Controllable acetylation of cellulose nanocrystal by uniform design and response surface methodology.

Acetylation of Cellulose nanocrystal (CNC) can reduce its surface polarity and therefore extends its application in biomedical and chemical fields. A method combining uniform design (UD) and response surface methodology (RSM) was developed to produce the acetylated CNC with arbitrary degree of substitution (DS) and crystallinity index (CrI). The effects of three factors (i.e., temperature, reaction time and the volume of acetic anhydride) on DS and CrI were investigated in their respective ranges (i.e., 60-90 oC, 1.0-5.0 h and 1.0-5.0 mL). Both mathematical models for DS and CrI were developed by multiple stepwise regression (MSR) based on UD data and their significances were evaluated by analysis of variance. The controllable acetylation of CNC was realized by using either UD alone or the combination of UD and RSM. Eight verification experiments show that the relative errors between the predicted and the measured results are less than 16.77 % and 6.08 % for DS and CrI, respectively, confirming the reliability and validity of the method. This developed methodology is ingenious and expected to be expanded to any other fields that controllable preparations are required.

A sulfur monoxide complex of platinum fluoride with a positively charged ligand.

A sulfur monoxide complex of platinum fluoride in the form of PtF2(η1-SO) was generated via the isomerization of a molecular complex Pt(SOF2) in cryogenic matrixes under UV-vis irradiation. The infrared absorptions observed at 1205.4, 619.8 and 594.9 cm-1 are assigned to the S-O, antisymmetric and symmetric F-Pt-F stretching vibrations of the PtF2(η1-SO) complex, which possesses nonplanar Cs symmetry with a singlet ground state according to density functional theory calculations. The experimental vibrational frequency and computed distance (1.449 Å) of the SO ligand indicate that the SO ligand features a positively charged character, which is further confirmed by natural bond orbital analysis and Mayer bond order. Such character is completely different from that for early transition metal-SO complexes and dioxygen complexes of platinum. Formation of the PtF2(η1-SO) complex was found to occur via the consecutive transfer of the two fluorine atoms from SOF2 to Pt in the sulfur bound Pt(SOF2) complex, which involves a series of intermediates on the basis of the mechanism study at the B3LYP level. Although the whole process is hindered by the large energy barrier encountered during the transfer of the first fluorine atom, UV-vis irradiation can provide sufficient energy to surmount this barrier and facilitates the formation of the nonplanar PtF2(η1-SO) complex stabilized in matrix.

Gas-phase formation of Grignard-type organolanthanide (III) ions RLnCl3 - : The influences of lanthanide center and hydrocarbyl group.

