Structure Of Hydrocarbon Chains Research Articles

A modified microwave hydrodistillation and simultaneous extraction in a rotating state to obtain essential oil, rosmarinic acid, and polysaccharides with sucrose stearate as an additive from Perilla frutescens

An improved approach was developed to obtain essential oil, rosmarinic acid, and polysaccharides with sucrose stearate as a green additive from Perilla frutescens (L.) Britt. Leaves using microwave-induced hydrodistillation and simultaneous extraction (MHDE). In this process, we realize the rotation of the material through a rotary motor so that the material is uniformly irradiated by microwaves. The influencing factors on MHDE were systematically optimized by single factor and central composite design. Under the obtained optimization conditions, the yields of essential oil, rosmarinic acid, and polysaccharides were 0.64% ± 0.03%, 0.18% ± 0.01%, and 4.35% ± 0.19%, respectively. GC-MS analysis results showed that the main component of essential oil prepared by MHDE was perillaldehyde, which accounted for 51.91% of the total essential oil, followed by caryophyllene, accounting for 15.79%. However, the ratio of perillaldehyde in the essential oil obtained by traditional hydrodistillation and extraction (HDE) was only 40.69%, and the proportion of caryophyllene was only 12.50%. MHDE uses sucrose stearate with a long hydrocarbon chain structure as an additive, which reduces the nonterpene aliphatics in the obtained essential oil.

Microwave-assisted intensification of transesterification reaction for biodiesel production from camelina oil: Optimization by Box-Behnken Design

The structure of hydrocarbon chain of fatty acids is similar to the petroleum products. Therefore, they are an ideal alternative for petroleum lubricant and diesel fuel, due to their renewability and biodegradability. In this study, intensification of transesterification reaction using microwave heating was applied to produce biodiesel with camelina oil. The heat energy required for the reaction was supplied by a microwave with a mechanical stirrer. H-NMR was used to analyze the transesterification reaction yield. The parameters namely reaction time, catalyst load and molar ratio of methanol to oil were investigated to maximize the yield using RSM-BBD design. The results showed that the highest biodiesel yield of 95.31% (desirability of 95%) was obtained at the reaction time of 5.85 min, catalyst concentration of 1.26 wt%, and the molar ratio of 6.91. Moreover, the physicochemical characteristics of the produced biodiesel could meet the requirements of EN14214 and ASTM D6751 biodiesel standards.

Quantitative structure-properties relationship and molecular design of some anti-wear lubricant additives

In-silico QSPR and MD simulation methods were adopted to effectively design new lubricant anti-wear additive compounds as an alternative to zinc dialkyl dithiophosphate (ZDDP) which was reported to contribute to environmental pollution. Some QSPR linear models were developed out of which the best model (With statistical analysis R2 = 0.990, R2pred. = 0.818, R2adj = 0.979, R2cv = 0.748) was used to design three new additive structures with an improved anti-wear lubricant properties. Three lubricant additives such as 2-(hept‑1-en-2 ylthio)benzo[d]oxazole, 2-((5-methylhex-5-en-1-yl)thio)benzo[d]oxazole and 2-((5-methyl-2-methylenehex-5-en-1-yl)thio)benzo[d]oxazole were designed and revealed to have anti-wear properties of 0.593, 0.512, and 0.367 mm respectively. These anti-wear lubricant properties of all the designed additives were found to be better than the bench-mark anti-wear additive, ZDDP (3.284 mm) and what other researchers proposed. Moreover, The dynamic binding energies of all the designed anti-wear lubricant additives were found to be bound better than the one calculated by other researchers and was found to be excellently bound also than the commercially sold (benchmark additive) additive (ZDDP) 24,365.405. The addition of acceptor substituent like =CH2 groups to the hydrocarbon chain structures of all the newly designed additives was noticed to have improved lubricant wear-reduction properties and binding dynamic energies of the new additives on the simulated steel coated surface. Therefore, these QSPR and MD methods could be used to provide a theoretical framework for researchers and industrialists to design an improved anti-wear additive properties and save resources before expensive laboratory trial and error method.

Ideal CdSe/CdS Core/Shell Nanocrystals Enabled by Entropic Ligands and Their Core Size-, Shell Thickness-, and Ligand-Dependent Photoluminescence Properties.

