Polymethylene Chain Research Articles

Diffusion in Polymethylene Chain Solutions with a Polar Component.

A hydrodynamic bead model based on Kirkwood-Riseman theory has been used to calculate the translational diffusion constant, D, for solutes with polymethylene chains in solutions with a polar component. A comparison with the experimental values for nonpolar n-alkanes in polar 2-propanol, tetrahydrofuran, chlorobenzene, chloroform, 1-octanol, quinoline, and chloroform (78 D values) and polar primary alcohols in nonpolar benzene and n-octane (24 D values) gives an average absolute percentage difference of ∼3% between the 102 experimental and calculated D values. Consideration of the solvent's temperature-dependent changes in the degree of aggregation due to hydrogen bonding was necessary for the n-alkanes in 1-octanol. Good agreement was not found for primary alcohols in 1-octanol due to solute-solvent hydrogen bonding. A correlation that depends on the solutes' molar volumes instead of their chain lengths gives worse agreement than the bead model for the n-alkanes in polar solvents and primary alcohols and n-alkanes in nonpolar solvents.

Tubular Magnetic Shielding Scan (TMSS): A New Technique for Molecular Space Exploration. (i) The Case of Aromaticity of Benzene and [n]Paracyclophanes.

Both traditional and novel techniques were employed in this work for magnetic shielding evaluation to shed new light on the magnetic and aromaticity properties of benzene and 12 [n]paracyclophanes with n = 3-14. Density functional theory (DFT) with the B3LYP functional and all-electron Jorge-ATZP and x2c-TZVPPall-s basis sets was utilized for geometry optimization and magnetic shielding calculations, respectively. Additionally, the 6-311+G(d,p) basis set was incorporated for the purpose of comparing the magnetic shielding results. In addition to traditional evaluations such as NICS/NICSzz-Scan, and 2D-3D σiso(r)/σzz(r) maps, two new techniques were implemented: bendable grids (BGs) and cylindrical grids (CGs) of ghost atoms (Bqs). BGs allow for the recording of magnetic shielding from the bent ring levels of [n]pCPs, while CGs provide tubular magnetic shielding scan (TMSS) maps detailing the magnetic shielding from a cylindrical region above and below the ring frame. Our findings suggest that smaller [n]pCPs with n < 6 exhibit deviations in the magnetic shielding above and below the ring, indicating a broken electron delocalization under the ring. In contrast, larger [n]pCPs tend to behave similarly to benzene in terms of magnetic shielding. Moreover, we found that shorter polymethylene chains of [n]pCPs exhibit significantly higher magnetic shielding interactions with the ring. Both of the above techniques offer new and promising tools for characterizing nonplanar aromatic compounds, thereby contributing to a deeper understanding of their magnetic and electronic properties.

Novel Uracil-Based Inhibitors of Acetylcholinesterase with Potency for Treating Memory Impairment in an Animal Model of Alzheimer's Disease.

Novel derivatives based on 6-methyluracil and condensed uracil, 2,4-quinazoline-2,4-dione, were synthesized with terminal meta- and para-benzoate moieties in polymethylene chains at the N atoms of the pyrimidine ring. In the synthesized compounds, the polymethylene chains were varied from having tris- to hexamethylene chains and quaternary ammonium groups; varying substituents (ester, salt, acid) at benzene ring were introduced into the chains and benzoate moieties. In vivo biological experiments demonstrated the potency of these compounds in decreasing the number of β-amyloid plaques and their suitability for the treatment of memory impairment in a transgenic model of Alzheimer's disease.

New Ceramides and Cerebrosides from the Deep-Sea Far Eastern Starfish Ceramaster patagonicus.

