bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of the biologically active conformers for prodine opiates and their derivatives
Authors: Froimowitz Mark , Kollman Peter
Published: December 2004

Conformational energy calculations using the empirical MM2 (molecular mechanics II) and semiempirical quantum mechanical PCILO (perturbative configuration interaction using localized orbitals) methods are reported for various prodine derivatives. These include 3‐demethylprodine, α‐prodine, β‐prodine, the α‐2‐methyl derivative, α‐promedol, the γ‐2,3‐dimethyl derivative, and γ‐isopromedol. The results are consistent with all of the compounds activating the opiate receptor in a phenyl equatorial conformation with optimum activity resulting from a particular orientation of the phenyl and propionoxyl groups. In disagreement with previous limited experimental data, α‐promedol is found to prefer a phenyl equatorial conformer. It is confirmed that, of the two mirror image phenyl equatorial conformers that are preferred for 3‐demethylprodine, the more active prodines antipodes consistently prefer the one in which the phenyl orientation is the opposite (mirror image) of that found in morphine and in the preferred conformer of the morphine‐like (+)‐phenylmorphan. This is a possible molecular basis for the nonmorphine‐like effects that occur with the introduction of a phenyl meta hydroxyl into some prodine derivatives. It is also suggested that the less active prodine antipodes, which have a morphine‐like phenyl orientation, may act in a morphine‐like manner at opiate receptors.
On the diatomic vibration–rotation eigenvalue equation: Highly accurate results for high levels
Authors: Dagher Mounzer , Kobeissi Hafez
Published: December 2004

Accurate vibration–rotation eigenvalues EvJ are sought for very high levels (up to dissociation) of a diatomic potential. The method used is the recent “eigenvalue equation” method [Kobeissi et al., J. Comput. Chem., 4, 218 (1983)] which dissociates the determination of the eigenvalue from that of the eigenfunction. A new mathematical formulation for any numerical potential is presented, which reduces the problem to the use of a single recurrent formula. A numerical application to the model potential used by Cashion [J. Chem. Phys., 39, 1872 (1963)], up to v = 23, gives results equal to the exact eigenvalues to approximately 10−14 cm−1. Another application to the model potential used by Johnson [J. Chem. Phys., 67, 4086 (1977)], up to v = 60, gives similar results.
Substituent effects in second‐row molecules: Basis set performance in calculations of normal valency phosphorus and sulfur compounds
Authors: Magnusson Eric
Published: December 2004

Ab inito molecular orbital calculations of the phosphorus‐ and sulfur‐containing series PH2X, PH3X+, SHX, and SH2X+ (X = H, CH3, NH2, OH, F) have been carried out over a range of Gaussian basis sets and the results (optimized geometrical structures, relative energies, and electron distributions) critically compared. As in first‐row molecules there are large discrepancies between substituent interaction energies at different basis set levels, particularly in electron‐rich molecules; use of basis sets lower than the supplemented 6‐31G basis incurs the risk of obtaining substituent stabilizations with large errors, including the wrong sign. Only a small part of the discrepancies is accounted for by structural differences between the optimized geometries. Supplementation of low level basis sets by d functions frequently leads to exaggerated stabilization energies for π‐donor substituents. Poor performance also results from the use of split valence basis sets in which the valence shell electron density is too heavily concentrated in diffuse component of the valence shell functions, again likely to occur in electron‐rich molecules. Isodesmic reaction energies are much less sensitive to basis set variation, but d function supplementation is necessary to achieve reliable results, suggesting a marginal valence role for d functions, not merely polarization of the bonding density. Optimized molecular geometries are relatively insensitive to basis set and electron population analysis data, for better‐than‐minimal bases, are uniform to an unexpected degree.
Polyatomic, anharmonic, vibrational–rotational analysis. Application to accurateab initioresults for formaldehyde
Authors: Harding Lawrence B. , Ermler Walter C.
Published: December 2004

A computer programSURVIBis described for calculating vibrational anharmonicity constants for polyatomic molecules. The program requires as input a grid of calculated energies in the vicinity of a stationary point. This grid is fit, in a least squares sense, to a polynomial function of the internal coordinates. This analytic representation of the energy surface is employed in a normal mode analysis, and the energy is reexpanded as a polynominal function of the normal mode coordinates (expressed as vectors in the mass‐weighted atomic Cartesian coordinate space). The resulting coefficients are used in a second‐order perturbation theory analysis to obtain the vibrational anharmonicity constants. Also reported is an application of this program to formaldehyde employingab initio,RHF,MP2,MP3, andRHF‐CIcalculations. The spectroscopic constants obtained for H2CO are in good agreement with experimentally derived values recently reported by Reisner.
Simple method of computing the partition coefficient
Authors: Klopman Gilles , Namboodiri Krishnan , Schochet Melvin
Published: December 2004

The values of log10 P (partition coefficient, in octanol/water) were calculated for about 200 organic molecules of diverse structures and functionalities. The method involves a simple procedure and appears accurate enough for semiquantitative applications. Further, this method of calculating log10 P values was shown to be successful in providing a better quantitative structure activity relationship (QSAR) than the Hansch‐type approach in the study of inhibitory activity of substituted phenols on Bacillus Subtilis spore germination.
Ab initio calculations of intermolecular potentials. The ground state of the ArH2 van der Waals molecule
Authors: Olivares Del Valle F. J. , Tolosa S. , Piñeiro A. Lopez , Requena A.
Published: December 2004

Hartree–Fock computations of the potential surface of ArH2 have been carried out and supplemented with calculations of the dispersion energy, with use of the counterpoise method to remove the basis set superposition error. The collinear and perpendicular bisector geometries are considered. The resulting potentials agree quite well with the actual experimental data.
Computer generation of matching polynimials of chemical graphs and lattices
Authors: Ramaraj Ramamani , Balasubramanian K.
Published: December 2004