RATIONALE: Compared with organomagnesium compounds (Grignard reagents), the Grignard-type organolanthanides (III) exhibit several utilizable differences in reactivity. However, the fundamental understanding of Grignard-type organolanthanides (III) is still in its infancy. Decarboxylation of metal carboxylate ions is an effective method to obtain organometallic ions that are well suited for gas-phase investigation using electrospray ionization (ESI) mass spectrometry in combination with density functional theory (DFT) calculations. METHODS: The (RCO2 )LnCl3 - (R = CH3 , Ln = La-Lu except Pm; Ln = La, R = CH3 CH2 , CH2 CH, HCC, C6 H5 , and C6 H11 ) precursor ions were produced in the gas phase via ESI of LnCl3 and RCO2 H or RCO2 Na mixtures in methanol. Collision-induced dissociation (CID) was employed to examine whether the Grignard-type organolanthanide (III) ions RLnCl3 - can be obtained via decarboxylation of lanthanide chloride carboxylate ions (RCO2 )LnCl3 - . DFT calculations can be used to determine the influences of lanthanide center and hydrocarbyl group on the formation of RLnCl3 - . RESULTS: When R = CH3 , CID of (CH3 CO2 )LnCl3 - (Ln = La-Lu except Pm) yielded decarboxylation products (CH3 )LnCl3 - and reduction products LnCl3 ·- with a variation in the relative intensity ratio of (CH3 )LnCl3 - /LnCl3 ·- . The trend is as follows: (CH3 )EuCl3 - /EuCl3 ·- < (CH3 )YbCl3 - /YbCl3 ·- ≈ (CH3 )SmCl3 - /SmCl3 ·- < other (CH3 )LnCl3 - /LnCl3 ·- , which complies with the trend of Ln (III)/Ln (II) reduction potentials in general. When Ln = La and hydrocarbyl groups were varied as CH3 CH2 , CH2 CH, HCC, C6 H5 , and C6 H11 , the fragmentation behaviors of these (RCO2 )LaCl3 - precursor ions were diverse. Except for (C6 H11 CO2 )LaCl3 - , the four remaining (RCO2 )LaCl3 - (R = CH3 CH2 , CH2 CH, HCC, and C6 H5 ) ions all underwent decarboxylation to yield RLaCl3 - . (CH2 CH)LaCl3 - and especially (CH3 CH2 )LaCl3 - are prone to undergo ß-hydride transfer to form LaHCl3 - , whereas (HCC)LaCl3 - and (C6 H5 )LaCl3 - are not. A minor reduction product, LaCl3 ·- , was formed via C6 H5 radical loss of (C6 H5 )LaCl3 - . The relative intensities of RLaCl3 - compared to (RCO2 )LaCl3 - decrease as follows: HCC > CH2 CH > C6 H5 > CH3 > CH3 CH2 >> C6 H11 (not visible). CONCLUSION: A series of Grignard-type organolanthanide (III) ions RLnCl3 - (R = CH3 , Ln = La-Lu except Pm; Ln = La, R = CH3 CH2 , CH2 CH, HCC, and C6 H5 ) were produced from (RCO2 )LnCl3 - via CO2 loss, whereas (C6 H11 )LaCl3 - did not. The experimental and theoretical results suggest that the reduction potentials of Ln (III)/Ln (II) couples as well as the bulkiness and hybridization of hydrocarbyl groups play important roles in promoting or limiting the formation of RLnCl3 - via decarboxylation of (RCO2 )LnCl3 - .

Dual-Ligand Strategy for the Preparation of Gas-Phase Uranyl(VI) Benzyne Complexes from Uranyl(VI) Benzoates.

The uranyl(VI) benzyne complex (η2-C6H4)UO2Cl- was prepared in the gas phase by electrospray ionization mass spectrometry coupled with collision-induced dissociation. It was formed via a dual-ligand strategy that requires the elimination of benzoic acid or benzene/CO2 from the uranyl dibenzoate precursor (C6H5CO2)2UO2Cl-. This contrasts the known strategy for the formation of gas-phase benzyne complexes that would result from CO2/HCl elimination from (C6H5CO2)UO2Cl2-, during which only one benzoate ligand is involved. Such dual-ligand strategy can be extended to the preparation of a series of methyl- and halo-substituted benzyne complexes of uranyl(VI). Density functional theory calculations at the B3LYP level reveal that the benzyne complex (η2-C6H4)UO2Cl- features a metallacyclopropene structure with the C6H42- ligand coordinated to uranium(VI) through two polarized U-Cbenzyne σ bonds, in accordance with the reactivity test toward water. Dehydrochlorination of the benzyne complex (η2-C6H4)UO2Cl- from (C6H5)UO2Cl2- that originates from decarboxylation of (C6H5CO2)UO2Cl2- with a single benzoate ligand is neither kinetically nor thermodynamically favorable than simple C6H5 radical loss to give UVO2Cl2-. This arises from the presence of an accessible V oxidation state for uranium and accounts for the necessity for the dual-ligand strategy in the preparation of uranyl(VI) benzyne complexes from uranyl benzoate precursors.

Influence of Metal Coordination on the Gas-Phase Chemistry of the Positional Isomers of Fluorobenzoate Complexes.

