bluuebunny/crossref_metadata_2025 huggingface dataset:
Industries using arsenic and arsenic compounds
Authors: Ishiguro Saburo
Published: January 2005

This paper reviews industries using arsenic and arsenic compounds such as wood preservatives and agricultural chemicals, the use of arsenic trioxide in glass manufacture, and the applications of metallic arsenic in non‐ferrous alloys and of high‐purity arsenic in the electronics industry.
Ethylalumoxanes and ethylchloroalumoxanes as components of catalyst for propylene polymerization
Authors: Pasynkiewicz S , Mańk B
Published: January 2005

Ethylalumoxanes and ethylchloroalumoxanes as components of Ziegler‐Natta catalysts for polymerization of propylene have been studied. The influence of the degree of hydrolysis of triethyl aluminium [(Et3Al) and diethylaluminium chlorilp (Et2AlCl)2] in the range 0.5–1.5:1 on the activity and the stereospecificity of the catalytic systems was determined (the degree of hydrolysis is defined as the molar ratio H2O/organoaluminium compound). It was found that the activity of the catalytic system ethylalumoxane‐ TiCl4 is a little higher than the activity of the Et2AlCl‐TiCl4 system. The ethylchloroalumoxane‐TiCl4 system is about six times more active than the classical Ziegler‐Natta system. Our studies showed that alumoxanes react with TiCl4 as follows: (a) to form compounds of the AlOTiCl3 type; (b) to exchange alkyl groups for chlorine; (c) to form donor‐acceptor complexes. Reactions of types (b) and (c) occur mainly in the cases of alumoxanes of low degree of hydrolysis (0.5–0.7). In cases of alumoxanes of a degree of hydrolysis equal to 0.7–1.0, reactions of all three types occur, and for alumoxanes of degree of hydrolysis >1.0 reactions of types (a) and (c) are preferred.
Determination of arsenic species by inductively coupled plasma mass spectrometry with ion chromatography
Authors: Kawabata Katsuhiko , Inoue Yoshinori , Takahashi Hiromitsu , Endo Ginji
Published: January 2005

Five arsenic species, trimethylarsine oxide, dimethylarsenic acid, monomethylarsonic acid, arsenobetaine and sodium arsenite, in urine were analysed by inductively coupled plasma mass spectrometry with ion chromatography (IC ICP MS).

Since the toxicities of different arsenic compounds are different, speciation of arsenic compounds is very important in the investigation of metabolisms. In this paper, we applied ion chromatography (IC) as a separation device and inductively coupled plasma mass spectrometry (ICP MS) as a detection device. For separation of the five arsenic compounds, an anion‐exchange column and, as mobile phase, tartaric acid were used. The eluent from the IC column was introduced directly into the nebulizer of the ICP MS and analysed at 75 amu. Detection limits were from 4 to 9 pg as arsenic.
Butyltin compounds in severn sound, lake huron, canada
Authors: Wong P. T. S. , Whittle D. M. , Chau Y. K. , Brown M.
Published: January 2005

Severn Sound is a heavily used recreational and beating area in the southeast corner of Georgian Bay, Lake Huron, Canada. Because of the concern over the possible release of tributyltin species (TBT) from antifouling paints on boat hulls and marinas, surveys were carried out in 1989 and 1992 to determine the presence of this species and its degradation products dibutyltin (DBT) and monobutyltin (MBT) in this area. Many fish (pike and young–of–the–year spottail shiners) and sediment samples collected in 1989 contained detectable levels of TBT. A maximum concentration of TBT was recorded in northern pike in the spring to be 240 ng Sn g−1. Maximum levels occurred in marinas during the beginning of the boating season and significantly reduced during the summer and early autumn, although the maximum value of TBT in sediment (392 ng Sn g−1) was observed in the summer of 1989. The seasonal variation of TBT levels was further substantiated in the subsequent 1992 study, in which sediments from three areas in a marina were sampled at monthly intervals from May to October. TBT levels were much higher in May and then generally decreased with time. Mussels (Elliptio complanta) caged in the marina for three months also contained TBT. DBT was frequently detected in the sediments but less frequently in fish and mussels. MBT was generally below detection limits. Plants (macrophytes and cladophora) contained very small amounts of butyltin compounds.
Ion—Molecule reactions of environmentally significant organotin compounds in a triple quadrupole mass spectrometer system
Authors: Lawson Graham , Ostah Naaman
Published: January 2005

Tandem MS techniques have been used to examine the formation of cluster ions derived from organotin compounds of environmental significance. The cluster formation was based on the addition of either water or methanol molecules (common HPLC solvents) to a cationic species derived from the organotin compound. For the compounds and conditions studied, cluster adducts were only observed from trisubstituted tin cations. The results show that, in high‐pressure ionization methods used in the interface between HPLC and MS, the tin atom may be associated with a range of ions depending on the system parameters, and that care should be taken if selection ion monitoring (SIM) is to be used.
Stability of alkyl‐lead compounds in blood
Authors: Nygren Olle
Published: January 2005

