Small Molecular Weight Material Research Articles

C-Si hybrid photonic structures by full infiltration of conjugated polymers into porous silicon rugate filters

Loading of one-dimensional (1-D) porous silicon photonic crystals (PS-PhCs), known as rugate filters, with luminescent materials is generally limited by the potential for (undesired) “pore clogging,” in relation to the size of the nanoparticles (e.g. quantum dots) or molecular species, and so far mainly restricted to small molecular weight materials or small nanocrystals, or in situ polymerized dyes. Here we report the infiltration 1-D PS-PhCs with a green-emitting commercial luminescent polymer (F8BT, poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)]), with a molecular weight of approximately 46 kDa across their whole depth (approximately 7.5 μm), thereby showing that pore clogging is not a concern for these structures. We also characterize the modification of the photoluminescence (PL) and decay rates, and investigate the detailed inner morphology of the filters with the help of (scanning) transmission electron microscopy. We observe both suppression (in the stop-band) and enhancement (at the high-energy band-edge) of the PL. We also find that the photonic stop-band is red-shifted after polymer infiltration, due to the increased effective refractive index of the polymer-infiltrated nanostructured system. The presence of just one unbroadened peak in the reflectance spectra after infiltration confirms that infiltration extends for the whole depth of the rugate filters.

Characterization of atmospheric organic matter using size-exclusion chromatography with inline organic carbon detection

The atmosphere contains a substantial amount of water-soluble organic material in aerosols, clouds and fogs. Despite years of efforts, little is known on the structure, composition and properties of this organic matter with most studies focusing on individual species while the bulk of the organic matter remains poorly characterized.In this work high-performance size-exclusion chromatography coupled with inline organic carbon detection (SEC-DOC) is used to characterize organic matter in fogs, clouds and aerosols collected in Fresno (CA), Whistler (BC), Davis (CA) and Selinsgrove (PA). The molecular weight distributions showed a fractional overlap of atmospheric samples and terrestrial fulvic acids although for clouds and aerosols the smaller molecular weight (MW) material is dominant. This smaller MW material is clearly resolved. Cloud and fog samples showed a larger fraction of small molecular weight organic species compared to the water-soluble fraction of aerosols, consistent with the partitioning of small molecular weight volatile species into the atmospheric aqueous phase. There are overall little differences between different sites for a same type of sample. These results obtained by one analytical set-up were confirmed with a second size-exclusion chromatography set-up using a different column and detection system. Size distributions for the same sampling location showed little inter-event variability and water-soluble organic carbon (WSOC) samples were slightly shifted toward larger sizes compared to clouds and fogs, consistent with an important contribution of volatile species to the latter ones. Cloud and aerosol samples contributed to a significant fraction (up to 21% of dissolved organic carbon (DOC)) of the macromolecular scale material.

Diffusion of triplet excitons in an operational organic light-emitting diode

Measurements of the diffusion length L for triplet excitons in small molecular-weight organic semiconductors are commonly carried out using a technique in which a phosphorescent-doped probe layer is set in the vicinity of a supposed exciton generation zone. However, analyses commonly used to retrieve $L$ ignore microcavity effects that may induce a strong modulation of the emitted light as the position of the exciton probe is shifted. The present paper investigates in detail how this technique may be improved to obtain more accurate results for L. The example of 4,4'-bis(carbazol-9-yl)1,1'-biphenyl (CBP) is taken, for which a triplet diffusion length of L=16 +/- 4 nm (at 3 mA/cm2) is inferred from experiments. The influence of triplet-triplet annihilation, responsible for an apparent decrease of L at high current densities, is theoretically investigated, as well as the 'invasiveness' of the thin probe layer on the exciton distribution. The interplay of microcavity effects and direct recombinations is demonstrated experimentally with the archetypal trilayer structure [N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)]-4,4'-diaminobiphenyl (NPB)/CBP/ 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (named bathocuproine, BCP). It is shown that in this device holes do cross the NPB/CBP junction, without the assistance of electrons and despite the high energetic barrier imposed by the shift between the HOMO levels. The use of the variable-thickness doped layer technique in this case is then discussed. Finally, some guidelines are given for improving the measure of the diffusion length of triplet excitons in operational OLEDs, applicable to virtually any small molecular-weight material.

