Quantitative Aspects of Electrochemical Detection of Amyloid‐β Aggregation

The tyrosine based electrochemical analysis of synthetic amyloid‐β (Aβ) peptide – an analog of natural peptide implicated in Alzheimer's disease pathogenesis – was applied for a quantitative estimation of peptide aggregation in vitro. The analysis was carried out by square wave voltammetry (SWV) on carbon screen printed electrodes (SPE). The electrooxidation peak current (I_p) for Aβ42 peptide in different aggregation states was directly compared with the size and structure of Aβ42 aggregates occurring in the analyzed sample. Dynamic light scattering (DLS) and thioflavin T (ThT) based fluorescence assay were employed to estimate the size and structure of Aβ42 aggregates. The I_p was found to decrease in a linear fashion when the average diameter of aggregates and the relative ThT fluorescence in Aβ42 solutions exceeded 35 nm and 3, respectively, while being nearly constant below these values. It was suggested that the electrooxidation current is mostly generated by peptide monomers and that a depletion of the monomer pool due to inclusion of Aβ42 molecules in aggregates is responsible for the decrease of electrooxidation current. The direct electrochemistry is emerging as a method complementary to methods based on aggregates’ detection and commonly employed for monitoring Aβ aggregation. The work further enlarges the basis for application of the cost‐effective and rapid electrochemical techniques, such as SWV on carbon SPE, to in vitro studies of Aβ aggregation.     

Conformation of Peptides Containing a Chiral α‐Ethylated α,α‐Disubstituted α‐Amino Acid: (S)‐α‐Ethylleucine (=(2S)‐2‐Amino‐2‐ethyl‐4‐methylpentanoic Acid) within Sequences of Dimethylglycine and Diethylglycine Residues

An optically active (S)‐α‐ethylleucine ((S)‐αEtLeu) as a chiral α‐ethylated α,α‐disubstituted α‐amino acid was synthesized by means of a chiral acetal auxiliary of (R,R)‐cyclohexane‐1,2‐diol. The chiral α‐ethylated α,α‐disubstituted amino acid (S)‐αEtLeu was introduced into the peptides constructed from 2‐aminoisobutyric acid (=dimethylglycine, Aib), and also into the peptide prepared from diethylglycine (Deg). The X‐ray crystallographic analysis revealed that both right‐handed (P) and left‐handed (M) 3₁₀‐helical structures exist in the solid state of CF₃CO‐(Aib)₂‐[(S)‐αEtLeu]‐(Aib)₂‐OEt ( 14 ) and CF₃CO‐[(S)‐αEtLeu]‐(Deg)₄‐OEt ( 18 ), respectively. The IR, CD, and ¹H‐NMR spectra indicated that the dominant conformation of pentapeptides 14 and CF₃CO‐[(S)‐αEtLeu]‐(Aib)₄‐OEt ( 16 ) in solution is a 3₁₀‐helical structure, and that of 18 in solution is a planar C₅ conformation. The conformation of peptides was also studied by molecular‐mechanics calculations.     

Cobalt(II)–metformin complexes containing α‐diimine/α‐diamine as auxiliary ligand: DNA binding properties

The cobalt(II) complexes [Co(Cl)₂(met)(o‐phen)] ( 1 ), [Co(Cl)₂(en)(met)] ( 2 ) and [Co(Cl)₂(met)(opda)] ( 3 ) (met = metformin, o‐phen = ortho‐phenanthroline, en = ethylenediamine, opda = ortho‐phenylenediamine) were synthesized and characterized using liquid chromatography–mass spectrometry, elemental analysis, molar conductance measurements, thermal analysis, infrared spectroscopy, magnetic moment measurements, electronic spectroscopy and X‐ray diffraction. The metal centre was found to be in an octahedral geometry. UV–visible absorption, fluorescence and viscosity measurements were conducted to assess the interaction of the complexes with calf thymus DNA. The complexes showed absorption hyperchromism in UV–visible spectra with DNA. The binding constants from UV–visible absorption studies were 1.38 × 10⁵, 2.1 × 10⁵ and 3.1 × 10⁵ M^?1 for 1 , 2 and 3 , respectively, and Stern–Volmer quenching constants from fluorescence studies were 0.146, 0.176 and 0.475, respectively. Viscosity measurements revealed that the binding of the complexes with DNA could be surface binding, mainly due to groove binding. The activities of the complexes in DNA cleavage decrease in the order 3 > 2 > 1 . The complexes were docked into DNA topoisomerase II using Discovery Studio 2.1 software.     

