Heteronuclear Multiple Quantum Correlation Research Articles

Multiblock poly(ether-b-amide) copolymers comprised of PA1212 and PPO-PEO-PPO with specific moisture-responsive and antistatic properties

Functional multiblock poly(ether-b-amide) (PEBA) copolymers, comprised of PA1212 (polyamide 1212) as hard segments and Jeffamine ED-2003 as soft segments, were successfully prepared via two-step melt polycondensation without any amidation catalyst. Here, using diamino-terminated poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEO-PPO), Jeffamine ED-2003, enhances the compatibility between polyamide oligomer and polyether, which is better than the traditional route using hydroxyl-terminated polyether. The chemical structure of multiblock PEBAs, as well as the microphase separated structure with crystalline phase of polyamide and polyether, were confirmed by heteronuclear multiple-bond correlation spectrum, heteronuclear multiple quantum correlation spectrum, Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry and dynamic mechanical analysis. The hydrophilic PEBA copolymers showed water adsorption ranging from 87.3% to 17.1% depending on the polyether content, and specially showed moisture responsive behavior within seconds when exposed to moisture. The corresponding mechanism was studied using time-resolved attenuated total reflectance FT-IR spectroscopy in the molecular level and the water diffusion coefficient was estimated to be 1.07 × 10–8 cm2∙s–1. Two-dimensional correlation FT-IR spectra analysis was performed to confirm that the interaction between water and polyether phase was in preference to that between water and polyamide matrix, and water molecule only forms hydrogen bond with the polyether segment. Due to the incorporation of PEO segments, the PEBAs have the surface resistivity varying from 5.6 × 109 to 6.5× 1010 Ω, which makes PEBA potential candidate as permanent antistatic agent.

Heteronuclear-filtered 1H homonuclear multi-quantum correlation experiment at 100 kHz magic-angle spinning

Remarkable advances in fast magic-angle spinning (MAS) techniques significantly improve the resolution of 1H solid-state nuclear magnetic resonance (NMR) spectra. Here, we introduce a heteronuclear-filtered 1H homonuclear multi-quantum (MQ) correlation strategy available at a MAS rate of 100 kHz by combining 1H{X} heteronuclear-filtered methods and 1H homonuclear MQ correlation experiments. The proposed strategy was applied to selectively extract 1H signals of aluminum lactate (Al-Lac) in a mixture of Al-Lac and zinc lactate (Zn-Lac) using 27Al-filtered methods (i.e., 1H{27Al} heteronuclear multiple quantum correlation (HMQC) or 1H{27Al} symmetry-based resonance-echo saturation-pulse double-resonance (S-RESPDOR)). We demonstrate that incorporating these 27Al-filtered methods into two-dimensional (2D) 1H–1H double-quantum (DQ)/single-quantum (SQ), triple-quantum (TQ)/SQ, and even three-dimensional (3D) 27Al/1H(DQ)/1H(SQ) experiments can facilitate the acquisition of spectra without signal overlap and targeted characterization of the 1H species surrounding 27Al sites. The proposed strategy is considered to efficiently extract key structural information from complex spin systems.

Synthesis of 5-fluorouracil-lactoside derivatives and experimental study on their anti-oral squamous cell carcinoma activity.

To reduce the toxicity of 5-fluorouracil (5-FU), design and synthesize 5-FU-lactoside derivatives, and preliminarily study their antitumor activities. Target compounds were prepared with Vorbrüggenglycation procedures, the structures were characterized through high resolution mass spectrometry (HRMS), 1H nuclear magnetic resonance (1HNMR), carbon-13 nuclear magnetic resonance (13CNMR), heteronuclear multiple quantum correlation (HMQC), and heteronuclear multiple bond correlation (HMBC). A cell counting kit (CCK)-8 test was performed to examine their in vitro toxicity and antitumor activity. Experimental data were tested by χ2, and statistically significant differences were denoted by P<0.05. The target compounds were synthesized through a simple and efficient method. 1HNMR, 13CNMR, HMQC, HMBC, and HRMS confirmed that Ⅰa and Ⅰb were 5-FU nucleoside derivatives substituted with lactoside groups at N-1 and N-3, respectively. The CCK-8 test verified that high concentrations (0.7 μmol·mL-1) of Ⅰa and Ⅰb inhibited the growth of normal oral keratinocytes (NOK) by 30.28% and 50.68% after 24 h of treatment. Both values were lower than the inhibitory effect of 5-FU (68.22%; P<0.05). Ⅰb had a significant inhibitory effect on the growth of two oral squamous cell carcinoma cell lines. The inhibition rates of Cal-27 cells and UM SCC-47 cells treated with 0.7 μmol·mL-1 for 24 h were 81.20% and 80.19%, respectively. Ⅰa and Ⅰb are less toxic than 5-FU. The antitumor activity of Ⅰb against oral squamous cell carcinoma cells is more obvious than that of Ⅰa.

