Infrared Spectroscopy of Protonated Trimethylamine–(Benzene)_<i>n</i> (<i>n</i> = 1–4) as Model Clusters of the Quaternary Ammonium–Aromatic Ring Interaction

The essence of the molecular recognition of the neurotransmitter acetylcholine has been attributed to the attractive interaction between a quaternary ammonium and aromatic rings. We employed protonated trimethylamine–(benzene)_<i>n</i> clusters (<i>n</i> = 1–4) in the gas phase as a model to study the recognition mechanism of acetylcholine at the microscopic level. We applied size-selective infrared spectroscopy to the clusters and observed the NH and CH stretching vibrational regions. We also performed density functional theory calculations of stable structures, charge distributions, and infrared spectra of the clusters. It was shown that the methyl groups of protonated trimethylamine are solvated by benzene one at a time in the <i>n</i> > 1 clusters, and the validity of these clusters as a model system of the acetylcholine recognition was demonstrated. The nature of the interactions between a quaternary ammonium and aromatic rings is discussed on the basis of the observed infrared spectra and the theoretical calculations

Fluorescence spectra of amplified products.

<p>The fluorescence spectra of amplified products were measured with excitation at 492 nm (A) and 585 nm (B) for oBP(SNP) and oBP(WT), respectively. The grey line, black solid line, and dotted line represent the fluorescence spectra of the amplification products of T/T (WT/WT), G/G (SNP/SNP), and T/G (WT/SNP), respectively.</p

Comparison of results obtained by PCR-RFLP (A) and sequence analysis (B).

<p>Arrows indicate SNP positions.</p

Clinicopathological characterization of primary lung cancer patients as well as presence of SNP (c.309T>G) in the <i>MDM2</i> gene and allele frequency.

<p>Clinicopathological characterization of primary lung cancer patients as well as presence of SNP (c.309T>G) in the <i>MDM2</i> gene and allele frequency.</p

Sequences of primers developed for the Duplex SmartAmp method.

<p>TP: The turn-back region is underlined.</p><p>FP: The folding region is underlined.</p><p>“Z” and “U” indicate thiazole pink- and thiazole orange-labeled thymines in oBP, respectively.</p

Ethnic differences of SNP (c.309 T>G) in the <i>MDM2</i> gene among lung cancer cases.

*<p>Squamous cell carcinoma.</p

SNP (c.309 T>G) in the <i>MDM2</i> gene and allele frequencies in primary lung cancer patients.

<p>SNP (c.309 T>G) in the <i>MDM2</i> gene and allele frequencies in primary lung cancer patients.</p

Analysis of DNA products formed in the Duplex SmartAmp reaction.

<p>A: Time course of typical Duplex SmartAmp reaction by real-time monitoring. B. Agarose gel electrophoresis of DNA products after Duplex SmartAmp reaction. We sampled aliquots of reaction mixtures at different reaction times (t = 0, 13, 16 and 30 minutes) and separated DNA products by agarose gel electrophoresis. The “Maker” represents a 100-bp DNA ladder.</p

Chemical structure of thymine labeled with fluorescent dyes.

<p>A : Thiazole pink-labeled thymine. B : Thiazole orange-labeled thymine.</p

Comparison of results obtained by the Duplex SmartAmp and PCR-RFLP methods.

<p>A total of 96 genomic DNA samples and 24 blood samples were subjected to the Duplex SmartAmp and PCR-RFLP assay methods to examine the genotypes of SNP (c.309T>G) in the <i>MDM2</i> gene.</p