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X-ray reflectivity measurements and surface-pressure isotherms of spread films of the fullerene-propylamine adduct C{sub 60} - [NH{sub 2}(CH{sub 2}){sub 2}CH{sub 3}]{sub 12} indicate that despite the lack of definite amphiphilic character, this material forms a homogeneous monomolecular layer on water surfaces. X-ray reflectivity data, taken at various lateral pressures, were fitted to a model structure defined in terms of the dimensions of an average cell and its chemical compositions. At T = 18 {sup 14}C, the lateral pressure versus area per molecule is indicative of a structural phase transition presumably from one closely-packed phase to another, as the total thickness of the film is consistent with a single layer of 15 A thickness. At pressures above 30 mN/m the film consists of an inhomogeneous bilayer, consistent with a layer thickness of 26 A. 16 refs., 3 figs., 1 tab.

Monolayers of surface-active hemicyanine dyes have been extensively studied owing in part to their potential importance for fabrication into non-linear optical materials. In an effort to increase the dipole moment to a value larger than that present in the typical hemicyanine, a neew compound was characterized, having the structure: (CH 3 ) 2 NC 6 H 4 CHCHCHCHC 6 H 4 N + C 22 H 45 B − which contains a more extended π-bonded system compared with some more commonly studied hemicyanines. It is known that hemicyanines may be present in various aggregated states as well as species having varying degrees of order when in monolayer form. For the new compound, monolayers could be produced having both ordered and disordered structures. On a pure water subphase, the new hemicyanine in a highly compressed monolayer had a narrow, blue-shifted absorption band with a maximum at 435 nm. Such a spectrum is characteristic of H-aggregate species. When the subphase contained cadmium chloride (1 × 10 −3 M) the optical absorption band was similar to that seen in chloroform solution for disaggregated species, with a broad absorption band at 485 nm, shifting only slightly as the monolayer was progressively compressed. Atomic force microscopy visualizing the two different films indicated that monolayers transferred from pure water subphase appeared inhomogeneous, discontinuous and indicative of island structures possibly in the original spread monolayer, or formed during transfer. Monolayers formed on Cd 2+ -containing subphases were uniform except for some small surface defects.

The size, structure and ease of manipulation of organized monolayer structures have been used to control reaction pathways for the formation of semiconductor particle clusters of cadmium sulfide and other semiconductors. The size and particle distributions are determined by the specific monolayer structure chosen. The present study reports a new technique for the formation of small clusters of cadmium and zinc sulfides. It combines monolayer methods with techniques based on inclusion formation in restricted volumes. Cadmium and zinc sulfides are formed within the cavity of a channel protein by a simple process in which a close-packed monolayer of the channel protein is formed on a neutral subphase, transported to a cadmium-chloride-containing subphase, transferred to a slide by Langmuir-Blodgett transfer and exposed to hydrogen sulfide. The channel protein is a membrane-bound entity with hydrophobic exterior walls and a hydrophilic inside channel (12 A diameter). It is cylindrical and in compressed monolayers is oriented normal to the interface with the channel mouth in communication with the subphase. Small water-soluble ions are rapidly taken into the channel interior. The size of the cluster formed is limited by the small number of ions capable of assimilation into the channel and, because each group of ions is compartmentalized, there is no possibility of spontaneous aggregation to produce macroscopic particulate inside of the protein channel. The cadmium and zinc sulfides were produced in the “quantum dot” size range as evidenced by their markedly blue-shifted optical spectra. The results of this study indicate more general potential application of channel protein structures as nanoscale reactors; in the case of the protein used here the channel opening and closing can be modulated by pH changes, affording the possibility of sealing or encapsuliting reactants or products in small defined volumes. Other types of channel structure are closed by changes in potential, specific small ions or biogenic messenger molecules. Some of these have significantly larger channel volumes that the protein used here. These too may be likely future systems for specific small-scale reactions.

