Pearson's hard soft acid base theory in bioinorganic Term Paper

Pearson's hard soft acid base theory in bioinorganic - Term Paper Example The theory implies that soft acids tend to bind to soft bases and hard acids to hard bases. An increase in the electronegativity of an element or ligand causes an increase in the polarizability; this in turn increases hardness. The theory is useful in predicting the pathways of chemical reactions. The chemical conditions in which a hard or soft base or acid in put in can cause the hardness (or softness) characteristics of the acid or base to change. Therefore, borderline elements and ligands might increase or decrease in hardness or softness depending on the chemical conditions. Because of this reason, the metals in various metalloenzymes may be subjected to chemical conditions that might alter their hardness or softness properties. Enzymes with metals that exhibit Pearson’s hard and soft acids and bases theory include: 1) Urease This is an enzyme with nickel at its active site found in many species of bacteria, algae, plants (such as Jack Bean) and invertebrates. It plays a k ey role in the catalytic hydrolysis of urea to form ammonia and carbon dioxide as pre the equation below: Urease in Jack Bean has a single catalytic unit made up of an ?-subunit that has the active site with a dimeric nickel center. One of the two Ni atoms (Ni-1) coordinates to histidine via the nitrogen atoms and a water molecule. The second Ni atom (Ni-2) is similarly coordinated to histidine via the N atoms, two water molecules and to aspartic acid via the O atom. Mechanism: There are several mechanisms that explain how urease works. These include: a) Zerner mechanism In this, a carbonyl oxygen in urea attacks one of the water ligands attached to Ni-1. A nitrogen atom in the urea molecule donates its lone pair electrons to a carbon atom forming an N=C bond (Dixon, Riddles and Blakeley). This then reacts with a carboxylate ion. A base-catalyzed deprotonation of one –OH ligand on Ni then occurs. The resultant electronegative O attacks the carbonyl carbon. The N=C bond initia lly formed donates two electrons to the nitrogen, cancelling out the charge on it. The intermediate carbon formed with a coordination of 4 is then broken down by a sulfhydryl group. Ammonia is released when the C-N bond is broken after an H atom bonds to the N. This occurs alongside the breaking of the bond between the octahedral nickel and oxygen. A carbamate ion coordinated to the Ni is then formed. Water displaces the carbamate. The resultant carbamate then degenerates to yield carbonic acid and urea. b) Mangani mechanism This mechanism stipulates that both Ni-1 and Ni-2 take part in the reaction. The first atom, Ni-1, binds to urea, causing its activation. The second, Ni-2 binds to a water molecule, causing its activation (Benini, Rypniewski and Wilson). Ni-1 is in a five-coordinate formation, bound to urea via a carbonyl O atom. The distance between the two Ni atoms is reduced by the movement of the urea molecule towards Ni-2. The relatively low Lewis base property of NH2 in ur ea makes it a poor chelating ligand. Its high basicity however, enables the binding to Ni to occur. 2) Carbon monoxide dehydrogenase This is a nickel-based enzyme found in various bacteria. The enzyme plays a role in the catalytic oxidation of carbon monoxide to form carbon dioxide as per the equation below: There are two classes of carbon monoxide hydrogenase enzymes: one has a Mo-[Fe2-S2] active site and the other a Ni-[Fe3-S4]

Intellectual Property Law assignment Essay Example | Topics and Well Written Essays - 3000 words

Intellectual Property Law assignment - Essay Example A copyrights issue, with regards to ownership and authorship of a book and photographs arises. Who between Burchill, the book author and Justin Timbersnake, the subject of the book, owns the copyright to the book and the photographs? Does Burchill own the rights to the photos of Justin Timberlake she took in the pretence of her personal use and do such rights allow her to publicly distribute the photos in question? As noted, this is purely a question of copyright law; most importantly, The Copyright, Designs and Patents Act, 1988 and the Copyright and Related Rights Regulations 2003, No. 2498. In particular, this case is about copyright laws because it touches on moral rights and obligations. In this case, the right of privacy for Justin’s photographs Burchill had taken for her personal use, of which she has now agreed to give to the editor of The Sunday Topical. Secondly, there is the issue of copyright infringement and moral infringement; has the editor of The Sunday Topical infringed on Justin Timbersnake’s rights to the contents of Burchill’s book and photos? It is a fact that Burchill is the author of the book biography of Justin Timbersnake and the photographs she took of Justin while at his mansion. ... Justin Timbersnake should not sue The Sun Topical for serialising the book since they have not in any way infringed on his copyright since Burchill owns the authorship rights. However, Timbersnake can go ahead and sue Burchill for giving his private photos to The Sun Topical for public display. Likewise, as the facts of this case those outlined above are concerned; the relevant law to this case is the Copyright, Designs and Patents Act, 1988, specifically in relation to authorship, ownership, infringements, moral rights and privacy. Based on the facts of the case, it is imperative that the issue of ownership of the book and of the photography needs to be established. It is also beneficial to determine whether, by allowing Burchill access to his personal diary, Justin Timbersnake’s granted or transferred his copyrights of the diary to Burchill. If there was an assignment or transfer of copyright ownership, it will be important to find out whether there is a written documentatio n signed by or on behalf of the assignor. Another issue that needs determining is the nature of relationship between Burchill and Justine Timbersnake with regards to both the photography and the book; was Burchill employed by Justin when she took the photographs? Or did Justin ask or commission her to write the book on his life? These questions help in determining the first owner of the copyright with regards to both the photographs and the book. In addition to solving the issue of copyright ownership and authorship, it is important that the issue of infringement is looked at. Determining whether liability exists is also important as is the issues of remedies in terms of damages and or criminal