Experimental resolution of early steps in protein folding: testing molecular dynamics simulations

Time-resolved Tyr fluorescence spectroscopy coupled with a laser-induced temperature-jump (T-jump) was employed to follow the folding relaxation dynamics of the B-domain of Staphylococcal protein A. The single Tyr is located in helix 1 (H1) and is a sensitive probe of the structure of this helix and the overall helical bundle structure. The results from this study were compared to those from a complementary infrared T-jump study on this protein [Vu, D. M.; Myers, J. K.; Oas, T. G.; Dyer, R. B. Biochemistry 2004, 43, 3582]. Both methods detect a microsecond process that follows the cooperative relaxation of the helical bundle core. However, a fast process (10-7 s) that follows the relaxation of the individual helices was observed only with the infrared probe. Thus, fast formation of H1 is not observed, but rather H1 forms in the microsecond phase, concomitantly with the docking to (and stabilization by) the other two helices to form the helical bundle structure. This observation validates the results of several previous molecular dynamics simulations that predict H1 formation only in the final assembly of the helix bundle.     

Partial thermal analysis of kerogen oxidation products

A method is proposed which, in principle, permits resolution of complex TG curves into elementary curves. The method is based on appropriate preheating of the substrate. In fact, the method represents partial differential thermogravimetric analysis (PDTG). In this paper it was used, together with IR spectroscopy, for analysis of the precipitated acids obtained by partial oxidation of the kerogen from an oil shale. The precipitated acids were found to consist of five components, characterized by similar thermal properties. General qualitative and quantitative characteristics of the individual components are suggested.

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Zusammenfassung Es wird eine Methode beschrieben, mit der es prinzipiell möglich ist, komplexe TG-Kurven in Elementarkurven zu zerlegen. Diese Methode beruht auf einem geeigneten Vorerhitzen des Substrates und stellt eigentlich ein partielles differentialthermogravimetrisches Verfahren (PDTG) dar, das in dieser Arbeit zusammen mit der IR-Spektroskopie angewendet wurde, um durch teilweise Oxydation von aus Kerogen eines Schieferöles gefällte Säuren zu untersuchen. Fünf Säuren, deren thermische Charakteristika einander ähnlich sind, konnten festgestellt werden. Es wurde eine allgemeine Charakteristik qualitativer and quantitativer Art der einzelnen Komponenten gegeben.

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Synthesis of 3-hydroxy-3-methyl-7-phenylbenzo[a]quinolizin-2-ones

Amino alcohols were prepared by debenzylation of l-benzyl-3-hydroxy-3-methyl-6(e) Phenyl-4 piperidone ethylene ketals, alkylation with phenacyl bromide, and subsequent reduction of the carbonyl group, and holding the alcohol in a mixture of sulfuric and trifluoroacetic acids yields 3-hydroxy-3-methyl-7(e)-pherrylbenzofafquirrolizin-2-ones. The possibility of recyclization of the latter while boiling in a mixture of acetic anhydride and acetic acid by -ketol rearrangement or rupture of the C-N bond was demonstrated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 221–224, February, 1994. Original article submitted January 18, 1994.     

Long-lived γ-radionuclidic impurities in spent99Mo/99mTc generators

The long-lived -radionuclidic impurities in the columns of spent⁹⁹Mo/^99mTc generators one year after the calibration date have been determined by -spectrometry. Three radionuclidic impuritiesfission products (¹⁰³Ru,¹⁰⁶Ru and¹²⁵Sb) were detected. Also in the majority of samples three radioisotopes of tungsten (¹⁸¹W,¹⁸⁵W and¹⁸⁸W) were also present. The contents of the impurities were found to vary greatly. According to the activity, energy and half-life, the main contribution to the residual activity in the spent generators is due to the presence of¹²⁵Sb.     

Kinetic determination of 1,3-propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid and in a mixture with ethylenediaminetetra-acetic acid

A kinetic method is proposed for the determination of propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid, based on its inhibitory effect on the acetonitrile-catalysed oxidation of Pyrocatechol Violet by hydrogen peroxide. The concentrations of 1,3-propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid determined ranged from 5.0 × 10^?7 to 4.0 × 10^?6 M with a relative standard deviation of up to 3.3%. The same indicator reaction can be applied to the determination of 1,3-propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid and ethylenediaminetetra-acetic acid in mixtures. Mixtures of these acids in molar ratios from 1 ∶ 4.5 to 10 ∶ 1 have been analysed. Concentrations of 1,3-propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid from 2.0 × 10^?7 to 1.0 × 10^?6 M and ethylenediaminetetra-acetic acid from 1.0 × 10^?7 to 9.0 × 10^?7 M were determined with relative standard deviations of up to 4.3 and 5.7%, respectively. The effect of foreign ions on the accuracy of these determinations was also investigated.     

Structural selection by microsolvation: conformational locking of tryptamine

The conformational space of tryptamine has been thoroughly investigated using rotationally resolved laser-induced fluorescence spectroscopy. Six conformers could be identified on the basis of the inertial parameters of several deuterated isotopomers. Upon attaching a single water molecule, the conformational space collapses into a single conformer. For the hydrogen-bonded water cluster, this conformer is identified unambiguously as tryptamine A. In the complex, the water molecule acts as proton donor with respect to the amino group. An additional interaction with one of the aromatic C-H bonds selectively stabilizes the observed conformer more than all other conformers. Ab initio calculations confirm much larger energy differences between the conformers of the water complex than between those of the monomers.     

Stability of semigroups commuting with a compact operator

It is proved that if are bounded -semigroups on Banach spaces and , resp., and , are bounded operators with dense ranges such that intertwines with and commutes with , then is strongly stable provided ---the generator of ---does not have eigenvalue on . An analogous result holds for power-bounded operators.

     

Microdisplacement and microvibration sensors based on semiconductor lasers

Conclusion The above analysis of a microvibration sensor based on a semiconductor laser has shown that in the optimal operating regime one can expect a detection ability of 10^–2 nm.It is preferable to record an optical signal (change of radiation power) than an optoelectronic one (change diode voltage).Several sensor variants were constructed: with an ILPN-202 commercial laser diode, with a laser cartridge, and with the LMF-1300 single-mode laser module. Since real sensors contain additional noise sources (pumping- and recording-system noise, fluctuations due to parasitic reflection, etc.), the sensitivity limit could not be reached. The detection ability ranges, depending on the scheme employed, from fraction of a nanometer to several nanometers, but is perfectly acceptable for many practical applications.Translation of Preprint No. 42 of the Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow, 1991.     

Tunneling Splittings in the S0 and S1 States of the Benzoic Acid Dimer Determined by High‐Resolution UV Spectroscopy

Five different isotopologues of the benzoic acid dimer and a vibronic band located 57 cm^?1 above the electronic origin, which is assigned to the out‐of‐plane butterfly motion, are studied by rotationally resolved UV spectroscopy. From these measurements a ground‐state structure with C_2h symmetry is deduced, whereas the symmetry is lowered to C_s in the S₁ state. The increase in the center‐of‐mass distance between the two monomers that is found on electronic excitation indicates a decrease in hydrogen‐bond strength. The tunneling splittings in the S₀ and S₁ states are 1385.2±0.7 and 271.2±0.7 MHz, respectively, corresponding to an increase in barrier height by 7.2 % on electronic excitation.