Monolayers on mica of two rigid amphiphiles of specific cross-sectional geometry have been studied by atomic force microscopy and are ordered over micron scale areas. An interlocking amphiphile shows disruption into crystalline shards on transfer from the aqueous subphase. A chiral amphiphile retains its integrity when transferred from the intermediate pressure phase but exhibits catastrophic changes when transferred from the high pressure phase. The results imply that the interlocked amphiphile has the same structure for both aqueous and solid subphases. The phases exhibited by the chiral amphiphile on mica are probably not those observed on the aqueous subphase.

Monolayer characteristics were determined for three isomeric cleavable phospholipids containing a ketal group on one of the alkyl chains: 1-octadecanoyl-2-[ trans -[8-(2,2-dimethyl-5-octyl-1,3-dioxolan-4-yl)octanoyl]]- sn -glycero-3-phosphatidylcholine ( 1a ); 1-octadecanoyl-2-[16-(2,2-dimethyl-1,3-dioxolan-4-yl)hexadecanoyl]- sn -glycero-3-phosphatidylcholine ( 1b ); and 1-octadecanoyl-2-[ trans -[1-(2,2-dimethyl-5-pentadecyl-1,3-dixolan-4-yl)methanoyl]]- sn -glycero-3-phosphatidylcholine ( 1c ). the monolayer characteristics were also determined for two of the daughter surfactants in which a vic -diol group replaces the ketal group: 1-octadecanoyl-2-( threo -9,10-dihydroxyloctadecanoyl)- sn -glycero-3-phosphatidylcholine ( 2a ) and 1-octadecanoyl-2-(17,18-dihydroxyoctadecanoyl)- sn -glycero-3-phospha-tidylcholine ( 2b ). Surfactants 1a-c displayed surprisingly high solubility in the water subphase; stable monolayers could not be formed even at 7–8 °C. Reproducible surface pressure isotherms were obtained for 1a-c, 2a and 2b v using a subphase of aqueous 30% polyethylene glycol. The apparent areas/molecule were larger than expected based on estimates from CPK models, even assuming that all alkyl chains are flat on the interface and are never elevated above it to any appreciable degree, even at high compressions. Surface potential measurements generally remained constant throughout the range of compression. The disparities between measured and estimated molecular areas are probably due to two effects: chirality in the systems and occlusion of void areas present in many of the planar conformational states.

Neutron and X-ray reflection measurements and surface pressure isotherms of spread films of the fullerene—dodecylamine adduct C60[NH2(CH2)11CH3]x all indicate that this material may form monomolecular layers on water surfaces. The reflection data sets (neutron on both H2O and D2O) can be accounted for by a single model structure defined in terms of the dimensions of an average cell and its chemical composition. This model ascribes a total thickness of about 29 A to the molecular interface layer with the following internal structure. The fullerenes (with several alkyl chains attached) form a central stratum and the remainder alkyl tails are located close to both the air and water interfaces. The alkyl moieties close to the aqueous substrate are hydrated. The reflection experiments and the isotherms suggest that on average 8 ± 3 dodecylamine molecules are present per fullerene, consistent within error, with elemental analysis 5 ± 2. By contrast, neutron reflection and surface pressure vs. area data of spread films of C60 fullerenes on aqueous surfaces indicate the formation of inhomogeneous multilayer films with a thickness and a surface roughness exceeding the molecular size. These underivatized fullerenes thus do not form monomolecular films.

A series of electrochemical and Raman studies were undertaken to investigate the effects of orientation of electroactive species on their electrochemical behavior. Raman, resonance Raman, surface-enhanced Raman scattering, and surface-enhanced resonance Raman scattering techniques provided information essential for determining species orientation on electrode surfaces. The paradigm compounds employed were a series of derivatized viologens. Synthesis of these compounds involved the incorporation of long alkyl chains, rendering them surface-active and capable of incorporation into various kinds of oriented systems at interfaces. Orientation control was effected by the use of three techniques which provided a hierarchy of progressively more stringently oriented systems. Viologens were incorporated into vesicles, spontaneously self-assembled systems, and Langmuir-Blodgett (LB) monolayer arrays. Whereas the ordering and orientation control was probably least effective in vesicles, a maximal ordering could be attained in LB systems. Analysis of the experimental findings indicates that the systems studied show varied behavior and a complex interaction of the important variables operative during electrochemical processes. The extent of orientation present in specific preparations, the electrochemical potentials, the presence of counterions, the density of monolayer packing, and the exact structures (relative contributions of alkyl chains and of the viologen moiety) were all found to influence the behavior observed.

