S. V. Eswaran

Photoresists for microlithography: 1. Role of organic chemistry in microelectronics

Characteristics of photoresists used in microlithography are highlighted. The microstructure of the matrix polymer used in these photoresists is critical for ensuring good lithographic performance and the same can be evaluated by using modern NMR spectroscopic techniques. It is now well-known that highly ordered ‘alternate’ and ‘semi-alternate’ tailor-made novolaks lead to better performing photoresists.

Designing of high-resolution photoresists: use of modern NMR techniques for evaluating lithographic performance

Applications of improved 1-D/ 2-D NMR spectroscopic techniques have been reviewed for quantitatively estimating the incorporation of different monomers and degree of linearity in resin microstructure. Comparison of the NMR data with those from lithography leads to a distinct correlation between resin micro-structure and lithographic performance. A novel photoresist mechanism is proposed in a positive photoresist; also, using modern NMR techniques, the crosslinking mechanism in a negative photoresist has been studied.

Electrical Studies on Pentacene Thin Film Transistors with Different Channel Widths

In order to conduct electrical studies on organic thin film transistors, top-contact devices are fabricated by growing polycrystalline films of freshly synthesized pentacene over Si/SiO2 substrates with two different channel widths under identical conditions. Reasonable field effect mobilities in order of 10−2-10−3 cm2V−1s−1 are obtained in these devices. An elaborative electrical characterization of all the devices is undertaken to study the variance in output saturation current, field effect mobility, and leakage current with aging under ambient conditions. As compared to the devices with longer channel width, the devices with shorter channel width exhibit better electrical performance initially. However, the former devices sustain the moderate performance much longer than the latter ones.

Woodward’s synthesis of vitamin B12

The synthesis of this molecule was a landmark in organic synthesis. It involved the masterful control of shapes of molecules to create 9 chiral centres with known absolute and relative configurations. The concepts of absolute and induced asymmetric synthesis are here explained.

Concomitant Nitrene and Carbene Insertion Accompanying Ring Expansion: Spectroscopic, X-ray, and Computational Studies

Reinvestigation of the thermolysis of azido-meta-hemipinate (I) yielded, in addition to known II, unusual products III and IV. These products are formed via a rare intramolecular nitrene insertion into an adjacent methoxy C-H bond followed by an intermolecular reaction during a ring-expansion and a ring-extrusion reaction followed by a carbene insertion. The structures of the new compounds were confirmed using a battery of techniques, including HRMS (ESI-QTOF) and 2D NMR as well as X-ray crystallography for compound IV. Density functional theory methods were used to support the proposed mechanism of formation of the products.

Evaluation of microlithographic performance of ‘deep UV’ resists: Synthesis, and 2D NMR studies on alternating ‘high ortho’ novolak resins

AbstractLithographic evaluation of a ‘deep UV’ negative photoresist is discussed along with the synthesis of an alternating ‘high-ortho’ novolak resin. 2-D NMR studies (COSY, NOESY, HSQC, HMBC) on this resin are also discussed. Graphical AbstractLithographic evaluation of a ‘deep UV’ negative photoresist is discussed along with the ‘two-step’ synthesis of an alternating ‘high-ortho’ novolak resin. The microstructure of the resin is stablished by TGA, DSC, 2-D NMR (COSY, NOESY, HSQC, HMBC) and energy minimisation studies.

A New Heterobifunctional Cross-linker Based on an “Introverted” Acid: Mass Spectrometric and Bioinformatics Studies, Analysis of Intermolecular Crosslinking of Proteins

A new NHS-aryl azido heterobifunctional cross-linker based on an “introverted” carboxylic acid has been used to bring about successful intermolecular cross-linking. As a ‘proof-of-concept’ Lysozyme was incubated with the crosslinker, then photolysed (366 nm, 6 W UV lamp), subjected to SDS-PAGE, excision of the ‘dimer’, trypsin digested and analyzed by ESI-MS and StavroX 3.6.0.1. Previous studies on crosslinking of Lysozyme (SI-I and SIII) using homobifunctional cross-linkers, either no cross-linking was observed or only two crosslinks were detected in the case of BS3, a smaller cross-linker. The heterobifunctional cross-linker described here leads to many more crosslinks, which have been identified by using mass spectrometry (ESI-MS) and StavroX 3.6.0.1, a bioinformatics software, especially suited for identifying intermolecular crosslinking.

ESI-MS and Stavrox 3.6.0.1 Investigations of Crosslinking by an Aryl-Azido-NHS-Heterobifunctional Crosslinker

Chemical cross-linking-mass spectrometry (CX-MS) combined with bioinformatics tools is increasingly being used to analyze large-scale protein–protein interactions. It has gained importance in studies in proteomics, lipidomics, in systems and structural biology. Recently it has gained importance in preparation of homogeneous antibody-drug conjugates, which has been described as “a pinnacle of such targeting efforts.” What makes these approaches exciting is that using the “Click” and Bertozzi protocols in vivo studies can be carried out successfully. Using CX-MS combined with cryo-EM, structures of protein complexes can now be probed at almost molecular resolution (upto 3 A). Chemical crosslinking is useful in materials science, as well. Major advances in both mass spectrometric techniques and bioinformatics tools today allow one to identify cross-linked peptides with highconfidence and with more user-friendly approaches. Crucial to this is the ability to capture intermolecular crosslinking reliably. The use of a new small NHS-aryl azido heterobifunctional cross-linker based is described here, which picks intermolecular crosslinking better. Thus, Lysozyme has been crosslinked successfully as established by the ‘dimeric’ band observed in SDS-PAGE. its tryptic digestion, ‘zip tip’ enrichment, ESI-MS, MS/MS and the data generated analyzed using StavroX 3.6.0.1, a bioinformatics software, especially suited for determining intermolecular crosslinking.

Azido-meta-hemipinic Acid: An "Introverted" Acid?

Reaction of Azido-m-hemipinic acid (IV) with N-hydroxy Succinimide (NHS) and Dicyclohexyl Carbodiimide (DCC) has been investigated. The product (IV) has been identified as a tri-NHS adduct of the elusive O-acylisourea intermediate in DCC catalyzed reactions of carboxylic acids and alcohols/amines. Based on these observations, a question is posed whether ‘azido-m-hemipinic acid’ is to be considered as an “introverted” acid?.