Naphthyl Ethylamine Research Articles

Dependence of the adsorption of chiral compounds on their enantiomeric composition

The adsorption of two different chiral molecules on platinum surfaces has been explored as a function of enantiomeric composition. In the first case, the saturation monolayers obtained by the adsorption of 1-(naphthyl)ethylamine (NEA) from CCl4 solutions were characterized in situ by reflection–absorption infrared spectroscopy (RAIRS). It was found that racemic mixtures yield different IR spectra than those obtained from enantiopure monolayers, a behavior that was interpreted as the result of the formation of racemate pairs via hydrogen bonding at the amine moiety also responsible for bonding to the surface. NEA adsorption under these conditions is reversible and can be modified by subsequent exposures to solutions of different chiral compositions, but that appears to take place only via changes in the relative fractions of enantiopure versus racemic domains on the surface; no other enantiomeric ratios are apparent in the IR data. The second study focused on the uptake of propylene oxide (PO) on Pt(111) under ultrahigh vacuum (UHV) conditions. In that case, racemic monolayers show densities up to ~20% lower than those obtained with one single enantiomer. This can be explained by kinetic arguments, since data from isothermal molecular-beam experiments indicated that the PO sticking coefficient depends on the chirality of the incoming PO molecules relative to that of the neighboring adsorbed PO species. Monte Carlo simulations could reproduce the experimental data by assuming adsorbate-assisted adsorption and enantiospecific adsorption geometries for molecules impinging on sites adjacent to previously adsorbed surface species.

LC Enantioseparation of 30-Component Diastereomeric Mixture of Amino Acids and Detection of d-Isomers Using New Reagents with Amines as Chiral Auxiliaries in Cyanuric Chloride

Two enantiomerically pure amines, viz., (R)-(+)-naphthylethyl amine and (S)-(+)-1-benzyl-3-aminopyrrolidine, were used as chiral auxiliaries for nucleophilic substitution of chlorine atoms in cyanuric chloride or its 6-butoxy derivative. The chiral derivatizing reagents so obtained were characterized and their chiral purity was ascertained. Diastereomers of 15 dl-proteinogenic amino acids were synthesized under microwave irradiation using these reagents. Separation of diastereomeric pairs along with separation of a mixture of 30 diastereomers in a single chromatographic run was carried out on a reversed-phase C18 column. Mixtures of acetonitrile with aqueous trifluoroacetic acid were used as mobile phase. The detection was made at 230 nm using photo diode array detector. The separation behavior in terms of retention times and resolutions was compared on the basis of effect of chiral auxiliaries (i.e. amines) and achiral substituents (i.e. chlorine or butoxy group) in the chiral derivatizing reagents and the hydrophobic side chains of amino acids. The separation method was validated in terms of accuracy, precision, linearity, recovery, limit of detection and limit of quantitation. The method was successful for determination of d-amino acids in the absence of pure d-enantiomers and for separation of 19 diastereomers from a mixture of 30.

Application of optically pure amines as chiral auxiliaries to develop trichloro‐s‐triazine‐based new chiral derivatizing reagents for reversed‐phase high‐performance liquid chromatographic enantioseparation of dl‐selenomethionine

(R)-(+)-naphthylethyl amine and (S)-(+)-1-benzyl-3-aminopyrrolidine were incorporated as chiral auxiliaries, by nucleophilic substitution of chlorine atoms, in cyanuric chloride (CC) or its 6-butoxy derivative. There were obtained four new chiral derivatizing reagents (CDRs) as two dichloro and two monochloro triazine reagents. The CDRs so obtained were characterized and their optical purity was ascertained. Diastereomers of dl-selenomethionine were synthesized under microwave irradiation for 60 or 90 s (at 80% power of 800 W). Reversed-phase high-performance liquid chromatographic separation of diastereomers was carried out on a C18 column using mixtures of acetonitrile with aqueous trifluoroacetic acid as mobile phase. The detection was made at 230 nm using a photodiode array detector. The separation behaviors in terms of retention times and resolutions were compared. The separation method was validated for limit of detection, linearity, accuracy, precision, and recovery.

Surface plasmon resonance study on binding interactions of multivalent cyclophane hosts with immobilized guests

AbstractGuest‐binding affinities of water‐soluble cyclophane heptadecamer (1) and pentamer (2) with immobilized guests such as 1‐pyrenylmethylamine (PMA) and 2‐(1‐ naphthyl)ethylamine (NEA) were investigated by surface plasmon resonance (SPR) measurements. As a typical example, the binding constants (K) for 1 and 2 with the immobilized PMA as a guest were evaluated to be 2.5 × 107 and 2.7 × 106 M−1, respectively, and were much larger than that of a monocyclic reference cyclophane (K, 2.5 × 104 M−1). Interestingly, in the complexation of 1 and 2 with the immobilized guests, more favorable association and dissociation rate constant values (ka and kd, respectively) were observed in comparison with those for the monocyclic cyclophane, reflecting multivalent effects in macrocycles. The multivalent effects in macrocycles as well as molecular recognition abilities of the cyclophane oligomers were confirmed even when the guest molecules were immobilized on SPR sensor chip surfaces. Copyright © 2009 John Wiley & Sons, Ltd.