Tunable Dual Fluorescence of 3‐(2,2′‐Bipyridyl)‐Substituted Iminocoumarin

3‐(2,2′‐Bipyridyl)‐substituted iminocoumarin molecules (compounds 1 and 2 ) exhibit dual fluorescence. Each molecule has one electron donor and two electron acceptors that are in conjugation, which leads to fluorescence from two independent charge transfer (CT) states. To account for the dual fluorescence, we subscribe to a kinetic model in which both CT states form after rapid decays from the directly accessed S₁ and S₂ excited states. Due to the slow internal conversion from S₂ to S₁, or more likely the slow interconversion between the two subsequently formed CT states, dual emission is allowed to occur. This hypothesis is supported by the following evidence: 1) the emission at short and long ends of the spectrum originates from two different excitation spectra, which eliminates the possibility that dual emission occurs after an adiabatic reaction at the S₁ level. 2) The fluorescence quantum yield of compound 2 grows with increasing excitation wavelength, which indicates that the high‐energy excitation elevates the molecule to a weakly emissive state that does not internally convert to the low‐energy, highly emissive state. The intensity of the two emission bands of 1 is tunable through the specific interactions between either of the two electron acceptors with another species, such as Zn²⁺ in the current demonstration. Therefore, the development of ratiometric fluorescent indicators based on the dual‐emitting iminocoumarin system is conceivable. Further fundamental studies on this series of compounds using time‐resolved spectroscopic techniques, and explorations of their applications will be carried out in the near future.     

Synthesis and Structure–Property Relationships of 2,2′‐Bis(benzo[b]phosphole) and 2,2′‐Benzo[b]phosphole–Benzo[b]heterole Hybrid π Systems

The first comprehensive study of the synthesis and structure–property relationships of 2,2′‐bis(benzo[b]phosphole)s and 2,2′‐benzo[b]phosphole–benzo[b]heterole hybrid π systems is reported. 2‐Bromobenzo[b]phosphole P‐oxide underwent copper‐assisted homocoupling (Ullmann coupling) and palladium‐catalyzed cross‐coupling (Stille coupling) to give new classes of benzo[b]phosphole derivatives. The benzo[b]phosphole–benzo[b]thiophene and ‐indole derivatives were further converted to P,X‐bridged terphenylenes (X=S, N) by a palladium‐catalyzed oxidative cycloaddition reaction with 4‐octyne through the C_β? H activation. X‐ray analyses of three compounds showed that the benzo[b]phosphole‐benzo[b]heterole derivatives have coplanar π planes as a result of the effective conjugation through inter‐ring C? C bonds. The π–π* transition energies and redox potentials of the cis and trans isomers of bis(benzo[b]phosphole) P‐oxide are very close to each other, suggesting that their optical and electrochemical properties are little affected by the relative stereochemistry at the two phosphorus atoms. The optical properties of the benzo[b]phosphole–benzo[b]heterole hybrids are highly dependent on the benzo[b]heterole subunits. Steady‐state UV/Vis absorption/fluorescence spectroscopy, fluorescence lifetime measurements, and theoretical calculations of the non‐fused and acetylene‐fused benzo[b]phosphole–benzo[b]heterole π systems revealed that their emissive excited states consist of two different conformers in rapid equilibrium.     

