Studies are presented on the two-dimensional (2-D) crystalline packing arrangements of enantiomerically pure and racemic α-amino acid RHC(NH3 +)CO2 - monolayers on water and on glycine aqueous solutions, as determined by synchrotron grazing incidence X-ray diffraction. The amphiphiles have been designed such that their racemic mixtures form 2-D crystals which are either heterochiral (for R = C n H2 n +1−, n = 10, 12, 16) due to the tendency for herringbone chain arrangements via glide symmetry or homochiral (for R = C n H2 n +1CONH(CH2)4−, n = 11, 17, 21) by virtue of hydrogen bonding by translation of the amide group in the chains leading to a spontaneous separation into islands of opposite chirality. The two different crystalline motifs led to a correlation between their packing arrangements and induced oriented nucleation of 3-D crystals of α-glycine by these monolayers. The relevance of the present results to the possibility of ordering and spontaneous segregation of racemates of the natural hydrophobic α-amino acids at the air-solution interface is discussed.

The packing arrangements of Langmuir films on aqueous solution of simple amphiphiles, such as fatty acids, alcohols, amides, and amino acids, are now established to near atomic resolution by the method of grazing incidence X-ray diffraction (GIXD), complemented by various spectroscopic and lattice energy computational techniques. For simple aliphatic chainlike amphiphilic molecules, it is possible to correlate the extent of two-dimensional (2-D) crystallinity of the Langmuir film with molecular interactions, in terms of the nature and length of the hydrophobic chain, the type of hydrophilic headgroup, and the binding properties thereto of solute ions and molecules from the aqueous subphase. The monolayer packing arrangements of amphiphilic molecules can be engineered for the performance of photoinduced topochemical reactions, and characterized by GIXD. Racemic mixtures of amphiphiles can also be engineered, by taking advantage of intermolecular hydrogen bonding, to undergo a spontaneous separation of the left-and right-handed molecules into 2-D chiral crystals at the air-solution interface. The geometry of binding of molecules or ions from the aqueous subphase to the hydrophilic headgroups can be pinpointed by GIXD, in favorable systems. The ordered binding of solutes to the amphiphile monolayer can lead to induced nucleation of oriented organic and inorganic crystals at the solution interface. GIXD has shown that such an induction can occur via even a partial lattice match, or by structural complementarity, sometimes involving a molecular rearrangement of the amphiphiles. It is possible from monolayer-induced crystallization to glean information on the process of nucleation and on the critical size of the nuclei. A variety of different types of crystalline multilayers, composed of waterinsoluble molecules such as bolaform amphiphiles, alkanes, heterosubstituted aromatics, can be formed at the air-solution interface. The number of layers formed and their polymorphic behavior can be controlled, albeit within limits, with the use of tailor-made additives. Their structures can be determined by GIXD, thus providing data on the initial stages of 3-D crystalization. Multilayers, comprising water-insoluble and watersoluble components, assembled in situ at the solution surface leading to thin film supramolecular architectures, have been engineered. These crystals have been found to be oriented vis-à-vis the solution surface and thus amenable to characterization by GIXD and other methods.

We report on the direct observation of collective electronic properties in assembled CdS quantum particles (QPs) arranged in periodic layers. Within each layer the QPs are of the same average size, either 2.5 or 5 nm, and the layers are arranged in a cascade-like pattern. The electronic properties of the QPs were studied using a new method, the attenuated low energy photoelectron spectroscopy (A-LEPS), in which a "pump" laser excites the QPs and a "probe" laser ejects photoelectrons from the QPs and from the metal substrate. The A-LEPS method provides information about the populated electronic states of the QPs (including the splitting between the light/heavy hole and split-off bands) and how these states depend on the interparticle interactions.

