Low-temperature (180 K) crystal structures of tetrakis-mu-(niflumato)di(aqua)dicopper(II) N,N-dimethylformamide and N,N-dimethylacetamide solvates, their EPR properties, and anticonvulsant activities of these and other ternary binuclear copper(II)niflumate complexes

Two pseudopolymorphs, solvates, of [Cu(2)(II)(niflumate)(4)(H(2)O)(2)] of unknown structure were obtained following solution of [Cu(2)(II)(niflumate)(4)(H(2)O)(2)] in N,N-dimethylacetamide (DMA) or N,N-dimethylformamide (DMF). Low-temperature crystal structures obtained for these solvates revealed that they were ternary aqua DMA and DMF solvates: [Cu(2)(II)(niflumate)(4)(H(2)O)(2)].4DMA and [Cu(2)(II)(niflumate)(4)(H(2)O)(2)].4DMF. Intermolecular hydrogen bonding interactions account for the formation of these stable DMA and DMF solvates. These pseudopolymorphs contain a centrosymmetric binuclear center with Cu-Cu bond distances ranging from 2.6439(7) to 2.6452(9) A; the coordination sphere of Cu(II) is characterized by one long Cu-O (water) bond length of 2.128(3)-2.135(3) A and four short Cu-O (carboxylate) bonds of 1.949(3)-1.977(3) A. Crystal parameters for the DMA pseudopolymorph: a=10.372(1), b=19.625(2), c=17.967(2) A, beta=97.40(1) degrees , V=3626.8(6) A(3); monoclinic system; space group: P2(1)/a and for the DMF pseudopolymorph: a=10.125(2), b=18.647(3), c=19.616(4) A, alpha=74.38(2)(o), beta=88.18(2)(o), gamma=79.28(2)(o), V=3504(1) A(3); triclinic system; space group: P1. EPR spectra of these solids are identical and show strong antiferromagnetic coupling between the copper atoms, similar to the spectrum obtained for [Cu(2)(II)(niflumate)(4)(DMSO)(2)]. The [Cu(2)(II)(niflumate)(4)(H(2)O)(2)], [Cu(2)(II)(niflumate)(4)(H(2)O)(2)].4DMA, [Cu(2)(II)(niflumate)(4)(H(2)O)(2)].4DMF, [Cu(2)(II)(niflumate)(4)(DMF)(2)], and[Cu(2)(II)(niflumate)(4)(DMSO)(2)] evidenced protection against maximal electroshock-induced seizures and Psychomotor seizures at various times after treatment, consistent with the well known antiinflammatory activities of Cu chelates, but failed to protect against Metrazol-induced seizures while evidencing some Rotorod Toxicity consistent with a mechanism of action involving sedative activity.     

Stereochemical Preference of 2'‐Deoxycytidine for Chiral Bis(diamido)‐bridged Basket Resorcin[4]arenes

Bis(diamido)‐bridged basket resorcin[4]arene (all-S)-1 and its (all-R)-1 enantiomer proved able to interact with 2'‐deoxycytidine ( 2 ) and pyrimidine nucleoside analogs in dimethyl sulfoxide (DMSO) solution. In such a solvent, the resorcinarene hosts adopt a preferential 1,3‐alternate‐like conformation, with a larger cavity delimited by two syn 3,5‐dimethoxyphenyl moieties, and two external pockets, each delimited by the other 3,5‐dimethoxyphenyl group and its diamido arm (the wing). Complexation phenomena were investigated by nuclear magnetic resonance (NMR) methods, including ¹H NMR DOSY and 1D ROESY experiments, and molecular modeling. Heteroassociation constants of [ (all-S)-1·2 ] and [ (all-R)-1·2 ] diastereoisomeric complexes were obtained from diffusion data by single point measurements, and from nonlinear fitting of ¹H NMR chemical shifts. Selective proton relaxation rate measurements allowed us to significantly discriminate the two complexes by identifying two different interaction sites of the guest in the resorcin[4]arene host, depending on its configuration. Chirality 25:840–851, 2013. © 2013 Wiley Periodicals, Inc.     

