ABSTRACT:Dissolution of cellulose into aqueous (aq) calcium thiocyanate solution was investigated with emphasis on solvent structure and interactions with cellulose. The aq calcium thiocyanate (Ca(SCNh) solution with concentration (CcaT) more than 48.5 wt% could dissolve any celluloses. Solvation measurement revealed that in wt%, the solvent system is formulated by Ca(NCS)2 • xH20 (x 4) + yH 2 0 (y 6), which exhibits mainly non-dissociated thiocyanate with high specific viscosity, as proved by electric conductivity, specific viscosity and IR or 13 C NMR measurements on solvent as a function of concentration of calcium thiocyanate. In this regard, the most stable 4 hydrate calcium thiocyanate is concluded from energy calculation as trans-trans configuration of Ca(-N = C = S) · 4H20. DSC and IR analyses suggested that dissolution of cellulose takes place by first attack of Ca(NCS)2 • xH2 0 (x 4) towards ring oxygen in cellulose. Ca(NCSh · xH2 0 (x 4) becomes 4-hydrates-like structure (sixcoordinate complex of Ca) and cellulose forms a 5-membered ring by coordinating two oxygen atoms (0(5) and 0(6)) in the glucopyranose unit, and then cellulose dissolves on heating. In this process, some ligand exchange might occur if the hydration number is more than 2. This coordination of cellulose is quite characteristic, compared with other solvents, such as cuprammonium hydroxide, which coordinate with 0(2) and 0(3) hydroxyl groups.

ABSTRACT:Attempt was made to clarify the structural change of wood pulp during the treatment of concentrated aqueous (aq) calcium thiocyanate (aq Ca(SCN)z) solution at room temperature. For this purpose, X-ray, DSC, and CPIMAS 13 C NMR were used to measure changes of crystalline structure and formation of cellulose-solvent complex. X-Ray data indicated that 55 wt% aq Ca(SCN)2 so ln. causes intracrystalline interplanar swelling of the wood pulp, forming cellulose--calcium thiocyanate addition compound. The interplanar spacing of (ITO), (110), and (200) planes increased for the former two planes and slightly decreased for the last one for treatment time td of 90 min. From DSC thermo grams of cellulose-55 wt% aq Ca(SCN)z soln. mixture, exothermic heat !'J.H for the formation of the addition compound was estimated to be ca. II kcal mol-1 , which was far iower than that for generation of cellulose sodium salt. The cellulose recovered from the system has quite different crystalline structure depending on treatment time and the reagents used for recovery. Up to td = 90 min, water recoverd the mixture of natural cellulose crystal (Cell

ABSTRACT:Attempt was made to investigate the solubility and the dissolved state of various cell uloses in aqueous (aq) calcium-and sodium-thiocyanate solution. Almost all cell uloses used in this study were soluble in 55 wt% aq calcium thiocyanate (Ca(SCN) 2) soln. at about 100°C, while 60wt% aq sodium thiocyanate (NaSCN) soln. dissolves only limited cellulose mainly regenerated from cellulose solution. The solubility of cellulose in 60wt% aq NaSCN was independent of the crystal form, crystallinity and the degree of polymerization of cellulose and this was explained only in terms of the degree of breakdown of intramolecular hydrogen bonds in the cellulose solid. Using 2-dimensional NMR six carbon peaks in 13 C NMR spectra of cellulose in two solvents were successfully assigned. The comparison of chemical shifts of cellulose in 55 wt% aq Ca(SCN)2 solution and 10% sodium hydroxide (NaOH) solution strongly suggested that calcium atoms as electron acceptors coordinate with oxygen atoms in glucose ring and primary alcohol at C(6) position, in the same manner of cellulose dipped in 55 wt% aq Ca(SCN)z solution at room temperature. In the 13 C NMR spectrum of cellulose-60% aq NaSCN solution system, C(3), C(2), and C(6) peaks were observed at lower magnetic field side, implying that sodium atoms interact with hydroxide groups at C(2), C(3), and C(6) positions of glucopyranose in cellulose molecules.

ABSTRACT:An attempt was made to evaluate molecular parameters of poly(hexamethyleneadipamide) (nylon 6,6) in mixture of calcium chloride and methanol with various calcium chloride concentrations (weight fraction Wea against weight of the solvent mixture) using light scattering method. Dissolved state of the polymer was discussed in connection with the chain conformation based on data of viscosity, adiabatic compressibility, infrared (IR) spectra and 1 H and 13 C NMR spectra. The second virial coefficient A 2 , obtained by the light scattering method, remarkably decreases with a decrease of Wea below 0.15 and is expected to become zero at Wea of ca. 0.115 (i.e., Flory's (9 solvent). From values of conformation parameter and characteristic ratio of the polymer, evaluated from radius of gyration at·the (9 state, the nylon 6,6 molecule is judged to be very flexible in the unperturbed state. The viscosity of the polymer solution showed specific Wea dependence, around Wea =0.15. The results of the viscosity, adiabatic compressibility, IR and NMR measurements on the solvent mixtures revealed that the above Wea= ca. 0.05, mole ratio of the undissociated CaCl2 monotonically increases with Wea and methanol molecules strongly interact with calcium chloride probably forming organometallic complex. The results of 1 H and 13 C NMR and IR measurements on the polymer solutions suggested that dissolution of nylon 6,6 in calcium chloride-methanol mixture with Wea~ 0.1 is realized at least by interaction of methanol and chlorine parts in the complex with amide carbonyl and amine: In the range of 0

Poly(8-aminoguanylic acid) has in neutral solution a novel ordered structure of high stability. The 8-amino group permits formation of three hydrogen bonds between two residues along the "top", or long axis, of the purines. The usual hydrogen bonding protons and Watson-Crick pairing sites are not involved in the association. The bonding scheme has a twofold rotation axis and is hemiprotonated at N(7). Poly(8NH2G) is converted by alkaline titration (pK = 9.7) to a quite different ordered structure, which is the favored form over the range approximately pH 10-11. The bonding scheme appears to be composed of a planar, tetrameric array of guanine residues, in which the 8-amino group does not participate in interbase hydrogen bonding. Poly (8NH2G) does not interact with poly(C) in neutral solution because of the high stability of the hemiprotonated G-G self-structure. Titration to the alkaline plateau, however, permits ready formation of a two-stranded Watson-Crick helix. In contrast to the monomer 8NH2GMP, poly(8NH2G) does not form a triple helix with poly(C) under any conditions. The properties of the ordered structures are interpreted in terms of a strong tendency of the 8-amino group to form a third interbase hydrogen bond, when this possibility is not prevented by high pH.