Rapid Quantification of 25-Hydroxyvitamin D<Subscript>3</Subscript> in Human Serum by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

LC-MS/MS is widely utilized today for quantification of vitamin D in biological fluids. Mass spectrometric assays for vitamin D require very careful method optimization for precise and interference-free, accurate analyses however. Here, we explore chemical derivatization and matrix-assisted laser desorption/ionization (MALDI) as a rapid alternative for quantitative measurement of 25-hydroxyvitamin D₃ in human serum, and compare it to results from LC-MS/MS. The method implemented an automated imaging step of each MALDI spot, to locate areas of high intensity, avoid sweet spot phenomena, and thus improve precision. There was no statistically significant difference in vitamin D quantification between the MALDI-MS/MS and LC-MS/MS: mean ± standard deviation for MALDI-MS—29.4?±?10.3 ng/mL—versus LC-MS/MS—30.3?±?11.2 ng/mL (P?=?0.128)—for the sum of the 25-hydroxyvitamin D epimers. The MALDI-based assay avoided time-consuming chromatographic separation steps and was thus much faster than the LC-MS/MS assay. It also consumed less sample, required no organic solvents, and was readily automated. In this proof-of-concept study, MALDI-MS readily demonstrated its potential for mass spectrometric quantification of vitamin D compounds in biological fluids.

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A Quantum Chemical Study of C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>, C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Molecules and Fe@C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Endocomplex

(U)PBE0/cc-pVDZ method is used to study the structure of C₆₀Cl₃₀, C₆₀(OH)₃₀ molecules and Fe@C₆₀(OH)₃₀ endocomplex. The triplet state of the endocomplex is shown to be the lowest in energy among its four states corresponding to different spin multiplicities and positions of Fe nucleus within the fullerene cavity. This state is characterized by bonding between the iron atom and one of two benzenoid cycles of the carbon cage, six internuclear Fe–C distances (208 pm), and 1s²2s²2p⁶3s²3p⁶3d^7.24s^0.14p^0.3 electron configuration of iron with spin population of 2.36.     

Endohedral Complex of Fullerene C<Subscript>60</Subscript> with Tetrahedral N<Subscript>4</Subscript>, N<Subscript>4</Subscript>@C<Subscript>60</Subscript>

B3LYP/6-31G(d) hybrid HF/DFT and BLYP/6-31G(d, p) DFT calculations were carried out to determine the structural and electronic properties of the endohedral complex of C₆₀ with Tetrahedral N₄ (T_d N₄), N₄@C₆₀. It was demonstrated that N₄ was seated in the center of the fullerene cage and the tetrahedral structure of N₄ is remained in the cage. The formation of this complex is endothermic with inclusion energy of 37.92 kcal/mol. N₄ endohedral doping perturbs the molecular orbitals of C₆₀ not so much, the calculated HOMO–LUMO gaps, the electron affinity (EA) and the ionizational potential (IP) of N₄@C₆₀ are similar to that of C₆₀.     

Mass spectrometric determination of the electron affinity of C<Subscript>60</Subscript>(CF<Subscript>3</Subscript>)<Subscript>10</Subscript> and C<Subscript>60</Subscript>(CF<Subscript>3</Subscript>)<Subscript>12</Subscript> molecules

Knudsen cell mass spectrometry was used to study ion-molecular electron exchange reactions between some trifluoromethyl derivatives of C₆₀ fullerene. Electron affinity values were experimentally determined for C₆₀(CF₃)₁₀ and the S ₆ isomer of C₆₀(CF₃)₁₂ and compared with the results of calculations and the data in the literature.     

Laser Desorption Ionization of As<Subscript>2</Subscript>Ch<Subscript>3</Subscript> (Ch = S,Se, and Te) Chalcogenides Using Quadrupole Ion Trap Time-of-Flight Mass Spectrometry: A Comparative Study

Laser desorption ionization using time-of-flight mass spectrometer afforded with quadrupole ion trap was used to study As₂Ch₃ (Ch = S, Se, and Te) bulk chalcogenide materials. The main goal of the study is the identification of species present in the plasma originating from the interaction of laser pulses with solid state material. The generated clusters in both positive and negative ion mode are identified as 10 unary (S _p ^+/– and As _m ^+/– ) and 34 binary (As _m S _p ^+/– ) species for As₂S₃ glass, 2 unary (Se _q ^+/– ) and 26 binary (As _m Se _q ^+/– ) species for As₂Se₃ glass, 7 unary (Te _r ^+/– ) and 23 binary (As _m Te _r ^+/– ) species for As₂Te₃ material. The fragmentation of chalcogenide materials was diminished using some polymers and in this way 45 new, higher mass clusters have been detected. This novel approach opens a new possibility for laser desorption ionization mass spectrometry analysis of chalcogenides as well as other materials.