High Chiral Induction in Cholesteric Liquid Crystal of Aromatic Polyesters with Chiral Naphthyl Ethylamine Groups at Their Polymer Ends

Chiral aromatic liquid crystal (LC) polyesters were prepared by incorporating (R)-(+)-1-(1-naphthyl)ethylamine (NEA) to both their ends, and the helical twisting powers were determined for the cholesteric LCs in mixtures with the homologous nematic polymer. The chiral NEA groups in the polymer ends were found to act as an effective chiral inducer so that only a small chiral content of 2–5 wt % can induce the helical pitches, which are comparable to the wavelength of visible light. Together with the easy preparation of chiral polymers and the simple processing to polymer cholesteric films, the high induction of chirality gives the opportunity to produce large-area nanostructures at low cost, which could be applied to the development of optical devices.

The Role of the Chiral Modifier on the Enantioselective Hydrogenation of Methyl Pyruvate on Pt(111)

Using density functional calculations we have investigated the enantioselective hydrogenation of methyl pyruvate (MP) to methyl lactate over Pt(111). Chirality was induced to the surface by adsorption of the chiral modifier naphthyl-ethylamine (NEA). In our calculations, we have investigated both the role of hydrogen in the formation of the observed docking complex and the role of the functional group of the modifier. As a result, we could identify the importance of the amine group for the interaction between reactant and modifier and propose that the observed docking complex is formed between semihydrogenated MP and NEA.

Adsorption and Stability of (R)-(+)- and (S)-(−)-1-(1-naphthyl) Ethylamine on a Series of Platinum Single Crystal Surfaces: Implications for Heterogeneous Chiral Hydrogenation

The adsorption, desorption, and stability of the powerful chiral modifier precursors R- and S- naphthylethylamine (NEA) on the {111}, {211}, {331}, {643}R, and “polycrystalline” platinum surfaces have been examined by cyclic voltammetry. NEA is effectively irreversibly adsorbed at room temperature to a saturation coverage that corresponds to occupancy of ∼80% of the available metal area and there is no detectable transport of adsorbate between the various adsorption sites present. Most importantly, the molecule adsorbs indiscriminately and with essentially equal rates at terrace and step sites, and in the case of the chiral {643}R surface, the adsorption behavior of the enantiomers R− and S−NEA is the same. Specifically, the intrinsically chiral kink sites neither favor nor disfavor the adsorption of either enantiomer. In every case, desorption of NEA occurs under electro-reducing conditions with {100} facets showing an enhanced desorption rate on the {643}R, {211}, and polycrystalline surfaces. The impli...

31P Nmr Determination of the Enantiomeric Composition of N-Phthaloyl-1-Aminoalkyl-Phosphonate Monoesters using 1-(1-Naphthyl)Ethylamine and Ephedrine as the Chiral Agents

Optically active 1-(1 -naphthyl)ethylamine as well as ephedrine with N-phthaloyl-1-aminoalkylphosphonate monoesters form in CDCl3 diastereoisomeric salts distinguished in 31P and in 1H NMR spectroscopy. The magnetic nonequivalence of phosphonate groups are in almost all cases large enough (Δδ 31P is up to 0.45 ppm) to determine enantiomeric excess values with a high level of accuracy. Ephedrine seems to be a better chiral agent for ee determination by means of 31P NMR. The larger chemical shift dispersions Δδ 31P NMR were recorded for the ephedrine salts. In contrast, the respective naphthylethylamine salts revealed greater Δδ 1H NMR values.

Stereoselective determination of R(−)- and S(+)-prilocaine in human serum using a brush-type chiral stationary phase, solid-phase extraction and UV detection

A chiral HPLC method was developed for the quantitation of R(−)- and S(+)-prilocaine in human serum. The method involves sensitive and selective detection of R(−)- and S(+)-prilocaine using normal-phase chiral HPLC on a pirkle-type naphthyl ethylamine stationary phase (Sumichiral OA-4700, 250 mm × 4 mm i.d.) at ambient temperature with a flow rate of 0.8 ml min −1. A sample clean-up procedure was used for isolation of the analytes of interest from human serum using Bond-Elut C 18 columns with high recovery and selectivity. The detection limits were 4 ng ml − for R-prilocaine and 5 ng ml −1 for S-prilocaine. The limits of quantitation were 10 ng ml −1 for both enantiomers. Linear calibration curves in the 10–1000 ng ml −1 range showed good coefficients of determination >0.999 ( n − 3). Precision and accuracy of the method were within 4–5.8% and 1.5–4.8% respectively for R(−)-prilocaine, and 2.8–5.7%, and 3.2–5.2% respectively for S(+)-prilocaine.