Revealing Brønsted Acidic Bridging SiOHAl Groups on Amorphous Silica-Alumina by Ultrahigh Field Solid-State NMR.

Amorphous silica-aluminas (ASAs) are important acidic catalysts and supports for many industrially essential and sustainable processes. The identification of surface acid sites with their local structures on ASAs is of critical importance for tuning their catalytic properties but still remains a great challenge and is under debate. Here, ultrahigh magnetic field (35.2 T) 27Al-{1H} D-HMQC (dipolar-mediated heteronuclear multiple-quantum correlation) two-dimensional NMR experiments demonstrate two types of Brønsted acid sites in ASA catalysts. In addition to the known pseudobridging silanol acid sites, the use of ultrahigh field NMR provides the first direct experimental evidence for the existence of bridging silanol (BS: SiOHAl) acid sites in ASAs, which has been hotly debated in the past few decades. This discovery provides new opportunities for scientists and engineers to develop and apply ASAs in various reaction processes due to the significance of BS in chemical and fuel productions based on its strong Brønsted acidity.

Through-space 11 B-27 Al correlation: Influence of the recoupling channel.

Through-space heteronuclear correlation (D-HETCOR) experiments based on heteronuclear multiple-quantum correlation (D-HMQC) and refocused insensitive nuclei enhanced by polarization transfer (D-RINEPT) sequences have been proven to be useful approaches for the detection of the spatial proximity between half-integer quadrupolar nuclei in solids under magic-angle spinning (MAS) conditions. The corresponding pulse sequences employ coherence transfers mediated by heteronuclear dipolar interactions, which are reintroduced under MAS by radiofrequency irradiation of only one of the two correlated nuclei. We investigate herein using numerical simulations of spin dynamics and solid-state NMR experiments on magnesium aluminoborate glass how the choice of the channel to which the heteronuclear dipolar recoupling is applied affects the transfer efficiency of D-HMQC and D-RINEPT sequences between 11 B and 27 Al nuclei. Experimental results show that maximum transfer efficiency is achieved when the recoupling scheme is applied to the channel, for which the spin magnetization is parallel to the B0 axis in average.

Elucidating the Location of Cd2+ in Post-synthetically Treated InP Quantum Dots Using Dynamic Nuclear Polarization 31P and 113Cd Solid-State NMR Spectroscopy

Indium phosphide quantum dots (InP QD) are a promising alternative to traditional QD materials that contain toxic heavy elements such as lead and cadmium. However, InP QD obtained from colloidal synthesis are often plagued by poor photoluminescence quantum yields (PL-QYs). In order to improve the PL-QY of InP QD, a number of post-synthetic treatments have been devised. Recently, it has been shown that InP post-synthetically treated with Lewis acid metal divalent cations (M-InP) exhibit enhanced PL-QY; however, the molecular structure and mechanism behind the improved PL-QY are not fully understood. To determine the surface structure of M-InP QD, dynamic nuclear polarization surface-enhanced nuclear magnetic resonance spectroscopy (DNP SENS) experiments were employed on a series of InP magic size clusters treated with Cd ions, InP QD, cadmium phosphide (Cd₃P₂) QD, and Cd-treated InP QD (Cd–InP QD). With the use of DNP SENS, we were able to obtain the 1D ³¹P and ¹¹³Cd NMR spectra, ¹¹³Cd{³¹P} rotational-echo double-resonance (REDOR) NMR spectra, and ³¹P{¹¹³Cd} dipolar heteronuclear multiple quantum correlation (D-HMQC) sequence. Changes in the phosphide ³¹P chemical shifts after Cd treatment provide indirect evidence that some Cd alloys into the sub-surface regions of the particle. DNP-enhanced ¹¹³Cd solid-state NMR spectra suggest that most Cd ions are coordinated by oxygen atoms from either carboxylate ligands or surface phosphate groups. ¹¹³Cd{³¹P} REDOR and ³¹P{¹¹³Cd} D-HMQC experiments confirm that a subset of Cd ions are located on the surface of Cd–InP QD and coordinated with phosphate groups.

