Effects Of Molecular Organization Research Articles

Effect of Molecular Organization on the Properties of Fractionated Lignin-Based Thiol-Ene Thermoset Materials.

In this study, the combination of sequential solvent fractionation of technical Kraft lignin was followed by allylation of most OH functionalities to give highly functional thermoset resins. All lignin fractions were highly functionalized on the phenolic (≥95%) and carboxylic acid OH (≥85%) and to a significant extent on the aliphatic OH moieties (between 43 and 75%). The resins were subsequently cross-linked using thiol-ene chemistry. The high amount of allyl functionalities resulted in a high cross-link density. Dynamic mechanical analysis measurements showed that the thioether content, directly related to the allyl content, strongly affects the performance of these thermosets with a glass transition temperature (Tg) between 81 and 95 °C and with a storage modulus between 1.9 and 3.8 GPa for all thermosets. The lignin fractions and lignin-based thermosets' morphology, at the nanoscale, was studied by wide-angle X-ray scattering measurements. Two π-π stacking interactions were observed: sandwich (≈4.1-4.7 Å) and T-shaped (≈5.5-7.2 Å). The introduction of allyl functionalities weakens the T-shaped π-π stacking interactions. A new signal corresponding to a distance of ≈3.5 Å was observed in lignin-based thermosets, which was attributed to a thioether organized structure. At the same time, a lignin superstructure was observed with a distance/size corresponding to 7.9-17.5 Å in all samples.

Effect of molecular organization on the image histograms of polarization SHG microscopy

Based on its polarization dependency, second harmonic generation (PSHG) microscopy has been proven capable to structurally characterize molecular architectures in different biological samples. By exploiting this polarization dependency of the SHG signal in every pixel of the image, average quantitative structural information can be retrieved in the form of PSHG image histograms. In the present study we experimentally show how the PSHG image histograms can be affected by the organization of the SHG active molecules. Our experimental scenario grounds on two inherent properties of starch granules. Firstly, we take advantage of the radial organization of amylopectin molecules (the SHG source in starch) to attribute shifts of the image histograms to the existence of tilted off the plane molecules. Secondly, we use the property of starch to organize upon hydration to demonstrate that the degree of structural order at the molecular level affects the width of the PSHG image histograms. The shorter the width is the more organized the molecules in the sample are, resulting in a reliable method to measure order. The implication of this finding is crucial to the interpretation of PSHG images used for example in tissue diagnostics.

Effect of Molecular Organization in Micelles and Bilayers on Binding and Conformation of Biologically Active Peptides

Amphiphiles form different types of aggregates, such as micelles and bilayers, depending on their shape and hydrophilic-hydrophobic balance. While bilayers form vesicles containing an inner aqueous compartment, micelles are smaller, approximately spherically-shaped, and have no internal aqueous compartment. Thus, molecular packing and mobility vary in these aggregates, and EPR spectra of spin probes can be used to examine these properties. EPR spectra evince tighter molecular packing and slower rate of motion in bilayers than in micelles. Such differences affect binding of peptides, both qualitatively and quantitatively. Fluorescence, CD, and EPR were employed to investigate interactions of micelles and vesicles with antimicrobial peptides, as well as fragments of GPCR and cytolytic toxins. EPR was also used for peptide analogues containing the paramagnetic amino acid TOAC. Two-component spectra indicated slow exchange between bound peptide and peptide tumbling fast in aqueous solution, allowing the calculation of binding constants. Peptide-membrane interaction was also monitored by changes in peptide fluorescence intensity and emission wavelengths, as well as accessibility to a water soluble quencher. CD spectra showed that upon binding the peptides acquired secondary structure due to formation of intramolecular hydrogen bonds, favored by the decreased polarity at the lipid interface. While in most cases, bilayer binding was only observed when electrostatic interactions occurred between positively charged peptides and negatively charged phospholipids, electrostatic effects played a less important role in peptide-micelle interaction. These differences were ascribed to differences in molecular packing and curvature in both types of aggregates. The positive curvature of micelles is proposed to mimic the lipid organization of toroidal pores. Thus, the conformational behavior in the presence of micelles would correspond to that of peptides forming toroidal pores in bilayer membranes.Supported by FAPESP, CNPq, CAPES.