Synthesis,spectral characterization,in vitro microbial and cytotoxic studies of lanthanum(III) and thorium(IV) complexes with 1,2,4-triazole Schiff bases

A series of metal complexes of La(III) and Th(IV) have been synthesized with newly derived biologically active ligands. These ligands were synthesized by the condensation of 3-substituted-4-amino-5-hydrazino-1,2,4-triazole with 8-formyl-7-hydroxy- 4-methylcoumarin. The structure of the complexes has been proposed by elemental analyses, spectroscopic data i.e. i.r., ¹H nmr, Uv-Vis, FAB-mass and thermal studies. The elemental analyses of the complexes conform to the stoichiometry of the type [La(L)·3H₂O]·2H₂O and [Th(L)(NO₃)·2H₂O]·2H₂O where (L = L^I-L^IV). All the complexes are soluble in DMF and DMSO and are non-electrolytes in DMF and DMSO. All these ligands and their complexes have also been screened for their antibacterial (Escherichia coli, Staphylococcus aureus, Staphylococcus pyogenes and Pseudomonas aeruginosa) and antifungal activities (Aspergillus niger, Aspergillus flavus and cladosporium) by the MIC method. The brine shrimp bioassay was also carried out to study their invitro cytotoxic properties.     

Conversion of 2,5-dimethylfuran to 2-hydroxy-5-hydroperoxy-2,5-dimethyldihydrofuran,a true 1O2-derived reaction in aqueous 1O2 generating systems

It has been studied whether 2,5-dimethylfuran (DMF) is a specific ¹O₂ trapping agent in aqueous system. The exposure of DMF to aqueous ¹O₂ generating system (Rose Bengal photooxygenation system) gave 2-hydroxy-5-hydroperoxy-2,5-dimethyldihydrofuran (a hydrated form of endoperoxide, ¹O₂-derived reaction product) and cis-diacetylethylene (cis-DAE), while the bromine-catalyzed autoxidation of DMF afforded only trans-DAE. In Fenton system (·OH generating system) DMF was converted in the main to cis-DAE, but not to the hydrated form of endoperoxide. The exposure of DMF to acetaldehyde-xanthine oxidase system failed to detect the hydrated form of endoperoxide, but chiefly yielded a non-specific oxidation product, cis-DAE.     

Use of amides as cryoprotectants in extenders for frozen sperm of tambaqui, Colossoma macropomum

Amides were tested as cryoprotectants in comparison with glycerol and DMSO (more traditional cryoprotectants) for recovery of Colossoma macropomum (tambaqui fish) sperm. Milt was extended in Beltsville Thawing Solution, then frozen with the addition of 2%, 5%, 8%, or 11% of: (1) dimethylacetamide (DMA), (2) dimethylformamide (DMF), (3) methylformamide (MF), or with 5% glycerol or 10% dimethylsulfoxide. Fertilization rates were greatest (P < 0.001) with amides; 8% DMF (91.6 ± 1.3%), 5% DMF (88.9 ± 1.6%), and 8% MF (83.0 ± 1.6%), which did not significantly differ among themselves, when compared with glycerol (51.6 ± 2.4%) and DMSO (61.9 ± 3.1%). The best hatching rates (P < 0.001) also occurred for 5% or 8% DMF and 8% MF (79.1 ± 3.1, 87.6 ± 1.5, and 74.8 ± 3.0, respectively) and were also similar (P > 0.05). For such treatments, both fertilization and hatching rates were similar (P > 0.05) to those with fresh sperm (91.7 ± 1.4 and 87.4 ± 1.4, respectively). The best sperm motility across extenders (at least 55.7%) was with 5%, 8%, and 11% DMF (P < 0.001). Those same treatments, along with 11% MF, provided the longest (P < 0.001) period of motility (at least 1 min). The greatest sperm integrity (more than 54%) was with 5% and 11% MF and with DMA and DMF at all tested concentrations (P < 0.001). The greatest (P < 0.001) sperm viability (at least 31%) was for 5%, 8%, and 11% DMA, and with 8% and 11% MF, and also for DMF at all tested concentrations. Sperm DNA integrity was best (more than 50%) for 2%, 5%, and 8% MF and for DMA and DMF at all concentrations (P < 0.001), whereas 2% DMA, 11% MF, 11% DMF, and the three amides at both 5% and 8% yielded the highest mitochondrial functionality (at least 44%; P < 0.001); thus, 8% MF and both 5% and 8% DMF were the cryoprotectants with the best postthaw quality for C. macropomum sperm.     

