BROMINATION OF NR WITH N-BROMOSUCCINIMIDE

ABSTRACT The mechanism of bromination of NR was studied by solution-state 1H-NMR spectroscopy. The bromination of NR was carried out at 20–50 °C with N-bromosuccinimide as the brominating agent, and the kinetic study of bromination was conducted under nitrogen atmosphere at 30–50 °C for various reaction times. The influence of bromine atom substituent on the bromination rate constant (k) also was investigated. Bromine atom content was found to be dependent upon the reaction time, indicating first-order kinetics. The activation energy of bromination of NR, calculated from the reaction rate constants, was 19.3, 5.5, and 5.8 kJ mol−1 for bromine atom linked to carbon atom with methylene proton and methylene protons, respectively.

<i>Geminal</i> parahydrogen-induced polarization: accumulating long-lived singlet order on methylene proton pairs

In the majority of hydrogenative parahydrogen-induced polarization (PHIP) experiments, the hydrogen molecule undergoes pairwise cis addition to an unsaturated precursor to occupy vicinal positions on the product molecule. However, some ruthenium-based hydrogenation catalysts induce geminal hydrogenation, leading to a reaction product in which the two hydrogen atoms are transferred to the same carbon centre, forming a methylene (CH2) group. The singlet order of parahydrogen is substantially retained over the geminal hydrogenation reaction, giving rise to a singlet-hyperpolarized CH2 group. Although the T1 relaxation times of the methylene protons are often short, the singlet order has a long lifetime, provided that singlet–triplet mixing is suppressed, either by chemical equivalence of the protons or by applying a resonant radiofrequency field. The long lifetime of the singlet order enables the accumulation of hyperpolarization during the slow hydrogenation reaction. We introduce a kinetic model for the behaviour of the observed hyperpolarized signals, including both the chemical kinetics and the spin dynamics of the reacting molecules. Our work demonstrates the feasibility of producing singlet-hyperpolarized methylene moieties by parahydrogen-induced polarization. This potentially extends the range of molecular agents which may be generated in a hyperpolarized state by chemical reactions of parahydrogen.

<i>Geminal</i> Parahydrogen-Induced Polarization: Accumulating Long-Lived Singlet Order on Methylene Proton Pairs

In the majority of hydrogenative PHIP (Parahydrogen Induced Polarization) experiments, the hydrogen molecule undergoes pairwise cis-addition to an unsaturated precursor to occupy vicinal positions on the product molecule. However, some ruthenium-based hydrogenation catalysts induce geminal hydrogenation, leading to a reaction product in which the twohydrogen atoms are transferred to the same carbon center, forming a methylene (CH2) group. The singlet order of parahydrogen is substantially retained over the geminal hydrogenation reaction, giving rise to a singlet-hyperpolarized CH2 group. Although the T1 relaxation times of the methylene protons are often short, the singlet order has a long lifetime, providing that singlet-triplet mixing is suppressed, either by chemical equivalence of the protons or by applying a resonant radiofrequency field. The long lifetime of the singlet order enables the accumulation of hyperpolarization during the slow hydrogenation reaction. We introduce a kinetic model for the behaviour of the observed hyperpolarized signals, including both the chemical kinetics and the spin dynamics of the reacting molecules. Our work demonstrates the feasibility of producing singlet-hyperpolarized methylene moieties by parahydrogen-induced polarization. This potentially extends the range of molecular agents which maybe generated in a hyperpolarized state by chemical reactions of parahydrogen.

Anhydrous Aluminum Chloride Catalyzed Methylene Group Inclusion: Mechanistic, Spectral and Single Crystal X-Ray Structural Study on Methanediyl Bis(Cyclohexylmethylcarbamodithioate)

In this study anhydrous AlCl3is used as a catalyst for the inclusion of a methylene group in to cyclohexylmethyldithiocarbamic acid to form methanediyl bis(cyclohexylmethylcarbamodithioate). Dichloromethane is used as a methylene group bearer in the reaction. A suitable mechanistic pathway involving+CH2Cl is discussed. FTIR, NMR and Mass spectral techniques have been used in the analysis. Single crystal X-ray structure of the compound was determined. FTIR spectrum of the compound showed υc-sband at 1073 cm-1and υC-Hvibrations appeared at 2853 and 2928 cm-1. Thioureide stretching band was observed at 1473 cm-1. The molecular ion peak in the Mass spectroscopy confirmed the proposed formula. H1NMR spectrum of the compound showed a signal at 4.33(s) ppm for α-CH of the cyclohexyl ring and -CH3protonsattached to nitrogen appeared at 3.40 ppm. Methylene proton (S-CH2-S) signal appeared at 3.16 ppm which is largely deshielded by the presence of two electronegative sulphur atoms on either side. The characteristic methylene carbon (S-CH2-S) signal appeared at 45.46 ppm in the13C NMR spectrum. Single crystal X-ray structural analysis of the compound showed it to be monomeric. Methylene carbon in S-CH2-S, C(9) is tetrahedrally bonded to two hydrogen atoms and two sulphur atoms S(2), S(3). The molecule stacks its cyclohexyl rings along ‘c’ axis of the unit cell. Short contacts in the form of supramolecular interactions such as C---S and S---S exist in the solid state at 3.49 and 3.50 Å respectively.

