Silicon-29 NMR Spectroscopy Study of the Effect of Tetraphenylammonium (TPA) as a Template on Distribution of Silicate Species on Alkaline Aqueous and Alcoholic Silicate Solutions

Silicon-29 nuclear magnetic resonance (NMR) spectroscopy is used to characterize aqueous and non-aqueous alkaline solutions of tetraphenylammonium (TPA) silicates. Effect of the TPA cation on the equilibrium of silicate oligomers in aqueous and non-aqueous alkaline silicate solutions is investigated using ²⁹Si NMR spectra. It was found that the TPA cation had a structural directing role, directing the silicate species to form minor amounts of high order silicate anion in the presence of a high concentration of silicon. ²⁹Si NMR spectra of TPA silicate solutions indicate that considerable changes occur by changing the Si/TPA ratio. Also the effect of different alcohols on the distribution of silicate species is investigated. The results obtained show that distribution of these species is affected by the presence of alcohols and that maximum variations in this distribution are observed in the presence of methanol.     

Silicon-29 NMR Study of Alkaline Aqueous and Alcoholic Tri-butylmethyl Ammonium (TBMA) Silicate Solutions

Silicon-29 NMR spectroscopy was used to characterize aqueous and alcoholic alkaline solutions of tri-butylmethyl ammonium (TBMA) silicates. The effect of TBMA cation on the equilibrium of silicate oligomers in aqueous alkaline silicate solutions was investigated using ²⁹Si NMR spectra. It was found that TBMA cation has a structure directing role and directs the silicate species to form minor amounts of silicate anion in the presence of high concentration of silicon. Silicon-29 NMR spectra of TBMA silicate solutions indicate that considerable changes occurred by changing the Si/TBMA ratio. The distribution of silicate species was affected by the presence of the alcohols, specifically methanol.     

Characterization of mixed micelles of sodium cumene sulfonate with sodium dodecyl sulfate and cetyl trimethylammonium bromide by SANS,FTIR spectroscopy and NMR spectroscopy

The aqueous solutions of sodium cumene sulfonate (NaCS) and its mixtures with cetyl trimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) are studied by Small Angle Neutron Scattering (SANS), Fourier Transform Infrared (FTIR) spectroscopy and Nuclear Magnetic Resonance (NMR) spectroscopy. The compositions of mixed micelles are determined using Rubingh's Regular Solution Theory. NaCS when added to CTAB solution leads to the formation of long rod shaped micelles with dramatic increase in the CTAB aggregation number. Its addition to SDS on the other hand results in the formation of smaller mixed micelles where parts of SDS molecules in the micelle are replaced by NaCS molecules. NaCS–SDS mixed micelles prefer elongated ellipsoidal geometry in order to accommodate short NaCS molecules. The FTIR spectroscopy results indicate enhanced ordering of CTAB tails inside the NaCS–CTAB mixed micelles with reduction in the gauche/trans conformer ratio. Addition of NaCS to SDS on the other hand results in decreased ordering of SDS tails, as compared to SDS micelles alone. The chemical shifts observed in ¹H NMR spectra of NaCS–SDS and NaCS–CTAB mixture indicate that NaCS resides near the surface of the SDS micelle.     

Spatial Structure of the Decapeptide Val-Ile-Lys-Lys-Ser-Thr-Ala-Leu-Leu-Gly in Water and in a Complex with Sodium Dodecyl Sulfate Micelles

We have studied the spatial structure of the decapeptide Val-Ile-Lys-Lys-Ser-Thr-Ala-Leu-Leu-Gly in aqueous solution and in a complex with sodium dodecyl sulfate (SDS) micelles by ¹H nuclear magnetic resonance (NMR) spectroscopy and two-dimensional (2-D) NMR spectroscopy (total correlation spectroscopy and nuclear Overhauser effect spectroscopy (NOESY)). The approach used to determine the decapeptide spatial structure was based on analysis of the ¹H?C¹³C residual dipolar couplings in the molecules partially aligned in lyotropic liquid crystalline media. Analysis of the interproton distances obtained from the 2-D NOESY NMR spectrum was used to reveal the spatial structure of the decapeptide in a complex with SDS micelles. Complex formation was confirmed by analysis of ¹H chemical shifts in the NMR spectrum of the decapeptide and analysis of the signs and values of NOEs in a solution with SDS micelles.     