α-D-Glycosyl-Substituted α,α-D-Trehaloses with (1 → 4)-Linkage: Syntheses and NMR Investigations

Two symmetrical trehalose glycosyl ‘acceptors’ 4 and 6 were prepared and three of the unsymmetrical type, 8 , 10 , and 11 . Glucosylation of symmetrical ‘acceptor’ 4 gave a higher yield of trisaccharide (44%) than protect ve-group manipulation, namely via selective debenzylidenation 2 → 9 or monoacetylation 2 → 5 which proceeded in moderate yields (33–34%). A comparison of catalysts in the cis-glucosylation of trehalose ‘acceptor’ 10 with tetra-O-benzyl-β-D -glucopyranosyl fluoride 13 profiled triflic anhydride ((Tf)₂O) as a new reactive promoter yielding 92% of trisaccharide 14 , deblocking gave the target saccharide α-D -glucopyranosyI-( 1 → 4 )-α,α-D -trehalose. ¹H-NMR spectra of most compounds were analyzed extensively. The use of the ID TOCSY technique is advocated for its time efficiency, if needed supplemented by ROESY experiments.     

Destabilized carbenium ions: α-carbomethoxy-α,α-dimethyl-methyl cations

Tertiary α-carbomethoxy-α,α-dimethyl-methyl cations a have been generated by electron impact induced fragmentation from the appropriately α-substituted methyl isobutyrates 1–4. The destabilized carbenium ions a can be distinguished from their more stable isomers protonated methyl methacrylate c and protonated methyl crotonate d by MIKE and CA spectra. The loss of I^— and Br˙ from the molecular ions of 1 and 2, respectively, predominantly gives rise to the destabilized ions a, whereas loss of Cl˙ from [3]^{+ ˙} results in a mixture of ions a and c. The loss of CH₃˙ from [4]⁺˙ favours skeletal rearrangement leading to ions d. The characteristic reactions of the destabilized ions a are the loss of CO and elimination of methanol. The loss of CO is associated by a very large KER and non-statistical kinetic energy release (T₅₀ = 920 meV). Specific deuterium labelling experiments indicate that the α-carbomethoxy-α,α-dimethyl-methyl cations a rearrange via a 1,4-H shift into the carbonyl protonated methyl methacrylate c and eventually into the alkyl-O protonated methyl methacrylate before the loss of methanol. The hydrogen rearrangements exhibit a deuterium isotope effect indicating substantial energy barriers between the [C₅H₉O₂]⁺ isomers. Thus the destabilized carbenium ion a exists as a kinetically stable species within a potential energy well.     

The First Fully Planar C5‐Conformation of Homooligopeptides Prepared from a Chiral α‐Ethylated α,α‐Disubstituted Amino Acid: (S)‐Butylethylglycine (=(2S)‐2‐Amino‐2‐ethylhexanoic Acid)

An optically active α‐ethylated α,α‐disubstituted amino acid, (S)‐butylethylglycine (=(2S)‐2‐amino‐2‐ethylhexanoic acid; (S)‐Beg; (S)‐ 2 ), was prepared starting from butyl ethyl ketone ( 1 ) by the Strecker method and enzymatic kinetic resolution of the racemic amino acid. Homooligopeptides containing (S)‐Beg (up to hexapeptide) were synthesized by conventional solution methods. An ethyl ester was used for the protection at the C‐terminus, and a trifluoroacetyl group was used for the N‐terminus of the peptides. The structures of tri‐ and tetrapeptides 5 and 6 in the solid state were solved by X‐ray crystallographic analysis, and were shown to have a bent planar C₅‐conformation (tripeptide) and a fully planar C₅‐conformation (tetrapeptide) (see Figs. 1 and 2, resp.). The IR and ¹H‐NMR spectra of hexapeptide 8 revealed that the dominant conformation in CDCl₃ solution was also a fully planar C₅‐conformation. These results show for the first time that the preferred conformation of homopeptides containing a chiral α‐ethylated α,α‐disubstituted amino acid is a planar C₅‐conformation.     

