Kinetics and Mechanism of the Pyridinolysis of Aryl Phenyl Isothiocyanophosphate in Acetonitrile

Adhikary, Keshab Kumar,Lee, Hai-Whang,Lee, Ik-Choon Korean Chemical Society 2003 Bulletin of the Korean Chemical Society Vol.24 No.8

The kinetics and mechanism of the pyridinolysis $(XC_5H_4N)$ of Y-aryl phenyl isothiocyanophosphates (1;$(YC_6H_4O)\;(C_6H_5O)$P(=O)NCS) are investigated in acetonitrile at 55.0 ℃. The Hammett plots for substituent (Y) variations in the substrate (log k₂ vs σY) exhibit a convex upward biphasic type with breaks at Y = H. For electron-donating Y groups the Hammett coefficients, ρY, are positive and cross-interaction constant ρXY is negative, while those for electron-withdrawing Y groups ρY values are negative with a positive ρXY. These results are interpreted to indicate mechanistic change at the breakpoint (σY = 0) from a concerted to a stepwise mechanism with rate-limiting expulsion of the $^-NCS$ group from a trigonal bipyramidal pentacoordinated (TBP-5C) intermediate. Biphasic plots of log k₂ vs σX or $pK_a$(X) with steeper slopes for the more basic nucleophiles are obtained suggesting an equatorial nucleophilic attack in contrast to an apical attack for the less basic nucleophiles with smaller magnitude of ρX or βx.

Kinetics and Mechanism of the Pyridinolysis of Diethyl Isothiocyanophosphate in Acetonitrile

Adhikary, Keshab Kumar,Lee, Hai-Whang Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.3

The kinetics and mechanism of the pyridinolysis ($XC_5H_4N$) of diethyl isothiocyanophosphate are investigated in acetonitrile at $55.0^{\circ}C$. The Hammett and Bronsted plots for substituent X variations in the nucleophiles exhibit the two discrete slopes with a break region between X = 3-Ac and 4-Ac. These are interpreted to indicate a mechanistic change at the break region from a concerted to a stepwise mechanism with rate-limiting expulsion of the isothiocyanate leaving group from a trigonal bipyramidal pentacoordinated intermediate. The relatively large ${\beta}_x$ values with more basic and less basic pyridines imply much greater fraction of frontside nucleophilic attack TSf than that of backside attack TSb.

Joint Spatial Division and Multiplexing—The Large-Scale Array Regime

Adhikary, Ansuman,Junyoung Nam,Jae-Young Ahn,Caire, Giuseppe IEEE 2013 IEEE transactions on information theory Vol.59 No.10

<P>We propose joint spatial division and multiplexing (JSDM), an approach to multiuser MIMO downlink that exploits the structure of the correlation of the channel vectors in order to allow for a large number of antennas at the base station while requiring reduced-dimensional channel state information at the transmitter (CSIT). JSDM achieves significant savings both in the downlink training and in the CSIT uplink feedback, thus making the use of large antenna arrays at the base station potentially suitable also for frequency division duplexing (FDD) systems, for which uplink/downlink channel reciprocity cannot be exploited. In the proposed scheme, the multiuser MIMO downlink precoder is obtained by concatenating a prebeamforming matrix, which depends only on the channel second-order statistics, with a classical multiuser precoder, based on the instantaneous knowledge of the resulting reduced dimensional “effective” channel matrix. We prove a simple condition under which JSDM incurs no loss of optimality with respect to the full CSIT case. For linear uniformly spaced arrays, we show that such condition is approached in the large number of antennas limit. For this case, we use Szego's asymptotic theory of Toeplitz matrices to show that a DFT-based prebeamforming matrix is near-optimal, requiring only coarse information about the users angles of arrival and angular spread. Finally, we extend these ideas to the case of a 2-D base station antenna array, with 3-D beamforming, including multiple beams in the elevation angle direction. We provide guidelines for the prebeamforming optimization and calculate the system spectral efficiency under proportional fairness and max-min fairness criteria, showing extremely attractive performance. Our numerical results are obtained via asymptotic random matrix theory, avoiding lengthy Monte Carlo simulations and providing accurate results for realistic (finite) number of antennas and users.</P>

One-Pot Conversion of Carbohydrates into Pyrrole-2-carbaldehydes as Sustainable Platform Chemicals

Adhikary, Nirmal Das,Kwon, Sunjeong,Chung, Wook-Jin,Koo, Sangho American Chemical Society 2015 Journal of organic chemistry Vol.80 No.15