Uncovering selective and active Ga surface sites in gallia-alumina mixed-oxide propane dehydrogenation catalysts by dynamic nuclear polarization surface enhanced NMR spectroscopy.

Gallia–alumina (Ga,Al)2O3(x : y) spinel-type solid solution nanoparticle catalysts for propane dehydrogenation (PDH) were prepared with four nominal Ga : Al atomic ratios (1 : 6, 1 : 3, 3 : 1, 1 : 0) using a colloidal synthesis approach. The structure, coordination environment and distribution of Ga and Al sites in these materials were investigated by X-ray diffraction, X-ray absorption spectroscopy (Ga K-edge) as well as 27Al and 71Ga solid state nuclear magnetic resonance. The surface acidity (Lewis or Brønsted) was probed using infrared spectroscopy with pyridine and 2,6-dimethylpyridine probe molecules, complemented by element-specific insights (Ga or Al) from dynamic nuclear polarization surface enhanced cross-polarization magic angle spinning 15N{27Al} and 15N{71Ga} J coupling mediated heteronuclear multiple quantum correlation NMR experiments using 15N-labelled pyridine as a probe molecule. The latter approach provides unique insights into the nature and relative strength of the surface acid sites as it allows to distinguish contributions from Al and Ga sites to the overall surface acidity of mixed (Ga,Al)2O3 oxides. Notably, we demonstrate that (Ga,Al)2O3 catalysts with a high Al content show a greater relative abundance of four-coordinated Ga sites and a greater relative fraction of weak/medium Ga-based surface Lewis acid sites, which correlates with superior propene selectivity, Ga-based activity, and stability in PDH (due to lower coking). In contrast, (Ga,Al)2O3 catalysts with a lower Al content feature a higher fraction of six-coordinated Ga sites, as well as more abundant Ga-based strong surface Lewis acid sites, which deactivate through coking. Overall, the results show that the relative abundance and strength of Ga-based surface Lewis acid sites can be tuned by optimizing the bulk Ga : Al atomic ratio, thus providing an effective measure for a rational control of the catalyst performance.

Low-power synchronous helical pulse sequences for large anisotropic interactions in MAS NMR: Double-quantum excitation of 14N.

We develop a theoretical framework for a class of pulse sequences in the nuclear magnetic resonance (NMR) of rotating solids, which are applicable to nuclear spins with anisotropic interactions substantially larger than the spinning frequency, under conditions where the radiofrequency amplitude is smaller than or comparable to the spinning frequency. The treatment is based on average Hamiltonian theory and allows us to derive pulse sequences with well-defined relationships between the pulse parameters and spinning frequency for exciting specific coherences without the need for any detailed calculations. This framework is applied to the excitation of double-quantum spectra of 14N and is used both to evaluate the existing low-power pulse schemes and to predict the new ones, which we present here. It is shown that these sequences can be designed to be γ-encoded and therefore allow the acquisition of sideband-free spectra. It is also shown how these new double-quantum excitation sequences are incorporated into heteronuclear correlation NMR, such as 1H-14N dipolar double-quantum heteronuclear multiple-quantum correlation spectroscopy. The new experiments are evaluated both with numerical simulations and experiments on glycine and N-acetylvaline, which represent cases with "moderate" and "large" quadrupolar interactions, respectively. The analyzed pulse sequences perform well for the case of a "moderate" quadrupolar interaction, however poorly with a "large" quadrupolar interaction, for which future work on pulse sequence development is necessary.

