Rapid separation of phenylthiohydantoin amino acids: ambient pressure ion-mobility mass spectrometry (IMMS)

An electrospray ionization (ESI) ambient pressure ion-mobility spectrometer (APIMS) interfaced to an orthogonal reflector time-of-flight mass spectrometer (TOFMS) was evaluated for the first time as a detector for the identification of phenylthiohydantoin (PTH)-derivatized amino acids, the final products in the Edman sequencing process of peptides and proteins. The drift and flight times of the twenty common PTH amino acids were characterized by a well-defined 2-D mobility/mass spectral pattern. The combination of mobility/mass modes of analysis gave rise to a unique trend-line formation for the series of PTH amino acids. In addition, each PTH amino acid had a unique reduced mobility constant K(o), thus enabling the differentiation of all the amino acid derivatives including the PTH-leucine and PTH-isoleucine isomers. More importantly it was shown that it was possible to resolve a complete reference mixture of PTH amino acids in a single experimental run in less than 1 min. Detection limits for the PTH amino acids were found to range from 1.04 to 3.52 ng; indicating that the limits of detection were less than 17.0 pmol for all of the PTH amino acids.     

How constant are Ritchie's "constant selectivity relationships"? A general reactivity scale for n-, pi-, and sigma-nucleophiles

The kinetics of 82 reactions of benzhydrylium ions (Ar(2)CH(+)) with n-nucleophiles has been determined at 20 degrees C. Evaluation by the equation log k = s(N + E) delivered the reactivity parameters N and s for 15 n-nucleophiles (water, hydroxide, amines, etc.). All nucleophiles except water (s = 0.89) and (-)SCH(2)CO(2)(-) (s = 0.43) have closely similar slope parameters (0.52 < s < 0.71), indicating that the reactions of most n-nucleophiles approximately follow Ritchie's constant selectivity relationship (s = constant). The different slope parameter for water is recognized as the main reason for the deviations from the Ritchie relationship reported in 1986. Correlation analysis of the rate constants for the reactions of benzhydrylium ions with the n-nucleophiles (except H(2)O) on the basis of Ritchie's equation log k = N(+) + log k(0) yields a statistically validated set of N(+) parameters for Ritchie-type nucleophiles and log k(0) parameters for benzhydrylium ions. The N and s parameters of the n-nucleophiles derived from their reactions with benzhydrylium ions were combined with literature data for the reactions of these nucleophiles with other carbocations to yield electrophilicity parameters E for tritylium, tropylium, and xanthylium ions. While the E parameters for tropylium and xanthylium ions appear to be generally applicable, it is demonstrated that the E parameters of tritylium ions can be used to predict reactivities toward n-nucleophiles as well as hydride transfer rate constants but not rates for the reactions of tritylium ions with pi-nucleophiles. It is now possible to merge the large data sets determined by Ritchie and others with our kinetic data and present a nucleophilicity scale comprising n- (e.g., amines), pi- (e.g., alkenes and arenes), and sigma-nucleophiles (e.g., hydrides).     

The use of the isotropic orientation factor in fluorescence resonance energy transfer (FRET) studies of the actin filament

A Dale-Eisinger style analysis (R. E. Daleet al., Biophys. J. 26, 161, 1979) is used to produce three-dimensional plots that display the limits on the average orientation factor k ² that is required to calculate molecular distances in F-actin from fluorescence resonance energy transfer measurements. Maxima and minima plots are generated for the transfer of energy from a donor to a single acceptor and for transfer to multiple acceptors that are related by F-actin helical symmetry. The analysis is performed in terms of dipole cone half-angles rather than depolarization factors, in order to facilitate the modeling of the multiple acceptor problem. Calculations are carried out under the restrictive condition of a single electric dipole moment per fluorophore. In addition, both surface and volume averaging of the donor and acceptor dipoles are considered. Comparisons between the plots show that for the multiple acceptor cases with F-actin symmetry, there is a great reduction in the range for maxima and minima limits on k ². The calculations also suggest guidelines for the choice of fluorescence label that will result in an average orientation factor occurring within acceptable limits, i.e., inside the limits for which k ²=2/3 may be employed. Thus, without having detailed knowledge of the mean donor or acceptor dipole relative orientations, the use of k ²=2/3 in radial coordinate studies of F-actin is more than reasonable and is fairly assured of being correct.     

FLASH—A superluminal communicator based upon a new kind of quantum measurement

The FLASH communicator consists of an apparatus which can distinguish between plane unpolarized (PUP) and circularly unpolarized (CUP) light plus a simple EPR arrangement. FLASH exploits the peculiar properties of measurements of the Third Kind. One purpose of this article is to focus attention on the operation of idealized laser gain tubes at the one-photon limit.FLASH: acronym for First Laser-Amplified Superluminal Hookup.     

