Batch‐to‐Batch Variation of Polymeric Photovoltaic Materials: its Origin and Impacts on Charge Carrier Transport and Device Performances

A detailed investigation of the impact of molecular weight distribution of a photoactive polymer, poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT), on photovoltaic device performance and carrier transport properties is reported. It is found that different batches of as‐received polymers have substantial differences in their molecular weight distribution. As revealed by gel permeation chromatography (GPC), two peaks can generally be observed. One of the peaks corresponds to a high molecular weight component and the other peak corresponds to a low molecular weight component. Photovoltaic devices fabricated with a higher proportion of low molecular weight component have power conversion efficiencies (PCEs) reduced from 5.7% to 2.5%. The corresponding charge carrier mobility at the short‐circuit region is also significantly reduced from 2.7 × 10^?5 to 1.6 × 10^?8 cm² V^?1 s^?1. The carrier transport properties of the polymers at various temperatures are further analyzed by the Gaussian disorder model (GDM). All polymers have similar energetic disorders. However, they appear to have significant differences in carrier hopping distances. This result provides insight into the origin of the molecular weight effect on carrier transport in polymeric semiconducting materials.     

Preparation and characterization of calcium-binding and other hydrophobic proteins from synaptic membranes

A number of hydrophobic proteins have been separated and purified to varying degrees from synaptic membranes derived from bovine brain. The proteins, which have been obtained using preparative acrylamide gel electrophoresis, have been analyzed for molecular weight, amino acid composition, peptide mapping, N-terminal amino acids, and for their ability to bind calcium and ATP. A number of the proteins bound calcium, the greatest binding being associated with a component having a molecular weight of 1.5 · 10⁴, a binding capacity of 4 calcium/molecule, and a K_m of 1.5 · 10^?5 M. An acidic tryptic peptide derived from this protein was evidently responsible for the calcium-binding. ATP binding appeared to be confined largely to the higher molecular weight proteins. From the peptide mapping there appears to be a similar acidic component in a number of the proteins exhibiting calcium-binding. ATP-binding was associated mainly with the high molecular weight proteins, particularly those which consisted of numerous basic tryptic peptides.     

Oligonucleotide Sequence of Replicase Initiation Site in Qβ RNA

THE single stranded RNA genome of bacteriophage Qβ has been variously estimated to consist of from 3,500¹ to 4,500² nucleotides. It contains three known cistrons³, which correspond to three of the four Qβ-specific proteins synthesized in vivo and in vitro^4–6. These are: (1) the gene for the maturation or A protein (molecular weight 41,000 (refs. 4, 5)), (2) that for the major coat protein of the virus (molecular weight 14,000 (ref. 9)) and (3) the gene for the phage-specific subunit of the Qβ replicase (molecular weight 64,000 (ref. 10) or 69,000 (ref. 24)), listed in the probable order^7,8 that they occur on the Qβ RNA. The fourth Qβ-specific protein, A₁ or IIb (molecular weight 36,000 (refs. 4–6, 10)), has recently been shown by Weiner and Weber to have an N-terminal sequence which is identical (for eight amino-acids) to that of the coat protein⁷. Because increased amounts of A₁ appear in virus particles grown in cells containing a UGA suppressor, Weiner and Weber postulate⁷ that this protein is the product of natural read-through at the UGA termination signal of the Qβ coat cistron. Such read-through (involving about 600 nucleotides) could occur entirely within a large “intercistronic” region between the coat and replicase genes, or could involve translation, either in or out of phase, of the replicase cistron. In hopes of distinguishing between these alternatives, I have isolated and examined the nucleotide sequence of the region surrounding the initiator codon of the Qβ replicase gene.     

The flexibility of low molecular weight double-stranded dna as a function of length: II. Light scattering measurements and the estimation of persistence lengths from light scattering,sedimentation and viscosity