The fragmentation behaviors of the o-, m-, and p-fluorobenzoate complexes of La3+, Ce3+, Fe3+, Cu2+, and UO22+ were investigated by electrospray ionization mass spectrometry, and the corresponding reaction mechanisms were explored by density functional theory (DFT) calculations. Fluoride transfer product LaIIIFCl3-/CeIIIFCl3- and decarboxylation product LaIIICl3(C6H4F)-/CeIIICl3(C6H4F)- were observed when the carboxylate precursors LaIIICl3(C6H4FCO2)-/CeIIICl3(C6H4FCO2)- were subjected to collision-induced dissociation. The variation in product ratios, which is not obvious in the meta and para cases, qualitatively follows the increasing overall energy barrier and reaction endothermicity of the two-step CO2/C6H4 elimination mechanism, and this aligns with the increase in U-F distance in the ortho, meta, and para decarboxylation product isomers. In contrast, the mass spectra of FeIIICl3(C6H4FCO2)-/CuIICl2(C6H4FCO2)- are dominated by the reduction product FeCl3-/CuCl2- regardless of the fluorobenzoate isomer. DFT/B3LYP calculations show that the two-step CO2/C6H4F elimination pathways are comparable in energy for all three positional isomers. It is energetically more favorable to give the reduction product than the fluoride transfer product, which is opposite to the lanthanum cases. Although the decarboxylation product was observed for all three UVIO2Cl2(C6H4FCO2)- isomers, the ortho isomer behaves more similarly to LaIIICl3(C6H4FCO2)-/CeIIICl3(C6H4FCO2)- as evidenced by the formation of UVIO2FCl2-, and the appearance of UVO2Cl2- in the cases of the meta and para isomers indicates the similarity with FeIIICl3(C6H4FCO2)-/CuIICl2(C6H4FCO2)-. The shorter U-F distance in UVIO2Cl2(o-C6H4F)- causes the decrease in the fluoride transfer barrier and thus makes this process more favorable over o-C6H4F radical loss to give UVO2Cl2-.

Gas-phase synthesis and structure of thorium benzyne complexes.

The thorium benzyne complex (η2-C6H4)ThCl3- was synthesized in the gas phase through consecutive decarboxylation and dehydrochlorination from the (C6H5CO2)ThCl4- precursor upon collision-induced dissociation. Theoretical calculations suggest that (η2-C6H4)ThCl3- exhibits a metallacyclopropene structure with two polarized Th-Cbenzyne σ bonds. This procedure can be generally extended to the synthesis of a wide range of gas-phase thorium benzyne complexes.

Cellulose nanofibrils (CNFs) in uniform diameter: Capturing the impact of carboxyl group on dispersion and Re-dispersion of CNFs suspensions.

The poor dispersibility and re-dispersibility of cellulose nanofibrils (CNFs) in various solvents and polymers have been recognized as the key factors limiting their potential applications. TEMPO oxidation, as the most common surface modification, can greatly improve the dispersion and re-dispersion of CNFs. However, the diameter of TEMPO-oxidized cellulose nanofibers (TOCNFs) has not been regulated in most researches, which was an important factor determining the dispersion and re-dispersion of TOCNFs. Herein, this work explored the effect of carboxyl groups on dispersion and re-dispersion of TOCNFs with uniform diameter in various solvents. Notably, fractal dimension was innovatively introduced to characterize the distribution of TOCNFs diameter. The fractal dimension and statistic diameter of TCONFs with different carboxyl group contents are ~1.56 and ~22 nm, demonstrating that the diameter of TOCNFs has been regulated in the same range. When the carboxyl group content is up to 1.58 mmol/g, the dispersion and re-dispersion of TOCNFs suspension in water and different organic solvents are the most uniform and stable. In a word, this work explores the dispersion and re-dispersion of TOCNFs with the uniform diameter and different carboxyl group contents, which can provide the theoretical guidance for various potential applications of nanofibrils in polymer matrix composites.

Discrimination and quantitation of halobenzoic acid positional isomers upon Th(IV) coordination by mass spectrometry.

A fast and reliable mass spectrometry-based method has been developed to discriminate the positional isomers of o-, m- and p-C6H4XCO2H (X = F, Cl and Br). This is based on the distinct fragmentation patterns of isomeric ThCl4(C6H4XCO2)- ions generated by electrospray ionization of the solutions with C6H4XCO2H isomers and ThCl4. Moreover, the composition of these positional isomers can be conveniently quantified without any pre-treatment according to the proportion of gas-phase fragmentation products.

Mass spectrometric and theoretical study on the formation of uranyl hydride from uranyl carboxylate.