The analysis of pH‐dependent protonated conformers of 1‐hydroxyethylidene‐1,1‐diphosphonic acid by means of FT‐Raman spectroscopy,multivariate curve resolution and DFT modelling

1‐Hydroxyethylidene‐1,1‐diphosphonic acid (HEDP) solutions in the pH range 0.98–13.00 were analysed using FT‐Raman spectroscopy and ³¹P and ²³Na NMR spectroscopy. Vibrational bands for different protonated species were observed in the Raman spectra, whereas only a single NMR signal that shifted with pH was observed for all samples over the entire pH range. No significant shift in the ²³Na NMR signal was observed, confirming that formation of Na⁺(aq) complexes did not take place; hence, no interference with the different protonated forms of HEDP occurred. Vibrational bands were assigned using density functional theory(DFT)‐calculated spectra of the most likely conformers in solution. Multivariate curve resolution was performed on the Raman spectra in the region containing the PO stretching vibrations to determine the number of protonated species formed over the entire pH range. Chemometric analysis compares very favourably with the experimental species distribution diagram which was generated using the reported log K_H values. Copyright © 2009 John Wiley & Sons, Ltd.     

Fabrication of oxide base nanostructures using pulsed laser ablation in aqueous solutions

Nanoparticles of TiO₂ and SnO₂ were obtained by laser ablation of Ti and Sn targets in both deionized water and sodium dodecyl sulfate (SDS) solutions. The crystallinity of the nanoparticles strongly depended on the SDS concentration in the solution. Well-crystallized oxide nanoparticles were most abundantly fabricated in SDS solution with around the critical micelle concentration. An inorganic/organic layered nanocomposite consisting of a zinc hydroxide layer and a SDS lamellar interlayer was obtained by the ablation of Zn in SDS solutions. The oxide and/or hydroxide can be formed by the rapid reactive quenching with water in the liquid–plasma interface, where ablated species can be oxidized by aqueous oxidation. The surfactant in the liquid medium could affect the aggregation and growth of nuclei after the oxidation. The preparation of Pt/TiO₂ nanocomposite particles by PLA of the bi-combinant target of Pt and TiO₂ is also reported. PACS 81.16.Mk; 81.10.Dn; 81.07.Bc     

Structural Study of N-(1-Benzoyl-3-Pyrrolidinyl) Benzamide

Oxazolidinones show potent activity against vancomycin-resistant Staphylococcus aureus(VRSA) species, and are currently under active development. We present NMR spectroscopy and molecular dynamics calculation studies on N-(1-benzoyl-3-pyrrolidinyl) benzamide, an oxazolidinone derivative with substitution at the amine group of 3-pyrrolidinamine. the ¹H-NMR and ¹³C-NMR spectra exhibited two sets of peaks, one major and one minor, giving rise to the existence of isomers at room temperature. In order to deduce the nature of its isomeric distribution, a series of derivatives were synthesized and analyzed using NMR spectroscopy and computer-aided molecular modeling (CAMM) simulations. the results suggest that rotation of the benzoyl group attached to the secondary amine in N-(1-benzoyl-3-pyrrolidinyl) benzamide is responsible for conformational heterogeneity.     

以TEOS为硅源的聚硅硫酸铁中铁的形态分布研究

利用正硅酸乙酯代替传统硅酸钠制备活性硅酸,使之与聚合硫酸铁反应而得到聚硅硫酸铁絮凝剂。 由于正硅酸乙酯水解很缓慢,容易控制,可得到铁硅分布均匀、重现性好的产物;这有利于进行聚硅硫酸铁中铁的形态研究。采用Fe-Ferron逐时络合比色法和红外光谱法研究了聚硅硫酸铁絮凝剂中铁和硅的形态分布。研究结果表明：聚硅硫酸铁絮凝剂中Fe(a)形态较多,Fe(b)和Fe(c)含量相对较少。在一定时间内,随着熟化时间的延长,Fe(a)和Fe(b)含量有所下降,Fe(c)含量有所增加;但是当熟化时间到达5 d后,三种形态的变化不大。研究还显示聚硅硫酸铁絮凝剂中铁和硅的形态与其在聚合硫酸铁和聚硅酸中是不同的;聚合硫酸铁与活性硅酸并非简单的复合,而是发生了复杂的化学反应,生成了一种重现性好的新型无机高分子聚硅硫酸铁絮凝剂。     

Silicon-29 NMR studies of aqueous silicate solutions part 7: Exchange rates between anions

Silicon-29 NMR evidence is presented regarding the linewidths and the rates of chemical exchange between the smaller silicate anions in alkaline aqueous solutions of sodium and potassium silicates. It is found that the linewidths of different species vary, being relatively large for the dimer under most conditions. Moreover, as well as decreasing with increasing temperature, linewidths also appear to decrease with increasing pH. Some semi-quantitative values for lifetimes in particular solutions under given conditions are presented, but it is emphasized that these are minimum values, since there may be other origins for line-broadening.     