A computer program in Pascal is developed for computing the matching polynomials of graphs and lattices. This program is based on the recursive relation for matching polynomials outlined by Hosoya [Bull. Chem. Soc. Jpn., 44, 2332 (1971)], Gutman and Hosoya [Theor. Chim. Acta, 48, 279 (1978)], and others. The graph whose matching polynomial is of interest is reduced recursively until the graph reduces to several trees. The characteristic polynomial of a tree is the same as the matching polynomial. The characteristic polynomials of resulting trees are computed using the computer program based on Frame's method developed by Balasubramanian [Theor. Chim. Acta, 65, 49 (1984)]; J. Comput. Chem., 5, 387 (1984). The resulting polynomials are then assembled to compute the matching polynomial of the initial graph. The program is especially useful in generating the matching polynomials of graphs containing a large number of vertices. The matching polynomials thus generated are potentially useful in several applications such as lattice statistics (dimer covering problem), aromaticity, valence bond methods (enumeration of perfect matchings) in the calculation of grand canonical partition functions, in the computation of thermodynamic properties of saturated hydrocarbons, and in chemical documentation.
Atom equivalents for relating ab initio energies to enthalpies of formation
Authors: Ibrahim Mustafa R. , Von Ragué Schleyer Paul
Published: December 2004

Sets of atom equivalents have been developed which permit the estimation of heats of formation, ΔH°(g), from ab initio total energies (3‐21G and 6‐31G* basis sets). This extends the isodesmic reaction scheme of Pople and the group equivalents of Wiberg. A variety of small inorganic and organic molecules, including fluorocarbons, free radicals, carbocations, and protonated species give excellent agreement with experiment; average errors are less than 1 kcal/mol with unstrained hydrocarbons (both basis sets), and are on the order of 2 kcal/mol for all molecules considered (6‐31G*; the 3‐21G basis errors, as expected, usually are somewhat higher). The results substantiate Pople's early conclusions that Hartree‐Fock theory provides a generally satisfactory description of classical molecules.
Stereodynamics of triethylamine: Molecular mechanics calculations on the direct rotational racemization of the C3‐symmetric conformers
Authors: Fleischman Stephen H. , Weltin Eugen E. , Hackett Bushweller C.
Published: December 2004

The direct interconversion of the two C3‐symmetric enantiomeric conformations of triethylamine, via CN bond rotation, has been studied by molecular mechanics (MM2) calculations. The MM2 calculations have been used to characterize the minima (equilibrium geometries) and first‐order saddle points (transition states) for this process. For one interconversion, there are five saddle points and six minima. The highest energy saddle point results from the uncoupled rotation of one ethyl group to eclipse the lone pair. Two of the barriers result from coupled rotation of two ethyl groups in close passage.
Relativistic effective potential SCF calculations of AgH and AuH
Authors: Krauss M. , Stevens W. J. , Basch Harold
Published: December 2004

Relativistic effective potentials (REP) are now widely used in molecular electronic structure calculations. Tests of these REP are needed to assess their accuracy. This can now be done for AgH and AuH since Lee and McLean have published Dirac‐Fock calculations for these molecules. Comparative SCF calculations have been performed for two types of effective potential. Satisfactory agreement between the effective potential results and Dirac‐Fock values is found for spectroscopic constants and dipole moments, which supports the use of these potentials for heavy atom containing molecules.
Usefulness of modified virtual orbitals in multireference CI procedure illustrated by calculations on lithium clusters
Authors: Fantucci P. , BonačiCć‐Koutecký V. , Koutecký J.
Published: December 2004

The maximization of the exchange interaction between the canonical Hartree–Fock virtual and occupied orbitals leads to a transformed set of virtual orbitals which are well suited as one‐electron functions for CI calculations. The procedure, generally known for a long time is seldom applied, despite its simplicity and very low computational demand. However, it is found to be particularly useful in the case of multireference CI, since an improved energy is obtained with a considerable shortening of the CI expansion. Moreover, in the final CI wave function, several configurations appear with considerable weight, thus allowing an easy choice of additional configurations to be inserted in the definition of a new zero‐order wave function. The efficiency of the computational procedure is discussed for the case of a Li6 cluster of D3h symmetry and for the NaCO and PdCO complexes. Results are reported for the relative stability of four different geometrical arrangements of the Li6 cluster.
Molecular structures and intramolecular interactions in dimethyl cyclohexane isomers
Authors: Klimkowski V. J. , Manning J. P. , Schäfer Lothar
Published: December 2004

The geometries of ten isomers of dimethyl cyclohexane were determined by ab initio gradient geometry refinement with the 4‐21G basis set. It is found that many intramolecular interactions are clearly manifested by correlated structural trends, and that they are consistent with strain energies calculated by employing previously defined ab initio group equivalents. Specifically, non‐bonded interactions are found between two adjacent methyl groups in some of the forms, and between axial methyl groups and adjacent axial CH bonds in others. Unperturbed axial CH and CC bonds are consistently longer than equatorial bonds. In general, CH bonds which are involved in non‐bonded repulsive interactions are shortened, i.e., strengthened, and the corresponding HCC angles are large, compared to non‐interacting parameters.
The effects of vinylic and allylic fluorine substitution in iso‐butylene
Authors: Ritchie James P.
Published: December 2004

