Pratik Verma

Redwood City, California, United States Contact Info
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Experienced serial entrepreneur, founder & C-level exec with a demonstrated history of…

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Publications

  • Security of IoT Data: Context, Depth and Breadth Across Hadoop

    John Wiley & Sons, Inc.

    This chapter describes security concerns associated with the devices, the network, and the data associated with Internet of Things (IoT) technologies and then addresses data security within IoT platforms built using Hadoop technologies. To manage the security and integrity of data, security admins create security policies to define which data each user is authorized to access using one or more rules. The internet is best understood as a globally distributed network of voluntarily interconnected…

    This chapter describes security concerns associated with the devices, the network, and the data associated with Internet of Things (IoT) technologies and then addresses data security within IoT platforms built using Hadoop technologies. To manage the security and integrity of data, security admins create security policies to define which data each user is authorized to access using one or more rules. The internet is best understood as a globally distributed network of voluntarily interconnected devices that can communicate with each other over well-defined protocols to enable business operations. Based on the type of intercommunication, different protocols have organically emerged: data distribution service (DDS) protocol, message queue telemetry transport (MQTT) and extensible messaging and presence protocol (XMPP) and advanced message queuing protocol (AMQP). There are other protocols that address how devices communicate over wireless connections that include radio frequency identification (RFID), Wi-Fi, or bluetooth technologies.

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  • Double Oxidation Localizes Spin in a Ni Bis-Phenoxyl Radical Complex

    Dalton Transactions

    The electronic structure of a doubly oxidized Ni salen complex NiSaltBu (SaltBu = N,N’-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) has been investigated by both experimental and theoretical methods. The doubly oxidized product was probed by Raman spectroscopy, UV-vis-NIR, and EPR to determine the locus of oxidation as well as the spectroscopic signature of the complex. It was determined that double oxidation of NiSaltBu affords a bis-ligand radical species in solution…

    The electronic structure of a doubly oxidized Ni salen complex NiSaltBu (SaltBu = N,N’-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-(1R,2R)-diamine) has been investigated by both experimental and theoretical methods. The doubly oxidized product was probed by Raman spectroscopy, UV-vis-NIR, and EPR to determine the locus of oxidation as well as the spectroscopic signature of the complex. It was determined that double oxidation of NiSaltBu affords a bis-ligand radical species in solution via the presence of phenoxyl radical bands at n7a (1504 cm-1) and n8a (1579 cm-1) in the Raman spectrum, and the loss of the intense NIR transition reported for the mono-radical complex (Angew. Chem. Int. Ed. 2007, 46, 5198). Spectroscopic experiments, complemented by DFT calculations, show that the two radical spins are predominantly localized on the phenolate moieties, in opposition to the extensive delocalization over the ligand framework observed for the mono-radical analogue.

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  • Sulfanyl stabilization of copper-bonded phenoxyls in model complexes and galactose oxidase.

    Proc. Natl. Acad. Sci. U S A

    Integrating sulfanyl substituents into copper-bonded phenoxyls significantly alters their optical and redox properties and provides insight into the influence of cysteine modification of the tyrosine cofactor in the enzyme galactose oxidase. The model complexes [1(SR2)](+) are class II mixed-valent Cu(II)-phenoxyl-phenolate species that exhibit intervalence charge transfer bands and intense visible sulfur-aryl π → π* transitions in the energy range, which provides a greater spectroscopic…

    Integrating sulfanyl substituents into copper-bonded phenoxyls significantly alters their optical and redox properties and provides insight into the influence of cysteine modification of the tyrosine cofactor in the enzyme galactose oxidase. The model complexes [1(SR2)](+) are class II mixed-valent Cu(II)-phenoxyl-phenolate species that exhibit intervalence charge transfer bands and intense visible sulfur-aryl π → π* transitions in the energy range, which provides a greater spectroscopic fidelity to oxidized galactose oxidase than non-sulfur-bearing analogs. The potentials for phenolate-based oxidations of the sulfanyl-substituted 1(SR2) are lower than the alkyl-substituted analogs by up to ca. 150 mV and decrease following the steric trend: -S(t)Bu > -S(i) Pr > -SMe. Density functional theory calculations suggest that reducing the steric demands of the sulfanyl substituent accommodates an in-plane conformation of the alkylsulfanyl group with the aromatic ring, which stabilizes the phenoxyl hole by ca. 8 kcal mol(-1) (1 kcal = 4.18 kJ; 350 mV) through delocalization onto the sulfur atom. Sulfur K-edge X-ray absorption spectroscopy clearly indicates a contribution of ca. 8-13% to the hole from the sulfur atoms in [1(SR2)](+). The electrochemical results for the model complexes corroborate the ca. 350 mV (density functional theory) contribution of hole delocalization on to the cysteine-tyrosine cross-link to the stability of the phenoxyl radical in the enzyme, while highlighting the importance of the in-plane conformation observed in all crystal structures of the enzyme.

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  • Tale of a twist: magnetic and optical switching in copper(II) semiquinone complexes.

    Inorg. Chem.

    An intermediate (C) that is observed in both phenol hydroxylation and catechol oxidation with the side-on peroxide species [Cu(2)O(2)(DBED)(2)](2+) (DBED = N(1),N(2)-di-tert-butylethane-1,2-diamine) is identified as a copper(II) semiquinone species ([1](+)) through independent synthesis and characterization. The reaction of the redox-active 3,5-di-tert-butylquinone ligand with [(DBED)Cu(I)(MeCN)](+) yields a copper(II) semiquinone [1](+) complex with a singlet ground state and an intense purple…

    An intermediate (C) that is observed in both phenol hydroxylation and catechol oxidation with the side-on peroxide species [Cu(2)O(2)(DBED)(2)](2+) (DBED = N(1),N(2)-di-tert-butylethane-1,2-diamine) is identified as a copper(II) semiquinone species ([1](+)) through independent synthesis and characterization. The reaction of the redox-active 3,5-di-tert-butylquinone ligand with [(DBED)Cu(I)(MeCN)](+) yields a copper(II) semiquinone [1](+) complex with a singlet ground state and an intense purple chromophore (ε(580) ~ 3500 M(-1) cm(-1)). All other copper(II) semiquinone complexes characterized to date are paramagnetic and weakly colored (ε(800) ~ 500 M(-1) cm(-1)). Antiferromagnetic coupling between the Cu(II) center and the semiquinone radical in [1](+) is characterized by paramagnetic (1)H NMR and SQUID magnetometry. Comparative X-ray crystal structures along with density functional theory calculations correlate the geometric structures of copper(II) semiquinone complexes with their magnetic and optical properties. The unique observable properties of [1](+) originate from an increase in the overlap of the Cu 3d and semiquinone π orbitals resulting from a large rhombic distortion in the structure with a twist of 51°, attributable to the large isotropic demands of the tert-butyl substituents of the DBED ligand. Independent characterization of [1](+) allows the spectroscopic yields of intermediate C to be quantified in this intriguing hydroxylation reaction.

    Other authors
    • John Weir
    • Liviu Mirica
    • T. Daniel P. Stack

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