Molecular Orientation and Intermolecular Interaction in Alanine on Cu(001)

• Published in: Langmuir Vol. 26; no. 4; pp. 2294 - 2300
• Main Authors: Iwai, Hidekazu, Egawa, Chikashi
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 16.02.2010
• Subjects: Adsorption; Alanine - chemistry; Binding Sites; Chemistry; Colloidal state and disperse state; Colloids: Surfactants and Self-Assembly, Dispersions, Emulsions, Foams; Copper - chemistry; Exact sciences and technology; General and physical chemistry; Hydrogen Bonding; Particle Size; Stereoisomerism; Surface physical chemistry; Surface Properties; Alanine; Oxygen; Amino group; Hydrogen; Nitrogen; Carbon; Intermolecular interaction; Scanning tunneling microscopy; Racemic; Molecular orientation; Adsorption; Aminoacid; Methyl group; Carboxylate; Bending; Frequency; Models; Structure; Functional group; Hydrogen bond
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la902716a

Molecular orientation of l-alanine and structure model of racemic alanine on Cu(001) have been studied by RAIRS, LEED, and STM. The appearance of characteristic frequencies of the NH2 wagging, the symmetric stretch of carboxylate group (COO−), the symmetric CH3 stretch, and the C*−H (C* denotes a chiral carbon) bending modes in RAIRS is consistent with an adsorption configuration in which alanine molecule is bonded to three Cu atoms through the two oxygen atoms of carboxylate group and the nitrogen atom of amino group in its anionic form with the methyl group standing up over near bridge sites. In the adlayer, hydrogen bonds between the hydrogen atoms of the amino group and the oxygen atom of the carboxylate group contribute to assemble d(l)-alanine molecules along [1̅30] ([3̅10]) as well as [110] directions with a c(2 × 4) periodicity. In the adsorption of racemic mixtures, dl-alanine, d- and l-alanine molecules segregate to form their own c(2 × 4) domains, thus creating the boundary lines along the [110] direction. A submolecular resolution STM image of these domains exhibits distinction between some functional groups and the surrounding intermolecular hydrogen bonds along the [1̅30] or [3̅10] direction. In the submolecular resolution STM, it is most reasonably interpreted that intermolecular network between adsorption alanines is connected by N−H1···O2 and N−H2···O2 hydrogen bonds to form each homochiral domain and the bond at the domain boundary is enhanced by scanning tip which is most probably modified.