Methyl 2‐acetamido‐2‐deoxy‐β‐d‐glucopyranoside dihydrate and methyl 2‐formamido‐2‐deoxy‐β‐d‐glucopyranoside

Methyl 2‐acetamido‐2‐deoxy‐β‐d ‐glucopyranoside (β‐GlcNAcOCH₃), (I), crystallizes from water as a dihydrate, C₉H₁₇NO₆·H₂O, containing two independent molecules [denoted (IA) and (IB)] in the asymmetric unit, whereas the crystal structure of methyl 2‐formamido‐2‐deoxy‐β‐d ‐glucopyranoside (β‐GlcNFmOCH₃), (II), C₈H₁₅NO₆, also obtained from water, is devoid of solvent water molecules. The two molecules of (I) assume distorted ⁴C₁ chair conformations. Values of ϕ for (IA) and (IB) indicate ring distortions towards B_C2,C5 and ^C3,O5B, respectively. By comparison, (II) shows considerably more ring distortion than molecules (IA) and (IB), despite the less bulky N‐acyl side chain. Distortion towards B_C2,C5 was observed for (II), similar to the findings for (IA). The amide bond conformation in each of (IA), (IB) and (II) is trans, and the conformation about the C—N bond is anti (C—H is approximately anti to N—H), although the conformation about the latter bond within this group varies by ∼16°. The conformation of the exocyclic hydroxymethyl group was found to be gt in each of (IA), (IB) and (II). Comparison of the X‐ray structures of (I) and (II) with those of other GlcNAc mono‐ and disaccharides shows that GlcNAc aldohexopyranosyl rings can be distorted over a wide range of geometries in the solid state.     

Lipophilic Functionalized Cobyrinic-Acid Derivatives. Part 1. Cobester α-monoacids (α,α,α,β,β,β-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates)

The four α,α,α, β,β,β,-hexamethyl α-hydrogen Coα, Coβ-dicyanocobyrinates 2b, d–f , with a free b-, d-, e-, and f-propionic-acid function, respectively, were prepared by partial hydrolysis of heptamethyl Coα, Coβ-dicyanocobyrinate (cobester; 1 ) in aqueous sulfuric acid. The cobester monoacids 2b, d–f were obtained as a ca. 1:1:1:1 mixture which was separated. The monoacids were purified by chromatography and isolated in crystalline form. The position of the free propionic-acid function was determined by an extensive analysis of 2b, d–f using 2D-NMR techniques; an analysis of the C,H-coupling network topology resulted in an alternative assignment strategy for cobyrinic-acid derivatives, based on pattern recognition. Additional information on the structure of the most polar of the four hexamethyl cobyrinates, of the b-isomer 2b , was also obtained in the solid state from a single-crystal X-ray analysis. Earlier structural assignments based on 1D-NMR spectra of the corresponding regioisomeric monoamides 3b, d–f (obtained from crystalline samples of the monoacids 2b, d–f ) were confirmed by the present investigations.     

Conformational Study of Heteropentapeptides Containing an α‐Ethylated α,α‐Disubstituted Amino Acid: (S)‐Butylethylglycine (=2‐Amino‐2‐ethylhexanoic Acid) within a Sequence of Dimethylglycine (=2‐Aminoisobutyric Acid) Residues

Heteropentapeptides containing the α‐ethylated α,α‐disubstituted amino acid (S)‐butylethylglycine and four dimethylglycine residues, i.e., CF₃CO‐[(S)‐Beg]‐(Aib)₄‐OEt ( 4 ) and CF₃CO‐(Aib)₂‐[(S)‐Beg]‐(Aib)₂‐OEt ( 7 ), were synthesized by conventional solution methods. In the solid state, the preferred conformation of 4 was shown to be both a right‐handed (P) and a left‐handed (M) 3₁₀‐helical structure, and that of 7 was a right‐handed (P) 3₁₀‐helical structure. IR, CD, and ¹H‐NMR spectra revealed that the dominant conformation of both 4 and 7 in solution was the 3₁₀‐helical structure. These conformations were also supported by molecular‐mechanics calculations.     