Structure of Na2O·MO·SiO2·CaF2 (M=Mg,Ca) oxyfluoride glasses

(9−x)CaO·xMgO·15Na₂O·60SiO₂·16CaF₂(x=0, 2, 4, 6, and 9) oxyfluoride glasses were prepared. Utilizing the Raman scattering technique together with ²⁹Si and ¹⁹F MAS NMR, the effect of alkaline metal oxides on the Q species of glass was characterized. Raman results show that as magnesia is added at the expense of calcium oxide, the disproportional reaction Q³→Q⁴+Q² (Qⁿ is a SiO₄ tetrahedron with n bridging oxygens) prompted due to the high ionic field strength of magnesia, magnesium oxide entered into the silicate network as tetrahedral MgO₄, and removed other modifying ions for charge compensation. This reaction was confirmed by ²⁹Si MAS NMR. ¹⁹F MAS NMR results show that fluorine exists in the form of mixed calcium sodium fluoride species in all glasses and no Si–F bonds were formed. As CaO is gradually replaced by MgO (x=6, 9), a proportion of the magnesium ions combines with fluorine to form the MgF⁺ species. Meanwhile, some part of Na⁺ ions complex F⁻ in the form of F–Na(6).     

硅酸钠与乙烯基三乙氧基硅烷的二维相关近红外光谱分析

关于超疏水涂层的制备有许多研究,其中硅衍生物涂层是一个重点,然而硅衍生物形成机理的研究还鲜有报道。以硅酸钠和乙烯基三乙氧基硅烷(VTES)作为硅衍生物的反应物,利用近红外光谱(near infrared, NIR)和二维相关分析(2D-correlation analysis, 2DCorr)方法探讨硅衍生物的反应机理。首先,采用德国Bruker公司的MPA型傅里叶近红外光谱仪采集样品的光谱信息,分析了17 Wt%硅酸钠、 97 Wt%VTES以及两者1:5摩尔比混合体系的分子结构变化特征,结果发现:混合体系在5 176~4 250 cm^-1范围内出现了Si-O-H和Si-O-Si基团的吸收峰,说明溶液中两者混合后发生了水解缩合反应;并发现10 262 cm^-1处的游离羟基减少并向低频方向偏移, 8 905 cm^-1处以氢键缔合的羟基增加;含氢键的醇从7 203 cm^-1偏移到6 846 cm^-1。将硅酸钠和VTES按照7种不同摩尔比混合并搅拌成溶胶凝胶状,采集这些样品的光谱信息,并且对吸收峰进行归属,结果发现:随着VTES的比例增加,游离羟基以及含氢键的醇减少,结合羟基增加,含硅基团也在增加。最后,对不同摩尔比的混合体系的光谱数据进行基线校正,运用软件Matlab 6.5计算基于摩尔比例扰动的二维相关光谱,提高近红外光谱的分辨率和分析不同官能团之间的变化顺序。结果发现:10 262 cm^-1处吸收峰的变化先于8 905 cm^-1处吸收峰的变化, 7 026(6 846) cm^-1处吸收峰的变化晚于5 859 cm^-1处吸收峰的变化, 5 264(5 176) cm^-1处吸收峰的变化晚于4 397 cm^-1处吸收峰的变化, 4 667 cm^-1处吸收峰的变化晚于4 397 cm^-1处吸收峰的变化。不同波数的吸收峰变化顺序对应其归属的官能团的变化顺序,进而揭示了近红外光谱中基团变化的原因。硅酸钠和VTES两种溶液混合后形成的溶胶凝胶是具有三维网状结构的硅-聚合物,这种聚合物具有疏水性质能被广泛应用。研究结果将有利于更深刻地理解硅酸钠和VTES混合体系水解缩合反应过程以及分子结构变化,为其进一步的研究和使用提供参考。     

Synthesis of Novel Fluorescent Cyclohexenone Derivatives and their Partitioning Study in Ionic Micellar Media

An approach is demonstrated toward the synthesis of four novel cyclohexenone derivatives (CDs) via a convenient route of Michael addition of ethyl acetoacetate. The molecular structures of CDs were confirmed by means of FT-IR, ¹H NMR, EIMS, UV and also by X-ray single crystal structure analysis. CDs are strongly fluorescent compounds and their fluorescent spectra exhibits intense violet fluorescence. To model the binding to biological membranes the behavior of CDs in micellar solutions of a cationic surfactant, cetyltrimethylammonium bromide (CTAB) and an anionic surfactant, sodium dodecylsulfate (SDS) has also been examined. The characteristics of partition and binding interactions of CDs with CTAB and SDS were investigated by UV-Visible and fluorescence spectroscopic techniques. Higher values of all mentioned interactions in case of CTAB, compared to SDS, indicate that there are greater interactions between the CDs and CTAB than with SDS.     