Effects of molecular organization on exciton diffusion in thin films of bioinspired light-harvesting molecules

Efficient exciton diffusion in light-harvesting organic materials is of great importance for the development of cheap and flexible photovoltaic devices. Bioinspired molecular materials such as derivatives of phthalocyanine and porphyrin offer promising prospects for the realization of efficient exciton diffusion. The chemical composition of these molecules is found to strongly affect the molecular organization in thin films and in turn the efficiency of exciton diffusion. High singlet exciton diffusion coefficients exceeding 10−6 m2 s−1 have been found. This value is similar to that for the natural chlorosomal bacterio-chlorophyll, which exhibits the highest exciton diffusion coefficient for self-assembled systems.

Effects of Molecular Organization on Photophysical Behavior. 2. Photoelectrochemical and Photocurrent Quantum Yield Studies of the Langmuir−Blodgett Monolayers of Some Surfactant Porphyrins

The photoelectrochemistry of two new groups of surfactant carboxyporphyrins is described. The surface active porphyrins deposited onto a SnO2 semiconductor surface exhibit an unusual photoelectrochemical effect: a substantial and stable photocurrent/photovoltage is generated in modified photoelectrode cells that possess porphyrins with electron-rich side chains. This is interpreted as resulting from enhanced electron injection at the illuminated interface, resulting from an enhanced through bond electron tunneling in these chains. The estimated electron-transfer rate constants (ket) obtained from fluorescence quenching measurements roughly agreed with the photocurrent quantum yields for these model compounds. All the model porphyrins behaved identically as a function of pH. An enhanced photocurrent quantum yield was exhibited by all the compounds on diluting their monolayers with dioleoylphosphatidylcholine, a nonfluorophore surface active compound. This is interpreted as resulting from minimization of t...

Effects of Molecular Organization on Photophysical Behavior. 1. Steady-State Fluorescence and Fluorescence Quantum Yield Studies of Langmuir−Blodgett Monolayers of Some Surfactant Porphyrins

The surface chemistry of two new groups of surfactant carboxyporphyrins is described. These materials exhibit well-behaved monomolecular films at an air−water interface. In compressed monolayers, the porphyrin ring appears to be oriented so that the plane of the ring is perpendicular to the surface. The surface-pressure−molecular area isotherms change with the length and nature of the side chains in a manner suggesting that a long side chain allows the porphyrin rings to acquire the most ordered packing. A rigid chain structure was found to restrict the orientational flexibility of the porphyrin rings and hence prevented them from acquiring a well-ordered monolayer structure. The solid-state photophysical properties of Langmuir−Blodgett monolayers of these materials are strongly dependent on their degree of order. The absorption, fluorescence, and fluorescence excitation spectra of single monolayer films transferred onto quartz and SnO2 slides using the Langmuir−Blodgett technique indicate that increasing the order in porphyrin monolayers leads to an increased red-shift of the Soret band and to decreased fluorescence quantum yields. On a SnO2 semiconductor surface, the monolayers exhibit enhanced fluorescence quenching. This is interpreted as evidence for isoenergetic electron transfer from the porphyrin to the semiconductor. An approximate interfacial electron-transfer rate (ket) was estimated on the basis of the fluorescence yields on quartz and SnO2 surfaces, respectively.

Conductivity in phthalocyanines and mixed phthalocyanine/lipid monolayers at the air-water interface

The effects of molecular organization in spread monolayers on AC conductivity at the air-water interface have been examined in systems of Al and Zn phthalocyanines mixed with dioleoylphosphatidylglycerol. While it is observed that conductivity decreases with increasing surface concentration under all conditions, it may be seen that certain phthalocyanine-lipid ratios produce marked enhancement of this effect. These results are interpreted in terms of changing orientation of the macrocycle ring which effects ring-water surface interactions and demonstrates the sensitivity of surface conductivity to molecular organization.

