Current Organic Chemistry - Volume 21, Issue 27, 2017

Magnetic criteria of aromaticity have been analyzed which are currently the most popular methods, considering the circular delocalization of electrons as the genesis of aromaticity. The concept of aromaticity as was visualized by Kekulé to the latest development in the field has been discussed. The other criteria for defining aromaticity such as the chemical behavior, the structural behavior and the energetic criteria are briefly defined keeping the main focus on the magnetic criteria. The various magnetic measures for defining aromaticity such as NMR chemical shifts which include 1H NMR shifts as well as Li+ NMR chemical shifts, Magnetic Susceptibility Anisotropy, Current Density Analysis Plots (CDA) and Nucleus Independent Chemical Shifts are explicitly discussed. The NMR chemical shift is explained with the help of the Ring Current Model (RCM) and its both experimental and computational applications are also discussed. Magnetic Susceptibility Anisotropy and its applicability as a magnetic criterion have been elaborated accordingly. A pictorial representation of Current density Analysis Plots and its relevance as a magnetic criterion have also been accounted for. Special attention is given to the NICS criteria, explaining the role of ghost atom, considering it to be the most popular magnetic criterion. Advantages and disadvantages of all the methods along with recent advances are discussed.

Carbon can form many allotropes. Because of the Carbon's valence and due to the atom arrangements in lattices, some of the allotropes can adopt different shapes and spatial conformations like planar sheets (graphene sheets), nanocones, nanotubes, nanobuds, nanoribbons, nanocages (pseudospheres or spheroids - fullerenes). Their extraordinary physical properties are promoting these structures as candidates with different applications in fields like Optoelectronics, Nanoelectronics, Biology (including Medicine and Pharmacy) and Electrochemistry. Because of their relatively new discovery, because of their complex molecular structures (presenting high numbers of possible isomers) and numerous possibilities of chemical transformations of these structures (addition reactions, substitution reactions, reactions through which two or more structures of this kind will covalently attach), their topology is still an object of great interest for scientists. Starting from the general aspects of connectivity in graphs, graph connectivity indices (Randic Index, Atom Bond Connectivity Index, Wiener Index, Balaban Index, Zagreb Indices, Hosoya Indices), new or adapted connectivity indices have been proposed for these structures to theoretically assess the atom arrangements. Because of their diverse dimensionality (Wiener dimensionality which refers to the atom connectivities and also geometrical one which refers to spatial conformations - planar or three dimensional structures), mathematical equations have been introduced to assess their atom bonding and topology (including volumes and surface areas). Computer software especially conceived for the calculus and design of these structures also exists today.

In the past decades, the advancement in system biology together with the expansion of analytical and biochemical techniques, pawed the way for investigating the complicated concept known as glycomics. The complexity and diversity of sugar chemical structures following the complex enzymatic biosynthesis, as well as all changes that take place in the glycome during growth, development and disease of the organism, have raised the interest in deciphering the glycan and glycoconjugate structure-to-function relationship and moreover, in profiling the glycome in view of potential disorder glycan biomarkers. The smallest modification within the normal degradation process of glycans causes a “domino effect”, hampering the subsequent degradation stages and finally, triggering specific disorders. This is also the case of the lysosomal storage disorders (LSDs), a heterogeneous group of inborn errors of metabolism caused by mutations in genes that encode mostly lysosomal hydrolases. The present paper summarizes relevant developments in the field of LSD investigation and diagnosis by employing various methodologies, such as fluorimetric assays and mass spectrometry (MS), with a particular emphasis on the detection and identification in a high throughput mode of various biomarkers in complex mixtures by high performance MS instruments, coupled with different microfluidic systems or with ion mobility spectrometry, the most proficient separation technique available nowadays. Monitoring biomarker expression in biological fluids is useful not just to measure the disease progression and to assess the most effective therapeutic regimens, but also to determine the susceptibility or recurrence degree of the disease.

