Synergetic impact of MgO on PMMA-ZrO2 hybrid composites: Evaluation of structural, morphological and improved mechanical behavior for dental applications.

This work aims to demonstrate the effect of ZrO2 and MgO inclusion into the Poly(methyl methacrylate) (PMMA). To fabricate novel hybrid composites via heat cure method, various composites (PZM2, PZM4 and PZM6) were synthesized in the system [(95-x) PMMA + 5 ZrO2 + x MgO] (x = 2, 4, and 6) respectively. Density of the prepared composites were determined and varying between 1.035-1.152 g/cm3. X-ray Diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) followed by EDAX and mechanical testing were performed to evaluate the fabricated composite properties. Moreover, to explore the structure of the fabricated composites the 13 C CP-MAS SSNMR and 1 H-13 C Phase-Modulated Lee Goldberg (PMLG) HETCOR Spectrum were recorded which clarify chemical shifting and motional dynamics of the composites. Mechanical tests were performed by UTM and the obtained parameters such as compressive strength, Young's modulus, fracture toughness, brittleness coefficient, flexural strength and flexural modulus are found to be in the range of 91-100 MPa, 0.48-0.51 GPa, 9.122-9.705 MPa.m1/2, 0.66-0.815, 51.03-42.78 MPa and 499-663 MPa respectively. Some more mechanical parameters such as proportional limit, elastic limit, failure strength, modulus of resilience and modulus of toughness were also calculated. Furthermore, tribological properties were also determined and the coefficient of friction (COF) was decreased by 17.4 % and 38 % for composite PZM6 at 20 N and 40 N as compared to the composite PZM2 and the lowest wear volume of 1.55 mm3 was observed for PZM2, whereas the maximum volume loss of 5.64 mm3 is observed for composite PZM6. To check out the biocompatibility, cytotoxicity and genotoxicity of the fabricated composites the Trypan-blue assay was also performed for PZM2 and PZM6 composites. Dissection on the gut of larvae was also performed on the both composites followed by DAPI and DCFH-DA staining. Therefore, these synthesized samples can be used for the fabrication of denture materials.

Analyzing atomic scale structural details and nuclear spin dynamics of four macrolide antibiotics: erythromycin, clarithromycin, azithromycin, and roxithromycin.

The current investigation centers on elucidating the intricate molecular architecture and dynamic behavior of four macrolide antibiotics, specifically erythromycin, clarithromycin, azithromycin, and roxithromycin, through the application of sophisticated solid-state nuclear magnetic resonance (SSNMR) methodologies. We have measured the principal components of chemical shift anisotropy (CSA) parameters, and the site-specific spin-lattice relaxation time at carbon nuclei sites. To extract the principal components of CSA parameters, we have employed 13C 2DPASS CP-MAS SSNMR experiments at two different values of magic angle spinning (MAS) frequencies, namely 2 kHz and 600 Hz. Additionally, the spatial correlation between 13C and 1H nuclei has been investigated using 1H-13C frequency switched Lee-Goldburg heteronuclear correlation (FSLGHETCOR) experiment at a MAS frequency of 24 kHz. Our findings demonstrate that the incorporation of diverse functional groups, such as the ketone group and oxime group with the lactone ring, exerts notable influences on the structure and dynamics of the macrolide antibiotic. In particular, we have observed a significant decrease in the spin-lattice relaxation time of carbon nuclei residing on the lactone ring, desosamine, and cladinose in roxithromycin, compared to erythromycin. Overall, our findings provide detailed insight into the relationship between the structure and dynamics of macrolide antibiotics, which is eventually correlated with their biological activity. This knowledge can be utilized to develop new and more effective drugs by providing a rational basis for drug discovery and design.

Functionality Modulation Toward Thianthrene-based Metal-Free Electrocatalysts for Water Splitting.

The development of metal-free bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) is significant but rarely demonstrated. Porous organic polymers (POPs) with well-defined electroactive functionalities show superior performance in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Precise control of the active sites' local environment requires careful modulation of linkers through the judicious selection of building units. Here, a systematic strategy is introduced for modulating functionality to design and synthesize a series of thianthrene-based bifunctional sp2 C═C bonded POPs with hollow spherical morphologies exhibiting superior electrocatalytic activity. This precise structural tuning allowed to gain insight into the effects of heteroatom incorporation, hydrophilicity, and variations in linker length on electrocatalytic activity. The most efficient bifunctional electrocatalyst THT-PyDAN achieves a current density of 10 mA cm─2 at an overpotential (η10) of ≈65 mV (in 0.5 m H2SO4) and ≈283 mV (in 1 m KOH) for HER and OER, respectively. THT-PyDAN exhibits superior activity to all previously reported metal-free bifunctional electrocatalysts in the literature. Furthermore, these investigations demonstrate that THT-PyDAN maintains its performance even after 36 h of chronoamperometry and 1000 CV cycling. Post-catalytic characterization using FT-IR, XPS, and microscopic imaging techniques underscores the long-term durability of THT-PyDAN.

