Solution conformations for the flexible 1-chloro-1,1-difluoro-2-pentanol unveiled using multinuclear magnetic resonance

The preferred conformations of a small polyfunctional molecule containing fluorine, chlorine and hydroxyl groups, the 1-chloro-1,1-difluoro-2-pentanol (CDP), were completely elucidated using ¹H, ¹³C and ¹⁹F NMR in three different solvents. While the Cl-C-C-O dihedral angle was asserted using coupling constant data for the diastereotopic fluorines, the Et-C-C-O torsional angle was analyzed by means of ¹H NMR spectra with selective irradiation of the diastereotopic hydrogens and fluorines. In addition, unusual couplings of the hydroxyl hydrogen with a diastereotopic hydrogen and fluorines provided information on the O-H orientation. The behavior of ¹J_C,F when the solvents varied agrees with a weak F???HO intramolecular hydrogen bond. These findings were corroborated, and the governing interactions rationalized with the aid of high level CCSD(T) theoretical calculations. Noteworthy, hyperconjugation involving the electron-acceptor σ*_C-Cl orbital drives the conformational equilibrium rather than the fluorine gauche effect.     

Test of special relativity in an ion storage ring

An accurate measurement of the Doppler effect in collinear laser spectroscopy has been performed at the TSR storage ring with electron cooled⁷Li⁺ ions at=0.064. This experiment is a sensitive test of the=(1– ²)^–1/2 factor(=v/c) in the special theory of relativity. The Doppler shifted frequencies of the moving⁷Li⁺ ions are compared with calibrated molecular lines at rest. The frequencies at rest for the⁷Li⁺ ions are known from independent measurements. The Doppler shifted frequencies in the collinear experiment have been measured with a precision ofv/v=6×10^–9, mainly limited by the signal width of the resonance. A corresponding upper limit of 8×10^–7 is deduced for any deviation of the time dilatation factor in special theory of relativity. A still higher accuracy is expected with a laser cooled ion beam. If such a beam is simultaneously subjected to RF bunching, the particle velocity and phase are exactly known. With an additional high resolution laser frequency measurement an improvement of at least one order of magnitude may be achieved.     

Hyperbolicity and invariant measures for generalC 2 interval maps satisfying the Misiurewicz condition

In this paper we will show that piecewiseC ² mappingsf on [0,1] orS ¹ satisfying the so-called Misiurewicz conditions are globally expanding (in the sense defined below) and have absolute continuous invariant probability measures of positive entropy. We do not need assumptions on the Schwarzian derivative of these maps. Instead we need the conditions thatf is piecewiseC ², that all critical points off are non-flat, and thatf has no periodic attractors. Our proof gives an algorithm to verify this last condition. Our result implies the result of Misiurewicz in [Mi] (where only maps with negative Schwarzian derivatives are considered). Moreover, as a byproduct, the present paper implies (and simplifies the proof of) the results of Mañé in [Ma], who considers generalC ² maps (without conditions on the Schwarzian derivative), and restricts attention to points whose forward orbit stay away from the critical points. One of the main complications will be that in this paper we want to prove the existence of invariant measures and therefore have to consider points whose iterations come arbitrarily close to critical points. Misiurewicz deals with this problem using an assumption on the Schwarzian derivative of the map. This assumption implies very good control of the non-linearity off ⁿ, even for highn. In order to deal with this non-linearity, without an assumption on the Schwarzian derivative, we use the tools of [M.S.]. It will turn out that the estimates we obtain are so precise that the existence of invariant measures can be proved in a very simple way (in some sense much simpler than in [Mi]). The existence of these invariant measures under such general conditions was already conjectured a decade ago.     

Surface selectivities in wet chemically modified PVC films. Influence of reaction conditions

Wet chemical modification reactions of PVC films in solvent/nonsolvent mixtures were performed. Three thiol compounds of different size and reactivity were used varying the solvent quality, temperature, and reaction times. The evolution of the concentration gradients within the films was studied using confocal Raman spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy. Surface selectivities were calculated and discussed in terms of the different relative reaction rate constants.     

