Single crystals of cellulose IVII: Influence of the cellulose molecular weight

The influence of the degree of polymerization (DP) of cellulose was evaluated in the preparation of micron-sized cellulose IV_II lamellar crystals in order to ascertain whether a regular chain-folded morphology could develop during their growth. For this purpose, sharp fractions of cellulose acetate were collected by preparative gel permeation chromatography. Aliquots of these fractions were deacetylated and crystallized in dilute solutions containing water, methylamine, and DMSO, and held at 150°C under pressure. Well-developed cellulose IV_II lamellar crystals were obtained with fractions of DP 22–24 whereas higher-DP material gave polycrystalline aggregates. This behavior indicates that large lamellar crystals of cellulose IV_II can be obtained only with unfolded short cellulose chains. The occurrence of chain-folded crystals with high–DP cellulose samples cannot be demonstrated.     

Decomposition behaviors of various crystalline celluloses as treated by semi-flow hot-compressed water

Various types of crystalline cellulose consisting of group I (cell I, III_I, IV_I) and group II (cell II, III_II, IV_II) prepared from cotton linter were adjusted for their degree of polymerization (DP) as starting materials. These celluloses were then treated by semi-flow hot-compressed water (HCW) at 230–270 °C/10 MPa/2–15 min to study their decomposition behaviors. The treatments performed resulted in residues of celluloses and water-soluble (WS) portions. Consequently, the crystallinity of the residues was found to remain the same, but the DP was reduced as the temperature increased. Additionally, X-ray diffractometry and Fourier transform-infrared analyses demonstrated that crystallographic changes occurred for residues of cell III_I, IV_I and III_II. Despite these changes, the overall results of the residues showed that group I has higher resistance to decomposing than group II. As for the WS portions, the yields of the hydrolyzed and degraded products were higher in group II than group I, indicating that group II is less resistant to decomposition by HCW treatment. Results for both the residues and WS portions are in agreement with each other, showing that the degree of difficulty of decomposition was higher in group I than group II. Therefore, the decomposition behaviors of the celluloses are due to differences in the crystalline forms.     

Hydrolysis behavior of various crystalline celluloses treated by cellulase of Tricoderma viride

Cellobiose and glucose are valuable products that can be obtained from enzymatic hydrolysis of cellulose. This study discusses changes in the crystalline form of celluloses to enhance the production of sugars and examines the effect on structural properties during enzymatic hydrolysis. Various crystalline celluloses consisting of group I (cell I, cell III_I, cell IV_I) and group II (cell II, cell III_II, cell IV_II) of similar DPs were prepared as starting materials. The similar DP values allowed a more direct comparison of the hydrolysis yields. The outcomes were analyzed and evaluated based on the residues and supernatants obtained from the treatment. As a result: (1) action of the cellulase of Trichoderma viride decreased both DP and crystallinity, with greater changes in group II celluloses, (2) the polymorphic interconversion process that occurred for cell III_I, cell IV_I, cell III_II and cell IV_II during the treatment was independent of the enzymatic hydrolysis, thus, the hydrolysis behaviors depended on the starting material of the celluloses, and (3) higher sugar production was obtained from cell III_I and group II. Therefore, the hydrolysis behavior of the various crystalline celluloses depended on the particular polymorph of the starting material.     

Photolysis and Thermolysis of Platinum(IV) 2,2′‐Bipyridine Complexes Lead to Identical Platinum(II)–DNA Adducts

Two Pt^IV and two Pt^II complexes containing a 2,2′‐bipyridine ligand were treated with a short DNA oligonucleotide under light irradiation at 37 °C or in the dark at 37 and 50 °C. Photolysis and thermolysis of the Pt^IV complexes led to spontaneous reduction of the Pt^IV to the corresponding Pt^II complexes and to binding of Pt^II 2,2′‐bipyridine complexes to N7 of guanine. When the reduction product was [Pt(bpy)Cl₂], formation of bis‐oligonucleotide adducts was observed, whereas [Pt(bpy)(MeNH₂)Cl]⁺ gave monoadducts, with chloride ligands substituted in both cases. Neither in the dark nor under light irradiation was the reductive elimination process of these Pt^IV complexes accompanied by oxidative DNA damage. This work raises the question of the stability of photoactivatable Pt^IV complexes toward moderate heating conditions.     