Molecular orbital calculations using the 3‐21G basis set have been performed for iso‐butylene (IB; 2‐methyl‐1‐propene), difluoro‐iso‐butylene (DFIB; 1,1‐difluoro‐2‐methyl‐1‐propene), hexafluoro‐iso‐butylene (HFIB; 3,3,3‐trifluoro‐2‐(trifluoromethyl)‐1‐propene), and perfluoro‐iso‐butylene (PFIB; 1,1,3,3,3‐pentafluoro‐2‐(trifluoromethyl)‐1‐propene). The effects of fluorine substitution were studied by comparison of several calculated quantities of the fluorinated compounds with those of IB. Through an analysis of the computed electron density distributions, it is suggested that a vinylic fluorine acts as a π acceptor, by electron transfer into the CF bond, and a π repeller, by polarization of the adjacent π electrons. An allylic fluorine acts as a π attractor through electrostatic effects, although in HFIB a minor contribution from hyperconjugation was evident. Finally, electrostatic potentials for the molecules were calculated. These show that fluorine substitution has large effects on the electrostatic potential associated with the π electrons. These effects change the sign of the calculated electrostatic potential in the plane containing the π bond to such an extent that PFIB is quite susceptible to nucleophilic attack.
Spatial geometric arrangements of disulfide‐crosslinked loops in proteins
Authors: Kikuchi Takeshi , Némethy George , Scheraga Harold A.
Published: December 2004

The classification of patterns of the three‐dimensional folding of a covalently crosslinked polypeptide chain can be used to introduce long‐range interactions into the theoretical search for the native conformation of a protein. This classification into Spatial Geometric Arrangements of Loops (SGAL) had been proposed earlier (H. Meirovitch and H. A. Scheraga, Macromolecules 14, 1250, 1981). It is based on the subdivision of the protein molecule into closed loops, defined by covalent crosslinks (such as disulfide bonds). Various SGAL classes correspond to the presence or absence of mutual penetration of loops, called entanglements or thrustings. A systematic and objective method is developed here to enumerate all theoretically possible SGAL's for a protein, based only on its covalent structure, i.e., the pattern of disulfide bonds or other crosslinks, regardless of whether the three‐dimensional structure is known or unknown. This information can be of use in structural predictions of folding patterns. Using a modification of the method, it is also possible to determine the SGAL class to which a protein of known structure belongs. Out of 18 proteins with known three‐dimensional structure and containing more than two disulfide bonds, five have a native structure with at least one entanglement or thrusting. Thus, threaded SGAL's represent a significant structural feature of native proteins. All five involve neighboring loops in the sequences. Their presence in a protein can suggest restrictions on the possible ways of folding the protein.
A force‐field study of the conformational characteristics of the iduronate ring
Authors: Ragazzi Massimo , Ferro Dino R. , Provasoli Augusto
Published: December 2004

Methods of molecular mechanics were applied to investigate the conformation of the (methyl 2‐O‐sulfate‐4‐methyl‐α‐L‐idopyranose) uronic acid (DMIS), in order to correlate the peculiar vicinal proton coupling constants observed in polysaccharides containing the iduronate ring to the conformational characteristics of this sugar ring. We found three conformers with comparable energies, namely the two chair forms 1C4 and 4C1 and the skew‐boat form 2S0(L); the latter is separated from each chair form by a barrier of about 9 kcal/mol. Along the pseudorotational path three additional minima (3S1, 1S3, and 1S5) were found, yet at least 4 kcal/mol higher than 2S0. The results obtained for the relative energies of the three conformers and the conformation of the side groups were affected by the inclusion of the electrostatic term and, in particular, by the charge assigned to the ionic groups of DMIS. However, the conformational properties of the idopyranosidic ring in DMIS (and in related compounds) should still be interpreted in terms of equilibrium among these three conformers only.
The computed force constants and vibrational spectra of toluene
Authors: Xie Yaoming , Boggs James E.
Published: December 2004

The complete harmonic force field and dipole moment derivatives have been computed for toluene at the Hartree‐Fock level using a 4‐21G basis set. The six scale factors optimized for benzene were used to scale the computed harmonic force constants of toluene. The vibrational frequencies of toluene computed from this scaled quantum mechanical force field are quite good. After a correction was made to two previously proposed spectral assignments, the mean deviation from the experimental frequencies is only 7.8 cm−1 except for the frequencies related to the methyl group. Five more scale factors for the vibrational modes of the methyl group were reoptimized. The final comparison showed an overall mean deviation of 7.5 cm−1 between the theoretical spectrum and the experimental spectrum. Computed intensities are qualitatively in agreement with experiments. They are highly useful in the investigation of questionable assignments.
Conformational study of the trinucleotide CpGpCp‐pentapeptide Gly5 complex: The important role of bridging water in the complex formation
Authors: Yoon Chang No , Jhon Mu Shik
Published: December 2004

Conformational changes in the RNA‐protein interaction were studied by calculating the intramolecular interaction energy of a model complex with the use of potential functions. The model complex has hydrogen‐bonded water molecules bridging polypeptide NH groups to 2'‐hydroxyl groups and sugar ring oxygen atoms. Since the sugar ring is constrained by the bridging water, preliminary calculations with the model compounds, the sugar ring, mononucleoside diphosphates, pCp and pGp, were carried out, and the flexibility and energetics of the sugar ring were compared with the previous results of DNA. The shift of the phase angle of the sugar ring occurred in the complex formation because of the hydrogen bond through the bridging water and the flexibility of the sugar ring. The free energy difference at 298 K is about −74.0 kcal/mol which was obtained from the intramolecular interaction energy difference of −67.5 kcal/mol by adding the conformational entropy change of 21.9 e.u., which in turn was calculated from the evaluation of the determinant of the matrix containing variances and covariances of the internal coordinates.
Matrix elements for anharmonic potentials: Application to I2 morse oscillator
Authors: Delgado‐barrio G. , Cortina A. M. , Varadé A. , Mareca P. , Villarreal P. , Miret‐artés S.
Published: December 2004

Many authors have contributed expressions for obtaining analytical matrix elements for Morse oscillators. In this work, we discuss the advantages of using these expressions. At the same time, we propose a full numerical method to calculate these matrix elements and we compare, for the I2 system, the different results given by Gallas, Vasan, and Cross, and the variational method.
The second limit of hydrogen + carbon monoxide + oxygen mixtures
Authors: Baldwin R. R. , Jackson D. , Melvin A. , Rossiter B. N.
Published: December 2004