Photocurrent Generation in Nanostructured Organic Solar Cells

Photocurrent generation in nanostructured organic solar cells is simulated using a dynamical Monte Carlo model that includes the generation and transport properties of both excitons and free charges. Incorporating both optical and electrical properties, we study the influence of the heterojunction nanostructure (e.g., planar vs bulk junctions) on donor-acceptor organic solar cell efficiencies based on the archetype materials copper phthalocyanine (CuPc) and C(60). Structures considered are planar and planar-mixed heterojunctions, homogeneous and phase-separated donor-acceptor (DA) mixtures, idealized structures composed of DA pillars, and nanocrystalline DA networks. The thickness dependence of absorption, exciton diffusion, and carrier collection efficiencies is studied for different morphologies, yielding results similar to those experimentally observed. The influences of charge mobility and exciton diffusion length are studied, and optimal device thicknesses are proposed for various structures. Simulations show that, with currently available materials, nanocrystalline network solar cells optimize both exciton diffusion and carrier collection, thus providing for highly efficient solar energy conversion. Estimations of achievable energy conversion efficiencies are made for the various nanostructures based on current simulations used in conjunction with experimentally obtained fill factors and open-circuit voltages for conventional small molecular weight materials combinations.

Solar cells utilizing small molecular weight organic semiconductors

AbstractIn this review, we focus on the field of organic photovoltaic cells based on small molecular weight materials. In particular, we discuss the physical processes that lead to photocurrent generation in organic solar cells, as well as the various architectures employed to optimize device performance. These include the donor–acceptor heterojunction for efficient exciton dissociation, the exciton blocking layer, the mixed or bulk heterojunction, and the stacked or tandem cell. We show how the choice of materials with known energy levels and absorption spectra affect device performance, particularly the open‐circuit voltage and short‐circuit current density. We also discuss the typical materials and growth techniques used to fabricate devices, as well as the issue of device stability, all of which are critical for the commercialization of low‐cost and high‐performance organic solar cells. Copyright © 2007 John Wiley & Sons, Ltd.

Strong exciton–photon coupling in organic materials

The study of strong exciton–photon coupling in organic materials has progressed at a rapid pace since the first observation of microcavity polaritons in tetra-(2,6-t-butyl)phenol-porphyrin zinc less than 10 years ago. The field is driven by the potential for revolutionary optoelectronic devices based on polaritonic phenomena such as ultrafast optical amplifiers and switches, structures with enhanced nonlinear optical properties, and coherent polariton light emitters, known as polariton lasers. This review examines recent experimental advances related to the general understanding of strong coupling in a range of small molecular weight and polymeric organic materials.

The Limits to Organic Photovoltaic Cell Efficiency

AbstractWe consider the fundamental limits to organic solar cell efficiency, and the schemes that have been used to overcome many of these limitations. In particular, the use of double and bulk heterojunctions, as well as tandem cells employing materials with high exciton diffusion lengths, is discussed.We show that in the last few years, a combination of strategies has led to a power conversion efficiency of ηp = 5.7% (under AM 1.5 G simulated solar radiation at 1 sun intensity) for tandem cells based on small-molecularweight materials, suggesting that even higher efficiencies are possible.We conclude by considering the ultimate power conversion efficiency that is expected from organic thinfilm solar cells.

