Studies on the graft copolymerization of cellulosic materials

Graft copolymers of acrylic acid on cellulosic materials were obtained by use of ceric ion in aqueous medium at various temperatures. The level of incorporation of poly(acrylic acid) grafts and the efficiency of grafting were significantly reduced as the temperature of polymerization was increased from 35° to 60°C. The uptake of cadmium and copperions from aqueous solution by the cellulose-g-poly(acrylic acid) copolymer was examined by equilibrium and dynamic sorption studies. The amount of metal ions removed from solution depended on the metal ion type, initial concentration of the metal ion solution, level of incorporation of poly(acrylic acid) in the graft copolymer and the temperature of the metal ion solution.     

Study on the formation of a supramolecular conjugated graft copolymer in solution

The formation in solution of a supramolecular graft copolymer bearing conjugated blocks is demonstrated using diffusion ordered NMR spectroscopy (DOSY). A tailor‐made poly(3‐(2‐ethylhexyl)thiophene) (P3EHT) with a phenol end group is synthesized. For this purpose, the chain‐growth mechanism of the polymerization of 2‐bromo‐5‐chloromagnesio‐3‐alkylthiophenes in the presence of a Ni(dppp) catalyst (dppp = 1,3‐bis(triphenylphosphino)propane) is exploited, as it enables the use of functionalized initiators to introduce specific end groups. The so‐obtained polythiophene was subsequently mixed in solution with poly(4‐vinylpyridine) (P4VP) to enable phenol‐pyridine hydrogen bonding. The formation of the supramolecular graft copolymer is studied using DOSY‐measurements. Based on the results thereof, the amount of P3EHT attached to the P4VP is calculated and the association constant of the hydrogen bond is estimated. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 804–809     

Molecular assembly composed of a dendrimer template and block polypeptides through stereocomplex formation

A 2nd generation polyamideamine (PAMAM) dendrimer bearing right-handed helices to its eight terminals was shown to accommodate eight left-handed helices via stereocomplex formation to generate molecular assemblies of disk structure with 13-14 nm diameter and 6 nm thickness.     

Combination of cellulosic materials and metallic ions

Cellulosic materials (DP, SCP) and PVA fibers were treated with four kinds of metallic ions (Ca²⁺, Fe²⁺, Fe³⁺, Ce⁴⁺), and the adsorption behavior was studied to elucidate the manner in which the celluloses and the metallic ions were combined. The effects of treatment temperature, time, and concentration upon the amount of the metallic ions adsorbed were examined. With Ca²⁺ and Fe²⁺, the effects of such factors on the adsorption were slight, while with Fe³⁺ and Ce⁴⁺ the effects of time, temperature, and ion concentration were pronounced. Also, it was evident that the amount (molar) of equilibrium adsorption of Ca²⁺ or Fe²⁺ was approximately the same as the content of carboxyl groups in the cellulose sample, and the amount of equilibrium adsorption of Fe³⁺ or Ce⁴⁺ was approximately the same as that of total carbonyl group content. When the samples which had adsorbed these metallic ions were treated with 0.1N hydrochloric acid, the Ca²⁺ and Fe²⁺ were completely desorbed while about 80% of the adsorbed Fe³⁺ and Ce⁴⁺ remained. These results indicate that there are two types of combinations of cellulosic materials and metallic ions involved: one is thought to be an ionic bond, while the other is considered to be a chelate bond.     

Chelate effect and thermodynamics of metal complex formation in solution: a quantum chemical study