In the preceding paper are described the isolation and physical characterization of seven narrowly disperse fractions of calf thymus DNA in the molecular weight range 0.3 to 1.3 × 10⁶ daltons. Herein, we have determined by light scattering the molecular weights and root mean square radii of these fractions in a solvent comprising 0.2 M NaCl, 2 mM EDTA, 2m MNa-PO₄, pH 7. Measurements were made in a modified Wippler—Scheibling photometer to a 20° lower limit of scattering angle on solutions rendered virtually dust-free by procedures described. The optical aniso tropics of the DNA fractions were measured permitting the experimental molecular weights and root mean square radii to be corrected to their true values. From these values, with appropriate polydispersity corrections, we calculate a Kratky—Porod persistence length, a, of 54.0 ± 5.6 nm which is invariant over the molecular weight range examined. From the sedimentation coefficients (preceding paper) and the theory of Yamakawa and Fujii, we calculate a to be 66 nm, a value found to apply equally well to several DNA samples of various origins whose sedimentation rates are known in the molecular weight range from about 4 × 10⁴ to 10⁸ daltons. Similarly, from the intrinsic viscosities and the theory of Yamakawa and Fujii, we calculate a to be 59 nm, which again adequately applies to a number of DNA samples whose viscosities have been measured by other workers in the molecular weight range 3 × 10⁵ to 10⁸ daltons. The Flory—Mandelkern parameter, β, was found to vary with molecular weight in the manner predicted by the theory of Yamakawa and Fujii. The average value of a from the three sets of measurements is 60 ± 6 nm, which we believe applies to double-stranded DNA molecules, independent of chain length, over the whole range of molecular weights for which reliable data exist.     

Structure and physico-chemical properties of bacteriophage G: III. A homogeneous DNA of molecular weight 5 × 108

The physico-chemical properties of the DNA released from bacteriophage G (active on Bacillus megatherium) are described. Phage G, an unusually large bacteriophage, has a nucleic acid content of 4 to 6 × 10⁸ daltons.Sedimentation velocity analysis at low angular speed and examination by electron microscopy, indicate that a single DNA molecule, sedimenting with s_{20, w}⁰ = 125 ± 1.5 S and at least 200 ± 20 μm long, is released upon thermal or osmotic shock. Melting temperature data and chromatographic analysis indicate a mean base composition of 70% A + T. CsCl and Cs₂SO₄ buoyant density data, circular dichroism spectra and sensitivity to specific nucleases indicate that phage G DNA is similar to the DNAs from T-even phages and is more glucosylated than phage T6 DNA. Direct glucose determination indicates a 185% molar ratio of glucose to cytosine. Linear density extrapolated from literature data and contour length measurement yield a lower limit for the molecular weight of phage G DNA of 4.9 × 10⁸. Comparison of this value with the s_20,w⁰ measured with the analytical ultracentrifuge seems to confirm the validity of the empirical relationship proposed by Freifelder (1970), between s_{20, w}⁰ and molecular weight, over a larger range than that previously known. A possible systematic error in defect in length determination, however, prevents a discrimination between this and other empirical formulae proposed by various authors, which predict a molecular weight that is 20 to 25% higher.     

Identification of the structural gene for a myosin heavy-chain in Caenorhabditis elegans

Mutants in the unc-54 gene of Caenorhabditis elegans have been characterized by cyanylation and sodium dodecyl sulphate/polyacrylamide gel electrophoresis of the total myosin present in each mutant. In the recessive mutants lacking a major fraction of the total myosin, the high molecular weight doublet of 15 × 10⁴ and 14 × 10⁴ which dominates the cyanylation pattern of the total wild-type myosin is absent. In the mutant E675, which possesses a novel heavy-chain with a molecular weight of 2 × 10⁵, each component of the cyanylation doublet is reduced by 10⁴ daltons, indicating that the doublet is derived from partial cleavage of a single polypeptide chain. This suggests that unc-54 is the structural gene for a myosin heavy-chain present in a major fraction of the total nematode myosin.     

Mechanism of reversible glycine cleavage reaction in Arthrobacter globiformis. Function of lipoic acid in the cleavage and synthesis of blycine.

The physical and chemical characterization of horse serum butyrylcholinesterase has been extended. The results show that the enzyme is a glycoprotein containing about 20% carbohydrate by weight. Mannose, glucosamine, galactose, and sialic acid are the sugar residues found. The extinction coefficient of butyrylcholinesterase, E_1cm^1% at 280 nm, was found to be 15.2 ± 0.3 by dry weight determination. The molecular weight of the protein in dilute phosphate buffer was determined to be (31.7 ± 1.2) × 10⁴ by high speed equilibrium sedimentation with a redetermined partial specific volume of 0.723 ± 0.003 ml/g. Subunit molecular weights for the dissociated protein were found to be (7.9 ± 0.4) × 10⁴ and (8.1 ± 0.1) × 10⁴, respectively, in guanidine hydrochloride and in a solution at pH 11.8. The subunit molecular weight was also estimated to be (8.8 ± 0.2) × 10⁴ by analytical sodium dodecyl sulfate-gel electrophoresis. This apparently higher subunit molecular weight from dodecyl sulfate gels is expected for glycoproteins containing significant amounts of carbohydrate. No free sulfhydryl group was detected, even though there are six half-cystines in each subunit. Therefore, it seems likely that there are three pairs of disulfide bonds per subunit. The available data indicate that native butyrylcholinesterase is a tetrameric glycoprotein consisting of subunits of equal molecular weight.     

