Dependence of equilibrium constants ofL-valine on ionic strength according to Guggenheim,Scatchard and Pitzer models

Summary A systematic study of the dependence of acid-base stoichiometric constants on the ionic strength has been carried out for the aminoacidL-valine in ClK and BrK solutions. The observed dependence has been interpreted by using Guggenheim, Scatchard and Pitzer models for the activity coefficients of the species involved in the equilibria.

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Die Abhängigkeit von Gleichgewichtskonstanten desL-Valin von der Ionenstärke entsprechend den Modellen von Guggenheim, Scatchard und Pitzer

Zusammenfassung Es wurde anL-Valin in KCl- und KBr-Lösungen eine systematische Studie der Abhängigkeit der Säure-Base-Stöchiometrie von der Ionenstärke durchgeführt. Die beobachteten Abhängigkeiten wurden aufgrund der nach den Modellen von Guggenheim, Scatchard und Pitzer erhaltenen Aktivitätskoeffizienten der an den Gleichgewichten beteiligten Spezies interpretiert.

     

Cyclodextrin effects on physical–chemical properties of novocaine

The UV-vis absorption and the fluorescence emission spectra of novocaine were analysed in aqueous cyclodextrin (CD) solutions. Either the absorbance read at λ_max 290 nm or the fluorescence emission intensity at λ_ems 346 nm increase in the presence of both α- and β-CD due to the formation of 1:1 inclusion complexes. The lower polarity of the CD-cavity sensed by the included drug enhances the emitted fluorescence; in fact, the same effect was observed in aqueous mixtures of acetonitrile, dioxane, or dimethylsulfoxide. The inclusion complex formation between the monocation of novocaine and CDs diminishes the electrical conductance of aqueous solutions of novocaine hydrochloride (NoHCl). Both the nitrosation reaction in aqueous acid medium and the ester hydrolysis in alkaline medium are retarded in the presence of CDs. The strongest effect was observed with β-CD as a consequence of the higher stability inclusion complex.     

Heritability of Stroop and flanker performance in 12-year old children

Background  

There is great interest in appropriate phenotypes that serve as indicator of genetically transmitted frontal (dys)function, such as ADHD. Here we investigate the ability to deal with response conflict, and we ask to what extent performance variation on response interference tasks is caused by genetic variation. We tested a large sample of 12-year old monozygotic and dizygotic twins on two well-known and closely related response interference tasks; the color Stroop task and the Eriksen flanker task. Using structural equation modelling we assessed the heritability of several performance indices derived from those tasks.     

The contribution of high frequencies to human brain activity underlying horizontal localization of natural spatial sounds

Background  

In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment.     

A kinetic study of the chlorination of tertiary alcoholamines in alkaline media

The kinetics of the chlorination of various tertiary alcoholamines by hypochlorite have been studied in alkaline media. A reaction mechanism consistent with the experimental results is put forward, and a relationship is established between the rate constants and the polar parameter (Σσ*) of the substituents.     

Precise mass measurement of a double-stranded 500 base-pair (309 kDa) polymerase chain reaction product by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd.