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Dr. Sameera  Daud-Ahmad  Md image

Dr. Sameera Daud-Ahmad Md

452 Old Hook Rd 2Nd Floor
Emerson NJ 07630
201 971-1072
Medical School: Other - Unknown
Accepts Medicare: No
Participates In eRX: No
Participates In PQRS: No
Participates In EHR: No
License #: 25MA08562600
NPI: 1073700381
Taxonomy Codes:
207RE0101X

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Publications

Highly Twisted N,N-Dialkylamines as a Design Strategy to Tune Simple Aromatic Hydrocarbons as Steric Environment-Sensitive Fluorophores. - Journal of the American Chemical Society
The steric-environment sensitivity of fluorescence of 9,10-bis(N,N-dialkylamino)anthracenes (BDAAs) was studied experimentally and theoretically. A new design strategy to tune simple aromatic hydrocarbons as efficient aggregation-induced emission (AIE) luminogens and molecular rotors is proposed. For a variety of BDAAs, prominent Stokes shifts and efficient solid-state fluorescence were observed. Calculations on BDAA-methyl suggested that in the ground state (S0) conformations, the pyramidal amine groups are highly twisted, so that their lone-pair orbitals cannot conjugate with the anthracene π orbitals. Fluorescence takes place from the S1 minima, in which one or both amine groups are planarized. The stability of the S1 excited state minima as well as destabilization of the S0 state is the origin of large Stokes shift. Experimental measurement of the nonadiabatic transition rate suggests that para disubstitution by dialkylamino (or strongly electron-donating) groups is a key for fast internal conversion. Minimum energy conical intersection (MECI) between S1 and S0 states was found to have a Dewar-benzene like structure. Although this can be reached efficiently in liquid phase for fast internal conversion, a large amplitude motion is required to reach this MECI, which is prohibited in the solid state and caused efficient AIE. This strategy is used to find experimentally that naphthalene analogues are also efficient AIE luminogens. The flexibility of alkyl chains on amino groups is also found to be important for allowed charge-transfer transition. Thus, three points [(1) highly twisted N,N-dialkylamines, (2) substitution at the para positions, (3) with flexible alkyl groups] were proposed for activation of small aromatic hydrocarbons.
DFT Rationalization of the Diverse Outcomes of the Iodine(III)-Mediated Oxidative Amination of Alkenes. - Chemistry (Weinheim an der Bergstrasse, Germany)
A computational study of the mechanism for the iodine(III)-mediated oxidative amination of alkenes explains the experimentally observed substrate dependence on product distribution. Calculations with the M06 functional have been carried out on the reaction between PhI(N(SO2 Me)2 )2 and three different representative substrates: styrene, α-methylstyrene, and (E)-methylstilbene. All reactions start with electrophilic attack by a cationic PhI(N(SO2 Me)2 )(+) unit on the double bond, and formation of an intermediate with a single C-I bond and a planar sp(2) carbocationic center. The major path, leading to 1,2-diamination, proceeds through a mechanism in which the bissulfonimide initially adds to the alkene through an oxygen atom of one sulfonyl group. This behavior is now corroborated by experimental evidence. An alternative path, leading to an allylic amination product, takes place through deprotonation at an allylic C-H position in the common intermediate. The regioselectivity of this amination depends on the availability of the resonant structures of an alternate carbocationic intermediate. Only in cases where a high electronic delocalization is possible, as in (E)-methylstilbene, does the allylic amination occur without migration of the double bond.© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Computational Catalysis Using the Artificial Force Induced Reaction Method. - Accounts of chemical research
The artificial force induced reaction (AFIR) method in the global reaction route mapping (GRRM) strategy is an automatic approach to explore all important reaction paths of complex reactions. Most traditional methods in computational catalysis require guess reaction paths. On the other hand, the AFIR approach locates local minima (LMs) and transition states (TSs) of reaction paths without a guess, and therefore finds unanticipated as well as anticipated reaction paths. The AFIR method has been applied for multicomponent organic reactions, such as the aldol reaction, Passerini reaction, Biginelli reaction, and phase-transfer catalysis. In the presence of several reactants, many equilibrium structures are possible, leading to a number of reaction pathways. The AFIR method in the GRRM strategy determines all of the important equilibrium structures and subsequent reaction paths systematically. As the AFIR search is fully automatic, exhaustive trial-and-error and guess-and-check processes by the user can be eliminated. At the same time, the AFIR search is systematic, and therefore a more accurate and comprehensive description of the reaction mechanism can be determined. The AFIR method has been used for the study of full catalytic cycles and reaction steps in transition metal catalysis, such as cobalt-catalyzed hydroformylation and iron-catalyzed carbon-carbon bond formation reactions in aqueous media. Some AFIR applications have targeted the selectivity-determining step of transition-metal-catalyzed asymmetric reactions, including stereoselective water-tolerant lanthanide Lewis acid-catalyzed