This work explored possibilities to obtain colloidal quantum dots (QDs) with ideal photoluminescence (PL) properties, i.e., monoexponential PL decay dynamics, unity PL quantum yield, ensemble PL spectrum identical to that at the single-dot level, single-dot PL nonblinking, and antibleaching. Using CdSe/CdS core/shell QDs as the model system, shell-epitaxy, ligand exchange, and shape conversion of the core/shell QDs were studied systematically to establish a strategy for reproducibly synthesizing QDs with the targeted properties. The key synthetic parameter during epitaxy was application of entropic ligands, i.e., mixed carboxylate ligands with different hydrocarbon chain length and/or structure. Well-controlled epitaxial shells with certain thickness (∼3-8 monolayers of the CdS shells) were found to be necessary to reach ideal photoluminescence properties, and the size of the core QDs was found to play a critical role in determining both photophysical and photochemical properties of the core/shell QDs. Effects of shape of the core QDs were unnoticeable, and shape of the core/shell QDs only affected photophysical properties quantitatively. Surface ligands, amines versus carboxylates, were important for photochemical properties (antiblinking and antibleaching) but barely affected photophysical properties as long as entropic ligands (mixed carboxylate ligands with distinguishable hydrocarbon chain lengths) were applied during epitaxy. Chemical environment (in polymer or in air), coupled with surface ligands, determined photochemical properties of the core/shell QDs with a given core size and shell thickness.

Evaporation and Hydrocarbon Chain Conformation of Surface Lipid Films

PurposeThe inhibition of the rate of evaporation (Revap) by surface lipids is relevant to reservoirs and dry eye. Our aim was to test the idea that lipid surface films inhibit Revap. MethodsRevap were determined gravimetrically. Hydrocarbon chain conformation and structure were measured using a Raman microscope. Six 1-hydroxyl hydrocarbons (11-24 carbons in length) and human meibum were studied. Reflex tears were obtained from a 62-year-old male. ResultsThe Raman scattering intensity of the lipid film deviated by about 7 % for hydroxyl lipids and varied by 21 % for meibum films across the entire film at a resolution of 5 μm2. All of the surface lipids were ordered. Revap of the shorter chain hydroxyl lipids were slightly (7%) but significantly lower compared with the longer chain hydroxyl lipids. Revap of both groups was essentially similar to that of buffer. A hydroxyl lipid film did not influence Revap over an estimated average thickness range of 0.69 to >6.9 μm. Revap of human tears and buffer with and without human meibum (34.4 μm thick) was not significantly different. Revap of human tears was not significantly different from buffer. ConclusionsHuman meibum and hydroxyl lipids, regardless of their fluidity, chain length, or thickness did not inhibit Revap of buffer or tears even though they completely covered the surface. It is unlikely that hydroxyl lipids can be used to inhibit Revap of reservoirs. Our data do not support the widely accepted (yet unconfirmed) idea that the tear film lipid layer inhibits Revap of tears.

Modeling and calculation of thermodynamic properties and phase equilibria of oil and gas condensate fractions based on two generalized multiparameter equations of state

Based on two generalized equations of state, previously developed by the authors, describing the properties of hydrocarbon chain and cyclic structures, a method for the predictive calculation of thermodynamic properties and phase equilibria of complex hydrocarbon mixtures (petroleum and gas-condensate fractions) has been developed. The method is applicable over a temperature range from the freezing point to 700 K and at pressures up to 100 MPa, including the liquid and gas phases as well as the supercritical region.The calculation of thermodynamic properties is made within the framework of the extended three-parameter corresponding states principle. The acentric factor was chosen as the third parameter of the corresponding states. The complex hydrocarbon mixture is treated as an individual substance, known as a “single-fluid model”. In this model, the mixture is a hypothetical individual hydrocarbon with an effective molar mass M and critical parameters, Tc, pc and ρc. This “substance” is characterized by the content of paraffin and cyclic structures in an effective molecule.For the calculation of phase equilibria, a method for modeling the composition of complex hydrocarbon mixtures using the concept of pseudo components has been developed. The method is based on the distillation curve and uses a minimum set of needed properties of mixtures, such as the average boiling temperature, relative density, and molar mass. Rules for generalization of the single-fluid model, used to calculate thermodynamic properties, to the linear model of mixtures, used for phase equlibria calculations, have been formulated.

Nanofluidity of fatty acid hydrocarbon chains as monitored by benchtop time-domain nuclear magnetic resonance.

