Anisotropy of the elastic properties of crystalline cellulose Iβ from first principles density functional theory with Van der Waals interactions

In spite of the significant potential of cellulose nanocrystals as functional nanoparticles for numerous applications, a fundamental understanding of the mechanical properties of defect-free, crystalline cellulose is still lacking. In this paper, the elasticity matrix for cellulose I_β with hydrogen bonding network A was calculated using ab initio density functional theory with a semi-empirical correction for van der Waals interactions. The computed Young’s modulus is found to be 206 GPa along [001] (c-axis), 98 GPa along [010] (b-axis), and 19 GPa along [100] (a-axis). Full compliance matrices are reported for 1.0, 1.5 and 2.0 % applied strains Color contour surfaces that show variations of the Young’s modulus and average Poisson’s ratio with crystallographic direction revealed the extreme anisotropies of these important mechanical properties. The sensitivity of the elastic parameters to misalignments in the crystal were examined with 2D polar plots within selected planes containing specific bonding characteristics; these are used to explain the substantial variability in the reported experimental Young’s moduli values. Results for the lattice directions [001], [010] and [100] are within the range of reported experimental and other numerical values.     

Solvent-extraction studies of phosphonium salts and their analytical applications—IV: Separation and determination of platinum

Platinum is very efficiently extracted with ethyl acetate from acidic solutions containing excess thiocyanate, after irradiation and precipitation with triphenylisopropylphosphonium ions. The extracted species has been isolated and found to be [(C₆H₅)₃C₃H₇P]₂-[Pt(SCN)₆]. Absorbance measurement of the organic extract at 365 mμ is used for quantitative determination of the platinum, the optimum concentration range being 5 to 20 ppm in the final dilution. Separation of platinum from palladium, rhodium, iridium, gold and silver are reported as well as the determination of platinum in the presence of moderate amounts of ruthenium.     

On approximate mathematical modeling of the vapor–liquid coexistence curves by the Van der Waals equation of state and non-classical value of the critical exponent

Van der Waals equation of state as well as power laws and critical exponent theories are prototypes to study the cubic shape, asymmetries and “flatness” of the vapor–liquid equilibrium curves near the critical point. In this work we study two similar methods to determine the phase curves in analytical form, which differ from each other by simplicity of mathematical calculation. We analyze temperature dependence of the coexistence curves asymptotically close to the vapor–liquid critical point. We explain the novelty of our method with respect to the standard thermodynamic limit discussed in the literature. Therefore we show that the shape of the coexistence curves can strongly influence the accepted value of the critical exponent. The results of theoretical studies have been compared with the ones obtained by experimental methods.     

Inclusion complexes of β-cyclodextrin with pyrazinamide and piperazine: Crystallographic and theoretical studies

The inclusion complexes of β-cyclodextrin (β-CD) with pyrazinamide (PYA) and piperazine (PIZ) have been investigated both in the solid phase by single-crystal X-ray diffraction analysis and in the gas phase by semi-empirical PM3 calculation. In the crystalline phase, the disordered PYA and PIZ molecules are entirely embedded in the β-CD cavity. The PYA pyrazine-centre displaces upwards by 1.15(1) Å from the β-CD plane, whereas the PIZ centre shifts downwards by 0.76(1) Å from the β-CD plane. The inclusion scenario changed in the gas phase. Two inclusion geometries of the PYA molecule are comparatively stable with binding energies of ? 22.28 and ? 25.29 kJ mol^? 1: the pyrazine centre shifts upwards by 0.5 Å and downwards by 2.0 Å from the β-CD plane. The PIZ molecule positioning at 2.0 Å below the β-CD plane gives a more stable inclusion complex than does the PYA molecule by 22–25 kJ mol^? 1.

Structural distinction of the β-CD–PYA and β-CD–PIZ inclusion complexes in the solid phase (by X-ray crystallography) and gas phase (by PM3 calculation) is a paradigm of the CD conformational flexibility, the induced-fit mechanism and the dynamics of the inclusion process.     

Excimer emission of caffeine with α- and β-cyclodextrins: spectral and molecular modelling studies

Excimer emission of caffeine with α-CD and β-CD were studied by UV-visible, fluorescence, time-resolved fluorescence, FTIR, ¹H NMR and molecular modelling techniques. Changes in the absorbance and fluorescence and lifetime of the caffeine with cyclodextrin (CD) solutions indicate (i) caffeine shows dual emission in the CD solutions, (ii) normal emission originates from a monomer and the longer wavelength emission is due to excimer and (iii) in both CDs caffeine forms 1:2 inclusion complex. Carbonyl stretching frequency moved to higher wave numbers and broadening of the N–H stretching band indicated the formation of inclusion complex. The resonance of the methyl protons of caffeine show remarkable upfield or downfield shift in the ¹H NMR, which indicates imidazole ring of the caffeine entrapped in the CD cavities. Investigations of energetic, thermodynamic and electronic properties of PM3 computational calculations confirmed the stability of the inclusion complex.     