Uranyl hydride in the form of HUO2Cl2- was prepared upon collision-induced dissociation of (RCO2)UO2Cl2- (R = H, CH3CH2, CH3CH2CH2, CH3CHCH, (CH3)2CH, C5H9, C6H11 and C6H5CH2CH2) in the gas phase. It was found that uranyl hydrides result from alkene and alkyne elimination with concomitant ß-hydride transfer of uranyl alkylides RUO2Cl2- following decarboxylation of the carboxylates with the exception of (HCO2)UO2Cl2-, and formation of HUVIO2Cl2- through alkene/alkyne loss is in competition with neutral ligand loss to give UVO2Cl2-. According to the calculations at the B3LYP level, loss of a neutral ligand is slightly less favorable in the cases of (CH3CH2)UO2Cl2- and (CH3CH2CH2)UO2Cl2-, and the situations of (CH3CHCH)UO2Cl2-, ((CH3)2CH)UO2Cl2-, (C5H9)UO2Cl2-, (C6H11)UO2Cl2- and (C6H5CH2CH2)UO2Cl2- with ß-hydrogen atoms should be similar despite the fact that the yield of uranyl hydride depends on the nature of the ligand. Although no uranyl hydride was observed when ß-hydrogen is not available in the carboxylate precursor, there is no HUO2Cl2- generated from (C6H5CO2)UO2Cl2-, (2-C6H4FCO2)UO2Cl2- and (CH2CHCH2CO2)UO2Cl2- with ß-hydrogen either. This is attributed to the much more favorable formation of UO2Cl2- over HUO2Cl2- as revealed by the B3LYP calculations, which is similar to the absence of HUO2Cl2- in the (CH3CO2)UO2Cl2- case where highly reactive CH2 would be formed.

Gas-phase structure, bonding, and fragmentation chemistry of the An (IV)-TMPDCAM complexes studied using mass spectrometry and theoretical calculation (An = Th and U).

RATIONALE: Pyridine-2,6-dicarboxamides (PDCAMs) exhibit a certain extraction ability for tetravalent actinide ions, but quite limited information regarding the structures and reactivities of the corresponding An4+ -PDCAMs complexes is available. Neutral diamides can form multiply charged complexes with lanthanide and actinide cations, which are well suited for gas-phase investigations using electrospray ionization (ESI) mass spectrometry in conjunction with theoretical calculation. METHODS: Binary Th (TMPDCAM)3 4+ /U (TMPDCAM)3 4+ (TMPDCAM = N,N,N',N'-tetramethylpyridine-2,6-dicarboxamide) complexes were generated in the gas phase via ES) of Th (ClO4 )4 /U (ClO4 )4 and TMPDCAM mixtures in acetonitrile; collision-induced dissociation (CID) was employed to reveal their fragmentation behaviors; the structure and bonding were investigated by density functional theory (DFT) calculation. RESULTS: An (TMPDCAM)3 4+ (An = Th and U) tetracations dominated the ESI mass spectra of An (ClO4 )4 and TMPDCAM mixtures in acetonitrile. DFT calculations indicate that the two An (TMPDCAM)3 4+ complexes have C3 geometry, and the bonding analyses demonstrate that the thorium or uranium center interacts with both Ocarbonyl and Npyridine , but the latter is weaker. CID of Th (TMPDCAM)3 4+ generated a series of multiply charged thorium-containing products via bond cleavages of the TMPDCAM ligand, whereas U (TMPDCAM)3 4+ yielded only oxygen extraction product UO (TMPDCAM)2+ and hydrolysis product UO (OH)+ . CONCLUSION: An4+ (An = Th and U) can form stable tetrapositive complexes in the gas phase on coordination of three neutral TMPDCAM ligands. The structure and bonding analyses indicate that the two An (TMPDCAM)3 4+ complexes possess twisted tricapped trigonal prismatic geometry and the An4+ centers are coordinated by six Ocarbonyl and three Npyridine atoms while the interactions between An4+ and Ocarbonyl are stronger. The fragmentation chemistry of Th (TMPDCAM)3 4+ and U (TMPDCAM)3 4+ is quite different from each other, which reveals that the gas-phase chemistry of quadruply charged actinide-diamide complexes is affected by the metal centers with distinct properties.