The thermal expansion of cellulose II and IIIII crystals

Highly crystalline samples of cellulose II and III_II have been prepared from repeated mercerization of ramie fibers and supercritical ammonia treatment of the mercerized ramie fibers, respectively. The thermal expansion behavior of cellulose II and III_II was investigated using X-ray diffraction at temperatures ranging from room temperature to 250 °C. With increasing temperature, the unit cell of cellulose II expanded in the lateral directions and contracted in the longitudinal direction, with the a and b axes increasing by 0.54 and 3.4%, respectively, and the c axis decreasing by 0.09%. The anisotropic thermal expansion in these three directions was closely related to the crystal structure and the hydrogen bonding in cellulose II. A similar anisotropic thermal expansion was also observed in cellulose III_II. Cellulose III_II expanded in the lateral direction but contracted in the longitudinal direction.     

Coordinatively Unsaturated Polynuclear Mixed-Valent Sn<Superscript>II</Superscript>–Sn<Superscript>IV</Superscript> and Cu<Superscript>II</Superscript>–Sn<Superscript>IV</Superscript> Oxo-Centered Carboxylates

The tetranuclear mixed-valent oxo-cluster [Sn^IISn^IVO(O₂CCF₃)₄]₂ (1) has been prepared by reacting SnCl₂ with AgO₂CCF₃ in a sealed ampoule at 90 °C. Alternatively, 1 was obtained by acidolysis of Ph₃SnSnPh₃ with trifluoroacetic acid in solution. The X-ray diffraction study of 1 revealed the presence of a Sn^IIOSn₂^IVOSn^II core comprised of the penta-coordinated divalent and six-coordinated tetravalent tin atoms. The ¹¹⁹Sn NMR studies confirmed the stability of the cluster in solution and the presence of two different oxidation states of tin. An acidolysis of Ph₃SnSnPh₃ in the presence of [Cu₂^II(O₂CCF₃)₄] followed by sublimation of the resulting product at 90 °C afforded the first trinuclear mixed metal Sn–Cu cluster [(C₆H₅)₂Sn₂^IVCu^IIO(O₂CCF₃)₆] (2). The X-ray diffraction analysis of 2 revealed the presence of two phenyl groups attached to the six-coordinated tin(IV) atoms and the tetragonal pyramidal environment of the copper(II) atom. Both complexes have been obtained free of exogenous ligands.     

π-Complexes of copper(I) halides with 3-(allylamino)-(C3H5NHC2H4CN, Apn) and 3-(diallylamino)-((C3H5)2NC2H4CN, Dapn)-propanenitrile. syntheses and crystal structures of compounds [CuCl(Apn)], [(H+Apn)Cu2Cl3], [(H+Dapn)CuCl2], and [(H+Dapn)CuBr2]

The ??-complexes [CuCl(C₃H₅NHC₂H₄CN)] (I), [(C₃H₅NH₂C₂H₄CN)Cu₂Cl₃] (II), [((C₃H₅)₂NHC₂H₄CN)CuCl₂] (III), and [((C₃H₅)₂NHC₂H₄CN)CuBr₂] (IV) are obtained as single crystals by the ac electrochemical synthesis on copper wire electrodes from ethanolic solutions of 3-(allylamino)propanenitrile, 3-(diallylamino)propanenitrile, and CuX₂ (X = Cl, Br). Their crystal structures are determined. The crystals of compounds I, III, and IV are monoclinic, space group P2₁/c, Z = 4. The crystals of compound II are triclinic, space group P $\bar 1$ , Z = 2. The unit cell parameters are a = 11.125(4), b = 8.769(4), c = 8.570(4) ?, ?? = 90.94(4)°, V = 835.9(6) ?³ (I); a = 6.2566(4), b = 7.5975(6), c = 11.1251(8) ?, ?? = 90.896(6)°, ?? = 92.827(5)°, ?? = 94.340(5)°, V = 526.57(7) ?³ (II); a = 11.656(4), b = 6.992(4), c = 14.681(5) ?, ?? = 100.89(4)°, V = 1174.9(9) ?³ (III); a =11.845(4), b = 7.282(4), c=14.855(5) ?, ?? = 100.37(4)°, V = 1260.4(9) ?³ (IV). The coordination mode of the Cu(I) atom in complex I includes two halogen atoms, the C=C bond, and the secondary amine N atom. The coordination environment in isostructural crystals of complexes III and IV is formed by the C=C bond and three halogen atoms as in complex II.     