ponents, as well as outgassing of CO 2 . Approximately 1 mg of vaterite spheroids was produced from 1 mL of supersaturated CaHCO 3 solution.Growth of the vaterite spheroids was followed in situ by optical microscopy and by removing samples at intervals of 2, 4, 6, and 18 h from an octane/SDS/CaHCO 3 microemulsion left partially uncovered at 25 C in a Petri dish. Samples of the uppermost dried powder layer, along with some of the thickening underlying microemulsion phase, were removed and immediately washed with methanol to remove SDS, filtered through a 1 mm poly(tetrafluoroethylene) (PTFE) membrane and rewashed with methanol. The remaining sediment was examined by SEM.Dissolution studies were undertaken by suspending the vaterite microsponges in distilled water. Samples were removed at various time intervals, dried in air and examined by SEM. Spheroids with an average size of 4.5 mm or 15 mm dissolved within 2 and 10 days, respectively.Control experiments on calcium carbonate crystallization were undertaken by mixing 0.5 g of SDS with 1.8 mL of supersaturated CaHCO 3 solution, prepared as above. A clear solution was obtained by probe sonication for 25 s, and the mixture left at 25 C in an open vial. The mixture transformed to a gel overnight. The precipitated CaCO 3 (vaterite) crystals were collected at intervals of 2, 4, 6, and 18 h by washing with methanol followed by sedimentation. Dissolution studies were performed by suspending the crystals, formed after 4 h, in distilled water for at least 1 day.Polymer-coated vaterite particles were prepared by adding 0.0011 g of the fully mineralized vaterite spheroids, 17.5 mm in diameter, to a saturated chlorobenzene solution of poly(vinyl chloride) (PVC) (M w = 95 000), followed by stirring for 2 h, sedimentation and air-drying of the inorganic material. The saturated PVC solution was prepared by adding 0.1 g of PVC to 25 mL of chlorobenzene, followed by overnight stirring, and removal of the saturated supernatent for further use. The PVC-coated vaterite spheres were then placed into 7 mL of distilled water and 1 mL liquid aliquots were removed at intervals of up to 7 days and the soluble Ca content analyzed by atomic absorption analysis. A control experiment involving the dissolution of 0.0013 g of uncoated 17.5 mm vaterite spheroids in 7 mL of distilled water was also undertaken.

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To provide more direct information on the role played by “tailor-made” auxiliary molecules in the early stages of crystal nucleation, the interplay between clusters of polar headgroups of monolayers of the copper complexes S −Cu− S ‘ and S −Cu− R ‘ and water-soluble copper complexes S ‘ −Cu− S ‘ and R ‘ −Cu− R ‘ were investigated [where S represents enantiomerically pure (S)-palmitoyl-N ε-lysine, and S ‘ and R ‘ represent chiral resolved (S) and (R) forms of alanine, serine, or valine]. The different monolayers were formed by spreading the amphiphilic (R) or (S) α-amino acid on an aqueous solution of copper acetate followed by injection of the water-soluble (S ‘) or (R ‘) α-amino acid into the subphase. The surface pressure−molecular area isotherms of the Langmuir monolayers of the two type of complexes (S −Cu− S ‘ and S −Cu− R ‘) are different, the former being substantially more expanded. The polar headgroups of the S −Cu− S ‘ and of the S −Cu− R ‘ monolayers transferred onto a solid support assume a trans and cis configuration, respectively, according to comparative X-ray photoelectron spectroscopy (XPS) studies with appropriate cis and trans three-dimensional (3-D) α-amino acid Cu complexes. A grazing incidence X-ray diffraction (GIXD) analysis demonstrated that the S −Cu− S ‘ and S −Cu− R ‘ monolayers have different 2-D crystal structures, in keeping with the XPS results. A model is presented suggesting that the water-soluble S ‘ −Cu− S ‘ copper complexes are enantioselectively bound to the periphery of the domains of the cis S −Cu− S ‘ monolayers, but not to the domains of the trans S −Cu− R ‘ monolayers. By symmetry, the same principal holds for the monolayers and water soluble copper complexes of α-amino acids of the opposite handedness.

Identification of the phase transition (see Figure) that occurs at the early stages of the topotactic transformation of Langmuir–Blodgett films of Cd or Pb behenate and arachidate with H2S has led to clarification of the structures of the hybrid films, previously in question. The ordered phase is stabilized by the addition of thio‐carboxylic acids to the system.

The electronic properties of hybrid Langmuir–Blodgett (LB) films containing CdS quantum particles (QP) of different size arranged in “cascade like” architectures on gold are studied. The energy distribution of photoelectrons ejected from the gold substrate and transmitted through the LB films is reported. The electronic properties were found to depend on the structure and the organization of the layers relative to the gold substrate, and on the interaction between the metal substrate and the film.