N-Methyl-N′-hexadecylviologen (C16MV) has been the subject of several electrochemical and spectroelectrochemical studies which characterized the species present in various redox states for C16MV monolayers on silver electrode surfaces. Both self-assembled monolayers (SA) and Langmuir-Blodgett (LB) transferred systems have been studied. These indicated inconsistencies regarding the presence or absence of splitting of the first reduction peak in its cyclic voltammogram (CV). The present study demonstrates the important influence of the specific anionic species present in the supporting electrolyte. Splitting may or may not take place, depending on the size and relative strength of the adsorption of specific anions contributed by the supporting electrolyte. Small, strongly adsorbing anions such as iodide produced peak splitting in the CV of C16MV monolayers; bulky but weakly adsorbing anions such as perchlorate may disrupt the ordered structure of monolayers but produce no splitting. Ancillary data provided by surface enhanced Raman spectroscopy (SERS) was consistent with the electrochemical measurements.

Monolayers of the reaction centers isolated from the photosynthetic bacteria Chloroflexus aurantiacus, Rhodobacter sphaeroides and Rhodopseudomonas viridis were prepared and investigated. The monolayer characteristics of these proteins were analyzed to determine the optimum conditions for stable film preparations. Monolayers were transfered onto quartz and metal supports by the Langmuir-Schaefer method to provide multilayers of definite thickness. These films retain the optical and photoelectrical properties of the native photosynthetic membranes. The sign of the photopotential provides evidence for a different orientation of the reaction centers of Rb. sphaeroides compared to those of Rps. viridis.

Surface enhanced Raman spectroscopy (SERS) was used to characterize electron transfer through mediators present as self-assembled monolayers on gold electrode surfaces. The surface active species were three alkyl sulfides with the general structure: [octadecyl]-S-[CH 2 ] n -[viologen]-[CH 2 ] m dibromide, in which n was 5, 7 and 10, and the sum of n and m held constant . These structures thus present the electroactive moiety at varying distances from the surface upon which they are adsorbed. Cyclic voltammetry was used to confirm results of previous measurements on silver, after which SERS spectroelectrochemistry was used to identify the electroactive species formed following the electron transfer steps. Electrochemistry imdicated that electron transfer was inversely proportional to the distance of the viologen from the gold surface; spectroelectrochemistry using SERS corroborated this, as the intensity of Raman scattering in SERS is a function of the distance of a scattering chromophore from the metal surface with which it is associated. Spectra of viologens were obtained for the neutral and radical species. Analysis of these data indicates agreement with the previous purely electrochemical studies of these compounds. These studies extend the utility of SERS spectroscopy for monolayer characterization by using gold surfaces to provide enhancement; silver surfaces have usually been used in previous SERS spectroelectrochemical studies, SERS employing gold surfaces may be especially significant in the case of biological molecules, because excitation in the red spectral regions greatly reduces background fluorescence, and a significantly decreased risk of photodecomposition is assured. For example, observation of gold SERS of chlorophyll or heme proteins by excitation into their Q -bands will permit acquisition of new information regarding these important compounds [cf. 6].

This study identifies the important chemical and physical factors determining the integrity of bacteriochlorophyll monolayers; these must be known if this pigment is to be used for model systems of the in vivo photosynthetic process. Spread monolayers of bacteriochlorophyll were subjected to variation of pH, temperature, subphase composition, incident light flux and atmospheres of various composition. Results were consistent with intuitive prediction as well as the known behavior of monolayers of chlorophyll a. Minimal decomposition was noted under conditions of darkness, presence of reducing agents either in the subphase or as an integral part of the monolayer, subambient temperatures, inert atmospheres and alkaline subphase pH. Major products arising from oxidative decomposition were 2′-desvinyl chlorophyll a, bacteriopheophytin, methyl bacteriopheophorbide and 10-hydroxy-bacteriochlorophyll a.

