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Controllable self-assembly and understanding of the interaction between single metabolite fibrils and live-cell membranes have paramount importance in providing minimal treatment in several neurodegenerative disorders. Here, utilizing the nonlinear nature and peculiar hydrogen bonding behavior of the dimethyl sulfoxide (DMSO)-water mixture, the selective self-assembly of a single metabolite 5-fluorouracil (5-FU) is achieved. A direct correlation between water availability and selective self-assembly of 5-FU is ratified from the excited-state dynamics. The specific fibrillar structures of 5-FU exhibit a great potential to modulate live cell membrane fluidity and model membrane lipid distribution. After 5-FU fibril addition, a disorder of H-bonded water molecules arises several layers beyond the first hydration shell of the polar headgroups, which essentially modifies interfacial water structure and dynamics. Overall, our results shed light on the role of solvent to govern specific self-assembly and also lay the foundation accounting for the earlier stage of several diseases and multidrug resistance.

A novel on-the-fly calibration method of optical tweezers is presented, which enables in situ control and measure of absolute temperature and viscosity at nanoscale dimensions. Such noncontact measurement and control at the nanoscale are challenging as the present techniques only provide off-line measurements that do not provide absolute values. Additionally, some of the present methods have a low spatial resolution. We simultaneously apply the high temporal sensitivity of position autocorrelation and equipartition theorem to precisely measure and control in situ temperature and the corresponding microrheological property around the focal volume of the trap at high spatial resolution. The femtosecond optical tweezers (FOTs) use a single-beam high repetition rate laser for optical trapping to result in finer temperature gradients in comparison to the continuous-wave laser tweezers. Such finer temperature gradients are due to the additional nonlinear optical (NLO) phenomena occurring only at the nanoscale focal plane of the FOTs. Because NLO processes are laser peak power-dependent, they promote an effective study of physical properties occurring only at the focal plane. Using FOTs at optically benign near-infrared wavelengths, we demonstrate microrheological control and measurement in water by adding a highly absorbing yet low fluorescent dye (IR780)., Competing Interests: The authors declare no competing financial interest.

In this article, we have investigated the excited-state intramolecular double proton transfer dynamics of [2,2'-bipyridyl]-3,3'-diol, BP(OH) 2 , in three alcohol-water binary mixtures, namely, ethanol (EtOH)-water, n -propanol (PrOH)-water, tert -butyl alcohol (TBA)-water, and dimethyl sulfoxide (DMSO)-water utilizing the femtosecond fluorescence upconversion technique. We have found that in alcohol-water binary mixtures the proton transfer (PT) pathway of BP(OH) 2 is sequential and the anomalous slowdown in PT dynamics is observed in mole fraction (χ) ranges χ EtOH = 0.04-0.07, χ EtOH = 0.23-0.28, χ PrOH = 0.17-0.30, χ TBA = 0.12-0.21, and χ TBA = 0.40-0.46. Our study sheds light on the involvement of water network in the PT dynamics. Reduction in water accessibility due to the involvement of water molecules in cluster formation results in hindered PT dynamics, and this retardation is more for the TBA-water binary mixture compared to that for the other two mixtures. Additionally, we have found two anomalous regions for the DMSO-water binary mixture in ranges χ DMSO = 0.12-0.16 and χ DMSO = 0.26-0.34. However, most interestingly, beyond χ DMSO = 0.40, we do not find any growth component in the femtosecond fluorescence upconversion trace, which may be due to the change in the PT mechanism from a sequential water-mediated pathway to a concerted intramolecular pathway., Competing Interests: The authors declare no competing financial interest.