Photopolymerization initiated by charge-transfer complex. I. Photopolymerization of methylmethacrylate with the use of quinaldine-bromine and lutidine–bromine charge-transfer complexes as photoinitiator

Photopolymerization of MMA was carried out with quinaldine–bromine (QN–Br₂) and lutidine–bromine (LU–Br₂) charge-transfer complexes as initiators. The rate of polymerization R_p increased with rising monomer concentration and the monomer exponent was computed as unity. At first the rate of polymerization accelerated and then reduced as the initiator concentration was increased. The initiator exponent was 0.5. The reaction was carried out at three different temperatures and overall activation energy was calculated at 4.0 kcal/mol. The kinetic data and other evidence indicate that the overall polymerization takes place in a radical mechanism. A suitable mechanism is suggested.     

A classical description of deep inelastic collisions with surface friction and deformation

The friction model for heavy ion induced fusion and deep inelastic nuclear reaction is extended to include deformation. Spheroidal deformation and relative motion of the mass centres of the two interacting nuclei are treated as dynamical variables. The radial frictional force has been assumed to be proportional to the rate of change of the separation between the two surfaces instead of the two centres of mass. The friction coefficients remain unaltered. The potential as a function of deformation and separation distance are generated by a single folding procedure. The model is applied to⁴⁰Ar+²³²Th at 379 MeV (Lab) and¹³⁶Xe+²⁰⁹Bi at 1,130 MeV (Lab). In case of the former, the energy loss, which has not been properly accounted for before, is now satisfactorily explained and in the case of the latter the model predicts the absence of fusion in agreement with experiment.     

THE 'OPSIN SHIFT' IN BACTERIORHODOPSIN: STUDIES WITH ARTIFICIAL BACTERIORHODOPSINS

Abstract— The difference (in cm⁻¹) in absorption maxima between the protonated Schiff base of retinals and the pigment derived therefrom has been defined as the opsin shift. It represents the influence of the opsin binding site on the chromophore. The analysis of the opsin shifts of a series of dihydrobacteriorhodopsins has led to the external point-charge model, which in addition to a counter anion near the Schiff base ammonium, carries another negative charge in the vicinity of the β-ionone ring. This is in striking contrast to the external point-charge model proposed earlier for the bovine visual pigment. The absorption maxima of rhodopsins formed from bromo- and phenyl retinals support the two models. A retinal carrying a photoaffinity label has yielded a nonbleachable bacteriorhodopsin.     

Enthalpic relaxation of convective desiccated trehalose-water glasses

Minimizing molecular mobility for desiccation preservation of biologics close to ambient temperature using trehalose glasses require quantitative characterization of their enthalpic relaxation at various end water contents. Differential scanning calorimetry (DSC) was used to characterize three different water contents: 0%, 1.5% and 10% over a wide range of aging temperatures. Results showed the characteristic time (τ) varies both with the water content and the aging temperature. τ increased with lowered aging temperature but showed a non-monotonous relationship as a function of water content. Fragility of trehalose glasses was analyzed using thermophysical parameters obtained from relaxation studies. The study showed trehalose to be a fragile glass former at all water contents, with 0% water samples showing a relatively stronger glass. A compromise between molecular mobility and glass fragility led to an optimal water content close to 1.5% and an aging temperature close to room temperature. This would ensure a τ value of 9000 h, which corresponds to a storage period of a year.     

Polymerization of methyl methacrylate initiated by Mn(III)–glycerol redox system

The kinetics of thermal polymerization of methyl methacrylate initiated by the redox system Mn(III)–glycerol was studied in aqueous sulfuric acid in the temperature range of 30–40°C, and the rates of polymerization, R_p, and Mn³⁺ disappearance, etc., were measured. The effect of certain water-miscible organic solvents and certain cationic and anionic surfactants on the rates of polymerization has been investigated. A mechanism involving the formation of a complex between Mn³⁺ and glycerol whose decomposition yields the initiating free radical with the polymerization being terminated by the metal ion has been suggested.     

Rapid spectrophotometric determination of phenothiazines with molybdophosphoric acid

A simple and rapid spectrophotometric method for the determination of six phenothiazines can be based on the formation of a coloured compound between molybdophosphoric acid and phenothiazines. The i.r. and e.s.r. spectra of the coloured compounds showed that molybdophosphoric acid oxidizes phenothiazines to a radical cation with which it then forms a coloured compound. The proposed method is employed for the determination of phenothiazines in pharmaceutical preparations. Calibration graphs are linear over ranges of about 100–2000 μg of the phenothiazine.     