Diketopeprazin and Methyl-5-docosenoate from endophytic fungi Aureobasidium pollulan BSS6 with α-Glucosidase inhibition and its validation through molecular docking

Endophytic fungi have been a focus of attention for producing diverse classes of bioactive metabolites but little is known about endophytic fungi Aureobasidium pullulan, isolated from the bark of frankincense producing tree (Boswellia sacra). Extensive chromatographic methods resulted in the isolation of two known diketopeprazin (1 and 2) along with three fatty acids derivatives (3–5) from the ethyl acetate fraction of Aureobasidium pollulan BSS6. The structures of mentioned compounds were characterized by advanced 1D and 2D spectroscopic techniques such as, ultraviolet–visible (UV), infrared (IR), electrospray ionization mass spectrometry (ESI-MS) 1H NMR, 13C NMR, heteronuclear multiple bond correlation (HMBC), heteronuclear multiple-quantum coherence (HMQC) and correlation spectroscopy (COSY). The resulted compounds were evaluated for α-glucosidase inhibition potential to know their hyperglycemic effect in type 2 diabetes mellitus. Compound 3 showed significant inhibition having an IC50 value of 23.3 µM. To know the binding energy and pharmacophore of compound 3 with in active site of enzyme, the molecular docking was performed. Compound 3 has shown π-alkyl type of interactions with Asp214 and Glu276, key amino acid residues in the catalytic triad of α-glucosidase. In conclusion, the current study reports novel sources of anti-diabetic constituent's from Aureobasidium sp. for the first time.

T1-Noise eliminated dipolar heteronuclear multiple-quantum coherence solid-state NMR spectroscopy.

Heteronuclear correlation (HETCOR) spectroscopy is one of the key tools in the arsenal of the solid-state NMR spectroscopist to probe chemical and spatial proximities between two different nuclei and enhance spectral resolution. Dipolar heteronuclear multiple-quantum coherence (D-HMQC) is a powerful technique that can be potentially utilized to obtain 1H detected 2D HETCOR solid-state NMR spectra of any NMR active nucleus. A long-standing problem in 1H detected D-HMQC solid-state NMR experiments is the presence of t1-noise which reduces sensitivity and impedes spectral interpretation. In this contribution, we describe novel pulse sequences, termed t1-noise eliminated (TONE) D-HMQC, that minimize t1-noise and can provide higher sensitivity and resolution than conventional D-HMQC. Monte-Carlo and numerical simulations confirm that t1-noise in conventional D-HMQC primarily occurs because random MAS frequency fluctuations cause variations in the NMR signal amplitude from scan to scan, leading to imperfect cancellation of uncorrelated signals by phase cycling. The TONE D-HMQC sequence uses 1H π-pulses to refocus the evolution of 1H CSA across each SR421 recoupling block, improving the stability of the pulse sequence to random MAS frequency fluctuations. The 1H refocusing pulses also restore the orthogonality of in-phase and anti-phase magnetization for all crystallite orientations at the end of each recoupling block, enabling the use of 90° flip-back or LG spin-lock trim pulses to reduce the intensity of uncorrelated signals. We demonstrate the application of these methods to acquire 1H detected 2D 1H{35Cl} and 1H{13C} HETCOR spectra of histidine·HCl·H2O with reduced t1-noise. To show generality, we also apply these methods to obtain 2D 1H{17O} spectra of 20%-17O fmoc-alanine and for the first time at natural abundance, 2D 1H{25Mg} HETCOR spectra of magnesium hydroxide. The TONE D-HMQC sequences are also used to probe 1H-25Mg and 1H-27Al proximities in Mg-Al layered double hydroxides and confirm the even mixing of Mg and Al in these materials.

Synthesis, crystal structure and biological activity of new phosphoester-p-substituted-methylparabens