Stabilization of Li Metal Anode in DMSO‐Based Electrolytes via Optimization of Salt–Solvent Coordination for Li–O2 Batteries

The conventional electrolyte of 1 m lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in dimethyl sulfoxide (DMSO) is unstable against the Li metal anode and therefore cannot be used directly in practical Li–O₂ batteries. Here, we demonstrate that a highly concentrated electrolyte based on LiTFSI in DMSO (with a molar ratio of 1:3) can greatly improve the stability of the Li metal anode against DMSO and significantly improve the cycling stability of Li–O₂ batteries. This highly concentrated electrolyte contains no free DMSO solvent molecules, but only complexes of (TFSI^?)_a ? Li⁺? (DMSO)_b (where a + b = 4), and thus enhances their stability with Li metal anodes. In addition, such salt–solvent complexes have higher Gibbs activation energy barriers than the free DMSO solvent molecules, indicating improved stability of the electrolyte against the attack of superoxide radical anions. Therefore, the stability of this highly concentrated electrolyte at both Li metal anodes and carbon‐based air electrodes has been greatly enhanced, resulting in improved cycling performance of Li–O₂ batteries. The fundamental stability of the electrolyte in the absence of free‐solvent against the chemical and electrochemical reactions can also be used to enhance the stability of other electrochemical systems.     

In situ synthesis of (5-phenyl-1H-pyrazole-3-carboxylic acid) metal complexes and their stable supramolecular microporous frameworks

By in situ generation of ppc ligand in the presence MCl₂ and 3-phenyl-1H-pyrazole-5-carbohydrazide at room temperature, the complexes, [M(ppc)₂(DMF)₂]·2H₂O (M = Co (1) and Ni (2); ppc = 5-phenyl-1H-pyrazole-3-carboxylic acid), were synthesized and characterized by single-crystal X-ray diffraction, IR spectrum, UV spectra and elemental analysis. X-ray structural analysis revealed that the complexes were formed into 3D supramolecular polymers via C-H?O and π?π interactions. The 3D supramolecular networks of two complexes were constructed from 1D nanochannels along the c-direction with the disorder DMF and water solvent molecules shuttling easily. TG and powder X-ray diffraction analysis showed two complexes had high stability when DMF and H₂O molecules were removed. Upon DMF molecules liberated, two complexes become stable microporous solid with coordination-unsaturated [M(ppc)₂] as center. The electrochemical properties were also investigated.     

Synthesis and characterization of the inclusion compound of a ferrocenyldiimine dioxomolybdenum complex with heptakis-2,3,6-tri-O-methyl-β-cyclodextrin

A dioxomolybdenum(VI) complex bearing the diimine ligand N,N′-bis(ferrocenylmethylene)ethylenediamine (FcNN) has been prepared in good yield by the reaction of FcNN with MoO₂Cl₂(THF)₂. One isomeric form was identified by ¹H NMR (including NOE experiments), corresponding to the cis,cis geometry with respect to the CN bonds of the free ligand. The polynuclear complex was immobilized in permethylated β-cyclodextrin (TRIMEB) by addition of the guest to a solution of TRIMEB in a mixture of dichloromethane and nitromethane. Removal of the solvent led to the isolation of an inclusion compound with a 2:1 host:guest stoichiometry. For comparison, an inclusion compound containing just the ligand FcNN and TRIMEB was prepared using a similar method. The products were characterized in the solid state by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), FT-IR and ¹³C CP MAS NMR spectroscopy. UV-Vis measurements were also carried out in solution. Both the complex MoO₂Cl₂(FcNN) and its inclusion compound with TRIMEB catalyze with high selectivity the liquid phase epoxidation of cyclooctene using tert-butyl hydroperoxide (TBHP) as the oxidant. In general, the catalytic behavior of the Mo^VI complex was not markedly affected by encapsulation in TRIMEB, although observed activities were slightly lower.     