Atomic-Scale Resolution Insights into Structural and Dynamic Differences between Ofloxacin and Levofloxacin.

This study employs advanced solid-state NMR techniques to investigate the atomic-level structure and dynamics of two enantiomers: ofloxacin and levofloxacin. The investigation focuses on critical attributes, such as the principal components of the chemical shift anisotropy (CSA) tensor, the spatial proximity of 1H and 13C nuclei, and site-specific 13C spin-lattice relaxation time, to reveal the local electronic environment surrounding specific nuclei. Levofloxacin, the levo-isomer of ofloxacin, exhibits higher antibiotic efficacy than its counterpart, and the dissimilarities in the CSA parameters indicate significant differences in the local electronic configuration and nuclear spin dynamics between the two enantiomers. Additionally, the study employs the 1H-13C frequency-switched Lee-Goldburg heteronuclear correlation (FSLGHETCOR) experiment to identify the presence of heteronuclear correlations between specific nuclei (C15 and H7 nuclei and C13 and H12 nuclei) in ofloxacin but not in levofloxacin. These observations offer insights into the link between bioavailability and nuclear spin dynamics, underscoring the significance of NMR crystallography approaches in advanced drug design.

Investigation of the Influence of Various Functional Groups on the Dynamics of Glucocorticoids.

The basic configuration of glucocorticoid consists of four-fused rings associated with one cyclohexadienone ring, two cyclohexane rings, and one cyclopentane ring. The ways the structure and dynamics of five glucocorticoids (prednisone, prednisolone, prednisolone acetate, methylprednisolone, and methylprednisolone acetate) are altered because of the substitution of various functional groups with these four-fused rings are studied thoroughly by applying sophisticated solid-state nuclear magnetic resonance (NMR) methodologies. The biological activities of these glucocorticoids are also changed because of the attachment of various functional groups with these four-fused rings. The substitution of the hydroxyl group (with the C11 atom of the cyclohexane ring) in place of the keto group enhances the potential of the glucocorticoid to cross the cellular membrane. As a result, the bioavailability of prednisolone (the hydroxyl group is attached with the C11 atom of the cyclohexane ring) is increased compared to prednisone (the keto group is attached with the C11 atom of cyclohexane rings). Another notable point is that the spin-lattice relaxation rate at crystallographically distinct carbon nuclei sites of prednisolone is increased compared to that of the prednisone, which implies that the motional degrees of freedom of glucocorticoid is increased because of the substitution of the hydroxyl group in place of the keto group of the cyclohexane ring. The attachment of the methyl group with the C6 atom of cyclohexane rings further reduces the spin-lattice relaxation time at crystallographically distinct carbon nuclei sites of glucocorticoid and its bioactivity is also increased. By comparing the spin-lattice relaxation time and the local correlation time at crystallographically different carbon nuclei sites of three steroids prednisone, prednisolone, and methylprednisolone, it is observed that both the spin-lattice relaxation time and the local correlation time gradually decrease at each crystallographically distinct carbon nuclei sites when we move from prednisone to prednisolone to methyl-prednisolone. On the other hand, if we compare the same for prednisolone, prednisolone acetate, and methylprednisolone acetate, then we also observe that both the spin-lattice relaxation time and the local-correlation time gradually decrease from prednisolone to prednisolone acetate to methylprednisolone acetate for all chemically different carbon nuclei. It is also noticeable that both the spin-lattice relaxation time and the local-correlation time gradually decrease from prednisone to prednisolone to prednisolone acetate to methylprednisolone to methylprednisolone acetate for most of the carbon nuclei sites. From in silico analysis, it is also revealed that the bioavailability and efficacy of the glucocorticoid increase from prednisone to prednisolone to prednisolone acetate to methylprednisolone to methylprednisolone acetate. Hence, it can be concluded that the biological activity and the motional degrees of freedom of the glucocorticoids are highly correlated. These types of studies provide a clear picture of the structure-activity relationship of the drug molecules, which will enlighten the path of developing highly potent glucocorticoids with minimum side effects. Another important aspect of these types of studies is to provide information about the electronics configuration and nuclear spin dynamics at crystallographically different carbon nuclei sites of five glucocorticoids, which will enrich the field of "NMR crystallography".