Previous studies by Buckler and Norrish of the second limit of CO and O2 mixtures containing small amounts (0.25–10%) of H2 have been used to obtain the velocity constant of the reaction

These estimates of k33 = 3.9 × 108 and 3.5 × 108 liter2 mole−2 sec−1 (M  H2) at 500° and 560°C, respectively, have been combined with other estimates over the range 300°–3500°K to give k33 = 3.0 × 108 exp (−3000/RT) for M  Ar; the considerable scatter in the available points does not encourage any great confidence in this expression and may be attributed at least partly to the different molecules used as M by different workers. For KCl‐coated and CsCl‐coated vessels at 540°C, studies of the second limit of H2 + O2 mixtures, to which CO has been added, have indicated that with both the surfaces, the effect of CO on the limit is masked by changes in the surface nature. In the case of CsCl, the results have enabled a lower limit of about 0.6 to be obtained for the efficiency of CO relative to H2 in the reaction

Use of a computer treatment to interpret the second limit of CO + H2 + O2 mixtures in aged boric‐acid‐coated vessels at 500°C gives a value of mCO = 0.74 ± 0.04 together with an estimate of k32 (H + CO + M″ = HCO + M″)/k4 = 0.022 ± 0.003, which leads to k32 = 2.3 × 108 liter2 mole−2 sec−1 (M  H2) at 500°C.
Vibrational excitation of deuterium fluoride and hydrogen fluoride by atomic and diatomic species
Authors: Blauer J. A. , Solomon W. C. , Owens T. W.
Published: December 2004

The vibrational excitation of HF and DF and the energy transfer efficiencies for various collision partners were investigated over the temperature and pressure ranges of 1400°K to 4100°K and 0.1 to 0.3 atm, respectively. The extent of excitation was determined as a function of time by continuously monitoring the infrared emission intensity at the center of the 1–0 vibration‐rotation band of the molecule. Collisional efficiencies of HF, N2, O2, F, Cl, and DF in relaxing HF and of DF, HF, and N2 in relaxing DF are reported. A comparison with relaxation data for pure HF taken at lower temperature suggests that long‐range attractive forces are mechanistically of major importance in the relaxation process. The relatively high efficiency of atomic chlorine in relaxing HF, i.e., (τP)HF–HF/(τP)HF–C1 ≥ 5 at 3000°K is discussed in terms of our previous result for atomic fluorine, i.e., (τP)HF–HF/(τP)HF–F = 18.
Reaction of H and D atoms with deuterated propylenes
Authors: Falconer W. E. , Sunder W. A.
Published: December 2004

Effects of deuterium substitution in propylene on the relative rates of H(D) atom abstraction from and addition to the olefin, and on the orientation of H(D) atom addition, have been studied in the gas phase at room temperature. Effects of isotopic substitution of the olefinic hydrogen atoms on abstraction could not be observed, but abstraction is reduced five‐ to tenfold by deuteration of the methyl group. Deuteration of either olefinic position enhances the rate of addition to the substituted carbon atom. Disproportionation‐combination ratios for deuterium‐substituted propyl radicals are not greatly different from those for unsubstituted radicals, the largest effect being for C3D7 radicals, for which the overall kd/kc is reduced 10–15%.
A flash photolysis study of the rate of the reaction OH + CH4→ CH3+ H2O over an extended temperature range
Authors: Zellner Reinhard , Steinert Wolfram
Published: December 2004

A flash photolysis system has been used to study the rate of reaction (1), OH + CH4→ CH3+ H2O, using time‐resolved resonance absorption to monitor OH. The temperature was varied between 300 and 900°K. It is found that the Arrhenius plot ofk1is strongly curved andk1(T) can best be represented by the expression

The apparent Arrhenius activation energy changes from 15±1 kJ/mole at 300°K to 32±2 kJ/mole at 1000°K. On either side of our temperature range, both absolute rates and their temperature dependence are in good agreement with the results from most previous investigations.
Reactions of O 3PJ atoms with halogens: The rate constants for the elementary reactions O + BrCl, O + Br2, and O + Cl2
Authors: Clyne Michael A. A. , Monkhouse Penelope B. , Townsend Leslie W.
Published: December 2004

Direct determinations of the rate constants (cm3/molec · sec) k1, k2, and k3 from 298 to 299°K are reported, using atomic resonance fluorescence in discharge flow systems:
equation image

One standard deviation.

The rate constant k1, which has not been determined previously, was found to possess an insignificant temperature coefficient (EA = (0 ± 700) J/mole) in the range of 299 to 619°K.

The present result for k2 agrees well with reinterpreted values from the one previous determination. Measurements of O atom consumption rates and Br atom production rates in the O + Br2 reaction are interpreted to give an estimate of the rate constant k4, which has not been reported previously, at 298°K:

equation image

k3 has been measured at three temperatures between 299 and 602°K. The present and previous results for k3 were combined to give the following rate expression:
Predicting gas phase organic molecule reaction rates using linear free‐energy correlations. I. O(3P) and OH addition and abstraction reactions
Authors: Gaffney J. S. , Levine S. Z.
Published: December 2004

Linear free‐energy (LFE) correlations for gas phase O(3P) and OH addition and abstraction reactions with a number of organic compounds have been established using existing room‐temperature rate constants evaluated from the literature. Addition reaction rate constant correlations with ionization potential and abstraction reaction rate constant correlations with bond dissociation energies are examined and compared to the LFE approach. Using multiple regression analysis, empirical linear equations are derived and used to predict rate constants for reactions of O(3P) and OH with a number of organic molecules. The use of LFE room‐temperature rate predictions permits chemical modeling efforts to be extended to compounds where experimental determinations of rate coefficients are lacking and also serves as a useful tool in evaluation of experimental rate measurements.
The ethylperoxy radical spectrum and rate constant for mutual interaction measured by flash photolysis and kinetic spectroscopy
Authors: Adachi Hiroyuki , Basco N. , James D. G. L.
Published: December 2004