Bis(4-(methoxycarbonyl)phenyl)phosphonate and bis(4-(methoxycarbonyl)phenyl) phosphate were prepared from the reaction of p-hydroxybenzoate with phenyl phosphonic dichloride and with phenyl dichlorophosphate, respectively, in the presence of CuCl as catalyst. The structure of the synthesized compounds was elucidated by FTIR, 1H NMR,13C NMR and 31P NMR spectroscopy. The assignments for the 1H, 13C and 31P chemical shifts are based on 1D and 2D NMR homo- and heteronuclear correlations (H,H-COSY (Correlation Spectroscopy), H,C-HMQC (Heteronuclear Multiple Quantum Correlation and H,C-HMBC (Heteronuclear Multiple Bond Correlation)) and 31P-13C couplings. The synthesized compounds revealed good solubility in common organic solvents. The crystal structure of the products was investigated by single-crystal X-ray diffraction, while the purity of the bulk product was confirmed by powder X-ray diffraction. The antimicrobial effect of the non-phosphoester-functionalized and phosphoester-functionalized p-hydroxybenzoate disc samples was investigated. Antimicrobial activities were evaluated against bacterial strains of Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923 and fungi Candidaalbicans ATCC 10321 used in this research. The non-phosphoester-functionalized p-hydroxybenzoate exhibit good antibacterial and antifungal effect compared to phosphoester-functionalized p-hydroxybenzoates. The synthesized compounds were screened in vitro for their cytotoxicity on primary Albino Rabbit dermal fibroblasts, by the 3-(4, 5-dimethyl-thiazol-2-yl)-2, 5-diphenyl-tetrazolium bromide (MTT) protocol. The results showed clearly that the synthesized phosphoesters promote cell viability and they have the potential to be developed into economical and reliable additives for skin cosmetics and pharmaceuticals.

A Cytotoxic Compound from n-Hexane Fraction of Lantana camara Linn Leaves

In this study, one triterpenoid compound from n-hexane fraction of Lantana camaraLinn leaves has cytotoxic activity was isolated. Isolation was carried out using gravity chromatographycolumnand purification by recrystallization method. Isolated compound was obtained white solid with melting point 252-253oC. The structure of isolated compound was elucidated using spectroscopic analysis Ultraviolet (UV), Infrared (IR), 1H-Nuclear Magnetic Resonance (1H-NMR), 13C-Nuclear Magnetic Resonance (13C-NMR) Heteronuclear Multiple Bond Connectivity (HMBC), Heteronuclear Multiple Quantum Correlation (HMQC), Distortionless Enhancement Polarization Transfer (DEPT) and comparative literature data, identified as Lantadene A (22β-angeloyloxy-3-oxoolean-12-en-28-oic-acid) with molecule formula C35H52O5. The Lantadene A compound was evaluated for cytotoxic activity against shrimp larvae Artemia SalinaLeach using Brine Shrimp Lethality Test(BSLT) method, showed strong cytotoxic activity with an LC50value of 48.97 µg/mL.

Rhodium(I)‐α‐Phenylvinylfluorenyl Complexes: Synthesis, Characterization, and Evaluation as Initiators in the Stereospecific Polymerization of Phenylacetylene

The synthesis, characterization and use, as initiators for phenylacetylene polymerizations, of three new rhodium(I)‐vinyl complexes containing fluorenyl functionality with fluorine‐functionalized phosphine ligands is described. Rh(nbd)(CPh=CFlu)P(4‐FC6H4)3, Rh(nbd)(CPh=CFlu)P(4‐CF3C6H4)3, and Rh(nbd)(CPh=CFlu)P[3,5‐(CF3)2C6H3]3 (nbd: 2,5‐norbornadiene; Flu: fluorenyl) were prepared and isolated as discrete, orange compounds and were readily recrystallized yielding X‐ray quality crystals. All complexes were characterized by a combination of 1H, 31P, 19F, 103Rh NMR spectroscopy and 2D 31P‐103Rh/31P‐103Rh{103Rh} heteronuclear multiple‐quantum correlation (HMQC) experiments, elemental analysis, and single‐crystal X‐ray analysis. The complexes were active as initiators in the co‐ordination insertion polymerization of phenylacetylene, with initiation efficiencies spanning the range 13–56 %, and yielded polyphenylacetylenes of low dispersity (Ð = Mw/Mn) with high cis‐transoidal stereoregularity.