In order to investigate occupational exposure to various chemicals, blood samples from exposed subjects may be used. Such samples are usually collected locally for transport to an analytical laboratory. It is therefore essential that the necessary transport is performed under such conditions that an adequate stability of the analytes in the samples is maintained. The stability of trimethyl‐ and dimethyl‐lead species in blood at various storage temperatures, as well as the insulation capacity of different transport packages for blood samples, were determined. The results showed that alkyl‐lead compounds in spiked blood stored at room temperature were stable for 6 h and in a refrigerator for up to one week. Only in spiked blood stored at −20°C were the alkyl‐lead compounds found to be stable for more than one month. Blood samples from exposed subjects stored at −20°C were found to be stable for at least two months. One transport package used, found to maintain this temperature of prefrozen samples for up to two days, was a polystyrene transport box filled with crushed dry ice. This packing procedure is therefore recommended for transport of blood samples collected for evaluation of occupational exposure to alkyl‐lead compounds.
Experiences with the analytical procedures for the determination of methylmercury in environmental samples
Authors: Lee Ying‐Hua , Munthe John , Iverfeldt ÅKe
Published: January 2005

The analytical method using ethylation, gas chromatography–cold vapor atomic fluorescence spectroscopy (GC–CV AFS), combined with different pretreatment procedures, has been used for the determination of methylmercury (MeHg) in various aqueous and solid environmental samples. Different types of samples with varying matrices and MeHg concentration levels require different pretreatment procedures in order to isolate/separate MeHg from the sample matrix, and to overcome interferences in the ethylation reaction process. Limitations of different pretreatment procedures (solvent extraction into methylene chloride, distillation under nitrogen flow and alkaline digestion) are discussed and recommendations are given. The influence of the quality of the ethylating reagent on the analytical results is also examined.
Interlaboratory study for the quality control of trimethyl‐lead determination in simulated rainwater and urban dust
Authors: Quevauviller Ph. , Wang Y. , Harrison R. M.
Published: January 2005

An interlaboratory programme has been started within the Measurements and Testing Programme (formerly BCR) of the European Commission to evaluate the performance of analytical techniques used for the determination of trimethyl‐lead in simulated rainwater and urban dust. A first interlaboratory study on solutions was successfully concluded in 1993 and a second exercise was organized, focusing on simulated rainwater and urban dust analysis. This paper reports the results of this second interlaboratory study, which is a preparatory step for a certification campaign of simulated rainwater (with representative contamination levels) and urban dust.
Anti‐Osteoporotic activity of metal complexes of amine carboxyboranes
Authors: Rajendran K. G. , Sood A. , Spielvogel B. F. , Hall I. H. , Norwood V. M. , Morse K. W.
Published: January 2005

Metal complexes of trimethylamine carboxyborane successfully suppressed calcium flux from both paired pup calvaria bones and rat UMR‐106 osteosarcoma cultured cells over a 48 h period. These agents increased uptake of calcium into the cell cultures and accelerated [3H]proline incorporation into collagen. Copper and iron complexes of the trimethylamine carboxyborane were more potent compared with the cobalt and chromium complexes. The agents effectively reduced Iysosomal enzyme activity and also proteolytic enzyme activities of macrophages. Since macrophages invade the bone surface and assist in the demineralization and digestion of collagen, those agents may be potentially useful to retard diseases involving bone reconstruction. Influx of white blood cells and macrophages to sites of degradation most probably would be inhibited by the agents, based on sponge test observations in mice. Osteoporosis induced by ovariectomy was minimized by injections of tetrakis[u‐(trimethylamine‐boranecarboxylato)‐bis(trimethylamine‐carboxyborane)dicopper(II)] into rats at 3.5 mg kg−1 day−1 for 14 days. Bone volume, density, weight and calcium content returned to normal baseline control values. In addition, the copper complex returned serum calcium, serum parathyroid hormone (PTH) and vitamin D3 values to normal levels. One possible mode of action of these derivatives is the regulation of the production and release of chemical mediators initiating bone loss, e.g. tumor necrosis factor, TNF α and interleukins 11 or 11‐2.
Negative ion mass spectrometry of organotin compounds—an aid to environmental monitoring?
Authors: Dahm Ralf H. , Lawson Graham , Ostah Naaman
Published: January 2005

Positive‐ion mass spectra of organotin compounds include a large number of different ions and therefore the absolute detection level is reduced. Negative‐ion mass spectra are usually less complex and detection levels may therefore be improved. The negative‐ion mass spectra of selected organotin compounds of the type R4Sn, R3SnCI, R2SnCI2 and RSnCl3 were investigated using conventional electron impact ionization conditions. Simplified mass spectra, suitable for compound speciation, were obtained for R3SnCI2 and R2SnCI2 materials but the same fragmentation product SnCI was obtained from all the RSnCI3 samples. R4Sn compounds produced no negative‐ion data in these studies. No significant gains in detection levels were noted but some interesting re‐arrangement reactions leading to the formation of compounds consisting of substituents from the original tin atom were identified. These reactions may be of synthetic importance.
Specific cation effects on the conformation of α‐poly‐L‐glutamic acid
Authors: Jacobson A. L.
Published: December 2004

The effect of the binding of the alkaline earth cations and of cupric and lanthanum ions on the dissociation of the sidechain carboxyl groups in α‐poly‐L‐glutamic acid has been measured by a modified titration technique. The α‐poly‐L‐glutamic acid was pretitrated with the strong base of a weakly bound counterion followed by addition of aliquots of the neutral salt, solution of the more strongly bound counterions. The changes in the ionization of the sidechain carboxyl groups were measured as a function of degree of poly acid pretitrated and the concentration of added salt. These changes were related to the helix‐coil transition in α‐poly‐L‐glutamic acid as a function of degree of ionization. pH titration data were used to delineate the helix, helix‐coil, and pure coil regions in α‐poly‐L‐glutamic acid.