The influences of water solvent on the structures and stabilities of Na+–AD conformers

The influences of water solvent on the structures and stabilities of the complex ion conformers formed by the coordination of alanine dipeptide (AD) and Na⁺ have been investigated using supramolecular and polarizable continuum solvation models at the level of B3LYP/6-311++G**, respectively; 12 monohydrated and 12 dihydrated structures of Na⁺–AD complex ion were obtained after full geometrical optimization. The results showed that H₂O molecules easily bind with Na⁺ of Na⁺–AD complex ion, forming an ion-lone pair interaction with the Na–O bond length of 2.1–2.3 Å. Besides, H₂O molecules also can form hydrogen bonds O_W–H_W···O(1), O_W–H_W···O(2), N(1)–H(1)···O_W or N(2)–H(2)···O_W with O or N groups of the Na⁺–AD backbone. The most stable gaseous bidentate conformer C7AB of Na⁺–AD is still the most stable one in the solvent of water. However, the structure of the most unstable gaseous conformer α′B of Na⁺–AD collapses under the attack of H₂O molecules and changes into C7AB conformation. Computations with IEFPCM solvation model of self-consistent reaction field theory give that aqueous C5A is more stable than C7_eqB and that the stabilization energies of water solvent on monodentate conformers of Na⁺–AD complex ion (about 272–294 kJ/mol) are more than those on bidentate ones (about 243 kJ/mol).     

Synthesis, structure and properties of copper(II) and manganese(II) coordination polymers with 1,5-dinitronaphthalene-3,7-dicarboxylate

Two new metal-organic coordination polymers with 1,5-dinitronaphthalene-3,7-dicarboxylate (NNDC), [Cu₂(NNDC)₂(DMF)_1.8(DMSO)_2.2(H₂O)₂]·H₂O (1) and [Mn₃(NNDC)₃(DMSO)₄]·2DMSO (2) have been synthesized under solvothermal conditions and characterized by single crystal X-ray diffraction and Thermogravimetric Analysis (TGA). The structure of compound 1 consists of one-dimensional chains with copper ions being linked by the dicarboxylate ligands. The coordination chains are associated into ladder-like double chains through O-H?O hydrogen bonds and π-π interactions, and the ladders are packed in a cross fashion through further π-π interactions to give the three-dimensional structure. The Mn(II) compound exhibits a 3D framework with the pcu topology, in which [Mn₃(COO)₆] clusters as octahedral secondary building blocks are linked by the naphthalene spacers. Magnetic analyses were carried out based on both temperature- and field-dependent data, consistently suggesting relatively weak antiferromagnetic interactions within the carboxylate bridged [Mn₃(COO)₆] cluster.     

Cryoprotection of lipid membranes for high-resolution solid-state NMR studies of membrane peptides and proteins at low temperature

