Cristian Opazo | New York University (original) (raw)

Papers by Cristian Opazo

Journal of Agricultural and Food Chemistry, 2008

The mechanism by which the naturally occurring polyphenolic compounds resveratrol (RES), C 14 H 1... more The mechanism by which the naturally occurring polyphenolic compounds resveratrol (RES), C 14 H 12 O 3 , and its metabolite piceatannol (PIC), C 14 H 12 O 4 , scavenge free radicals is studied using experimental and density functional theory (DFT) methods. PIC's crystal structure shows a strong intermolecular hydrogen bond network, which, through a concerted motion of the hydroxyl hydrogen atoms, can produce a second hydrogen bond chain. This reorganization offers a low-energy pathway for the transfer of hydrogen atoms and is a contributing factor to PIC's biological activity. Additionally, DFT calculations describing the entire reaction mechanism of RES, PIC, and 3,3′,4′,5,5′-pentahydroxystilbene with hydroxyl and peroxyl radicals agree with experimental results, showing that increased hydroxylation aids in scavenging activity. PIC is more efficient than RES because (i) by sharing its 3′-OH hydrogen atom with its adjacent neighbor, O-4′, the abstraction and transfer of the 4′-H atom to the free radical becomes easier and (ii) the resulting PIC semiquinone radical is more stable. As a result of the reaction with OH • , both RES and PIC form water; with the peroxyl radical, both RES and PIC form hydrogen peroxide. Also, docking of PIC onto the protein transthyretin suggests better performance than RES and confirms its possible application in neurodegenerative conditions such as Alzheimer's disease.

The COVID-19 pandemic forced more technology-enhanced simulated practice to accommodate remote st... more The COVID-19 pandemic forced more technology-enhanced simulated practice to accommodate remote student learning. 1 It also provided an opportunity to explore this innovative learning method and reflect on prior traditional methods. 1 In dental school, students must be competent in the delivery of local anaesthesia to be safe providers. The inferior alveolar nerve block (IANB) is an injection most students struggle with as the target is invisible and the technique relies on knowledge of anatomy. Without sufficient clinical training, this

Journal of Dental Education, 2021

PURPOSE The ultimatum bargaining game has been devised by economists to measure fairness and gene... more PURPOSE The ultimatum bargaining game has been devised by economists to measure fairness and generosity during negotiations. This study sought to adapt the game to classroom application with the intent of (a) determining whether the known outcomes would be replicated given modifications needed to make the game suitable as an educational tool and (b) sharing the resulting self-appraisal with students themselves. METHODS A total of 452 first-year dental students participated in this adaptation as part of a classroom exercise. Students, identified as donors, were allocated an imaginary stake of 100andaskedtosharesomeamountofitwitharecipientclassmatebymakinganonnegotiable,one−timeoffer.Iftheofferisaccepted,thedonorstudentretainsanyresidualamount.Iftheofferisrejected,neitherthedonornorrecipientreceivesanything.Thequestionbeingtestediswhetherstudentfairnessand/orgenerositychangewhenthepreferreddonorstatusisassignedatrandomversusonthebasisofanearnedpropertyentitlementrepresentedherebyahigher−classrank.RESULTSANDCONCLUSIONWhenstatusasGroupAdonorswasestablishedatrandom,themajorityofstudentsofferedtheirfictitiousGroupBcounterpartthefairestpossibleamountof100 and asked to share some amount of it with a recipient classmate by making a nonnegotiable, one-time offer. If the offer is accepted, the donor student retains any residual amount. If the offer is rejected, neither the donor nor recipient receives anything. The question being tested is whether student fairness and/or generosity change when the preferred donor status is assigned at random versus on the basis of an earned property entitlement represented here by a higher-class rank. RESULTS AND CONCLUSION When status as Group A donors was established at random, the majority of students offered their fictitious Group B counterpart the fairest possible amount of 100andaskedtosharesomeamountofitwitharecipientclassmatebymakinganonnegotiable,one−timeoffer.Iftheofferisaccepted,thedonorstudentretainsanyresidualamount.Iftheofferisrejected,neitherthedonornorrecipientreceivesanything.Thequestionbeingtestediswhetherstudentfairnessand/orgenerositychangewhenthepreferreddonorstatusisassignedatrandomversusonthebasisofanearnedpropertyentitlementrepresentedherebyahigher−classrank.RESULTSANDCONCLUSIONWhenstatusasGroupAdonorswasestablishedatrandom,themajorityofstudentsofferedtheirfictitiousGroupBcounterpartthefairestpossibleamountof50 (70.4% in 2020 and 61% in 2018). However, when students were told that their status as Group A donors would be established based on their ranking in the upper half of the class, the percentage offering the fairest amount declined to 49.5% in 2020 and to 51.8% in 2018. This outcome was available for immediate disclosure to students during the classroom session; it was consistent with results previously reported for the ultimatum bargaining game; and it showed that when a property entitlement is perceived as having been earned (manifested by a higher-class rank), fairness and generosity decline.