The structure of R-NiF3, and synthesis,and magnetism of new R3 MIINiIVF6 (M = Fe,Co, Cu,Zn), and MIINiIIF4 (M = Co,Cu)

Neutron diffraction, at 2 K, of R-NiF₃ indicates the formulation approaches Ni^IINi^IVF₆, with Ni^II − F = 1.959(3) and Ni^IV − F = 1.811(3) Å, but 295 K data allow for only a slight increase in any Ni^III. Relatives have been precipitated from liquid anhydrous HF, at ≤ 20 °C, by adding K₂NiF₆ to M(SbF₆)₂ (M = Co, Cu, Zn) or M(AsF₆)₂ (M = Fe). CuNiF₆ like NiNiF₆ is metastable and loses F₂ easily, above 40 °C. CuNiF₆ is reduced by Xe or C₃F₆ at −20 °C; CoNiF₆ by H₂ at 350 °C, each giving pseudo-rutile MNiF₄. Magnetic data indicate the dominant formulation is M^IINi^IVF₆ (Ni(IV) low spin d⁶) with field dependence in CoNiF₆ (≤ 220 K) and FeNiF₆ (≤ 295 K).     

Cellulose nanocrystals obtained from microcrystalline cellulose by p-toluene sulfonic acid hydrolysis,NaOH and ethylenediamine treatment

Cellulose nanocrystals (CNCs) were first isolated from microcrystalline cellulose (MCC) by p-toluene sulfonic acid (p-TsOH) hydrolysis. Cellulose II nanocrystal (CNC II) and cellulose III nanocrystal (CNC III) were then formed by swelling the obtained cellulose I nanocrystal (CNC I) in concentrated sodium hydroxide solutions and ethylenediamine (EDA) respectively. The properties of CNC I, CNC II and CNC III were subjected to comprehensive characterization by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The results indicated that CNC I, CNC II and CNC III obtained in this research had high crystallinity index and good thermal stability. The degradation temperatures of the resulted CNC I, CNC II and CNC III were 300 °C, 275 °C and 242 °C, respectively. No ester bonds were found in the resulting CNCs. CNCs prepared in this research also had large aspect ratio and high negative zeta potential.

     

Iα → Iβ transition of cellulose under ultrasonic radiation

Aqueous suspensions of dispersed Glaucocystis cellulose microfibrils were sonicated at 4 °C for 3 h, using 24 kHz ultrasonic waves. This treatment induced a variety of ultrastructural defects, as the microfibrils became not only shortened, but also presented substantial damage materialized by kinks and subfibrillation. Upon analysis by X-ray diffraction and ¹³C solid-state NMR spectroscopy, it was found that the initial sample that contained 90 % of cellulose I_α allomorph became, to a large extent, unexpectedly converted into the I_β phase, while the loss of crystallinity was only moderate during the sonication treatment.     

Preparation and characterization of cellulose nanofibers from partly mercerized cotton by mixed acid hydrolysis

Cellulose nanofibers with a diameter of 70 nm and lengths of approximately 400 nm were fabricated from partly mercerized cotton fibers by acid hydrolysis. Morphological evolution of the hydrolyzed cotton fibers was investigated by powder X-ray diffraction, Fourier transform infrared analysis and field emission scanning electron microscopy. The XRD results show that the cellulose I was partially transformed into cellulose II by treatment with 15 % NaOH at 150° for 3 h. The crystallinity of this partially mercerized sample was lower than the samples that were converted completely to cellulose II by higher concentrations of NaOH. The intensities of all of the diffraction peaks were noticeably increased with increased hydrolysis time. Fourier transform infrared results revealed that the chemical composition of the remaining nanofibers of cellulose I and II had no observable change after acidic hydrolysis, and there was no difference between the hydrolysis rates for cellulose I or II. The formation of cellulose nanofibers involves three stages: net-like microfibril formation, then short microfibrils and finally nanofibers.     

Hemilabile imino-phosphine palladium(II) complexes: synthesis,molecular structure,and evaluation in Heck reactions

The ligands 2-(diphenylphosphino)benzyl-(2-thiophene)methylimine (V) and 2-(diphenylphosphino) benzyl-(2-thiophene)ethylimine (VI) were prepared from 2-(diphenylphosphino)benzaldehyde and thiophene amines with very good yields. An equimolar reaction of V and VI with either PdCl₂(cod) (cod = cyclooctadiene) or PdClMe(cod) afforded palladium(II) complexes I–IV. The molecular structure of II was confirmed by X-ray crystallography. The coordination geometry around the palladium atom exhibited distorted square planar geometry at the palladium centre. Complexes I, II, and IV were evaluated as catalysts for Heck coupling reactions of iodobenzene with methyl acrylate under mild reaction conditions; 0.1 mole % catalyst, Et₃N base, MeCN reflux for 8 h, 80°C; isolated yield on a 10 mmol scale with catalyst I (64 %), II (68 %), and IV (58 %). They all exhibited significant activities.     

