R.A. Uphaus

Monolayers of photosynthetic reaction centers of green and purple bacteria

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.

Langmuir-Blodgett and X-ray Diffraction Studies of Isolated Photosystem II Reaction Centers in Monolayers and Multilayers: Physical Dimensions of the Complex*

Abstract— The photosystem II (PSII) reaction center (RC) is a hydrophobic intrinsic protein complex that drives the water‐oxidation process of photosynthesis. Unlike the bacterial RC complex, an X‐ray crystal structure of the PSII RC is not available. In order to determine the physical dimensions of the isolated PSII RC complex, we applied Langmuir techniques to determine the cross‐sectional area of an isolated RC in a condensed monolayer film. Low‐angle X‐ray diffraction results obtained by examining Langmuir‐Blodgett multilayer films of alternating PSII RC/Cd stearate monolayers were used to determine the length (or height; z‐direction, perpendicular to the plane of the original membrane) of the complex. The values obtained for a PSII RC monomer were 26 nm2and 4.8 nm, respectively, and the structural integrity of the RC in the multilayer film was confirmed by several approaches. Assuming a cylindrical‐type RC structure, the above dimensions lead to a predicted volume of about 125 nm3. This value is very close to the expected volume of 118 nm3, calculated from the known molecular weight and partial specific volume of the PSII RC proteins. This same type of comparison was also made with the Rhodobacter sphaeroides RC based on published data, and we conclude that the PSII RC is much shorter in length and has a more regular solid geometric structure than the bacterial RC. Furthermore, the above dimensions of the PSII RC and those of PSII core (RC plus proximal antenna) proteins protruding outside the plane of the PSII membrane into the lumenal space as imaged by scanning tunneling microscopy (Seibert, Aust. J. PL Physiol. 22,161–166, 1995) fit easily into the known dimensions of the PSII core complex visualized by others as electron‐density projection maps. From this we conclude that the in situ PSII core complex is a dimeric structure containing two copies of the PSII RC.

Crystal engineering in two dimensions: control of planar packing by design of new amphiphiles

Abstract 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.

Imaging of structured and disordered hemicyanine monolayers by atomic force microscopy

Abstract 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.

Monolayer study of cleavable phospholipids

Abstract 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.

Factors determining stability of bacteriochlorophyll monolayers

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.