1‐(β‐d‐Erythrofuranosyl)adenosine

The title compound, also known as β‐erythroadenosine, C₉H₁₁N₅O₃, (I), a derivative of β‐adenosine, (II), that lacks the C5′ exocyclic hydroxymethyl (–CH₂OH) substituent, crystallizes from hot ethanol with two independent molecules having different conformations, denoted (IA) and (IB). In (IA), the furanose conformation is ^OT₁–E₁ (C1′‐exo, east), with pseudorotational parameters P and τ_m of 114.4 and 42°, respectively. In contrast, the P and τ_m values are 170.1 and 46°, respectively, in (IB), consistent with a ²E–²T₃ (C2′‐endo, south) conformation. The N‐glycoside conformation is syn (+sc) in (IA) and anti (−ac) in (IB). The crystal structure, determined to a resolution of 2.0 Å, of a cocrystal of (I) bound to the enzyme 5′‐fluorodeoxyadenosine synthase from Streptomyces cattleya shows the furanose ring in a near‐ideal ^OE (east) conformation (P = 90° and τ_m = 42°) and the base in an anti (−ac) conformation.     

Interplay of α,α‐ versus α,β‐Conjugation in the Excited States and Charged Defects of Branched Oligothiophenes as Models for Dendrimeric Materials

This article investigates the excited and charged states of three branched oligothiophenes with methyl–thienyl side groups as models to promote 3D arrangements. A comparison with the properties of the parent systems, linear all‐α,α‐oligothiophenes, is proposed. A wide variety of spectroscopic methods (i.e., absorption, emission, triplet–triplet transient absorption, and spectroelectrochemistry) in combination with DFT calculations have been used for this purpose. Whereas the absorption spectra are slightly blueshifted upon branching, both the emission spectra and triplet–triplet absorption spectra are moderately redshifted; this indicates a larger contribution of the β‐linked thienyl groups in the delocalization of the S₁ and T₁ states rather than into the S₀ state. The delocalization through the α,β‐conjugated path was found to be crucial for the stabilization of the trication species in the larger branched systems, whereas the linear sexithiophene homologue can only be stabilized up to the dication species.     

Structure and Properties of γ‐Brass‐Type Pt2Zn11—δ (0.2 < δ < 0.3)

The γ‐brass type phase Pt₂Zn_11—δ (0.2 < δ < 0.3) was prepared by reaction of the elements in evacuated silica ampoules. The structures of crystals grown in the presence of excess zinc or alternatively excess platinum were determined from single crystal X‐ray diffraction intensities and confirmed by Rietveld profile fits. Pt₂Zn_10.72(1) crystallizes in the space group I4¯3m, a = 908.55(4) pm, Z = 4. The structure refinement converged at R_F = 0.0302 for I_o > 2σ (I_o) for 293 symmetrically independent intensi ties and 19 variables. The structure consists of a 26 atom cluster which is comprised of four crystallographically distinct atoms. The atoms Zn(1), Pt(1), Zn(2) and Zn(3) form an inner tetrahedron IT, an outer tetrahedron OT, an octahedron OH, and a distorted cuboctahedron CO respectively. About 14 % of the Zn(1) sites are unoccupied. Pt₂Zn_10.73 melts at 1136(2) K. It is a moderate metallic conductor (ρ₂₉₈ = 0.2—0.9 mΩ cm) whose magnetic properties (χ_mol = —4.6 10^—10 to —5.4 10^—10 m³ mol^—1) are dominated by the core diamagnetism of its components.     

Synthesis,crystal structure,spectral characterization,and DFT studies on 4‐((1‐phenyl‐1H‐tetrazol‐5‐ylthio)methyl)benzoic acid

A new thiotetrazole compound, 4‐((1‐phenyl‐1H‐tetrazol‐5‐ylthio)methyl) benzoic acid ( 1 ), has been synthesized and characterized by elemental analysis, ¹H and ¹³C NMR, ESI‐MS, FT‐IR, UV–vis, fluorescence spectra, and single‐crystal X‐ray diffraction analysis. The structural analysis reveals that compound 1 adopts a nonplanar geometric structure and exhibits an extensive but not uniform π delocalization with all members of the tetrazolyl ring and the exocyclic sulfur atom. A density functional theory (DFT) calculation at B3LYP/6‐31G** level of theory was performed to elucidate the structure of this thiotetrazole system. And the time‐dependent DFT (TD‐DFT) calculations of absorption spectra reveal two electron‐transition bands derived from the contribution of π → π* transitions, which are in agreement with experimental results. Moreover, compound 1 exhibits a blue‐light emission (λ_em = 441 nm) in the solid state at room temperature. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:435–443, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21034     

