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排序方式: 共有150条查询结果,搜索用时 15 毫秒
51.
S. Barman C. Rajesh G. P. Das C. Majumder 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(3):613-625
Here we report a systematic theoretical study of the structure and
electronic properties of Snn-1Pb and Pbn-1Sn (n = 2-13) clusters
and compare these results with pure Snn and Pbn to understand the
influence of the dopant elements. The calculations were carried out using
the density functional theory with generalized gradient approximation for
the exchange-correlation potential. Extensive search based on large number
of initial configurations has been carried out to locate the stable isomers
of Snn-1Pb and Pbn-1Sn (n = 2-13) clusters. The relative
stability of Snn-1Pb and Pbn-1Sn (n = 2-13) clusters is analyzed
based on the calculated binding energies and second difference in energy.
The stability analysis of these clusters suggests that, while the
substitution of Sn by Pb lowers the stability of Snn clusters, presence
of Sn enhances the stability of the Pbn clusters. The results suggest
that while for Snn-1Pb, n=4, 7, 10, 12 clusters are more stable than
their respective neighbors, Pbn-1Sn clusters with n = 4, 7 and 9 are
found to be more stable. Based on the fragmentation pattern it is seen that
for Snn-1Pb and Pbn-1Sn clusters favor monomer evaporation of the
Pb atom up to n =11 and n =12, respectively. Unlike this trend, the
Sn11Pb undergoes fission type fragment into Sn5Pb and Sn6
clusters. A comparison between our theoretical results and surface induced
dissociation experiment shows good agreement, which gives confidence on the
prediction of the ground state geometries. 相似文献
52.
Dr. Zufang Huang Dr. Soumik Siddhanta Prof. Dr. Gang Zheng Prof. Dr. Thomas Kickler Prof. Ishan Barman 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(15):6028-6034
The use of surface-enhanced Raman spectroscopy (SERS) to determine spectral markers for the diagnosis of heparin-induced thrombocytopenia (HIT), a difficult-to-diagnose immune-related complication that often leads to limb ischemia and thromboembolism, is proposed. The ability to produce distinct molecular signatures without the addition of labels enables unbiased inquiry and makes SERS an attractive complementary diagnostic tool. A capillary-tube-derived SERS platform offers ultrasensitive, label-free measurement as well as efficient handling of blood serum samples. This shows excellent reproducibility, long-term stability and provides an alternative diagnostic rubric for the determination of HIT by leveraging machine-learning-based classification of the spectroscopic data. We envision that a portable Raman instrument could be combined with the capillary-tube-based SERS analytical tool for diagnosis of HIT in the clinical laboratory, without perturbing the existing diagnostic workflow. 相似文献
53.
Zufang Huang Soumik Siddhanta Gang Zheng Thomas Kickler Ishan Barman 《Angewandte Chemie (International ed. in English)》2020,59(15):5972-5978
The use of surface‐enhanced Raman spectroscopy (SERS) to determine spectral markers for the diagnosis of heparin‐induced thrombocytopenia (HIT), a difficult‐to‐diagnose immune‐related complication that often leads to limb ischemia and thromboembolism, is proposed. The ability to produce distinct molecular signatures without the addition of labels enables unbiased inquiry and makes SERS an attractive complementary diagnostic tool. A capillary‐tube‐derived SERS platform offers ultrasensitive, label‐free measurement as well as efficient handling of blood serum samples. This shows excellent reproducibility, long‐term stability and provides an alternative diagnostic rubric for the determination of HIT by leveraging machine‐learning‐based classification of the spectroscopic data. We envision that a portable Raman instrument could be combined with the capillary‐tube‐based SERS analytical tool for diagnosis of HIT in the clinical laboratory, without perturbing the existing diagnostic workflow. 相似文献
54.
55.
Nikita Barman Saikat Banerjee Paula Brandão Antonio Bauzá 《Journal of Coordination Chemistry》2016,69(7):1188-1205
Four complexes based on N,N′-bis(2-pyridylmethylene)-1,3-propanediamine (L) and different Cd(II) salts have been synthesized and characterized by single-crystal X-ray diffraction analysis. The complexes are [Cd2(L)2(μ-Cl)2](ClO4)2 (1), [Cd2(L)2(μ-Br)2](ClO4)2 (2), [Cd(L)I](ClO4) (3), and [Cd(L)(NCS)2] (4). L exhibits the same coordination mode in 1–4. The radius of each anion plays a role in affecting the structures and luminescent intensities of the final products. CdCl2, CdBr2, and CdI2 react with L to produce chloride or bromido-bridged binuclear complexes and mononuclear iodido complex, respectively, whereas an unusual mononuclear trigonal prismatic (TP) 4 is obtained when thiocyanate was used as a coligand. Photoluminescence properties of all the complexes show that the trend of fluorescence intensity is 1 > 4 > 2 > 3. All four complexes exhibit different supramolecular interactions such as C–H/σ, π–π, and C–H/π and hydrogen bonding interactions. The experimental findings are complemented by density functional theory (DFT) calculations. 相似文献
56.
