International Journal of Advanced Computer Science and Applications, 2015
Cloud computing enables the sharing of resources such as storage, network, applications and softw... more Cloud computing enables the sharing of resources such as storage, network, applications and software through internet. Cloud users can lease multiple resources according to their requirements, and pay only for the services they use. However, despite all cloud benefits there are many security concerns related to hardware, virtualization, network, data and service providers that act as a significant barrier in the adoption of cloud in the IT industry. In this paper, we survey the top security concerns related to cloud computing. For each of these security threats we describe, i) how it can be used to exploit cloud components and its effect on cloud entities such as providers and users, and ii) the security solutions that must be taken to prevent these threats. These solutions include the security techniques from existing literature as well as the best security practices that must be followed by cloud administrators.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Organic fluoronium ions can be described as positively charged molecules in which the most electr... more Organic fluoronium ions can be described as positively charged molecules in which the most electronegative and least polarizable element fluorine engages in two partially covalent bonding interactions to two carbon centers. While recent solvolysis experiments and NMR spectroscopic studies on a metastable [C–F–C]+fluoronium ion strongly support the divalent fluoronium structure over the alternative rapidly equilibrating classical carbocation, the model system has, to date, eluded crystallographic analysis to confirm this phenomenon in the solid state. Herein, we report the single crystal structure of a symmetrical [C–F–C]+fluoronium cation. Besides its synthesis and crystallographic characterization as the [Sb2F11]−salt, vibrational spectra are discussed and a detailed analysis concerning the nature of the bonding situation in this fluoronium ion and its heavier halonium homologues is performed, which provides detailed insights on this molecular structure.
Switching a HO···π Interaction to a Nonconventional OH···π Hydrogen Bond: A Completed Crystallographic Puzzle
The Journal of Organic Chemistry, 2020
In this article, we present crystallographic and spectroscopic evidence of a tunable system where... more In this article, we present crystallographic and spectroscopic evidence of a tunable system wherein a HO···π interaction switches incrementally to a nonconventional OH···π hydrogen bonding (HB) interaction. More specifically, we report the synthesis of substituted forms of model system 1 to study the effects of aryl ring electronic density on the qualitative characteristics of OH···π hydrogen bonds therein. The OH stretch in experimental IR data, in agreement with DFT calculations, shows continuous red shifts as the adjacent ring becomes more electron-rich. For example, the OH stretch of an ¬amino-substituted analogue is red shifted by roughly 50 cm-1 compared to the same stretch in the CF3 analogue, indicating a significantly stronger HB interaction in the former. Moreover, DFT calculations (ωB97XD/6-311+G**) predict that increasing electronic density on the adjacent top ring reduces the aryl π-OH σ* energy gap with a concomitant enhancement of the OH n-π* energy gap. Consequently, a dominant π-σ* interaction in the amino substituted analogue locks the system in the in-form while a favorable n-π* interaction reverses the orientation of the oxygen bound hydrogen in its protonated form. Additionally, the 1H NMR data of various analogues reveal that stronger OH···π interactions in systems with electron rich aromatic rings slow exchange of the alcoholic proton, thereby revealing coupling with the geminal proton. Finally, X-ray crystallographic analyses of a spectrum of analogues clearly visualize the three distinct stages of "switch" - starting with exclusive HO···π, to partitioned HO···π/OH···π, finally to achieving exclusive OH···π forms. Furthermore, the crystal structure of the amino analogue reveals an interesting feature in which an extended hydrogen bonding network, involving two conventional (NH···O) and two nonconventional (OH···π) HBs, dimerizes and anchors the molecule in the unit cell.
In this note, we present a series of N-(8-fluoronaphthalen-1-yl)benzamide derivatives designed to... more In this note, we present a series of N-(8-fluoronaphthalen-1-yl)benzamide derivatives designed to maximize amide-NH•••F hydrogen bond interactions therein. A combination of IR and NMR spectroscopy indicates a linear correlation between the high energy shift in NH stretching frequency and the electron withdrawing nature of the substituent, consistent with the trend predicted by DFT calculations. Additionally, a limiting case of hydrogen bonding is observed when the benzamide derivatives are replaced with trifluoroacetamide, causing an additional red shift of 44 cm -1 in the NH stretching frequency. Most importantly, 1 H-19 F coupling constants in this series are among the largest measured for amide-NH•••F interactions. X-ray crystallography reveals face-to-face alignment of naphthalene rings in these derivatives resulting in part from the NH•••F hydrogen bonds. This motif also dictates the formation of sheets composed of stacked naphthalene rings in the crystal structure as opposed to unfluorinated analogues wherein NH•••OC hydrogen-bonding interactions force benzamide and naphthalene rings to engage in T-shaped π-π interactions instead. Additionally, the NH proton in the trifluoroacetamide derivative engages in extended H-bond interactions in its crystal structure.
Compound 2 was dissolved in 3 mL dichloromethane in a 3-dram vial and the solvent was evaporated ... more Compound 2 was dissolved in 3 mL dichloromethane in a 3-dram vial and the solvent was evaporated slowly with the vial in slanted position. Small crystals of compound 2 were formed when all the solvent had evaporated. xs1924a Crystal data Chemical formula C 29 H 20 O 5 M r 448.45 Crystal system, space group Triclinic, P-1 Temperature (K) 110 a, b, c (Å) 8.0663 (5), 12.7882 (6), 13.3392 (11) , , (°) 102.324 (5), 103.153 (6), 102.371 (4) V (Å 3 ) 1258.07 (15) Z 2 Radiation type Cu K (mm -1 ) 0.66 Crystal size (mm) 0.21 × 0.11 × 0.02 Data collection S5 Diffractometer SuperNova, Dual, Cu at zero, Atlas Absorption correction Analytical CrysAlis PRO 1.171.39.29c (Rigaku Oxford Diffraction, 2017) Analytical numeric absorption correction using a multifaceted crystal model based on expressions derived by R.C.
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Papers by Muhammad Kazim