The functional properties of lipid-rich assemblies such as serum lipoproteins, cell membranes, and intracellular lipid droplets are modulated by the fluidity of the hydrocarbon chain environment. Existing methods for monitoring hydrocarbon chain fluidity include fluorescence, electron spin resonance, and nuclear magnetic resonance (NMR) spectroscopy; each possesses advantages and limitations. Here we introduce a new approach based on benchtop time-domain (1)H NMR relaxometry (TD-NMR). Unlike conventional NMR spectroscopy, TD-NMR does not rely on the chemical shift resolution made possible by homogeneous, high-field magnets and Fourier transforms. Rather, it focuses on a multiexponential analysis of the time decay signal. In this study, we investigated a series of single-phase fatty acid oils, which allowed us to correlate (1)H spin-spin relaxation time constants (T2) with experimental measures of sample fluidity, as obtained using a viscometer. Remarkably, benchtop TD-NMR at 40 MHz was able to resolve two to four T2 components in biologically relevant fatty acids, assigned to nanometer-scale domains in different segments of the hydrocarbon chain. The T2 values for each domain were exquisitely sensitive to hydrocarbon chain structure; the largest values were observed for pure fatty acids or mixtures with the highest cis-double bond content. Moreover, the T2 values for each domain exhibited positive linear correlations with fluidity. The TD-NMR T2 and fluidity measurements appear to be monitoring the same underlying phenomenon: variations in hydrocarbon chain packing. The results from this study validate the use of benchtop TD-NMR T2 as a nanofluidity meter and demonstrate its potential for probing nanofluidity in other systems of biological interest.

Enhancing nucleic acid delivery, insights from the cationic phospholipid carriers.

The development of nucleic acid-based drugs has attracted considerable interest in the past two decades as a new category of biologics. A key challenge in successfully achieving the full potential of nucleotide therapeutics is their efficient delivery. Synthetic cationic lipids are currently the most extensively used non-viral nucleotide carriers because of their ability to form complexes with the nucleic acids. Here we examine the properties of oligonucleotide lipoplexes with a particularly noteworthy cationic lipid class, the cationic phosphatidylcholines (PCs) which exhibit low toxicity and good nucleotide delivery efficacy. Studies on a set of cationic PCs reveal the existence of a strong, systematic dependence of their carrier efficiency on the lipid hydrocarbon chain structure. Their activity rises with the increase in chain unsaturation and declines with the increase in chain length. Maximum transfection is detected for ethyl-PC (ePC) with monounsaturated 14:1 chains. The same lipid exhibits maximum activity also in intracellular delivery of siRNA. As the lipid phase behavior is known to depend substantially on the hydrocarbon chain structure, the above relationships validate a view that cationic PC phase properties are an important factor for their activity. Indeed, time-resolved X-ray diffraction studies showed that the rate of the nucleotide release from the lipoplexes, as well as their transfection activity, correlate with the non-lamellar phase progressions detected in mixtures of cationic PCs with biomembrane lipids. These findings emphasize the role of the non-lamellar lipid mesophases in the nucleic acid transport across the cellular membranes and their intracellular release.

Electron microscopy and theoretical modeling of cochleates.

Cochleates are self-assembled cylindrical condensates that consist of large rolled-up lipid bilayer sheets and represent a novel platform for oral and systemic delivery of therapeutically active medicinal agents. With few preceding investigations, the physical basis of cochleate formation has remained largely unexplored. We address the structure and stability of cochleates in a combined experimental/theoretical approach. Employing different electron microscopy methods, we provide evidence for cochleates consisting of phosphatidylserine and calcium to be hollow tubelike structures with a well-defined constant lamellar repeat distance and statistically varying inner and outer radii. To rationalize the relation between inner and outer radii, we propose a theoretical model. Based on the minimization of a phenomenological free energy expression containing a bending, adhesion, and frustration contribution, we predict the optimal tube dimensions of a cochleate and estimate ratios of material constants for cochleates consisting of phosphatidylserines with varied hydrocarbon chain structures. Knowing and understanding these ratios will ultimately benefit the successful formulation of cochleates for drug delivery applications.

