Mass spectometry of aralkyl compounds with a functional group—VI1: Mass spectra of 1-phenylethyanol-1, 2-phenylethanol-1 and 1-phenylpropanol-2

Mass spectra of 1-phenylethanol-1 and its analogues, specifically deuterated in the aliphatic chain, suggest that the [M? CH₃]⁺ ion is represented partly by an α-hydroxybenzyl fragment. Moreover, the molecular ion loses successively—after scrambling of all hydrogen atoms, except those of CH₃? a hydrogen atom and C₆H₆, generation the CH₃CO⁺ ion. Diffuse peaks, found in the spectra of of 2-phenylethanol-1 and its analogues, specifically deuterated in the aliphatic chain and in the phenyl ring, show that the molecular ion loses C₂H₄O, possibly via a four-center mechanism, after an exchange of aromatic and hydroxylic hydrogens. Mass spectra of 1-phenylpropanol-2 and its analogues, specifically, deuterated in the aliphatic chain, demonstrate that in the molecular ion exclusively the hydroxyl hydrogen atom is transferred to one of the ortho-positions of the phenyl ring via a McLafferty rearrangement, generating the [M ? C₂H₄O]⁺ ion. Furtherore, an eight-membered ring structure is proposed for the [M ? CH₃]⁺ ion to explain the loss of H₂O and C₂H₂O from this ion after an extensive scrambling of hydrogen atoms.     

Reactive polymeric nanoparticles based on unconventional dextran derivatives

Unconventional dextran derivatives with reactive tosyl- and deoxy-azido moieties were synthesized homogeneously under various reaction conditions. Well soluble tosyl dextran of a high degree of substitution up to 1.66 was prepared applying N,N-dimethylacetamide/LiCl as solvent. Almost 50% of secondary toslyate moieties could be replaced by nucleophilic displacement reaction with azide ions. The structure of the products was efficiently analyzed by NMR spectroscopy also after peracylation of the unconventional dextran derivatives. Applying a simple dialysis technique, nanospheres with a size in the range from 160 to 420 nm (D50%) were obtained that possess reactive functional tosyl- and deoxy-azido groups.     

Coupling of narrow-bore liquid chromatography to thin-layer chromatography : Part 2. Application of fluorescence-based spectroscopic techniques for off-line detection

The effluent from a narrow-bore liquid chromatographic (l.c.) separation can be immobilized on thin-layer chromatographic (t.l.c.) plates with little loss of resolution. The deposited compounds are then available for further inspection. For off-line detection, direct fluorescence emission, fluorescence excitation emission spectra, and fluorescence line-narrowing spectroscopy are investigated with tetracene and benz[k] fluoranthene as model compounds. Detection based on direct emission measurements and on measurements for which complete spectra are obtained for the separated compounds, is suitable for identification and determination. Detection limits are of the same order of magnitude as those for on-line detection in narrow-bore l.c. The fluorescence spectra of immobilized compounds can be obtained with a conventional fluorescence spectrometer equipped with a solid-sample accessory. No other special apparatus is needed. The immobilized chromatogram is also suitable for techniques incompatible with flow systems, e.g., fluorescence line-narrowing spectroscopy, which yields fluorescence spectra via laser excitation of low-temperature solid samples. Very selective narrow-line fluorescence spectra were obtained for tetracene deposited on t.l.c. plates in amounts down to the low picogram level.     

Influence of substrate morphology on organic layer growth: PTCDA on Ag(1 1 1)

By UV-excited photoelectron emission microscopy (UV-PEEM) we investigated the microscopic growth behavior of organic thin films using 3,4,9,10-perylene-tetracarboxylicacid dianhydride (PTCDA) on a Ag(1 1 1) single crystal substrate as example. Direct, real time observation allows to correlate the initial growth modes and the related kinetic parameters with substrate properties like terrace width, step density, and step bunches from the submonolayer range up to 5 layers or more. Above room temperature PTCDA grows in a Stranski–Krastanov fashion: after completion of the first two stable layers three-dimensional islands are formed. The nucleation density strongly depends on the temperature and the substrate morphology thus affecting the properties of the organic film.     