Objective: In this review we present the general principles that are at the basis of the construction of artificial molecular devices and machines and the main characteristics of these systems with a special focus for the kind of energy inputs needed to make them work. Methodology: By the bottom-up (chemical) approach science and technology move from micro- to nanoworld, and due to the nature of inputs (light and chemical) they move from electronics to photonics and chemionics. Furthermore the chemical molecule-by-molecule bottom-up approach offers unlimited opportunities for design and construction of nanoscale supramolecular structures, by combining the high precision of the chemical synthesis and scientists with a device driven-ingenuity. Furthermore, because the ability to perform specific functions as a response to external stimuli depends directly on the chemical nature and properties of the component units, in this review, we illustrate some examples of molecular devices and machines based on specific molecular units that have been developed in the research group of one of the authors. They are systems exhibiting pseudorotaxane, rotaxane, catenane and dendrimer structures that incorporate redox- and/or photoactive moieties. Conclusion: The future development of this kind of research will lead to more and more sophisticated artificial molecular devices and machines with better performances regarding their stability, switching, speed, and functions performed. We foresee that they will find useful applications in various fields, like energy conversion, sensoring, catalysis, and will give a great contribution in solving the present-day main problems regarding food, health, energy supply, and environment protection.

Immobilization of biomolecules in porous supports, especially in silica matrices, is probably one of the most successful processes in biomaterials synthesis in the last three decades. The flexibility and versatility offered by the sol-gel process, ensured its leading position in the biomolecules immobilization. Functionalization with organic groups of the silica precursors leads to so-called organically modified silica gels. While there are many studies published recently about organically modified silica gels, the relationship between the functionalized support properties and the biomolecules activity is still poorly understood. The aim of this review is to summarize the available results on the influence of the organic functionalization of the silica support on the performance of immobilized biomolecules.

Linear polyacene hydrocarbons C4n+2H2n+2 consisting in the linear condensation of n aromatic hexagonal rings, have been used in prototypical studies of electronic delocalization, relevant for conduction effects. The results of density functional theory (DFT) calculations were interpreted by analytical simplified models, such as Huckel simple orbital schemes and the Heisenberg spin Hamiltonian, generating a Valence Bond phenomenology. The latter model shows how the manifold of excited states of the hydrocarbons assumes a band-like structure with increasing n. It is also shown that the “aromatic” resonance structures form a configuration interaction space in which electron mobility, expressed as the electronic polarization of the molecule, arises from a mixing of the ground and low lying excited states, responsive to an externally applied electric field.

Background: Claisen rearrangement is an important reaction, and some "variants" are brought out under the inspiration of Claisen reaction, e.g. Bellus-Claisen rearrangement, Eschenmoser-Claisen rearrangement, Ireland-Claisen rearrangement, and Johnson-Claisen rearrangement. Objective: The application of tandem Claisen rearrangement in organic synthesis was analyzed and discussed herein. Method: We chose some important synthetic studies utilizing the tandem Claisen rearrangement as the key transformation and concisely described and discussed their contents. Results: The tandem reaction could shorten the reaction steps and improve the reaction yield. Conclusion: So, the tandem Claisen rearrangement would greatly improve the efficiency of reaction.

Background: In order to be suitable for biomedical applications, the iron oxide based magnetic materials require appropriate characteristics such as superparamagnetic behaviour, high saturation magnetization, high specific surface area, small particle size and narrow distribution. Objective: The objective of the present study was to find the optimum conditions for obtaining iron oxidesilica nanocomposites with superparamagnetic behaviour by thermolysis of sol-gel derived inorganic-organic hybrid xerogels. Method: The tetraethylorthosilicate, TEOS, and iron (III) acetylacetonate precursors were processed at room temperature by acid catalysed sol-gel route in the presence of polyvinyl alcohol (molecular weight of 145000) as an additive. The thermal treatment at 180 °C, 220 °C, 260 °C, 300 °C, 400 °C and 500 °C respectively, of obtained inorganic-organic hybrid xerogel resulted in six Fe2O3-SiO2 (20% Fe2O3-target composition) nanocomposite samples. All the samples were investigated by means of X-ray diffraction technique, transmission electron microscopy, Mossbauer spectroscopy, and submitted to magnetic measurements. Results: The maghemite unique crystalline phase was obtained at 300°C along with a certain amount of amorphous iron oxide. By further raising the calcination temperature, this initialized the γ- to α-Fe2O3 transition process. At 400 °C, the maghemite and hematite coexist, and at 500 °C only the hematite crystalline phase was found. Conclusion: Both structural and magnetic properties of the nanocomposite sample annealed at 260°C, recommend it. The sample consists in γ-Fe2O3 phase exhibiting superparamagnetic behavior with approx. 48 emu/g saturation magnetization value and approx. 10 nm average particle diameter. A promising response was obtained when the sample was tested as a contrast agent in medical imaging application.