Pressure Viscosity Coefficient of Vegetable Oils

The pressure viscosity coefficient (PVC) of ten vegetable oils from commodity and new crops, and two petroleum-based oils [polyalphaolefin (PAO) and hexadecane], were investigated. PVC was estimated using two different methods: from analysis of oil physical properties (viscosity and density); and from analysis of elastohydrodynamic (EHD) film thickness data. Estimated PVC of vegetable and petroleum-based oils decreased with increasing temperature, which was expected. PVC values derived from physical properties were generally much higher than the values from the literature or those derived from EHD film thickness. PVC values increased with increasing viscosity of the tested oils. Based on further examination of PVC data for a wide range of oils from the literature and this work, it is proposed that lubricating oils can be roughly divided into three structural categories, each with defined range of PVC values: low PVC oils ( 20 GPa−1) with predominantly entangled molecular structures, and intermediate PVC oils (10–20 GPa−1) with negligible layering or entangling molecular structures. It is proposed that vegetable oils, along with PAO and hexadecane, have flexible hydrocarbon chain structures, with little or no branching or layering, and, hence, belong to the intermediate PVC category.

Structure determination of the nonlinear hydrocarbon chains C9H3 and C11H3 by deuterium labeling

A systematic deuterium labeling experiment is presented that aims at an unambiguous determination of the geometrical ground state structure of the C(9)H(3) and C(11)H(3) hydrocarbon chains. Cavity ring-down spectroscopy and special plasma expansions constituting C/H, C/D, and C/H/D are used to record optical transitions of both species and their (partially) deuterated equivalents in the 19,000 cm(-1) region. The number of observed bands, the quantitative determination of isotopic shifts, and supporting calculations show that the observed C(9)H(3) and C(11)H(3) spectra originate from HC(4)(CH)C(4)H and HC(4)[C(C(2)H)]C(4)H species with C(2v) symmetry. This result illustrates the potential of deuterium labeling as a useful approach to characterize the molecular structure of nonlinear hydrocarbon chains.

Synthesis, structure and morphology of organic layered double hydroxide (LDH) hybrids: Comparison between aliphatic anions and their oxygenated analogs

Intercalation of organic anions is an important aspect of layered double hydroxide (LDH) chemistry in the development of polymer–LDH composites. In the research, we intercalated short and lengthy straight-chain organic anions with the carbon number up to 50 into the interlayer of MgAl and ZnAl-LDHs. We also noted that the packing mode of the straight-chain organic species and the basal spacing are somewhat predictable. In most cases, the hydrocarbon chain (or oxygenated) is packed in an anti-parallel inter-penetrating style at an angle of around 55°. Only when the hydrocarbon chain contains 14–18 carbons and the supplied amount of the organic anion is more than the anion exchange capacity, a so-called bi-layer packing mode is also observed. Due to the variety in the structure and property of organic hydrocarbon chains, the organo-LDH crystallites show various morphologies, where the hydrophobic forces are expected to play an important role in determining the crystallite shape.

Cationic phospholipids: structure–transfection activity relationships

Synthetic cationic lipids are presently the most widely used non-viral gene carriers. Examined here is a particularly attractive cationic lipid class, triester phosphatidylcholines (PCs) exhibiting low toxicities and good transfection efficiency. Similarly to other cationic lipids, they form stable complexes (lipoplexes) with the polyanionic nucleic acids. A summary of studies on a set of ∼30 cationic PCs reveals the existence of a strong, systematic dependence of their transfection efficiency on the lipid hydrocarbon chain structure: transfection activity increases with increase of chain unsaturation from 0 to 2 double bonds per lipid and decreases with increase of chain length in the range ∼30–50 total number of chain carbon atoms. Maximum transfection was observed for ethyl phosphate PCs (EPCs) with monounsaturated 14:1 chains (total of 2 double bonds and 30 chain carbon atoms). Lipid phase behavior is known to depend strongly on the chain molecular structure and the above relationships thus substantiate a view that cationic PC phase propensities are an important determinant of their activity. Indeed, X-ray structural studies show that the rate of DNA release from lipoplexes as well as transfection activity well correlate with non-lamellar phase progressions observed in cationic PC mixtures with membrane lipids. These findings appear to be of considerable interest because, according to current views, key processes in lipid-mediated transfection such as lipoplex disassembly and DNA release within the cells are believed to take place upon cationic lipid mixing with cellular lipids.