Model systems which display the essential characteristics of the photo-induced electron transfer process in the photosynthetic reaction center have been studied using electrochemical methods together with resonance Raman (RR) and surface-enhanced Raman scattering (SERS) spectroscopy. The objective is to develop an understanding of the experimental factors which are important for producing highly efficient charge separation between an electron donor molecule and an electron acceptor. In the photosynthetic reaction center complex the quantum yield for charge separation is near 1.0. The primary electron transfer between the bacteriochlorophyll (BChl) special pair (P) and bacteriopheophytin (BPh) is extremely fast (ca. 3 ps) and the energy depleting charge recombination reaction is prevented by a series of dark electron transfer steps from BPh to secondary electron acceptors. The dark process is thermodynamically driven, as each of the successive acceptor species have decreasing reduction potentials. Various approaches have been used to mimic the photosynthetic process including covalently bonded donor-acceptor species, triads, tetrads, etc. as reviewed recently [1]. Another approach has been to prepare organized systems in which the donor and acceptor species are separated spatially. Vesicles [2], bilayers [3] and Langmuir-Blodgett [4] monolayers have all been used for this purpose. The success of the model system studies has been evaluated in terms of the kinetics of the charge separation step and the quantum yield.

Surface pressure-area isotherms were established for a series of seven derivatized phthalocyanine compounds containing from one to four covalently linked macrocycles. Good solubility in spreading solvents was conferred by the presence of four neopentoxyl groups per macrocycle. All compounds studied formed strong, stable monolayers with high breaking pressures (about 50 mN m−1 or greater). Observed surface pressure-area isotherms were of the most simple kind, with no indication of phase transitions or discontinuities, with one exception. Minimal molecular areas were seen at lowest compression rates and higher temperatures, indicating that these systems have a large number of configurational states which are not capable of restructuring quickly into a compact monolayer of highest density. For some compounds it appears that orientation on the water surface can be essentially flat. Most previously studied phthalocyanine monolayers suggest that the macrocycles tend always to orient edge-on at some acute angle to the water surface because of the very strong cofacial energies of interaction. With other compounds of this group, it is evident that the macrocycles can assume orientations either parallel or perpendicular to the surface, others having intermediate orientations as well. In addition, one multinucleate compound probably assumes a bilayer structure at high surface pressures. The range of orientations available in these systems should appreciably extend the utility of phthalocyanines in monolayers transferred by the Langmuir-Blodgett technique. The present study indicates that a more complete exploitation of the possibilities of organic synthesis can result in a more varied monolayer behavior than seen hitherto.

The current emphasis in efforts to produce systems capable of highly specific molecular recognition has produced a wide variety of compounds such as crown ethers, cryptands, cyclodextrins and other inclusion systems. A more desirable approach, and one obviating laborious organic synthesis, would be based upon a mechanism more like that seen in the in vivo antigen-antibody reaction. Sites having the capability for specific molecular recognition based on a predetermined template molecule would allow realization of systems of the desired specificity. The technique of cosorption of a silane and a surface-active molecule onto a glass surface has been comprehensively described by Sagiv and by Maoz and Sagiv and has indicated the feasibility of this approach, e.g. with surface-active dyes. In the present study, adsorbed monolayers were produced with sites based on chosen template molecules, using the Sagiv method, and the systems then reconstituted with the original template molecule as well with molecules of closely similar structure (i.e. porphyrins or chlorophylls). A high degree of recognition was evidenced, as shown by the use of surface-enhanced resonance Raman spectroscopy as the detection tool. It was also shown that chemically dissimilar species can be reconstituted into sites formed by other species, provided that the molecular shapes are compatible. The ease of resorption into performed sites is strongly dependent on the presence of amphiphilic character in the molecule re-entering a site.