HMNTA Complexes of Tetravalent Metal Ions: On the Roles of Carbonyl Oxygen and Amine Nitrogen in the Stabilization of Gas-Phase M(HMNTA)24+ Complexes.

Gas-phase tetrapositively charged M(HMNTA)24+ (M = Zr, Hf, Th, and U) ions were generated via electrospray ionization of the M(ClO4)4 and N,N,N',N',N″,N″-hexamethylnitrilotriacetamide (HMNTA) mixtures in acetonitrile. In these complexes, the Zr4+, Hf4+, Th4+, and U4+ metal centers are coordinated by two neutral HMNTA ligands forming antitriangular prism geometry on the basis of DFT calculations. Bonding analysis reveals that the M4+ center is stabilized by six carbonyl oxygen atoms, while the interactions between M4+ and two central amine nitrogen atoms are negligible. This is further confirmed by the calculation results of two tetrapositive model complexes without either central amine nitrogen or carbonyl oxygen atoms, indicating the central nitrogen atom of HMNTA is not necessary in forming tetrapositive metal complexes that can be stabilized in gas phase. Collision-induced dissociation of Zr(HMNTA)24+, Hf(HMNTA)24+, and Th(HMNTA)24+ shows the formation of similar charge reducing products with the oxidation state of metal retaining IV whereas ions with other oxidation states were observed for the fragmentation products of U(HMNTA)24+.

Complexation of Ln3+ with Pyridine-2,6-dicarboxamide: Formation of the 1:2 Complexes in Solution and Gas Phase.

Electrospray ionization of LnCl3 and tetramethylpyridine-2,6-dicarboxamide (TMPDA) mixtures in methanol generated abundant tripositively charged Ln(TMPDA)23+ ions with an unprecedented 1:2 stoichiometry in the gas phase. Different from the very common 1:3 Ln(L)33+ (L = TMGA, tetramethyl glutaramide; TMOGA, tetramethyl-3-oxaglutaramide; TMTDA, tetramethyl-3-thiodiglycolamide) complexes, Ln3+ is coordinated by four Ocarbonyl and two Npyridine atoms from two perpendicular TMPDA ligands based on the DFT calculations. The observation of 1:2 Ln(TMPDA)23+ in the gas phase is due to the desolvation of Ln(TMPDA)2(MeOH)23+ that is predominant in the methanol solution of LnCl3 and TMPDA according to the extended X-ray absorption fine structure analysis, and the 1:3 Ln(TMOGA)33+ and Ln(TMGA)33+ complexes observed in the gas phase also parallel the speciation in relevant solutions. Such a difference in solution speciation is most likely a result of the unfavorable steric effect caused by the pyridine ring of TMPDA.

End-On Cyanogen Complexes of Iridium, Palladium, and Platinum.

The cyanogen complexes of iridium, palladium, and platinum were prepared via the reactions of noble metal atoms with cyanogen in argon matrixes, and the product structures were determined by infrared spectroscopy and density functional theory calculations. These complexes were predicted to possess linear geometries with the metal center coordinated by the nitrogen atom of cyanogen in end-on fashions. On the basis of the B3LYP calculations, doublet, singlet, and singlet spin states are most stable for [Ir(NCCN)], [Pd(NCCN)], and [Pt(NCCN)]. Bonding analysis revealed the presence of electron donation from the polarized σ orbital of cyanogen into the empty metal dz2 orbital and back-donation from the metal dxz/yz orbitals to the 2πu orbitals of cyanogen, the latter of which destabilizes the C-N bond and stabilizes the C-C bond. Such an effect causes an increase in C-N bond length by 0.01-0.015 Å and a decrease in C-C bond length by 0.013-0.02 Å for noble-metal-cyanogen complexes in comparison to the same bond in neutral cyanogen, and this is also consistent with the changes in vibrational frequencies. Although [Ir(NCCN)], [Pd(NCCN)], and [Pt(NCCN)] were formed spontaneously during sample annealing, neither cyanide nor isocyanide product was observed in the experiments, which is different from the cases of early transition, lanthanide, and actinide metals.