The crystal polymorphs of metazachlor

Five crystal polymorphs of the herbicide metazachlor (MTZC) were characterized by means of hot stage microscopy, differential scanning calorimetry, IR- and Raman spectroscopy as well as X-ray powder diffractometry. Modification (mod.) I, II and III° can be crystallized from solvents and the melt, respectively, whereas the unstable mod. IV and V crystallize exclusively from the super-cooled melt. Based on the results of thermal analysis and solvent mediated transformation studies, the thermodynamic relationships among the polymorphic phases of metazachlor were evaluated and displayed in a semi-schematic energy/temperature-diagram. At room temperature, mod. III° (T _fus =76°C, Δ_fus H _III =26.6 kJ mol^-1) is the thermodynamically stable form, followed by mod. II (T _fus =80°C, Δ_fus H _II =23.0 kJ mol^-1) and mod. I (T _fus =83°C, Δ_fus H _II=19.7 kJ mol^-1). These forms are enantiotropically related showing thermodynamic transition points at ~55°C (T _{trs, III/II}), ~60°C (T _{trs, III/I}) and ~63°C (T _{trs, II/I}). Thus mod. I is the thermodynamically stable form above 63°C, mod. III° below 55°C and mod. II in a small window between these temperatures. Mod. IV (T _fus =72-74°C, Δ_fus H _II =18.7 kJ mol^-1) and mod. V (T _fus =65°C) are monotropically related to each other as well as to all other forms. The metastable mod. I and II show a high kinetic stability. They crystallize from solvents, and thus these forms can be present in commercial samples. Since metazachlor is used as an aqueous suspension, the use of the metastable forms is not advisable because of a potential transformation to mod. III°. This may result in problematic formulations, due to caking and aggregation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Crystalline Intermediates during Polycondensation Reactions in the C–N–Cl System – The Paddle‐Wheel Molecule N(C6N7Cl2)3

Solid state metathesis reactions between cyanuric chloride and C–N–H or alkali metal–(B–)C–N compounds, respectively, were carried out in the temperature range between 150 °C to 500 °C, studying intermediate stages of reactions and targeting the formation of carbon nitride materials by elimination of HCl or alkali metal chlorides. Although cyanuric chloride was reacted with quite a number of different reaction partners such as melamine, cyanamide, lithium nitride, lithium or sodium carbodiimide, lithium nitridoborate or sodium dicyandiamide, always the same intermediate compounds appeared in the reactions mixtures. Colorless, needle‐shaped crystals of the tertiary amine N(C₃N₃Cl₂)₃ ( 1 ) were obtained at temperatures around 200–250 °C. Temperatures as high as 400 °C yielded yellow, plate‐like crystals of the heptazine compound C₆N₇Cl₃ ( 2 ). At even higher temperatures, the reaction products were of poorer crystallinity, but evidence of the formation of another crystalline intermediate was given by X‐ray powder diffraction and electron diffraction experiments. This third intermediate is assumed to be a tertiary amine, quite similar to 1 , however, having heptazine ligands instead of triazine ligands and is assigned with the formula N(C₆N₇Cl₂)₃ ( 3 ). Theoretical calculations were performed for the structures and the vibrational spectra of 1 and 3 . Theoretical calculations and a structure refinement based of X‐ray powder diffraction data yielded a plausible structural model for compound 3 .     

Ethanol production from olive oil extraction residue pretreated with hot water

The olive pulp fraction contained in the residue generated in olive oil extraction by a two-step centrifugation process can be upgraded by using the cellulose fraction to produce ethanol and recovering high value phenols (tyrosol and hydroxytyrosol). Olive pulp was pretreated in a laboratory scale stirred autoclave at different temperatures (150–250°C). Pretreatment was evaluated regarding cellulose recovery, enzymatic hydrolysis effectiveness ethanol production by a simultaneous saccharification and fermentation process (SSF), and phenols recovery in the filtrate. The pretreatment of olive pulp using water at temperatures between 200°C and 250°C enhanced enzymatic hydrolysis. Maximum ethanol production (11.9 g/L) was obtained after pretreating pulp at 210°C in a SSF fed-batch procedure. Maximum hydroxytyrosol recovery was obtained in the liquid fraction when pretreated at 230°C.     

A new phase in the MnII–SeIV–MoVI–O system,Mn(MoO3)(SeO3)(H2O): Hydrothermal synthesis,crystal structure and properties

A new phase in the Mn^II–Se^IV–Mo^VI–O system, Mn(MoO₃)(SeO₃)(H₂O) (1), has been hydrothermally synthesized with a high yield (82%), and characterized by IR, TG-DSC, magnetism measurement and single crystal X-ray diffraction. The structure of Mn(MoO₃)(SeO₃)(H₂O) features a complicated 3D network composed of the 1D molybdenum(VI) oxide chains and the 1D manganese(II) selenite chains interconnected via Se–O–Mo and Mn–O–Mo bridges. It is stable up to approximately 340 °C, and losses water molecule at 340 °C, then release SeO₂ at about 420 °C. The result of magnetic property measurements has indicated that there exist antiferromagnetic interactions between Mn(II) centers. Photocatalysis experimental result illustrates that the compound exhibits good photocatalytic performance for degradation of RhB under visible light irradiation.     