For the alkaline earth cations, the binding strength in the helical region is calcium > strontium > magnesium > barium. The more strongly bound cations produced much larger poly acid dissociation with the binding strength alkaline earths ≪ cupric < lanthanum at equivalent ionic strength. All results indicated that the helix conformation promoted ion binding. The binding of the alkaline earth cations in the random coil form was similar to that reported with other coiled polyelectrolytes. The cupric and lanthanum ions appeared to stabilize the helical structure against changes due to increased poly‐acid ionization.
Light‐scattering molecular weight of rabbit myosin A
Authors: Tomimatsu Yoshio
Published: December 2004

Proper correction of angular light‐scattering data for reflection effects results in agreement between determinations by light scattering and by sedimentation equilibrium of the molecular weight of rabbit myosin A prepared in the same manner. This leaves the question of molecular weight dependence on the method of sample preparation unsettled. Reflection corrections for angular light‐scattering measurements by the more exact Tomimatsu–Palmer (T–P) method are compared to those by the less adequate Sheffer–Hyde (S–H) method.
Reconstruction of protein and nucleic acid sequences. I. Systematics and computer program
Authors: Bradley Dan F. , Merril Carl R. , Shapiro Marvin B.
Published: December 2004

The protein sequences now known have been reconstructed as a kind of intriguing logical‐mathematical puzzle using information about fragments of the molecules. We wish to show that the reconstruction can be done systematically by repeating a series of elementary operations on these same data governed by a set of well‐defined rules. The completely automatic reconstruction of polymer sequences by a high speed digital computer using these operations and rules is demonstrated.
Statistical mechanics of noncovalent bonds in polyamino acids. VIII. Covalent loops in proteins
Authors: Poland Douglas C. , Scheraga Harold A.
Published: December 2004

The effect of covalently crosslinked loops on the entropy of polypeptide chains is discussed. Since the available theory applies to single, independent loops, this theory has been extended to cases where the chains are multiply crosslinked and, therefore, dependent. Multiply crosslinked loops are present in many proteins, e.g., ribonuclease. It is shown that, whereas in general there is a significant difference between the entropy computed with the present treatment of dependent chains and that incorrectly computed by applying the theory of independent chains to multiply crosslinked loops, the difference in the two procedures is not very great for ribonuclease (and well within the uncertainty of our knowledge of the residue conformational entropy) because the chains of ribonuclease are only slightly dependent even though they are multiply crosslinked. Specifically, estimates of the entropy losses per residue are: −0.45 e.u. for chains in a single, independent loop, −0.58 to −0.66 e.u. for dependent chains in multiply crosslinked loops, and −0.51 e.u. for a simplified model of ribonuclease. With this information, a treatment is given of a helix–coil transition in two chains, assumed to be polyglycine, connected at each end by disulfide bonds. The results of a previous theory for short chains are combined here with the results for the entropy loss on loop formation. It is seen that the presence of the loop stabilizes the helical forms (because of the lowering of the entropy of the random state) and broadens the transition (because of the increased importance of intermediate states).
Complexes of silver ion with natural and synthetic polynucleotides
Authors: Daune M. , Dekker C. A. , Schachman H. K.
Published: December 2004

A study of silver‐ion binding by nucleic acids and synthetic ribo and deoxyribopolynucleotides, has been carried out by means of potentiometric titration, thermal transition, and difference spectra. It is clearly demonstrated that a strong complex between Ag+ and nitrogen atoms of bases is made reversibly. Binding constants and site numbers are determined for each type of polynucleotide. Base reactivity varies strongly with chain length, and a cooperative phenomenon is found in each case. Two successive complexes with DNA are seen in all the three techniques, and they have the same characteristics as complexes with respectively poly‐dGC and poly dAT. In the first complex, Ag+ is linked to four bases, provided two of them are a G‐C pair. Calculated and experimental values of site numbers agree very well for DNA of different G‐C content. Thermal stabilization occurs simultaneously, and the increase of melting temperature corresponds to calculated changes of stacking energy between base pairs. In the second complex a new ordered structure insensitive to temperature is formed, with simultaneous release of protons. The stoichiometry can be related to base sequence. Complexing with silver increases the resistance of TMV RNA to both temperature and ribonuclease; a tentative explanation is given in the latter case.
Polynucleotide synthesis at oligomeric templates
Authors: Volkenstein M. V. , Fishman S. N.
Published: December 2004

The theory of kinetics of polynucleotide synthesis at oligomeric templates is developed. It is shown that the dependence of oligomer efficacy on its size cannot be explained without taking into account the probability of separation of the oligomer from the growing chain. If such a possibility exists, the maximal size which can be achieved by the growing chain is determined by the ratio of the probability of proposed propagation and of the probability of separation. Without any models of the separation mechanism, the study of experimental kinetic data shows that two such mechanisms exist. Very short oligomers can be easily separated from the growing chain, but there is a critical size of oligomer after which the probability of separation is much smaller. The oligomers whose size is equal to or greater than the critical one form helices with growing chains.
Electronic spectrum, optical activity, and structure of the acridine orange complex with poly‐α,L‐glutamic acid
Authors: Ballard R. E. , McCaffery A. J. , Mason S. F.
Published: December 2004