The accuracy of quantum chemical predictions of structures and thermodynamic data for metal complexes depends both on the quantum chemical methods and the chemical models used. A thermodynamic analogue of the Eigen-Wilkins mechanism for ligand substitution reactions (Model A) turns out to be sufficiently simple to catch the essential chemistry of complex formation reactions and allows quantum chemical calculations at the ab initio level of thermodynamic quantities both in gas phase and solution; the latter by using the conductor-like polarizable continuum (CPCM) model. Model A describes the complex formation as a two-step reaction: 1. [M(H2O)x](aq) + L(aq) <==>[M(H2O)x], L(aq); 2. [M(H2O)x], L(aq) <==>[M(H2O)(x-1)L],(H2O)(aq). The first step, the formation of an outer-sphere complex is described using the Fuoss equation and the second, the intramolecular exchange between an entering ligand from the second and water in the first coordination shell, using quantum chemical methods. The thermodynamic quantities for this model were compared to those for the reaction: [M(H2O)x](aq) + L(aq) <==>[M(H2O)(x-1)L](aq) + (H2O)(aq) (Model B), as calculated for each reactant and product separately. The models were tested using complex formation between Zn(2+) and ammonia, methylamine, and ethylenediamine, and complex formation and chelate ring closure reactions in binary and ternary UO(2)(2+)-oxalate systems. The results show that the Gibbs energy of reaction for Model A are not strongly dependent on the number of water ligands and the structure of the second coordination sphere; it provides a much more precise estimate of the thermodynamics of complex formation reactions in solution than that obtained from Model B. The agreement between the experimental and calculated data for the formation of Zn(NH(3))(2+)(aq) and Zn(NH(3))(2)(2+)(aq) is better than 8 kJ/mol for the former, as compared to 30 kJ/mol or larger, for the latter. The Gibbs energy of reaction obtained for the UO(2)(2+) oxalate systems using model B differs between 80 and 130 kJ/mol from the experimental results, whereas the agreement with Model A is better. The errors in the quantum chemical estimates of the entropy and enthalpy of reaction are somewhat larger than those for the Gibbs energy, but still in fair agreement with experiments; adding water molecules in the second coordination sphere improves the agreement significantly. Reasons for the different performance of the two models are discussed. The quantum chemical data were used to discuss the microscopic basis of experimental enthalpy and entropy data, to determine the enthalpy and entropy contributions in chelate ring closure reactions and to discuss the origin of the so-called "chelate effect". Contrary to many earlier suggestions, this is not even in the gas phase, a result of changes in translation entropy contributions. There is no simple explanation of the high stability of chelate complexes; it is a result of both enthalpy and entropy contributions that vary from one system to the other.     

Enzymatic conversion of cellulosic materials to sugars and alcohol

This techno-economic study deals with the production of sugars and alcohols from cellulosic materials. It covers such key subjects as: potential raw materials; the state-of-the-art on production technologies; the economics of extant processes; and finally infers implications for developing countries from the foregoing. It is clear that a large number of cellulose-, starch-, and sugarcontaining plants can be processed to produce sugars and alcohols. Sugar-containing plants such as sugarcane, sweet sorghum, and nipa palm are the best candidates for the high-yield production of alcohol fuel. Likewise, the starch-containing crops such as cassava, sweet potatoes, yams, taro, and tannia are good candidates, but require an additional step to break down starch to sugar. However, the emphasis of this report is on the major part of biomass containing cellulose and which, therefore, needs special treatment before it can be used to produce glucose and alcohols. To utilize cellulosic containing raw materials the following steps are necessary:

1. Growth, harvest, and delivery of raw materials to processing plants; or, alternatively, the collection and delivery of cellulosic “waste” products.
2. Pretreatment or conversion of the raw material by mechanical, physical, chemical, or enzymatic methods to break down the cellulose to sugars and to modify or remove unwanted side-products, usually lignin and hemicellulose.
3. Recovery and purification of sugars from reaction mixture.
4. Fermentation of sugars to alcohol and purification by distillation.
5. Treatment of process residues to reduce pollution and to recover potentially valuable side-products.

From the considerable research and development work carried out in all areas of pretreatment, it appears acid and enzymatic hydrolysis processes hold the most promise for developing countries. Though acid hydrolysis technology is more advanced, greater ultimate potential is seen in the enzymatic hydrolysis, which is, therefore, recommended for developing countries. The economics of producing alcohol from cellulosic materials is at this time not favorable. Nevertheless, it is recommended that further research and development be undertaken in this area in order to accomplish one or more commercially attractive processes for producing alcohol from fermenting cellulose. If this was accomplished, the developing countries could gain in the following manner:

? Increase self-sufficiency since alcohols can to a great part substitute for petroleum fuels.

? Achieve a better balance of trade.

? Be able to increase employment, especially in rural areas.

? Achieve a higher level of technical competence in biotechnology and related areas.

? Be in a position to expand chemical industries.

? Establish an improved agricultural base by being able to utilize alternative crops and by being able to use what was previously termed agricultural wastes.

     

A study of structure formation processes occurring with the gelation of polysulfonamide solution in dimethylacetamide

This work investigates spontaneous gelatination of polysulfonamide in the solution of dimethylacetamide by nuclear magnetic relaxation, small-angle light scattering, and refractive index measurement. Two stages of the gelatination process were found to occur. Spherulites are formed in the first stage while the mobility of the solvent molecules decreases sharply. The second stage is characterized mainly by perfection of the inside structure of spherulites without a change in their size. The degree of decreasing mobility of the solvent molecules is much less in this stage than in the first stage.     

A calorimetric investigation of the formation of a stereocomplex in poly(methyl methacrylate) solutions

The heat of formation ΔH of the stereocomplex of iso + syndiotactic poly(methyl methacrylate) in a 1 per cent solution in dimethylformamide and in toluene was measured. From the concentration dependence of ΔH it may be inferred that multimolecular aggregates are formed, with a composition given by the ratio syn: iso = 1·5: 1 to 2: 1. The measurements also indicate a strong dependence of the thermal effect on the quality of the solvent and on the tacticity of both polymer components.     