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The thermodynamic properties of the [(Me<Subscript>3</Subscript>Si)<Subscript>7</Subscript>C<Subscript>60</Subscript>]<Subscript>2</Subscript> fullerene complex

The temperature dependence of the heat capacity C _p ^o of the [(Me₃Si)₇C₆₀]₂ fullerene complex was measured for the first time using precision adiabatic vacuum calorimetry over the temperature range 6.7–340 K and high-accuracy differential scanning calorimetry at 320–635 K. For the most part, the error in the C _p ^o values was about ±0.5%. An irreversible endothermic effect caused by the splitting of the dimeric bond between fullerene fragments and the thermal decomposition of the complex was observed at 448–570 K. The thermodynamic characteristics of this transformation were calculated and analyzed. Multifractal analysis of the low-temperature (T < 50 K) heat capacity was performed, and conclusions were drawn concerning the character of the heterodynamicity of the structure. The experimental data obtained were used to calculate the standard thermodynamic functions C _p ^o (T), H ^o (T) ? H ^o (0), S ^o (T) ? S ^o (0), and G ^o (T) ? H ^o (0) over the temperature range from T → 0 to 445 K and estimate the standard entropy of formation of the compound from simple substances at 298.15 K. The standard thermodynamic properties of [(Me₃Si)₇C₆₀]₂ are compared with those of the (C₆₀)₂ dimer, the [(η⁶-Ph₂)₂Cr]⁺[C₆₀]^?? fulleride, and the initial C₆₀ fullerene.     

Self-assembling of fullerene C<Subscript>60</Subscript> into (C<Subscript>60</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> clasters in aromatic solvents

Self-assembling of fullerene C₆₀ into (C₆₀) _n clusters in aromatic solvents was studied. The role of the π-π interactions and dispersion forces in the (C₆₀) _n cluster formation in these media is demonstrated using the data on the solubility of fullerene C₆₀ in these solvents and their ionization potentials and also spectral characteristics of fullerene C₆₀ in the range of 326–340 nm in different solvents.     

Structure,energy, and spin characteristics of La@C<Subscript>60</Subscript>-Lu@C<Subscript>60</Subscript> lanthanide endofullerenes

Calculations of the equilibrium geometric and electronic structure of lanthanide endofullerenes are presented. Two types of the Ln@C₆₀ structure are found. For endofullerenes of the first type (La@C₆₀-Dy@C₆₀), the stable position of the lanthanide atom is achieved at a distance of 0.67R from the center of fullerene (R is the fullerene radius); in endofullerenes of the second type (Ho@C₆₀-Lu@C₆₀), the character of the interaction between the lanthanide atom and fullerene changes because of the transfer of unpaired electrons from the corresponding atom to fullerene. It is found that in endofullerenes of the second type, metal atom mobility increases, and two minima of the potential energy appear, which corresponds to the Ln position in the center and at a distance of 0.5R from the center. Based on the obtained spin density distribution for La@C₆₀-Lu@C₆₀ endofullerenes, we conclude that there is spin leakage.     

The saturated hydrides of C<Subscript>60</Subscript>:F<Subscript>5</Subscript>F<Subscript>6</Subscript> PK F<Subscript>5</Subscript>F<Subscript>7</Subscript> isomers

The carbon cages composed of pentagons and heptagons (F₅F₇ isomers) are the analogs of fullerenes composed of pentagons and hexagons (F₅F₆ isomers). To provide insight into the structures and stability of the hydrides of F₅F₆ and F₅F₇ isomers, systematical density functional theory calculations are performed on all the 1,812 F₅F₆–C₆₀H₆₀ and 56 F₅F₇–C₆₀H₆₀. The calculated results demonstrate that the isomer with lowest/highest energy has most/fewest fused pentagons for both F₅F₆ and F₅F₇ hydrides and the stability of these hydrides increase with the number of fused pentagons roughly. The lowest energy F₅F₆–C₆₀H₆₀ and F₅F₇–C₆₀H₆₀ are 237.1 and 152.5 kcal/mol lower in energy than the isolated pentagon rule (IPR) C₆₀H₆₀, respectively; however, these two parent cages are 529.6 and 660.0 kcal/mol higher in energy than the IPR C₆₀. The calculations suggest that heptagon-containing cages, not only those violating the IPR can be the candidate cages for fullerene derivatives and the possible repulsion between the added atoms may play an important role in determining the structures and stability of the hydrides of carbon cages.     