The electronic absorption and circular dichroism spectra of the complex formed by acridine orange with poly‐α,L‐glutamic acid in the α‐helix conformation have been measured in aqueous solution over a range of glutamate residue‐to‐dye ratios. Three Cotton effects (circular dichroism bands) associated with the long wavelength absorption band of acridine orange at 4950 A. are induced by complex formation between the dye and the polypeptide, and further circular dichroism bands are observed in the ultraviolet region associated with the 2700 A., but not with the 2950 A. absorption band of the dye. The induced optical activity is found to be relatively insensitive to the glutamate residue‐to‐dye ratio and to be more dependent upon the ionic strength of the solution. By Measuring the circular dichroism spectrum of the complex in aqueous solution under streaming conditions with the light propagated along the direction of flow the observed circular dichroism bands are assigned to electronic transitions polarized parallel or perpendicular to the axis of the polypeptide α‐helix. From the spectroscopic data it is inferred that the dye aggregate in the L‐PGA–AO complex has the form of a left‐handed superhelix bound to the core of the right‐handed α‐helix of poly‐α,L‐glutamic acid. It is shown that the longer and the shorter of the in‐plane axes of the dye molecule are probably orientated respectively at a small angle, and radially, with respect to the axis of the α‐helix in the complex.
Protonation of cytosine in DNA
Authors: Zimmer Ch. , Venner H.
Published: December 2004

Spectrophotometric acid titrations of DNA samples of different GC content were performed at different wavelengths. From the acid titration profile and absorbance changes of deoxycytidine‐5′‐monophosphate and DNA the extent of protonated cytosine within the DNA double‐stranded molecule was estimated (pK 3.65 at 25°C. in 0.02M KCl). At constant counterion concentration and temperature the maximum of protonated cytosine in DNA before denaturation occurs depends on the base composition and can exceed 50%. The thermal stability of the DNA secondary structure is strongly reduced with increasing amount of ionized cytosine residues. The degree of protonation of cytosine in DNA is decreased with increasing counterion concentration.
Conformations and interactions of excited stales. I. Model compounds for polymers
Authors: Longworth J. W. , Bovey F. A.
Published: December 2004

From observations on model compounds having two or more benzene rings and structures analogous to high polymers of interest (polystyrene and aromatic polypeptides), we conclude that interactions of pairs of benzene rings sufficiently strong to cause observable excimer emission requires that these rings be separated by no more than 2–3 A. and that they be in an approximately parallel‐stacked, face‐to‐face arrangement. If a molecule does not have such a configuration of its aromatic rings in its ground‐state conformation, strong excimer emission can still occur provided there is a conformation with the appropriate ring configuration which can be attained within the radiative lifetime of the excited state.
Temperature‐dependent properties of dinucleoside phosphates
Authors: Davis Robert C. , Tinoco Ignacio
Published: December 2004

The optical rotatory dispersion, hypochromism, and proton magnetic resonance were measured for a number of dinucleoside phosphates in both dilute salt solutions and in 25.2% LiCl (which freezes below −70°C.) as a function of temperature. Two models for the “disordering” of dinucleoside phosphates: the two‐state model and the oscillating dimer model, are used to analyze the data. Both models fit some of the data, but neither are completely satisfactory. Evidence is given for a dynamic structure of dinucleoside phosphates, in which the bases oscillate with respect to one another, remaining parallel to one another with no solvent in between, even at high temperatures. Implications of this model to the structures of single‐strand sections of RNA's are discussed.
Low temperature infrared spectra of polyglycines and C—H …︁ OC hydrogen bonding in polyglycine II
Authors: Krimm S. , Kuroiwa K.
Published: December 2004

Infrared spectra of polyglycines I and II obtained at −170°C. have been compared with those obtained at room temperature. The changes in frequency of some of the C—H stretching bands are consistent with the earlier suggestion that C—H …︁ OC hydrogen bonds are present in the structure of polyglycine II.
Temperature dependence of the hydrogen ion equilibria in poly(riboadenylic acid)
Authors: Holcomb D. N. , Timasheff Serge N.
Published: December 2004

Hydrogen ion titration curves have been obtained for poly (riboadenylic acid) (poly A) at temperatures of 0–40°C, and ionic strengths of 0.001, 0.01, and 0.15. Where comparable, the data are in general agreement with those previously reported by other investigators. Correlations between the titration data and thermal denaturation curves have been obtained. Formation of a two‐stranded helix is catalyzed by the uptake of protons by the adenine base. Partial protonation of the base is required for formation of the two‐stranded helix, but under appropriate conditions it is stable at degrees of ionization less than 0.2. The degree of ionization required for formation of the two‐stranded helix increases with temperature and decreases with ionic strength.
Molecular weight of T7 and calf thymus DNA by low‐angle light scattering
Authors: Harpst J. A. , Krasna Alvin I. , Zimm B. H.
Published: December 2004

A low‐angle light‐scattering instrument has been used to measure molecular weights of native calf‐thymus and T7 DNA. Molecular weights obtained by extrapolation of angular data to 0° from measurements above 30° are less than molecular weights from extrapolation of data taken at low angles (below 30°). The low‐angle molecular weights determined for calf‐thymus DNA and for T7 DNA agree well with estimates of weight‐average molecular weight obtained with other techniques. The low‐angle light‐scattering molecular weight for calf‐thymus DNA is higher than previously reported values by light scattering at angles above 30°. A concentration dependence in the scattering from DNA solutions is also observed.
The ultrasonic degradation of biological macromolecules under conditions of stable cavitation. II. Degradation of deoxyribonucleic acid
Authors: Peacocke A. R. , Pritchard N. J.
Published: December 2004