The release and stability of the large subunit of DNA from T2 and T4 bacteriophage

T₂ and T₄ bacteriophage have been exposed to various treatments which are known to release the encapsulated DNA. The unseparated reaction products have been examined by autoradiography. The results indicate the presence of one large subunit of DNA (molecular weight 45 x 10⁶) for each former phage particle. Some smaller subunits of molecular weight 12 x 10⁶ have been observed. The large subunit is sensitive to very small amounts of DNAase, and is resistant to mixed proteases and cannot be dispersed by banding in cesium chloride density gradients. The sensitivity to fragmentation by P³² decay and the increase in this sensitivity following heat treatment are best explained by assuming that the large subunit is a duplex of polynucleotide strands over most of its length. The presence of hypothetical non-DNA interconnections is considered.     

Human Serum Cholinesterase,a Tetramer

AFTER electrophoresis of human serum in starch gel¹, there are at least four bands of Cholinesterase activity. Most of the enzyme is concentrated in the band with least mobility (C₄) while three faster moving bands (C₁, C₂, C₃) are of lower molecular weight as shown by gel filtration². Although electrophoresis in Polyacrylamide reveals additional bands³, all seem to be a single genetic entity as shown by experiments on persons homozygous for the silent gene^4,5. The C₄ enzyme has a molecular weight of at least 250,000 (ref. 6) and can be assumed to be composed of more than one polypeptide chain. By preparing an enzyme of altered mobility and forming hybrids of it with the usual enzyme, we have obtained results that suggest that Cholinesterase is a tetramer.     

Preparation and solution properties of pullulan fractions as standard samples for water-soluble polymers

A series of pullulan fractions with molecular weights in the range 5 × 10³ to 8 × 10⁵ were prepared. The weight-average molecular weight (M_w) of all the samples was determined by sedimentation equilibrium. The hydrodynamic properties of pullulan in aqueous solution were investigated by viscometry and ultracentrifugation. The experimental results indicate that pullulan molecules in water are fairly stable and behave as expanded random coils when M_w is above 2 × 10⁴. The molecular weight distributions of the fractions were measured by gel filtration. The ratio M_w/M_n was close to 1·1, except for a sample with the highest M_w.It is concluded that the pullulan fractions prepared by the present work are well characterized and have a narrow molecular weight distribution. They may be useful as standard samples for studies of water-soluble polymers.     

Low Molecular Weight Active Form of Inducible Liver Tyrosine Aminotransferase

RECENT experiments^1–4 suggest that there are several forms of inducible liver tyrosine aminotransferase and that they may be stimulated by different hormones and expressed differently by genetic mutation. We now report the occurrence of a low molecular weight form of enzymatically active soluble tyrosine aminotransferase, which is inducible as is the larger molecular weight enzyme. Assuming that the latter is a tetramer⁵, the former has a tentative molecular weight equivalent to a subunit of the larger enzyme.     

Molecular weight estimation using sodium dodecyl sulfate-pore gradient electrophoresis

Pore gradient electrophoresis (PGE) in the presence of sodium dodecyl sulfate (SDS) provides a means for high resolution fractionation of multicomponent protein systems and permits estimation of molecular weights for macromolecules ranging from 10³ to 10⁶. We have evaluated the performance of several methods used to construct calibration curves for estimation of molecular weights using SDS-PGE. A linear relationship between the logarithm of molecular weight, log (M_r), and the logarithm of the relative mobility, log (R_l), can be obtained for a 30-fold range of molecular weights. However, this range of linearity depends on the choice of the concentration gradient, the degree of crosslinking of the gel, and on the nature of the underlying relationship between the retardation coefficient, K_R, and the molecular weight. An empirical relationship, first introduced by Lambin et al. (1976, Anal. Biochem.74, 567) between log (M_r) and the logarithm of the gel concentration at the position reached by the protein, log (%T), provides better linearity over a wider molecular weight range than does the use of log (R_l). We have compared these relatienships by experimental analysis of 10 standard proteins and by a theoretical analysis of an idealized model system. A computer program has been developed which provides appropriate statistical estimation of the molecular weight for an unknown protein, together with its standard error and 95% confidence limits. A new method has also been developed for analysis of nonlinear calibration curves in terms of molecular weight versus distance migrated, based on a theoretically justifiable, physical-chemical model. This model implies that either the relationship between log (M_r) and log (R_l) or the one between log (M_r) and log (%T) will become nonlinear as the range of molecular weight is extended. We suggest that the use of a nonlinear least-squares curve-fitting procedure provides an optimal method for molecular weight estimation when sufficient data are available. Based on these findings, a general strategy is presented for estimation of molecular weights by polyacrylamide gel electrophoresis.     