Three new ceramides (1–3) and three new cerebrosides (4, 8, and 9), along with three previously known cerebrosides (ophidiocerebrosides C (5), D (6), and CE-3-2 (7)), were isolated from a deep-sea starfish species, the orange cookie starfish Ceramaster patagonicus. The structures of 1−4, 8, and 9 were determined by the NMR and ESIMS techniques and also through chemical transformations. Ceramides 1–3 contain iso-C21 or C23 Δ9-phytosphingosine as a long-chain base and have C16 or C17 (2R)-2-hydroxy-fatty acids of the normal type. Cerebroside 4 contains C22 Δ9-sphingosine anteiso-type as a long-chain base and (2R)-2-hydroxyheptadecanoic acid of the normal type, while compounds 8 and 9 contain saturated C-17 phytosphingosine anteiso-type as a long-chain base and differ from each other in the length of the polymethylene chain of (2R)-2-hydroxy-fatty acids of the normal type: C23 in 8 and C24 in 9. All the new cerebrosides (4, 8, and 9) have β-D-glucopyranose as a monosaccharide residue. The composition of neutral sphingolipids from C. patagonicus was described for the first time. The investigated compounds 1–3, 5–7, and 9 exhibit slight to moderate cytotoxic activity against human cancer cells (HT-29, SK-MEL-28, and MDA-MB-231) and normal embryonic kidney cells HEK293. Compounds 2, 5, and 6 at a concentration of 20 µM inhibit colony formation of MDA-MB-231 cells by 68%, 54%, and 68%, respectively. The colony-inhibiting activity of compounds 2, 5, and 6 is comparable to the effect of doxorubicin, which reduces the number of colonies by 70% at the same concentration.

Ditopic pyridyl-benzothiazole – Pyridylmethylene-2-thiohydantoin conjugates: Synthesis and study in complexation with CuCl2

New ditopic ligands (L) consisting of 2-(2-pyridyl)benzothiazole and 5-pyridylmethylene-2-thioimidazol-4-one moieties linked with polymethylene chains of various lengths (compounds 4) or triazole-containing linker (compounds 9, 11) were synthesized and their coordination properties in the reactions with CuCl2 were investigated. All the obtained copper complexes had the LCuCl2 composition. Ligands 4 with polymethylene linkers coordinate CuCl2 initially at the 5-pyridylmethylene-2-thioimidazolone moiety, but then copper chloride migrates to the 2-pyridylbenzothiazole fragment. In contrast, ligands 9, 11 with the triazole-containing linkers coordinate CuCl2 at 5-pyridylmethylene-2-thio-imidazolone and triazole fragments, and then the structure of the complex in the solution does not change. In DMF, the initially formed Cu2+ complexes may be reduced to Cu1+ compounds, based on electrochemical investigation data.

Toporosides A and B, Cyclopentenyl-Containing ω-Glycosylated Fatty Acid Amides, and Toporosides C and D from the Northwestern Pacific Marine Sponge Stelodoryx toporoki.

Toporosides A-D (1-4), new ω-glycosylated fatty acid amides, were isolated from the sponge Stelodoryx toporoki. The structures of these compounds, including absolute configurations of stereogenic centers, were established using analysis of 1D and 2D NMR, ECD, and HR mass spectra as well as chemical transformations. Toporosides A (1) and B (2) are the first lipids containing a cyclopentenyl α,β-unsaturated carbonyl moiety in the polymethylene chain. Toporoside C (3) is likely a precursor, which undergoes intramolecular aldol condensation to produce 1 and 2. Toporosides A, C, and D showed protective effects against TNF-α-induced injury in H9c2 cardiomyocytes.

Ultramacrocyclization in water via external templation.

Condensing a dihydrazide and each of a series of cationic bisaldehyde compounds bearing polymethylene chains in weakly acidic water produces either a macrocycle in a [1 + 1] manner or its dimer namely a [2]catenane, or their mixture. The product distribution is determined by the length of the bisaldehydes. Addition of cucurbit[8]uril (CB[8]) drives the catenane/macrocycle equilibria to the side of macrocycles, by forming ring-in-ring complexes with the latter. When the polymethylene unit of the bisaldehyde is replaced with a more rigid p-xylene linker, its self-assembly with the dihydrazide leads to quantitative formation of a [2]catenane. Upon addition of CB[8], the [2]catenane is transformed into an ultra-large macrocycle condensed in a [2 + 2] manner, which is encircled by two CB[8] rings. The framework of this macrocycle contains one hundred and two atoms, whose synthesis would be a formidable task without the external template CB[8]. Removal of CB[8] with a competitive guest leads to recovery of the [2]catenane.