Study of the Variation of the Electronic Distribution and Motional Dynamics of Two Independent Molecules of an Asymmetric Unit of Atorvastatin Calcium by Solid-State NMR Measurements.

Significant changes in the spin-lattice time and chemical shift anisotropy (CSA) parameters are observed in two independent molecules of an asymmetric unit of atorvastatin calcium (ATC-I) (which is referred to as "a"- and "b"-type molecules by following Wang et al.). The longitudinal magnetization decay curve is fitted by two exponentials-one with longer relaxation time and another with shorter relaxation time for most of the carbon nuclei sites. The local correlation time also varies significantly. This is the experimental evidence of the coexistence of two different kinds of motional degrees of freedom within ATC-I molecule. The solubility and bioavailability of the drug molecule are enhanced due to the existence of two different kinds of dynamics. Hence, the macroscopic properties like solubility and bioavailability of a drug molecule are highly correlated with its microscopic properties. The motional degrees of freedom of "a"- and "b"-type molecules are also varied remarkably at certain carbon nuclei sites. This is the first time the change in the molecular dynamics of two independent molecules of an asymmetric unit of atorvastatin calcium is quantified using solid-state NMR methodology. These types of studies, in which the chemical shift anisotropy (CSA) parameters and spin-lattice relaxation time provide information about the change in electronic distribution and the spin dynamics at the various crystallographic location of the drug molecule, will enrich the field "NMR crystallography". It will also help us to understand the electronic distribution around a nucleus and the nuclear spin dynamics at various parts of the molecule, which is essential to develop the strategies for the administration of the drug.

Study of the structure and dynamics at various parts of the antibacterial drug molecule cefpodoxime proxetil.

The structure and dynamics of cefpodoxime proxetil are elucidated by measuring chemical shift anisotropy (CSA) tensor, spin-lattice relaxation time, and local correlation time at twenty-one crystallographically different 13C nuclei sites. The principal components of CSA tensor of cefpodoxime proxetil are extracted by the two-dimensional phase adjusted sinning sideband (2DPASS) cross-polarization magic angle spinning (CP-MAS) solid-state NMR experiment, and the spin-lattice relaxation time is measured by the method outlined by Torchia(T1CP). The local correlation time is calculated by bearing in mind that the spin-lattice relaxation mechanism of 13C nuclei is mainly governed by the CSA interaction and the heteronuclear dipole-dipole interaction. The aminothiazole ring, ß-lactam ring, and dihydrothiazine ring provide stability to the drug molecule and increase the affinity of the drug to penicillin-binding proteins (PBPs) receptors. The principal components of CSA parameters, spin-lattice relaxation time, and local correlation time vary substantially for carbon nuclei residing on these three rings. These signify that not only the electronic environment, but the molecular conformation, and the local dynamics are also altered within the ring. The substitution of the acyl side chain, oxime group, and the aminothiazole ring at the C7 position of the ß-lactam ring enhances the antibacterial activity and the binding affinity of the drug. A huge variation of the spin-lattice relaxation time and local correlation time is observed in those regions. The change in the electron charge distribution and nuclear spin dynamics at different parts of the drug molecule is clear by CSA and spin-lattice relaxation measurements, which will enrich the field "NMR crystallography".

Structure and dynamics of sodium alginate as elucidated by chemical shift anisotropy and site-specific spin-lattice relaxation time measurements.