New bioactive C15 acetogenins from the red alga Laurencia obtusa

Background and Objective: With regard to the uniqueness of the red algae of the genus Laurencia as the source of C15-acetogenins, along with the diversity of biological applications; the acetogenin content of the Red Sea Laurencia obtusa was investigated. Materials and Methods: Fractionation and purification of the CH2Cl2/MeOH extract were carried out by applying several chromatographic techniques, including column and preparative thin-layer chromatography; followed by a series of 1H nuclear magnetic resonance measurements to give rise of some interesting notes. Toxicity to Artemia salina was evaluated. The apoptosis induced by these two compounds was demonstrated by DNA fragmentation assay and microscopic observation. Results: A new rare chloroallene-based C15 acetogenin, laurentusenin (1) along with a new furan ring containing C15 acetogenin, laurenfuresenin (2), were isolated from the red alga L. obtusa. Comparing 1D and 2D NMR, MS, ultraviolet and infrared radiation spectral data for the newly isolated compounds with the reported bromoallene containing acetogenins spectral data was played the crucial role for characterization of their chemical structures. 1 and 2 exhibited bare toxicity (LD50 >12 mM) in test organism, A. salina and induced apoptotic death confirmed by DNA fragmentation and microscopic investigations. Conclusion: The isolated metabolite 1 showed unusual substituted allene side chain, while 2 inserted furan ring as a new acetogenin nucleus. Both compounds may play a role in apoptosis induction and initiation and propagation of inflammatory responses. Abbreviations used: NMR: Nuclear magnetic resonance; MS: Mass spectrometry; UV: Ultraviolet spectroscopy; IR: infrared radiation; EIMS: Electron ionization mass spectra; TLC: Thin-layer chromatography; PPP: Platelet poor plasma; PRPDS: platelet-rich plasma derived serum. DEPT: Destortionless Enhancement by Polarization Transfer; NOESY: Nuclear Overhauser Effect Spectroscopy; HSQC: Heteronuclear Single Quantum Coherence; HMBC: Heteronuclear Multiple-quantum Correlation; 1H-1H COSY: Correlation Spectroscopy.

Reducing t1 noise through rapid scanning.

The so-called t1 noise, which arises due to random instabilities in the spectrometer hardware, remains the primary source of noise that limits the sensitivity of most 2D NMR experiments, particularly in the expanding group of solid-state NMR methods that utilize dipolar-recoupling. In this communication we revisit the relationship between the signal intensity and the t1 noise produced. It is shown that since the latter scales linearly with the signal strength, the use of a conventional relaxation delay of 1.3T1 may prove far from optimal. In cases where the fluctuations occur on a shorter timescale than the recycle delay, a considerably faster repetition rate should be used to maximize the time sensitivity in a 2D experiment than what is used to maximize the sensitivity in 1D. This is demonstrated with the acquisition of 1H{13C} Dipolar-mediated Heteronuclear Multiple-Quantum Correlation (D-HMQC) type spectra in which the sensitivity could be nearly doubled by choosing a very short relaxation delay corresponding to 0.2T1.

Observation of proximities between spin-1/2 and quadrupolar nuclei in solids: Improved robustness to chemical shielding using adiabatic symmetry-based recoupling

We introduce a novel heteronuclear dipolar recoupling based on the R21−1 symmetry, which uses the tanh/tan (tt) shaped pulse as a basic inversion element and is denoted R21−1(tt). Using first-order average Hamiltonian theory, we show that this sequence is non-γ-encoded and that it reintroduces the |m| = 1 spatial component of the Chemical Shift Anisotropy (CSA) of the irradiated isotope and its heteronuclear dipolar interactions. Using numerical simulations and one-dimensional (1D) 27Al-{31P} through-space D-HMQC (Dipolar Heteronuclear Multiple-Quantum Correlation) experiments on VPI-5, we compare the performances of this recoupling to those of other non-γ-encoded |m| = 1 heteronuclear recoupling schemes: REDOR (Rotational-Echo DOuble Resonance), SFAM (Simultaneous Frequency and Amplitude Modulation) and R42−1(tt). Such comparison indicates that the R21−1(tt) scheme is more robust to CSA, offset and radiofrequency field inhomogeneities than the other schemes. We take advantage of the high robustness of R21−1(tt) to CSA and offset to demonstrate the possibility to correlate the signals of 207Pb isotope with those of neighboring half-integer spin quadrupolar nuclei. Such approach is demonstrated experimentally by acquiring 11B-{207Pb} D-HMQC 2D spectra of Pb4O(BO3)2 crystalline powder.

