Acetylcysteine (C5H9NO3S) is a drug with the notable property of being used to treat a variety of ailments. Paracetamol overdose is a particularly important use, but it also is used to treat bronchitis, chemotherapy side effects, HIV and also has found a use as a psychiatric treatment. It is known for being quite safe with side affects such as vomiting and redness of the skin being quite manageable. The most serious side effect is that 5% percent of people experience an anaphylactic shock that may require immediate treatment when they take acetylcysteine. However it is none of these purely medical concerns that are relevant for today’s paper. Instead the focus is on another property this drug possesses. A physical antimicrobial mechanism which has been reported as being effective at disrupting bacterial adhesion, hampering of their polysaccharide production and ultimately breaks up biofilms.
Entropy and enthalpy are related but distinct concepts. The enthalpy of an activity is the heat energy released (or taken in) at a constant pressure during that activity. A positive enthalpy is an endothermic event, a negative enthalpy an exothermic one. The entropy change is the heat energy change at a constant temperature.
The two values of enthalpy, H, and entropy, S, can be combined with temperature to produce the Gibbs free energy for an event as shown on the right. The Gibbs free energy reveals whether an event is feasible or not. If the energy, G, is negative then the event can occur spontaneously, if positive, it cannot. The array below the equation explains the scenarios in which G is less than zero. If we take the second row, where H is positive and S is negative. It is clear that no matter how temperature changes (as the temperature is in kelvin it can never drop below zero) a positive number minus a negative number will always be positive, so an event with positive enthalpy (endothermal) and negative entropy (such as a gas becoming a solid) will never happen on its own.
Zinc oxide (ZnO) nanoparticles have noticeably wide band gap of 3.37 eV at room temperature. This means that these nanoparticles, normally between 1 and 100 nm, are often included in sunscreens as they excel at absorbing ultraviolet light. Another great application of these zinc nanoparticles is to combat bacteria and some cancers due to the nanoparticles ability to produce reactive oxidative species that destroy the cells they interact with. Previous studies have shown that this antimicrobial activity is most effective at pH 7; keep that in mind as we move on. Unfortunately nanoparticles have a tendency to stick together due to a high surface energy caused by their small size. In order to ensure dispersion occurs in such applications such as the sunscreen is to coat them with some other material which increases the electrostatic repulsion between the particles. Organosilanes are a popular choice for zinc oxide nanoparticles.
Non-Newtonian fluids are liquids which have become quite well known by the general public. The example most recognised is cornstarch and water, which exhibits a phenomenon called shear thickening. When a shear force is applied, the liquid’s viscosity increases to the point that it acts like a solid. The opposite effect can also happen. This video gives a demonstration of the effect of shear thinning where the fluid can be ejected from the syringe but once it is allowed to rest, it can no longer flow and begins acting much more like a solid. Glassy materials, which this post should cover in sufficient detail, often demonstrate this effect when their temperature brings them close to the glass transition temperature.
The concept of a glass and the glassy transition have been covered quite concisely in this previous post. Now the viscous liquids produced when a glass undergoes the glass-liquid transition will normally form a molecular liquid sometimes described as a mesoscopic liquid. This is because the particles have noticeable and nonignorable size. As the density of these particles increases a process called jamming occurs. The jamming principle is that viscosity will increase with particle density and the jamming transition is when the viscosity gets so great that the particles begin being physically held in place with a very limited movement range. This is reminiscent of the molecular structure of a solid and that is exactly what the liquid becomes. Sufficient stresses or increased volume to decrease particle density can unjam the system.
In this post published a few days ago I talked about the potential for terahertz spectroscopy to analyse the chemical properties of drugs.
Today’s instead looks at the possible uses in computer and technology development for terahertz radiation. Of course for any communication system modulation of the wave that’s transferring the message is important. It may have crossed the reader’s mind at some point, the question of why sound waves cannot be radiated from aerials despite a frequency existing within them. This is because at the frequency of 15kHz, the upper range of audio frequencies, the energy radiated from an aerial is basically zero. The phrase “radio frequencies” was coined because it’s literally frequencies which are high enough for radio waves to be noticeably produced. In order to actually radiate sound energy, you need to create a wave of higher frequency, called the carrier wave, that mimics the wave you want to transmit. The diagram above shows the two most common ways of doing this, AM for amplitude modulated has a carrier wave that matches amplitude with the signal while frequency modulated has a higher frequency at the peaks than at the troughs.
Despite having been writing these posts for almost two years I cannot remember explicitly mentioning terahertz spectroscopy once. There have been times when I have talked about analysis at the near infrared scale and of course referred to the terahertz frequency range but the exact details of terahertz spectroscopy have not been described in a way I’m satisfied with. Time to remedy that. Terahertz spectroscopy is a spectroscopic technique that uses photons in the area of terahertz (1012 Hz) to interact with the matter being studied.