Mukaiyama aldol reactions. In terms of establishing the selectivity of a reaction, systematic sampling of the transition states is critical. In this direction, AFIR is very useful for performing a systematic and automatic determination of TSs. In the presence of a comprehensive description of the transition states, the selectivity of the reaction can be calculated more accurately. For relatively large molecular systems, the computational cost of AFIR searches can be reduced by using the ONIOM(QM:QM) or ONIOM(QM:MM) methods. In common practice, density functional theory (DFT) with a relatively small basis set is used for the high-level calculation, while a semiempirical approach or a force field description is used for the low-level calculation. After approximate LMs and TSs are determined, standard computational methods (e.g., DFT with a large basis set) are used for the full molecular system to determine the true LMs and TSs and to rationalize the reaction mechanism and selectivity of the catalytic reaction. The examples in this Account evidence that the AFIR method is a powerful approach for accurate prediction of the reaction mechanisms and selectivities of complex catalytic reactions. Therefore, the AFIR approach in the GRRM strategy is very useful for computational catalysis.
The Mechanism of Iron(II)-Catalyzed Asymmetric Mukaiyama Aldol Reaction in Aqueous Media: Density Functional Theory and Artificial Force-Induced Reaction Study. - Journal of the American Chemical Society
Density functional theory (DFT), combined with the artificial force-induced reaction (AFIR) method, is used to establish the mechanism of the aqueous Mukaiyama aldol reactions catalyzed by a chiral Fe(II) complex. On the bases of the calculations, we identified several thermodynamically stable six- or seven-coordinate complexes in the solution, where the high-spin quintet state is the ground state. Among them, the active intermediates for the selectivity-determining outer-sphere carbon-carbon bond formation are proposed. The multicomponent artificial force-induced reaction (MC-AFIR) method found key transition states for the carbon-carbon bond formation, and explained the enantioselectivity and diastereoselectivity. The overall mechanism consists of the coordination of the aldehyde, carbon-carbon bond formation, the rate-determining proton transfer from water to aldehyde, and dissociation of trimethylsilyl group. The calculated full catalytic cycle is consistent with the experiments. This study provides important mechanistic insights for the transition metal catalyzed Mukaiyama aldol reaction in aqueous media.
Binary classification using multivariate receiver operating characteristic curve for continuous data. - Journal of biopharmaceutical statistics
The classification scenario needs handling of more than one biomarker. The main objective of the work is to propose a multivariate receiver operating characteristic (MROC) model which linearly combines the markers to classify them into one of the two groups and also to determine an optimal cut point. Simulation studies are conducted for four sets of mean vectors and covariance matrices and a real dataset is also used to demonstrate the proposed model. Linear and quadratic discriminant analysis has also been applied to the above datasets in order to explain the ease of the proposed model. Bootstrapped estimates of the parameters of the ROC curve are also estimated.
Remarkable changes in the photoluminescent properties of Y2Ce2O7:Eu(3+) red phosphors through modification of the cerium oxidation states and oxygen vacancy ordering. - Physical chemistry chemical physics : PCCP
A new series of red phosphors based on Eu(3+)-doped yttrium cerate [Y1.9Ce2O7:0.1Eu(3+), Y2Ce1.9O7:0.1Eu(3+) and Y2Ce2-xO7:xEu(3+) (x = 0.05, 0.10, 0.15, 0.20, 0.25 and 0.50)] was prepared via a conventional solid-state method. The influence of the substitution of Eu(3+) at the aliovalent site on the photoluminescent properties was determined by powder X-ray diffraction, FT Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy with energy-dispersive spectroscopy, UV-visible absorption spectroscopy, photoluminescence spectroscopy and lifetime measurements. The substitution of Eu(3+) at the Ce(4+) site induces a structural transition from a defect fluorite to a C-type structure, which increases the oxygen vacancy ordering and the distortion of the Eu(3+) environment, and decreases the formation of Ce(3+) states. In contrast, phosphors with isovalent substitution at the Y(3+) site exhibit the biphasic nature of defect fluorite and a C-type structure, thereby increasing the number of Ce(3+) oxidation states. These modifications resulted in remarkable changes in the photoluminescent properties of Y2Ce1.9O7:0.1Eu(3+) red phosphors, with emission intensities 3.8 times greater than those of the Ce0.9O2:0.1Eu(3+) and Y1.9Ce2O7:0.1Eu(3+). The photoluminescent properties of Y2Ce2-xO7:xEu(3+) were studied at different Eu(3+) concentrations under excitation with blue light. These phosphors emit intense red light due to the (5)D0-(7)F2 transition under excitation at 466 nm and no concentration quenching is observed with up to 50 mol% Eu(3+). They show increased lifetimes in the range 0.62-0.72 ms at Eu(3+) concentrations. The cation ordering linked to the oxygen vacancy ordering led to the uniform distribution of Eu(3+) ions in the lattice, thus allowing higher doping concentrations without quenching and consequently increasing the lifetime of the (5)D0 states. Our results demonstrate that significant improvements in the photoluminescence properties can be achieved by the structural alteration of a fluorite CeO2 to a C-type lattice.