Quantitative Analysis of Organic Liquid Three-Component Systems: Near-Infrared Transmission versus Raman Spectroscopy, Partial Least Squares versus Classical Least Squares Regression Evaluation and Volume versus Weight Percent Concentration Units.

The band shapes and band positions of near-infrared (NIR) and Raman spectra change depending on the concentrations of specific chemical functionalities in a multicomponent system. To elucidate these effects in more detail and clarify their impact on the analytical measurement techniques and evaluation procedures, NIR transmission spectra and Raman spectra of two organic liquid three-component systems with variable compositions were analyzed by two different multivariate calibration procedures, partial least squares (PLS) and classical least-squares (CLS) regression. Furthermore, the effect of applying different concentration units (volume percent (%V) and weight percent (%W) on the performance of the two calibration procedures have been tested. While the mixtures of benzene/cyclohexane/ethylbenzene (system 1) can be regarded as a blended system with comparatively low molecular interactions, hydrogen bonding plays a dominant role in the blends of ethyl acetate/1-heptanol/1,4-dioxane (system 2). Whereas system 1 yielded equally good calibrations by PLS and CLS regression, for system 2 acceptable results were only obtained by PLS regression. Additionally, for both sample systems, Raman spectra generally led to lower calibration performance than NIR spectra. Finally, volume and weight percent concentration units yielded comparable results for both chemometric evaluation procedures.

Protective effect of polysaccharide from Ligusticum chuanxiong hort against H2O2-induced toxicity in zebrafish embryo.

A protein-containing polysaccharide, LCP, showing strong antioxidant activity from the rhizome of Ligusticum chuanxiong Hort was fractionated and purified. Its physicochemical properties were characterised by gel permeation chromatography (GPC), gas chromatography-mass spectrometry (GC-MS), UV and IR analysis. The results showed that LCP was proteoglycan containing 85.7% total carbohydrate, 2.79% protein, 5.14% uronic acid, and four kinds of monosaccharides including xylose, glucose, mannose and galactose with molar ratios of 1.2: 7.8: 1: 2.1, respectively. The average molecular weight of LCP was 15.8 × 104 Da. In addition, the results indicated that LCP exhibited good radical scavenging abilities. Furthermore, LCP partially attenuated the incidence of mortalities and pericardial edema in zebrafish embryos exposed to hydrogen peroxide (H2O2). Moreover, LCP provided protection against H2O2-induced ROS generation and cell death in zebrafish embryo. These results indicated that LCP could be a potential approach for oxidative stress damage reversal.

Stimulus-responsive reversible thermochromism and exciplex emission of a Zn(ii) complex and selective sensing of NH3 gas.

A multifunctional smart binuclear Zn(ii) complex (1) was synthesized by a simple process. 1 contains unique water pentamers in its crystals and undergoes reversible thermochromism and exciplex emission on and off during the dehydration and rehydration processes. A thermally induced redox reaction occurred in the charge transfer of complex 1 giving rise to a persistent radical species which shows fast response and high selectivity toward gaseous NH3 as a solid-state colorimetric and fluorescent bifunctional sensor.

Evaluating the Molecular Interaction of Organic Liquid Mixtures Using Near-Infrared Spectroscopy.

The near-infrared transmission spectra of two organic liquid three-component systems of variable compositions were investigated in detail. To evaluate the interaction of the different components in the two systems the experimental spectra of the pure components were compared to mathematically constructed "pure component" spectra. Though usually the correlation coefficient (CC) and Manhattan distance (MD) are used to measure the similarity of spectra, in the present investigations principal component analysis (PCA) was found to be a more effective tool to investigate the difference between these spectra and derive parameters characterizing the interaction between the different components. Thus, PC scores for the two types of spectra established some distinct patterns which clearly expressed their differences. For a three-dimensional coordinate system of selected principal components, the Euclidean distances between the mathematically constructed and the experimental spectra of the pure components were calculated. Finally, the mean values of the distances for each component provided indices to rank the interaction of the components in the mixtures. Thus, the results offer a convenient approach that can quantitatively evaluate the molecular interactions of the individual components in organic liquid mixtures by various spectroscopies.