Synthesis of fullerene C<Subscript>60</Subscript> monoadducts. Cyclopropanation of C<Subscript>60</Subscript> with sulfonium ylides

3′H-Cyclopropa[1,9](C₆₀-I_h)[5,6]fullerene-3′-carboxylic acid can be synthesized in a good yield by cyclopropanation of fullerene C₆₀ with 2-(dimethyl-λ⁴-sulfanylidene)acetates provided that the ester residue is readily hydrolyzable in acid medium.     

纳米金淀积的多孔硅靶增强样品的激光解吸/电离质谱信号

硅片类型和多孔硅结构的多样性影响了多孔硅表面的激光解吸/离子化质谱(DIOS)(无辅助基质的激光解吸/电离飞行时间质谱(LDI-TOF-MS))数据的重复性和靶的耐储时间。本工作通过在多孔硅的表面淀积金纳米颗粒并将其作为目标靶来增强软物质分子如聚乙二醇和多肽的激光解吸/电离质谱信号。纳米金的淀积钝化了多孔硅表面的Si-H活性基团,增加了靶的耐储时间。用场发射扫描电镜表征了多孔硅淀积金纳米颗粒前后的形貌,用X射线能量色散光谱法分析金的百分含量,结果表明其含量随沉积时间的延长而增加。激光解吸/电离质谱信号的增强可能是由多孔硅及其支持的金纳米颗粒的光学和物理性质引起的,该类型的样品靶在激光解吸/电离飞行时间质谱的应用上结合了多孔硅和金纳米颗粒的双重优势。     

Reactivity of fullerene C<Subscript>60</Subscript>

The results of a quantum-chemical study of the reactivity of fullerene C₆₀ in such reactions as polymerization (dimerization), cycloaddition, addition of valence-saturated molecules are presented. The mechanisms of these reactions are also discussed.     

New Hybrid Material: (C<Subscript>3</Subscript>H<Subscript>6</Subscript>N<Subscript>3</Subscript>)<Subscript>4</Subscript>Bi<Subscript>2</Subscript>Cl<Subscript>10</Subscript>. Synthesis,Structural Study and Spectroscopic Behavior

The structure of (C₃H₆N₃)₄Bi₂Cl₁₀ was determined by single crystal X-ray diffraction at room temperature. It crystallizes in the orthorhombic space group Pcmn, with a = 9.430 (1) Å, b = 17.426 (3) Å, c = 19.883(5) Å, V = 3267.3 (11) ų and Z = 4. The structure consists of discrete binuclear [Bi₂Cl₁₀]^4– anions and 3-aminopyrazolium cations. The crystal packing is governed by weak N–H···Cl hydrogen bonds, π–π and electrostatic Cl···Cl interactions. Infrared spectrum is used to gain more information on the title compound. An assignment of the observed vibration modes is reported. The crystal morphology is studied using the BFDH laws. The calculated HOMO and LUMO energies show that charge transfer occur within organic and inorganic molecules. The optical absorption of the zero-dimensional hybrid was also investigated.     

Sorption of light fullerenes C<Subscript>60</Subscript> and C<Subscript>70</Subscript> on NORIT-AZO carbon

Sorption of fullerenes C₆₀ and C₇₀ from o-xylene, toluene, and dichlorobenzene solutions on NORIT-AZO carbons was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1638–1642.Original Russian Text Copyright © 2004 by Semenov, Seregin, Arapov, Charykov.     

Molecular modeling of hydration properties of hydrophobic ions Li<Superscript>+</Superscript>@C<Subscript>60</Subscript> and K<Superscript>+</Superscript>@C<Subscript>60</Subscript>

The Gibbs free energies of solvation (ΔG _s) and the electronic structures of endohedral metallofullerenes M⁺@C₆₀ (M⁺= Li⁺, K⁺) were calculated within the framework of the density functional theory and the polarizable continuum model. In water environment, the equilibrium position of K⁺ is at the center of the fullerene cavity whereas that of Li⁺ is shifted by 0.14 nm toward the fullerene cage. The Li⁺ cation is stabilized by interactions with both the fullerene and solvent. The equilibrium structures of both endohedral metallofullerenes are characterized by very close ΔG _s values. In particular, the calculated ΔG _s values for K⁺@C₆₀ are in the range from −124 to −149 kJ mol⁻¹ depending on the basis set and on the type of the density functional. Molecular dynamics simulations (TIP3P H₂O, OPLS force field, water sphere of radius 1.9 nm) showed that the radial distribution functions of water density around C₆₀ and M⁺@C₆₀ are very similar, whereas orientations of water dipoles around the endohedral metallofullerenes resemble the hydration pattern of isolated metal ions.     

