Conformation energies of «-butane and «-pentane have been calculated as functions of their C-C bond rotation angles using semiempirical expressions for the repulsive and attractive energies between nonbonded atom pairs and an intrinsic threefold torsion potential having a barrier height of 2.8 kcal mole-1 for each C-C bond. Parameters for the nonbonded repulsions were adjusted to reproduce the experimental energy difference Ea of 500 cal mole-1 between the gauche and the trans states. The same parameters yield barrier heights for rotations in propane, «-butane, isobutane, and neopentane which agree with experiment. The potential wells about gauche and trans minima in «-butane and «-pentane are similar in breadth. The former have been found to occur at ca.
45)a1 is the thermal expansion coefficient of pure component 1 (see eq. 41). If s1 = s2, the coefficients simplify in eq. 43-45.Series expansions for the partial molar enthalpy and entropy may be obtained from eq. 43 by differentiation. Concluding RemarksAdaptation of the reduced partition function expressed by eq. 7 to mixtures and adoption of eq. 20 for the intermolecular energy on the assumption of random mixing underlies the theory developed above.The expressions derived for the various residual (or excess) properties of a binary mixture involve a single parameter, X12, beyond those furnished by the properties of the two pure components. The thermodynamic properties (e.g., H , Y , and S ) are thus related explicitly to one another in terms of this parameter characterizing the given mixture. Treatment of mixtures of small, nonpolar molecules on this basis is demonstrated in the following paper.I4 Application to polymer solutions will be presented in a future communication.Acknowledgment. The excess enthalpies, volumes, and entropies of 23 equimolar binary liquid mixtures f o r which necessary data are available in the literature are interpreted according to the relationships presented in the preceding paper. Most of the mixtures comprise pairs of small globular molecules from the group c-CsHlz, C 6 H 6 , C(CH3)4, CCI4, SiCI4, TiCI4, and SnCl, or f r o m the condensed gases CH4, Ar, 0 2 , and N2. Also included are mixtures of C6H6 and of c-csH,2 with n-hexane and n-heptane, the benzenediphenyl system, and two hydrocarbon-fluorocarbon mixtures. Previously unaccounted equation of state terms, which depend on properties of the pure components, make important contributions to each of the excess quantities. Through use oj pair interaction parameters chosen to achieve agreement with the observed excess enthalpies, excess volumes are calculated which agree in nearly all cases with those observed within limits set b y experimental errors. Although excess entropies calculated on the same basis tend to be somewhat lower than those observed, the agreement is favorable f o r most systems. Exceptions involve benzene as one component or cyclohexane in admixture with n-alkanes. Because account was taken of equation of state contributions, the present interaction parameters differ f r o m those deduced from experimental results b y previous procedures. Departures from the Berthelot geometric mean rule are discussed. (1) P. J. Flory, J . A m . Chem.Analysis of the dependence of the various excess quantities on composition has not been undertaken for the reason that comparison of theoretical prediction with the observed compositional dependence would be indecisive for the mixtures of nonpolar, small molecules considered. Hence, results are quoted only for
Conformational energies of the first four members 0, = 1-4) of the polyoxide series CH3O[(CH2),,-O-IxCH3 were calculated using semiempirical potential energy functions in the usual manner. Experimental values of the same energies were also obtained by means of critical analysis of the unperturbed dimensions and dipole moments of these chain molecules in terms of the rotational isomeric state theory of chain configurations. The semiempirical methods do not in general successfully predict conformational energies in this class of chain molecules, as was pointed out in several earlier but more limited comparisons of this type. The present study implicates the intramolecular interactions involving oxygen atoms as the origin of this disagreement between theory and experiment and gives a quantitative estimate of the magnitude of the discrepancy for each of the interactions thus involved. The energy differences thus established should be included, as carrectims, in conformational energy calculations on such molecules until more reliable potential energy functions can be derived. In any case, the energies obtained in the present investigation by direct correlation of theoretical and experimental values of the dimensions and dipole moments should be useful in the prediction of any configuration-dependent property of any member of the polyoxide series.In recent years a variety of configuration-dependent properties of polymeric chains have been succesqfully treated within the framework of the rotational isomeric state approximation, provided that the neighbor-dependent character of the conformational energies is taken into accounts2 Of fundamental importance in such treatments is information by means of which one may locate suitable rotational states and establish their relative energies. The most reliable information of this type is often obtained by direct measurements, either sgectroscopic or thermodynamic, on small molecules having structural features similar to those of the chain molecule under in~estigation.~ In addition, semiempirical conformational energy calculations frequently provide supplementary information useful in accessing the overall conformatiopal energy surface as a function of the skeletal rotational angles. Such calculations also provide very important information regarding the high energy conformations, which generally elude direct observation by conventional techniques. Since the potential energy functions used in such calculations ale semiempirical,2a however, their reliability must be carefully tested against appropriate experimental data. A typical example of this approach is the calculation4 of the conformational energies of the n-alkanes, including polymethylene (PM) [CH2-Ix. The results thus obtained were found to be in satisfactory agreement with those required to reproduce the observed values of the unperturbed dimension ( r2)o and its temperature coefficient d In (r2)o/dT for the PM chain.The PM chain may be converted schematically to any member of the polyoxide series [(CH2)y-O-]x by simply ...