Observation of "hidden" magnesium: first-principles calculations and 25Mg solid-state NMR of enstatite

²⁵Mg NMR parameters have been determined for two polymorphs of enstatite (MgSiO₃), an important magnesium silicate phase present as a major component of the Earth's upper mantle. The crystal structures of both polymorphs contain two crystallographically distinct magnesium sites; however, only a single resonance is observed in ²⁵Mg MAS NMR spectra recorded at 14.1 and 20.0 T. First-principles calculations performed on geometry-optimised crystal structures reveal that the quadrupolar interaction for the second site is expected to be very large, resulting in extensive broadening of the spectral resonance, explaining its apparent absence in the NMR spectrum. ²⁵Mg QCPMG NMR experiments employing variable offset cumulative spectroscopy (VOCS) are used to observe the broadened site and enable measurement of NMR parameters. The large difference in quadrupolar interaction between the two crystallographic magnesium sites is rationalised qualitatively in terms of the distortion of the local coordination environment as well as longer-range effects using a simple point charge model.     

Structure solution of network materials by solid-state NMR without knowledge of the crystallographic space group

An algorithm is presented for solving the structures of silicate network materials such as zeolites or layered silicates from solid-state ²⁹Si double-quantum NMR data for situations in which the crystallographic space group is not known. The algorithm is explained and illustrated in detail using a hypothetical two-dimensional network structure as a working example. The algorithm involves an atom-by-atom structure building process in which candidate partial structures are evaluated according to their agreement with SiOSi connectivity information, symmetry restraints, and fits to ²⁹Si double quantum NMR curves followed by minimization of a cost function that incorporates connectivity, symmetry, and quality of fit to the double quantum curves. The two-dimensional network material is successfully reconstructed from hypothetical NMR data that can be reasonably expected to be obtained for real samples. This advance in “NMR crystallography” is expected to be important for structure determination of partially ordered silicate materials for which diffraction provides very limited structural information.     

水溶性聚合物与十二烷基硫酸钠相互作用的1H NMR研究

用¹H NMR方法研究了分别在2 g/L聚乙烯吡咯烷酮(PVP)和2 g/L聚乙烯醇（PVA）存在下，一系列不同浓度的十二烷基硫酸钠(SDS)溶液. 二维NOESY实验表明，SDS在浓度为2.5 mmol/L时形成胶束，且PVP被增溶到胶束内部；当SDS浓度低于2.5 mmol/L时，PVP与SDS之间没有明显的相互作用. 自旋-自旋弛豫时间的测量结果支持这一结论. 实验中没有检测到PVA与SDS之间的相互作用.     

An NMR crystallographic approach to monitoring cation substitution in the aluminophosphate STA-2

The substitution of the divalent cations Mg²⁺ and Zn²⁺ into the aluminophosphate (AlPO) framework of STA-2 has been studied using an “NMR crystallographic” approach, combining multinuclear solid-state NMR spectroscopy, X-ray diffraction and first-principles calculations. Although the AlPO framework itself is inherently neutral, the positive charge of the organocation template in an as-made material is usually balanced either by the coordination to the framework of anions from the synthesis solution, such as OH⁻ or F⁻, and/or by the substitution of aliovalent cations. However, the exact position and distribution of the substituted cations can be difficult to determine, but can have a significant impact upon the catalytic properties a material exhibits once calcined.For as-made Mg substituted STA-2, the positive charge of the organocation template is balanced by the substitution of Mg²⁺ for Al³⁺ and, where required, by hydroxide anions coordinated to the framework [27] Al MAS NMR spectra show that Al is present in both tetrahedral and five-fold coordination, with the latter dependent on the amount of substituted cations, and confirms the bridging nature of the hydroxyl groups, while high-resolution MQMAS spectra are able to show that Mg appears to preferentially substitute on the Al1 site. This conclusion is also supported by first-principles calculations. The calculations also show that ³¹P chemical shifts depend not only on the topologically-distinct site in the SAT framework, but also on the number of next-nearest-neighbour Mg species, and the exact nature of the coordinated hydroxyls (whether the P atom forms part of a six-membered ring, P(OAl)₂OH, where OH bridges between two Al atoms). The calculations demonstrate a strong correlation between the ³¹P isotropic chemical shift and the average 〈P–O–M〉 bond angle. In contrast, for Zn substituted STA-2, both X-ray diffraction and NMR spectroscopy show less preference for substitution onto Al1 or Al2, with both appearing to be present, although that into Al1 appears slightly more favoured.     