Synthese und konformationsstudien von selen-analoga der metallocen-dithiolen-chelate früher übergangsmetalle

The reaction of the metallocene dichlorides Cp₂MCl₂ (Cp = η⁵-C₅H₅; M = Ti, Zr, Hf, Mo, W) and Cp₂′TiCl₂ (Cp′ = η⁵-C₅H₄CH₃) with equimolar amounts of dilithium-benzene-o-diselenolate, 1,2-(LiSe)₂C₆H₄, gives the chelate complexes Cp₂M(Se₂C₆H₄) (M = Ti (I), Zr (II), Hf (III), Mo (IV), W (V)) and Cp₂′Ti(Se₂C₆H₄) (VI). CpTiCl₃ reacts with 1,2-(LiSe)₂C₆H₄ to give CpTiCl(Se₂C₆H₄) (VII). The ring inversion activation parameters for I–VI can be determined by means of temperature-dependent ¹H NMR spectroscopy in solution. The fragmentation behaviour of I–VII in the mass spectrometer has been investigated by pursuing metastable transitions, using linked-scan techniques.     

Random walks on inhomogeneous lattices

For lattices with two kinds of points (black and white), distributed according to a translation-invariant joint probability distribution, we study statistical properties of the sequence of consecutive colors encountered by a random walker moving through the lattice. The probability distribution for the single steps of the walk is considered to be independent of the colors of the points. Several exact results are presented which are valid in any number of dimensions and for arbitrary probability distributions for the coloring of the points and the steps of the walk. They are used to derive a few general properties of random walks on lattices containing traps.Presented at the Symposium on Random Walks, Gaithersburg, MD, June 1982.     

Defect trapping by100Pd in fcc metals

Lattice defects in Al, Cu, Ag and Au were studied by the perturbed angular correlation technique (PAC) using the probe atom¹⁰⁰Pd/¹⁰⁰Rh. The comparison of data obtained on interstitial trapping in Cu and Au at different probe atoms (¹⁰⁰pd,¹¹¹In) allows defect characterisation less affected by the respective probe. The trapping efficiency of¹⁰⁰Pd for vacancy like defects is quite different to that of¹¹¹In atoms.     

Beitrag zur Deutung des Cryotrapping-Effektes

Zusammenfassung Die Dampfdruckerniedrigung, die kondesierendes Argon bei 4,2° K auf Wasserstoff ausübt, wurde unter der Annahme, da die Stammfunktion desRaoultschen Gesetzes unter den herrschenden Bedingungen gültig ist, berechnet und mit Mewerten vonHengevoss undTrendelenburg verglichen. Aus der guten Übereinstimmung der Ergebnisse kann mit gro Wahrscheinlichkeit auf die Richtigkeit dieser Voraussetzungen geschlossen werden.     

Universal quenching of common fluorescent probes by water and alcohols

Although biological imaging is mostly performed in aqueous media, it is hardly ever considered that water acts as a classic fluorescence quencher for organic fluorophores. By investigating the fluorescence properties of 42 common organic fluorophores recommended for biological labelling, we demonstrate that H₂O reduces their fluorescence quantum yield and lifetime by up to threefold and uncover the underlying fluorescence quenching mechanism. We show that the quenching efficiency is significantly larger for red-emitting probes and follows an energy gap law. The fluorescence quenching finds its origin in high-energy vibrations of the solvent (OH groups), as methanol and other linear alcohols are also found to quench the emission, whereas it is restored in deuterated solvents. Our observations are consistent with a mechanism by which the electronic excitation of the fluorophore is resonantly transferred to overtones and combination transitions of high-frequency vibrational stretching modes of the solvent through space and not through hydrogen bonds. Insight into this solvent-assisted quenching mechanism opens the door to the rational design of brighter fluorescent probes by offering a justification for protecting organic fluorophores from the solvent via encapsulation.

Overtones and combinations of O–H vibrations in the solvent efficiently quench red-emitting fluorophores by resonant energy transfer.