ABSTRACT:Conformational studies on 1,2-dimethoxyethane (DME), a monomer model compound of poly(oxyethylene), have been carried out by using NMR technique. The observed temperature dependence of the vicinal coupling constants was analyzed on the basis of the rotational isomeric state scheme. For the C-C bond, the 13 CH satellite side bands provide the desired information. Conformational energy E., representing the energy of the gauche state expressed relative to the trans, was found to vary in a range -0.5 to -I .2 kcal mol-t, depending on the solvent system. Values of JT and fa for the vicinal 1 H-1 H coupling were determined concomitantly: JT =I 1.4 ± 0.3 and fa= 2.3 ± 0. I Hz. For the rotation about the C-0 bond, the vicinal 13 C-1 H coupling constant associated with the terminal methyl group was studied. Adoption of fa= 1.3 Hz leads to an estimate of E" = 0.8 to 1.1 kcal mol-1 for the energy difference between the gauche and trans states. In these treatments, the neighbor-dependent character of the bond rotation along the chain was rigorously taken into account. The values of E. and EP derived for the polymer are comparable with those of DME. The results are compared with those reported previously by Viti et a/. and Mastuzaki et a/.KEY WORDS 1,2-Dimethoxyethane I Poly(oxyethylene) I 13 CH Satellite NMR 1 13 C NMR I Vicinal Coupling Constant I Potential Energy Calculation I Conformational Energy I In a series of papers, 1 -3 we have investigated conformational characteristics of polyoxide chains having a general formula fCH 2 C-(R1)(R2)0tn• in which gauche 0 · · · 0 interactions take place around the skeletal C-C bond. The major purpose of these studies is to evaluate the gauche oxygen effect associated with these polymers in terms of the extra stabilization energies, which have been defined as the difference between the conformational energies calculated by using conventional semiempirical expressions 1 and those derived from the analysis of the experimental data on some relevant conformation-dependent properties such as the unperturbed dimension. dipole moment, and bond conformation. In the case of poly(oxyethylene) (POE), where R 1 = R 2 = H, the semiempirical energy calculation (0.6 kcal mol-1 ) failed to reproduce the observed preference (-0.4 kcal mol-1 ) for the gauche over the trans state. 4 · 5 The discrepancy amounts to ca. I kcal mol-1 • In the poly-(oxypropylene) (POP) chain, 2 two gauche states occurring around the skeletal C-C bond are sterically unequivalent to each other. The gauche oxygen effect estimated for the ga conformation, in which the articulated methyl group is situated trans to the preceding oxygen, is in the same order of magnitude as that of POE. Such a stabilization effect, however, was found to be largely suppressed in the sterically more hindered g fJ conformation, in which the preceding oxygen atom is syn to both the following oxygen and the methyl group. A value of Eg=0.5kcal mol-1 (expressed relative to trans) was derived from the 641
The TEL gene on 12p12-13 is a target for a number of translocations associated with various hematological malignancies. The fusion of the TEL gene to the Syk gene in a patient with myelodysplastic syndrome (MDS) with t(9;12)(q22;p12) is reported. Southern blot analysis of patient bone marrow cells with TEL and Syk gene probes detected rearranged fragments. Anchored polymerase chain reaction identified the Syk gene, a nonreceptor tyrosine kinase, on 9q22 fused downstream of TEL exon 5. The TEL gene was fused in-frame to Syk and produced a fusion protein that was constitutively phosphorylated in tyrosine with dimerization that was mediated by the helix-loop-helix domain of TEL. A TEL-Syk fusion product transformed the murine hematopoietic cell line BaF3 to interleukin-3 growth factor independence. TEL-Syk is a novel transforming protein and leads to the transformation of hematopoietic cells. These data implicate that the rearranged Syk gene is involved in the pathogenesis of hematopoietic malignancies.
Conformational analysis has been performed on semiflexible polyesters having repeat units such as -[X-0-C0(CH2)nC0-0]-and -[X-C0-0(CH2)"0-C0]-. These polymers are known to exhibit thermotropic mesophases when (aromatic) rigid cores X are sufficiently anisotropic. Spatial orientations of a given core have been elucidated in a Cartesian coordinate system fixed to the preceding core. The angle defined by unit vectors attached to two successive rigid cores has been evaluated for each conformation of the intervening flexible segment. When the number of methylene units n in the flexible segment is even, the angle is found to be distributed in the range 0-30°( 30-40%) and 85-130°(60-70%). For polymers with = odd, the major portion of the calculated angle is located in the region 50-90°, and to a varying degree (0-20%), orientations are also permitted in the range > 160°. Only the = even polymers conform to the concept of an ordinary nematic ordering. Based on these results, an explanation has been offered for the observed odd-even oscillation in the entropy change ASni at the isotropization temperature. For the n = even polymers, the orientational and combinatorial contributions to the entropy change at the nematicisotropic transition have been estimated from the calculated distribution curves within the framework of the modified Flory-Ronca theory. The results are compared with experimental data reported in the literature. = even series are unmistakable. Recently, Blumstein and collaborators3,4 reported other examples of the odd-even effect for polyesters having the same backbone structure as depicted above.
The combinatory partition function for a system of rodlike particles of diverse axis ratios mixed with a quasispherical solvent has been derived by use of the model and elaboration of the procedure previously employed for a binary system in which the solute is monodisperse. A single disorder parameter y = x sin " where x is the axis ratio for solute particles of a given component and sin measures their average inclination with respect to the axis of the domain, or phase, characterizes all solute components for which x > y. Components with x < y are unoriented. Chemical potentials are given for the various components, and the basic relations required for treatment of the equilibria between an isotropic and an anisotropic, or liquid crystalline, phase are derived.
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