5‐Fluorouracil solutions: NMR study of acid–base equilibrium in water and DMSO

A comprehensive analysis of solutions of 5‐fluorouracil (5FU) in water and an organic medium (dimethylsulfoxide, DMSO) was carried out using quantum chemical methods and nuclear magnetic resonance (NMR) spectroscopy. The details of anionic form generation in the solution of 5FU with an equimolar amount of potassium hydroxide were studied by ¹³С, ¹Н, ¹⁵N and ¹⁹F NMR. Interpretation of NMR spectral data was carried out using quantum chemical calculations at the TPSSTPSS/6‐311+G(d,p) level of theory. Specific solvation of 5FU and 1THF‐5FU was modeled in approximation using the five‐water cluster model and solvate complex including two DMSO molecules. It was established that in an alkaline medium in DMSO 5FU occurred mainly as a type of an anion with a deprotonation on N(1) position of a pyrimidine ring whereas in water alkaline solution—as a mixture of two anions with a deprotonation on N(1) and N(3) positions with a predominant content of the latter form. For the quantitative definition of the deprotonation forms of 5FU the technique based on the data of theoretical and experimental NMR ¹³C spectroscopy, tested on a model compound 1‐(tetrahydrofuranyl‐2)‐5‐fluoro‐pyrimidinedione‐2,4 (tegafur, THF‐5FU), was offered. The N(3) anion was found from spectral data to be more thermodynamically stable than the N(1) anion by 2.40 kJ mol^?1 (calculated value 2.24 kJ mol^?1) in an alkaline–water solution. Both alkaline–water and alkaline–DMSO solutions of THF‐5FU (THF‐5FU/KOH = 1/1) were characterized by the ratio of the equilibrium concentrations of the anion and diketo‐tautomer as 9:1 and 4.3:1, respectively. Copyright © 2014 John Wiley & Sons, Ltd.     

NMR Studies of Heat-Induced Transitions in Structure and Cation Binding Environments of a Strontium-Saturated Swelling Mica

In this work, we combine ²⁷Al, ²⁹Si, ¹⁹F, and ²³Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) to characterize the structure and interlayer cation environments in a strontium-saturated member of the swelling mica family before and after a heat-induced collapse of the interlayer space. The ²⁷Al and ²⁹Si MAS NMR demonstrate that the sample consists mainly of swelling mica, though the composition does not match the ideal structural formula. Aluminum NMR also shows that a portion of the aluminum shifts from a tetrahedral to an octahedral coordination environment upon heating. Changes in the ²⁹Si and ¹⁹F NMR after heating are consistent with a structural rearrangement of the tetrahedral sheet to permit the binding of larger cations in the ditrigonal cavity. The ²³Na MAS NMR results indicate the presence of three unique sodium environments before and after heating. The heat-invariant resonance is consistent with the presence of sodium carbonate. The other two resonances are associated with interlayer sodium and reflect a migration of sodium to a dominantly anhydrous ditrigonal binding structure with heating. Quantitative elemental analysis and NMR data presented here suggest strontium is bound deep within the ditrigonal cavity of the collapsed micas. Authors' address: Karl T. Mueller, 104 Chemistry Building, Penn State University, University Park, PA 16802, USA     

129Xe NMR study of the homogeneity and the size distribution of small sodium metal particles in NaY zeolite

NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using¹²⁹Xe NMR spectroscopy. At low sodium concentration, the¹²⁹Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields.     

Azetidin‐2‐one Versus Chroman‐2‐one: Application of 1H‐13C COSY NMR and Mass Spectroscopy in Structure Elucidation–Class of Compounds

Azetidin‐2‐ones, commonly known as β‐lactams, constitute a biologically important class of compound. Treatment of azetidin‐2‐ones with alkali is known to form diverse types of compounds depending on the stability of the ring. In many cases, the ring is retained in the product at the cost of transformation of substituents. Spectroscopy is the most important tool to characterize the organic compounds. However, in some cases the structures of the products are so closely related that simple IR, ¹H NMR, and ¹³C NMR spectra do not lead to unambiguous structure elucidation. This article reports a novel application of ¹H‐¹³C COSY NMR and mass spectroscopy in determining unequivocally an azetidin‐2‐one ring structure instead of a chroman‐2‐one ring structure for the product obtained by treatment of 1‐benzhydryl‐3,3‐bis(4‐methylphenyl)‐4‐[2‐(o‐dip‐tolylacyl)hydroxyphenyl]‐2‐azetidinone with ethanolic sodium hydroxide at room temperature.