A study of interaction in the lowest singlet and triplet states of H2

The potential energy curves of the ground state and the first excited state of H₂ are examined in terms of the electronic force acting on each nucleus. The results reveal the detailed course of events that occur when two hydrogen atoms with parallel and antiparallel electron spins approach one another from a large internuclear separation.     

Facile preparation of potassium 32P-phosphonate

Simple and easy to operate experimental assemblies were for the first time designed for the successful preparation of potassium ³²P-phosphonate from ³²P-orthophosphate. Phosphate was first converted to phosphoryl chloride by reacting with phosphorus pentachloride. Then the phosphoryl chloride formed was reduced to phosphorus trichloride by heating with charcoal at 650 °C. The latter was absorbed in aqueous potassium hydroxide to obtain potassium ³²P-phosphonate at a yield of about 75%. The chemical purity of ³²P-phosphonate was assayed using ion-chromatography and the radiochemical purity was also determined.The authors thank Shri. J. K. Ghosh, Chief Executive, BRIT and Dr. N. Sivaprasad, General Manager, RPh & ILCJ, BRIT for their support and encouragement throughout this work.     

bryA: an unusual modular polyketide synthase gene from the uncultivated bacterial symbiont of the marine bryozoan Bugula neritina

"Candidatus Endobugula sertula," the uncultivated bacterial symbiont of Bugula neritina, is the proposed source of the bryostatin family of anticancer compounds. We cloned a large modular polyketide synthase (PKS) gene complex from "Candidatus Endobugula sertula" and characterized one gene, bryA, which we propose is responsible for the initial steps of bryostatin biosynthesis. Typical PKS domains are present. However, acyltransferase domains are lacking in bryA, and beta-ketoacyl synthase domains of bryA cluster with those of PKSs with discrete, rather than integral, acyltransferases. We propose a model for biosynthesis of the bryostatin D-lactate starter unit by the bryA loading module, utilizing atypical domains homologous to FkbH, KR, and DH. The bryA gene product is proposed to synthesize a portion of the pharmacologically active part of bryostatin and may be useful in semisynthesis of clinically useful bryostatin analogs.     

New and efficient synthesis of 5′-amino-5′-(S)-methyl-2′,5′-dideoxynucleosides

A short, efficient synthesis of 5′-amino-5′-(S)-methyl-2′,5′-dideoxynucleosides 1 has been developed through the diastereoselective addition of methylmagnesium bromide or methyllithium to an intermediate tert-butylsulfinimide.     

Enantioselective hydrogenation of alkenes with iridium-PHOX catalysts: a kinetic study of anion effects

In the asymmetric hydrogenation of unfunctionalized olefins with cationic iridium-PHOX catalysts, the reaction kinetics and, as a consequence, catalyst activity and productivity depend heavily on the counterion. A strong decrease in the reaction rate is observed in the series [Al[OC(CF3)3]4]- >BArF- >[B(C6F5)4]- >PF6- >BF4- >CF3SO3-. With the first two anions, high rates, turnover frequencies (TOF >5000 h(-1) at 4 degrees C), and turnover numbers (TONs) of 2000-5000 are routinely achieved. The hexafluorophosphate salt reacts with lower rates, although they are still respectable; however, this salt suffers from deactivation during the reaction and extreme water-sensitivity, especially at low catalyst loading. Triflate and tetrafluoroborate almost completely inhibit the catalyst. In contrast to the hexafluorophosphate salt, catalysts with [Al[OC(CF3)3]4]-, BArF-, and [B(C6F5)4]- as counterions do not lose activity during the reaction and remain active, even after all the substrate has been consumed. In addition they are much less sensitive to moisture and, in general, rigorous exclusion of water and oxygen is not necessary. A first-order rate dependence on the hydrogen pressure was determined for the BArF- and the PF6- salts. At low catalyst loading, the rate dependence on catalyst concentration was also first order. The rate dependence on the alkene concentration was strikingly different for the two salts. While the reaction rate observed for the BArF- salt slightly decreased with increasing alkene concentration (rate order -0.2), a rate order of approximately 1 was determined for the corresponding hexafluorophosphate at low alkene concentrations.