Phosphorescence as a probe of exciton formation and energy transfer in organic light emitting diodes

The development of highly efficient phosphorescent molecules has approximately quadrupled the quantum efficiency of organic light emitting devices (OLEDs). By harnessing triplet as well as singlet excitons, efficient molecular phosphorescence has also enabled novel studies of exciton physics in organic semiconductors. In this review, we will summarize recent progress in understanding exciton formation and energy transfer using phosphorescent molecular probes. Particular emphasis is given to two topics of current interest: energy transfer in blue phosphorescent OLEDs, and quantifying the formation ratio of singlet to triplet excitons in small-molecular weight materials and polymers. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Redox effects on resin extraction of herbicides from soil

Relative soil aeration affects the surfaces upon which pesticides adsorb and non-ionic resins offer a means of observing and evaluating this factor. A non-ionic resin extractor, developed for pesticide extraction under reducing conditions, was used to adsorb a fraction of the reversibly adsorbed (active portion) herbicides. The extractor consists of cleaned XAD-2 resin encased in a dialysis membrane composed of regenerated cellulose. Anaerobiosis was achieved by incubating soil suspensions with glucose under a 95% N 2–5% H 2 environment until the redox potential reached −150 mV. Nine soils with a range of physical and chemical characteristics were examined for atrazine, metribuzin, and alachlor content. Amounts of atrazine, metribuzin, and alachlor extracted from soil ranged to 100, 140, and 75 ng g −1, respectively. Resin extractions (RE) conducted under aerobic conditions recovered about 25–50% of the pesticide extractable with conventional solid phase solvent extraction at 60 °C (SPE 60). Under anaerobic conditions, equal amounts of atrazine were extracted with RE and SPE 60. Slightly less metribuzin was recovered under anaerobic extraction with the exception of those soils lacking detectable amounts by SPE 60. Larger amounts of alachlor were extracted with resins under anaerobic conditions than under aerobic conditions but the amounts were not correlated with those determined by SPE 60. Large amounts of soil organic matter were solublized under anaerobiosis and smaller molecular weight material was extracted with the herbicides. The nature and amounts of co-extracted organic matter varied among soils. RE directly from soil suspensions enabled simultaneous determination of all three herbicides.

Molecular cloning and characterization of the polypeptide backbone of Schistosomamansoni circulating cathodic antigen

One of the candidate schistosome antigens for the development of a circulating antigen detection diagnostic assay is the circulating cathodic antigen (CCA). Detection of CCA in urine provides a non-invasive assay with high sensitivity. Previously we reported that CCA is secreted in patients’ urine as a small molecular weight material which is probably of a proteinaceous nature. In an attempt to further characterize the secreted component of CCA, we used a monoclonal antibody (MAb) reactive with urine-CCA to isolate an adult worm cDNA clone (SmN3-1) that encodes the polypeptide backbone of CCA. The sequence, gene organization and expression of SmN3-1 were analyzed. The 1.6 kb nucleotide and 347 amino acid sequences of SmN3-1 showed no significant homology to any published sequence. The size and antigenic properties of the expression product of SmN3-1 in Escherichia coli greatly resembled the CCA molecule excreted in urine, suggesting that the latter is primarily composed of the protein element of CCA.

Possibility of lymphatic absorption of epidermal growth factor from intestine

Epidermal growth factor (EGF) in the milk fat globule membrane (MFGM) emulsion enhanced the absorption of this factor from the intestine, especially to the intestinal lymph. Most of the radioactive EGF administered was degraded to small molecular weight materials. These degraded materials were absorbed and appeared in both the intestinal lymph and portal vein blood. However, a certain portion of EGF, although small, appeared in the lymph maintaining the original molecular mass. The MFGM emulsion used enhanced the lymphatic absorption of intact EGF, suggesting that this dosage form increased the absorption of EGF, protected the degradation of EGF in the intestine or promoted the absorption of intact EGF. The enhancing effect on the absorbed dose percentage of EGF recovered using MFGM emulsion was also observed in the portal vein plasma. However, the effect on the absorption of intact EGF was much larger in the lymph than in the portal vein.

