₆₉₅ from Chlide₆₆₈ within a few seconds. It increased to a transient maximum during the Shibata shift (15–25 min) that resulted in Chl(ide)₆₈₂. A final, slow decrease to a steady state occurred during the final red shift to Chl₆₈₅. Pretreatments with δ-aminolevulinic acid, chloramphenicol or 1, 10-phenanthroline resulted in correlated modifications of Chl(ide) fluorescence yield transients and shifts of the low-temperature Chl(ide) emission band. The complex response of the final decrease phase of the fluorescence yield to these compounds suggests that it results both from the assembly of photosynthetic Chl proteins and from the reorganization of the etioplast membrane system. From these results it is concluded that continuous recordings of Chl(ide) fluorescence yield after a short light pulse represent a useful tool to monitor the kinetics of pigment–protein organization and primary thylakoid assembly triggered by Pchlide photoreduction.     

COPPER QUENCHING OF THE VARIABLE FLUORESCENCE IN Dunaliella tertiolecta. NEW EVIDENCE FOR A COPPER INHIBITION EFFECT ON PSII PHOTOCHEMISTRY

Abstract— The copper quenching effect on fluorescence in Dunaliella tertiolecta was studied. 30% of variable fluorescence was quenched in the presence of 70 μ,M CuS0₄. We confirmed that the copper inhibitory effect on photosystem II (PSII) activity is located on its oxidizing side. Further, we indicate that the complementary area is decreased by copper. Since the quantum yield of PSII photochemistry was lowered and the rate of PSII primary electron acceptor Q_A remained unaffected, we can conclude that some PSII reaction centers were inactivated by copper.     

A tetragonal polymorph of caesium hydroxide monohydrate,CsOH·H2O,from X‐ray powder data

Tetragonal caesium hydro­xide monohydrate, CsOH·H₂O, a clathrate hydrate, is a polymorph of three known hexagonal or pseudo‐hexagonal modifications. It was obtained as a by‐product in a high‐pressure experiment. Whether it is a high‐pressure polymorph, however, remains to be verified. The Cs atoms are situated in cavities of the form of a bicapped pentagonal prism, within an infinite three‐dimensional hydrogen‐bonded oxy­gen framework that is locally identical to layers found in the hexagonal modifications. The Cs atom and one of the two H atoms are at sites with symmetry, the O atom has mm site symmetry and the second H atom has 2/m symmetry.     

Preparation of (S,S)‐Fmoc‐β2hIle‐OH, (S)‐Fmoc‐β2hMet‐OH,and (S)‐Fmoc‐β2hTyr(tBu)‐OH for Solid‐Phase Syntheses of β2‐ and β2/β3‐Peptides

The preparation of three new N‐Fmoc‐protected (Fmoc=[(9H‐fluoren‐9‐yl)methoxy]carbonyl) β²‐homoamino acids with proteinogenic side chains (from Ile, Tyr, and Met) is described, the key step being a diastereoselective amidomethylation of the corresponding Ti‐enolates of 3‐acyl‐4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐ones with CbzNHCH₂OMe/TiCl₄ (Cbz=(benzyloxy)carbonyl) in yields of 60–70% and with diastereoselectivities of >90%. Removal of the chiral auxiliary with LiOH or NaOH gives the N‐Cbz‐protected β‐amino acids, which were subjected to an N‐Cbz/N‐Fmoc (Fmoc=[(9H‐fluoren‐9‐yl)methoxy]carbonyl) protective‐group exchange. The method is suitable for large‐scale preparation of Fmoc‐β²hXaa‐OH for solid‐phase syntheses of β‐peptides. The Fmoc‐amino acids and all compounds leading to them have been fully characterized by melting points, optical rotations, IR, ¹H‐ and ¹³C‐NMR, and mass spectra, as well as by elemental analyses.     

The quadrupole moment of the 3/2+ nuclear ground state of 197Au from electric field gradient relativistic coupled cluster and density-functional theory of small molecules and the solid state

An attempt is made to improve the currently accepted muonic value for the 197Au nuclear quadrupole moment [+0.547(16)x10(-28) m2] for the 3/2+ nuclear ground state obtained by Powers et al. [Nucl. Phys. A230, 413 (1974)]. From both measured Mossbauer electric quadrupole splittings and solid-state density-functional calculations for a large number of gold compounds a nuclear quadrupole moment of +0.60x10(-28) m2 is obtained. Recent Fourier transform microwave measurements for gas-phase AuF, AuCl, AuBr, and AuI give accurate bond distances and nuclear quadrupole coupling constants for the 197Au isotope. However, four-component relativistic density-functional calculations for these molecules yield unreliable results for the 197Au nuclear quadrupole moment. Relativistic singles-doubles coupled cluster calculations including perturbative triples [CCSD(T) level of theory] for these diatomic systems are also inaccurate because of large cancellation effects between different field gradient contributions subsequently leading to very small field gradients. Here one needs very large basis sets and has to go beyond the standard CCSD(T) procedure to obtain any reliable field gradients for gold. From recent microwave experiments by Gerry and co-workers [Inorg. Chem. 40, 6123 (2001)] a significantly enhanced (197)Au nuclear quadrupole coupling constant in (CO)AuF compared to free AuF is observed. Here, these cancellation effects are less important, and relativistic CCSD(T) calculations finally give a nuclear quadrupole moment of +0.64x10(-28) m2 for 197Au. It is argued that it is currently very difficult to improve on the already published muonic value for the 197Au nuclear quadrupole moment.     

