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Chemical bonding in Period 2 homonuclear diatomic molecules: a comprehensive relook
No full textTheoretical and experimental studies of bonding in the main group homonuclear diatomic molecules have been pursued for many years, and they possess serious challenges for scientists. Most of the early experimental work have been carried out by Herzberg.1,2 We take a relook at the bonding motifs of Period 2 homonuclear diatomic molecules (from Li-2 to Ne-2) using varieties of quantum chemical tools, commonly used for intermolecular bonding/interactions now. The methods employed include Atoms in Molecules (AIM), Non-covalent Index plot (NCI), Electrostatic potential (ESP), and Potential Acting on one Electron in a Molecule (PAEM). The spectroscopic constants i.e., equilibrium bond distances (r(e)), harmonic frequencies (omega), bond dissociation energies (D-e) have all been evaluated using high-level ab initio methods and critically compared with the experimental results. Multi-reference calculations (CASSCF) on B-2 and C-2 have been carried out as they have a large number of low lying electronic states. Bonding within these homonuclear diatomic molecules show all the diversities that are encountered in inter/intra-molecular bonding in chemistry. Based on the AIM analysis, these 8 homonuclear diatomic molecules could be divided into three different groups, based on the correlation between binding energy and the electron density at the bond critical point. However, PAEM/ESP analysis allows us to analyse all eight of them as one group having a good correlation between binding energy and the PAEM/ESP at the critical point between the two atoms. Our results highlight the arbitrariness in relying on some computational tools to characterize a bond as covalent (shared) or ionic/electrostatic (closed). In contrast, they also show the usefulness of the various methods in exploring similarities and differences in bonding. We propose that from Li-2 to Ne-2, all homonuclear diatomic molecules are bound by `chemical bonds'
The unexplained success of stentplasty vasospasm treatment: Insights using Mechanistic Mathematical Modeling
No full textBackgroundCerebral vasospasm (CVS) following subarachnoid hemorrhage occurs in up to 70% of patients. Recently, stents have been used to successfully treat CVS. This implies that the force required to expand spastic vessels and resolve vasospasm is lower than previously thought.ObjectiveWe develop a mechanistic model of the spastic arterial wall to provide insight into CVS and predict the forces required to treat it.Material and MethodsThe arterial wall is modelled as a cylindrical membrane using a constrained mixture theory that accounts for the mechanical roles of elastin, collagen and vascular smooth muscle cells (VSMC). We model the pressure diameter curve prior to CVS and predict how it changes following CVS. We propose a stretch-based damage criterion for VSMC and evaluate if several commercially available stents are able to resolve vasospasm.ResultsThe model predicts that dilatation of VSMCs beyond a threshold of mechanical failure is sufficient to resolve CVS without damage to the underlying extracellular matrix. Consistent with recent clinical observations, our model predicts that existing stents have the potential to provide sufficient outward force to successfully treat CVS and that success will be dependent on an appropriate match between stent and vessel.ConclusionMathematical models of CVS can provide insights into biological mechanisms and explore treatment approaches. Improved understanding of the underlying mechanistic processes governing CVS and its mechanical treatment may assist in the development of dedicated stents
The unexplained success of stentplasty vasospasm treatment: Insights using Mechanistic Mathematical Modeling (vol 29, pg 763, 2019)
No full textNaphthalene and its BN analogues in the weak coupling regime: a general rule for their I-V characteristics
No full textWehave computed the current-voltage (I-V) characteristics of naphthalene and its Boron-Nitrogen (BN) analogues coupled weakly to electrodes in quantum many-body basis. The master equation method has been employed to compute the current by obtaining the tunneling rate of charges from molecule to electrodes. We find that the nature of the I-V curve is solely governed by the charge density distributions of the excited states of the singly charged molecular device. We also find that the nature of the I-V curve is independent of the atoms involved in bridging the molecule to the electrode. We have further verified these inferences by obtaining the I-V curves of biphenyl molecule
Transferrin conjugates of antitubercular drug isoniazid: Synthesis and in vitro efficacy
No full textTuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) has become the world's leading killer disease due to a single infectious agent which survives in the host macrophage for the indefinite period. Hence, it is necessary to enhance the efficacy of the clinically existing antitubercular agents or to discover new anti antitubercular agents. Here, we report the synthesis, characterization and antimycobacterial evaluation of protein-drug conjugates. A carrier protein, Transferrin (Tf) was covalently conjugated to isoniazid (INH) utilizing hydrazone and amide linkers. The purity of the reactions was confirmed by SDS-PAGE while conjugation was confirmed by UV-visible spectrophotometry, MALDI-TOF analysis, and FFIR spectrophotometry. The in vitro antitubercular assay result showed that the inhibitory activity of the parent drug was conserved in both the conjugates. The conjugates were effective against intracellular Mtb H37Rv and were devoid of cytotoxic effect at therapeutic concentration
de Sitter, alpha `-corrections & duality invariant cosmology