Effects of molecular organization on photophysical photochemical behavior. Interactions of oxygen and pyrene-bearing probes across the air-lipid boundary in spread monolayers

Oxygen quenching of excited singlet pyrene probes in spread monolayers of dioleoylphosphatidylcholine (DOL), dipalmitylphosphatidylcholine (DPL), and dielaidylphosphatidylcholine (DEL), has been measured by time-resolved fluorescence. The probes used were a pyrene-bearing phosphatidylcholine (2-PyPC) and 1-pyrenedodecanoic acid (Py-22). In all cases, oxygen quenching was diminished by compression of the monolayer system

Effects of molecular organization on photophysical behavior: steady-state and real-time behavior of chlorophyll a fluorescence in spread monolayers of dipalmitoylphosphatidylcholine

Fluorescence spectra, intensities, and lifetimes of chlorophyll a have been determined in monolayers of dipalmitoylphosphatidylcholine as functions of chlorophyll concentration and monolayer compression over the range of (0.5-20) x 10/sup 12/ molecules/cm/sup 2/ and 2-30 dyn/cm surface pressure. This lipid exhibits three different phases over the surface pressure region examined: liquid-expanded, liquid-condensed, and solid-condensed. The fluorescence spectrum observed at 680 nm indicates that monomeric chlorophyll a is the predominant fluorescent form throughout. However, fluorescence intensities and lifetimes both respond dramatically to changes in lipid phase. In the region of the transition from liquid-expanded to liquid-condensed phase, intensity falls dramatically while lifetime shows no response to phase change. In the second transition from liquid-condensed to solid-condensed, the intensity again increases somewhat, while the lifetime exhibits two-component decay, one dependent on surface pressure and one essentially constant, exhibiting the value expected in dilute systems. These variations are interpreted in terms of changing interactions among chlorophyll molecules with alterations in the microenvironment.

Effects of molecular organization on photophysical and photochemical behavior: Quenching by subphase iodide of fluorescence in pyrene-bearing probes at the nitrogen-water interface

The quenching by subphase iodide of pyrene covalently bound to amphiphatic molecules in spread monolayers has been measured. The probes employed were 2-(6-pyreneylhexanoyl)-3-palmitoyl-sn-glycero-1-phosphorylcholine, 10-(6(8)-octadecylpyrenyl) decanoic acid and 1-pyrenedocosanoic acid; the host lipids utilized were dioleoylphosphatidylcholine (DOL) and dipalmitoylphosphatidylcholine (DPL). It has been observed in all cases that pyrene fluorescence is significantly quenched in the uncompressed layer and that this quenching diminishes markedly as the surface pressure is increased over the liquid expanded region. Beyond this range a plateau in the fluorescence decay is reached in DOL, while in DPL changes in quenching are related to phase transitions. These findings indicate significant probe-water interaction at low surface pressure. Residual iodide quenching in DOL above 10 dyn cm −1 indicates some continued water-probe contact which may be due to the liquid character of the host layer and the double-bond character of the lipid while the very small residual quenching in DPL suggests tight packing in the non-liquid phases.

Effects of molecular organization on photophysical behavior: time-resolved fluorescence of a pyrene-labeled phosphatidylcholine in spread monolayers of dioleoylphosphatidylcholine

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffects of molecular organization on photophysical behavior: time-resolved fluorescence of a pyrene-labeled phosphatidylcholine in spread monolayers of dioleoylphosphatidylcholineMaria Bohorquez and L. K. PattersonCite this: J. Phys. Chem. 1988, 92, 7, 1835–1839Publication Date (Print):April 1, 1988Publication History Published online1 May 2002Published inissue 1 April 1988https://doi.org/10.1021/j100318a028RIGHTS & PERMISSIONSArticle Views39Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (556 KB) Get e-Alerts

ChemInform Abstract: Effects of Molecular Organization on Photophysical Behavior. Excimer Kinetics and Diffusion of l‐Pyrenedecanoic Acid in Lipid Monolayers at the Nitrogen‐Water Interface.

ChemInform Abstract: Effects of Molecular Organization on Photophysical Behavior. Excimer Kinetics and Diffusion of l‐Pyrenedecanoic Acid in Lipid Monolayers at the Nitrogen‐Water Interface.

