Notes: Ionization Constants for Some Piperazine Derivatives

Keyworth, D.A.

doi:10.1021/jo01091a614

Cited by 8 publications

(9 citation statements)

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“…However, the charge distribution in the molecule varies according to the other functional groups. Therefore, the more electrophilic the substituent group, the less protonated will be the pyrazine nucleus, which results in a decreased net charge [13]. In fact, this trend is confirmed by the electropherogram shown in Fig.…”

Section: Effect Of the Bge Composition On Analytes Migration Ordermentioning

confidence: 55%

“…The pyrazine nucleus is a weak base (pK a 5 12.9) and a replacement of a hydrogen atom by one alkyl group roughly doubles its base strength [13]. Further alkyl substitutions increase basicity, but the whole effect depends on the switch position [13]. Normally, if both alkyl substituents act at the same nitrogen, by mesomeric or inductive effects, the base characteristic will be strengthened, i.e.…”

Section: Effect Of the Bge Composition On Analytes Migration Ordermentioning

confidence: 99%

“…Normally, if both alkyl substituents act at the same nitrogen, by mesomeric or inductive effects, the base characteristic will be strengthened, i.e. this phenomenon explains the reason why 2,6-dimethylpyrazine is a stronger base than 2,5-dimethylpyrazine [13,19,20,21]. However, the charge distribution in the molecule varies according to the other functional groups.…”

Section: Effect Of the Bge Composition On Analytes Migration Ordermentioning

confidence: 99%

“…However, some of the impairments of GC analyses of such compounds include their basic character, which make them Besides, GC analysis is frequently time consuming and requires specific sample extraction methods, such as solidphase microextraction (SPME) [8]. Nevertheless, beyond their high volatility, these heterocycles are also sufficiently basic to be ionized in great extension in aqueous media, which indicates the potentiality of analysis of such compounds by CZE [13,14]. Few methodologies have been described for the analysis of volatile compounds [15,16] as well as amines [17] by CE.…”

Section: Introductionmentioning

confidence: 99%

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Simple and rapid CE‐UV method for the assessment of trail pheromone compounds of leaf‐cutting ants' venom glands

2011

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Leaf-cutting ants cause large losses in several crops around the world. In the ant species Atta sexdens, each colony comprises up to 5 million individuals. In order to keep a close connection among such a large number of individuals, an efficient chemical communication system is necessary. Among other different substances, these animals use alkylpyrazines to mark their trails and to guide ant workers from the nest to their sources of food. In this study, CE-UV was used to apply a method for qualitative analysis of venom gland components of leaf-cutting ants. Mobility of these compounds proved to be a function of the ionization capability of these bases as well as their volumes. Migration order was thoroughly explained in terms of such parameters. The best analysis conditions were achieved with a BGE composed by 0.8% formic acid plus 20% methanol in water, hydrodynamic injection, and application of external pressure. Such analysis conditions may be easily applied in CE-MS analyses as well. CE-UV analyses proved to be as adequate as GC to analyze such compounds due to system detectability (LD ≅ 0.005 mmol/L), separation efficiency (from 5.07×10(4) to 1.23×10(5) theoretical plates), and resolution (minimum of 2.35). In addition, analysis time was ca. 15 min, which shows another advantage of CE analysis when compared with GC. Although the analytes are found in concentrations as low as 50 ng/venom glands, four putative pyrazine ring moiety substances could be detected in real samples, due to sample stacking and use of a capillary with extended detection cell.

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Section: Effect Of the Bge Composition On Analytes Migration Ordermentioning

confidence: 55%

Section: Effect Of the Bge Composition On Analytes Migration Ordermentioning

confidence: 99%

Section: Effect Of the Bge Composition On Analytes Migration Ordermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Simple and rapid CE‐UV method for the assessment of trail pheromone compounds of leaf‐cutting ants' venom glands

2011

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“…the imidazole derivatives are much stronger bases than the diazine derivatives. For example pK a values of 6.95 and 2.8 have been reported for the conjugate acids of imidazole [30] and tetramethylpyrazine, [31] respectively.…”

Section: Resultsmentioning

confidence: 99%

Correlation between proton transfer and ³⁵Cl NQR frequency as well as molecular geometry of chloranilic acid in co‐crystals with some organic bases

Asaji¹,

Seliger²,

Žagar³

et al. 2010

Magnetic Reson in Chemistry

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Proton transfer in hydrogen-bonded organic co-crystals of chloranilic acid with some organic bases was investigated by nuclear quadrupole resonance (NQR) spectroscopy. The (35)Cl NQR frequencies of chloranilic acid molecule as well as (14)N NQR frequencies of the organic base molecule were measured with the conventional pulse methods as well as double-resonance methods, respectively. The extent of proton transfer in the O...H...N hydrogen bond was estimated from Townes-Dailey analysis of the (14)N NQR parameters. The (35)Cl NQR frequency and molecular geometry of chloranilic acid are correlated to the extent of proton transfer in the protonation process of the organic base molecule. It is shown that the hydrogen bond affects the pi-electron system of chloranilic acid. Geometry dependence of the O...H...N hydrogen bond, i.e. the H-N valence bond order versus the hydrogen-bond geometry correlation is also discussed.

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High-temperature protonic motion and low-temperature lattice deformation in one-dimensional hydrogen-bonded molecular chain in tetramethylpyrazine–chloranilic acid (1:1)

2007

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The phase transition of tetramethylpyrazine-chloranilic acid (1:1) was studied by 35 Cl NQR measurements. The frequency splits into a doublet below T c = 83.0 ± 0.5 K. The averaged frequency of 36.98 MHz at 77 K suggests an electrically neutral electronic state of the chloranilic acid molecule, that is, no proton transfer between the acid and base molecules. An enhancement of the relaxation rate was observed at T c : it is presumably due to critical slowing down of a hydrogen motion in the one-dimensional hydrogen bond network. The excitation of a hightemperature hydrogen motion at T > 250 K is also suggested by the steep decrease of T 1 observed above 250 K. From the slope of the Arrhenius plots, an activation energy of 35 kJ mol −1 is calculated for the motion.

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Notes: Ionization Constants for Some Piperazine Derivatives

Cited by 8 publications

References 0 publications

Simple and rapid CE‐UV method for the assessment of trail pheromone compounds of leaf‐cutting ants' venom glands

Simple and rapid CE‐UV method for the assessment of trail pheromone compounds of leaf‐cutting ants' venom glands

Correlation between proton transfer and ³⁵Cl NQR frequency as well as molecular geometry of chloranilic acid in co‐crystals with some organic bases

High-temperature protonic motion and low-temperature lattice deformation in one-dimensional hydrogen-bonded molecular chain in tetramethylpyrazine–chloranilic acid (1:1)

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Notes: Ionization Constants for Some Piperazine Derivatives

Cited by 8 publications

References 0 publications

Simple and rapid CE‐UV method for the assessment of trail pheromone compounds of leaf‐cutting ants' venom glands

Simple and rapid CE‐UV method for the assessment of trail pheromone compounds of leaf‐cutting ants' venom glands

Correlation between proton transfer and 35Cl NQR frequency as well as molecular geometry of chloranilic acid in co‐crystals with some organic bases

High-temperature protonic motion and low-temperature lattice deformation in one-dimensional hydrogen-bonded molecular chain in tetramethylpyrazine–chloranilic acid (1:1)

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Correlation between proton transfer and ³⁵Cl NQR frequency as well as molecular geometry of chloranilic acid in co‐crystals with some organic bases