Solid-state NMR spectra of membrane proteins often show significant line broadening at cryogenic temperatures. Here we investigate the effects of several cryoprotectants to preserve the spectral resolution of lipid membranes and membrane peptides at temperatures down to ~200 K. Trehalose, glycerol, dimethylsulfoxide (DMSO), dimethylformamide (DMF), and polyethylene glycol (PEG), were chosen. These compounds are commonly used in protein crystallography and cryobiology. ¹³C and ¹H magic-angle-spinning spectra of several types of lipid membranes show that DMSO provides the best resolution enhancement over unprotected membranes and also best retards ice formation at low temperature. DMF and PEG-400 show slightly weaker cryoprotection, while glycerol and trehalose neither prevent membrane line broadening nor prevent ice formation under the conditions of our study. Neutral saturated-chain phospholipids are the most amenable to cryoprotection, whereas negatively charged and unsaturated lipids attenuate cryoprotection. ¹³C–¹H dipolar couplings and ³¹P chemical shift anisotropies indicate that high spectral resolution at low temperature is correlated with stronger immobilization of the lipids at high temperature, indicating that line narrowing results from reduction of the conformational space sampled by the lipid molecules at high temperature. DMSO selectively narrowed the linewidths of the most disordered residues in the influenza M2 transmembrane peptide, while residues that exhibit narrow linewidths in the unprotected membrane are less impacted. A relatively rigid β-hairpin antimicrobial peptide, PG-1, showed a linewidth increase of ~0.5 ppm over a ~70 K temperature drop both with and without cryoprotection. Finally, a short-chain saturated lipid, DLPE, exhibits excellent linewidths, suggesting that it may be a good medium for membrane protein structure determination. The three best cryoprotectants found in this work—DMSO, PEG, and DMF—should be useful for low-temperature membrane-protein structural studies by SSNMR without compromising spectral resolution.     

Thermal effects in guest–host systems: [Zn2(bdc)(S‐lac)(dmf)]•PhEtOH: A DSC and NMR study

Differential scanning calorimetry and nuclear magnetic resonance were used to investigate thermal effects in the guest–host systems where homochiral metal–organic sorbent [Zn₂(bdc)(S ‐lac)(dmf)] is considered as a host while 1‐phenylethanol enantiomers and their racemic mixture serve as guest molecules. A maximum energy gain from the guest–host interaction was observed in the system with the racemic mixture. The effect of host–guest recognition was revealed for the case of the host and guest having a similar type of chirality in the presence of antipode guest molecules.     

Measurement of preferential solvation of some glucans in mixed solvent systems by gel-permeation chromatography

Preferential solvation of the glucans amylose, pullulan, and dextran in binary dimethyl-sulfoxide/water (DMSO/H₂O) solvent mixtures has been measured using gel-permeation chromatography. The preferential solvation behavior of the three glucans in DMSO/H₂O solvent mixtures is indistinguishable in the experiments reported. In solvent mixtures with mol ratio DMSO/H₂O less than 1:2, all three glucans are solvated preferentially by H₂O. The maximum extent of preferential solvation by H₂O is about 2.5 mol H₂O/mol of glucose residues. When the DMSO/H₂O mol ratio exceeds 1:2, DMSO solvates the glucans preferentially to a maximum extent of about 1 mol DMSO/mol of glucose residues. An interpretation of the change in preferential solvation with mixed solvent composition is suggested in terms of the known characteristics of the binary solvent system, and the relationship of preferential solvation, reported here, to the absolute solvation of the glucan chains is discussed.     

The effect of solvent on preparation of CH3NH3PbI3 photodetectors via an antisolvent-free method

During the fabrication of lateral-structured photodetectors based on CH₃NH₃PbI₃ film, antisolvents represented by toluene are usually used to accelerate the crystallization of perovskite. Using antisolvent not only leads to the formation of shrinkage holes at the bottom of the perovskite layer, but the toxicity of antisolvents would also hinder the industrial preparation of perovskite devices. An antisolvent-free method is a possible solution to avoid these problems. Here, we report a lateral-structured photodetector based on an antisolvent-free method. The lateral photodetector exhibited a high responsivity of 1.75 A⋅W⁻¹ and specific detectivity (D*) of 3.54 × 10¹² Jones. In particular, the results indicated that the solvent had an influence on perovskite film morphology, crystallization, and device performance. The prepared CH₃NH₃PbI₃ film presented needle-like crystals and low performance with single precursor solvent N,N-dimethylformamide (DMF). In comparison, appropriate mixing of dimethyl sulfoxide (DMSO) could improve the morphology, crystallization, and performance of the film. In addition, the solvent volume ratio of the precursor had a profound effect on the performance of the as-prepared photodetectors. At a DMSO:DMF volume ratio of 5:5, the as-prepared film had massive perovskite crystals and fewer defects, resulting in optimal device performance, which can be explained by Urbach energy.     

