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Il Dipartimento di Fisica ospita Seminari di Dipartimento, Seminari organizzati dai gruppi di ricerca, e Physics Colloquia organizzati dalla Scuola di Dottorato.

I Seminari vengono inseriti nel Calendario.

Di seguito gli eventuali Seminari in programma nel mese in corso:

28/02/2018 Ore 14:30 - 17:00

Superfluid phases of dipolar bosons

28/2/2018 14:30:00 Dip. Fisica. Aula D

Superfluid phases of dipolar bosons  - dott. Fabio Cinti
National Institute for Theoretical Physics (NITheP), Stellenbosch University, Stellenbosch, South Africa

Very recently, experimental investigations on BECs of dysprosium or erbium have brought to light surprising outcomes. In particular, it has been observed that the interplay between dipole-dipole and short-range interactions produce an ordered arrangement of self-bounded droplets. Such remarkable results rekindled interest in systems characterised by anisotropic dipolar-interactions. Yet, the microscopic mechanisms that cause these interesting quantum regimes is still under debate. In particular a few authors have only provided a first simplified mean-field description in the framework of an extended Gross-Pitaevskii equation.
In this talk I will present new outcomes that extend the knowledge of the dipolar quantum droplets applying quantum Monte Carlo techniques, probing regions of parameter space where the attractive part of the dipolar interaction dominates and the system forms an ordered array of parallel filaments or a cluster phase. Most interestingly, considering a relevant parameter regime for experiments, I will be discussing quantum observables such as global/local superfluidity and condensate fraction, and comment on the role of temperature as well. Furthermore I will also put the attention on systems composed of mixtures of dipolar bosons. In this last case dipolar interactions should establish droplet demixing purely due to quantum statistic.

Informazioni: Dott. Davide.Galli@unimi.it

09/02/2018 Ore 12:30 - 13:30

Linking mechanochemistry with protein folding with single bond resolution

9 febbraio 2018 alle ore 12:30 in Aula BS via Celoria 16 a Milano

Relatore: Sergi Garcia-Manyes
Department of Physics and Randall Division of Cell and Molecular Biophysics King’s College London

The nanomechanical properties of elastomeric proteins determine the elasticity of a variety of tissues. Post-translational modifications (PTMs) have recently emerged as a useful tactic to regulate protein nanomechanics. In particular, the presence of covalent disulfide bonds, arguably the most relevant PTM with a significant mechanical role, is a widespread natural strategy to regulate protein extensibility and enhance protein stiffness. The prevalent in-vivo strategy to form disulfide bonds requires the presence of dedicated enzymes. Here we propose two alternative chemical routes to promote non-enzymatic oxidative protein folding through the reactivity of protein based chemical modifications. Using single-molecule force-clamp spectroscopy and mass spectrometry, we first captured the reactivity of an individual sulfenic acid, a PTM that functions as a key sensor of oxidative stress, when embedded within the core of a single Ig domain of the titin protein. Our results demonstrated that sulfenic acid is a crucial short-lived intermediate that dictates the protein’s fate in a conformation-dependent manner. When exposed to the solution, sulfenic acid rapidly undergoes further chemical modification, leading to irreversible protein misfolding; when cryptic in the protein’s microenvironment, it readily condenses with a neighbouring thiol to create a protective disulfide bond, which assists the functional folding of the protein. A second, alternative method to induce disulfide reformation occurs via disulfide isomerization of naturally occurring small thiols. Our single molecule approach, complemented with DFT calculations revealed that subtle changes in the chemical structure of a transient mixed-disulfide intermediate adduct between a protein cysteine and an attacking low molecular-weight thiol have a dramatic effect on the protein’s mechanical stability. Combined, these chemistry-based mechanisms for non-enzymatic oxidative folding provide a plausible explanation for redox-modulated stiffness of proteins that are physiologically exposed to mechanical forces, such as cardiac titin.


Stefano Zapperi    mail : stefano.zapperi@unimi.it

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