Characterisation of interferon α‐2b by liquid chromatography and mass spectrometry techniques

Interferon α‐2b produced by Escherichia coli consists of 165 amino acids and contains two disulphide bonds; its purity was confirmed by LC‐UV (DAD)‐FLD and LC‐MS techniques. A C₄ column was used with UV detection at 214 nm; diode array detector (DAD) spectra were recorded from 200–400 nm and fluorescence detection was performed at specific wavelengths of trypthophan emission and excitation. Peptide mapping was performed with trypsin. Peptides produced by trypsin digestion were analysed by LC‐UV (DAD)‐FLD, LC‐MS, and LC‐MS/MS using a C₁₈ column. Amino acid sequence coverage was about 95%. UV spectra in the range from 200 nm to 400 nm, emission (Em) and excitation (Ex) spectra of each separated peptide were additionally compared with spectra of the same peptide produced by digestion of European Pharmacopaeia interferon α‐2b standard (spectral matching). The chromatogram of any interferon α‐2b (drug substance or certificated standard) sample produced in the same manner with the same amino acid composition should be similar to the chromatogram obtained by the method described in this paper. Molecular masses of peptides were obtained from MS experiments and MS/MS experiments gave additional structural information. The molecular mass of interferon α‐2b was obtained by MALDI‐TOF MS analysis in linear mode, with an accuracy comparable to the theoretical average mass ± 5 atomic mass units. The molecular mass was obtained from the deconvoluted ESI mass spectrum.     

Photochemische Reaktionen 49. Mitteilung [1] Spezifisch π → π*-induzierte Keton-Photoreaktionen: Die Doppelbindungsverschiebung von O-Acetyl-10α-testosteron Protonisierung der Doppelbindung seines δ5-Isomeren

The α,β-unsatured ketone 10α-testosterone has been reported previously [6] to photoisomerize in t-butanol solution to the β,γ-unsaturated ketone. The irradiation had been carried out using a high-pressure mercury lamp in a quartz vessel. For structural reasons this double bond shift cannot proceed through a photoenolization mechanism involving an intramolecular hydrogen transfer from the γ-position to the enone oxygen as has been suggested to operate in several formally analogous cases of aliphatic enone isomerizations. In the present reinvestigation, O-acetyl 10α-testosterone ( 1 ) was used, employing selectively either excitation of its n → π* (with wavelengths > 300 nm) or its π → π* absorption band (with 253,7 nm). In t-butanol solution the doublebond shift 1 → 2 could be effected with π→* excitation only. Experiments in deuterated solvent (t-BuOD) resulted in deuterium in corporation in both the δ5-ketone in the C(4)-position, cf.( 3 ) and in the conjugated ketone. These results indicate that the reactions is initiated either in the, S_π,π* state or in a high vibrational mode of the S₀ or t_ππ*state. n→ π* Excitation of 1 in t-butanol gave essentially no over-all chemical change, while in benzene solution it resulted again in a double bond isomerization ( 1 → 2 ). In analogy to results with similar enones [28] under identical conditions the deconjugation in benzene may be the consequence of an intermolecular hydrogen abstraction of the T_n,π* excited state of the enone. Another specifically π →π* induced photoreaction was observed on irradiation of the β, γ-unsaturated ketone 2 in t-BuOD with 253,7 nm. The olefinic hydrogen at C-6 of 2 was exchanged with deuterium and, to a small extent, isomerization to the conjugated ketone 1 with concomitant deuterium incorporation occurred. It is concluded that from the higher excited state of the β, γ-unsaturated ketone, but not from its S_n,π* state, an activation mode of the double bond is accessible to effect D+ addition at C-6 followed by deprotonation to 4 and to deuterated 1 , respectively.     

