A time-gated fluorescence detector using a tuning fork chopper

We describe an affordable gated fluorescence detection system to measure fluorescent compounds with long-lifetimes that uses a tuning fork chopper to block the intense excitation pulse from a flash lamp or short-lived fluorescence. A conventional non-gated inexpensive photosensor module is used to collect the luminescence signal. Using the long-lived luminescence from the terbium(III)–dipicolinic acid (DPA) chelate, we demonstrate a limit of detection (LOD) of 120 pM for DPA. This system is not only an order of magnitude less expensive than an electronically gateable phototomultiplier tube (GPMT), it exhibits no evidence of gradual loss of sensitivity, due likely to photocathode fatigue and deterioration, observed with a GPMT.     

Anti-Markovnikov hydration of α-olefins and the other pathways to n-alcohols

Three possible mechanisms of the direct hydration of α-olefins under conditions of catalysis with metal complexes in solution are considered, and information that confirms the possible realization of the reaction steps of various types is presented. Factors determining the regioselectivity of reaction steps are considered in the framework of various mechanisms, and the available published data about catalytic systems capable of ensuring the direct hydration of α-olefins are analyzed. New approaches to organization of the synthesis of n-alcohols from olefins and dienes are discussed, which are based on the systems of consecutive reactions, conjugated, and combined (associated) processes.     

Liquid-state stereospecific reactions for inertially rotating molecules

A study has been made on how inertial rotation affects the rate of a bimolecular diffusion-controlled stereospecific reaction in solution. The rate constants have been calculated in the kinematic approximation for a reaction between anisotropic and isotropic partners. The orientation motion is considered as rotation with angular momentum relaxing by the strong-collision mechanism (Jordan J diffusion). The averaging in the reaction anisotropy due to the rotation has been calculated for diffusion-type and jump-type translational mobility.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 257–265, May–June, 1989.     

The acidity scale of HCl solutions in N,N-dimethylformamide

The scale of the thermodynamic acidity of HCl solutions in DMF has been measured at 25 and 39.5 °C up to 15 mol L^–1 acid concentration by the indicator method. It is shown that in the HCl-DMF system the ionization of the nitroaniline-derived indicators occurs by the ion pair mechanism. Within the temperature range studied acidity is independent of temperature. Indicators of the nitroaniline series are used.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1025–1028, June, 1994.     

Experimental verification of the theory of J-diffusion in nitrogen gas

The measured linewidths of NMR spectra for ¹⁵N₂ and ¹⁴N₂ have been used to calculate rotational (τJ) and orientational (τθ₂) relaxation times. Within the density range studied (0–100 amagat) τθ₂ is proportional to τ_J in line with the impact theory of orientational and rotational relaxation.     

Ab initio calculations of potential energy surface for reaction of nucleophilic addition of H− ion to methylacetylene

Within the framework of the Hartree-Fock-Roothaan Method, using double- basis sets 3-21++G and (6-31-H-G//3-21++G), the minimum energy paths (MEPs) have been calculated for reactions of nucleophilic addition of the hydride ion H^– to the methylacetylene molecule: CH₃-CCH+H^–[CH₃-CH=CH]^– (1) CH₃-CCH+H^–[CH₃-C=CH₂]^– (2). It has been established that the activation energy for reaction (2) is 7.02 kJ/mole lower than for reaction (1). An analysis has been made of the character of electron density distribution along the MEP of each reaction. It has been shown that distortion of geometry of the reactants plays an important role in intensifying the interaction of the frontier orbitals. The reasons for nonfulfillment of Markownikoff's rule for these reactions have been determined. The results from the calculations are compared with calculations reported in the literature for the related reaction of nucleophilic addition of the hydride ion H^– to the acetylene molecule: HCCH+H^–[CH₂=CH]^–.Translated from Teoreticheskaya i Éxperimental'naya Khimiya, Vol. 21, No. 3, pp. 303–309, May–June, 1985.     

High-frequency dynamic nuclear polarization in MAS spectra of membrane and soluble proteins

One of the principal promises of solid-state NMR (SSNMR) magic angle spinning (MAS) experiments has been the possibility of determining the structures of molecules in states that are not accessible via X-ray or solution NMR experiments-e.g., membrane or amyloid proteins. However, the low sensitivity of SSNMR often restricts structural studies to small-model compounds and precludes many higher-dimensional solid-state MAS experiments on such systems. To address the sensitivity problem, we have developed experiments that utilize dynamic nuclear polarization (DNP) to enhance sensitivity. In this communication, we report the successful application of MAS DNP to samples of cryoprotected soluble and membrane proteins. In particular, we have observed DNP signal enhancements of up to 50 in 15N MAS spectra of bacteriorhodopsin (bR) and alpha-lytic protease (alpha-LP). The spectra were recorded at approximately 90 K where MAS is experimentally straightforward, and the results suggest that the described protocol will be widely applicable.     

Oxidative carbonylation of alkynes in self-oscillating mode. Effect of the nature of substrates on the dynamic behavior of reaction system

The oxidative carbonylation of alkynes in the oscillation mode was studied. The influence of the nature of substrates, alkynes and alcohols, on the pattern of oscillations was considered. The role of oxidants, I₂ and H₂O₂, in this process was demonstrated. The reaction network of the process was formulated, and four hypothetical mechanisms were selected.