<P>A practical conversion method of carbohydrates into <I>N</I>-substituted 5-(hydroxymethyl)pyrrole-2-carbaldehydes (pyrralines) was developed by the reaction with primary amines and oxalic acid in DMSO at 90 °C. Further cyclization of the highly functionalized pyrralines afforded the pyrrole-fused poly-heterocyclic compounds as potential intermediates for drugs, food flavors, and functional materials. The mild Maillard variant of carbohydrates and amino esters in heated DMSO with oxalic acid expeditiously produced the pyrrole-2-carbaldehyde skeleton, which can be concisely transformed into the pyrrole alkaloid natural products, 2-benzyl- and 2-methylpyrrolo[1,4]oxazin-3-ones <B>8</B> and <B>9</B>, lobechine <B>10</B>, and (−)-hanishin <B>11</B> in 23–32% overall yields from each carbohydrate.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/joceah/2015/joceah.2015.80.issue-15/acs.joc.5b01349/production/images/medium/jo-2015-01349v_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jo5b01349'>ACS Electronic Supporting Info</A></P>

Kinetics and Mechanism of the Pyridinolysis of Aryl Ethyl Chlorothiophosphates in Acetonitrile

Adhikary, Keshab Kumar,Lee, Hai-Whang Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.11

The nucleophilic substitution reactions of Y-aryl ethyl chlorothiophosphates with X-pyridines are studied kinetically in acetonitrile at $55.0^{\circ}C$. The Hammett and Bronsted plots for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a break point at X = 3-Me. The substituents of X = 4-CN and 4-Ac show great positive deviations from both the Hammett and Bronsted plots. The Hammett plots for substituent Y variations in the substrates exhibit biphasic concave upwards with a minimum point at Y = H. The obtained values of the cross-interaction constants (${\rho}_{XY}$) are all in spite of the biphasic free energy correlations for both substituent X and Y variations, since the ${\rho}_X$values with both the strongly and weakly basic pyridines are almost constant. A stepwise mechanism with a rate-limiting leaving group departure from the intermediate is proposed where the distance between X and Y does not vary from the intermediate to the second transition state. A frontside attack is proposed with the strongly basic pyridines based on the considerably great magnitudes of ${\rho}_X$ and ${\beta}_X$ values and a backside attack is proposed with the weakly basic pyridines based on the relatively small magnitudes of ${\rho}_X$ and ${\beta}_X$. The positive deviations of the two strong ${\pi}$-acceptor parasubstituents, X = 4-Ac and 4-CN, from both the Hammett and Bronsted plots are rationalized by the great extents of bond formation and breaking.

Significant Substituent Effects on Pyridinolysis of Aryl Ethyl Chlorophosphates in Acetonitrile

Adhikary, Keshab Kumar,Lee, Hai Whang Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.5

The substituent effects on the pyridinolysis (XC5H4N) of Y-aryl ethyl chlorophosphates are investigated in acetonitrile at $35.0^{\circ}C$. The two strong ${\pi}$-acceptor substituents, X = 4-Ac and 4-CN in the X-pyridines, exhibit large positive deviations from the Hammett plots but little positive deviations from the Br$\ddot{o}$nsted plots. The substituent Y effects on the rates are really significant and the Hammett plots for substituent Y variations in the substrates invariably change from biphasic concave downwards via isokinetic at X = H to biphasic concave upwards with a break point at Y = 3-Me as the pyridine becomes less basic. These are interpreted to indicate a mechanistic change at the break point from a stepwise mechanism with a rate-limiting bond formation (${\rho}_{XY}$ = -6.26) for Y = (4-MeO, 4-Me, 3-Me) to with a rate-limiting leaving group expulsion from the intermediate (${\rho}_{XY}$ = +5.47) for Y = (4-Me, H, 3-MeO). The exceptionally large magnitudes of ${\rho}_{XY}$ values imply frontside nucleophilic attack transition state.

Modern Contraception and Anaemia Among Reproductive-age Women in India: Results From a Household Survey

Adhikary Mihir,Barman Poulami,Singh Bharti,Anand Abhishek 대한예방의학회 2024 예방의학회지 Vol.57 No.4

