Relationship between kinetic chain length and radical polymerization rate

In the copolymerization of monomers M₁ and M₂ which form polymer radicals of chain length n of N¹_n with electron on a M₁ type and N²_n with one on a M₂ type, it is assumed that the specific rates of termination between N¹_n and N¹_n and N¹_s, N¹_n and N²_s, and N²_n and N²_s are k_α(ns)^?a, k_β(ns)^?a, and k_γ(ns)^?a, respectively, where k_α, k_β, and k_γ are the rate constants of reaction between segment radicals in the respective termination, and a is constant. The relation between kinetic chain length n? and polymerization rate R_p is derived as: 1/n? = 1/n?₀ + const. (R_p)^A(a), where n?₀ is the kinetic chain length of the polymer formed by transfer and A (a) is unity (predominance of transfer) and 1/(1–2a) (no transfer). In the copolymerization between methyl methacrylate (M₁) and styrene (M₂) at 60°C, when R_p → 0, k_r12/k₁₂ + k_r21/k₂₁ = 5.9× 10^?5 is obtained, where k_r12 and k_r21 are the rate constants of transfer of N¹ to M₂ and N² to M₁, and k₁₂ and k₂₁ are the rate constants of propagation of N¹ to M₂ and N² to M₁. In the absence of transfer, the a value is found to be 0.065 ± 0.008, from the relation between n? and R_p, regardless of the monomer composition. Such a value is also estimated by setting b = 0.72 in a = 0.153 (2b–1), where b is the constant in the Mark-Houwink equation. Further, the value of k_β is found to be 1.18 × 10⁹l./mole-sec, which is comparable with the diffusion-controlled rate of reaction between small molecules. The rate of reaction between segment radicals is fivefold larger than the polymer-polymer termination when transfer predominates.     

Application of preparative high-speed counter-current chromatography for separation of methyl gallate from Acer truncatum Bunge

Preparative separation of methyl gallate in leaves extract of Acer truncatum Bunge was conducted using high-speed counter-current chromatography (HSCCC) with a solvent system composed of ethyl acetate-ethanol-water at volume ratios of 5:1:5 (v/v/v). In a single operation, 57.5 mg of methyl gallate was obtained from 120 mg of the extract. HPLC analyses of the counter-current chromatography (CCC) fraction revealed that the methyl gallate was having over 97% purity. Its structure was identified by 1H NMR and 13C NMR.     

Radiation-induced solid-state polymerization of trioxane under high pressure

The in-source polymerization of trioxane in the solid state was investigated over a wide range of temperature and pressure, i.e., from 30 to 140°C and up to 7000 kg/cm², respectively. In the polymerization that was carried out slightly below the melting point under pressure, the higher the pressure, the higher the rate of polymerization. It was confirmed that the maximum rate of solid-state polymerization of trioxane occurs near the melting points, even under elevated pressure. The rate of polymerization decreased with increasing pressure at constant temperature. The shape of the time–conversion curves may be classified into two types, i.e., one which is typical of high pressure and low temperature, and the other which is typical of low pressure and high temperature. Changes in the shape of the conversion—intrinsic viscosity curves occurred coincidentally. Thus, three regions for the different “polymerization characteristic” were determined as functions of polymerization temperature and pressure. Explanations are given for the above-mentioned polymerization characteristic.     

Reaction of carboxamide with Cu2Oisonitrile complex; formation of a new chelated copper(I) complex

Reaction of carboxamides with Cu₂O in the presence of t-butyl isocyanide gave new chelated copper(I) complexes, which probably are formed by the insertion of t-butyl isocyanide into the coppernitrogen bond of copper(I) amide isonitrile complexes, which were initially produced from the carboxamides and Cu₂Ot-butyl isocyanide complex. The same chelated copper(I) complexes were prepared more readily by the reaction of the corresponding N-trimethylsilyl-carboxamides with Cu₂Ot-butyl isocyanide complex. Reactions of the copper(I) complexes thus obtained with alkylating agents, such as alkyl halides, alkyl tosylates and triethyloxonium tetrafluoroborate, also were described.     