Intrinsic spectral and kinetic parameters have been measured for the ethylperoxy radical, which was formed in the gas phase by the flash photolysis of azoethane in the presence of an adequate excess of oxygen. Absolute values of the extinction coefficient ϵ(λ) were derived from complementary measurements of the yield of nitrogen and the absorbance of an equivalent concentration of ethylperoxy radicals. The absorption spectrum is broad, structureless and comparatively weak; ϵ(236) = 1.02 × 103 liter mole−1 cm−1 at the maximum, and the oscillator strength is 3.4 × 10−2. This spectrum resembles the spectrum of the methylperoxy radical closely in form, but it is less intense; the ratio of the values of oscillator strength is 0.5. The bimolecular reactions of mutual interaction of ethylperoxy radicals are not exclusively terminating, and ethoxy and hydroperoxy radicals are formed in kinetically significant quantities. A computer program was designed to simulate the rise and fall of the concentration of each radical species, and to perform the related kinetic analysis. This program predicted that a second‐order plot of the decline of the absorbance of the ethylperoxy radical during the dark period would not show a significant departure from linearity, a conclusion which was confirmed by experiment. Accordingly, the gradient of each such plot yielded a value of k'/ϵ(λ), where k' is the apparent value of the rate constant for the collective reactions of mutual interaction. This rate constant was evaluated from the product of corresponding values of k'/ϵ(λ) and ϵ(λ); individual values are independent of the wavelength of measurement, and the mean value is k' = (6.6 ± 0.5) × 107 liter mole−1 sec−1. Further kinetic analysis yielded the corresponding absolute value: k = (6.0 ± 0.6) × 107 liter mole−1 sec−1. This value fits the pattern of a relationship between rate constant and structure shown by the methylperoxy, isopropylperoxy, and tert‐butylperoxy radicals. Adequate sensitivity for the characterization of the spectrum of the ethylperoxy radical was achieved by the use of a pulsed xenon arc as the monitoring light source in conjunction with a dual beam detection system with twin cells and balanced photomultipliers, and the apparatus is described in detail.
A study of the reactions of fluorine with hydrogen and methane in the initiation phase using a miniature tubular reactor
Authors: Seeger C. , Rotzoll G. , Lübbert A. , Schügerl K.
Published: December 2004

A small tubular reactor having an inner diameter of 1–2 mm andused as the source in a molecular beam apparatus is described in detail. This arrangement allows the study of fast reactions with reaction times smaller than 1 msec. The preexplosive reaction phase between F2 and H2 and CH4, respectively, is investigated to find out the initiation reactions. In the F2/H2 reaction, initiation is brought about by heterogeneous generation of F atoms or some other surface reaction. Evidence is also obtained for chain branching reactions. In the F2/CH4 case the dominant initiation reaction is the homogeneous reaction CH4 + F2 → CH3 + HF + F. The rate constant for the reaction between 300 and 400 K is 1012.3±0.3 exp[−47 ± 8 kJ/mol/RT] cm3/mol sec. The analysis of the experimental data also yields the rate constant for the propagation reaction CH3 + F2 → CH3 F + F, which is 1012.3±0.3 exp[−4.6 ±2.1 kJ/mol/RT] cm3/mol sec.
The reaction of atomic oxygen O(3P) with propane
Authors: Jewell Steven P. , Holbrook Kenneth A. , Oldershaw Geoffrey A.
Published: December 2004

The reaction of O(3P) atoms with propanehas been studied at temperatures near 300 K by using a discharge flow system. Oxygen atoms were generated in the absence of molecular oxygen by the reaction N + NO → N2 + O, nitrogen atoms having been generated in a microwave discharge. Rate constants for the reaction were measured in two ways, either by measurement of O‐atom decay in the presence of excess propane or by measuring the change in propane concentration after an appropriate time in the presence of an excess of oxygen atoms. The two methods were in good agreement, and the mean rate constant at 306 K is given by

A study of the products of the reaction under conditions corresponding to complete removal of oxygen atoms has shown that an important product of the reaction in the early stages is propene. This is difficult to explain interms of a mechanism involving alkoxy radicals similar to that which has been proposed for some other O(3P)–hydrocarbon reactions. An alternative mechanism is proposed in terms of successive hydrogen abstraction reactions.
Coupling rates and kinetics of arenediazonium cations with couplers utilized in the diazo reprographic process
Authors: Cox A. , Goodman P. D. , Kemp T. J. , de Moira P. Pinot
Published: December 2004

Stoichiometric and, in most cases, absolute rates of coupling of a series of m‐ and p‐substituted benzenediazonium ions with 2,3‐dihydroxynaphthalene‐6‐sulfonate ion (1) have been determined (i) at pH 5.6 (when one OH group is partly monoionized) and (ii) at pH 9.9 (when one OH group is completely ionized and the second slightly so). The rates at both pH values correlate with the σ+ parameter (except for the most reactive ArN at pH 9.9) and the contributions of the two reactive forms of the coupler evaluated. Detailed pH dependences of the coupling rate of the p‐chlorobenzenediazonium ion with (1) reveal a strong interaction between (1) and the borate ion, which strongly influences the coupling rate. Coupling rates have also been measured for both diazonium ions and couplers of importance in the diazo reprographic process.
Rate constants for the quenching of metastable O2(1Σ) molecules
Authors: Choo Kwang Yul , Leu Ming‐Taun
Published: December 2004

Singlet molecular oxygen, O2(1Σ), is one of the important intermediate species in the atmospheres of Earth, Mars, and Venus. To elucidate the chemistry of this excited molecular oxygen, a series of kinetic measurements have been undertaken using the flow‐discharge/optical‐emission technique. By monitoring the characteristic emission (762 nm for 1Σ), the quenching rates for several important molecules have been obtained at room temperature. The following table summarizes measurements.