On the complexation of quercetin with methyl-??-cyclodextrin: photostability and antioxidant studies

Quercetin, a plant-derived flavonoid, has been extensively investigated for a wide range of potential health benefits linked to its antioxidant properties. Unfortunately the topical administration of this molecule is restricted by its fast photodegradation. In the attempt to overcome this limitation the inclusion complex between quercetin (Q) and methyl-??-cyclodextrin (Me-??-CD) was prepared and previously investigated by a molecular modelling study, a solubility diagram and a DSC analysis. Successively the kinetics of photodegradation, the antiradical, metal chelating and anti-lipoperoxidative activities were studied by comparing the complex with free Q. In addition the accumulation of Q in porcine skin was evaluated after in vitro topical application by means of vertical Franz cells. The complex formation resulted useful in enhancing the solubility of Q without significantly reducing its antioxidant ability. A modest improvement in the photostability was also observed.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms—III : Configurational and conformational studies with Derivatives of 8-oxal-azabicyclo [4.3.0] nonane

Some Me substituted 8-oxa-1-azabicyclo[4.3.0] nonanes have been prepared and their configurations and preferred conformations assigned. The importance of geminal coupling constants in studying the conformations of these compounds is demonstrated.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms—XI : Configurational and conformational studies with derivatives of 1,3-diazabicyclo[4.4.0]decanes

The configurations and preferred conformations of a number of 1,3-diazabicyclo[4.4.0]decanes have been assigned on the basis of their NMR spectra. Dipolar interactions are shown to be important in determining the position of conformational equilibria.     

“Aggregation-induced emission” of transition metal compounds: Design,mechanistic insights,and applications

In the last decades, compounds with ‘Aggregation-Induced Emission’ (AIE), which are weakly or non-emissive at all in solution but exhibit a strong luminescence in aggregated states, have emerged as an extraordinary breakthrough in the field of luminescent materials, allowing to circumvent ‘Aggregation Caused Quenching’ (ACQ), which in many cases prevents the development of efficient solid-state materials for optoelectronic applications.Since the discovery of AIE, many AIE-active materials have been developed, most of them composed of organic molecules, and thus fluorescent in nature. Although a wide range of applications such as bioimaging, sensing, multi-stimuli responsive materials, and optoelectronic devices have been proposed for this new class of materials, triplet harvesting phosphorescent materials have much longer lifetimes as compared to their singlet harvesting analogues, and for this particular reason, the development of AIE-active phosphorescent materials seems to be a promising strategy from the applications point of view. In this respect, the synthesis of new AIE-active systems including heavy metals that would facilitate the population of low-lying excited triplet states via spin-orbit coupling (SOC), for which the strength increases as the fourth power of atomic number, i.e. Z⁴, is highly desirable. This review covers the design and synthetic strategies used to obtain the AIEgens reported in the literature that contain either d-block metals such as Cu(I), Zn(II), Re(I), Ru(II), Pd(II), Ir(III), Pt(II), Au(I), and Os(IV), describing the mechanisms proposed to explain their AIE. New emerging high-tech applications such as OLEDs, chemical sensors or bioimaging probes proposed for these materials are also discussed in a separate section.     

The determination of Miconazole and its related production impurities together with basic solution stability studies using a sub 2 μm chromatographic column

A selective and sensitive method for the analysis of Miconazole and its associated impurities is developed. The separation is carried out using a Thermo Scientific Hypersil Gold C18 Column (50 mm x 4.6 mm i.d., 1.9 μm particle size) with a mobile phase of acetonitrile-methanol-ammonium acetate (1.5 w/v) (30:32:38 v/v) at a flow rate of 2.5 mL/min and UV detection at 235 nm. The method is validated according to ICH guidelines with respect to precision, accuracy, linearity, specificity, robustness, and limits of detection and quantification. All parameters examined are found to be well within the stated guidelines. Naturally aged samples are also tested to determine sample stability. A profile of sample and impurity breakdown was presented. The analysis time was more than halved from just under 20 min (the current European Pharmacopeia Method) to under 8 min (developed method) and the method is applicable for assay and related substance determination.     

Hydroaminations of unactivated alkenes with basic alkylamines: group 4 metal halide catalysts and Brønsted-acid organocatalysts

Two distinct economical catalysts for intramolecular hydroaminations of electronically unactivated alkenes with basic amines are described, which are based on (a) group 4 metal halides under basic reaction conditions or (b) Br?nsted-acid organocatalysts.     

Infrared studies with terpenoid compounds—VI: Infrared spectra of penicillic acid and its derivatives

An abnormally persistent self-association of penicillic acid in solution has been observed. With all compounds studied an unusually high molar absorptivity of (ν_cc) is reported.     