The applicability of surface-enhanced resonance Raman scattering (SERRS) spectroscopy to the study of transferred Langmuir-Blodgett (LB) monolayers was investigated. Three surface-active cyanine dyes, as well as chlorophyll a, bacteriochlorophyll a, and bacteriopheophytin a were incorporated into monolayers with inert matrix diluent molecules and the monolayers were transferred to glass slides which had previously been coated with 50 A silver films. Good-quality SERRS spectra were obtained of the compounds studied, at monolayer concentrations of less than 10 mole-per cent. Appreciable quenching of intrinsic fluorescence was evident for those systems in which the chromophore was in immediate contact with the metal surfaces. When the chromophore was removed a distance of two spacer layers (about 56 A) from the silver surface, a reduction of approximately 40% in SERRS signal intensity was observed for each of the dyes. These latter results indicate that an electrodynamic enhancement mechanism is operative for these systems. Significant photobleaching occurred in all of the samples studied and photooxidation occurred in the bacteriochlorophyll monolayers. These problems were minimized by the use of low laser power and short exposure times through the use of diode array detection. The present results illustrate that SERRS is a highly sensitive technique for the study of transferred LB monolayers arrays.

The monolayer behavior of a group of short-chain alkyl phosphates was investigated with Langmuir trough techniques. The compounds were all octyl or ethylhexyl phosphates or phosphinates; the exceptionally small hydrophobic moieties in these compounds do not permit the formation of stable, coherent films at room temperatures. Stable monolayers were formed, however, on subphases of 1 M nitric acid at 5–10°C. The apparent areas per molecule are consequently strongly temperature dependent with total desorption evidently taking place at room temperature. When compared to molecular areas estimated from space-filling models, the experimentally determined limiting molecular areas are greater by factors of 1.1 to 2. Compounds containing ethylhexyl groups yielded limiting molecular areas in much closer agreement with model estimates than did the octyl-containing compounds. A limiting minimal area per molecule, particularly for the ethylhexyl systems, was approached only after several cycles of compression and reexpansion. This result indicates that the weak van der Waals interactions present and the high viscosity of the systems allow coherent film formation only after repeated partial structuring of the system after several compressions. Expansion of previously compressed monolayers revealed marked hysteresis effects. The systems investigated included: di-n-octyl phosphoric acid, di-n-octyl phosphinic acid, tri-n-octyl phosphate, tri-n-octyl phosphine oxide, bis-2,2 dimethylhexyl phosphoric acid, bis (2-ethylhexyl) phosphoric acid, bis (2-ethylhexyl) phosphinic acid, 2-ethylhexyl, 2-ethylhexyl phosphonic acid, and tris (2-ethylhexyl) phosphate.

Results of film compression studies on monolayers of di(2-ethylhexyl)phosphate (HDEHP) and other alkyl phosphoric acid derivatives are reported. HDEDP was found to form coherent monolayers below room temperature with apparent molecular areas which progressively decreased with increasing cycles of compression. Marked hysterisis was noted upon expansion and recompression of a compressed film. Expanded layers of HDEHP were found to gradually lose coherency and become destructured if left expanded for hours or days. This behavior was attributed to molecular disengagement due to weakly interacting alkyl chains and the presence of chain branching. Results of studies of other alkyl phosphoric acid derivatives indicate similar behavior, but the consequences of branching were apparently more important than the physical state (solid or liquid) of the monolayer. (BLM)

Representative sections of leaf, stem, and root of peppermint plants grown in 70 per cent D 2 O nutrient were examined microscopically; comparison was made of the significant histological features with sections from plants grown in an aqueous nutrient. The major effect of deuterium on the growth of peppermint appears to be inhibition of cell divisions. Parenchyma cells are enlarged and vascular tissue appears to be reduced in the deuteriated plants. In general, the effects were more pronounced in growing tissues than in tissue exposed to deuterium after differentiation had occurred.

The effect of varying concentrations of D 2 O on the growth of peppermint plants was studied over a period of at least 50 days. The extent of deuterium uptake is reported. This appears to be the first detailed study of the effects of extensive replacement of hydrogen by deuterium on the growth of a higher plant.

The growth of belladonna is strongly inhibited by D 2 O concentrations greater than 50 per cent. The alkaloid content decreases progressively as the deuterium level in the plant increases. Germinative ability of seeds containing up to 40 per cent deuterium is unimpaired.