Quencher
Rate Constants (cm3/s)

CH2
(4.6 ± 0.5) × 10−13

H2
(7.0 ± 0.3) × 10−13

N2
(1.7 ± 0.1) × 10−15

Cl2
(4.5 ± 0.8) × 10−16

CO
(4.5 ± 0.5) × 10−15

O3
(2.2 ± 0.3) × 10−11

2,3 DBM‐2
(6.0 ± 0.1) × 10−13

The error limits represent one standard deviation. The systematic error is estimated to be about 15%. For CO2 and O3 molecules, the quenching rate constants were also measured in the temperature range of 245–362 K. In both reactions, negligible temperature dependences (with the activation energy less than 0.6 kcal/mole) were observed.
Pulse radiolysis study of the reaction of OH radicals with C2H4 over the temperature range 343–1173 K
Authors: Liu An‐Dong , Mulac William A. , Jonah Charles D.
Published: December 2004

The reaction of OH and OD radicals with ethylene in the presence of 1 atm argon and 6 Torr water vapor was studied in the temperature range 343–1173 K. The results reveal three kinetically separate temperature regions: (1) 343–563 K, where the disappearance of OH radical is dominated by the addition of OH to the double bond of ethylene; (2) 563–748 K, where concurrent reactions of addition, the reverse reaction of addition and H‐atom abstraction is dominant; and (3) 748–1173 K, where H‐atom abstraction is likely the main reaction. The rate for hydrogen abstraction is 2.4 × 10−11 exp[(−2104 ± 125)/T] cm3/molec‐s (for OD 2.1 × 10−11 exp[(−2130 ± 172)/T] cm3/molec‐s). There was no obvious pyrolysis of ethylene below 1073 K. The study of OD radical with ethylene shows a small isotope effect.
Das Korrosionsverhalten von Aluminiumbrozen
Authors: Franke Erich
Published: December 2004

Es wird ein Überblick gegeben über Struktur, Schmelzen, Vergießen, mechanisch‐technologische Eigenschaften, Korrosionsverhalten und Einsatzmöglichkeiten von Aluminiumbronzen, die eine Gruppe von Legierungen umfassen, die sich hauptsächlich aus Kupfer und Aluminium zusammensetzen und denen im Laufe der Jahre zur Steigerung ihrer Güte und Erfüllung spezieller Anforderungen noch weitere Elemente, wie Zinn, Nickel und Mangan beigefügt worden sind. Als charakteristische Besonderheit dieser Bronzen ist ihre außerordentliche Fähigkeit anzusehen, durch Oxydation des in den Legierungen enthaltenen Aluminiums dünne, jedoch sehr dichte und festhaftende Filme auf ihren Oberflächen zu bilden, die die Bronzen gegen Korrosion und vor allem gegen Oxydation schnisch wichtigsten Kupferlegierungen gemacht, die ihre optimalen Eigenschaften bei mittleren Temperaturen zeigen, da in diesem Bereich auch ihre mechanischen Kennwerte besonders günstig sind.
Säurefeste Zemente
Authors: Waeser Bruno
Published: December 2004

Nach einigen geschichtlichen Ausführungen und notwendigen Begriffsbestimmungen werden zunächst die Silikatzemente besprochen, die aus Wasserglas und Füllstoffen aufgebaut werden, wobei recht erhebliche Festigkeiten erreicht werden können. Sie leiten über zu den Säuremörtel Hoechst, Keralith, Asplit, Kera Keranol, Kerasolitih oder dgl., Haveg, Prodorit und andere Kunstharz‐ bzw. Bitumenzemente sowie Asphaltmassen gehören, die im einzelnen behandelt werden. Den Abschluß für bilden die sonstigen Säurebaustoffe, für die sich die Bezeichnungen Phenolzemente, Schwefelzemente usw. eingeführt haben. Misch‐ bzw. Asbestzemente und säurefeste Bekleidungen auf Zement‐ bzw. Betongrundlage werden, soweit notwendig, gewürdigt. Den Prüfmethoden ist stärkste Beachtung zu schenken, um vor Schwierigkeiten geschützt zu sein.
Über die biologische Eisenkorrosion
Authors: Seelmeyer Günther
Published: December 2004

Die Arbeit gibt eine Zusammenstellung unseres heutigen Wissens über die Korrosionsersheutigen, die durch Mikroorganismen auf Eisen hervorgebracht werden. Nach einem kurzen überblick über die Eigenschaften der hierfür in Frage kommenden Organismen werden die praktisch vorkommenden Erscheinungsformen und Begleiterscheinungen der biologischen Eisenkorrosion, sowie die Theorien, die bisher darüber aufgestellt wurden, besprochen. Die Arbeit endet mit einer Zusammenstellung der bis heute bekannten Verhütungsmöglichkeiten dieser Korrosionsart.
Die Rostschutzwirkung des Zements
Authors: Hebberling Hans
Published: December 2004