Solutions of T7 bacteriophage or calf thymus DNA arc degraded in solution by ultrasonic fields of low intensity in the presence of vibrating air bubbles but are not degraded at these low intensities when such bubbles are absent. Evidence is presented for the hydrodynamic nature of the observed degradation and theoretical simulation of a plausible degradation mechanism is compared with experimental degradation studies. It is concluded that degradation of such linear macromolecules as DNA may occur as a result of stresses induced in the macromolecule; these stresses are the result of a relative movement of solvent molecules and the macromolecules in the time‐independent flow of solvent near the vibrating bubbles.
Conformational studies of polymers and copolymers of L‐aspartate esters. I. Preparation and solution studies
Authors: Bradbury E. M. , Carpenter B. G. , Goldman H.
Published: December 2004

An alcoholysis method is described for the modification of high molecular weight poly(β‐benzyl L‐asparatate); by this method the benzyl groups in the polypeptide have been replaced by methyl, ethyl, isopropyl, n‐propyl, and phenethyl groups to give a series of copolymers of each of the corresponding aspartate esters with benzyl L‐aspartate. By repeating the reactions, replacement of better than 99% has been achieved in some cases to give in effect the homopolymer. Optical rotatory dispersion studies show that of all the systems studied only poly(β‐methyl L‐aspartate) has the left‐handed helix sense, the others are right‐handed. It is shown further that the helix sense is not an intrinsic property of the nature of the aspartate side chain. Raising the temperature of chloroform solutions of the right‐handed form of the copolymers of benzyl L‐aspartate and ethyl L‐aspartate results in a transition to the left‐handed helix, the temperature of the transition being dependent on the composition of the copolymer. Also poly(β‐n‐propyl L‐aspartate) undergoes a transition from the right‐ to the left‐handed helix form at 59°C. These results suggest a general pattern of behavior of poly(aspartate esters) and that with suitable conditions of solvent and temperature they may be in either the right‐ or left‐handed helical form.
Conformations of poly‐L‐valine in solution
Authors: Epand Raquel F. , Scheraga Harold A.
Published: December 2004

In order to test theoretical predictions that poly‐L‐valine can exist in an α‐helical conformation, water‐soluble block copolymers of L‐valine and D, L‐lysine were prepared. By carrying out the synthesis on a resin support (with the use of N‐carboxyanhydrides) contamination of the individual blocks by any unreacted monomer from the previous block was avoided. A single glycine residue was incorporated at the C‐terminus of the chain for use in amino acid analyses. Using optical rotatory dispersion and circular dichroism criteria, about 50% of the short valine block of (D, L‐lysine HCl)18‐(L‐valine)15‐(D, L‐lysine‐HCl)16‐glycine was found to be in the right‐handed α‐helical conformation in 98% aqueous methanol, in water, the polymer appears to be a dimer, with the valine block being involved in the formation of an intermolecular β‐structure.
Interaction of heat‐denatured HeLa cell DNA with synthetic and natural polysaccharides
Authors: Graves I. L.
Published: December 2004

Heat‐denatured DNA from HeLa cells interacts with natural as well as synthetic polysaccharides. Glucose does not inhibit the interaction nor will it produce it. Polysaccharides with a molecular weight of 10000 or greater are required before the interaction takes place.
Ultraviolet dichroic ratio of DNA from T2 and T5 bacteriophages
Authors: Gray Donald M. , Rubenstein Irwin
Published: December 2004

The dichroic ratios of T5st‐O and T2H bacteriophage DNA molecules were measured throughout the ultraviolet region of the spectrum. Two methods of DNA orientation were studied: (1) orientation in solution in a Shimadzu flow dichroism instrument attached to a Beckman DU spectrophotometer, and (2) alcohol precipitation of the DNA from solution and orientation in a thin film on the quartz face of a humidity chamber. Spectra in the latter case were recorded using a Gary Model 14 spectrophotomcter fitted with Glan prisms. The lower wavelength limit was 215 mμ in both systems. The DNA preparations were carefully characterized as to spectral purity, sedimentation coefficient, hyperchromicity, protein content, and DNA content. In addition, the structure of the DNA oriented in films was inferred from x‐ray diffraction patterns of fibers of the precipitated DXA. The A and B configurations of DNA in films could not be distinguished by the dichroic ratio measuiements. The dichroic ratio obtained for the film‐oriented DNA at high relative humidity shows the same wavelength dependence as for the flow‐oriented DNA. The same wavelength dependence for DNA in the fibrous state and in solution, when considered together with the x‐ray diffract ion results, indicates that DNA in solution maintains an orientation of bases which is similar to that in fibers. I1Or both solutions and films of DNA, the dichroic ratio is constant from 290mμ to 240 mμ and increases at wavelengths below 240 mμ. The increased parallel absorption below 240 mμ is consistent with the existence of an n→π* transition. The inherent molecular dichroic ratio is found to be the same for T5st‐O DNA and T2H DNA in solution, and is a maximum of 0.09 ± 0.02 at 260 mμ.
Conformational changes in histone IV
Authors: Li H. J. , Wickett R. , Craig A. Morrie , Isenberg I.
Published: December 2004

