The stereochemistry of selected supramolecular complexes of cucurbiturils and the effect of homogeneous equilibria and electron transfer of the guest

From a practical perspective, host-guest complexes are vehicles for understanding and using supramolecular interactions for purposeful function in sensors, molecular machines and switches, while from a fundamental perspective they may lead to novel supramolecular protection schemes in basic organic reactions. This dissertation examines the interactions of cucurbiturils as barrel-shaped hosts, exhibiting a hydrophobic cavity, with substituted benzoylpyrydinium, phenypyrylium, and diazaanthraquinonediium cations as guests. In water, N-methyl-4-(p-substituted benzoyl)pyridinium cations exist in equilibrium with their hydrated forms (gem-diols), whose concentrations depend on the para substituent. In the presence of cucurbit7uril (CB[7]), the benzoyl group shows a preference for the CB[7] cavity, and the ketone to gem-diol equilibrium is shifted toward the keto form, meaning that the stabilization through hydrophobic interactions of the benzoyl group in the CB[7] cavity exceeds the hydrogen bonding stabilization of the gem-diols in the aqueous environment. In an aprotic polar solvent such as dimethylsulfoxide, 4-benzoylpyridinium cations undergo heterogeneous electron transfer simultaneously from both their free state as well as their complexes with CB[7]. In the same line of work, N,N\u27-dimethyl-2,6-diaza-9,10-anthraquinonediium dication in water not only exists in equilibrium with its gem-diol but also forms aggregates which cause line-broadening in ¹H NMR. At low pH (\u3c1), the aggregates break up and the equilibrium is shifted exclusively toward the quinone form. In the presence of CB[7], the quinone form undergoes inclusion with CB[7] by slow exchange in both water and aqueous acid. Both free and CB[7]-intercalated quinone forms are observed by ¹H NMR. To gain more insight on the intercalation of monocationic guests in the cucurbituril cavity not only as a function of their hydrophobic properties but also in terms of their shape, size and the size of the cavity, 4-phenylpyrylium cation (Pylm) was chosen as a guest and both CB[7] and CB[8] as hosts. The size and shape of the guest was modified by 2,6-substitution (Me, iPr, Ph, t-Bu). In water, 2,6-disubsituted-Pylm form dimers, but they enter as such only in CB[8]. All guests insert their 4-phenyl groups in either cavity, except (iPr-Pylm)₂@CB[8] where iPr-groups are inserted. Stereochemistry is interpreted by an interplay of size and hydrophobicity of pyrylium substituents, solvation effects, and size and flexibility of the hosts --Abstract, page iv

Probing the Steric Effect of 2,6-disubstituted-4-phenylpyrilium Inclusion Complexes with Cucurbit{[}7]uril

2,6,-disubstitued-4-phenylpyrylium compounds form inclusion complexes with cucurbit[7]uril (CB[7]), a macrocyclic host made of repeating units of glycoluril. To study the effect of steric hindrance on the mode and extent of inclusion, four different 2,6-disubstituted-4-phenylpyrilium tetrafluoborate salts (1a-d) were synthesized and their complexation with cucurbit[7]uril was studied by 1H NMR. Based on the nature of the substituents at 2,6 positions (R = Me, i-Pr, t-Bu, Ph) of 4-phenylpyrylium tetrafluoborate salts, different degree of inclusion was observed and the extent of inclusion was further confirmed by measuring their binding constants with CB[7] via UV-Vis titrations

DISTRIBUTION AND SEASONAL VARIATION OF HEAVY METALS IN SEDIMENTS OF MUTHUPET LAGOON, SOUTHEAST COAST OF INDIA

This study deals with seasonal variation of heavy metals in sediments of Muthupet lagoon, Southeast coast of India from September 2011 to August 2012. The bulk sediments were association with sand, silt and clay. Geo-accumulation index (lgeo) was used to quantitatively assess the influences of heavy metal pollution. Heavy metals were determined by using Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) and the results were compared to permissible limits of WHO/USEPA. The minimum concentration of heavy metals in all the stations were found during the post monsoon and summer seasons and the maximum concentration of heavy metals in all the stations were found during the pre-monsoon and monsoon seasons. The reason for the pollution was land drainage, irrigation through channels and municipal wastes and also the peak agricultural activities due to the release of fresh water from reservoirs. Among all the metals iron was found to be maximum in all the stations in post-monsoon and summer season followed by magnesium and manganese. Apart from these three metal, all other six metals are recorded in moderate range. The reason for the high concentration of these metals are anthropogenic activity, agriculture, aquaculture and the rivers regular in and out flow throughout the study duration in the lagoon area

FIGURE 12 in Distribution of Tetraodontiformes (Family: Tetraodontidae) along the Parangipettai Coast, Southeast coast of India