Application of “abnormal” X-ray yields from primary targets of compounds in XSQR studies with proton and alpha particle beams

Previous reports on abnormal yields from charge induced X-ray studies (CHIX) have demonstrated conclusively that such yields are exceptionally high when compared to PIXE at low incident particle energies. A combination of low incident energies and high X-ray yields could be useful for XSQR investigations with low energy accelerators, particularly in studies where the sample matrix swamps the signals from the impurities of interest such as chromium in steels (overwhelming Fe peak) and Cu in brass (high Zn peak). This work discusses the possible applications of CHIX to XSQR studies with primary targets of compressed powders of selected compounds under bombardment with 3000 keV alphas and 800 and 1000 keV protons. A feature of interest in the use of comparatively low beam currents (between 100–150 nA) in the absence of sample cooling. The advantages and limitations of the application are discussed.     

Titrimetric analysis with chloramine-t—VIII: The chloramine-t-thalliumi and -thiocyanate reactions and some further applications employing excess of reagent

Direct oxidation of thallium^I in chloride or bromide media at acid concentrations of 0.05 to 3.0M is too slow to permit the use of visual indicators, and potentiometric titration reveals large positive errors. Double excess back titration following oxidation in acid chloride or bromide media gives excellent results provided the excess of oxidant is limited to 0.5 ml; oxidation in the absence of bromide is preferred. No satisfactory procedure for the determination of thiocyanate other than that previously advocated⁴ could be devised. Reactions with hydrazine and thiosulphate give poor results, oxidation of nitrite is unsatisfactory, and hydroxylamine and vanadium^IV are not oxidised.Examples of reactions involving excess of oxidant have been examined. Determination of sulphite in which chloramine-T is used quantitatively to liberate an excess of iodine is satisfactory. Determination of 8-hydroxyquinoline and of metals precipitated as oxinates by double excess back titration in which chloramine-T is used for the quantitative generation of bromine affords excellent results. Hexacyanoferrate(II) cannot be directly titrated, but determination by double excess back titration is possible, although the results are of poor accuracy.     

Encapsulation of ciprofloxacin,sparfloxacin, and ofloxacin drugs with α- and β-cyclodextrins: spectral and molecular modelling studies

Inclusion complexation of ciprofloxacin (CIP), sparfloxacin (SPA), and ofloxacin (OFL) drugs with α-CD and β-CD was studied by UV-visible, fluorescence, time-resolved fluorescence, Fourier transform infrared spectroscopy (FTIR), hydrogen nuclear magnetic resonance (¹HNMR), scanning electron microscopy (SEM), and molecular modelling techniques. Changes in the absorbance and fluorescence intensities and fluorescence lifetime of the drugs in the cyclodextrin (CD) solutions suggest the formation of inclusion complexes. Carbonyl stretching frequency moved to higher wave numbers and broadening of the N–H stretching band indicated the formation of inclusion complex. Cyclohexane ring protons of the drugs show remarkable upfield or downfield shift in the ¹HNMR spectrum, indicating that the cyclohexane part of the guest molecule is entrapped inside CD cavities. SEM images of CIP/CD, SPA/CD, and OFL/CD complexes have a crystal structure with different morphology from the isolated CIP, SPA, OFL, and CDs. Investigations of the energetic, thermodynamic, and electronic properties of parametric model number 3 computational calculations confirmed the stability of the inclusion complex.     

Phosphorus-nitrogen compounds: Reinvestigation of the reactions of hexachlorocyclotriphosphazene with 1,4-butane- and 1,6-hexane-diols—NMR studies of the products

Reactions of hexachlorocyclotriphosphazene N₃P₃Cl₆ (1) with 1,4-butane-(2) and 1,6-hexane-diols (3) in (1:1:2, 1:2:4, and 1:3:6) stoichiometries in THF solution at room temperature (r.t.) and under refluxing conditions yield a total of 15 products: two open chain, N₃P₃Cl₅[O(CH₂)_nOH] (n = 4, 6) (4, 5), two mono-spiro, N₃P₃Cl₄[O(CH₂)_nO] (n = 4, 6) (6, 7), two mono-ansa, N₃P₃Cl₄[O(CH₂)_nO] (n = 4,6) (8, 9), two dispiro, N₃P₃Cl₂[O(CH₂)_nO]₂ (n = 4, 6) (10, 11), two spiro-ansa, N₃P₃Cl₂[O(CH₂)_nO]₂ (n = 4, 6) (12, 13), one tri-spiro, N₃P₃[O(CH₂)₄O]₃ (14), two single-bridged, N₃P₃Cl₅[O(CH₂)_nO]N₃P₃Cl₅ (n = 4, 6) (15, 16), one double-bridged, N₃P₃Cl₄[O(CH₂)₆O]₂N₃P₃Cl₄ (17), and one tri-bridged, N₃P₃Cl₃[O(CH₂)₆O]₃N₃P₃Cl₃ (18) derivatives. Their structures have been elucidated by MS, ³¹P, and ¹H NMR spectroscopy. The results obtained, based on the synthesis, characterization, product types, and the relative yields, are compared with those of previous studies on the reactions of 1 with 1,2-ethane-, 1,3-propane-, 1,4-butane-, 1,5-pentane-, and 1,6-hexane-diols.