Identification of a monocyte-derived factor which regulates synthesis of insulin receptors on activated T-lymphocytes (MIRRF)

The regulation of the insulin receptor on the activated T-lymphocyte was studied. It has been previously shown that the monocyte with its constitutive insulin receptor can signal the quiescent T-lymphocyte with respect to ambient insulin concentration which regulates the copies of insulin receptors synthesized during the lymphocyte activation event. In this communication it is shown that the vehicle by which the monocyte signals the T-lymphocyte is a soluble, small molecular weight protein. Initially a bioassay was established to test the putative monocyte-derived factor in which freshly prepared purified populations of monocytes were incubated with insulin, extensively washed, and replated with lymphocytes in microwells or across a 3 μm filter from lymphocytes using the appearance of insulin receptors on T lymphocytes responding to lectin as measured by a radioligand binding assay as the outcome variable. Dose response and time course relationships were established to develop the ideal conditions for the bioassay. It was shown that the monocyte-derived insulin receptor regulatory factor (MIRRF) could be readily detected in conditioned medium of insulin-incubated and then washed monocytes as a starting point for attempts at later purification. Using rats fed an essential fatty acid deficient diet (EFAD), incapable of generating standard prostanoids, it was demonstrated that the MIRRF was readily detectable in our standard bioassay revealing that the factor was not a member of the arachidonic acid family. Lastly, it was shown that MIRRF is cycloheximide sensitive and either is a protein or requires protein synthesis. These studies reveal that the monocyte insulin regulatory factor (MIRRF) is a small molecular weight material dependent on protein synthesis derived from insulin-incubated monocytes capable of passing a 3 μm filter and providing a regulatory signal to quiescent, insulin receptor negative lymphocytes. Furthermore, the ready detection of the factor in conditioned medium and the characterization of ideal conditions for a bioassay permit further studies to purify to homogeneity, to sequence, and to ascertain a full range of biological activities of this putatively novel cytokine.

The structure, size and solution chemistry of a polysaccharide iron complex(Niferex)

A polysaccharide-iron complex(PIC), synthesized by the neutralization of an FeCl 3 carbohydrate solution, is marketed as an oral hematinic(‘Niferex’). The chemistry, structure and solution chemistry of this complex have been examined by a variety of techniques. Elemental analyses are consistent with the report that solid PIC contains ferrihydrite in the core. Treatment of this material with ammonium oxalate yields a small molecular weight material which rapidly becomes a second, larger material, a result also consistent with the idenfication of ferrihydrite in PIC. The complex itself appears to be spherical with diameters ranging from 3 to 10 nm as determined by gel permeation chromatography and electron microscopy. The relationship between the charge and pH on the complex was studied by electrophoresis and acid—base titration. The material is negatively charged and soluble above pH 4.6. Between pH 4.0 and 4.6, PIC is neutral and insoluble, and below 4.0 it is positively charged and soluble. The carbohydrate component apparently contributes to its solubility at near neutral pHs and may be important in the reported bioavailability of the iron in this supplement.

Isolation of insulin degradation products from endosomes derived from intact rat liver.

Rats were injected with [125I]iodoinsulin labeled at either the A14 or B26 tyrosine, and the animals were killed and livers subcellularly fractionated to yield light (early or neutral) endosomes and heavy (late or acidic) endosomes. 125I-Labeled material was extracted from endosomes and analyzed by Sephadex G-50 filtration and high performance liquid chromatography (HPLC). Radiolabeled material in both types of endosomes is comprised of high molecular weight, insulin-sized, and low molecular weight components, with B chain-labeled small molecular weight material in two peaks, one corresponding to iodotyrosine and one to small peptides (Mr less than 1500). As compared with A chain label, however, less of the B chain material appears in the degradation components (both high and low molecular weight fractions) suggesting that a fragment of B chain containing the B26 residue is lost from the endosomes. Analysis on HPLC shows that significant amounts of the insulin-sized and high molecular weight material have proteolytic cleavage(s) in the B chain with an intact A chain. The B chain-derived labeled peptides elute from HPLC identically with products generated by insulin protease. These results therefore show substantial insulin degradation occurring in light endosomes prior to endosomal acidification and to receptor dissociation, suggesting receptor-bound insulin is a substrate for insulin protease.

