Amide interactions in chlorinated solvents

Enthalpies of solution and of transfer of amides for the solvents chloroform (CHCl₃), methylenechloride (CH₂Cl₂), carbontetrachloride (CCl₄), cyclohexane (C₆H₁₂), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), and ethylacetate (EtOAc) have been used to isolate and quantify the solvation interactions of amides in chlorinated solvents. Specific interactions at the aminde carbonyl and N–H groups have been identified. An analysis of the transfer enthalpies of pyrrole and methylpyrrole from cyclohexane to the chlorinated solvents shows that specific interactions between the pyrroles and these solvents are similar in nature. A means of calculating differences in the transfers of different solutes between the same solvent pair is given.Work done at Lebanon Valley College.     

Optimization of offset frequency in the SORC pulse sequence using feedback.

The low signal-to-noise ratio (SNR) of nuclear quadrupolar resonance measurements has motivated research on signal enhancement methods, including multipulse sequences that facilitate signal averaging, the development of interlaced pulse sequences, and super-Q coils. More recently, it has been shown that feedback can be used to automatically optimize pulse sequence parameters, maximizing the SNR. This paper extends this work by using feedback to optimize the offset frequency in the strong off-resonant comb pulse sequence. Analysis and results are presented for a sample of sodium nitrite at both liquid nitrogen and room temperatures.     

Redox transformations of bis(2,2'-bipyridine)(1-methyl-1-pyridin-2-yl-ethylamine)ruthenium(II)

The amineruthenium(II) complex Ru(bpy)2(mpea)2+ has been prepared by the direct reaction of 1-methyl-1-pyridin-2-yl-ethylamine (mpea) with Ru(bpy)2Cl2 in ethanol/water and isolated as the hexafluorophosphate salt. Electrochemical analysis of this complex shows that it undergoes sequential one-electron oxidations to an amidoruthenium(III) intermediate (E degrees' = 1.086 V vs NHE) and then to an amidoruthenium(IV) (E degrees' = 0.928 V) or imidoruthenium(IV) (E degrees' = 1.083 V) complex, depending upon the solution pH (pKa = 2.62 for the amidoruthenium(IV) species). At higher potentials ( Epa = 1.5 V in 1.0 M H2SO4), the amido- or imidoruthenium(IV) species is irreversibly oxidized to the corresponding nitrosoruthenium(II) complex. The mechanism for this transformation appears, on the basis of b3lyp/cpcm/cep-31g(d) computations, to proceed through an imidoruthenium(V) intermediate, which is rapidly attacked by water to yield a Ru(II)-bound hydroxylamine radical, which is readily oxidized and deprotonated to produce the nitrosoruthenium(II) complex. The nitrosoruthenium(II) complex is quantitatively reduced to the original [Ru(bpy)2(mpea)]2+ complex at relatively negative potentials ( Epc = -0.2 V in 1.0 M H2SO4).     

Java classes for managing chemical information and solving generalized equilibrium problems

Java classes have been created for organizing chemical information and solving generalized equilibrium problems. An object-oriented approach is employed for the organization and manipulation of chemical information. Classes have been created to represent chemical species, phases, and chemical reactions. The representation of the entire chemical system is encapsulated in the ChemSystem class. The Equilibria class provides methods for analyzing a chemical system, as described by a ChemSystem object, and determining the amounts of each species in the system at equilibrium. The ChemEquilibria applet has been created to facilitate deployment of this software over the World Wide Web.     

Feedback optimization of pulse width in the SORC sequence.

A method for increasing the signal-to-noise ratio (SNR) of nuclear quadrupole resonance (NQR) measurements by automatically adjusting a pulse parameter in real-time is presented. This approach is useful in situations where the optimal pulse parameters cannot be chosen beforehand due to lack of knowledge regarding the system. For example, NQR provides a means for detecting explosives by revealing the presence of (14)N. In this particular application, the distance between the search coil and the explosive, as well as the temperature of the explosive, is unknown. As a result, a fixed set of pulse parameters will not yield the largest SNR for all possible search applications. This paper describes a feedback algorithm that uses measurements of the NQR signal to automatically adjust the pulse width in the strong off-resonant comb sequence to maximize the SNR of the NQR measurement. Experimental results obtained using a sample of sodium nitrite are presented.     

A secretory phospholipase A2-mediated neuroprotection and anti-apoptosis

Background  

Phospholipase A₂ liberates free fatty acids and lysophospholipids upon hydrolysis of phospholipids and these products are often associated with detrimental effects such as inflammation and cerebral ischemia. The neuroprotective effect of neutral phospholipase from snake venom has been investigated.     

Synthesis and characterization of bis(di-2-pyridylmethanamine)ruthenium(II)

The complex Ru(dipa)(2)(2+) (dipa = di-2-pyridylmethanamine) has been prepared, yielding approximately a statistical ratio of the meso and rac isomers. The electronic spectra of both isomers show pyridyl pi --> pi transitions in the UV region and MLCT bands in the visible region. The solvent dependence of the spectra provides evidence of hydrogen bond formation between the solvent and the NH(2) site on the ligand. The electrochemical properties of the two isomers are identical; each undergoes a reversible one-electron oxidation in acetonitrile (E(1/2) = 0.933 V vs Ag/AgCl) and in aqueous solution below pH 3 (E(1/2) = 0.786 V vs Ag/AgCl). In aqueous solution above pH 3, one-electron oxidation of the ruthenium center is followed by deprotonation of the ligand NH(2) site yielding a reactive amidoruthenium(III) species. The ruthenium-bound dipa ligand possesses structural constraints that prevent the usual oxidative dehydrogenation reaction, which would yield exclusively the corresponding imine. Instead the amidoruthenium(III) intermediate finds alternative reaction routes leading to multiple products.     

Detection of nuclear resonance signals: modification of the receiver operating characteristics using feedback

The performance of a nuclear resonance detection system can be quantified using binary detection theory. Within this framework, signal averaging increases the probability of a correct detection and decreases the probability of a false alarm by reducing the variance of the noise in the average signal. In conjunction with signal averaging, we propose another method based on feedback control concepts that further improves detection performance. By maximizing the nuclear resonance signal amplitude, feedback raises the probability of correct detection. Furthermore, information generated by the feedback algorithm can be used to reduce the probability of false alarm. We discuss the advantages afforded by feedback that cannot be obtained using signal averaging. As an example, we show how this method is applicable to the detection of explosives using nuclear quadrupole resonance.