FIGURE 12. Distribution of puffer fishes in all the three stations along the Parangipettai coast

Development of hybrid multi-head, multi-material paste and ink extrusion type 3D printer for biomedical applications

ABSTRACTAdditive manufacturing is a fabrication technique where materials are built up layer-by-layer allowing the realization of complex designs. Ceramic additive manufacturing is steadily increasing in the market and industries are developing 3D printers that are economical and efficient to print single/multi-material. The development of free-form extrusion-type printers has been of great significance due to their wide range of materials used, availability of technology, low development cost, and design freedom in developing the structures. We have successfully developed a hybrid multi-head 3D printer with four print heads capable of operating individually or together to print multiple layers using different materials. The three mechanically actuated print heads are provided to print ceramic, metallic slurry, and polymeric materials, and one pneumatic actuated print head is for printing bio-ink. The developed hybrid multi-head 3D printer can be beneficial in printing a wide range of materials such as metals, ceramics, polymers, and composites due to its flexibility in printing materials of different viscosities at different pressure. The optimization of the printing of calcium silicate bio-ceramics and multi-material is also studied and reported

<span style="mso-bidi-font-weight:bold">First record of Titan cardinal fish, <i>Holapogon maximus </i>(Apogonidae) <span style="mso-bidi-font-weight:bold">along the South east coast of Tamilnadu, India </span></span>

229-232Titan cardinal fish, Holapogon maximus is described based on the basis of 3 specimens 154 to 190 mm SL, collected from Mudasalodai landing center, east coast of India (Lat. 11º 29’N; Long. 79º 46’E). This species was caught from the shrimp trawl net which is operated at a depth of 25-35 m and it is distinct by having following combination of characters: 9 dorsal fin spine whereas the 8th spine is hidden into the body, 2 anal fin spine and 7 rays and 13 pectoral fin rays

Immobilization of Pd Catalysts on Mesoporous Silica for Amine-, and Copper-free Sonogashira Coupling Reactions

Immobilization of catalysts on solid supports is a promising approach to combine the advantages of heterogeneous and homogeneous catalysts. Pd(PPh3)2Cl2, known as an extremely active homogeneous catalyst for the Sonogashira coupling reaction, has been immobilized on high-surface-area MCF (mesocellular foams)-type mesoporous silica powder modified with 3-aminopropyltriethoxysilane and subsequently with diphenylphosphine. The functionalized MCF-type silica and supported catalysts have been characterized by x-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopy (FTIR), elemental analysis, nitrogen sorption porosimetry, and scanning electron microscopy (SEM). Such supported Pd catalysts have proven to be useful recyclable reagents for copper- and amine-free Sonogashira coupling reactions of haloaromatic compounds with terminal alkynes

Host-guest Interactions of Cucurbit[7]uril with N-quaternized-4-(p-substituted Benzoyl)pyridinium Cations and Control of the Ketone to Gem-diol Equilibrium

N-Methyl-4-(p-substituted benzoyl) pyridinium cations show affinity towards cucurbit[7]uril (CB[7]) and they form either endo or exo complexes. The mode of complexation is controlled by solvent polarity and also by the chemical identity of the group that is attached on the positively charged nitrogen atom. For example, the N-methyl derivative prefers the endo form in water and the exo form in DMSO. The N-benzyl analogue prefers the exo form in both water and DMSO. Interestingly, in water, the N-methyl-4-(p-substituted benzoyl) pyridinium cations exist in equilibrium of their keto and gem-diol forms, whereas the ratio of the gem-diol versus the keto form is controlled by the p-substituent: with electron withdrawing substituents (e.g., nitro, formyl) the gem-diol form dominates. However, in the presence of CB[7], the stabilization realized by having the keto group inside the hydrophobic interior of CB[7] is greater than the stabilization realized via hydrogen bonding of the two hydroxyl groups of the gem-diol with water, shifting the equilibrium towards the keto for

Simultaneous Electron Transfer from Free and Intercalated 4-benzoylpyridinium Cations in Cucurbit[7]uril

N-Substituted 4-benzoylpyridinium monocations form stable host−guest complexes with cucurbit[7]uril (CB[7]) in DMSO (Keq ≈ 0.6−1.9 × 103 M−1). Observation of simultaneous reversible and quasi-reversible e-transfer processes from the free and intercalated quests, respectively, is attributed to the pre-e-transfer host−guest equilibrium. The standard rate constant for Me-BP@CB[7] (ks = 1.0 × 10−4 cm·s−1) reflects e-transfer across 5.7 Å, corresponding to the distance of the intercalated guest from the outmost perimeter of CB[7] (5.3 Å)