Aggregation of amyloid Aβ(1–40) peptide in perdeuterated 2,2,2‐trifluoroethanol caused by ultrasound sonication

Ultrasound sonication of protein and peptide solutions is routinely used in biochemical, biophysical, pharmaceutical and medical sciences to facilitate and accelerate dissolution of macromolecules in both aqueous and organic solvents. However, the impact of ultrasound waves on folding/unfolding of treated proteins, in particular, on aggregation kinetics of amyloidogenic peptides and proteins is not understood. In this work, effects of ultrasound sonication on the misfolding and aggregation behavior of the Alzheimer's Aβ_(1–40)‐peptide is studied by pulsed‐field gradient (PFG) spin–echo diffusion NMR and UV circular dichroism (CD) spectroscopy. Upon simple dissolution of Aβ_(1–40) in perdeuterated trifluoroethanol, CF₃‐CD₂‐OD (TFE‐d₃), the peptide is present in the solution as a stable monomer adopting α‐helical secondary structural motifs. The self‐diffusion coefficient of Aβ_(1–40) monomers in TFE‐d₃ was measured as 1.35 × 10^?10 m² s^?1, reflecting its monomeric character. However, upon ultrasonic sonication for less than 5 min, considerable populations of Aβ molecules (ca 40%) form large aggregates as reflected in diffusion coefficients smaller than 4.0 × 10^?13 m² s^?1. Sonication for longer times (up to 40 min in total) effectively reduces the fraction of these aggregates in ¹H PFG NMR spectra to ca 25%. Additionally, absorption below 230 nm increased significantly upon sonication treatment, an observation, which also clearly confirms the ongoing aggregation process of Aβ_(1–40) in TFE‐d₃. Surprisingly, upon ultrasound sonication only small changes in the peptide secondary structure were detected by CD: the peptide molecules mainly adopt α‐helical motifs in both monomers and aggregates formed upon sonication. Copyright © 2010 John Wiley & Sons, Ltd.     

Reaktionen cyclischer Carbonsäureanhydride mit (α, α′-Dipyridyl)-(Cyclooctadien-1, 5)-nickel

Reactions of Cyclic Carbonic Acid Anhydrides with (α,α′-Dipyridyl)-(Cyclooctadiene-1,5) Nickel With maleic anhydride (dipy)Ni(COD) reacts by substitution forming (dipy)Ni(MSA)₂ (I) and (dipy)Ni(MSA) (II). While in I the bonding of MSA occurs only by the C = C group, in II MSA coordinates additionally by one of the carbonyl functions. With phthalic anhydride (PSA) and succinic anhydride (dipy)Ni(COD) by a redox addition gives six membered metalacycles V and VII, which are decarbonylated at higher temperatures producing the five-membered metalacycles VI and VIII. The IR spectra of the new compounds are discussed.     

Bis(8‐quinolinolato‐N,O)platinum(II) and its synthetic intermediate, 8‐hydroxyquinolinium dichloro(8‐quinolinolato‐N,O)platinate(II) tetrahydrate

Bis(8‐quinolinolato‐N,O)­platinum(II), [Pt(C₉H₆NO)₂], (I), has a centrosymmetric planar structure with trans coordination. The molecules form an inclined π stack, with an interplanar spacing of 3.400 (6) Å. 8‐Hydroxy­quinolinium dichloro(8‐quinolinolato‐N,O)­platinate(II) tetrahydrate, (C₉H₈NO)[PtCl₂(C₉H₆NO)]·4H₂O, (II), is soluble in water and is regarded as the synthetic intermediate of the insoluble neutral compound (I). The uncoordinated 8‐hydroxy­quinolinium cations and the monoquinolinolate complexes form an alternating π stack. The origins of fluorescence and phosphorescence in (II) are assigned to the 8‐hydroxy­quinolinium cation and the monoquinolinolate–Pt complex, respectively.