No full textDemanding O(d, d)-duality covariance, Hohm and Zwiebach have written down the action for the most general cosmology involving the metric, b-field and dilaton, to all orders in alpha' in the string frame. Remarkably, for an FRW metric-dilaton ansatz the equations of motion turn out to be quite simple, except for the presence of an unknown function of a single variable. If this unknown function satisfies some simple properties, it allows de Sitter solutions in the string frame. In this note, we write down the Einstein frame analogues of these equations, and make some observations that make the system tractable. Perhaps surprisingly, we find that a necessary condition for de Sitter solutions to exist is that the unknown function must satisfy a certain second order non-linear ODE. The solutions of the ODE do not have a simple power series expansion compatible with the leading supergravity expectation. We discuss possible interpretations of this fact. After emphasizing that all (potential) string and Einstein frame de Sitter solutions have a running dilaton, we write down the most general cosmologies with a constant dilaton in string/Einstein frame: these have power law scale factors
Double-L Cantilever-Based Fiber Bragg Grating Accelerometer
No full textOptical accelerometers, especially the fiber Bragg grating accelerometers are the preferred sensors for vibration, and acceleration measurement in several fields of engineering. They are light, compact, immune to electromagnetic interference, and provide better noise immunity due to wavelength encoded nature of signal transduction. In the present work, analytical modeling, numerical simulation, fabrication, and characterization of a novel double-L cantilever based fiber Bragg grating accelerometer is presented. This design not only enhances the sensitivity in comparison to its single-L counterpart, but also provides selferature compensation. Modular design of the accelerometer provides flexibility in replacing specific components to achieve desired performance characteristics. Resonant frequency of 86 Hz, sensitivity of 406.7 pm/g with an excellent linearity of 99.86 , and small temperature sensitivity of 0.016 pm/°C have been demonstrated for the fabricated model. The FBG accelerometer has a linear operating range of ±6 g
Influence of cadmium(II) source upon the formation of a discrete monomer Cd(kappa(2)-OC(O)Bu-t)(2)(H2O)(2)] and a trinuclear heterobimetallic 1D CP, {Na-2Cd(mu(5)-kappa(3):kappa(3)-OAc)(mu(3)-kappa(2):kappa(3)-OC(O)Bu -t)(mu(3)-kappa(1):kappa(2)-OC(O)Bu-t)(2)].2(t)BuC(O)OH}(infinity)
No full textThe reaction of CdCl2 center dot 2.5H(2)O with two equiv of aq. NaOH followed by treatment of the resulting solution with two equiv of pivalic acid gave Cd(kappa(2)-OC(O)Bu-t)(2) (H2O)(2)] (1) in 83% yield while the aforementioned reaction with Cd(OAc)(2)center dot 2H(2)O as Cd2+ source afforded a trinuclear heterobimetallic 1D-CP, {Na-2Cd(mu(5)-kappa(3):kappa(3)-OAc)(mu(3)-kappa(2):kappa(3) OC(O)Bu-t)(mu(3)-kappa(1):kappa(2)-OC(O)Bu-t)(2)]center dot 2(t)BuC(O)OH}(infinity) (2) in 90% yield. Complexes 1 and 2 were characterized by elemental analyses, IR spectroscopy, solution H-1 and C-13 {H-1} NMR spectroscopy and solid state CP-MAS C-13{H-1} NMR spectroscopy, TG-DTA analyses and single crystal X-ray diffraction. The phase purity of 2 was also verified by powder X-ray diffraction. Complex 1 represents the first structurally characterised discrete mono-nuclear cadmium(II) carboxylate complex which is known to contain a pair of chelating carboxylate ligand, while 2 represents the first structurally characterized trinuclear heterobimetallic 1D-CP formed through aggregation via covalent coordinate bond
Supervised i-vector Modeling - Theory and Applications
No full textOver the last decade, the factor analysis based modeling of a variable length speech utterance into a fixed dimensional vector (termed as i-vector) has been prominently used for many tasks like speaker recognition, language recognition and even in speech recognition. The i-vector model is an unsupervised learning paradigm where the data is initially clustered using a Gaussian Mixture Universal Background Model (GMM-UBM). The adapted means of the Gaussian mixture components are dimensionality reduced using the Total Variability Matrix (TVM) where the latent variables are modeled with a single Gaussian distribution. In this paper, we propose to rework the theory of i-vector modeling using a supervised framework where the speech utterances are associated with a label. Class labels arc introduced in the i-vector model using a mixture Gaussian prior. We show that the proposed model is a generalized i-vector model and the conventional i-vector model turns out to be a special case of this model. This model is applied for a language recognition task using the NIST Language Recognition Evaluation (LRE) 2017 dataset. In these experiments, the supervised i-vector model provides significant improvements over the conventional i-vector model (average relative improvements of 5 % in terms of C-avg)
EFFICIENT SYNTHESIS OF O-LINKED GLYCOCONJUGATES OF AMINO ACIDS FROM CARBOHYDRATE-DERIVED DONOR-ACCEPTOR CYCLOPROPANES
No full textN-Iodosuccinimide (NIS) mediated ring opening of carbohydrate-derived donor-acceptor cyclopropanes with free ``CO2H'' group of N-protected L-amino acids at ambient conditions afforded iodo derivatives of glycosyl ester of L-amino acids. The iodides were subsequently converted easily into corresponding azides using NaN3 in DMF followed by reduction with Zn/AcOH to produce ester linked glycosyl amino acids. A similar strategy was adopted to synthesize C-linked glycoamino acid derivatives from different N-protected L-amino alcohols. By using an orthogonal strategy C- and O-linked glycopeptides were also synthesized