Doyel Barman 《Topology and its Applications》2012,159(3):806-813
We continue the study of Selectively Separable (SS) and, a game-theoretic strengthening, strategically selectively separable spaces (SS+) (see Barman, Dow (2011) [1]). The motivation for studying SS+ is that it is a property possessed by all separable subsets of Cp(X) for each σ-compact space X. We prove that the winning strategy for countable SS+ spaces can be chosen to be Markov. We introduce the notion of being compactlike for a collection of open sets in a topological space and with the help of this notion we prove that there are two countable SS+ spaces such that the union fails to be SS+, which contrasts the known result about SS spaces. We also prove that the product of two countable SS+ spaces is again countable SS+. One of the main results in this paper is that the proper forcing axiom, PFA, implies that the product of two countable Fréchet spaces is SS, a statement that was shown in Barman, Dow (2011) [1] to consistently fail. An auxiliary result is that it is consistent with the negation of CH that all separable Fréchet spaces have π-weight at most ω1. 相似文献
57.
Tirtha Bhattacharjee Prasanta Gogoi Vedavati G. Puranik Rupesh L. Gawade Pranjit Barman 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(12):o485-o487
In the title compound, C21H18N2OS2, a strong intramolecular N—H...O hydrogen bond [N...O = 2.642 (3) Å] between the amide N atom and the benzoyl O atom forms an almost planar six‐membered ring in the central part of the molecule. In the crystal, molecules are packed through weak N—H...S interactions. Intra‐ and intermolecular hydrogen bonds and van der Waals interactions are the stabilizing forces for the crystal structure. 相似文献
58.
59.
Honcharenko D Varghese OP Plashkevych O Barman J Chattopadhyaya J 《The Journal of organic chemistry》2006,71(1):299-314
[structures: see text] The synthesis of novel 1',2'-aminomethylene bridged (6-aza-2-oxabicyclo[3.2.0]heptane) "azetidine" pyrimidine nucleosides and their transformations to the corresponding phosphoramidite building blocks (20, 39, and 42) for automated solid-phase oligonucleotide synthesis is reported. The novel bicyclonucleoside "azetidine" monomers were synthesized by two different strategies starting from the known sugar intermediate 6-O-benzyl-1,2:3,4-bis-O-isopropylidene-D-psicofuranose. Conformational analysis performed by molecular modeling (ab initio and MD simulations) and NMR showed that the azetidine-fused furanose sugar is locked in a North-East conformation with pseudorotational phase angle (P) in the range of 44.5-53.8 degrees and sugar puckering amplitude (phi(m)) of 29.3-32.6 degrees for the azetidine-modified T, U, C, and 5-Me-C nucleosides. Thermal denaturation studies of azetidine-modified oligo-DNA/RNA heteroduplexes show that the azetidine-fused nucleosides display improved binding affinities when compared to that of previously synthesized North-East sugar constrained oxetane fused analogues. 相似文献
60.
Varghese OP Barman J Pathmasiri W Plashkevych O Honcharenko D Chattopadhyaya J 《Journal of the American Chemical Society》2006,128(47):15173-15187
The 2'-deoxy-2'-N,4'-C-ethylene-bridged thymidine (aza-ENA-T) has been synthesized using a key cyclization step involving 2'-ara-trifluoromethylsufonyl-4'-cyanomethylene 11 to give a pair of 3',5'-bis-OBn-protected diastereomerically pure aza-ENA-Ts (12a and 12b) with the fused piperidino skeleton in the chair conformation, whereas the pentofuranosyl moiety is locked in the North-type conformation (7 degrees < P < 27 degrees, 44 degrees < phi m < 52 degrees). The origin of the chirality of two diastereomerically pure aza-ENA-Ts was found to be due to the endocyclic chiral 2'-nitrogen, which has axial N-H in 12b and equatorial N-H in 12a. The latter is thermodynamically preferred, while the former is kinetically preferred with Ea = 25.4 kcal mol-1, which is thus far the highest observed inversion barrier at pyramidal N-H in the bicyclic amines. The 5'-O-DMTr-aza-ENA-T-3'-phosphoramidite was employed for solid-phase synthesis to give four different singly modified 15-mer antisense oligonucleotides (AONs). Their AON/RNA duplexes showed a Tm increase of 2.5-4 degrees C per modification, depending upon the modification site in the AON. The relative rates of the RNase H1 cleavage of the aza-ENA-T-modified AON/RNA heteroduplexes were very comparable to that of the native counterpart, but the RNA cleavage sites of the modified AON/RNA were found to be very different. The aza-ENA-T modifications also made the AONs very resistant to 3' degradation (stable over 48 h) in the blood serum compared to the unmodified AON (fully degraded in 4 h). Thus, the aza-ENA-T modification in the AON fulfilled three important antisense criteria, compared to the native: (i) improved RNA target affinity, (ii) comparable RNase H cleavage rate, and (iii) higher blood serum stability. 相似文献