Tracking variations in the abundance and composition of dissolved organic matter in solar ponds of oilfield-produced brine

The quantity and quality of dissolved organic matter (DOM) in the brine of solar ponds influence the efficiency of mineral extraction and brine evaporation rates. Here we report a characterization study of DOM in solar ponds of oilfield-produced brines using different approaches. The results showed that the concentrations of dissolved organic carbon and total dissolved solids exhibited a 2–3 fold increase with exposure time in the ponds. Analyses with two-dimensional correlation spectroscopy of attenuated total reflectance Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, indicated that the aromatic and carboxylic acid structures in the DOM, were more susceptible to degradation/transformation compared with aliphatics, while aliphatics exhibited a preferential decline with increasing exposure time in the solar ponds. The relative abundance of aliphatic compounds (including functionalized ones) gradually decreased by 17.1% (r = −0.94, P < 0.001), in the solar pond process, while the opposite was observed for carbohydrates, which increased by 88.7% (r = 0.93, P < 0.001). Pyrolysis–gas chromatography–mass spectrometry revealed that the DOM in oilfield-produced brine contained polymethylene chain, terpenoid-like, carbohydrate (or carbohydrate-like) and aromatic structures. Terpenoid-like compounds were depleted while isoprenoid and linear polymethylene chain compounds increased upon irradiation in solar ponds. Finally, the guidelines for removing DOM from brine, and their ecological impacts and consequences in the process of brine resource exploitation, were discussed.

Quantum dynamics of vibrational energy flow in oscillator chains driven by anharmonic interactions

A new model of vibrational energy transfer in molecular systems taking into account anharmonic (third order) interactions of localized vibrations with a chain of harmonic oscillators is developed. The role of the energy spectrum of the chain and of the magnitude of the non-linear coupling is discussed in detail by an exact numerical solution of the quantum dynamical problem based on the tensor-train (matrix product state) representation of the vibrational wave function. Results show that the type of wave packet motion is determined by the eigen-spectrum of the chain and by its excitation time. It is found that when the excitation of the chain takes place on a much shorter timescale than the energy transfer along the chain the vibrational wave packet moves in a ballistic way independently of the length of the chain. On the other hand when the excitation of the chain takes place on the timescale of the energy transfer along the chain the overall motion becomes superballistic. These findings shed new light on recent observations of ballistic energy transfer along polymethylene chains.

Molecular dynamic simulations of diacridine binding to DNA: Indications that C6 diacridine can bisintercalate spanning two base pairs.

Dimers of 9-aminoacridine linked via the 9-amino group with polymethylene chains, termed diacridines, are known to bisintercalate into DNA when the linker comprises 6 or more methylene units. There are no literature reports of crystal or NMR solution structures for bisintercalated diacridine-DNA complexes, and the issue of the structure of the C6 ([CH2 ]n linker where n = 6) diacridine complex remains unresolved. Previously, based on simple geometric considerations, it was proposed that C6 diacridine could only span a single base pair, which requires that its bifunctional reaction violates the widely-observed "neighbor exclusion principle" where bound intercalators are separated by at least 2 base pairs. Here we have explored the structure of diacridine-DNA complexes using unrestrained molecular dynamics in explicit solvent using the parmbsc0 forcefield in AMBER14. We studied the C4 to C8 dimers, intercalated via both the minor and major DNA grooves, to a variety of nucleotide sequences. We find that C6, C7, and C8 diacridine are able to form 2 base pair bisintercalated complexes from either groove, whereas the C4 and C5 homologues cannot. We conclude that C6 diacridine does have the capacity to bisintercalate without violating neighbor exclusion, and that the previous proposed binding model needs revision.

Novel Acetylcholinesterase Inhibitors Based on Uracil Moiety for Possible Treatment of Alzheimer Disease.

In this study, novel derivatives based on 6-methyluracil and condensed uracil were synthesized, namely, 2,4-quinazoline-2,4-dione with ω-(ortho-nitrilebenzylethylamino) alkyl chains at the N atoms of the pyrimidine ring. In this series of synthesized compounds, the polymethylene chains were varied from having tetra- to hexamethylene chains, and secondary NH, tertiary ethylamino, and quaternary ammonium groups were introduced into the chains. The molecular modeling of the compounds indicated that they could function as dual binding site acetylcholinesterase inhibitors, binding to both the peripheral anionic site and active site. The data from in vitro experiments show that the most active compounds exhibit affinity toward acetylcholinesterase within a nanomolar range, with selectivity for acetylcholinesterase over butyrylcholinesterase reaching four orders of magnitude. In vivo biological assays demonstrated the potency of these compounds in the treatment of memory impairment using an animal model of Alzheimer disease.