Conformational change of histone IV, induced by phosphate, have been investigated by observing the intrinsic fluorescence of tyrosine residues and circular dichroism (CD). There is a fast conformational change upon the addition of phosphate, followed by a slow process with time constants in the range of minutes to hours depending upon both the phosphate and histone concentrations. The CD results indicate α‐helix formation in the fast process, and β‐sheet formation in the slow one, although other secondary and tertiary structural changes also may occur. The histone concentration dependence of the fast process is consistent with dimerization. Divalent phosphate is about ten times more effective than monovalent phosphate in inducing conformational changes. All of the changes are reversible.
Lysine oligopeptides. Preparation by ion‐exchange chromatography
Authors: Yaron A. , Otey M. C. , Sober H. A. , Katchalski E. , Ehrlich‐Rogozinski S. , Berger A.
Published: December 2004

The preparation of L‐lysine peptides (Lysn, n = 2–14) from polyL‐lysine is described. Fractionation by ion‐exchange column chromatography of poly‐L‐lysine hydrolysates on a preparative scale resulted in 0.2–1.0 g quantities of individual members of the poly‐L‐lysine series. The peptides isolated proved to be analytically pure and the optical configuration was fully retained, as demonstrated by complete enzymic digestion. Peptides higher than n = 14 were also prepared. They consisted of oligolysine groups of narrow and accurately determined size distribution. Potentiometric titrations were used both to characterize the products and to demonstrate the characteristic dependence of the dissociation constants on size of the peptide.
Proof of the charging of polypeptides and polyamides in organic acids
Authors: Bradbury J. H. , Yuan H. H. H.
Published: December 2004

The electrophoresis of poly‐γ‐benzyl‐L‐glutamate (PBLG), poly‐L‐alanine (PLA) and nylon dissolved in various solvents was studied in a glass cell containing three sintered glass partitions. After the passage of a measured amount of charge the concentration of PBLG remained constant in all four chambers when the helicogenic solvents dimethylformamide and ethylene dichloride were used, but in mixtures of ethylene dichloride and dichloroacetic acid and in trifluoroacetic acid, polypeptide migrated to the cathode. Electrophoresis also occurred with PLA in trifluoroacetic acid and with nylon in formic acid. Although the total charge on the polyion could not be determined, the results show beyond reasonable doubt that polypeptides and polyamides are protonated in the presence of moderately strong organic acids.
Small‐angle x‐ray scattering by poly‐L‐alanine solutions
Authors: Brumberger H. , Anderson L. C.
Published: December 2004

The radius of gyration and “persistence length” of poly‐L‐alanine, calculated from small‐angle x‐ray scattering data, have values of 56 Å and 44 Å, respectively, in dichloroacetic acid, and 78 Å and ∼30 Å in a 1:1 v/v mixture of trifluoroacetic acid and trifluoroethanol. This can be interpreted to mean that poly‐L‐alanine exists in a relatively rigid, predominantly α‐helical conformation in dichloroacetic acid and in an extended, more flexible form in the mixed solvent system.
A Calorimetric Investigation of the Heats of Binding of Mg++ to Poly A, to Poly U, and to Their Complexes
Authors: Krakauer H.
Published: December 2004

The heats of binding of Mg++ ions to poly A, poly U, and to their complexes, in the presence of Na+ ions, have been measurd calorimetrically. In all cases the heat, ΔH(θ), exhibitis a distinct dependence on the extent of binding, θ, and in the cases of poly A and poly U also on the Na+ concentration. The values of ΔH(θ) range from +2 to +3 kcal/mole of Mg++ bound at θ = 0 to 1.3 kcal/mole at θ = 0.5 except in poly A where at θ = 0 ΔH(θ) = −2 to −3 kcal/mole. This is interpreted as being due to a facilitation of base stacking by the binding of Mg++. The extent of facilitation is consistent with current estimates of base stacking. A similar effect but of much smaller magnitude is believed to obtain in poly A poly U. An interpretation of the dependence of ΔH(θ) on θ in terms of simple electrostatic interactions, but neglecting solvent effects, was attempted and found to be inadequate.
The ultraviolet circular dichroism of some natural DNAs and an analysis of the spectra for sequence information
Authors: Allen F. S. , Gray Donald M. , Roberts Gary P. , Tinoco Ignacio
Published: December 2004

The circular dichroism spectra of many natural DNAs and double‐stranded synthetic polynucleotides were obtained. The eight first‐neighbor contributions to the CD spectra of a DNA have been extracted from these data. Therefore, the CD spectrum for any DNA with known first‐neighbor frequencies may be easily calculated. For a natural DNA the CD spectrum may be approximated by assuming the first‐neighbor frequencies have the most probable values consistent with the base composition. Under favorable conditions, the measured CD spectrum can be used to determine thirteen of the sixteen first‐neighbor frequencies of a DNA to ± 0.02 mole percent. The TG, CA, and TA first‐neighbor cannot be unambiguously resolved by our method. The accuracy of the first‐neighbor frequency analysis depends on the number of different first‐neighbors present in the DNA and the extent to which they differ from the most probable value.