Studies on some aspects of peroxidase from submaxillary gland

A peroxidase has been purified 25- to 30-fold over crude homogenate from goat submaxillary gland, which shows a single band of protein on polyacrylamide gel electrophoresis at four different pH values (4.6–10.0). A molecular weight (M_r) of approximately 2 × 10⁴ per heme binding site has been found. The molecular weight of the enzyme determined by Sephadex-gel filtration method, appeared to be 4 × 10⁴. The sedimentation pattern of the purified enzyme shows a symmetrical peak, although there was evidence of some small heterogenous material near the meniscus. The sedimentation coefficient of the enzyme (s^o 20^wat 0.4% of the enzyme concentration) was found to be 4.18, which indicates the molecular weight of the enzyme to be approximately 6 × 10⁴.     

Synthesis of RNA in isolated polytene nuclei from salivary gland cells of Chironomus thummi

The incorporation of [³H]UTP into RNA by isolated polytene salivary gland nuclei of Chironomus thummi was investigated under different incubation conditions; the labeled RNA fractions were characterized by electrophoresis. The results suggested that at two characteristic ionic conditions most of the RNA synthesized was the product of RNA polymerase I or RNA polymerase II as distinguished by their differential sensitivities to α-amanitin. Electrophoretical analysis of the RNA synthesized under conditions favouring polymerase I showed that this RNA population consisted mainly of four distinct molecular weight fractions within a range between 2.8 × 10⁴ and 2.5 × 10⁶. Under conditions favouring polymerase II two fractions were detected: one with a broad molecular weight distribution around 0.4 × 10⁶ containing considerable amounts of poly(A)-bearing RNA molecules, and a second with a peak at a molecular weight of 2.8 × 10⁴.     

Time course of gold-induced accumulation of copper and zinc and the effects of dimercaptosuccinate and cadmium on gold metabolism in rat kidney

After the s.c. administration of sodium aurothiomalate (SATM, 10 mg Au/kg) to male rats, the gold content of the kidney increased to a maximum after 4 days and thereafter declined slowly. The total copper content of the kidney increased at least until 11 days after SATM treatment but was not simply a function of the renal gold content. Gold and copper accumulated in the metallothionein-like, low molecular weight protein fraction and the initial uptake of gold by this fraction appeared to be related to the accumulation of copper. The Zn²⁺ content of the kidney was initially unchanged but later increased with the additional Zn²⁺ bound predominantly to the non-soluble components. The accumulation of low molecular weight protein-bound copper was not related either to the Zn²⁺ content of this fraction or to the total Zn²⁺ content of the kidney.Daily administration of dimercaptosuccinic acid (DMSA, 50 mg/kg, i.p.) for 2 weeks to SATM-pretreated rats resulted in a 50% reduction in the concentration of gold in the non-soluble fraction and in both the high and low molecular weight protein components of the soluble fraction. Copper, which accumulated in the non-soluble components and in the soluble low molecular weight protein, was lost only from the non-soluble components.Uptake of gold by the kidneys was increased when rats were pretreated with Cd²⁺. The accumulation of gold in the low molecular weight protein fraction was also increased, but most of the additional gold in the kidneys was accumulated by the non-soluble components. SATM had no effect on the renal concentration or subcellular distribution of Cd²⁺. It was concluded that the soluble low molecular weight metal binding protein does not have prominent regulatory or protective functions in the renal metabolism of gold.     

Purification and characterisation of leukotriene A4 hydrolase from rat neutrophils

Leukotriene A₄ hydrolase was rapidly and extensively purified from rat neutrophils using anion exchange and gel filtration high-pressure liquid chromatography. The enzyme which converts the allylic epoxide leukotriene A₄ to the 5,12-dihydroxyeicosatetraenoic acid leukotriene B₄ was localized in the cytosolic fraction and exhibited an optimum activity at pH 7.8 and apparent K_m for leukotriene A₄ between 2 · 10^?5 and 3 · 10^?5 M. The purified leukotriene A₄ hydrolase was shown to have a molecular weight of 68 000 on sodium dodecylsulfate polyacrylamide gel electrophoresis and of 50 000 by gel filtration. The molecular weight and monomeric native form of this enzyme are unique characteristics which distinguish leukotriene A₄ hydrolase from previously purified epoxide hydrolases.     