Self-assembly involving hydrogen bonds. Spectral properties and structure of supramolecular complexes of bis-aza-18-crown-6-containing dienones with alkanediammonium salts

Dienones (ketocyanine dyes) containing two aza-18-crown-6 ether residues were synthesized. The complex formation of these dyes with the EtNH3+ and +H3N(CH2)nNH3+ ions (n = 2–10, 12) in MeCN was studied by electronic and 1H NMR spectroscopy, including spectrophotometric and 1H NMR titration. It was found that homoditopic bis-azacrown dienones and alkanediammonium ions with a short polymethylene chain form 1:1, 2:2, and 1:2 complexes, whereas alkanediammonium ions with a long polymethylene chain form only pseudocyclic 1:1 complexes. The stability constants of the resulting complexes were determined (logK1:1 varies in the range from 2.74 to 5.62 [M–1], logK2:2 = 2.1 [M–1], and logK1:2 varies in the range from 2.03 to 2.96 [M–1]). The most stable complexes are formed by diammonium ions with a long polymethylene chain owing to simultaneous binding of both NH3+ groups to the azacrown ether residues of the dye. The structure of supramolecular complexes was confirmed by quantum chemical calculations.

Molecular Origin of the Odd-Even Effect of Macroscopic Properties of n-Alkanethiolate Self-Assembled Monolayers: Bulk or Interface?

Elucidating the influence of the monolayer interface versus bulk on the macroscopic properties (e.g., surface hydrophobicity, charge transport, and electron transfer) of organic self-assembled monolayers (SAMs) chemically anchored to metal surfaces is a challenge. This article reports the characterization of prototypical SAMs of n-alkanethiolates on gold (CH3(CH2)nSAu, n = 6-19) at the macroscopic scale by electrochemical impedance spectroscopy and contact angle goniometry, and at the molecular level, by infrared reflection absorption spectroscopy. The SAM capacitance, dielectric constant, and surface hydrophobicity exhibit dependencies on both the length (n) and parity (nodd or neven) of the polymethylene chain. The peak positions of the CH2 stretching modes indicate a progressive increase in the chain conformational order with increasing n between n = 6 and 16. SAMs of nodd have a greater degree of structural gauche defects than SAMs of neven. The peak intensities and positions of the CH3 stretching modes are chain length independent but show an odd-even alternation of the spatial orientation of the terminal CH3. The correlations between the different data trends establish that the chain length dependencies of the dielectric constant and surface hydrophobicity originate from changes in the polymethylene chain conformation (bulk), while the odd-even variation arises primarily from a difference in the chemical composition of the interface related to the terminal group orientation. These findings provide new physical insights into the structure-property relation of SAMs for the design of ultrathin film dielectrics as well as the understanding of stereostructural effects on the electrical characteristics of tunnel junctions.

Diffusion of Polymethylene Chain Molecules in Nonpolar Solvents.

The translational diffusion constants, D, for solutes with polymethylene chains are compared with the predictions of a hydrodynamic bead model based on Kirkwood-Riseman theory. The solute-solvent combinations include (a) n-alkanes in n-alkanes; (b) n-alkanes in benzene, toluene, tetralin, decalin, and CCl4; (c) 1-alkenes in n-alkanes; (d) 1-phenylalkanes in n-alkanes; and (e) 1-phenylalkanes in isocetane (2,2,4,4,6,8,8-heptamethylnonane), pristane (2,6,10,14-tetramethylpentadecane), and squalane (2,6,10,15,19,23-hexamethyltetracosane). The bead model gives good overall agreement with an average difference of less than 3% between 207 experimental and calculated diffusion constants that include published data as well as new D values determined for 1-alkenes and 1-phenylalkanes using capillary flow techniques. The calculated values are obtained using chain element (bead) radii that decrease as the solvent viscosity increases. The bead model's results are comparable to those obtained using cylinder and lollipop diffusion for many of the same solute-solvent systems; the three models are compared and discussed. The results for the 1-alkenes and n-alkanes in the n-alkanes are the first from a Kirkwood-Riseman analysis in a homologous series of solvents.

Pheophorbide–phenazinium conjugate as a fluorescent light-up probe for G-quadruplex structure