The biocompatible, biodegradable, linear copolymer sodium alginate is fabricated from [Formula: see text] linked [Formula: see text]-D-mannuronic acid (M block) and [Formula: see text]-L-guluronic acid (G-block). It has wide applications in drug delivery, cell encapsulation, and commercial application in the textile, cosmetics, paper, food, biomedical, and pharmaceutical industries. The structure and dynamics of sodium alginate were here investigated by measuring chemical shift anisotropy (CSA) parameters, spin-lattice relaxation time, and molecular correlation time. The principal components of the CSA tensor were determined by two-dimensional phase-adjusted spinning sideband (2DPASS) cross-polarization magic angle spinning (CP-MAS) SSNMR. The alternating M and G blocks of both equatorial and axial links are associated with greater overall flexibility. The molecular correlation time of the carboxyl carbon of both G and M blocks is faster than for the anomeric carbon and pyranose carbon. This is further experimental evidence of the coexistence of two different dynamics within the polysaccharide chains of sodium alginate, which was previously established by 1H-13C dipolar profile analysis. The relaxation time of the para-crystalline region of sodium alginate is comparable with that of chitosan, but it is much shorter than that of cellulose and chitin. The order of the molecular correlation time of sodium alginate and chitosan is also the same. Hence, it can be concluded that sodium alginate exhibits greater flexibility than cellulose and chitin. These types of investigation into the local electronic configuration and nuclear spin dynamics at various carbon nuclei sites of the biopolymer at atomic-scale resolution will help in the design of biomimetic materials.

Probing Atomistic Behavior To Unravel Dielectric Phenomena in Charge Transfer Cocrystals.

Six new binary charge-transfer (CT) cocrystals have been synthesized by solvent drop-assisted mechanochemical grinding method, and all of them exhibited remarkable color changes during the grinding process. Crystal structure analysis reveals the donor (D) and acceptor (A) molecules have assembled primarily via cofacial π···π stacking interactions displaying mixed D-A-D-A stacked columns. Interestingly these cocrystals exhibited very diverse dielectric response in the presence of an alternating current (ac) external electric field, and their dielectric behavior can be explained from the nature and strength of CT interactions in the cocrystal assembly. Strong CT cocrystals were found to display a rigid supramolecular framework while weakly bound CT complexes allowed its constituent polar molecules to relax and hence the observed rotational dynamics contributed to their dielectric properties. Chemical shift anisotropy parameters, spin-lattice relaxation, and molecular correlation times obtained from 13C solid-state NMR spectroscopy measurements establish the occurrence of molecular dynamics at the atomistic scale in cocrystals, thereby displaying high permittivity. Furthermore, we also propose a strategy directed toward the design of CT cocrystals that allows us to introduce rotational dynamics in noncentrosymmetric molecules, which significantly enhances their dielectric properties due to orientation polarization. The results indicate that D-A-based organic CT systems, particularly with a mixed stack, have a wide range of potential applications in materials science.

Investigation of the Structure and Dynamics of Antiviral Drug Adefovir Dipivoxil by Site-Specific Spin-Lattice Relaxation Time Measurements and Chemical Shift Anisotropy Tensor Measurements.

Adefovir is regarded as a potential antiviral agent. However, it cannot be considered as a valuable drug candidate due to its high polarity that limits its permeability across the human intestinal mucosa. When the ribose phosphate group of adefovir is replaced by the isopolar phosphonomethyl ether functionality, it neutralizes the negative charge of the drug. This makes the drug lipid-soluble and potent to diffuse across the cell membrane. The prodrug adefovir dipivoxil is regarded as a potent antiviral drug against hepatitis B virus (HBV), human immunodeficiency virus (HIV), Rauscher murine leukemia virus (R-MuLV), murine cytomegalovirus (MCMV), herpes simplex virus (HSV), simian immunodeficiency virus (SIV), and feline immunodeficiency virus (FIV). The correlation between the structure and the dynamics of adefovir dipivoxil is determined by measuring the principal components of chemical shift anisotropy (CSA) tensor, site-specific spin-lattice relaxation time, and molecular correlation time at crystallographically different carbon nuclei sites. The CSA parameters, spin-lattice relaxation time, and molecular correlation time of phosphorous nucleus of the organophosphate group of adefovir dipivoxil molecule are also determined. The spin-lattice relaxation time of carbon nuclei varies from 1 to 107 s. The range of molecular correlation time also varies from 10-4 to 10-8 s. These remarkable diversities of motional dynamics of the molecules imply that there exist various motional degrees of freedom within this valuable drug and these motional degrees of freedom are independent of each other, which may be the reason for the biological activities exhibited by the drug. The correlation between structure and dynamics of such an important antiviral drug adefovir dipivoxil can be visualized by these types of extensive spectroscopic measurements, which will enlighten the path of inventing advanced medicine in the pharmaceutical industry, and it will also illuminate the understanding of the structure-activity relationships of antiviral drug.

Understanding the correlation between structure and dynamics of clocortolone pivalate by solid state NMR measurement.

