Cation-π interaction of N,N-Dimethyltryptamine in hydrochloric acid solution characteristic to gastric acid

N,N-DMT molecule is known in many cultures as endogenous hallucinogen and most research has been directed towards the psychological effects or structural definition while molecular interactions in conditions of the human body are poorly understood. We have complemented past structural research of N,N-DMT and investigated molecular interactions of N,N-DMT in the environment of 0.1 M hydrochloric acid which is characteristic to gastric fluid. Experimentally we have measured spectra of N,N-DMT with IR and Raman techniques and computed individual vibrational frequencies at DFT–B3LYP level of theory. Furthermore we put N,N-DMT in solution similar to gastric fluid environment and experimentally detected shift in vibrational frequency which is confirmed in our calculation. Our theoretical model shows that the cause of this shift is cationπ bond between N,N-DMT and HCl in the vicinity of the benzene ring. Abbreviations: N,N-DMT: N,N-dimethyltryptamine; HCl: Hydrocloric acid, FTIR: Fourier transform infrared; IR: Infrared


Introduction
The N,N-dimethyltryptamine (N,N-DMT) is an endogenous compound, first synthesized in 1931. It was confirmed to have hallucinogenic properties in 1956. It was natural derived from the essential amino acid tryptophan and ultimately produced by the enzyme indolethylamine-N-methyltransferase (INMT) during normal metabolism [1]. Structurally speaking N,N-DMT consists of indole ring connected through propyl chain with dimethylamino group. Research proved his natural existence in the human blood and urine other mammals and wide range of plants [2][3][4][5][6]. Some authors have conducted research about therapeutic potential of this compound [7]. The latest research demonstrated that N,N-DMT has immunomodulatory potential that may contribute to significant anti-inflammatory effects and tissue regeneration [8]. In Brazil there are drinks containing N,N-DMT as ingredient and are legally used during the course of religious activities and for healing purposes [5]. During oral intake of those drinks, N,N-dimethyltryptamine interacts with hydrochloric acid inside the stomach. Interactions between N,N-dimethyltryptamine and hydrochloric acid within the gastric fluid are not widely researched on molecular level, so our motivation is to investigate these interactions of N,N-DMT and HCl, theoretically and experimentally.

Materials and methods
95%> pure N,N-dimethyltryptamine was purchased from AKos Consulting & Solutions GmbH company and used without further purification. The supplier of 37% Hydrocloric acid was Sigma-Aldrich. To simulate natural conditions in stomach we prepared experimental solution in a manner that we first diluted Hydrocloric acid with water to get natural concentration of HCl in gastric fluid [9,10] which is in our experiment 0,1M and then we put N,N-DMT in a solution. To observe interactions, solution was characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR FTIR), Spectrum One FT-IR spectrometer, Perkin Elmer (model 2000), in the range from 4000 to 650 cm −1 . The FT-IR spectrometer was connected to a PC with the installed IRDM (IR Data Manager) program to process the recorded spectra. FTIR spectra were normalized using baseline correction from software Essential FTIR. First we recorded spectrum of an aqueous solution sample of N,N-DMT and HCl, and then we put solution in a desiccator over silica gel for 24 hours and then we recorded dry sample. Pure N,N-DMT Raman spectrum from 4000-155 cm −1 was recorded on a Nicolet 6700 FT-IR spectrometer with NXR FT-Raman module coupled with an IBM AT computer. The 1064 nm YVO 4 laser was used for excitation.
The quantum chemical calculations were performed with the Gaussian 09 package program at DFT-B3LYP level of theory [11]. The standard 6-311++G(d,p) basis set was used to carry out the calculations of molecular geometries, PE hypersurfaces, force fields, vibrational frequencies, as well as IR intensities and Raman scattering activities.

Conformational analysis
We have found three stable conformations and we selected the lowest-energy conformation for further analysis. This conformation is shown in Figure 1. The potential energy has been scanned by changing the dihedral angle C12-C15-C16-N17 from 0° to 360° in one hundred steps, which is equivalent to rotation about C15-C16 bond. At each scanning step configuration was optimized.