Isolation and characterization of proteoglycans synthesized by adult human gingival fibroblasts in vitro

The proteoglycans synthesized by fibroblasts derived from healthy human gingivae were isolated and characterized. The largest medium proteoglycan was excluded from Sepharose CL-4B but not from Sepharose CL-2B; it was recovered in the most-dense density gradient fraction and identified as a chondroitin sulfate proteoglycan. The medium contained two smaller proteoglycans; one contained predominantly chondroitin sulfate proteoglycan, while the other was comprised predominantly of dermatan sulfate proteoglycan and was quantitatively the major species. The largest proteoglycan in the cell layer fraction, excluded from both Sepharose CL-2B and Sepharose CL-4B, was found in the least-dense density gradient fraction and contained heparan sulfate and chondroitin sulfate proteoglycan. It could be further dissociated by treatment with detergent, suggesting an intimate association with cell membranes. Two other proteoglycan populations of intermediate size were identified in the cell layer extracts which contained variable proportions of heparan sulfate, dermatan sulfate, or chondroitin sulfate proteoglycan. Some small molecular weight material indicative of free glycosaminoglycan chains was also associated with the cell layer fraction. Carbohydrate analysis of the proteoglycans demonstrated the glycosaminoglycan chains to have approximate average molecular weights of 25,000. In addition, N- and O-linked oligosaccharides which were associated with the proteoglycans appeared to be sulfated in varying degrees.

Human beta-melanocyte-stimulating hormone revisited.

It is generally accepted that human beta-melanocyte-stimulating hormone (h beta MSH) does not normally exist in humans but was merely an artifactually generated 22-amino acid peptide corresponding to a lipotropin (LPH) fragment (residues 35-56). We examined whether the shorter 18-amino acid peptide h beta MSH-(5-22) could be detected in some human tissues. Normal human pituitaries and hypothalami as well as corticotropin-secreting pituitary and nonpituitary tumors were extracted and chromatographed on Sephadex G-50, and the fractions were measured with two radioimmunoassays using either a COOH-terminal human gamma LPH (h gamma LPH) antiserum that recognized equally h gamma LPH, h beta MSH, and h beta MSH-(5-22) or a mid-portion h gamma LPH antiserum that recognized h gamma LPH and h beta MSH but not h beta MSH-(5-22). Normal pituitaries and pituitary tumors contained a single immunoreactive material coeluting with h gamma LPH. The hypothalami and the nonpituitary tumors all contained h gamma LPH and a smaller molecular weight material that was only detected in the COOH-terminal h gamma LPH radioimmunoassay; its elution volume (Ve/V, 0.75) was identical to that of h beta MSH-(5-22) but different from that of h beta MSH (Ve/V, 0.60); on reversed-phase HPLC, it coeluted with synthetic h beta MSH-(5-22) with a retention time different from that of h beta MSH. It is concluded that h beta MSH-(5-22) that corresponds to the 18-amino acid peptide h beta LPH-(39-56), flanked by two pairs of basic amino acids within the h beta LPH molecule, is a normal maturation product of proopiomelanocortin in human nonpituitary tissues.

Colloidal and dissolved organic carbon dynamics in undisturbed boreal forest catchments: a seasonal study of apparent molecular weight spectra

SUMMARY. 1. Colloidal and dissolved organic carbon (CDOC) was monitored in six pristine boreal rivers in Northern Quebec, Canada, using ultrafiltration to obtain apparent molecular weight spectra.2. The concentration and proportional contribution of small (<1K) molecular weight material (potentially microbially labile) and high (0.7μm to 300 K) molecular weight material was not significantly different between streams of order 2–9.3. The dominant component of CDOC (0.7μm to 300 K fraction) was probably derived in streams other than first order, from surface or sub‐surface run‐off, whereas a peak concentration in the <1 K fraction during August was probably due to autochthonous exudates.4. The two first order streams included in this survey had very low CDOC concentrations. However, further work on twelve other first order streams showed that they had high concentrations and we consider that this is the more typical situation. The finding offered a potential explanation for the otherwise anomalous longitudinal CDOC distribution pattern throughout the study area.