Structural Characterization of Natural Rubber Recent Research Advancements

The micro-structure of the surface of Hevea brasiliensis latex particles has been found by the means of atomic force microscopy (AFM), confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cryogenic transmission electron microscopy (cryo-TEM), and electrokinetics over a broad range of KNO3electrolyte concentrations (4-300 mM) and pH values (1-8). Based on the atomic force microscopy analysis of the fresh natural rubber latex, it could be estimated that the protein-lipid layer is covered with the rubber particles. The molecules in the particle were labeled with fluorescent Rhodamine (RB), and were monitored by CLSM. SEM and TEM were used to observe the surface of fresh natural rubber particles and were dyed by osmium tetroxide. Fourier Transform Infrared Spectroscopy (FTIR) has been used to characterize the nitrogenous groups in natural rubber and deproteinized natural rubber (DPNR). The FTIR and1H-NMR analysis of phosphatase-treated DPNR confirmed that the presence of mono- and diphosphate terminations without phospholipids was also unlikely owing to the presence of a methylene proton signal of an isoprene unit linked to mono- and diphosphate groups. The , [η] and Higgins’ k’ of DPNR decreased after being treated with lipase.

Combination of Nanogel Polyethylene Glycol-Polyethylenimine and 6(hydroxymethyl)-1,4-anthracenedione as an Anticancer Nanomedicine

Polyethylene glycol-polyethylenimine (PEG-PEI) nanogels have been used to deliver nucleic acids and oligonucleotides into cells. First, we synthesized PEG-PEI nanogels with methylene proton ratios (CH2O:CH2N) in PEG-PEI ranging from ∼6.8:1 to 4:1 and less, as shown by 1H NMR spectra. We first synthesized various nanogels with varying ratios of CH2O:CH2N (methylene proton) in PEG-PEI as shown by 1H NMR spectra and tested their cytotoxicity using a rodent pancreatic adenocarcinoma cell line (Pan 02). We showed that the nanogel PEG-PEI with methylene proton ratio of 4:1 was strongly cytotoxic to Pan 02 cells in vitro, while the nanogel with the methylene proton ratio of 6.8:1 was not toxic. We incorporated a novel anti-cancer drug, 6-(hydroxymethyl)-1,4-anthracenedione (AQ) analogue (AQ10) into nontoxic nanogel PEG-PEI and tested the effect of AQ10 loaded nanogel PEG-PEI (AQ10-nanogel PEG-PEI) and AQ10 dissolved in DMSO on Pan 02 cell growth. The size of this AQ10-nanogel PEG-PEI was characterized using atomic force microscopy (AFM). Our studies showed that the AQ10-nanogel PEG-PEI is readily taken up by Pan 02 cells. Growth attenuation of Pan 02 cells treated with AQ10-nanogel PEG-PEI was three to four times that of cells treated with AQ10 dissolved in DMSO. These results suggest that PEG-PEI, usually used to deliver nucleic acids into cells, can also be used to deliver an insoluble small molecule anticancer drug, AQ10.

Measurement of intracellular triglyceride stores by H spectroscopy: validation in vivo

We validate the use of 1H magnetic resonance spectroscopy (MRS) to quantitatively differentiate between adipocyte and intracellular triglyceride (TG) stores by monitoring the TG methylene proton signals at 1.6 and 1.4 ppm, respectively. In two animal models of intracellular TG accumulation, intrahepatic and intramyocellular TG accumulation was confirmed histologically. Consistent with the histological changes, the methylene signal intensity at 1.4 ppm increased in both liver and muscle, whereas the signal at 1.6 ppm was unchanged. In response to induced fat accumulation, the TG concentration in liver derived from 1H MRS increased from 0 to 44.9 ± 13.2 μmol/g, and this was matched by increases measured biochemically (2.1 ± 1.1 to 46.1 ± 10.9 μmol/g). Supportive evidence that the methylene signal at 1.6 ppm in muscle is derived from investing interfascial adipose tissue was the finding that, in four subjects with generalized lipodystrophy, a disease characterized by absence of interfacial fat, no signal was detected at 1.6 ppm; however, a strong signal was seen at 1.4 ppm. An identical methylene chemical shift at 1.4 ppm was obtained in human subjects with fatty liver where the fat is located exclusively within hepatocytes. In experimental animals, there was a close correlation between hepatic TG content measured in vivo by 1H MRS and chemically by liver biopsy [ R = 0.934; P < .0001; slope 0.98, confidence interval (CI) 0.70–1.17; y-intercept 0.26, CI −0.28 to 0.70]. When applied to human calf muscle, the coefficient of variation of the technique in measuring intramyocellular TG content was 11.8% in nonobese subjects and 7.9% in obese subjects and of extramyocellular (adipocyte) fat was 22.6 and 52.5%, respectively. This study demonstrates for the first time that noninvasive in vivo 1H MRS measurement of intracellular TG, including that within myocytes, is feasible at 1.5-T field strengths and is comparable in accuracy to biochemical measurement. In addition, in mixed tissue such as muscle, the method is clearly advantageous in differentiating between TG from contaminating adipose tissue compared with intramyocellular lipids.