Synthesis,and Helix or Hairpin‐Turn Secondary Structures of ‘Mixed’ α/β‐Peptides Consisting of Residues with Proteinogenic Side Chains and of 2‐Amino‐2‐methylpropanoic Acid (Aib)

Twelve peptides, 1 – 12 , have been synthesized, which consist of alternating sequences of α‐ and β‐amino acid residues carrying either proteinogenic side chains or geminal dimethyl groups (Aib). Two peptides, 13 and 14 , containing 2‐methyl‐3‐aminobutanoic acid residues or a ‘random mix’ of α‐, β²‐, and β³‐amino acid moieties were also prepared. The new compounds were fully characterized by CD (Figs. 1 and 2), and ¹H‐ and ¹³C‐NMR spectroscopy, and high‐resolution mass spectrometry (HR‐MS). In two cases, 3 and 14 , we discovered novel types of turn structures with nine‐ and ten‐membered H‐bonded rings forming the actual turns. In two other cases, 8 and 11 , we found 14/15‐helices, which had been previously disclosed in mixed α/β‐peptides containing unusual β‐amino acids with non‐proteinogenic side chains. The helices are formed by peptides containing the amino acid moiety Aib in every other position, and their backbones are primarily not held together by H‐bonds, but by the intrinsic conformations of the containing amino acid building blocks. The structures offer new possibilities of mimicking peptide–protein and protein–protein interactions (PPI).     

Changes in the room-temperature emission spectrum of chlorophyll during fast and slow phases of the Kautsky effect in intact leaves

Changes in the room-temperature emission spectrum of chlorophyll (Chl) were analyzed using fast diode-array recordings during the Kautsky effect in mature and in greening barley leaves. In mature leaves, the comparison of F(O) (basal level of fluorescence yield at transient O) and F(M) (maximum level of fluorescence yield at transient M) spectra showed that the relative amplitude of total variable fluorescence was maximal for the 684 nm Photosystem II (PSII) band and minimal for the 725 nm Photosystem I band. During the increase from F(O) to F(M), a progressive redshift of the spectrum of variable fluorescence occurred. This shift reflected the different fluorescence rise kinetics of different layers of chloroplasts inside the leaf. This was verified by simulating the effect of screening on the emission spectrum of isolated chloroplasts and by experiments on greening leaves with low Chl content. In addition, experiments performed at different greening stages showed that the presence of uncoupled Chl at early-greening stages and light-harvesting complex II (LHCII) at later stages have detectable but minor effects on the shape of room-temperature emission spectra. When strong actinic light was applied to mature green leaves, the slow fluorescence yield, which declined from F(M) to F(T) (steady-state level of fluorescence yield at transient T), was accompanied by a slight redshift of the 684 nm PSII band because of nonphotochemical quenching of short-wavelength-emitting Chl ascribed to LHCII.     

Proteotypic peptides of hairs for the identification of common European domestic and wild animal species revealed by in-sample protein digestion and mass spectrometry analysis

The aim of this work is to offer an alternative or complementary analytical tool to the time-consuming and expensive methods commonly used for the recognition of animal species according to their hair. The paper introduces a simple and fast way for species differentiation of animal hairs called in-sample digestion. A total of 10 European animal species, including cat, cow, common degu, dog, fallow deer, goat, horse, sika deer, rabbit, roe deer, and 17 different breeds of dogs were examined using specific tryptic cleavage directly in hair followed by matrix-assisted laser desorption/ionization–time of flight mass spectrometry and liquid chromatography-electrospray ionization quadrupole time of flight. Principal component analysis was used for the subsequent mass spectrometric data evaluation. This novel approach demonstrates the ability to distinguish among individual animal species, which is supported by finding characteristic m/z values obtained by the mass spectrometry for each animal species. The approach was successfully tested on two “blind” samples. On the other hand, the attempt to distinguish among hairs of different dog breeds has not been successful due to the very similar protein composition and their amino acid sequences.     

Characterization of vestibular schwannoma tissues using liquid chromatography-tandem mass spectrometry analysis of specific peptide fragments separated by in-sample tryptic protein digestion followed by mathematical analysis

Vestibular schwannoma is the most common benign neoplasm of the cerebellopontine angle. Its first symptoms include hearing loss, tinnitus, and vestibular symptoms, followed by cerebellar and brainstem symptoms, along with palsy of the adjacent cranial nerves. However, the clinical picture has unpredictable dynamics and currently, there are no reliable predictors of tumor behavior. Hence, it is desirable to have a fast routine method for analysis of vestibular schwannoma tissues at the molecular level. The major objective of this study was to verify whether a technique using in-sample specific protein digestion with trypsin would have the potential to provide a proteomic characterization of these pathological tissues. The achieved results showed that the use of this approach with subsequent liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of released peptides allowed a fast identification of a considerable number of proteins in two differential parts of vestibular schwannoma tissue as well as in tissues of control healthy samples. Furthermore, mathematical analysis of MS data was able to discriminate between pathological vestibular schwannoma tissues and healthy tissues. Thus, in-sample protein digestion combined with LC-MS/MS separation and identification of released specific peptides followed by mathematical analysis appears to have the potential for routine characterization of vestibular schwannomas at the molecular level. Data are available via ProteomeXchange with identifier PXD045261.