“Stat” methods in continuous flow analysis : Determination of Copper,Iron, Iodide and Hydrochloric Acid

A continuous flow “stat” method is described in which a certain arbitrarily imposed state in the flowing stream is automatically maintained by regulating the rate of flow of one of the components. The electronic system is regulated by measuring a physical phenomenon in the flowing solution. The method is illustrated by the examples of a continuous flow absorptiostat [Fe(III)/S₂O₃^2-/Cu(II)]for determinations of copper(II) (1–10 μg ml^-1), iron(III) (25–250 or 12.5–125 μg ml^-1), as well as for determination of iodide (12.8–128 μg ml^-1). A continuous flow conductostat [HCl/NaOH] for determination of 1–2.5 × 10^-4 M HCl is also described. This analytical technique is intended for automatic continuous monitoring of sample streams.     

A general formalism of deriving the pair potential of polymer chains for arbitrary interaction potentials between isolated chain segments at and close to the theta-point

A formalism has been worked out which allows to transform any non-punctiform segment-segment potential of isolated polymer segments ε of fairly short-ranged character into the pair-potentialU operating between linear polymer chains with a certain reference to the arguments as they have been originally put forward byFlory andKrigbaum. Although no restrictions are made in the derivation as to the repulsive or attractive contribution of the segment-segment potential ε because of some known general deficiencies of theFlory-Krigbaum treatment for exclusively repulsive interaction, the resulting equations are primarily intended to describe the thermodynamic situation at and close to the θ-point where repulsion and attraction—though working at different ranges of segment separation—cancel. As the equation derived is somewhat complicated two different approximate forms have been developed: The first one is based on aTaylor series expansion retaining terms up to the fourth order which allows to characterizeU by the second and the fourth moment of the pair segment-segment distribution function, β and γ (β being the so-called binary cluster integral of segment-segment interaction, which is considered to be zero for θ-conditions). In this caseU may be represented by an expression of the general form $$U/kT = A(1 - BR^2 )\exp \{ - bR^2 \} .$$ The second method is based on a separate integration over the repulsive and attractive ranges of ε giving the repulsive (U ₊) and the attractive (U _?) part ofU finally after some approximations leading to an equation of the general form $$U/kT = (U_ + + U_ - )/kT = A_1 \exp \{ - b_1 R^2 \} - A_2 \exp \{ - b_2 R^2 \} .$$ In both cases the knowledge of the exact form of ε is dispensable, only β and γ—or for the second case their repulsive (β₊ and γ₊) and attractive (β_? and γ_?) parts have to be known. It is shown that the approximations are in excellent accordance with the exact form so that they may be conveniently used to describe pair potentials of polymer chains and to analyze pair potentials of segment-segment interactions under the limitations and conditions indicated.     

Synthesis of 3-nitro- and 3-aminoquinoline-2,4-diones. An unexpected route to 3-hydroxyquinoline-2,4-diones

Nitration of 3-substituted-4-hydroxy-2(1H)-quinolones 1 with nitric acid leads either to 3-nitro- 2 or 3-hydroxyquinolinediones 3 , depending on the reaction conditions. 3-Substituted-3-hydroxyquinolinediones 3 are also obtained by oxidative hydroxylation with peracetic acid. Amination of 3-substituted-3-chloroquinolinediones 4 with ammonium hydroxide predominantly leads again to 3-substituted-3-hydroxyquinolinediones 3 , only in one case the 3-aminoquinolinedione 5 could be isolated. With morpholine or pyridine as amines the expected 3-aminoquinolinediones 6 and 7 were obtained.     

Analytical determination of non-born—oppenheimer matrix elements between different molecular electronic states

Matrix elements for the nonadiabatic correction between different adiabatic Born—Oppenheimer (ABO) states are discussed in terms of a generating function (nonadiabatic coupling function, NAF) which was introduced earlier. Recursion relations are derived for the case where different vibronic states are coupled via a single non-totally symmetric mode. The formalism is applied to the estimation of non-Born—Oppenheimer coupling between vibronic states of pyrazine.     

Eine gemeinsame Basis für die Theorie der Eulerschen Graphen und den Satz von Petersen

The main result states: Lete ₁,e ₂,e ₃ be three lines incident to the pointv (degv4) of the connected bridgeless graphG such thate ₁ ande ₃ belong to different blocks ifv is a cutpoint. Split the pointv in two ways: Lete ₁,e _j ,j=2, 3, be incident to a new pointv _1j and leave the remainder ofG unchanged, thus obtainingG _1j . Then at least one of the two graphsG ₁₂,G ₁₃ is connected and bridgeless. — A classical result ofFrink follows from this theorem which is the key to a simple proof of Petersen's theorem. Moreover, the above result can be used to prove practically all classical results on Eulerian graphs, including best upper and lower bounds for the number of Eulerian trails in a connected Eulerian graph. In the theory of Eulerian graphs, it can be viewed as the basis for good algorithms checking on several properties of this class of graphs.

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Herrn Prof. Dr. H. Hornich zum 70. Geburtstag gewidmet