Journal of Biological Chemistry, 2002

An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Journal of Dental Education

ACM SIGGRAPH 2021 Educators Forum

LocalAnesthesiaVR is a virtual reality training system for dental anesthesia, a clinical procedur... more LocalAnesthesiaVR is a virtual reality training system for dental anesthesia, a clinical procedure every dentist must be competent with, and one that is particularly challenging to master throughout the demanding dental curriculum. This unique VR-based system provides learners with visual, auditory and haptic feedback enabling experiential learning in pre-clinical education.

Proceedings of SIGGRAPH 2021 by the Association for Computing Machinery, 2021

COMPLEX SYSTEMS-CHAMPAIGN-, Jan 1, 2007

This study examines goal-free viewing of cellular automaton (CA) images to address the nature of ... more This study examines goal-free viewing of cellular automaton (CA) images to address the nature of the bottom-up process, the robustness of salience as a framework for explaining fixation points, and the particular features that can characterize salience. The influence of familiarity on oculomotor strategy is also addressed. A qualitative study of the results show promising trends. Higher-level structural features such as pockets of regularity within randomness or localized structures within regularity were salient for most participants. These results raise interesting questions about the kinds of visual features that can be used to characterize salience. An unexpected result is that many fixations occur in blank regions within images featuring nested (fractal) structures. Many of these findings escape current psychophysical models of oculomotor strategy. Hence, future eye-tracking studies with CAs as stimuli could greatly improve our current understandings of the human visual system.

Journal of medicinal …, Jan 1, 2012

The in vitro antiproliferative activity of the title compound on five tumor cell lines shows pref... more The in vitro antiproliferative activity of the title compound on five tumor cell lines shows preference for the colon−rectal tumor HCT116, IC 50 = 13.98 μM, followed by breast MCF7 (19.58 μM) and ovarian A2780 (23.38 μM) cell lines; human glioblastoma U-87 and lung carcinoma A549 are less sensitive. A commercial curcumin reagent, also containing demethoxy and bis-demethoxy curcumin, was used to synthesize the title compound, and so (p-cymene)Ru(demethoxycurcuminato)chloro was also isolated and chemically characterized. The crystal structure of the title compound shows (1) the chlorine atom linking two neighboring complexes through H-bonds with two O-(hydroxyl), forming an infinite two-step network; (2) significant twist in the curcuminato, 20°between the planes of the two phenyl rings. This was also seen in the docking of the Ru-complex onto a rich guanine B-DNA decamer, where a Ru−N7(guanine) interaction is detected. This Ru−N7(guanine) interaction is also seen with ESI-MS on a Rucomplex-guanosine derivative.