Quantum-chemical modeling of endohedral derivatives of buckminsterfullerenes Gd@C<Subscript>60</Subscript>(CHR)<Subscript>2</Subscript> and Gd@C<Subscript>80</Subscript>(CHR)<Subscript>2</Subscript>

The structural energies of the endohedral derivatives of buckminsterfullerenes Gd@C₆₀(CHR)₂ and Gd@C₈₀(CHR)₂ were calculated by quantum-chemical methods – semiempirical PM3 and nonempirical RHF SCF MO LCAO with the S. Huzinaga MINI minimum basis set and GAMESS software.     

The structural-phase state of C<Subscript>60</Subscript>-C<Subscript>70</Subscript> fullerene mixtures

The structural and phase state of the C₆₀-C₇₀ system at various C₆₀/C₇₀ ratios in mixtures obtained by the vaporization of solutions in toluene at ∼98°C was studied by X-ray structure analysis, differential scanning calorimetry, and infrared spectroscopy. Solid solutions based on the face-centered cubic packing of C₆₀ are not formed in the C₆₀-C₇₀ system at C₇₀ contents from 0.5 to 50 wt %. The hexagonal close packing of a solid solution of C₆₀ in C₇₀ can be formed as a result of the thermally activated decomposition of the ternary crystal solvate in the C₆₀-C₇₀-C₆H₅CH₃ system. The structural state of multiphase mixtures formed under conditions far from equilibrium is characterized by a high degree of structure imperfection and greater ability to undergo oxidation compared with C₆₀ and C₇₀.     

Influence of ZnO coating on the structure,morphology and electrochemical performances for LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> material

In this paper, ZnO was applied to modify the surface of LiNi_1/3Co_1/3Mn_1/3O₂ cathode material by a simple method. Powder X-ray diffraction (XRD) results show that both of the pristine material and the modified material were well crystallized and closely similar to each other. The crystal parameters of pristine material increased by modified measure. Scan electron microscope (SEM) pictures exhibit that the quasispherical pristine material was modified to the squareness one. Transmission electron microscope (TEM) image clearly elucidates that ZnO (several nanometers to 20 nm) was successful coated on surface of LiNi_1/3Co_1/3Mn_1/3O₂. X-ray photo-electron spectrometry (XPS) is used to characterize the composite of the coating layer on the surface of modified material. Electrochemical performance results present that the ZnO coating layer decrease the initial capacities of LiNi_1/3Co_1/3Mn_1/3O₂ by increasing the surface layer resistances. However, the cycling performance of LiNi_1/3Co_1/3Mn_1/3O₂ was effectively improved by the ZnO coating layer.     

Influence of composition on corroding process of Na<Subscript>2</Subscript>O-K<Subscript>2</Subscript>O-CaO-ZrO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript> glasses

The corroding process of six glasses of the Na₂O-K₂O-CaO-ZrO₂-SiO₂ system with ZrO₂content 0–2.13 mass % by water was observed during static tests at 121°C and pressure of 0.25 MPa in steam sterilizer. Significant increase of Na⁺ and K⁺ content in leachates was observed after the addition of ZrO₂ into glass. Further increase of the content of ZrO₂ in glasses slowed down the rate of Na⁺ and K⁺ leaching. The leaching process of SiO₂ as well as Na⁺, K⁺, and Ca²⁺ ions was evaluated on the basis of comparison with model leaching processes. Variation of the concentrations of Na⁺, K⁺, Ca²⁺, and SiO₂ in leachates with time was described by empirical equation. Observed changes in the initial leaching rates of Na⁺, K⁺, Ca²⁺, and SiO₂ can be ascribed to the content of ZrO₂ in glasses. The presence of ZrO₂ in glasses reduced the overall rate of glass dissolution.     

Electron interactions in the (η<Superscript>2</Superscript>-C<Subscript>60</Subscript>)Pd[P(Ph<Subscript>2</Subscript>)C<Subscript>5</Subscript>H<Subscript>4</Subscript>]<Subscript>2</Subscript>Fe complex

The electronic structure of the (η²-C₆₀)Pd[P(Ph₂)C₅H₄]₂Fe complex was calculated by the “hybrid” B3LYP method. Comparison of the experimental X-ray emission C-Kα spectrum and theoretical spectrum of the compound demonstrated that the electron interactions between the C₆₀ core, palladium atom, and organometallic fragment are described correctly in the framework of the quantum chemical method used. The electronic structure of the organometallic fullerene complex can be presented as a set of blocks of orbitals corresponding to different types of chemical bond. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2640–2644, December, 2005.