Mitochondrial morphology and function impaired by dimethyl sulfoxide and dimethyl Formamide

In this work, the effects of two non-ionic, non-hydroxyl organic solvents, dimethyl sulfoxide (DMSO) and dimethyl formamide (DMF) on the morphology and function of isolated rat hepatic mitochondria were investigated and compared. Mitochondrial ultrastructures impaired by DMSO and DMF were clearly observed by transmission electron microscopy. Spectroscopic and polarographic results demonstrated that organic solvents induced mitochondrial swelling, enhanced the permeation to H⁺/K⁺, collapsed the potential inner mitochondrial membrane (IMM), and increased the IMM fluidity. Moreover, with organic solvents addition, the outer mitochondrial membrane (OMM) was broken, accompanied with the release of Cytochrome c, which could activate cell apoptosis signaling pathway. The role of DMSO and DMF in enhancing permeation or transient water pore formation in the mitochondrial phospholipid bilayer might be the main reason for the mitochondrial morphology and function impaired. Mitochondrial dysfunctions induced by the two organic solvents were dose-dependent, but the extents varied. Ethanol (EtOH) showed the highest potential damage on the mitochondrial morphology and functions, followed by DMF and DMSO.     

Porous coordination polymer of copper(II) assembled from mixed organic ligands pyridine-2,4-dicarboxylic acid and trans-1,2-bis(4-pyridyl)ethylene: Synthesis, crystal structure and magnetic study

A 3-D porous coordination polymer of Cu(II) has been synthesized using two different organic bridging ligands, pyridine-2,4-dicarboxylate (pydc) and trans-1,2-bis(4-pyridyl)ethylene (bpe). Here, pydc and bpe connect two adjacent Cu(II) centers, resulting in a rectangular grid-like 2-D sheet with grid dimensions 10.058 × 15.258 Å. The channels are formed when 2-D networks running along the b-axis which are filled by solvent water molecules. The stability of porous networks, after removal of guest water molecules is confirmed by thermogravimetric analysis and X-ray powder diffraction technique. The low temperature magnetic study has been carried out, which indicates the presence of weak antiferromagnetic coupling with J = −0.59 cm⁻¹.     

Temperature dependence of the electronic spin-lattice relaxation time in a 2-iron-2-sulphur model complex

The complex [Fe2S2(S2-o-xylyl)2]2- in DMF (dimethylformamide), DMSO (dimethylsulphoxide) or a 1:1 DMF/DMSO mixture, a model for the chromophore in the 2Fe-2S proteins (ferredoxins), has been reduced and studied by conventional EPR over a temperature range. The low-field feature of the spectrum, Hz, has been computer simulated in order to analyse the lineshape in terms of a convolution product of Lorentzian and Gaussian distributions. The Gaussian contribution to the linewidth and a fixed part of the Lorentzian contribution, which is a function of the solvent and the way it freezes, were measured at a low temperature (less than or equal to 100 K) and subtracted from the linewidths in the higher-temperature range (130-200 K). The variable Lorentzian contribution thus obtained was related to spin-lattice relaxation times. The spin-lattice relaxation times of the sample having 1:1 DMSO/DMF solvent were measured in the range 6 to 11 K by the saturating pulse technique and in the range 10 to 65 K by continuous saturation methods. Up to 65 K the results follow the law 1/T1 alpha T4.5, a relationship which is not readily interpreted in terms of a simple Debye model. At higher temperatures the results may be interpreted in terms either of a dominant Orbach mechanism involving excited states at approx. 900 +/- 50 cm-1 (DMSO, DMF) or 770 +/- 50 cm-1 (1:1 DMSO/DMF), or of a Raman process in which 1/T1 alpha T7.5. The former is compatible with the two-phonon process already described in some ferredoxins, especially those with little anisotropy (gy - gx approximately 0.0) which have characteristically high [J] values.     