The extinction coefficient at 260 nm and the base composition can also be calculated from the CD spectrum.
On the Application of Polyelectrolyte “Limiting Laws” to the Helix‐Coil Transition of DNA. II. The Effect of Mg++ Counterions
Authors: Manning Gerald S.
Published: December 2004

The techniques of the previous article are here applied to the case for which the solution contains, in addition to excess uni–univalent salt, one equivalent of divalent counterions per mole nucleotide. In agreement with the melting temperature measurements of Dove and Davidson for Mg++, it is predicted that a region of uni–univalent salt concentration then exists in which (dT m/d log m A+) is negative. It is further predicted, in accord with experiment, that in the presence of divalent counterions, the helical form of DNA is much more stable than in their absence.
The action of hemoglobin. Cooperative effects in tetrameric proteins
Authors: Saroff H. A. , Yap W. T.
Published: December 2004

The cooperative effect is developed for proteins containing four subunits. The extension of the primitive Adair model is considered and the present models based on this extension are compared.
Optical properties and base pairing of E. coil 5S RNA
Authors: Richards E. G. , Geroch M. E. , Simpkins H. , Lecanidou R.
Published: December 2004

The ultraviolet absorption, optical rotatory dispersion, circular dichroism, and infrared absorption spectra of renatured 5S RNA have been measured at pH 7.0 in 0.1M NaCl at 25° and used to obtain four independent estimates of the number of base pairs. These four estimations are in reaonable agreement and average values of 28 ± 4 G.C and 13 ± 4 A.U. base pairs.
Optical activity of polypeptides and proteins
Authors: Madison Vincent , Schellman John
Published: December 2004

Using methods described in a previous publication the optical activity of a number of polypeptides and proteins has been calculated. The systems included the α‐helix, the two β‐structures, polyproline I, polyproline II, collagen and collagen models, and poly‐N‐methylalanine. In addition to these orderded structures, calculations were also performed on the α, β and nonperiodic regions of myoglobin, lysozyme, ribonuclease‐S and β‐chymotrypsin. The α and β structures in prteins differ from the polypeptide models by being very short and partially disordered. It is concluded that the 222‐nm band of the α‐helix is a good method for detecting helices in proteins but that the 207‐and 191‐nm bands of the helix will not fit a linear superposition model. The circular dichroism of the so‐called β regions of proteins differs markedly from that for ideal β structure because of breakdownin symmetry. As a result estimates of β‐structure in proteins based on polypeptide models are not likely to be quantitative.

The theoretical methods give an adequate account of the optical activity of all the ordered polypeptides except polyproline II and collagen and (by inference) the nonperiodic chains in the various proteins. This difficulty is the remaining barrier to a complete theory of the optical activity of the polypeptide backbone in globular proteins.
Electro‐optic decay analysis for polydisperse systems
Authors: Schweitzer J. , Jennings B. R.
Published: December 2004

The decay curves of electro‐optic transients are generally used to measure the rotary diffusion contants (D) of colloidal particles in suspension or biopolymers in solution. Analysis usually is made by plotting the logarithm of the decay as a function of time, t. Curvature in such plots the presence of several values of D and hence a distribution of particle sizes. In this case, analysis of the complete curve to yield the distribution is severely restricted by lack of precision in the experimental data. The most reliable and reproducible part of the decay curve is the initial (t =0)slope.

This paper develops theory for the initial slope for dilute suspensions of long thin cylinders with various electrical properties. It is shown that the inital slope depends not only on the particle‐size distribution and electric field strength, but also on the nature of the electrical properties of the molecules. Futhermore, for an identical polydisperse system. transient electric birefringence, electric optical rotation, and electric dichroism on the one hand, and transient electric light scattering on the other, yield different initial slopes and hence apperently different values for D. These important conclusions have not been appereciated in previous studies and indicate the need for caution when comparing data from different experimental methods. I11ustrative calculations are presented for a polydisperse system of long thin cylinders having a normal distribution in lengths, but of uniform diameter. Some preliminary measurement support the theory.
Synthesis and conformational study of poly(Nϵ‐benzyl‐L‐lysine) and its benzyloxycarbonyl derivative
Authors: Yamamoto Hiroyuki , Hayakawa Tadao
Published: December 2004

The solvent‐and pH‐induced conformational changes are examined in order to investigate the influence of benzyl group. Polymer was prepared via Nϵ‐benzyloxycarbonyl, Nϵ‐benzyl‐Nα‐carboxy‐L‐lysine anhydride. The resulting poly (Nϵ‐benzyloxycarbonyl, Nϵ‐benzyl‐L‐lysine) was obtained in high yield and had a high molecular weight. The protected polymer was removed into poly (Nϵ‐benzyl‐L‐lysine) by treating it with hydrogen bromide. From the results of the ORD and CD, the protected polymer has a righthanded α‐helix, showing [m′]233 = –10,300, [θ]220 = –27,600 and [θ]207 = –25,100 in dioxane. The breakdown of the helical conformation is found to occur at 8% dichloroacetic acid in chloroform‐dichloroacetic acid mixture. In the pH range 3.35–6.90, poly (Nϵ‐benzyl‐L‐lysine) is in a random coil structure. In the pH range 7.50–13.0, the polypeptide has a right‐handed α‐helix structure; [m′]233 = –12,000, [0]220 = –27,200, and [0]207 = –27,000. In comparison with poly‐L‐lysine, the coil‐to‐helix transition is observed at lower pH range in 50% n‐propanol. Above pH 8 by heating, the α ⇀ β transition of poly (Nϵ‐benzyl‐L‐lysine) is not observed in an aqueous media.
Phase relationships of an equivalent mixture of sulfated polyvinyl alcohol and aminoacetalyzed polyvinyl alcohol in microsalt aqueous solution
Authors: Nakajima Akio , Sato Hiroko
Published: December 2004