Organization of Lipid Molecules within Biomembranes

In this review, we report on the organization of lipid molecules forming biomembranes. More precisely, the question is how these amphiphiles phase separate under a change of a suitable parameter, like temperature, pressure or membrane environment. The mixture may undergo a lateral or transversal phase separations. This essentially depends on two principal factors, which are the structure (length) of hydrocarbon chains of lipid molecules and the curvature asymmetry of membranes. When the former dominates, a lateral separation is then expected. In contrary, for those biomembranes of high curvature asymmetry, a vertical separation is rather observed. We examine the problem from a static (phase diagrams) and kinetics (relaxation in time) point of view. Finally, the discussion is also extended to the phase separation between lipid molecules and cholesterol in biomembranes (formation of rafts), between phospholipids and grafted polymers on liposomes, or between surfactant and its co-surfactant in bilayer systems.

Skin Constituents as Cosmetic Ingredients. Part II: A Study of Bio‐Mimetic Monoglycerides Behavior at the Squalene‐Water Interface by the “Pendant Drop” Method in a Dynamic Mode

This work aims at presenting the viscoelastic behavior of bio‐mimetic monoglycerides used as emulsifier in a mixture made of two non‐miscible liquids, squalene and water. The measurement of the interfacial tension, carried out by the “pendant drop” method in “dynamic” mode, made it possible to characterize these amphiphilic molecules according to the value of their elastic modulus, ϵ, as well as their relaxation time, τR. The analysis of these parameters, as well as those developed in the previous publication [L. Blasco et al. (2006) Skin constituents as cosmetic ingredients. Part I: A Study of bio‐mimetic monoglyceride behavior at the squalene‐water interface by the “pendant drop” method in a static mode. J. Dispers. Sci. Technol., 27(6).] shows that the hydrocarbon chain structure, such as its length, the presence of one or more unsaturations, hydroxyl function, affects the behavior of surfactant molecules at the squalene/water interface.

Molecular dynamics studies on monolayer of cetyltrimethylammonium bromide surfactant formed at the air/water interface

An atomistic molecular dynamics (MD) simulation has been carried out to investigate the structural and dynamic properties of a monolayer of cationic surfactant cetyltrimethylammonium bromide (C 16TAB) formed at the air/water interface. The simulation was performed at room temperature, and two systems I and II containing different surface areas 45 and 68 Å 2 per molecule, respectively, were selected. Through the radial distribution function (RDF) among the headgroups, water molecules and bromide ions, the thickness of the adsorbed layer was estimated. The hydrocarbon chain structure was analyzed by taking into account the length distributions between headgroups and different methyl(ene) groups in the chain, and it is shown that two systems have a big difference in the structures of the monolayer, especially for the last several methyl(ene) groups normal to the interface. The disordered monolayer for system I is proved by the orientation correlation function and the fractions of gauche conformations in the chain. It indicates that the structure of monolayers depends on the vertical position with respect to the interface. We found that water molecules around the headgroups at the interface have smaller diffusion coefficient than those in the hydrocarbon tails or in the bulky water. It is shown that the diffusion of water molecules mostly depends on the surroundings, and the electrostatic and H-bonding interactions are the reason that water molecule has small diffusion coefficient in the chains of the monolayer.

Structural Study on Polymorphism of Cis-Unsaturated Triacylglycerol: Triolein

To clarify the influence of cis-unsaturation on solid-state structures of triacylglycerols (TAGs), the crystal structures of three crystalline phases (alpha, beta' and beta) of triolein [C3H5(OCOC17H33)3] were investigated by powder X-ray diffractometry and IR and Raman spectroscopy. The influence on the structural change of the alpha phase in the course of cooling was also studied. With respect to the subcell structure and conformational order of hydrocarbon chains in the beta and beta' phases, triolein resembles saturated TAGs; trans-zigzag hydrocarbon chains are adopted in the T(parallel) subcell for the beta phase and in the O(perpendicular) subcell for the beta' phase. The influence of cis-unsaturation was most obvious in the structure of the alpha phase and its temperature dependence. The alpha phase of triolein does not form the ordinary hexagonal subcell but a rather loose distorted subcell, which hardly changes in cooling, forming a striking contrast to the hexagonal-->pseudohexagonal subcell transformation found in the alpha phase of saturated TAGs.