Red‐ and green‐emitting nano‐clay materials doped with Eu3+ and/or Tb3+

Trivalent europium (Eu³⁺) and terbium (Tb³⁺) ions are important activator centers used in different host lattices to produce red and green emitting materials. The current work shows the design of new clay minerals to act as host lattices for rare earth (RE) ions. Based on the hectorite structure, nano‐chlorohectorites and nano‐fluorohectorites were developed by replacing the OH^? present in the hectorite structure with Cl^? or F^?, thus avoiding the luminescence quenching expected due to the OH^? groups. The produced matrices were characterized through X‐ray powder diffraction (XPD), transmission electron microscopy (TEM), FT‐IR, ²⁹Si MAS (magic angle spinning) NMR, nitrogen sorption, thermogravimetry‐differential scanning calorimetry (TGA‐DSC) and luminescence measurements, indicating all good features expected from a host lattice for RE ions. The nano‐clay materials were successfully doped with Eu³⁺ and/or Tb³⁺ to yield materials preserving the hectorite crystal structure and showing the related luminescence emissions. Thus, the present work shows that efficient RE³⁺ luminescence can be obtained from clays without the use of organic ‘antenna’ molecules.     

Optimization of the Water-Insoluble Procedures for <Emphasis Type="Italic">USP</Emphasis> General Chapter <Emphasis Type="Italic">Residual Solvents</Emphasis> <467>

The water-insoluble procedures in US Pharmacopeia (USP) General Chapter Residual Solvents <467>, which are based on European Pharmacopoeia procedures, were optimized and modified before their inclusion in the chapter to improve their scope, performance, and ruggedness. The optimized procedures use a static headspace introduction system with a gas chromatograph equipped with a flame ionization detector. This article describes some of the key changes made to the USP published procedures, including use of dimethyl sulfoxide (DMSO) or dimethylformamide (DMF) as the solvent, addition of 5 mL of water and 1 mL of sample (dissolved in DMSO or DMF) to the headspace vial, use of a 3:1 GC split ratio, and use of new matrix-matched system suitability solutions. These procedures were verified with two different active pharmaceutical ingredients—hydroxyzine pamoate and prednisone. In the investigation, the more polar material (hydroxyzine pamoate) showed greater recoveries for the optimized procedures when prepared in DMSO. The less polar material (prednisone) typically had greater recoveries in DMF for the optimized procedures. During experimentation, insights into sample preparation, additional types of headspace instrumentation, solvent purity, and other parameters were also gained.     

Conditions for Reversible Na Intercalation in Graphite: Theoretical Studies on the Interplay Among Guest Ions,Solvent, and Graphite Host

Graphite is the most widely used anode material for Li‐ion batteries and is also considered a promising anode for K‐ion batteries. However, Na⁺, a similar alkali ion to Li⁺ or K⁺, is incapable of being intercalated into graphite and thus, graphite is not considered a potential electrode for Na‐ion batteries. This atypical behavior of Na has drawn considerable attention; however, a clear explanation of its origin has not yet been provided. Herein, through a systematic investigation of alkali metal graphite intercalation compounds (AM‐GICs, AM = Li, Na, K, Rb, Cs) in various solvent environments, it is demonstrated that the unfavorable local Na‐graphene interaction primarily leads to the instability of Na‐GIC formation but can be effectively modulated by screening Na ions with solvent molecules. Moreover, it is shown that the reversible Na intercalation into graphite is possible only for specific conditions of electrolytes with respect to the Na‐solvent solvation energy and the lowest unoccupied molecular orbital level of the complexes. It is believed that these conditions are applicable to other electrochemical systems involving guest ions and an intercalation host and hint at a general strategy to tailor the electrochemical intercalation between pure guest ion intercalation and cointercalation.