Degradation of cellulosic key chromophores by ozone: a mechanistic and kinetic study

Cellulose - Chromophores, colored substances of rather high stability that reduce brightness, are present in all kinds of cellulosic products, such as pulp, fibers, aged cellulosic material, and...     

Studies of the graft copolymerization of methyl methacrylate by means of the photochemical reduction of ceric ion adsorbed on cellulosic materials

It was observed that the rate of reduction of ceric ion adsorbed on cellulose was remarkably accelerated by irradiation with ultraviolet light, and this behavior depended upon the kind of cellulose. When the graft copolymerization of methyl methacrylate on cellulose with adsorbed ceric ion was carried out by irradiation with ultraviolet light, the percent grafting decreased for softwood, bleached sulfite pulp and increased for hardwood semichemical pulp. The average molecular weight of the grafts was observed generally to decrease. If it is assumed that the ceric ions, which are reduced at an accelerated rate in the early stages of reaction with SCP, do not participate in the graft formation, a relation is observed between the modified amount of reduced ceric ion and the number of grafted chains formed, and the molar ratios of these quantities are 12:1 without irradiation and 75:1 to 100:1 with irradiation. Even when the rate of reduction of ceric ion is accelerated, the increase in the number of grafted chains is found to be very small.     

Diversity of the gramicidin a spatial structure: two-dimensional 1H nmr study in solution

Theoretical consideration reveals a unique relationship between NMR spectral parameters and possible types of the gramididin A spatial structure. By means of two dimensional NMR spectroscopy four distinct species were detected simultaneously in ethanol solution. Comparison of experimental data and theoretical conclusions demonstrates that species 1 and 2 are left-handed parallel double helices

differing in relative arrangement of the two polypeptide chains within the dimers, species 3 is left-handed antiparallel double helix

, and species 4 is a mirror image of species 1, i.e. right-handed parallel double helix

. The results are compared with those on spatial structures of the peptide in complex with cesium (right-handed antiparallel double helix

) and of the gramicidin A transmembrane ionchannel (N-terminal to N-terminal single-stranded dimer

).     

In-situ UV-visible study of Pd nanocluster formation in solution

The formation of Pd nanoclusters in solution is studied. This system has two types of light-absorbing species: Pd ions which absorb light via electronic transitions and Pd clusters and aggregates which absorb light via valence-conduction transitions and also scatter light due to their nanometric dimensions. Here we monitor these dynamic changes using UV-visible spectroscopy. The reduction and clustering concentration profiles are extracted from the raw data using a combination of net analyte signal (NAS) and principal component analysis (PCA) methods. PdCl2, Pd(OAc)2 and Pd(NO3)2 are used as Pd2+ precursors and various tetra-n-octylammonium carboxylates are applied as reducing and stabilising agents. This in situ approach enables the quantification of both the reduction of the Pd2+ ions and the growth of the Pd clusters. Kinetic models that account for ion reduction, cluster growth and aggregation are presented and the influence of the counteranions and the reducing agents on these processes is discussed.     

Nitrilotriacetato-monoperoxo complexes of vanadium(V): formation in aqueous solution,synthesis and structure

Summary M₂[VO(nta)(O₂)]·xH₂O, where M⁺ is NH _inf4 ^p+ , K⁺ or Rb⁺ and nta is nitrilotriacetate, and Sr[VO(nta)(O₂)]·2H₂O were synthesized. The electronic spectra of aqueous KVO₃-H₂O₂-H₃nta-HClO₄(KOH) solutions (pH 1.45–5.62) and the thermal decomposition of K₂[VO(nta)(O₂)]· 2H₂O with active oxygen release at 275° C showed that the nta-monoperoxo complex is the most stable vanadium(V) peroxo complex so far investigated. The anhydrous potassium salt was prepared on heating the crystallohydrate under dynamic conditions. The i.r. spectra indicate the same anion structure in solution and in the solid state where nta is coordinated as a tetradentate ligand.     

Positron lifetime study of several chiral materials in aqueous solution

The most obvious symmetry breaking in Nature is the left-right asymmetry of living beings: sugars and amino acids are almost exclusively represented by one of their stereoisomers (D-isomer for sugars and L-isomer for amino acids) at the expense of other possible isomers. In our experiment we studied the aqueous solutions of tartaric acid, alanine, and cysteine in the function of temperature by positron lifetime spectroscopy. The results were compared with those obtained in pure water under similar conditions. We always observed a sharp minimum of the positron lifetime at around 41 °C in water and in the solutions of the natural stereo-isomers. On the other hand, the same minimum occurred at considerably lower temperatures in the solutions of the unnatural isomers.     