Functions and molecular structure of organic binders for iron ore pelletization

Organic binders of iron ore pellets were widely investigated in past decades because they do not contaminate the product. This paper mainly involves the functions and molecular structure of ideal organic binders for iron ore pelletization based on fundamental principles of molecular design, interface chemistry, polymer science as well as failure model of a binding system. Investigation shows that good wettability, great adhesive and cohesive forces as well as fine thermal stability are essential functions of binders for iron ore pelletization. The molecular structure mold [XPY]n of organic binders is proposed. Ionization potential, electron affinity, group electronegativity, bond ionicity and bond energy are calculated and/or applied in the selection and judgement of polar group (X) and hydrophilic group (Y). Organic chain skeleton (P) and polymerization degree (n) are investigated on the basis of the structure–property relationships of polymers. It is shown that COO− and OH are excellent polar group and hydrophilic group of organic binders of iron ore pellet, respectively, and organic skeletons with unsaturated hydrocarbon chain and ring aromatic structure are the best for organic binders of iron pellets. Two kinds of organic binders are synthesized and prepared on the basis of the investigations and they are found to be effective for pelletizing of iron ore concentrates. One of them has been used in commercial production of iron ore pellets in China.

Influence of the structure of polysulphide additives on the shiftability of manual transmissions

AbstractThe shiftability of manual transmissions is known to be strongly affected by the nature of the transmission oil. When conventional sulphur—phosphorus (SP) additives are used in the oil, gear clashing, sticking, and other problems occur. As reported previously, these problems are caused mainly by the polysulphide used in the SP additives. This paper reports on a study of the effect of the structure of the polysulphide's hydrocarbon chain on the synchromesh characteristics. It is found that polysulphides with long hydrocarbon chains have high kinematic friction coefficients and low static friction coefficients. It is also shown that this phenomenon occurs because of the adsorption of the polysulphide on to the copper alloy of which the gear synchroniser ring is made. By using a polysulphide with a long hydrocarbon chain it is possible to develop transmission oils that have superior load‐carrying capacity and better shiftability even when compared with the latest transmission oils that contain metallic detergents.

Effect of independent variations in fatty acid structure and chain length on lipid polar headgroup composition in Acholeplasma laidlawii B membranes: regulation of lamellar/nonlamellar phase propensity.

We have studied the biosynthetic regulation of the membrane lipid polar headgroup distribution in Acholeplasma laidlawii B cells made fatty acid auxotrophic by growth in the presence of the biotin-binding agent avidin to test whether this organism has the ability to coherently regulate the lamellar/nonlamellar phase propensity of its membrane lipids. The addition of various single normal growth-supporting exogenous fatty acids to such cell cultures produces fatty acid-homogeneous cells in which the hydrocarbon chain length and structure of the fatty acyl chains of the membrane lipids can be independently varied. Moreover, in analyzing our results, we consider the fact that the individual membrane lipid classes of this organism can form either normal micellar, lamellar, or reversed cubic or hexagonal phases in isolation (Lewis, R. N. A. H., and McElhaney, R. N. (1995) Biochemistry 34, 13818-13824). When A. laidlawii cells are highly enriched in one of a homologous series of methyl isobranched, methyl anteisobranched, or omega-cyclohexyl fatty acids, neither the ratio of normal micellar/lamellar nor of inverted cubic or hexagonal/lamellar phase-forming lipids are coherently regulated, and in fact in the former case, the changes in lipid polar headgroup composition observed are generally in a direction opposite to that required to maintain the overall lamellar/nonlamellar phase preference of the total membrane lipids constant when hydrocarbon chain length is varied. Similarly, when lipid hydrocarbon structure is varied at a constant effective chain length, a similar lack of coherent regulation of membrane lipid polar headgroup distribution is also observed, although in this case a weak overall trend in the expected direction occurs. We also confirm our previous finding (Foht, P. J., Tran, Q. M., Lewis, R. N. A. H., and McElhaney, R. N. (1995) Biochemistry 34, 13811-13817) that the ratio of inverted phase-forming monoglucosyl diacylglycerol to the lamellar phase-forming glycolipid diglucosyl diacylglycerol, previously used to estimate membrane lipid phase preference in A. laidlawii A and B, is not by itself a reliable indicator of the overall lamellar/nonlamellar phase propensity of the total membrane lipids of these organisms. Our results indicate that A. laidlawii B lacks a coherent mechanism to biosynthetically regulate the polar headgroup distribution of its membrane lipids to maintain the micellar/lamellar/inverted phase propensity constant in the face of induced variations in either the chain length or the structure of its lipid hydrocarbon chains. Finally, we suggest that the lack of a coherent regulatory mechanism to regulate the overall phase-forming propensity of the total membrane lipids of this organism under these circumstances may result in part from its inability to optimize all of the biologically relevant physical properties of its membrane lipid bilayer simultaneously.