Unter den Handelssorten des Zements und Betons sind mit Traß versetzter Portlandzement, Bimsbeton und Gipsschlackenzement besonders zur chemischen Rostumwandlung befähigt. Der Schutzwert dieser Baustroffe wird mehr von ihrem pH‐Wert als von der Dicke der Einbettung beeinflußt. Im Stahlbau verwendeter Beton muß in der Regel mindestens 300kg/m3 Zement enthateln. Der „ vorläufige”︁ Rostschutz durch Aufbringen dünner Zementschlämme hat sich in Fällen höherer Beanspruchung nicht durchweg bewährt. Es erscheint sodann eine einmalige Grundierung mit Bleimennige empfehlenswert, deren billigere Beisorte “V 40” das Eissen erwiesenermaßen auch ohne schützenden Deckanstrich 4½ Jahre und länger gegen Rostbildung zu schützen vermag. Alte Anstriche werden vor dem Einbetonieren am besten mit autogenen Flammstrahlern entfernt.
Mantelbeanspruchung von ausgekleideten Behältern am Beispiel des Zellstoffkochers
Authors: Kirschbaum Emil
Published: December 2004

Zellstoffkocher zerknallten häufig einige Stunden nach Dampfeinlaß, bei Inbetriebsetzung, nach Stillstand oder im Winter unter Einfluß kalter Zugluft. Auf Grund dieses Tatbestandes wurde die zusätzliche Beanspruchung des Eisenmantels durch die Wärmedehnung der Kocherauskleidung an einer technischen Anlage untersucht. Theoretische Ableitungen ergeben, daß die zusätzliche Beanspruchung unter sonst gleichen Bedingungen mit der Dicke der Ausmauerung zunimmt. Der Temperaturverlauf in der Wand eines Kochers wurde bei verschiedenen Ankochzeiten an 3 Stellen durch Einbau von je 10 Thermoelementen im Betrieb gemessen. Die Ergebnisse erhärten die theoretischen Betrachtungen und führen zu der Forderung, daß die Wärmeausdehnungszahl der säurefesten Auskleidung nicht größer als 0,92 × 10−5 m/m.° C sein darf. Dies ist insbesondere bei älteren Kochern zu beachten, deren Rundlaschenverbindungen nur auf die kleinere Beanspruchung in achsialer Richtung abgestimmt sind, wobei die zusätzliche Beanspruchung durch die warme Auskleidung nicht berücksichtigt ist. Weitere Ergebnisse der Untersuchung zeigen, daß aufgeheizte Kocher vor Abkühlung durch Zugluft besonders in der kalten Jahreszeit zu schüzen sind.
Über die Witterungsbeständigkeit von Graufarben durch Pinsel‐ und Spritzauftragverfahren
Authors: Buser Karl
Published: December 2004

Gegenstand der Untersuchung war die Klärung des Einflusses des Auftragsverfahrens auf die Witterungsbeständigkeit von Rostschutzfarben. In mehrjährigen Bewitterungsversuchen verhielten sich im Streichverfahren aufgebrachte Anstriche im allgemeinen besser als im Spritzverfahren aufgebrachte.
Säurebeständige Stähle in der Holzessigfabrikation
Authors: Wetternik L. , Zitter H.
Published: December 2004

Die chemische Beanspruchung in der Holzessigindustrie ist größer als die in der Gärungsfabrikation, was durch Gehalte an homologen Säuren und empyrheumatischen Stoffen bedingt ist.

Ein Stahl mit 18% Cr, 10% Ni und 2% Mo, der im allgemeinen für diese Essigsäure Verwendung findet, versagte an den Stellen stärkster Beanspruchung in Holzessigsäure. Es wurde daher versucht, durch Erhöhung des Cr‐ und Ni‐Gehaltes eine Verbesserung zu erzielen.

Die besten Ergebnisse wurden mit einem bereits in der schwedischen Zellulosefabrikation verwendeten Stahl mit 27% Cr, 4,5% Ni und 1,5% Mo erreicht, der nach den Laboratoriumsversuchen im gesamten Konzentrations‐Temperaturbereich bis zum Siedepunkt voll beständig ist.

Dieser Stahl besteht nur zum geringen Teil aus Austenit und weist daher eine größere Härte auf. Trotzdem ist er gut verarbeitbar und läßt sich auch befriedigend schweißen.
Schallemissionsmessungen an beschichteten Stahlblechen
Authors: Moslé H. G. , Wellenkötter B.
Published: December 2004

Die Schallemissionsmessungen an unterschiedlich beschichteten Stahlblechen zeigten, daß es mit Hilfe dieses Verfahrens möglich ist, das Schädigungsverhalten dieser Werkstoffgruppe zu untersuchen.

Bei den galvanisch beschichteten Blechen war die Schallemission bei gleichem Substrat abhängig von:

dem abgeschiedenen Metall

der Zusammensetzung des Elektrolyten

der Abscheidungsstromdichte

der Schichtdicke.

Die Untersuchungen an den phosphatierten und/oder lackierten Blechen zeigten eine Abhängigkeit der Schallemission von:

der Art der Phosphatierung

der chemischen Zusammensetzung des Lackes

der Höhe der Einbrenntemperatur

der Bewitterung

der Schichtdicke.

Bei den bisherigen Untersuchungen wurde die Schallemission lediglich als Impulsrate registriert. Um gezieltere Aussagen über Enthaftungen und Rißbildungen zu ermöglichen und um Haftungsmechanismen über die Enthaftungsvorgänge aufzuklären wurde begonnen, Amplituden‐ und Frequenzanalysen der Schallemission von beschichteten Metallen vorzunehmen.
Kohlenstoff‐faserverstärktes Al2O3 und Mullit
Authors: Yasuda E. , Schlichting J.
Published: December 2004

Die Hydrolyse von Metallalkoxyden (Al‐tri‐sec‐butylat und Methylsilanester) läßt sich zur Herstellung von kohlenstoffaserverstärkten Al2O3‐ und Mullit‐Verbundwerkstoffen heranziehen. Hierbei zeigte es sich, daß für Al2O3‐Matrix eine zusätzliche SiC‐Zwischenschicht die Haftung zwischen Faser und Matrix verbessert. Die hergestellten Verbundwerkstoffe zeigen deutlich verbesserte Werte für die Bruchzähigkeit.
Aufbau und Eigenschaften glasfaserverstärkter Eisenverbundwerkstoffe
Authors: Abels U. , Bergmann H. W.
Published: December 2004

Aus Karbonyleisenpulver und gemahlenen Glasfasern, Duran 50®, gelang es, durch Mahlen und gemeinsame Höchstverformung mittels Strangpressen eine neue Werkstoffvariante herzustellen.