A novel fluorescent light-up probe for G-quadruplex (G4) structures based on fluorescence quenching mechanism was designed. It is a conjugate of two fluorophores, Pheophorbide-a (Pheo-a) and cationic intercalative aminophenazinium dye (Pzn), linked with polymethylene chain. Pheo-a is a natural porphyrin known as efficient photosensitizer for antitumor photodynamic therapy. Cationic Pzn part of the conjugate enhances its binding to anionic nucleic acid. Spectroscopic properties of Pheo-Pzn and its binding to polyribonucleotides of different secondary structures (double-stranded poly(A)·poly(U), poly(G)·poly(C) and four-stranded poly(G)) were studied in a wide range of molar phosphate-to-dye ratios (P/D) by absorption spectroscopy, polarized fluorescence and fluorimetric titration methods. In aqueous medium free Pheo-Pzn exhibits strongly quenched fluorescence due to formation of stacked intramolecular heterodimer. DFT calculations demonstrated that it is energetically favored over the open form of Pheo-Pzn. The conjugate is able to discriminate between duplex and quadruplex polynucleotides exhibiting 50-fold emission increase upon binding to quadruplex poly(G) and quenched fluorescence in the case of ds-polymers. The observed spectral changes evidence disintegration of the heterodimer and separate binding of both Pheo-Pzn fragments to poly(G) with intercalation of Pheo-a moiety between guanine tetrads, while binding of the heterodimer as a whole to duplex polynucleotides is suggested. Pheo-Pzn conjugate can be proposed as efficient probe for the recognition of G-quadruplex structures.

Macromolecular Effect Stabilized Color-Tunable and Room Temperature Charge-Transfer Complexes Based on Donor–Acceptor Assemblies

We report one of the first examples of room temperature stable solid-state charge transfer (CT) complexes based on a segmented π-conjugated polymer and rylene diimide donor–acceptor system having tunable optical transitions from the visible to NIR region in the solar spectrum. Semicrystalline and amorphous segmented oligo-phenylenevinylene (OPV) chromophore containing polymers were tailor-made with flexible polymethylene chains in the backbone. The electron rich segmented OPV polymers were complexed with two electron-deficient diimides based on naphthalene (NDI) and phenylene (PDI) core. The binary complexes of segmented OPV polymers and rylene diimides produced unique classes of CT complexes based on OPV-NDI and OPV-PDI chromophore diads. Electron microscope, polarizing microscope, and X-ray diffraction analyses provided direct evidence for the two-dimensional lamellar packing of D–A self-assembly in the solid state. Detailed absorption and emission photophysical studies revealed that the donor OPV polymers and acceptor chromophores exhibited a 1:1 complex with respect to the long-range order of D–A–D–A–D–A π-stacked supramolecular assemblies. The role of the macromolecular effect on the CT complexation was further investigated using structurally identical OPV monomers. The monomer OPV-NDI complexes (or PDI complexes) were found to exhibit CT complex in the solution; however, they underwent uncontrollable phase separation into their individual D and A crystalline domains and lost their CT self-assembly in the solid state. Interestingly, the macromolecular effect driven supramolecular self-organization of long chain segmented OPV polymers produced stable CT complexes both in solution and solid state under ambient conditions. Segmented OPV polymer + PDI and segmented OPV polymer + NDI complexes were produced as red and green colored CT complexes, respectively. This enabled the accomplishment of room temperature stable CT complexes in π-conjugated polymers having absorption ranging from 350 to 1100 nm. These donor–acceptor CT self-assemblies are processable into thin films under solvent free melt crystallization process; thus, the present segmented polymer design strategy opens up a platform for donor–acceptor CT complexes.

Syntheses of terpyridine-pyridylbenzothiazole linked ditopic ligands and their copper(II) complexes

New binary ligands consisting of 2,2′:6′,2″-terpyridine and 2-(2-pyridyl)benzothiazole linked with polymethylene chains of various lengths (3a-d, n = 4–11, where n is the number of CH2 units) were synthesized. Cu(II) complexes of these ligands with both CuLCl2 (4a-d) and CuL2ClO4 (5a-d) composition were also synthesized. Single crystals of the chloride complex 4b and perchlorate complex 5b were obtained, and their crystal structures were determined using X-ray diffraction. Both compounds are mononuclear Cu(II) coordination compounds with five-coordinate distorted tetragonal pyramidal geometry in the chloride complex and six-coordinate octahedral geometry in the perchlorate complex. Only terpyridine moieties coordinate with the copper ion, while pyridylbenzothiazole fragments do not participate in the coordination. Cyclic voltammograms of complexes 4 and 5 showed a Cu(II) → Cu(I) reduction at approximately −0.15 V; the observed oxidation and reduction potentials were almost identical for complexes with (CH2)4 and (CH2)11 linkers. Complex 5b, based on cyclic voltammetry data, could be turned into a heteronuclear Rh(III)–Cu(II) complex by treatment with [S-(11-(4-([2,2′:6′,2″-terpyridin]-4′-yl)phenoxy)undecyl)ethanethioate]rhodium(III) trichloride.