Vibrational analysis N,N-Dimethyltyptamine:
Objective of the vibrational analysis was to find vibrational modes connected with specific molecular structure of calculated molecule. Molecule was investigated using Raman spectroscopy ( Figure 2) in the region of 50-3500 cm -1 and IR spectroscopy ( Figure 3) in the region of 650-4000 cm -1 .

Discussion
Hydrocloric acid molecules with intermolecular hydrogen bonding have stretching band around 2930 cm -1 . Various clusters of HCl can be formed by intermolecular hydrogen bond which shifts the only HCl stretching mode to lower frequencies. The shift is about 100 cm -1 and is observed in (Figure 4) as 2854 cm -1 band. The frequency band around 2350 cm -1 very probably originates from HCl clusters encapsulating one molecule of water. The calculations shows that such HCl clusters exist and the calculated frequency is around 2350 cm -1 . On Figure 4 we can see frequencies around 1700-1900 cm -1 belonging to combination and overtone bands that are typical for benzenoid compounds [12]. We argue that HCl molecule interacts with N,N-DMT through cation-π type of interaction. It is well known that electrons in the benzene ring are delocalized and can form a new type of bond with electron deficient atom, which in our case is hydrogen atom of HCl molecule. This chemical bond shifts the frequency to the lower value. Therefore we have noticed that the measured frequency of this vibration in the spectra of pure Dimethyltryptamine was 1599 cm -1 and in the spectra of Dimethyltryptamine in hydrochloric acid solution is shifted to 1546 cm -1 in Figure 5. The experimental data shows that the frequency shift of stretching in benzene ring is about 53 cm -1 . Calculation of this frequency shift with B3LYP functional indicates, but generally underestimates this shift. The idea is to put molecules of hydrochloric acid in the vicinity of benzene ring and optimize the whole structure composed of DMT and HCl molecules. As an example we are presenting structure shown in Figure 7. The calculated shift is 7 cm -1 and is obtained with four HCl molecules agglomerated in the vicinity of benzene ring. We argue that calculated shift with more than four HCl molecules could be even greater, having in mind that calculated shift is slighter when we used smaller number of HCl molecules. The same rule applies to low frequency C-H out of plane bending modes. However, the calculated frequency shift is toward higher frequencies in contrast to before mentioned C-C ring stretching frequency shift. These two opposite tendencies could be understood if we take into account that the hydrochloric interacts with delocalized electrons in the ring and thus weakening C-C bonds in contrast to hydrogen atoms bonded to ring which through additional interaction with chlorine atom stiffen their bonds with carbon atoms. We can corroborate this interpretation with experimental data in Figure 6 where we clearly see one very broad band around 750 cm -1 . We argue that this broad band comes from both sides of the peak; frequency modes lower than 750 cm -1 are shifted toward higher, and higher frequency modes are shifted to lower frequencies.
We should also take into account that we are working here with   unscaled frequencies. The scaling factors would bring closer calculated and observed frequencies. The interaction between DMT and HCl can be very complex. It includes cation-π interaction between HCl and benzene ring and hydrogen bonding between HCl molecules. The calculated configuration shown in Figure 7 is just one possible simple example of DMT-HCl interaction, as we expect much more complex configurations due to higher concentrations of HCl and DMT molecules.
It is obvious that the calculations confirm experimentally observed shift which is a strong indication that cation-π interaction exists. When we had left N,N-DMT inside HCl solution of 0.1 M over a period of several hours up to a few days we didn't detect the presence of N,N-DMT molecule. The significance of these facts in biology and medicine is that the HCl is an inhibitor of N,N-DMT activity and that it is the main agents for the decomposition of that molecule in the gastric fluid. Therefore, such an influence of HCl significantly reduces efficiency of N,N-DMT at oral intake.