A new type of polymer salt was prepared from an equivalent mixture of partly sulfated polyvinyl alcohol (polyanion, Q−) and partly aminoacetalyzed polyvinyl alcohol (polycation, P+). With respect to a three‐component system composed of this polymer salt (P+Q−), water, and a microsalt (K+A−), phase relationships, as represented by complex coacervation, were investigated. Experimental results were discussed according to a theoretical equation for the free energy of mixing derived by taking into account the entropy and enthalpy contributions as ascribed for non‐ionic polymer solution, and the electrostatic free energy expression as derived by Voorn.
Conformational studies of α‐glucans
Authors: Sathyanarayana B. K. , Rao V. S. R.
Published: December 2004

A study of the effect of linkage on the possible conformations of di‐and polysaccharides of α‐D‐glucose and also the probable intramolecular hydrogen bonds has been made. The differences in the nature of linkage is shown to effect the energetically preferred conformations; (1 → 2) linkages lead only to righthanded helical conformations, (1 → 3) linkages lead to extended as well as both left and righthanded helical conformations; (1 → 4) linkages lead to both right‐and lefthanded wide helical conformations. The possible hydrogen bonds between adjacent residues are also dependent on the nature of the linkage. A comparison of the conformational data of α‐D‐glucans with those of β‐D‐glucans has indicated that the favored conformations and hydrogen bonds between contiguous residues in the chain are influenced by the configuration at the anomeric carbon atom in all the three types of polysaccharides. From the energy calculations a probable conformation (ϕM = −10°, ψM = −30°, ϕN = −23°, ψN = −19°) has also been proposed for crystalline mycodextran in conformity with x‐ray data. This conformation contains two types of hydrogen bonds between contiguous residues one between 0–2 and 0–3 atoms at (1 → 4) linkage and the other between 0−2 and 0–4 atoms at (1 → 3) linkage in the chain. The conformation of maltose unit (−10°,−30°) that is likely to occur in the crystalline mycodextran coincides with the minimum energy conformation of maltose.
Cooperative nonenzymic base recognition—a study of interaction of oligoguanylic acid with poly C
Authors: Podder S. K.
Published: December 2004

The interaction between poly C and (Gp)nG(n = 1,2) in dilute solution was investigated spectrophotometrically in 0.1M phosphate buffer pH 7.2 under conditions unfavorable for the formation of self‐associated complexes of oligoguanylic acids. Two isosbestic points were observed when poly C was titrated gradually with GpGpG, one at 232–233 mμ(in the range of 0–33% poly C) and one around 238 mμ (in the range of 50–100% poly C). The melting temperature (Tm) of the 1:1 poly C: (Gp)nG complexes (n = 1,2) of varying concentration were determined. The equilibrium properties of the 1:1 complexes can be described by two interaction parameters, namely, (i) cooperative stacking interaction between the first nearest neighbor of the adsorbed oligomer, and (ii) intrinsic association constant of the adsorbed oligomer with its polymeric site, since the cooperative helix–coil transition particularly in the smaller oligonucleotide can be described by an “all or none” model. Based on such a model the enthalpy of stacking inteaction‐dependent Tm values yielded directly the sum of the enthalpy of stacking interaction and of basepairing (which is dependent on the chain length of the oligomer) and the value of S, the stability constant of a G–C pair within a helix. The enthalpy of formation of G–C pair is then calculated as −6.3 kcal/base pair either from the chain length dependent enthalpy term or from the temperature coefficient of S values. From the S value and the association constant of 1:1 GpGpGpC:GpCpCpC complex, other thermodynamic parameters such as nucleation parameter (β) and free energy of stacking interaction can be obtained.
Induced cotton effects of tRNA–acridine orange complex and tRNA conformation
Authors: Ito Takashi , Zama Mitsuo , Amagasa Jumpei
Published: December 2004

Circular dichroism spectra of acridine orange bound to E. coli tRNA were studied at varying tRNA phosphate‐to‐dye (P/D) ratios for both unfractionated and purified materials in the absence of Mg++. From the rather discrete features exhibited in the circular dichroism spectra three types of interactions were observed: (1) A high P/D ratio such as 75.2 or 49.8 indicates the interaction between the nucleotide base and dye molecule. The spectra with a large positive peak at 515 mμ are, however, quite different from that of DNA–AO complex under similar conditions. (2) With an intermediate P/D ratio (26.5 to 9.6) dye molecules bound strongly to the polynucleotide chain. (3) With low P/D ratios (≤7.5) the interaction appears to be due to the stacked dye molecules in the single‐stranded part of tRNA. The spectra of the third group have an isobestic point at 477 mμ. Below a P/D ratio of 4 the spectrum shows one positive and two negative bands which may be the characteristics of circular dichroism of stacked dyes in polynucleotide chain.

Although no drastic change in the conformation of tRNA itself was detectable in the presence of Mg++ in the ultraviolet region, a dramatic change was observed in the circular dichroism of tRNA–acridine orange complex when Mg++ concentration was increased to 10−3M. It was inferred that certain conformational changes other than simple hydrogen bond formation occured in tRNA molecules at this high Mg++ concentration, so that the amount of bound dye in the stacking condition was increased through the transition.