The structure of aqueous sodium hydroxide solutions: a combined solution x-ray diffraction and simulation study

To determine the structure of aqueous sodium hydroxide solutions, results obtained from x-ray diffraction and computer simulation (molecular dynamics and Car-Parrinello) have been compared. The capabilities and limitations of the methods in describing the solution structure are discussed. For the solutions studied, diffraction methods were found to perform very well in describing the hydration spheres of the sodium ion and yield structural information on the anion's hydration structure. Classical molecular dynamics simulations were not able to correctly describe the bulk structure of these solutions. However, Car-Parrinello simulation proved to be a suitable tool in the detailed interpretation of the hydration sphere of ions and bulk structure of solutions. The results of Car-Parrinello simulations were compared with the findings of diffraction experiments.     

Light scattering studies of stereocomplex formation of stereoregular poly(methyl methacrylate) in solutions

The structure and stereocomplex formation of multi-stereoblock poly(methyl methacrylates) in three different solvents, acetone, tetrahydrofuran (THF) and chloroform, corresponding to strongly-, weakly- and non-complexing solvent, respectively, were investigated by a combination of static and dynamic laser light scattering. Our results revealed that the stereocomplex was caused by weak interactions, and could be melted at higher temperatures. In THF, the intermolecular and intramolecular interactions could be clearly separated at lower temperatures, and the structure of aggregated chains was linear. In acetone, a more compact structure was obtained, which was corroborated by the fact that the stereocomplex had a higher melting temperature than in THF.     

Assembling molecular species into 3D frameworks: Computational design and structure solution of hybrid materials

We present here the computational prediction of hybrid organic–inorganic extended lattices. The production of candidate crystal structures is successfully performed by direct-space assembly of building-units using the AASBU (Automated Assembly of Secondary Building Units) method, mixing independent organic and inorganic units. Hybrid candidates that are compatible with the imposed metal:organic ratio are generated with their cell parameters, space group, atomic positions, along with their simulated diffraction pattern. Since no explicit limit regarding the nature, number, and size of the inorganic and organic units, or hybrid building-block is involved, the method offers boundless potential for exploring hybrid frameworks in terms of the topological diversity. The most appealing development arises from the computer-assisted design of hybrid frameworks. Indeed, in a significant number of systems, it is well-known that controlled synthesis conditions can promote the occurrence of specific building-units, which serve to “propagate” the infinite crystal structure. We believe that the computational approach presented herein is valuable to create virtual libraries of viable hybrid polymorphs. We further show how it has proven to be, for the first time in the realm of hybrids, a tangible route towards structure solution in direct space, exemplified here with the computational structure determination of two complex hybrid structures, MIL-100 and MIL-101. This challenging area is of special interest when high quality diffraction data are not available or when very large cell sizes are involved. The development of a structural model in direct space, starting with minimal knowledge such as the metal:organic ratio, is shown here to be possible. With such a method in hand, formerly intractable structural problems when using methods based on conventional reciprocal space become feasible in direct space.     

Triphenyltin substituted benzoates: A spectroscopic study of structure in solution and solid phases

¹¹⁹Sn NMR and Mössbauer spectroscopic data have been recorded for 12 compounds of formula Ph₃SnO₂CC₆H₄X(X = H, Me-2, NH₂-2, NMe₂-2, Cl-2, Cl-3, Cl-4, OH-2, OH-4, SMe-4 or OMe-2) and Ph₃SnO₂CC₁₀H₇-1. On the basis of these measurements all the compounds are assigned a coordination number of four at tin in solution, and, with the exception of the Cl-2 and OH-2 derivatives, retain this structure in the solid. Both of these latter compounds exhibit enhanced Mössbauer quadrupole splittings (3.71 and 2.97 mm s⁻¹), which are attributed to carboxylate- and hydroxyl-bridged structures, respectively. The variable-temperature Mössbauer spectra of two compounds (X = OMe-2 or OH-2) are discussed.     

Search for memory effects in methane hydrate: structure of water before hydrate formation and after hydrate decomposition

Neutron diffraction with HD isotope substitution has been used to study the formation and decomposition of the methane clathrate hydrate. Using this atomistic technique coupled with simultaneous gas consumption measurements, we have successfully tracked the formation of the sI methane hydrate from a water/gas mixture and then the subsequent decomposition of the hydrate from initiation to completion. These studies demonstrate that the application of neutron diffraction with simultaneous gas consumption measurements provides a powerful method for studying the clathrate hydrate crystal growth and decomposition. We have also used neutron diffraction to examine the water structure before the hydrate growth and after the hydrate decomposition. From the neutron-scattering curves and the empirical potential structure refinement analysis of the data, we find that there is no significant difference between the structure of water before the hydrate formation and the structure of water after the hydrate decomposition. Nor is there any significant change to the methane hydration shell. These results are discussed in the context of widely held views on the existence of memory effects after the hydrate decomposition.