Structural characteristics of clocortolone pivalate are unique in the topical corticosteroid field having high penetration power through the stratum corneum of skin as well as low corticosteroid-related adverse effects. The molecule was thoroughly studied by 13C 2DPASS CP MAS NMR and spin-lattice relaxation time measurements. Molecular correlation time at different carbon nuclei positions was calculated by assuming that the chemical shift anisotropy interaction and heteronuclear dipole-dipole interaction play vital roles in the 13C spin-lattice relaxation mechanism. The CSA parameters are substantially varied at different carbon nuclei sites. This suggests that the electronic distribution surrounding the carbon nuclei varies widely when the same carbon atom is placed in different chemical surroundings of the molecule. The spinning CSA sideband pattern for C11, C17, C26 nuclei is axially symmetric. The asymmetry parameter is very small (≤0.3) for C2, C5, C10, C22, C23, C24 nuclei, and it is reasonably high (≥0.9) for C3, C4, C6, C18, C19, C21 nuclei. The anisotropy parameter is very high for double bonded C14, C15, C18, C19, C21, C22, and C23 nuclei. Spin-lattice relaxation time and molecular correlation time are also varied substantially for carbon nuclei situated at various positions of the molecule. The spin-lattice relaxation time is slow for carbon nuclei residing at the carbon ring, and it is very fast for C12, C17, C16, C26 carbon nuclei situated at the side portion of the molecule. Molecular correlation time is of the order of 10-4 s for those carbon nuclei attached with neighbouring carbon or oxygen atoms by double bonds like C14, C15, C18, C19, C21, C22, and C23. It implies that the molecular correlation time is very high for those carbon nuclei associated with high values of the chemical shift anisotropy parameter. In contrast, the molecular correlation time is of the order of 10-8 s for C12, C16, and C17 carbon nuclei. From these studies, it is clear that the various portions of the molecule exhibit different degrees of motion and the dynamics is related with the structural characteristics of the molecule. These investigations on important drug clocortolone pivalate by solid state NMR will help researchers to understand the structure and dynamics of the molecule, which will give a direction to develop advance corticosteroids.

An atomic resolution description of folic acid using solid state NMR measurements.

The chemical shift anisotropy tensor and site-specific spin-lattice relaxation time of folic acid were determined by a 13C 2DPASS CP-MAS NMR experiment and Torchia CP experiment respectively. The molecular correlation time at various carbon nuclei sites of folic acid was evaluated by assuming that the 13C spin-lattice relaxation mechanism is mainly governed by chemical shift anisotropy interaction and hetero-nuclear dipole-dipole coupling. CSA parameters are larger for the carbon nuclei residing at the heteroaromatic ring and aromatic ring, and those attached to double-bonded electronegative oxygen atoms. It is comparatively low for C9, C19, C21, and C22. The molecular correlation time is of the order of 10-4/10-5 s for C9, C19, C21 and C22 carbon nuclei, whereas it is of the order of 10-3 s for the rest of the carbon nuclei sites. Spin lattice relaxation time varies from 416 s to 816 s. For C23 and C14, the value is 816 s, and it is 416 s for C7 nuclei. The correlation between structure and dynamics on an atomic scale of such an important drug as folic acid can be visualized by these types of extensive spectroscopic measurements, which will help to develop an advanced drug for DNA replication.

Understanding the structure and dynamics of anti-inflammatory corticosteroid dexamethasone by solid state NMR spectroscopy.

For decades corticosteroid dexamethasone has been applied as an anti-inflammatory, immunosuppressant, and decongestant, in the prevention of postoperative nausea and vomiting (PONV), and for auto-immune diseases, allergic reactions, total hip arthroplasty (THA), and cancer. Recently in vitro studies suggested that it may be beneficial to deal with the COVID-19 pandemic. This important drug molecule was investigated by solid state NMR measurements to provide more complete features of its structure and dynamics at atomic scale resolution. The spin-lattice relaxation time at twenty-two different carbon sites of dexamethasone was determined by the Torchia CP method. The principle components of the chemical shift anisotropy tensor were determined by 13C two-dimensional phase adjusted spinning sideband (2DPASS) cross-polarization magic angle spinning (CP-MAS) solid state NMR experiments. The molecular correlation time at twenty-two crystallographically different carbon sites of dexamethasone was calculated by considering that the spin-lattice relaxation mechanism of the 13C nucleus is mainly governed by the chemical shift anisotropy interaction and the heteronuclear dipole-dipole coupling. The spin-lattice relaxation time of carbon nuclei resides on 'A', 'B', 'C', and 'D' rings and the side-chain of dexamethasone is quite large, which implies the close-packed arrangement of the molecule. The difference in molecular correlation time at various regions of the molecule demonstrates the existence of different degrees of freedom within the molecule. This may be the reason for the various biological activities exhibited by the molecule. These types of detailed features of the structure and dynamics of such an important drug with multiple biological activities are necessary to develop the advanced medicine and it will also help to understand the structure-activity relationships of corticosteroid.