Design and synthesis of fluorescent ligands for the detection of cannabinoid type 2 receptor (CB2R)

The Cannabinoid 2 receptor, CB2R, belonging to the endocannabinoid system, ECS, is involved in the first steps of neurodegeneration and cancer evolution and progression and thus its modulation may be exploited in the therapeutic and diagnostic fields. However, CB2Rs distribution and signaling pathways in physiological and pathological conditions are still controversial mainly because of the lack of reliable diagnostic tools. With the aim to produce green and safe systems to detect CB2R, we designed a series of fluorescent ligands with three different green fluorescent moieties (4-dimethylaminophthalimide, 4-DMAP, 7-nitro-4-yl-aminobenzoxadiazole, NBD, and Fluorescein-thiourea, FTU) linked to the N1-position of the CB2R pharmacophore N-adamantyl-4-oxo-1,4-dihydroquinoline-3-carboxamide through polymethylene chains. Compound 28 emerged for its compromise between good pharmacodynamic properties (CB2R Ki = 130 nM and no affinity vs the other subtype CB1R) and optimal fluorescent spectroscopic properties. Therefore, compound 28 was studied through FACS (saturation and competitive binding studies) and fluorescence microscopy (visualization and competitive binding) in engineered cells (CB2R-HEK293 cells) and in diverse tumour cells. The fluoligand binding assays were successfully set up, and affinity values for the two reference compounds GW405833 and WIN55,212-2, comparable to the values obtained by radioligand binding assays, were obtained. Fluoligand 28 also allowed the detection of the presence and quantification of the CB2R in the same cell lines. The interactions of compound 28 within the CB2R binding site were also investigated by molecular docking simulations, and indications for the improvement of the CB2R affinity of this class of compounds were provided. Overall, the results obtained through these studies propose compound 28 as a safe and green alternative to the commonly used radioligands for in vitro investigations.

Star-shaped oligomers with truxenone centre and triphenylene branches: mesomorphism, optical and electronic properties

ABSTRACT Three star-shaped oligomers with an electron-deficient truxenone (TrO) as the central core and three electron-rich triphenylenes (TP) as the peripheral arms were prepared, in which the triphenylenes groups are, respectively, connected to the central truxenone core at 2, 7 and 12 positions through a highly flexible O(CH2)nO (n = 6,8,10) polymethylene chain. All these triphenylene-armed oligomers TrO[O(CH2)nOTP]3 (n = 6,8,10) exhibit liquid crystalline over broad mesophase ranges including room temperature. Oligomer TrO[O(CH2)6OTP]3 exhibit a rectangular columnar mesophase, while others with the linkage longer show a hexagonal columnar mesophase. This modulation of phase behaviours was demonstrated to be generated by steric perturbations introduced between the three decyloxy substituents in central truxenone core and the linkages with different lengths, which cause the disturbance of the intracolumnar structure and influence the degree of ordering in columnar phases. No new electronic absorption except for the usual bands of the individual truxenone or triphenylene part was observed in dichloromethane solution of TrO[O(CH2)6OTP]3 . However, two new emission peaks emerged and the intensity and position of the emission peaks were found to exhibit pronounced changes upon concentration variation, which can be attributed to the formation of intermolecular excimers.

Photoionization mass spectrometry of ω-phenylalkylamines: Role of radical cation-π interaction

Linear ω-phenylalkylamines of increasing alkyl chain length have been investigated employing synchrotron radiation in the photon energy range from 7 to 15 eV. These molecules have received considerable interest because they bear the skeleton of biologically relevant compounds including neurotransmitters and because of the possible interaction between the amino moiety and the phenyl ring. Recently, the contribution of this interaction has been assayed in both neutral and protonated species, pointing to a role of the polymethylene chain length. In this work, the ionization energy (IE) values of benzylamine (BA), 2-phenylethylamine (2-PEA), 3-phenylpropylamine (3-PPA), and 4-phenylbutylamine (4-PBA) were investigated in order to ascertain the impact of the different alkyl chain lengths and to verify an amino radical cation-π interaction. The IEs obtained experimentally, 8.54, 8.37, 8.29, and 8.31 eV for BA, 2-PEA, 3-PPA and 4-PBA, respectively, show a decreasing trend that is discussed employing calculations at the CBS-QB3 level. Moreover, the appearance energy values for major fragments produced by the photofragmentation process are reported.