Isolation of acetylcholine receptor-- -bungarotoxin complexes from Torpedo californica electroplax

Affinity chromatography has been utilized to purify acetylcholine receptors from Torpedo californica electroplax membranes. These have been isolated as their [¹²⁵I]α-bungarotoxin complexes. The major protein subunit found had a molecular weight of 3.5–4.5 × 10⁴ on gel electrophoresis under denaturing conditions. Other components of higher molecular weight were also present in smaller amounts even in the best preparations. This is interpreted as most likely due to either a multiple subunit structure or to more than one type of receptor in the tissue used.     

Neutron scattering study of the 13 S fragment of 16 S RNA and its complex with ribosomal protein S4

A fragment with a molecular weight of 170,000 and a sedimentation coefficient of 13 S which is capable of specifically binding ribosomal protein S4 has been obtained by digestion of Escherichia coli 16 S RNA with ribonuclease A. The 13 S fragment of 16 S RNA and its complex with protein S4 have been studied by different physical methods; in the first place, by neutron scattering. It has been shown that this fragment is very compact in solution. The radii of gyration of this fragment (50 ± 3 Å) and of protein S4 within the complex (17 ± 3 Å) coincide, within the limits of experimental error, with the radii of gyration for the free RNA fragment (47 ± 2 Å) and the free ribosomal protein S4 in solution (18 ± 2 Å). Hence the conclusion is drawn that the compactness of the RNA fragment and the ribosomal protein does not change on complex formation. The compact 13 S fragment of 16 S RNA is shown to be contrast-matched in solvent containing 70% ²H₂O which corresponds to a value for the partial specific volume of RNA of 0.537 cm³/g.     

Plant 5.8S RNA is a Component of 80S but not 70S Ribosomes

LIVING organisms contain two classes of ribosomes that can be distinguished by differences in their size, the molecular weights of their constituent high molecular weight RNAs and their sensitivity to certain inhibitors of protein synthesis. The ribosomes of one type occur in bacteria, blue-green algae and chloroplasts. They have sedimentation coefficients of approximately 70S^1,2, contain RNA with molecular weights of about 1.1 × 10⁶ (23S) and 0.56 × 10⁶ (16S)³ and their activity is inhibited by chloramphenicol^4,5, lincomycin and spectinomycin⁶. The ribosomes of the other type are found in the cytoplasm of animal and plant cells, have sedimentation coefficients of 80S^1,2, contain RNA with molecular weights of 1.3?1.75 × 10⁶ (25–28S) and 0.7 × 10⁶ (18S)³ and are prevented from functioning by cycloheximide⁴.     

Studies on the metabolic fate of 111In-labeled antibodies

Indium-111-labeled antibodies, though providing superior photon flux to iodine-labeled antibodies, can exhibit high levels of accumulation in some non-target organs. In an effort to understand the nature of this non-target uptake we have evaluated the molecular weight of ¹¹¹In species retained in several tissues by radio-FPLC (sizing chromatography) following injection of [¹¹¹In]DTPA 5G6.4, a murine monoclonal antibody, into normal mice. Blood, liver and kidneys were removed, and liver and kidneys were homogenized at several time points after antibody injection. The proportion of ¹¹¹In-containing species was found to vary with the tissue and with time. Analysis of blood showed only radiolabeled antibody. In the liver, several ¹¹¹In species were identified with molecular weights compatible with intact antibody, [¹¹¹In]transferrin, and low molecular weight complexes, with an increase in the proportion of [¹¹¹In]transferrin and low molecular weight species occurring over time. While the same molecular weight species were also identified in the kidneys, the kidneys contained the largest percentage of low molecular weight species which increased over time. When ¹²⁵I-labeled 5G6.4 was injected and the tissues similarly analyzed, only radioactive material with the molecular weight of intact antibody was detected. Comparison of two methods of purification of [¹¹¹In]labeled antibody after labeling revealed a significant difference in the organ uptake of radiolabeled products for ¹¹¹In. Although dialysis was sufficient for the removal of labile ¹¹¹In, as determined by TLC, subsequent sizing chromatography on Bio-Gel P-60 dramatically dropped the hepatic and renal uptake of ¹¹¹In relative to blood and diminished the proportion of the low molecular weight species present on sizing FPLC of extracts from tissues. These data indicate that low and intermediate molecular weight ¹¹¹In compounds are accreted in the liver and kidneys following the i.p. injection of ¹¹¹In-labeled monoclonal antibodies and that their uptake can be diminished by more stringent radioantibody purification. This knowledge may be valuable in developing methods for reducing non-target ¹¹¹In uptake.