Investigation of the Detailed Internal Structure and Dynamics of Itraconazole by Solid-State NMR Measurements.

The structure and dynamics of itraconazole were investigated by 13C 2DPASS MAS SSNMR and spin-lattice relaxation time measurement to get an insight into its multiple biological activities, e.g., antifungal, antiviral, anticancer activities, etc. The molecular correlation time at chemically different sites of carbon nuclei was calculated by considering that the spin-lattice relaxation mechanism is mainly dominated by chemical shift anisotropy interaction and heteronuclear dipole-dipole interaction. The spin-lattice relaxation time is long for C35, C6, C5, and C34 carbon nuclei that participated in the 1, 2, 4-triazole ring. On the contrary, it is comparatively shorter for C1, C2, C3, and C4 carbon nuclei associated with the sec-butyl group in the triazolane side-chain region. Chemical shift anisotropy (CSA) parameters of C5, C6, C34, and C35 nuclei are much higher than those of C1, C2, C3, C4 nuclei, indicating that the relaxation mechanism at a high value of magnetic field is predominated by chemical shift anisotropy interaction. The molecular correlation time of carbon nuclei residing at the side-chain region is 2-3 orders of magnitude lesser than that of those participated in the 1,2,4-triazole ring. The spin-lattice relaxation time is very long for carbon nuclei C28 and C30 bonded with chlorine. Asymmetry and anisotropy parameters are also very high for the spinning CSA sideband pattern corresponding to the C28 and C30 nuclei. The molecular correlation time is on the order of 10-3 s for C28 and 10-4 s for C30, whereas for side-chain carbon nuclei, it is on the order of 10-6 s. This suggests that the effective magnetic field experienced by C28 and C30 nuclei is affected by the polarization of the chemical bond. A huge variation in molecular correlation time is observed for chemically different sites of carbon nuclei of the itraconazole molecule. These investigations vividly portrayed how the structure is correlated with the dynamics of a valuable drug, itraconazole, with multiple biological activities. This study will enlighten the way of inventing advance medicine for multiple biological activities in the pharmaceutical industry.

Investigation of the internal structure and dynamics of cellulose by 13C-NMR relaxometry and 2DPASS-MAS-NMR measurements.

Internal structure and dynamics of commercial and natural cellulose were studied by measuring chemical shift anisotropy (CSA) parameters, and spin-lattice relaxation rate (1/T1) at each and every chemically different carbon nuclear site. CSA parameters were measured by 13C two-dimensional phase adjusted spinning sideband (2DPASS) cross-polarization magic angle spinning (CP-MAS) NMR experiment. Site specific spin-lattice relaxation time was measured by Torchia-CP method. Anisotropy parameters of C4 and C6 regions are higher than C1 and C235 regions and asymmetry of C4 line is lower than any other carbon site. The higher values of CSA parameters of C4 and C6 nuclei arise due to the rotation of O4-C4, C1-O4, O5-C5-C6-O6 and C4-C5-C6-O6 bonds at torsion angles ψ, Φ, χ and χ' respectively and the influence of interchain and intrachain hydrogen bondings. Two distinct peaks are also observed for C4 and C6 resonance line position-one peak arises primarily due to the nuclei in amorphous region and another one arises due to the same nuclei resides in paracrystalline region. The spin-lattice relaxation time and the CSA parameters are different at these two distinct peak positions of C4 and C6 line. Molecular correlation time of each and every chemically different carbon site was calculated with the help of CSA parameters and spin-lattice relaxation time. The molecular correlation time of the amorphous region is one order of magnitude less than the crystalline region. The distinction between amorphous and paracrystalline regions of cellulose is more vividly portrayed by determining spin-lattice relaxation time, CSA parameters, and molecular correlation time at each and every chemically different carbon site. This type of study correlating the structure and dynamics of cellulose will illuminate the path of inventing biomimetic materials.