Expression of inducible nitric oxide synthase in the epithelial linings of odontogenic keratocyst, dentigerous cyst and radicular cyst: a pathological insight. - Annals of medical and health sciences research
The present study is aimed at analyzing the expression of inducible nitric oxide synthase (iNOS) in the epithelial lining of odontogenic keratocyst (OKC), dentigerous cyst (DC), radicular cyst (RC) in order to understand the possible role of iNOS with special reference to its neoplastic nature and local aggressive of cysts.The primary aim of the following study is to analyze the immunohistochemical expression of iNOS and secondary aim is to compare the iNOS expression, pattern and intensity of staining among the epithelial linings of OKC, DC and RC.iNOS in the epithelial lining cells were analyzing in 10 OKC's, 10 DC's and 10 RC's using immunohistochemistry. The percentage of positive cells was assessed and presented as mean ± standard deviation. The correlation with respect to the intensity and percentage of staining within the epithelial linings of OKCs, DCs and RCs was carried out using (analysis of variance and Student's t-test) Chi-square test.Staining intensity of iNOS portion was seen in the entire thickness of the epithelial linings of OKC, whereas in DC's only one case had entire thickness of the epithelial lining staining and in RC's none of the cases showed entire thickness of staining. On comparing the staining intensity of iNOS between OKC, DC and RC groups, using Chi-square test, there was a statistically significant difference between these groups (P < 0.01). On analyzing the immuno-reactivity of iNOS in OKC, DC and RC there was a positive variable expression iNOS between the cysts.iNOS was over expressed in OKCs when compared with DC and RC suggesting that iNOS may contribute to the aggressive behavior of OKC. This is yet another evidence to support that OKC is the neoplasm.
Double exchange in a mixed-valent octanuclear iron cluster, [Fe8(μ4-O)4(μ-4-Cl-pz)12Cl4](-). - Dalton transactions (Cambridge, England : 2003)
A combination of SQUID and pulsed high-field magnetometry is used to probe the nature of mixed valency in an Fe(II)Fe7(III) cluster. DFT-computed spin Hamiltonian parameters suggest that antiferromagnetic coupling dominates, and that electron transfer both between the four irons of the cubane core (t1) and between a cubane and three neighboring irons (t2) is significant. Simulations using the computed parameters are able to reproduce the key features of the measured effective magnetic moment, μeff(T), over the 2 < T < 300 K temperature range. In contrast, the field dependence of the molar magnetization, Mmol, measured at 0.4 K is inconsistent with substantial electron transfer: only values of t2∼ 0 place the separation between ground and first excited states in the region indicated by experiment. The apparent quenching of the cubane-outer electron transfer at very low temperatures indicates that vibronic coupling generates one or more shallow minima on the adiabatic potential energy surfaces that serve to trap the itinerant electron in the cubane core.
Chemo-, regio-, and stereoselective silver-catalyzed aziridination of dienes: scope, mechanistic studies, and ring-opening reactions. - Journal of the American Chemical Society
Silver complexes bearing trispyrazolylborate ligands (Tp(x)) catalyze the aziridination of 2,4-diene-1-ols in a chemo-, regio-, and stereoselective manner to give vinylaziridines in high yields by means of the metal-mediated transfer of NTs (Ts = p-toluensulfonyl) units from PhI═NTs. The preferential aziridination occurs at the double bond neighboring to the hydroxyl end in ca. 9:1 ratios that assessed a very high degree of regioselectivity. The reaction with the silver-based catalysts proceeds in a stereospecific manner, i.e., the initial configuration of the C═C bond is maintained in the aziridine product (cis or trans). The degree of regioselectivity was explained with the aid of DFT studies, where the directing effect of the OH group of 2,4-diene-1-ols plays a key role. Effective strategies for ring-opening of the new aziridines, deprotection of the Ts group, and subsequent formation of β-amino alcohols have also been developed.
Trace elements in diabetes mellitus. - Journal of clinical and diagnostic research : JCDR
Diabetes Mellitus is the commonest major metabolic disease and most prevalent diseases worldwide.Its related morbidity is due to its micro and macro angiopathic complications.The aim of this study was to measure and compare the serum levels of zinc and magnesium in normal individuals and in diabetic patients.Analysis of minerals was done in plasma by using a Varian Spectra AA 220 model atomic absorption spectrophotometer.Our observations showed a definite lowering of serum magnesium (p<0.001) and serum zinc levels (p<0.001) were significant in diabetic group.The cause of diabetic hypomagnesaemia is multifactorial. An altered metabolism, a poor glycaemic control and osmotic diuresis may be contributory factors. Decreased serum zinc levels in diabetes may be caused by an increase in urinary loss. These decreased levels of trace elements cause disturbances in glucose transport across cell membrane lead to insufficient formation and secretion of insulin by pancreas which compromise in the antioxidant defense mechanisms.

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