Trotz des niedrigen E‐Moduls der Glasphase kommt es zu einer anomalen Festigkeitssteigerung der Komposite bei zum Teil guten Dehnungswerten. Der lineare Abfall des E‐Moduls und der Gleichstromleitfähigkeit des Verbundmaterials bis zu 50 Vol% des Additives erklärt sich aus dem fasergerüstartigen Aufbau in Verformungsrichtung. Die starke Dämpfungsabnahme im KHz‐Bereich und der starke Abfall der Wärmeleitfähigkeit ist durch Phononenstreuprozesse an den Phasengrenzflächen Glas/Metall bedingt, die aufgrund des gelockten Querschnittgefüges in mannigfaltiger Form vorliegen.
Untersuchung verschiedener Schweißverfahren für die Nickel‐Basislegierung NiMo 16 Cr 16 Ti
Authors: Merz D. , Poweleit B. , Thiessen W.
Published: December 2004

Die allgemeine gute Korrosionsbeständigkeit der Nickelbasislegierung NiMo 16 Cr 16 Ti gegen den Angriff stark oxidierender Säuren sichert diesem Werkstoff ein breites Einsatzgebiet. Die Legierung ist mit umhüllten Stabelektroden und nach Schutzgasschweißverfahren gut zu verarbeiten. Bevorzugt sollte jedoch das Schutzgasschweißen eingesetzt werden, da erhebliche Analyseunterschiede zwischen dem niedergeschmolzenen Schweißgut aus umhüllten Stabelektroden und aus blanken Stäben und Drähten bestehen. Das unterschiedliche Schweißgut hat Einfluß auf das Korrosionsverhalten und die Warmformgebungsmöglichkeiten von geschweißten Konstruktionen.
Mechanical properties of mica‐reinforced polypropylene composites
Authors: Trotignon J. P. , Sanschagrin B. , Piperaud M. , Verdu J.
Published: December 2004

The influence of muscovite mica on the tensile, flexural, and mold shrinkage properties of composites with polypropylene (PP) were investigated. The best results in tensile and flexural properties at room temperature were observed for the physicochemical‐treated mica followed by silane‐treated mica. The mechanical properties could be correlated with the PP‐mica interactions, as observed in the scanning electron microscope (SEM). In the present study, with mica aspect ratio equal to about 30, the optimum performance was obtained for the average flake diameter 80 ⩽ d (μm) ⩽ 280. Finally, the results of coloration and weathering are discussed. It was found that the PP/30 percent mica formulation has superior weathering characteristics over the neat PP resin.
Industrial applications and properties of short glass fiber‐reinforced plastics
Authors: Santrach Drago
Published: December 2004

Short glass fibers for reinforcements of plastics have been commercially produced for over three decades. During this period, they have been used in virtually every polymer, as well as in other matrices, such as concrete and plaster. Their tensile strength/cost performance is still three times that of Kevlar® and more than 30 times better than carbon fibers. Similarly, excellent modulus/cost performance and high temperature/cost performance can be achieved. This article gives a review of short‐fiber composites: their properties and use. Included is a comparison of compounding vs. in‐house blending, fiber/flake hybrids, and reinforced polymer blends. Finally, several new materials still in development stages will be examined.
Time‐dependence of crystal orientation in crystalline polymers
Authors: Stein R. S.
Published: December 2004

The results of two methods for studying molecular processes accompanying the deformation of polyethylene are described. The examination of spherulite deformation by observing light scattering patters along with measurement of the birefringence, stress and strain during the rapid extension of polyethylene shows that this initial structural deformation is essentially instantaneous. Dynamic x‐ray diffraction shows that this is followed by a slower relaxation involving change in the orientation of the crystals by two processes, the lower temperature one involving slipping of lamellae past each other and the higher temperature one involving viscoelastic flow of the crystals.
Effects of high hydrostatic pressure on the mechanical behavior of a crystalline polymer–polyoxymethylene
Authors: Sardar D. , Radcliffe S. V. , Baer E.
Published: December 2004

The true stress‐true strain behavior of polyoxymethylene, n(‐CH2O), as an example of a bulk semi‐crystalline polymer, has been investigated for constant hydrostatic environmental pressures from 1 atmosphere to 8 kilobars with the principal objectives of elucidating the factors controlling flow and fracture. Experiments were conducted in uniaxial tension at room temperature and constant strain rate. The tensile observations were supplemented by measurements of bulk compressibility and stress relaxation behavior at pressure.

In contrast with metals and inorganic compounds, the modulus, yield stress and fracture stress of POM increase strongly with pressure by a factor of approximately three at 8 kilobars. The modulus increase is shown from the stress relaxation measurements to be associated with a pressure‐induced increase in the β‐transition temperature which points to the potential usefulness of the concept of pressure‐temperature super‐position of mechanical behavior. The characteristics of the pressure dependence of the yield stress demonstrate that yield criteria based on continum mechanics considerations, including the Mohr or Coulomb‐Navier criterion, are not valid for general deformation (non‐plane strain) conditions in this polymer. The concept of a critical volume change determining the initiation of yielding is suggested to be applicable to semi‐crystalline polymers. Comparison with analogous changes in yield stress with temperature points to an increasing contribution to the control of yielding by the initially disordered regions with increasing pressure or decreasing temperature. The fracture behavior observed at pressure eliminates the concepts of a critical stress as a fracture criterion for POM and of a simple reduction in normal stress at points of stress concentration as the principal effect of the applied pressure on fracture.