Ozone-related fluorescent compounds in mouse liver and lung

Groups of ten female, weanling mice were fed a basal, vitamin E-deficient diet or a basal diet supplemented with RRR-α-tocopheryl acetate for 14 months. During the last month one group from each dietary regimen was exposed for 30–60 min/day to 1.5 ppm ozone (25 hr total ozone exposure) and the remaining groups to control ambient air. The liver and lung tissues were homogenized and extracted with 2:1 chloroform:methanol and water. The water-soluble and organic solvent-soluble fluorescent materials were separated on Sephadex G-25 and LH-20 columns, respectively. Excitation and emission wavelengths for the eluting fractions were determined by continuous emission scans from 250 to 600 nm for each excitation wavelength between 250 and 500 nm (in increments of 25 nm). Ozone exposure did not effect the concentration of any of the fluorescent materials examined in the lung, but it resulted in a significant increase in two of four water-soluble compounds in the liver with excitation wavelength maxima/emission wavelength maxima of 270 nm/310 nm and 275 nm/350 nm (smaller molecular weight material) suggesting in vivo lipid oxidation.

Pro-enkephalin peptides possessing Met-enkephalin-Arg 6-Gly 7-Leu 8-immunoreactivity in rat CSF, striatum and adrenal gland

Cerebrospinal fluid (CSF) taken from rats implanted with chronic cisternal cannulae and extracts prepared from rat adrenal gland and striatum were subjected to Sephadex G-50 chromatography and HPLC. Fractions were monitored using specific radioimmunoassays (RIA) for the pentapeptide methionine enkephalin (Met-Enk) and methionine enkephalin-Arg 6-Gly 7-Leu 8 (Met-EnkRGL). In rat CSF, striatum and adrenal gland, three Met-EnkRGL-immunoreactive (IR) peaks of Mrs 8000, 5000 and 1000 daltons were detected. The same peaks were also found to possess Met-Enk-immunoreactivity after enzyme digestion of Sephadex G-50 fractions with trypsin and carboxypeptidase B (CPB), suggesting their derivation from pro-enkephalin. HPLC of the 8K and 5K peaks on a column of Ultrapore RPSC showed them to elute discretely with similar retention times, indicative of hydrophobic peptides of large molecular weight. Their similar hydrophobicities yet significant separation during gel filtration would suggest that the 8K and 5K peptides are sstructurally closely related yet different with respect to their molecular weights. HPLC of the small molecular weight material from rat striatum and adrenal gland revealed the presence of Met-EnkRGL and Met-EnkRGL sulphoxide in both tissues. In rat striatum Met-Enk and its sulphoxide were also detected. The oxidised pentapeptide was found to be present in rat CSF, together with two unidentified small molecular weight Met-Enk-IR peaks detected without prior enzyme digestion of fractions. The small molecular weight Met-EnkRGL-IR material in rat CSF was found to be comprised of two unknown peptides which were less hydrophobic than Met-EnkRGL and its sulphoxide derivative.

Protection of suckling mice from heat-stable enterotoxin of Escherichia coli by infant formulas.

Human milk contains factors that protect suckling infants against enteropathogen-induced diarrhea. One nonspecific protective factor found in human milk is a small molecular weight material that protects suckling mice from death due to the heat-stable enterotoxin of Escherichia coli. This study demonstrated that cow's milk and most formulas derived from cow's milk also contain a factor(s) that can protect against heat-stable enterotoxin of E. coli in suckling mice.