Effects of molecular organization on photophysical behavior: Steady-state and real-time behavior of chlorophyll- b fluorescence in spread monolayers of dioleoylphosphatidylcholine

Fluorescence lifetimes, spectra, and intensities of chlorophyll- b have been determined in monolayers of dioleoylphosphatidylcholine as functions of monolayer compression up to 30 dyn cm −1 over the chlorophyll- b concentration range of 1–30 x 10 12 molecules cm −2. The fluorescence spectrum observed at 661 nm indicates that monomeric chlorophyll- b is the only fluorescent form. The fluorescence lifetime at the low concentration limit approaches 3.8 ns, quite close to that observed in non-polar media. Both fluorescence lifetime and intensity decrease with increasing concentration, the behavior reflecting the expected concentration quenching. Unlike previous studies with chlorophyll- a, however, Stern-Volmer-type plots indicate that static quenching plays a marked role in the fluorescence behavior observed.

Effects of molecular organization on photophysical behavior. Excimer kinetics and diffusion of 1-pyrenedecanoic acid in lipid monolayers at the nitrogen-water interface

The time resolved behavior of pyrenedecanoic acid excimers in spread phospholipid monolayers at the air-water interface is reported herein. Interactions of the pyrene-bearing probe, 1-pyrenedecanoic (PDecA) have been compared as functions of probe concentration and hydrocarbon structure of the host liquid to the character of the lipid environment. The time resolved fluorescence measurements of mixed PDecA-lipid monolayers exhibit two features at 480 nm: a very fast rise in excimer intensity and a dependence of the excimer decay on PDecA mole fraction in the layer. 9 references, 3 figures.

Effects of molecular organization on photophysical behavior: lifetime and steady-state fluorescence of chlorophyll a singlets in monolayers of dioleoylphosphatydylcholine at the nitrogen-water interface

Effects of molecular organization on photophysical behavior: lifetime and steady-state fluorescence of chlorophyll a singlets in monolayers of dioleoylphosphatydylcholine at the nitrogen-water interface

Effects of molecular organization on photophysical and photochemical behavior. Exciplex formation in 1-pyrenedodecanoic acid and 4-dodecylaniline at the nitrogen-water interface

Effects of molecular organization on photophysical and photochemical behavior. Exciplex formation in 1-pyrenedodecanoic acid and 4-dodecylaniline at the nitrogen-water interface

PROTEIN AGGREGATION IN INTACT AND DISRUPTED PEROXIDIZING ERYTHROCYTE MEMBRANES

The effects of molecular organization on the interaction of peroxidizing lipids with proteins were studied by using human red cell membranes. Intact and chloroform-disrupted membranes were oxidized. Disruption of membranes was achieved by treatment with chloroform and subsequent elimination of the solvent. Lipid oxidation rates and SDS-electrophoretic protein patterns in the two types of membranes were compared. Specific 3H-DIDS label of band 3 allowed the study of the role of intrinsic proteins in the aggregation process. Lipid oxidation rate is not greatly affected by chloroform disruption although disrupted membranes show a higher rate of protein aggregation. α-Tocopherol decreases lipid oxidation and protein aggregation rates. Band 3 protein dimers (188,000 M.W.) appear earlier than the higher molecular weight protein aggregates (400,000 M.W.). The results suggest that native membrane organization prevents protein damage upon lipid peroxidation.

Structural origin of the cryogenic relaxations in poly(ethylene terephthalate)

AbstractThe effect of molecular organization (crystallinity, orientation) on the internal friction of poly(ethylene terephthalate) was studied by means of dynamic mechanical measurements at temperatures from 300 to 4.2°K, with a free‐oscillating torsion pendulum at 1 Hz. It was found that crystallinity decreases the intensity of the composite γ relaxation at 210°K and gives rise to an additional loss maximum ε at 26°K. Uniaxial orientation broadens the γ relaxation and gives rise to an additional loss peak δ, at 46°K. The δ and ε losses are dependent on molecular organization, occurring only in samples containing aligned, taut chain segments and crystalline structures, respectively. They have a common activation energy of 4 kcal/mole. All three low‐temperature relaxations in oriented specimens show pronounced directional anisotropy, which, in the γ loss, may be due to the preferred orientation of noncrystalline chain segments, while in the δ and ε losses, may be associated with the direction of defect structures. On the basis of the observed behavior of the δ and ε relaxations it is suggested that they may involve motions of defect structures and may thus participate in stress‐transfer mechanisms at large deformations.