The electronic structures and spectra of proflavine,acridine orange,and their DNA complexes

The electronic structure of the proflavine cation is studied by the SCF –ASMO –CI method using the Pariser–Parr–Pople approximations. It is shown that the band at 445 mμ may be assigned to the ¹A₁ → ¹B₁, transition polarized along the long axis of the molecule. The bands in the neighbourhood of 260 mμ, which are composed of three absorption bands, are tentatively assigned to the ¹A₁ → ¹B₁, ¹A₁ → ¹B₁, and ¹A₁ → ¹A₁ transitions, respectively, in order of decreasing wavelength. The spectrum of the acridine orange cation may be understood to have the same assignment as that of the proflavine cation. The acridine dye cations are well known for their dimerization with concentration. The intermolecular distances in these dimers are estimated from the band shifts due to the formation of dimers, using the exciton theory. The main contribution to the molecular interaction is shown to be the electrostatic dipole–dipole interaction. Since the first excitation band of the dye molecule which exhibits a remarkable change due to the formation of the DNA–acridine dye complex, is suggested to be polarized along the long axis, preference of the outside stacking or the intercalation model is qualitatively discussed from the spectral shift of the acridine dye bound to the DNA, assuming simple models.     

Termination rate constants in radical polymerization

A rate constant is generally derived by using Fick's equation corresponding to the spherical interdiffusion of particles. By using this rate constant, chain and primary radical termination rate constants can be approximated to rate constants for the bimolecular reactions between two radical chain ends, and primary radical and radical chain end, respectively. The former is given by k_s = 8πN_LD_sL_s exp { ? L_s/R_s} × 10^?3 1./mole-sec. The latter is given by k_si = 4πN_L(D_s + D_i)L_si exp { ? L_si/R_si} × 10^?3 1./mole-sec. Here, N_L is Avogadro's number; D_s and D_i are the diffusion constants of radical chain end and primary radical, respectively; L_s and L_si are, respectively, the distances between two radical chain ends and between a primary radical and a radical chain end at a thermal energy equal to the coulombic energy of interaction of the net charges; and R_s and R_si are, respectively, the average distances between two radical chain ends and primary radical on a collision.     

Further evidence of the vibronic coupling of pyrazine as revealed by preresonance raman effect

The excitation wavelength dependences of the intensities of the Raman lines of pyrazine have been measured. The intensity enhancement of the non-totally symmetric Raman line at 925 cm^?1 provided firm evidence of the vibronic coupling between the lowest ¹B_3u(n,π^*) and second lowest ¹B_2u(π,π^*) states. The excitation wavelength dependences of other non-totally symmetric Raman lines suggest also the various vibronic coupling schemes.     

Kunzeanones A, B, and C: novel alkylated phloroglucinol metabolites from Kunzea ambigua

Three new metabolites, kunzeanones A (1), B (2), and C (3), along with three known compounds, cryptostrobin (4), (+)-spathulenol (5), and (−)-globulol (6), were isolated from the non-polar fraction of the dried leaves of Kunzea ambigua (Myrtaceae), which shows ichthyotoxicity toward a small fish, medaka. The structures of these new compounds were elucidated as condensates of alkylated phloroglucinol with methylflavanone and germacrane-type sesquiterpene, respectively, on the basis of spectral analyses including 1-D and 2-D NMR spectra. The stereochemistries of kunzeanones A and B were determined by X-ray crystallographic analysis. A sesquiterpene, (+)-spathulenol (5), among the isolates was characterized as the ichthyotoxic principle of the extract.     

Biogenetically inspired approach to the Strychnos alkaloids. Concise syntheses of (+/-)-akuammicine and (+/-)-strychnine

A linear synthesis of the indole alkaloid (+/-)-akuammicine (2) was completed by a novel sequence of reactions requiring only 10 steps from commercially available starting materials. The approach features a tandem vinylogous Mannich addition and an intramolecular hetero Diels-Alder reaction to rapidly assemble the pentacyclic heteroyohimboid derivative 8 from the readily available hydrocarboline 6. Oxidation of the E ring of 8 gave the lactone 9 that was converted into deformylgeissoschizine (11). The subsequent elaboration of 11 into 2 was effected by a biomimetically patterned transformation that involved sequential oxidation and base-induced skeletal reorganization. A variation of these tactics was then applied to the synthesis of the C(18) hydroxylated akuammicine derivative 36. Because 36 had previously been converted into strychnine (1) in four steps, its preparation constitutes a concise, formal synthesis of this complex alkaloid.