Getting a better insight into the chemistry of decomposition of complex flame retarded formulation: New insights using solid state NMR

This paper aims at developing an innovative approach to characterize the char residue of an intumescent coating obtained after a UL1709 furnace test. The intumescent formulation is based on an epoxy resin and contains numerous additives including zinc borate, ammonium polyphosphate and silicate fibers. The purpose is to characterize the numerous reactions that can occur upon burning using crossed methods including Electron Probe Micro-Analysis (EPMA), X-ray diffraction (XRD) and 1D/2D solid state Nuclear Magnetic Resonance (NMR). In particular, it emphasizes the potential of the advanced NMR technique namely two-dimensional Dipolar Heteronuclear Multiple Quantum Correlation (2D D-HMQC) NMR. As a result, EPMA evidenced that B/P and B/Si are located in the same domain suggesting the formation of boron-phosphorus and/or boron-silicone containing compounds on the sample surface. H3BO3 was identified by XRD as a main crystalline specie, additional species (e.g. SiO2, Zn4O(BO2)6) were also identified. The borate, silicate and phosphate chemical species were then characterized using 1D NMR but no definitive assignments could be given. To specify those assignments, 2D D-HMQC NMR was performed and the formation of amorphous borophosphates and borosilicates was evidenced emphasizing the chemical reactivity between the ingredients of the formulation. It was suggested that these species allow reinforcing the char and improving the fire protective properties of the coatings. This work highlights the particular interest of advanced NMR technique, which provides unique information on the characterization of intumescent char.

Improving reliability of chemometric models for authentication of species origin of heparin by switching from 1D to 2D NMR experiments

Nuclear magnetic resonance (NMR) spectroscopy is regarded as one of the most powerful and versatile analytical approaches to assure the quality of heparin preparations. In particular, it was recently demonstrated that by using 1H NMR coupled with chemometrics heparin and low molecular weight heparin (LMWH) samples derived from three major animal species (porcine, ovine and bovine) can be differentiated [Y.B. Monakhova et al. J. Pharm. Anal. 149 (2018) 114–119].In this study, significant improvement of existing chemometric models was achieved by switching to 2D NMR experiments (heteronuclear multiple-quantum correlation (HMQC) and diffusion-ordered spectroscopy (DOSY)). Two representative data sets (sixty-nine heparin and twenty-two LMWH) belonged to different batches and distributed by different commercial companies were investigated. A trend for animal species differentiation was observed in the principal component analysis (PCA) score plot built based on the DOSY data. A superior model was constructed using HMQC experiments, where individual heparin (LMWH) clusters as well as their blends were clearly differentiated. The predictive power of different classification methods as well as unsupervised techniques (independent components analysis, ICA) clearly proved applicability of the model for routine heparin and LMWH analysis.The switch from 1D to 2D NMR techniques provides a wealth of additional information, which is beneficial for multivariate modeling of NMR spectroscopic data for heparin preparations.

Spin-Noise-Detected Two-Dimensional Nuclear Magnetic Resonance at Triple Sensitivity.

A major breakthrough in speed and sensitivity of 2 D spin‐noise‐detected NMR is achieved owing to a new acquisition and processing scheme called “double block usage” (DBU) that utilizes each recorded noise block in two independent cross‐correlations. The mixing, evolution, and acquisition periods are repeated head‐to‐tail without any recovery delays and well‐known building blocks of multidimensional NMR (constant‐time evolution and quadrature detection in the indirect dimension as well as pulsed field gradients) provide further enhancement and artifact suppression. Modified timing of the receiver electronics eliminates spurious random excitation. We achieve a threefold sensitivity increase over the original snHMQC (spin‐noise‐detected heteronuclear multiple quantum correlation) experiment (K. Chandra et al., J. Phys. Chem. Lett. 2013, 4, 3853) and demonstrate the feasibility of spin‐noise‐detected long‐range correlation.

Heteronuclear Correlation Experiments Such as Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC), Heteronuclear Multiple-Quantum Correlation Spectroscopy (HMQC) and Heteronuclear Multiple-Bond Correlation Spectroscopy (HMBC) Comparative Study On Malignant and Benign Human Endocrinology and Thyroid Cancer Cells and Tissues Under Synchrotron Radiation

Heteronuclear Correlation Experiments Such as Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC), Heteronuclear Multiple-Quantum Correlation Spectroscopy (HMQC) and Heteronuclear Multiple-Bond Correlation Spectroscopy (HMBC) Comparative Study On Malignant and Benign Human Endocrinology and Thyroid Cancer Cells and Tissues Under Synchrotron Radiation