PloS one, Jan 1, 2010

The taurine amino-acid derivative, taurolidine, bis-(1,1-dioxoperhydro-1,2,4-thiabiazinyl-4)metha... more The taurine amino-acid derivative, taurolidine, bis-(1,1-dioxoperhydro-1,2,4-thiabiazinyl-4)methane, shows broad antibacterial action against gram-positive and gram-negative bacteria, mycobacteria and some clinically relevant fungi. It inhibits, in vitro, the adherence of Escherichia coli and Staphylococcus aureus to human epithelial and fibroblast cells. Taurolidine is unstable in aqueous solution and breaks down into derivatives which are thought to be responsible for the biological activity. To understand the taurolidine antibacterial mechanism of action, we provide the experimental single crystal X-ray diffraction results together with theoretical methods to characterize the hydrolysis/decomposition reactions of taurolidine. The crystal structure features two independent molecules linked through intermolecular H-bonds with one of them somewhat positively charged. Taurolidine in a biological environment exists in equilibrium with taurultam derivatives and this is described theoretically as a 2-step process without an energy barrier: formation of cationic taurolidine followed by a nucleophilic attack of O(hydroxyl) on the exocyclic C(methylene). A concerted mechanism describes the further hydrolysis of the taurolidine derivative methylol-taurultam. The interaction of methylol-taurultam with the diaminopimelic NH 2 group in the E. coli bacteria cell wall (peptidoglycan) has a negative DG value (238.2 kcal/mol) but a high energy barrier (45.8 kcal/ mol) suggesting no reactivity. On the contrary, taurolidine docking into E. coli fimbriae protein, responsible for bacteria adhesion to the bladder epithelium, shows it has higher affinity than mannose (the natural substrate), whereas methyloltaurultam and taurultam are less tightly bound. Since taurolidine is readily available because it is administered in high doses after peritonitis surgery, it may successfully compete with mannose explaining its effectiveness against bacterial infections at laparoscopic lesions.

Journal of agricultural …, Jan 1, 2008

Bioinorganic Chemistry and …, Jan 1, 2005

Previous studies established some Ti compounds as having marked activity against tumors of the ga... more Previous studies established some Ti compounds as having marked activity against tumors of the gastrointestinal tract and lack of side effects common to widely used cytostatic agents. We describe pertinent structural features of known antitumor Ti agents and other potentially active compounds. Particularly noteworthy features are that Ti-O bonds are short and Ti-O-Ti bond angles are large, demonstrating that in these compounds the O binding has high s-character approaching sp hybridization. /'he successful drug development/1/of the antitumor agent cis-diaminodichloroplatinum(II) (cisplatin) 1, generated a search for other active metal compounds and cis-diethoxy-bis(1-phenylbutane-l,3dionato)titanium(IV), [(bzac)2Ti(OEt)2] (budotitane) 2, was the first non-Pt metal antitumor compound that reached clinical trials /2/. The ligand 1-phenylbutane-l,3-dionato bzac benzoylacetonato, is an asymmetric [3-diketone chelator useful tbr establishing one key structural feature tbr activity in budotitane, namely, the existence of two OEt cis leaving groups, which arc analogous to the 2 CI in cisplatin. Another Ti antitumor agent is titanocene dichloride, (Cp)2TiCI2 3, Cp cyclopentadienyl, which possesses 2 CI leaving groups/5/. Among the differences between Ti antitumor drugs and cisplatin is the spectrum of activity, as Ti drugs operate against gastrointestinal tumors whereas Pt drugs do not. On the other hand, P338 and LI210 leukemia are sensitive targets for Pt drugs but not for budotitane/4/. Other differences include a much faster hydrolysis rate of the leaving groups in the former, and the environment where the metal-leaving group bonds cleave: outside the cell for Ti drugs and inside the cell tbr Pt drugs/1/. Titanocenc dichloride shows a larger spectrum of activity compared to budotitane. This is likely due to better solubility in physiological medium and it is currently in phase II clinical tests /5/, whereas the Structural Features of Antitumor Titanium. Agents and Related Compounds development of budotitane is limited by formulation problems /6/. Titanocene dichloride interacts with transferrin, a protein associated with iron transport, and suggests a possible mode of entry into the tumor cell. That is, the protein, with a Ti atom bound to one of its 2 domains/7,8/, could cross the tumor cell wall, which is characterized by greater amount of transferrin receptors than present in normal cells, and allow metal interaction with unknown targets.