Simulation of X-ray diffractograms relevant to the purported polymorphs cellulose IV<Subscript>I</Subscript> and IV<Subscript>II</Subscript>

Diffractograms were simulated for model nanocrystals of cellulose I_β, using numerical summation of radiation scattered from all carbon and oxygen atoms in the nanocrystal. Diffractogram peaks were sometimes displaced by a few degrees from positions calculated by the Bragg equation, as predicted in a published study based on a different mathematical approach. Simulated diffractograms showed 2 or 3 peaks, depending on the cross-sectional size and shape of the model nanocrystal. Some of the 2-peak diffractograms resembled published results for the purported polymorph cellulose IV_I, or for cell-wall cellulose, supporting suggestions that cellulose IV_I is simply cellulose I fragmented into nanocrystals with relatively small cross-sectional dimensions. A published diffractogram for cellulose IV_II could not be simulated with acceptable precision, suggesting that this polymorph might have a crystal structure distinctly different from that of cellulose I_β.     

Investigation of the change in the fine structure of Valonia cellulose upon wet heating and mercerization

A Valonia cellulose (NV), a cellulose II derived from NV by mercerization (MV), and a cast cellulose II film (F) were deuterated repeatedly (wetting-drying cycle) in vapor phase at 25°C; the integrated deuteration time amounts to 5 × 10⁵ min. A region C, which cannot be attacked by the exchange reaction, exists in NV and MV, amounting to 80 and 18% in the respective samples. In the case of F, it could not be determined exactly due to the too large scattering of the data. On heating in liquid D₂O for 5 or 10 min., OD groups develop within C above 190 and 170°C in NV and MV, respectively. Above 190°C. the exchange is larger in NV than in MV. These OD groups within the pre-existing crystallites begin to disappear after treating with NaOH solution at the concentration at which cellulose begins to be converted to alkali cellulose I. The resistant OD groups developed within the amorphous and intermediate regions are rehydrogenated by the more dilute alkaline solutions.     

Synthesis and Crystal Structure of Bis(methyltriphenylphosphonium) Hexabromotellurate(IV)‐bis{dibromoselenate(II)}, [PMePh3]2[TeBr6(SeBr2)2], the Salt of a Mixed‐valence Bromotellurate(IV)‐Selenate(II) Anion

Brown crystals of [PMePh₃]₂[TeBr₆(SeBr₂)₂] ( 1 ) were obtained when selenium and bromine (1:1) react in acetonitrile solution in the presence of tellurium(IV) bromide and methyltriphenylphosphonium bromide. The salt 1 crystallizes in the triclinic space group P1¯ with the cell dimensions a = 10.3630(14)Å, b = 11.5140(12)Å, c = 11.7605(17)Å, α = 108.643(9)°, β = 106.171(10)° and γ = 99.077(9)° (296 K). In the solid state the [TeBr₆(SeBr₂)₂]^2— anion contains a nearly regular [TeBr₆] octahedron where the four equatorial bromo ligands each have developed a bond to the Se^II atom of a SeBr₂ molecule. The contacts between the bridging bromo and the Se^II atoms of the SeBr₂ molecules are observed in the range 3.11—3.21Å, and can be interpreted as bonds of the donor‐acceptor type with the bridging bromo ligands as donors and the SeBr₂ molecules as acceptors. The Te^IV—Br distances are in the range 2.67—2.72Å, and the Se^II—Br bond lengths in coordinated SeBr₂ molecules in the range 2.33—2.34Å.     

Elastic modulus of the crystalline regions of cellulose polymorphs

The elastic modulus E_l of the crystalline regions of cellulose polymorphs in the direction parallel to the chain axis was measured by x-ray diffraction. The E_l values of cellulose I, II, III_I, III_II, and IV_I were 138, 88, 87, 58, 75 GPa, respectively. This indicates that the skeletons of these polymorphs are completely different from each other in the mechanical point of view. The crystal transition induces a skeletal contraction accompanied by a change in intramolecular hydrogen bonds, which is considered to result in a drastic change in the E_l value of the cellulose polymorphs. © 1995 John Wiley & Sons, Inc.