The deselenization of selenocysteine selectively removes the selenol group to give alanine under anaerobic conditions or serine under aerobic conditions (oxygen saturation).

Although native chemical ligation has enabled the synthesis of hundreds of proteins, not all proteins are accessible through typical ligation conditions. The challenging protein, 125-residue human phosphohistidine phosphatase 1 (PHPT1), has three cysteines near the C-terminus, which are not strategically placed for ligation. Herein, we report the first sequential native chemical ligation/deselenization reaction. PHPT1 was prepared from three unprotected peptide segments using two ligation reactions at cysteine and alanine junctions. Selenazolidine was utilized as a masked precursor for N-terminal selenocysteine in the middle segment, and, following ligation, deselenization provided the native alanine residue. This approach was used to synthesize both the wild-type PHPT1 and an analogue in which the active-site histidine was substituted with the unnatural and isosteric amino acid β-thienyl-l-alanine. The activity of both proteins was studied and compared, providing insights into the enzyme active site.

The development of chemically-addressable N-heterocyclic carbene (NHC) based self-assembled monolayers (SAMs) requires in-depth understanding of the influence of NHCs anchoring geometry on its chemical functionality. Herein, it is demonstrated that the chemical reactivity of surface anchored NO 2 -functionalized NHCs (NO 2 -NHCs) can be tuned by modifying the distance between the functional group and the reactive surface, which is governed by the deposition technique. Liquid-deposition of NO 2 -NHCs on Pt (111) induced a SAM in which the NO 2 -aryl groups were flat-lying on the surface. The high proximity between the NO 2 groups and the Pt surface led to high reactivity and 85% of the NO 2 groups were reduced at room temperature. Lower reactivity was obtained with vapor-deposited NO 2 -NHCs that assumed a preferred upright geometry. The separation between the NO 2 groups in the vapor-deposited NO 2 -NHCs and the reactive surface circumvented their surface-induced reduction, which was facilitated only after exposure to harsher reducing conditions. KEYWORDS Self-assembled monolayers; N-Heterocyclic Carbene; NEXAFS; Anchoring geometry;The high chemical tunability and metal-affinity of N-heterocyclic carbene molecules (NHCs) have enabled to form robust NHCs-based self-assembled monolayers (SAMs) with exceptional stability and functionality. [1][2][3][4][5][6][7][8][9][10] Chemically-functionalized NHCs have been utilized for the formation of SAMs with varied applications range, including molecular patterning, biosensing and catalysis. [11][12][13][14][15][16] Two main approaches have been developed for surface-anchoring of NHCs: 1. Liquiddeposition; in which deprotonation is facilitated by a strong base, such as potassium tert-butoxide (KO t Bu), for the formation of an active carbene that can be anchored on metallic surfaces (Scheme 1a). 12, 17 2. Vapor-deposition; in this approach hydrogen carbonates counteranion serves as a base for deprotonation of the imidazolium cation, enabling active carbene formation and its surface-anchoring under ultra-high vacuum (UHV) conditions (Scheme 1b). 11 Scheme 1. Schematic illustration of liquid-(a) and vapor-deposition (b) of NO 2 -functionalized NHCs.

The human body contains 25 selenoproteins, but challenges in their preparations have prevented biological characterizations thus far. Here we report the first total chemical syntheses of two human selenoproteins, selenoprotein M (SELM) and selenoprotein W (SELW).

IR nanospectroscopy measurements revealed the influence of oxidizing reaction conditions on the reactivity of different surface sites on Pt particles.