A comprehensive and comparative study of the internal structure and dynamics of natural ß-keratin and regeneratedß-keratin by solid state NMR spectroscopy.

Structure and dynamics of natural and regenerated chicken feather ß-keratin were investigated by 13C cross-polarization (CP) magic angle spinning (MAS) solid state nuclear magnetic resonance (SSNMR) spectral analysis, 13C and 1H spin-lattice relaxation time measurements, and 13C two dimensional phase adjusted spinning sidebands (2DPASS) MAS SSNMR measurements. Chemical shift anisotropy (CSA) parameters of both natural and regenerated chicken feather ß-keratin were extracted by using 2DPASS MAS SSNMR experiment. The beauty of 2DPASS MAS SSNMR experiment is it can correlate the isotropic and anisotropic dimension with the help of shearing transformation and two dimensional Fourier Transformation. Molecular correlation time at each and every magnetically inequivalent carbon site of both natural and regenerated chicken feather ß-keratin were also determined. The change in molecular dynamics of structural protein after pretreatment was monitored by 2DPASS MAS SSNMR and 13C relaxation measurement. This type of comprehensive study will provide the information about the interrelation between the structure and dynamics of structural protein and will also shed light in the way of developing methods for conversion of animal by-products to novel product.

Elucidating the internal structure and dynamics of α-chitin by 2DPASS-MAS-NMR and spin-lattice relaxation measurements.

The structure and dynamics of the second most abundant biopolymer α-chitin were studied by high resolution solid state 13C cross-polarization magic angle spinning nuclear magnetic resonance (CP-MAS-NMR) spectral analysis, 13C relaxation measurements at eight chemically different carbon sites and chemical shift anisotropy measurement by two-dimensional phase-adjusted spinning sidebands (2DPASS) magic angle spinning (MAS) solid state NMR method.13C spin-lattice relaxation time was measured by high resolution Torchia CP method. Spin-lattice relaxation rate (1/T1) of side chain carbon nuclei were remarkably high, because those nuclei possess higher degree of motional freedom. Chemical shift anisotropy parameters of eight chemically different carbon nuclei were determined by 2DPASS-MAS-NMR experiment. Large value of chemical shift anisotropy was observed for carbonyl group carbon (C7) nuclei, because of electrostatic effect, hydrogen bonding and molecular magnetic susceptibility. 13C relaxation mechanism is mainly governed by chemical shift anisotropy interaction, especially at high value of external magnetic field (11.74 T). Thus, the correlation time at different carbon sites were also calculated by using the spin-lattice relaxation times and chemical shift anisotropy values. The correlation time of side chain carbon (C8) was two orders of magnitude less than the carbonyl group carbon. These types of investigations would enlighten the correlation between the structure and dynamics of long polysaccharide chain compound.

"Perfect echo" HMQC: sensitivity and resolution enhancement by broadband homonuclear decoupling.

Homonuclear (1)H-(1)H J-modulation leads to J-multiplets in F1 dimension of 2D (1)H-(13)C HMQC spectra. This hampers unambiguous signal assignment for overcrowded (13)C spectra. Broadband homonuclear decoupling has been achieved in the indirect t1 evolution period by incorporating blocks of perfect echo. This method of perfect echo HMQC demonstrates better resolution and sensitivity than conventional HMQC spectra. The results on Cyclosporine demonstrate that the method is very efficient for refocusing geminal couplings in weakly coupled -(13)CH2 groups. Partial refocusing of vicinal couplings is also observed for -(13)CH and -(13)CH3 groups. Interpretation of the result based on product operator formalism is also given. Comparison of pe-HMQC, HMQC and HSQC reveals that the F1 linewidth of pe-HMQC is much narrower than HMQC and very close to that of HSQC for CH2 groups.

Use of spatial encoding in NMR photography.

NMR photography has gained significant attention as a method of storing and retrieving information using NMR spectroscopy. Among the commonly practiced methods the most important is the frequency encoding by use of a multi-frequency pulse on a liquid crystal molecule. We propose and demonstrate another robust method which relies on spatial encoding. Spatial information is mapped onto the spectrum, if excited and recorded in the presence of a gradient. The encoding is performed by applying a multi-frequency pulse in the presence of a gradient. The subsequent acquisition, under a gradient, helps storing this spatial information on a one-dimensional spectrum. Series of such spectra can also store two-dimensional patterns. This procedure is described and exemplified in this paper.