Objectives: Chronic anaemia is a significant health concern, particularly among women of childbearing age. Factors such as menstrual blood loss, childbirth, inadequate nutrition, closely spaced pregnancies, and recurrent gastrointestinal bleeding increase the risk of anaemia. This study investigated whether current contraceptive methods are associated with anaemia in Indian women of reproductive age.Methods: Cross-sectional data from the fifth round of the National Family Health Survey, conducted in 2019-2021, were used for this investigation. We included only non-pregnant and non-amenorrhoeic women in our analysis, resulting in a final analytical sample of 673 094 women aged 15-49. Bivariate cross-tabulations and multivariable logistic regression were employed to analyse the data.Results: The prevalence of anaemia was 57%, and the adjusted regression models found no significant association between the use of any contraceptive methods and women’s haemoglobin status. Women using traditional contraceptive methods had 1.08 (95% confidence interval, 1.05 to 1.11) times higher odds of having anaemia. Among the modern methods, other than injectables, all other methods—such as an intrauterine device, barrier use, and sterilisation—were associated with higher odds of anaemia compared to women who used contraceptive pills.Conclusions: This study explored the relationship between modern contraceptives and haemoglobin levels in India, revealing that injectables were associated with a notable reduction in the odds of anaemia, whereas traditional contraceptives and other modern methods exhibited positive associations with anaemia. These findings prompt policymakers to focus on anaemia reduction and safe contraceptives. More research is needed to inform decisions, given the scant literature.

Dynamic analysis of water storage tank with rigid block at bottom

Adhikary, Ranjan,Mandal, Kalyan Kumar Techno-Press 2018 Ocean systems engineering Vol.8 No.1

The present paper deals with the finite element analysis of water tanks with rigid baffle. Fluid is discretized by two dimensional eight-node isoparametric elements and the governing equation is simulated by pressure based formulation to reduce the degrees of freedom in the domain. Both free vibration and force vibration analysis are carried out for different sizes and positions of block at tank bottom. The fundamental frequency depends on block height and it reduces with the increase of block height. The variation of hydrodynamic pressure on tank walls not only depends of the exciting frequency but also on the size and position of rigid block at tank bottom. The hydrodynamic pressure has higher value when the exciting frequency is equal and lower than the fundamental frequency of the water in the tank. Similarly, the hydrodynamic pressure increases with the increase of width of the block for all exciting frequencies when the block is at the centre of tank. The left and right walls of tank have experienced different hydrodynamic pressure when the block is placed at off-centre. However, the increase in hydrodynamic pressure on nearest tank wall becomes insignificant after a certain value of the distance between the wall and the rigid block.

Nucleophilic Substitution Reactions of α-Bromoacetanilides with Benzylamines

Adhikary, Keshab Kumar,Kim, Chan-Kyung,Lee, Bon-Su,Lee, Hai-Whang Korean Chemical Society 2008 Bulletin of the Korean Chemical Society Vol.29 No.1

Kinetic studies of the reactions of a-bromoacetanilides [YC6H4NHC(=O)CH2Br] with substituted benzylamines (XC6H4CH2NH2) have been carried out in dimethyl sulfoxide at 35.0 oC. The Hammett plots for substituent (Y) variations in the substrate (log kN vs. sY) are biphasic concave upwards/downwards with breaks at Y = 4-Cl (sY = 0.23). The Hammett coefficients rY and the cross-interaction constant rXY (= +0.16) are positive for sY 0.23, while the rY values are positive/negative [rY > 0 for X = (4-MeO and 4-Me) and rY < 0 for X = (H, 4-Cl and 3-Cl)] and the rXY (= -1.51) value is negative for sY ³ 0.23. Based on these and other results, the benzylaminolyses of a-bromoacetanilides are proposed to proceed through rate-limiting expulsion of the bromide leaving group from a zwitterionic tetrahedral intermediate, T, with a bridged transition state for s Y 0.23, while the reaction proceeds through concerted mechanism with an enolate-like TS in which the nucleophile attacks the a-carbon for s Y ³ 0.23.

Pyridinolysis of O,O-Diphenyl S-Phenyl Phosphorothiolates in Acetonitrile

Adhikary, Keshab Kumar,Lumbiny, Bilkis Jahan,Kim, Chan-Kyung,Lee, Hai Whang Korean Chemical Society 2008 Bulletin of the Korean Chemical Society Vol.29 No.4

The reactions of O,O-diphenyl Z-S-phenyl phosphorothiolates with X-pyridines have been studied kinetically in acetonitrile at $35.0{^{\circ}C}$. The Hammett plots for substituent (Z) variations in the leaving group (log $k_2$ vs. $\sigma$ Z) are biphasic concave downwards with breaks at Z = H. The large magnitudes of ${\rho}X(\rho_{nuc})$, ${\beta}X(\rho_{nuc})$, and the cross-interaction constant, $\rho$XZ, suggest frontside nucleophilic attack toward the leaving group. The sign reversal of $\rho$Z from positive in $\sigma$ Z $\leq$ 0 to negative in $\sigma$ Z $\geq$ 0 is interpreted as the change in mechanism from concerted to stepwise with rate-limiting expulsion of the leaving group. The anomalous negative sign of $\rho$ Z for leaving groups with electron-withdrawing substituents is interpreted as the intramolecular ligand exchange process of the leaving group from the equatorial position in the intermediate to the apical position in the TS.