The synthesis and conformational analysis of tetrahydro-1,2,4-oxadiazines

The synthesis and variable temperature ¹H and ¹³C NMR spectra of three tetrahydro-1,2,4-oxadiazines are reported. The N(4)-Me inversion barriers are 6.8–7.0 (ax→ts) and 7.4–7.9 kcal mol^?1 (eq→ts) with ΔG° 0.6–0.9 kcal mol^?1. The N(2)-Me inversion barriers are 10.4–11.4 (ax→ts) and 11.6–13.1 kcal mol^?1 (eq→ts) with ΔGδ 1.2–1.7 kcal mol^?1. The barrier to ring inversion is ca. 12.7 kcal mol^?1. “R value” analysis shows the ring to have a 56.5±2δ dihedral angle about the C(5)-(6) bond, indicative of the expected chair conformation.     

A study on the electronic effect of <Emphasis Type="Italic">para</Emphasis> substituents in the aryloxy ring of the hydrazone ligands on the vanadium centre in a family of mixed-ligand [V<Superscript>V</Superscript>O(ONO)(OO)] complexes

[V^IVO(acac)₂] reacts with the methanolic solutions of tridentate dibasic ONO donor hydrazone ligands derived from the condensation of benzoyl hydrazine with either 2-hydroxyacetophenone (H₂L¹) or its para-substituted derivatives (H₂L^2–4) (general abbreviation H₂L), in the presence of vanillin (Hvan) in equimolar ratio under aerobic conditions generating the mixed-ligand oxovanadium(V) complexes of the type [V^VO(L)(van)], (1)–(4) in good yield. All the complexes are diamagnetic and exhibit only ligand-to-metal charge transfer (l.m.c.t.) band near 510 nm in addition to intra-ligand (π → π*) transition band near 330 nm in CH₂Cl₂ solution. ¹H-n.m.r. spectra of the complexes in CDCl₃ solution indicate the presence of two isomeric forms [(1A), (1B); (2A), (2B); (3A), (3B) and (4A), (4B)] in different ratios, which is explained by the interchange of the two binding sites of van⁻ motif between its coordinated equatorial and axial positions. Complexes display two quasi-reversible one electron reduction peaks near +0.10 V and near +0.30 V versus s.c.e. in CH₂Cl₂ solution which are attributed to the successive reduction of V^V→ V^IV and the V^IV→ V^III motifs, respectively. λ_max (for l.m.c.t. transition), and the two reduction potential values (E _1/2)^I (average of the first step anodic and first step cathodic peak potentials) and (E _1/2)^II (average of the second step anodic and second step cathodic peak potentials) of the complexes, are found to be linearly related to the Hammett constants (σ) of the substituents in the aryloxy ring of the hydrazone ligands. λ_max, (E _1/2)^I and (E _1/2)^II values show large dependence: dλ_max/dσ = 37.29 nm, d(E _1/2)^I/dσ = 0.21 V and d(E _1/2)^II/dσ = 0.21 V, respectively, on σ.     

A characterization based on the equidistribution of the first two spacings of record values

Summary For a sequence {X _n:n=0, 1, 2,...} of i.i.d. discrete random variables let X ₀ denote the zeroeth record value and X _L(1), the first record value. It is shown that X ₀ and X _L(1) –X ₀ are identically distributed if and only if X ₀ has the geometric distribution over the lattice k :k=1, 2,... for some >0.     

Aqueous polymerization of acrylonitrile initiated by the bromate–thiourea redox system

The aqueous polymerization of acrylonitrile initiated by an acidified bromate–thiourea redox system has been studied under nitrogen atmosphere. The rate of polymerization is independent of thiourea concentration over the range 2–9 × 10^?3M and reaches maximum at 9 × 10^?3M. The rate varies linearly with [monomer]. The initial rate of polymerization as well as the maximum conversion increases within the range of 4–22.5 × 10^?3M KBrO₃, but beyond 22.5 × 10^?3M the rate of polymerization decreases. The initial rate and the limiting conversion increases with increasing polymerization temperature in the range 30–45°C; and beyond 45°C they decrease. The effect of certain neutral salts, water-soluble solvents, and micelles of cationic, anionic, and nonionic surfactants on the rate of polymerization has been investigated.